Guido, I., Vilfan, A., Ishibashi, K., Sakakibara, H., Shiraga, M., Bodenschatz, E., Golestanian, R. and Oiwa, K., "A Synthetic Minimal Beating Axoneme", Small, July 2022, Vol. 2107854, 1 pp. |
Abstract: Cilia and flagella are beating rod-like organelles that enable the directional movement of microorganisms in fluids and fluid transport along the surface of biological organisms or inside organs. The molecular motor axonemal dynein drives their beating by interacting with microtubules. Constructing synthetic beating systems with axonemal dynein capable of mimicking ciliary beating still represents a major challenge. Here, the bottom-up engineering of a sustained beating synthoneme consisting of a pair of microtubules connected by a series of periodic arrays of approximately eight axonemal dyneins is reported. A model leads to the understanding of the motion through the cooperative, cyclic association–dissociation of the molecular motor from the microtubules. The synthoneme represents a bottom-up self-organized bio-molecular machine at the nanoscale with cilia-like properties. |
BibTeX:
@article{Guidoa, author = {Guido, I. and Vilfan, A. and Ishibashi, K. and Sakakibara, H. and Shiraga, M. and Bodenschatz, E. and Golestanian, R. and Oiwa, K.}, title = {A Synthetic Minimal Beating Axoneme}, journal = {Small}, month = {July}, year = {2022}, volume = {2107854}, pages = {1}, doi = {10.1002/smll.202107854},, url = {https://onlinelibrary.wiley.com/doi/10.1002/smll.202107854} } |
Yerragolam, G., Stevens, R. J. A. M., Verzicco, R., Lohse, D. and Shishkina, O., "Passive scalar transport in Couette flow", J. Fluid Mech., July 2022, Vol. 943(A17) |
Abstract: A scaling theory for the passive scalar transport in Couette flow, i.e. the flow between two parallel plates moving with different velocities, is proposed. This flow is determined by the bulk Reynolds number Re-b and the Prandtl number Pr. In the turbulent regime, for moderate shear Reynolds number Re-tau and moderate Pr, we derive that the passive scalar transport characterised by the Nusselt number Nu scales as Nu similar to (PrRe tau Reb-1)-Re-1/-Re-2-Re-2. We then use the well-established scaling for the friction coefficient C-f similar to Re-b(-1/4) (corresponding to a shear Reynolds number Re-tau similar to Re-b(7/)8) which holds reasonably well within the range 3 x 10(3) <= Re-b <= 10(5), to obtain Nu similar to pr(1/2)Re(b)(3/4) for the Nusselt number scaling. The theoretical results are tested against direct numerical simulations of Couette flows for the parameter ranges 81 <= Re-b <= 22361 and 0.1 <= Pr <= 10, finding good agreement. Analyses of the numerically obtained turbulent flow fields confirm logarithmic mean wall-parallel profiles of the velocity and the passive scalar in the inertial sublayer. |
BibTeX:
@article{Yerragolam, author = {Yerragolam, G.S. and Stevens, R. J. A. M. and Verzicco, R. and Lohse, D. and Shishkina, O.}, title = {Passive scalar transport in Couette flow}, journal = {J. Fluid Mech.}, month = {July}, year = {2022}, volume = {943}, number = {A17}, doi = {10.1017/jfm.2022.368},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/passive-scalar-transport-in-couette-flow/FE8771FDA4A3F90CD92AF0800B81A64C} } |
Ahmad, R., Bae, A., Su, Y.-J., Pozveh, S. G., Bodenschatz, E., Pumir, A. and Gholami, A., "Bio-hybrid micro-swimmers propelled by flagella isolated from C. reinhardtii", Soft Matter, June 2022, Vol. 18(25), 4767 pp. |
Abstract: Bio-hybrid micro-swimmers, composed of biological entities integrated with synthetic constructs, actively transport cargo by converting chemical energy into mechanical work. Here, using isolated and demembranated flagella from green algae Chlamydomonas reinhardtii (C. reinhardtii), we build efficient axonemally-driven micro-swimmers that consume ATP to propel micron-sized beads. Depending on the calcium concentration, we observed two main classes of motion: whereas beads move along curved trajectories at calcium concentrations below 0.03 mM, they are propelled along straight paths when the calcium concentration increases. In this regime, they reached velocities of approximately 20 ìm s-1, comparable to human sperm velocity in vivo. We relate this transition to the properties of beating axonemes, in particular the reduced static curvature with increasing calcium concentration. Our designed system has potential applications in the fabrication of synthetic micro-swimmers, and in particular, bio-actuated medical micro-robots for targeted drug delivery. |
BibTeX:
@article{Ahmad2022, author = {Ahmad, R. and Bae, A. and Su, Y.-J. and Pozveh, S. G. and Bodenschatz, E. and Pumir, A. and Gholami, A.}, title = {Bio-hybrid micro-swimmers propelled by flagella isolated from C. reinhardtii}, journal = {Soft Matter}, month = {June}, year = {2022}, volume = {18}, number = {25}, pages = {4767}, doi = {10.1039/d2sm00574c},, url = {https://pubs.rsc.org/en/content/articlelanding/2022/SM/D2SM00574C} } |
Hejazi, B., Schlenczek, O., Thiede, B., Bagheri, G. and Bodenschatz, E., "On the Risk of Infection by Infectious Aerosols in Large Indoor Spaces", Aerosol and Air Quality Research, June 2022 |
Abstract: Airborne diseases can be transmitted by infectious aerosols in the near field, i.e., in close proximity, or in the far field, i.e., by infectious aerosols that are well mixed within the indoor air. Is it possible to say which mode of disease transmission is predominant in large indoor spaces? We addressed this question by measuring the transport of aerosols equivalent to the size of human respiratory particles in two large hardware stores (V > 10000 m3). We found that aerosol concentrations in both stores decreased rapidly and almost independently of aerosol size, despite the different ventilation systems. A persistent and directional airflow on the order of a few cm/s was observed in both stores. Consequently, aerosol dynamics in such open settings can be expected to be dominated by turbulent dispersion and sweeping flows, and the accumulation of infectious aerosols in the indoor air is unlikely to contribute significantly to the risk of infection as long as the occupancy of the store is not too high. Under these conditions, well-fitting face masks are an excellent means of preventing disease transmission by human aerosols. |
BibTeX:
@article{Hejazi, author = {Hejazi, B. and Schlenczek, O. and Thiede, B. and Bagheri, G. and Bodenschatz, E.}, title = {On the Risk of Infection by Infectious Aerosols in Large Indoor Spaces}, journal = {Aerosol and Air Quality Research}, month = {June}, year = {2022}, doi = {10.4209/aaqr.220117},, url = {https://aaqr.org/articles/aaqr-22-03-oa-0117} } |
Huang, M., Wang, Y., Bao, Y. and He, X., "Heat transport and temperature boundary-layer profiles in closed turbulent Rayleigh-Benard convection with slippery conducting surfaces", J. Fluid Mech., June 2022, Vol. 943(A2) |
Abstract: We report direct numerical simulations (DNS) of the Nusselt number Nu, the vertical profiles of mean temperature Theta(z) and temperature variance Omega(7) across the thermal boundary layer (BL) in closed turbulent Rayleigh-Bénard convection (RBC) with slippery conducting surfaces (z is the vertical distance from the bottom surface). The DNS study was conducted in three RBC samples: a three-dimensional cuboid with length L = H and width W = H/4 (H is the sample height), and two-dimensional rectangles with aspect ratios Gamma L/H = 1 and 10. The slip length b for top and bottom plates varied from 0 to infinity. The Rayleigh numbers Ra were in the range 10(6) <= Ra <= 10(10) and the Prandtl number Pr was fixed at 4.3. As b increases, the normalised Nu/Nu(0) (Nu(0) is the global heat transport for b = 0) from the three samples for different Ra and Gamma can be well described by the same function Nu/Nu(0) = N-0 tanh(b/lambda(0)) + 1, with N-0 = 0.8 +/- 0.03. Here lambda(0) L/(2Nu(0)) is the thermal boundary layer thickness for b = 0. Considering the BL fluctuations for Pr > 1, one can derive solutions of temperature profiles Theta(z) and Omega(z) near the thermal BL for b >= 0. When b = 0, the solutions are equivalent to those reported by Shishkina et al. (Phys. Rev. Lett., vol. 114, 2015, 114302) and Wang et al. (Phys. Rev. Fluids, vol. 1, 2016, 082301(R)), respectively, for no-slip plates. For b > 0, the derived solutions are in excellent agreement with our DNS data for slippery plates. |
BibTeX:
@article{2022b, author = {Huang, M. and Wang, Y. and Bao, Y. and He, X.}, title = {Heat transport and temperature boundary-layer profiles in closed turbulent Rayleigh-Benard convection with slippery conducting surfaces}, journal = {J. Fluid Mech.}, month = {June}, year = {2022}, volume = {943}, number = {A2}, doi = {10.1017/jfm.2022.391},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/heat-transport-and-temperature-boundarylayer-profiles-in-closed-turbulent-rayleighbenard-convection-with-slippery-conducting-surfaces/4943682F3C97286122C44F1A2518DF64} } |
Majumder, R., Zykov, V. and Bodenschatz, E., "From Disorder to Normal Rhythm: Traveling-Wave Control of Cardiac Arrhythmias", Phys. Rev. Applied, June 2022, Vol. 17, 064033 pp. |
Abstract: Lethal cardiac arrhythmias often involve the occurrence of spiral waves, whose control is essential for the treatment of the disease. While high-voltage shock-based control methods rely on ensuring an abrupt electrical synchronization of the heart, low-energy techniques mostly cause drift-induced termination of these waves. In particular, such a drift can be induced by a spatiotemporal modulation of domain excitability in optogenetically modified cardiac tissue. Here we demonstrate a low-energy optogenetics-based approach to suppress spiral waves via their transient chaotization and rapid drift. |
BibTeX:
@article{Majumder2022, author = {Majumder, R. and Zykov, V. and Bodenschatz, E.}, title = {From Disorder to Normal Rhythm: Traveling-Wave Control of Cardiac Arrhythmias}, journal = {Phys. Rev. Applied}, month = {June}, year = {2022}, volume = {17}, pages = {064033}, doi = {10.1103/PhysRevApplied.17.064033},, url = {https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.17.064033} } |
Detert, M., Chen, Y., Zandvliet, H. J. W. and Lohse, D., "Transition in the growth mode of plasmonic bubbles in binary liquids", Soft Matter, May 2022, Vol. 18, 4136 pp. |
Abstract: Multi-component fluids with phase transitions show a plethora of fascinating phenomena with rich physics. Here we report on a transition in the growth mode of plasmonic bubbles in binary liquids. By employing high-speed imaging we reveal that the transition is from slow evaporative to fast convective growth and accompanied by a sudden increase in radius. The transition occurs as the three-phase contact line reaches the spinodal temperature of the more volatile component leading to massive, selective evaporation. This creates a strong solutal Marangoni flow along the bubble which marks the beginning of convective growth. We support this interpretation by simulations. After the transition the bubble starts to oscillate in position and in shape. Though different in magnitude the frequencies of both oscillations follow the same power law image (file: d2sm00315e-t1.tif), which is characteristic of bubble shape oscillations, with the surface tension ó as the restoring force and the bubble's added mass as inertia. The transitions and the oscillations both induce a strong motion in the surrounding liquid, opening doors for various applications where local mixing is beneficial. |
BibTeX:
@article{Detert, author = {Detert, M. and Chen, Y. and Zandvliet, H. J. W. and Lohse, D.}, title = {Transition in the growth mode of plasmonic bubbles in binary liquids}, journal = {Soft Matter}, month = {May}, year = {2022}, volume = {18}, pages = {4136}, doi = {10.1039/d2sm00315e},, url = {https://pubs.rsc.org/en/content/articlehtml/2022/sm/d2sm00315e} } |
Gholami, A., Ahmad, R., Bae, A. J., Pumir, A. and Bodenschatz, E., "Waveform of free, hinged and clamped axonemes isolated from C. reinhardtii: influence of calcium", New J. Phys., May 2022, Vol. 24(053025) |
Abstract: The beating of cilia and flagella is essential to perform many important biological functions, including generating fluid flows on the cell surface or propulsion of micro-organisms. In this work, we analyze the motion of isolated and demembranated flagella from green algae Chlamydomonas reinhardtii, which act as ATP-driven micro-swimmers. The beating flagella of Chlamydomonas exhibit an asymmetric waveform that is known to involve the superposition of a static component, corresponding to a fixed, intrinsic curvature, and a dynamic wave component traveling from base-to-tip at the fundamental beat frequency, plus higher harmonics. Here, we analyse free, hinged and clamped axonemes using principal component analysis. The axonemal motion is described with a high degree of accuracy, taking into account only the first four dominant eigenmodes. Our analysis suggests that the wave motion can be alternatively described with Fourier modes, with a wavelength ë, larger than the length of the filament L (ë/L ≈ 1.3). Within this representation, we demonstrate that the main base-to-tip traveling wave component coexists with standing waves. Finally, we report the effect of calcium on the constituting wave components and find that the static mode is the most sensitive component to the calcium ion concentration. |
BibTeX:
@article{Gholami, author = {Gholami, A. and Ahmad, R. and Bae, A. J. and Pumir, A. and Bodenschatz, E.}, title = {Waveform of free, hinged and clamped axonemes isolated from C. reinhardtii: influence of calcium}, journal = {New J. Phys.}, month = {May}, year = {2022}, volume = {24}, number = {053025}, doi = {10.1088/1367-2630/ac688d},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ac688d} } |
Zykov, V. and Bodenschatz, E., "Two Domains of Meandering Spiral Waves in a Modified Barkley Model", Front. Appl. Math. Stat., May 2022, Vol. 8(903563) |
Abstract: The stability of rigidly rotating spiral waves is a very important topic in the study of nonlinear reaction-diffusion media. Computer experiments carried out with a slightly modified Barkley model showed that, in addition to one region of instability observed earlier in the original Barkley model, there is another one exhibiting completely different properties. The wave instability in the second region is not related to the Hopf bifurcation. Moreover, hysteresis effects are observed at the boundary of the region. This means that in the vicinity of this region of instability, direct integration of the model equations leads either to a rigidly rotating or meandering spiral, depending on the initial conditions. |
BibTeX:
@article{Zykov2022a, author = {Zykov, V. and Bodenschatz, E.}, title = {Two Domains of Meandering Spiral Waves in a Modified Barkley Model}, journal = {Front. Appl. Math. Stat.}, month = {May}, year = {2022}, volume = {8}, number = {903563}, doi = {10.3389/fams.2022.903563},, url = {https://www.frontiersin.org/articles/10.3389/fams.2022.903563/full?&utm_source=Email_to_authors_&utm_medium=Email&utm_content=T1_11.5e1_author&utm_campaign=Email_publication&field=&journalName=Frontiers_in_Applied_Mathematics_and_Statistics&id=903563} } |
Guido, I., "Spontaneously Beating Biomimetic Structures", Springer, April 2022, Vol. 2430, 205 pp. |
Abstract: The propulsion of motile cells such as sperms and the transport of fluids on cell surfaces rely on oscillatory bending of cellular appendages that can perform periodic oscillations. These structures are flagella and cilia. Their beating is driven by the interaction between microtubules and motor proteins and the mechanism regulating this is still a puzzle. One approach to address this issue is the assembling of synthetic minimal systems by using natural building blocks, e.g., microtubules and kinesin motors, which undergo persistent oscillation in the presence of ATP. An example of an autonomous molecular system is reported in this chapter. It dynamically self-organizes through its elasticity and the interaction with the environment represented by the active forces exerted by motor proteins. The resulting motion resembles the beating of sperm flagella. Assembling such minimal systems able to mimic the behavior of complex biological structures might help to unveil basic mechanisms underlying the beating of natural cilia and flagella. |
BibTeX:
@article{Guido, author = {Guido, I.}, title = {Spontaneously Beating Biomimetic Structures}, journal = {Springer}, month = {April}, year = {2022}, volume = {2430}, pages = {205}, doi = {10.1007/978-1-0716-1983-4_13},, url = {https://link.springer.com/protocol/10.1007/978-1-0716-1983-4_13} } |
Güttler, J. M., "Experimental Investigation of Micrometric Droplets and Artificial Particles", April 2022 |
Abstract: Clouds and atmospheric particles (e.g. ice crystals, smoke, dust or pollen) heavily influence Earth's energy budget and contribute to the largest uncertainties in climate prediction models. Their treatment involves a huge variety of scales, from sub-micrometer particles that act as cloud condensation nuclei (CCN) to turbulent mixing and entrainment processes, up to coherent atmospheric flows that can span tens to thousands of kilometers. This causes challenges for both simulations and theory as most climate models cannot resolve scale differences on that order. Combining simulations and theory with in situ and laboratory work, however, can enhance our understanding significantly. Different approaches exist, ranging from satellite observations to airborne, ship-based and field-site studies to controlled experiments. In this work, micrometer-sized droplets and particles are created and studied in a laboratory setting. For this, several apparatus and software were designed and tested: 1) A droplet generator able to produce droplets with diameters smaller 100 micron, 2) A settling chamber to study ellipsoidal particles within the intermediate regime 3) Single- and multi-camera tracking codes to determine particle trajectories and orientations for non-spherical particles. Together, these methods compose a first step in determining particle drag, terminal velocities and particle relaxation times for so far unexplored particle shapes and density ratios. |
BibTeX:
@phdthesis{Guettler, author = {Güttler, J. M.}, title = {Experimental Investigation of Micrometric Droplets and Artificial Particles}, month = {April}, year = {2022}, doi = {10.53846/goediss-9205},, url = {https://ediss.uni-goettingen.de/handle/11858/14017} } |
Reiter, P., Zhang, X. and Shishkina, O., "Flow states and heat transport in Rayleigh-Bénard convection with different sidewall boundary conditions", J. Fluid Mech., April 2022, Vol. 936(A32), 1 pp. |
Abstract: This work addresses the effects of different thermal sidewall boundary conditions on the formation of flow states and heat transport in two- and three-dimensional Rayleigh–Bénard convection (RBC) by means of direct numerical simulations and steady-state analysis for Rayleigh numbers Ra up to 4x1010 and Prandtl numbers Pr=0.1,1 and 10. We show that a linear temperature profile imposed at the conductive sidewall leads to a premature collapse of the single-roll state, whereas a sidewall maintained at a constant temperature enhances its stability. The collapse is caused by accelerated growth of the corner rolls with two distinct growth rate regimes determined by diffusion or convection for small or large Ra, respectively. Above the collapse of the single-roll state, we find the emergence of a double-roll state in two-dimensional RBC and a double-toroidal state in three-dimensional cylindrical RBC. These states are most prominent in RBC with conductive sidewalls. The different states are reflected in the global heat transport, so that the different thermal conditions at the sidewall lead to significant differences in the Nusselt number for small to moderate Ra. However, for larger Ra, the heat transport and flow dynamics become increasingly alike for different sidewalls and are almost indistinguishable for Ra>109. This suggests that the influence of imperfectly insulated sidewalls in RBC experiments is insignificant at very high Ra - provided that the mean sidewall temperature is controlled. |
BibTeX:
@article{Reiter2022, author = {Reiter, P. and Zhang, X. and Shishkina, O.}, title = {Flow states and heat transport in Rayleigh-Bénard convection with different sidewall boundary conditions}, journal = {J. Fluid Mech.}, month = {April}, year = {2022}, volume = {936}, number = {A32}, pages = {1}, doi = {10.1017/jfm.2022.56},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/flow-states-and-heat-transport-in-rayleighbenard-convection-with-different-sidewall-boundary-conditions/ADE8D211CF7E439AD2660ECD5CD633C8} } |
Buaria, D. and Pumir, A., "Vorticity-Strain Rate Dynamics and the Smallest Scales of Turbulence", Phys. Rev. Lett., March 2022, Vol. 128(9), 094501 pp. |
Abstract: Building upon the intrinsic properties of Navier-Stokes dynamics, namely the prevalence of intense vortical structures and the interrelationship between vorticity and strain rate, we propose a simple framework to quantify the extreme events and the smallest scales of turbulence. We demonstrate that our approach is in excellent agreement with the best available data from direct numerical simulations of isotropic turbulence, with Taylor-scale Reynolds numbers up to 1300. We additionally highlight a shortcoming of prevailing intermittency models due to their disconnection from the observed correlation between vorticity and strain. Our work accentuates the importance of this correlation as a crucial step in developing an accurate understanding of intermittency in turbulence. |
BibTeX:
@article{Buariaa, author = {Buaria, D. and Pumir, A.}, title = {Vorticity-Strain Rate Dynamics and the Smallest Scales of Turbulence}, journal = {Phys. Rev. Lett.}, month = {March}, year = {2022}, volume = {128}, number = {9}, pages = {094501}, doi = {10.1103/PhysRevLett.128.094501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.094501} } |
Wedi, M., Moturi, V. M., Funfschilling, D. and Weiss, S., "Experimental evidence for the boundary zonal flow in rotating Rayleigh-Bénard convection", J. Fluid Mech., March 2022, Vol. 939(A14), 1 pp. |
Abstract: We report on the presence of the boundary zonal flow in rotating Rayleigh-Bénard convection evidenced by two-dimensional particle image velocimetry. Experiments were conducted in a cylindrical cell of aspect ratio Ã=D/H=1 between its diameter (D) and height (H). As the working fluid, we used various mixtures of water and glycerol, leading to Prandtl numbers in the range 6.6 <= Pr <= 76. The horizontal velocity components were measured at a horizontal cross-section at half height. The Rayleigh numbers were in the range 108 <= Ra <= 3x109. The effect of rotation is quantified by the Ekman number, which was in the range 1.5x10-5 <= Ek <= 1.2x10-3 in our experiment. With our results we show the first direct measurements of the boundary zonal flow (BZF) that develops near the sidewall and was discovered recently in numerical simulations as well as in sparse and localized temperature measurements. We analyse the thickness ä0 of the BZF as well as its maximal velocity as a function of Pr, Ra and Ek, and compare these results with previous results from direct numerical simulations. |
BibTeX:
@article{Wedi2022, author = {Wedi, M. and Moturi, V. M. and Funfschilling, D. and Weiss, S.}, title = {Experimental evidence for the boundary zonal flow in rotating Rayleigh-Bénard convection}, journal = {J. Fluid Mech.}, month = {March}, year = {2022}, volume = {939}, number = {A14}, pages = {1}, doi = {10.1017/jfm.2022.195},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/experimental-evidence-for-the-boundary-zonal-flow-in-rotating-rayleighbenard-convection/6CC0CCA5412E2D34AC772BE066C15416} } |
Ahlers, G., Bodenschatz, E., Hartmann, R., He, X., Lohse, D., Reiter, P., Stevens, R. J. A. M., Verzicco, R., Wedi, M., Weiss, S., Zhang, X., Zwirner, L. and Shishkina, O., "Aspect Ratio Dependence of Heat Transfer in a Cylindrical Rayleigh-Bénard Cell", Phys. Rev. Lett., February 2022, Vol. 128(8), 084501 pp. |
Abstract: While the heat transfer and the flow dynamics in a cylindrical Rayleigh-Benard (RB) cell are rather independent of the aspect ratio Gamma (diameter/height) for large Gamma, a small-Gamma cell considerably stabilizes the flow and thus affects the heat transfer. Here, we first theoretically and numerically show that the critical Rayleigh number for the onset of convection at given Gamma follows Ra-c,Ra-Gamma similar to Ra-c,Ra-infinity(1 + C Gamma(-2))(2), with C less than or similar to 1.49 for Oberbeck-Boussinesq (OB) conditions. We then show that, in a broad aspect ratio range (1/32) <= Gamma <= 32, the rescaling Ra -> Ra-l Ra[Gamma(2)/(C+Gamma(2))](3/2) collapses various OB numerical and almost-OB experimental heat transport data Nu(Ra,Gamma). Our findings predict the Gamma dependence of the onset of the ultimate regime Ra-u,Ra-Gamma similar to [Gamma(2)/(C+Gamma(2))](-3/2) in the OB case. This prediction is consistent with almost-OB experimental results (which only exist for Gamma = 1, 1/2, and 1/3) for the transition in OB RB convection and explains why, in small-Gamma cells, much larger Ra (namely, by a factor Gamma(-3)) must be achieved to observe the ultimate regime. |
BibTeX:
@article{Ahlers, author = {Ahlers, G. and Bodenschatz, E. and Hartmann, R. and He, X. and Lohse, D. and Reiter, P. and Stevens, R. J. A. M. and Verzicco, R. and Wedi, M. and Weiss, S. and Zhang, X. and Zwirner, L. and Shishkina, O.}, title = {Aspect Ratio Dependence of Heat Transfer in a Cylindrical Rayleigh-Bénard Cell}, journal = {Phys. Rev. Lett.}, month = {February}, year = {2022}, volume = {128}, number = {8}, pages = {084501}, doi = {10.1103/PhysRevLett.128.084501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.128.084501} } |
Cabrera, F., Sheikh, M. Z., Mehlig, B., Plihon, N., Bourgoin, M., Pumir, A. and Naso, A., "Experimental validation of fluid inertia models for a cylinder settling in a quiescent flow", Phys. Rev. Fluids, February 2022, Vol. 7(2), 024301-1 pp. |
Abstract: The precise description of the motion of anisotropic particles in a flow rests on the understanding of the force and torque acting on them. Here, we study experimentally small, very elongated particles settling in a fluid at small Reynolds number. In our experiments, we can, to a very good approximation, relate the rate of rotation of cylindrical tungsten rods, of aspect ratios = 8 and = 16, settling in pure glycerol, to the torque they are experiencing. This allows us to compare the measured torque with expressions obtained either in the slender-rod limit or in the case of spheroids. Both theories predict a simple angle dependence for the torque, which is found to capture very well the experimental results. The slender-rod theory overestimates the results for the two aspect ratios considered, while the expression obtained for a spheroid provides a better approximation for = 16. Comparing our results with those of previous experiments provides further insight on the conditions of validity of the slender-rod theory. The translational dynamics is shown to be in qualitative agreement with the slender-rod and spheroid models, the former one being found to represent better the experimental data. |
BibTeX:
@article{Cabrera2022, author = {Cabrera, F. and Sheikh, M. Z. and Mehlig, B. and Plihon, N. and Bourgoin, M. and Pumir, A. and Naso, A.}, title = {Experimental validation of fluid inertia models for a cylinder settling in a quiescent flow}, journal = {Phys. Rev. Fluids}, month = {February}, year = {2022}, volume = {7}, number = {2}, pages = {024301-1}, doi = {10.1103/PhysRevFluids.7.024301},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.7.024301} } |
Kim, J. J., Kim, H., Kim, J., Lee, I., Kim, H. and Lee, S. J., "Effect of the flow structure on the indoor deposition of particulate matter", J Vis, February 2022 |
Abstract: Indoor air quality, especially in terms of particulate matter (PM), is a critical public health concern. Although various methods for removing indoor PM have been suggested, the effects of various influential factors on PM deposition have not been clearly understood. Here, the effect of the flow structure inside a test chamber on PM deposition was quantitatively investigated using flow visualization techniques. To elucidate the flow parameters that influence the PM deposition, the efficiency of PM removal and deposition constant were examined for different flow directions, flow velocities, and distances between the fan and the surface of the test chamber. The spatial distributions of the mean velocity and turbulence intensity inside the test chamber were obtained experimentally using a particle image velocimetry technique to understand the mechanism associated with PM deposition. The overall mean velocity, recirculating flow region, and turbulent intensity in the near-wall regions may partially explain the difference in the PM deposition under various flow conditions. |
BibTeX:
@article{2022, author = {Kim, J. J. and Kim, H.J. and Kim, J. and Lee, I. and Kim, H. and Lee, S. J.}, title = {Effect of the flow structure on the indoor deposition of particulate matter}, journal = {J Vis}, month = {February}, year = {2022}, doi = {10.1007/s12650-021-00825-4},, url = {https://link.springer.com/article/10.1007/s12650-021-00825-4} } |
Mohammadi, M., Nowak, J. L., Bertens, G., Molacek, J., Kumala, W. and Malinowski, S. P., "Cloud microphysical measurements at a mountain observatory: comparison between shadowgraph imaging and phase Doppler interferometry", Atmos. Meas. Tech., February 2022, Vol. 15(4), 965 pp. |
Abstract: The microphysical properties of cloud droplets, such as droplet size distribution and droplet number concentration, were studied. A series of field experiments was performed in the summer of 2019 at the Umweltforschungsstation Schneefernerhaus (UFS), an environmental research station located just below the peak of the Zugspitze mountain in the German Alps. A VisiSize D30 manufactured by Oxford Laser Ltd., which is a shadowgraph imaging instrument, was utilized for the first time to measure the size and velocity of cloud droplets during this campaign. Furthermore, a phase Doppler interferometer (PDI) device, manufactured by Artium Tech. Inc., was simultaneously measuring cloud droplets. After applying modifications to the built-in software algorithms, the results from the two instruments show reasonable agreement regarding droplet sizing and velocimetry for droplet diameters larger than 13 mu m. Moreover, discrepancies were observed concerning the droplet number concentration results, especially with smaller droplet sizes. Further investigation by applying appropriate filters to the data allowed the attribution of the discrepancies to two phenomena: the different optical performance of the sensors with regard to small droplets and high turbulent velocity fluctuations relative to the mean flow that result in an uncertain estimate of the volume of air passing through the PDI probe volume. |
BibTeX:
@article{2022a, author = {Mohammadi, M. and Nowak, J. L. and Bertens, G. and Molacek, J. and Kumala, W. and Malinowski, S. P.}, title = {Cloud microphysical measurements at a mountain observatory: comparison between shadowgraph imaging and phase Doppler interferometry}, journal = {Atmos. Meas. Tech.}, month = {February}, year = {2022}, volume = {15}, number = {4}, pages = {965}, doi = {10.5194/amt-15-965-2022},, url = {https://amt.copernicus.org/articles/15/965/2022/amt-15-965-2022.html} } |
Buaria, D., Pumir, A. and Bodenschatz, E., "Generation of intense dissipation in high Reynolds number turbulence", Phil. Trans. R. Soc. A, January 2022, Vol. 380(2218) |
Abstract: Intense fluctuations of energy dissipation rate in turbulent flows result from the self-amplification of strain rate via a quadratic nonlinearity, with contributions from vorticity (via the vortex stretching mechanism) and pressure-Hessian-which are analysed here using direct numerical simulations of isotropic turbulence on up to 12 288(3) grid points, and Taylor-scale Reynolds numbers in the range 140-1300. We extract the statistics involved in amplification of strain and condition them on the magnitude of strain. We find that strain is self-amplified by the quadratic nonlinearity, and depleted via vortex stretching, whereas pressure-Hessian acts to redistribute strain fluctuations towards the mean-field and hence depletes intense strain. Analysing the intense fluctuations of strain in terms of its eigenvalues reveals that the net amplification is solely produced by the third eigenvalue, resulting in strong compressive action. By contrast, the self-amplification acts to deplete the other two eigenvalues, whereas vortex stretching acts to amplify them, with both effects cancelling each other almost perfectly. The effect of the pressure-Hessian for each eigenvalue is qualitatively similar to that of vortex stretching, but significantly weaker in magnitude. Our results conform with the familiar notion that intense strain is organized in sheet-like structures, which are in the vicinity of, hut never overlap with tube-like regions of intense vorticity due to fundamental differences in their amplifying mechanisms. |
BibTeX:
@article{Buaria2022, author = {Buaria, D. and Pumir, A. and Bodenschatz, E.}, title = {Generation of intense dissipation in high Reynolds number turbulence}, journal = {Phil. Trans. R. Soc. A}, month = {January}, year = {2022}, volume = {380}, number = {2218}, doi = {10.1098/rsta.2021.0088},, url = {https://royalsocietypublishing.org/doi/full/10.1098/rsta.2021.0088} } |
Collesano, L., Guido, I., Golestanian, R. and Vilfan, A., "Active beating modes of two clamped filaments driven by molecular motors", J. R. Soc. Interface, January 2022, Vol. 19(186), 20210693 pp. |
Abstract: Biological cilia pump the surrounding fluid by asymmetric beating that is driven by dynein motors between sliding microtubule doublets. The complexity of biological cilia raises the question about minimal systems that can re-create similar patterns of motion. One such system consists of a pair of microtubules that are clamped at the proximal end. They interact through dynein motors that cover one of the filaments and pull against the other one. Here, we study theoretically the static shapes and the active dynamics of such a system. Using the theory of elastica, we analyse the shapes of two filaments of different lengths with clamped ends. Starting from equal lengths, we observe a transition similar to Euler buckling leading to a planar shape. When further increasing the length ratio, the system assumes a non-planar shape with spontaneously broken chiral symmetry after a secondary bifurcation and then transitions to planar again. The predicted curves agree with experimentally observed shapes of microtubule pairs. The dynamical system can have a stable fixed point, with either bent or straight filaments, or limit cycle oscillations. The latter match many properties of ciliary motility, demonstrating that a two-filament system can serve as a minimal actively beating model. |
BibTeX:
@article{Collesano2022, author = {Collesano, L. and Guido, I. and Golestanian, R. and Vilfan, A.}, title = {Active beating modes of two clamped filaments driven by molecular motors}, journal = {J. R. Soc. Interface}, month = {January}, year = {2022}, volume = {19}, number = {186}, pages = {20210693}, doi = {10.1098/rsif.2021.0693},, url = {https://royalsocietypublishing.org/doi/full/10.1098/rsif.2021.0693} } |
Ecke, R. E., Zhang, X. and Shishkina, O., "Connecting wall modes and boundary zonal flows in rotating Rayleigh-Bénard convection", Phys. Rev. Fluids, January 2022, Vol. 7(1), L011501 pp. |
Abstract: Using direct numerical simulations, we study rotating Rayleigh-Bénard convection in a cylindrical cell with aspect ratio Gamma = 1/2, for Prandtl number 0.8, Ekman number 10(-6), and Rayleigh numbers from the onset of wall modes to the geostrophic regime, an extremely important one in geophysical and astrophysical contexts. We connect linear wall-mode states that occur prior to the onset of bulk convection with the boundary zonal flow that coexists with turbulent bulk convection in the geostrophic regime through the continuity of length and timescales and of convective heat transport. We quantitatively collapse drift frequency, boundary length, and heat transport data from numerous sources over many orders of magnitude in Rayleigh and Ekman numbers. Elucidating the heat transport contributions of wall modes and of the boundary zonal flow are critical for characterizing the properties of the geostrophic regime of rotating convection in finite, physical containers and is crucial for connecting the geostrophic regime of laboratory convection with geophysical and astrophysical systems. |
BibTeX:
@article{Ecke2022, author = {Ecke, R. E. and Zhang, X. and Shishkina, O.}, title = {Connecting wall modes and boundary zonal flows in rotating Rayleigh-Bénard convection}, journal = {Phys. Rev. Fluids}, month = {January}, year = {2022}, volume = {7}, number = {1}, pages = {L011501}, doi = {10.1103/PhysRevFluids.7.L011501},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.7.L011501} } |
Li, A., Luo, Y.-X., Liu, Y., Xu, Y.-Q., Tian, F.-B. and Wang, Y., "Hydrodynamic behaviors of self-propelled sperms in confined spaces", Engineering Applications of Computational Fluid Mechanics, January 2022, Vol. 16(1), 141 pp. |
Abstract: The hydrodynamic behaviors of sperms in confined spaces (e.g. Poiseuille flow and quiescent flow between two parallel walls) are studied with a two-dimensional self-propelled sperm model based on the immersed boundary-lattice Boltzmann method (IB-LBM). For single-sperm swimming in Poiseuille flow, four typical swimming patterns, including wall-adhesion, focusing, tumbling and oscillating, are observed. The occurrence conditions including flow strength, inter-wall distance, initialization of sperm are studied in detail for the four patterns. For multiple-sperm swimming in quiescent flow between two parallel walls, it is observed that the sperm population tends to swim nearby the walls, leading to wall accumulation. To explore the hydrodynamic behaviors of the sperm population in Poiseuille flows, the effects of flow velocities on the sperm rheotaxis and the wall accumulation are investigated in detail. It is found that an appropriate flow velocity is essential to guide the swimming direction, as well as the wall accumulation. In addition, collision and adsorption between adjacent sperms may facilitate wall accumulation. Finally, we study the propulsion rate of different combination modes of sperms. We found that the wedge-shaped mode leads to the optimal propulsive speed, and reducing the combining distance can increase the propulsive speed. |
BibTeX:
@article{Li2022, author = {Li, A. and Luo, Y.-X. and Liu, Y. and Xu, Y.-Q. and Tian, F.-B. and Wang, Y.}, title = {Hydrodynamic behaviors of self-propelled sperms in confined spaces}, journal = {Engineering Applications of Computational Fluid Mechanics}, month = {January}, year = {2022}, volume = {16}, number = {1}, pages = {141}, doi = {10.1080/19942060.2021.2008500},, url = {https://www.tandfonline.com/doi/full/10.1080/19942060.2021.2008500} } |
Yang, R., Zhang, X., Reiter, P., Lohse, D., Shishkina, O. and Linkmann, M., "Data-driven identification of the spatiotemporal structure of turbulent flows by streaming dynamic mode decomposition", GAMM, January 2022, e202200003 pp. |
Abstract: Streaming Dynamic Mode Decomposition (sDMD) is a low-storage version of dynamic mode decomposition (DMD), a data-driven method to extract spatiotemporal flow patterns. Streaming DMD avoids storing the entire data sequence in memory by approximating the dynamic modes through incremental updates with new available data. In this paper, we use sDMD to identify and extract dominant spatiotemporal structures of different turbulent flows, requiring the analysis of large datasets. First, the efficiency and accuracy of sDMD are compared to the classical DMD, using a publicly available test dataset that consists of velocity field snapshots obtained by direct numerical simulation of a wake flow behind a cylinder. Streaming DMD not only reliably reproduces the most important dynamical features of the flow; our calculations also highlight its advantage in terms of the required computational resources. We subsequently use sDMD to analyse three different turbulent flows that all show some degree of large-scale coherence: rapidly rotating Rayleigh-Bénard convection, horizontal convection and the asymptotic suction boundary layer (ASBL). Structures of different frequencies and spatial extent can be clearly separated, and the prominent features of the dynamics are captured with just a few dynamic modes. In summary, we demonstrate that sDMD is a powerful tool for the identification of spatiotemporal structures in a wide range of turbulent flows. |
BibTeX:
@article{Yang, author = {Yang, R. and Zhang, X. and Reiter, P. and Lohse, D. and Shishkina, O. and Linkmann, M.}, title = {Data-driven identification of the spatiotemporal structure of turbulent flows by streaming dynamic mode decomposition}, journal = {GAMM}, month = {January}, year = {2022}, pages = {e202200003}, doi = {10.1002/gamm.202200003},, url = {https://onlinelibrary.wiley.com/doi/10.1002/gamm.202200003} } |
Zykov, V. and Bodenschatz, E., "Spiral waves within a bistability parameter region of an excitable Medium", New J. Phys., January 2022, Vol. 24(013036) |
Abstract: Spiral waves are a well-known and intensively studied dynamic phenomenon in excitable media of various types. Most studies have considered an excitable medium with a single stable resting state. However, spiral waves can be maintained in an excitable medium with bistability. Our calculations, performed using the widely used Barkley model, clearly show that spiral waves in the bistability region exhibit unique properties. For example, a spiral wave can either rotate around a core that is in an unexcited state, or the tip of the spiral wave describes a circular trajectory located inside an excited region. The boundaries of the parameter regions with positive and 'negative' cores have been defined numerically and analytically evaluated. It is also shown that the creation of a positive or 'negative' core may depend on the initial conditions, which leads to hysteresis of spiral waves. In addition, the influence of gradient flow on the dynamics of the spiral wave, which is related to the tension of the scroll wave filaments in a three-dimensional medium, is studied. |
BibTeX:
@article{Zykov2022, author = {Zykov, V. and Bodenschatz, E.}, title = {Spiral waves within a bistability parameter region of an excitable Medium}, journal = {New J. Phys.}, month = {January}, year = {2022}, volume = {24}, number = {013036}, doi = {10.1088/1367-2630/ac47ca},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ac47ca} } |
Bagheri, G., Schlenczek, O., Turco, L., Thiede, B., Stieger, K., Kosub, J.-M., Pöhlker, M. L., Pöhlker, C., Molacek, J., Scheithauer, S. and Bodenschatz, E., "Exhaled particles from nanometre to millimetre and their origin in the human respiratory tract", (submitted), 2021 |
BibTeX:
@article{Bagheri2021a, author = {Bagheri, G. and Schlenczek, O. and Turco, L. and Thiede, B. and Stieger, K. and Kosub, J.-M. and Pöhlker, M. L. and Pöhlker, C. and Molacek, J. and Scheithauer, S. and Bodenschatz, E.}, title = {Exhaled particles from nanometre to millimetre and their origin in the human respiratory tract}, journal = {(submitted)}, year = {2021},, url = {https://www.medrxiv.org/content/10.1101/2021.10.01.21264333v1} } |
Hejazi, B., Schlenczek, O., Thiede, B., Bagheri, G. and Bodenschatz, E., "Aerosol transport measurements and assessment of riskfrom infectious aerosols: a case study of two Germancash-and-carry hardware/DIY stores", (submitted), 2021 |
Abstract: We report experimental results on aerosol dispersion in two large German cash-and-carry hardware/DIY stores to better understand the factors contributing to disease transmission by infectious human aerosols in large indoor environments. We examined the transport of aerosols similar in size to human respiratory aerosols (0.3-10 ìm) in representative locations, such as high-traffic areas and restrooms. In restrooms, the observed decay of aerosol concentrations was consistent with well-mixed air exchange. In all other locations, fast decay times were measured, which were found to be independent of aerosol size (typically a few minutes). From this, we conclude that in the main retail areas, including at checkouts, rapid turbulent mixing and advection is the dominant feature in aerosol dynamics. With this, the upper bound of risk for airborne disease transmission to a susceptible is determined by direct exposure to the exhalation cloud of an infectious. For the example of the SARS-CoV-2 virus, we find when speaking without a face mask and aerosol sizes up to an exhalation (wet) diameter of 50 ìm, a distance of 1.5 m to be unsafe. However, at the smallest distance between an infectious and a susceptible, while wearing typical surgical masks and for all sizes of exhaled aerosol, the upper bound of infection risk is only -5% and decreases further by a factor of 100 (-0.05%) for typical FFP2 masks for a duration of 20 minutes. This upper bound is very conservative and we expect the actual risk for typical encounters to be much lower. The risks found here are comparable to what might be expected in calm outdoor weather. |
BibTeX:
@article{Hejazi2021, author = {Hejazi, B. and Schlenczek, O. and Thiede, B. and Bagheri, G. and Bodenschatz, E.}, title = {Aerosol transport measurements and assessment of riskfrom infectious aerosols: a case study of two Germancash-and-carry hardware/DIY stores}, journal = {(submitted)}, year = {2021},, url = {https://arxiv.org/abs/2105.10357} } |
Pöhlker, M. L., Krüger, O., Förster, J.-D., Elbert, W., Fröhlich-Nowoisky, J., Pöschl, U., Pöhlker, C., Bagheri, G., Bodenschatz, E., Huffman, J. A., Scheithauer, S. and Mikhailov, E., "Respiratory aerosols and droplets in the transmission of infectious diseases", (submitted), 2021 |
Abstract: Knowing the physicochemical properties of exhaled droplets and aerosol particles is a prerequisite for a detailed mechanistic understanding and effective prevention of the airborne transmission of infectious human diseases. This article provides a critical review and synthesis of scientific knowledge on the number concentrations, size distributions, composition, mixing state, and related properties of respiratory particles emitted upon breathing, speaking, singing, coughing, and sneezing. We derive and present a parametrization of respiratory particle size distributions based on five lognormal modes related to different origins in the respiratory tract, which can be used to trace and localize the sources infectious particles. This approach may support the medical treatment as well as the risk assessment for aerosol and droplet transmission of infectious diseases. It was applied to analyze which respiratory activities may drive the spread of specific pathogens, such as Mycobacterium tuberculosis, influenza viruses, and SARS-CoV-2 viruses. The results confirm the high relevance of vocalization for the transmission of SARS-CoV-2 as well as the usefulness of face masks, including community, medical, and N95/FFP2 masks, as preventive measures against COVID-19 and other airborne infectious diseases. |
BibTeX:
@article{2021, author = {Pöhlker, M. L. and Krüger, O. and Förster, J.-D. and Elbert, W. and Fröhlich-Nowoisky, J. and Pöschl, U. and Pöhlker, C. and Bagheri, G. and Bodenschatz, E. and Huffman, J. A. and Scheithauer, S. and Mikhailov, E.}, title = {Respiratory aerosols and droplets in the transmission of infectious diseases}, journal = {(submitted)}, year = {2021},, url = {https://arxiv.org/abs/2103.01188} } |
Bagheri, G., Thiede, B., Hejazi, B., Schlenczek, O. and Bodenschatz, E., "An upper bound on one-to-one exposure to infectious human respiratory particles", PNAS, December 2021, Vol. 118(49), e2110117118 pp. |
Abstract: There is ample evidence that masking and social distancing are effective in reducing severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission. However, due to the complexity of airborne disease transmission, it is difficult to quantify their effectiveness, especially in the case of one-to-one exposure. Here, we introduce the concept of an upper bound for one-to-one exposure to infectious human respiratory particles and apply it to SARS-CoV-2. To calculate exposure and infection risk, we use a comprehensive database on respiratory particle size distribution; exhalation flow physics; leakage from face masks of various types and fits measured on human subjects; consideration of ambient particle shrinkage due to evaporation; and rehydration, inhalability, and deposition in the susceptible airways. We find, for a typical SARS-CoV-2 viral load and infectious dose, that social distancing alone, even at 3.0 m between two speaking individuals, leads to an upper bound of 90% for risk of infection after a few minutes. If only the susceptible wears a face mask with infectious speaking at a distance of 1.5 m, the upper bound drops very significantly; that is, with a surgical mask, the upper bound reaches 90% after 30 min, and, with an FFP2 mask, it remains at about 20% even after 1 h. When both wear a surgical mask, while the infectious is speaking, the very conservative upper bound remains below 30% after 1 h, but, when both wear a well-fitting FFP2 mask, it is 0.4%. We conclude that wearing appropriate masks in the community provides excellent protection for others and oneself, and makes social distancing less important. |
BibTeX:
@article{Bagheri2021, author = {Bagheri, G. and Thiede, B. and Hejazi, B. and Schlenczek, O. and Bodenschatz, E.}, title = {An upper bound on one-to-one exposure to infectious human respiratory particles}, journal = {PNAS}, month = {December}, year = {2021}, volume = {118}, number = {49}, pages = {e2110117118}, doi = {10.1073/pnas.2110117118},, url = {https://www.pnas.org/content/118/49/e2110117118}, altmetric = {https://www.altmetric.com/details/117997034} } |
Bertens, G., Bagheri, G., Xu, H., Bodenschatz, E. and Molacek, J., "In situ cloud particle tracking experiment", Rev. Sci. Instrum., December 2021, Vol. 92(12), 125105 pp. |
Abstract: The collision-coalescence process of inertial particles in turbulence is held responsible for the quick growth of cloud droplets from -15 to -50 µm in diameter, but it is not well understood. Turbulence has two effects on cloud droplets: (1) it brings them closer together, preferentially concentrating them in certain parts of the flow, and (2) it sporadically creates high accelerations, causing droplets to detach from the underlying flow. These turbulence-cloud droplet interactions are difficult to study numerically or in the laboratory due to the large range of scales involved in atmospheric turbulence, so in situ measurements are needed. Here, we present a Lagrangian particle tracking (LPT) experimental setup situated close to the summit of Mt. Zugspitze at an altitude of 2650 m above the sea level on top of the environmental research station Schneefernerhaus. Clouds naturally occur at this location about a quarter of the time. The LPT experiment probes a volume of -40 x 20 x 12 mm3, has a spatial resolution of 5 µm and a temporal resolution of 0.1 ms, and measures accelerations to within 0.1 m s-2. Furthermore, the experiment can slide over a set of rails, driven by a linear motor, to compensate for the mean wind. It can slide up to 7.5 m s-1. By doing so, the average residence time of the particles in the measurement volume increases. The mean wind compensation allows us to study various dynamical quantities, such as the velocity autocorrelation, or the dynamics of clustering. Moreover, it is beneficial for particle tracking, in general, since longer particle tracks allow us to apply better filtering to the tracks and thus increase accuracy. We present the radial distribution function, which quantifies clustering, the longitudinal relative velocity distribution, and the Lagrangian velocity autocorrelation, all computed from cloud droplet trajectories.
I. INTRODUCTION |
BibTeX:
@article{Bertensa, author = {Bertens, G. and Bagheri, G. and Xu, H. and Bodenschatz, E. and Molacek, J.}, title = {In situ cloud particle tracking experiment}, journal = {Rev. Sci. Instrum.}, month = {December}, year = {2021}, volume = {92}, number = {12}, pages = {125105}, doi = {10.1063/5.0065806},, url = {https://aip.scitation.org/doi/10.1063/5.0065806} } |
Zwirner, L., Emran, M. S., Schindler, F., Singh, S., Eckert, S., Vogt, T. and Shishkina, O., "Dynamics and length scales in vertical convection of liquid metals", J. Fluid Mech., December 2021, Vol. 932, A9 pp. |
Abstract: Using complementary experiments and direct numerical simulations, we study turbulent thermal convection of a liquid metal (Prandtl number Pr ≈ 0.03) in a box-shaped container, where two opposite square sidewalls are heated/cooled. The global response characteristics like the Nusselt number Nu and the Reynolds number Re collapse if the side height L is used as the length scale rather than the distance H between heated and cooled vertical plates. These results are obtained for various Rayleigh numbers 5x10^3 RaH 10^8 (based on H) and the aspect ratios L/H=1,2,3 and 5. Furthermore, we present a novel method to extract the wind-based Reynolds number, which works particularly well with the experimental Doppler-velocimetry measurements along vertical lines, regardless of their horizontal positions. The extraction method is based on the two-dimensional autocorrelation of the time-space data of the vertical velocity. |
BibTeX:
@article{Zwirner, author = {Zwirner, L. and Emran, M. S. and Schindler, F. and Singh, S. and Eckert, S. and Vogt, T. and Shishkina, O.}, title = {Dynamics and length scales in vertical convection of liquid metals}, journal = {J. Fluid Mech.}, month = {December}, year = {2021}, volume = {932}, pages = {A9}, doi = {10.1017/jfm.2021.977},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/dynamics-and-length-scales-in-vertical-convection-of-liquid-metals/28BB5EDD17943194B74618617B4F31CC} } |
Bertens, G., "Experimental investigation of cloud droplet dynamics at the research station Schneefernerhaus", November 2021 |
Abstract: The collision–coalescence of droplets in turbulence is responsible for the fast growth of cloud droplets from 15 to 40 ìm in radius, but how exactly it causes this quick growth is not understood. The growth of cloud droplets through collision–coalescence is governed by two quantities: the radial distribution function (RDF), which is a measure for the degree of clustering the droplets exhibit, and the radial relative velocity (RRV), which is a measure for the velocity difference between nearby droplets. In this thesis an in-situ experiment is described, that is designed to simultaneously measure all aspects relevant to turbulent collision-coalescence of cloud droplets: droplet motions, droplet sizes, and properties of the turbulent carrier flow. The experiment is located in the German Alps, on top of the environmental research station Schneefernerhaus, at an altitude of 2650 m where clouds naturally occur. Droplet motions are measured using a particle tracking setup; turbulence statistics are measured with a sonic anemometer that is mounted close by. Droplet sizes are measured using a novel technique that relies only on the droplet intensities as recorded by the particle tracking experiment. A complete derivation of the technique based on Lorentz-Mie scattering theory is given. Droplet sizes measured with this approach are compared to those obtained with a holographic instrument. The experiment is used to measure droplet rms accelerations and the radial distribution function conditioned on (pairs of) Stokes numbers. Both qualitatively agree with literature values, but further research is needed to see why there is no quantitative agreement. |
BibTeX:
@phdthesis{Bertens, author = {Bertens, G.}, title = {Experimental investigation of cloud droplet dynamics at the research station Schneefernerhaus}, month = {November}, year = {2021},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0008-598E-5} } |
Buaria, D. and Pumir, A., "Nonlocal amplification of intense vorticity in turbulent flows", Phys. Rev. Research, November 2021, Vol. 3(4), L042020 pp. |
Abstract: The nonlinear and nonlocal coupling of vorticity and strain rate constitutes a major hindrance in understanding the self-amplification of velocity gradients in turbulent fluid flows. Utilizing highly resolved direct numerical simulations of isotropic turbulence in periodic domains of up to 122883 grid points and Taylor-scale Reynolds number Rë in the range 140-1300, we investigate this nonlocality by decomposing the strain-rate tensor into local and nonlocal contributions obtained through Biot-Savart integration of vorticity in a sphere of radius R. We find that vorticity is predominantly amplified by the nonlocal strain coming beyond a characteristic scale size, which varies as a simple power law of vorticity magnitude. The underlying dynamics preferentially align vorticity with the most extensive eigenvector of nonlocal strain. The remaining local strain aligns vorticity with the intermediate eigenvector and does not contribute significantly to amplification; instead it surprisingly attenuates intense vorticity, leading to breakdown of the observed power law and ultimately also the scale invariance of vorticity amplification, with important implications for prevailing intermittency theories. |
BibTeX:
@article{Buaria, author = {Buaria, D. and Pumir, A.}, title = {Nonlocal amplification of intense vorticity in turbulent flows}, journal = {Phys. Rev. Research}, month = {November}, year = {2021}, volume = {3}, number = {4}, pages = {L042020}, doi = {10.1103/PhysRevResearch.3.L042020},, url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.3.L042020} } |
He, X., Bodenschatz, E. and Ahlers, G., "Universal scaling of temperature variance in Rayleigh–Bénard convection near the transition to the ultimate state", J. Fluid Mech., November 2021, Vol. 931, A7 pp. |
Abstract: We report measurements of the temperature frequency spectra P(f,z,r), the variance ó2(z,r) and the Nusselt number Nu in turbulent Rayleigh-Bénard convection (RBC) over the Rayleigh number range 4 × 1011<-Ra<-5 × 1015 and for a Prandtl number Pr= 0.8 (z is the vertical distance from the bottom plate and r is the radial position). Three RBC samples with diameter D=1.12 m yet different aspect ratios Ã ≡ D/L=1.00, 0.50 and 0.33 (L is the sample height) were used. In each sample, the results for ó2/Ä2 (Ä is the applied temperature difference) in the classical state over the range 0.018<-z/L<-0.5 can be collapsed onto a single curve, independent of Ra, by normalizing the distance z by the thermal boundary layer thickness ë=L/(2Nu). One can derive the equation ó2/Ä2=c1 × ln(z/ë)+c2+c3(z/ë)-0.5 from the observed f-1 scaling of the temperature frequency spectrum. It fits the collapsed ó2(z/ë) data in the classical state over the large range 20<-z/ë<-104. In the ultimate state (Ra>-Ra∗ 2) the data can be collapsed only when an adjustable parameter ë =L/(2Nu ) is used to replace ë. The values of Nu are larger by about 10 % than the experimentally measured Nu but follow the predicted Ra dependence of Nu for the ultimate RBC regime. The data for both the global heat transport and the local temperature fluctuations reveal the ultimate-state transitions at Ra2(Ã). They yield Ra∗ 2 ∝ Ã-3.0 in the studied Ã range. |
BibTeX:
@article{He2021a, author = {He, X. and Bodenschatz, E. and Ahlers, G.}, title = {Universal scaling of temperature variance in Rayleigh–Bénard convection near the transition to the ultimate state}, journal = {J. Fluid Mech.}, month = {November}, year = {2021}, volume = {931}, pages = {A7}, doi = {10.1017/jfm.2021.940},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/universal-scaling-of-temperature-variance-in-rayleighbenard-convection-near-the-transition-to-the-ultimate-state/6160313A60A9828CCEE1AD2AEB53B93D} } |
Herzog, S., Schiepel, D., Guido, I., Barta, R. and Wagner, C., "A Probabilistic Particle Tracking Framework for Guided and Brownian Motion Systems with High Particle Densities", SN COMPUT. SCI., October 2021, Vol. 2, 485 pp. |
Abstract: This paper presents a new framework for particle tracking based on a Gaussian Mixture Model (GMM). It is an extension of the state-of-the-art iterative reconstruction of individual particles by a continuous modeling of the particle trajectories considering the position and velocity as coupled quantities. The proposed approach includes an initialization and a processing step. In the first step, the velocities at the initial points are determined after iterative reconstruction of individual particles of the first four images to be able to generate the tracks between these initial points. From there on, the tracks are extended in the processing step by searching for and including new points obtained from consecutive images based on continuous modeling of the particle trajectories with a Gaussian Mixture Model. The presented tracking procedure allows to extend existing trajectories interactively with low computing effort and to store them in a compact representation using little memory space. To demonstrate the performance and the functionality of this new particle tracking approach, it is successfully applied to a synthetic turbulent pipe flow, to the problem of observing particles corresponding to a Brownian motion (e.g., motion of cells), as well as to problems where the motion is guided by boundary forces, e.g., in the case of particle tracking velocimetry of turbulent Rayleigh–Bénard convection. |
BibTeX:
@article{Herzog2021, author = {Herzog, S. and Schiepel, D. and Guido, I. and Barta, R. and Wagner, C.}, title = {A Probabilistic Particle Tracking Framework for Guided and Brownian Motion Systems with High Particle Densities}, journal = {SN COMPUT. SCI.}, month = {October}, year = {2021}, volume = {2}, pages = {485}, doi = {10.1007/s42979-021-00879-z},, url = {https://link.springer.com/article/10.1007/s42979-021-00879-z} } |
Majumder, R., Hussaini, S., Zykov, V. S., Luther, S. and Bodenschatz, E., "Pulsed low-energy stimulation initiates electric turbulence in cardiac tissue", PLoS Comput Biol, October 2021, Vol. 17(10), 1009476 pp. |
Abstract: Interruptions in nonlinear wave propagation, commonly referred to as wave breaks, are typical of many complex excitable systems. In the heart they lead to lethal rhythm disorders, the so-called arrhythmias, which are one of the main causes of sudden death in the industrialized world. Progress in the treatment and therapy of cardiac arrhythmias requires a detailed understanding of the triggers and dynamics of these wave breaks. In particular, two very important questions are: 1) What determines the potential of a wave break to initiate re-entry? and 2) How do these breaks evolve such that the system is able to maintain spatiotemporally chaotic electrical activity? Here we approach these questions numerically using optogenetics in an in silico model of human atrial tissue that has undergone chronic atrial fibrillation (cAF) remodelling. In the lesser studied sub-threshold illumination regime, we discover a new mechanism of wave break initiation in cardiac tissue that occurs for gentle slopes of the restitution characteristics. This mechanism involves the creation of conduction blocks through a combination of wavefront-waveback interaction, reshaping of the wave profile and heterogeneous recovery from the excitation of the spatially extended medium, leading to the creation of re-excitable windows for sustained re-entry. This finding is an important contribution to cardiac arrhythmia research as it identifies scenarios in which low-energy perturbations to cardiac rhythm can be potentially life-threatening. |
BibTeX:
@article{Maju, author = {Majumder, R. and Hussaini, S. and Zykov, V. S. and Luther, S. and Bodenschatz, E.}, title = {Pulsed low-energy stimulation initiates electric turbulence in cardiac tissue}, journal = {PLoS Comput Biol}, month = {October}, year = {2021}, volume = {17}, number = {10}, pages = {1009476}, doi = {10.1371/journal.pcbi.1009476},, url = {https://journals.plos.org/ploscompbiol/article?id=10.1371/journal.pcbi.1009476} } |
Mishra, A., Pumir, A. and Ostilla-Monico, R., "Instability and disintegration of vortex rings during head-on collisions and wall interactions", Phys. Rev. Lett., October 2021, Vol. 6(10), 104702 pp. |
Abstract: The head-on collision of two vortex rings can produce diverse phenomena: A tiara of secondary rings, vortex sheets which flatten and interact iteratively, or the violent disintegration of the rings into a turbulent cloud. The outcome of the interaction is determined by the nature of the instability affecting two impinging vortex rings. Here we carry out a systematic study to determine the dominant instability as a function of the parameters of the problem. To this end, we numerically simulate the head-on collision of vortex rings with circulation Reynolds numbers between 1000 and 3500 and varying slenderness ratios Ë=a/R ranging from Ë=0.1 to 0.35, with a the core radius and R the ring radius. By studying the temporal evolution of the energy and viscous dissipation, we elucidate the role azimuthal instabilities play in determining what the outcomes of the collision are. We then compare these collisions to the head-on impact of a vortex ring on a free-slip and a no-slip wall. The free-slip wall imposes a mirror symmetry, which impedes certain instabilities and at sufficiently large Reynolds numbers leads to the formation of a half-tiara of vortices. Impact against a no-slip wall results in the process where a secondary vortex ring is formed after the ejection of the resulting boundary layer. When the Reynolds number is above a certain threshold, which increases with Ë, the vortices disintegrate through azimuthal instabilities, resulting in a turbulent cloud. |
BibTeX:
@article{Mishra, author = {Mishra, A. and Pumir, A. and Ostilla-Monico, R.}, title = {Instability and disintegration of vortex rings during head-on collisions and wall interactions}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2021}, volume = {6}, number = {10}, pages = {104702}, doi = {10.1103/PhysRevFluids.6.104702},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.104702} } |
Kamprad, N., "Mechanics and Dynamics of Dictyostelium discoideum adhesion", September 2021 |
Abstract: The amoeba Dictyostelium discoideum (D.d.) is an excellent laboratory model system for studying amoeboid adhesion. In its natural habitat, D.d. lives in the soil and hunts for bacteria, an environment, which is very heterogeneous, where surface properties change rapidly. This phenomenon requires a high degree of flexibility from the adhesion apparatus of D.d.. To block amoeboid adhesion of D.d., first studies used polyethylene glycol (PEG) “brushes” as surface functionalization. In the present study, it was shown that gels of PEG are a good alternative, and it was possible to identify that developmental stage of D.d., axenic background and cytoskeletal fluorescence labelling can reduce the effect of surface passivation. In a second set of experiments conducted in the present work, the focus lay on the adhesion versatility of D.d. to a variety of substrates, which bases on several non-specific driving forces. To specify these forces, model substrates made of silicon were used, which influence DLVO forces based in their layered structure. It was found that Van der Waals forces, hydrophobic effects and electrostatic interactions are involved in D.d. adhesion. Besides membrane- and glycocalyx-based interactions, these forces are complemented by additional structures, individual adhesion bonds and adhesion bond clusters of the transmembrane protein SadA (Substrate Adhesion-deficient A), while D.d. does not possess integrins and thus focal contacts. Furthermore, actin foci, dynamic structures of freshly polymerised actin in the ventral membrane, have been shown to be involved in amoeboid adhesion and migration. In the present work, it was possible to analyse SadA adhesion bonds and actin foci both from a mechanical point of view employing step spectroscopy based on single cell force spectroscopy, but also in a more dynamical approach using reflection interference contrast and total internal reflection microscopy. Several established axenic laboratory strains as well as corresponding mutants deficient for components of actin-adhesome and endocytosis-signalling were analysed. The following two phenomena could were observed: I) reduction of the adhesion forces and step as well as spot density for inhibition of the Arp2/3 complex II) manipulation of adhesion apparatus (anchoring protein TalA, transmembrane protein SadA) increases the number of actin foci, with a simultaneous reduction in adhesion force. Finally, a quantification of the role of actin foci in adhesion and endocytosis was achieved. It was possible to show that actin foci exist independently of clathrin-mediated endocytosis, which also affects the lifetime of actin foci. Furthermore, clathrin-containing structures could also be detected after the appearance of actin foci, which may stabilise adhesive structures. It was shown that D.d. is a very versatile organism that adapts substrate-dependently to the environment by non-specific adhesion. Furthermore, it could also be shown that specific adhesion of D.d. works very similarly to that of integrins. |
BibTeX:
@phdthesis{Kamprad, author = {Kamprad, N.}, title = {Mechanics and Dynamics of Dictyostelium discoideum adhesion}, month = {September}, year = {2021},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0008-5921-F} } |
Shishkina, O., "Rayleigh-Bénard convection: The container shape matters", Phys. Rev. Fluids, September 2021, Vol. 6(9), 090502 pp. |
Abstract: To study turbulent thermal convection, one often chooses a Rayleigh-Benard flow configuration, where a fluid is confined between a heated bottom plate, a cooled top plate of the same shape, and insulated vertical sidewalls. When designing a Rayleigh-Benard setup, for specified fluid properties under Oberbeck-Boussinesq conditions, the maximal size of the plates (diameter or area), and maximal temperature difference between the plates, Delta(max), one ponders: Which shape of the plates and aspect ratio Gamma of the container (ratio between its horizontal and vertical extensions) would be optimal? In this article, we aim to answer this question, where under the optimal container shape, we understand such a shape, which maximizes the range between the maximal accessible Rayleigh number and the critical Rayleigh number for the onset of convection in the considered setup, Ra-c,Ra- Gamma. First we prove that Ra-c,Ra- Gamma proportional to (1 + c(u) Gamma(-2))(1 + c(theta) Gamma(-2)), for some c(u) > 0 and c(theta) > 0. This holds for all containers with no-slip boundaries, which have a shape of a right cylinder, whose bounding plates are convex domains, not necessarily circular. Furthermore, we derive accurate estimates of Ra-c,Ra- (Gamma), under the assumption that in the expansions (in terms of the Laplace eigenfunctions) of the velocity and reduced temperature at the onset of convection, the contributions of the constant-sign eigenfunctions vanish, both in the vertical and at least in one horizontal direction. With that we derive Ra-c,Ra- Gamma approximate to (2 pi)(4)(1 + c(u)Gamma(-2))(1 + c(theta)Gamma(-2)), where c(u) and c(theta) are determined by the container shape and boundary conditions for the velocity and temperature, respectively. In particular, for circular cylindrical containers with no-slip and insulated sidewalls, we have c(u) = j(11)(2)/pi(2) approximate to 1.49 and c(theta) = ((j) over tilde (11))(2)/pi(2) approximate to 0.34, where j(11) and (j) over tilde (11) are the first positive roots of the Bessel function J(1) of the first kind or its derivative, respectively. For parallelepiped containers with the ratios Gamma(x) and Gamma(y), Gamma(y) <= Gamma(x) equivalent to Gamma, of the side lengths of the rectangular plates to the cell height, for no-slip and insulated sidewalls we obtain Ra-c,Ra- Gamma approximate to (2 pi)(4)(1 + Gamma(-2)(x))(1 + Gamma(-2)(x)/4 + Gamma(-2)(y)/4). Our approach is essentially different to the linear stability analysis, however, both methods lead to similar results. For Gamma less than or similar to 4.4, the derived Ra-c,Ra-Gamma is larger than Jeffreys' result Ra-c,infinity(J) approximate to 1708 for an unbounded layer, which was obtained with linear stability analysis of the normal modes restricted to the consideration of a single perturbation wave in the horizontal direction. In the limit Gamma -> infinity, the difference between Ra-c,Ra-Gamma ->infinity = (2 pi)(4) for laterally confined containers and Jeffreys' Ra-c,infinity(J) for an unbounded layer is about 8.8%.
We further show that in Rayleigh-Benard experiments, the optimal rectangular plates are squares, while among all convex plane domains, circles seem to match the optimal shape of the plates. The optimal Gamma is independent of Delta(max) and of the fluid properties. For the adiabatic sidewalls, the optimal Gamma is slightly smaller than 1/2 (for cylinder, about 0.46), which means that the intuitive choice of Gamma = 1/2 in most Rayleigh-Benard experiments is right and justified. For the given plate diameter D and maximal temperature difference Delta(max), the maximal attainable Rayleigh number range is about 3.5 orders of magnitudes smaller than the order of the Rayleigh number based on D and Delta(max). Deviations from the optimal Gamma lead to a reduction of the attainable range, namely, as log(10) (Gamma) for Gamma -> 0 and as log(10) (Gamma(-3)) for Gamma -> infinity. Our theory shows that the relevant length scale in Rayleigh-Benard convection in containers with no-slip boundaries is l similar to D/root Gamma(2) + c(u) = H/root 1 + c(u)/Gamma(2). This means that in the limit Gamma -> infinity, l equals the cell height H, while for Gamma -> 0, it is rather the plate diameter D. |
BibTeX:
@article{Shi, author = {Shishkina, O.}, title = {Rayleigh-Bénard convection: The container shape matters}, journal = {Phys. Rev. Fluids}, month = {September}, year = {2021}, volume = {6}, number = {9}, pages = {090502}, doi = {10.1103/PhysRevFluids.6.090502},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.090502} } |
Xu, H., Zhang, W. and Wang, Y., "Explore missing flow dynamics by physics-informed deep learning: The parameterized governing systems", Physics of Fluids, September 2021, Vol. 33(9), 095116 pp. |
Abstract: Gaining and understanding flow dynamics have much importance in a wide range of disciplines, e.g., astrophysics, geophysics, biology, mechanical engineering, and biomedical engineering. For turbulent flows, local flow information such as velocity and its statistics, can be measured experimentally. Due to the poor fidelity or experimental limitations, some information may not be resolved in a region of interest. On the other hand, detailed flow features are described by the governing equations, e.g., the Navier–Stokes equations for viscous fluid, and can be resolved numerically, which is heavily dependent on the capability of either computing resources or modeling. Alternatively, we address this problem by employing the physics-informed deep learning and treat the governing equations as a parameterized constraint to recover the missing flow dynamics. We demonstrate that with limited data, no matter from experiment or others, the flow dynamics in the region where the required data are missing or not measured, can be reconstructed with the parameterized governing equations. Meanwhile, a richer dataset, with spatial distribution of the control parameter (e.g., eddy viscosity of turbulence modelings), can be obtained. The method provided in this paper may shed light on the data-driven scale-adaptive turbulent structure recovering and understanding of complex fluid physics and can be extended to other parameterized governing systems beyond fluid mechanics. |
BibTeX:
@article{Xu, author = {Xu, H. and Zhang, W. and Wang, Y.}, title = {Explore missing flow dynamics by physics-informed deep learning: The parameterized governing systems}, journal = {Physics of Fluids}, month = {September}, year = {2021}, volume = {33}, number = {9}, pages = {095116}, doi = {10.1063/5.0062377},, url = {https://aip.scitation.org/doi/full/10.1063/5.0062377} } |
Stevens, B. e. a., "EUREC^{4}A", Earth Syst. Sci. Data, August 2021, Vol. 13(8), 4067 pp. |
Abstract: The science guiding the EUREC4A campaign and its measurements is presented. EUREC4A comprised roughly 5 weeks of measurements in the downstream winter trades of the North Atlantic - eastward and southeastward of Barbados. Through its ability to characterize processes operating across a wide range of scales, EUREC4A marked a turning point in our ability to observationally study factors influencing clouds in the trades, how they will respond to warming, and their link to other components of the earth system, such as upper-ocean processes or the life cycle of particulate matter. This characterization was made possible by thousands (2500) of sondes distributed to measure circulations on meso- (200 km) and larger (500 km) scales, roughly 400 h of flight time by four heavily instrumented research aircraft; four global-class research vessels; an advanced ground-based cloud observatory; scores of autonomous observing platforms operating in the upper ocean (nearly 10000 profiles), lower atmosphere (continuous profiling), and along the air–sea interface; a network of water stable isotopologue measurements; targeted tasking of satellite remote sensing; and modeling with a new generation of weather and climate models. In addition to providing an outline of the novel measurements and their composition into a unified and coordinated campaign, the six distinct scientific facets that EUREC4A explored - from North Brazil Current rings to turbulence-induced clustering of cloud droplets and its influence on warm-rain formation - are presented along with an overview of EUREC4A's outreach activities, environmental impact, and guidelines for scientific practice. Track data for all platforms are standardized and accessible at https://doi.org/10.25326/165 (Stevens, 2021), and a film documenting the campaign is provided as a video supplement. |
BibTeX:
@article{Bodenschatz, author = {Stevens, B. et al.}, title = {EUREC^{4}A}, journal = {Earth Syst. Sci. Data}, month = {August}, year = {2021}, volume = {13}, number = {8}, pages = {4067}, doi = {10.5194/essd-13-4067-2021},, url = {https://essd.copernicus.org/articles/13/4067/2021/} } |
Majumder, R., Nazer, A. N. M., Panfilov, A. V., Bodenschatz, E. and Wang, Y., "Electrophysiological Characterization of Human Atria: The Understated Role of Temperature", Front. Physiol., July 2021, Vol. 12, 639149 pp. |
Abstract: Ambient temperature has a profound influence on cellular electrophysiology through direct control over the gating mechanisms of different ion channels. In the heart, low temperature is known to favor prolongation of the action potential. However, not much is known about the influence of temperature on other important characterization parameters such as the resting membrane potential (RMP), excitability, morphology and characteristics of the action potential (AP), restitution properties, conduction velocity (CV) of signal propagation, etc. Here we present the first, detailed, systematic in silico study of the electrophysiological characterization of cardiomyocytes from different regions of the normal human atria, based on the effects of ambient temperature (5-50°C). We observe that RMP decreases with increasing temperature. At 48°C, the cells lose their excitability. Our studies show that different parts of the atria react differently to the same changes in temperature. In tissue simulations a drop in temperature correlated positively with a decrease in CV, but the decrease was region-dependent, as expected. In this article we show how this heterogeneous response can provide an explanation for the development of a proarrhythmic substrate during mild hypothermia. We use the above concept to propose a treatment strategy for atrial fibrillation that involves severe hypothermia in specific regions of the heart for a duration of only 200 ms. |
BibTeX:
@article{Majum, author = {Majumder, R. and Nazer, A. N. M. and Panfilov, A. V. and Bodenschatz, E. and Wang, Y.}, title = {Electrophysiological Characterization of Human Atria: The Understated Role of Temperature}, journal = {Front. Physiol.}, month = {July}, year = {2021}, volume = {12}, pages = {639149}, doi = {10.3389/fphys.2021.639149},, url = {https://www.frontiersin.org/articles/10.3389/fphys.2021.639149/full} } |
Nasirimarekani, V., Struebing, T., Vilfan, A. and Guido, I., "Tuning the Properties of Active Microtubule Networks by Depletion Forces", Langmuir, July 2021, Vol. 37(26), 7919 pp. |
Abstract: Suspensions of microtubules and nonadsorbing particles form thick and long bundles due to depletion forces. Such interactions act at the nanometer scale and define the structural and dynamical properties of the resulting networks. In this study, we analyze the depletion forces exerted by two types of nonadsorbing particles, namely, the polymer, poly(ethylene glycol) (PEG), and the block copolymer, Pluronic. We characterize their effects both in passive and active networks by adding motor proteins to the suspensions. By exploiting its bundling effect via entropic forces, we observed that PEG generates a network with thick structures showing a nematic order and larger mesh size. On the other hand, Pluronic builds up a much denser gel-like network without a recognizable mesh structure. This difference is also reflected in the network activity. PEG networks show moderate contraction in lateral directions while Pluronic networks exhibit faster and isotropic contraction. Interestingly, by mixing the two nonadsorbing polymers in different ratios, we observed that the system showed a behavior that exhibited properties of both agents, leading to a robust and fast responsive structure compared to the single-depletant networks. In conclusion, we show how passive osmotic compression modifies the distribution of biopolymers. Its combination with active motors results in a new active material with potential for nanotechnological applications. |
BibTeX:
@article{Nas, author = {Nasirimarekani, V. and Struebing, T. and Vilfan, A. and Guido, I.}, title = {Tuning the Properties of Active Microtubule Networks by Depletion Forces}, journal = {Langmuir}, month = {July}, year = {2021}, volume = {37}, number = {26}, pages = {7919}, doi = {10.1021/acs.langmuir.1c00426},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.1c00426} } |
Nunnari, G. G., "Experimental investigation of a sheared thermally unstable boundary layer", July 2021 |
Abstract: In many natural and industrial systems, heat is transported by mixed convection, where an externally driven flow causes advection of the temperature field in addition to the fluid motion due to buoyancy of differentially heated areas. We investigate experimentally the heat flux across a thermally unstable boundary layer subject to a shear flow. In the experiment, we use a two meter long aluminium plate that is subject to a shear flow above its heated surface. For varying Richardson, Reynolds and Grashof numbers, we measure the heat flux from the plate, as well as the vertical velocity and temperature profiles above it by using hot-wire anemometry and thermistors arrays. The fluid is air at atmospheric pressure, resulting in a Prandtl number of Pr = 0.75. The goal of this research is not only to investigate the transition from fully forced to dominantly free convection, but we also hope to better understand the difference between a shear driven turbulent boundary layer and a laminar boundary layer which is perturbed by thermal plumes. |
BibTeX:
@phdthesis{Nunn, author = {Nunnari, G. G.}, title = {Experimental investigation of a sheared thermally unstable boundary layer}, month = {July}, year = {2021},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0008-5889-B} } |
Poulidis, A. P., Biass, S., Bagheri, G., Takemi, T. and Iguchi, M., "Atmospheric vertical velocity -a crucial component in understanding proximal deposition of volcanic ash", Earth and Planetary Science Letters, July 2021, Vol. 566, 116980 pp. |
Abstract: The simulation of volcanic ash transport and deposition (VATD) for distances within a few kilometres from the vent (proximal region) is challenging owing to a combination of unresolved volcanogenic effects and the impact of the volcano's orography. Due to the urgency of calculations or sometimes lack of access to computational resources or expertise, atmospheric vertical velocity (w) is often underestimated in VATD modelling. The error associated with this underestimation has, however, never been properly quantified. Here, we use a weak vulcanian eruption that occurred at Sakurajima volcano on 1/10/2017 as a first step to addressing this limitation. We combine deposit characteristics observed by disdrometer measurements with high-resolution atmospheric and VATD modelling to validate and illustrate the differences in modelled trajectories when w is either ignored or accounted for. The Weather Research and Forecasting (WRF) model is used to model the orogenic effects down to a resolution of 50 m. Eulerian and Lagrangian VATD models (FALL3D and LagTrack, a newly-developed Matlab code, respectively) are used to describe the particle trajectories. Results confirm the importance of w in the case of low-altitude eruptions for capturing the complex, near-vent trajectory of ash particles: when neglected fall velocities were seen to differ up to 2–5 m s-1 depending on the particle size. Although the impact of w is most notable within 10 km from the vent, the forced sedimentation of low terminal velocity particles can have a significant secondary effect at larger distances. |
BibTeX:
@article{Pouli, author = {Poulidis, A. P. and Biass, S. and Bagheri, G. and Takemi, T. and Iguchi, M.}, title = {Atmospheric vertical velocity -a crucial component in understanding proximal deposition of volcanic ash}, journal = {Earth and Planetary Science Letters}, month = {July}, year = {2021}, volume = {566}, pages = {116980}, doi = {10.1016/j.epsl.2021.116980},, url = {https://www.sciencedirect.com/science/article/abs/pii/S0012821X21002399} } |
Reiter, P., Shishkina, O., Lohse, D. and Krug, D., "Crossover of the relative heat transport contributions of plume ejecting and impacting zones in turbulent Rayleigh-Bénard convection", EPL, July 2021, Vol. 134(3), 34002 pp. |
Abstract: Turbulent thermal convection is characterized by the formation of large-scale structures and strong spatial inhomogeneity. This work addresses the relative heat transport contributions of the large-scale plume ejecting vs. plume impacting zones in turbulent Rayleigh-Bénard convection. Based on direct numerical simulations of the two dimensional (2-D) problem, we show the existence of a crossover in the wall heat transport from initially impacting dominated to ultimately ejecting dominated at Ra ≈ 3 × 10^11 . This is consistent with the trends observed in 3-D convection at lower Ra, and we therefore expect a similar crossover to also occur there. We identify the development of a turbulent mixing zone, connected to thermal plume emission, as the primary mechanism for the takeover. The mixing zone gradually extends vertically and horizontally, therefore becoming more and more dominant for the overall heat transfer. |
BibTeX:
@article{Reiter, author = {Reiter, P. and Shishkina, O. and Lohse, D. and Krug, D.}, title = {Crossover of the relative heat transport contributions of plume ejecting and impacting zones in turbulent Rayleigh-Bénard convection}, journal = {EPL}, month = {July}, year = {2021}, volume = {134}, number = {3}, pages = {34002}, doi = {10.1209/0295-5075/134/34002},, url = {https://iopscience.iop.org/article/10.1209/0295-5075/134/34002#Acknowledgments} } |
Teimurazov, A., Reiter, P., Shishkina, O. and Frick, P., "Heat transport in a cell heated at the bottom and the side", EPL, July 2021, Vol. 134(3), 34001 pp. |
Abstract: Turbulent thermal convection of water (Prandtl number 5.4) in a cubic cell heated from the bottom and the side and cooled from the top and the opposite side is studied numerically by means of direct numerical simulations and large-eddy simulations. The temperature difference between the bottom and top horizontal walls, Ä, is fixed, whereas the temperature difference between the two vertical walls, è, is varied in the range 0 ≤ /Δ ≤ 1.5 . The other vertical walls are adiabatic. The Rayleigh number determined by Ä equals Ra_Δ = 5.2 × 10^8 . General laws on the momentum and heat transport in turbulent convection under a joint action of the vertical and horizontal temperature gradients are not yet known, and our study sheds light on the effect of additional horizontal thermal driving (as in vertical convection) on turbulent Rayleigh-Bénard convection. We show that the effective heat transfer and the structure of the flow are strongly affected by the additional heating from the side. Even weak side heating (/Δ = 0.05) turns the large-scale circulation (LSC), directing it along the walls rather than diagonally. The total kinetic energy and heat flux through the heated walls increase, while the mean flow and vertical heat flux even decrease slightly. Further increase of the side heating accelerates the mean flow, the LSC continues to accelerate up to /Δ = 0.4 , but the turbulent energy starts to decrease at /Δ > 0.25 indicating a change in the flow structure. For /Δ > 0.4 , the effect of the increasing heat flux is complimented by a strong suppression of the LSC and small-scale turbulence. At highest considered side heating (/Δ = 1.5) , the vertical heat flux is increased by 43% compared to RBC, while the Reynolds number is lower than in RBC. Thus, the rearranged global flow structure allows a stronger heat transport with a weaker flow. For the studied Ra Δ , the contribution to the total kinetic energy of the system (characterized by the Reynolds number) from the large-scale flow is higher than the contribution from the turbulent fluctuations for all values of θ / Δ . |
BibTeX:
@article{Teimura, author = {Teimurazov, A. and Reiter, P. and Shishkina, O. and Frick, P.}, title = {Heat transport in a cell heated at the bottom and the side}, journal = {EPL}, month = {July}, year = {2021}, volume = {134}, number = {3}, pages = {34001}, doi = {10.1209/0295-5075/134/34001},, url = {https://iopscience.iop.org/article/10.1209/0295-5075/134/34001} } |
Wang, Q., Reiter, P., Lohse, D. and Shishkina, O., "Universal properties of penetrative turbulent Rayleigh-Bénard convection", Phys. Rev. Fluids, June 2021, Vol. 6(6), 063502 pp. |
Abstract: Penetrative turbulence, which occurs in a convectively unstable fluid layer and penetrates into an adjacent, originally stably stratified layer, is numerically and theoretically analyzed. As example we pick the canonical Rayleigh-Bénard geometry, but now with the bottom plate temperature Tb > 4°C, the top plate temperature Tt ≤ 4°C, and the density maximum around Tm ≈ 4°C in between, resulting in penetrative turbulence. Next to the Rayleigh number Ra, the crucial new control parameter as compared to standard Rayleigh-Bénard convection is the density inversion parameter èm ≡ (Tm-Tt)/(Tb-Tt). The crucial response parameters are the relative mean midheight temperature èc and the overall heat transfer (i.e., the Nusselt number Nu). We numerically show (for Ra up to 1010) and theoretically derive that èc(èm) and Nu(èm)/Nu(0) are universally(i.e., independently of Ra) determined only by the density inversion parameter èm and succeed to derive these universal dependences. In particular, èc(èm)=(1+è2m)/2, which holds for èm below a Ra-dependent critical value, beyond which èc(èm) sharply decreases and drops down to èc=1/2 at èm=èm,c. This critical density inversion parameter èm,c can be precisely predicted by a linear stability analysis. Finally, we numerically identify and discuss rare transitions between different turbulent flow states for large èm. |
BibTeX:
@article{Wanga, author = {Wang, Q. and Reiter, P. and Lohse, D. and Shishkina, O.}, title = {Universal properties of penetrative turbulent Rayleigh-Bénard convection}, journal = {Phys. Rev. Fluids}, month = {June}, year = {2021}, volume = {6}, number = {6}, pages = {063502}, doi = {10.1103/PhysRevFluids.6.063502},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.063502} } |
, "Measuring the full dissipation rate tensor in homogeneous turbulence", June 2021 |
Abstract: Recent developments in dense Lagrangian Particle Tracking with Shake-The-Box (Schanz et al. 2016) and data assimilation techniques, like FlowFit (Gesemann et al. 2016), raises hope that for moderate Reynolds numbers the full (time-resolved) velocity gradient tensor might be capturedexperimentally at high-spatial resolution more accurately than in previous generic turbulence measurements by e.g. Tomo-PIV. Here we present measurements of the full velocity gradient and dissipation rate tensor based on dense fields of fluid particle trajectories in homogeneous turbulence at Re-lambda 270 and 370 in a von Karman flow between two counter-rotating propellers. Applying the Shake-The-Box (STB) particle tracking algorithm (Schanz et al. 2016) we are able to instantaneously track up to 100,000 particles in a measurement volume of 40 x 40 x 15 mm³. The data assimilation scheme FlowFit (Gesemann et al. 2016) applies Navier-Stokes- constraints by imposing conservation of mass and momentum to interpolate the scattered velocity and acceleration data by continuous 3D B-Splines in a cubic grid of cells, enabling to recover (locally) the smallest flow scales in the center of tetrahedrons of particles in close proximity (r < 3-Eta for the time-resolved 3D velocity, acceleration and pressure fields. Measuring Aij and 3D pressure fields at full temporal- and spatial resolution in experimental fluid mechanics is a highly desired capability since its beginning. Based on such data many derived quantities of high importance for data driven developments of advanced CFD methods and related turbulence models can be delivered which in turn can enhance their applicability towards higher Reynolds numbers and full coupled FSI problems e.g. for innovative aircraft design purposes. |
BibTeX:
@proceedings{2021g,, title = {Measuring the full dissipation rate tensor in homogeneous turbulence}, month = {June}, year = {2021},, url = {https://elib.dlr.de/142922/} } |
Bai, X.-D., Zhang, J.-S., Zheng, J.-H. and Wang, Y., "Energy extraction performance of a flapping wing with active elastic airbag deformation at the leading edge", Ocean Engineering, May 2021, Vol. 228, 108901 pp. |
Abstract: To promote energy extraction efficiency, an active deformation method to implant an elastic airbag at the leading edge of flapping wings is proposed in this study. The charging and discharging processes of the airbag are accomplished by sinusoidally adjusting the local deformation angle. We investigated numerically the effect of both the reduced frequency and the local deformation amplitude on the energy extraction efficiency with the chord based Reynolds number . Our results show that as the reduced frequency increases, the energy extraction efficiency of flapping wings with various local deformation first rises and then drops with a maximum energy efficiency around 0.4. Energy extraction efficiency via local deformation of the leading edge can be enhanced up to 25%, compared with the non-deformed flapping wing in the lower reduced frequency range. Analysis on flow field and the working coefficients indicates, due to the airbag deformation, the leading edge vortex is more closely attached to the suction side of the flapping wing with larger local deformation elastic airbag ( α =20° and 25°), inducing more preferable pressure distribution and higher power coefficients with less oscillation throughout the motion cycle. |
BibTeX:
@article{2021d, author = {Bai, X.-D. and Zhang, J.-S. and Zheng, J.-H. and Wang, Y.}, title = {Energy extraction performance of a flapping wing with active elastic airbag deformation at the leading edge}, journal = {Ocean Engineering}, month = {May}, year = {2021}, volume = {228}, pages = {108901}, doi = {10.1016/j.oceaneng.2021.108901},, url = {https://www.sciencedirect.com/science/article/abs/pii/S002980182100336X} } |
Mojiri, S., Isbaner, S., Mühle, S., Jang, H., Bae, A. J., Gregor, I., Gholami, A. and Enderlein, J., "Rapid multi-plane phase-contrast microscopy reveals torsional dynamics in flagellar motion", Biomedical Optics Express, May 2021, Vol. 12(6), 3169 pp. |
Abstract: High speed volumetric optical microscopy is an important tool for observing rapid processes in living cells or for real-time tracking of sub-cellular components. However, the 3D imaging capability often comes at the price of a high technical complexity of the imaging system and/or the requirement of demanding image analysis. Here, we propose a combination of conventional phase-contrast imaging with a customized multi-plane beam-splitter for enabling simultaneous acquisition of images in eight different focal planes. Our method is technically straightforward and does not require complex post-processing image analysis. We apply our multi-plane phase-contrast microscope to the real-time observation of the fast motion of reactivated Chlamydomonas axonemes with sub-µm spatial and 4 ms temporal resolution. Our system allows us to observe not only bending but also the three-dimensional torsional dynamics of these micro-swimmers. |
BibTeX:
@article{Moji, author = {Mojiri, S. and Isbaner, S. and Mühle, S. and Jang, H. and Bae, A. J. and Gregor, I. and Gholami, A. and Enderlein, J.}, title = {Rapid multi-plane phase-contrast microscopy reveals torsional dynamics in flagellar motion}, journal = {Biomedical Optics Express}, month = {May}, year = {2021}, volume = {12}, number = {6}, pages = {3169}, doi = {10.1364/BOE.419099},, url = {https://www.osapublishing.org/boe/fulltext.cfm?uri=boe-12-6-3169&id=450859} } |
Le-The, H., Küchler, C., van den Berg, A., Bodenschatz, E., Lohse, D. and Krug, D., "Fabrication of freestanding Pt nanowires for use as thermal anemometry probes in turbulence measurements", Microsyst Nanoeng, April 2021, Vol. 7(28), 1 pp. |
Abstract: We report a robust fabrication method for patterning freestanding Pt nanowires for use as thermal anemometry probes for small-scale turbulence measurements. Using e-beam lithography, high aspect ratio Pt nanowires ( 300 nm width, 70 µm length, 100 nm thickness) were patterned on the surface of oxidized silicon (Si) wafers. Combining wet etching processes with dry etching processes, these Pt nanowires were successfully released, rendering them freestanding between two silicon dioxide (SiO2) beams supported on Si cantilevers. Moreover, the unique design of the bridge holding the device allowed gentle release of the device without damaging the Pt nanowires. The total fabrication time was minimized by restricting the use of e-beam lithography to the patterning of the Pt nanowires, while standard photolithography was employed for other parts of the devices. We demonstrate that the fabricated sensors are suitable for turbulence measurements when operated in constant-current mode. A robust calibration between the output voltage and the fluid velocity was established over the velocity range from 0.5 to 5 m s-1 in a SF6 atmosphere at a pressure of 2 bar and a temperature of 21 °C. The sensing signal from the nanowires showed negligible drift over a period of several hours. Moreover, we confirmed that the nanowires can withstand high dynamic pressures by testing them in air at room temperature for velocities up to 55 m s-1. |
BibTeX:
@article{2021c, author = {Le-The, H. and Küchler, C. and van den Berg, A. and Bodenschatz, E. and Lohse, D. and Krug, D.}, title = {Fabrication of freestanding Pt nanowires for use as thermal anemometry probes in turbulence measurements}, journal = {Microsyst Nanoeng}, month = {April}, year = {2021}, volume = {7}, number = {28}, pages = {1}, doi = {10.1038/s41378-021-00255-0},, url = {https://www.nature.com/articles/s41378-021-00255-0} } |
Nordsiek, F., Bodenschatz, E. and Bagheri, G., "Risk assessment for airborne disease transmission by poly-pathogen aerosols", PLOS ONE, April 2021, Vol. 16(4), 1 pp. |
Abstract: In the case of airborne diseases, pathogen copies are transmitted by droplets of respiratory tract fluid that are exhaled by the infectious that stay suspended in the air for some time and, after partial or full drying, inhaled as aerosols by the susceptible. The risk of infection in indoor environments is typically modelled using the Wells-Riley model or a Wells-Riley-like formulation, usually assuming the pathogen dose follows a Poisson distribution (mono-pathogen assumption). Aerosols that hold more than one pathogen copy, i.e. poly-pathogen aerosols, break this assumption even if the aerosol dose itself follows a Poisson distribution. For the largest aerosols where the number of pathogen in each aerosol can sometimes be several hundred or several thousand, the effect is non-negligible, especially in diseases where the risk of infection per pathogen is high. Here we report on a generalization of the Wells-Riley model and dose-response models for poly-pathogen aerosols by separately modeling each number of pathogen copies per aerosol, while the aerosol dose itself follows a Poisson distribution. This results in a model for computational risk assessment suitable for mono-/poly-pathogen aerosols. We show that the mono-pathogen assumption significantly overestimates the risk of infection for high pathogen concentrations in the respiratory tract fluid. The model also includes the aerosol removal due to filtering by the individuals which becomes significant for poorly ventilated environments with a high density of individuals, and systematically includes the effects of facemasks in the infectious aerosol source and sink terms and dose calculations. |
BibTeX:
@article{Nordsi, author = {Nordsiek, F. and Bodenschatz, E. and Bagheri, G.}, title = {Risk assessment for airborne disease transmission by poly-pathogen aerosols}, journal = {PLOS ONE}, month = {April}, year = {2021}, volume = {16}, number = {4}, pages = {1}, doi = {10.1371/journal.pone.0248004},, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0248004} } |
Wang, Q., Liu, H.-R., Verzicco, R., Shishkina, O. and Lohse, D., "Regime transitions in thermally driven high-Rayleigh number vertical convection", J. Fluid Mech., April 2021, Vol. 917, A6 pp. |
Abstract: Thermally driven vertical convection (VC) - the flow in a box heated on one side and cooled on the other side, is investigated using direct numerical simulations with Rayleigh numbers over the wide range of 10^7<=Ra<=10^14 and a fixed Prandtl number Pr=10 in a two-dimensional convection cell with unit aspect ratio. It is found that the dependence of the mean vertical centre temperature gradient S on Ra shows three different regimes: in regime I (Ra<=5x10^10), S is almost independent of Ra; in the newly identified regime II (5x10^10<=Ra<=10^13), S first increases with increasing Ra (regime IIa), reaches its maximum and then decreases again (regime IIb); and in regime III (Ra > 1013), S again becomes only weakly dependent on Ra, being slightly smaller than in regime I. The transition from regime I to regime II is related to the onset of unsteady flows arising from the ejection of plumes from the sidewall boundary layers. The maximum of S occurs when these plumes are ejected over approximately half of the area (downstream) of the sidewalls. The onset of regime III is characterized by the appearance of layered structures near the top and bottom horizontal walls. The flow in regime III is characterized by a well-mixed bulk region owing to continuous ejection of plumes over large fractions of the sidewalls, and, as a result of the efficient mixing, the mean temperature gradient in the centre S is smaller than that of regime I. In the three different regimes, significantly different flow organizations are identified: in regime I and regime IIa, the location of the maximal horizontal velocity is close to the top and bottom walls; however, in regime IIb and regime III, banded zonal flow structures develop and the maximal horizontal velocity now is in the bulk region. The different flow organizations in the three regimes are also reflected in the scaling exponents in the effective power law scalings Nu-Raâ and Re-Raã. Here, Nu is the Nusselt number and Re is the Reynolds number based on maximal vertical velocity (averaged over vertical direction). In regime I, the fitted scaling exponents (â ≈ 0.26 and ã ≈ 0.51) are in excellent agreement with the theoretical predictions of â=1/4 and ã=1/2 for laminar VC (Shishkina, Phys. Rev. E., vol. 93, 2016, 051102). However, in regimes II and III, â increases to a value close to 1/3 and ã decreases to a value close to 4/9. The stronger Ra dependence of Nu is related to the ejection of plumes and the larger local heat flux at the walls. The mean kinetic dissipation rate also shows different scaling relations with Ra in the different regimes. |
BibTeX:
@article{Wng, author = {Wang, Q. and Liu, H.-R. and Verzicco, R. and Shishkina, O. and Lohse, D.}, title = {Regime transitions in thermally driven high-Rayleigh number vertical convection}, journal = {J. Fluid Mech.}, month = {April}, year = {2021}, volume = {917}, pages = {A6}, doi = {10.1017/jfm.2021.262},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/regime-transitions-in-thermally-driven-highrayleigh-number-vertical-convection/2C6892CA314FB35E39818039C64ED799} } |
Yang, P.-F., Pumir, A. and Xu, H., "Return to isotropy of homogeneous shear-released turbulence", Phys. Rev. Fluids, April 2021, Vol. 6(4), 044601 pp. |
Abstract: The presence of mean velocity gradients induces anisotropies in turbulent flows, which affect even the smallest scales of motion at finite Reynolds numbers. By performing direct numerical simulations of the Navier-Stokes equations, we study the return to isotropy of a homogeneous turbulent flow initially in a statistically stationary state under a uniform shear, S= ∂ U1/ ∂ x2, in the conceptually simple situation where the mean shear is suddenly released. In particular, we characterize the timescales involved in the dynamics. We observe that the Reynolds stress tensor, which measures the large-scale flow anisotropy, relaxes towards an isotropic form over a timescale of the order of the large-eddy turnover time of turbulence, in qualitative agreement with previous studies with different types of initially imposed mean velocity gradient. We also investigate how the correlations of the velocity gradient tensor relax to isotropy with time. In particular, we focus on the properties of the one-point vorticity correlations ‹ ùiùj › and ‹ ùiùjùk guilsinglright. The nonzero off-diagonal term of the second-order correlation tensor, i.e., the correlation between the streamwise and the transverse components of vorticity, ‹ ù1ù2 › , decreases towards 0 over a time of the order of the Kolmogorov timescale. In comparison, the anisotropies in the diagonal components ‹ ù2i › (i=1, 2, or 3) relax over a time significantly longer than the Kolmogorov timescale. This difference can be explained by an elementary theoretical analysis of the dynamics of the anisotropy tensor bùij ≡ ‹ ùiùj › ‹ ùkùk › -13äij at the instant when the shear is released. We also observe that the skewness of the spanwise component of vorticity, Sù3, relaxes slowly towards zero. The relaxation of a small-scale quantity over a time much longer than the Kolmogorov timescale, as surprising as it may seem, is in fact consistent with a known relation between velocity-gradient correlations and the pressure-rate-of-strain correlation, and raises the important question of separation between the timescales characterizing the return to isotropy at large and small scales. |
BibTeX:
@article{2021e, author = {Yang, P.-F. and Pumir, A. and Xu, H.}, title = {Return to isotropy of homogeneous shear-released turbulence}, journal = {Phys. Rev. Fluids}, month = {April}, year = {2021}, volume = {6}, number = {4}, pages = {044601}, doi = {10.1103/PhysRevFluids.6.044601},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.044601} } |
Zhang, Y.-B., Bodenschatz, E., Xu, H. and Xi, H.-D., "Experimental observation of the elastic range scaling in turbulent flow with polymer additives", Science Advances, April 2021, Vol. 7(14), eabd3525 pp. |
Abstract: A minute amount of long-chain flexible polymer dissolved in a turbulent flow can drastically change flow properties, such as reducing the drag and enhancing mixing. One fundamental riddle is how these polymer additives interact with the eddies of different spatial scales existing in the turbulent flow and, in turn, alter the turbulence energy transfer. Here, we show how turbulent kinetic energy is transferred through different scales in the presence of the polymer additives. In particular, we observed experimentally the emerging of a previously unidentified scaling range, referred to as the elastic range, where increasing amount of energy is transferred by the elasticity of the polymers. In addition, the existence of the elastic range prescribes the scaling of high-order velocity statistics. Our findings have important implications to many turbulence systems, such as turbulence in plasmas or superfluids where interaction between turbulent eddies and other nonlinear physical mechanisms are often involved. |
BibTeX:
@article{Zhang, author = {Zhang, Y.-B. and Bodenschatz, E. and Xu, H. and Xi, H.-D.}, title = {Experimental observation of the elastic range scaling in turbulent flow with polymer additives}, journal = {Science Advances}, month = {April}, year = {2021}, volume = {7}, number = {14}, pages = {eabd3525}, doi = {10.1126/sciadv.abd3525},, url = {https://advances.sciencemag.org/content/7/14/eabd3525.abstract} } |
Ahmad, R., Kleineberg, K., Nasirimarekani, V., Su, Y.-J., Pozveh, S. G., Bae, A., Sundmacher, K., Bodenschatz, E., Guido, I., Vidakovic-Koch, T. and Gholami, A., "Light-Powered Reactivation of Flagella and Contraction of Microtubule Networks: Toward Building an Artificial Cell", ACS Synth. Biol., March 2021, Vol. 10(6), 1490 pp. |
Abstract: Artificial systems capable of self-sustained movement with self-sufficient energy are of high interest with respect to the development of many challenging applications, including medical treatments, but also technical applications. The bottom-up assembly of such systems in the context of synthetic biology is still a challenging task. In this work, we demonstrate the biocompatibility and efficiency of an artificial light-driven energy module and a motility functional unit by integrating light-switchable photosynthetic vesicles with demembranated flagella. The flagellar propulsion is coupled to the beating frequency, and dynamic ATP synthesis in response to illumination allows us to control beating frequency of flagella in a light-dependent manner. In addition, we verified the functionality of light-powered synthetic vesicles in in vitro motility assays by encapsulating microtubules assembled with force-generating kinesin-1 motors and the energy module to investigate the dynamics of a contractile filamentous network in cell-like compartments by optical stimulation. Integration of this photosynthetic system with various biological building blocks such as cytoskeletal filaments and molecular motors may contribute to the bottom-up synthesis of artificial cells that are able to undergo motor-driven morphological deformations and exhibit directional motion in a light-controllable fashion. |
BibTeX:
@article{Ahma, author = {Ahmad, R. and Kleineberg, K. and Nasirimarekani, V. and Su, Y.-J. and Pozveh, S. G. and Bae, A. and Sundmacher, K. and Bodenschatz, E. and Guido, I. and Vidakovic-Koch, T. and Gholami, A.}, title = {Light-Powered Reactivation of Flagella and Contraction of Microtubule Networks: Toward Building an Artificial Cell}, journal = {ACS Synth. Biol.}, month = {March}, year = {2021}, volume = {10}, number = {6}, pages = {1490}, doi = {10.1021/acssynbio.1c00071},, url = {https://pubs.acs.org/doi/abs/10.1021/acssynbio.1c00071} } |
Küchler, C., "Measurements of Turbulence at High Reynolds Numbers", March 2021 |
Abstract: The effective description and fundamental understanding of turbulent flows remains elusive to modern physics despite centuries of research and its great importance in numerous fields. The theoretical difficulties of the topic (nonlinear, nonlocal, or unclosed equations) are accompanied by the multiscale characteristics, large number of degrees of freedom, and strong sensitivity to initial conditions that make numerical and laboratory experiments equally challenging. One potential way to unravel the dynamics underlying turbulent motions is the separation of inertial forces from viscous forces, i.e. the study of turbulence at very large Reynolds numbers. The Max Planck Variable Density Turbulence Tunnel (VDTT) is a facility well-suited for the study of such large Reynolds numbers under controlled conditions. Its active grid allows the creation of turbulence at Taylor-scale Reynolds numbers Rë > 6000 that can be investigated with state-of-the-art subminiature hot wires and whose turbulence generation can be controlled with great flexibility. This allows the study of fine details of the turbulence energy spectrum, such as the bottleneck effect, which are difficult to investigate even at small Rë. We show for the first time experimentally that the bottleneck effect decreases with increasing Reynolds number up to Rë ≈ 5000 confirming previous numerical studies at lower Reynolds numbers. A very influential phenomenological model is the seminal self-similar model of the velocity increment statistics by Kolmogorov and its intermittency refinements. In this thesis the cornerstones of this scaling theory are confirmed approximately throughout the range of Rë studied (150-6000) using hot wire data from the VDTT. This constitutes the most extensive dataset in this range of Rë to the author’s best knowledge. The local scaling exponents of the increment statistics becomes Rë-independent for Rë > 2000. They do however not allow the immediate identification of an inertial range scaling exponent, but carry the imprints of the turbulence decay and certain dissipative effects. The effect of decay is more dramatic, but can be explained by a model for the statistics of decaying turbulence. This allows the extraction of an inertial range scaling exponent that agrees with those obtained by the extended self-similarity technique. The dissipative effects take the form of log-periodic oscillations on the scaling functions, whose exact physical origin remains elusive. The remainder of the thesis deals with the design and implementation of a particle tracking system in the VDTT. The system allows the measurement of statistics in the Lagrangian framework, where instead of a multi-location measurement, individual fluid parcels are followed throughout the flow and multi-time statistics are obtained. The setup records the motion of cellulose particles of Stokes numbers between 0.0001 and 2 illuminated by a high-power laser using four stationary high-speed cameras. It is shown that the setup is capable of acquiring acceleration statistics and record particle tracks of up to 15 viscous time scales. This allows the systematic investigation of Lagrangian turbulence at Rë > 2000 where such investigations were impossible hereto- fore. |
BibTeX:
@phdthesis{K, author = {Küchler, C.}, title = {Measurements of Turbulence at High Reynolds Numbers}, month = {March}, year = {2021},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0005-15A8-6} } |
O'Shea, S., Crosier, J., Dorsey, J., Gallagher, L., Schledewitz, W., Bower, K., Schlenczek, O., Borrmann, S., Cotton, R., Westbrook, C. and Ulanowski, Z., "Characterising optical array particle imaging probes: implications for small-ice-crystal observations", Atmos. Meas. Tech., March 2021, Vol. 14(3), 1917 pp. |
Abstract: The cloud particle concentration, size, and shapedata from optical array probes (OAPs) are routinely used toparameterise cloud properties and constrain remote sensingretrievals. This paper characterises the optical response ofOAPs using a combination of modelling, laboratory, and fieldexperiments. Significant uncertainties are found to exist withsuch probes for ice crystal measurements. We describe andtest two independent methods to constrain a probe’s sam-ple volume that remove the most severely mis-sized parti-cles: (1) greyscale image analysis and (2) co-location usingstereoscopic imaging. These methods are tested using fieldmeasurements from three research flights in cirrus. For thesecases, the new methodologies significantly improve agree-ment with a holographic imaging probe compared to con-ventional data-processing protocols, either removing or sig-nificantly reducing the concentration of small ice crystals(< 200 ìm) in certain conditions. This work suggests that theobservational evidence for a ubiquitous mode of small iceparticles in ice clouds is likely due to a systematic instrumentbias. Size distribution parameterisations based on OAP mea-surements need to be revisited using these improved method-ologies. |
BibTeX:
@article{2021a, author = {O'Shea, S. and Crosier, J. and Dorsey, J. and Gallagher, L. and Schledewitz, W. and Bower, K. and Schlenczek, O. and Borrmann, S. and Cotton, R. and Westbrook, C. and Ulanowski, Z.}, title = {Characterising optical array particle imaging probes: implications for small-ice-crystal observations}, journal = {Atmos. Meas. Tech.}, month = {March}, year = {2021}, volume = {14}, number = {3}, pages = {1917}, doi = {10.5194/amt-14-1917-2021},, url = {https://amt.copernicus.org/articles/14/1917/2021/amt-14-1917-2021-discussion.html} } |
Tai, N. C., Ching, E. S. C., Zwirner, L. and Shishkina, O., "Heat flux in turbulent Rayleigh-Bénard convection: Predictions derived from a boundary layer theory", Phys. Rev. Fluids, March 2021, Vol. 6, 033501 pp. |
Abstract: Using a closed set of boundary layer equations [E. S. C. Ching et al., Phys. Rev. Research 1, 033037 (2019)] for turbulent Rayleigh-Bénard convection, we derive analytical results for the dependence of the heat flux, measured by the Nusselt number (Nu), on the Reynolds (Re) and Prandtl (Pr) numbers and two parameters that measure fluctuations in the regime where the horizontal pressure gradient is negligible. This regime is expected to be reached at sufficiently high Rayleigh numbers for a fluid of any given Prandtl number. In the high-Pr limit, Nu=F1(k1)Re1/2Pr1/3 and, in the low-Pr limit, Nu tends to ð-1/2Re1/2Pr1/2, where F1(k1) has a weak dependence on the parameter k1 in the eddy viscosity that measures velocity fluctuations. These theoretical results further reveal a close resemblance of the scaling dependencies of heat flux in steady forced convection and turbulent Rayleigh-Bénard convection and this finding solves a puzzle in our present understanding of heat transfer in turbulent Rayleigh-Bénard convection. |
BibTeX:
@article{2021f, author = {Tai, N. C. and Ching, E. S. C. and Zwirner, L. and Shishkina, O.}, title = {Heat flux in turbulent Rayleigh-Bénard convection: Predictions derived from a boundary layer theory}, journal = {Phys. Rev. Fluids}, month = {March}, year = {2021}, volume = {6}, pages = {033501}, doi = {10.1103/PhysRevFluids.6.033501},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.6.033501} } |
Yan, B., Shishkina, O. and He, X., "Thermal boundary-layer structure in laminar horizontal convection", JFM, March 2021, Vol. 915, R5 pp. |
Abstract: We present experimentally obtained time-averaged vertical temperature profiles è(z) in horizontal convection (HC) in water (Prandtl number Pr=6), which were measured near the heating and cooling plates that are embedded in the bottom of HC samples. Three HC rectangular samples of different sizes but the same aspect ratio Ã ≡ L:W:H=10:1:1 (L, W and H are the length, width and height of the sample, respectively) were used in the experiments, which allowed us to study HC in a Rayleigh-number range 2x10^10 ≲ Ra ≲ 9x10^12. The measurements revealed that above the cooling plate, the mean temperature profiles have a universal scaling form è(z/ëc) with ëc being a Ra-dependent thickness of the cold thermal boundary layer (BL). The è(z/ëc)-profiles agree well with solutions to a laminar BL equation in HC, which is derived under assumption that the large-scale horizontal velocity achieves its maximum near the plate and vanishes in the bulk. Above the heating plate, the mean temperature field has a double-layer structure: in the lower layer, the è profiles scale with the hot thermal BL thickness ëh, while in the upper layer, they again scale with ëc. Both scaling forms are in good agreement with the solutions to the BL equation with a proper parameter choice. |
BibTeX:
@article{Yan, author = {Yan, B. and Shishkina, O. and He, X.}, title = {Thermal boundary-layer structure in laminar horizontal convection}, journal = {JFM}, month = {March}, year = {2021}, volume = {915}, pages = {R5}, doi = {10.1017/jfm.2021.226},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/thermal-boundarylayer-structure-in-laminar-horizontal-convection/281E63EEB124C6D19E70A0AF98342491} } |
Zhang, X., Ecke, R. and Shishkina, O., "Boundary zonal flows in rapidly rotating turbulent thermal convection", March 2021, Vol. 915, A62 pp. |
Abstract: Recently, in Zhang et al. (Phys. Rev. Lett., vol. 124, 2020, 084505), it was found that, in rapidly rotating turbulent Rayleigh-Bénard convection in slender cylindrical containers (with diameter-to-height aspect ratio Ã=1/2) filled with a small-Prandtl-number fluid (Pr ≈ 0.8), the large-scale circulation is suppressed and a boundary zonal flow (BZF) develops near the sidewall, characterized by a bimodal probability density function of the temperature, cyclonic fluid motion and anticyclonic drift of the flow pattern (with respect to the rotating frame). This BZF carries a disproportionate amount (>60%) of the total heat transport for Pr < 1, but decreases rather abruptly for larger Pr to approximately 35%. In this work, we show that the BZF is robust and appears in rapidly rotating turbulent Rayleigh-Bénard convection in containers of different Ã and over a broad range of Pr and Ra. Direct numerical simulations for Prandtl number 0.1 ≤ Pr ≤ 12.3, Rayleigh number 10^7 ≤ Ra ≤ 5x10^9, inverse Ekman number 10^5 1/Ek ≤ 10^7 and Ã=1/3, 1/2, 3/4, 1 and 2 show that the BZF width ä0 scales with the Rayleigh number Ra and Ekman number Ek as ä0/H-Ã0Pr-1/4,0Ra1/4Ek2/3 (Pr<1,Pr>1) and with the drift frequency scales as ù/Ù-Ã0Pr-4/3RaEk5/3, where H is the cell height and Ù the angular rotation rate. The mode number of the BZF is 1 for Ã ≲ 1 and 2Ã for Ã=1,2 independent of Ra and Pr. The BZF is quite reminiscent of wall mode states in rotating convection. |
BibTeX:
@article{Zhanga, author = {Zhang, X. and Ecke, R. and Shishkina, O.}, title = {Boundary zonal flows in rapidly rotating turbulent thermal convection}, month = {March}, year = {2021}, volume = {915}, pages = {A62}, doi = {10.1017/jfm.2021.74},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/boundary-zonal-flows-in-rapidly-rotating-turbulent-thermal-convection/0CACBDB849F79B4C249EAFA92D54DC2E} } |
He, X., Bodenschatz, E. and Ahlers, G., "A model for universal spatial variations of temperature fluctuations in turbulent Rayleigh-Bénard convection", Theoretical and Applied Mechanics Letters, February 2021, Vol. 11(2), 100237 pp. |
Abstract: We propose a theoretical model for spatial variations of the temperature variance (z is the distance from the sample bottom and r the radial coordinate) in turbulent Rayleigh-Bénard convection (RBC). Adapting the “attached-eddy” model of shear flow to the plumes of RBC, we derived an equation for which is based on the universal scaling of the normalized RBC temperature spectra. This equation includes both logarithmic and power-law dependences on , where is the thermal boundary layer thickness. The equation parameters depend on r and the Prandtl number Pr, but have only an extremely weak dependence on the Rayleigh number Ra Thus our model provides a near-universal equation for the temperature variance profile in turbulent RBC. |
BibTeX:
@article{He, author = {He, X. and Bodenschatz, E. and Ahlers, G.}, title = {A model for universal spatial variations of temperature fluctuations in turbulent Rayleigh-Bénard convection}, journal = {Theoretical and Applied Mechanics Letters}, month = {February}, year = {2021}, volume = {11}, number = {2}, pages = {100237}, doi = {10.1016/j.taml.2021.100237},, url = {https://www.sciencedirect.com/science/article/pii/S2095034921000441} } |
Reiter, P., Zhang, X., Stepanov, R. and Shishkina, O., "Generation of zonal flows in convective systems by travelling thermal waves", J. Fluid Mech., February 2021, Vol. 913, A13 pp. |
Abstract: This work addresses the effect of travelling thermal waves applied at the fluid layer surface, on the formation of global flow structures in two-dimensional (2-D) and 3-D convective systems. For a broad range of Rayleigh numbers (103 ≤ Ra ≤ 107) and thermal wave frequencies (10-4 ≤ Ù ≤ 100), we investigate flows with and without imposed mean temperature gradients. Our results confirm that the travelling thermal waves can cause zonal flows, i.e. strong mean horizontal flows. We show that the zonal flows in diffusion dominated regimes are driven purely by the Reynolds stresses and end up always travelling retrograde. In convection dominated regimes, however, mean flow advection, caused by tilted convection cells, becomes dominant. This generally leads to prograde directed mean zonal flows. By means of direct numerical simulations we validate theoretical predictions made for the diffusion dominated regime. Furthermore, we make use of the linear stability analysis and explain the existence of the tilted convection cell mode. Our extensive 3-D simulations support the results for 2-D flows and thus provide further evidence for the relevance of the findings for geophysical and astrophysical systems. |
BibTeX:
@article{reit, author = {Reiter, P. and Zhang, X. and Stepanov, R. and Shishkina, O.}, title = {Generation of zonal flows in convective systems by travelling thermal waves}, journal = {J. Fluid Mech.}, month = {February}, year = {2021}, volume = {913}, pages = {A13}, doi = {10.1017/jfm.2020.1186},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/generation-of-zonal-flows-in-convective-systems-by-travelling-thermal-waves/AA697C58A404B7A5FB12E20F53EDCBE8} } |
Rossi, E., Bagheri, G., Beckett, F. and Bonadonna, C., "The fate of volcanic ash: premature or delayed sedimentation?", Nature Communications, February 2021, Vol. 12(1303), 1 pp. |
Abstract: A large amount of volcanic ash produced during explosive volcanic eruptions has been found to sediment as aggregates of various types that typically reduce the associated residence time in the atmosphere (i.e., premature sedimentation). Nonetheless, speculations exist in the literature that aggregation has the potential to also delay particle sedimentation (rafting effect) even though it has been considered unlikely so far. Here, we present the first theoretical description of rafting that demonstrates how delayed sedimentation may not only occur but is probably more common than previously thought. The fate of volcanic ash is here quantified for all kind of observed aggregates. As an application to the case study of the 2010 eruption of Eyjafjallajökull volcano (Iceland), we also show how rafting can theoretically increase the travel distances of particles between 138–710?ìm. These findings have fundamental implications for hazard assessment of volcanic ash dispersal as well as for weather modeling. |
BibTeX:
@article{Rossi, author = {Rossi, E. and Bagheri, G. and Beckett, F. and Bonadonna, C.}, title = {The fate of volcanic ash: premature or delayed sedimentation?}, journal = {Nature Communications}, month = {February}, year = {2021}, volume = {12}, number = {1303}, pages = {1}, doi = {10.1038/s41467-021-21568-8},, url = {https://www.nature.com/articles/s41467-021-21568-8} } |
Wedi, M., van Gils, D., Bodenschatz, E. and Weiss, S., "Rotating turbulent thermal convection at very large Rayleigh numbers", J. Fluid Mech., February 2021, Vol. 912, A30 pp. |
Abstract: We report on turbulent thermal convection experiments in a rotating cylinder with a diameter (D) to height (H) aspect ratio of Ã=D/H=0.5. Using nitrogen and pressurised sulphur hexafluoride we cover Rayleigh numbers (Ra) from 8x10^9 to 8x10^14 at Prandtl numbers 0.72 ≲ Pr ≲ 0.94. For these Ra we measure the global vertical heat flux (i.e. the Nusselt number – Nu), as well as statistical quantities of local temperature measurements, as a function of the rotation rate, i.e. the inverse Rossby number – 1/Ro. In contrast to measurements in fluids with a higher Pr we do not find a heat transport enhancement, but only a decrease of Nu with increasing 1/Ro. When normalised with Nu(0) for the non-rotating system, data for all different Ra collapse and, for sufficiently large 1/Ro, follow a power law Nu/Nu0 ∝ (1/Ro)-0.43. Furthermore, we find that both the heat transport and the temperature field qualitatively change at rotation rates 1/Ro ∗ 1=0.8 and 1/Ro ∗ 2=4. We interpret the first transition at 1/Ro ∗ 1 as change from a large-scale circulation roll to the recently discovered boundary zonal flow (BZF). The second transition at rotation rate 1/Ro ∗ 2 is not associated with a change of the flow morphology, but is rather the rotation rate for which the BZF is at its maximum. For faster rotation the vertical transport of warm and cold fluid near the sidewall within the BZF decreases and hence so does Nu. |
BibTeX:
@article{2021b, author = {Wedi, M. and van Gils, D. and Bodenschatz, E. and Weiss, S.}, title = {Rotating turbulent thermal convection at very large Rayleigh numbers}, journal = {J. Fluid Mech.}, month = {February}, year = {2021}, volume = {912}, pages = {A30}, doi = {10.1017/jfm.2020.1149},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/rotating-turbulent-thermal-convection-at-very-large-rayleigh-numbers/18114099E6030E3C224E2CE60ADDF60A} } |
Gallemí-Pérez, A. and Chávez-Medina, V., "Current and future challenges in interdisciplinary Ph.D. education as perceived by students", Communications Physics, January 2021, Vol. 4(6), 1 pp. |
Abstract: Göttingen is home to the Third Infinity conference, a biennial event organized by Ph.D. candidates that aims, beyond discussing complex systems physics, at providing a platform to discuss themes central to doctoral life and education. As part of the organizing committee of Third Infinity 2020, in this comment we would like to raise attention on the main issues faced by today’s European interdisciplinary Ph.D. students as we learnt them from direct experience during the organization process, as well as from discussion with our peers during the event. |
BibTeX:
@article{Ga, author = {Gallemí-Pérez, A. and Chávez-Medina, V.}, title = {Current and future challenges in interdisciplinary Ph.D. education as perceived by students}, journal = {Communications Physics}, month = {January}, year = {2021}, volume = {4}, number = {6}, pages = {1}, doi = {10.1038/s42005-020-00497-w},, url = {https://www.nature.com/articles/s42005-020-00497-w} } |
Bai, X.-D., Wang, Y. and Zhang, W., "Applying physics informed neural network for flow data assimilation", Journal of Hydrodynamics, December 2020, Vol. 32, 1050 pp. |
Abstract: Data assimilation (DA) refers to methodologies which combine data and underlying governing equations to provide an estimation of a complex system. Physics informed neural network (PINN) provides an innovative machine learning technique for solving and discovering the physics in nature. By encoding general nonlinear partial differential equations, which govern different physical systems such as fluid flows, to the deep neural network, PINN can be used as a tool for DA. Due to its nature that neither numerical differential operation nor temporal and spatial discretization is needed, PINN is straightforward for implementation and getting more and more attention in the academia. In this paper, we apply the PINN to several flow problems and explore its potential in fluid physics. Both the mesoscopic Boltzmann equation and the macroscopic Navier-Stokes are considered as physics constraints. We first introduce a discrete Boltzmann equation informed neural network and evaluate it with a one-dimensional propagating wave and two-dimensional lid-driven cavity flow. Such laminar cavity flow is also considered as an example in an incompressible Navier-Stokes equation informed neural network. With parameterized Navier-Stokes, two turbulent flows, one within a C-shape duct and one passing a bump, are studied and accompanying pressure field is obtained. Those examples end with a flow passing through a porous media. Applications in this paper show that PINN provides a new way for intelligent flow inference and identification, ranging from mesoscopic scale to macroscopic scale, and from laminar flow to turbulent flow. |
BibTeX:
@article{Bai, author = {Bai, X.-D. and Wang, Y. and Zhang, W.}, title = {Applying physics informed neural network for flow data assimilation}, journal = {Journal of Hydrodynamics}, month = {December}, year = {2020}, volume = {32}, pages = {1050}, doi = {10.1007/s42241-020-0077-2},, url = {https://link.springer.com/article/10.1007/s42241-020-0077-2} } |
He, X., Bodenschatz, E. and Ahlers, G., "Aspect ratio dependence of the ultimate-state transition in turbulent thermal convection", PNAS, December 2020, Vol. 117(48), 30022 pp. |
Abstract: Iyer et al. (1) report heat (Nu) and momentum (Re) transport results for turbulent Rayleigh-Bénard convection (RBC) for a Prandtl number Pr=1 from direct numerical simulation (DNS) for a cylindrical sample of aspect ratio (diameter D/height H ) Ã=1/10. The data show the classic scaling Nu=0.0525Ra0.331 in the range 1010<=Ra<=1015. The authors emphasize that their data do not reveal a transition Rayleigh number Ra* to the RBC ultimate state (2, 3), but neglect to point out that sidewall stabilization, and thus Ra*, is expected to increase with decreasing Ã. Here, we point out that experimental Ra* values do indeed show a strong Ã dependence with Ra* well above 1015 for Ã=0.1. |
BibTeX:
@article{He2021, author = {He, X. and Bodenschatz, E. and Ahlers, G.}, title = {Aspect ratio dependence of the ultimate-state transition in turbulent thermal convection}, journal = {PNAS}, month = {December}, year = {2020}, volume = {117}, number = {48}, pages = {30022}, doi = {10.1073/pnas.2007399117},, url = {https://www.pnas.org/content/117/48/30022.short} } |
Pozveh, S. G., Bae, A. J. and Gholami, A., "Resistive force theory and wave dynamics in swimming flagellar apparatus isolated from C. reinhardtii", Soft Matter, December 2020, Vol. 17, 1601 pp. |
Abstract: Cilia-driven motility and fluid transport are ubiquitous in nature and essential for many biological processes, including swimming of eukaryotic unicellular organisms, mucus transport in airway apparatus or fluid flow in the brain. The-biflagellated micro-swimmer Chlamydomonas reinhardtii is a model organism to study the dynamics of flagellar synchronization. Hydrodynamic interactions, intracellular mechanical coupling or cell body rocking is believed to play a crucial role in the synchronization of flagellar beating in green algae. Here, we use freely swimming intact flagellar apparatus isolated from a wall-less strain of Chlamydomonas to investigate wave dynamics. Our analysis on phase coordinates shows that when the frequency difference between the flagella is high (10–41% of the mean), neither mechanical coupling via basal body nor hydrodynamics interactions are strong enough to synchronize two flagella, indicating that the beating frequency is perhaps controlled internally by the cell. We also examined the validity of resistive force theory for a flagellar apparatus swimming freely in the vicinity of a substrate and found quantitative agreement between the experimental data and simulations with a drag anisotropy of ratio 2. Finally, using a simplified wave form, we investigated the influence of phase and frequency differences, intrinsic curvature and wave amplitude on the swimming trajectory of flagellar apparatus. Our analysis shows that by controlling the phase or frequency differences between two flagella, steering can occur. |
BibTeX:
@article{Poz, author = {Pozveh, S. G. and Bae, A. J. and Gholami, A.}, title = {Resistive force theory and wave dynamics in swimming flagellar apparatus isolated from C. reinhardtii}, journal = {Soft Matter}, month = {December}, year = {2020}, volume = {17}, pages = {1601}, doi = {10.1039/d0sm01969k},, url = {https://pubs.rsc.org/en/content/articlehtml/2021/sm/d0sm01969k} } |
Scheller, V., "Switchable polymeric microcarriers forremodeling of wound healing", December 2020 |
BibTeX:
@mastersthesis{Sch, author = {Scheller, V.}, title = {Switchable polymeric microcarriers forremodeling of wound healing}, month = {December}, year = {2020},, url = {http://www.lfpn.ds.mpg.de/Thesis/Masterarbeit_Vanessa_Scheller.pdf} } |
Wang, Q., Lohse, D. and Shishkina, O., "Scaling in Internally Heated Convection: A Unifying Theory", Geophysical Research Letters, December 2020, Vol. 48(4), e2020GL091198 pp. |
Abstract: We offer a unifying theory for turbulent, purely internally heated convection, generalizing the unifying theories of Grossmann and Lohse (2000, https://doi.org/10.1017/S0022112099007545; 2001, https://doi.org/10.1103/PhysRevLett.86.3316) for Rayleigh-Bénard turbulence and of Shishkina et al. (2016, https://doi.org/10.1002/2015GL067003) for turbulent horizontal convection, which are both based on the splitting of the kinetic and thermal dissipation rates in respective boundary and bulk contributions. We obtain the mean temperature of the system and the Reynolds number (which are the response parameters) as function of the control parameters, namely the internal thermal driving strength (called, when nondimensionalized, the Rayleigh-Roberts number) and the Prandtl number. The results of the theory are consistent with our direct numerical simulations of the Boussinesq equations. |
BibTeX:
@article{Wangb, author = {Wang, Q. and Lohse, D. and Shishkina, O.}, title = {Scaling in Internally Heated Convection: A Unifying Theory}, journal = {Geophysical Research Letters}, month = {December}, year = {2020}, volume = {48}, number = {4}, pages = {e2020GL091198}, doi = {10.1029/2020GL091198},, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091198} } |
Bhowmick, T., Wang, Y., Iovieno, M., Bagheri, G. and Bodenschatz, E., "Supersaturation in the Wake of a Precipitating Hydrometeor and its Impact on Aerosol Activation", Geophysical Research Letters, November 2020, Vol. 47(22), e2020GL091179 pp. |
Abstract: The activation of aerosols impacts the life cycle of a cloud. A detailed understanding is necessary for reliable climate prediction. Recent laboratory experiments demonstrate that aerosols can be activated in the wake of precipitating hydrometeors. However, many quantitative aspects of this wake-induced activation of aerosols remain unclear. Here, we report a detailed numerical investigation of the activation potential of wake-induced supersaturation. By Lagrangian tracking of aerosols we show that a significant fraction of aerosols are activated in the supersaturated wake. These 'lucky aerosols' are entrained in the wake's vortices and reside in the supersaturated environment sufficiently long to be activated. Our analyses show that this wake-induced activation of aerosols can contribute to the life cycle of the clouds. |
BibTeX:
@article{Bh, author = {Bhowmick, T. and Wang, Y. and Iovieno, M. and Bagheri, G. and Bodenschatz, E.}, title = {Supersaturation in the Wake of a Precipitating Hydrometeor and its Impact on Aerosol Activation}, journal = {Geophysical Research Letters}, month = {November}, year = {2020}, volume = {47}, number = {22}, pages = {e2020GL091179}, doi = {10.1029/2020GL091179},, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091179} } |
Buaria, D., Pumir, A. and Bodenschatz, E., "Self-attenuation of extreme events in Navier-Stokes turbulence", Nat. Commun., November 2020, Vol. 11(5852), 1 pp. |
Abstract: Turbulent fluid flows are ubiquitous in nature and technology, and are mathematically described by the incompressible Navier-Stokes equations. A hallmark of turbulence is spontaneous generation of intense whirls, resulting from amplification of the fluid rotation-rate (vorticity) by its deformation-rate (strain). This interaction, encoded in the non-linearity of Navier-Stokes equations, is non-local, i.e., depends on the entire state of the flow, constituting a serious hindrance in turbulence theory and even establishing regularity of the equations. Here, we unveil a novel aspect of this interaction, by separating strain into local and non-local contributions utilizing the Biot-Savart integral of vorticity in a sphere of radius R. Analyzing highly-resolved numerical turbulent solutions to Navier-Stokes equations, we find that when vorticity becomes very large, the local strain over small R surprisingly counteracts further amplification. This uncovered self-attenuation mechanism is further shown to be connected to local Beltramization of the flow, and could provide a direction in establishing the regularity of Navier-Stokes equations. |
BibTeX:
@article{bua, author = {Buaria, D. and Pumir, A. and Bodenschatz, E.}, title = {Self-attenuation of extreme events in Navier-Stokes turbulence}, journal = {Nat. Commun.}, month = {November}, year = {2020}, volume = {11}, number = {5852}, pages = {1}, doi = {10.1038/s41467-020-19530-1},, url = {https://www.nature.com/articles/s41467-020-19530-1} } |
Buaria, D., Bodenschatz, E. and Pumir, A., "Vortex stretching and enstrophy production in high Reynolds number turbulence", Phys. Rev. Fluids, October 2020, Vol. 5(10), 104602 pp. |
Abstract: An essential ingredient of turbulent flows is the vortex stretching mechanism, whichemanates from the nonlinear interaction of vorticity and strain-rate tensor and leads toformation of extreme events. We analyze the statistical correlations between vorticity andstrain rate by using a massive database generated from very well-resolved direct numericalsimulations of forced isotropic turbulence in periodic domains. The grid resolution is upto 12 288^3, and the Taylor-scale Reynolds number is in the range 140-1300. In orderto understand the formation and structure of extreme vorticity fluctuations, we obtainstatistics conditioned on enstrophy (vorticity-squared). The magnitude of strain, as well asits eigenvalues, is approximately constant when conditioned on weak enstrophy; whereasthey grow approximately as power laws for strong enstrophy, which become steeper withincreasing Rë. We find that the well-known preferential alignment between vorticity andthe intermediate eigenvector of strain tensor is even stronger for large enstrophy, whereasvorticity shows a tendency to be weakly orthogonal to the most extensive eigenvector (for large enstrophy). Yet the dominant contribution to the production of large enstro-phy events arises from the most extensive eigendirection, the more so as Rë increases. Nevertheless, the stretching in intense vorticity regions is significantly depleted, consistentwith the kinematic properties of weakly curved tubes in which they are organized. Furtheranalysis reveals that intense enstrophy is primarily depleted via viscous diffusion, thoughviscous dissipation is also significant. Implications for modeling are nominally addressedas appropriate. |
BibTeX:
@article{Buar, author = {Buaria, D. and Bodenschatz, E. and Pumir, A.}, title = {Vortex stretching and enstrophy production in high Reynolds number turbulence}, journal = {Phys. Rev. Fluids}, month = {October}, year = {2020}, volume = {5}, number = {10}, pages = {104602}, doi = {10.1103/PhysRevFluids.5.104602},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.104602} } |
Eckstein, T., Vidal-Henriquez, E., Bae, A. J. and Gholami, A., "Spatial heterogeneities shape the collective behavior of signaling amoeboid cells", Sci. Signal, October 2020, Vol. 13(655), eaaz3975 pp. |
Abstract: In its natural habitat in the forest soil, the cellular slime mold Dictyostelium discoideum is exposed to obstacles. Starving Dictyostelium cells secrete cAMP, which is the key extracellular signaling molecule that promotes the aggregation process required for their long-term survival. Here, we investigated the influence of environmental inhomogeneities on the signaling and pattern formation of Dictyostelium cells. We present experimental data and numerical simulations on the pattern formation of signaling Dictyostelium cells in the presence of periodic arrays of millimeter-sized pillars. We observed concentric cAMP waves that initiated almost synchronously at the pillars and propagated outward. In response to these circular waves, the Dictyostelium cells streamed toward the pillars, forming aggregates arranged in patterns that reflected the periodicity of the lattice of pillars. Our results suggest that, in nature, the excitability threshold and synchronization level of the cells are two key parameters that control the nature of the interaction between cells and spatial heterogeneities in their environment. |
BibTeX:
@article{Eck, author = {Eckstein, T. and Vidal-Henriquez, E. and Bae, A. J. and Gholami, A.}, title = {Spatial heterogeneities shape the collective behavior of signaling amoeboid cells}, journal = {Sci. Signal}, month = {October}, year = {2020}, volume = {13}, number = {655}, pages = {eaaz3975}, doi = {10.1126/scisignal.aaz3975},, url = {https://stke.sciencemag.org/content/13/655/eaaz3975} } |
Gabellini, P., Rossi, E., Bonadonna, C., Pistolesi, M., Bagheri, G. and Cioni, R., "Physical and Aerodynamic Characterization of Particle Clusters at Sakurajima Volcano (Japan)", Front. Earth Sci., October 2020, Vol. 8(575874), 1 pp. |
Abstract: The process of particle aggregation significantly affects ash settling dynamics associated with volcanic explosive eruptions. Several experiments have been carried out to investigate the physics of ash aggregation and dedicated numerical schemes have been developed to produce more accurate forecasting of ash dispersal and sedimentation. However, numerical description of particle aggregation is complicated by the lack of complete datasets on natural samples required for model validation and calibration. Here we present a first comprehensive dataset for the internal structure, aerodynamical properties (e.g., size, density, terminal velocity) and grain size of constituting particles of a variety of aggregate types collected in the natural laboratory of Sakurajima Volcano (Japan). Even though the described particle clusters represent the most common types of aggregates associated with ash-rich fallouts, they are of difficult characterization due to the very low potential of preservation in tephra-fallout deposits. Properties were, therefore, derived based on a combination of high-resolution-high-speed videos of tephra fallout, scanning electron microscope analysis of aggregates collected on adhesive paper and analysis of tephra samples collected in dedicated trays. Three main types of particle clusters were recognized and quantitively characterized: cored clusters (PC3), coated particles (PC2), and ash clusters (PC1) (in order of abundance). A wide range of terminal velocities (0.5–4 m/s) has been observed for these aggregates, with most values varying between 1 and 2 m/s, while aggregate size varies between 200 and 1,200 µm. PC1, PC2, and PC3 have densities between 250 and 500, 1,500 and 2,000, and 500 and 1,500 kg/m3, respectively. The size of the aggregate core, where present, varies between 200 and 750 µm and increases with aggregate size. Grain size of tephra samples was deconvoluted into a fine and a coarse Gaussian subpopulation, well correlated with the grain size of shells and of the internal cores of aggregates, respectively. This aspect, together with the revealed abundance of PC3 aggregates, reconciles the presence of a large amount of fine ash (aggregate shells) with coarse ash (aggregate cores) and better explains the grain size distribution bimodality, the high settling velocity with respect to typical PC1 velocities and the low settling velocities of large aggregates with respect to typical PC2 velocity. Furthermore, ash forming the aggregates was shown to be always finer than 45 µm, confirming the key role played by aggregation processes in fine ash deposition at Sakurajima. |
BibTeX:
@article{2020d, author = {Gabellini, P. and Rossi, E. and Bonadonna, C. and Pistolesi, M. and Bagheri, G. and Cioni, R.}, title = {Physical and Aerodynamic Characterization of Particle Clusters at Sakurajima Volcano (Japan)}, journal = {Front. Earth Sci.}, month = {October}, year = {2020}, volume = {8}, number = {575874}, pages = {1}, doi = {10.3389/feart.2020.575874},, url = {https://www.frontiersin.org/articles/10.3389/feart.2020.575874/full} } |
Momper, R., Ibanez Landeta, A., Yang, L., Halim, H., Therien-Aubin, H., Bodenschatz, E., Landfester, K. and Riedinger, A., "Plasmonic and Semiconductor Nanoparticles Interfere with Stereolithographic 3D Printing", ACS Appl. Mater. Interfaces, October 2020, Vol. 12(45), 50834 pp. |
Abstract: Two-photon polymerization stereolithographic three-dimensional (3D) printing is used for manufacturing a variety of structures ranging from microdevices to refractive optics. Incorporation of nanoparticles in 3D printing offers huge potential to create even more functional nanocomposite structures. However, this is difficult to achieve since the agglomeration of the nanoparticles can occur. Agglomeration not only leads to an uneven distribution of nanoparticles in the photoresin but also induces scattering of the excitation beam and altered absorption profiles due to interparticle coupling. Thus, it is crucial to ensure that the nanoparticles do not agglomerate during any stage of the process. To achieve noninteracting and well-dispersed nanoparticles on the 3D printing process, first, the stabilization of nanoparticles in the 3D printing resin is indispensable. We achieve this by functionalizing the nanoparticles with surface-bound ligands that are chemically similar to the photoresin that allows increased nanoparticle loadings without inducing agglomeration. By systematically studying the effect of different nanomaterials (Au nanoparticles, Ag nanoparticles, and CdSe/CdZnS nanoplatelets) in the resin on the 3D printing process, we observe that both, material-specific (absorption profiles) and unspecific (radical quenching at nanoparticle surfaces) pathways co-exist by which the photopolymerization procedure is altered. This can be exploited to increase the printing resolution leading to a reduction of the minimum feature size. |
BibTeX:
@article{Momp, author = {Momper, R. and Ibanez Landeta, A. and Yang, L. and Halim, H. and Therien-Aubin, H. and Bodenschatz, E. and Landfester, K. and Riedinger, A.}, title = {Plasmonic and Semiconductor Nanoparticles Interfere with Stereolithographic 3D Printing}, journal = {ACS Appl. Mater. Interfaces}, month = {October}, year = {2020}, volume = {12}, number = {45}, pages = {50834}, doi = {10.1021/acsami.0c14546},, url = {https://pubs.acs.org/doi/abs/10.1021/acsami.0c14546} } |
Stricker, L., Guido, I., Breithaupt, T., Mazza, M. G. and Vollmer, J., "Hybrid sideways/longitudinal swimming in the monoflagellate Shewanella oneidensis: from aerotactic band to biofilm", Royal Soc., October 2020, Vol. 17(20200559), 171 pp. |
Abstract: Shewanella oneidensis MR-1 are facultative aerobic electroactive bacteria with an appealing potential for sustainable energy production and bioremediation. They gather around air sources, forming aerotactic bands and biofilms. Here, we experimentally follow the evolution of the band around an air bubble, and we find good agreement with the numerical solutions of the pertinent transport equations. Video microscopy reveals a transition between motile and non-motile MR-1 upon oxygen depletion, preventing further development of the biofilm. We discover that MR-1 can alternate between longitudinal fast and sideways slow swimming. The resulting bimodal velocity distributions change in response to different oxygen concentrations and gradients, supporting the biological functions of aerotaxis and confinement. |
BibTeX:
@article{Strick, author = {Stricker, L. and Guido, I. and Breithaupt, T. and Mazza, M. G. and Vollmer, J.}, title = {Hybrid sideways/longitudinal swimming in the monoflagellate Shewanella oneidensis: from aerotactic band to biofilm}, journal = {Royal Soc.}, month = {October}, year = {2020}, volume = {17}, number = {20200559}, pages = {171}, doi = {10.1098/rsif.2020.0559},, url = {https://royalsocietypublishing.org/doi/abs/10.1098/rsif.2020.0559} } |
Witt, H., Yandrapalli, N., Sari, M., Turco, L., Robinson, T. and Steinem, C., "Precipitation of Calcium Carbonate Inside Giant Unilamellar Vesicles Composed of Fluid-Phase Lipids", Langmuir, October 2020, Vol. 36, 13244 pp. |
Abstract: Biomineralization of CaCO3 commonly involves the formation of amorphous CaCO3 precursor particles that are produced in a confined space surrounded by a lipid bilayer. While the influence of confinement itself has been investigated with different model systems, the impact of an enclosing continuous lipid bilayer on CaCO3 formation in a confined space is still poorly understood as appropriate model systems are rare. Here, we present a new versatile method based on droplet-based microfluidics to produce fluid-phase giant unilamellar vesicles (GUVs) in the presence of high CaCl2 concentrations. These GUVs can be readily investigated by means of confocal laser scanning microscopy in combination with bright-field microscopy, demonstrating that the formed CaCO3 particles are in conformal contact with the fluid-phase lipid bilayer and thus suggesting a strong interaction between the particle and the membrane. Atomic force microscopy adhesion studies with membrane-coated spheres on different CaCO3 crystals corroborated this notion of a strong interaction between the lipids and CaCO3. |
BibTeX:
@article{Witt, author = {Witt, H. and Yandrapalli, N. and Sari, M. and Turco, L. and Robinson, T. and Steinem, C.}, title = {Precipitation of Calcium Carbonate Inside Giant Unilamellar Vesicles Composed of Fluid-Phase Lipids}, journal = {Langmuir}, month = {October}, year = {2020}, volume = {36}, pages = {13244}, doi = {10.1021/acs.langmuir.0c02175},, url = {https://pubs.acs.org/doi/10.1021/acs.langmuir.0c02175} } |
Yang, R., Chong, K. L., Wang, Q., Verzicco, R., Shishkina, O. and Lohse, D., "Periodically Modulated Thermal Convection", Phys. Rev. Lett., October 2020, Vol. 125(15), 154502 pp. |
Abstract: Many natural and industrial turbulent flows are subjected to time-dependent boundary conditions. Despite being ubiquitous, the influence of temporal modulations (with frequency f) on global transport properties has hardly been studied. Here, we perform numerical simulations of Rayleigh-Bénard convection with time periodic modulation in the temperature boundary condition and report how this modulation can lead to a significant heat flux (Nusselt number Nu) enhancement. Using the concept of Stokes thermal boundary layer, we can explain the onset frequency of the Nu enhancement and the optimal frequency at which Nu is maximal, and how they depend on the Rayleigh number Ra and Prandtl number Pr. From this, we construct a phase diagram in the 3D parameter space (f, Ra, Pr) and identify the following: (i) a regime where the modulation is too fast to affect Nu; (ii) a moderate modulation regime, where Nu increases with decreasing f, and (iii) slow modulation regime, where Nu decreases with further decreasing f. Our findings provide a framework to study other types of turbulent flows with time-dependent forcing. |
BibTeX:
@article{2020c, author = {Yang, R. and Chong, K. L. and Wang, Q. and Verzicco, R. and Shishkina, O. and Lohse, D.}, title = {Periodically Modulated Thermal Convection}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2020}, volume = {125}, number = {15}, pages = {154502}, doi = {10.1103/PhysRevLett.125.154502},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.154502} } |
Yik, H., Valori, V. and Weiss, S., "Turbulent Rayleigh-Bénard convection under strong non-Oberbeck-Boussinesq conditions", Phys. Rev. Fluids, October 2020, Vol. 5(10), 103502 pp. |
Abstract: We report on Rayleigh-Bénard convection with strongly varying fluid properties experimentally and theoretically. Using pressurized sulfur-hexafluoride (SF6) above its critical point, we are able to make measurements at mean temperatures (Tm) and pressures (Pm) along Prandtl-number isolines in the (T,P) parameter space. This allows us to keep the mean Rayleigh- (Ram) and Prandtl number (Prm) constant while changing the temperature dependences of the fluid properties independently, e.g., probing the liquidlike or gaslike region that are left and right of the supercritical isochore. Hence, non-Oberbeck-Boussinesq (NOB) effects can be measured and analyzed cleanly. We measure the temperature at midheight (Tc) as well as the global vertical heat flux. We observe a significant heat transport enhancement of up to 112% under strong NOB conditions. Furthermore, we develop a theoretical model for the global vertical heat flux based on ideas of Grossmann and Lohse (GL) in OB systems, adjusted for nonconstant fluid properties. In this model, the NOB effects influence the boundary layer and hence Tc, but the change of the heat flux is predominantly due to a change of the fluid properties in the bulk, in particular the heat capacity cp and density ñ. Predictions from our model are consistent with our experimental results as well as with previous measurements carried out in pressurized ethane and cryogenic helium. |
BibTeX:
@article{Yik, author = {Yik, H. and Valori, V. and Weiss, S.}, title = {Turbulent Rayleigh-Bénard convection under strong non-Oberbeck-Boussinesq conditions}, journal = {Phys. Rev. Fluids}, month = {October}, year = {2020}, volume = {5}, number = {10}, pages = {103502}, doi = {10.1103/PhysRevFluids.5.103502},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.103502} } |
Bhowmick, T., Wang, Y., Iovieno, M., Bagheri, G. and Bodenschatz, E., "Population Distribution in the Wake of a Sphere", Symmetry, September 2020, Vol. 12(9), 1498 pp. |
Abstract: The physics of heat and mass transfer from an object in its wake has significant importance in natural phenomena as well as across many engineering applications. Here, we report numerical results on the population density of the spatial distribution of fluid velocity, pressure, scalar concentration, and scalar fluxes of a wake flow past a sphere in the steady wake regime (Reynolds number 25 to 285). Our findings show that the spatial population distributions of the fluid and the transported scalar quantities in the wake follow a Cauchy-Lorentz or Lorentzian trend, indicating a variation in its sample number density inversely proportional to the squared of its magnitude. We observe this universal form of population distribution both in the symmetric wake regime and in the more complex three dimensional wake structure of the steady oblique regime with Reynolds number larger than 225. The population density distribution identifies the increase in dimensionless kinetic energy and scalar fluxes with the increase in Reynolds number, whereas the dimensionless scalar population density shows negligible variation with the Reynolds number. Descriptive statistics in the form of population density distribution of the spatial distribution of the fluid velocity and the transported scalar quantities is important for understanding the transport and local reaction processes in specific regions of the wake, which can be used e.g., for understanding the microphysics of cloud droplets and aerosol interactions, or in the technical flows where droplets interact physically or chemically with the environment. |
BibTeX:
@article{Bhowmick, author = {Bhowmick, T. and Wang, Y. and Iovieno, M. and Bagheri, G. and Bodenschatz, E.}, title = {Population Distribution in the Wake of a Sphere}, journal = {Symmetry}, month = {September}, year = {2020}, volume = {12}, number = {9}, pages = {1498}, doi = {doi.org/10.3390/sym12091498},, url = {https://www.mdpi.com/2073-8994/12/9/1498} } |
Buaria, D. and Sreenivasan, K. R., "Dissipation range of the energy spectrum in high Reynolds number turbulence", Phys. Rev. Fluids, September 2020, Vol. 5(9), 092601(R) pp. |
Abstract: We seek to understand the kinetic energy spectrum in the dissipation range of fully developed turbulence. The data are obtained by direct numerical simulations (DNS) of forced Navier-Stokes equations in a periodic domain, for Taylor-scale Reynolds numbers up to R-lambda = 650, with excellent small-scale resolution of k(max) eta approximate to 6, and additionally at R-lambda = 1300 with k(max) eta approximate to 3, where k(max) is the maximum resolved wave number and eta is the Kolmogorov length scale. We find that for a limited range of wave numbers k past the bottleneck, in the range 0.15 less than or similar to k eta <= 0.5, the spectra for all R-lambda display a universal stretched exponential behavior of the form exp(-k(2/3)), in rough accordance with recent theoretical predictions. In contrast, the stretched exponential fit does not possess a unique exponent in the near dissipation range 1 <= k eta <= 4, but one that persistently decreases with increasing R-lambda. This region serves as the intermediate dissipation range between the exp(-k(2/3)) region and the far dissipation range k eta >> 1 where analytical arguments as well as DNS data with superfine resolution [S. Khurshid et al., Phys. Rev. Fluids 3, 082601 (2018)] suggest a simple exp(-k eta) dependence. We briefly discuss our results in connection to the multifractal model. |
BibTeX:
@article{Buara, author = {Buaria, D. and Sreenivasan, K. R.}, title = {Dissipation range of the energy spectrum in high Reynolds number turbulence}, journal = {Phys. Rev. Fluids}, month = {September}, year = {2020}, volume = {5}, number = {9}, pages = {092601(R)}, doi = {10.1103/PhysRevFluids.5.092601},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.092601} } |
Cattelaens, J., Turco, L., Berclaz, L. M., Huelsse, B., Hitzl, W., Vollkommer, T. and Bodenschatz, K. J., "The Impact of a Nanocellulose-Based Wound Dressing in the Management of Thermal Injuries in Children: Results of a Retrospective Evaluation", Life, September 2020, Vol. 10(9), 212 pp. |
Abstract: The aim of this retrospective study is to evaluate for the first time the impact of a nanocellulose-based wound dressing in the treatment of pediatric patients with both partial- and deep-thickness burns. Usability and effectiveness were defined based on parameters such as frequency of dressing changes under narcosis, duration of hospital stay, onset of complications, need for additional treatments, and follow up scar formation assessment. Fifty-six children who sustained burns in the year 2018 and were treated with a nanocellulose-based wound dressing were included in the trial. The mean stay in hospital was 6.7 days. Patients underwent dressing changes under narcosis 2.4 times on average, and none had wound-associated infection. In all, 82% of the patients were treated only with nanocellulose-based wound dressings, and reepithelialization occurred after ten days. The majority of patients had scars with normal pigmentation (98%), vascularization (91%), height (92%), and pliability (92%). In conclusion, using a nanocellulose-based wound dressing for the treatment of both superficial, partial-thickness and deep, full-thickness burns has several advantages. Compared with the results published in literature on other wound dressings, it requires a moderate number of dressing changes under narcosis and results in short hospital stays. Additionally, it has a low associated infection rate and promotes wound healing. |
BibTeX:
@article{Cattelaens2020, author = {Cattelaens, J. and Turco, L. and Berclaz, L. M. and Huelsse, B. and Hitzl, W. and Vollkommer, T. and Bodenschatz, K. J.}, title = {The Impact of a Nanocellulose-Based Wound Dressing in the Management of Thermal Injuries in Children: Results of a Retrospective Evaluation}, journal = {Life}, month = {September}, year = {2020}, volume = {10}, number = {9}, pages = {212}, doi = {10.3390/life10090212},, url = {https://www.mdpi.com/2075-1729/10/9/212} } |
Guido, I., Diehl, D., Olszok, N. A. and Bodenschatz, E., "Cellular velocity, electrical persistence and sensing in developed and vegetative cells during electrotaxis", PLOS ONE, September 2020, Vol. 15(9), 0239379 pp. |
Abstract: Cells have the ability to detect electric fields and respond to them with directed migratory movement. Investigations identified genes and proteins that play important roles in defining the migration efficiency. Nevertheless, the sensing and transduction mechanisms underlying directed cell migration are still under discussion. We use Dictyostelium discoideum cells as model system for studying eukaryotic cell migration in DC electric fields. We have defined the temporal electric persistence to characterize the memory that cells have in a varying electric field. In addition to imposing a directional bias, we observed that the electric field influences the cellular kinematics by accelerating the movement of cells along their paths. Moreover, the study of vegetative and briefly starved cells provided insight into the electrical sensing of cells. We found evidence that conditioned medium of starved cells was able to trigger the electrical sensing of vegetative cells that would otherwise not orient themselves in the electric field. This observation may be explained by the presence of the conditioned medium factor (CMF), a protein secreted by the cells, when they begin to starve. The results of this study give new insights into understanding the mechanism that triggers the electrical sensing and transduces the external stimulus into directed cell migration. Finally, the observed increased mobility of cells over time in an electric field could offer a novel perspective towards wound healing assays. |
BibTeX:
@article{Gui, author = {Guido, I. and Diehl, D. and Olszok, N. A. and Bodenschatz, E.}, title = {Cellular velocity, electrical persistence and sensing in developed and vegetative cells during electrotaxis}, journal = {PLOS ONE}, month = {September}, year = {2020}, volume = {15}, number = {9}, pages = {0239379}, doi = {10.1371/journal.pone.0239379},, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0239379#abstract0} } |
Karstensen, J., Lavik, G., Acquistapace, C., Bagheri, G., Begler, C., Bendinger, A., Bodenschatz, E., Böck, T., Güttler, J., Hall, K., Körner, M., Kopp, A., Lange, D., Mehlmann, M., Nordsiek, F., Reus, K., Ribbe, J., Philippi, M., Piosek, S., Ritschel, M., Tschitschko, B. and Wiskandt, J., "EUREC4A Campaign, Cruise No. MSM89, 17. January - 20. February 2020, Bridgetown (Barbados) - Bridgetown (Barbados), The ocean mesoscale component in the EUREC4A++ field study", September 2020 |
Abstract: The MSM89 expedition of Maria S Merian was a contribution to the international research initiative EUREC4A (www.eurec4a.eu). The cruise was carried out in concert with the M161 campaign on RV METEOR (Germany) and the EUREC4A-OA campaign on NO L’ATALANTE (France). Airplane and drone operations as well as well as continuous observations from the ground-based site on the Island of Barbados (BCO) were considered during the MSM89 campaign.
Moreover, the cruise was coordinated with ships and Saildrone© operations in the context of the US American ATOMIC project. The overall goal of the EUREC4A field campaign was to collect observational data that will enable research on dynamic and thermodynamic processes in the atmosphere and ocean that will bring the understanding of the role of clouds in the climate system to a new level. MSM89 had its focus on the ocean/atmosphere coupling across ocean mesoscale vortices. For this purpose, both ocean and atmosphere profile measurements were carried out to observe the temporal evolution and spatial heterogeneity of the atmospheric and oceanic boundary layer. Autonomous observing platforms (underwater glider) and a ship towed platform (Cloudkite) augmented the ship-based observations. Incubation experiments were performed to determine Nitrogen fixation rates, the gas exchange for carbon dioxide and oxygen uptake. |
BibTeX:
@article{2020a, author = {Karstensen, J. and Lavik, G. and Acquistapace, C. and Bagheri, G. and Begler, C. and Bendinger, A. and Bodenschatz, E. and Böck, T. and Güttler, J. and Hall, K. and Körner, M. and Kopp, A. and Lange, D. and Mehlmann, M. and Nordsiek, F. and Reus, K. and Ribbe, J. and Philippi, M. and Piosek, S. and Ritschel, M. and Tschitschko, B. and Wiskandt, J.}, title = {EUREC4A Campaign, Cruise No. MSM89, 17. January - 20. February 2020, Bridgetown (Barbados) - Bridgetown (Barbados), The ocean mesoscale component in the EUREC4A++ field study}, month = {September}, year = {2020}, doi = {10.2312/cr_msm89},, url = {https://doi.org/10.2312/cr_msm89} } |
Kim, H., Jo, S.-M., Meng, F., Guo, Y., Therien-Aubin, H., Golestanian, R., Landfester, K. and Bodenschatz, E., "One-Step Generation of Core-Gap-Shell Microcapsulesfor Stimuli-Responsive Biomolecular Sensing", Adv. Funct. Mater, September 2020, Vol. 30(50), 2006019 pp. |
Abstract: The versatile design of stimuli-responsive microparticles embedding valuable biomolecules has great potential in a variety of engineering fields, such as sensors, actuators, drug delivery, and catalysis. Here, results are reported on thermoresponsive core-gap-shell (TCGS) microcapsules made of poly(N-isopropylacrylamide) (PNIPAm), which encapsulate hydrophilic payloads in a simple and stable manner. These are realized by a one-step microfluidic approach using the phase separation of a supersaturated aqueous solution of NIPAm. Various designs of the microcapsules are achieved by individual control of the swelling or by incorporating pH-responsive comonomers of the inner core and outer shell. The gap, i.e., the space between the inner core and outer shell, can be loaded with cargo-like nanoparticles. The outer shell can serve as a stimuli-responsive gateway for the transport of smaller molecules from the external solution. It is shown that the TCGS microcapsules are suitable as temperature controllable glucose sensors and hold promise in the design of controllable enzymatic reactions. The proposed platform provides an avenue for developing a new?generation of microparticles for diverse and efficient engineering applications. |
BibTeX:
@article{Ki, author = {Kim, H. and Jo, S.-M. and Meng, F. and Guo, Y. and Therien-Aubin, H. and Golestanian, R. and Landfester, K. and Bodenschatz, E.}, title = {One-Step Generation of Core-Gap-Shell Microcapsulesfor Stimuli-Responsive Biomolecular Sensing}, journal = {Adv. Funct. Mater}, month = {September}, year = {2020}, volume = {30}, number = {50}, pages = {2006019}, doi = {10.1002/adfm.202006019},, url = {https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202006019} } |
Schich, C., "Interplay of actin foci and clathrin rich areasupon Dictyostelium discoideum adhesion", September 2020 |
BibTeX:
@mastersthesis{Schi, author = {Schich, C.}, title = {Interplay of actin foci and clathrin rich areasupon Dictyostelium discoideum adhesion}, month = {September}, year = {2020},, url = {http://www.lfpn.ds.mpg.de/Thesis/Masterarbeit_Christoph_Schich.pdf} } |
Shishkina, O., "Tenacious wall states in thermal convection in rapidly rotating containers", J. Fluid Mech., September 2020, Vol. 898(F1), F1 pp. |
Abstract: Convection in a container, heated from below, cooled from above and rapidly rotated around a vertical axis, starts from its sidewall. When the imposed vertical temperature gradient is not sufficiently large for bulk modes to set in, thermal convection can start in the form of wall modes, which are observed near the sidewall as pairs of hot ascending and cold descending plumes that drift along the wall. With increasing temperature gradient, different wall and bulk modes occur and interact, leading finally to turbulence. A recent numerical study by Favier & Knobloch (J. Fluid Mech., 895, 2020, R1) reveals an extreme robustness of the wall states. They persist above the onset of bulk modes and turbulence, thereby relating them to the recently discovered boundary zonal flows in highly turbulent rotating thermal convection. More exciting is that the wall modes can be thought of as topologically protected states, as they are robust with respect to the sidewall shape. They stubbornly drift along the wall, following its contour, independent of geometric obstacles. |
BibTeX:
@article{S, author = {Shishkina, O.}, title = {Tenacious wall states in thermal convection in rapidly rotating containers}, journal = {J. Fluid Mech.}, month = {September}, year = {2020}, volume = {898}, number = {F1}, pages = {F1}, doi = {10.1017/jfm.2020.420},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/tenacious-wall-states-in-thermal-convection-in-rapidly-rotating-containers/705A9E1320801296E9ECC1CDDFEF9BA8} } |
Zwirner, L., "Superstructures, heat and momentum transport in inclined turbulent thermal convection of low-Prandtl-number fluids", September 2020 |
Abstract: Recent experiments by Vasil’ev et al. (2015a) using liquid sodium as working fluid inside an extremely slender Rayleigh-Bénard convection (RBC) cell of the diameter-to-height aspect ratio Ã = 1/20, which was inclined with respect to gravity, showed astonishing results: the heat transport through the system can be tenfold stronger for an inclination of â 65° , compared to classical RBC without inclination, â = 0°. As liquid metals are opaque and the flow structure is hardly accessible by experimental means, the main objective of this work is to conduct high-fidelity direct numerical simulations (DNS), where the full temperature and velocity fields are available, and to understand the complex relationship between the flow structures and the heat transport. It is found that inside slender cylinders of Ã = 1/5 at Prandtl numbers 1 and 0.1, the heat transport is generally enhanced through inclination. This enhancement is related to a stronger single large-scale circulation (LSC) roll, which helps to create a hot and a cold plume column that eventually span the whole cylinder and impinge on the opposite boundary layer. Furthermore, for low-Prandtl-number fluids (Pr = 0.1) and slender cylinders (Ã = 1/5), the DNS reveal a global flow structure, that consists of up to four distinguishable rolls on top of each other. The heat transport is strongly determined by the number of rolls and decreases significantly as the number of rolls increases. Additionally, the elliptical instability is identified as the mechanism to break up the single-roll flow structure into multiple rolls. Finally, DNS for Ã = 1, extremely low Prandtl number (Pr = 0.0094) and Ra = 1.67 x 10^7 are directly compared to measurements in liquid sodium. The study demonstrates a quantitative agreement of the experimental and numerical results, in particular with respect to the global heat and momentum transport, temperature and velocity profiles, as well as the dynamics of the LSC. The DNS reveal that the twisting and sloshing of the LSC at small inclination angles periodically affects the instantaneous heat transport (with a variation of up to ±44 % of the mean heat transport). The twisted LSC is associated with a weak heat transport, while the sloshing mode that brings together the hot and cold streams of the LSC is associated with a strong heat transport. |
BibTeX:
@phdthesis{Zwira, author = {Zwirner, L.}, title = {Superstructures, heat and momentum transport in inclined turbulent thermal convection of low-Prandtl-number fluids}, month = {September}, year = {2020},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0005-1490-1} } |
Cordes, A., Witt, H., Gallemi-Perez, A., Brückner, B., Grimm, F., Vache, M., Oswald, T., Bodenschatz, J., Flormann, D., Lautenschläger, F., Tarantola, M. and Janshoff, A., "Prestress and Area Compressibility of Actin Cortices Determine the Viscoelastic Response of Living CellsCordes", Phys. Rev. Lett., August 2020, Vol. 125(6-7), 068101 pp. |
Abstract: Shape, dynamics, and viscoelastic properties of eukaryotic cells are primarily governed by a thin, reversibly cross-linked actomyosin cortex located directly beneath the plasma membrane. We obtain time-dependent rheological responses of fibroblasts and MDCK II cells from deformation-relaxation curves using an atomic force microscope to access the dependence of cortex fluidity on prestress. We introduce a viscoelastic model that treats the cell as a composite shell and assumes that relaxation of the cortex follows a power law giving access to cortical prestress, area-compressibility modulus, and the power law exponent (fluidity). Cortex fluidity is modulated by interfering with myosin activity. We find that the power law exponent of the cell cortex decreases with increasing intrinsic prestress and area-compressibility modulus, in accordance with previous finding for isolated actin networks subject to external stress. Extrapolation to zero tension returns the theoretically predicted power law exponent for transiently cross-linked polymer networks. In contrast to the widely used Hertzian mechanics, our model provides viscoelastic parameters independent of indenter geometry and compression velocity. |
BibTeX:
@article{Cordes2020, author = {Cordes, A. and Witt, H. and Gallemi-Perez, A. and Brückner, B. and Grimm, F. and Vache, M. and Oswald, T. and Bodenschatz, J. and Flormann, D. and Lautenschläger, F. and Tarantola, M. and Janshoff, A.}, title = {Prestress and Area Compressibility of Actin Cortices Determine the Viscoelastic Response of Living CellsCordes}, journal = {Phys. Rev. Lett.}, month = {August}, year = {2020}, volume = {125}, number = {6-7}, pages = {068101}, doi = {10.1103/PhysRevLett.125.068101},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.068101} } |
Strübing, T., Khosravanizadeh, A., Vilfan, A., Bodenschatz, E., Golestanian, R. and Guido, I., "Wrinkling Instability in 3D Active Nematics", Nano Lett., August 2020, Vol. 20(9), 6281 pp. |
Abstract: In nature, interactions between biopolymers and motor proteins give rise to biologically essential emergent behaviors. Besides cytoskeleton mechanics, active nematics arise from such interactions. Here we present a study on 3D active nematics made of microtubules, kinesin motors, and depleting agent. It shows a rich behavior evolving from a nematically ordered space-filling distribution of microtubule bundles toward a flattened and contracted 2D ribbon that undergoes a wrinkling instability and subsequently transitions into a 3D active turbulent state. The wrinkle wavelength is independent of the ATP concentration and our theoretical model describes its relation with the appearance time. We compare the experimental results with a numerical simulation that confirms the key role of kinesin motors in cross-linking and sliding the microtubules. Our results on the active contraction of the network and the independence of wrinkle wavelength on ATP concentration are important steps forward for the understanding of these 3D systems. |
BibTeX:
@article{2020, author = {Strübing, T. and Khosravanizadeh, A. and Vilfan, A. and Bodenschatz, E. and Golestanian, R. and Guido, I.}, title = {Wrinkling Instability in 3D Active Nematics}, journal = {Nano Lett.}, month = {August}, year = {2020}, volume = {20}, number = {9}, pages = {6281}, doi = {10.1021/acs.nanolett.0c01546},, url = {https://pubs.acs.org/doi/10.1021/acs.nanolett.0c01546} } |
Wang, Q., Verzicco, R., Lohse, D. and Shishkina, O., "Multiple States in Turbulent Large-Aspect-Ratio Thermal Convection: What Determines the Number of Convection Rolls?", Phys. Rev. Lett., August 2020, Vol. 125(7), 074501 pp. |
Abstract: Wall-bounded turbulent flows can take different statistically stationary turbulent states, with different transport properties, even for the very same values of the control parameters. What state the system takes depends on the initial conditions. Here we analyze the multiple states in large-aspect ratio (Ã) two-dimensional turbulent Rayleigh-Bénard flow with no-slip plates and horizontally periodic boundary conditions as model system. We determine the number n of convection rolls, their mean aspect ratios Ãr=Ã/n, and the corresponding transport properties of the flow (i.e., the Nusselt number Nu), as function of the control parameters Rayleigh (Ra) and Prandtl number. The effective scaling exponent â in Nu-Raâ is found to depend on the realized state and thus Ãr, with a larger value for the smaller Ãr. By making use of a generalized Friedrichs inequality, we show that the elliptical shape of the rolls and viscous damping determine the Ãr window for the realizable turbulent states. The theoretical results are in excellent agreement with our numerical finding 2/3<=Ãr<=4/3, where the lower threshold is approached for the larger Ra. Finally, we show that the theoretical approach to frame Ãr also works for free-slip boundary conditions. |
BibTeX:
@article{Wang, author = {Wang, Q. and Verzicco, R. and Lohse, D. and Shishkina, O.}, title = {Multiple States in Turbulent Large-Aspect-Ratio Thermal Convection: What Determines the Number of Convection Rolls?}, journal = {Phys. Rev. Lett.}, month = {August}, year = {2020}, volume = {125}, number = {7}, pages = {074501}, doi = {10.1103/PhysRevLett.125.074501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.074501} } |
Yang, P.-F., Pumir, A. and Xu, H., "Dynamics and invariants of the perceived velocity gradient tensor in homogeneous and isotropic turbulence", J. Fluid Mech., August 2020, Vol. 897(A9), 1 pp. |
Abstract: The perceived velocity gradient tensor (PVGT), constructed from four fluid tracers forming a tetrahedron, provides a natural way to study the structure of velocity fluctuations and its dependence on spatial scales. It generalizes and shares qualitatively many properties with the true velocity gradient tensor. Here, we establish the evolution equation for the PVGT, and, for homogeneous and isotropic incompressible turbulent flows, we analyse the dynamics of the PVGT in particular using its second- and third-order invariants. We show that, for PVGT based on regular tetrads with lateral size R-0, the second-order invariants can be expressed solely in terms of the usual second-order velocity structure functions, while the third-order invariants involve the usual third-order longitudinal velocity structure function and a less well known three-point velocity correlation function. For homogeneous and isotropic turbulence, exact relations between the second moments of strain and vorticity, as well as enstrophy production and the third moments of the strain, are derived. These generalized relations are valid for all ranges of R-0, and reduce to classical results for the velocity gradient tensor when R-0 is in the dissipative range. With the help of these relations, we quantify the importance of the various terms, such as vortex stretching, as a function of the scale R-0. Our analysis, which is supported by the results of direct numerical simulations of turbulent flows in the Reynolds-number range 100 <= R-lambda <= 610, allows us to demonstrate that strain prevails over vorticity when R-0 is in the inertial range. |
BibTeX:
@article{Yang2020, author = {Yang, P.-F. and Pumir, A. and Xu, H.}, title = {Dynamics and invariants of the perceived velocity gradient tensor in homogeneous and isotropic turbulence}, journal = {J. Fluid Mech.}, month = {August}, year = {2020}, volume = {897}, number = {A9}, pages = {1}, doi = {10.1017/jfm.2020.375},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/dynamics-and-invariants-of-the-perceived-velocity-gradient-tensor-in-homogeneous-and-isotropic-turbulence/A102CC220F53EF74DC3CD907042C67F2} } |
Clay, M. P., Buaria, D., Yeung, P. K. and Gotoh, T., "GPU acceleration of a petascale application for turbulent mixing at high Schmidt number using OpenMP 4.5", Comput. Phys. Commun., July 2020, Vol. 228, 100 pp. |
Abstract: This paper reports on the successful implementation of a massively parallel GPU-accelerated algorithm for the direct numerical simulation of turbulent mixing at high Schmidt number. The work stems from a recent development (Comput. Phys. Commun., vol. 219, 2017, 313–328), in which a low-communication algorithm was shown to attain high degrees of scalability on the Cray XE6 architecture when overlapping communication and computation via dedicated communication threads. An even higher level of performance has now been achieved using OpenMP 4.5 on the Cray XK7 architecture, where on each node the 16 integer cores of an AMD Interlagos processor share a single Nvidia K20X GPU accelerator. In the new algorithm, data movements are minimized by performing virtually all of the intensive scalar field computations in the form of combined compact finite difference (CCD) operations on the GPUs. A memory layout in departure from usual practices is found to provide much better performance for a specific kernel required to apply the CCD scheme. Asynchronous execution enabled by adding the OpenMP 4.5 NOWAIT clause to TARGET constructs improves scalability when used to overlap computation on the GPUs with computation and communication on the CPUs. On the 27-petaflops supercomputer Titan at Oak Ridge National Laboratory, USA, a GPU-to-CPU speedup factor of approximately 5 is consistently observed at the largest problem size of grid points for the scalar field computed with 81923 XK7 nodes. |
BibTeX:
@article{Clay, author = {Clay, M. P. and Buaria, D. and Yeung, P. K. and Gotoh, T.}, title = {GPU acceleration of a petascale application for turbulent mixing at high Schmidt number using OpenMP 4.5}, journal = {Comput. Phys. Commun.}, month = {July}, year = {2020}, volume = {228}, pages = {100}, doi = {10.1016/j.cpc.2018.02.020},, url = {https://www.sciencedirect.com/science/article/pii/S0010465518300596} } |
Karmakar, R., Schich, C., Kamprad, N., Scheller, V., Gutierrez, E., Groisman, A., Rappel, W. and Tarantola, M., "Novel micropatterning technique reveals dependence of cell-substrate adhesion and migration of social amoebas on parental strain, development, and fluorescent markers", PLOS ONE, July 2020, Vol. 15(7), 0236171 pp. |
Abstract: Cell-substrate adhesion of the social amoeba Dictyostelium discoideum, a model organism often used for the study of chemotaxis, is non-specific and does not involve focal adhesion complexes. Therefore, micropatterned substrates where adherent Dictyostelium cells are constrained to designated microscopic regions are difficult to make. Here we present a micropatterning technique for Dictyostelium cells that relies on coating the substrate with an -1ìm thick layer of polyethylene glycol (PEG) gel. We show that, when plated on a substrate with narrow parallel stripes of PEG-gel and glass, Dictyostelium cells nearly exclusive adhere to and migrate along the glass stripes, thus providing a model system to study one-dimensional migration of amoeboid cells. Surprisingly, we find substantial differences in the adhesion to PEG-gel and glass stripes between vegetative and developed cells and between two different axenic laboratory strains of Dictyostelium, AX2 and AX4. Even more surprisingly, we find that the distribution of Dictyostelium cells between PEG-gel and glass stripes is significantly affected by the expression of several fluorescent protein markers of the cytoskeleton. We carry out atomic force microscopy based single cell force spectroscopy measurements that confirm that the force of adhesion to PEG-gel substrate can be significantly different between vegetative and developed cells, AX2 and AX4 cells, and cells with and without fluorescent markers. Thus, the choice of parental background, the degree of development, and the expression of fluorescent protein markers can all have a profound effect on cell-substrate adhesion and should be considered when comparing migration of cells and when designing micropatterned substrates. |
BibTeX:
@article{Karmakar2020, author = {and Karmakar, R. and Schich, C. and Kamprad, N. and Scheller, V. and Gutierrez, E. and Groisman, A. and Rappel, W. and Tarantola, M.}, title = {Novel micropatterning technique reveals dependence of cell-substrate adhesion and migration of social amoebas on parental strain, development, and fluorescent markers}, journal = {PLOS ONE}, month = {July}, year = {2020}, volume = {15}, number = {7}, pages = {0236171}, doi = {10.1371/journal.pone.0236171},, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0236171} } |
Kim, H., Witt, H., Oswald, T. and Tarantola, M., "Adhesion of Epithelial Cells to PNIPAm Treated Surfaces for Temperature-Controlled Cell-Sheet Harvesting", ACS Applied Materials & Interfaces, July 2020, Vol. 12(30), 33516 pp. |
Abstract: Stimuli responsive polymer coatings are a common motive for designing surfaces for cell biological applications. In the present study, we have characterized temperature dependent adhesive properties of poly(N-isopropylacrylamide) (PNIPAm) microgel coated surfaces (PMS) using various atomic force microscopy based approaches. We imaged and quantified the material properties of PMS upon a temperature switch using quantitative AFM imaging but also employed single-cell force spectroscopy (SCFS) before and after decreasing the temperature to assess the forces and work of initial adhesion between cells and PMS. We performed a detailed analysis of steps in the force-distance curves. Finally, we applied colloid probe atomic force microscopy (CP-AFM) to analyze the adhesive properties of two major components of the extracellular matrix to PMS under temperature control, namely collagen I and fibronectin. In combination with confocal imaging, we could show that these two ECM components differ in their detachment properties from PNIPAm microgel films upon cell harvesting, and thus gained a deeper understanding of cell-sheet maturation and harvesting process and the involved partial ECM dissolution. |
BibTeX:
@article{Kim2020, author = {Kim, H. and Witt, H. and Oswald, T. and Tarantola, M.}, title = {Adhesion of Epithelial Cells to PNIPAm Treated Surfaces for Temperature-Controlled Cell-Sheet Harvesting}, journal = {ACS Applied Materials & Interfaces}, month = {July}, year = {2020}, volume = {12}, number = {30}, pages = {33516}, doi = {/10.1021/acsami.0c09166},, url = {https://pubs.acs.org/doi/abs/10.1021/acsami.0c09166} } |
Lohse, D. and Zhang, X., "Physicochemical hydrodynamics of droplets out of equilibrium", Nat Rev Phys, July 2020, Vol. 2, 426 pp. |
Abstract: Droplets abound in nature and technology. In general, they are multicomponent, and, when out of equilibrium, have gradients in concentration, implying flow and mass transport. Moreover, phase transitions can occur, in the form of evaporation, solidification, dissolution or nucleation of a new phase. The droplets and their surrounding liquid can be binary, ternary or contain even more components, with several in different phases. Since the early 2000s, rapid advances in experimental and numerical fluid dynamical techniques have enabled major progress in our understanding of the physicochemical hydrodynamics of such droplets, further narrowing the gap from fluid dynamics to chemical engineering and colloid and interfacial science, arriving at a quantitative understanding of multicomponent and multiphase droplet systems far from equilibrium, and aiming towards a one-to-one comparison between experiments and theory or numerics. This Perspective discusses examples of the physicochemical hydrodynamics of droplet systems far from equilibrium and the relevance of such systems for applications. |
BibTeX:
@article{Lohsea, author = {Lohse, D. and Zhang, X.}, title = {Physicochemical hydrodynamics of droplets out of equilibrium}, journal = {Nat Rev Phys}, month = {July}, year = {2020}, volume = {2}, pages = {426}, doi = {10.1038/s42254-020-0199-z},, url = {https://www.nature.com/articles/s42254-020-0199-z} } |
Zwirner, L., Tilgner, A. and Shishkina, O., "Elliptical Instability and Multiple-Roll Flow Modes of the Large-Scale Circulation in Confined Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., July 2020, Vol. 125, 054502 pp. |
Abstract: The large-scale circulation (LSC) of fluid is one of the main concepts in turbulent thermal convection as it is known to be important in global heat and mass transport in the system. In turbulent Rayleigh-Bénard convection (RBC) in slender containers, the LSC is formed of several dynamically changing convective rolls that are stacked on top of each other. The present study reveals the following two important facts: (i) the mechanism which causes the twisting and breaking of a single-roll LSC into multiple rolls is the elliptical instability and (ii) the heat and momentum transport in RBC, represented by the Nusselt (Nu) and Reynolds (Re) numbers, is always stronger (weaker) for smaller (larger) number n of the rolls in the LSC structure. Direct numerical simulations support the findings for n=1,…,4 and the diameter-to-height aspect ratio of the cylindrical container Ã=1/5, the Prandtl number Pr=0.1 and Rayleigh number Ra=5x105. Thus, Nu and Re are, respectively, 2.5 and 1.5 times larger for a single-roll LSC (n=1) than for a LSC with n=4 rolls. |
BibTeX:
@article{Zwir, author = {Zwirner, L. and Tilgner, A. and Shishkina, O.}, title = {Elliptical Instability and Multiple-Roll Flow Modes of the Large-Scale Circulation in Confined Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {July}, year = {2020}, volume = {125}, pages = {054502}, doi = {10.1103/PhysRevLett.125.054502},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.125.054502} } |
Buaria, D., Pumir, A., Feraco, F., Marino, R., Pouquet, A., Rosenberg, D. and Primavera, L., "Single-particle Lagrangian statistics from direct numerical simulations of rotating-stratified turbulence", Phys. Rev. Fluids, June 2020, Vol. 5(6), 064801 pp. |
Abstract: Geophysical fluid flows are predominantly turbulent and often strongly affected by the Earth's rotation, as well as by stable density stratification. Using direct numerical simulations of forced Boussinesq equations, we study the influence of these effects on the motion of fluid particles. We perform a detailed study of Lagrangian statistics of acceleration, velocity, and related quantities, focusing on cases where the frequencies associated with rotation and stratification (RaS), f and N, respectively, are held at a fixed ratio N/f=5. The simulations are performed in a periodic domain, at Reynolds number Re 4000, and Froude number Fr in the range 0.03? Fr<- 0.2 (with Rossby number Ro=5Fr). As the intensity of RaS increases, a sharp transition is observed between a regime dominated by eddies to a regime dominated by waves, which corresponds to Fr varleq 0.07. For the given runs, this transition to a wave-dominated regime can also be seemingly described by simply comparing the timescales 1/N and ôç, the latter being the Kolmogorov timescale based on the mean kinetic energy dissipation. Due to the known anisotropy induced by RaS, we consider separately the motion in the horizontal and vertical directions. In the regime Nôç<1, acceleration statistics exhibit well known characteristics of isotropic turbulence in both directions, such as probability density functions with wide tails and acceleration variance approximately scaling as per Kolmogorov's theory. In contrast for Nôç>1, they behave very differently, experiencing the direct influence of the imposed rotation and stratification. On the other hand, the Lagrangian velocity statistics exhibit visible anisotropy for all runs; nevertheless the degree of anisotropy becomes very strong in the regime Nôç>1. We observe that in the regime Nôç<1, rotation enhances the mean-square displacements in horizontal planes in the ballistic regime at short times but suppresses them in the diffusive regime at longer times. This suppression of the horizontal displacements becomes stronger in the regime Nôç>1, with no clear diffusive behavior. In contrast, the displacements in the vertical direction are always reduced. This inhibition is extremely strong in the Nôç>1 regime, leading to a scenario where particles almost appear to be trapped in horizontal planes. |
BibTeX:
@article{2020b, author = {Buaria, D. and Pumir, A. and Feraco, F. and Marino, R. and Pouquet, A. and Rosenberg, D. and Primavera, L.}, title = {Single-particle Lagrangian statistics from direct numerical simulations of rotating-stratified turbulence}, journal = {Phys. Rev. Fluids}, month = {June}, year = {2020}, volume = {5}, number = {6}, pages = {064801}, doi = {10.1103/PhysRevFluids.5.064801},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.064801} } |
He, X., Funfschilling, D., Nobach, H., Bodenschatz, E. and Ahlers, G., "Reply to C.R. Doering: Absence of Evidence for the Ultimate State of Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., June 2020, Vol. 124(22), 229402 pp. |
BibTeX:
@article{Hea, author = {He, X. and Funfschilling, D. and Nobach, H. and Bodenschatz, E. and Ahlers, G.}, title = {Reply to C.R. Doering: Absence of Evidence for the Ultimate State of Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {June}, year = {2020}, volume = {124}, number = {22}, pages = {229402}, doi = {10.1103/PhysRevLett.124.229402},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.229402} } |
Kalhöfer-Köchling, M., Bodenschatz, E. and Wang, Y., "Structure Tensors for Dispersed Fibers in Soft Materials", Phys. Rev. Applied, June 2020, Vol. 13(6), 064039 pp. |
Abstract: Soft tissues, such as skin, myocardium, and chordae tendineae, typically display anisotropic mechanical behavior due to their fibrous nature. In constitutive modeling, fiber families frequently are assumed to be unidirectional. Recent numerical results, however, display the need to incorporate dispersion of fiber orientation. This evidence gets supplemented by new experimental results based on high-resolution second-harmonic imaging microscopy. Generalized structure-tensor (GST) models are frequently utilized to model fiber dispersion, as they are mathematically easy to treat and demand only a little effort to implement. They can be regarded as Taylor-series expansions of the numerically more challenging angular-integration (AI) method, which encompasses a distribution of fiber orientations together with the associated fiber stress. In this work, we show how low-order GST models give rise to numerical instabilities as they show strong sensitivity with regards to the mean fiber orientation. To overcome these instabilities, we propose a different class of GST models, termed squared GST (SGST), which computes faster, is easier to implement, and converges to the AI faster than previous GST models of similar order. The SGST models promise to be adaptable to generalized problems, such as functional decomposition of fiber density as well as coupling between different fiber families. Advanced simulations with the proposed models will shed light on the complex behavior of fiber reinforced soft materials. |
BibTeX:
@article{KalhoeferKoechling2020, author = {Kalhöfer-Köchling, M. and Bodenschatz, E. and Wang, Y.}, title = {Structure Tensors for Dispersed Fibers in Soft Materials}, journal = {Phys. Rev. Applied}, month = {June}, year = {2020}, volume = {13}, number = {6}, pages = {064039}, doi = {10.1103/PhysRevApplied.13.064039},, url = {https://journals.aps.org/prapplied/abstract/10.1103/PhysRevApplied.13.064039} } |
Knutsen, A. N., Baj, P., Lawson, J. M. and Bodenschatz, E., "The inter-scale energy budget in a von Karman mixing flow", J. Fluid Mech., May 2020, Vol. 895(A11), 1 pp. |
Abstract: A detailed assessment of the inter-scale energy budget of the turbulent flow in a von Karman mixing tank has been performed based on two extensive experimental data sets. Measurements were performed at a Taylor microscale Reynolds number of Re = 199 in the central region of the tank, using scanning particle image velocimetry (PIV) to fully resolve the velocity gradient tensor (VGT), and stereoscopic PIV for an expanded field of view. Following a basic flow characterisation, the Karman-Howarth-Monin-Hill equation was used to investigate the inter-scale energy transfer. Access to the full VGT enabled the contribution of the different terms of the energy budget to be evaluated without any assumptions or approximations. The scale-space distribution of the dominant terms was also reported to assess the isotropy of the energy transfer. The results show a highly anisotropic distribution of energy transfer in scale space. Energy transfer was shown in a spherically averaged sense to be dominated at the small scales by the nonlinear inter-scale transfer term. However, in contrast to flows considered in previous studies, the local energy transfer is found to depend heavily on the linear contribution associated with the mean flow. Analysis of the scale-to-scale transfer of energy also allowed direct assessment of the classical picture of the energy cascade. It was found that while the inter-scale energy cascade driven by the turbulent fluctuations always proceeds in the forward direction, the total energy cascade driven by both the turbulent fluctuations and the mean flow exhibits significant inverse cascade regions, where energy is transferred from smaller to larger scales. |
BibTeX:
@article{Knutsen2020, author = {Knutsen, A. N. and Baj, P. and Lawson, J. M. and Bodenschatz, E.}, title = {The inter-scale energy budget in a von Karman mixing flow}, journal = {J. Fluid Mech.}, month = {May}, year = {2020}, volume = {895}, number = {A11}, pages = {1}, doi = {10.1017/jfm.2020.277},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/interscale-energy-budget-in-a-von-karman-mixing-flow/99F33E99DF76CBA05D5BBA35A4841AE9} } |
Bocanegra Evans, H., Dam, N., Bertens, G. and van de Water, W., "Making droplets glow in turbulence", Phys. Rev. Fluids, April 2020, Vol. 5(4), 044303 pp. |
Abstract: We present a new technique to study preferential concentration of droplets in a turbulent air flow. Preferential concentration is the tendency of droplets to cluster in regions of strain, while avoiding regions of rotation. We study the properties of the droplet concentration field in zero mean flow turbulence that was created using an array of synthetic jets. The droplets are made of a phosphorescent solution of Europium chelate. They are excited by a laser sheet from a pulsed UV laser, after which the glowing droplets are followed using a high-speed intensified camera. We quantify preferential concentration through measurement of moments of the coarse-grained local droplet density. At the Stokes numbers studied (St approximate to 2) the fractal dimension, a scaling property of this coarse-grained density field, points to clustering. Clustering is a consequence of the compressibility of the droplet velocity field. We also quantify the dynamical behavior of clustering by moving with this velocity field. We find a preference for clustering in the Lagrangian frame during the time interval set by the decay of the phosphorescence. |
BibTeX:
@article{BocanegraEvans.Dam.ea2020, author = {Bocanegra Evans, H. and Dam, N. and Bertens, G. and van de Water, W.}, title = {Making droplets glow in turbulence}, journal = {Phys. Rev. Fluids}, month = {April}, year = {2020}, volume = {5}, number = {4}, pages = {044303}, doi = {10.1103/PhysRevFluids.5.044303},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.5.044303} } |
Prabhakaran, P., Kinney, G., Cantrell, W., Shaw, R. A. and Bodenschatz, E., "High supersaturation in the wake of falling hydrometeors: Implications for cloud invigoration and ice nucleation", Geophys. Res. Lett., April 2020, Vol. 47(023214), 1 pp. |
Abstract: Aerosol particles, cloud droplets, and ice crystals, coupled through the supersaturation field, play an important role in the buoyancy and life cycle of convective clouds. This letter reports laboratory observations of copious cloud droplets and ice crystals formed in the wake of a warm, falling water drop, which is a laboratory surrogate for a relatively warm hydrometeor in atmospheric clouds, such as a graupel particle in the wet growth regime. Aerosols were activated in the regions of very high supersaturation due to mixing in the wake. A mechanism is explored for attaining very high supersaturations capable of activating significant fractions of the interstitial aerosols within the lifetime of a convective cloud. The latent heat released from the activation of interstital aerosols and subsequent growth may provide an additional source of buoyancy for cloud invigoration and may lead to larger concentrations of ice crystals. |
BibTeX:
@article{Prabhakaran.Kinney.ea2020, author = {Prabhakaran, P. and Kinney, G. and Cantrell, W. and Shaw, R. A. and Bodenschatz, E.}, title = {High supersaturation in the wake of falling hydrometeors: Implications for cloud invigoration and ice nucleation}, journal = {Geophys. Res. Lett.}, month = {April}, year = {2020}, volume = {47}, number = {023214}, pages = {1}, doi = {10.1029/2020GL088055},, url = {https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088055} } |
Reiter, P. and Shishkina, O., "Classical and symmetrical horizontal convection: detaching plumes and oscillations", J. Fluid Mech., April 2020, Vol. 892, R1 pp. |
Abstract: Classical and symmetrical horizontal convection is studied by means of direct numerical simulations for Rayleigh numbers up to 3 x 10? and Prandtl numbers , 1 and 10. For both set-ups, a very good agreement in global quantities with respect to heat and momentum transport is attained. Similar to Shishkina & Wagner (Phys. Rev. Lett., vol. 116, 2016, 024302), we find Nusselt number versus scaling transitions in a region . Above a critical , the flow undergoes either a steady-oscillatory transition (small ) or a transition from steady state to a transient state with detaching plumes (large ). The onset of the oscillations takes place at and the onset of detaching plumes at . These onsets coincide with the onsets of scaling transitions. |
BibTeX:
@article{Reiter.Shishkina2020, author = {Reiter, P. and Shishkina, O.}, title = {Classical and symmetrical horizontal convection: detaching plumes and oscillations}, journal = {J. Fluid Mech.}, month = {April}, year = {2020}, volume = {892}, pages = {R1}, doi = {10.1017/jfm.2020.211},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/classical-and-symmetrical-horizontal-convection-detaching-plumes-and-oscillations/4839285AFFC011BD2D157F377E9D8A84} } |
Eckstein, T., Vidal-Henriquez, E. and Gholami, A., "Experimental observation of boundary-driven oscillations in a reaction-diffusion-advection system", Soft Matter, March 2020, Vol. 16, 4243 pp. |
Abstract: Boundary-driven oscillations were numerically predicted to exist in a reaction-diffusion-advection system, namely in the signaling population of social amoeba D. discoideum. If deprived of nutrients, D. discoideum aggregates by producing cAMP waves at precisely timed intervals. In the presence of an advecting flow, holding the upstream boundary to a zero concentration of cAMP produces an instability that sends periodic wave trains downstream. This instability is expected to exist at lower degradation rates of cAMP and thus provides a mechanism for wave creation in phosphodiesterase deficient systems, such as PdsA- cells. Degradation of extracellular cAMP by the enzyme phosphodiesterase PdsA is fundamental to successfully producing waves, regulating the external cAMP gradient field and preventing the accumulation of cAMP. Using a flow-through microfluidic setup filled with PdsA- cells, we confirm experimentally that boundary-driven oscillations indeed exist. Above a minimum flow velocity, decaying waves are induced, with a decay length that increases with the imposed flow velocity. We performed extensive numerical simulations and showed that these waves have a boundary-driven origin, where the lack of cAMP in the upstream flow destabilizes the system. We explored the properties of these waves and the parameter region where they exist, finding good agreement with our experimental observations. These results provide experimental confirmation of the destabilizing effect of the upstream boundary in an otherwise stable reaction-diffusion system. We expect this mechanism to be relevant for wave creation in other oscillatory or excitable systems that are incapable of wave generation in the absence of flow. |
BibTeX:
@article{Eckstein.Vidal-Henriquez.ea2020, author = {Eckstein, T. and Vidal-Henriquez, E. and Gholami, A.}, title = {Experimental observation of boundary-driven oscillations in a reaction-diffusion-advection system}, journal = {Soft Matter}, month = {March}, year = {2020}, volume = {16}, pages = {4243}, doi = {10.1039/C9SM02291K},, url = {https://pubs.rsc.org/en/content/articlehtml/2020/sm/c9sm02291k} } |
Lloyd, G., Choularton, T., Bower, K., Crosier, J., Gallagher, M., Flynn, M., Dorsey, J., Liu, D., Taylor, J. W., Schlenczek, O., Fugal, J., Borrmann, S., Cotton, R., Field, P. and Blyth, A., "Small ice particles at slightly supercooled temperatures in tropical maritime convection", Atmos. Chem. Phys., March 2020, Vol. 20, 3895 pp. |
Abstract: In this paper we show that the origin of the ice phase in tropical cumulus clouds over the sea may occur by primary ice nucleation of small crystals at temperatures just between 0 and -5°C. This was made possible through use of a holographic instrument able to image cloud particles at very high resolution and small size (6 µm). The environment in which the observations were conducted was notable for the presence of desert dust advected over the ocean from the Sahara. However, there is no laboratory evidence to suggest that these dust particles can act as ice nuclei at temperatures warmer than about -10°C, the zone in which the first ice was observed in these clouds. The small ice particles were observed to grow rapidly by vapour diffusion, riming, and possibly through collisions with supercooled raindrops, causing these to freeze and potentially shatter. This in turn leads to the further production of secondary ice in these clouds. Hence, although the numbers of primary ice particles are small, they are very effective in initiating the rapid glaciation of the cloud, altering the dynamics and precipitation production processes. |
BibTeX:
@article{Lloyd.Choularton.ea2020, author = {Lloyd, G. and Choularton, T. and Bower, K. and Crosier, J. and Gallagher, M. and Flynn, M. and Dorsey, J. and Liu, D. and Taylor, J. W. and Schlenczek, O. and Fugal, J. and Borrmann, S. and Cotton, R. and Field, P. and Blyth, A.}, title = {Small ice particles at slightly supercooled temperatures in tropical maritime convection}, journal = {Atmos. Chem. Phys.}, month = {March}, year = {2020}, volume = {20}, pages = {3895}, doi = {10.5194/acp-20-3895-2020},, url = {https://www.semanticscholar.org/paper/Small-Ice-Particles-at-Slightly-Supercooled-in-Lloyd-Choularton/b73dfdc096c9f86c9d8f0d3800e0905154c3822c} } |
Negrete, J., Pumir, A., Westendorf, C., Tarantola, M., Bodenschatz, E. and Beta, C., "Receptor-induced transient responses in cells with oscillatory actin dynamics", Phys. Rev. Research, March 2020, Vol. 2(1), 013239 pp. |
Abstract: Living cells adjust their sensing and migratory machinery in response to changes in their environment.In this work, we show that cells of the social amoebaDictyostelium discoideummodulate the dynamicalstate of their actin cytoskeleton in response to an external pulse of the chemoattractant cyclic adenosinemonophosphate (cAMP). In particular, we focus on a population of cells that exhibits noisy oscillatory cyclesof actin polymerization and systematically study receptor-induced transitions in their cytoskeletal dynamics.In response to a short external pulse of cAMP, these cells adopt a noisy quiescent state, before returning totheir initial, oscillatory dynamics. The response exhibits a biphasic time profile, with a duration that showsstrong variability between cells; it can extend as long as approximately twelve oscillation cycles. We propose amodel that is based on a generic nonlinear noisy oscillator. Our theoretical analysis suggests that the transienttermination of oscillations in response to a receptor stimulus occurs via a Hopf bifurcation. |
BibTeX:
@article{Negrete.Pumir.ea2020, author = {Negrete, J. and Pumir, A. and Westendorf, C. and Tarantola, M. and Bodenschatz, E. and Beta, C.}, title = {Receptor-induced transient responses in cells with oscillatory actin dynamics}, journal = {Phys. Rev. Research}, month = {March}, year = {2020}, volume = {2}, number = {1}, pages = {013239}, doi = {10.1103/PhysRevResearch.2.013239},, url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.2.013239} } |
Zimik, S., Pandit, R. and Majumder, R., "Anisotropic shortening in the wavelength of electrical waves promotes onset of electrical turbulence in cardiac tissue: An in silico study", PLOS ONE, March 2020, Vol. 15(3), e0230214 pp. |
Abstract: Several pathological conditions introduce spatial variations in the electrical properties of cardiac tissue. These variations occur as localized or distributed gradients in ion-channel functionality over extended tissue media. Electrical waves, propagating through such affected tissue, demonstrate distortions, depending on the nature of the ionic gradient in the diseased substrate. If the degree of distortion is large, reentrant activity may develop, in the form of rotating spiral (2d) and scroll (3d) waves of electrical activity. These reentrant waves are associated with the occurrence of lethal cardiac rhythm disorders, known as arrhythmias, such as ventricular tachycardia (VT) and ventricular fibrillation (VF), which are believed to be common precursors of sudden cardiac arrest. By using state-of-the-art mathematical models for generic, and ionically-realistic (human) cardiac tissue, we study the detrimental effects of these ionic gradients on electrical wave propagation. We propose a possible mechanism for the development of instabilities in reentrant wave patterns, in the presence of ionic gradients in cardiac tissue, which may explain how one type of arrhythmia (VT) can degenerate into another (VF). Our proposed mechanism entails anisotropic reduction in the wavelength of the excitation waves because of anisotropic variation in its electrical properties, in particular the action potential duration (APD). We find that the variation in the APD, which we induce by varying ion-channel conductances, imposes a spatial variation in the spiral- or scroll-wave frequency ù. Such gradients in ù induce anisotropic shortening of wavelength of the spiral or scroll arms and eventually leads to instabilitites. |
BibTeX:
@article{Zimik.Pandit.ea2020, author = {Zimik, S. and Pandit, R. and Majumder, R.}, title = {Anisotropic shortening in the wavelength of electrical waves promotes onset of electrical turbulence in cardiac tissue: An in silico study}, journal = {PLOS ONE}, month = {March}, year = {2020}, volume = {15}, number = {3}, pages = {e0230214}, doi = {10.1371/journal.pone.0230214},, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0230214} } |
Bai, X.-D., Zhang, W. and Wang, Y., "Deflected oscillatory wake pattern behind two side-by-side circular cylinders", Ocean Engineering, February 2020, Vol. 197, 106847 pp. |
Abstract: Wake flow behind structures is of fundamental significance and practical interest in ocean engineering. Several asymmetric flow patterns, such as the deflected stationary, flip-flop and deflected oscillatory wakes, behind two cylinders in a side-by-side arrangement have been reported most recently. In the present work, direct numerical simulations together with the state-of-art dynamic mode decomposition are used to reveal the underlying physics of deflected oscillatory wake pattern with low Reynolds number and intermediate gap ratio. Asymmetric flow structures are observed numerically in certain arrangements. Specially, the structure for gap flow is similar to that observed in flip-flop pattern induced by the secondary instability, but asymmetric here. It is found that the drag coefficient and lift coefficient under such circumstances are dominated by the asymmetric gap flow structure rather than the vortex street in the downstream. The present work provides a new scenario to the wake flow patterns behind two side-by-side cylinders with intermediate gap ratios, and it is potentially helpful in understanding the vibrating behaviors of adjacent cylinders. |
BibTeX:
@article{Bai.Zhang.ea2020, author = {Bai, X.-D. and Zhang, W. and Wang, Y.}, title = {Deflected oscillatory wake pattern behind two side-by-side circular cylinders}, journal = {Ocean Engineering}, month = {February}, year = {2020}, volume = {197}, pages = {106847}, doi = {10.1016/j.oceaneng.2019.106847},, url = {https://www.sciencedirect.com/science/article/abs/pii/S0029801818307716} } |
Koltai, P. and Weiss, S., "Diffusion maps embedding and transition matrix analysis of the large-scale flow structure in turbulent Rayleigh-Bénard convection", Nonlinearity, February 2020, Vol. 33(4), 1723 pp. |
Abstract: By utilizing diffusion maps embedding and transition matrix analysis we investigate sparse temperature measurement time-series data from Rayleigh-Bénard convection experiments in a cylindrical container of aspect ratio between its diameter (D) and height (L). We consider the two cases of a cylinder at rest and rotating around its cylinder axis. We find that the relative amplitude of the large-scale circulation (LSC) and its orientation inside the container at different points in time are associated to prominent geometric features in the embedding space spanned by the two dominant diffusion-maps eigenvectors. From this two-dimensional embedding we can measure azimuthal drift and diffusion rates, as well as coherence times of the LSC. In addition, we can distinguish from the data clearly the single roll state (SRS), when a single roll extends through the whole cell, from the double roll state (DRS), when two counter-rotating rolls are on top of each other. Based on this embedding we also build a transition matrix (a discrete transfer operator), whose eigenvectors and eigenvalues reveal typical time scales for the stability of the SRS and DRS as well as for the azimuthal drift velocity of the flow structures inside the cylinder. Thus, the combination of nonlinear dimension reduction and dynamical systems tools enables to gain insight into turbulent flows without relying on model assumptions. |
BibTeX:
@article{Koltai.Weiss2020, author = {Koltai, P. and Weiss, S.}, title = {Diffusion maps embedding and transition matrix analysis of the large-scale flow structure in turbulent Rayleigh-Bénard convection}, journal = {Nonlinearity}, month = {February}, year = {2020}, volume = {33}, number = {4}, pages = {1723}, doi = {10.1088/1361-6544/ab6a76},, url = {https://iopscience.iop.org/article/10.1088/1361-6544/ab6a76} } |
Majumder, R., Zykov, V. S. and Panfilov, A. V., "In silico optical control of pinned electrical vortices in an excitable biological medium", New J. Phys., February 2020, Vol. 22, 023034 pp. |
Abstract: Vortices of excitation are generic to any complex excitable system. In the heart, they occur as rotors, spirals (2D) and scroll waves (3D) of electrical activity that are associated with rhythm disorders, known as arrhythmias. Lethal cardiac arrhythmias often result in sudden death, which is one of the leading causes of mortality in the industrialized world. Irrespective of the nature of the excitable medium, the rotation of a rotor is driven by its dynamics at the (vortex) core. In a recent study, Majumder et al (2018 eLife 7 e41076) demonstrated, using in silico and in vitro cardiac optogenetics, that light-guided manipulation of the core of free rotors can be used to establish real-time spatiotemporal control over the position, number and rotation of these rotors in cardiac tissue. Strategic application of this method, called 'Attract-Anchor-Drag' (AAD) can also be used to eliminate free rotors from the heart and stop cardiac arrhythmias. However, rotors in excitable systems, can pin (anchor) around local heterogeneities as well, thereby limiting their dynamics and possibility for spatial control. Here, we expand our results and numerically demonstrate, that AAD method can also detach anchored vortices from inhomogeneities and subsequently control their dynamics in excitable systems. Thus, overall we demonstrate that AAD control is one of the first universal methods that can be applied to both free and pinned vortices, to ensure their spatial control and removal from the heart and, possibly, other excitable systems. |
BibTeX:
@article{Majumder.Zykov.ea2020, author = {Majumder, R. and Zykov, V. S. and Panfilov, A. V.}, title = {In silico optical control of pinned electrical vortices in an excitable biological medium}, journal = {New J. Phys.}, month = {February}, year = {2020}, volume = {22}, pages = {023034}, doi = {10.1088/1367-2630/ab704f},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ab704f} } |
Zhang, X., van Gils, D., Horn, S., Wedi, M., Zwirner, L., Ahlers, G., Ecke, R., Weiss, S., Bodenschatz, E. and Shishkina, O., "Boundary Zonal Flow in Rotating Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., February 2020, Vol. 124(8), 084505 pp. |
Abstract: For rapidly rotating turbulent Rayleigh-Bénard convection in a slender cylindrical cell, experiments and direct numerical simulations reveal a boundary zonal flow (BZF) that replaces the classical large-scale circulation. The BZF is located near the vertical side wall and enables enhanced heat transport there. Although the azimuthal velocity of the BZF is cyclonic (in the rotating frame), the temperature is an anticyclonic traveling wave of mode one, whose signature is a bimodal temperature distribution near the radial boundary. The BZF width is found to scale like Ra1/4Ek2/3 where the Ekman number Ek decreases with increasing rotation rate. |
BibTeX:
@article{Zhang.Gils.ea2020, author = {Zhang, X. and van Gils, D. and Horn, S. and Wedi, M. and Zwirner, L. and Ahlers, G. and Ecke, R. and Weiss, S. and Bodenschatz, E. and Shishkina, O.}, title = {Boundary Zonal Flow in Rotating Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {February}, year = {2020}, volume = {124}, number = {8}, pages = {084505}, doi = {10.1103/PhysRevLett.124.084505},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.084505?utm_source=email&utm_medium=email&utm_campaign=prl-alert} } |
Emran, M. S. and Shishkina, O., "Natural convection in cylindrical containers with isothermal ring-shaped obstacles", J. Fluid Mech., January 2020, Vol. 882, A3 pp. |
Abstract: By means of three-dimensional direct numerical simulations, we investigate the influence of the regular roughness of heated and cooled plates on the mean heat transport in a cylindrical Rayleigh-Bénard convection cell of aspect ratio one. The roughness is introduced by a set of isothermal obstacles, which are attached to the plates and have a form of concentric rings of the same width. The considered Prandtl number equals 1, the Rayleigh number varies from to , the number of rings on each plate is 1, 2, 4, 8 or 10, the height of the rings is varied from 1.5 % to 49 % of the cylinder height and the gap between the rings is varied from 1.5 % to 18.8 % of the cell diameter. Totally, 135 different cases are analysed. Direct numerical simulations show that with small and wide roughness rings, a small reduction of the mean heat transport (the Nusselt number ) is possible, but, in most cases, the presence of the heated and cooled obstacles generally leads to an increase of , compared to the case of classical Rayleigh-Bénard convection with smooth plates. When the rings are very tall and the gaps between them are sufficiently wide, the effective mean heat flux can be several times larger than in the smooth case. For a fixed geometry of the obstacles, the scaling exponent in the versus scaling first increases with growing up to approximately 0.5, but then smoothly decreases back towards the exponent in the no-obstacle case. |
BibTeX:
@article{Emran.Shishkina2020, author = {Emran, M. S. and Shishkina, O.}, title = {Natural convection in cylindrical containers with isothermal ring-shaped obstacles}, journal = {J. Fluid Mech.}, month = {January}, year = {2020}, volume = {882}, pages = {A3}, doi = {10.1017/jfm.2019.797},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/natural-convection-in-cylindrical-containers-with-isothermal-ringshaped-obstacles/DEE19B2976E67B7A356501553F44E013} } |
Glienke, S., Kostinski, A. B., Shaw, R. A., Larsen, M. L., Fugal, J. P., Schlenczek, O. and Borrmann, S., "Holographic Observations of Centimeter-Scale Nonuniformities within Marine Stratocumulus Clouds", JAS, January 2020, Vol. 77(2), 499 pp. |
Abstract: Data collected with a holographic instrument [Holographic Detector for Clouds (HOLODEC)] on board the High-Performance Instrumented Airborne Platform for Environmental Research Gulfstream-V (HIAPER GV) aircraft from marine stratocumulus clouds during the Cloud System Evolution in the Trades (CSET) field project are examined for spatial uniformity. During one flight leg at 1190 m altitude, 1816 consecutive holograms were taken, which were approximately 40 m apart with individual hologram dimensions of 1.16 cm x 0.68 cm x 12.0 cm and with droplet concentrations of up to 500 cm-3. Unlike earlier studies, minimally intrusive data processing (e.g., bypassing calculation of number concentrations, binning, and parametric fitting) is used to test for spatial uniformity of clouds on intra- and interhologram spatial scales (a few centimeters and 40 m, respectively). As a means to test this, measured droplet count fluctuations are normalized with the expected standard deviation from theoretical Poisson distributions, which signifies randomness. Despite the absence of trends in the mean concentration, it is found that the null hypothesis of spatial uniformity on both spatial scales can be rejected with compelling statistical confidence. Monte Carlo simulations suggest that weak clustering explains this signature. These findings also hold for size-resolved analysis but with less certainty. Clustering of droplets caused by, for example, entrainment and turbulence, is size dependent and is likely to influence key processes such as droplet growth and thus cloud lifetime. |
BibTeX:
@article{Glienke.Kostinski.ea2020, author = {Glienke, S. and Kostinski, A. B. and Shaw, R. A. and Larsen, M. L. and Fugal, J. P. and Schlenczek, O. and Borrmann, S.}, title = {Holographic Observations of Centimeter-Scale Nonuniformities within Marine Stratocumulus Clouds}, journal = {JAS}, month = {January}, year = {2020}, volume = {77}, number = {2}, pages = {499}, doi = {10.1175/JAS-D-19-0164.1},, url = {https://journals.ametsoc.org/doi/10.1175/JAS-D-19-0164.1} } |
Eichele, G., Bodenschatz, E., Ditte, Z., Günther, A.-K., Kapoor, S., Wang, Y. and Westendorf, C., "Cilia-driven flows in the brain third ventricle", Philosophical Transactions B, December 2019, Vol. 375(1792), 20190154 pp. |
Abstract: The brain ventricles are interconnected, elaborate cavities that traverse the brain. They are filled with cerebrospinal fluid (CSF) that is, to a large part, produced by the choroid plexus, a secretory epithelium that reaches into the ventricles. CSF is rich in cytokines, growth factors and extracellular vesicles that glide along the walls of ventricles, powered by bundles of motile cilia that coat the ventricular wall. We review the cellular and biochemical properties of the ventral part of the third ventricle that is surrounded by the hypothalamus. In particular, we consider the recently discovered intricate network of cilia-driven flows that characterize this ventricle and discuss the potential physiological significance of this flow for the directional transport of CSF signals to cellular targets located either within the third ventricle or in the adjacent hypothalamic brain parenchyma. Cilia-driven streams of signalling molecules offer an exciting perspective on how fluid-borne signals are dynamically transmitted in the brain. |
BibTeX:
@article{Eichele.Bodenschatz.ea2019, author = {Eichele, G. and Bodenschatz, E. and Ditte, Z. and Günther, A.-K. and Kapoor, S. and Wang, Y. and Westendorf, C.}, title = {Cilia-driven flows in the brain third ventricle}, journal = {Philosophical Transactions B}, month = {December}, year = {2019}, volume = {375}, number = {1792}, pages = {20190154}, doi = {10.1098/rstb.2019.0154},, url = {https://royalsocietypublishing.org/doi/full/10.1098/rstb.2019.0154} } |
Zhang, W., Zhu, B., Xu, H. and Wang, Y., "Applying extended intrinsic mean spin tensor in evolution algorithm for RANS modelling of turbulent rotating channel flow", Journal of Hydrodynamics, December 2019, Vol. 31(6), 1255 pp. |
Abstract: We present a machine learning based method for RANS modeling in the rotating frame of reference (RFR). The extended intrinsic mean spin tensor (EIMST) is adopted in a novel expansion of the evolution algorithm, named multi-dimensional gene expression programming (MGEP). Based on DNS data, a constrain free model for Reynolds stress is created by considering system rotating. The anisotropy behavior of Reynolds stress is considered in the model, which is then for the first time applied for modeling turbulent flow inside a rotating channel. Compared with the traditional RANS model, the new model can predict the non-symmetric profile of Reynolds stress. Meanwhile, the Taylor-Görtler vortex is captured in our simulations with the new model. It is demonstrated that the application of EIMST in MGEP can be successfully adopted for RANS modeling in the RFR. |
BibTeX:
@article{Zhang.Zhu.ea2019, author = {Zhang, W. and Zhu, B. and Xu, H. and Wang, Y.}, title = {Applying extended intrinsic mean spin tensor in evolution algorithm for RANS modelling of turbulent rotating channel flow}, journal = {Journal of Hydrodynamics}, month = {December}, year = {2019}, volume = {31}, number = {6}, pages = {1255}, doi = {10.1007/s42241-019-0093-2},, url = {https://link.springer.com/article/10.1007/s42241-019-0093-2} } |
Zwirner, L., Khalilov, R., Kolesnichenko, I., Mamykin, A., Mandrykin, S., Pavlinov, A., Shestakov, A., Teimurazov, A., Frick, P. and Shishkina, O., "The influence of the cell inclination on the heat transport and large-scale circulation in liquid metal convection", J. Fluid Mech., December 2019, Vol. 884, A18-1 pp. |
Abstract: Inclined turbulent thermal convection in liquid sodium is studied at large Rayleigh numbers based on the results of both experimental measurements and high-resolution numerical simulations. For a direct comparison, the considered system parameters are set to be similar: in the direct numerical simulations (DNS), in the large-eddy simulations and in the experiments, while the Prandtl number of liquid sodium is very small (Pr 0.009). The cylindrical convection cell has an aspect ratio of one; one circular surface is heated, while the other one is cooled. Additionally, the cylinder is inclined with respect to gravity and the inclination angle varies from =0° , which corresponds to Rayleigh-Bénard convection (RBC), to =90° , as in a vertical convection (VC) set-up. Our study demonstrates quantitative agreement of the experimental and numerical results, in particular with respect to the global heat and momentum transport, temperature and velocity profiles, as well as the dynamics of the large-scale circulation (LSC). The DNS reveal that the twisting and sloshing of the LSC at small inclination angles periodically affects the instantaneous heat transport (up to of the mean heat transport). The twisted LSC is associated with a weak heat transport, while the sloshing mode that brings together the hot and cold streams of the LSC is associated with a strong heat transport. The experiments show that the heat transport scales as in both limiting cases (RBC and VC) for Rayleigh numbers around , while any inclination of the cell, 0<<90° , leads to an increase of . |
BibTeX:
@article{Zwirner.Khalilov.ea2020, author = {Zwirner, L. and Khalilov, R. and Kolesnichenko, I. and Mamykin, A. and Mandrykin, S. and Pavlinov, A. and Shestakov, A. and Teimurazov, A. and Frick, P. and Shishkina, O.}, title = {The influence of the cell inclination on the heat transport and large-scale circulation in liquid metal convection}, journal = {J. Fluid Mech.}, month = {December}, year = {2019}, volume = {884}, pages = {A18-1}, doi = {10.1017/jfm.2019.935},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/influence-of-the-cell-inclination-on-the-heat-transport-and-largescale-circulation-in-liquid-metal-convection/64FE07D0075BBBE1FFDF92962DCE0AD0} } |
Hsu, H.-F., Krekhov, A., Tarantola, M., Beta, C. and Bodenschatz, E., "Interplay between myosin II and actin dynamics in chemotactic amoeba", New J. Phys., November 2019, Vol. 21, 113055 pp. |
Abstract: The actin cytoskeleton and its response to external chemical stimuli is fundamental to the mechano-biology of eukaryotic cells and their functions. One of the key players that governs the dynamics of the actin network is the motor protein myosin II. Based on a phase space embedding we have identi?ed from experiments three phases in the cytoskeletal dynamics of starved Dictyostelium discoideum in response to a precisely controlled chemotactic stimulation. In the first two phases the dynamics of actin and myosin II in the cortex is uncoupled, while in the third phase the time scale for the recovery of cortical actin is determined by the myosin II dynamics. We report a theoretical model that captures the experimental observations quantitatively. The model predicts an increase in the optimal response time of actin with decreasing myosin II-actin coupling strength highlighting the role of myosin II in the robust control of cell contraction. |
BibTeX:
@article{Hsu.Krekhov.ea2019, author = {Hsu, H.-F. and Krekhov, A. and Tarantola, M. and Beta, C. and Bodenschatz, E.}, title = {Interplay between myosin II and actin dynamics in chemotactic amoeba}, journal = {New J. Phys.}, month = {November}, year = {2019}, volume = {21}, pages = {113055}, doi = {10.1088/1367-2630/ab5822},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ab5822} } |
Wu, H. X., Xu, H. and Bodenschatz, E., "Measuring vorticity vector from the spinning of micro-sized mirror-encapsulated spherical particles in the flow", Rev. Sci. Instrum., November 2019, Vol. 90, 115111 pp. |
Abstract: We demonstrate a nonintrusive technique that is capable of measuring all three-components of vorticity following small tracer particles in the flow. The vorticity is measured by resolving the instantaneous spin of the microsized spherical hydrogel particles, in which small mirrors are encapsulated. The hydrogel particles have the same density and refractive index as the working fluid-water. The trajectory of the light reflected by the spinning mirror, recorded by a single camera, is sufficient to determine the 3D rotation of the hydrogel particle, and hence the vorticity vector of the flow at the position of the particle. Compared to more conventional methods that measure vorticity by resolving velocity gradients, this technique has much higher spatial resolution. We describe the principle of the measurement, the optical setup to eliminate the effect of particle translation, the calibration procedure, and the analysis of measurement uncertainty. We validate the technique by measurements in a Taylor-Couette flow. Our technique can be used to obtain the multipoint statistics of vorticity in turbulence. |
BibTeX:
@article{Wu.Xu.ea2019, author = {Wu, H. X. and Xu, H. and Bodenschatz, E.}, title = {Measuring vorticity vector from the spinning of micro-sized mirror-encapsulated spherical particles in the flow}, journal = {Rev. Sci. Instrum.}, month = {November}, year = {2019}, volume = {90}, pages = {115111}, doi = {10.1063/1.5121016},, url = {https://aip.scitation.org/doi/10.1063/1.5121016} } |
Bagheri, G. and Bonadonna, C., "Comment on “A New One-Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a WideRange of Reynolds Number"", JGL Solid Earth, October 2019, Vol. 124(10), 10261 pp. |
Abstract: With this comment we want to clarify a number of aspects of the paper recently published by Dioguardi, Mele, and Dellino “A New One-Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a Wide Range of Reynolds Number” (hereafter referred to as DMD2018). In particular, we show that contrary to the conclusions of DMD2018, the model of Bagheri and Bonadonna (2016, https://doi.org/10.1016/j.powtec.2016.06.015), hereafter referred to as BB2016, is the best model in predicting the drag and terminal velocity of particles measured by DMD2018, as demonstrated here by comparison of estimation errors. The discrepancy is mainly due to a production error (misplaced parentheses) introduced in BB2016 during the publication process and partly due to the incorrect methodology used by DMD2018 to calculate particle terminal velocity. Here we present the correct sets of equations and methodology to show that typo-free model of BB2016 outperforms all existing drag models including the new model suggested by DMD2018. |
BibTeX:
@article{Bagheri.Bonadonna2019, author = {Bagheri, G. and Bonadonna, C.}, title = {Comment on “A New One-Equation Model of Fluid Drag for Irregularly Shaped Particles Valid Over a WideRange of Reynolds Number"}, journal = {JGL Solid Earth}, month = {October}, year = {2019}, volume = {124}, number = {10}, pages = {10261}, doi = {10.1029/2019JB017697},, url = {https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JB017697} } |
Ching, E. S. C., Leung, H. S., Zwirner, L. and Shishkina, O., "Velocity and thermal boundary layer equations for turbulent Rayleigh-Bénard convection", Phys. Rev. Research, October 2019, Vol. 1(3), 033037 pp. |
Abstract: In turbulent Rayleigh-Bénard convection, the boundary layers are nonsteady with fluctuations, the time-averaged large-scale circulating velocity vanishes far away from the top and bottom plates, and the motion arises from buoyancy. In this paper, we derive the full set of boundary layer equations for both the temperature and velocity fields from the Boussinesq equations for a quasi-two-dimensional flow above a heated plate, taking into account all the above effects. By solving these boundary layer equations, both the time-averaged temperature and velocity boundary layer profiles are obtained. |
BibTeX:
@article{Ching.Leung.ea2019, author = {Ching, E. S. C. and Leung, H. S. and Zwirner, L. and Shishkina, O.}, title = {Velocity and thermal boundary layer equations for turbulent Rayleigh-Bénard convection}, journal = {Phys. Rev. Research}, month = {October}, year = {2019}, volume = {1}, number = {3}, pages = {033037}, doi = {10.1103/PhysRevResearch.1.033037},, url = {https://journals.aps.org/prresearch/abstract/10.1103/PhysRevResearch.1.033037} } |
Günther, A.-K., "Transport of lipid vesicles via the cilia logistic network in the brain of mice", September 2019 |
Abstract: The ventricular system of the mammalian brain consists of four interconnected cavities, which are lined by ciliated ependymal cells. Constant and coordinated movement of the cilia results in a directed flow of cerebrospinal fluid (CSF) along the ependymal walls. In the ventral part of the third ventricle (v3V) the cilia give rise to a complex network of flow that confines and connects regions. This so-called ciliary logistic network (CLN) may provide transport routes for CSF components (e.g. extracellular vesicles) and has the potential to guide and restrict the distribution of local secretions. It is unclear, how extracellular vesicles like exosomes are distributed throughout the ventricular system and whether the CLN mediates site-specific deliveries of exosomes. In this thesis, a characterization of exosome-like cargo transport along the CLN and potential target sites in the v3V of the mouse brain are presented. To investigate the transport and interaction of exosome-like cargo, fluorescently-labelled liposomes of defined composition and size were applied to the cilia-generated near wall flow via microinjections. The results of this work reveal that the transport of lipid vesicles within the v3V is determined by the cilia-generated flow. Liposomes are transported with high precision and interact with ependymal cilia in specific regions. |
BibTeX:
@phdthesis{Guenther2019, author = {Günther, A.-K.}, title = {Transport of lipid vesicles via the cilia logistic network in the brain of mice}, month = {September}, year = {2019},, url = {https://ediss.uni-goettingen.de/handle/21.11130/00-1735-0000-0003-C1B9-2} } |
Berghout, P., Zhu, X., Chung, D., Verzicco, R., Stevens, R. J. A. M. and Lohse, D., "Direct numerical simulations of Taylor-Couette turbulence: the effects of sand grain roughness", J. Fluid Mech., August 2019, Vol. 873, 260 pp. |
Abstract: Progress in roughness research, mapping any given roughness geometry to its fluid dynamic behaviour, has been hampered by the lack of accurate and direct measurements of skin-friction drag, especially in open systems. The Taylor–Couette (TC) system has the benefit of being a closed system, but its potential for characterizing irregular, realistic, three-dimensional (3-D) roughness has not been previously considered in depth. Here, we present direct numerical simulations (DNSs) of TC turbulence with sand grain roughness mounted on the inner cylinder. The model proposed by Scotti (Phys. Fluids, vol. 18, 031701, 2006) has been modified to simulate a random rough surface of monodisperse sand grains. Taylor numbers range from (corresponding to ) to ( ). We focus on the influence of the roughness height in the transitionally rough regime, through simulations of TC with rough surfaces, ranging from up to . We analyse the global response of the system, expressed both by the dimensionless angular velocity transport and by the friction factor . An increase in friction with increasing roughness height is accompanied with enhanced plume ejection from the inner cylinder. Subsequently, we investigate the local response of the fluid flow over the rough surface. The equivalent sand grain roughness is calculated to be , where is the size of the sand grains. We find that the downwards shift of the logarithmic layer, due to transitionally rough sand grains exhibits remarkably similar behaviour to that of the Nikuradse (VDI-Forsch., vol. 361, 1933) data of sand grain roughness in pipe flow, regardless of the Taylor number dependent constants of the logarithmic layer. Furthermore, we find that the dynamical effects of the sand grains are contained to the roughness sublayer with . |
BibTeX:
@article{Berghout.Zhu.ea2019, author = {Berghout, P. and Zhu, X. and Chung, D. and Verzicco, R. and Stevens, R. J. A. M. and Lohse, D.}, title = {Direct numerical simulations of Taylor-Couette turbulence: the effects of sand grain roughness}, journal = {J. Fluid Mech.}, month = {August}, year = {2019}, volume = {873}, pages = {260}, doi = {10.1017/jfm.2019.376},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/direct-numerical-simulations-of-taylorcouette-turbulence-the-effects-of-sand-grain-roughness/7D74C435AD8B464E689A47B45F10CC5B} } |
Jiang, H., Zhu, X., Mathai, V., Yang, X., Verzicco, R., Lohse, D. and Sun, C., "Convective heat transfer along ratchet surfaces in vertical natural convection", J. Fluid Mech., August 2019, Vol. 873, 1055 pp. |
Abstract: We report on a combined experimental and numerical study of convective heat transfer along ratchet surfaces in vertical natural convection (VC). Due to the asymmetry of the convection system caused by the asymmetric ratchet-like wall roughness, two distinct states exist, with markedly different orientations of the large-scale circulation roll (LSCR) and different heat transport efficiencies. Statistical analysis shows that the heat transport efficiency depends on the strength of the LSCR. When a large-scale wind flows along the ratchets in the direction of their smaller slopes, the convection roll is stronger and the heat transport is larger than the case in which the large-scale wind is directed towards the steeper slope side of the ratchets. Further analysis of the time-averaged temperature profiles indicates that the stronger LSCR in the former case triggers the formation of a secondary vortex inside the roughness cavity, which promotes fluid mixing and results in a higher heat transport efficiency. Remarkably, this result differs from classical Rayleigh–Bénard convection (RBC) with asymmetric ratchets (Jiang et al., Phys. Rev. Lett., vol. 120, 2018, 044501), wherein the heat transfer is stronger when the large-scale wind faces the steeper side of the ratchets. We reveal that the reason for the reversed trend for VC as compared to RBC is that the flow is less turbulent in VC at the same Ra. Thus, in VC the heat transport is driven primarily by the coherent LSCR, while in RBC the ejected thermal plumes aided by gravity are the essential carrier of heat. The present work provides opportunities for control of heat transport in engineering and geophysical flows. |
BibTeX:
@article{Jiang.Zhu.ea2019, author = {Jiang, H. and Zhu, X. and Mathai, V. and Yang, X. and Verzicco, R. and Lohse, D. and Sun, C.}, title = {Convective heat transfer along ratchet surfaces in vertical natural convection}, journal = {J. Fluid Mech.}, month = {August}, year = {2019}, volume = {873}, pages = {1055}, doi = {10.1017/jfm.2019.446},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/convective-heat-transfer-along-ratchet-surfaces-in-vertical-natural-convection/DD0A6EACC30AA21AC6AEBB6CDEF6E086} } |
Alards, K. M. J., Kunnen, R. P. J., Stevens, R. J. A. M., Lohse, D., Toschi, F. and Clercx, H. J. H., "Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number", Phys. Rev. Fluids, July 2019, Vol. 4(7), 074601 pp. |
Abstract: In Rayleigh-Benard convection (RBC) for fluids with Prandtl number Pr greater than or similar to 1, rotation beyond a critical (small) rotation rate is known to cause a sudden enhancement of heat transfer, which can be explained by a change in the character of the boundary layer (BL) dynamics near the top and bottom plates of the convection cell. Namely, with increasing rotation rate, the BL signature suddenly changes from Prandtl-Blasius type to Ekman type. The transition from a constant heat transfer to an almost linearly increasing heat transfer with increasing rotation rate is known to be sharp and the critical Rossby number Ro(c) occurs typically in the range 2.3 less than or similar to Ro(c) less than or similar to 2.9 (for Rayleigh number Ra = 1.3 x 10(9), Pr = 6.7, and a convection cell with aspect ratio Gamma = D/H = 1, with D the diameter and H the height of the cell). The explanation of the sharp transition in the heat transfer points to the change in the dominant flow structure. At 1/Ro less than or similar to 1/Ro(c) (slow rotation), the well-known large-scale circulation (LSC) is found: a single domain-filling convection roll made up of many individual thermal plumes. At 1/Ro greater than or similar to 1/Ro(c) (rapid rotation), the LSC vanishes and is replaced with a collection of swirling plumes that align with the rotation axis. In this paper, by numerically studying Lagrangian acceleration statistics, related to the small-scale properties of the flow structures, we reveal that this transition between these different dominant flow structures happens at a second critical Rossby number, Ro(c2) approximate to 2.25 (different from Ro(c1) approximate to 2.7 for the sharp transition in the Nusselt number Nu; both values for the parameter settings of our present numerical study). When statistical data of Lagrangian tracers near the top plate are collected, it is found that the root-mean-square values and the kurtosis of the horizontal acceleration of these tracers show a sudden increase at Ro(c2). To better understand the nature of this transition we compute joint statistics of the Lagrangian velocity and acceleration of fluid particles and vertical vorticity near the top plate. It is found that for Ro greater than or similar to 2.25 there is hardly any correlation between the vertical vorticity and extreme acceleration events of fluid particles. For Ro less than or similar to 2.25, however, vortical regions are much more prominent and extreme horizontal acceleration events are now correlated to large values of positive (cyclonic) vorticity. This suggests that the observed sudden transition in the acceleration statistics is related to thermal plumes with cyclonic vorticity developing in the Ekman BL and subsequently becoming mature and entering the bulk of the flow for Ro less than or similar to 2.25. |
BibTeX:
@article{Alards.Kunnen.ea2019, author = {Alards, K. M. J. and Kunnen, R. P. J. and Stevens, R. J. A. M. and Lohse, D. and Toschi, F. and Clercx, H. J. H.}, title = {Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number}, journal = {Phys. Rev. Fluids}, month = {July}, year = {2019}, volume = {4}, number = {7}, pages = {074601}, doi = {10.1103/PhysRevFluids.4.074601},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.074601} } |
Bakhuis, D., Mathai, V., Verschoof, R. A., Ezeta, R., Lohse, D., Huisman, S. G. and Sun, C., "Statistics of rigid fibers in strongly sheared turbulence", Phys. Rev. Fluids, July 2019, Vol. 4(7), 072301(R) pp. |
Abstract: Practically all flows are turbulent in nature and contain some kind of irregularly shaped particles, e.g., dirt, pollen, or life forms such as bacteria or insects. The effects of the particles on such flows and vice versa are highly nontrivial and are not completely understood, particularly when the particles are finite sized. Here, we report an experimental study of millimetric fibers in a strongly sheared turbulent flow. We find that the fibers show a preferred orientation of -0.38ð±0.05ð (-68±9 ) with respect to the mean flow direction in high-Reynolds-number Taylor-Couette turbulence, for all studied Reynolds numbers, fiber concentrations, and locations. Despite the finite size of the anisotropic particles, we can explain the preferential alignment by using Jefferey's equation, which provides evidence of the benefit of a simplified point-particle approach. Furthermore, the fiber angular velocity is strongly intermittent, again indicative of point-particle-like behavior in turbulence. Thus large anisotropic particles still can retain signatures of the local flow despite classical spatial and temporal filtering effects. |
BibTeX:
@article{Bakhuis.Mathai.ea2019, author = {Bakhuis, D. and Mathai, V. and Verschoof, R. A. and Ezeta, R. and Lohse, D. and Huisman, S. G. and Sun, C.}, title = {Statistics of rigid fibers in strongly sheared turbulence}, journal = {Phys. Rev. Fluids}, month = {July}, year = {2019}, volume = {4}, number = {7}, pages = {072301(R)}, doi = {10.1103/PhysRevFluids.4.072301},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.072301} } |
Cavallini, F. and Tarantola, M., "ECIS based wounding and reorganization of cardiomyocytes and fibroblasts in co-cultures", Prog. Biophys. Mol. Biol., July 2019, Vol. 144, 116 pp. |
Abstract: The crosstalk of two major heart cell groups, cardiomyocytes and fibroblasts, relies on direct electromechanical cellular coupling as well as indirect mechanical signal transmission through the surrounding viscoelastic extracellular matrix. Upon injury of cardiac tissue, this communication becomes unbalanced: fibrosis is initiated leading to increased collagen deposition, accompanied by an activation of fibroblasts – the key players of fibrosis. They undergo a reorganization or partial transformation to myofibroblasts during this process, which precedes scar formation within the infarcted heart in vivo. Here, we induce wound formation in an in vitro system as a model for these fibrotic conditions: we assessed the dynamics of wound healing in co-cultures of fibroblasts and myocytes upon targeted wound initiation using Electric Cell Substrate Impedance Sensing (ECIS) under optical control. We discovered distinct wound closure dynamics for mono- and co-cultures of myocytes and fibroblasts and observed a cessation of the contractile behavior for recovering cardiomyocyte cultures. We furthermore identified a change of cellular impedance for recovering fibroblasts and the presence of á-SMA, suggesting a partial transformation into myofibroblasts. This was concomitant with a modulation of connectivity, cell-substrate dynamics and membrane capacitance of all wounded cell cultures. Qualitatively, connexin 43 observation confirmed the ECIS trend found for cell-cell connectivity. Finally, we were able to validate the ECIS based wounding approach against an ECIS based barrier assay – the so-called electric fence. In particular the cell-cell connectivity and thus cell layer integrity dominates the healing dynamics within the two intrinsically different assays. |
BibTeX:
@article{Cavallini.Tarantola2018, author = {Cavallini, F. and Tarantola, M.}, title = {ECIS based wounding and reorganization of cardiomyocytes and fibroblasts in co-cultures}, journal = {Prog. Biophys. Mol. Biol.}, month = {July}, year = {2019}, volume = {144}, pages = {116}, doi = {10.1016/j.pbiomolbio.2018.06.010},, url = {https://www.sciencedirect.com/science/article/pii/S0079610718300658?via%3Dihub} } |
Krastel, S., Kinne, S., Nitsche, F., Ahlers, J., Bischof, S., Bodenschatz, E., Cremanns, M., Düring, A., Höhne, P., Jeuck, A., Lenz, K.-F., Meyer, M., Pereyra, N., Rachid, J., Schiwitza, S., Schlenczek, O., Schopenhauer, M., Schröder, M., Stevens, B., Tewes, S., Vietheer, C. and Wagner, T., "Morphology of the headwall area of the Sahara slide, NW-Africa, Measuring Over Ocean References, Mapping sequences to protists morphospecies from the Atlantic, Cruise No. MSM82/2, 26.04.19 - 14.05.19, Montevideo (Uruguay) - Las Palmas (Spain)", July 2019 |
Abstract: RV MARIA S. MERIAN Cruise MSM82/2 realized three proposals. Hydroacoustic data and gravity cores were collected in the headwall area of the Sahara slide (Proposal ‘Morphology of the headwall area of the Sahara Slide, NW-Africa’. The new data show a very high (>100 m) and wide (> 60 km wide) lower headwall. Flow structures can be traced across the lower headwall suggesting the it is older than the upper headwall area. Three gravity cores were taken for dating different flows. Atmospheric data were collected in the frame of the proposal ‘Measuring Over Ocean References’. These measurements included shipboard-based estimates of atmospheric aerosol and trace-gases as well as cloud properties. A major success was the successful test of a CloudKite, which was used onboard of a German research vessel for the first time. Five Argo Floats were deployed and underway hydroacoustic data were collected for the Seabed 2030 project of the Nippon Foundation and GEBCO in order to create improved maps of the sea floor. The proposal ‘Mapping sequences to protists morphospecies from the Atlantic’ aimed in studying the biodiversity of pelagic protists in an area, which has not been investigated extensively yet. Surface water samples were taken every 5° latitude. In addition, three CTDs sampled deeper water masses, especially the area around the chlorophyll maximum. 15 protist species were isolated onboard. Several species are in mixed cultures and need to be isolated after the cruise. |
BibTeX:
@article{2019, author = {Krastel, S. and Kinne, S. and Nitsche, F. and Ahlers, J. and Bischof, S. and Bodenschatz, E. and Cremanns, M. and Düring, A. and Höhne, P. and Jeuck, A. and Lenz, K.-F. and Meyer, M. and Pereyra, N. and Rachid, J. and Schiwitza, S. and Schlenczek, O. and Schopenhauer, M. and Schröder, M. and Stevens, B. and Tewes, S. and Vietheer, C. and Wagner, T.}, title = {Morphology of the headwall area of the Sahara slide, NW-Africa, Measuring Over Ocean References, Mapping sequences to protists morphospecies from the Atlantic, Cruise No. MSM82/2, 26.04.19 - 14.05.19, Montevideo (Uruguay) - Las Palmas (Spain)}, month = {July}, year = {2019}, doi = {10.2312/cr_msm82_2},, url = {https://www.tib.eu/de/suchen/id/awi:doi 10.2312%2Fcr_msm82_2/} } |
Tan, H. S., Diddens, C., Mohammed, A. A., Li, J., Versluis, M., Zhang, X. and Lohse, D., "Microdroplet nucleation by dissolution of a multicomponent drop in a host liquid", J. Fluid Mech., July 2019, Vol. 870, 217 pp. |
Abstract: Multicomponent liquid drops in a host liquid are very relevant in various technological applications. Their dissolution or growth dynamics is complex. Differences in solubility between the drop components combined with the solutal Marangoni effect and natural convection contribute to this complexity, which can be even further increased in combination with the ouzo effect, i.e. the spontaneous nucleation of microdroplets due to composition-dependent miscibilities in a ternary system. The quantitative understanding of this combined process is important for applications in industry, particularly for modern liquid–liquid microextraction processes. In this work, as a model system, we experimentally and theoretically explore water–ethanol drops dissolving in anethole oil. During the dissolution, we observed two types of microdroplet nucleation, namely water microdroplet nucleation in the surrounding oil at drop mid-height, and oil microdroplet nucleation in the aqueous drop, again at mid-height. The nucleated oil microdroplets are driven by Marangoni flows inside the aqueous drop and evolve into microdroplet rings. A one-dimensional multiphase and multicomponent diffusion model in combination with thermodynamic equilibrium theory is proposed to predict the behaviour of spontaneous emulsification, i.e. microdroplet nucleation, that is triggered by diffusion. A scale analysis together with experimental investigations of the fluid dynamics of the system reveals that both the solutal Marangoni flow inside the drop and the buoyancy-driven flow in the host liquid influence the diffusion-triggered emulsification process. Our work provides a physical understanding of the microdroplet nucleation by dissolution of a multicomponent drop in a host liquid. |
BibTeX:
@article{Tan.Diddens.ea2019, author = {Tan, H. S. and Diddens, C. and Mohammed, A. A. and Li, J. and Versluis, M. and Zhang, X. and Lohse, D.}, title = {Microdroplet nucleation by dissolution of a multicomponent drop in a host liquid}, journal = {J. Fluid Mech.}, month = {July}, year = {2019}, volume = {870}, pages = {217}, doi = {10.1017/jfm.2019.207},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/microdroplet-nucleation-by-dissolution-of-a-multicomponent-drop-in-a-host-liquid/D92FC384C0B2112A2DFA5D0124C92823} } |
Tarantola, M., Meyer, T., Schmidt, C. F. and Zimmermann, W.-H., "Physics meets medicine - At the heart of active matter", Prog. Biophys. Mol. Biol., July 2019, Vol. 144, 1 pp. |
Abstract: Active matter is loosely defined as a soft material set in motion by integrated force-generating entities, such as motor proteins in a network of cytoskeletal protein polymers. In biological systems, energy dissipating dynamics are essential to tissue structure and function, and the heart is a prime example of a central and highly complex organ built of active matter. Unfortunately there is a knowledge gap between fundamental insight gained from experimental and theoretical studies of non-equilibrium statistical physics of active matter and the complex structures and functions found at the tissue level. Such an understanding will be of direct practical value to medicine. |
BibTeX:
@article{Tarantola.Meyer.ea2019, author = {Tarantola, M. and Meyer, T. and Schmidt, C. F. and Zimmermann, W.-H.}, title = {Physics meets medicine - At the heart of active matter}, journal = {Prog. Biophys. Mol. Biol.}, month = {July}, year = {2019}, volume = {144}, pages = {1}, doi = {10.1016/j.pbiomolbio.2019.03.009},, url = {https://www.sciencedirect.com/science/article/pii/S0079610719300707?via%3Dihub} } |
Zhu, X., Stevens, R. J. A. M., Shishkina, O., Verzicco, R. and Lohse, D., "Nu Ra1/2 scaling enabled by multiscale wallroughness in Rayleigh-Bénard turbulence", J. Fluid Mech., June 2019, Vol. 869, R4 pp. |
Abstract: In turbulent Rayleigh-Bénard (RB) convection with regular, mono-scale, surface roughness, the scaling exponent ? in the relationship between the Nusselt number and the Rayleigh number Ra , Nu Ra? 1/2 can be locally, provided that Ra is large enough to ensure that the thermal boundary layer thickness ? is comparable to the roughness height. However, at even larger , Ra , ? becomes thin enough to follow the irregular surface and ? saturates back to the value for smooth walls (Zhu et al., Phys. Rev. Lett., vol. 119, 2017, 154501). In this paper, we prevent this saturation by employing multiscale roughness. We perform direct numerical simulations of two-dimensional RB convection using an immersed boundary method to capture the rough plates. We find that, for rough boundaries that contain three distinct length scales, a scaling exponent of ?=0.49+-0.02 can be sustained for at least three decades of . The physical reason is that the threshold at which the scaling exponent ? saturates back to the smooth wall value is pushed to larger , when the smaller roughness elements fully protrude through the thermal boundary layer. The multiscale roughness employed here may better resemble the irregular surfaces that are encountered in geophysical flows and in some industrial applications. |
BibTeX:
@article{Zhu.Stevens.ea2019, author = {Zhu, X. and Stevens, R. J. A. M. and Shishkina, O. and Verzicco, R. and Lohse, D.}, title = {Nu Ra1/2 scaling enabled by multiscale wallroughness in Rayleigh-Bénard turbulence}, journal = {J. Fluid Mech.}, month = {June}, year = {2019}, volume = {869}, pages = {R4}, doi = {10.1017/jfm.2019.228},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/nusim-ra12-scaling-enabled-by-multiscale-wall-roughness-in-rayleighbenard-turbulence/115F3B409B43FF8A8BB0E99B49DC9A40} } |
Küchler, C., Bewley, G. P. and Bodenschatz, E., "Experimental Study of the Bottleneck in Fully Developed Turbulence", Journal of Statistical Physics, May 2019, Vol. 175(3-4), 617 pp. |
Abstract: The energy spectrum of incompressible turbulence is known to reveal a pileup of energy at those high wavenumbers where viscous dissipation begins to act. It is called the bottleneck effect. Based on direct numerical simulations of the incompressible Navier-Stokes equations, results from Donzis & Sreenivasan (2010) pointed to a decrease of the strength of the bottleneck with increasing intensity of the turbulence, measured by the Taylor micro-scale Reynolds number Rë. Here we report first experimental results on the dependence of the amplitude of the bottleneck as a function of Rë in a wind-tunnel flow. We used an active grid in the Variable Density Turbulence Tunnel (VDTT) (see Bodenschatz et al. (2014)) to reach Rë > 5000, which is unmatched in laboratory flows of decaying turbulence. The VDTT with the active grid permitted us to measure energy spectra from flows of different Rë, with the small-scale features appearing always at the same frequencies. We relate those spectra recorded to a common reference spectrum, largely eliminating systematic errors which plague hotwire measurements at high frequencies. The data are consistent with a power law for the decrease of the bottleneck strength for the finite range of Rë in the experiment. |
BibTeX:
@article{Kuechler.Bewley.ea2018, author = {Küchler, C. and Bewley, G P and Bodenschatz, E.}, title = {Experimental Study of the Bottleneck in Fully Developed Turbulence}, journal = {Journal of Statistical Physics}, month = {May}, year = {2019}, volume = {175}, number = {3-4}, pages = {617}, doi = {10.1007/s10955-019-02251-1},, url = {https://link.springer.com/article/10.1007%2Fs10955-019-02251-1} } |
Lee, S. J., Ha, N. and Kim, H., "Superhydrophilic-Superhydrophobic Water Harvester Inspired by Wetting Property of Cactus Stem", ACS Sustainable Chem. Eng., May 2019, Vol. 7(12), 10641 pp. |
Abstract: Water harvesting is a core technology for collecting fresh water in arid areas. In this study, we design a three-dimensional cactus stem-inspired water harvesting system (WHS) with directional transport of absorbed fog. The bioinspired WHS consists of two distinct functions. One is an effective water-absorbing function with an antievaporating feature, and the other is an on-demand water-releasing function. The excellent water absorption capability of a mucilage-filled cactus stem covered with a cuticle is mimicked by a cylindrical double structural system (DS) comprising an interpenetrating polymer network (IPN) hydrogel with good water retention capacity and a superhydrophobic copper mesh (SHPM) that prevents the re-evaporation of absorbed water. DS harvests water at a rate of 209 mg cm–2 h–1 and exhibits enhanced water collecting performance, i.e., 1.2, 1.3, and 2 times higher than that of the superhydrophilic IPN hydrogel, SHPM, and pristine copper mesh (PTM), respectively. The detailed fog harvesting mechanism of DS is examined through an X-ray imaging technique, and the water harvesting mechanism is described in terms of volumetric expansion of IPN hydrogel, absorption of microdroplets on mesh humps, and thickness of the water-film between mesh fibers. In addition, the function of water release is demonstrated with the aid of the thermoresponsive property of the IPN hydrogel. This biomimetic WHS may aid in developing effective three-dimensional plant-inspired fog collectors. |
BibTeX:
@article{Lee.Ha.ea2019, author = {Lee, S. J. and Ha, N. and Kim, H.}, title = {Superhydrophilic-Superhydrophobic Water Harvester Inspired by Wetting Property of Cactus Stem}, journal = {ACS Sustainable Chem. Eng.}, month = {May}, year = {2019}, volume = {7}, number = {12}, pages = {10641}, doi = {10.1021/acssuschemeng.9b01113},, url = {https://pubs.acs.org/doi/10.1021/acssuschemeng.9b01302} } |
Buaria, D., Pumir, A., Bodenschatz, E. and Yeung, P. K., "Extreme velocity gradients in turbulent flows", New J. Phys., April 2019, Vol. 21, 043004 pp. |
Abstract: Fully turbulent flows are characterized by intermittent formation of very localized and intense velocity gradients. These gradients can be orders of magnitude larger than their typical value and lead to many unique properties of turbulence. Using direct numerical simulations of the Navier–Stokes equations with unprecedented small-scale resolution, we characterize such extreme events over a significant range of turbulence intensities, parameterized by the Taylor-scale Reynolds number (R_λ ). Remarkably, we find the strongest velocity gradients to empirically scale as τ _K^-1R_λ ^β , with β ≈ 0.775± 0.025, where τ _K is the Kolmogorov time scale (with its inverse, τ _K^-1, being the rms of velocity gradient fluctuations). Additionally, we observe velocity increments across very small distances r⩽ η , where ç is the Kolmogorov length scale, to be as large as the rms of the velocity fluctuations. Both observations suggest that the smallest length scale in the flow behaves as η R_λ ^-α , with α =β -12, which is at odds with predictions from existing phenomenological theories. We find that extreme gradients are arranged in vortex tubes, such that strain conditioned on vorticity grows on average slower than vorticity, approximately as a power law with an exponent γ lt 1, which weakly increases with R_λ . Using scaling arguments, we get β =(2-γ )^-1, which suggests that â would also slowly increase with R_λ . We conjecture that approaching the mathematical limit of infinite R_λ , strain and vorticity would scale similarly resulting in γ =1 and hence extreme events occurring at a scale η R_λ ^-1/2 corresponding to β =1. |
BibTeX:
@article{Buaria.Pumir.ea2019, author = {Buaria, D. and Pumir, A. and Bodenschatz, E. and Yeung, P. K.}, title = {Extreme velocity gradients in turbulent flows}, journal = {New J. Phys.}, month = {April}, year = {2019}, volume = {21}, pages = {043004}, doi = {10.1088/1367-2630/ab0756},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/ab0756} } |
Karpinska, K., Bodenschatz, J. F. E., Malinowski, S. P., Nowak, J. L., Risius, S., Schmeissner, T., Shaw, R. A., Siebert, H., Xi, H., Xu, H. and Bodenschatz, E., "Turbulence-induced cloud voids: observation and interpretation", Atmos. Chem. Phys., April 2019, Vol. 19(7), 4991 pp. |
Abstract: The phenomenon of “cloud voids”, i.e., elongatedvolumes inside a cloud that are devoid of droplets, was ob-served with laser sheet photography in clouds at a mountain-top station. Two experimental cases, similar in turbulenceconditions yet with diverse droplet size distributions andcloud void prevalence, are reported. A theoretical explana-tion is proposed based on the study of heavy inertial sed-imenting particles inside a Burgers vortex. A general con-clusion regarding void appearance is drawn from theoreticalanalysis. Numerical simulations of polydisperse droplet mo-tion with realistic vortex parameters and Mie scattering vi-sual effects accounted for can explain the presence of voidswith sizes similar to that of the observed ones. Clustering andsegregation effects in a vortex tube are discussed for reason-able cloud conditions. |
BibTeX:
@article{Karpinska.Bodenschatz.ea2019, author = {Karpinska, K. and Bodenschatz, J. F. E. and Malinowski, S. P. and Nowak, J. L. and Risius, S. and Schmeissner, T. and Shaw, R. A. and Siebert, H. and Xi, H. and Xu, H. and Bodenschatz, E.}, title = {Turbulence-induced cloud voids: observation and interpretation}, journal = {Atmos. Chem. Phys.}, month = {April}, year = {2019}, volume = {19}, number = {7}, pages = {4991}, doi = {10.5194/acp-19-4991-2019},, url = {https://www.atmos-chem-phys.net/19/4991/2019/acp-19-4991-2019-discussion.html} } |
Lu, J., Zhu, X., Peters, E., Verzicco, R., Lohse, D. and Kuipers, J., "Moving from momentum transfer to heat transfer – A comparative study of an advanced Graetz-Nusselt problem using immersed boundary methods", Chemical Engineering Science, April 2019, Vol. 198, 317 pp. |
Abstract: In this paper two immersed boundary methods (IBM), specifically a continuous forcing method (CFM) and a discrete forcing method (DFM), are applied to perform direct numerical simulations (DNSs) of heat transfer problems in tubular fluid-particle systems. Both IBM models are built on the well-developed models utilized in momentum transfer studies, and have the capability to handle mixed boundary conditions at the particle surface as encountered in industrial applications with both active and passive particles.
Following a thorough verification of both models for the classical Graetz-Nusselt problem, we subsequently apply them to study a much more advanced Graetz-Nusselt problem of more practical importance with a dense stationary array consisting of hundreds of particles randomly positioned inside a tube with adiabatic wall. The influence of particle sizes and fractional amount of passive particles is analyzed at varying Reynolds numbers, and the simulation results are compared between the two IBM models, finding good agreement. Our results thus qualify the two employed IBM modules for more complex applications. |
BibTeX:
@article{Lu.Zhu.ea2019, author = {Lu, J. and Zhu, X. and Peters, E.A.J.F. and Verzicco, R. and Lohse, D. and Kuipers, J.A.M.}, title = {Moving from momentum transfer to heat transfer – A comparative study of an advanced Graetz-Nusselt problem using immersed boundary methods}, journal = {Chemical Engineering Science}, month = {April}, year = {2019}, volume = {198}, pages = {317}, doi = {10.1016/j.ces.2018.08.046},, url = {https://www.sciencedirect.com/science/article/pii/S0009250918306250} } |
Nobach, H., "Note on nonparametric spectral analysis of wideband spectrum with missing data via sample-and-hold interpolation and deconvolution", Digital Signal Processing, April 2019, Vol. 87, 19 pp. |
Abstract: In [1] a procedure for bias-free estimation of the autocorrelation function is introduced for equidistantly sampled data with randomly occurring samples being invalid. The method incorporates sample-and-hold interpolation of the missing data points. The occurring dynamic error of the primary estimate of the correlation function is treated by a deconvolution procedure with two parameters and with , which are the on-diagonal and the aside-diagonal parameters of a specific correction matrix (at all lag times except zero). The parameters and were obtained as a function of the probability á of a sample to be valid by numerical simulation. However, explicit expressions for the parameters and can be derived, which might improve the usability of the deconvolution procedure in [1]. |
BibTeX:
@article{Nobach2019, author = {Nobach, H.}, title = {Note on nonparametric spectral analysis of wideband spectrum with missing data via sample-and-hold interpolation and deconvolution}, journal = {Digital Signal Processing}, month = {April}, year = {2019}, volume = {87}, pages = {19}, doi = {10.1016/j.dsp.2019.01.008},, url = {https://www.sciencedirect.com/science/article/pii/S1051200418303646} } |
Prabhakaran, P., Krekhov, A., Bodenschatz, E. and Weiss, S., "Leidenfrost Pattern Formation and Boiling", Journal of Statistical Physics, April 2019, Vol. 175(3-4), 598 pp. |
Abstract: We report on Leidenfrost patterns and boiling with compressed sulfur hexafluoride (SF6). The experiments were carried out in a large aspect ratio Rayleigh-Bénard convection cell, where the distance between the horizontal plates is comparable with the capillary length of the working fluid. Pressures and temperatures were chosen such that the bottom plate was above and the top plate was below the liquid-vapor transition temperature of SF6. As a result, SF6 vapor condenses at the top plate and forms drops that grow in size. Leidenfrost patterns are formed as the drops do not fall but levitate by the vapor released in the gap between the hot bottom plate and the colder drops. When the size of these drops became too large, one or more vapor bubbles-chimneys-form inside them. We determine the critical size for the formation of a chimney as a function of the capillary length. For even larger drops and extended puddles many disconnected chimneys occur that can grow to sizes large enough for the formation of new drops inside them. By varying the temperatures and the pressure in the system, we observe various such patterns. When the area covered by a puddle becomes large it touches the hot bottom plate locally and boils off rapidly. This can be attributed to a local reduction of the bottom plate surface temperature below the Leidenfrost temperature. |
BibTeX:
@article{Prabhakaran.Krekhov.ea2019, author = {Prabhakaran, P. and Krekhov, A. and Bodenschatz, E. and Weiss, S.}, title = {Leidenfrost Pattern Formation and Boiling}, journal = {Journal of Statistical Physics}, month = {April}, year = {2019}, volume = {175}, number = {3-4}, pages = {598}, doi = {10.1007/s10955-019-02283-7},, url = {https://link.springer.com/article/10.1007/s10955-019-02283-7?wt_mc=Internal.Event.1.SEM.ArticleAuthorOnlineFirst&utm_source=ArticleAuthorOnlineFirst&utm_medium=email&utm_content=AA_en_06082018&ArticleAuthorOnlineFirst_20190412} } |
Vilfan, A., Subramani, S., Bodenschatz, E., Golestanian, R. and Guido, I., "Flagella-like Beating of a Single Microtubule", Nano Letters, April 2019, Vol. 19(5), 3359 pp. |
Abstract: Kinesin motors can induce a buckling instability in a microtubule with a fixed minus end. Here we show that by modifying the surface with a protein-repellent functionalization and using clusters of kinesin motors, the microtubule can exhibit persistent oscillatory motion resembling the beating of sperm flagella. The observed period is of the order of 1 min. From the experimental images we theoretically determine a distribution of motor forces that explains the observed shapes using a maximum likelihood approach. A good agreement is achieved with a small number of motor clusters acting simultaneously on a microtubule. The tangential forces exerted by a cluster are mostly in the range 0-8 pN toward the microtubule minus end, indicating the action of 1 or 2 kinesin motors. The lateral forces are distributed symmetrically and mainly below 10 pN, while the lateral velocity has a strong peak around zero. Unlike well-known models for flapping filaments, kinesins are found to have a strong “pinning” effect on the beating filaments. Our results suggest new strategies to utilize molecular motors in dynamic roles that depend sensitively on the stress built-up in the system. |
BibTeX:
@article{Vilfan.Subramani.ea2019, author = {Vilfan, A. and Subramani, S. and Bodenschatz, E. and Golestanian, R. and Guido, I.}, title = {Flagella-like Beating of a Single Microtubule}, journal = {Nano Letters}, month = {April}, year = {2019}, volume = {19}, number = {5}, pages = {3359}, doi = {10.1021/acs.nanolett.9b01091},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.nanolett.9b01091} } |
Zykov, V. S., "Kinematics of Spiral Waves in Excitable Media", April 2019, 265 pp. |
Abstract: Spiral waves rigidly rotating in excitable media sometimes play a constructive role in self-organization, while in many cases they cause an undesirable and dangerous activity. An understanding of spiral wave kinematics can help to control or to prevent this self-sustained activity. A description of the spiral wave kinematics performed by use of a free-boundary approach, reveals the selection principle which determines the shape and the rotation frequency of spiral waves in an unbounded medium with a given excitability. It is shown that a rigidly rotating spiral in a medium with strongly reduced refractoriness is supported within an excitability range restricted by two universal limits. At the low excitability limit, the spiral core radius diverges, while it vanishes at the high excitability limit and the spiral wave resembles the Yin-Yang pattern. |
BibTeX:
@incollection{Zykov2019a, author = {Zykov, V. S.}, title = {Kinematics of Spiral Waves in Excitable Media}, month = {April}, year = {2019}, pages = {265}, doi = {10.1007/978-3-030-05798-5_16},, url = {https://link.springer.com/chapter/10.1007/978-3-030-05798-5_16} } |
Atakhani, A., Mohammad-Rafiee, F. and Gholami, A., "Influence of cross-linking and retrograde flow on formation and dynamics of lamellipodium", PLOS ONE, March 2019, Vol. 14(3), 0213810 pp. |
Abstract: The forces that arise from the actin cortex play a crucial role in determining the membrane deformation. These include protrusive forces due to actin polymerization, pulling forces due to transient attachment of actin filaments to the membrane, retrograde flow powered by contraction of actomyosin network, and adhesion to the extracellular matrix. Here we present a theoretical model for membrane deformation resulting from the feedback between the membrane shape and the forces acting on the membrane. We model the membrane as a series of beads connected by springs and determine the final steady-state shape of the membrane arising from the interplay between pushing/pulling forces of the actin network and the resisting membrane tension. We specifically investigate the effect of the gel dynamics on the spatio-temporal deformation of the membrane until a stable lamellipodium is formed. We show that the retrograde flow and the cross-linking velocity play an essential role in the final elongation of the membrane. Interestingly, in the simulations where motor-induced contractility is switched off, reduced retrograde flow results in an increase in the rate and amplitude of membrane protrusion. These simulations are consistent with experimental observations that report an enhancement in protrusion efficiency as myosin II molecular motors are inhibited. |
BibTeX:
@article{Atakhani.Mohammad-Rafiee.ea2019, author = {Atakhani, A. and Mohammad-Rafiee, F. and Gholami, A.}, title = {Influence of cross-linking and retrograde flow on formation and dynamics of lamellipodium}, journal = {PLOS ONE}, month = {March}, year = {2019}, volume = {14}, number = {3}, pages = {0213810}, doi = {10.1371/journal.pone.0213810},, url = {https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0213810} } |
Griffin, K. P., Wei, N. J., Bodenschatz, E. and Bewley, G. P., "Control of long-range correlations in turbulence", Experiments in Fluids, March 2019, Vol. 60(55), 1 pp. |
Abstract: The character of turbulence depends on where it develops. Turbulence near boundaries, for instance, is different than in a free stream. To elucidate the differences between flows, it is instructive to vary the structure of turbulence systematically, but there are few ways of stirring turbulence that make this possible. In other words, an experiment typically examines either a boundary layer or a free stream, say, and the structure of the turbulence is fixed by the geometry of the experiment. We introduce a new active grid with many more degrees of freedom than the previous active grids. The additional degrees of freedom make it possible to control various properties of the turbulence. We show how long-range correlations in the turbulent velocity fluctuations can be shaped by changing the way the active grid moves. Specifically, we show how not only the correlation length, but also the detailed shape of the correlation function depends on the correlations imposed in the motions of the grid. Until now, large-scale structure had not been adjustable in experiments. This new capability makes possible new systematic investigations into turbulence dissipation and dispersion, for example, and perhaps in flows that mimic features of boundary layers, free streams, and flows of intermediate character. |
BibTeX:
@article{Griffin.Wei.ea2019, author = {Griffin, K. P. and Wei, N. J. and Bodenschatz, E. and Bewley, G. P.}, title = {Control of long-range correlations in turbulence}, journal = {Experiments in Fluids}, month = {March}, year = {2019}, volume = {60}, number = {55}, pages = {1}, doi = {10.1007/s00348-019-2698-1},, url = {https://link.springer.com/article/10.1007/s00348-019-2698-1?wt_mc=Internal.Event.1.SEM.ArticleAuthorIncrementalIssue&utm_source=ArticleAuthorIncrementalIssue&utm_medium=email&utm_content=AA_en_06082018&ArticleAuthorIncrementalIssue_20190306#copyrightInformation} } |
Kim, H., Kim, K. and Lee, S., "Flattened-Top Domical Droplet Formed by a Poly(pyrrole) Membrane", Macromol. Mater. Eng., March 2019, Vol. 304(3), 1800707 pp. |
Abstract: Polypyrrole (PPy) is a promising conductive polymer (CP) with electrical versatility, easy synthesis and functionalization, stability, and biocompatibility. Diverse architectures have been adopted to improve PPy performance, but the direct and precise patterning of various architectures remains challenging. Here, the unique formation of a PPy membrane on the air/water interface of a droplet solution containing ammonium persulfate and phytic acid is investigated. When a PPy thin film forms on the air/water interface, the top of the droplet rapidly flattens. The formation procedure and final structure of the PPy thin film are visualized and quantitatively investigated. Unlike the typical globular structure of PPy, the self assembled PPy film surface fabricated in this study is very organized and regularly shaped. This well ordered membrane may have a very high buckling strength greater than the surface tension of the solution. The proposed precise fabrication method is simple and inexpensive for fabricating patterned functional membranes. These results provide new insight into the fabrication of CP and their applications in various practical electromaterial engineering fields. |
BibTeX:
@article{Kim.Kim.ea2019, author = {Kim, H. and Kim, K. and Lee, S.L.}, title = {Flattened-Top Domical Droplet Formed by a Poly(pyrrole) Membrane}, journal = {Macromol. Mater. Eng.}, month = {March}, year = {2019}, volume = {304}, number = {3}, pages = {1800707}, doi = {10.1002/mame.201800707},, url = {https://onlinelibrary.wiley.com/doi/full/10.1002/mame.201800707} } |
Li, Y., Diddens, C., Lv, P., Wijshoff, H., Versluis, M. and Lohse, D., "Gravitational Effect in Evaporating Binary Microdroplets", Phys. Rev. Lett., March 2019, Vol. 122(114501), 1 pp. |
Abstract: The flow in an evaporating glycerol-water binary submillimeter droplet with a Bond number Bo<<1 is studied both experimentally and numerically. First, we measure the flow fields near the substrate by microparticle image velocimetry for both sessile and pendant droplets during the evaporation process, which surprisingly show opposite radial flow directions--inward and outward, respectively. This observation clearly reveals that in spite of the small droplet size, gravitational effects play a crucial role in controlling the flow fields in the evaporating droplets. We theoretically analyze that this gravity-driven effect is triggered by the lower volatility of glycerol which leads to a preferential evaporation of water then the local concentration difference of the two components leads to a density gradient that drives the convective flow. We show that the Archimedes number Ar is the nondimensional control parameter for the occurrence of the gravitational effects. We confirm our hypothesis by experimentally comparing two evaporating microdroplet systems, namely, a glycerol-water droplet and a 1,2-propanediol-water droplet. We obtain different Ar, larger or smaller than a unit by varying a series of droplet heights, which corresponds to cases with or without gravitational effects, respectively. Finally, we simulate the process numerically, finding good agreement with the experimental results and again confirming our interpretation. |
BibTeX:
@article{Li.Diddens.ea2019, author = {Li, Y. and Diddens, C. and Lv, P. and Wijshoff, H. and Versluis, M. and Lohse, D.}, title = {Gravitational Effect in Evaporating Binary Microdroplets}, journal = {Phys. Rev. Lett.}, month = {March}, year = {2019}, volume = {122}, number = {114501}, pages = {1}, doi = {10.1103/PhysRevLett.122.114501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.114501} } |
Vidal-Henriquez, E. and Gholami, A., "Spontaneous center formation in Dictyostelium discoideum", Scientific Reports, March 2019, Vol. 9, 3935 pp. |
Abstract: Dictyostelium discoideum (D.d.) is a widely studied amoeba due to its capabilities of development, survival, and self-organization. During aggregation it produces and relays a chemical signal (cAMP) which shows spirals and target centers. Nevertheless, the natural emergence of these structures is still not well understood. We present a mechanism for creation of centers and target waves of cAMP in D.d. by adding cell inhomogeneity to a well known reaction-diffusion model of cAMP waves and we characterize its properties. We show how stable activity centers appear spontaneously in areas of higher cell density with the oscillation frequency of these centers depending on their density. The cAMP waves have the characteristic dispersion relation of trigger waves and a velocity which increases with cell density. Chemotactically competent cells react to these waves and create aggregation streams even with very simple movement rules. Finally we argue in favor of the existence of bounded phosphodiesterase to maintain the wave properties once small cell clusters appear. |
BibTeX:
@article{Vidal-Henriquez.Gholami2019, author = {Vidal-Henriquez, E. and Gholami, A.}, title = {Spontaneous center formation in Dictyostelium discoideum}, journal = {Scientific Reports}, month = {March}, year = {2019}, volume = {9}, pages = {3935}, doi = {10.1038/s41598-019-40373-4},, url = {https://www.nature.com/articles/s41598-019-40373-4} } |
Bae, A., Hanstorp, D. and Chang, K., "Juggling with Light", Phys. Rev. Lett., February 2019, Vol. 122(4), 043902 pp. |
Abstract: We discovered that when a pair of small particles is optically levitated, the particles execute a “dance” whose motion resembles the orbits of balls being juggled. This motion lies in a plane perpendicular to the polarization of the incident light. We ascribe the dance to a mechanism by which the dominant force on each particle cyclically alternates between radiation pressure and gravity as each particle takes turns eclipsing the other. We explain the plane of motion by considering the anisotropic scattering of polarized light at a curved interface. |
BibTeX:
@article{Bae.Hanstorp.ea2019, author = {Bae, A. and Hanstorp, D. and Chang, K.}, title = {Juggling with Light}, journal = {Phys. Rev. Lett.}, month = {February}, year = {2019}, volume = {122}, number = {4}, pages = {043902}, doi = {10.1103/PhysRevLett.122.043902},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.043902} } |
Capelo, H. L., Molacek, J., Lambrechts, M., Lawson, J. M., Johansen, A., Blum, J., Bodenschatz, E. and Xu, H., "Observation of aerodynamic instability in the flow of a particle stream in a dilute gas", Astronomy & Astrophysics, February 2019, Vol. 622(A151), 20 pp. |
Abstract: Forming macroscopic solid bodies in circumstellar discs requires local dust concentration levels significantly higher than the mean. Interactions of the dust particles with the gas must serve to augment local particle densities, and facilitate growth past barriers in the metre size range. Amongst a number of mechanisms that can amplify the local density of solids, aerodynamic streaming instability (SI) is one of the most promising. This work tests the physical assumptions of models that lead to SI in protoplanetary discs (PPDs). We conduct laboratory experiments in which we track the three-dimensional motion of spherical solid particles fluidised in a low-pressure, laminar, incompressible, gas stream. The particle sizes span the Stokes–Epstein drag regime transition and the overall dust-to-gas mass density ratio, E, is close to unity. A recently published study establishes the similarity of the laboratory flow to a simplified PPD model flow. We study velocity statistics and perform time-series analysis of the advected flow to obtain experimental results suggesting an instability due to particle-gas interaction: (i) there exist variations in particle concentration in the direction of the mean relative motion between the gas and the particles, that is the direction of the mean drag forces; (ii) the particles have a tendency to “catch up” to one another when they are in proximity; (iii) particle clumping occurs on very small scales, which implies local enhancements above the background E by factors of several tens; (iv) the presence of these density enhancements occurs for a mean E approaching or greater than 1; (v) we find evidence for collective particle drag reduction when the local particle number density becomes high and when the background gas pressure is high so that the drag is in the continuum regime. The experiments presented here are precedent-setting for observing SI under controlled conditions and may lead to a deeper understanding of how it operates in nature. |
BibTeX:
@article{Capelo.Molacek.ea2019, author = {Capelo, H. L. and Molacek, J. and Lambrechts, M. and Lawson, J. M. and Johansen, A. and Blum, J. and Bodenschatz, E. and Xu, H.}, title = {Observation of aerodynamic instability in the flow of a particle stream in a dilute gas}, journal = {Astronomy & Astrophysics}, month = {February}, year = {2019}, volume = {622}, number = {A151}, pages = {20}, doi = {10.1051/0004-6361/201833702},, url = {https://www.aanda.org/articles/aa/abs/2019/02/aa33702-18/aa33702-18.html} } |
Chung, H., Kim, S., Kim, K.-T., Hwang, B.-G., Kim, H.-J., Lee, S. and Lee, Y.-H., "A novel approach to investigate hypoxic microenvironment during rice colonization by Magnaporthe oryzae", Environmental Microbiology, February 2019, Vol. 21(3), 1151 pp. |
Abstract: Because molecular oxygen functions as the final acceptor of electrons during aerobic respiration and a substrate for diverse enzymatic reactions, eukaryotes employ various mechanisms to maintain cellular homeostasis under varying oxygen concentration. Human fungal pathogens change the expression of genes involved in virulence and oxygen-required metabolisms such as ergosterol (ERG) synthesis when they encounter oxygen limitation (hypoxia) during infection. The oxygen level in plant tissues also fluctuates, potentially creating hypoxic stress to pathogens during infection. However, little is known about how in planta oxygen dynamics impact pathogenesis. In this study, we investigated oxygen dynamics in rice during infection by Magnaporthe oryzae via two approaches. First, rice leaves infected by M. oryzae were noninvasively probed using a microscopic oxygen sensor. Second, an immunofluorescence assay based on a chemical probe, pimonidazole, was used. Both methods showed that oxygen concentration in rice decreased after fungal penetration. We also functionally characterized five hypoxia-responsive genes participating in ERG biosynthesis for their role in pathogenesis. Resulting insights and tools will help study the nature of in planta oxygen dynamics in other pathosystems. |
BibTeX:
@article{Chung.Kim.ea2019, author = {Chung, H. and Kim, S. and Kim, K.-T. and Hwang, B.-G. and Kim, H.-J. and Lee, S. and Lee, Y.-H.}, title = {A novel approach to investigate hypoxic microenvironment during rice colonization by Magnaporthe oryzae}, journal = {Environmental Microbiology}, month = {February}, year = {2019}, volume = {21}, number = {3}, pages = {1151}, doi = {10.1111/1462-2920.14563},, url = {https://onlinelibrary.wiley.com/doi/full/10.1111/1462-2920.14563} } |
Escobar, J., Garcia-Gonzales, D., Devic I. Zhang, X. and Lohse, D., "Morphology of Evaporating Sessile Microdroplets on Lyophilic Elliptical Patches", Langumir, February 2019, Vol. 35(6), 2099 pp. |
Abstract: The evaporation of droplets occurs in a large variety of natural and technological processes such as medical diagnostics, agriculture, food industry, printing, and catalytic reactions. We study the different droplet morphologies adopted by an evaporating droplet on a surface with an elliptical patch with a different contact angle. We perform experiments to observe these morphologies and use numerical calculations to predict the effects of the patched surfaces. We observe that tuning the geometry of the patches offers control over the shape of the droplet. In the experiments, the drops of various volumes are placed on elliptical chemical patches of different aspect ratios and imaged in 3D using laser scanning confocal microscopy, extracting the droplet’s shape. In the corresponding numerical simulations, we minimize the interfacial free energy of the droplet, by employing Surface Evolver. The numerical results are in good qualitative agreement with our experimental data and can be used for the design of micropatterned structures, potentially suggesting or excluding certain morphologies for particular applications. However, the experimental results show the effects of pinning and contact angle hysteresis, which are obviously absent in the numerical energy minimization. The work culminates with a morphology diagram in the aspect ratio vs relative volume parameter space, comparing the predictions with the measurements. |
BibTeX:
@article{Escobar.Garcia-Gonzales.ea2019, author = {Escobar, J.M.E. and Garcia-Gonzales, D. and Devic, I. Zhang, X. and Lohse, D.}, title = {Morphology of Evaporating Sessile Microdroplets on Lyophilic Elliptical Patches}, journal = {Langumir}, month = {February}, year = {2019}, volume = {35}, number = {6}, pages = {2099}, doi = {10.1021/acs.langmuir.8b03393},, url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374750/} } |
Huang, H., Wang, X., Yu, J., Chen, Y., Ji, H., Zhang, Y., Rehfeldt, F., Wang, Y. and Zhang, K., "Liquid-Behaviors-Assisted Fabrication of Multidimensional Birefringent Materials from Dynamic Hybrid Hydrogels", ACS Nano, February 2019, Vol. 13(4), 3867 pp. |
Abstract: Liquid-solid transition is a widely usedstrategy to shape polymeric materials and encode theirmicrostructures. However, it is still challenging to fullyexploit liquid behaviors of material precursors. Inparticular, the dynamic and static liquid behaviors naturallyconflict with each other, which makes it difficult tointegrate their advantages in the same materials. Here, byutilizing a shear-thinning phenomenon in the dynamichybrid hydrogels, we achieve a hydrodynamic alignment ofcellulose nanocrystals (CNC) and preserve it in the relaxedhydrogel networks due to the much faster relaxation ofpolymer networks (within 500 s) than CNC after theunloading of external force. During the following dryingprocess, the surface tension of hydrogels further enhances the orientation index of CNC up to 0.872 in confinedgeometry, and these anisotropic microstructures demonstrate highly tunable birefringence (up to 0.004 14). Due to thepresence of the boundaries of dynamic hydrogels, diverse xerogels includingfibers,films, and even complex three-dimensional structures with variable anisotropic microstructures can be fabricated without any external molds. |
BibTeX:
@article{Huang.Wang.ea2019, author = {Huang, H. and Wang, X. and Yu, J. and Chen, Y. and Ji, H. and Zhang, Y. and Rehfeldt, F. and Wang, Y. and Zhang, K.}, title = {Liquid-Behaviors-Assisted Fabrication of Multidimensional Birefringent Materials from Dynamic Hybrid Hydrogels}, journal = {ACS Nano}, month = {February}, year = {2019}, volume = {13}, number = {4}, pages = {3867}, doi = {10.1021/acsnano.9b00551},, url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.9b00551} } |
Lawson, J. M., Bodenschatz, E., Knutsen, A. N., Dawson, J. R. and Worth, N. A., "Direct assessment of Kolmogorov's first refined similarity hypothesis", Phys. Rev. Fluids, February 2019, Vol. 4(2), 022601 pp. |
Abstract: Using volumetric velocity data from a turbulent laboratory water flow and numerical simulations of homogeneous, isotropic turbulence, we present a direct experimental and numerical assessment of Kolmogorov's first refined similarity hypothesis based on three-dimensional measurements of the local energy dissipation rate år measured at dissipative scales r. We focus on the properties of the stochastic variables VL=Äu(r)/(rår)1/3 and VT=Äv(r)/(rår)1/3, where Äu(r) and Äv(r) are longitudinal and transverse velocity increments. Over one order of magnitude of scales r within the dissipative range, the distributions of VL and VT from both experiment and simulation collapse when parametrized by a suitably defined local Reynolds number, providing conclusive experimental evidence in support of the first refined similarity hypothesis and its universality. |
BibTeX:
@article{Lawson.Bodenschatz.ea2019, author = {Lawson, J. M. and Bodenschatz, E. and Knutsen, A. N. and Dawson, J. R. and Worth, N. A.}, title = {Direct assessment of Kolmogorov's first refined similarity hypothesis}, journal = {Phys. Rev. Fluids}, month = {February}, year = {2019}, volume = {4}, number = {2}, pages = {022601}, doi = {10.1103/PhysRevFluids.4.022601},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.4.022601} } |
Wilkinson, M., Pradas, M., Huber, G. and Pumir, A., "Lacunarity exponents", Journal of Physics A: Mathematical and Theoretical, February 2019, Vol. 52(11), 115101 pp. |
Abstract: Many physical processes result in very uneven, apparently random, distributions of matter, characterised by fluctuations of the local density varying over orders of magnitude. The density of matter in the sparsest regions can have a power-law distribution, with an exponent that we term the lacunarity exponent. We discuss a mechanism which explains the wide occurrence of these power laws, and give analytical expressions for the exponent in some simple models. |
BibTeX:
@article{Wilkinson.Pradas.ea2019, author = {Wilkinson, M. and Pradas, M. and Huber, G. and Pumir, A.}, title = {Lacunarity exponents}, journal = {Journal of Physics A: Mathematical and Theoretical}, month = {February}, year = {2019}, volume = {52}, number = {11}, pages = {115101}, doi = {10.1088/1751-8121/ab0349},, url = {https://iopscience.iop.org/article/10.1088/1751-8121/ab0349/meta} } |
Gauthier, A., Diddens, C., Proville, R., Lohse, D. and van der Meer, D., "Self-propulsion of inverse Leidenfrost drops on a cryogenic bath", PNAS, January 2019, Vol. 116(4), 1174 pp. |
Abstract: When deposited on a hot bath, volatile drops are observed to stay in levitation: the so-called Leidenfrost effect. Here, we discuss drop dynamics in an inverse Leidenfrost situation where room-temperature drops are deposited on a liquid-nitrogen pool and levitate on a vapor film generated by evaporation of the bath. In the seconds following deposition, we observe that the droplets start to glide on the bath along a straight path, only disrupted by elastic bouncing close to the edges of the container. Initially at rest, these self-propelled drops accelerate within a few seconds and reach velocities on the order of a few centimeters per second before slowing down on a longer time scale. They remain self-propelled as long as they are sitting on the bath, even after freezing and cooling down to liquid-nitrogen temperature. We experimentally investigate the parameters that affect liquid motion and propose a model, based on the experimentally and numerically observed (stable) symmetry breaking within the vapor film that supports the drop. When the film thickness and the cooling dynamics of the drops are also modeled, the variations of the drop velocities can be accurately reproduced. |
BibTeX:
@article{Gauthier.Diddens.ea2019, author = {Gauthier, A. and Diddens, C. and Proville, R. and Lohse, D. and van der Meer, D.}, title = {Self-propulsion of inverse Leidenfrost drops on a cryogenic bath}, journal = {PNAS}, month = {January}, year = {2019}, volume = {116}, number = {4}, pages = {1174}, doi = {10.1073/pnas.1812288116},, url = {https://www.pnas.org/content/116/4/1174.short} } |
Peng, S., Spandan, V., Verzicco, R., Lohse, D. and Zhang, H., "Growth dynamics of microbubbles on microcavity arrays by solvent exchange: Experiments and numerical simulations", Journal of Colloid and Interface Science, December 2018, Vol. 532, 103 pp. |
Abstract: Solvent exchange is a flow process to induce a transient oversaturation for forming nanobubbles or nanodroplets on solid surfaces by displacing the solution of gases or droplet liquids with a controlled flow of a poor solvent. In this work, we experimentally and numerically investigate the effect of the flow rate and other control parameters on the formation of microbubbles on hydrophobic cavity arrays during the solvent exchange process. We find that the growth rate, location, and number density of microbubbles are closely related to flow rate, solvent concentration, cavity distance, and spatial arrangement. Higher growth rates and number densities of the bubbles were obtained for faster solvent exchange flow rates. The competition of neighbouring growing bubbles for dissolved gas is greatly alleviated when the inter cavity distance is increased from 13 mu m to 40 mu m. The effects of the flow rate and the cavity spacing on the bubble growth are in agreement with the observations from our three-dimensional numerical simulations. The findings reported in this work provide important insight into the formation of multiple interacting surface microbubbles under various flow conditions. The understanding may be extended to a smaller scale for the growth of surface nanobubbles during solvent exchange, which is much harder to visualize in experiments. |
BibTeX:
@article{Peng.Spandan.ea2018, author = {Peng, S.H. and Spandan, V. and Verzicco, R. and Lohse, D. and Zhang, H.}, title = {Growth dynamics of microbubbles on microcavity arrays by solvent exchange: Experiments and numerical simulations}, journal = {Journal of Colloid and Interface Science}, month = {December}, year = {2018}, volume = {532}, pages = {103}, doi = {10.1016/j.jcis.2018.07.111},, url = {https://www.sciencedirect.com/science/article/pii/S0021979718308750} } |
Spandan, V., Lohse, D., de Tullio, M. and Verzicco, R., "A fast moving least squares approximation with adaptive Lagrangian mesh refinement for large scale immersed boundary simulations", Journal of Computational Physics, December 2018, Vol. 375, 228 pp. |
Abstract: In this paper we propose and test the validity of simple and easy-to-implement algorithms within the immersed boundary framework geared towards large scale simulations involving thousands of deformable bodies in highly turbulent flows. First, we introduce a fast moving least squares (fast-MLS) approximation technique with which we speed up the process of building transfer functions during the simulations which leads to considerable reductions in computational time. We compare the accuracy of the fast-MLS against the exact moving least squares (MLS) for the standard problem of uniform flow over a sphere. In order to overcome the restrictions set by the resolution coupling of the Lagrangian and Eulerian meshes in this particular immersed boundary method, we present an adaptive Lagrangian mesh refinement procedure that is capable of drastically reducing the number of required nodes of the basic Lagrangian mesh when the immersed boundaries can move and deform. Finally, a coarse-grained collision detection algorithm is presented which can detect collision events between several Lagrangian markers residing on separate complex geometries with minimal computational overhead. |
BibTeX:
@article{Spandan.Lohse.ea2018, author = {Spandan, V. and Lohse, D. and de Tullio, M.D. and Verzicco, R.}, title = {A fast moving least squares approximation with adaptive Lagrangian mesh refinement for large scale immersed boundary simulations}, journal = {Journal of Computational Physics}, month = {December}, year = {2018}, volume = {375}, pages = {228}, doi = {10.1016/j.jcp.2018.08.040},, url = {https://www.sciencedirect.com/science/article/pii/S0021999118305710} } |
Zaytsev, M. E., Lajoinie, G., Wang, Y., Lohse, D., Zandvliet, H. J. W. and Zhang, H., "Plasmonic Bubbles in n-Alkanes", Journal of Physical Chemistry, December 2018, Vol. 122(49), 28375 pp. |
Abstract: In this paper, we study the formation of microbubbles upon the irradiation of an array of plasmonic Au nanoparticles with a laser in n-alkanes (CnH2n+2, with n = 5-10). Two different phases in the evolution of the bubbles can be distinguished. In the first phase, which occurs after a delay time tau(d) of about 100 mu s, an explosive microbubble is formed, reaching a diameter in the range from 10 to 100 mu m. The exact size of this explosive microbubble barely depends on the carbon chain length of the alkane but more so on the laser power P-I. With increasing laser power, the delay time prior to bubble nucleation as well as the size of the microbubble both decrease. In the second phase, which sets in right after the collapse of the explosive microbubble, a new bubble forms and starts growing due to the vaporization of the surrounding liquid, which is highly gas-rich. The final bubble size in this second phase strongly depends on the alkane chain length; namely, it increases with a decreasing number of carbon atoms. Our results have important implications for using plasmonic heating to control chemical reactions in organic solvents. |
BibTeX:
@article{Zaytsev.Lajoinie.ea2019, author = {Zaytsev, M. E. and Lajoinie, G. and Wang, Y. and Lohse, D. and Zandvliet, H. J. W. and Zhang, H.}, title = {Plasmonic Bubbles in n-Alkanes}, journal = {Journal of Physical Chemistry}, month = {December}, year = {2018}, volume = {122}, number = {49}, pages = {28375}, doi = {10.1021/acs.jpcc.8b09617},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b09617} } |
Zykov, V., "Spiral wave initiation in excitable media", Royal Society A, December 2018, Vol. 376(2135), 20170379 pp. |
Abstract: Spiral waves represent an important example of dissipative structures observed in many distributed systems in chemistry, biology and physics. By definition, excitable media occupy a stationary resting state in the absence of external perturbations. However, a perturbation exceeding a threshold results in the initiation of an excitation wave propagating through the medium. These waves, in contrast to acoustic and optical ones, disappear at the medium's boundary or after a mutual collision, and the medium returns to the resting state. Nevertheless, an initiation of a rotating spiral wave results in a self-sustained activity. Such activity unexpectedly appearing in cardiac or neuronal tissues usually destroys their dynamics which results in life-threatening diseases. In this context, an understanding of possible scenarios of spiral wave initiation is of great theoretical importance with many practical applications. |
BibTeX:
@article{Zykov2018, author = {Zykov, V.}, title = {Spiral wave initiation in excitable media}, journal = {Royal Society A}, month = {December}, year = {2018}, volume = {376}, number = {2135}, pages = {20170379}, doi = {10.1098/rsta.2017.0379},, url = {https://royalsocietypublishing.org/doi/pdf/10.1098/rsta.2017.0379} } |
Lohse, D., "Bubble puzzles: From fundamentals to applications", Phys. Rev. Fluids, November 2018, Vol. 3(11), 110504 pp. |
Abstract: For centuries, bubbles have fascinated artists, engineers, and scientists alike. In spite of century-long research on them, new and often surprising bubble phenomena, features, and applications keep popping up. In this paper I sketch my personal scientific bubble journey, starting with single-bubble sonoluminescence, continuing with sound emission and scattering of bubbles, cavitation, snapping shrimp, impact events, air entrainment, and surface micro- and nanobubbles, and finally arriving at effective force models for bubbles and dispersed bubbly two-phase flow. In particular, I also cover various applications of bubbles, namely, in ultrasound diagnostics, drug and gene delivery, piezoacoustic inkjet printing, immersion lithography, sonochemistry, electrolysis, catalysis, acoustic marine geophysical survey, and bubble drag reduction for naval vessels, and show how these applications crossed my way. I also try to show that good and interesting fundamental science and relevant applications are not a contradiction, but mutually stimulate each other in both directions. |
BibTeX:
@article{Lohse, author = {Lohse, D.}, title = {Bubble puzzles: From fundamentals to applications}, journal = {Phys. Rev. Fluids}, month = {November}, year = {2018}, volume = {3}, number = {11}, pages = {110504}, doi = {10.1103/PhysRevFluids.3.110504},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.3.110504} } |
Kamprad, N., Witt, H., Schröder, M., Kreis, C., Bäumchen, O., Janshoff, A. and Tarantola, M., "Adhesion Strategies of Dictyostelium discoideum - a Force Spectroscopy Study", RSC Nanoscale, October 2018, Vol. 10, 22504 pp. |
Abstract: Biological adhesion is essential for all motile cells and generally limits locomotion to suitably functionalized substrates displaying a compatible surface chemistry. However, organisms that face vastly varying environmental challenges require a different strategy. The model organism Dictyostelium discoideum (D.d.), a slime mould dwelling in the soil, faces the challenge of overcoming variable chemistry by employing the fundamental forces of colloid science. To understand the origin of D.d. adhesion, we realized and modified a variety of conditions for the amoeba comprising the absence and presence of the specific adhesion protein Substrate Adhesion A (sadA), glycolytic degradation, ionic strength, surface hydrophobicity and strength of van der Waals interactions by generating tailored model substrates. Employing AFM-based single cell force spectroscopy we could show that experimental force curves upon retraction exhibit two regimes. The first part up to the critical adhesion force can be described in terms of a continuum model, while the second regime of the curve beyond the critical adhesion force is governed by stochastic unbinding of individual binding partners and bond clusters. We found that D.d. relies on adhesive interactions based on EDL-DLVO (Electrical Double Layer-Derjaguin-Landau-Verwey-Overbeek) forces as well as contributions from the glycocalix and specialized adhesion molecules like sadA. This versatile mechanism allows the cells to adhere to a large variety of natural surfaces and conditions. |
BibTeX:
@article{Kamprad.Witt.ea, author = {Kamprad, N. and Witt, H. and Schröder, M. and Kreis, C. and Bäumchen, O. and Janshoff, A. and Tarantola, M.}, title = {Adhesion Strategies of Dictyostelium discoideum - a Force Spectroscopy Study}, journal = {RSC Nanoscale}, month = {October}, year = {2018}, volume = {10}, pages = {22504}, doi = {10.1039/C8NR07107A},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/C8NR07107A.pdf} } |
Lawson, J. M., Bodenschatz, E., Lalescu, C. C. and Wilczek, M., "Bias in particle tracking acceleration measurement", Experments in Fluids, October 2018, Vol. 59, 172 pp. |
Abstract: We investigate sources of systematic error (bias) in acceleration statistics derived from Lagrangian particle tracking data and demonstrate techniques to eliminate or minimise these bias errors introduced during processing. Numerical simulations of particle tracking experiments in isotropic turbulence show that the main sources of bias error arise from noise due to random position errors and selection biases introduced during numerical differentiation. We outline the use of independent measurements and filtering schemes to eliminate these biases. Moreover, we test the validity of our approach in estimating the statistical moments and probability densities of the Lagrangian acceleration. Finally, we apply these techniques to experimental particle tracking data and demonstrate their validity in practice with comparisons to available data from the literature. The general approach, which is not limited to acceleration statistics, can be applied with as few as two cameras and permits a substantial reduction in the position accuracy and sampling rate required to adequately measure the statistics of Lagrangian acceleration. |
BibTeX:
@article{Lawson.Bodenschatz.ea2018, author = {Lawson, J. M. and Bodenschatz, E. and Lalescu, C. C. and Wilczek, M.}, title = {Bias in particle tracking acceleration measurement}, journal = {Experments in Fluids}, month = {October}, year = {2018}, volume = {59}, pages = {172}, doi = {doi.org/10.1007/s00348-018-2622-0},, url = {https://link.springer.com/article/10.1007/s00348-018-2622-0} } |
Verschoof, R. A., Zhu, X., Bakhuis, D., Huisman, S. G., Verzicco, R., Sun, C. and Lohse, D., "Rough-wall turbulent Taylor-Couette flow: The effect of the rib height", Eur. Phys. J. E, October 2018, Vol. 41(10), 125 pp. |
Abstract: In this study, we combine experiments and direct numerical simulations to investigate the effects of the height of transverse ribs at the walls on both global and local flow properties in turbulent Taylor-Couette flow. We create rib roughness by attaching up to 6 axial obstacles to the surfaces of the cylinders over an extensive range of rib heights, up to blockages of 25% of the gap width. In the asymptotic ultimate regime, where the transport is independent of viscosity, we emperically find that the prefactor of the scaling (corresponding to the drag coefficient being constant) scales with the number of ribs and by the rib height . The physical mechanism behind this is that the dominant contribution to the torque originates from the pressure forces acting on the rib which scale with the rib height. The measured scaling relation of is slightly smaller than the expected scaling, presumably because the ribs cannot be regarded as completely isolated but interact. In the counter-rotating regime with smooth walls, the momentum transport is increased by turbulent Taylor vortices. We find that also in the presence of transverse ribs these vortices persist. In the counter-rotating regime, even for large roughness heights, the momentum transport is enhanced by these vortices. |
BibTeX:
@article{Verschoof.Zhu.ea2018, author = {Verschoof, R. A. and Zhu, X. and Bakhuis, D. and Huisman, S. G. and Verzicco, R. and Sun, C. and Lohse, D.}, title = {Rough-wall turbulent Taylor-Couette flow: The effect of the rib height}, journal = {Eur. Phys. J. E}, month = {October}, year = {2018}, volume = {41}, number = {10}, pages = {125}, doi = {10.1140/epje/i2018-11736-2},, url = {https://link.springer.com/article/10.1140/epje/i2018-11736-2} } |
Yang, P.-F., Pumir, A. and Xu, H., "Generalized self-similar spectrum and the effect of large-scale in decaying homogeneous isotropic turbulence", New J. Phys., October 2018, Vol. 20, 103055 pp. |
Abstract: In statistically stationary conditions, the turbulent energy spectrum in a high Reynolds number flow exhibits a k -5/3 (Kolmogorov) regime, with a faster decay at larger, dissipative wavenumbers. Here, we investigate how the energy spectrum of a turbulent flow evolves in time when turbulence decays freely, in the absence of forcing. Results from direct numerical simulation of decaying turbulence in a periodic box with several different initial conditions suggest a generalized self-similar spectrum, depending on k_s=k× η (t) and k_l=k× L(t), where ç(t) and L(t) are, respectively, the small (Kolmogorov) and large scales of the flow. A closure method allows us to obtain an explicit form of the spectrum, which reproduces the deviations from the Kolmogorov spectrum at small k observed numerically. The solution can also be used to determine the second and third order structure functions in decaying turbulent flows, and to study their scaling behavior. Our results compare favorably with high-Reynolds number wind tunnel data. Moreover, our theoretical results provide support to the interesting empirical observation by Pearson et al (2002 Phys. Fluids 14 1288–90) that, independent of the large scale structure of the flow, the dimensionless energy dissipation rate is a universal constant when scaled in terms of the turbulent kinetic energy of the flow, and of the length scale corresponding to the peak of the compensated energy spectrum. |
BibTeX:
@article{Yang.Pumir.ea2018, author = {Yang, P.-F. and Pumir, A. and Xu, H.}, title = {Generalized self-similar spectrum and the effect of large-scale in decaying homogeneous isotropic turbulence}, journal = {New J. Phys.}, month = {October}, year = {2018}, volume = {20}, pages = {103055}, doi = {10.1088/1367-2630/aae72d},, url = {http://iopscience.iop.org/article/10.1088/1367-2630/aae72d/meta} } |
Feraco, F., Marino, R., Pumir, A., Primavera, L., Mininni, P. D., Pouquet, A. and Rosenberg, D., "Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number", EPL, September 2018, Vol. 123(4), 44002 pp. |
Abstract: We investigate the large-scale intermittency of vertical velocity and temperature, and the mixing properties of stably stratified turbulent flows using both Lagrangian and Eulerian fields from direct numerical simulations of the Boussinesq equations with periodic boundary conditions, in a parameter space relevant for the atmosphere and the oceans. Over a range of Froude numbers of geophysical interest (≈ 0.05--0.3) we observe very large fluctuations of the vertical components of the velocity and the potential temperature, localized in space and time, with a sharp transition leading to non-Gaussian wings of the probability distribution functions. This behavior is captured by a simple model representing the competition between gravity waves on a fast time scale and nonlinear steepening on a slower time scale. The existence of a resonant regime characterized by enhanced large-scale intermittency, as understood within the framework of the proposed model, is then linked to the emergence of structures in the velocity and potential temperature fields, localized overturning and mixing. Finally, in the same regime we observe a linear scaling of the mixing efficiency with the Froude number and an increase of its value of roughly one order of magnitude. |
BibTeX:
@article{Feraco.Marino.ea2018, author = {Feraco, F. and Marino, R. and Pumir, A. and Primavera, L. and Mininni, P. D. and Pouquet, A. and Rosenberg, D.}, title = {Vertical drafts and mixing in stratified turbulence: Sharp transition with Froude number}, journal = {EPL}, month = {September}, year = {2018}, volume = {123}, number = {4}, pages = {44002}, doi = {10.1209/0295-5075/123/44002},, url = {http://iopscience.iop.org/article/10.1209/0295-5075/123/44002/meta} } |
Kamprad, N. and Tarantola, M., "The dual role of actin foci in adhesion and endocytosis of Dictyostelium discoideum", September 2018 |
BibTeX:
@proceedings{Kamprad.Tarantola, author = {Kamprad, N. and Tarantola, M.}, title = {The dual role of actin foci in adhesion and endocytosis of Dictyostelium discoideum}, month = {September}, year = {2018},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/Tarantola-087.pdf} } |
Maheshwari, S., van der Hoef, M., Prosperetti, A. and Lohse, D., "Dynamics of Formation of a Vapor Nanobubble Around a Heated Nanoparticle", Journal of Physical Chemistry, September 2018, Vol. 122(36), 20571 pp. |
Abstract: We study the formation of a nanobubble around a heated nanoparticle in a bulk liquid by using molecular dynamics simulations. The nanoparticle is kept at a temperature above the critical temperature of the surrounding liquid, leading to the formation of a vapor nanobubble attached to it. First, we study the role of both the temperature of the bulk liquid far away from the nanoparticle surface and the temperature of the nanoparticle itself on the formation of a stable vapor nanobubble. We determine the exact conditions under which it can be formed and compare this with the conditions that follow from a macroscopic heat balance argument. Next, we demonstrate the role of dissolved gas on the conditions required for nucleation of a nanobubble and on its growth dynamics. We find that beyond a certain threshold concentration, the dissolved gas dramatically facilitates vapor bubble nucleation due to the formation of gaseous weak spots in the surrounding liquid. |
BibTeX:
@article{Maheshwari.Hoef.ea2018a, author = {Maheshwari, S. and van der Hoef, M. and Prosperetti, A. and Lohse, D.}, title = {Dynamics of Formation of a Vapor Nanobubble Around a Heated Nanoparticle}, journal = {Journal of Physical Chemistry}, month = {September}, year = {2018}, volume = {122}, number = {36}, pages = {20571}, doi = {10.1021/acs.jpcc.8b04017},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpcc.8b04017} } |
Pesch, W., Krekhov, A., Eber, N. and Buka, A., "Nonlinear analysis of flexodomains in nematic liquid crystals", Phys. Rev. E, September 2018, Vol. 98(3), 032702 pp. |
Abstract: We investigate flexodomains, which are observed in planar layers of certain nematic liquid crystals, when a dc voltage U above a critical value Uc is applied across the layer. They are characterized by stationary stripelike spatial variations of the director in the layer plane with a wave number p(U). Our experiments for different nematics demonstrate that p(U) varies almost linearly with U for U>Uc. That is confirmed by a numerical analysis of the full nonlinear equations for the director field and the induced electric potential. Beyond this numerical study, we demonstrate that the linearity of p(U) follows even analytically, when considering a special parameter set first used by Terent'ev and Pikin [Sov. Phys. JETP 56, 587 (1982)]. Their theoretical paper serves until now as the standard reference on the nonlinear analysis of flexodomains, since it has arrived at a linear variation of p(U) for large U>>Uc. Unfortunately, the corresponding analysis suffers from mistakes, which in a combination led to that result. |
BibTeX:
@article{Pesch.Krekhov.ea2018, author = {Pesch, W. and Krekhov, A. and Eber, N. and Buka, A.}, title = {Nonlinear analysis of flexodomains in nematic liquid crystals}, journal = {Phys. Rev. E}, month = {September}, year = {2018}, volume = {98}, number = {3}, pages = {032702}, doi = {10.1103/PhysRevE.98.032702},, url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.98.032702} } |
Mathai, V., Huisman, S. G., Sun, C., Lohse, D. and Bourgoin, M., "Dispersion of Air Bubbles in Isotropic Turbulence", Phys. Rev. Lett., August 2018, Vol. 121(5), 054501 pp. |
Abstract: Bubbles play an important role in the transport of chemicals and nutrients in many natural and industrial flows. Their dispersion is crucial to understanding the mixing processes in these flows. Here we report on the dispersion of millimetric air bubbles in a homogeneous and isotropic turbulent flow with a Taylor Reynolds number from 110 to 310. We find that the mean squared displacement (MSD) of the bubbles far exceeds that of fluid tracers in turbulence. The MSD shows two regimes. At short times, it grows ballistically (aT2), while at larger times, it approaches the diffusive regime where the MSD T. Strikingly, for the bubbles, the ballistic-to-diffusive transition occurs one decade earlier than for the fluid. We reveal that both the enhanced dispersion and the early transition to the diffusive regime can be traced back to the unsteady wake-induced motion of the bubbles. Further, the diffusion transition for bubbles is not set by the integral timescale of the turbulence (as it is for fluid tracers and microbubbles), but instead, by a timescale of eddy crossing of the rising bubbles. The present findings provide a Lagrangian perspective towards understanding mixing in turbulent bubbly flows. |
BibTeX:
@article{Mathai.Huisman.ea2018, author = {Mathai, V. and Huisman, S. G. and Sun, C. and Lohse, D. and Bourgoin, M.}, title = {Dispersion of Air Bubbles in Isotropic Turbulence}, journal = {Phys. Rev. Lett.}, month = {August}, year = {2018}, volume = {121}, number = {5}, pages = {054501}, doi = {10.1103/PhysRevLett.121.054501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.054501} } |
Sun, D., Wang, Y., Yu, H. and Han, Q., "A lattice Boltzmann study on dendritic growth of a binary alloy in the presence of melt convection", Int. J. Heat Mass Transfer, August 2018, Vol. 123, 213 pp. |
Abstract: A multi-relaxation-time (MRT) lattice Boltzmann (LB) based model is utilized to simulate the dendritic growth with melt convection in solidification of alloys. It models melt convection by the MRT-LB equation and solute transport by a conservation equation with a pseudo-potential function. The D2Q9 lattice vectors are proposed to describe interface advancement in the liquid-solid transition. Effects of undercoolings, interface curvature and preferred growth orientation are incorporated into the model implicitly. After model validation, dendritic growth under several conditions of pure diffusion and melt convection was numerically investigated, and the solidification entropies were proposed to quantitatively characterize the solidification system. The result shows that the growth behavior, microstructure formation and solute segregation are significantly influenced by melt convection. The solidification entropies reflecting complexity of the solidification system are useful to characterize dendritic growth and solute segregation. This work offers a potential solution for studies of microstructure evolution in solidification of alloys. |
BibTeX:
@article{Sun.Wang.ea2018, author = {Sun, D. and Wang, Y. and Yu, H. and Han, Q.}, title = {A lattice Boltzmann study on dendritic growth of a binary alloy in the presence of melt convection}, journal = {Int. J. Heat Mass Transfer}, month = {August}, year = {2018}, volume = {123}, pages = {213}, doi = {10.1016/j.ijheatmasstransfer.2018.02.053},, url = {https://www.sciencedirect.com/science/article/pii/S0017931017331733} } |
Verschoof, R. A., Bakhuis, D., Bullee, P. A., Huisman, S. G., Sun, C. and Lohse, D., "Air cavities at the inner cylinder of turbulent Taylor-Couette flow", International Journal of Multiphase Flow, August 2018, Vol. 105, 264 pp. |
Abstract: Air cavities, i.e. air layers developed behind cavitators, are seen as a promising drag reducing method in the maritime industry. Here we utilize the Taylor–Couette (TC) geometry, i.e. the flow between two concentric, independently rotating cylinders, to study the effect of air cavities in this closed setup, which is well-accessible for drag measurements and optical flow visualizations. We show that stable air cavities can be formed, and that the cavity size increases with Reynolds number and void fraction. The streamwise cavity length strongly depends on the axial position due to buoyancy forces acting on the air. Strong secondary flows, which are introduced by a counter-rotating outer cylinder, clearly decrease the stability of the cavities, as air is captured in the Taylor rolls rather than in the cavity. Surprisingly, we observed that local air injection is not necessary to sustain the air cavities; as long as air is present in the system it is found to be captured in the cavity. We show that the drag is decreased significantly as compared to the case without air, but with the geometric modifications imposed on the TC system by the cavitators. As the void fraction increases, the drag of the system is decreased. However, the cavitators itself significantly increase the drag due to their hydrodynamic resistance (pressure drag): In fact, a net drag increase is found when compared to the standard smooth-wall TC case. Therefore, one must first overcome the added drag created by the cavitators before one obtains a net drag reduction. |
BibTeX:
@article{Verschoof.Bakhuis.ea2018, author = {Verschoof, R. A. and Bakhuis, D. and Bullee, P. A. and Huisman, S. G. and Sun, C. and Lohse, D.}, title = {Air cavities at the inner cylinder of turbulent Taylor-Couette flow}, journal = {International Journal of Multiphase Flow}, month = {August}, year = {2018}, volume = {105}, pages = {264}, doi = {10.1016/j.ijmultiphaseflow.2018.04.016},, url = {https://www.sciencedirect.com/science/article/pii/S0301932217309503} } |
Zhu, X., Phillips, E., Spandan, V., Donners, J., Ruetsch, G., Romero, J., Ostilla-Monico, R., Yang, Y., Lohse, D., Verzicco, R., Fatica, M. and Stevens, R. J. A. M., "AFiD-GPU: A versatile Navier-Stokes solver for wall-bounded turbulent flows on GPU clusters", Computer Physics Communications, August 2018, Vol. 229, 199 pp. |
Abstract: The AFiD code, an open source solver for the incompressible Navier–Stokes equations (http://www.afid.eu), has been ported to GPU clusters to tackle large-scale wall-bounded turbulent flow simulations. The GPU porting has been carried out in CUDA Fortran with the extensive use of kernel loop directives (CUF kernels) in order to have a source code as close as possible to the original CPU version; just a few routines have been manually rewritten. A new transpose scheme has been devised to improve the scaling of the Poisson solver, which is the main bottleneck of incompressible solvers. For large meshes the GPU version of the code shows good strong scaling characteristics, and the wall-clock time per step for the GPU version is an order of magnitude smaller than for the CPU version of the code. Due to the increased performance and efficient use of memory, the GPU version of AFiD can perform simulations in parameter ranges that are unprecedented in thermally-driven wall-bounded turbulence. To verify the accuracy of the code, turbulent Rayleigh–Bénard convection and plane Couette flow are simulated and the results are in excellent agreement with the experimental and computational data that have been published in literature. |
BibTeX:
@article{Zhu.Phillips.ea2018, author = {Zhu, X. and Phillips, E. and Spandan, V. and Donners, J. and Ruetsch, G. and Romero, J. and Ostilla-Monico, R. and Yang, Y. and Lohse, D. and Verzicco, R. and Fatica, M. and Stevens, R. J. A. M.}, title = {AFiD-GPU: A versatile Navier-Stokes solver for wall-bounded turbulent flows on GPU clusters}, journal = {Computer Physics Communications}, month = {August}, year = {2018}, volume = {229}, pages = {199}, doi = {10.1016/j.cpc.2018.03.026},, url = {https://www.sciencedirect.com/science/article/pii/S0010465518300985} } |
Bakhuis, D., Verschoof, R. A., Mathai, V., Huisman, S. G., Lohse, D. and Sun, C., "Finite-sized rigid spheres in turbulent Taylor-Couette flow: effect on the overall drag", J. Fluid Mech., July 2018, Vol. 850, 246 pp. |
Abstract: We report on the modification of drag by neutrally buoyant spherical finite-sized particles in highly turbulent Taylor–Couette (TC) flow. These particles are used to disentangle the effects of size, deformability and volume fraction on the drag, and are contrasted to the drag in bubbly TC flow. From global torque measurements, we find that rigid spheres hardly decrease or increase the torque needed to drive the system. The size of the particles under investigation has a marginal effect on the drag, with smaller diameter particles showing only slightly lower drag. Increase of the particle volume fraction shows a net drag increase. However, this increase is much smaller than can be explained by the increase in apparent viscosity due to the particles. The increase in drag for increasing particle volume fraction is corroborated by performing laser Doppler anemometry, where we find that the turbulent velocity fluctuations also increase with increasing volume fraction. In contrast to rigid spheres, for bubbles, the effective drag reduction also increases with increasing Reynolds number. Bubbles are also much more effective in reducing the overall drag. |
BibTeX:
@article{Bakhuis.Verschoof.ea2018, author = {Bakhuis, D. and Verschoof, R. A. and Mathai, V. and Huisman, S. G. and Lohse, D. and Sun, C.}, title = {Finite-sized rigid spheres in turbulent Taylor-Couette flow: effect on the overall drag}, journal = {J. Fluid Mech.}, month = {July}, year = {2018}, volume = {850}, pages = {246}, doi = {10.1017/jfm.2018.462},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/finitesized-rigid-spheres-in-turbulent-taylorcouette-flow-effect-on-the-overall-drag/F5711D08AE9BD758D3EA6D16C1B3B3D0} } |
Wang, Y., Zaytsev, M. E., Lajoinie, G., Le The, H., Eijkel, J. C. T., van den Berg, A., Versluis, M., Weckhuysen, B., Zhang, X., Zandvliet, H. J. W. and Lohse, D., "Giant and explosive plasmonic bubbles by delayed nucleation", Proc. Natl. Acad. Sci. U.S.A., July 2018, Vol. 115(30), 7676 pp. |
Abstract: When illuminated by a laser, plasmonic nanoparticles immersed in water can very quickly and strongly heat up, leading to the nucleation of so-called plasmonic vapor bubbles. While the long-time behavior of such bubbles has been well-studied, here, using ultrahigh-speed imaging, we reveal the nucleation and early life phase of these bubbles. After some delay time from the beginning of the illumination, a giant bubble explosively grows, and collapses again within 200 ìs (bubble life phase 1). The maximal bubble volume Vmax remarkably increases with decreasing laser power, leading to less total dumped energy E. This dumped energy shows a universal linear scaling relation with Vmax, irrespective of the gas concentration of the surrounding water. This finding supports that the initial giant bubble is a pure vapor bubble. In contrast, the delay time does depend on the gas concentration of the water, as gas pockets in the water facilitate an earlier vapor bubble nucleation, which leads to smaller delay times and lower bubble nucleation temperatures. After the collapse of the initial giant bubbles, first, much smaller oscillating bubbles form out of the remaining gas nuclei (bubble life phase 2). Subsequently, the known vaporization dominated growth phase takes over, and the bubble stabilizes (life phase 3). In the final life phase 4, the bubble slowly grows by gas expelling due to heating of the surrounding. Our findings on the explosive growth and collapse during the early life phase of a plasmonic vapor bubble have strong bearings on possible applications of such bubbles. |
BibTeX:
@article{Wang.Zaytsev.ea2018, author = {Wang, Y. and Zaytsev, M. E. and Lajoinie, G. and Le The, H. and Eijkel, J. C. T. and van den Berg, A. and Versluis, M. and Weckhuysen, B. and Zhang, X. and Zandvliet, H. J. W. and Lohse, D.}, title = {Giant and explosive plasmonic bubbles by delayed nucleation}, journal = {Proc. Natl. Acad. Sci. U.S.A.}, month = {July}, year = {2018}, volume = {115}, number = {30}, pages = {7676}, doi = {10.1073/pnas.1805912115},, url = {http://www.pnas.org/content/115/30/7676.short} } |
Weiss, S., He, X., Ahlers, G., Bodenschatz, E. and Shishkina, O., "Bulk temperature and heat transport in turbulent Rayleigh-Bénard convection of fluids with temperature-dependent properties", J. Fluid Mech., July 2018, Vol. 851, 374 pp. |
Abstract: We critically analyse the different ways to evaluate the dependence of the Nusselt number (Nu) on the Rayleigh number (Ra) in measurements of the heat transport in turbulent Rayleigh-Bénard convection under general non-Oberbeck–Boussinesq conditions and show the sensitivity of this dependence to the choice of the reference temperature at which the fluid properties are evaluated. For the case when the fluid properties depend significantly on the temperature and any pressure dependence is insignificant we propose a method to estimate the centre temperature. The theoretical predictions show very good agreement with the Goettingen measurements by He et al. (New J. Phys., vol. 14, 2012, 063030). We further show too the values of the normalized heat transport are independent of whether they are evaluated in the whole convection cell or in the lower or upper part of the cell if the correct reference temperatures are used. |
BibTeX:
@article{Weiss.He.ea2018, author = {Weiss, S. and He, X. and Ahlers, G. and Bodenschatz, E. and Shishkina, O.}, title = {Bulk temperature and heat transport in turbulent Rayleigh-Bénard convection of fluids with temperature-dependent properties}, journal = {J. Fluid Mech.}, month = {July}, year = {2018}, volume = {851}, pages = {374}, doi = {10.1017/jfm.2018.507},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/bulk-temperature-and-heat-transport-in-turbulent-rayleighbenard-convection-of-fluids-with-temperaturedependent-properties/42633DB06FE8EB4D0F6537CE3DF2D02F} } |
Zwirner, L. and Shishkina, O., "Confined inclined thermal convection in low-Prandtl-number fluids", J. Fluid Mech., July 2018, Vol. 850, 984 pp. |
Abstract: Any tilt of a Rayleigh-Bénard convection cell against gravity changes the global flow structure inside the cell, which leads to a change of the heat and momentum transport. Especially sensitive to the inclination angle is the heat transport in low-Prandtl-number fluids and confined geometries. The purpose of the present work is to investigate the global flow structure and its influence on the global heat transport in inclined convection in a cylindrical container of diameter-to-height aspect ratio =1/5. The study is based on direct numerical simulations where two different Prandtl numbers and Pr=0.1 and 1.0 are considered, while the Rayleigh number, Ra, ranges from to 10_6 to 10_9. For each combination of Ra and Pr, the inclination angle is varied between 0 and Pi/2 . An optimal inclination angle of the convection cell, which provides the maximal global heat transport, is determined. For inclined convection we observe the formation of two system-sized plume columns, a hot and a cold one, that impinge on the opposite boundary layers. These are related to a strong increase in the heat transport. |
BibTeX:
@article{Zwirner.Shishkina2018, author = {Zwirner, L. and Shishkina, O.}, title = {Confined inclined thermal convection in low-Prandtl-number fluids}, journal = {J. Fluid Mech.}, month = {July}, year = {2018}, volume = {850}, pages = {984}, doi = {10.1017/jfm.2018.477},, url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6374750/} } |
Bourgoin, M., Baudet, C., Kharche, S., Mordant, N., Vandenberghe, T., Sumbekova, S., Stelzenmuller N. Aliseda, A., Gibert, M., Roche, P.-E., Volk, R., Barois, T., Lopez Caballero, M., Chevillard, L., Pinton, J.-F., Fiabane, L., Delville, J., Fourment, C., Bouha, A., Danaila, L., Bodenschatz, E., Bewley, G., Sinhuber, M., Segalini, A., Örlü, R., Torrano, I., Mantik, J., Guariglia, D., Uruba, V., Skala, V. and Puczylowski J. Peinke, J., "Investigation of the small-scale statistics of turbulence in the Modane S1MA wind tunnel", CEAS Aeronautical Journal, June 2018, Vol. 9(2), 269 pp. |
Abstract: This article describes the planning, set-up, turbulence characterization and analysis of measurements of a passive grid turbulence experiment that was carried out in the S1MA wind-tunnel from ONERA in Modane, in the context of the ESWIRP European project. This experiment aims at a detailed investigation of the statistical properties of turbulent flows at large Reynolds numbers. The primary goal is to take advantage of the unequaled large-scale dimensions of the ONERA S1MA wind-tunnel facility, to make available to the broad turbulence community high-quality experimental turbulence data with unprecendented resolution (both spatial and temporal) and accuracy (in terms of statistical convergence). With this goal, we designed the largest grid-generated turbulence experiment planned and performed to date. Grid turbulence is a canonical flow known to produce almost perfectly homogeneous and isotropic turbulence (HIT) which remains a unique framework to investigate fundamental physics of turbulent flows. Here, we present a brief description of the measurements, in particular those based on hot-wire diagnosis. By comparing results from classical hot-wires and from a nano-fabricated wire (developed at Princeton University), we show that our goal of resolving down to the smallest dissipative scales of the flow has been achieved. We also present the full characterization of the turbulence here, in terms of turbulent energy dissipation rate, injection and dissipation scales (both spatial and temporal) and Reynolds number. |
BibTeX:
@article{Bourgoin.Baudet.ea2018, author = {Bourgoin, M. and Baudet, C. and Kharche, S. and Mordant, N. and Vandenberghe, T. and Sumbekova, S. and Stelzenmuller, N. Aliseda, A. and Gibert, M. and Roche, P.-E. and Volk, R. and Barois, T. and Lopez Caballero, M. and Chevillard, L. and Pinton, J.-F. and Fiabane, L. and Delville, J. and Fourment, C. and Bouha, A. and Danaila, L. and Bodenschatz, E. and Bewley, G. and Sinhuber, M. and Segalini, A. and Örlü, R. and Torrano, I. and Mantik, J. and Guariglia, D. and Uruba, V. and Skala, V. and Puczylowski, J. Peinke, J.}, title = {Investigation of the small-scale statistics of turbulence in the Modane S1MA wind tunnel}, journal = {CEAS Aeronautical Journal}, month = {June}, year = {2018}, volume = {9}, number = {2}, pages = {269}, doi = {10.1007/s13272-017-0254-3},, url = {https://link.springer.com/article/10.1007/s13272-017-0254-3#enumeration} } |
Li, Y., Lv, P., Diddens, C., Tan, H., Wijshoff, H., Versluis, M. and Lohse, D., "Evaporation-Triggered Segregation of Sessile Binary Droplets", Phys. Rev. Lett., June 2018, Vol. 120, 224501 pp. |
Abstract: Droplet evaporation of multicomponent droplets is essential for various physiochemical applications, e.g., in inkjet printing, spray cooling, and microfabrication. In this work, we observe and study the phase segregation of an evaporating sessile binary droplet, consisting of a miscible mixture of water and a surfactantlike liquid (1,2-hexanediol). The phase segregation (i.e., demixing) leads to a reduced water evaporation rate of the droplet, and eventually the evaporation process ceases due to shielding of the water by the nonvolatile 1,2-hexanediol. Visualizations of the flow field by particle image velocimetry and numerical simulations reveal that the timescale of water evaporation at the droplet rim is faster than that of the Marangoni flow, which originates from the surface tension difference between water and 1,2-hexanediol, eventually leading to segregation. |
BibTeX:
@article{Li.Lv.ea2018, author = {Li, Y. and Lv, P. and Diddens, C. and Tan, H. and Wijshoff, H. and Versluis, M. and Lohse, D.}, title = {Evaporation-Triggered Segregation of Sessile Binary Droplets}, journal = {Phys. Rev. Lett.}, month = {June}, year = {2018}, volume = {120}, pages = {224501}, doi = {10.1103/PhysRevLett.120.224501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.224501} } |
Schröder, M., "Cell-Substrate Adhesion and Contact Guidance of Dictyostelium discoideum on Surfaces of Varying Curvatures", June 2018 |
BibTeX:
@mastersthesis{Schroeder2018, author = {Schröder, M.}, title = {Cell-Substrate Adhesion and Contact Guidance of Dictyostelium discoideum on Surfaces of Varying Curvatures}, month = {June}, year = {2018},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/Schroeder-M_MasterThesis.pdf} } |
Yang, Y., Verzicco, R. and Lohse, D., "Two-scalar turbulent Rayleigh-Bénard convection: numerical simulations and unifying theory", J. Fluid Mech., June 2018, Vol. 848, 848 pp. |
Abstract: We conduct direct numerical simulations for turbulent Rayleigh-Bénard (RB) convection, driven simultaneously by two scalar components (say, temperature and concentration) with different molecular diffusivities, and measure the respective fluxes and the Reynolds number. To account for the results, we generalize the Grossmann–Lohse theory for traditional RB convection (Grossmann & Lohse, J. Fluid Mech., vol. 407, 2000, pp. 27–56; Phys. Rev. Lett., vol. 86 (15), 2001, pp. 3316–3319; Stevens et al., J. Fluid Mech., vol. 730, 2013, pp. 295–308) to this two-scalar turbulent convection. Our numerical results suggest that the generalized theory can successfully capture the overall trends for the fluxes of two scalars and the Reynolds number without introducing any new free parameters. In fact, for most of the parameter space explored here, the theory can even predict the absolute values of the fluxes and the Reynolds number with good accuracy. The current study extends the generality of the Grossmann–Lohse theory in the area of buoyancy-driven convection flows. |
BibTeX:
@article{Yang.Verzicco.ea2018, author = {Yang, Y. and Verzicco, R. and Lohse, D.}, title = {Two-scalar turbulent Rayleigh-Bénard convection: numerical simulations and unifying theory}, journal = {J. Fluid Mech.}, month = {June}, year = {2018}, volume = {848}, pages = {848}, doi = {10.1017/jfm.2018.378},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/twoscalar-turbulent-rayleighbenard-convection-numerical-simulations-and-unifying-theory/13C81A0AF85BBB4E3E1897FE1F6F7198} } |
Capelo, H., "Dynamics of Suspended Dust Grains: Experimental Investigations and Implications for Protoplanetary Discs", May 2018 |
Abstract: The collective interaction of solid particulate matter with flowing gas is one of the fundamental processes occurring in planet-forming discs. Small dust grains and pebbles are comparable to or smaller than the mean free path of the gas in observed and simulated discs, where the collective force of particles on the gas has been predicted to create a fluid 'streaming instability' that can produce a turbulent flow and associated localised solid-density enhancements. Such fluid instabilities are therefore favoured amongst candidate mechanisms that concentrate solids in the initial stages of planet formation, which requires sufficiently compact mass concentrations for gravity to play its role in assembling matter, first by producing precursor planetesimals via gravitational instabilities, and subsequently via accretion. Previously, the streaming instability was studied analytically and with numerical simulations. This is the first work to test the mechanism directly in laboratory experiments. In this thesis, I show that the non-linear phase of the streaming instability is manifest, both in experiments and simulations, when fluidised particles settle against a pressure gradient and the solid-to-gas density ratio is close to unity. The experimental results set a precedent for empirical studies of scalable two-phase flows with properties similar to the fluids in protoplanetary discs. These experimental findings provide a test case to calibrate codes that include additional physical processes important for mass assembly such as collisions and charge attraction. Having established a facility to study low-pressure gas flows will enable myriad additional tests of the dynamical interaction between rarefied gas and sample materials. |
BibTeX:
@phdthesis{Capelo2018, author = {Capelo, H.}, title = {Dynamics of Suspended Dust Grains: Experimental Investigations and Implications for Protoplanetary Discs}, month = {May}, year = {2018},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-002E-E402-0} } |
van Limbeek, M. A. J., Hoefnagels, P. B. J., Shirota, M., Sun, C. and Lohse, D., "Boiling regimes of impacting drops on a heated substrate under reduced pressure", Phys. Rev. Fluids, May 2018, Vol. 3(5), 053601 pp. |
Abstract: We experimentally investigate the boiling behavior of impacting ethanol drops on a heated smooth sapphire substrate at pressures ranging from P=0.13 bar to atmospheric pressure. We employ frustrated total internal reflection imaging to study the wetting dynamics of the contact between the drop and the substrate. The spreading drop can be in full contact (contact boiling), it can partially touch (transition boiling), or the drop can be fully levitated (Leidenfrost boiling). We show that the temperature of the boundary between contact and transition boiling shows at most a weak dependence on the impact velocity, but a significant decrease with decreasing ambient gas pressure. A striking correspondence is found between the temperature of this boundary and the static Leidenfrost temperature for all pressures. We therefore conclude that both phenomena share the same mechanism and are dominated by the dynamics taking place at the contact line. On the other hand, the boundary between transition boiling and Leidenfrost boiling, i.e., the dynamic Leidenfrost temperature, increases for increasing impact velocity for all ambient gas pressures. Moreover, the dynamic Leidenfrost temperature coincides for pressures between P=0.13 and 0.54 bar, whereas for atmospheric pressure the dynamic Leidenfrost temperature is slightly elevated. This indicates that the dynamic Leidenfrost temperature is at most weakly dependent on the enhanced evaporation by the lower saturation temperature of the liquid. |
BibTeX:
@article{Limbeek.Hoefnagels.ea2018, author = {van Limbeek, M. A. J. and Hoefnagels, P. B. J. and Shirota, M. and Sun, C. and Lohse, D.}, title = {Boiling regimes of impacting drops on a heated substrate under reduced pressure}, journal = {Phys. Rev. Fluids}, month = {May}, year = {2018}, volume = {3}, number = {5}, pages = {053601}, doi = {10.1103/PhysRevFluids.3.053601},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.3.053601} } |
Mathai, V., Zhu, X., Sun, C. and Lohse, D., "Flutter to tumble transition of buoyant spheres triggered by rotational inertia changes", Nature Communications, May 2018, Vol. 9(1792) |
Abstract: Heavy particles sink straight in water, while buoyant bubbles and spheres may zigzag or spiral as they rise. The precise conditions that trigger such path-instabilities are still not completely understood. For a buoyant rising sphere, two parameters are believed to govern the development of unsteady dynamics: the particle’s density relative to the fluid, and its Galileo number. Consequently, with these parameters specified, the opportunities for variation in particle dynamics appear limited. In contrast to this picture, here we demonstrate that vigorous path-oscillations can be triggered by modulating a spherical particle’s moment of inertia (MoI). For a buoyant sphere rising in a turbulent flow, MoI reduction triggers a tumble–flutter transition, while in quiescent liquid, it induces a modification of the sphere wake resulting in large-amplitude path-oscillations. The present finding opens the door for control of particle path- and wake-instabilities, with potential for enhanced mixing and heat transfer in particle-laden and dispersed multiphase environments. |
BibTeX:
@article{Mathai.Zhu.ea2018, author = {Mathai, V. and Zhu, X. and Sun, C. and Lohse, D.}, title = {Flutter to tumble transition of buoyant spheres triggered by rotational inertia changes}, journal = {Nature Communications}, month = {May}, year = {2018}, volume = {9}, number = {1792}, doi = {10.1038/s41467-018-04177-w},, url = {https://www.nature.com/articles/s41467-018-04177-w} } |
Schwille, P., Spatz, J., Landfester, K., Bodenschatz, E., Herminghaus, S., Sourjik, V., Erb, T., Bastiaens, P., Lipowsky, R., Hyman, A., Dabrock, P., Baret, J.-C., Vidakovic-Koch, T., Bieling, P., Dimova, R., Mutschler, H., Robinson, T., Tang, D., Wegner, S. and Sundmacher, K., "MaxSynBio - Avenues towards creating cells from the bottom up", Angewandte Chemie, May 2018 |
Abstract: A large Max Planck based German research consortium ('MaxSynBio') was formed to investigate living systems from a fundamental perspective. The research program of MaxSynBio relies solely on the bottom up approach to Synthetic Biology. MaxSynBio focuses on the detailed analysis and understanding of essential processes of life, via their modular reconstitution in minimal synthetic systems. The ultimate goal is to construct a basic living unit entirely from non-living components. The fundamental insights gained from the activities in MaxSynBio can eventually be utilized for establishing a new generation of biotechnological processes, which would be based on synthetic cell constructs that replace natural cells currently used in conventional biotechnology. |
BibTeX:
@article{Schwille.Spatz.ea2018, author = {Schwille, P. and Spatz, J. and Landfester, K. and Bodenschatz, E. and Herminghaus, S. and Sourjik, V. and Erb, T. and Bastiaens, P. and Lipowsky, R. and Hyman, A. and Dabrock, P. and Baret, J.-C. and Vidakovic-Koch, T. and Bieling, P. and Dimova, R. and Mutschler, H. and Robinson, T. and Tang, D. and Wegner, S. and Sundmacher, K.}, title = {MaxSynBio - Avenues towards creating cells from the bottom up}, journal = {Angewandte Chemie}, month = {May}, year = {2018}, doi = {10.1002/anie.201802288},, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.201802288} } |
Turco, L., "Mechanoelectrical Coupling and Reorganisation of Cardiomyocytes and Fibroblasts under Shear Stress", May 2018 |
Abstract: In this work, I studied the influence of changes such as the abundance of myofibroblasts in fibrotic conditions and the increased shear stress on cellular mechanical properties, morphology, contractility and connectivity. By using co-cultures of cardiomyocytes and myofibroblasts as an in vitro model system for fibrosis I observed that their communication occurs via both electrical and mechanical junctions. Co-cultures with low ratios of cardiomyocytes overexpressed electrical and mechanical junction proteins, Connexin43 (Cx43) and N-Cadherin (N-Cad), respectively, inducing alterations in the electrophysiology of cardiomyocytes: decrease of beating frequency and outbreak of spiral waves. The enhanced expression of N-Cad shows that myofibroblasts may influence the function of cardiomyocytes by applying contractile forces via mechanical junctions. N-Cad in turn is responsible for the transmission of contractile forces between myofibroblasts throughout the fibrotic scar. AFM-based microrheological measurements revealed that viscoelastic properties change under fibrotic conditions. Co-culture was observed to be stiffer than both cardiomyocytes and fibroblasts monocultures and was characterised by a solid-like behaviour at almost all frequencies. Another physiological change that occurs in LVR is the increase of mechanical load on cardiomyocytes, in particular shear stress, which is often neglected in vitro and in silico models. By combining impedance spectroscopy and optical microscopy I have shown that high values of shear stress stimulation lead to an immediate decrease of cell-substrate distances at the flow onset, cell spreading up to 48 hours, and a gradual reorientation of the actin fibers along the direction of the flow that took upto 108 hours. Additionally, beating frequency and cell-cell connectivity of cardiomyocytes increased under shear stress. Furthermore, contraction of cardiomyocytes synchronised in the presence of shear stress. The application of shear stress leads to the increase of beating frequency of co-cultures and induces contractility of fibrotic co-cultures with 9:1 ratio of myofibroblasts and cardiomyocytes, which do not present any activity without flow stimulation. Flow stimulation increased the beating frequency of the cardiomyocytes and myofibroblasts co-cultures similar to the monocultures, and for the first time, I observed contractility in co-cultures with 9:1 ratio of myofibroblasts after shear stimulation, whereas the non-sheared co-cultures did not show any activity. In conclusion this work proves that stimulating cardiomyocytes with high shear stress is a reliable in vitro pathological model to reproduce conditions similar to the in vivo situation. Furthermore, experimental and modelling studies used to understand pathophysiology during LVR should take into account the presence of high shear stress and its influence on mechanoelectrical coupling and cellular morphology. |
BibTeX:
@phdthesis{Turco2018, author = {Turco, L.}, title = {Mechanoelectrical Coupling and Reorganisation of Cardiomyocytes and Fibroblasts under Shear Stress}, month = {May}, year = {2018},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-002E-E401-1} } |
Verschoof, R. A., te Nijenhuis, A. K., Huisman, S. G. and Sun, C., "Periodically driven Taylor–Couette turbulence", J. Fluid Mech., May 2018, Vol. 846, 834 pp. |
Abstract: We study periodically driven Taylor–Couette turbulence, i.e. the flow confined between two concentric, independently rotating cylinders. Here, the inner cylinder is driven sinusoidally while the outer cylinder is kept at rest (time-averaged Reynolds number is Re=5x10-5). Using particle image velocimetry, we measure the velocity over a wide range of modulation periods, corresponding to a change in Womersley number in the range 15 |
BibTeX:
@article{Verschoof.Nijenhuis.ea2018, author = {Verschoof, R. A. and te Nijenhuis, A. K. and Huisman, S. G. and Sun, C.}, title = {Periodically driven Taylor–Couette turbulence}, journal = {J. Fluid Mech.}, month = {May}, year = {2018}, volume = {846}, pages = {834}, doi = {10.1017/jfm.2018.276},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/periodically-driven-taylorcouette-turbulence/3D44457FBDF7BAF44DBE2B09E30A2629} } |
Wedi, M., "Effects of rotation on the Nusselt number in large-scale Rayleigh-Bénard convection", May 2018 |
BibTeX:
@mastersthesis{Wedi2018, author = {Wedi, M.}, title = {Effects of rotation on the Nusselt number in large-scale Rayleigh-Bénard convection}, month = {May}, year = {2018},, url = {http://www.lfpn.ds.mpg.de/turbulence/documents/Wedi-masterarbeit.pdf} } |
Escobar, J. M. E., Dietrich, E., Arscott, S., Zandvliet, H. J. W., Zhang, X. and Lohse, D., "Zipping-Depinning: Dissolution of Droplets on Micropatterned Concentric Rings", Langmuir, April 2018, Vol. 34(19), 5396 pp. |
Abstract: The control of the surface wettability is of great interest for technological applications as well as for the fundamental understanding of surface phenomena. In this article, we describe the dissolution behavior of droplets wetting a micropatterned surface consisting of smooth concentric circular grooves. In the experiments, a droplet of alcohol (1-pentanol) is placed onto water-immersed micropatterns. When the drops dissolve, the dynamics of the receding contact line occurs in two different modes. In addition to the stick-jump mode with jumps from one ring to the next inner one, our study reveals a second dissolution mode, which we refer to as zipping-depinning. The velocity of the zipping-depinning fronts is governed by the dissolution rate. At the early stage of the droplet dissolution, our experimental results are in good agreement with the theoretical predictions by Debuisson et al. [ Appl. Phys. Lett. 2011, 99, 184101]. With an extended model, we can accurately describe the dissolution dynamics in both stick-jump and zipping-depinning modes. |
BibTeX:
@article{Escobar.Dietrich.ea2018, author = {Escobar, J. M. E. and Dietrich, E. and Arscott, S. and Zandvliet, H. J. W. and Zhang, X. and Lohse, D.}, title = {Zipping-Depinning: Dissolution of Droplets on Micropatterned Concentric Rings}, journal = {Langmuir}, month = {April}, year = {2018}, volume = {34}, number = {19}, pages = {5396}, doi = {10.1021/acs.langmuir.8b00256},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.langmuir.8b00256} } |
Kooij, G. L., Botchev, M. A., Frederix, E. M. A., Geurts, B. J., Horn, S., Lohse, D., van der Poel, E. P., Shishkina, O., Stevens, R. J. A. M. and Verzicco, R., "Comparison of computational codes for direct numerical simulations of turbulent Rayleigh-Bénard convection", Computer & Fluids, April 2018, Vol. 166, 1 pp. |
Abstract: Computational codes for direct numerical simulations of Rayleigh-Bénard (RB) convection are compared in terms of computational cost and quality of the solution. As a benchmark case, RB convection at and in a periodic domain, in cubic and cylindrical containers is considered. A dedicated second-order finite-difference code (AFID/RBflow) and a specialized fourth-order finite-volume code (Goldfish) are compared with a general purpose finite-volume approach (OpenFOAM) and a general purpose spectral-element code (Nek5000). Reassuringly, all codes provide predictions of the average heat transfer that converge to the same values. The computational costs, however, are found to differ considerably. The specialized codes AFID/RBflow and Goldfish are found to excel in efficiency, outperforming the general purpose flow solvers Nek5000 and OpenFOAM by an order of magnitude with an error on the Nusselt number Nu below 5%. However, we find that Nu alone is not sufficient to assess the quality of the numerical results: in fact, instantaneous snapshots of the temperature field from a near wall region obtained for deliberately under-resolved simulations using Nek5000 clearly indicate inadequate flow resolution even when Nu is converged. Overall, dedicated special purpose codes for RB convection are found to be more efficient than general purpose codes. |
BibTeX:
@article{Kooij.Botchev.ea2018, author = {Kooij, G. L. and Botchev, M. A. and Frederix, E. M. A. and Geurts, B. J. and Horn, S. and Lohse, D. and van der Poel, E. P. and Shishkina, O. and Stevens, R. J. A. M. and Verzicco, R.}, title = {Comparison of computational codes for direct numerical simulations of turbulent Rayleigh-Bénard convection}, journal = {Computer & Fluids}, month = {April}, year = {2018}, volume = {166}, pages = {1}, doi = {10.1016/j.compfluid.2018.01.010},, url = {https://www.sciencedirect.com/science/article/pii/S0045793018300100} } |
Stevens, R. J. A. M., Blass, A., Zhu, X., Verzicco, R. and Lohse, D., "Turbulent thermal superstructures in Rayleigh-Bénard convection", Phys. Rev. Fluids, April 2018, Vol. 3(4), 041501(R) pp. |
Abstract: We report the observation of superstructures, i.e., very large-scale and long living coherent structures in highly turbulent Rayleigh-Bénard convection up to Rayleigh Ra=109. We perform direct numerical simulations in horizontally periodic domains with aspect ratios up to Ã=128. In the considered Ra number regime the thermal superstructures have a horizontal extend of six to seven times the height of the domain and their size is independent of Ra. Many laboratory experiments and numerical simulations have focused on small aspect ratio cells in order to achieve the highest possible Ra. However, here we show that for very high Ra integral quantities such as the Nusselt number and volume averaged Reynolds number only converge to the large aspect ratio limit around Ã 4, while horizontally averaged statistics such as standard deviation and kurtosis converge around Ã 8, the integral scale converges around Ã 32, and the peak position of the temperature variance and turbulent kinetic energy spectra only converge around Ã 64. |
BibTeX:
@article{Stevens.Blass.ea2018, author = {Stevens, R. J. A. M. and Blass, A. and Zhu, X. and Verzicco, R. and Lohse, D.}, title = {Turbulent thermal superstructures in Rayleigh-Bénard convection}, journal = {Phys. Rev. Fluids}, month = {April}, year = {2018}, volume = {3}, number = {4}, pages = {041501(R)}, doi = {10.1103/PhysRevFluids.3.041501},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.3.041501} } |
Zhu, X., Mathai, V., Stevens, R. J. A. M., Verzicco, R. and Lohse, D., "Transition to the Ultimate Regime in Two-Dimensional Rayleigh-Bénard Convection", Phys. Rev. Lett., April 2018, Vol. 120(14), 144502 pp. |
Abstract: The possible transition to the so-called ultimate regime, wherein both the bulk and the boundary layers are turbulent, has been an outstanding issue in thermal convection, since the seminal work by Kraichnan [Phys. Fluids 5, 1374 (1962)]. Yet, when this transition takes place and how the local flow induces it is not fully understood. Here, by performing two-dimensional simulations of Rayleigh-Bénard turbulence covering six decades in Rayleigh number Ra up to 1014 for Prandtl number Pr=1, for the first time in numerical simulations we find the transition to the ultimate regime, namely, at Ra =1013. We reveal how the emission of thermal plumes enhances the global heat transport, leading to a steeper increase of the Nusselt number than the classical Malkus scaling Nu Ra1/3 [Proc. R. Soc. A 225, 196 (1954)]. Beyond the transition, the mean velocity profiles are logarithmic throughout, indicating turbulent boundary layers. In contrast, the temperature profiles are only locally logarithmic, namely, within the regions where plumes are emitted, and where the local Nusselt number has an effective scaling Nu Ra0.38, corresponding to the effective scaling in the ultimate regime. |
BibTeX:
@article{Zhu.Mathai.ea2018, author = {Zhu, X. and Mathai, V. and Stevens, R. J. A. M. and Verzicco, R. and Lohse, D.}, title = {Transition to the Ultimate Regime in Two-Dimensional Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {April}, year = {2018}, volume = {120}, number = {14}, pages = {144502}, doi = {10.1103/PhysRevLett.120.144502},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.144502} } |
Eckstein, T., Vidal-Henriquez, E., Bae, A., Zykov, V., Bodenschatz, E. and Gholami, A., "Influence of fast advective flows on pattern formation of Dictyostelium discoideum", PLOS ONE, March 2018, Vol. 13(3), e0194859 pp. |
Abstract: We report experimental and numerical results on pattern formation of self-organizing Dictyostelium discoideum cells in a microfluidic setup under a constant buffer flow. The external flow advects the signaling molecule cyclic adenosine monophosphate (cAMP) downstream, while the chemotactic cells attached to the solid substrate are not transported with the flow. At high flow velocities, elongated cAMP waves are formed that cover the whole length of the channel and propagate both parallel and perpendicular to the flow direction. While the wave period and transverse propagation velocity are constant, parallel wave velocity and the wave width increase linearly with the imposed flow. We also observe that the acquired wave shape is highly dependent on the wave generation site and the strength of the imposed flow. We compared the wave shape and velocity with numerical simulations performed using a reaction-diffusion model and found excellent agreement. These results are expected to play an important role in understanding the process of pattern formation and aggregation of D. discoideum that may experience fluid flows in its natural habitat. |
BibTeX:
@article{Eckstein.Vidal-Henriquez.ea2018, author = {Eckstein, T. and Vidal-Henriquez, E. and Bae, A. and Zykov, V. and Bodenschatz, E. and Gholami, A.}, title = {Influence of fast advective flows on pattern formation of Dictyostelium discoideum}, journal = {PLOS ONE}, month = {March}, year = {2018}, volume = {13}, number = {3}, pages = {e0194859}, doi = {10.1371/journal.pone.0194859},, url = {http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0194859} } |
Mandemaker, L., Filez, M., Delen, G., Tan, H., Zhang, X., Lohse, D. and Weckhuysen, B., "Time-Resolved In Situ Liquid-Phase Atomic Force Microscopy and Infrared Nanospectroscopy during the Formation of Metal-Organic Framework Thin Films", J. Phys. Chem., March 2018, Vol. 9, 1838 pp. |
Abstract: Metal–organic framework (MOF) thin films show unmatched promise as smart membranes and photocatalytic coatings. However, their nucleation and growth resulting from intricate molecular assembly processes are not well understood yet are crucial to control the thin film properties. Here, we directly observe the nucleation and growth behavior of HKUST-1 thin films by real-time in situ AFM at different temperatures in a Cu-BTC solution. In combination with ex situ infrared (nano)spectroscopy, synthesis at 25 °C reveals initial nucleation of rapidly growing HKUST-1 islands surrounded by a continuously nucleating but slowly growing HKUST-1 carpet. Monitoring at 13 and 50 °C shows the strong impact of temperature on thin film formation, resulting in (partial) nucleation and growth inhibition. The nucleation and growth mechanisms as well as their kinetics provide insights to aid in future rational design of MOF thin films. |
BibTeX:
@article{Mandemaker.Filez.ea2018, author = {Mandemaker, L. and Filez, M. and Delen, G. and Tan, H. and Zhang, X. and Lohse, D. and Weckhuysen, B.}, title = {Time-Resolved In Situ Liquid-Phase Atomic Force Microscopy and Infrared Nanospectroscopy during the Formation of Metal-Organic Framework Thin Films}, journal = {J. Phys. Chem.}, month = {March}, year = {2018}, volume = {9}, pages = {1838}, doi = {10.1021/acs.jpclett.8b00203},, url = {https://pubs.acs.org/doi/abs/10.1021/acs.jpclett.8b00203} } |
Shen Ng, C., Ooi, A., Lohse, D. and Chung, D., "Bulk scaling in wall-bounded and homogeneous vertical natural convection", J. Fluid Mech., March 2018, Vol. 841, 825 pp. |
Abstract: Previous numerical studies on homogeneous Rayleigh-Bénard convection, which is Rayleigh-Bénard convection (RBC) without walls, and therefore without boundary layers, have revealed a scaling regime that is consistent with theoretical predictions of bulk-dominated thermal convection. In this so-called asymptotic regime, previous studies have predicted that the Nusselt number ( ) and the Reynolds number ( ) vary with the Rayleigh number ( ) according to and at small Prandtl numbers ( ). In this study, we consider a flow that is similar to RBC but with the direction of temperature gradient perpendicular to gravity instead of parallel to it; we refer to this configuration as vertical natural convection (VC). Since the direction of the temperature gradient is different in VC, there is no exact relation for the average kinetic dissipation rate, which makes it necessary to explore alternative definitions for , and and to find physical arguments for closure, rather than making use of the exact relation between and the dissipation rates as in RBC. Once we remove the walls from VC to obtain the homogeneous set-up, we find that the aforementioned -power-law scaling is present, similar to the case of homogeneous RBC. When focusing on the bulk, we find that the Nusselt and Reynolds numbers in the bulk of VC too exhibit the -power-law scaling. These results suggest that the -power-law scaling may even be found at lower Rayleigh numbers if the appropriate quantities in the turbulent bulk flow are employed for the definitions of , and . From a stability perspective, at low- to moderate- , we find that the time evolution of the Nusselt number for homogenous vertical natural convection is unsteady, which is consistent with the nature of the elevator modes reported in previous studies on homogeneous RBC. |
BibTeX:
@article{ShenNg.Ooi.ea2018, author = {Shen Ng, C. and Ooi, A. and Lohse, D. and Chung, D.}, title = {Bulk scaling in wall-bounded and homogeneous vertical natural convection}, journal = {J. Fluid Mech.}, month = {March}, year = {2018}, volume = {841}, pages = {825}, doi = {10.1017/jfm.2018.102},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/bulk-scaling-in-wallbounded-and-homogeneous-vertical-natural-convection/FCA7F9872616912439163BE898E15E33} } |
Zykov, V. S. and Bodenschatz, E., "Periodic sequence of stabilized wave segments in an excitable medium", Phys. Rev. E, March 2018, Vol. 97(3), 030201(R) pp. |
Abstract: Numerical computations show that a stabilization of a periodic sequence of wave segments propagating through an excitable medium is possible only in a restricted domain within the parameter space. By application of a free-boundary approach, we demonstrate that at the boundary of this domain the parameter H introduced in our Rapid Communication is constant. We show also that the discovered parameter predetermines the propagation velocity and the shape of the wave segments. The predictions of the free-boundary approach are in good quantitative agreement with results from numerical reaction-diffusion simulations performed on the modified FitzHugh-Nagumo model. |
BibTeX:
@article{Zykov.Bodenschatz2018, author = {Zykov, V. S. and Bodenschatz, E.}, title = {Periodic sequence of stabilized wave segments in an excitable medium}, journal = {Phys. Rev. E}, month = {March}, year = {2018}, volume = {97}, number = {3}, pages = {030201(R)}, doi = {10.1103/PhysRevE.97.030201},, url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.97.030201} } |
Zykov, V. S. and Bodenschatz, E., "Wave Propagation in Inhomogeneous Excitable Media", Annual Reviews, March 2018, Vol. 9, 435 pp. |
Abstract: Excitable media are ubiquitous in nature and can be found in physical, chemical, and biological systems that are far from thermodynamic equilibrium. The spatiotemporal self-organization of these systems has long attracted the deep interest of condensed matter physicists and applied mathematicians alike. Spatial inhomogeneity of excitable media leads to nontrivial spatiotemporal dynamics. Here, we report on well-established as well as recent developments in the experimental and theoretical studies of inhomogeneous excitable media. |
BibTeX:
@article{Zykov.Bodenschatz2018a, author = {Zykov, V. S. and Bodenschatz, E.}, title = {Wave Propagation in Inhomogeneous Excitable Media}, journal = {Annual Reviews}, month = {March}, year = {2018}, volume = {9}, pages = {435}, doi = {10.1146/annurev-conmatphys-033117-054300},, url = {https://www.annualreviews.org/doi/abs/10.1146/annurev-conmatphys-033117-054300} } |
Bao, L., Spandan, V., Yang, Y., Dyett, B., Verzicco, R., Lohse, D. and Zhang, X., "Flow-induced dissolution of femtoliter surface droplet arrays", Lab Chip, February 2018, Vol. 18, 1066 pp. |
Abstract: The dissolution of liquid nanodroplets is a crucial step in many applied processes, such as separation and dispersion in the food industry, crystal formation of pharmaceutical products, concentrating and analysis in medical diagnosis, and drug delivery in aerosols. In this work, using both experiments and numerical simulations, we quantitatively study the dissolution dynamics of femtoliter surface droplets in a highly ordered array under a uniform flow. Our results show that the dissolution of femtoliter droplets strongly depends on their spatial positions relative to the flow direction, drop-to-drop spacing in the array, and the imposed flow rate. In some particular cases, the droplet at the edge of the array can dissolve about 30% faster than the ones located near the centre. The dissolution rate of the droplet increases by 60% as the inter-droplet spacing is increased from 2.5 ìm to 20 ìm. Moreover, the droplets close to the front of the flow commence to shrink earlier than those droplets in the center of the array. The average dissolution rate is faster for the faster flow. As a result, the dissolution time (Ti) decreases with the Reynolds number (Re) of the flow as Ti Re-3/4. The experimental results are in good agreement with the numerical simulations where the advection-diffusion equation for the concentration field is solved and the concentration gradient on the surface of the drop is computed. The findings suggest potential approaches to manipulate nanodroplet sizes in droplet arrays simply by dissolution controlled by an external flow. The obtained droplets with varying curvatures may serve as templates for generating multifocal microlenses in one array. |
BibTeX:
@article{Bao.Spandan.ea2018, author = {Bao, L. and Spandan, V. and Yang, Y. and Dyett, B. and Verzicco, R. and Lohse, D. and Zhang, X.}, title = {Flow-induced dissolution of femtoliter surface droplet arrays}, journal = {Lab Chip}, month = {February}, year = {2018}, volume = {18}, pages = {1066}, doi = {10.1039/C7LC01321C},, url = {http://pubs.rsc.org/en/content/articlehtml/2018/lc/c7lc01321c} } |
Damaschke, N., Kühn, V. and Nobach, H., "A fair review of non-parametric bias-free autocorrelation and spectral methods for randomly sampled data in laser Doppler velocimetry", Digital Signal Processing, February 2018, Vol. 76, 22 pp. |
Abstract: This paper presents a comparison of currently available methods for non-parametric and bias-free estimation of the autocorrelation function and power spectral density from randomly sampled data. The primary motivation is the processing of velocity data obtained using laser Doppler techniques in turbulent flows. However, the methods are applicable to various other cases of random sampling, including those with small deviations from the ideal Poisson process. Whilst these methods have been compared in the literature before, a fair comparison of their relative performance requires that they be tested under identical conditions. This includes identical use of special processing options and identical processing parameters. This has not been achieved in the literature to date. An example application on publicly available laser Doppler data shows agreement between the results obtained with the different methods. Under this fair comparison, the methods converge in terms of their systematic and random errors, indicating that they are comparably efficient at using the available information content of the randomly sampled signal. The results also identify that the available methods are interchangeable and indicate a possible replacement for the current best-practice procedure in the laser Doppler community. |
BibTeX:
@article{Damaschke.Kuehn.ea2018, author = {Damaschke, N. and Kühn, V. and Nobach, H.}, title = {A fair review of non-parametric bias-free autocorrelation and spectral methods for randomly sampled data in laser Doppler velocimetry}, journal = {Digital Signal Processing}, month = {February}, year = {2018}, volume = {76}, pages = {22}, doi = {10.1016/j.dsp.2018.01.018},, url = {https://www.sciencedirect.com/science/article/pii/S1051200418300307} } |
Gao, X., Krekhov, A., Zykov, V. and Bodenschatz, E., "Initiation of Rotors by Fast Propagation Regions in Excitable Media: A Theoretical Study", Front. Phys., February 2018, Vol. 6, 8 pp. |
Abstract: We study the effect of geometry of a fast propagation region (FPR) in an excitable medium on the rotor initiation using a generic two-dimensional reaction-diffusion model. We find that, while the flat boundary of a rectangularly shaped FPR may block the propagation of the excitation wave, a large local curvature at the rounded corners of the FPR would prevent the blockage and thus initiate a rotor. Our simulations demonstrate that the prerequisites for the rotor initiation are the degree of the heterogeneity, its shape and size. These results may explain the incidence of arrhythmias by local heterogeneities induced, for example, by a cardiac tissue remodeling. |
BibTeX:
@article{Gao.Krekhov.ea2018, author = {Gao, X. and Krekhov, A. and Zykov, V. and Bodenschatz, E.}, title = {Initiation of Rotors by Fast Propagation Regions in Excitable Media: A Theoretical Study}, journal = {Front. Phys.}, month = {February}, year = {2018}, volume = {6}, pages = {8}, doi = {10.3389/fphy.2018.00008},, url = {https://www.frontiersin.org/articles/10.3389/fphy.2018.00008/full} } |
Maheshwari, S., van der Hoef, M., Rodriguez, J. and Lohse, D., "Leakiness of Pinned Neighboring Surface Nanobubbles Induced by Strong Gas-Surface Interaction", ACS Nano, February 2018, Vol. 12(3), 2603 pp. |
Abstract: The stability of two neighboring surface nanobubbles on a chemically heterogeneous surface is studied by molecular dynamics (MD) simulations of binary mixtures consisting of Lennard-Jones (LJ) particles. A diffusion equation-based stability analysis suggests that two nanobubbles sitting next to each other remain stable, provided the contact line is pinned, and that their radii of curvature are equal. However, many experimental observations seem to suggest some long-term kind of ripening or shrinking of the surface nanobubbles. In our MD simulations we find that the growth/dissolution of the nanobubbles can occur due to the transfer of gas particles from one nanobubble to another along the solid substrate. That is, if the interaction between the gas and the solid is strong enough, the solid–liquid interface can allow for the existence of a “tunnel” which connects the liquid–gas interfaces of the two nanobubbles to destabilize the system. The crucial role of the gas–solid interaction energy is a nanoscopic element that hitherto has not been considered in any macroscopic theory of surface nanobubbles and may help to explain experimental observations of the long-term ripening. |
BibTeX:
@article{Maheshwari.Hoef.ea2018, author = {Maheshwari, S. and van der Hoef, M. and Rodriguez, J. and Lohse, D.}, title = {Leakiness of Pinned Neighboring Surface Nanobubbles Induced by Strong Gas-Surface Interaction}, journal = {ACS Nano}, month = {February}, year = {2018}, volume = {12}, number = {3}, pages = {2603}, doi = {10.1021/acsnano.7b08614},, url = {https://pubs.acs.org/doi/abs/10.1021/acsnano.7b08614} } |
Tian, F.-B., Wang, Y., Liu, H. and Zhang, Y., "The lattice Boltzmann method and its applications in complex flows and fluid-structure interactions", J. Mechanical Engineering Science, February 2018, Vol. 232(3), 403 pp. |
Abstract: The lattice Boltzmann (LB) method has been developed into an alternative and robust numerical tool for computational fluid dynamics, heat transfer and beyond since its introduction in 1980s. Instead of discretising the partial differential equation, the LB method is an approach based on particle kinetics. It has achieved considerable success in the past years and has been proven to be an efficient computational method for complex flows and fluid–structure interactions, important research topics for mechanical engineering science, due to the local nature of its operations, simplicity of formulation and implementation and high level of scalability on parallel processing systems. |
BibTeX:
@article{Tian.Wang.ea2018, author = {Tian, F.-B. and Wang, Y. and Liu, H. and Zhang, Y.}, title = {The lattice Boltzmann method and its applications in complex flows and fluid-structure interactions}, journal = {J. Mechanical Engineering Science}, month = {February}, year = {2018}, volume = {232}, number = {3}, pages = {403}, doi = {10.1177/0954406218754913},, url = {http://journals.sagepub.com/doi/full/10.1177/0954406218754913} } |
Zhu, X., Verschoof, R. A., Bakhuis, D., Huisman, S. G., Verzicco, R., Sun, C. and Lohse, D., "Wall roughness induces asymptotic ultimate turbulence", Nature Physics, February 2018, Vol. 14, 417 pp. |
Abstract: Turbulence governs the transport of heat, mass and momentum on multiple scales. In real-world applications, wall-bounded turbulence typically involves surfaces that are rough; however, characterizing and understanding the effects of wall roughness on turbulence remains a challenge. Here, by combining extensive experiments and numerical simulations, we examine the paradigmatic Taylor-Couette system, which describes the closed flow between two independently rotating coaxial cylinders. We show how wall roughness greatly enhances the overall transport properties and the corresponding scaling exponents associated with wall-bounded turbulence. We reveal that if only one of the walls is rough, the bulk velocity is slaved to the rough side, due to the much stronger coupling to that wall by the detaching flow structures. If both walls are rough, the viscosity dependence is eliminated, giving rise to asymptotic ultimate turbulence-the upper limit of transport-the existence of which was predicted more than 50 years ago. In this limit, the scaling laws can be extrapolated to arbitrarily large Reynolds numbers. |
BibTeX:
@article{Zhu.Verschoof.ea2018, author = {Zhu, X. and Verschoof, R. A. and Bakhuis, D. and Huisman, S. G. and Verzicco, R. and Sun, C. and Lohse, D.}, title = {Wall roughness induces asymptotic ultimate turbulence}, journal = {Nature Physics}, month = {February}, year = {2018}, volume = {14}, pages = {417}, doi = {10.1038/s41567-017-0026-3},, url = {https://www.nature.com/articles/s41567-017-0026-3} } |
Chong, K. L., Wagner, S., Kaczorowski, M., Shishkina, O. and Xia, K.-Q., "Effect of Prandtl number on heat transport enhancement in Rayleigh-Bénard convection under geometrical confinement", Phys. Rev. Fluids, January 2018, Vol. 3(1), 013501 pp. |
Abstract: We study, using direct numerical simulations, the effect of geometrical confinement on heat transport and flow structure in Rayleigh-Bénard convection in fluids with different Prandtl numbers. Our simulations span over two decades of Prandtl number Pr, 0.1?Pr?40, with the Rayleigh number Ra fixed at 108. The width-to-height aspect ratio spans between 0.025 and 0.25, while the length-to-height aspect ratio is fixed at one. We first find that for Pr?0.5, geometrical confinement can lead to a significant enhancement in heat transport as characterized by the Nusselt number Nu. For those cases, Nu is maximal at a certain opt and the maximal relative enhancement generally increases with Pr over the explored parameter range. As opposed to the situation of Pr?0.5, confinement-induced enhancement in Nu is not realized for smaller values of Pr, such as 0.1 and 0.2. The Pr dependence of the heat transport enhancement can be understood in its relation to the coverage area of the thermal plumes over the thermal boundary layer (BL) where larger coverage is observed for larger Pr due to a smaller thermal diffusivity. We further show that opt is closely related to the crossing of thermal and momentum BLs and find that Nu declines sharply when the thickness ratio of the thermal and momentum BLs exceeds a certain value of about one. In addition, through examining the temporally averaged flow fields and two-dimensional mode decomposition, it is found that for smaller Pr the large-scale circulation is robust against the geometrical confinement of the convection cell. We further found that opt exhibits a power-law relation with Pr as opt=0.11Pr?0.060±0.004. Together with the result opt=29.37Ra-0.31 found by Chong et al. [Phys. Rev. Lett. 115, 264503 (2015)], our findings provide a more complete picture of the geometrical confinement. |
BibTeX:
@article{Chong.Wagner.ea2018, author = {Chong, K. L. and Wagner, S. and Kaczorowski, M. and Shishkina, O. and Xia, K.-Q.}, title = {Effect of Prandtl number on heat transport enhancement in Rayleigh-Bénard convection under geometrical confinement}, journal = {Phys. Rev. Fluids}, month = {January}, year = {2018}, volume = {3}, number = {1}, pages = {013501}, doi = {10.1103/PhysRevFluids.3.013501},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.3.013501} } |
Jiang, H., Zhu, X., Mathai, V., Verzicco, R., Lohse, D. and Sun, C., "Controlling Heat Transport and Flow Structures in Thermal Turbulence Using Ratchet Surfaces", Phys. Rev. Lett., January 2018, Vol. 120(4), 044501 pp. |
Abstract: In this combined experimental and numerical study on thermally driven turbulence in a rectangular cell, the global heat transport and the coherent flow structures are controlled with an asymmetric ratchetlike roughness on the top and bottom plates. We show that, by means of symmetry breaking due to the presence of the ratchet structures on the conducting plates, the orientation of the large scale circulation roll (LSCR) can be locked to a preferred direction even when the cell is perfectly leveled out. By introducing a small tilt to the system, we show that the LSCR orientation can be tuned and controlled. The two different orientations of LSCR give two quite different heat transport efficiencies, indicating that heat transport is sensitive to the LSCR direction over the asymmetric roughness structure. Through a quantitative analysis of the dynamics of thermal plume emissions and the orientation of the LSCR over the asymmetric structure, we provide a physical explanation for these findings. The current work has important implications for passive and active flow control in engineering, biofluid dynamics, and geophysical flows. |
BibTeX:
@article{Jiang.Zhu.ea2018, author = {Jiang, H. and Zhu, X. and Mathai, V. and Verzicco, R. and Lohse, D. and Sun, C.}, title = {Controlling Heat Transport and Flow Structures in Thermal Turbulence Using Ratchet Surfaces}, journal = {Phys. Rev. Lett.}, month = {January}, year = {2018}, volume = {120}, number = {4}, pages = {044501}, doi = {10.1103/PhysRevLett.120.044501},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.120.044501} } |
Miroshnikova, Y. A., Le, H. Q., Schneider, D., Thalheim, T., Rübsam, M., Bremicker, N., Polleux, J., Kamprad, N., Tarantola, M., Wang, I., Balland, M., Niessen, C. M., Galle, J. and Wickström, A., "Adhesion forces and cortical tension couple cell proliferation and differentiation to drive epidermal stratification", Nature Cell Biology, January 2018, Vol. 20, 69 pp. |
Abstract: To establish and maintain organ structure and function, tissues need to balance stem cell proliferation and differentiation rates and coordinate cell fate with position. By quantifying and modelling tissue stress and deformation in the mammalian epidermis, we find that this balance is coordinated through local mechanical forces generated by cell division and delamination. Proliferation within the basal stem/progenitor layer, which displays features of a jammed, solid-like state, leads to crowding, thereby locally distorting cell shape and stress distribution. The resulting decrease in cortical tension and increased cell–cell adhesion trigger differentiation and subsequent delamination, reinstating basal cell layer density. After delamination, cells establish a high-tension state as they increase myosin II activity and convert to E-cadherin-dominated adhesion, thereby reinforcing the boundary between basal and suprabasal layers. Our results uncover how biomechanical signalling integrates single-cell behaviours to couple proliferation, cell fate and positioning to generate a multilayered tissue. |
BibTeX:
@article{Miroshnikova.Le.ea2017, author = {Miroshnikova, Y. A. and Le, H. Q. and Schneider, D. and Thalheim, T. and Rübsam, M. and Bremicker, N. and Polleux, J. and Kamprad, N. and Tarantola, M. and Wang, I. and Balland, M. and Niessen, C. M. and Galle, J. and Wickström, A.}, title = {Adhesion forces and cortical tension couple cell proliferation and differentiation to drive epidermal stratification}, journal = {Nature Cell Biology}, month = {January}, year = {2018}, volume = {20}, pages = {69}, doi = {10.1038/s41556-017-0005-z},, url = {https://www.nature.com/articles/s41556-017-0005-z} } |
Zhu, X., Verzicco, R., Zhang, X. and Lohse, D., "Diffusive interaction of multiple surface nanobubbles: shrinkage, growth, and coarsening", Soft Matter, January 2018, Vol. 14(11), 1967 pp. |
Abstract: Surface nanobubbles are nanoscopic spherical-cap shaped gaseous domains on immersed substrates which are stable, even for days. After the stability of a single surface nanobubble has been theoretically explained, i.e. contact line pinning and gas oversaturation are required to stabilize it against diffusive dissolution [Lohse and Zhang, Phys. Rev. E, 2015, 91, 031003(R)], here we focus on the collective diffusive interaction of multiple nanobubbles. For that purpose we develop a finite difference scheme for the diffusion equation with the appropriate boundary conditions and with the immersed boundary method used to represent the growing or shrinking bubbles. After validation of the scheme against the exact results of Epstein and Plesset for a bulk bubble [J. Chem. Phys., 1950, 18, 1505] and of Lohse and Zhang for a surface bubble, the framework of these simulations is used to describe the coarsening process of competitively growing nanobubbles. The coarsening process for such diffusively interacting nanobubbles slows down with advancing time and increasing bubble distance. The present results for surface nanobubbles are also applicable for immersed surface nanodroplets, for which better controlled experimental results of the coarsening process exist. |
BibTeX:
@article{Zhu.Verzicco.ea2018, author = {Zhu, X. and Verzicco, R. and Zhang, X. and Lohse, D.}, title = {Diffusive interaction of multiple surface nanobubbles: shrinkage, growth, and coarsening}, journal = {Soft Matter}, month = {January}, year = {2018}, volume = {14}, number = {11}, pages = {1967}, doi = {10.1039/C7SM02523H},, url = {http://pubs.rsc.org/en/content/articlehtml/2018/sm/c7sm02523h} } |
Westendorf, C., Gholami, A., Faubel, R., Guido, I., Wang, Y., Bae, A., Eichele, G. and Bodenschatz, E., "Koordinierter Flüssigkeitstransport durch zilienbesetzte Oberflächen", 2017 |
Abstract: Aktiver und gerichteter Flüssigkeitstransport sind lebenswichtig f?r eukaryotische Organismen. Die Aufgabe des Transportes übernehmen oft zilienbesetzte Gewebe wie z. B. die Innenseite des Ventrikelsystems in Säugetiergehirnen. Durch eine neuartige Methode wurde eine hohe Komplexität der durch Zilien generierten Ströme im dritten Hirnventrikel nachgewiesen. Ziliengewebe, die mit einer derartigen Präzision arbeiten sind auch für die synthetische Biologie und technische Anwendungen interessant. Daher versucht unsere AG am MPI für Dynamik und Selbstorganisation solche Zilienteppiche nachzubilden. |
BibTeX:
@research_report{Westendorf.Gholami.ea2017, author = {Westendorf, C. and Gholami, A. and Faubel, R. and Guido, I. and Wang, Y. and Bae, A. and Eichele, G. and Bodenschatz, E.}, title = {Koordinierter Flüssigkeitstransport durch zilienbesetzte Oberflächen}, year = {2017}, doi = {10.17617/1.51},, url = {https://www.mpg.de/11009414/mpids_jb_2017} } |
Buaria, D. and Yeung, P. K., "A highly scalable particle tracking algorithm using partitioned global address space (PGAS) programming for extreme-scale turbulence simulations", ScienceDirect, December 2017, Vol. 221, 246 pp. |
Abstract: A new parallel algorithm utilizing a partitioned global address space (PGAS) programming model to achieve high scalability is reported for particle tracking in direct numerical simulations of turbulent fluid flow. The work is motivated by the desire to obtain Lagrangian information necessary for the study of turbulent dispersion at the largest problem sizes feasible on current and next-generation multi-petaflop supercomputers. A large population of fluid particles is distributed among parallel processes dynamically, based on instantaneous particle positions such that all of the interpolation information needed for each particle is available either locally on its host process or neighboring processes holding adjacent sub-domains of the velocity field. With cubic splines as the preferred interpolation method, the new algorithm is designed to minimize the need for communication, by transferring between adjacent processes only those spline coefficients determined to be necessary for specific particles. This transfer is implemented very efficiently as a one-sided communication, using Co-Array Fortran (CAF) features which facilitate small data movements between different local partitions of a large global array. The cost of monitoring transfer of particle properties between adjacent processes for particles migrating across sub-domain boundaries is found to be small. Detailed benchmarks are obtained on the Cray petascale supercomputer Blue Waters at the University of Illinois, Urbana-Champaign. For operations on the particles in a simulation (0.55 trillion grid points) on 262,144 Cray XE6 cores, the new algorithm is found to be orders of magnitude faster relative to a prior algorithm in which each particle is tracked by the same parallel process at all times. This large speedup reduces the additional cost of tracking of order 300 million particles to just over 50% of the cost of computing the Eulerian velocity field at this scale. Improving support of PGAS models on major compilers suggests that this algorithm will be of wider applicability on most upcoming supercomputers. |
BibTeX:
@article{Buaria.Yeung2017, author = {Buaria, D. and Yeung, P. K.}, title = {A highly scalable particle tracking algorithm using partitioned global address space (PGAS) programming for extreme-scale turbulence simulations}, journal = {ScienceDirect}, month = {December}, year = {2017}, volume = {221}, pages = {246}, doi = {10.1016/j.cpc.2017.08.022},, url = {https://www.sciencedirect.com/science/article/pii/S0010465517302680} } |
Ezeta, R., Huisman, S. G., Sun, C. and Lohse, D., "Turbulence strength in ultimate Taylor-Couette turbulence", J. Fluid Mech., December 2017, Vol. 836, 397 pp. |
Abstract: We provide experimental measurements for the effective scaling of the Taylor–Reynolds number within the bulk , based on local flow quantities as a function of the driving strength (expressed as the Taylor number ), in the ultimate regime of Taylor-Couette flow. We define , where is the bulk-averaged standard deviation of the azimuthal velocity, is the bulk-averaged local dissipation rate and is the liquid kinematic viscosity. The data are obtained through flow velocity field measurements using particle image velocimetry. We estimate the value of the local dissipation rate using the scaling of the second-order velocity structure functions in the longitudinal and transverse directions within the inertial range – without invoking Taylor’s hypothesis. We find an effective scaling of , (corresponding to for the dimensionless local angular velocity transfer), which is nearly the same as for the global energy dissipation rate obtained from both torque measurements ( ) and direct numerical simulations ( ). The resulting Kolmogorov length scale is then found to scale as and the turbulence intensity as . With both the local dissipation rate and the local fluctuations available we finally find that the Taylor–Reynolds number effectively scales as in the present parameter regime of . |
BibTeX:
@article{Ezeta.Huisman.ea2017, author = {Ezeta, R. and Huisman, S. G. and Sun, C. and Lohse, D.}, title = {Turbulence strength in ultimate Taylor-Couette turbulence}, journal = {J. Fluid Mech.}, month = {December}, year = {2017}, volume = {836}, pages = {397}, doi = {10.1017/jfm.2017.795},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/turbulence-strength-in-ultimate-taylorcouette-turbulence/4BC09E959D0A6D1C18C6F0317F2A7D0F} } |
Zhang, W., Bai, X.-D., Ma, Z., Chen, G. and Wang, Y., "Compressible effect on the cavitating flow: A numeric study", ScienceDirect, December 2017, Vol. 29(6), 1089 pp. |
Abstract: To understand the effect of the compressibility on the cavitating flow, a compressible, multiphase, single component Reynolds averaged Navier-Stokes (RANS) solver is used to study the cavitating flow on a wedge in the present work. A barotropic equation of status is used. A non-linear model for compressibility in the mixture is adopted to capture the effect of the compressibility within the complex cavitation bubbly mixtures. An unsteady cavitation phenomenon is found in the numerical simulation. The numerical results of local compressibility and Mach number in the bubbly mixture are given. The mechanism responsible for the unsteady shedding of the bubbly mixture is discussed based on the numerical results. |
BibTeX:
@incollection{Zhang.Bai.ea2017, author = {Zhang, W. and Bai, X.-D. and Ma, Z. and Chen, G. and Wang, Y.}, title = {Compressible effect on the cavitating flow: A numeric study}, journal = {ScienceDirect}, month = {December}, year = {2017}, volume = {29}, number = {6}, pages = {1089}, doi = {10.1016/S1001-6058(16)60823-5},, url = {https://www.sciencedirect.com/science/article/abs/pii/S1001605816608235} } |
Liu, C.-C., "Phenomenological Nusselt-Rayleigh Scaling of Turbulent Thermal Convection", J. Phys. Soc. Jpn., November 2017, Vol. 86(12), 123401 pp. |
Abstract: Natural convection between the hot floor and the cool ceiling, so called Rayleigh-Bénard convection, is pervasive and of both fundamental and industrial interests. One key issue is how heat transfer varies with increasing thermal potential, or equivalently how the Nusselt number (Nu) scales with the Rayleigh number (Ra). The overview of experimental findings remains to show the need of extra explanation complemental to the current theories. Here we present a model based on the phenomenological theory of turbulence, where the power-law spectral exponent of the energy spectrum is the only input parameter required. The goal aims to elucidate the unexplained aspect in the Nu–Ra scaling. We find that Kolmogorov turbulence in the current model leads to Nu Ra0.3, in good agreement with the modern experimental results. We hope that this model could stimulate the discussion as to the effects of the spectral phenomena on the Nu–Ra scaling, and thus augment our understanding of buoyancy-driven thermal convection. |
BibTeX:
@article{Liu2017, author = {Liu, C.-C.}, title = {Phenomenological Nusselt-Rayleigh Scaling of Turbulent Thermal Convection}, journal = {J. Phys. Soc. Jpn.}, month = {November}, year = {2017}, volume = {86}, number = {12}, pages = {123401}, doi = {10.7566/JPSJ.86.123401},, url = {http://journals.jps.jp/doi/abs/10.7566/JPSJ.86.123401} } |
Prabhakara, K. H., Gholami, A., Zykov, V. S. and Bodenschatz, E., "Effects of developmental variability on the dynamics and self-organization of cell populations", New J. Phys., November 2017, Vol. 19, 113024 pp. |
Abstract: We report experimental and theoretical results for spatiotemporal pattern formation in cell populations, where the parameters vary in space and time due to mechanisms intrinsic to the system, namely Dictyostelium discoideum (D.d.) in the starvation phase. We find that different patterns are formed when the populations are initialized at different developmental stages, or when populations at different initial developmental stages are mixed. The experimentally observed patterns can be understood with a modified Kessler–Levine model that takes into account the initial spatial heterogeneity of the cell populations and a developmental path introduced by us, i.e. the time dependence of the various biochemical parameters. The dynamics of the parameters agree with known biochemical studies. Most importantly, the modified model reproduces not only our results, but also the observations of an independent experiment published earlier. This shows that pattern formation can be used to understand and quantify the temporal evolution of the system parameters. |
BibTeX:
@article{Prabhakara.Gholami.ea2017, author = {Prabhakara, K. H. and Gholami, A. and Zykov, V. S. and Bodenschatz, E.}, title = {Effects of developmental variability on the dynamics and self-organization of cell populations}, journal = {New J. Phys.}, month = {November}, year = {2017}, volume = {19}, pages = {113024}, doi = {10.1088/1367-2630/aa9391},, url = {http://iopscience.iop.org/article/10.1088/1367-2630/aa9391/meta} } |
Shishkina, O., Horn, S., Emran, M. S. and Ching, E. S. C., "Mean temperature profiles in turbulent thermal convection", Phys. Rev. Fluids, November 2017, Vol. 2(11), 113502 pp. |
Abstract: To predict the mean temperature profiles in turbulent thermal convection, the thermal boundary layer (BL) equation including the effects of fluctuations has to be solved. In Shishkina et al. [Phys. Rev. Lett. 114, 114302 (2015)], the thermal BL equation with the fluctuations taken into account as an eddy thermal diffusivity has been solved for large Prandtl-number fluids for which the eddy thermal diffusivity and the velocity field can be approximated, respectively, as a cubic and a linear function of the distance from the plate. In the present work, we make use of the idea of Prandtl's mixing length model and relate the eddy thermal diffusivity to the stream function. With this proposed relation, we can solve the thermal BL equation and obtain a closed-form expression for the dimensionless mean temperature profile in terms of two independent parameters for fluids with a general Prandtl number. With a proper choice of the parameters, our predictions of the temperature profiles are in excellent agreement with the results of our direct numerical simulations for a wide range of Prandtl numbers from 0.01 to 2547.9 and Rayleigh numbers from 107 to 109. |
BibTeX:
@article{Shishkina.Horn.ea2017, author = {Shishkina, O. and Horn, S. and Emran, M. S. and Ching, E. S. C.}, title = {Mean temperature profiles in turbulent thermal convection}, journal = {Phys. Rev. Fluids}, month = {November}, year = {2017}, volume = {2}, number = {11}, pages = {113502}, doi = {10.1103/PhysRevFluids.2.113502},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.2.113502} } |
Shy, S. S., Nguyen, M. T., Huang, S.-Y. and Liu, C.-C., "Is turbulent facilitated ignition through differential diffusion independent of spark gap?", ScienceDirect, November 2017, Vol. 185, 1 pp. |
Abstract: In 2014, Wu et al. discovered an unexpected result. Turbulence can facilitate ignition through differential diffusion when the effective Lewis number (Le) of mixtures is sufficiently larger than unity using small electrode gaps (dgap?<=?0.8?mm) in near-isotropic turbulence generated by a fan-stirred burner. This suggested that the required minimum ignition energy (MIE) in intense turbulence can be smaller than that in quiescence (Wu et al. did not measure MIE). This work explores whether the aforesaid turbulent facilitated ignition (TFI) for Le?>?1 is independent of dgap. We apply the same hydrogen mixtures at the equivalence ratio o?=?5.1 (Le? ?2.3) and o?=?0.18 (Le? ?0.3) as Wu et al. in our large fan-stirred cruciform bomb capable of generating near-isotropic turbulence to measure values of MIE as a function of dgap at both quiescence and intense turbulence (the rms turbulent fluctuating velocity u'=?5.4?m/s) conditions. A drastic fall of values of laminar and turbulent MIE (MIEL and MIET) with increasing dgap is observed. TFI only occurs for Le?>?1 (o?=?5.1) and it is restricted at smaller dgap?=?0.58?mm, where MIEL?=?61.5?mJ?>>?MIET?=?26?mJ (0.25-mm tungsten electrodes) and MIEL?=?255.5?mJ?>>?MIET?=?36.8?mJ (2-mm tungsten electrodes) in support of Wu et al.’s finding. However, we discover that the MIEL and MIET curves versus dgap can cross each other at larger dgap, at which no TFI for Le?>?1 at dgap?=?2?mm where MIEL?=?0.52?mJ?< |
BibTeX:
@article{Shy.Nguyen.ea2017, author = {Shy, S. S. and Nguyen, M. T. and Huang, S.-Y. and Liu, C.-C.}, title = {Is turbulent facilitated ignition through differential diffusion independent of spark gap?}, journal = {ScienceDirect}, month = {November}, year = {2017}, volume = {185}, pages = {1}, doi = {10.1016/j.combustflame.2017.06.022},, url = {https://www.sciencedirect.com/science/article/pii/S0010218017302432} } |
Eidi, Z., Mohammad-Rafiee, F., Khorrami, M. and Gholami, A., "Modelling of Dictyostelium discoideum movement in a linear gradient of chemoattractant", Royal Society of Chemistry, October 2017, Vol. 13, 8209 pp. |
Abstract: Chemotaxis is a ubiquitous biological phenomenon in which cells detect a spatial gradient of chemoattractant, and then move towards the source. Here we present a position-dependent advection–diffusion model that quantitatively describes the statistical features of the chemotactic motion of the social amoeba Dictyostelium discoideum in a linear gradient of cAMP (cyclic adenosine monophosphate). We fit the model to experimental trajectories that are recorded in a microfluidic setup with stationary cAMP gradients and extract the diffusion and drift coefficients in the gradient direction. Our analysis shows that for the majority of gradients, both coefficients decrease over time and become negative as the cells crawl up the gradient. The extracted model parameters also show that besides the expected drift in the direction of the chemoattractant gradient, we observe a nonlinear dependency of the corresponding variance on time, which can be explained by the model. Furthermore, the results of the model show that the non-linear term in the mean squared displacement of the cell trajectories can dominate the linear term on large time scales. |
BibTeX:
@article{Eidi.Mohammad-Rafiee.ea2017, author = {Eidi, Z. and Mohammad-Rafiee, F. and Khorrami, M. and Gholami, A.}, title = {Modelling of Dictyostelium discoideum movement in a linear gradient of chemoattractant}, journal = {Royal Society of Chemistry}, month = {October}, year = {2017}, volume = {13}, pages = {8209}, doi = {10.1039/C7SM01568B},, url = {http://pubs.rsc.org/en/content/articlehtml/2017/sm/c7sm01568b} } |
Hsu, H.-F., Bodenschatz, E., Westendorf, C., Gholami, A., Pumir, A., Tarantola, M. and Beta, C., "Variability and Order in Cytoskeletal Dynamics of Motile Amoeboid Cells", Phys. Rev. Lett., October 2017, Vol. 119(14), 148101 pp. |
Abstract: The chemotactic motion of eukaryotic cells such as leukocytes or metastatic cancer cells relies on membrane protrusions driven by the polymerization and depolymerization of actin. Here we show that the response of the actin system to a receptor stimulus is subject to a threshold value that varies strongly from cell to cell. Above the threshold, we observe pronounced cell-to-cell variability in the response amplitude. The polymerization time, however, is almost constant over the entire range of response amplitudes, while the depolymerization time increases with increasing amplitude. We show that cell-to-cell variability in the response amplitude correlates with the amount of Arp2/3, a protein that enhances actin polymerization. A time-delayed feedback model for the cortical actin concentration is consistent with all our observations and confirms the role of Arp2/3 in the observed cell-to-cell variability. Taken together, our observations highlight robust regulation of the actin response that enables a reliable timing of cell movement. |
BibTeX:
@article{Hsu.Bodenschatz.ea2017, author = {Hsu, H.-F. and Bodenschatz, E. and Westendorf, C. and Gholami, A. and Pumir, A. and Tarantola, M. and Beta, C.}, title = {Variability and Order in Cytoskeletal Dynamics of Motile Amoeboid Cells}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2017}, volume = {119}, number = {14}, pages = {148101}, doi = {10.1103/PhysRevLett.119.148101},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.148101} } |
Shishkina, O., Emran, M. S., Grossmann, S. and Lohse, D., "Scaling relations in large-Prandtl-number natural thermal convection", Phys. Rev. Lett., October 2017, Vol. 2(10), 103502 pp. |
Abstract: In this study, we follow Grossmann and Lohse [Phys. Rev. Lett. 86, 3316 (2001)], who derived various scalings regimes for the dependence of the Nusselt number Nu and the Reynolds number Re on the Rayleigh number Ra and the Prandtl number Pr. We focus on theoretical arguments as well as on numerical simulations for the case of large-Pr natural thermal convection. Based on an analysis of self-similarity of the boundary layer equations, we derive that in this case the limiting large-Pr boundary-layer dominated regime is I<°°, introduced and defined by Grossmann and Lohse [Phys. Rev. Lett. 86, 3316 (2001)], with the scaling relations Nu Pr0Ra1/3 and Re Pr-1Ra2/3. Our direct numerical simulations for Ra from 104 to 109 and Pr from 0.1 to 200 show that the regime I<°° is almost indistinguishable from the regime III°°, where the kinetic dissipation is bulk-dominated. With increasing Ra, the scaling relations undergo a transition to those in IVu of Grossmann and Lohse [Phys. Rev. Lett. 86, 3316 (2001)], where the thermal dissipation is determined by its bulk contribution. |
BibTeX:
@article{Shishkina.Emran.ea2017, author = {Shishkina, O. and Emran, M. S. and Grossmann, S. and Lohse, D.}, title = {Scaling relations in large-Prandtl-number natural thermal convection}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2017}, volume = {2}, number = {10}, pages = {103502}, doi = {doi.org/10.1103/PhysRevFluids.2.103502},, url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.2.103502} } |
Vidal-Henriquez, E., Zykov, V., Bodenschatz, E. and Gholami, A., "Convective instability and boundary driven oscillations in a reaction-diffusion-advection model", Chaos, October 2017, Vol. 27, 103110 pp. |
Abstract: In a reaction-diffusion-advection system, with a convectively unstable regime, a perturbation creates a wave train that is advected downstream and eventually leaves the system. We show that the convective instability coexists with a local absolute instability when a fixed boundary condition upstream is imposed. This boundary induced instability acts as a continuous wave source, creating a local periodic excitation near the boundary, which initiates waves traveling both up and downstream. To confirm this, we performed analytical analysis and numerical simulations of a modified Martiel-Goldbeter reaction-diffusion model with the addition of an advection term. We provide a quantitative description of the wave packet appearing in the convectively unstable regime, which we found to be in excellent agreement with the numerical simulations. We characterize this new instability and show that in the limit of high advection speed, it is suppressed. This type of instability can be expected for reaction-diffusion systems that present both a convective instability and an excitable regime. In particular, it can be relevant to understand the signaling mechanism of the social amoeba Dictyostelium discoideum that may experience fluid flows in its natural habitat. |
BibTeX:
@article{Vidal-Henriquez.Zykov.ea2017, author = {Vidal-Henriquez, E. and Zykov, V. and Bodenschatz, E. and Gholami, A.}, title = {Convective instability and boundary driven oscillations in a reaction-diffusion-advection model}, journal = {Chaos}, month = {October}, year = {2017}, volume = {27}, pages = {103110}, doi = {10.1063/1.4986153},, url = {https://arxiv.org/abs/1706.02530} } |
Weiss, M., Frohnmayer, J. P., Benk, L. T., Haller, B., Janiesch, J.-W., Heitkamp, T., Börsch, M., Lira, R. B., Dimova, R., Lipowsky, R., Bodenschatz, E., Baret, J.-C., Vidakovic-Koch, T., Sundmacher, K., Platzman, I. and Spatz, J. P., "Sequential bottom-up assembly of mechanically stabilized synthetic cells by microfluidics", Nature Materials, October 2017, Vol. 17, 89 pp. |
Abstract: Compartments for the spatially and temporally controlled assembly of biological processes are essential towards cellular life. Synthetic mimics of cellular compartments based on lipid-based protocells lack the mechanical and chemical stability to allow their manipulation into a complex and fully functional synthetic cell. Here, we present a high-throughput microfluidic method to generate stable, defined sized liposomes termed ‘droplet-stabilized giant unilamellar vesicles (dsGUVs)’. The enhanced stability of dsGUVs enables the sequential loading of these compartments with biomolecules, namely purified transmembrane and cytoskeleton proteins by microfluidic pico-injection technology. This constitutes an experimental demonstration of a successful bottom-up assembly of a compartment with contents that would not self-assemble to full functionality when simply mixed together. Following assembly, the stabilizing oil phase and droplet shells are removed to release functional self-supporting protocells to an aqueous phase, enabling them to interact with physiologically relevant matrices. |
BibTeX:
@article{Weiss.Frohnmayer.ea2017, author = {Weiss,M. and Frohnmayer, J. P. and Benk, L. T. and Haller, B. and Janiesch, J.-W. and Heitkamp, T. and Börsch, M. and Lira, R. B. and Dimova, R. and Lipowsky, R. and Bodenschatz, E. and Baret, J.-C. and Vidakovic-Koch, T. and Sundmacher, K. and Platzman, I. and Spatz, J. P.}, title = {Sequential bottom-up assembly of mechanically stabilized synthetic cells by microfluidics}, journal = {Nature Materials}, month = {October}, year = {2017}, volume = {17}, pages = {89}, doi = {10.1038/nmat5005},, url = {https://www.nature.com/articles/nmat5005} } |
Kliesch, T. T., Dietz, J., Turco, L., Halder, P., Polo, E., Tarantola, M., Jahn, R. and Janshoff, A., "Membrane tension increases fusion efficiency of model membranes in the presence of SNAREs", Sci. Rep., September 2017, Vol. 7(1), 12070 pp. |
Abstract: The large gap in time scales between membrane fusion occurring in biological systems during neurotransmitter release and fusion observed between model membranes has provoked speculations over a large number of possible factors that might explain this discrepancy. One possible reason is an elevated lateral membrane tension present in the presynaptic membrane. We investigated the tension-dependency of fusion using model membranes equipped with a minimal fusion machinery consisting of syntaxin 1, synaptobrevin and SNAP 25. Two different strategies were realized; one based on supported bilayers and the other one employing sessile giant liposomes. In the first approach, isolated patches of planar bilayers derived from giant unilamellar vesicles containing syntaxin 1 and preassembled SNAP 25 (ÄN-complex) were deposited on a dilatable PDMS sheet. In a second approach, lateral membrane tension was controlled through the adhesion of intact giant unilamellar vesicles on a functionalized surface. In both approaches fusion efficiency increases considerably with lateral tension and we identified a threshold tension of 3.4 mN m-1, at which the number of fusion events is increased substantially. |
BibTeX:
@article{Kliesch.Dietz.ea2017, author = {Kliesch, T. T. and Dietz, J. and Turco, L. and Halder, P. and Polo, E. and Tarantola, M. and Jahn, R. and Janshoff, A.}, title = {Membrane tension increases fusion efficiency of model membranes in the presence of SNAREs}, journal = {Sci. Rep.}, month = {September}, year = {2017}, volume = {7}, number = {1}, pages = {12070}, doi = {10.1038/s41598-017-12348-w},, url = {https://www.ncbi.nlm.nih.gov/pubmed/28935937} } |
Knutsen, A. N., Lawson, J. M., Dawson, J. R. and Worth, N. A., "A laser sheet self-calibration method for scanning PIV", Experiments in Fluids, September 2017, Vol. 58, 145 pp. |
Abstract: Knowledge of laser sheet position, orientation, and thickness is a fundamental requirement of scanning PIV and other laser-scanning methods. This paper describes the development and evaluation of a new laser sheet self-calibration method for stereoscopic scanning PIV, which allows the measurement of these properties from particle images themselves. The approach is to fit a laser sheet model by treating particles as randomly distributed probes of the laser sheet profile, whose position is obtained via a triangulation procedure enhanced by matching particle images according to their variation in brightness over a scan. Numerical simulations and tests with experimental data were used to quantify the sensitivity of the method to typical experimental error sources and validate its performance in practice. The numerical simulations demonstrate the accurate recovery of the laser sheet parameters over range of different seeding densities and sheet thicknesses. Furthermore, they show that the method is robust to significant image noise and camera misalignment. Tests with experimental data confirm that the laser sheet model can be accurately reconstructed with no impairment to PIV measurement accuracy. The new method is more efficient and robust in comparison with the standard (self-) calibration approach, which requires an involved, separate calibration step that is sensitive to experimental misalignments. The method significantly improves the practicality of making accurate scanning PIV measurements and broadens its potential applicability to scanning systems with significant vibrations. |
BibTeX:
@article{Knutsen.Lawson.ea2017, author = {Knutsen, A. N. and Lawson, J. M. and Dawson, J. R. and Worth, N. A.}, title = {A laser sheet self-calibration method for scanning PIV}, journal = {Experiments in Fluids}, month = {September}, year = {2017}, volume = {58}, pages = {145}, doi = {10.1007/s00348-017-2428-5},, url = {https://link.springer.com/article/10.1007/s00348-017-2428-5} } |
Prabhakaran, P., Weiss, S., Krekhov, A., Pumir, A. and Bodenschatz, E., "Can Hail and Rain Nucleate Cloud Droplets?", Phys. Rev. Lett., September 2017, Vol. 119(12), 128701 pp. |
Abstract: We present results from moist convection in a mixture of pressurized sulfur hexafluoride (liquid and vapor), and helium (gas) to model the wet and dry components of the Earth’s atmosphere. To allow for homogeneous nucleation, we operate the experiment close to critical conditions. We report on the nucleation of microdroplets in the wake of large cold liquid drops falling through the supersaturated atmosphere and show that the homogeneous nucleation is caused by isobaric cooling of the saturated sulfur hexafluoride vapor. Our results carry over to atmospheric clouds: falling hail and cold rain drops may enhance the heterogeneous nucleation of microdroplets in their wake under supersaturated atmospheric conditions. We also observed that under appropriate circumstances settling microdroplets form a rather stable horizontal cloud layer, which separates regions of super- and subcritical saturation. |
BibTeX:
@article{Prabhakaran.Weiss.ea2017, author = {Prabhakaran, P. and Weiss, S. and Krekhov, A. and Pumir, A. and Bodenschatz, E.}, title = {Can Hail and Rain Nucleate Cloud Droplets?}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2017}, volume = {119}, number = {12}, pages = {128701}, doi = {10.1103/PhysRevLett.119.128701},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.128701} } |
Sinhuber, M., Bewley, G. P. and Bodenschatz, E., "Dissipative Effects on Inertial-Range Statistics at High Reynolds Numbers", Phys. Rev. Lett., September 2017, Vol. 119(13), 134502 pp. |
Abstract: Using the unique capabilities of the Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization, Goettingen, we report experimental measurements in classical grid turbulence that uncover oscillations of the velocity structure functions in the inertial range. This was made possible by measuring extremely long time series of up to 1010 samples of the turbulent fluctuating velocity, which corresponds to O(107) integral length scales. The measurements were conducted in a well-controlled environment at a wide range of high Reynolds numbers from Rë=110 up to Rë=1600, using both traditional hot-wire probes as well as the nanoscale thermal anemometry probe developed at Princeton University. An implication of the observed oscillations is that dissipation influences the inertial-range statistics of turbulent flows at scales significantly larger than predicted by current models and theories. |
BibTeX:
@article{Sinhuber.Bewley.ea2017, author = {Sinhuber, M. and Bewley, G. P. and Bodenschatz, E.}, title = {Dissipative Effects on Inertial-Range Statistics at High Reynolds Numbers}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2017}, volume = {119}, number = {13}, pages = {134502}, doi = {10.1103/PhysRevLett.119.134502},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.134502} } |
Li, T.-C., Gao, X., Zheng, F. F., Pan, D. B., Zheng, B. and Zhang, H., "A theory for spiral wave drift induced by ac and polarized electric fields in chemical excitable media", Sci. Rep., August 2017, Vol. 7, 8657 pp. |
Abstract: Spiral waves are shown to undergo directional drifts in the presence of ac and polarized electric fields when their frequencies are twice of the spiral frequencies. Here, we propose a quantitative description for the spiral wave drift induced by weak electric fields, and provide the explicit equations for the spiral wave drift speed and direction. Numerical simulations are performed to demonstrate the quantitative agreement with analytical results in both weakly and highly excitable media. |
BibTeX:
@article{Li.Gao.ea2017, author = {Li, T.-C. and Gao, X. and Zheng, F. F. and Pan, D. B. and Zheng, B. and Zhang, H.}, title = {A theory for spiral wave drift induced by ac and polarized electric fields in chemical excitable media}, journal = {Sci. Rep.}, month = {August}, year = {2017}, volume = {7}, pages = {8657}, doi = {10.1038/s41598-017-09092-6},, url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561252/} } |
Zykov, V., Krekhov, A. and Bodenschatz, E., "Geometrical factors in propagation block and spiral wave initiation", Chaos, August 2017, Vol. 27, 093923 pp. |
Abstract: Many theoretical and experimental studies indicate that a propagation block represents an important factor in spiral wave initiation in excitable media. The analytical and numerical results we obtained for a generic two-component reaction-diffusion system demonstrate quantitative conditions for the propagation block in a one-dimensional and a two-dimensional medium due to a sharp spatial increase of the medium's excitability or the coupling strength above a certain critical value. Here, we prove that this critical value strongly depends on the medium parameters and the geometry of the inhomogeneity. For an exemplary two-dimensional medium, we show how the propagation block can be used to initiate spiral waves by a specific choice of the size and shape of the medium's inhomogeneity. |
BibTeX:
@article{Zykov.Krekhov.ea2017a, author = {Zykov, V. and Krekhov, A. and Bodenschatz, E.}, title = {Geometrical factors in propagation block and spiral wave initiation}, journal = {Chaos}, month = {August}, year = {2017}, volume = {27}, pages = {093923}, doi = {10.1063/1.4999473},, url = {http://aip.scitation.org/doi/10.1063/1.4999473} } |
Franz, J., Tarantola, M. and Riethmüller, C., "How tetraspanins shape endothelial and leukocyte nano-architecture during inflammation", Biochemical Society Transactions, July 2017, Vol. 45(4), 999 pp. |
Abstract: Tetraspanins are ubiquitous membrane proteins that induce local membrane curvature and hence co-ordinate cell-to-cell contacts. This review highlights their role in inflammation, which requires control of the nano-architecture of attachment sites between endothelial cells and leukocytes. The active role of endothelial cells in preparing for transmigration of leukocytes and determining the severity of an inflammation is often underscored. A clear hint to endothelial pre-activation is their ability to protrude clustered adhesion proteins upward prior to leukocyte contact. The elevation of molecular adhesive platforms toward the blood stream is crucially dependent on tetraspanins. In addition, leukocytes require tetraspanins for their activation. The example of the B-cell receptor is referenced in some detail here, since it provides deeper insights into the receptor–coreceptor interplay. To lift the role of tetraspanins from an abstract model of inflammation toward a player of clinical significance, two pathologies are analyzed for the known contributions of tetraspanins. The recent publication of the first crystal structure of a full-length tetraspanin revealed a cholesterol-binding site, which provides a strong link to the pathophysiological condition of atherosclerosis. Dysregulation of the inflammatory cascade in autoimmune diseases by endothelial cells is exemplified by the involvement of tetraspanins in multiple sclerosis. |
BibTeX:
@article{Franz.Tarantola.ea2017, author = {Franz, J. and Tarantola, M. and Riethmüller, C.}, title = {How tetraspanins shape endothelial and leukocyte nano-architecture during inflammation}, journal = {Biochemical Society Transactions}, month = {July}, year = {2017}, volume = {45}, number = {4}, pages = {999}, doi = {10.1042/BST20170163},, url = {http://www.biochemsoctrans.org/content/45/4/999} } |
Lampert, T. J., Kamprad, N., Edwards, M., Borleis, J., Watson, A. J., Tarantola, M. and Devreotes, P. N., "Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity", Proceedings of the National Academy of Science of the United States of America, July 2017, Vol. 114(37), E7727 pp. |
Abstract: The model organism Dictyostelium discoideum has greatly facilitated our understanding of the signal transduction and cytoskeletal pathways that govern cell motility. Cell–substrate adhesion is downstream of many migratory and chemotaxis signaling events. Dictyostelium cells lacking the tumor suppressor PTEN show strongly impaired migratory activity and adhere strongly to their substrates. We reasoned that other regulators of migration could be obtained through a screen for overly adhesive mutants. A screen of restriction enzyme-mediated integration mutagenized cells yielded numerous mutants with the desired phenotypes, and the insertion sites in 18 of the strains were mapped. These regulators of adhesion and motility mutants have increased adhesion and decreased motility. Characterization of seven strains demonstrated decreased directed migration, flatness, increased filamentous actin-based protrusions, and increased signal transduction network activity. Many of the genes share homology to human genes and demonstrate the diverse array of cellular networks that function in adhesion and migration. |
BibTeX:
@article{Lampert.Kamprad.ea2017, author = {Lampert, T. J. and Kamprad, N. and Edwards, M. and Borleis, J. and Watson, A. J. and Tarantola, M. and Devreotes, P. N.}, title = {Shear force-based genetic screen reveals negative regulators of cell adhesion and protrusive activity}, journal = {Proceedings of the National Academy of Science of the United States of America}, month = {July}, year = {2017}, volume = {114}, number = {37}, pages = {E7727}, doi = {10.1073/pnas.1616600114},, url = {http://www.pnas.org/content/114/37/E7727.short} } |
Clay, M. P., Buaria, D., Gotoh, T. and Yeung, P. K., "A dual communicator and dual grid-resolution algorithm for petascale simulations of turbulent mixing at high Schmidt number", ScienceDirect, June 2017, Vol. 219, 313 pp. |
Abstract: A new dual-communicator algorithm with very favorable performance characteristics has been developed for direct numerical simulation (DNS) of turbulent mixing of a passive scalar governed by an advection–diffusion equation. We focus on the regime of high Schmidt number (), where because of low molecular diffusivity the grid-resolution requirements for the scalar field are stricter than those for the velocity field by a factor . Computational throughput is improved by simulating the velocity field on a coarse grid of points with a Fourier pseudo-spectral (FPS) method, while the passive scalar is simulated on a fine grid of points with a combined compact finite difference (CCD) scheme which computes first and second derivatives at eighth-order accuracy. A static three-dimensional domain decomposition and a parallel solution algorithm for the CCD scheme are used to avoid the heavy communication cost of memory transposes. A kernel is used to evaluate several approaches to optimize the performance of the CCD routines, which account for 60% of the overall simulation cost. On the petascale supercomputer Blue Waters at the University of Illinois, Urbana–Champaign, scalability is improved substantially with a hybrid MPI-OpenMP approach in which a dedicated thread per NUMA domain overlaps communication calls with computational tasks performed by a separate team of threads spawned using OpenMP nested parallelism. At a target production problem size of 81923 (0.5 trillion) grid points on 262,144 cores, CCD timings are reduced by 34% compared to a pure-MPI implementation. Timings for 163843 (4 trillion) grid points on 524,288 cores encouragingly maintain scalability greater than 90%, although the wall clock time is too high for production runs at this size. Performance monitoring with CrayPat for problem sizes up to 40963 shows that the CCD routines can achieve nearly 6% of the peak flop rate. The new DNS code is built upon two existing FPS and CCD codes. With the grid ratio , the disparity in the computational requirements for the velocity and scalar problems is addressed by splitting the global communicator MPI_COMM_WORLD into disjoint communicators for the velocity and scalar fields, respectively. Inter-communicator transfer of the velocity field from the velocity communicator to the scalar communicator is handled with discrete send and non-blocking receive calls, which are overlapped with other operations on the scalar communicator. For production simulations at and on 262,144 cores for the scalar field, the DNS code achieves 94% strong scaling relative to 65,536 cores and 92% weak scaling relative to and on 512 cores. |
BibTeX:
@article{Clay.Buaria.ea2017, author = {Clay, M. P. and Buaria, D. and Gotoh, T. and Yeung, P. K.}, title = {A dual communicator and dual grid-resolution algorithm for petascale simulations of turbulent mixing at high Schmidt number}, journal = {ScienceDirect}, month = {June}, year = {2017}, volume = {219}, pages = {313}, doi = {10.1016/j.cpc.2017.06.009},, url = {http://www.sciencedirect.com/science/article/pii/S0010465517301911} } |
Shishkina, O., "Heat Transport in Horizontal and Inclined Convection", June 2017, Vol. 196, 245 pp. |
Abstract: We discuss three classical paradigmatic systems of thermally driven flows: Rayleigh-Bénard convection, where a fluid is confined between a heated bottom plate and a cooled top plate, horizontal convection, where the fluid is heated at one part of the bottom and cooled at some other part, and vertical convection, where the fluid is confined between two differently heated isothermal vertical plates. Rayleigh-Bénard and vertical convection can be also considered as limiting cases of so-called inclined convection. For these systems we study how the heat and momentum transport, which is represented by the Nusselt number and Reynolds number, scales with the main governing parameters of the system, which are the Rayleigh number and Prandtl number. We show that different boundary conditions generally lead to different scaling diagrams in the Prandtl–Rayleigh plane. For laminar vertical convection the scalings can be derived from the boundary layer equations, see Shishkina (Phys Rev E 93:051102, 2016, [8]). In the case of horizontal convection, the scalings can be derived from the analysis of the boundary-layer and bulk contributions of the kinetic and thermal dissipation rates, see Shishkina et al. (Geophys Res Lett 43:1219–1225, 2016, [5]). Here we summarize some previous results and discuss the applicability of the developed theory to global ocean circulation. |
BibTeX:
@proceedings{Shishkina2017a, author = {Shishkina, O.}, title = {Heat Transport in Horizontal and Inclined Convection}, month = {June}, year = {2017}, volume = {196}, pages = {245}, doi = {10.1007/978-3-319-57934-4_35},, url = {https://link.springer.com/chapter/10.1007/978-3-319-57934-4_35} } |
Clerc, M. G., Davila, J. D., Kowalczyk, M., Smyrnelis, P. and Vidal-Henriquez, E., "Theory of light-matter interaction in nematic liquid crystals and the second Painlevé equation", Calc. Var., May 2017, Vol. 56(93) |
Abstract: We study global minimizers of an energy functional arising as a thin sample limit in the theory of light-matter interaction in nematic liquid crystals. We show that depending on the parameters various defects are predicted by the model. In particular we show existence of a new type of topological defect which we call the shadow kink. Its local profile is described by the generalized Hastings and McLeod solutions of the second Painlevvé equation (Claeys et al. in Ann Math 168(2):601–641, 2008; Hastings and McLeod in Arch Ration Mech Anal 73(1):31–51, 1980). As part of our analysis we give a new proof of existence of these solutions. |
BibTeX:
@article{Clerc.Davila.ea2017, author = {Clerc, M. G. and Davila, J. D. and Kowalczyk, M. and Smyrnelis, P. and Vidal-Henriquez, E.}, title = {Theory of light-matter interaction in nematic liquid crystals and the second Painlevé equation}, journal = {Calc. Var.}, month = {May}, year = {2017}, volume = {56}, number = {93}, doi = {DOI 10.1007/s00526-017-1187-8},, url = {https://link.springer.com/article/10.1007/s00526-017-1187-8} } |
Gao, X., Feng, X., Li, T.-C., Qu, S., Wang, X. and Zhang, H., "Dynamics of spiral waves rotating around an obstacle and the existence of a minimal obstacle", Phys. Rev. E, May 2017, Vol. 95(5), 052218 pp. |
Abstract: Pinning of vortices by obstacles plays an important role in various systems. In the heart, anatomical reentry is created when a vortex, also known as the spiral wave, is pinned to an anatomical obstacle, leading to a class of physiologically very important arrhythmias. Previous analyses of its dynamics and instability provide fine estimates in some special circumstances, such as large obstacles or weak excitabilities. Here, to expand theoretical analyses to all circumstances, we propose a general theory whose results quantitatively agree with direct numerical simulations. In particular, when obstacles are small and pinned spiral waves are destabilized, an accurate explanation of the instability in two-dimensional media is provided by the usage of a mapping rule and dimension reduction. The implications of our results are to better understand the mechanism of arrhythmia and thus improve its early prevention. |
BibTeX:
@article{Gao.Feng.ea2017, author = {Gao, X. and Feng, X. and Li, T.-C. and Qu, S. and Wang, X. and Zhang, H.}, title = {Dynamics of spiral waves rotating around an obstacle and the existence of a minimal obstacle}, journal = {Phys. Rev. E}, month = {May}, year = {2017}, volume = {95}, number = {5}, pages = {052218}, doi = {10.1103/PhysRevE.95.052218},, url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.95.052218} } |
Krekhov, A. and Shliomis, M., "Spontaneous Core Rotation in Ferrofluid Pipe Flow", Phys. Rev. Lett., March 2017, Vol. 118(11), 114503 pp. |
Abstract: Ferrofluid flow along a tube of radius R in a constant axial magnetic field is revisited. Our analytical solution and numerical simulations predict a transition from an initially axial flow to a steady swirling one. The swirl dynamo arises above some critical pressure drop and magnetic field strength. The new flow pattern consists of two phases of different symmetry: The flow in the core resembles Poiseuille flow in a rotating tube of the radius r* |
BibTeX:
@article{Krekhov.Shliomis2017, author = {Krekhov, A. and Shliomis, M.}, title = {Spontaneous Core Rotation in Ferrofluid Pipe Flow}, journal = {Phys. Rev. Lett.}, month = {March}, year = {2017}, volume = {118}, number = {11}, pages = {114503}, doi = {10.1103/PhysRevLett.118.114503},, url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.114503} } |
Ching, E. S., Dung, O.-Y. and Shishkina, O., "Fluctuating Thermal Boundary Layers and Heat Transfer in Turbulent Rayleigh-Bénard Convection", J. Stat. Phys., February 2017, Vol. 167(3), 626 pp. |
Abstract: We investigate the effect of fluctuations in thermal boundary layer on heat transfer in turbulent Rayleigh-Bénard convection for Prandtl number greater than one in the regime where the thermal dissipation rate is dominated by boundary layer contribution and in the presence of a large-scale circulating flow. |
BibTeX:
@article{Ching.Shishkina, author = {Emily S.C. Ching and Dung, O.-Y. and Shishkina, O.}, title = {Fluctuating Thermal Boundary Layers and Heat Transfer in Turbulent Rayleigh-Bénard Convection}, journal = {J. Stat. Phys.}, month = {February}, year = {2017}, volume = {167}, number = {3}, pages = {626}, doi = {10.1007/s10955-017-1739-5},, url = {http://link.springer.com/article/10.1007%2Fs10955-017-1739-5} } |
Weiss, S. and Deegan, R., "Weakly and strongly coupled Belousov-Zhabotinsky patterns", Phys. Rev. E, February 2017, Vol. 95(2), 022215 pp. |
Abstract: We investigate experimentally and numerically the synchronization of two-dimensional spiral wave patterns in the Belousov-Zhabotinsky reaction due to point-to-point coupling of two separate domains. Different synchronization modalities appear depending on the coupling strength and the initial patterns in each domain. The behavior as a function of the coupling strength falls into two qualitatively different regimes. The weakly coupled regime is characterized by inter-domain interactions that distorted but do not break wave fronts. Under weak coupling, spiral cores are pushed around by wave fronts in the other domain, resulting in an effective interaction between cores in opposite domains. In the case where each domain initially contains a single spiral, the cores form a bound pair and orbit each other at quantized distances. When the starting patterns consist of multiple randomly positioned spiral cores, the number of cores decreases with time until all that remains are a few cores that are synchronized with a partner in the other domain. The strongly coupled regime is characterized by interdomain interactions that break wave fronts. As a result, the wave patterns in both domains become identical. |
BibTeX:
@article{Weiss.Deegan2017, author = {Weiss, S. and Deegan, R.D.}, title = {Weakly and strongly coupled Belousov-Zhabotinsky patterns}, journal = {Phys. Rev. E}, month = {February}, year = {2017}, volume = {95}, number = {2}, pages = {022215}, doi = {10.1103/PhysRevE.95.022215},, url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.95.022215} } |
Zykov, V., Krekhov, A. and Bodenschatz, E., "Fast propagation regions cause self-sustained reentry in excitable media", Proc. Natl. Acad. Sci. U.S.A., February 2017, Vol. 114(6), 1281 pp. |
Abstract: Self-sustained waves of electrophysiological activity can cause arrhythmia in the heart. These reentrant excitations have been associated with spiral waves circulating around either an anatomically defined weakly conducting region or a functionally determined core. Recently, an ablation procedure has been clinically introduced that stops atrial fibrillation of the heart by destroying the electrical activity at the spiral core. This is puzzling because the tissue at the anatomically defined spiral core would already be weakly conducting, and a further decrease should not improve the situation. In the case of a functionally determined core, an ablation procedure should even further stabilize the rotating wave. The efficacy of the procedure thus needs explanation. Here, we show theoretically that fundamentally in any excitable medium a region with a propagation velocity faster than its surrounding can act as a nucleation center for reentry and can anchor an induced spiral wave. Our findings demonstrate a mechanistic underpinning for the recently developed ablation procedure. Our theoretical results are based on a very general and widely used two-component model of an excitable medium. Moreover, the important control parameters used to realize conditions for the discovered phenomena are applicable to quite different multicomponent models. |
BibTeX:
@article{Zykov.Krekhov.ea2017, author = {Zykov, V. and Krekhov, A. and Bodenschatz, E.}, title = {Fast propagation regions cause self-sustained reentry in excitable media}, journal = {Proc. Natl. Acad. Sci. U.S.A.}, month = {February}, year = {2017}, volume = {114}, number = {6}, pages = {1281}, doi = {10.1073/pnas.1611475114},, url = {http://www.pnas.org/content/114/6/1281.short} } |
Shishkina, O., "Mean flow structure in horizontal convection", J. Fluid Mech., January 2017, Vol. 812, 525 pp. |
Abstract: We analyse the global flow structures in horizontal convection systems, where the heat supply and removal takes place through separated parts of a lower horizontal surface of a fluid layer. The results are based on direct numerical simulations for the length-to-height aspect ratio of the convection cell I=10 , Rayleigh number Ra from 3x108 to 3x1011 and Prandtl number Pr from 0.05 to 50. The structure of the mean flows in horizontal convection is described in terms of time-averaged spatial distributions of the temperature, velocity, kinetic energy, thermal and kinetic dissipation rates. A possible scenario of transition to turbulent horizontal convection in the whole convection cell of a large aspect ratio is discussed. |
BibTeX:
@article{Shishkina2017, author = {Shishkina, O.}, title = {Mean flow structure in horizontal convection}, journal = {J. Fluid Mech.}, month = {January}, year = {2017}, volume = {812}, pages = {525}, doi = {10.1017/jfm.2016.866},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/mean-flow-structure-in-horizontal-convection/759294BE5E272703205AF21D228F5D95} } |
Bagheri, G. and Bonadonna, C., "On the drag of freely falling non-spherical particles", ScienceDirect, November 2016, Vol. 301, 526 pp. |
Abstract: We present a new general model for the prediction of the drag coefficient of non-spherical solid particles of regular and irregular shapes falling in gas or liquid valid for sub-critical particle Reynolds numbers (i.e. Re < 3 x 105). Results are obtained from experimental measurements on 300 regular and irregular particles in the air and analytical solutions for ellipsoids. Depending on their size, irregular particles are accurately characterized with a 3D laser scanner or SEM micro-CT method. The experiments are carried out in settling columns with height of 0.45 to 3.60 m and in a 4 m-high vertical wind tunnel. In addition, 881 additional experimental data points are also considered that are compiled from the literature for particles of regular shapes falling in liquids. New correlation is based on the particle Reynolds number and two new shape descriptors defined as a function of particle flatness, elongation and diameter. New shape descriptors are easy-to-measure and can be more easily characterized than sphericity. The new correlation has an average error of 10%, which is significantly lower than errors associated with existing correlations. Additional aspects of particle sedimentation are also investigated. First, it is found that particles falling in dense liquids, in particular at Re > 1000, tend to fall with their maximum projection area perpendicular to their falling direction, whereas in gases their orientation is random. Second, effects of small-scale surface vesicularity and roughness on the drag coefficient of non-spherical particles found to be < 10%. Finally, the effect of particle orientation on the drag coefficient is discussed and additional correlations are presented to predict the end members of drag coefficient due to change in the particle orientation. |
BibTeX:
@article{Bagheri.Bonadonna2016, author = {Bagheri, G. and Bonadonna, C.}, title = {On the drag of freely falling non-spherical particles}, journal = {ScienceDirect}, month = {November}, year = {2016}, volume = {301}, pages = {526}, doi = {10.1016/j.powtec.2016.06.015},, url = {http://www.sciencedirect.com/science/article/pii/S0032591016303539} } |
Bagheri, G., Rossi, E., Biass, S. and Bonadonna, C., "Timing and nature of volcanic particle clusters based on field and numerical investigations", J. Volcanol. Geotherm. Res., November 2016, Vol. 327, 520 pp. |
Abstract: Aggregation processes are known to play an important role in volcanic particle dispersal and sedimentation. They are also a primary source of uncertainty in ash dispersal forecasting since fundamental questions, such as the timing and deposition dynamics of volcanic aggregates, still remain unanswered. Here, we applied a state-of-the-art combination of field and numerical strategies to characterize volcanic aggregates. We introduce a new category of aggregates observed with high-speed-high-resolution videos, namely cored clusters. Cored clusters are mostly sub-spherical fragile aggregates that have never been observed in the deposits nor on adhesive tape as they typically break at impact with the ground. They consist of a core particle (200–500ìm) fully covered by a thick shell of particles < 90ìm. The low preservation potential of cored clusters in ash deposits explains the poor documentation in the literature and the low consideration attributed so far. Cored clusters can also better explain the deposition of fine ash in proximal and medial regions and the polymodality observed in many ash deposits. In addition, numerical inversions show how cored clusters can rapidly form within 175s from eruption onset. Finally, our observations represent the first field-based evidence of the so-called rafting effect, in which the sedimentation of coarse ash in cored clusters is delayed due to aggregation. |
BibTeX:
@article{Bagheri.Rossi.ea, author = {Bagheri, G. and Rossi, E. and Biass, S. and Bonadonna, C.}, title = {Timing and nature of volcanic particle clusters based on field and numerical investigations}, journal = {J. Volcanol. Geotherm. Res.}, month = {November}, year = {2016}, volume = {327}, pages = {520}, doi = {10.1016/j.jvolgeores.2016.09.009},, url = {http://www.sciencedirect.com/science/article/pii/S0377027316303547} } |
Shishkina, O., Weiss, S. and Bodenschatz, E., "Conductive heat flux in measurements of the Nusselt number in turbulent Rayleigh-Bénard convection", Phys. Rev. Fluids, October 2016, Vol. 1(6), 062301(R) pp. |
Abstract: We propose a recipe to calculate accurately the Nusselt number Nu in turbulent Rayleigh-Bénard convection, using the measured total heat flux q and known parameters of the fluid and convection cell. More precisely, we present a method to compute the conductive heat flux q^, which is a normalization of q in the definition of Nu, for conditions where the fluid parameters may vary strongly across the fluid layer. We show that in the Oberbeck-Boussinesq approximation and also when the thermal conductivity depends exclusively on the temperature, the value of q^ is determined by simple explicit formulas. For a general non-Oberbeck-Boussinesq (NOB) case we propose an iterative procedure to compute q^. Using our procedure, we critically analyze some already conducted and some hypothetical experiments and show how q^ is influenced by the NOB effects. |
BibTeX:
@article{Shishkina.Weiss.ea2016, author = {Shishkina, O. and Weiss, S. and Bodenschatz, E.}, title = {Conductive heat flux in measurements of the Nusselt number in turbulent Rayleigh-Bénard convection}, journal = {Phys. Rev. Fluids}, month = {October}, year = {2016}, volume = {1}, number = {6}, pages = {062301(R)}, doi = {10.1103/PhysRevFluids.1.062301},, url = {http://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.1.062301} } |
Negrete, J., Pumir, A., Hsu, H.-F., Westendorf, C., Tarantola, M., Beta, C. and Bodenschatz, E., "Noisy Oscillations in the Actin Cytoskeleton of Chemotactic Amoeba", Phys. Rev. Lett., September 2016, Vol. 117(14), 148102 pp. |
Abstract: Biological systems with their complex biochemical networks are known to be intrinsically noisy. Here we investigate the dynamics of actin polymerization of amoeboid cells, which are close to the onset of oscillations. We show that the large phenotypic variability in the polymerization dynamics can be accurately captured by a generic nonlinear oscillator model in the presence of noise. We determine the relative role of the noise with a single dimensionless, experimentally accessible parameter, thus providing a quantitative description of the variability in a population of cells. Our approach, which rests on a generic description of a system close to a Hopf bifurcation and includes the effect of noise, can characterize the dynamics of a large class of noisy systems close to an oscillatory instability. |
BibTeX:
@article{Negrete.Pumir.ea2016, author = {Negrete, J. and Pumir, A. and Hsu, H.-F. and Westendorf, C. and Tarantola, M. and Beta, C. and Bodenschatz, E.}, title = {Noisy Oscillations in the Actin Cytoskeleton of Chemotactic Amoeba}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2016}, volume = {117}, number = {14}, pages = {148102}, doi = {10.1103/PhysRevLett.117.148102},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.148102} } |
Pumir, A., Xu, H. and Siggia, E., "Small-scale anisotropy in turbulent boundary layers", J. Fluid Mech., August 2016, Vol. 804, 5 pp. |
Abstract: In a channel flow, the velocity fluctuations are inhomogeneous and anisotropic. Yet, the small-scale properties of the flow are expected to behave in an isotropic manner in the very-large-Reynolds-number limit. We consider the statistical properties of small-scale velocity fluctuations in a turbulent channel flow at moderately high Reynolds number (Reô 1000), using the Johns Hopkins University Turbulence Database. Away from the wall, in the logarithmic layer, the skewness of the normal derivative of the streamwise velocity fluctuation is approximately constant, of order 1, while the Reynolds number based on the Taylor scale is Rë 150. This defines a small-scale anisotropy that is stronger than in turbulent homogeneous shear flows at comparable values of Rë. In contrast, the vorticity-strain correlations that characterize homogeneous isotropic turbulence are nearly unchanged in channel flow even though they do vary with distance from the wall with an exponent that can be inferred from the local dissipation. Our results demonstrate that the statistical properties of the fluctuating velocity gradient in turbulent channel flow are characterized, on one hand, by observables that are insensitive to the anisotropy, and behave as in homogeneous isotropic flows, and on the other hand by quantities that are much more sensitive to the anisotropy. How this seemingly contradictory situation emerges from the simultaneous action of the flux of energy to small scales and the transport of momentum away from the wall remains to be elucidated. |
BibTeX:
@article{Pumir.Xu.ea2016a, author = {Pumir, A. and Xu, H. and Siggia, E.D.}, title = {Small-scale anisotropy in turbulent boundary layers}, journal = {J. Fluid Mech.}, month = {August}, year = {2016}, volume = {804}, pages = {5}, doi = {10.1017/jfm.2016.529},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/small-scale-anisotropy-in-turbulent-boundary-layers/099DC1792A7D0021DFDC2D0764F1FC70#} } |
Faubel, R., Westendorf, C., Bodenschatz, E. and Eichele, G., "Cilia-based flow network in the brain ventricles", Science, July 2016, Vol. 353(6295), 176 pp. |
Abstract: Cerebrospinal fluid conveys many physiologically important signaling factors through the ventricular cavities of the brain. We investigated the transport of cerebrospinal fluid in the third ventricle of the mouse brain and discovered a highly organized pattern of cilia modules, which collectively give rise to a network of fluid flows that allows for precise transport within this ventricle. We also discovered a cilia-based switch that reliably and periodically alters the flow pattern so as to create a dynamic subdivision that may control substance distribution in the third ventricle. Complex flow patterns were also present in the third ventricles of rats and pigs. Our work suggests that ciliated epithelia can generate and maintain complex, spatiotemporally regulated flow networks. |
BibTeX:
@article{Faubel.Westendorf.ea2016, author = {Faubel, R. and Westendorf, C. and Bodenschatz, E. and Eichele, G.}, title = {Cilia-based flow network in the brain ventricles}, journal = {Science}, month = {July}, year = {2016}, volume = {353}, number = {6295}, pages = {176}, doi = {10.1126/science.aae0450},, url = {http://science.sciencemag.org/content/353/6295/176} } |
Yan, W., Wu, J., Yang, S. and Wang, Y., "Numerical investigation on characteristic flow regions for three staggered stationary circular cylinders", European Journal of Mechanics B/Fluids, July 2016, Vol. 60, 48 pp. |
Abstract: In this work, the characteristic flow regions for three stationary circular cylinders were numerically investigated by the multiple-relaxation-time (MRT) based lattice Boltzmann method (LBM). The immersed boundary method (IBM) was employed to handle the solid boundary of cylinders to account for the fluid–solid interaction. The cylinders were arranged in a staggered configuration, which means that one cylinder was placed in front of the others with side-by-side arrangement. The calculations were carried out at different spacing ratios T/DT/D (varying from 1 to 10) and fixed spacing ratio S/D=3S/D=3 with a constant Reynolds number Re=200Re=200, which represents a typical unsteady laminar flow. Here, DD is the diameter of the cylinders, TT is the spacing between the centers of two downstream cylinders, and SS is the distance between the centers of the upstream cylinder and downstream cylinders. The experiments based on the laser-induced fluorescence (LIF) flow visualization were performed to verify the reliability of simulation results. The results indicated that the spacing ratio T/DT/D has a significant influence on the wake structures. Two different characteristic steady and unsteady flow regions behind the upstream cylinder were observed. The characteristic steady flow occurs at the regions of 1?T/D?1.21?T/D?1.2 and 2.5?T/D?3.12.5?T/D?3.1, and the characteristic unsteady flow happens at the regions of 1.3?T/D?2.41.3?T/D?2.4 and 3.2?T/D?103.2?T/D?10. The present results would be helpful for designing multiple piers in the practical application. |
BibTeX:
@article{Yan.Wu.ea2016, author = {Yan, W. and Wu, J. and Yang, S. and Wang, Y.}, title = {Numerical investigation on characteristic flow regions for three staggered stationary circular cylinders}, journal = {European Journal of Mechanics B/Fluids}, month = {July}, year = {2016}, volume = {60}, pages = {48}, doi = {10.1016/j.euromechflu.2016.07.006},, url = {http://www.sciencedirect.com/science/article/pii/S0997754615304027} } |
Schütz, S. and Bodenschatz, E., "Two-particle dispersion in weakly turbulent thermal convection", New J. Phys., June 2016, Vol. 18, 065007 pp. |
Abstract: We present results from a numerical study of particle dispersion in the weakly nonlinear regime of Rayleigh-Bénard convection of a fluid with Prandtl number around unity, where bi-stability between ideal straight convection rolls and weak turbulence in the form of spiral defect chaos exists. While Lagrangian pair statistics has become a common tool for studying fully developed turbulent flows at high Reynolds numbers, we show that key characteristics of mass transport can also be found in convection systems that show no or weak turbulence. Specifically, for short times, we find an interval of t 3-scaling of pair dispersion, which we explain quantitatively with the interplay of advection and diffusion. For long times we observe diffusion-like dispersion of particles that becomes independent of the individual particles' stochastic movements. The spreading rate is found to depend on the degree of spatio-temporal chaos. |
BibTeX:
@article{Schuetz.Bodenschatz2016, author = {Schütz, S. and Bodenschatz, E.}, title = {Two-particle dispersion in weakly turbulent thermal convection}, journal = {New J. Phys.}, month = {June}, year = {2016}, volume = {18}, pages = {065007}, doi = {10.1088/1367-2630/18/6/065007},, url = {http://iopscience.iop.org/article/10.1088/1367-2630/18/6/065007/pdf} } |
Barboza, R., Bortolozzo, U., Clerc, M. G., Davila, J. D., Kowalczyk, M., Resodori, S. and Vidal-Henriquez, E., "Light-matter interaction induces a shadow vortex", Phys. Rev. E, May 2016, Vol. 93(5), 050201(R) pp. |
Abstract: By sending a light beam on a homeotropic nematic liquid-crystal cell subjected to a voltage with a photosensitive wall, a stable matter vortex can be induced at the center of the beam. When the applied voltage is decreased, the vortex disappears from the illuminated region; however, the system shows a stationary molecular texture. Based on a forced Ginzburg-Landau amplitude equation, we show that the vortex with a core of exponentially suppressed amplitude always remains in a shadow region below instability threshold and that the observed texture is induced by its phase distribution. This is a different type of vortex phase singularity solution. Numerical simulations and experimental observations show a quite fair agreement. |
BibTeX:
@article{Barboza.Bortolozzo.ea2016, author = {Barboza, R. and Bortolozzo, U. and Clerc, M. G. and Davila, J. D. and Kowalczyk, M. and Resodori, S. and Vidal-Henriquez, E.}, title = {Light-matter interaction induces a shadow vortex}, journal = {Phys. Rev. E}, month = {May}, year = {2016}, volume = {93}, number = {5}, pages = {050201(R)}, doi = {10.1103/PhysRevE.93.050201},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.050201} } |
Shishkina, O., "Momentum and heat transport scalings in laminar vertical convection", Phys. Rev. E, May 2016, Vol. 93(5), 051102(R) pp. |
Abstract: We derive the dependence of the Reynolds number Re and the Nusselt number Nu on the Rayleigh number Ra and the Prandtl number Pr in laminar vertical convection (VC), where a fluid is confined between two differently heated isothermal vertical walls. The boundary layer equations in laminar VC yield two limiting scaling regimes: Nu?Pr1/4Ra1/4, Re?Pr?1/2Ra1/2 for Pr?1 and Nu?Pr0Ra1/4, Re?Pr?1Ra1/2 for Pr?1. These theoretical results are in excellent agreement with direct numerical simulations for Ra from 105 to 1010 and Pr from 10?2 to 30. The transition between the regimes takes place for Pr around 10?1. |
BibTeX:
@article{Shishkina2016, author = {Shishkina, O.}, title = {Momentum and heat transport scalings in laminar vertical convection}, journal = {Phys. Rev. E}, month = {May}, year = {2016}, volume = {93}, number = {5}, pages = {051102(R)}, doi = {10.1103/PhysRevE.93.051102},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.051102} } |
Bai, X.-D., Zhang, W., Guo, A.-X. and Wang, Y., "The flip-flopping wake pattern behind two side-by-side circular cylinders: A global stability analysis", Phys. Fluids, April 2016, Vol. 28, 044102 pp. |
Abstract: A global stabilityanalysis is performed for the flip-flopping wake pattern behind two side-by-side cylinders with emphasis on the unstable vorticity field. The combination of direct numerical simulation with the state-of-art lattice Boltzmann method and dynamic mode decomposition is used to analyse such wake pattern for the first time. The vorticity mode of the secondary instability is extracted from the flow. Such mode is found to be symmetrical with respect to the geometric axis of symmetry. Furthermore, a new scenario is found for the high order harmonics that there is a pair of two tertiary modes as a result of nonlinear interaction between the mode related to the secondary instability and the global mode of the in-phase synchronized vortex shedding base flow. Besides, the reason for the Fourier spectra of the lift on the two cylinders being the same is also illustrated for this case. |
BibTeX:
@article{Bai.Zhang.ea2016, author = {Bai, X.-D. and Zhang, W. and Guo, A.-X. and Wang, Y.}, title = {The flip-flopping wake pattern behind two side-by-side circular cylinders: A global stability analysis}, journal = {Phys. Fluids}, month = {April}, year = {2016}, volume = {28}, pages = {044102}, doi = {10.1063/1.4944685},, url = {http://scitation.aip.org/content/aip/journal/pof2/28/4/10.1063/1.4944685} } |
Eber, N., Salamon, P., Fekete, B. A., Karapinar, R., Krekhov, A. and Buka, A., "Suppression of spatially periodic patterns by dc voltage", Physical Review E, April 2016, Vol. 93, 042701 pp. |
Abstract: The effect of superposed dc and ac applied voltages on two types of spatially periodic instabilities in nematic liquid crystals, flexoelectric domains (FD), and electroconvection (EC) was studied. The onset characteristics, threshold voltages, and critical wave vectors were determined. We found that in general the superposition of driving with different time symmetries inhibits the pattern forming mechanisms for FD and EC as well. As a consequence, the onset extends to much higher voltages than the individual dc or ac thresholds. A dc-bias-induced reduction of the crossover frequency from the conductive to the dielectric EC regimes and a peculiar transition between two types of flexodomains with different wavelengths were detected. Direct measurements of the change of the electrical conductivity and its anisotropy, induced by the applied dc voltage component, showed that the dc bias substantially affects both parameters. Taking into account the experimentally detected variations of the conductivity in the linear stability analysis of the underlying nematohydrodynamic equations, a qualitative agreement with the experimental findings on the onset behavior of spatially periodic instabilities was obtained. |
BibTeX:
@article{Krekhov.Dressel.ea2015a, author = {Eber, N. and Salamon, P. and Fekete, B. A. and Karapinar, R. and Krekhov, A. and Buka, A.}, title = {Suppression of spatially periodic patterns by dc voltage}, journal = {Physical Review E}, month = {April}, year = {2016}, volume = {93}, pages = {042701}, doi = {10.1103/PhysRevE.93.042701},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.042701} } |
Weiss, S., Wei, P. and Ahlers, G., "Heat-transport enhancement in rotating turbulent Rayleigh-Bénard convection", Phys. Rev, April 2016, Vol. 93, 043102 pp. |
Abstract: We present new Nusselt-number (Nu) measurements for slowly rotating turbulent thermal convection in cylindrical samples with aspect ratio Ã=1.00 and provide a comprehensive correlation of all available data for that Ã. In the experiment compressed gasses (nitrogen and sulfur hexafluride) as well as the fluorocarbon C6F14 (3M Fluorinert FC72) and isopropanol were used as the convecting fluids. The data span the Prandtl-number (Pr) range 0.74 |
BibTeX:
@article{Weiss.Wei.ea2016, author = {Weiss, S. and Wei, P. and Ahlers, G.}, title = {Heat-transport enhancement in rotating turbulent Rayleigh-Bénard convection}, journal = {Phys. Rev}, month = {April}, year = {2016}, volume = {93}, pages = {043102}, doi = {10.1103/PhysRevE.93.043102},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.043102} } |
Pumir, A., Xu, H., Bodenschatz, E. and Grauer, R., "Single-Particle Motion and Vortex Stretching in Three-Dimensional Turbulent Flows", Phys. Rev. Lett., March 2016, Vol. 116(12), 124502 pp. |
Abstract: Three-dimensional turbulent flows are characterized by a flux of energy from large to small scales, which breaks the time reversal symmetry. The motion of tracer particles, which tend to lose energy faster than they gain it, is also irreversible. Here, we connect the time irreversibility in the motion of single tracers with vortex stretching and thus with the generation of the smallest scales. |
BibTeX:
@article{Pumir.Xu.ea2016, author = {Pumir, A. and Xu, H. and Bodenschatz, E. and Grauer, R.}, title = {Single-Particle Motion and Vortex Stretching in Three-Dimensional Turbulent Flows}, journal = {Phys. Rev. Lett.}, month = {March}, year = {2016}, volume = {116}, number = {12}, pages = {124502}, doi = {10.1103/PhysRevLett.116.124502},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.124502} } |
Sun, D.-K., Wang, Y., Dong, A.-P. and Sun, B.-D., "A three-dimensional quantitative study on the hydrodynamic focusing of particles with the immersed boundary - Lattice Boltzmann method", International Journal of Heat and Mass Transfer, March 2016, Vol. 94, 306 pp. |
Abstract: Hydrodynamic focusing of particles is numerically studied by the immersed boundary – lattice Boltzmann method. Particle focusing entropy is proposed to quantitatively characterize processing performance and final results of hydrodynamic focusing. Simulations of hydrodynamic focusing in several straight microchannels are carried out to evaluate versatility of the focusing entropy. Time evolutions of focusing entropies and particle trajectories are analyzed contrastively. The results demonstrate that the focusing entropy is an effective scale to measure particles ordering degree and hydrodynamic focusing performance. Higher ordering degree determines lower focusing entropy, which indicates better focusing performance. Channel cross section, particle rigidness and channel Reynolds number are three major factors influencing focusing dynamics and final results. Rectangular microchannel is more advantageous than circular and square ones in hydrodynamic focusing. Particles of different rigidness in rectangular microchannel can be separated significantly with the flow mediation. Increasing channel Reynolds numbers can lead to higher efficiency and better focusing performance. |
BibTeX:
@article{Sun.Wang.ea2016, author = {Sun, D.-K. and Wang, Y. and Dong, A.-P. and Sun, B.-D.}, title = {A three-dimensional quantitative study on the hydrodynamic focusing of particles with the immersed boundary - Lattice Boltzmann method}, journal = {International Journal of Heat and Mass Transfer}, month = {March}, year = {2016}, volume = {94}, pages = {306}, doi = {10.1016/j.ijheatmasstransfer.2015.11.012},, url = {http://www.sciencedirect.com/science/article/pii/S0017931015307304} } |
Di Lorenzo, F., "Scale-dependent Response of Fluid Turbulence under Variation of the Large-scale Forcing", February 2016 |
Abstract: In this work, an experiment to measure the temporal evolution of energy transfer at different scales in a turbulent flow that was subject to a perturbation of the energy injection is described. Two types of experiments were performed. In the first type a step-function-like increase of the energy input was used to force the turbulent flow. In the second case the forcing of a fully developed turbulent flow was switched off to observe the decay of the turbulence. Experiments investigating the scale dependent response of a turbulent flow to a perturbation of the large-scale forcing have, to the best knowledge of the author, not been done so far. This is due to the complexity of the endeavor and the limitations of state-of-the-art measurement techniques. The approach to overcome these limitations and the hardware developed for this purpose is also documented in this thesis. |
BibTeX:
@phdthesis{DiLorenzo2016, author = {Di Lorenzo, F.}, title = {Scale-dependent Response of Fluid Turbulence under Variation of the Large-scale Forcing}, month = {February}, year = {2016},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-86B1-C} } |
He, X., Bodenschatz, E. and Ahlers, G., "Azimuthal diffusion of the large-scale-circulation plane, and absence of significant non-Boussinesq effects, in turbulent convection near the ultimate-state transition", J. Fluid Mech., February 2016, Vol. 791, R3 pp. |
Abstract: We present measurements of the orientation è0 and temperature amplitude ä of the large-scale circulation in a cylindrical sample of turbulent Rayleigh–B?nard convection (RBC) with aspect ratio Ã?D/L=1.00 (D and L are the diameter and height respectively) and for the Prandtl number Pr?0.8. The results for è0 revealed a preferred orientation with up-flow in the west, consistent with a broken azimuthal invariance due to the Earth’s Coriolis force (see Brown & Ahlers (Phys. Fluids, vol. 18, 2006, 125108)). They yielded the azimuthal diffusivity Dè and a corresponding Reynolds number Reè for Rayleigh numbers over the range 2?1012?Ra?1.5?1014. In the classical state (Ra?2?1013) the results were consistent with the measurements by Brown & Ahlers (J. Fluid Mech., vol. 568, 2006, pp. 351–386) for Ra?1011 and Pr=4.38, which gave Reè?Ra0.28, and with the Prandtl-number dependence Reè?Pr?1.2 as found previously also for the velocity-fluctuation Reynolds number ReV (He et al., New J. Phys., vol. 17, 2015, 063028). At larger Ra the data for Reè(Ra) revealed a transition to a new state, known as the ‘ultimate’ state, which was first seen in the Nusselt number Nu(Ra) and in ReV(Ra) at Ra?1?2?1013 and Ra?2?8?1013. In the ultimate state we found Reè?Ra0.40±0.03. Recently, Skrbek & Urban (J. Fluid Mech., vol. 785, 2015, pp. 270–282) claimed that non-Oberbeck–Boussinesq effects on the Nusselt and Reynolds numbers of turbulent RBC may have been interpreted erroneously as a transition to a new state. We demonstrate that their reasoning is incorrect and that the transition observed in the G?ttingen experiments and discussed in the present paper is indeed to a new state of RBC referred to as ‘ultimate’. |
BibTeX:
@article{He.Bodenschatz.ea2016, author = {He, X. and Bodenschatz, E. and Ahlers, G.}, title = {Azimuthal diffusion of the large-scale-circulation plane, and absence of significant non-Boussinesq effects, in turbulent convection near the ultimate-state transition}, journal = {J. Fluid Mech.}, month = {February}, year = {2016}, volume = {791}, pages = {R3}, doi = {10.1017/jfm.2016.56},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10193782&fulltextType=RA&fileId=S0022112016000562} } |
Shishkina, O., Grossmann, S. and Lohse, D., "Heat and momentum transport scalings in horizontal convection", Geophys. Res. Lett., February 2016, Vol. 43, 1219 pp. |
Abstract: In a horizontal convection (HC) system heat is supplied and removed exclusively through a single, top, or bottom, surface of a fluid layer. It is commonly agreed that in the studied Rayleigh number (Ra) range, the convective heat transport, measured by the Nusselt number, follows the Rossby (1965) scaling, which is based on the assumptions that the HC flows are laminar and determined by their boundary layers. However, the universality of this scaling is questionable, as these flows are observed to become more turbulent with increasing Ra. Here we propose a theoretical model for heat and momentum transport scalings with Ra, which is based on the Grossmann and Lohse (2000) ideas, applied to HC flows. The obtained multiple scaling regimes include in particular the Rossby scaling and the ultimate scaling by Siggers et al. (2004). Our results have bearing on the understanding of the convective processes in many geophysical systems and engineering applications. |
BibTeX:
@article{Shishkina.Grossmann.ea2016, author = {Shishkina, O. and Grossmann, S. and Lohse, D.}, title = {Heat and momentum transport scalings in horizontal convection}, journal = {Geophys. Res. Lett.}, month = {February}, year = {2016}, volume = {43}, pages = {1219}, doi = {10.1002/2015GL067003},, url = {http://onlinelibrary.wiley.com/doi/10.1002/2015GL067003/full} } |
Shishkina, O. and Horn, S., "Thermal convection in inclined cylindrical containers", J. Fluid Mech., February 2016, Vol. 790, R3 pp. |
Abstract: By means of direct numerical simulations (DNS) we investigate the effect of a tilt angle , 06 6p=2, of a Rayleigh–B?nard convection (RBC) cell of aspect ratio 1, on the Nusselt number Nu and Reynolds number Re. The considered Rayleigh numbers Ra range from 106 to 108, the Prandtl numbers range from 0.1 to 100 and the total number of the studied cases is 108. We show that the Nu ./=Nu.0/ dependence is not universal and is strongly influenced by a combination of Ra and Pr.
Thus, with a small inclination of the RBC cell, the Nusselt number can decrease or increase, compared to that in the RBC case, for large and small Pr, respectively. A slight cell tilt may not only stabilize the plane of the large-scale circulation (LSC) but can also enforce an LSC for cases when the preferred state in the perfect RBC case is not an LSC but a more complicated multiple-roll state. Close to D p=2, Nu and Re decrease with increasing in all considered cases. Generally, the Nu./=Nu.0/ dependence is a complicated, non-monotonic function of . |
BibTeX:
@article{Shishkina.Horn2016, author = {Shishkina, O. and Horn, S.}, title = {Thermal convection in inclined cylindrical containers}, journal = {J. Fluid Mech.}, month = {February}, year = {2016}, volume = {790}, pages = {R3}, doi = {10.1017/jfm.2016.55},, url = {http://journals.cambridge.org/download.php?file=%2FFLM%2FFLM790%2FS0022112016000550a.pdf&code=36e97ccd95fa88ecd990e75cf703ee45} } |
Leonhardt, H., Gerhardt, M., Höppner, N., Krüger, K., Tarantola, M. and Beta, C., "Cell-substrate impedance fluctuations of single amoeboid cells encode cell-shape and cell-substrate adhesion dynamics", Phys. Rev. E, January 2016, Vol. 93, 012414 pp. |
Abstract: We show systematic electrical impedance measurements of single motile cells on microelectrodes. Wild-type cells and mutant strains were studied that differ in their cell-substrate adhesion strength. We recorded the projected cell area by time-lapse microscopy and observed irregular oscillations of the cell shape. These oscillations were correlated with long-term variations in the impedance signal. Superposed to these long-term trends, we observed fluctuations in the impedance signal. Their magnitude clearly correlated with the adhesion strength, suggesting that strongly adherent cells display more dynamic cell-substrate interactions. |
BibTeX:
@article{Leonhardt.Gerhardt.ea, author = {Leonhardt, H. and Gerhardt, M. and Höppner, N. and Krüger, K.. and Tarantola, M. and Beta, C.}, title = {Cell-substrate impedance fluctuations of single amoeboid cells encode cell-shape and cell-substrate adhesion dynamics}, journal = {Phys. Rev. E}, month = {January}, year = {2016}, volume = {93}, pages = {012414}, doi = {10.1103/PhysRevE.93.012414},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.012414#fulltext#fulltext} } |
Shishkina, O. and Wagner, S., "Prandtl-Number Dependence of Heat Transport in Laminar Horizontal Convection", Phys. Rev. Lett., January 2016, Vol. 116, 024302 pp. |
Abstract: We report the Prandtl-number (Pr) and Rayleigh-number (Ra) dependencies of the Reynolds number (Re) and mean convective heat transport, measured by the Nusselt number (Nu), in horizontal convection (HC) systems, where the heat supply and removal are provided exclusively through a lower horizontal surface of a fluid layer. For laminar HC, we find that Re Ra2/5Pr?4/5, Nu Ra1/5Pr1/10 with a transition to Re Ra1/2Pr?1, Nu Ra1/4Pr0 for large Pr. The results are based on direct numerical simulations for Ra from 3?108 to 5?1010 and Pr from 0.05 to 50 and are explained by applying the Grossmann-Lohse approach [J. Fluid Mech. 407, 27 (2000)] transferred from the case of Rayleigh-Bénard convection to the case of laminar HC. |
BibTeX:
@article{Shishkina.Wagner2016, author = {Shishkina, O. and Wagner, S.}, title = {Prandtl-Number Dependence of Heat Transport in Laminar Horizontal Convection}, journal = {Phys. Rev. Lett.}, month = {January}, year = {2016}, volume = {116}, pages = {024302}, doi = {10.1103/PhysRevLett.116.024302},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.024302} } |
Xu, H., Pumir, A. and Bodenschatz, E., "Lagrangian view of time irreversibility of fluid turbulence", Science China, January 2016, Vol. 59(1), 614702 pp. |
Abstract: A turbulent flow is maintained by an external supply of kinetic energy, which is eventually dissipated into heat at steep velocity gradients. The scale at which energy is supplied greatly differs from the scale at which energy is dissipated, the more so as the turbulent intensity (the Reynolds number) is larger. The resulting energy flux over the range of scales, intermediate between energy injection and dissipation, acts as a source of time irreversibility. As it is now possible to follow accurately fluid particles in a turbulent flow field, both from laboratory experiments and from numerical simulations, a natural question arises: how do we detect time irreversibility from these Lagrangian data? Here we discuss recent results concerning this problem. For Lagrangian statistics involving more than one fluid particle, the distance between fluid particles introduces an intrinsic length scale into the problem. The evolution of quantities dependent on the relative motion between these fluid particles, including the kinetic energy in the relative motion, or the configuration of an initially isotropic structure can be related to the equal-time correlation functions of the velocity field, and is therefore sensitive to the energy flux through scales, hence to the irreversibility of the flow. In contrast, for singleparticle Lagrangian statistics, the most often studied velocity structure functions cannot distinguish the “arrow of time”. Recent observations from experimental and numerical simulation data, however, show that the change of kinetic energy following the particle motion, is sensitive to time-reversal. We end the survey with a brief discussion of the implication of this line of work. |
BibTeX:
@article{Xu.Pumir.ea2016, author = {Xu, H. and Pumir, A. and Bodenschatz, E.}, title = {Lagrangian view of time irreversibility of fluid turbulence}, journal = {Science China}, month = {January}, year = {2016}, volume = {59}, number = {1}, pages = {614702}, doi = {10.1007/s11433-015-5736-x},, url = {http://link.springer.com/article/10.1007/s11433-015-5736-x} } |
Krekhov, A., Dressel, B., Pesch, W. and Delev V. Batyrshin, E., "Spatiotemporal complexity of electroconvection patterns in nematic liquid crystals", Phys. Rev. E, December 2015, Vol. 92(6), 062510 pp. |
Abstract: We investigate a number of complex patterns driven by the electroconvection instability in a planarly aligned layer of a nematic liquid crystal. They are traced back to various secondary instabilities of the ideal roll patterns bifurcating at onset of convection, whereby the basic nematohydrodynamic equations are solved by common Galerkin expansion methods. Alternatively these equations are systematically approximated by a set of coupled amplitude equations. They describe slow modulations of the convection roll amplitudes, which are coupled to a flow field component with finite vorticity perpendicular to the layer and to a quasihomogeneous in-plane rotation of the director. It is demonstrated that the Galerkin stability diagram of the convection rolls is well reproduced by the corresponding one based on the amplitude equations. The main purpose of the paper is, however, to demonstrate that their direct numerical simulations match surprisingly well new experiments, which serves as a convincing test of our theoretical approach. |
BibTeX:
@article{Krekhov.Dressel.ea2015, author = {Krekhov, A. and Dressel, B. and Pesch, W. and Delev, V. Batyrshin, E.}, title = {Spatiotemporal complexity of electroconvection patterns in nematic liquid crystals}, journal = {Phys. Rev. E}, month = {December}, year = {2015}, volume = {92}, number = {6}, pages = {062510}, doi = {10.1103/PhysRevE.92.062510},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.92.062510} } |
Sinhuber, M., "On the Scales of Turbulent Motion at High Reynolds Numbers", December 2015 |
Abstract: Turbulence is a physical state of a fluid far from equilibrium. In turbulent flows, a huge number of degrees of freedom is excited and a wide range of interacting scales determines the flow characteristics. Turbulent flows are nonlinear and non-local. They exhibit chaotic spatial and temporal dynamics and extreme events are likely to occur. Up to today, there is no unified theory of turbulence, very few exact predictions from the governing equations are available and the precise predictability of the behavior of turbulent flows is limited. Additionally, it is not known exactly, how the flow quantities depend on the turbulent flow’s vigorousness that is given by the so-called Reynolds number. In this thesis, high-Reynolds number turbulence and its dependencies on the Reynolds number are investigated by the means of hot-wire measurements in the Variable Density Turbulence Tunnel at the Max-Planck-Institute for Dynamics and Self-Organization in G?ttingen. The Reynolds number dependence of the decay exponent of freely decaying turbulence is found to be consistent with Saffmans prediction. Furthermore, with extremely long datasets, the statistical properties of turbulence in the inertial range are investigated in great detail, finding deviations from the expected scaling behavior. |
BibTeX:
@phdthesis{Sinhuber2015, author = {Sinhuber, M.}, title = {On the Scales of Turbulent Motion at High Reynolds Numbers}, month = {December}, year = {2015},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-8662-F} } |
Negrete, J., "Fluctuations and Oscillatory Instabilities of Intracellular Fiber networks", November 2015 |
Abstract: Biological systems with their complex biochemical networks are known to be intrinsically noisy. The interplay between noise and dynamical behavior is particularly relevant in the case of chemotactic amoeboid cells as their cytoskeleton operates close to an oscillatory instability. Here, we investigate the oscillatory dynamics in the actin system of chemotactic amoeboid cells. We show that the large phenotypic variability in the polymerization dynamics can be accurately captured by a generic nonlinear oscillator model, in the presence of noise. The relative role of the noise is fully determined by a single dimensionless parameter, experimentally measurable, and whose distribution completely characterizes the possible cellular behavior. We find that cells operate either below or above the threshold of self-oscillation, always in a regime where noise plays a very substantial role. To test the limits of this phenomenological description, we perturbed experimentally the cytoskeletal dynamics by a short chemoattractant pulse and measured the spatio-temporal response of filamentous actin reporter, LimE, and depolymerization regulators Coronin1 and Aip1. After pulsing, we observed self oscillating cells to relax back to their oscillatory state after a noisy transient. Particularly long transients were observed for cells initially displaying highly correlated oscillations. The observation of a slow recovery time of the actin polymerizing network provides a link to the long times scales, characteristic of chemotactic cell motility. In the second part of this work, we have characterized the response of LimE, Aip1, and Coronin to cAMP in non oscillating cells. We have used a proposed method that transforms the observed time series into symbolic dynamics, that gives partial information on the interactions between these proteins. We tested the predictions by studying the LimE response in mutant cells that either lacked Aip1 or Coronin. Finally, a model is proposed where Aip1 and Coronin synergizes to control actin polymerization. |
BibTeX:
@phdthesis{Negrete2015, author = {Negrete, J.}, title = {Fluctuations and Oscillatory Instabilities of Intracellular Fiber networks}, month = {November}, year = {2015},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0023-9683-E} } |
Winkel, F., "On Turbulent Rayleigh-Bénard Convection in a Two-Phase Binary Gas Mixture", November 2015 |
Abstract: In this thesis an attempt is made to generate cloud patterns in a laboratory scale experiment. A two-phase binary gas mixture is employed as a physical model system. The fluid mixture is composed of a condensable gas which forms a liquid and a vapor phase and a noncondensable gas which serves as a background or carrier gas. The fluid mixture is confined between a bottom and a top plate. If the fluid mixture is exposed to a constant temperature difference, two intriguing phenomena can be observed. First a film condensation sets in at the cold top plate that results in the formation of a very regular hexagonal droplet pattern. The temporal evolution of the droplet pattern is quantified and it is shown that a stable mass flux is essential in order to the maintain the hexagonal symmetry of the droplet patten. Second cloud-like patterns occur in a thin layer above the liquid-vapor interface. The dynamics of the cloud-like patterns reveal the turbulent flow inside the gaseous phase. An area-perimeter analysis of the cloud-like patterns results in a fractal dimension that is similar to the one obtained by the fractal analysis of two-dimensional cloud and rain areas in satellite and radar data. This thesis is meant as a proof of concept which is why most of the results are still qualitative. However, a physical model system is presented that is appropriate in order to study the dynamics of cloud-like patterns in a turbulent Rayleigh-Bénard convection experiment. The origin of the cloud-like patterns is still a matter of debate. Therefore further experiments that could reveal the nature of these patterns must be performed. |
BibTeX:
@phdthesis{Winkel2015, author = {Winkel, F.}, title = {On Turbulent Rayleigh-Bénard Convection in a Two-Phase Binary Gas Mixture}, month = {November}, year = {2015},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-8645-2} } |
Bodenschatz, E., "Clouds resolved", Science, October 2015, Vol. 350(6256), 40-41 pp. |
Abstract: The pillowing structure and filamentary detail of clouds has inspired many paintings as well as associations to down pillows. Turbulence is at the source of this beauty. It affects aerosol-cloud droplet interaction, cloud particle collisions and merging, and entrainment and mixing of environmental air with clouds (1, 2). These microphysical processes are important for predicting weather and climate (3). Yet it has remained very difficult to observe clouds at the temporal and spatial scales required to gain understanding of these processes. On page 87 of this issue, Beals et al. (4) show that the filamentary structure of entrainment and mixing reaches to the centimeter scale in a cloud. |
BibTeX:
@article{Bodenschatz2015, author = {Bodenschatz, E.}, title = {Clouds resolved}, journal = {Science}, month = {October}, year = {2015}, volume = {350}, number = {6256}, pages = {40-41}, doi = {10.1126/science.aad1386},, url = {http://www.sciencemag.org/content/350/6256/40.summary?sid=cb42e5f4-2ef2-44b5-96ba-c78ad569f4d9} } |
Kaoui, B., Guckenberger, A., Krekhov, A., Ziebert, F. and Zimmermann, W., "Coexistence of stable branched patterns in anisotropic inhomogeneous systems", New J. Phys., October 2015, Vol. 17(10), 103015 pp. |
Abstract: A new class of pattern forming systems is identified and investigated: anisotropic systems that are spatially inhomogeneous along the direction perpendicular to the preferred one. By studying the generic amplitude equation of this new class and a model equation, we show that branched stripe patterns emerge, which for a given parameter set are stable within a band of different wave numbers and different numbers of branching points (defects). Moreover, the branched patterns and unbranched ones (defect-free stripes) coexist over a finite parameter range. We propose two systems where this generic scenario can be found experimentally, surface wrinkling on elastic substrates and electroconvection in nematic liquid crystals, and relate them to the findings from the amplitude equation. |
BibTeX:
@article{Kaoui.Guckenberger.ea2015, author = {Kaoui, B. and Guckenberger, A. and Krekhov, A. and Ziebert, F. and Zimmermann, W.}, title = {Coexistence of stable branched patterns in anisotropic inhomogeneous systems}, journal = {New J. Phys.}, month = {October}, year = {2015}, volume = {17}, number = {10}, pages = {103015}, doi = {10.1088/1367-2630/17/10/103015},, url = {http://iopscience.iop.org/article/10.1088/1367-2630/17/10/103015} } |
Gholami, A., Zykov, V., Steinbock, O. and Bodenschatz, E., "Flow-driven two-dimensional waves in colonies of Dictyostelium discoideum", New J. Phys., September 2015, Vol. 17, 093040 pp. |
Abstract: Dictyostelium discoideum (D.d.) is a valuable model organism to study self-organization and pattern formation in biology. Recently we reported flow-driven waves in experiments with uniformly distributed populations of signaling amobae, D.d., and carried out a theoretical study in a one-dimensional model. In this work, we perform two-dimensional numerical simulations using the well-known Martiel–Golbeter model to study the effect of the flow profile and intrinsic noise on the flow-driven waves. We show that, in the presence of flow, a persistence noise due to spontaneous cell firing events can lead to sustained structures that fill the whole length of the system. We also show that external periodic stimuli of cyclic adenosine monophosphate can induce 1:1 and 2:1 entrainments which are in agreement with our experimental observations. |
BibTeX:
@article{Gholami.Zykov.ea2015, author = {Gholami, A. and Zykov, V. and Steinbock, O. and Bodenschatz, E.}, title = {Flow-driven two-dimensional waves in colonies of Dictyostelium discoideum}, journal = {New J. Phys.}, month = {September}, year = {2015}, volume = {17}, pages = {093040}, doi = {10.1088/1367-2630/17/9/093040},, url = {http://iopscience.iop.org/article/10.1088/1367-2630/17/9/093040/meta} } |
Nobach, H., "LDA-Korrelations- und Spektralschätzung - Ein Zwischenstand", September 2015 |
BibTeX:
@proceedings{Nobach2015b, author = {Nobach, H}, title = {LDA-Korrelations- und Spektralschätzung - Ein Zwischenstand}, month = {September}, year = {2015},, url = {http://www.nambis.de/publications/gala15.html} } |
Nobach, H., "Fuzzy time quantization and local normalization for the direct spectral estimation from laser Doppler velocimetry data", Experiments in Fluids, September 2015, Vol. 56, 182 pp. |
Abstract: An adaptation of the fuzzy slotting method and the local normalization to the direct type of power spectral estimation are given. Using experimentally obtained data, it is shown that the two optional processing methods have equivalent influence on the estimated turbulence spectra, for the two processing types, the direct spectral estimation and the slotting technique. The question about the estimation quality of the fuzzy slotting and the local normalization is not addressed here. However, it is shown that the impact of fuzzy time quantization on the spectral density is that of a low-pass filter of a sinc2 shape. |
BibTeX:
@article{Nobach2015c, author = {Nobach, H}, title = {Fuzzy time quantization and local normalization for the direct spectral estimation from laser Doppler velocimetry data}, journal = {Experiments in Fluids}, month = {September}, year = {2015}, volume = {56}, pages = {182}, doi = {10.1007/s00348-015-2050-3},, url = {http://link.springer.com/article/10.1007/s00348-015-2050-3} } |
Wilkinson, M., Guichardaz, R., Pradas, M. and Pumir, A., "Power-law distributions in noisy dynamical systems", EPL, September 2015, Vol. 111(5), 50005 pp. |
Abstract: We consider a dynamical system which is non-autonomous, has a stable attractor and which is perturbed by an additive noise. We establish that under some quite typical conditions, the intermittent fluctuations from the attractor have a probability distribution with power-law tails. We show that this results from a stochastic cascade of amplification of fluctuations due to transient periods of instability. The exponent of the power-law is interpreted as a negative fractal dimension, and is explicitly determined, using numerics or perturbation expansion, in the case of a model of colloidal particles in one-dimension. |
BibTeX:
@article{Wilkinson.Guichardaz.ea2015, author = {Wilkinson, M. and Guichardaz, R. and Pradas, M. and Pumir, A.}, title = {Power-law distributions in noisy dynamical systems}, journal = {EPL}, month = {September}, year = {2015}, volume = {111}, number = {5}, pages = {50005}, doi = {10.1209/0295-5075/111/50005},, url = {http://iopscience.iop.org/article/10.1209/0295-5075/111/50005/meta} } |
Blum, C., "Curvotaxis and Pattern Formation in the Actin Cortex of Motile Cells", August 2015 |
Abstract: Amoeboid cell migration is a crucial part of life. Neutrophil granulocytes, a kind of phagocytes of the mammalian immune system, migrate from blood vessels through tissue towards spots of inflammation. To find this inflammation, they use a chemical “compass” that contains a system to receive and process a chemical signal that guides the neutrophil to the inflammation by leading it towards higher concentration of a chemoattractant molecule. This process is known as chemotaxis, plays also major role is cancer metastasis. The social amoeba Dictyostelium discoideum (D.d.) is a commonly used model organism to study migration as well as chemotaxis. In this study the cell migration of D.d. was investigated within the concept of chemotaxis as well as regarding the geometrical environment of the cells. Here it was found that cells prefere to migrate along paths of high curvature. Hence this finding was called “Curvotaxis”. The open question of a temporal shift between the signalling molecule Ras-G the actin polymerization and the forming of pseudopods was solved by the finding the Ras-G was visible before actin and the propulsion. |
BibTeX:
@phdthesis{Blum2015, author = {Blum, C.}, title = {Curvotaxis and Pattern Formation in the Actin Cortex of Motile Cells}, month = {August}, year = {2015},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-8667-5} } |
Prabhakaran, P., Winkel, F., Krekhov, A., Nobach, H. and Bodenschatz, E., "MOIST RAYLEIGH-BENARD CONVECTION", August 2015 |
Abstract: We report the observations from turbulent thermal Rayleigh-Benard convection experiment with a two-phase liquid-vapor binary mixture. Evaporation/condensation processes in a turbulent convection are accompanied by the formation of cloud like structures above the liquid-vapor interface. We also found that a liquid film condensation on the underside of the top plate results in regular hexagonal patterns of falling droplets. |
BibTeX:
@proceedings{Prabhakaran.Winkel.ea2015, author = {Prabhakaran, P. and Winkel, F. and Krekhov, A. and Nobach, H and Bodenschatz, E.}, title = {MOIST RAYLEIGH-BENARD CONVECTION}, month = {August}, year = {2015},, url = {http://www.etc15.nl/proceedings/proceedings/display_manuscript/298.htm} } |
Risius, S., Xu, H., Di Lorenzo, F., Xi, H., Siebert, H., Shaw, R. A. and Bodenschatz, E., "Schneefernerhaus as a mountain research station for clouds and turbulence", Atmos. Meas. Tech., August 2015, Vol. 8(8), 3209 pp. |
Abstract: Cloud measurements are usually carried out with airborne campaigns, which are expensive and are limited by temporal duration and weather conditions. Ground based measurements at high-altitude research stations therefore play a complementary role in cloud study. Using the meteorological data (wind speed, direction, temperature, humidity, visibility, etc.) collected by the German Weather Service (DWD) from 2000 to 2012 and turbulence measurements recorded by multiple ultrasonic sensors (sampled at 10 Hz) in 2010, we show that the Umweltforschungsstation Schneefernerhaus (UFS) located just below the peak of Zugspitze in the German Alps, at a height of 2650 m, is a well-suited station for cloud-turbulence research. The wind at UFS is dominantly in the east–west direction and nearly horizontal. During the summer time (July and August) the UFS is immersed in warm clouds about 25% of the time. The clouds are either from convection originating in the valley in the east, or associated with synoptic-scale weather systems typically advected from the west. Air turbulence, as measured from the second and third order velocity structure functions that exhibit well-developed inertial ranges, possesses Taylor microscale Reynolds numbers up to 104, with the most probable value at 3000. In spite of the complex topography, the turbulence appears to be nearly as isotropic as many laboratory flows when evaluated on the so called "Lumley-triangle". |
BibTeX:
@article{Risius.Xu.ea2015, author = {Risius, S. and Xu, H. and Di Lorenzo, F. and Xi, H. and Siebert, H. and Shaw, R. A. and Bodenschatz, E.}, title = {Schneefernerhaus as a mountain research station for clouds and turbulence}, journal = {Atmos. Meas. Tech.}, month = {August}, year = {2015}, volume = {8}, number = {8}, pages = {3209}, doi = {10.5194/amtd-8-541-2015},, url = {http://www.atmos-meas-tech-discuss.net/8/541/2015/amtd-8-541-2015.html} } |
Siebert, H., Shaw, R. A., Ditas, J., Schmeissner, T., Malinowski, S. P., Bodenschatz, E. and Xu, H., "High-resolution measurement of cloud microphysics and turbulence at a mountaintop station", Atmos. Meas. Tech., August 2015, Vol. 8, 3219 pp. |
Abstract: Mountain research stations are advantageous not only for long-term sampling of cloud properties but also for measurements that are prohibitively difficult to perform on airborne platforms due to the large true air speed or adverse factors such as weight and complexity of the equipment necessary. Some cloud–turbulence measurements, especially Lagrangian in nature, fall into this category. We report results from simultaneous, high-resolution and collocated measurements of cloud microphysical and turbulence properties during several warm cloud events at the Umweltforschungsstation Schneefernerhaus (UFS) on Zugspitze in the German Alps. The data gathered were found to be representative of observations made with similar instrumentation in free clouds. The observed turbulence shared all features known for high-Reynolds-number flows: it exhibited approximately Gaussian fluctuations for all three velocity components, a clearly defined inertial subrange following Kolmogorov scaling (power spectrum, and second- and third-order Eulerian structure functions), and highly intermittent velocity gradients, as well as approximately lognormal kinetic energy dissipation rates. The clouds were observed to have liquid water contents on the order of 1 g m?3 and size distributions typical of continental clouds, sometimes exhibiting long positive tails indicative of large drop production through turbulent mixing or coalescence growth. Dimensionless parameters relevant to cloud–turbulence interactions, the Stokes number and settling parameter are in the range typically observed in atmospheric clouds. Observed fluctuations in droplet number concentration and diameter suggest a preference for inhomogeneous mixing. Finally, enhanced variance in liquid water content fluctuations is observed at high frequencies, and the scale break occurs at a value consistent with the independently estimated phase relaxation time from microphysical measurements. |
BibTeX:
@article{Siebert.Shaw.ea, author = {Siebert, H. and Shaw, R. A. and Ditas, J. and Schmeissner, T. and Malinowski, S. P. and Bodenschatz, E. and Xu, H.}, title = {High-resolution measurement of cloud microphysics and turbulence at a mountaintop station}, journal = {Atmos. Meas. Tech.}, month = {August}, year = {2015}, volume = {8}, pages = {3219}, doi = {10.5194/amt-8-3219-2015},, url = {http://www.atmos-meas-tech.net/8/3219/2015/amt-8-3219-2015.html} } |
Vosskuhle, M., Pumir, A., Leveque, E. and Wilkinson, M., "Collision rate for suspensions at large Stokes numbers - comparing Navier–Stokes and synthetic turbulence", Journal of Fluid Mechanics, August 2015, Vol. 16(1), 15 pp. |
Abstract: The use of simplified models of turbulent flows provides an appealing possibility to study the collision rate of turbulent suspensions, especially in conditions relevant to astrophysics, which require large timescale separations. To check the validity of such approaches, we used a direct numerical simulation (DNS) velocity field, which satisfies the Navier–Stokes equations (although it neglects the effect of the suspended particles on the flow field), and a kinematic simulation (KS) velocity field, which is a random field designed so that its statistics are in accord with the Kolmogorov theory for fully-developed turbulence. In the limit where the effects of particle inertia (characterised by the Stokes number) are negligible, the collision rates from the two approaches agree. As the Stokes number St increases, however, we show that the DNS collision rate exceeds the KS collision rate by orders of magnitude. We propose an explanation for this phenomenon and explore its consequences. We discuss the collision rate R for particles in high Reynolds number flows at large Stokes number, and present evidence that . |
BibTeX:
@article{Vosskuhle.Pumir.ea2015, author = {Vosskuhle, M. and Pumir, A. and Leveque, E. and Wilkinson, M.}, title = {Collision rate for suspensions at large Stokes numbers - comparing Navier–Stokes and synthetic turbulence}, journal = {Journal of Fluid Mechanics}, month = {August}, year = {2015}, volume = {16}, number = {1}, pages = {15}, doi = {10.1080/14685248.2014.948628},, url = {http://www.tandfonline.com/doi/abs/10.1080/14685248.2014.948628} } |
Cisse, M., Saw, E. W., Gibert, M., Bodenschatz, E. and Bec, J., "Turbulence attenuation by large neutrally buoyant particles", Phys. Fluids, June 2015, Vol. 27, 061702 pp. |
Abstract: Turbulence modulation by inertial-range-size, neutrally buoyant particles is investigated experimentally in a von K?rm?n flow. Increasing the particle volume fraction Öv, maintaining constant impellers Reynolds number attenuates the fluid turbulence. The inertial-range energy transfer rate decreases as ? Ö2/3 v , suggesting that only particles located on a surface affect the flow. Small-scale turbulent properties, such as structure functions or acceleration distribution, are unchanged. Finally, measurements hint at the existence of a transition between two different regimes occurring when the average distance between large particles is of the order of the thickness of their boundary layers. |
BibTeX:
@article{Cisse.Saw.ea2015acceptedforpublication, author = {Cisse, M. and Saw, E. W. and Gibert, M. and Bodenschatz, E. and Bec, J.}, title = {Turbulence attenuation by large neutrally buoyant particles}, journal = {Phys. Fluids}, month = {June}, year = {2015}, volume = {27}, pages = {061702}, doi = {10.1063/1.4922241},, url = {http://scitation.aip.org/content/aip/journal/pof2/27/6/10.1063/1.4922241#} } |
Gholami, A., Steinbock, O., Zykov, V. and Bodenschatz, E., "Flow-driven instabilities during pattern formation of Dictyostelium discoideum", New J. Phys., June 2015, Vol. 17(1), 063007 pp. |
Abstract: The slime mold Dictyostelium discoideum is a well known model system for the study of biological pattern formation. In the natural environment, aggregating populations of starving Dictyostelium discoideum cells may experience fluid flows that can profoundly change the underlying wave generation process. Here we study the effect of advection on the pattern formation in a colony of homogeneously distributed Dictyostelium discoideum cells described by the standard Martiel–Goldbeter model. The external flow advects the signaling molecule cyclic adenosine monophosphate (cAMP) downstream, while the chemotactic cells attached to the solid substrate are not transported with the flow. The evolution of small perturbations in cAMP concentrations is studied analytically in the linear regime and by corresponding numerical simulations. We show that flow can significantly influence the dynamics of the system and lead to a flow-driven instability that initiate downstream traveling cAMP waves. We also show that boundary conditions have a significant effect on the observed patterns and can lead to a new kind of instability. |
BibTeX:
@article{Gholami.Steinbock.ea2015a, author = {Gholami, A. and Steinbock, O. and Zykov, V. and Bodenschatz, E.}, title = {Flow-driven instabilities during pattern formation of Dictyostelium discoideum}, journal = {New J. Phys.}, month = {June}, year = {2015}, volume = {17}, number = {1}, pages = {063007}, doi = {10.1088/1367-2630/17/6/063007},, url = {http://iopscience.iop.org/1367-2630/17/6/063007/article} } |
He, X., van Gils, D., Bodenschatz, E. and Ahlers, G., "Reynolds numbers and the elliptic approximation near the ultimate state of turbulent Rayleigh-Bénard convection", New J. Phys., June 2015, Vol. 17(6), 063028 pp. |
Abstract: We report results of Reynolds-number measurements, based on multi-point temperature measurements and the elliptic approximation (EA) of He and Zhang (2006 Phys. Rev. E 73 055303), Zhao and He (2009 Phys. Rev. E 79 046316) for turbulent Rayleigh–B?nard convection (RBC) over the Rayleigh-number range 10^11≲ textRa≲ 2× 10^14 and for a Prandtl number Pr sime 0.8. The sample was a right-circular cylinder with the diameter D and the height L both equal to 112 cm. The Reynolds numbers ReU and ReV were obtained from the mean-flow velocity U and the root-mean-square fluctuation velocity V, respectively. Both were measured approximately at the mid-height of the sample and near (but not too near) the side wall close to a maximum of ReU. A detailed examination, based on several experimental tests, of the applicability of the EA to turbulent RBC in our parameter range is provided. The main contribution to ReU came from a large-scale circulation in the form of a single convection roll with the preferred azimuthal orientation of its down flow nearly coinciding with the location of the measurement probes. First we measured time sequences of ReU(t) and ReV(t) from short (10 s) segments which moved along much longer sequences of many hours. The corresponding probability distributions of ReU(t) and ReV(t) had single peaks and thus did not reveal significant flow reversals. The two averaged Reynolds numbers determined from the entire data sequences were of comparable size. For textRalt textRa_1^*≃ 2× 10^13 both ReU and ReV could be described by a power-law dependence on Ra with an exponent æ close to 0.44. This exponent is consistent with several other measurements for the classical RBC state at smaller Ra and larger Pr and with the Grossmann–Lohse (GL) prediction for ReU (Grossmann and Lohse 2000 J. Fluid. Mech. 407 27; Grossmann and Lohse 2001 86 3316; Grossmann and Lohse 2002 66 016305) but disagrees with the prediction ζ ≃ 0.33 by GL (Grossmann and Lohse 2004 Phys. Fluids 16 4462) for ReV. At textRa=textRa_2^*≃ 7× 10^13 the dependence of ReV on Ra changed, and for larger Ra textRe_V∼ textRa^0.50± 0.02, consistent with the prediction for ReU (Grossmann and Lohse 2000 J. Fluid. Mech. 407 27; Grossmann and Lohse Phys. Rev. Lett. 2001 86 3316; Grossmann and Lohse Phys. Rev. E 2002 66 016305; Grossmann and Lohse 2012 Phys. Fluids 24 125103) in the ultimate state of RBC. |
BibTeX:
@article{He.Gils.ea2015, author = {He, X. and van Gils, D. and Bodenschatz, E. and Ahlers, G.}, title = {Reynolds numbers and the elliptic approximation near the ultimate state of turbulent Rayleigh-Bénard convection}, journal = {New J. Phys.}, month = {June}, year = {2015}, volume = {17}, number = {6}, pages = {063028}, doi = {10.1088/1367-2630/17/6/063028},, url = {http://iopscience.iop.org/1367-2630/17/6/063028/} } |
Rother, J., Richter, C., Turco, L., Knoch, F., Mey, I., Luther, S., Janshoff, A., Bodenschatz, E. and Tarantola, M., "Crosstalk of cardiomyocytes and fibroblasts in co-cultures", Open Biology, June 2015, Vol. 5, 150038 pp. |
Abstract: Electromechanical function of cardiac muscle depends critically on the crosstalk of myocytes with non-myocytes. Upon cardiac fibrosis, fibroblasts translocate into infarcted necrotic tissue and alter their communication capabilities. In the present in vitro study, we determined a multiple parameter space relevant for fibrotic cardiac tissue development comprising the following essential processes: (i) adhesion to substrates with varying elasticity, (ii) dynamics of contractile function, and (iii) electromechanical connectivity. By combining electric cell-substrate impedance sensing (ECIS) with conventional optical microscopy, we could measure the impact of fibroblast–cardiomyocyte ratio on the aforementioned parameters in a non-invasive fashion. Adhesion to electrodes was quantified via spreading rates derived from impedance changes, period analysis allowed us to measure contraction dynamics and modulations of the barrier resistance served as a measure of connectivity. In summary, we claim that: (i) a preferred window for substrate elasticity around 7 kPa for low fibroblast content exists, which is shifted to stiffer substrates with increasing fibroblast fractions. (ii) Beat frequency decreases nonlinearly with increasing fraction of fibroblasts, while (iii) the intercellular resistance increases with a maximal functional connectivity at 75% fibroblasts. For the first time, cardiac cell–cell junction density-dependent connectivity in co-cultures of cardiomyocytes and fibroblasts was quantified using ECIS. |
BibTeX:
@article{Rother.Richter.ea, author = {Rother, J. and Richter, C. and Turco, L. and Knoch, F. and Mey, I. and Luther, S. and Janshoff, A. and Bodenschatz, E. and Tarantola, M.}, title = {Crosstalk of cardiomyocytes and fibroblasts in co-cultures}, journal = {Open Biology}, month = {June}, year = {2015}, volume = {5}, pages = {150038}, doi = {10.1098/rsob.150038},, url = {http://rsob.royalsocietypublishing.org/content/5/6/150038.abstract?ijkey=1VhwXRIwbtlK84d&keytype=ref} } |
Hsu, H.-F., "Oscillatory instabilities of intracellular fiber networks", May 2015 |
Abstract: D. discoideum shares many common features of actin dynamics and essential responses with eukaryotic cells and cancer cells. Therefore, most properties of the oscillations are well studied in the simpler biological model system. However, the properties and the underlying mechanisms of the recently found autonomous cytoskeletal oscillations are still unexplored. Questions such as what the roles of this autonomous oscillation in chemotaxis are, and how external stimulation affects autonomous oscillations are intriguing but unanswered. This study starts by investigating actin dynamics of cells in the absence of external stimuli. We analyze thousands of cells to get a stochastically significant mean. In the part on intrinsic oscillations, we report on the properties like the distribution of oscillations, role of actin regulating proteins such as Aip1, coronin and myosin II and propose an underlying mechanism. In the second chapter, we investigated how external stimulation alters the intrinsic frequency. With dose dependence experiments and careful examination of the different sections of the actin polymerization, depolymerization and recovery, we extend our model to account for the chemotatic responses. We also use the experimental data to verify an existing model of actin dynamics and modify it according to our experimental results. Finally, we investigate the role of myosin II in actin dynamics. Although myosin II is not directly involved in actin regulation, it is essential for effective cellular functions such as movement, chemotaxis and cytokinesis. |
BibTeX:
@phdthesis{Hsu2015, author = {Hsu, Hsin-Fang}, title = {Oscillatory instabilities of intracellular fiber networks}, month = {May}, year = {2015},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0028-8652-4} } |
Nobach, H., "Corrections to the direct spectral estimation for laser Doppler data", Experiments in Fluids, May 2015, Vol. 56(5), 109 pp. |
Abstract: An algorithm for estimating the power spectral density and the correlation function of laser Doppler-generated data sets is introduced. The algorithm is of the type of direct spectral estimators including weighting of individual velocity values to correct statistical biases caused by the correlation of instantaneous data rate and velocity values. It is extended by the forward–backward inter-arrival time weighting, the correction of the wraparound error, that of dead-time influences, and an error due to the removal of estimated block mean values. A temporal limitation of the correlation function as an alternative to the block averaging allows the block lengths to be chosen in a wide range with less necessities for compromises between systematic and random errors. |
BibTeX:
@article{Nobach2015, author = {Nobach, H}, title = {Corrections to the direct spectral estimation for laser Doppler data}, journal = {Experiments in Fluids}, month = {May}, year = {2015}, volume = {56}, number = {5}, pages = {109}, doi = {10.1007/s00348-015-1980-0},, url = {http://link.springer.com/article/10.1007/s00348-015-1980-0} } |
Nobach, H., "A model-free noise removal for the interpolation method of correlation and spectral estimation from laser Doppler data", Experiments in Fluids, May 2015, Vol. 56, 100 pp. |
Abstract: A procedure to estimate and remove the contribution of data noise to the correlation function and the power spectral density calculated from laser Doppler data with the interpolation method is introduced. In comparison with earlier approaches, the new procedure is model free and, therefore, more objective. The new procedure is proven based on experimental data taken with a laser Doppler system, where the power spectral density obtained with the interpolation method is compared directly to data from a hot-wire reference measurement. |
BibTeX:
@article{Nobach2015a, author = {Nobach, H}, title = {A model-free noise removal for the interpolation method of correlation and spectral estimation from laser Doppler data}, journal = {Experiments in Fluids}, month = {May}, year = {2015}, volume = {56}, pages = {100}, doi = {10.1007/s00348-015-1975-x},, url = {http://link.springer.com/article/10.1007/s00348-015-1975-x} } |
Oikawa, N., Bodenschatz, E. and Zykov, V., "Unusual spiral wave dynamics in the Kessler-Levine model of an excitable medium", Chaos, May 2015, Vol. 25(5), 053115 pp. |
Abstract: The Kessler-Levine model is a two-component reaction-diffusion system that describes spatiotemporal dynamics of the messenger molecules in a cell-to-cell signaling process during the aggregation of social amoeba cells. An excitation wave arising in the model has a phase wave at the wave back, which simply follows the wave front after a fixed time interval with the same propagation velocity. Generally speaking, the medium excitability and the refractoriness are two important factors which determine the spiral wave dynamics in any excitable media. The model allows us to separate these two factors relatively easily since the medium refractoriness can be changed independently of the medium excitability. For rigidly rotating waves, the universal relationship has been established by using a modified free-boundary approach, which assumes that the front and the back of a propagating wave are thin in comparison to the wave plateau. By taking a finite thickness of the domain boundary into consideration, the validity of the proposed excitability measure has been essentially improved. A novel method of numerical simulation to suppress the spiral wave instabilities is introduced. The trajectories of the spiral tip observed for a long refractory period have been investigated under a systematic variation of the medium refractoriness. |
BibTeX:
@article{a, author = {Oikawa, N. and Bodenschatz, E. and Zykov, V.}, title = {Unusual spiral wave dynamics in the Kessler-Levine model of an excitable medium}, journal = {Chaos}, month = {May}, year = {2015}, volume = {25}, number = {5}, pages = {053115}, doi = {10.1063/1.4921879},, url = {http://scitation.aip.org/content/aip/journal/chaos/25/5/10.1063/1.4921879?Track=CHAOSJUNE2015&utm_source=Researcher+Account&utm_medium=email&utm_campaign=5834052_Chaos+June+2015&dm_i=1XPS,3H1L0,J5FZ71,CFMT8,1} } |
Shishkina, O., Horn, S., Wagner, S. and Ching, E., "Thermal Boundary Layer Equation for Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., March 2015, Vol. 114, 114302 pp. |
Abstract: We report a new thermal boundary layer equation for turbulent Rayleigh-Benard convection for Prandtl number Pr>1 that takes into account the effect of turbulent fluctuations. These fluctuations are neglected in existing equations, which are based on steady-state and laminar assumptions. Using this new equation, we derive analytically the mean temperature profiles in two limits: (a) Pr>1, Pr 1 and (b) Pr>>1. These two theoretical predictions are in excellent agreement with the results of our direct numerical simulations for Pr=4.38 (water) and Pr=2547.9 (glycerol) respectively. |
BibTeX:
@article{Shishkina.Horn.ea2015, author = {Shishkina, O. and Horn, S. and Wagner, S. and Ching, E.S.C.}, title = {Thermal Boundary Layer Equation for Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {March}, year = {2015}, volume = {114}, pages = {114302}, doi = {10.1103/PhysRevLett.114.114302},, url = {http://arxiv.org/abs/1411.5826} } |
Xu, J., Menon, S. N., Singh, R., Garnier, N. B., Sinha, S. and Pumir, A., "The Role of Cellular Coupling in the Spontaneous Generation of Electrical Activity in Uterine Tissue", PLOS ONE, March 2015, Vol. 10(3), e0118443 pp. |
Abstract: The spontaneous emergence of contraction-inducing electrical activity in the uterus at the beginning of labor remains poorly understood, partly due to the seemingly contradictory observation that isolated uterine cells are not spontaneously active. It is known, however, that the expression of gap junctions increases dramatically in the approach to parturition, by more than one order of magnitude, which results in a significant increase in inter-cellular electrical coupling. In this paper, we build upon previous studies of the activity of electrically excitable smooth muscle cells (myocytes) and investigate the mechanism through which the coupling of these cells to electrically passive cells results in the generation of spontaneous activity in the uterus. Using a recently developed, realistic model of uterine muscle cell dynamics, we investigate a system consisting of a myocyte coupled to passive cells. We then extend our analysis to a simple two-dimensional lattice model of the tissue, with each myocyte being coupled to its neighbors, as well as to a random number of passive cells. We observe that different dynamical regimes can be observed over a range of gap junction conductances: at low coupling strength, corresponding to values measured long before delivery, the activity is confined to cell clusters, while the activity for high coupling, compatible with values measured shortly before delivery, may spread across the entire tissue. Additionally, we find that the system supports the spontaneous generation of spiral wave activity. Our results are both qualitatively and quantitatively consistent with observations from in vitro experiments. In particular, we demonstrate that the increase in inter-cellular electrical coupling observed experimentally strongly facilitates the appearance of spontaneous action potentials that may eventually lead to parturition. |
BibTeX:
@article{Xu.Menon.ea2015, author = {Xu, J. and Menon, S. N. and Singh, R. and Garnier, N. B. and Sinha, S. and Pumir, A.}, title = {The Role of Cellular Coupling in the Spontaneous Generation of Electrical Activity in Uterine Tissue}, journal = {PLOS ONE}, month = {March}, year = {2015}, volume = {10}, number = {3}, pages = {e0118443}, doi = {10.1371/journal.pone.0118443},, url = {http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118443} } |
Gao, Y., Xu, H. and Law, C. K., "Turbulence decay and cloud core relaxation in molecular clouds", Astrophys. J., February 2015, Vol. 799(2), 227 pp. |
Abstract: The turbulent motion within molecular clouds is a key factor controlling star formation. Turbulence supports molecular cloud cores from evolving to gravitational collapse and hence sets a lower bound on the size of molecular cloud cores in which star formation can occur. On the other hand, without a continuous external energy source maintaining the turbulence, such as in molecular clouds, the turbulence decays with an energy dissipation time comparable to the dynamic timescale of clouds, which could change the size limits obtained from Jean's criterion by assuming constant turbulence intensities. Here we adopt scaling relations of physical variables in decaying turbulence to analyze its specific effects on the formation of stars. We find that the decay of turbulence provides an additional approach for Jeans' criterion to be achieved, after which gravitational infall governs the motion of the cloud core. This epoch of turbulence decay is defined as cloud core relaxation. The existence of cloud core relaxation provides a more complete understanding of the effect of the competition between turbulence and gravity on the dynamics of molecular cloud cores and star formation. |
BibTeX:
@article{Gao.Xu.ea2015, author = {Gao, Y. and Xu, H. and Law, C. K.}, title = {Turbulence decay and cloud core relaxation in molecular clouds}, journal = {Astrophys. J.}, month = {February}, year = {2015}, volume = {799}, number = {2}, pages = {227}, doi = {10.1088/0004-637X/799/2/227},, url = {http://iopscience.iop.org/0004-637X/799/2/227} } |
Hohenberg, P. C. and Krekhov, A., "An introduction to the Ginzburg-Landau theory of phase transitions and nonequilibrium patterns", Phys. Rep., February 2015, Vol. 572, 1-42 pp. |
Abstract: This paper presents an introduction to phase transitions and critical phenomena on the one hand, and nonequilibrium patterns on the other, using the Ginzburg-Landau theory as a unified language. In the first part, mean-field theory is presented, for both statics and dynamics, and its validity tested self-consistently. As is well known, the mean-field approximation breaks down below four spatial dimensions, where it can be replaced by a scaling phenomenology. The Ginzburg-Landau formalism can then be used to justify the phenomenological theory using the renormalization group, which elucidates the physical and mathematical mechanism for universality. In the second part of the paper it is shown how near pattern forming linear instabilities of dynamical systems, a formally similar Ginzburg-Landau theory can be derived for nonequilibrium macroscopic phenomena. The real and complex Ginzburg-Landau equations thus obtained yield nontrivial solutions of the original dynamical system, valid near the linear instability. Examples of such solutions are plane waves, defects such as dislocations or spirals, and states of temporal or spatiotemporal (extensive) chaos. |
BibTeX:
@article{Hohenberg.Krekhov2015, author = {Hohenberg, P. C. and Krekhov, A.}, title = {An introduction to the Ginzburg-Landau theory of phase transitions and nonequilibrium patterns}, journal = {Phys. Rep.}, month = {February}, year = {2015}, volume = {572}, pages = {1-42}, doi = {10.1016/j.physrep.2015.01.001},, url = {https://www.sciencedirect.com/science/article/pii/S0370157315000514} } |
Breus, V., Pietuch, A., Tarantola, M., Basche, T. and Janshoff, A., "The Effect of Surface Charge on Non-Specific Uptake and Cytotoxicity of CdSe/ZnS Core/Shell Quantum Dots", Beilstein J. Nanotechnol., January 2015, Vol. 6, 281 pp. |
Abstract: In this work, cytotoxicity and cellular impedance response was compared for CdSe/ZnS core/shell quantum dots (QDs) with positively charged cysteamine–QDs, negatively charged dihydrolipoic acid–QDs and zwitterionic D-penicillamine–QDs exposed to canine kidney MDCKII cells. Pretreatment of cells with pharmacological inhibitors suggested that the uptake of nanoparticles was largely due to receptor-independent pathways or spontaneous entry for carboxylated and zwitterionic QDs, while for amine-functionalized particles involvement of cholesterol-enriched membrane domains is conceivable. Cysteamine–QDs were found to be the least cytotoxic, while D-penicillamine–QDs reduced the mitochondrial activity of MDCKII by 20–25%. Although the cell vitality appeared unaffected (assessed from the changes in mitochondrial activity using a classical MTS assay after 24 h of exposure), the binding of QDs to the cellular interior and their movement across cytoskeletal filaments (captured and characterized by single-particle tracking), was shown to compromise the integrity of the cytoskeletal and plasma membrane dynamics, as evidenced by electric cell–substrate impedance sensing. |
BibTeX:
@article{Beus.Pietuch.ea2014, author = {Breus, V. and Pietuch, A. and Tarantola, M. and Basche, T. and Janshoff, A.}, title = {The Effect of Surface Charge on Non-Specific Uptake and Cytotoxicity of CdSe/ZnS Core/Shell Quantum Dots}, journal = {Beilstein J. Nanotechnol.}, month = {January}, year = {2015}, volume = {6}, pages = {281}, doi = {10.3762/bjnano.6.26},, url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-6-26&vt=f&tpn=0&bpn=searchResult} } |
Gholami, A., Steinbock, O., Zykov, V. S. and Bodenschatz, E., "Flow-Driven Waves and Phase-Locked Self-Organization in Quasi-One-Dimensional Colonies of Dictyostelium discoideum", Phys. Rev. Lett., January 2015, Vol. 114, 018103 pp. |
Abstract: We report experiments on flow-driven waves in a microfluidic channel containing the signaling slime mold Dictyostelium discoideum. The observed cyclic adenosine monophosphate (cAMP) wave trains developed spontaneously in the presence of flow and propagated with the velocity proportional to the imposed flow velocity. The period of the wave trains was independent of the flow velocity. Perturbations of flow-driven waves via external periodic pulses of the signaling agent cAMP induced 1:1, 2:1, 3:1, and 1:2 frequency responses, reminiscent of Arnold tongues in forced oscillatory systems. We expect our observations to be generic to active media governed by reaction-diffusion-advection dynamics, where spatially bound autocatalytic processes occur under flow conditions. |
BibTeX:
@article{Gholami.Steinbock.ea2015, author = {Gholami, A. and Steinbock, O. and Zykov, V. S. and Bodenschatz, E.}, title = {Flow-Driven Waves and Phase-Locked Self-Organization in Quasi-One-Dimensional Colonies of Dictyostelium discoideum}, journal = {Phys. Rev. Lett.}, month = {January}, year = {2015}, volume = {114}, pages = {018103}, doi = {10.1103/PhysRevLett.114.018103},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.018103} } |
Pietuch, A., Brückner, B., Schneider, D., Tarantola, M., Rosman, C., Sönnichsen, C. and Janshoff, A., "Mechanical properties of MDCK II cells exposed to gold nanorods", Beilstein J. Nanotechnol., January 2015, Vol. 6, 223 pp. |
Abstract: Background: The impact of gold nanoparticles on cell viability has been extensively studied in the past. Size, shape and surface functionalization including opsonization of gold particles ranging from a few nanometers to hundreds of nanometers are among the most crucial parameters that have been focussed on. Cytoxicity of nanomaterial has been assessed by common cytotoxicity assays targeting enzymatic activity such as LDH, MTT and ECIS. So far, however, less attention has been paid to the mechanical parameters of cells exposed to gold particles, which is an important reporter on the cellular response to external stimuli.
Results: Mechanical properties of confluent MDCK II cells exposed to gold nanorods as a function of surface functionalization and concentration have been explored by atomic force microscopy and quartz crystal microbalance measurements in combination with fluorescence and dark-field microscopy. Conclusion: We found that cells exposed to CTAB coated gold nanorods display a concentration-dependent stiffening that cannot be explained by the presence of CTAB alone. The stiffening results presumably from endocytosis of particles removing excess membrane area from the cell’s surface. Another aspect could be the collapse of the plasma membrane on the actin cortex. Particles coated with PEG do not show a significant change in elastic properties. This observation is consistent with QCM measurements that show a considerable drop in frequency upon administration of CTAB coated rods suggesting an increase in acoustic load corresponding to a larger stiffness (storage modulus). |
BibTeX:
@article{Pietuch.Brueckner.ea2014, author = {Pietuch, A. and Brückner, B.R. and Schneider, D. and Tarantola, M. and Rosman, C. and Sönnichsen, C. and Janshoff, A.}, title = {Mechanical properties of MDCK II cells exposed to gold nanorods}, journal = {Beilstein J. Nanotechnol.}, month = {January}, year = {2015}, volume = {6}, pages = {223}, doi = {10.3762/bjnano.6.21},, url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-6-21&vt=f&tpn=0&bpn=searchResult} } |
Sinhuber, M., Bodenschatz, E. and Bewley, G. P., "Decay of Turbulence at High Reynolds Numbers", Phys. Rev. Lett., January 2015, Vol. 114, 034501 pp. |
Abstract: Turbulent motions in a fluid decay at a certain rate once stirring has stopped. The role of the most basic parameter in fluid mechanics, the Reynolds number, in setting the decay rate is not generally known. This Letter concerns the high-Reynolds-number limit of the process. In a classical grid-turbulence wind-tunnel experiment that both reaches higher Reynolds numbers than ever before and covers a wide range of them (104 |
BibTeX:
@article{Sinhuber.Bodenschatz.ea2015, author = {Sinhuber, M. and Bodenschatz, E. and Bewley, G P}, title = {Decay of Turbulence at High Reynolds Numbers}, journal = {Phys. Rev. Lett.}, month = {January}, year = {2015}, volume = {114}, pages = {034501}, doi = {10.1103/PhysRevLett.114.034501},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.034501} } |
Horn, S. and Shishkina, O., "Toroidal and poloidal energy in rotating Rayleigh-Bénard convection", J. Fluid Mech., December 2014, Vol. 762, 232 pp. |
Abstract: We consider rotating Rayleigh–Bénard convection of a fluid with a Prandtl number of Pr=0.8 in a cylindrical cell with an aspect ratio Ã=1/2. Direct numerical simulations (DNS) were performed for the Rayleigh number range 105?Ra?109 and the inverse Rossby number range 0?1/Ro?20. We propose a method to capture regime transitions based on the decomposition of the velocity field into toroidal and poloidal parts. We identify four different regimes. First, a buoyancy-dominated regime occurring while the toroidal energy etor is not affected by rotation and remains equal to that in the non-rotating case, e0tor. Second, a rotation-influenced regime, starting at rotation rates where etor>e0tor and ending at a critical inverse Rossby number 1/Rocr that is determined by the balance of the toroidal and poloidal energy, etor=epol. Third, a rotation-dominated regime, where the toroidal energy etor is larger than both epol and e0tor. Fourth, a geostrophic regime for high rotation rates where the toroidal energy drops below the value for non-rotating convection. |
BibTeX:
@article{Horn.Shishkina2014, author = {Horn, S. and Shishkina, O.}, title = {Toroidal and poloidal energy in rotating Rayleigh-Bénard convection}, journal = {J. Fluid Mech.}, month = {December}, year = {2014}, volume = {762}, pages = {232}, doi = {10.1017/jfm.2014.652},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9449002&fileId=S0022112014006521} } |
Priebe, M., Bernhardt, M., Blum, C., Tarantola, M., Bodenschatz, E. and Salditt, T., "Scanning X-Ray Nanodiffraction on Dictyostelium discoideum", Biophys. J., December 2014, Vol. 107(11), 2662 pp. |
Abstract: We have performed scanning x-ray nanobeam diffraction experiments on single cells of the amoeba Dictyostelium discoideum. Cells have been investigated in 1), freeze-dried, 2), frozen-hydrated (vitrified), and 3), initially alive states. The spatially resolved small-angle x-ray scattering signal shows characteristic streaklike patterns in reciprocal space, which we attribute to fiber bundles of the actomyosin network. From the intensity distributions, an anisotropy parameter can be derived that indicates pronounced local variations within the cell. In addition to nanobeam small-angle x-ray scattering, we have evaluated the x-ray differential phase contrast in view of the projected electron density. Different experimental aspects of the x-ray experiment, sample preparation, and data analysis are discussed. Finally, the x-ray results are correlated with optical microscopy (differential phase contrast and confocal microscopy of mutant strains with fluorescently labeled actin and myosin II), which have been carried out in live and fixed states, including optical microscopy under cryogenic conditions. |
BibTeX:
@article{Priebe.Bernhardt.ea2014accepted, author = {Priebe, M. and Bernhardt, M. and Blum, C. and Tarantola, M. and Bodenschatz, E. and Salditt, T.}, title = {Scanning X-Ray Nanodiffraction on Dictyostelium discoideum}, journal = {Biophys. J.}, month = {December}, year = {2014}, volume = {107}, number = {11}, pages = {2662}, doi = {10.1016/j.bpj.2014.10.027},, url = {http://www.cell.com/biophysj/abstract/S0006-3495(14)01105-9} } |
Rosman, C., Pierrat, S., Tarantola, M., Sunnick, E., Schneider, D., Janshoff, A. and Sönnichsen, C., "Mammalian cell growth on gold nanoparticle-decorated substrates is influenced by the nanoparticle coating", Beilstein J. Nanotechnol., December 2014, Vol. 5, 2479 pp. |
Abstract: In this work, we study epithelial cell growth on substrates decorated with gold nanorods that are functionalized either with a positively charged cytotoxic surfactant or with a biocompatible polymer exhibiting one of two different end groups, resulting in a neutral or negative surface charge of the particle. Upon observation of cell growth for three days by live cell imaging using optical dark field microscopy, it was found that all particles supported cell adhesion while no directed cell migration and no significant particle internalization occurred. Concerning cell adhesion and spreading as compared to cell growth on bare substrates after 3 days of incubation, a reduction by 45% and 95%, respectively, for the surfactant particle coating was observed, whereas the amino-terminated polymer induced a reduction by 30% and 40%, respectively, which is absent for the carboxy-terminated polymer. Furthermore, interface-sensitive impedance spectroscopy (electric cell–substrate impedance sensing, ECIS) was employed in order to investigate the micromotility of cells added to substrates decorated with various amounts of surfactant-coated particles. A surface density of 65 particles/ìm2 (which corresponds to 0.5% of surface coverage with nanoparticles) diminishes micromotion by 25% as compared to bare substrates after 35 hours of incubation. We conclude that the surface coating of the gold nanorods, which were applied to the basolateral side of the cells, has a recognizable influence on the growth behavior and thus the coating should be carefully selected for biomedical applications of nanoparticles. |
BibTeX:
@article{Rosman.Pierrat.ea, author = {Rosman, C. and Pierrat, S. and Tarantola, M. and Sunnick, E. and Schneider, D. and Janshoff, A. and Sönnichsen, C.}, title = {Mammalian cell growth on gold nanoparticle-decorated substrates is influenced by the nanoparticle coating}, journal = {Beilstein J. Nanotechnol.}, month = {December}, year = {2014}, volume = {5}, pages = {2479}, doi = {10.3762/bjnano.5.257},, url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-5-257} } |
Wagner, S. and Shishkina, O., "Heat Flux enhancement by regular surface roughness in turbulent thermal convection", J. Fluid Mech., December 2014, Vol. 763, 109 pp. |
Abstract: Direct numerical simulations (DNS) of turbulent thermal convection in a box-shaped domain with regular surface roughness at the heated bottom and cooled top surfaces are conducted for Prandtl number Pr=0.786 and Rayleigh numbers Ra between 106 and 108. The surface roughness is introduced by four parallelepiped equidistantly distributed obstacles attached to the bottom plate, and four obstacles located symmetrically at the top plate. By varying Ra and the height and width of the obstacles, we investigate the influence of the regular wall roughness on the turbulent heat transport, measured by the Nusselt number Nu. For fixed Ra, the change in the value of Nu is determined not only by the covering area of the surface, i.e. the obstacle height, but also by the distance between the obstacles. The heat flux enhancement is found to be largest for wide cavities between the obstacles which can be ‘washed out’ by the flow. This is also manifested in an empirical relation, which is based on the DNS data. We further discuss theoretical limiting cases for very wide and very narrow obstacles and combine them into a simple model for the heat flux enhancement due to the wall roughness, without introducing any free parameters. This model predicts well the general trends and the order of magnitude of the heat flux enhancement obtained in the DNS. In the Nu versus Ra scaling, the obstacles work in two ways: for smaller Ra an increase of the scaling exponent compared to the smooth case is found, which is connected to the heat flux entering the cavities from below. For larger Ra the scaling exponent saturates to the one for smooth plates, which can be understood as a full washing-out of the cavities. The latter is also investigated by considering the strength of the mean secondary flow in the cavities and its relation to the wind (i.e. the large-scale circulation), that develops in the core part of the domain. Generally, an increase in the roughness height leads to stronger flows both in the cavities and in the bulk region, while an increase in the width of the obstacles strengthens only the large-scale circulation of the fluid and weakens the secondary flows. An increase of the Rayleigh number always leads to stronger flows, both in the cavities and in the bulk. |
BibTeX:
@article{Wagner.Shiskina2014, author = {Wagner, S. and Shishkina, O.}, title = {Heat Flux enhancement by regular surface roughness in turbulent thermal convection}, journal = {J. Fluid Mech.}, month = {December}, year = {2014}, volume = {763}, pages = {109}, doi = {10.1017/jfm.2014.665},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9464672&fileId=S002211201400665X} } |
Ahlers, G., Bodenschatz, E. and He, X., "Logarithmic temperature profiles of turbulent Rayleigh-Bénard convection in the classical and ultimate state for a Prandtl number of 0.8", J. Fluid Mech., November 2014, Vol. 758, 436 pp. |
Abstract: We report on experimental determinations of the temperature field in the interior (bulk) of turbulent Rayleigh–Bénard convection for a cylindrical sample with an aspect ratio (diameter D over height L) equal to 0.50, in both the classical and the ultimate state. The measurements are for Rayleigh numbers Ra from 6?1011 to 1013 in the classical and 7?1014 to 1.1?1015 (our maximum accessible Ra) in the ultimate state. The Prandtl number was close to 0.8. Although to lowest order the bulk is often assumed to be isothermal in the time average, we found a ‘logarithmic layer’ (as reported briefly by Ahlers et al., Phys. Rev. Lett., vol. 109, 2012, 114501) in which the reduced temperature È=[?T(z)??Tm]/ÄT (with Tm the mean temperature, ÄT the applied temperature difference and ??? a time average) varies as Aln(z/L)+B or A?ln(1?z/L)+B? with the distance z from the bottom plate of the sample. In the classical state, the amplitudes ?A and A? are equal within our resolution, while in the ultimate state there is a small difference, with ?A/A??0.95. For the classical state, the width of the log layer is approximately 0.1L, the same near the top and the bottom plate as expected for a system with reflection symmetry about its horizontal midplane. For the ultimate state, the log-layer width is larger, extending through most of the sample, and slightly asymmetric about the midplane. Both amplitudes A and A? vary with radial position r, and this variation can be described well by A=A0[(R?r)/R]?0.65, where R is the radius of the sample. In the classical state, these results are in good agreement with direct numerical simulations (DNS) for Ra=2?1012; in the ultimate state there are as yet no DNS. The amplitudes ?A and A? varied as Ra?ç, with ç?0.12 in the classical and ç?0.18 in the ultimate state. A close analogy between the temperature field in the classical state and the ‘law of the wall’ for the time-averaged downstream velocity in shear flow is discussed. A two-sublayer mean-field model of the temperature profile in the classical state was analysed and yielded a logarithmic z dependence of È. The Ra dependence of the amplitude A given by the model corresponds to an exponent çth=0.106, in good agreement with the experiment. In the ultimate state the experimental result ç?0.18 differs from the prediction çth?0.043 by Grossmann & Lohse (Phys. Fluids, vol. 24, 2012, 125103). |
BibTeX:
@article{Ahlers.Bodenschatz.ea2014, author = {Ahlers, G. and Bodenschatz, E. and He, X.}, title = {Logarithmic temperature profiles of turbulent Rayleigh-Bénard convection in the classical and ultimate state for a Prandtl number of 0.8}, journal = {J. Fluid Mech.}, month = {November}, year = {2014}, volume = {758}, pages = {436}, doi = {10.1017/jfm.2014.543},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9377080&fileId=S0022112014005436} } |
Saw, E. W., Bewley, G. P., Bodenschatz, E., Ray, S. S. and Bec, J., "Extreme fluctuations of the relative velocities between droplets in turbulent airflow", Phys. Fluids, November 2014, Vol. 26, 111702 pp. |
Abstract: We compare experiments and direct numerical simulations to evaluate the accuracy of the Stokes-drag model, which is used widely in studies of inertial particles in turbulence. We focus on statistics at the dissipation scale and on extreme values of relative particle velocities for moderately inertial particles (St < 1). The probability distributions of relative velocities in the simulations were qualitatively similar to those in the experiments. The agreement improved with increasing Stokes number and decreasing relative velocity. Simulations underestimated the probability of extreme events, which suggests that the Stokes drag model misses important dynamics. Nevertheless, the scaling behavior of the extreme events in both the experiments and the simulations can be captured by the same multi-fractal model. |
BibTeX:
@article{Saw.Bewley.ea2014, author = {Saw, E. W. and Bewley, G. P. and Bodenschatz, E. and Ray, S. S. and Bec, J.}, title = {Extreme fluctuations of the relative velocities between droplets in turbulent airflow}, journal = {Phys. Fluids}, month = {November}, year = {2014}, volume = {26}, pages = {111702}, doi = {10.1063/1.4900848},, url = {http://scitation.aip.org/content/aip/journal/pof2/26/11/10.1063/1.4900848} } |
Good, G., Ireland, P., Bewley, G., Bodenschatz, E., Collins, L. and Warhaft, Z., "Settling regimes of inertial particles in isotropic turbulence", J. Fluid Mech., October 2014, Vol. 759, R3 pp. |
Abstract: We investigate the settling speeds and root mean square (r.m.s.) velocities of inertial particles in isotropic turbulence with gravity using experiments with water droplets in air turbulence from 32 loudspeaker jets and direct numerical simulations (DNS). The dependence on particle inertia, gravity and the scales of both the smallest and largest turbulent eddies is investigated. We isolate the mechanisms of turbulence settling modification and find that the reduced settling speeds of large particles in experiments are due to nonlinear drag effects. We demonstrate using DNS that reduced settling speeds with linear drag (e.g. see Nielsen, J. Sedim. Petrol., vol. 63, 1993, pp. 835–838) only arise in artificial flows that, by design, eliminate preferential sweeping by the eddies. Gravity and inertia both reduce the particle r.m.s. velocities and falling particles are more responsive to vertical than to horizontal fluctuations. The model by Wang & Stock (J. Atmos. Sci., vol. 50, 1993, pp. 1897–1913) captures these trends. |
BibTeX:
@article{Good.Ireland.ea2014, author = {Good, G.H. and Ireland, P.J. and Bewley, G.P. and Bodenschatz, E. and Collins, L.R. and Warhaft, Z.}, title = {Settling regimes of inertial particles in isotropic turbulence}, journal = {J. Fluid Mech.}, month = {October}, year = {2014}, volume = {759}, pages = {R3}, doi = {10.1017/jfm.2014.602},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9395167&fileId=S0022112014006028} } |
Jucha, J., "Time-Symmetry Breaking in Turbulent Multi-Particle Dispersion", October 2014 |
Abstract: In fluid dynamics, the term turbulence usually describes a special state of a continuous medium in which many interacting degrees of freedom are excited. Turbulent flows therefore exhibit strong temporal and spatial fluctuations in velocity, pressure and other flow properties. This behavior can be found in the atmospheric flows that determine our weather and climate, water flows in rivers and oceans, and even in the coffee we drink and the air we breathe. One of the interesting phenomena observed in turbulent flows is their time irreversibility. When milk is stirred into coffee, for example, turbulent flow generates very complicated, interwoven layer structures of the two substances. Reversing the stirring direction does not untangle the produced layers, but instead enhances the complexity of their structure. The initial condition of the two unmixed fluids can never be reproduced. The irreversibility of turbulent flows arises from instabilities that lead to a flux of energy through scales. For a three-dimensional flow, the spatial scale at which energy is injected is always larger than the scale at which it is viscously dissipated. Energy is therefore transported from large to small scales in a cascade-like manner. Reversing the time direction would lead to a change of direction of this energy flux, showing that turbulent flows are not symmetric in time. Since mixing is a good indicator for the irreversibility of a flow, it seems natural to use the dispersion of particle clusters as a tool to analyze time asymmetry. The simplest case is the dispersion of a set of two particles, called relative dispersion. First experimental and numerical studies on the time asymmetry in relative dispersion have indicated that particles separate faster backwards than forwards in time, but no conclusive explanation has been be given. In this thesis, I present a rigorous theoretical connection between the time asymmetry in the short-time evolution of particle clusters and the intrinsic irreversibility of turbulent flows due to the energy cascade. I confirm my theoretical findings with experimental data conducted in a turbulent water flow produced by two counterrotating propellers. Additionally, I examine how a change of the energy cascade, induced by the addition of minute amounts of polymers to the flow, is reflected in the particle dispersion. I present experimental data showing that the addition of polymers to the flow has a significant impact on time asymmetry in both two- and four-particle dispersion. |
BibTeX:
@phdthesis{Jucha2014, author = {Jucha, J.}, title = {Time-Symmetry Breaking in Turbulent Multi-Particle Dispersion}, month = {October}, year = {2014},, url = {http://ediss.uni-goettingen.de/handle/11858/00-1735-0000-0023-98F1-4} } |
Pumir, A., Xu, H., Boffetta, G., Falkovich, G. and Bodenschatz, E., "Redistribution of Kinetic Energy in Turbulent Flows", Phys. Rev. X, October 2014, Vol. 4, 041006 pp. |
Abstract: In statistically homogeneous turbulent flows, pressure forces provide the main mechanism to redistribute kinetic energy among fluid elements, without net contribution to the overall energy budget. This holds true in both two-dimensional (2D) and three-dimensional (3D) flows, which show fundamentally different physics. As we demonstrate here, pressure forces act on fluid elements very differently in these two cases. We find in numerical simulations that in 3D pressure forces strongly accelerate the fastest fluid elements, and that in 2D this effect is absent. In 3D turbulence, our findings put forward a mechanism for a possibly singular buildup of energy, and thus may shed new light on the smoothness problem of the solution of the Navier-Stokes equation in 3D. |
BibTeX:
@article{Pumir.Xu.ea2014, author = {Pumir, A. and Xu, H. and Boffetta, G. and Falkovich, G. and Bodenschatz, E.}, title = {Redistribution of Kinetic Energy in Turbulent Flows}, journal = {Phys. Rev. X}, month = {October}, year = {2014}, volume = {4}, pages = {041006}, doi = {10.1103/PhysRevX.4.041006},, url = {https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041006} } |
Weiss, S., Seiden, G. and Bodenschatz, E., "Resonance patterns in spatially forced Rayleigh-Bénard convection", J. Fluid Mech., October 2014, Vol. 756, 293 pp. |
Abstract: We report on the influence of a quasi-one-dimensional periodic forcing on the pattern selection process in Rayleigh-Benard convection (RBC). The forcing was introduced by a lithographically fabricated periodic texture on the bottom plate. We study the convection patterns as a function of the Rayleigh number (Ra) and the dimensionless forcing wavenumber (q(f)). For small Ra, convection takes the form of straight parallel rolls that are locked to the underlying forcing pattern. With increasing Ra, these rolls give way to more complex patterns, due to a secondary instability. The forcing wavenumber q(f) was varied in the experiment over the range of 0.6q(c) < q(f) < 1.4q(c), with q(c) being the critical wavenumber of the unforced system. We investigate the stability of straight rolls as a function of q(f) and report patterns that arise due to a secondary instability. |
BibTeX:
@article{Weiss.Seiden.ea2014, author = {Weiss, S. and Seiden, G. and Bodenschatz, E.}, title = {Resonance patterns in spatially forced Rayleigh-Bénard convection}, journal = {J. Fluid Mech.}, month = {October}, year = {2014}, volume = {756}, pages = {293}, doi = {10.1017/jfm.2014.456},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9338307&fileId=S002211201400456X} } |
Bodenschatz, E., Bewley, G. P., Nobach, H., Sinhuber, M. and Xu, H., "Variable density turbulence tunnel facility", Rev. Sci. Instrum., September 2014, Vol. 85, 093908 pp. |
Abstract: The Variable Density Turbulence Tunnel at the Max Planck Institute for Dynamics and Self-Organization in G?ttingen, Germany, produces very high turbulence levels at moderate flow velocities, low power consumption, and adjustable kinematic viscosity between 10?4 m2/s and 10?7 m2/s. The Reynolds number can be varied by changing the pressure or flow rate of the gas or by using different non-flammable gases including air. The highest kinematic viscosities, and hence lowest Reynolds numbers, are reached with air or nitrogen at 0.1 bar. To reach the highest Reynolds numbers the tunnel is pressurized to 15 bars with the dense gas sulfur hexafluoride (SF6). Turbulence is generated at the upstream ends of two measurement sections with grids, and the evolution of this turbulence is observed as it moves down the length of the sections. We describe the instrumentation presently in operation, which consists of the tunnel itself, classical grid turbulence generators, and state-of-the-art nano-fabricated hot-wire anemometers provided by Princeton University [M. Vallikivi, M. Hultmark, S. C. C. Bailey, and A. J. Smits, Exp. Fluids51, 1521 (2011)]. We report measurements of the characteristic scales of the flow and of turbulent spectra up to Taylor Reynolds number R ë ? 1600, higher than any other grid-turbulence experiment. We also describe instrumentation under development, which includes an active grid and a Lagrangian particle tracking system that moves down the length of the tunnel with the mean flow. In this configuration, the properties of the turbulence are adjustable and its structure is resolvable up to R ë ? 8000. |
BibTeX:
@article{Bodenschatz.Bewley.ea2014, author = {Bodenschatz, E. and Bewley, G. P. and Nobach, H. and Sinhuber, M. and Xu, H.}, title = {Variable density turbulence tunnel facility}, journal = {Rev. Sci. Instrum.}, month = {September}, year = {2014}, volume = {85}, pages = {093908}, doi = {10.1063/1.4896138},, url = {http://scitation.aip.org/content/aip/journal/rsi/85/9/10.1063/1.4896138} } |
Bush, J. W. M., Oza, A. U. and Molacek, J., "The wave-induced added mass of walking droplets", J. Fluid Mech., September 2014, Vol. 755, R7 pp. |
Abstract: It has recently been demonstrated that droplets walking on a vibrating fluid bath exhibit several features previously thought to be peculiar to the microscopic realm. The walker, consisting of a droplet plus its guiding wavefield, is a spatially extended object. We here examine the dependence of the walker mass and momentum on its velocity. Doing so indicates that, when the walker’s time scale of acceleration is long relative to the wave decay time, its dynamics may be described in terms of the mechanics of a particle with a speed-dependent mass and a nonlinear drag force that drives it towards a fixed speed. Drawing an analogy with relativistic mechanics, we define a hydrodynamic boost factor for the walkers. This perspective provides a new rationale for the anomalous orbital radii reported in recent studies. |
BibTeX:
@article{Bush.Oza.ea2014, author = {Bush, J. W. M. and Oza, A. U. and Molacek, J.}, title = {The wave-induced added mass of walking droplets}, journal = {J. Fluid Mech.}, month = {September}, year = {2014}, volume = {755}, pages = {R7}, doi = {10.1017/jfm.2014.459},, url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/waveinduced-added-mass-of-walking-droplets/46F140AA8C92329E965EAB1C2A011513} } |
Nobach, H., "LDV measurement of longitudinal correlations in a turbulent flow", September 2014 |
Abstract: Die Transformation einer zeitlichen Korrelationsfunktion der Geschwindigkeit an einem Messpunkt in einer turbulenten Str?mung in die longitudinale r?umliche Korrelationsfunktion bzw. in Zeit-Raum-Korrelationen auf der Grundlage eines statistischen Transportmodells soll dargestellt und sowohl mit dem als Taylorsche Hypothese einer eingefrorenen Str?mung bekannten Modell sowie mit LDA-Zweipunktmessungen verglichen werden. |
BibTeX:
@conference{Nobach2014, author = {Nobach, H}, title = {LDV measurement of longitudinal correlations in a turbulent flow}, month = {September}, year = {2014},, url = {http://www.gala-ev.org/images/Beitraege/Beitraege%202014/pdf/12.pdf} } |
Tarantola, M., Bae, A., Fuller, D., Bodenschatz, E., Rappel, W. and Loomis, W. F., "Cell substratum adhesion during early development of Dictyostelium discoideum", PLOS ONE, September 2014, Vol. 9(9), e106574 pp. |
Abstract: Vegetative and developed amoebae of Dictyostelium discoideum gain traction and move rapidly on a wide range of substrata without forming focal adhesions. We used two independent assays to quantify cell-substrate adhesion in mutants and in wild-type cells as a function of development. Using a microfluidic device that generates a range of hydrodynamic shear stress, we found that substratum adhesion decreases at least 10 fold during the first 6 hr of development of wild type cells. This result was confirmed using a single-cell assay in which cells were attached to the cantilever of an atomic force probe and allowed to adhere to untreated glass surfaces before being retracted. Both of these assays showed that the decrease in substratum adhesion was dependent on the cAMP receptor CAR1 which triggers development. Vegetative cells missing talin as the result of a mutation in talA exhibited slightly reduced adhesive properties compared to vegetative wildtype cells. In sharp contrast to wild-type cells, however, these talA mutant cells did not show further reduction of adhesion during development such that after 5 hr of development they were significantly more adhesive than developed wild type cells. In addition, both assays showed that substrate adhesion was reduced in 0 hr cells when the actin cytoskeleton was disrupted by latrunculin. Consistent with previous observations, substrate adhesion was also reduced in 0 hr cells lacking the membrane proteins SadA or SibA as the result of mutations in sadA or sibA. However, there was no difference in the adhesion properties between wild type AX3 cells and these mutant cells after 6 hr of development, suggesting that neither SibA nor SadA play an essential role in substratum adhesion during aggregation. Our results provide a quantitative framework for further studies of cell substratum adhesion in Dictyostelium. |
BibTeX:
@article{Tarantola.Bae.ea2014, author = {Tarantola, M. and Bae, A. and Fuller, D. and Bodenschatz, E. and Rappel, W. and Loomis, W. F.}, title = {Cell substratum adhesion during early development of Dictyostelium discoideum}, journal = {PLOS ONE}, month = {September}, year = {2014}, volume = {9}, number = {9}, pages = {e106574}, doi = {10.1371/journal.pone.0106574},, url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0106574} } |
He, X., Shang, X. and Tong, P., "Test of the anomalous scaling of passive temperature fluctuations in turbulent Rayleigh-Bénard convection with spatial inhomogeneity", J. Fluid Mech., August 2014, Vol. 753, 104 pp. |
Abstract: The scaling properties of the temperature structure function (SF) and temperature–velocity cross-structure function (CSF) are investigated in turbulent Rayleigh-Bénard convection (RBC). The measured SFs and CSFs exhibit good scaling in space and time and the resulting SF and CSF exponents are obtained both at the centre of the convection cell and near the sidewall. A universal relationship between the CSF exponent and the thermal dissipation exponent is found, confirming that the anomalous scaling of passive temperature fluctuations in turbulent RBC is indeed caused by the spatial intermittency of the thermal dissipation field. It is also found that the difference in the functional form of the measured SF and CSF exponents at the two different locations in the cell is caused by the change of the geometry of the most dissipative structures in the (inhomogeneous) temperature field from being sheetlike at the cell centre to filament-like near the sidewall. The experiment thus provides direct evidence showing that the universality features of turbulent cascade are linked to the degree of anisotropy and inhomogeneity of turbulent statistics. |
BibTeX:
@article{He.Shang.ea2014, author = {He, X. and Shang, X. and Tong, P.}, title = {Test of the anomalous scaling of passive temperature fluctuations in turbulent Rayleigh-Bénard convection with spatial inhomogeneity}, journal = {J. Fluid Mech.}, month = {August}, year = {2014}, volume = {753}, pages = {104}, doi = {10.1017/jfm.2014.325},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9302687&fulltextType=RA&fileId=S0022112014003255} } |
Jucha, J., Xu, H., Pumir, A. and Bodenschatz, E., "Time-reversal-symmetry Breaking in Turbulence", Phys. Rev. Lett., July 2014, Vol. 113, 054501 pp. |
Abstract: In three-dimensional turbulent flows, the flux of energy from large to small scales breaks time symmetry. We show here that this irreversibility can be quantified by following the relative motion of several Lagrangian tracers. We find by analytical calculation, numerical analysis, and experimental observation that the existence of the energy flux implies that, at short times, two particles separate temporally slower forwards than backwards, and the difference between forward and backward dispersion grows as t3. We also find the geometric deformation of material volumes, defined by four points spanning an initially regular tetrahedron, to show sensitivity to the time reversal with an effect growing linearly in t. We associate this with the structure of the strain rate in the flow. |
BibTeX:
@article{Jucha.Xu.ea2014, author = {Jucha, J. and Xu, H. and Pumir, A. and Bodenschatz, E.}, title = {Time-reversal-symmetry Breaking in Turbulence}, journal = {Phys. Rev. Lett.}, month = {July}, year = {2014}, volume = {113}, pages = {054501}, doi = {10.1103/PhysRevLett.113.054501},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.054501} } |
Knoch, F., Tarantola, M., Bodenschatz, E. and Rappel, W., "Modeling self-organized spatio-temporal patterns of PIP3 and PTEN during spontaneous cell polarization", Phys. Biol., July 2014, Vol. 11(4), 046002 pp. |
Abstract: During spontaneous cell polarization of Dictyostelium discoideum cells, phosphatidylinositol (3,4,5)-triphoshpate (PIP3) and PTEN (phosphatase tensin homolog) have been identified as key signaling molecules which govern the process of polarization in a self-organized manner. Recent experiments have quantified the spatio-temporal dynamics of these signaling components. Surprisingly, it was found that membrane-bound PTEN can be either in a high or low state, that PIP3 waves were initiated in areas lacking PTEN through an excitable mechanism, and that PIP3 was degraded even though the PTEN concentration remained low. Here we develop a reaction-diffusion model that aims to explain these experimental findings. Our model contains bistable dynamics for PTEN, excitable dynamics for PIP3, and postulates the existence of two species of PTEN with different dephosphorylation rates. We show that our model is able to produce results that are in good qualitative agreement with the experiments, suggesting that our reaction-diffusion model underlies the self-organized spatio-temporal patterns observed in experiments. |
BibTeX:
@article{Knoch.Tarantola.ea, author = {Knoch, F. and Tarantola, M. and Bodenschatz, E. and Rappel, W.}, title = {Modeling self-organized spatio-temporal patterns of PIP3 and PTEN during spontaneous cell polarization}, journal = {Phys. Biol.}, month = {July}, year = {2014}, volume = {11}, number = {4}, pages = {046002}, doi = {10.1088/1478-3975/11/4/046002},, url = {http://iopscience.iop.org/1478-3975/11/4/046002/article?fromSearchPage=true} } |
Nobach, H. and Bodenschatz, E., "Longitudinal Cross-correlation Function in Fully Turbulent Flow", July 2014 |
Abstract: The application of a simple statistical model to transform temporal correlation functions from one-point measurements into two-point longitudinal spatial cross-correlation functions is investigated. Instead of Taylor’s frozenflow hypothesis a simple advection model with fluctuating velocities and their probability density function is used. This model is valid for long Lagrangian correlation. Based on two-point laser Doppler measurements taken in a turbulent round free air jet, it is shown that it correctly reproduces the time shift including the observed lagging of the correlation peak compared to the mean velocity, the decaying correlation strength, the blur and the arising skewness. This transform is extended to a more flexible advection model, including the decrease of the Lagrangian correlation during the passage of fluid portions through the arrangement of measurement volumes. |
BibTeX:
@proceedings{Nobach.Bodenschatz2014, author = {Nobach, H and Bodenschatz, E.}, title = {Longitudinal Cross-correlation Function in Fully Turbulent Flow}, month = {July}, year = {2014} } |
Wilczek, M., Xu, H. and Narita, Y., "A note on Taylor's hypothesis under large-scale flow variation", Nonlinear Proc. Geoph., June 2014, Vol. 21, 645 pp. |
Abstract: Experimental investigations of turbulent velocity fields often invoke Taylor's hypothesis (also known as frozen turbulence approximation) to evaluate the spatial structure based on time-resolved single-point measurements. A crucial condition for the validity of this approximation is that the turbulent fluctuations are small compared to the mean velocity, in other words, that the turbulence intensity must be low. While turbulence intensity is a well-controlled parameter in laboratory flows, this is not the case in many geo- and astrophysical settings. Here we explore the validity of Taylor's hypothesis based on a simple model for the wavenumber-frequency spectrum that has recently been introduced as a generalization of Kraichnan's random sweeping hypothesis. In this model, the fluctuating velocity is decomposed into a large-scale random sweeping velocity and small-scale fluctuations, which allows for a precise quantification of the influence of large-scale flow variations. For turbulence with a power-law energy spectrum, we find that the wavenumber spectrum estimated by Taylor's hypothesis exhibits the same power-law as the true spectrum, yet the spectral energy is overestimated due to the large-scale flow variation. The magnitude of this effect, and specifically its impact on the experimental determination of the Kolmogorov constant, are estimated for typical turbulence intensities of laboratory and geophysical flows. |
BibTeX:
@article{Wilczek.Xu.ea2014, author = {Wilczek, M. and Xu, H. and Narita, Y.}, title = {A note on Taylor's hypothesis under large-scale flow variation}, journal = {Nonlinear Proc. Geoph.}, month = {June}, year = {2014}, volume = {21}, pages = {645}, doi = {10.5194/npg-21-645-2014},, url = {http://www.nonlin-processes-geophys.net/21/645/2014/npg-21-645-2014.html} } |
He, X., van Gils, D., Bodenschatz, E. and Ahlers, G., "Logarithmic Spatial Variations and Universal f^-1 Power Spectra of Temperature Fluctuations in Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., May 2014, Vol. 112, 174501 pp. |
Abstract: We report measurements of the temperature variance 2(z,r) and frequency power spectrum P(f,z,r) (z is the distance from the sample bottom and r the radial coordinate) in turbulent Rayleigh-Bénard convection (RBC) for Rayleigh numbers Ra = 1.610^13 and 1.110^15 and for a Prandtl number Pr ≃ 0.8 for a sample with a height L = 224 cm and aspect ratio D/L = 0.50 (D is the diameter). For z/L less than or similar to 0.1 2(z,r) was consistent with a logarithmic dependence on z, and there was a universal (independent of Ra, r, and z) normalized spectrum which, for 0.02 less than or similar to f_0 less than or similar to 0.2, had the form P(f_0) = P_0 (f_0)^-1 with P_0 =0.208 ± 0.008 a universal constant. Here _0 = 2R where R is the radius of curvature of the temperature autocorrelation function C() at τ = 0. For z/L ≃ 0.5 the measurements yielded P(f_0) ∼ (f_0)^-α with α in the range from 3/2 to 5/3. All the results are similar to those for velocity fluctuations in shear flows at sufficiently large Reynolds numbers, suggesting the possibility of an analogy between the flows that is yet to be determined in detail. |
BibTeX:
@article{He.Gils.ea2014, author = {He, X. and van Gils, D. and Bodenschatz, E. and Ahlers, G.}, title = {Logarithmic Spatial Variations and Universal f^-1 Power Spectra of Temperature Fluctuations in Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {May}, year = {2014}, volume = {112}, pages = {174501}, doi = {10.1103/PhysRevLett.112.174501},, url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.174501} } |
Horn, S. and Shishkina, O., "Rotating non-Oberbeck–Boussinesq Rayleigh-Bénard convection in water", Phys. Fluids, May 2014, Vol. 26, 055111 pp. |
Abstract: Rotating Rayleigh–Bénard convection in water is studied in direct numerical simulations, where the temperature dependence of the viscosity, the thermal conductivity, and the density within the buoyancy term is taken into account. In all simulations, the arithmetic mean of the lowest and highest temperature in the system equals 40 °C, corresponding to a Prandtl number of Pr = 4.38. In the non-rotational case, the Rayleigh number Ra ranges from 107 to 1.16 ? 109 and temperature differences Ä up to 70 K are considered, whereas in the rotational case the inverse Rossby number range from 0.07 ≤ 1/Ro ≤ 14.1 is studied for Ä = 40°K with the focus on Ra = 108. The non-Oberbeck–Boussinesq (NOB) effects in water are reflected in an up to 5.5?K enhancement of the center temperature and in an up to 5% reduction of the Nusselt number. The top thermal and viscous boundary layer thicknesses increase and the bottom ones decrease, while the sum of the corresponding top and bottom thicknesses remains as in the classical Oberbeck–Boussinesq (OB) case. Rotation applied to NOB thermal convection reduces the central temperature enhancement. Under NOB conditions the top (bottom) thermal and viscous boundary layers become equal for a slightly larger (smaller) inverse Rossby number than in the OB case. Furthermore, for rapid rotation the thermal bottom boundary layers become thicker than the top ones. The Nusselt number normalized by that in the non-rotating case depends similarly on 1/Ro? in both, the NOB and the OB cases. The deviation between the Nusselt number under OB and NOB conditions is minimal when the thermal and viscous boundary layers are equal. |
BibTeX:
@article{Horn.Shiskina2014, author = {Horn, S. and Shishkina, O.}, title = {Rotating non-Oberbeck–Boussinesq Rayleigh-Bénard convection in water}, journal = {Phys. Fluids}, month = {May}, year = {2014}, volume = {26}, pages = {055111}, doi = {10.1063/1.4878669},, url = {http://scitation.aip.org/content/aip/journal/pof2/26/5/10.1063/1.4878669} } |
Krekhov, A., Decker, W., Pesch, W., Eber, N., Salamon, P., Fekete, B. and Buka, A., "Patterns driven by combined ac and dc electric fields in nematic liquid crystals", Phys. Rev. E, May 2014, Vol. 89, 052507 pp. |
Abstract: The effect of superimposed ac and dc electric fields on the formation of electroconvection and flexoelectric patterns in nematic liquid crystals was studied. For selected ac frequencies, an extended standard model of the electrohydrodynamic instabilities was used to characterize the onset of pattern formation in the two-dimensional parameter space of the magnitudes of the ac and dc electric field components. Numerical as well as approximate analytical calculations demonstrate that depending on the type of patterns and on the ac frequency, the combined action of ac and dc fields may either enhance or suppress the formation of patterns. The theoretical predictions are qualitatively confirmed by experiments in most cases. Some discrepancies, however, seem to indicate the need to extend the theoretical description. |
BibTeX:
@article{Krekhov.Decker.ea2014, author = {Krekhov, A. and Decker, W. and Pesch, W. and Eber, N. and Salamon, P. and Fekete, B. and Buka, A.}, title = {Patterns driven by combined ac and dc electric fields in nematic liquid crystals}, journal = {Phys. Rev. E}, month = {May}, year = {2014}, volume = {89}, pages = {052507}, doi = {10.1103/PhysRevE.89.052507},, url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.89.052507} } |
Vosskuhle, M., Pumir, A., Leveque, E. and Wilkinson, M., "Prevalence of the sling effect for enhancing collision rates in turbulent suspensions", Journal of Fluid Mechanics, May 2014, Vol. 749, 841 pp. |
Abstract: Turbulence facilitates collisions between particles suspended in a turbulent flow. Two effects have been proposed that can enhance the collision rate at high turbulence intensities: ‘preferential concentration’ (a clustering phenomenon) and the ‘sling effect’ (arising from the formation of caustic folds in the phase space of the suspended particles). We have determined numerically the collision rate of small heavy particles as a function of their size and densities. The dependence on particle densities allows us to quantify the contribution of the sling effect to the collision rate. Our results demonstrate that the sling effect provides the dominant mechanism to the enhancement of the collision rate of particles, when inertia becomes significant. |
BibTeX:
@article{Vosskuhle.Pumir.ea2014, author = {Vosskuhle, M. and Pumir, A. and Leveque, E. and Wilkinson, M.}, title = {Prevalence of the sling effect for enhancing collision rates in turbulent suspensions}, journal = {Journal of Fluid Mechanics}, month = {May}, year = {2014}, volume = {749}, pages = {841}, doi = {10.1017/jfm.2014.259},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9270846&fileId=S0022112014002596} } |
Xu, H., Pumir, A., Falkovich, G., Bodenschatz, E., Shats, M., Xia, H., Francois, N. and Boffetta, G., "Flight-crash events in turbulence", Proc. Natl. Acad. Sci. U.S.A., May 2014, Vol. 111(21), 7558 pp. |
Abstract: The statistical properties of turbulence differ in an essential way from those of systems in or near thermal equilibrium because of the flux of energy between vastly different scales at which energy is supplied and at which it is dissipated. We elucidate this difference by studying experimentally and numerically the fluctuations of the energy of a small fluid particle moving in a turbulent fluid. We demonstrate how the fundamental property of detailed balance is broken, so that the probabilities of forward and backward transitions are not equal for turbulence. In physical terms, we found that in a large set of flow configurations, fluid elements decelerate faster than accelerate, a feature known all too well from driving in dense traffic. The statistical signature of rare "flight-crash" events, associated with fast particle deceleration, provides away to quantify irreversibility in a turbulent flow. Namely, we find that the third moment of the power fluctuations along a trajectory, nondimensionalized by the energy flux, displays a remarkable power law as a function of the Reynolds number, both in two and in three spatial dimensions. This establishes a relation between the irreversibility of the system and the range of active scales. We speculate that the breakdown of the detailed balance characterized here is a general feature of other systems very far from equilibrium, displaying a wide range of spatial scales. |
BibTeX:
@article{Xu.Pumir.ea2014a, author = {Xu, H. and Pumir, A. and Falkovich, G. and Bodenschatz, E. and Shats, M. and Xia, H. and Francois, N. and Boffetta, G.}, title = {Flight-crash events in turbulence}, journal = {Proc. Natl. Acad. Sci. U.S.A.}, month = {May}, year = {2014}, volume = {111}, number = {21}, pages = {7558}, doi = {10.1073/pnas.1321682111},, url = {http://www.pnas.org/content/111/21/7558.short} } |
Luther, S., Bodenschatz, E., Krinski, V., Gilmour, R. and Fenton, F., "Apparatus for and Method of Terminating a High Frequency Arrhythmic Electric State of a Biological Tissue", Patent, April 2014(US20140107721 A1) |
Abstract: For terminating a high frequency arrhythmic electric state of a biological tissue an electric signal representative of the present electric state of the biological tissue is obtained. From the electric signal a dominant frequency of the present electric state is determined, and from the dominant frequency it is determined whether the present electric state of the biological tissue is a high frequency arrhythmic electric state. Further, a dominance level indicative of how dominant the dominant frequency is in the high frequency arrhythmic electric state is determined from the electric signal. Depending on the at least one dominant frequency, at least one series of electric pulses at intervals is generated. The electric pulses are applied to the biological tissue starting at a point in time at which the dominance level exceeds a predefined threshold value for the biological tissue being in a determined high frequency arrhythmic electric state. |
BibTeX:
@article{Luther.Bodenschatz.ea2014, author = {Luther, S. and Bodenschatz, E. and Krinski, V. and Gilmour, R. and Fenton, F.}, title = {Apparatus for and Method of Terminating a High Frequency Arrhythmic Electric State of a Biological Tissue}, journal = {Patent}, month = {April}, year = {2014}, number = {US20140107721 A1},, url = {http://www.google.com/patents/US20140107721} } |
Zykov, V. S. and Bodenschatz, E., "Stabilized wave segments in an excitable medium with a phase wave at the wave back", New J. Phys., April 2014, Vol. 16(4), 043030 pp. |
Abstract: The propagation velocity and the shape of a stationary propagating wave segment are determined analytically for excitable media supporting excitation waves with trigger fronts and phase backs. The general relationships between the medium?s excitability and the wave segment parameters are obtained in the framework of the free boundary approach under quite usual assumptions. Two universal limits restricting the region of existence of stabilized wave segments are found. The comparison of the analytical results with numerical simulations of the well-known Kessler–Levine model demonstrates their good quantitative agreement. The findings should be applicable to a wide class of systems, such as the propagation of electrical waves in the cardiac muscle or wave propagation in autocatalytic chemical reactions, due to the generality of the free-boundary approach used. |
BibTeX:
@article{Zykov.Bodenschatz2014a, author = {Zykov, V. S. and Bodenschatz, E.}, title = {Stabilized wave segments in an excitable medium with a phase wave at the wave back}, journal = {New J. Phys.}, month = {April}, year = {2014}, volume = {16}, number = {4}, pages = {043030}, doi = {10.1088/1367-2630/16/4/043030},, url = {http://iopscience.iop.org/1367-2630/16/4/043030} } |
Xiang, G., Hong, Z., Zykov, V. S. and Bodenschatz, E., "Stationary propagation of a wave segment along an inhomogeneous excitable stripe", New J. Phys., March 2014, Vol. 16(3), 033012 pp. |
Abstract: We report a numerical and theoretical study of an excitation wave propagating along an inhomogeneous stripe of an excitable medium. The stripe inhomogeneity is due to a jump of the propagation velocity in the direction transverse to the wave motion. Stationary propagating wave segments of rather complicated curved shapes are observed. We demonstrate that the stationary segment shape strongly depends on the initial conditions which are used to initiate the excitation wave. In a certain parameter range, the wave propagation is blocked at the inhomogeneity boundary, although the wave propagation is supported everywhere within the stripe. A free-boundary approach is applied to describe these phenomena which are important for a wide variety of applications from cardiology to information processing. |
BibTeX:
@article{Xiang.Hong.ea, author = {Xiang, G. and Hong, Z. and Zykov, V. S. and Bodenschatz, E.}, title = {Stationary propagation of a wave segment along an inhomogeneous excitable stripe}, journal = {New J. Phys.}, month = {March}, year = {2014}, volume = {16}, number = {3}, pages = {033012}, doi = {10.1088/1367-2630/16/3/033012},, url = {http://iopscience.iop.org/1367-2630/16/3/033012} } |
Zykov, V. S. and Bodenschatz, E., "Continous Transition between Two Limits of Spiral Wave Dynamics in an Excitable Medium", Phys. Rev. Lett., February 2014, Vol. 112, 054101 pp. |
Abstract: By application of a free-boundary approach, we prove the existence of a continuous transition and a full spectrum of solutions between the two known limits of spiral wave dynamics. We identify a control parameter whose essential importance was not realized in earlier studies of spatiotemporal pattern selection in excitable media. The predictions of the free-boundary approach are in good quantitative agreement with results from numerical reaction-diffusion simulations performed on the modified Barkley model. |
BibTeX:
@article{Zykov.Bodenschatz2014, author = {Zykov, V. S. and Bodenschatz, E.}, title = {Continous Transition between Two Limits of Spiral Wave Dynamics in an Excitable Medium}, journal = {Phys. Rev. Lett.}, month = {February}, year = {2014}, volume = {112}, pages = {054101}, doi = {10.1103/PhysRevLett.112.054101},, url = {http://prl.aps.org/abstract/PRL/v112/i5/e054101} } |
Xi, H., Xu, H. and Bodenschatz, E., "Effects of Polymer Additive on Turbulent Bulk Flow: The Polymer Concentration Dependence", January 2014, 57 pp. |
Abstract: We report an experimental study of the effects of polymer additives on the turbulent bulk flow. Our results confirm that both the acceleration fluctuation a and the velocity fluctuation u of the flow are suppressed when the polymer additives are present and the suppression effect on a is much stronger. We further found that polymer additives enhance the anisotropy of the flow at small scales, but do not affect the anisotropy at large scale very much. These results are qualitatively in agreement with a recent theory which predicts that only scales smaller than a critical scale are affected by the polymer additives. |
BibTeX:
@inbook{Xi.Xu.ea2014, author = {Xi, H. and Xu, H. and Bodenschatz, E.}, title = {Effects of Polymer Additive on Turbulent Bulk Flow: The Polymer Concentration Dependence}, month = {January}, year = {2014}, pages = {57}, doi = {10.1007/978-3-642-40371-2_7},, url = {http://link.springer.com/chapter/10.1007/978-3-642-40371-2_7} } |
Banerjee, D., Ray, S. S., Sahoo, G. and Pandit, R., "Multiscaling in Hall-Magnetohydrodynamic Turbulence: Insights from a Shell Model", Phys. Rev. Lett., October 2013, Vol. 111, 174501 pp. |
Abstract: We show that a shell-model version of the three-dimensional Hall-magnetohydrodynamic (3D Hall-MHD) equations provides a natural theoretical model for investigating the multiscaling behaviors of velocity and magnetic structure functions. We carry out extensive numerical studies of this shell model, obtain the scaling exponents for its structure functions, in both the low-k and high-k power-law ranges of 3D Hall-MHD, and find that the extended-self-similarity (ESS) procedure is helpful in extracting the multiscaling nature of structure functions in the high-k regime, which otherwise appears to display simple scaling. Our results shed light on intriguing solar-wind measurements. |
BibTeX:
@article{Banerjee.Ray.ea2013, author = {Banerjee, D. and Ray, S. S. and Sahoo, G. and Pandit, R.}, title = {Multiscaling in Hall-Magnetohydrodynamic Turbulence: Insights from a Shell Model}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2013}, volume = {111}, pages = {174501}, doi = {10.1103/PhysRevLett.111.174501},, url = {http://arxiv.org/abs/1303.0650} } |
Westendorf, C., "Oscillatory Dynamics of the Actin Cytoskeleton", October 2013 |
Abstract: The actin cytoskeleton is ubiquitously distributed among eukaryotic organisms and determines the shape and the movement of eukaryotic cells. In single migratory cells, rapid and localized actin polymerization often follows an external stimulus, engaging migration towards or away from the stimulus. This process is termed chemotaxis and plays a crucial role in several different eukaryotic processes, for instance the inflammatory response of neutrophils and macrophages, cancer metastasis or the growth of axons. A suitable model system to study the chemotactically induced response of the actin cytoskeleton is the social amoeba Dictyostelium discoideum. Within its life cycle, it exists as an autonomously living and proliferating single cell as well as a differentiated and multicellular organism. The developmental program to multicellularity is engaged under starvation conditions and serves as a survival mechanism. Within this development, the cells become chemotactic towards 3’-5’ cyclic adenosine monophosphate (cAMP), which is emitted spontaneously by cells to attract other amoebae. If a D. discoideum amoeba is exposed to a sudden upshift of external cAMP concentration, the actin cytoskeleton responds biphasically, i.e. an initial sharp increase in filamentous actin concentration is followed by a broader and smaller maximum. This biphasic behavior resembles a damped oscillation, if the input is shortened to a brief pulse of cAMP. Within this thesis, the oscillatory properties of the actin cytoskeleton and the chemotactic signaling cascade, controlling the actin polymerization were probed by different periodic input functions of externally administered cAMP. The pulses were created using the flow photolysis method, in which chemically caged molecules are photochemically released in the microfluidic flow. Pulse lengths down to 1.5 s are possible with concentration switching times below 1 s. The response of the D. discoideum actin cytoskeleton, which was labeled via LimE-GFP (a protein specifically associated with filamentous actin) suggests a resonance of the actin cytoskeleton at input periods equal to 20 s. The second harmonic frequency becomes apparent, above the resonance timescale. Furthermore, the response to short periods suggest an onset of oscillatory behavior, i.e. the actin cytoskeleton follows the external forcing, above input periods of 8 s. This is considerably shorter than the 20 s timescale, previously estimated for the chemotactic signaling cascade. In conjunction with these observations and the observation that a minor fraction of all cells showed selfsustained oscillations of the LimE-GFP fluorescence intensity, we proposed that the actin cytoskeleton and/or the signal processing cascade operate close to an oscillatory instability. A delay differential equation, which shows this type of Hopf bifurcation was successfully used to model the principal observed temporal patterns. The delay was experimentally verified by measuring the delay between LimE-GFP, the polymerization marker and CoroninGFP as well as Aip1-GFP, two labels of the actin depolymerization process. Interestingly self-sustained oscillations of the LimE-GFP label have been reported previously in a D. discoideum knockout mutant of the Arp2/3 regulatory SCAR-complex. One could speculate that, within this mutant, a larger fraction of cells passed the instability criterion, explaining the higher rate of observed oscillations. The oscillatory patterns, obtained by confocal laser scanning microscopy (CLSM), lacked verification by other microscopy techniques and a possible light dependence of the oscillations was supposed. Additional CLSM experiments were conducted within this thesis and such light dependence was not observed. However, it was verified that the oscillations occur globally within the cell. Assuming that the constant polymerization and depolymerization cycles act directly on the cell membrane gave rise to the possibility to read out the height of a cell as a non-optical parameter. Atomic force microscopy (AFM) height measurements over time characterized the difference as stronger fluctuations of the cell height within the SCAR(-)/PIR121(-) knockout mutant. To study the actin cytoskeleton on the timescales of polymerizing filamentous actin bundles other microscopy techniques than CLSM need to be applied. Most prominently the total internal reflection fluorescence microscopy (TIRF) images solely the lower boundary of the specimen on a high time resolution. One way to improve the quality of TIRF imaging is to compress the cell and therefore to confine its lower membrane to the glass surface, increasing the observable parts of the cell. Previous approaches involved overlaying techniques, which lack precise control and stability. Here, easy-to-handle microfluidic-based flattening techniques were developed and characterized. Microfluidic compression devices greatly improved the degree of control over flattening and duration of the experiments, but are nevertheless generable within one to two hours. |
BibTeX:
@phdthesis{Westendorf2013, author = {Westendorf, C.}, title = {Oscillatory Dynamics of the Actin Cytoskeleton}, month = {October}, year = {2013},, url = {http://hdl.handle.net/11858/00-1735-0000-0001-BBAF-E} } |
Bewley, G. P., Saw, E. W. and Bodenschatz, E., "Observation of the sling effect", New J. Phys., August 2013, Vol. 15, 083051 pp. |
Abstract: When cloud particles are small enough, they move with the turbulent air in the cloud. On the other hand, as particles become larger their inertia affects their motions, and they move differently than the air. These inertial dynamics impact cloud evolution and ultimately climate prediction, since clouds govern the Earth's energy balances. However, we lack a simple description of the dynamics. Falkovich et al describe theoretically a new dynamical mechanism called the 'sling effect' by which extreme events in the turbulent air cause idealized inertial cloud particles to break free from the airflow (Falkovich et al 2002 Nature 419 151). The sling effect thereafter causes particle trajectories to cross each other within isolated pockets in the flow, which increases the chance of collisions that forms larger particles. We combined experimental techniques that allow for precise control of a turbulent flow with three-dimensional tracking of multiple particles at unprecedented resolution. In this way, we could observe both the sling effect and crossing trajectories between real particles. We isolated the inertial sling dynamics from those caused by turbulent advection by conditionally averaging the data. We found the dynamics to be universal in terms of a local Stokes number that quantifies the local particle velocity gradients. We measured the probability density of this quantity, which shows that sharp gradients became more frequent as the global Stokes number increased. We observed that sharp compressive gradients in the airflow initiated the sling effect, and that thereafter gradients in the particle flow ran away and steepened in a way that produced singularities in the flow in finite time. During this process both the fluid motions and gravity became unimportant. The results underpin a framework for describing a crucial aspect of inertial particle dynamics and predicting collisions between particles. |
BibTeX:
@article{Bewley.Saw.ea2013, author = {Bewley, G P and Saw, E. W. and Bodenschatz, E.}, title = {Observation of the sling effect}, journal = {New J. Phys.}, month = {August}, year = {2013}, volume = {15}, pages = {083051}, doi = {10.1088/1367-2630/15/8/083051},, url = {http://iopscience.iop.org/1367-2630/15/8/083051/pdf/1367-2630_15_8_083051.pdf} } |
Papke, A. and Battiato, I., "A reduced complexity model for dynamic similarity in obstructed shear flows", Geophys. Res. Lett., August 2013, Vol. 40(15), 3888 pp. |
Abstract: [1] Coupled flows through and over permeable media, also known as obstructed shear flows, are ubiquitous to many environmental systems at different scales, including aquatic flows over sediment beds, and atmospheric flows over crops and cities. Despite their differences, such flows exhibit strong dynamic similarities among systems and scales, as evidenced by the recent finding of empirical universal scaling laws correlating relevant length and velocity scales. We propose a reduced complexity model for obstructed shear channel flows, which couples Brinkman with Reynolds equations to describe the flow within and above the obstruction. We derive scaling laws by intermediate asymptotic analysis of a Darcy-Brinkman type solution in the low permeability limit. The approach highlights the importance of the effective permeability of the obstruction as a critical parameter governing the system dynamical response. The model results are in good agreement with the scaling laws empirically calculated in other studies. |
BibTeX:
@article{Papke.Battiato2013, author = {Papke, A. and Battiato, I.}, title = {A reduced complexity model for dynamic similarity in obstructed shear flows}, journal = {Geophys. Res. Lett.}, month = {August}, year = {2013}, volume = {40}, number = {15}, pages = {3888}, doi = {10.1002/grl.50759},, url = {http://onlinelibrary.wiley.com/doi/10.1002/grl.50759/abstract} } |
Xi, H., Bodenschatz, E. and Xu, H., "Elastic Energy Flux by Flexible Polymers in Fluid Turbulence", Phys. Rev. Lett., July 2013, Vol. 111(2), 024501 pp. |
Abstract: We present a study of the energy transfer in the bulk of a turbulent flow with dilute long-chain polymer additives. Based on prior work by Tabor and de Gennes [ Europhys. Lett. 2 519 (1986)], we propose a theory on the energy flux into the elastic degrees of freedom of the polymer chains. This elastic energy flux, which increases as the length scale decreases, gradually reduces the energy transferred to smaller scales through turbulence cascade and hence suppresses small scale fluctuations. The balance of the elastic energy flux and the turbulence energy cascade gives an elastic length scale, which describes the effect of polymer elasticity on turbulence in the inertial range. Predictions of this new “energy flux balance theory” agree excellently with our experimental results. |
BibTeX:
@article{Xi.Bodenschatz.ea2013, author = {Xi, H. and Bodenschatz, E. and Xu, H.}, title = {Elastic Energy Flux by Flexible Polymers in Fluid Turbulence}, journal = {Phys. Rev. Lett.}, month = {July}, year = {2013}, volume = {111}, number = {2}, pages = {024501}, doi = {10.1103/PhysRevLett.111.024501},, url = {http://prl.aps.org/abstract/PRL/v111/i2/e024501} } |
He, X., Funfschilling, D., Nobach, H., Bodenschatz, E. and Ahlers, G., "Comment on ``Effect of Boundary Layers Asymmetry on Heat Transfer Efficiency in Turbulent Rayleigh-Bénard Convection at Very High Rayleigh Numbers''", Phys. Rev. Lett., May 2013, Vol. 110(19), 199401 pp. |
BibTeX:
@article{He.Funfschilling.ea2013, author = {He, X. and Funfschilling, D. and Nobach, H. and Bodenschatz, E. and Ahlers, G.}, title = {Comment on ``Effect of Boundary Layers Asymmetry on Heat Transfer Efficiency in Turbulent Rayleigh-Bénard Convection at Very High Rayleigh Numbers''}, journal = {Phys. Rev. Lett.}, month = {May}, year = {2013}, volume = {110}, number = {19}, pages = {199401}, doi = {10.1103/PhysRevLett.110.199401},, url = {http://prl.aps.org/abstract/PRL/v110/i19/e199401} } |
Schäfer, E., Aue, D., Tarantola, M., Polo, E., Westendorf, C., Oikawa, N., Bodenschatz, E., Geil, B. and Janshoff, A., "Collective behavior of Dictyostelium discoideum monitored by impedance analysis", Commun. Integr. Biol., May 2013, Vol. 6(3), e23894 pp. |
Abstract: Dictyostelium discoideum cells respond to periodic signals of extracellular cAMP by collective changes of cell-cell and cell-substrate contacts. This was confirmed by dielectric analysis employing electric cell-substrate impedance sensing (ECIS) and impedance measurements involving cell-filled micro channels in conjunction with optical microscopy providing a comprehensive picture of chemotaxis under conditions of starvation. |
BibTeX:
@article{Schafer.Aue.ea2013, author = {Schäfer, E. and Aue, D. and Tarantola, M. and Polo, E. and Westendorf, C. and Oikawa, N. and Bodenschatz, E. and Geil, B. and Janshoff, A.}, title = {Collective behavior of Dictyostelium discoideum monitored by impedance analysis}, journal = {Commun. Integr. Biol.}, month = {May}, year = {2013}, volume = {6}, number = {3}, pages = {e23894}, doi = {10.1371/journal.pone.0054172},, url = {http://www.landesbioscience.com/journals/cib/article/23894/?show_full_text=true&#} } |
Westendorf, C., Bodenschatz, E. and Beta, C., "Amöben mit Rhythmus", ChemieXtra, May 2013, Vol. 5, 16 pp. |
BibTeX:
@article{Westendorf.Bodenschatz.ea2013, author = {Westendorf, C. and Bodenschatz, E. and Beta, C.}, title = {Amöben mit Rhythmus}, journal = {ChemieXtra}, month = {May}, year = {2013}, volume = {5}, pages = {16},, url = {http://www.lfpn.ds.mpg.de/Docs/amoeben-mit-rhytmus.pdf} } |
Wilczek, M., Xu, H., Ouellette, N. T., Friedrich, R. and Bodenschatz, E., "Generation of Lagrangian intermittency in turbulence by a self-similar mechanism", New J. Phys., May 2013, Vol. 15, 055015 pp. |
Abstract: Intermittency, i.e., extreme fluctuations at small scales, causes the deviation of turbulence statistics from Kolmogorov's 1941 theoretical predictions. Intermittency effects are especially strong for Lagrangian statistics. Our understanding of how Lagrangian intermittency manifests, however, is still elusive. Here, we study the Lagrangian intermittency in the framework of an exact, yet unclosed probability density function (PDF) equation. Combining this theoretical approach with data from experiments and simulations, no a priori phenomenological assumptions about the structure or properties of the flow have to be made. In this description, the non-self-similar evolution of the velocity increment PDF is determined at all scales by a single function, which is accessible through data from experiments and simulations. This 'intermittency generating function' arises from the dependence of the acceleration of a fluid element on its velocity history, thereby coupling different scales of turbulent motion. Empirically, we find that the intermittency generating function has a simple, approximately self-similar form, which has the surprising implication that Lagrangian intermittency—the absence of self-similarity in the Lagrangian velocity increment statistics—is driven by a self-similar mechanism. The simple form of the intermittency generating function furthermore allows us to formulate a simple model parametrization of the velocity increment PDFs. |
BibTeX:
@article{Wilczek.Xu.ea2013, author = {Wilczek, M. and Xu, H. and Ouellette, N. T. and Friedrich, R. and Bodenschatz, E.}, title = {Generation of Lagrangian intermittency in turbulence by a self-similar mechanism}, journal = {New J. Phys.}, month = {May}, year = {2013}, volume = {15}, pages = {055015}, doi = {10.1088/1367-2630/15/5/055015},, url = {http://iopscience.iop.org/1367-2630/15/5/055015/} } |
Pumir, A., Bodenschatz, E. and Xu, H., "Tetrahedron deformation and alignment of perceived vorticity and strain in a turbulent flow", Phys. Fluids, March 2013, Vol. 25(3), 035101 pp. |
Abstract: We describe the structure and dynamics of turbulence by the scale-dependent perceived velocity gradient tensor as supported by following four tracers, i.e., fluid particles, that initially form a regular tetrahedron. We report results from experiments in a von K?rm?n swirling water flow and from numerical simulations of the incompressible Navier-Stokes equation. We analyze the statistics and the dynamics of the perceived rate of strain tensor and vorticity for initially regular tetrahedron of size r0 from the dissipative to the integral scale. Just as for the true velocity gradient, at any instant, the perceived vorticity is also preferentially aligned with the intermediate eigenvector of the perceived rate of strain. However, in the perceived rate of strain eigenframe fixed at a given time t = 0, the perceived vorticity evolves in time such as to align with the strongest eigendirection at t = 0. This also applies to the true velocity gradient. The experimental data at the higher Reynolds number suggests the existence of a self-similar regime in the inertial range. In particular, the dynamics of alignment of the perceived vorticity and strain can be rescaled by t0, the turbulence time scale of the flow when the scale r0 is in the inertial range. For smaller Reynolds numbers we found the dynamics to be scale dependent. |
BibTeX:
@article{Pumir.Bodenschatz.ea2013, author = {Pumir, A. and Bodenschatz, E. and Xu, H.}, title = {Tetrahedron deformation and alignment of perceived vorticity and strain in a turbulent flow}, journal = {Phys. Fluids}, month = {March}, year = {2013}, volume = {25}, number = {3}, pages = {035101}, doi = {10.1063/1.4795547},, url = {http://pof.aip.org/resource/1/phfle6/v25/i3/p035101_s1?isAuthorized=no} } |
Westendorf, C., Negrete, J. j., Bae, A., Sandmann, R., Bodenschatz, E. and Beta, C., "Actin cytoskeleton of chemotactic amoebae operates close to the onset of oscillations", Proc. Natl. Acad. Sci. U.S.A., March 2013, Vol. 110(10), 3853 pp. |
Abstract: The rapid reorganization of the actin cytoskeleton in response to external stimuli is an essential property of many motile eukaryotic cells. Here, we report evidence that the actin machinery of chemotactic Dictyostelium cells operates close to an oscillatory instability. When averaging the actin response of many cells to a short pulse of the chemoattractant cAMP, we observed a transient accumulation of cortical actin reminiscent of a damped oscillation. At the single-cell level, however, the response dynamics ranged from short, strongly damped responses to slowly decaying, weakly damped oscillations. Furthermore, in a small subpopulation, we observed self-sustained oscillations in the cortical F-actin concentration. To substantiate that an oscillatory mechanism governs the actin dynamics in these cells, we systematically exposed a large number of cells to periodic pulse trains of different frequencies. Our results indicate a resonance peak at a stimulation period of around 20 s. We propose a delayed feedback model that explains our experimental findings based on a time-delay in the regulatory network of the actin system. To test the model, we performed stimulation experiments with cells that express GFP-tagged fusion proteins of Coronin and actin-interacting protein 1, as well as knockout mutants that lack Coronin and actin-interacting protein 1. These actin-binding proteins enhance the disassembly of actin filaments and thus allow us to estimate the delay time in the regulatory feedback loop. Based on this independent estimate, our model predicts an intrinsic period of 20 s, which agrees with the resonance observed in our periodic stimulation experiments. |
BibTeX:
@article{Westendorf.Negrete.ea2013, author = {Westendorf, C. and Negrete, J. jr. and Bae, A. and Sandmann, R. and Bodenschatz, E. and Beta, C.}, title = {Actin cytoskeleton of chemotactic amoebae operates close to the onset of oscillations}, journal = {Proc. Natl. Acad. Sci. U.S.A.}, month = {March}, year = {2013}, volume = {110}, number = {10}, pages = {3853}, doi = {10.1073/pnas.1216629110},, url = {http://www.pnas.org/content/110/10/3853.short} } |
Belan, M., Massaglia, S., Mirzaei, M., Tordella, D., De Ponte, S., Mignone, A., Ferrari, A. and Bodenschatz, E., "An investigation of the hydrodynamics of hypersonic jets in astrophysical conditions", EDP sciences, February 2013, Vol. 58, 137 pp. |
Abstract: Hypersonic, collimated jets are being lately intensively studied in Earth laboratories, trying to reproduce some of the physical properties of a subclass of astrophysical jets that are the Herbig-Haro (HH) jets. These jets are produced in the regions around Young Stellar Objects (YSOs), that are proto-stars located inside galactic Giant Molecular Clouds. In addition to the novel experimental approach, HH or YSO jets have been object of interest by the astrophysical community since a few decades and studied by means of observations at different wavelengths and analytical and numerical modeling. We present laboratory experiments and 2D numerical simulations of hypersonic jets, comparing the results of experiments and simulations that reproduce the evolution of the above mentioned jets. The experimental flows match two main scaling parameter requirements for proto-stellar jets, i.e. the ejection Mach number M and the jet/ambient density ratio eta. In particular, eta goes from slightly underdense to overdense values. Furthermore, as a development of previous works, we consider here the dependence of the jet structure and morphology on the Mach number, in the range 10 to 15. |
BibTeX:
@article{Belan.Massaglia.ea2013, author = {Belan, M. and Massaglia, S. and Mirzaei, M. and Tordella, D. and De Ponte, S. and Mignone, A. and Ferrari, A. and Bodenschatz, E.}, title = {An investigation of the hydrodynamics of hypersonic jets in astrophysical conditions}, journal = {EDP sciences}, month = {February}, year = {2013}, volume = {58}, pages = {137}, doi = {10.1051/eas/1258022},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8838091&fileId=S1633476058000223} } |
Frisch, U., Ray, S. S., Sahoo, G., Banerjee, D. and Pandit, R., "Real-Space Manifestations of Bottlenecks in Turbulence Spectra", Phys. Rev. Lett., February 2013, Vol. 110(6), 064501 pp. |
Abstract: An energy-spectrum bottleneck, a bump in the turbulence spectrum between the inertial and dissipation ranges, is shown to occur in the nonturbulent, one-dimensional, hyperviscous Burgers equation and found to be the Fourier-space signature of oscillations in the real-space velocity, which are explained by boundary-layer-expansion techniques. Pseudospectral simulations are used to show that such oscillations occur in velocity correlation functions in one- and three-dimensional hyperviscous hydrodynamical equations that display genuine turbulence. |
BibTeX:
@article{Frisch.Ray.ea2013, author = {Frisch, U. and Ray, S. S. and Sahoo, G. and Banerjee, D. and Pandit, R.}, title = {Real-Space Manifestations of Bottlenecks in Turbulence Spectra}, journal = {Phys. Rev. Lett.}, month = {February}, year = {2013}, volume = {110}, number = {6}, pages = {064501}, doi = {10.1103/PhysRevLett.110.064501},, url = {http://prl.aps.org/abstract/PRL/v110/i6/e064501} } |
Klein, S., Gibert, M., Bérut, A. and Bodenschatz, E., "Simultaneous 3D Measurement of the Translation and Rotation of Finite-size Particles and the flow Field in a Fully Developed Turbulent Water Flow", Meas. Sci. Technol., February 2013, Vol. 24(2), 024006 pp. |
Abstract: We report a novel experimental technique that measures simultaneously in three dimensions the trajectories, the translation and the rotation of finite-size inertial particles together with the turbulent flow. The flow field is analyzed by tracking the temporal evolution of small fluorescent tracer particles. The inertial particles consist of a super-absorbent polymer that renders them index and density matched with water and thus invisible. The particles are marked by inserting at various locations tracer particles into the polymer. Translation and rotation, as well as the flow field around the particle are recovered dynamically from the analysis of the marker and tracer particle trajectories. We apply this technique to study the dynamics of inertial particles much larger in size ( R p /eta ap 100) than the Kolmogorov length scale eta in a von Kaacutermaacuten swirling water flow ( R lambda ap 400). We show, using the mixed (particle/fluid) Eulerian second-order velocity structure function, that the interaction zone between the particle and the flow develops in a spherical shell of width 2 R p around the particle of radius R p . This we interpret as an indication of a wake induced by the particle. This measurement technique has many additional advantages that will make it useful to address other problems such as particle collisions, dynamics of non-spherical solid objects, or even of wet granular matter. |
BibTeX:
@article{Klein.Gibert.ea2013, author = {Klein, S. and Gibert, M. and Bérut, A. and Bodenschatz, E.}, title = {Simultaneous 3D Measurement of the Translation and Rotation of Finite-size Particles and the flow Field in a Fully Developed Turbulent Water Flow}, journal = {Meas. Sci. Technol.}, month = {February}, year = {2013}, volume = {24}, number = {2}, pages = {024006}, doi = {10.1088/0957-0233/24/2/024006},, url = {http://iopscience.iop.org/0957-0233/24/2/024006/} } |
Schäfer, E., Tarantola, M., Polo, E., Westendorf, C., Oikawa, N., Bodenschatz, E., Geil, B. and Janshoff, A., "Chemotaxis of Dictyostelium discoideum: Collective Oscillation of Cellular Contacts", PLOS ONE, January 2013, Vol. 8, e54172 pp. |
Abstract: Chemotactic responses of Dictyostelium discoideum cells to periodic self-generated signals of extracellular cAMP comprise a large number of intricate morphological changes on different length scales. Here, we scrutinized chemotaxis of single Dictyostelium discoideum cells under conditions of starvation using a variety of optical, electrical and acoustic methods. Amebas were seeded on gold electrodes displaying impedance oscillations that were simultaneously analyzed by optical video microscopy to relate synchronous changes in cell density, morphology, and distance from the surface to the transient impedance signal. We found that starved amebas periodically reduce their overall distance from the surface producing a larger impedance and higher total fluorescence intensity in total internal reflection fluorescence microscopy. Therefore, we propose that the dominant sources of the observed impedance oscillations observed on electric cell-substrate impedance sensing electrodes are periodic changes of the overall cell-substrate distance of a cell. These synchronous changes of the cell-electrode distance were also observed in the oscillating signal of acoustic resonators covered with amebas. We also found that periodic cell-cell aggregation into transient clusters correlates with changes in the cell-substrate distance and might also contribute to the impedance signal. It turned out that cell-cell contacts as well as cell-substrate contacts form synchronously during chemotaxis of Dictyostelium discoideum cells. |
BibTeX:
@article{Schafer.Tarantola.ea2013, author = {Schäfer, E. and Tarantola, M. and Polo, E. and Westendorf, C. and Oikawa, N. and Bodenschatz, E. and Geil, B. and Janshoff, A.}, title = {Chemotaxis of Dictyostelium discoideum: Collective Oscillation of Cellular Contacts}, journal = {PLOS ONE}, month = {January}, year = {2013}, volume = {8}, pages = {e54172}, doi = {10.1371/journal.pone.0054172},, url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0054172} } |
Nobach, H. and Tropea, C., "A statistical method for transforming temporal correlation functions from one-point measurements into longitudinal spatial and spatio-temporal correlation functions", Exp. Fluids, December 2012, Vol. 53(6), 1815 pp. |
Abstract: The transformation of temporal, one-point correlation functions into longitudinal spatial and spatio-temporal correlation functions in turbulent flows using a simple statistical convection model is introduced. To illustrate and verify the procedure, experimental data (one-point and two-point) have been obtained with a laser Doppler system from a turbulent, round, free-air jet. |
BibTeX:
@article{Nobach.Tropea2012, author = {Nobach, H. and Tropea, C.}, title = {A statistical method for transforming temporal correlation functions from one-point measurements into longitudinal spatial and spatio-temporal correlation functions}, journal = {Exp. Fluids}, month = {December}, year = {2012}, volume = {53}, number = {6}, pages = {1815}, doi = {10.1007/s00348-012-1392-3},, url = {http://link.springer.com/article/10.1007%2Fs00348-012-1392-3} } |
Rosman, C., Pierrat, S., Henkel, A., Tarantola, M., Schneider, D., Sunnick, E., Janshoff, A. and Sönnichsen, C., "A New Approach to Assess Gold Nanoparticle Uptake by Mammalian Cells: Combining Optical Dark-Field and Transmission Electron Microscopy", Small, December 2012, Vol. 8(23), 3683 pp. |
Abstract: Toxicological effects of nanoparticles are associated with their internalization into cells. Hence, there is a strong need for techniques revealing the interaction between particles and cells as well as quantifying the uptake at the same time. For that reason, herein optical dark-field microscopy is used in conjunction with transmission electron microscopy to investigate the uptake of gold nanoparticles into epithelial cells with respect to shape, stabilizing agent, and surface charge. The number of internalized particles is strongly dependent on the stabilizing agent, but not on the particle shape. A test of metabolic activity shows no direct correlation with the number of internalized particles. Therefore, particle properties besides coating and shape are suspected to contribute to the observed toxicity. |
BibTeX:
@article{Rosman.Pierrat.ea2012, author = {Rosman, C. and Pierrat, S. and Henkel, A. and Tarantola, M. and Schneider, D. and Sunnick, E. and Janshoff, A. and Sönnichsen, C.}, title = {A New Approach to Assess Gold Nanoparticle Uptake by Mammalian Cells: Combining Optical Dark-Field and Transmission Electron Microscopy}, journal = {Small}, month = {December}, year = {2012}, volume = {8}, number = {23}, pages = {3683}, doi = {10.1002/smll.201200853},, url = {http://onlinelibrary.wiley.com/doi/10.1002/smll.201200853/abstract} } |
Gholami, A., Enculescu, M. and Falcke, M., "Membrane waves driven by forces from actin filaments", New J. Phys., November 2012, Vol. 14, 115002 pp. |
Abstract: Membrane waves propagating along the cell circumference in a top down view have been observed with several eukaryotic cells (Dobereiner et al 2006 Phys. Rev. Lett. 97 10; Machacek and Danuser 2006 Biophys. J. 90 1439-52). We present a mathematical model reproducing these traveling membrane undulations during lamellipodial motility of cells on flat substrates. The model describes the interplay of pushing forces exerted by actin polymerization on the membrane, pulling forces of attached actin filaments on the cell edge, contractile forces powered by molecular motors across the actin gel and resisting membrane tension. The actin filament network in the bulk of lamellipodia obeys gel flow equations. We investigated in particular the dependence of wave properties on gel parameters and found that inhibition of myosin motors abolishes waves in some cells but not in others in agreement with experimental observations. The model provides a unifying mechanism explaining the dynamics of actin-based motility in a variety of systems. |
BibTeX:
@article{Gholami.Enculescu.ea2012, author = {Gholami, A. and Enculescu, M. and Falcke, M.}, title = {Membrane waves driven by forces from actin filaments}, journal = {New J. Phys.}, month = {November}, year = {2012}, volume = {14}, pages = {115002}, doi = {10.1088/1367-2630/14/11/115002},, url = {http://iopscience.iop.org/1367-2630/14/11/115002/} } |
Wu, H. X., Miorini, R. L., Tan, D. and Katz, J., "Turbulence Within the Tip-Leakage Vortex of an Axial Waterjet Pump", AIAA Journal, November 2012, Vol. 50(11), 2574 pp. |
Abstract: Stereoscopic particle image velocimetry measurements are performed in an optical refractive index matched facility to investigate the evolution of turbulence in the tip region of an axial waterjet pump rotor. Presented analysis of mean flow velocity, vorticity, Reynolds stresses, and turbulence production/transport within the rotor passage focus on the tip-leakage vortex and associated flows. Turbulence production peaks in the shear layer that connects the blade-tip suction side with the vortex as well as in a region of flow contraction situated at the casing wall. Flow separation occurring there, as the leakage backflow meets the throughflow, detaches the boundary-layer vorticity, which is entrained into the tip-vortex perimeter. Upon the inclusion of turbulence transport in the analysis, a discrepancy between distributions of turbulent stresses and associated production vanishes, except at the vortex core. There, the elevated turbulent energy (but relatively low production of Reynolds stresses) is presumably due to low dissipation. Within the aft part of the rotor passage, shortly after vortex bursting, the tip-leakage backflow reaches the neighboring blade. There, radial motion induced by the tip-vortex residual swirl detaches the pressure-side boundary-layer vorticity and injects it into the rotor passage. |
BibTeX:
@article{Wu.Miorini.ea2012, author = {Wu, H. X. and Miorini, R. L. and Tan, D. and Katz, J.}, title = {Turbulence Within the Tip-Leakage Vortex of an Axial Waterjet Pump}, journal = {AIAA Journal}, month = {November}, year = {2012}, volume = {50}, number = {11}, pages = {2574}, doi = {10.2514/1.J051491},, url = {http://arc.aiaa.org/doi/abs/10.2514/1.J051491} } |
Ahlers, G., He, X., Funfschilling, D. and Bodenschatz, E., "Heat transport by turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and 3×10^12 less than or similar to Ra less than or similar to 10^15: aspect ratio Gamma=0.50", New J. Phys., October 2012, Vol. 14, 103012 pp. |
Abstract: We report on the experimental results for heat-transport measurements, in the form of the Nusselt number Nu, by turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratio Gamma equivalent to D/L = 0.50 (D = 1.12m is the diameter and L = 2.24m the height). The measurements were made using sulfur hexafluoride at pressures up to 19 bar as the fluid. They are for the Rayleigh-number range 3 x 10(12) less than or similar to Ra less than or similar to 10(15) and for Prandtl numbers Pr between 0.79 and 0.86. For Ra < Ra-1* similar or equal to 1.4 x 10(13) we find Nu = N-0 Ra-gamma eff with gamma(eff) = 0.312 +/- 0.002, which is consistent with classical turbulent RBC in a system with laminar boundary layers below the top and above the bottom plate. For Ra-1* < Ra < Ra-2* (with Ra-2* similar or equal to 5 x 10(14)) gamma(eff) gradually increases up to 0.37 +/- 0.01. We argue that above Ra-2* the system is in the ultimate state of convection where the boundary layers, both thermal and kinetic, are also turbulent. Several previous measurements for Gamma = 0.50 are re-examined and compared with our results. Some of them show a transition to a state with gamma(eff) in the range from 0.37 to 0.40, albeit at values of Ra in the range from 9 x 10(10) to 7 x 10(11) which is much lower than the present Ra-1* or Ra-2*. The nature of the transition found by them is relatively sharp and does not reveal the wide transition range observed in this work. In addition to the results for the genuine Rayleigh-Bénard system, we present measurements for a sample which was not completely sealed; the small openings permitted external currents, imposed by density differences and gravity, to pass through the sample. That system should no longer be regarded as genuine RBC because the externally imposed currents modified the heat transport in a major way. It showed a sudden decrease of gamma(eff) from 0.308 for Ra < Ra-t similar or equal to 4 x 10(13) to 0.25 for larger Ra. A number of possible experimental effects are examined in a sequence of appendices; none of these effects is found to have a significant influence on the measurements. |
BibTeX:
@article{Ahlers.He.ea2012, author = {Ahlers, G. and He, X. and Funfschilling, D. and Bodenschatz, E.}, title = {Heat transport by turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and 3×10^12 less than or similar to Ra less than or similar to 10^15: aspect ratio Gamma=0.50}, journal = {New J. Phys.}, month = {October}, year = {2012}, volume = {14}, pages = {103012}, doi = {10.1088/1367-2630/14/10/103012},, url = {http://iopscience.iop.org/1367-2630/14/10/103012/} } |
Baptista, M. S., Rubinger, R. M., Viana, E. R., Sartorelli, J. C., Parlitz, U. and Grebogi, C., "Mutual Information Rate and Bounds for It", PLOS ONE, October 2012, Vol. 7(10), e46745 pp. |
Abstract: The amount of information exchanged per unit of time between two nodes in a dynamical network or between two data sets is a powerful concept for analysing complex systems. This quantity, known as the mutual information rate (MIR), is calculated from the mutual information, which is rigorously defined only for random systems. Moreover, the definition of mutual information is based on probabilities of significant events. This work offers a simple alternative way to calculate the MIR in dynamical (deterministic) networks or between two time series (not fully deterministic), and to calculate its upper and lower bounds without having to calculate probabilities, but rather in terms of well known and well defined quantities in dynamical systems. As possible applications of our bounds, we study the relationship between synchronisation and the exchange of information in a system of two coupled maps and in experimental networks of coupled oscillators. |
BibTeX:
@article{Baptista.Rubinger.ea2012, author = {Baptista, M. S. and Rubinger, R. M. and Viana, E. R. and Sartorelli, J. C. and Parlitz, U. and Grebogi, C.}, title = {Mutual Information Rate and Bounds for It}, journal = {PLOS ONE}, month = {October}, year = {2012}, volume = {7}, number = {10}, pages = {e46745}, doi = {10.1371/journal.pone.0046745},, url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046745} } |
Benczik, I. J. and Vollmer, J., "A Diffusion-induced Transition in the Phase Separation of Binary Fluid Mixtures Subjected to a Temperature Ramp", EPL, October 2012, Vol. 100(1), 16001 pp. |
Abstract: Demixing of binary fluids under slow temperature ramps shows repeated waves of nucleation which arise as a consequence of the competition between generation of supersaturation by the temperature ramp and relaxation of supersaturation by diffusive transport and flow. Here, we use an advection-reaction-diffusion model to study the oscillations in the weak- and strong-diffusion regime. There is a sharp transition between the two regimes, which can only be understood based on the spatial distribution of the composition, rather than in terms of the average composition. Our results shed light on the parameter drift and secondary features observed in phase separating fluids subjected to a temperature ramp, and they bear intriguing communalities with macroscopic oscillations due to synchronization of life cycles in ageing populations. |
BibTeX:
@article{Benczik.Vollmer2012, author = {Benczik, I. J. and Vollmer, J.}, title = {A Diffusion-induced Transition in the Phase Separation of Binary Fluid Mixtures Subjected to a Temperature Ramp}, journal = {EPL}, month = {October}, year = {2012}, volume = {100}, number = {1}, pages = {16001}, doi = {10.1209/0295-5075/100/16001},, url = {http://iopscience.iop.org/0295-5075/100/1/16001/} } |
Kuptsov, P. V. and Parlitz, U., "Theory and Computation of Covariant Lyapunov Vectors", J. Nonlinear Sci., October 2012, Vol. 22(5), 727 pp. |
Abstract: Lyapunov exponents are well-known characteristic numbers that describe growth rates of perturbations applied to a trajectory of a dynamical system in different state space directions. Covariant (or characteristic) Lyapunov vectors indicate these directions. Though the concept of these vectors has been known for a long time, they became practically computable only recently due to algorithms suggested by Ginelli et al. [Phys. Rev. Lett. 99, 2007, 130601] and by Wolfe and Samelson [Tellus 59A, 2007, 355]. In view of the great interest in covariant Lyapunov vectors and their wide range of potential applications, in this article we summarize the available information related to Lyapunov vectors and provide a detailed explanation of both the theoretical basics and numerical algorithms. We introduce the notion of adjoint covariant Lyapunov vectors. The angles between these vectors and the original covariant vectors are norm-independent and can be considered as characteristic numbers. Moreover, we present and study in detail an improved approach for computing covariant Lyapunov vectors. Also we describe how one can test for hyperbolicity of chaotic dynamics without explicitly computing covariant vectors. |
BibTeX:
@article{Kuptsov.Parlitz2012, author = {Kuptsov, P. V. and Parlitz, U.}, title = {Theory and Computation of Covariant Lyapunov Vectors}, journal = {J. Nonlinear Sci.}, month = {October}, year = {2012}, volume = {22}, number = {5}, pages = {727}, doi = {10.1007/s00332-012-9126-5},, url = {http://link.springer.com/article/10.1007%2Fs00332-012-9126-5} } |
Saw, E. W., Salazar, J. P. L. C., Collins, L. R. and Shaw, R. A., "Spatial clustering of polydisperse inertial particles in turbulence: I. Comparing simulation with theory", New J. Phys., October 2012, Vol. 14, 105030 pp. |
Abstract: Particles that are heavy compared to the fluid in which they are embedded (inertial particles) tend to cluster in turbulent flow, with the degree of clustering depending on the particle Stokes number. The phenomenon is relevant to a variety of systems, including atmospheric clouds; in most realistic systems particles have a continuous distribution of sizes and therefore the clustering of 'polydisperse' particle populations is of special relevance. In this work a theoretical expression for the radial distribution function (RDF) for mono- and bidisperse inertial particles in the low Stokes number limit (Chun et al 2005 J. Fluid Mech. 536 219-51) is compared with the results of a direct numerical simulation of particle-laden turbulence. The results confirm the power-law form of the RDF for monodisperse particles with St less than or similar to 0.3. The clustering signature occurs at scales less than or similar to 10-30 times the Kolmogorov scale, consistent with a dissipation-scale mechanism. The theory correctly predicts the decorrelation scale below which bidisperse particles cease to cluster because of their distinct inertial response. A 'saturation' effect was observed, however, in which the power-law exponent is limited by the least clustered particle population. An expression is presented with which a polydisperse RDF can be obtained from the mono-and bidisperse RDFs and the particle size distribution. The DNS data clearly show that the effect of polydispersity is to diminish clustering, and place a bound on the level of polydispersity required to approximate a monodisperse system; this result is of relevance to experimental studies and realistic systems. |
BibTeX:
@article{Saw.Salazar.ea2012, author = {Saw, E. W. and Salazar, J. P. L. C. and Collins, L. R. and Shaw, R. A.}, title = {Spatial clustering of polydisperse inertial particles in turbulence: I. Comparing simulation with theory}, journal = {New J. Phys.}, month = {October}, year = {2012}, volume = {14}, pages = {105030}, doi = {10.1088/1367-2630/14/10/105030},, url = {http://iopscience.iop.org/1367-2630/14/10/105030/} } |
Saw, E. W., Shaw, R. A., Salazar, J. P. L. C. and Collins, L. R., "Spatial clustering of polydisperse inertial particles in turbulence: II. Comparing simulation with experiment", New J. Phys., October 2012, Vol. 14, 105031 pp. |
Abstract: Particles that are heavy compared to the fluid in which they are embedded (inertial particles) tend to cluster in turbulent flow, with the degree of clustering depending on the particle Stokes number. The phenomenon is relevant to a variety of multiphase flows, including atmospheric clouds; in most realistic systems, particles have a continuous distribution of sizes and therefore the clustering of 'polydisperse' particle populations is of special relevance. In this part of the study, measurements of spatial correlations of particles in high-Reynolds-number turbulence are compared with the results of a direct numerical simulation of particle-laden turbulence. The experimentally derived radial distribution functions (RDFs) exhibit a pronounced scale break at approximately 10-30 times the Kolmogorov scale, with large-scale clustering arising from 'scalar mixing' of the droplet field, and smaller-scale clustering depending on the particle Stokes numbers. A procedure is outlined for isolating the RDF due to inertial clustering from that resulting from large-scale mixing. Reasonable agreement between the experiment and the direct numerical simulations (DNS) is obtained for St less than or similar to 0.3 when particle Stokes number distributions in the DNS match those existing in the experiments. The experimental RDFs are consistent with the flattening or saturation scale appearing for bidisperse particles, but as in the companion paper, also support the 'saturation' effect in the asymmetric response of the power-law slope. The evidence for a universal scale break, as observed in both the DNS and the experiments, suggests that the pre-factor in the theoretical expression for the RDF is inherently tied to the power-law exponent, and an empirical form for this is given. Finally, no strong influence of the turbulence Reynolds number was observed for the clustering phenomenon. The consistency between the carefully analyzed DNS and experiments, in terms of St dependence, dissipation-range scale break and saturation of clustering for polydisperse particles, provides an indirect confirmation of the diffusion-drift theory of Chun et al (2005 J. Fluid Mech. 536 219-51). |
BibTeX:
@article{Saw.Shaw.ea2012, author = {Saw, E. W. and Shaw, R. A. and Salazar, J. P. L. C. and Collins, L. R.}, title = {Spatial clustering of polydisperse inertial particles in turbulence: II. Comparing simulation with experiment}, journal = {New J. Phys.}, month = {October}, year = {2012}, volume = {14}, pages = {105031}, doi = {10.1088/1367-2630/14/10/105031},, url = {http://iopscience.iop.org/1367-2630/14/10/105031/} } |
Ahlers, G., Bodenschatz, E., Funfschilling, D., Grossmann, S., He, X., Lohse, D., Stevens, R. J. A. M. and Verzicco, R., "Logarithmic Temperature Profiles in Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., September 2012, Vol. 109(11), 114501 pp. |
Abstract: We report results for the temperature profiles of turbulent Rayleigh-Bénard convection (RBC) in the interior of a cylindrical sample of aspect ratio Gamma equivalent to D/L = 0.50 (D and L are the diameter and height, respectively). Both in the classical and in the ultimate state of RBC we find that the temperature varies as A X ln(z/L) + B, where z is the distance from the bottom or top plate. In the classical state, the coefficient A decreases in the radial direction as the distance from the side wall increases. For the ultimate state, the radial dependence of A has not yet been determined. These findings are based on experimental measurements over the Rayleigh-number range 4 X 10(12) less than or similar to Ra less than or similar to 10(15) for a Prandtl number Pr similar or equal to 0.8 and on direct numerical simulation at Ra = 2 X 10(12), 2 X 10(11), and 2 X 10(10), all for Pr = 0.7. |
BibTeX:
@article{Ahlers.Bodenschatz.ea2012, author = {Ahlers, G. and Bodenschatz, E. and Funfschilling, D. and Grossmann, S. and He, X. and Lohse, D. and Stevens, R. J. A. M. and Verzicco, R.}, title = {Logarithmic Temperature Profiles in Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2012}, volume = {109}, number = {11}, pages = {114501}, doi = {10.1103/PhysRevLett.109.114501},, url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.114501} } |
Amselem, G., Theves, M., Bae, A., Beta, C. and Bodenschatz, E., "Control Parameter Description of Eukaryotic Chemotaxis", Phys. Rev. Lett., September 2012, Vol. 109(10), 108103 pp. |
Abstract: The chemotaxis of eukaryotic cells depends both on the average concentration of the chemoattractant and on the steepness of its gradient. For the social amoeba Dictyostelium discoideum, we test quantitatively the prediction by Ueda and Shibata [Biophys. J. 93, 11 (2007)] that the efficacy of chemotaxis depends on a single control parameter only, namely, the signal-to-noise ratio (SNR), determined by the stochastic fluctuations of (i) the binding of the chemoattractant molecule to the transmembrane receptor and (ii) the intracellular activation of the effector of the signaling cascade. For SNR less than or similar to 1, the theory captures the experimental findings well, while for larger SNR noise sources further downstream in the signaling pathway need to be taken into account. |
BibTeX:
@article{Amselem.Theves.ea2012a, author = {Amselem, G. and Theves, M. and Bae, A. and Beta, C. and Bodenschatz, E.}, title = {Control Parameter Description of Eukaryotic Chemotaxis}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2012}, volume = {109}, number = {10}, pages = {108103}, doi = {10.1103/PhysRevLett.109.108103},, url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.108103} } |
Bewley, G. P. and Vollmer, J., "The journey of hydrogen to quantized vortex cores", Physica Scripta, September 2012, Vol. T155, 014055 pp. |
Abstract: Nanoscale hydrogen particles in superfluid helium track the motions of quantized vortices. This provides a way to visualize turbulence in the superfluid. Here, we trace the evolution of the hydrogen from a gas to frozen particles migrating toward the cores of quantized vortices. Not only are the intervening processes interesting in their own right, but understanding them better leads to more revealing experiments. |
BibTeX:
@article{bewley:2013, author = {G P Bewley and J Vollmer}, title = {The journey of hydrogen to quantized vortex cores}, journal = {Physica Scripta}, month = {September}, year = {2012}, volume = {T155}, pages = {014055}, doi = {10.1088/0031-8949/2013/T155/014055},, url = {http://arxiv.org/abs/1209.4335} } |
Bittihn, P., Hörning, M. and Luther, S., "Negative Curvature Boundaries as Wave Emitting Sites for the Control of Biological Excitable Media", Phys. Rev. Lett., September 2012, Vol. 109, 118106 pp. |
Abstract: Understanding the interaction of electric fields with the complex anatomy of biological excitable media is key to optimizing control strategies for spatiotemporal dynamics in those systems. On the basis of a bidomain description, we provide a unified theory for the electric-field-induced depolarization of the substrate near curved boundaries of generalized shapes, resulting in the localized recruitment of control sites. Our findings are confirmed in experiments on cardiomyocyte cell cultures and supported by two-dimensional numerical simulations on a cross section of a rabbit ventricle. |
BibTeX:
@article{Bittihn.Hoerning.ea2012, author = {Bittihn, P. and Hörning, M. and Luther, S.}, title = {Negative Curvature Boundaries as Wave Emitting Sites for the Control of Biological Excitable Media}, journal = {Phys. Rev. Lett.}, month = {September}, year = {2012}, volume = {109}, pages = {118106}, doi = {10.1103/PhysRevLett.109.118106},, url = {http://prl.aps.org/abstract/PRL/v109/i11/e118106} } |
Capelo, H. L., Herbst, W., Leggett, S. K., Hamilton, C. M. and Johnson, J. A., "Locating the Trailing Edge of the Circumbinary Ring In the KH 15D System", Astrophys. J. Lett., September 2012, Vol. 757(1), L18 pp. |
Abstract: Following two years of complete occultation of both stars in the binary T Tauri star KH 15D by its opaque circumbinary ring, KH 15D has abruptly brightened again during apastron phases, reaching I = 15 mag. Here, we show that the brightening is accompanied by a change in spectral class from K6/K7 (the spectral class of star A) to similar to K1, and a bluing of the system in V - I by about 0.3 mag. A radial velocity measurement confirms that, at apastron, we are now seeing direct light from star B, which is more luminous and of earlier spectral class than star A. Evidently, the trailing edge of the occulting screen has just become tangent to one anse of star B's projected orbit. This confirms a prediction of the precession models, supports the view that the tilted ring is self-gravitating, and ushers in a new era of the system's evolution that should be accompanied by the same kind of dramatic phenomena observed from 1995 to 2009. It also promotes KH 15D from a single-lined to a double-lined eclipsing binary, greatly enhancing its value for testing pre-main-sequence models. The results of our study strengthen the case for truncation of the outer ring at around 4 AU by a sub-stellar object such as an extremely young giant planet. The system is currently at an optimal configuration for detecting the putative planet and we urge expedient follow-up observations. |
BibTeX:
@article{Capelo.Herbst.ea2012, author = {Capelo, H. L. and Herbst, W. and Leggett, S. K. and Hamilton, C. M. and Johnson, J. A.}, title = {Locating the Trailing Edge of the Circumbinary Ring In the KH 15D System}, journal = {Astrophys. J. Lett.}, month = {September}, year = {2012}, volume = {757}, number = {1}, pages = {L18}, doi = {10.1088/2041-8205/757/1/L18},, url = {http://iopscience.iop.org/2041-8205/757/1/L18/} } |
He, X., Funfschilling, D., Nobach, H., Bodenschatz, E. and Ahlers, G., "Measurements of Reynolds numbers near the transition to the ultimate state of turbulent Rayleigh-Bénard convection", September 2012 |
Abstract: A Reynolds number Reeff was measured in turbulent Rayleigh-B?nard convection (RBC) of a cylindrical sample over the Rayleigh-number range 1012 ? Ra ? 1015 and for Prandtl numbers Pr near 0.8 (He et al., 2012). The aspect ratio Ã ? D / L of the cylindrical sample was 0.50 (D = 1.12 m was the diameter and L = 2.24 m was the height). The measurements of Reeff were conducted at a distance L/4 above the bottom plate and 1.0 cm away from the sidewall inside the sample. For Ra ? 1013 the results showed Reeff á Raæeff with æeff ? 0.43, consistent with classical turbulent RBC. After a transition region for 1013 ? Ra ? 5?1014, where multi-stability occurred, we found an exponent æ ? 0.50, in agreement with the predictions of Grossmann and Lohse (2011) for the large-Ra asymptotic state. We believe that our measurements revealed the transition of RBC to the ultimate state predicted by Kraichnan (1962). |
BibTeX:
@inproceedings{He.Funfschilling.ea2012a, author = {He, X. and Funfschilling, D. and Nobach, H. and Bodenschatz, E. and Ahlers, G.}, title = {Measurements of Reynolds numbers near the transition to the ultimate state of turbulent Rayleigh-Bénard convection}, month = {September}, year = {2012},, url = {http://www.dl.begellhouse.com/references/1bb331655c289a0a,7c69ce3452e09525,2b8f6a20709b5d5b.html} } |
Schumacher, J. and Bodenschatz, E., "Focus on new perspectives in high-Rayleigh-number turbulent convection", New J. Phys., September 2012, Vol. 14, 095004 pp. |
Abstract: Part of Focus on New Perspectives in High-Rayleigh-Number Turbulent Convection
Thermal convection in a gravitational field is the source of most large-scale flows on Earth, planets and stars. It is also used to heat houses or to cool passively with metal vanes, as for example in most electronic equipment. The driving force for thermal convection is buoyancy. When a fluid is heated it expands, i.e., it changes its mass density. If the fluid in a gravitational field and heating is applied in such a way that cold, dense fluid is on top of that which is warmer and lighter, the warm fluid will rise when the driving forces of buoyancy overcome viscous drag and thermal diffusion. The experimentally best defined and most studied example is Rayleigh–B?nard convection (RBC), where a horizontal fluid layer is heated from below and cooled from above. For an incompressible fluid and Boussinesq conditions, where due to modest temperature gradients only the linear temperature dependence of density governs the physics, two dimensionless parameters describe the physics. One is the Rayleigh number, Ra, which is proportional to the temperature difference across the fluid layer of thickness, d, and to d3, implying that high Ra can be achieved experimentally at modest temperature differences only with a large d. The other parameter is the Prandtl number, Pr, which describes the relative importance of the convective nonlinearities in the momentum and heat equations. The geometry and thermal boundary conditions of the experimental apparatus are other important factors. Experiments usually strive to realize the theoretically most easily studied boundary conditions, i.e. perfectly conducting top and bottom plates and insulating sidewalls. As mentioned above, situations with large Ra require large cell heights. In experiments, typical geometries chosen are mostly cylindrical, with aspect ratios Ã = diameter/height between 1/4 and 2. For RBC, the onset of convection in an infinitely extended layer between no-slip walls is independent of the Prandtl number and occurs at Ra = 1708 in the form of convection rolls, whose periodicity is given by the layer height. When the temperature difference, and thus the Rayleigh number, increases, i.e., to the order of Ra 107 and larger, the fluid flow becomes turbulent in the bulk and the flow is controlled by instabilities at the boundary layer. The turbulent fluctuations in turn conspire to create large-scale sweeping flows, the so-called 'mean winds' that couple back to the boundary layer dynamics. In addition to the idealized situation of RBC in a Boussinesq fluid, situations closer to the convective flows occuring in nature are of increasingly central interest. One such is the influence of rotation around a vertical axis, with its application to planetary flows, and another is convection with phase changes, with its application to convection and cloud formation in the atmosphere. The global transport of heat and momentum is the persistent riddle in high-Rayleigh number turbulent convection. Detailed knowledge of the physics is required to better understand the energy budgets in the atmospheric flows of stars and planets. The fundamental challenge lies in basic physics, namely the understanding of the complex interaction of boundary layer instabilities, bulk turbulence, coupling to the large-scale sweeping flows, and the trends of the dynamics with increasing Rayleigh number. In this focus issue, the cutting-edge questions of the field are addressed. How important are the boundary layers of the temperature and velocity fields for the global transport? Which flow structures are connected with the local transport processes of heat and momentum? Is there an 'ultimate' regime for heat transport for very high Rayleigh number? How are the transport properties affected when thermodynamic phase changes of the working fluid or rotation are present? These are some of the topics discussed in the contributions to this issue, invited papers from around the world, comprising numerical, theoretical and experimental state-of-the-art works from this research field. We would like to thank all of the contributors for their efforts, and also the referees, whose careful revision added much value to each of the contributions. This focus issue gives a comprehensive overview of recent progress in this exciting and rapidly developing field. |
BibTeX:
@article{Schumacher.Bodenschatz2012, author = {Schumacher, J. and Bodenschatz, E.}, title = {Focus on new perspectives in high-Rayleigh-number turbulent convection}, journal = {New J. Phys.}, month = {September}, year = {2012}, volume = {14}, pages = {095004}, doi = {10.1088/1367-2630/14/9/095004},, url = {http://iopscience.iop.org/1367-2630/14/9/095004?fromSearchPage=true} } |
Suetani, H., Soejima, K., Matsuoka, R., Parlitz, U. and Hata, H., "Manifold learning approach for chaos in the dripping faucet", Phys. Rev. E, September 2012, Vol. 86(3), 036209 pp. |
Abstract: Dripping water from a faucet is a typical example exhibiting rich nonlinear phenomena. For such a system, the time stamps at which water drops separate from the faucet can be directly observed in real experiments, and the time series of intervals tau(n) between drop separations becomes a subject of analysis. Even if the mass m(n) of a drop at the onset of the nth separation, which is difficult to observe experimentally, exhibits perfectly deterministic dynamics, it may be difficult to obtain the same information about the underlying dynamics from the time series tau(n). This is because the return plot tau(n-1) vs. tau(n) may become a multivalued relation (i.e., it doesn't represent a function describing deterministic dynamics). In this paper, we propose a method to construct a nonlinear coordinate which provides a "surrogate" of the internal state m(n) from the time series of tau(n). Here, a key of the proposed approach is to use ISOMAP, which is a well-known method of manifold learning. We first apply it to the time series of tau(n) generated from the numerical simulation of a phenomenological mass-spring model for the dripping faucet system. It is shown that a clear one-dimensional map is obtained by the proposed approach, whose characteristic quantities such as the Lyapunov exponent, the topological entropy, and the time correlation function coincide with the original dripping faucet system. Furthermore, we also analyze data obtained from real dripping faucet experiments, which also provide promising results. |
BibTeX:
@article{Suetani.Soejima.ea2012, author = {Suetani, H. and Soejima, K. and Matsuoka, R. and Parlitz, U. and Hata, H.}, title = {Manifold learning approach for chaos in the dripping faucet}, journal = {Phys. Rev. E}, month = {September}, year = {2012}, volume = {86}, number = {3}, pages = {036209}, doi = {10.1103/PhysRevE.86.036209},, url = {http://pre.aps.org/abstract/PRE/v86/i3/e036209} } |
Chebbok, M., Squires, A., Schroeder-Schetelig, J., Zabel, M., Hasenfuss, G., Bodenschatz, E., Fenton, F. and Luther, S., "Low-energy anti-fibrillation pacing (LEAP): a gentle, non traumatic defibrillation Option", Eur. Heart J., August 2012, Vol. 33, 381 pp.
[DOI] |
BibTeX:
@article{Chebbok.Squires.ea2012, author = {Chebbok, M. and Squires, A. and Schroeder-Schetelig, J. and Zabel, M. and Hasenfuss, G. and Bodenschatz, E. and Fenton, F. and Luther, S.}, title = {Low-energy anti-fibrillation pacing (LEAP): a gentle, non traumatic defibrillation Option}, journal = {Eur. Heart J.}, month = {August}, year = {2012}, volume = {33}, pages = {381} } |
Wagner, E., Lauterbach, M. A., Kohl, T., Westphal, V., Williams, G. S. B., Steinbrecher, J. H., Streich, J. H., Korff, B., Tuan, H. M., Hagen, B., Luther, S., Hasenfuss, G., Parlitz, U., Jafri, M. S., Hell, S. W., Lederer, W. J. and Lehnart, S. E., "Stimulated Emission Depletion Live-Cell Super-Resolution Imaging Shows Proliferative Remodeling of T-Tubule Membrane Structures After Myocardial Infarction", Circ. Res., August 2012, Vol. 111(4), 402 pp. |
Abstract: Rationale: Transverse tubules (TTs) couple electric surface signals to remote intracellular Ca2+ release units (CRUs). Diffraction-limited imaging studies have proposed loss of TT components as disease mechanism in heart failure (HF). Objectives: Objectives were to develop quantitative super-resolution strategies for live-cell imaging of TT membranes in intact cardiomyocytes and to show that TT structures are progressively remodeled during HF development, causing early CRU dysfunction. Methods and Results: Using stimulated emission depletion (STED) microscopy, we characterized individual TTs with nanometric resolution as direct readout of local membrane morphology 4 and 8 weeks after myocardial infarction (4pMI and 8pMI). Both individual and network TT properties were investigated by quantitative image analysis. The mean area of TT cross sections increased progressively from 4pMI to 8pMI. Unexpectedly, intact TT networks showed differential changes. Longitudinal and oblique TTs were significantly increased at 4pMI, whereas transversal components appeared decreased. Expression of TT-associated proteins junctophilin-2 and caveolin-3 was significantly changed, correlating with network component remodeling. Computational modeling of spatial changes in HF through heterogeneous TT reorganization and RyR2 orphaning (5000 of 20 000 CRUs) uncovered a local mechanism of delayed subcellular Ca2+ release and action potential prolongation. Conclusions: This study introduces STED nanoscopy for live mapping of TT membrane structures. During early HF development, the local TT morphology and associated proteins were significantly altered, leading to differential network remodeling and Ca2+ release dyssynchrony. Our data suggest that TT remodeling during HF development involves proliferative membrane changes, early excitation-contraction uncoupling, and network fracturing. (Circ Res. 2012; 111:402-414.) |
BibTeX:
@article{Wagner.Lauterbach.ea2012, author = {Wagner, E. and Lauterbach, M. A. and Kohl, T. and Westphal, V. and Williams, G. S. B. and Steinbrecher, J. H. and Streich, J. H. and Korff, B. and Tuan, H. M. and Hagen, B. and Luther, S. and Hasenfuss, G. and Parlitz, U. and Jafri, M. S. and Hell, S. W. and Lederer, W. J. and Lehnart, S. E.}, title = {Stimulated Emission Depletion Live-Cell Super-Resolution Imaging Shows Proliferative Remodeling of T-Tubule Membrane Structures After Myocardial Infarction}, journal = {Circ. Res.}, month = {August}, year = {2012}, volume = {111}, number = {4}, pages = {402}, doi = {10.1161/CIRCRESAHA.112.274530},, url = {http://circres.ahajournals.org/content/111/4/402} } |
Falkovich, G., Xu, H., Pumir, A., Bodenschatz, E., Biferale, L., Boffetta, G., Lanotte, A. S. and Toschi, F., "On Lagrangian single-particle statistics", Phys. Fluids, July 2012, Vol. 24(5), 055102 pp. |
Abstract: In turbulence, ideas of energy cascade and energy flux, substantiated by the exact Kolmogorov relation, lead to the determination of scaling laws for the velocity spatial correlation function. Here we ask whether similar ideas can be applied to temporal correlations. We critically review the relevant theoretical and experimental results concerning the velocity statistics of a single fluid particle in the inertial range of statistically homogeneous, stationary and isotropic turbulence. We stress that the widely used relations for the second structure function, D2(t) ? ?[v(t) ? v(0)]2??åt, relies on dimensional arguments only: no relation of D2(t) to the energy cascade is known, neither in two- nor in three-dimensional turbulence. State of the art experimental and numerical results demonstrate that at high Reynolds numbers, the derivative math has a finite non-zero slope starting from t ? 2ôç. The analysis of the acceleration spectrum ÖA(ù) indicates a possible small correction with respect to the dimensional expectation ÖA(ù) ? ù0 but present data are unable to discriminate between anomalous scaling and finite Reynolds effects in the second order moment of velocity Lagrangian statistics. |
BibTeX:
@article{Falkovich.Xu.ea2012, author = {Falkovich, G. and Xu, H. and Pumir, A. and Bodenschatz, E. and Biferale, L. and Boffetta, G. and Lanotte, A. S. and Toschi, F.}, title = {On Lagrangian single-particle statistics}, journal = {Phys. Fluids}, month = {July}, year = {2012}, volume = {24}, number = {5}, pages = {055102}, doi = {10.1063/1.4711397},, url = {http://pof.aip.org/resource/1/phfle6/v24/i5/p055102_s1} } |
Lambertz, S., "Experimentelle Untersuchung der Basset Gedächtniskraft auf eine starre Kugel in instationärer Bewegung and Experimental measurement of the history forces on a rigid sphere in unsteady motion", July 2012 |
BibTeX:
@mastersthesis{Lambertz2012, author = {Lambertz, S.}, title = {Experimentelle Untersuchung der Basset Gedächtniskraft auf eine starre Kugel in instationärer Bewegung and Experimental measurement of the history forces on a rigid sphere in unsteady motion}, month = {July}, year = {2012},, url = {http://www.lfpn.ds.mpg.de/turbulence/documents/Diploma-S-Lambertz-ExpBassetForce.pdf} } |
Bewley, G. P., Chang, K. and Bodenschatz, E., "On integral length scales in anisotropic turbulence", Phys. Fluids, June 2012, Vol. 24(6), 061702 pp. |
Abstract: We found experimentally a dependence of the integral length scales of correlation functions measured in different directions in a turbulent flow on the velocity fluctuation anisotropy in those same directions. We derive invariants for anisotropic turbulence that is locally isotropic, and so a relationship between the velocity and length scales. The results emphasize the importance of defining the Reynolds number, which was about 480, in terms of scalar quantities instead of these scales. We also find that the normalized energy dissipation rate was approximately independent of the anisotropy. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4726077] |
BibTeX:
@article{Bewley.Chang.ea2012, author = {Bewley, G. P. and Chang, K. and Bodenschatz, E.}, title = {On integral length scales in anisotropic turbulence}, journal = {Phys. Fluids}, month = {June}, year = {2012}, volume = {24}, number = {6}, pages = {061702}, doi = {10.1063/1.4726077},, url = {http://pof.aip.org/resource/1/phfle6/v24/i6/p061702_s1} } |
He, X., Funfschilling, D., Bodenschatz, E. and Ahlers, G., "Heat transport by turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and 4×10^11 less than or similar to Ra less than or similar to 2×10^14: ultimate-state transition for aspect ratio Gamma=1.00", New J. Phys., June 2012, Vol. 14, 063030 pp. |
Abstract: We report experimental results for heat-transport measurements, in the form of the Nusselt number Nu, by turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratio Gamma equivalent to D/L = 1.00 (D = 1.12m is the diameter and L = 1.12m the height) and compare them with previously reported results for Gamma = 0.50. The measurements were made using sulfur hexafluoride at pressures up to 19 bars as the fluid. They are for the Rayleigh-number range 4 x 10(11) less than or similar to Ra less than or similar to 2 x 10(14) and for Prandtl numbers Pr between 0.79 and 0.86. For Ra < Ra-1* similar or equal to 2 x 10(13) we find Nu = N0Ra gamma eff with gamma(eff) = 0.321 +/- 0.002 and N-0 = 0.0776, consistent with classical turbulent RBC in a system with laminar boundary layers (BLs) below the top and above the bottom plate and with the prediction of Grossmann and Lohse. For Ra > Ra-1* the data rise above the classical-state power-law and show greater scatter. In analogy to similar behavior observed for Gamma = 0.50, we interpret this observation as the onset of the transition to the ultimate state. Within our resolution this onset occurs at nearly the same value of Ra-1* as it does for Gamma = 0.50. This differs from an earlier estimate by Roche et al (2010 New J. Phys. 12 085014), which yielded a transition at Ra-U similar or equal to 1.3 x 10(11) Gamma(-2.5 +/- 0.5). A Gamma-independent Ra-1* would suggest that the BL shear transition is induced by fluctuations on a scale less than the sample dimensions rather than by a global Gamma-dependent flow mode. Within the resolution of the measurements the heat transport above Ra-1* is equal for the two Gamma values, suggesting a universal aspect of the ultimate-state transition and properties. The enhanced scatter of Nu in the transition region, which exceeds the experimental resolution, indicates an intrinsic irreproducibility of the state of the system. Several previous measurements for Gamma = 1.00 are re-examined and compared with the present results. None of them identified the ultimate-state transition. |
BibTeX:
@article{He.Funfschilling.ea2012, author = {He, X. and Funfschilling, D. and Bodenschatz, E. and Ahlers, G.}, title = {Heat transport by turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and 4×10^11 less than or similar to Ra less than or similar to 2×10^14: ultimate-state transition for aspect ratio Gamma=1.00}, journal = {New J. Phys.}, month = {June}, year = {2012}, volume = {14}, pages = {063030}, doi = {10.1088/1367-2630/14/6/063030},, url = {http://iopscience.iop.org/1367-2630/14/6/063030/} } |
Többens, A., Mettin, R. and Parlitz, U., "Dynamics of A Driven Oscillator Carrying A Freely Sliding Mass", Int. J. Bifurcat. Chaos, June 2012, Vol. 22(6), 1250132 pp. |
Abstract: A mathematical model for a nonlinear oscillator, which is composed of an oscillating mass interacting with a freely sliding friction damper, is introduced and investigated. This oscillator is a strongly simplified model for a damping principle applied to turbine blades to suppress oscillations induced by inhomogeneous flow fields. It exhibits periodic, quasi-periodic, as well as chaotic dynamics occuring suddenly due to adding sliding bifurcations. Mathematically, the oscillator is given as a piecewise smooth (Filippov) system with a switching manifold corresponding to the sticking phase of the damper mass. The rich dynamics of this system is analyzed and illustrated by means of resonance curves, Lyapunov diagrams, Poincare sections and reductions to iterated one-dimensional maps. |
BibTeX:
@article{Toebbens.Mettin.ea2012, author = {Többens, A. and Mettin, R. and Parlitz, U.}, title = {Dynamics of A Driven Oscillator Carrying A Freely Sliding Mass}, journal = {Int. J. Bifurcat. Chaos}, month = {June}, year = {2012}, volume = {22}, number = {6}, pages = {1250132}, doi = {10.1142/S0218127412501325},, url = {http://www.worldscientific.com/doi/abs/10.1142/S0218127412501325} } |
Amselem, G., Theves, M., Bae, A., Bodenschatz, E. and Beta, C., "A Stochastic Description of Dictyostelium Chemotaxis", PLOS ONE, May 2012, Vol. 7(5), e37213 pp. |
Abstract: Chemotaxis, the directed motion of a cell toward a chemical source, plays a key role in many essential biological processes. Here, we derive a statistical model that quantitatively describes the chemotactic motion of eukaryotic cells in a chemical gradient. Our model is based on observations of the chemotactic motion of the social ameba Dictyostelium discoideum, a model organism for eukaryotic chemotaxis. A large number of cell trajectories in stationary, linear chemoattractant gradients is measured, using microfluidic tools in combination with automated cell tracking. We describe the directional motion as the interplay between deterministic and stochastic contributions based on a Langevin equation. The functional form of this equation is directly extracted from experimental data by angle-resolved conditional averages. It contains quadratic deterministic damping and multiplicative noise. In the presence of an external gradient, the deterministic part shows a clear angular dependence that takes the form of a force pointing in gradient direction. With increasing gradient steepness, this force passes through a maximum that coincides with maxima in both speed and directionality of the cells. The stochastic part, on the other hand, does not depend on the orientation of the directional cue and remains independent of the gradient magnitude. Numerical simulations of our probabilistic model yield quantitative agreement with the experimental distribution functions. Thus our model captures well the dynamics of chemotactic cells and can serve to quantify differences and similarities of different chemotactic eukaryotes. Finally, on the basis of our model, we can characterize the heterogeneity within a population of chemotactic cells. |
BibTeX:
@article{Amselem.Theves.ea2012b, author = {Amselem, G. and Theves, M. and Bae, A. and Bodenschatz, E. and Beta, C.}, title = {A Stochastic Description of Dictyostelium Chemotaxis}, journal = {PLOS ONE}, month = {May}, year = {2012}, volume = {7}, number = {5}, pages = {e37213}, doi = {10.1371/journal.pone.0037213},, url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0037213} } |
Gibert, M., Xu, H. and Bodenschatz, E., "Where do small, weakly inertial particles go in a turbulent flow?", J. Fluid Mech., May 2012, Vol. 698, 160 pp. |
Abstract: We report experimental results on the dynamics of heavy particles of the size of the Kolmogorov scale in a fully developed turbulent flow. The mixed Eulerian structure function of two-particle velocity and acceleration difference vectors |
BibTeX:
@article{Gibert.Xu.ea2012, author = {Gibert, M. and Xu, H. and Bodenschatz, E.}, title = {Where do small, weakly inertial particles go in a turbulent flow?}, journal = {J. Fluid Mech.}, month = {May}, year = {2012}, volume = {698}, pages = {160}, doi = {10.1017/jfm.2012.72},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8539092} } |
Nobach, H., "The Particle Image Velocimetry --- Characteristics, Limits and Possible Applications", May 2012, 29 pp. |
Abstract: Individual variations of intensity of tracer particles, e.g., due to out-of-plane displacements between exposures, strongly limit the achievable accuracy of correlation-based PIV processing. The RMS error originated by this effect correlates with the spatial resolution that can be achieved with the processing algorithm making especially high-resolution algorithms like iterative image deformation affected by this error. Both aspects are shown, the gain of resolution by iterative image deformation and the loss of accuracy due to individual variations of particle intensities. |
BibTeX:
@inbook{Nobach2012, author = {Nobach, H.}, title = {The Particle Image Velocimetry --- Characteristics, Limits and Possible Applications}, month = {May}, year = {2012}, pages = {29}, doi = {10.5772/34671},, url = {http://www.intechopen.com/books/the-particle-image-velocimetry-characteristics-limits-and-possible-applications/limits-in-planar-piv-due-to-individual-variations-of-particle-image-intensities} } |
Szewcyk, M., Richter, C., Briese, V. and Richter, D. U., "A Retrospective In Vitro Study of the Impact of Anti-diabetics and Cardioselective Pharmaceuticals on Breast Cancer", Anticancer Res., May 2012, Vol. 32(5), 2133 pp. |
Abstract: Background: In a retrospective controlled study, a tumor-protective effect, regarding breast cancer, was determined for the medicines metformin and glitazone (antidiabetics), bisoprolol, and propranolol (cardioselective beta 1 adrenoceptor antagonists). Our main goal was to provide evidence, showing the tumor-protective effects of beta-blockers and of antidiabetics via investigations in vitro. Materials and Methods: Four different medicines were tested in cell cultures: Propranolol: 2.4 mg/ml and 0.3 mg/ml; bisoprolol: 0.1 mg/ml and 0.05 mg/ml; metformin: 7.5 mg/ml, 2.5 mg/ml, and 0.15 mg/ml; and glitazone: 2.5 mg/ml, 0.15 mg/ml, and 0.05 mg/ml. The human breast cancer cell lines MCF7 and BT20 (estrogen receptor-positive and -negative; ATCC; cell density: 5x10(5) cells/ml) were used. Both cell lines were cultured under sterile conditions in incubators at 37 degrees C, with a humidified atmosphere of 5% CO2. The influences of the drugs were determined through cytotoxicity and proliferation assays and performance of a hydrogen peroxide assay. Morphological observations (light microscopy) and metabolic investigations (pH value, glucose) were also performed. Results: The application of the beta-blocker propranolol resulted in highly cytotoxic effects (>90%) in both cell lines. In contrast, bisoprolol did not have any effects, neither in cytotoxicity tests nor in cell proliferation assays. The anti-diabetic metformin had a higher cytotoxic influence on the BT20 than did on the MCF7 cell line. The cell proliferation of BT20 was significantly inhibited after the addition of 2.5 mg/ml metformin and of 2.5 mg/ml glitazone. The application of glitazone also resulted in an increase of hydrogen peroxide and a decrease of the pH value. Conclusion: The strongest cytotoxic effect was observed with propranolol suggesting that, in clinical practice, this pharmaceutical can be used in patients with breast cancer who have hypertension. A specific clinical recommendation for anti-diabetics is not yet possible. |
BibTeX:
@inproceedings{Szewcyk.Richter.ea2012, author = {Szewcyk, M. and Richter, C. and Briese, V. and Richter, D. U.}, title = {A Retrospective In Vitro Study of the Impact of Anti-diabetics and Cardioselective Pharmaceuticals on Breast Cancer}, journal = {Anticancer Res.}, month = {May}, year = {2012}, volume = {32}, number = {5}, pages = {2133},, url = {http://ar.iiarjournals.org/content/32/5/2133.full.pdf} } |
Weiss, S., Seiden, G. and Bodenschatz, E., "Pattern formation in spatially forced thermal convection", New J. Phys., May 2012, Vol. 14, 053010 pp. |
Abstract: In this paper, we present experimental results on the interplay between two different symmetry breaking mechanisms in a pattern forming system, namely inclined layer convection (ILC) with a spatially modulated heated plate. By varying the relative strength and relative orientation, we explored in detail the interplay of these symmetry breaking mechanisms. We found a stabilization of spatio-temporal chaos and resonant interactions that led to superlattice patterns. The fundamental mechanisms observed should be equally applicable to other pattern forming systems. |
BibTeX:
@article{Weiss.Seiden.ea2012, author = {Weiss, S. and Seiden, G. and Bodenschatz, E.}, title = {Pattern formation in spatially forced thermal convection}, journal = {New J. Phys.}, month = {May}, year = {2012}, volume = {14}, pages = {053010}, doi = {10.1088/1367-2630/14/5/053010},, url = {http://iopscience.iop.org/1367-2630/14/5/053010/pdf/1367-2630_14_5_053010.pdf} } |
Parlitz, U., Berg, S., Luther, S., Schirdewan, A., Kurths, J. and Wessel, N., "Classifying cardiac biosignals using ordinal pattern statistics and symbolic dynamics", Comput. Biol. Med., March 2012, Vol. 42(3), 319 pp. |
Abstract: The performance of (bio-)signal classification strongly depends on the choice of suitable features (also called parameters or biomarkers). In this article we evaluate the discriminative power of ordinal pattern statistics and symbolic dynamics in comparison with established heart rate variability parameters applied to beat-to-beat intervals. As an illustrative example we distinguish patients suffering from congestive heart failure from a (healthy) control group using beat-to-beat time series. We assess the discriminative power of individual features as well as pairs of features. These comparisons show that ordinal patterns sampled with an additional time lag are promising features for efficient classification. (C) 2011 Elsevier Ltd. All rights reserved. |
BibTeX:
@article{Parlitz.Berg.ea2012, author = {Parlitz, U. and Berg, S. and Luther, S. and Schirdewan, A. and Kurths, J. and Wessel, N.}, title = {Classifying cardiac biosignals using ordinal pattern statistics and symbolic dynamics}, journal = {Comput. Biol. Med.}, month = {March}, year = {2012}, volume = {42}, number = {3}, pages = {319}, doi = {10.1016/j.compbiomed.2011.03.017},, url = {http://www.sciencedirect.com/science/article/pii/S0010482511000618} } |
Risius, S., "Untersuchung turbulenter Strömungen auf der Umweltforschungsstation Schneefernerhaus (Zugspitze) and Investigation of turbulent flows at the Umweltforschungsstation Schneefernerhaus (Zugspitze)", March 2012 |
BibTeX:
@mastersthesis{Risius2012, author = {Risius, S.}, title = {Untersuchung turbulenter Strömungen auf der Umweltforschungsstation Schneefernerhaus (Zugspitze) and Investigation of turbulent flows at the Umweltforschungsstation Schneefernerhaus (Zugspitze)}, month = {March}, year = {2012},, url = {http://www.lfpn.ds.mpg.de/turbulence/documents/Diplom-Zugspitze-Steffen-Risius.pdf} } |
Chang, K., Bewley, G. P. and Bodenschatz, E., "Experimental study of the influence of anisotropy on the inertial scales of turbulence", J. Fluid Mech., February 2012, Vol. 692, 464 pp. |
Abstract: We ask whether the scaling exponents or the Kolmogorov constants depend on the anisotropy of the velocity fluctuations in a turbulent flow with no shear. According to our experiment, the answer is no for the Eulerian second-order transverse velocity structure function. The experiment consisted of 32 loudspeaker-driven jets pointed toward the centre of a spherical chamber. We generated anisotropy by controlling the strengths of the jets. We found that the form of the anisotropy of the velocity fluctuations was the same as that in the strength of the jets. We then varied the anisotropy, as measured by the ratio of axial to radial root-mean-square (r.m.s.) velocity fluctuations, between 0.6 and 2.3. The Reynolds number was approximately constant at around R-lambda = 481. In a central volume with a radius of 50 mm, the turbulence was approximately homogeneous, axisymmetric, and had no shear and no mean flow. We observed that the scaling exponent of the structure function was 0.70 +/- 0.03, independent of the anisotropy and regardless of the direction in which we measured it. The Kolmogorov constant, C-2, was also independent of direction and anisotropy to within the experimental error of 4%. |
BibTeX:
@article{Chang.Bewley.ea2012, author = {Chang, K. and Bewley, G. P. and Bodenschatz, E.}, title = {Experimental study of the influence of anisotropy on the inertial scales of turbulence}, journal = {J. Fluid Mech.}, month = {February}, year = {2012}, volume = {692}, pages = {464}, doi = {10.1017/jfm.2011.529},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8478322} } |
Chakraborty, S., Frisch, U., Pauls, W. and Ray, S. S., "Nelkin scaling for the Burgers equation and the role of high-precision calculations", Phys. Rev. E, January 2012, Vol. 85(1), 015301 pp. |
Abstract: Nelkin scaling, the scaling of moments of velocity gradients in terms of the Reynolds number, is an alternative way of obtaining inertial-range information. It is shown numerically and theoretically for the Burgers equation that this procedure works already for Reynolds numbers of the order of 100 (or even lower when combined with a suitable extended self-similarity technique). At moderate Reynolds numbers, for the accurate determination of scaling exponents, it is crucial to use higher than double precision. Similar issues are likely to arise for three-dimensional Navier-Stokes simulations. |
BibTeX:
@article{Chakraborty.Frisch.ea2012, author = {Chakraborty, S. and Frisch, U. and Pauls, W. and Ray, S. S.}, title = {Nelkin scaling for the Burgers equation and the role of high-precision calculations}, journal = {Phys. Rev. E}, month = {January}, year = {2012}, volume = {85}, number = {1}, pages = {015301}, doi = {10.1103/PhysRevE.85.015301},, url = {http://pre.aps.org/abstract/PRE/v85/i1/e015301} } |
Chang, K., "Explorations into the Inertial and Integral Scalse of Homogeneous Axisymmetric Turbulence", January 2012 |
Abstract: A flow generator is described in which homogeneous axisymmetric turbulent air flows with varying and fully controllable degrees of anisotropy, including the much studied isotropic case, are generated by the combined agitations produced by 32 acoustic mixers focusing at the center of the system. The axisymmetric turbulence in a central volume of the size of the inertial scale is shown to have negligible mean and shear. The Taylor Reynolds number is about 480. The influence of large scale anisotropy on the turbulence is examined from three aspects, namely the velocity structure functions, the velocity correlation functions, and the integral lengths. The directional dependence of two different second order transverse structure functions, in which one of them has separations stretched along the axis of symmetry of the turbulence and the other one normal to it, is studied. It is shown that the inertial range scaling exponents, determined using the extended-self-similarity procedure, and the Kolmogorov constants of the two structure functions are unaffected by the direction in which the structure functions are measured. As an extension, because of its relevance to the study of intermittency, the directional dependence of transverse structure functions of the fourth to the sixth order is studied. Despite some issues with measurement noise and statistical convergence, some indications are found that anisotropy in the velocity field intensifies the asymmetry of the probability density of the velocity increments. In addition, some evidence is found that the inertial range scaling exponents of the fourth, fifth, and sixth order are independent of the anisotropy. Finally, it is found that, except in the isotropic case, the second order transverse velocity correlation functions deviate from each other at the large scale with increasing anisotropy. A self-similarity argument similar to one found in the study of critical phenomena is proposed. It is shown that the argument leads to a power-law relationship between the large scale velocity fluctuation and the correlation length, with an exponent that depends on the inertial range scaling exponent of the turbulence. The data collapse predicted by the self-similarity hypothesis is verified. It is demonstrated that the value of the power-law exponent is consistent with the value of the inertial range scaling exponent. |
BibTeX:
@phdthesis{Chang2012, author = {Chang, K.}, title = {Explorations into the Inertial and Integral Scalse of Homogeneous Axisymmetric Turbulence}, month = {January}, year = {2012},, url = {http://ecommons.library.cornell.edu/handle/1813/29150} } |
He, X., Funfschilling, D., Nobach, H., Bodenschatz, E. and Ahlers, G., "Transition to the Ultimate State of Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., January 2012, Vol. 108(2), 024502 pp. |
Abstract: Measurements of the Nusselt number Nu and of a Reynolds number Re(eff) for Rayleigh-Bénard convection (RBC) over the Rayleigh-number range 10(12) less than or similar to & Ra less than or similar to 10(15) and for Prandtl numbers Pr near 0.8 are presented. The aspect ratio Gamma equivalent to D/L of a cylindrical sample was 0.50. For Ra less than or similar to 10(13) the data yielded Nu alpha Ra(gamma eff) with gamma(eff) similar or equal to 0.31 and Re(eff) alpha Ra(zeta eff) with zeta(eff) similar or equal to 0.43, consistent with classical turbulent RBC. After a transition region for 10(13) less than or similar to Ra less than or similar to 5x 10(14), where multistability occurred, we found gamma(eff) similar or equal to 0: 38 and zeta(eff) = zeta similar or equal to 0.50, in agreement with the results of Grossmann and Lohse for the large-Ra asymptotic state with turbulent boundary layers which was first predicted by Kraichnan. |
BibTeX:
@article{He.Funfschilling.ea2012d, author = {He, X. and Funfschilling, D. and Nobach, H. and Bodenschatz, E. and Ahlers, G.}, title = {Transition to the Ultimate State of Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {January}, year = {2012}, volume = {108}, number = {2}, pages = {024502}, doi = {10.1103/PhysRevLett.108.024502},, url = {http://link.aps.org/doi/10.1103/PhysRevLett.108.024502} } |
Klein, S., "Dynamics of large particles in turbulence", January 2012 |
BibTeX:
@mastersthesis{Klein2012, author = {Klein, S.}, title = {Dynamics of large particles in turbulence}, month = {January}, year = {2012},, url = {http://www.lfpn.ds.mpg.de/turbulence/documents/Dipl-thesis-SimonKlein.pdf} } |
Schneider, D., Tarantola, M. and Janshoff, A., "Dynamics of TGF-beta induced epithelial-to-mesenchymal transition monitored by Electric Cell-Substrate Impedance Sensing", Biochim. Biophys. Acta Mol. Cell Res., December 2011, Vol. 1813(12), 2099 pp. |
Abstract: The epithelial-to-mesenchymal transition (EMT) is a program of cellular development associated with loss of cell-cell contacts, a decreased cell adhesion and substantial morphological changes. Besides its importance for numerous developmental processes, EMT has also been held responsible for the development and progression of tumors and formation of metastases. The influence of the cytokine transforming growth factor beta 1 (TGF-beta 1) induced EMT on structure, migration, cytoskeletal dynamics and long-term correlations of the mammalian epithelial cell lines NMuMG, A549 and MDA-MB231 was investigated with time-resolved impedance analysis. The three cell lines show important differences in concentration dependency, cellular morphology and dynamics upon their response to TGF-beta 1. A549 cells and the non-tumor mouse epithelial cell line NMuMG show a substantial change in morphology mirrored in stepwise changes of their phenotype upon cytokine treatment. Impedance based measurements of micromotility reveal a complex dynamic response to TGF-beta 1 exposure which leads to a transient increase in fluctuation amplitude and long-term correlation. These changes in fluctuation amplitude are also detectable for MDA-MB231 cells, whereas the long-term correlation remains unvaried. We were able to distinguish three time domains during EMT. Initially, all cell lines display an increase in micromotion lasting 4 to 9 h termed transitional state I. This regime is followed by transitional state II lasting approximately 20 h, where cellular dynamics are diminished and, in case of the NMuMG cell line, a loss of cell-cell contacts occurs. Finally, the transformation into the mesenchymal-like phenotype occurs 24-30 h after exposure to TGF-beta 1. (C) 2011 Elsevier B.V. All rights reserved. |
BibTeX:
@article{Schneider.Tarantola.ea2011, author = {Schneider, D. and Tarantola, M. and Janshoff, A.}, title = {Dynamics of TGF-beta induced epithelial-to-mesenchymal transition monitored by Electric Cell-Substrate Impedance Sensing}, journal = {Biochim. Biophys. Acta Mol. Cell Res.}, month = {December}, year = {2011}, volume = {1813}, number = {12}, pages = {2099}, doi = {10.1016/j.bbamcr.2011.07.016},, url = {http://www.sciencedirect.com/science/article/pii/S0167488911002151} } |
Zykov, V. S., Oikawa, N. and Bodenschatz, E., "Selection of Spiral Waves in Excitable Media with a Phase Wave at the Wave Back", Phys. Rev. Lett., December 2011, Vol. 107(25), 254101 pp. |
Abstract: Universal relationships between the medium excitability and the angular velocity and the core radius of rigidly rotating spiral waves in excitable media are derived for situations where the wave front is a trigger wave and the wave back is a phase wave. Two universal limits restricting the region of existence of spiral waves in the parameter space are demonstrated. The predictions of the free-boundary approach are in good quantitative agreement with results from numerical reaction-diffusion simulations performed on the Kessler-Levine model. |
BibTeX:
@article{Zykov.Oikawa.ea2011, author = {Zykov, V. S. and Oikawa, N. and Bodenschatz, E.}, title = {Selection of Spiral Waves in Excitable Media with a Phase Wave at the Wave Back}, journal = {Phys. Rev. Lett.}, month = {December}, year = {2011}, volume = {107}, number = {25}, pages = {254101}, doi = {10.1103/PhysRevLett.107.254101},, url = {http://link.aps.org/doi/10.1103/PhysRevLett.107.254101} } |
Belan, M., de Ponte, S., Tordella, D., Massaglia, S., Mignone, A., Bodenschatz, E. and Ferrari, A., "Hydrodynamics of hypersonic jets: experiments and numerical simulations", Astrophys. Space Sci., November 2011, Vol. 336(1), 9 pp. |
Abstract: Stars form in regions of the galaxy that are denser and cooler than the mean interstellar medium. These regions are called Giant Molecular Clouds. At the beginning of their life, up to 10(5)-10(6) years, stars accrete matter from their rich surrounding environment and are origin of a peculiar phenomenon that is the jet emission. Jets from Young Stellar Objects (YSOs) are intensively studied by the astrophysical community by observations at different wavelengths, analytical and numerical modeling and laboratory experiments. Indications about the jet propagation and its resulting morphologies are here obtained by means of a combined study of hypersonic jets carried out both in the laboratory and by numerical simulations. |
BibTeX:
@article{Belan.Ponte.ea2011, author = {Belan, M. and de Ponte, S. and Tordella, D. and Massaglia, S. and Mignone, A. and Bodenschatz, E. and Ferrari, A.}, title = {Hydrodynamics of hypersonic jets: experiments and numerical simulations}, journal = {Astrophys. Space Sci.}, month = {November}, year = {2011}, volume = {336}, number = {1}, pages = {9}, doi = {10.1007/s10509-011-0600-6},, url = {http://link.springer.com/article/10.1007%2Fs10509-011-0600-6} } |
Blum, D. B., Bewley, G. P., Bodenschatz, E., Gibert, M., Gylfason, A., Mydlarski, L., Voth, G. A., Xu, H. and Yeung, P. K., "Signatures of non-universal large scales in conditional structure functions from various turbulent flows", New J. Phys., November 2011, Vol. 13, 113020 pp. |
Abstract: We present a systematic comparison of conditional structure functions in nine turbulent flows. The flows studied include forced isotropic turbulence simulated on a periodic domain, passive grid wind tunnel turbulence in air and in pressurized SF(6), active grid wind tunnel turbulence (in both synchronous and random driving modes), the flow between counter-rotating discs, oscillating grid turbulence and the flow in the Lagrangian exploration module (in both constant and random driving modes). We compare longitudinal Eulerian second-order structure functions conditioned on the instantaneous large-scale velocity in each flow to assess the ways in which the large scales affect the small scales in a variety of turbulent flows. Structure functions are shown to have larger values when the large-scale velocity significantly deviates from the mean in most flows, suggesting that dependence on the large scales is typical in many turbulent flows. The effects of the large-scale velocity on the structure functions can be quite strong, with the structure function varying by up to a factor of 2 when the large-scale velocity deviates from the mean by +/- 2 standard deviations. In several flows, the effects of the large-scale velocity are similar at all the length scales we measured, indicating that the large-scale effects are scale independent. In a few flows, the effects of the large-scale velocity are larger on the smallest length scales. |
BibTeX:
@article{Blum.Bewley.ea2011, author = {Blum, D. B. and Bewley, G. P. and Bodenschatz, E. and Gibert, M. and Gylfason, A. and Mydlarski, L. and Voth, G. A. and Xu, H. and Yeung, P. K.}, title = {Signatures of non-universal large scales in conditional structure functions from various turbulent flows}, journal = {New J. Phys.}, month = {November}, year = {2011}, volume = {13}, pages = {113020}, doi = {10.1088/1367-2630/13/11/113020},, url = {http://iopscience.iop.org/1367-2630/13/11/113020/} } |
Brandt, C., Grulke, O., Klinger, T., Negrete, J., Bousselin, G., Brochard, F., Bonhomme, G. and Oldenbürger, S., "Spatiotemporal mode structure of nonlinearly coupled drift wave modes", Phys. Rev. E, November 2011, Vol. 84, 056405 pp. |
Abstract: This paper presents full cross-section measurements of drift waves in the linear magnetized plasma of the Mirabelle device. Drift wave modes are studied in regimes of weakly developed turbulence. The drift wave modes develop azimuthal space-time structures of plasma density, plasma potential, and visible light fluctuations. A fast camera diagnostic is used to record visible light fluctuations of the plasma column in an azimuthal cross section with a temporal resolution of 10ìs corresponding approximately to 10% of the typical drift wave period. Mode coupling and drift wave dispersion are studied by spatiotemporal Fourier decomposition of the camera frames. The observed coupling between modes is compared to calculations of nonlinearly coupled oscillators described by the Kuramoto model. |
BibTeX:
@article{PhysRevE.84.056405, author = {Brandt, Christian and Grulke, Olaf and Klinger, Thomas and Negrete, José and Bousselin, Guillaume and Brochard, Frédéric and Bonhomme, Gérard and Oldenbürger, Stella}, title = {Spatiotemporal mode structure of nonlinearly coupled drift wave modes}, journal = {Phys. Rev. E}, month = {November}, year = {2011}, volume = {84}, pages = {056405}, doi = {10.1103/PhysRevE.84.056405},, url = {http://link.aps.org/doi/10.1103/PhysRevE.84.056405} } |
Schumann-Bischoff, J. and Parlitz, U., "State and parameter estimation using unconstrained optimization", Phys. Rev. E, November 2011, Vol. 84(5), 056214 pp. |
Abstract: We present an efficient method for estimating variables and parameters of a given system of ordinary differential equations by adapting the model output to an observed time series from the (physical) process described by the model. The proposed method is based on (unconstrained) nonlinear optimization exploiting the particular structure of the relevant cost function. To illustrate the features and performance of the method, simulations are presented using chaotic time series generated by the Colpitts oscillator, the three-dimensional Hindmarsh-Rose neuron model, and a nine-dimensional extended Rossler system. |
BibTeX:
@article{Schumann-Bischoff.Parlitz2011, author = {Schumann-Bischoff, J. and Parlitz, U.}, title = {State and parameter estimation using unconstrained optimization}, journal = {Phys. Rev. E}, month = {November}, year = {2011}, volume = {84}, number = {5}, pages = {056214}, doi = {10.1103/PhysRevE.84.056214},, url = {http://pre.aps.org/abstract/PRE/v84/i5/e056214} } |
Seiden, G. and Thomas, P. J., "Complexity, segregation, and pattern formation in rotating-drum flows", Rev. Mod. Phys., November 2011, Vol. 83(4), 1323 pp. |
Abstract: Rotating-drum flows span a variety of research areas, ranging from physics of granular matter through hydrodynamics of suspensions to pure liquid coating flows. Recent years have seen an intensified scientific activity associated with this unique geometrical configuration, which has contributed to our understanding of related subjects such as avalanches in granules and segregation in suspensions. The existing literature related to rotating-drum flows is reviewed, highlighting similarities and differences between the various flow realizations. Scaling laws expressing the importance of different mechanisms underlying the observed phenomena have been focused on. An emphasis is placed on pattern formation phenomena. Rotating-drum flows exhibit stationary patterns as well as traveling and oscillating patterns; they exhibit reversible transitions as well as hysteresis. Apart from the predominant cylindrical configuration, this review covers recent work done with tumblers having other geometries, such as the sphere and the Hele-Shaw cell. |
BibTeX:
@article{Seiden.Thomas2011, author = {Seiden, G. and Thomas, P. J.}, title = {Complexity, segregation, and pattern formation in rotating-drum flows}, journal = {Rev. Mod. Phys.}, month = {November}, year = {2011}, volume = {83}, number = {4}, pages = {1323}, doi = {10.1103/RevModPhys.83.1323},, url = {http://rmp.aps.org/abstract/RMP/v83/i4/p1323_1} } |
Beta, C. and Bodenschatz, E., "Microfluidic tools for quantitative studies of eukaryotic chemotaxis", Eur. J. Cell Biol., October 2011, Vol. 90(10), 811 pp. |
Abstract: Over the past decade, microfluidic techniques have been established as a versatile platform to perform live cell experiments under well-controlled conditions. To investigate the directional responses of cells, stable concentration profiles of chemotactic factors can be generated in microfluidic gradient mixers that provide a high degree of spatial control. However, the times for built-up and switching of gradient profiles are in general too slow to resolve the intracellular protein translocation events of directional sensing of eukaryotes. Here, we review an example of a conventional microfluidic gradient mixer as well as the novel flow photolysis technique that achieves an increased temporal resolution by combining the photo-activation of caged compounds with the advantages of microfluidic chambers. (C) 2011 Elsevier GmbH. All rights reserved. |
BibTeX:
@article{Beta.Bodenschatz2011, author = {Beta, C. and Bodenschatz, E.}, title = {Microfluidic tools for quantitative studies of eukaryotic chemotaxis}, journal = {Eur. J. Cell Biol.}, month = {October}, year = {2011}, volume = {90}, number = {10}, pages = {811}, doi = {10.1016/j.ejcb.2011.05.006},, url = {http://www.sciencedirect.com/science/article/pii/S0171933511001038} } |
Ouellette, N. T., Bodenschatz, E. and Xu, H., "Path Lengths in Turbulence", J. Stat. Phys., October 2011, Vol. 145(1), 93 pp. |
Abstract: By tracking tracer particles at high speeds and for long times, we study the geometric statistics of Lagrangian trajectories in an intensely turbulent laboratory flow. In particular, we consider the distinction between the displacement of particles from their initial positions and the total distance they travel. The difference of these two quantities shows power-law scaling in the inertial range. By comparing them with simulations of a chaotic but non-turbulent flow and a Lagrangian Stochastic model, we suggest that our results are a signature of turbulence. |
BibTeX:
@article{Ouellette.Bodenschatz.ea2011, author = {Ouellette, N. T. and Bodenschatz, E. and Xu, H.}, title = {Path Lengths in Turbulence}, journal = {J. Stat. Phys.}, month = {October}, year = {2011}, volume = {145}, number = {1}, pages = {93}, doi = {10.1007/s10955-011-0323-7},, url = {http://link.springer.com/article/10.1007%2Fs10955-011-0323-7} } |
Berg, S., Luther, S. and Parlitz, U., "Synchronization based system identification of an extended excitable system", Chaos, September 2011, Vol. 21(3), 033104 pp. |
Abstract: A basic state and parameter estimation scheme for an extended excitable system is presented, where time series from a spatial grid of sampling points are used to drive and synchronize corresponding model equations. Model parameters are estimated by minimizing the synchronization error. This estimation scheme is demonstrated using data from generic models of excitable media exhibiting spiral wave dynamics and chaotic spiral break-up that are implemented on a graphics processing unit. (C) 2011 American Institute of Physics. [doi:10.1063/1.3613921] |
BibTeX:
@article{Berg.Luther.ea2011, author = {Berg, S. and Luther, S. and Parlitz, U.}, title = {Synchronization based system identification of an extended excitable system}, journal = {Chaos}, month = {September}, year = {2011}, volume = {21}, number = {3}, pages = {033104}, doi = {10.1063/1.3613921},, url = {http://chaos.aip.org/resource/1/chaoeh/v21/i3/p033104_s1} } |
Tarantola, M., Sunnick, E., Schneider, D., Marel, A. K., Kunze, A. and Janshoff, A., "Dynamic Changes of Acoustic Load and Complex Impedance as Reporters for the Cytotoxicity of Small Molecule Inhibitors", Chem. Res. Toxicol., September 2011, Vol. 24(9), 1494 pp. |
Abstract: Cellular motility is the major driving force of numerous biological phenomena including wound healing, immune response, embryogenesis, cancer formation, and metastasis. We studied the response of epithelial FaDu monolayers cultured on gold electrodes of an acoustic resonator (quartz crystal microbalance, QCM) and impedance sensor (electric cell-substrate impedance sensing, ECIS) to externally applied chemical stimuli interfering with cytoskeleton organization. Epithelial cell motility of confluent monolayers is characterized by subtle cell shape changes and variations in the cell-substrate as well as cell-cell distance without net directionality of individual cells. The impact of small molecules such as cytochalasin D, phalloidin, and blebbistatin as well as paclitaxel, nocodazol, and colchicin on actin and microtubules organization was quantified by conventional sensors' readouts and by comparing the noise pattern of the signals which is attributed to cellular dynamics. The responsiveness of noninvasive and label-free techniques relying on cellular dynamics is compared to classical viability assays and changes of the overall impedance of ultrasmall electrodes or acoustic loads of a thickness shear mode resonator. Depending on the agent used, a distinct sensor response was found, which can be used as a fingerprint of the cellular response. Cytoskeletal rearrangements and nuclear integrity were corroborated by fluorescence microscopy and correlated to the readouts of QCM and ECIS. |
BibTeX:
@article{Tarantola.Sunnick.ea2011, author = {Tarantola, M. and Sunnick, E. and Schneider, D. and Marel, A. K. and Kunze, A. and Janshoff, A.}, title = {Dynamic Changes of Acoustic Load and Complex Impedance as Reporters for the Cytotoxicity of Small Molecule Inhibitors}, journal = {Chem. Res. Toxicol.}, month = {September}, year = {2011}, volume = {24}, number = {9}, pages = {1494}, doi = {10.1021/tx200115q},, url = {http://pubs.acs.org/doi/abs/10.1021/tx200115q} } |
Xu, H., Pumir, A. and Bodenschatz, E., "The pirouette effect in turbulent flows", Nat. Phys., September 2011, Vol. 7(9), 709 pp. |
Abstract: The disorganized fluctuations of turbulence are crucial in the transport of particles or chemicals(1,2) and could play a decisive role in the formation of rain in clouds(3), the accretion process in protoplanetary disks(4), and how animals find their mates or prey(5,6). These and other examples(7) suggest a yet-to-be-determined unifying structure of turbulent flows(8,9). Here, we unveil an important ingredient of turbulence by taking the perspective of an observer who perceives its world with respect to three distant neighbours all swept by the flow. The time evolution of the observer's world can be decomposed into rotation and stretching. We show that, in this Lagrangian frame, the axis of rotation aligns with the initially strongest stretching direction, and that the dynamics can be understood by the conservation of angular momentum. This 'pirouette effect' thus appears as an important structural component of turbulence, and elucidates the mechanism for small-scale generation in turbulence. |
BibTeX:
@article{Xu.Pumir.ea2011, author = {Xu, H. and Pumir, A. and Bodenschatz, E.}, title = {The pirouette effect in turbulent flows}, journal = {Nat. Phys.}, month = {September}, year = {2011}, volume = {7}, number = {9}, pages = {709}, doi = {10.1038/nphys2010},, url = {http://www.nature.com/nphys/journal/v7/n9/full/nphys2010.html} } |
Yu, D. and Parlitz, U., "Inferring Network Connectivity by Delayed Feedback Control", PLOS ONE, September 2011, Vol. 6(9), e24333 pp. |
Abstract: We suggest a control based approach to topology estimation of networks with N elements. This method first drives the network to steady states by a delayed feedback control; then performs structural perturbations for shifting the steady states M times; and finally infers the connection topology from the steady states' shifts by matrix inverse algorithm ( M = N) or l(1-)norm convex optimization strategy applicable to estimate the topology of sparse networks from M << N perturbations. We discuss as well some aspects important for applications, such as the topology reconstruction quality and error sources, advantages and disadvantages of the suggested method, and the influence of ( control) perturbations, inhomegenity, sparsity, coupling functions, and measurement noise. Some examples of networks with Chua's oscillators are presented to illustrate the reliability of the suggested technique. |
BibTeX:
@article{Yu.Parlitz2011, author = {Yu, D. and Parlitz, U.}, title = {Inferring Network Connectivity by Delayed Feedback Control}, journal = {PLOS ONE}, month = {September}, year = {2011}, volume = {6}, number = {9}, pages = {e24333}, doi = {10.1371/journal.pone.0024333},, url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0024333} } |
Schneider, D., Tarantola, M. and Janshoff, A., "Morphological and dynamical changes during TGF-beta induced epithelial-to-mesenchymal transition", Eur. Biophys. J. Biophy., August 2011, Vol. 40, 163 pp.
[DOI] |
BibTeX:
@conference{Schneider.Tarantola.ea2011a, author = {Schneider, D. and Tarantola, M. and Janshoff, A.}, title = {Morphological and dynamical changes during TGF-beta induced epithelial-to-mesenchymal transition}, journal = {Eur. Biophys. J. Biophy.}, month = {August}, year = {2011}, volume = {40}, pages = {163} } |
Luther, S., Fenton, F. H., Kornreich, B. G., Squires, A., Bittihn, P., Hornung, D., Zabel, M., Flanders, J., Gladuli, A., Campoy, L., Cherry, E. M., Luther, G., Hasenfuss, G., Krinsky, V. I., Pumir, A., Gilmour R. F., J. and Bodenschatz, E., "Low-energy control of electrical turbulence in the heart", Nature, July 2011, Vol. 475(7355), 235 pp. |
Abstract: Controlling the complex spatio-temporal dynamics underlying life-threatening cardiac arrhythmias such as fibrillation is extremely difficult, because of the nonlinear interaction of excitation waves in a heterogeneous anatomical substrate(1-4). In the absence of a better strategy, strong, globally resetting electrical shocks remain the only reliable treatment for cardiac fibrillation(5-7). Here we establish the relationship between the response of the tissue to an electric field and the spatial distribution of heterogeneities in the scale-free coronary vascular structure. We show that in response to a pulsed electric field, E, these heterogeneities serve as nucleation sites for the generation of intramural electrical waves with a source density rho(E) and a characteristic time, tau, for tissue depolarization that obeys the power law tau proportional to E(alpha). These intramural wave sources permit targeting of electrical turbulence near the cores of the vortices of electrical activity that drive complex fibrillatory dynamics. Weshow in vitro that simultaneous and direct access to multiple vortex cores results in rapid synchronization of cardiac tissue and therefore, efficient termination of fibrillation. Using this control strategy, we demonstrate low-energy termination of fibrillation in vivo. Our results give new insights into the mechanisms and dynamics underlying the control of spatio-temporal chaos in heterogeneous excitable media and provide new research perspectives towards alternative, life-saving low-energy defibrillation techniques. |
BibTeX:
@article{Luther.Fenton.ea2011, author = {Luther, S. and Fenton, F. H. and Kornreich, B. G. and Squires, A. and Bittihn, P. and Hornung, D. and Zabel, M. and Flanders, J. and Gladuli, A. and Campoy, L. and Cherry, E. M. and Luther, G. and Hasenfuss, G. and Krinsky, V. I. and Pumir, A. and Gilmour, R. F., Jr. and Bodenschatz, E.}, title = {Low-energy control of electrical turbulence in the heart}, journal = {Nature}, month = {July}, year = {2011}, volume = {475}, number = {7355}, pages = {235}, doi = {10.1038/nature10216},, url = {http://www.nature.com/nature/journal/v475/n7355/full/nature10216.html} } |
Pauls, W., "Some remarks on Li-Sinai-type solutions of the Burgers equation", J. Phys. A, July 2011, Vol. 44(28), 285209 pp. |
Abstract: For a class of complex-valued initial conditions, we construct solutions for the inviscid Burgers equations of the same type as those recently introduced by Li and Sinai. Obtained by very simple considerations, these solutions correspond to stable distributions with 1 < alpha <= 2. We furthermore show that solutions of non-Gaussian type can be constructed for the viscous Burgers equation. |
BibTeX:
@article{Pauls2011, author = {Pauls, W.}, title = {Some remarks on Li-Sinai-type solutions of the Burgers equation}, journal = {J. Phys. A}, month = {July}, year = {2011}, volume = {44}, number = {28}, pages = {285209}, doi = {10.1088/1751-8113/44/28/285209},, url = {http://iopscience.iop.org/1751-8121/44/28/285209/} } |
Ahlers, G., Funfschilling, D. and Bodenschatz, E., "Heat transport in turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and Ra less than or similar to 10^15", 13th European Turbulence Conference (etc13): Convection, Rotation, Stratification and Buoyancy Effects, June 2011, Vol. 318, 082001 pp. |
Abstract: We report experimental results for the heat transport, as expressed by the Nusselt number Nu, by turbulent Rayleigh-Bénard convection in a cylindrical sample of aspect ratio Gamma equivalent to D/L = 0.50 (D = 1.12 m is the diameter and L = 2.24 m the height). The measurements are for the Rayleigh-number range 10(12) less than or similar to Ra less than or similar to 10(15) and for a Prandtl number Pr similar or equal to 0.86. At these large Ra the results were exceptionally sensitive to details of the experiment. Near Ra = 10(15) the Nusselt number could be caused to vary over the range 3500 less than or similar to Nu less than or similar to 5800 by minor changes in the apparatus or operating procedure. |
BibTeX:
@article{Ahlers.Funfschilling.ea2011, author = {Ahlers, G. and Funfschilling, D. and Bodenschatz, E.}, title = {Heat transport in turbulent Rayleigh-Bénard convection for Pr similar or equal to 0.8 and Ra less than or similar to 10^15}, journal = {13th European Turbulence Conference (etc13): Convection, Rotation, Stratification and Buoyancy Effects}, month = {June}, year = {2011}, volume = {318}, pages = {082001}, doi = {10.1088/1742-6596/318/8/082001},, url = {http://iopscience.iop.org/1742-6596/318/8/082001/} } |
Parlitz, U., Schlemmer, A. and Luther, S., "Synchronization patterns in transient spiral wave dynamics", Phys. Rev. E, May 2011, Vol. 83(5), 057201 pp. |
Abstract: Transient dynamics of spiral waves in a two-dimensional Barkley model is shown to be governed by pattern formation processes resulting in regions of synchronized activity separated by moving interfaces. During the transient the number of internally synchronized regions decreases as synchronization fronts move to the boundary of the simulated area. This spatiotemporal transient dynamics in an excitable medium is detected and visualized by means of an analysis of the local periodicity and by evaluation of prediction errors across the spatial domain. During the (long) transient both analyses show patterns that must not be misinterpreted as any information about (spatial) structure of the underlying (completely homogeneous) system. |
BibTeX:
@article{Parlitz.Schlemmer.ea2011, author = {Parlitz, U. and Schlemmer, A. and Luther, S.}, title = {Synchronization patterns in transient spiral wave dynamics}, journal = {Phys. Rev. E}, month = {May}, year = {2011}, volume = {83}, number = {5}, pages = {057201}, doi = {10.1103/PhysRevE.83.057201},, url = {http://pre.aps.org/abstract/PRE/v83/i5/e057201} } |
Ahlers, G., Funfschilling, D. and Bodenschatz, E., "Transitions in heat transport by turbulent convection at Rayleigh numbers up to 10^15 (vol 11, 123001, 2009)", New J. Phys., April 2011, Vol. 13, 049401 pp. |
Abstract: In the original paper by Ahlers et al ( 2009 New J. Phys. 11 123001) a transition was reported at a Rayleigh number Ra = Ra* similar or equal to 4x10(13). For Ra > Ra*, the Nusselt number Nu rose less rapidly with increasing Ra than it did below Ra*. In a note added in proof the authors reported the subsequent discovery of a coexisting additional 'upper branch' where Nu increased more rapidly with Ra. This addendum reports more extensive measurements of Nu( Ra) on the upper branch, which yield Nu alpha Ra-0.36. |
BibTeX:
@article{Ahlers.Funfschilling.ea2011a, author = {Ahlers, G. and Funfschilling, D. and Bodenschatz, E.}, title = {Transitions in heat transport by turbulent convection at Rayleigh numbers up to 10^15 (vol 11, 123001, 2009)}, journal = {New J. Phys.}, month = {April}, year = {2011}, volume = {13}, pages = {049401}, doi = {10.1088/1367-2630/13/4/049401},, url = {http://iopscience.iop.org/1367-2630/13/4/049401/pdf/1367-2630_13_4_049401.pdf} } |
Nobach, H., "Influence of individual variations of particle image intensities on high-resolution PIV", Exp. Fluids, April 2011, Vol. 50(4), 919 pp. |
Abstract: Individual variations of intensity of tracer particles, e.g., due to out-of-plane displacements between exposures, strongly limit the achievable accuracy of correlation-based PIV processing. The RMS error originated by this effect correlates with the spatial resolution that can be achieved with the processing algorithm making especially high-resolution algorithms like iterative image deformation affected by this error. Both aspects are shown, the gain of resolution by iterative image deformation and the loss of accuracy due to individual variations of particle intensities. |
BibTeX:
@article{Nobach2011, author = {Nobach, H.}, title = {Influence of individual variations of particle image intensities on high-resolution PIV}, journal = {Exp. Fluids}, month = {April}, year = {2011}, volume = {50}, number = {4}, pages = {919}, doi = {10.1007/s00348-010-0948-3},, url = {http://link.springer.com/article/10.1007%2Fs00348-010-0948-3} } |
Tordella, D., Belan, M., Massaglia, S., De Ponte, S., Mignone, A., Bodenschatz, E. and Ferrari, A., "Astrophysical jets: insights into long-term hydrodynamics", New J. Phys., April 2011, Vol. 13, 043011 pp. |
Abstract: Astrophysical jets are ubiquitous throughout the universe. They can be observed to emerge from protostellar objects, stellar x-ray binaries and supermassive black holes located at the center of active galaxies, and they are believed to originate from a central object that is surrounded by a magnetized accretion disc. With the motivations to understand whether hypersonic Newtonian jets produce any similarity to the morphologies observed in jets from young stellar objects (YSOs) and whether numerical codes, based on Godunov-type schemes, capture the basic physics of shocked flows, we have conceived a laboratory experiment and performed three-dimensional (3D) numerical simulations that reproduce the mid-to-long-term evolution of hypersonic jets. Here we show that these jets propagate, maintaining their collimation over long distances, in units of the jet initial radius. The jets studied are quasi-isentropic, are both lighter and heavier than the ambient and meet the two main scaling parameter requirements for proto-stellar jets: the ejection Mach number and the ambient/jet density ratio. |
BibTeX:
@article{Tordella.Belan.ea2011, author = {Tordella, D. and Belan, M. and Massaglia, S. and De Ponte, S. and Mignone, A. and Bodenschatz, E. and Ferrari, A.}, title = {Astrophysical jets: insights into long-term hydrodynamics}, journal = {New J. Phys.}, month = {April}, year = {2011}, volume = {13}, pages = {043011}, doi = {10.1088/1367-2630/13/4/043011},, url = {http://iopscience.iop.org/1367-2630/13/4/043011/} } |
Abel, M., Bodenschatz, E. and Toschi, F., "COST Action MP0806 'Particles in Turbulence': International Conference on Fundamentals, Experiments, Numeric and Applications", J. Phys., March 2011, Vol. 333, 011001 pp. |
Abstract: Turbulent flows are ubiquitous in nature and technology. Turbulent flows govern the transport of particulate matter in nature. For example, in atmospheric flows turbulence impacts the dynamics of aerosols, droplets, spores and of the living world by either chemo-attractant transport or transport of the insects themselves. In marine flows examples include the bubble dynamics that governs the uptake of oxygen and carbon dioxide at the ocean air interface, or the impact of turbulence on the life of phyto- and zoo-plankton, or the spread of pollutants in the oceans and estuaries. Turbulence is equally important for technology from process engineering in chemical and pharmaceutical industries to energy transport and energy generation.
The COST Action MP0806 'Particles in Turbulence' has as the primary objective the support of the fundamental research on the statistical properties of particle transport in turbulent flows. The Action provides excellent opportunities for the exchange of ideas by bringing together scientists from different areas of research and applications, or different views on the problem. The COST Action MP0806 organizes several events annually. The conference held at the University of Potsdam from 16 to 18 March 2011 was the main meeting of the Action in 2011. In total 87 researchers from 18 countries (of which 12 were European) met and presented their work, discussed new ideas on theoretical, numerical and experimental approaches, as well as on applications to various scientific domains. The conference attracted also a number of participants from outside the COST Action. The scientific presentations focused on inertial and finite-size particles, particle collisions, as well as advection and reaction in simple and complex flow geometries. Very interesting results were presented at the forefront of the field: the increasing computational power combined with novel numerical techniques now allows for the first time simulation of the dynamics of finites size particles, of bubbles, or of the large scale dynamics of convective clouds. Similarly the technical evolution provided major leaps on the experimental side. High-speed cameras, refined turbulence setups, specially prepared particles, etc allow high-precision measurements of larger span in space- and time-scales and quantitative comparison with simulations and theoretical models. The formation of rain, one of the key ingredients of climate models, still attracts considerable attention and this topic motivated many studies presented during the conference. Finally, new theoretical developments are emerging further demonstrating the vitality of this research field. In total, 83 contributed talks were presented (60 presentations have been made available for download from the COST Action website, http://mp0806.cineca.it), 16 keynote speakers gave plenary talks, while 3 specifically invited speakers provided overviews on important application areas: aerosol control in nuclear safety applications ('Postulated Nuclear Accidents: Evaluating Radioactive Releases with Special Emphasis on Particulate' by Martin Kissane), formation of rain in warm clouds ('Growth of cloud droplets and raindrops in turbulent clouds' by by Wojciech Grabowski) and evolution of biological aggregates in marine environments ('Aggregation and fragmentation of marine aggregates in random flows' by Ulrike Feudel). The scientific level of all presentations was very high and participants really enjoyed the conference despite (or maybe thanks to) the very intense program. Motivated by the very rapid pace of progress in the field, we have scheduled another conference for next year to be held at Lorentz Center in Leiden (The Netherlands). We expect that this conference shall be the start of a conference series on 'Particles in Turbulence'. The conference would have neither been possible without the financial support of the COST Office, nor without the contagious enthusiasm of the many participants. We would also like to thank the students from Potsdam University for their exquisite help. We are very thankful to Anita Peeters for her unwavering support and help in the organization of this particular event, as well as, for the efforts ensuring the smooth running of the COST Action 'Particles in turbulence'. |
BibTeX:
@article{Abel.Bodenschatz.ea2011, author = {Abel, M. and Bodenschatz, E. and Toschi, F.}, title = {COST Action MP0806 'Particles in Turbulence': International Conference on Fundamentals, Experiments, Numeric and Applications}, journal = {J. Phys.}, month = {March}, year = {2011}, volume = {333}, pages = {011001}, doi = {10.1088/1742-6596/333/1/011001},, url = {http://iopscience.iop.org/1742-6596/333/1/011001?fromSearchPage=true} } |
van den Berg, T. H., Wormgoor, W. D., Luther, S. and Lohse, D., "Phase-Sensitive Constant Temperature Anemometry", Macromol. Mater. Eng., March 2011, Vol. 296(3), 230 pp. |
Abstract: Hot-film measurements in bubbly flows provide time series that contain information about the liquid and the gas phase. Signal classification is required to disentangle the corresponding segments. The classification algorithms are prone to detection bias, which makes hot-film measurements in two-phase flows very difficult. We present a new phase-sensitive hot-film probe that provides velocity data and optical phase classification in a single device. We report a proof of concept of this method and demonstrate its accuracy and robustness. Furthermore, we discuss its application to turbulent bubbly flows. |
BibTeX:
@article{Berg.Wormgoor.ea2011, author = {van den Berg, T. H. and Wormgoor, W. D. and Luther, S. and Lohse, D.}, title = {Phase-Sensitive Constant Temperature Anemometry}, journal = {Macromol. Mater. Eng.}, month = {March}, year = {2011}, volume = {296}, number = {3}, pages = {230}, doi = {10.1002/mame.201000339},, url = {http://onlinelibrary.wiley.com/doi/10.1002/mame.201000339/abstract;jsessionid=E33D7B5F89A07C2D8918F4F64F80BD18.d02t02} } |
Bodenschatz, E., "Trendwende beim Publizieren?", Physik Journal, March 2011 |
BibTeX:
@article{Bodenschatz2011, author = {Bodenschatz, E.}, title = {Trendwende beim Publizieren?}, journal = {Physik Journal}, month = {March}, year = {2011},, url = {http://www.lfpn.ds.mpg.de/Docs/2011PhysikJournalEditorialBodenschatz.pdf} } |
Gilbert, A. D. and Pauls, W., "Complex manifolds for the Euler equations: a hierarchy of ODEs and the case of vanishing angle in two dimensions", Fluid Dynamics Research, March 2011, Vol. 43(2), 025505 pp. |
Abstract: This paper considers the two-dimensional Euler equation for complex spatial variables and two complex modes in the initial condition. A hierarchy of third-order ordinary differential equations (ODEs) is used to study the location and structure of the complex singular manifold for short times. The system has two key parameters, the ratio eta of the wave numbers of the two modes, and the angle phi between the two wave vectors. Using this hierarchy for the case phi = pi/2 the results of earlier authors (Pauls et al 2006 Physica D 219 40-59) are reproduced numerically. To make analytical progress, the paper considers the limit phi -> 0 in which the wave vectors become parallel, rescaling time also. By considering the limiting behaviour of the ODE hierarchy, an asymptotic framework is set up that describes the geometry of the singular manifold and local behaviour of vorticity in this limiting case phi = 0 of parallel modes. In addition, the hierarchy of ODEs can be solved analytically, order by order, in the parallel case using computer algebra. This is used to confirm the asymptotic theory and to give evidence for a scaling exponent beta = 1 for the blow-up of vorticity on the singular manifold, omega = O(s(-beta)) in this case of vanishing angle phi. |
BibTeX:
@article{Gilbert.Pauls2011, author = {Gilbert, A. D. and Pauls, W.}, title = {Complex manifolds for the Euler equations: a hierarchy of ODEs and the case of vanishing angle in two dimensions}, journal = {Fluid Dynamics Research}, month = {March}, year = {2011}, volume = {43}, number = {2}, pages = {025505}, doi = {10.1088/0169-5983/43/2/025505},, url = {http://iopscience.iop.org/article/10.1088/0169-5983/43/2/025505/meta} } |
Schäfer, E., Westendorf, C., Bodenschatz, E., Beta, C., Geil, B. and Janshoff, A., "Shape Oscillations of Dictyostelium discoideum Cells on Ultramicroelectrodes Monitored by Impedance Analysis", Small, March 2011, Vol. 7(6), 723 pp. |
Abstract: Time-resolved analysis employing electric cell–substrate impedance sensing reveals periodic impedance changes of small ensembles of Dictyostelium discoideum amoebae oscillating synchronously upon deprivation of food. Impedance changes are attributed to periodic alterations of cell shape and cell–substrate distance. Ultrasmall electrodes allow the detection of single cell traces. |
BibTeX:
@article{Schaefer.Westendorf.ea2011, author = {Schäfer, E. and Westendorf, C. and Bodenschatz, E. and Beta, C. and Geil, B. and Janshoff, A.}, title = {Shape Oscillations of Dictyostelium discoideum Cells on Ultramicroelectrodes Monitored by Impedance Analysis}, journal = {Small}, month = {March}, year = {2011}, volume = {7}, number = {6}, pages = {723}, doi = {10.1002/smll.201001955},, url = {http://onlinelibrary.wiley.com/doi/10.1002/smll.201001955/abstract;jsessionid=47D3864DC27C6F80BC839166BB16120F.d01t04} } |
Foote, A. D., Vilstrup, J. T., de Stephanis, R., Verborgh, P., Nielsen, S. C. A., Deaville, R., Kleivane, L., Martin, V., Miller, P. J. O., Oien, N., Perez-Gil, M., Rasmussen, M., Reid, R. J., Robertson, K. M., Rogan, E., Simila, T., Tejedor, M. L., Vester, H., Vikingsson, G. A., Willerslev, E., Gilbert, M. T. P. and Piertney, S. B., "Genetic differentiation among North Atlantic killer whale populations", Mol. Ecol., February 2011, Vol. 20(3), 629 pp. |
Abstract: Population genetic structure of North Atlantic killer whale samples was resolved from differences in allele frequencies of 17 microsatellite loci, mtDNA control region haplotype frequencies and for a subset of samples, using complete mitogenome sequences. Three significantly differentiated populations were identified. Differentiation based on microsatellite allele frequencies was greater between the two allopatric populations than between the two pairs of partially sympatric populations. Spatial clustering of individuals within each of these populations overlaps with the distribution of particular prey resources: herring, mackerel and tuna, which each population has been seen predating. Phylogenetic analyses using complete mitogenomes suggested two populations could have resulted from single founding events and subsequent matrilineal expansion. The third population, which was sampled at lower latitudes and lower density, consisted of maternal lineages from three highly divergent clades. Pairwise population differentiation was greater for estimates based on mtDNA control region haplotype frequencies than for estimates based on microsatellite allele frequencies, and there were no mitogenome haplotypes shared among populations. This suggests low or no female migration and that gene flow was primarily male mediated when populations spatially and temporally overlap. These results demonstrate that genetic differentiation can arise through resource specialization in the absence of physical barriers to gene flow. |
BibTeX:
@article{Foote.Vilstrup.ea2011, author = {Foote, A. D. and Vilstrup, J. T. and de Stephanis, R. and Verborgh, P. and Nielsen, S. C. A. and Deaville, R. and Kleivane, L. and Martin, V. and Miller, P. J. O. and Oien, N. and Perez-Gil, M. and Rasmussen, M. and Reid, R. J. and Robertson, K. M. and Rogan, E. and Simila, T. and Tejedor, M. L. and Vester, H. and Vikingsson, G. A. and Willerslev, E. and Gilbert, M. T. P. and Piertney, S. B.}, title = {Genetic differentiation among North Atlantic killer whale populations}, journal = {Mol. Ecol.}, month = {February}, year = {2011}, volume = {20}, number = {3}, pages = {629}, doi = {10.1111/j.1365-294X.2010.04957.x},, url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2010.04957.x/abstract} } |
Giewekemeyer, K., Krüger, S., Kalbfleisch, S., Bartels, M., Beta, C. and Salditt, T., "X-ray propagation microscopy of biological cells using waveguides as a quasipoint source", Phys. Fluids, February 2011, Vol. 83(2), e023804 pp. |
Abstract: We have used x-ray waveguides as highly confining optical elements for nanoscale imaging of unstained biological cells using the simple geometry of in-line holography. The well-known twin-image problem is effectively circumvented by a simple and fast iterative reconstruction. The algorithm which combines elements of the classical Gerchberg-Saxton scheme and the hybrid-input-output algorithm is optimized for phase-contrast samples, well-justified for imaging of cells at multi-keV photon energies. The experimental scheme allows for a quantitative phase reconstruction from a single holographic image without detailed knowledge of the complex illumination function incident on the sample, as demonstrated for freeze-dried cells of the eukaryotic amoeba Dictyostelium discoideum. The accessible resolution range is explored by simulations, indicating that resolutions on the order of 20 nm are within reach applying illumination times on the order of minutes at present synchrotron sources. |
BibTeX:
@article{Giewekemeyer.Krueger.ea2011, author = {Giewekemeyer, K. and Krüger, S.P. and Kalbfleisch, S. and Bartels, M. and Beta, C. and Salditt, T.}, title = {X-ray propagation microscopy of biological cells using waveguides as a quasipoint source}, journal = {Phys. Fluids}, month = {February}, year = {2011}, volume = {83}, number = {2}, pages = {e023804}, doi = {10.1103/PhysRevA.83.023804},, url = {http://pra.aps.org/abstract/PRA/v83/i2/e023804} } |
Petitprez, S., Zmoos, A.-F., Ogrodnik, J., Balse, E., Raad, N., El-Haou, S., Albesa, M., Bittihn, P., Luther, S., Lehnart, S. E., Hatem, S. N., Coulombe, A. and Abriel, H., "SAP97 and Dystrophin Macromolecular Complexes Determine Two Pools of Cardiac Sodium Channels Na_v 1.5 in Cardiomyocytes", Circ. Res., February 2011, Vol. 108(3), 294 pp. |
Abstract: Rationale: The cardiac sodium channel Nav1.5 plays a key role in excitability and conduction. The 3 last residues of Nav1.5 (Ser-Ile-Val) constitute a PDZ-domain binding motif that interacts with the syntrophin–dystrophin complex. As dystrophin is absent at the intercalated discs, Nav1.5 could potentially interact with other, yet unknown, proteins at this site.
Objective: The aim of this study was to determine whether Nav1.5 is part of distinct regulatory complexes at lateral membranes and intercalated discs. Methods and Results: Immunostaining experiments demonstrated that Nav1.5 localizes at lateral membranes of cardiomyocytes with dystrophin and syntrophin. Optical measurements on isolated dystrophin-deficient mdx hearts revealed significantly reduced conduction velocity, accompanied by strong reduction of Nav1.5 at lateral membranes of mdx cardiomyocytes. Pull-down experiments revealed that the MAGUK protein SAP97 also interacts with the SIV motif of Nav1.5, an interaction specific for SAP97 as no pull-down could be detected with other cardiac MAGUK proteins (PSD95 or ZO-1). Furthermore, immunostainings showed that Nav1.5 and SAP97 are both localized at intercalated discs. Silencing of SAP97 expression in HEK293 and rat cardiomyocytes resulted in reduced sodium current (INa) measured by patch-clamp. The INa generated by Nav1.5 channels lacking the SIV motif was also reduced. Finally, surface expression of Nav1.5 was decreased in silenced cells, as well as in cells transfected with SIV-truncated channels. Conclusions: These data support a model with at least 2 coexisting pools of Nav1.5 channels in cardiomyocytes: one targeted at lateral membranes by the syntrophin-dystrophin complex, and one at intercalated discs by SAP97. |
BibTeX:
@article{Petitprez.Zmoos.ea2011, author = {Petitprez, S. and Zmoos, A.-F. and Ogrodnik, J. and Balse, E. and Raad, N. and El-Haou, S. and Albesa, M. and Bittihn, P. and Luther, S. and Lehnart, S. E. and Hatem, S. N. and Coulombe, A. and Abriel, H.}, title = {SAP97 and Dystrophin Macromolecular Complexes Determine Two Pools of Cardiac Sodium Channels Na_v 1.5 in Cardiomyocytes}, journal = {Circ. Res.}, month = {February}, year = {2011}, volume = {108}, number = {3}, pages = {294}, doi = {10.1161/CIRCRESAHA.110.228312},, url = {http://circres.ahajournals.org/content/108/3/294} } |
Sahoo, G., Perlekar, P. and Pandit, R., "Systematics of the magnetic-Prandtl-number dependence of homogeneous, isotropic magnetohydrodynamic turbulence", New J. Phys., January 2011, Vol. 13, 013036 pp. |
Abstract: We present the results of our detailed pseudospectral direct numerical simulation (DNS) studies, with up to 1024(3) collocation points, of incompressible, magnetohydrodynamic (MHD) turbulence in three dimensions, without a mean magnetic field. Our study concentrates on the dependence of various statistical properties of both decaying and statistically steady MHD turbulence on the magnetic Prandtl number Pr-M over a large range, namely 0.01 <= Pr-M <= 10. We obtain data for a wide variety of statistical measures, such as probability distribution functions (PDFs) of the moduli of the vorticity and current density, the energy dissipation rates, and velocity and magnetic-field increments, energy and other spectra, velocity and magnetic-field structure functions, which we use to characterize intermittency, isosurfaces of quantities, such as the moduli of the vorticity and current density, and joint PDFs, such as those of fluid and magnetic dissipation rates. Our systematic study uncovers interesting results that have not been noted hitherto. In particular, we find a crossover from a larger intermittency in the magnetic field than in the velocity field, at large Pr-M, to a smaller intermittency in the magnetic field than in the velocity field, at low Pr-M. Furthermore, a comparison of our results for decaying MHD turbulence and its forced, statistically steady analogue suggests that we have strong universality in the sense that, for a fixed value of Pr-M, multiscaling exponent ratios agree, at least within our error bars, for both decaying and statistically steady homogeneous, isotropic MHD turbulence. |
BibTeX:
@article{Sahoo.Perlekar.ea2011, author = {Sahoo, G. and Perlekar, P. and Pandit, R.}, title = {Systematics of the magnetic-Prandtl-number dependence of homogeneous, isotropic magnetohydrodynamic turbulence}, journal = {New J. Phys.}, month = {January}, year = {2011}, volume = {13}, pages = {013036}, doi = {10.1088/1367-2630/13/1/013036},, url = {http://iopscience.iop.org/1367-2630/13/1/013036/} } |
Amselem, G., "Directional sensing and chemotaxis in eukaryotic cells – a quantitative study", 2010 |
BibTeX:
@phdthesis{Amselem2010, author = {Amselem, G.}, title = {Directional sensing and chemotaxis in eukaryotic cells – a quantitative study}, year = {2010},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/Amselem-Thesis.pdf} } |
Nobach, H., Kinzel, M., Zimmermann, R., Tropea, C. and Bodenschatz, E., "Measurement of Particle Accelerations with the Laser Doppler Technique", Turbulence and Interactions, 2010, Vol. 110 |
Abstract: An extension of the laser Doppler technique for measuring particle acceleration is presented. The basic principles of the technique follow closely those introduced in [11], although numerous improvements have been implemented in the signal processing for increasing the reliability of individual estimates of particle acceleration. The main contribution of this study is to identify and quantify the errors due to optical fringe divergence in the detection volume of the present laser Doppler system, to introduce an appropriate experiment involving a falling wire and to compare the acceleration measurements of the laser Doppler system to the results of a particle tracking system with high-speed cameras in a highly turbulent flow. Noteworthy is the fact that all measurements were performed with a commercial off-the-shelf laser Doppler system. |
BibTeX:
@proceedings{Nobach.Kinzel.ea2010, author = {Nobach, H. and Kinzel, M. and Zimmermann, R. and Tropea, C. and Bodenschatz, E.}, title = {Measurement of Particle Accelerations with the Laser Doppler Technique}, journal = {Turbulence and Interactions}, year = {2010}, volume = {110}, doi = {10.1007/978-3-642-14139-3_33},, url = {http://link.springer.com/chapter/10.1007%2F978-3-642-14139-3_33} } |
Bae, A. J. and Bodenschatz, E., "On the swimming of Dictyostelium amoebae", Proc. Natl. Acad. Sci. U.S.A., November 2010, Vol. 107(44), E165 pp. |
BibTeX:
@article{Bae.Bodenschatz2010, author = {Bae, A. J. and Bodenschatz, E.}, title = {On the swimming of Dictyostelium amoebae}, journal = {Proc. Natl. Acad. Sci. U.S.A.}, month = {November}, year = {2010}, volume = {107}, number = {44}, pages = {E165}, doi = {10.1073/pnas.1011900107},, url = {http://www.pnas.org/content/107/44/E165} } |
Schröder-Schetelig, J., Manoonpong, P. and Wörgötter, F., "Using efference copy and a forward internal model for adaptive biped walking", Auton. Robot., November 2010, Vol. 29(3), 357 pp. |
Abstract: To behave properly in an unknown environment, animals or robots must distinguish external from self-generated stimuli on their sensors. The biologically inspired concepts of efference copy and internal model have been successfully applied to a number of robot control problems. Here we present an application of this for our dynamic walking robot RunBot. We use efference copies of the motor commands with a simple forward internal model to predict the expected self-generated acceleration during walking. The difference to the actually measured acceleration is then used to stabilize the walking on terrains with changing slopes through its upper body component controller. As a consequence, the controller drives the upper body component (UBC) to lean forwards/backwards as soon as an error occurs resulting in dynamical stable walking. We have evaluated the performance of the system on four different track configurations. Furthermore we believe that the experimental studies pursued here will sharpen our understanding of how the efference copies influence dynamic locomotion control to the benefit of modern neural control strategies in robots. |
BibTeX:
@article{Schroeder-Schetelig.Manoonpong.ea2010, author = {Schröder-Schetelig, J. and Manoonpong, P. and Wörgötter, F.}, title = {Using efference copy and a forward internal model for adaptive biped walking}, journal = {Auton. Robot.}, month = {November}, year = {2010}, volume = {29}, number = {3}, pages = {357}, doi = {10.1007/s10514-010-9199-7},, url = {http://link.springer.com/article/10.1007%2Fs10514-010-9199-7} } |
Otani, N. F., Luther, S., Singh, R. and . Gilmour, R. F. J., "Transmural Ultrasound-based Visualization of Patterns of Action Potential Wave Propagation in Cardiac Tissue", Ann. Biomed. Eng., October 2010, Vol. 38(10), 3112 pp. |
Abstract: The pattern of action potential propagation during various tachyarrhythmias is strongly suspected to be composed of multiple re-entrant waves, but has never been imaged in detail deep within myocardial tissue. An understanding of the nature and dynamics of these waves is important in the development of appropriate electrical or pharmacological treatments for these pathological conditions. We propose a new imaging modality that uses ultrasound to visualize the patterns of propagation of these waves through the mechanical deformations they induce. The new method would have the distinct advantage of being able to visualize these waves deep within cardiac tissue. In this article, we describe one step that would be necessary in this imaging process—the conversion of these deformations into the action potential induced active stresses that produced them. We demonstrate that, because the active stress induced by an action potential is, to a good approximation, only nonzero along the local fiber direction, the problem in our case is actually overdetermined, allowing us to obtain a complete solution. Use of two- rather than three-dimensional displacement data, noise in these displacements, and/or errors in the measurements of the fiber orientations all produce substantial but acceptable errors in the solution. We conclude that the reconstruction of action potential-induced active stress from the deformation it causes appears possible, and that, therefore, the path is open to the development of the new imaging modality. |
BibTeX:
@article{Otani.Luther.ea2010, author = {Otani, N. F. and Luther, S. and Singh, R. and . Gilmour, Robert F. Jr.}, title = {Transmural Ultrasound-based Visualization of Patterns of Action Potential Wave Propagation in Cardiac Tissue}, journal = {Ann. Biomed. Eng.}, month = {October}, year = {2010}, volume = {38}, number = {10}, pages = {3112}, doi = {10.1007/s10439-010-0071-x},, url = {http://link.springer.com/article/10.1007%2Fs10439-010-0071-x} } |
Nobach, H., "Reduktion des Fehlers durch Intensitutsänderung von Streuteilchen bei planarer PIV", September 2010 |
Abstract: Individuelle Intensit?ts?nderungen von Streuteilchen bei Bewegung senkrecht zum Lichtschnitt oder nicht ausreichende ?berlappung der beiden aufeinanderfolgenden Lichtpulse wurden zuvor als eine wesentliche Fehlerquelle bei der planaren PIV-Messtechnik erkannt. Es wird ein Verfahren vorgestellt, das der Ursache des Fehlers, n?mlich ?berlappenden Teilchenabbildungen mit unterschiedlichen, relativen Helligkeits?nderungen, entgegenwirkt. Das Verfahren beruht auf einer Maskierung der betroffenen Bereiche. Als Kriterium zum Erkennen der betroffenen Bereichen wird der lokale Kreuzkorrelationskoeffizient ausgewertet. Das gesamte Verfahren ist als Zwischenschritt in der PIV-Analyse ausgelegt, der auf die zur Bestimmung der Verschiebung zu korrelierenden Bildausschnitte wirkt. Die notwendigen Informationen werden direkt aus den Bildern gewonnen, hieraus eine Maske erstellt, die wiederum direkt auf die zu korrelierenden Bilder angewendet wird. Die Wirksamkeit des Verfahrens wird anhand von Rechnersimulationen mit homogenem Geschwindigkeitsfeld und Experimenten mit einem bewegten Glasblock demonstriert. Durch die vorgestellte Korrektur wird der Fehler besonders im Bereich
mittlerer Verschiebungen senkrecht zum Lichtschnitt reduziert und damit der Anwendungsbereich der planaren PIV-Messtechnik mit akzeptablen Fehlern zu deutlich gr??eren Verschiebungen senkrecht zur Lichtschnittebene erweitert. Geschwindigkeitsgradienten k?nnen zu Einschr?nkungen der Wirksamkeit des Verfahrens f?hren, was Potential f?r weitere Entwicklungen und Tests gibt. |
BibTeX:
@proceedings{Nobach2010a, author = {Nobach, H.}, title = {Reduktion des Fehlers durch Intensitutsänderung von Streuteilchen bei planarer PIV}, month = {September}, year = {2010},, url = {http://www.gala-ev.org/images/Beitraege/Beitraege%202010/pdf/22.pdf} } |
Benczik, I. J. and Vollmer, J., "A reactive-flow model of phase separation in fluid binary mixtures with continuously ramped temperature", EPL, August 2010, Vol. 91(3), 36003 pp. |
Abstract: We suggest to revisit the phase separation of binary mixtures subjected to a sustained change of temperature from the point of view of reactive flows. Exploiting this new perspective, we describe the demixing dynamics by a spatial model of advection-reaction-diffusion completed with nucleation and coaguation of droplets. In this approach several features of the dynamics-in particular an oscillatory variation of the droplet density-become numerically and analytically accessible. Hence, this model helps to clarify why the oscillation frequency is hardly affected by the flow. Copyright (C) EPLA, 2010 |
BibTeX:
@article{Benczik.Vollmer2010, author = {Benczik, I. J. and Vollmer, J.}, title = {A reactive-flow model of phase separation in fluid binary mixtures with continuously ramped temperature}, journal = {EPL}, month = {August}, year = {2010}, volume = {91}, number = {3}, pages = {36003}, doi = {10.1209/0295-5075/91/36003},, url = {http://iopscience.iop.org/0295-5075/91/3/36003/} } |
Nobach, H., "Influence of individual variations of particle image intensities on high-resolution PIV", Exp. Fluids, August 2010, Vol. 50(4), 919 pp. |
Abstract: Individual variations of intensity of tracer particles, e.g., due to out-of-plane displacements between exposures, strongly limit the achievable accuracy of correlation-based PIV processing. The RMS error originated by this effect correlates with the spatial resolution that can be achieved with the processing algorithm making especially high-resolution algorithms like iterative image deformation affected by this error. Both aspects are shown, the gain of resolution by iterative image deformation and the loss of accuracy due to individual variations of particle intensities. |
BibTeX:
@article{Nobach2010, author = {Nobach, H.}, title = {Influence of individual variations of particle image intensities on high-resolution PIV}, journal = {Exp. Fluids}, month = {August}, year = {2010}, volume = {50}, number = {4}, pages = {919}, doi = {10.1007/s00348-010-0948-3},, url = {http://link.springer.com/article/10.1007/s00348-010-0948-3} } |
Nobach, H., "Suppression of planar PIV errors due to particle intensity variations", July 2010 |
Abstract: One of the major sources of error in planar PIV is due to particle intensity variations when e.g. particles with out-of-plane motion change their intensity or disappear completely. The same effect comes e.g. from different laser beam profiles for the first and second laser pulse or from non-spherical rotating particles changing reflectivity. It has been shown that the error due to this effect can be as large as 0.05 to 0.1 pixel for typical out-of-plane displacements. The paper introduces a method to suppress the influence of this error source based on selective pixel weighting using local correlation values over a 3?3 pixel area. The method has been applied to synthetic data and a moving glass block with markers. In most cases a substantial
reduction in error of 20 to 50% has been achieved. |
BibTeX:
@proceedings{Nobach2010b, author = {Nobach, H.}, title = {Suppression of planar PIV errors due to particle intensity variations}, month = {July}, year = {2010},, url = {http://ltces.dem.ist.utl.pt/LXLASER/LXLASER2010/upload/1697_gzkfbi_1.12.2.Full_1697.pdf} } |
Pauls, W., "On complex singularities of the 2D Euler equation at short times", Physica D, July 2010, Vol. 239(13), 1159 pp. |
Abstract: We present a study of complex singularities of a two-parameter family of solutions for the two-dimensional Euler equation with periodic boundary conditions and initial conditions psi(0)(z(1), z(2)) = (F) over cap (p) cos p . z + (F) over cap (q) cos q . z in the short-time asymptotic regime. As has been shown numerically in Pails et al. [W. Pauls, T. Matsumoto, U. Frisch, J. Bec, Nature of complex singularities for the 2D Euler equation, Physica D 219 (2006) 40-59], the type of the singularities depends on the angle theta between the modes p and q. Thus, the Fourier coefficients of the solutions decrease as G(k, theta) similar to C(theta)k(-alpha)e(-delta(theta)k) with the exponent alpha depending on phi. Here we show for the two particular cases of phi going to zero and to pi that the type of the singularities can be determined very accurately, being characterised by alpha = 5/2 and alpha = 3 respectively. In these two cases we are also able to determine the subdominant corrections. Furthermore, we find that the geometry of the singularities in these two cases is completely different, the singular manifold being located "over" different points in the real domain. (C) 2010 Elsevier B.V. All rights reserved. |
BibTeX:
@article{Pauls2010, author = {Pauls, W.}, title = {On complex singularities of the 2D Euler equation at short times}, journal = {Physica D}, month = {July}, year = {2010}, volume = {239}, number = {13}, pages = {1159}, doi = {10.1016/j.physd.2010.03.004},, url = {http://www.sciencedirect.com/science/article/pii/S0167278910000989} } |
Tisserand, J.-C., Creyssels, M., Gibert, M., Casting, B. and Chilla, F., "Convection in a vertical channel", New J. Phys., July 2010, Vol. 12, 075024 pp. |
Abstract: The flow generated by heat convection in a long, vertical channel is studied by means of particle imagery velocimetry techniques, with the help of the thermal measurements from a previous paper (Gibert et al 2009 Phys. Fluids 21 035109). We analyse the mean velocity profiles and the Reynolds stresses, and compare the present results with the previous ones obtained in a larger cell and at a larger Reynolds number. We calculate the horizontal temperature profile and the related horizontal heat flux. The pertinence of effective turbulent diffusivity and viscosity is confirmed by the low value of the associated mixing length. We study the one-point and two-point statistics of both velocity components. We show how the concept of turbulent viscosity explains the relations between the local probability density functions (pdf) of fluctuations for temperature, vertical and horizontal velocity components. Despite the low Reynolds number values explored, some conclusions can be drawn about the small scale velocity differences and the related energy cascade. |
BibTeX:
@article{Tisserand, author = {Tisserand, J.-C. and Creyssels, M. and Gibert, M. and Casting, B. and Chilla, F.}, title = {Convection in a vertical channel}, journal = {New J. Phys.}, month = {July}, year = {2010}, volume = {12}, pages = {075024}, doi = {10.1088/1367-2630/12/7/075024},, url = {https://iopscience.iop.org/article/10.1088/1367-2630/12/7/075024} } |
Beta, C., "Bistability in the actin cortex", PMC Biophysics, June 2010 |
Abstract: Multi-color fluorescence imaging experiments of wave forming Dictyostelium cells have revealed that actin waves separate two domains of the cell cortex that differ in their actin structure and phosphoinositide composition. We propose a bistable model of actin dynamics to account for these experimental observation. The model is based on the simplifying assumption that the actin cytoskeleton is composed of two distinct network types, a dendritic and a bundled network. The two structurally different states that were observed in experiments correspond to the stable fixed points in the bistable regime of this model. Each fixed point is dominated by one of the two network types. The experimentally observed actin waves can be considered as trigger waves that propagate transitions between the two stable fixed points. |
BibTeX:
@openaccess{Beta2010, author = {Beta, C.}, title = {Bistability in the actin cortex}, journal = {PMC Biophysics}, month = {June}, year = {2010}, doi = {10.1186/1757-5036-3-12},, url = {http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907310/} } |
Gibert, M., Xu, H. and Bodenschatz, E., "Inertial effects on two-particle relative dispersion in turbulent flows", EPL, June 2010, Vol. 90(6), 64005 pp. |
Abstract: We report experimental results on the relative motion of pairs of solid spheric particles with initial separations in the inertial range of fully developed turbulence in water. The particle densities were in the range of 1 approximate to rho(p)/rho f approximate to 8, i.e., from neutrally buoyant to highly inertial; and their sizes were of the Kolmogorov scale. For all particles, we observed a Batchelor-like regime, in which particles separated ballistically. Similar to the Batchelor regime for tracers, this regime was observed in the early stages of the relative separation for times t similar to 0.1t(0) with t(0) determined by the turbulence energy dissipation rate and the initial separation between particle pairs. In this time interval heavier particles separated faster than fluid tracers. The second-order Eulerian velocity structure functions was found to increase with density. In other words, both observations show that the relative velocity between inertial particles was larger than that between tracers. Based on the widely used, simplified equation of motion for inertial point-particles, we derived a model that shows an increase in relative velocity between inertial particles. In its scale dependence, however, it disagrees quantitatively with the experimental results. This we attribute to the preferential sampling of the flow field by inertial particles, which is not captured by the model. |
BibTeX:
@article{Gibert.Xu.ea2010, author = {Gibert, M. and Xu, H. and Bodenschatz, E.}, title = {Inertial effects on two-particle relative dispersion in turbulent flows}, journal = {EPL}, month = {June}, year = {2010}, volume = {90}, number = {6}, pages = {64005}, doi = {10.1209/0295-5075/90/64005},, url = {http://iopscience.iop.org/0295-5075/90/6/64005/} } |
Bittihn, P., Squires, A., Luther, G., Bodenschatz, E., Krinsky, V., Parlitz, U. and Luther, S., "Phase-resolved analysis of the susceptibility of pinned spiral waves to far-field pacing in a two-dimensional model of excitable media", Phil. Trans. R. Soc. A, May 2010, Vol. 368(1918), 2221 pp. |
Abstract: Life-threatening cardiac arrhythmias are associated with the existence of stable and unstable spiral waves. Termination of such complex spatio-temporal patterns by local control is substantially limited by anchoring of spiral waves at natural heterogeneities. Far-field pacing (FFP) is a new local control strategy that has been shown to be capable of unpinning waves from obstacles. In this article, we investigate in detail the FFP unpinning mechanism for a single rotating wave pinned to a heterogeneity. We identify qualitatively different phase regimes of the rotating wave showing that the concept of vulnerability is important but not sufficient to explain the failure of unpinning in all cases. Specifically, we find that a reduced excitation threshold can lead to the failure of unpinning, even inside the vulnerable window. The critical value of the excitation threshold (below which no unpinning is possible) decreases for higher electric field strengths and larger obstacles. In contrast, for a high excitation threshold, the success of unpinning is determined solely by vulnerability, allowing for a convenient estimation of the unpinning success rate. In some cases, we also observe phase resetting in discontinuous phase intervals of the spiral wave. This effect is important for the application of multiple stimuli in experiments. |
BibTeX:
@article{Bittihn.Squires.ea2010, author = {Bittihn, P. and Squires, A. and Luther, G. and Bodenschatz, E. and Krinsky, V. and Parlitz, U. and Luther, S.}, title = {Phase-resolved analysis of the susceptibility of pinned spiral waves to far-field pacing in a two-dimensional model of excitable media}, journal = {Phil. Trans. R. Soc. A}, month = {May}, year = {2010}, volume = {368}, number = {1918}, pages = {2221}, doi = {10.1098/rsta.2010.0038},, url = {http://rsta.royalsocietypublishing.org/content/368/1918/2221} } |
Zimmermann, R., Xu, H., Gasteuil, Y., Bourgoin, M., Volk, R., Pinton, J.-F. and Bodenschatz, E., "The Lagrangian exploration module: An apparatus for the study of statistically homogeneous and isotropic turbulence", Rev. Sci. Instrum., May 2010, Vol. 81(5), 055112 pp. |
Abstract: We present an apparatus that generates statistically homogeneous and isotropic turbulence with a mean flow that is less than 10% of the fluctuating velocity in a volume of the size of the integral length scale. The apparatus is shaped as an icosahedron where at each of the 12 vertices the flow is driven by independently controlled propellers. By adjusting the driving of the different propellers the isotropy and homogeneity of the flow can be tuned, while keeping the mean flow weak. (c) 2010 American Institute of Physics. [doi: 10.1063/1.3428738] |
BibTeX:
@article{Zimmermann.Xu.ea2010, author = {Zimmermann, R. and Xu, H. and Gasteuil, Y. and Bourgoin, M. and Volk, R. and Pinton, J.-Fr. and Bodenschatz, E.}, title = {The Lagrangian exploration module: An apparatus for the study of statistically homogeneous and isotropic turbulence}, journal = {Rev. Sci. Instrum.}, month = {May}, year = {2010}, volume = {81}, number = {5}, pages = {055112}, doi = {10.1063/1.3428738},, url = {http://rsi.aip.org/resource/1/rsinak/v81/i5/p055112_s1} } |
Bödeker, H. U., Beta, C., Frank, T. D. and Bodenschatz, E., "Quantitative analysis of random ameboid motion", EPL, April 2010, Vol. 90(2), 28005 pp. |
Abstract: We quantify random migration of the social ameba Dictyostelium discoideum. We demonstrate that the statistics of cell motion can be described by an underlying Langevin-type stochastic differential equation. An analytic expression for the velocity distribution function is derived. The separation into deterministic and stochastic parts of the movement shows that the cells undergo a damped motion with multiplicative noise. Both contributions to the dynamics display a distinct response to external physiological stimuli. The deterministic component depends on the developmental state and ambient levels of signaling substances, while the stochastic part does not. Copyright (C) EPLA, 2010 |
BibTeX:
@article{Boedeker.Beta.ea2010, author = {Bödeker, H. U. and Beta, C. and Frank, T. D. and Bodenschatz, E.}, title = {Quantitative analysis of random ameboid motion}, journal = {EPL}, month = {April}, year = {2010}, volume = {90}, number = {2}, pages = {28005}, doi = {10.1209/0295-5075/90/28005},, url = {http://iopscience.iop.org/0295-5075/90/2/28005/} } |
Westendorf, C., Bae, A. J., Erlenkamper, C., Galland, E., Franck, C., Bodenschatz, E. and Beta, C., "Live cell flattening - traditional and novel approaches", PMC Biophysics, April 2010, Vol. 3(9), 15 pp. |
Abstract: Eukaryotic cell flattening is valuable for improving microscopic observations, ranging from bright field (BF) to total internal reflection fluorescence (TIRF) microscopy. Fundamental processes, such as mitosis and in vivo actin polymerization, have been investigated using these techniques. Here, we review the well known agar overlayer protocol and the oil overlay method. In addition, we present more elaborate microfluidics-based techniques that provide us with a greater level of control. We demonstrate these techniques on the social amoebae Dictyostelium discoideumiota comparing the advantages and disadvantages of each method. |
BibTeX:
@openaccess{Westendorf.Bae.ea2010, author = {Westendorf, C. and Bae, A. J. and Erlenkamper, C. and Galland, E. and Franck, C. and Bodenschatz, E. and Beta, C.}, title = {Live cell flattening - traditional and novel approaches}, journal = {PMC Biophysics}, month = {April}, year = {2010}, volume = {3}, number = {9}, pages = {15}, doi = {10.1186/1757-5036-3-9},, url = {http://link.springer.com/article/10.1186/1757-5036-3-9} } |
Di Lorenzo, F., "Development of a receiver system for the RTO", March 2010 |
BibTeX:
@mastersthesis{DiLorenzo2010, author = {Di Lorenzo, F.}, title = {Development of a receiver system for the RTO}, month = {March}, year = {2010},, url = {http://www.lfpn.ds.mpg.de/turbulence/documents/DiLorenzo_MScThesis_2010.pdf} } |
Sahoo, G., Mitra, D. and Pandit, R., "Dynamo onset as a first-order transition: Lessons from a shell model for magnetohydrodynamics", Phys. Rev. E, March 2010, Vol. 81(3), 036317 pp. |
Abstract: We carry out systematic and high-resolution studies of dynamo action in a shell model for magnetohydro-dynamic (MHD) turbulence over wide ranges of the magnetic Prandtl number Pr(M) and the magnetic Reynolds number Re(M). Our study suggests that it is natural to think of dynamo onset as a nonequilibrium first-order phase transition between two different turbulent, but statistically steady, states. The ratio of the magnetic and kinetic energies is a convenient order parameter for this transition. By using this order parameter, we obtain the stability diagram (or nonequilibrium phase diagram) for dynamo formation in our MHD shell model in the (Pr(M)(-1), Re(M)) plane. The dynamo boundary, which separates dynamo and no-dynamo regions, appears to have a fractal character. We obtain a hysteretic behavior of the order parameter across this boundary and suggestions of nucleation-type phenomena. |
BibTeX:
@article{Sahoo.Mitra.ea2010, author = {Sahoo, G. and Mitra, D. and Pandit, R.}, title = {Dynamo onset as a first-order transition: Lessons from a shell model for magnetohydrodynamics}, journal = {Phys. Rev. E}, month = {March}, year = {2010}, volume = {81}, number = {3}, pages = {036317}, doi = {10.1103/PhysRevE.81.036317},, url = {http://pre.aps.org/abstract/PRE/v81/i3/e036317} } |
Bodenschatz, E., Malinowski, S. P., Shaw, R. A. and Stratmann, F., "Can We Understand Clouds Without Turbulence?", Science, February 2010, Vol. 327(5968), 970 pp. |
BibTeX:
@article{Bodenschatz.Malinowski.ea2010, author = {Bodenschatz, E. and Malinowski, S. P. and Shaw, R. A. and Stratmann, F.}, title = {Can We Understand Clouds Without Turbulence?}, journal = {Science}, month = {February}, year = {2010}, volume = {327}, number = {5968}, pages = {970}, doi = {10.1126/science.1185138},, url = {http://www.sciencemag.org/content/327/5968/970} } |
Bardos, C., Frisch, U., Pauls, W., Ray, S. S. and Titi, E. S., "Entire Solutions of Hydrodynamical Equations with Exponential Dissipation", Commun. Math. Phys., January 2010, Vol. 293(2), 519 pp. |
Abstract: We consider a modification of the three-dimensional Navier-Stokes equations and other hydrodynamical evolution equations with space-periodic initial conditions in which the usual Laplacian of the dissipation operator is replaced by an operator whose Fourier symbol grows exponentially as e(vertical bar k vertical bar/kd) at high wavenumbers vertical bar k vertical bar. Using estimates in suitable classes of analytic functions, we show that the solutions with initially finite energy become immediately entire in the space variables and that the Fourier coefficients decay faster than e-(C(k/kd) ln(vertical bar k vertical bar/kd)) for any C < 1/(2 ln 2). The same result holds for the one-dimensional Burgers equation with exponential dissipation but can be improved: heuristic arguments and very precise simulations, analyzed by the method of asymptotic extrapolation of van der Hoeven, indicate that the leading-order asymptotics is precisely of the above form with C = C(*) = 1/ ln 2. The same behavior with a universal constant C(*) is conjectured for the Navier-Stokes equations with exponential dissipation in any space dimension. This universality prevents the strong growth of intermittency in the far dissipation range which is obtained for ordinary Navier-Stokes turbulence. Possible applications to improved spectral simulations are briefly discussed. |
BibTeX:
@article{Bardos.Frisch.ea2010, author = {Bardos, C. and Frisch, U. and Pauls, W. and Ray, S. S. and Titi, E. S.}, title = {Entire Solutions of Hydrodynamical Equations with Exponential Dissipation}, journal = {Commun. Math. Phys.}, month = {January}, year = {2010}, volume = {293}, number = {2}, pages = {519}, doi = {10.1007/s00220-009-0916-z},, url = {http://link.springer.com/article/10.1007%2Fs00220-009-0916-z} } |
Pumir, A., Sinha, S., Sridhar S.and Argentina, M., Hörning, M., Filippi, S., Cherubini, C., Luther, S. and Krinsky, V., "Wave-train-induced termination of weakly anchored vortices in excitable media", Phys. Rev. E, January 2010, Vol. 81(1), 010901 pp. |
Abstract: A free vortex in excitable media can be displaced and removed by a wave train. However, simple physical arguments suggest that vortices anchored to large inexcitable obstacles cannot be removed similarly. We show that unpinning of vortices attached to obstacles smaller than the core radius of the free vortex is possible through pacing. The wave-train frequency necessary for unpinning increases with the obstacle size and we present a geometric explanation of this dependence. Our model-independent results suggest that decreasing excitability of the medium can facilitate pacing-induced removal of vortices in cardiac tissue. |
BibTeX:
@article{Pumir.Sinha.ea2010, author = {Pumir, A. and Sinha, S. and Sridhar,S.and Argentina, M. and Hörning, M. and Filippi, S. and Cherubini, C. and Luther, S. and Krinsky, V.}, title = {Wave-train-induced termination of weakly anchored vortices in excitable media}, journal = {Phys. Rev. E}, month = {January}, year = {2010}, volume = {81}, number = {1}, pages = {010901}, doi = {10.1103/PhysRevE.81.010901},, url = {http://pre.aps.org/abstract/PRE/v81/i1/e010901} } |
Ahlers, G., Bodenschatz, E., Funfschilling, D. and Hogg, J., "Turbulent Rayleigh-Bénard convection for a Prandtl number of 0.67", J. Fluid Mech., December 2009, Vol. 641, 157 pp. |
Abstract: For the Rayleigh-number range 10(7) less than or similar to Ra less than or similar to 10(11) we report measurements of the Nusselt number Nu and of properties of the large-scale circulation (LSC) for cylindrical samples of helium gas (Prandtl number Pr = 0.674) that have aspect ratio Gamma equivalent to D/L = 0.50 (D and L are the diameter and the height respectively) and are heated from below. The results for Nu are consistent with recent direct numerical Simulations. We measured the amplitude delta of the azimuthal temperature variation induced by the LSC at the sidewall, and the LSC circulation-plane orientation theta(0), at three vertical positions. For the entire Ra range the LSC involves a convection roll that is coherent over the height of the system. However, this structure frequently collapses completely at irregular time intervals and then reorganizes from the incoherent flow. At small delta the probability distribution p(delta) increases linearly from zero; for Gamma = 1 and Pr = 4.38 this increase is exponential. No evidence of a two-roll structure, with one above the other, was observed. This differs from recent direct numerical simulations for Gamma = 0.5 and Pr = 0.7, where a one-roll LSC was Found to exist only for Ra less than or similar to 10(9) to 10(10), and from measurements for Gamma = 0.5 and Pr similar or equal to 5, where one- and two-roll structures were observed with transitions between them at random time intervals. |
BibTeX:
@article{Ahlers.Bodenschatz.ea2009, author = {Ahlers, G. and Bodenschatz, E. and Funfschilling, D. and Hogg, J.}, title = {Turbulent Rayleigh-Bénard convection for a Prandtl number of 0.67}, journal = {J. Fluid Mech.}, month = {December}, year = {2009}, volume = {641}, pages = {157}, doi = {10.1017/S0022112009991959},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6837836} } |
Ahlers, G., Funfschilling, D. and Bodenschatz, E., "Transitions in heat transport by turbulent convection at Rayleigh numbers up to 10^15", New J. Phys., December 2009, Vol. 11, 123001 pp. |
Abstract: We describe a pressure vessel for conducting experiments in helium (He), air, nitrogen (N-2) or sulfur hexafluoride (SF6) under pressures of up to 19 bars, and facilities for the study of Rayleigh-Bénard convection inside this pressure vessel. The convection cells, known as the high pressure convection facilities (HPCFs), can have interior heights up to L = 2.3 m and diameters up to D = 1.2 m. Measurements of the Nusselt number Nu for Rayleigh numbers Ra up to Ra* = 4 x 10(13) and a Prandtl number Pr similar or equal to 0.8 gave Nu proportional to Ra-gamma eff with gamma(eff) similar or equal to 0.308. At Ra* there was a sharp transition to a new regime. The Nusselt number was continuous at Ra*, but the exponent characterizing its dependence on Ra changed suddenly to gamma(eff) = 0.25. Near Ra = Ra** similar or equal to 3 x 10(14), there was a further change in the Ra-dependence of Nu. A new state with gamma(eff) similar or equal to 0.17 evolved and there was bistability of the gamma(eff) = 0.25 and the gamma(eff) = 0.17 branches. |
BibTeX:
@article{Ahlers.Funfschilling.ea2009, author = {Ahlers, G. and Funfschilling, D. and Bodenschatz, E.}, title = {Transitions in heat transport by turbulent convection at Rayleigh numbers up to 10^15}, journal = {New J. Phys.}, month = {December}, year = {2009}, volume = {11}, pages = {123001}, doi = {10.1088/1367-2630/11/12/123001},, url = {http://iopscience.iop.org/1367-2630/11/12/123001/} } |
Seiden, G., Weiss, S. and Bodenschatz, E., "Superlattice patterns in forced thermal convection", Chaos, December 2009, Vol. 19(4), 041102 pp. |
BibTeX:
@article{Seiden.Weiss.ea2009, author = {Seiden, G. and Weiss, S. and Bodenschatz, E.}, title = {Superlattice patterns in forced thermal convection}, journal = {Chaos}, month = {December}, year = {2009}, volume = {19}, number = {4}, pages = {041102}, doi = {10.1063/1.3176902},, url = {http://chaos.aip.org/resource/1/chaoeh/v19/i4/p041102_s1} } |
Bewley, G. P., "The generation of particles to observe quantized vortex dynamics in superfluid helium", Cryogenics, October 2009, Vol. 49(10), 549 pp. |
Abstract: We describe a method to prepare a sample of superfluid helium-4 with hydrogen particles suspended within it. The method is to dilute hydrogen gas with helium at room temperature, and bubble the mixture through liquid helium at a temperature above the superfluid phase transition temperature, T(lambda) approximate to 2.17 K. The procedure yields a suspension of micron-sized particles whose total volume is about 10(5) times smaller than the fluid volume. The fluid and suspension are then cooled to a temperature below T(lambda). We show that the particles, so prepared in superfluid helium, are useful for studying superfluid flows and, in particular, the dynamics of quantized vortices. In addition, the particle-superfluid helium system is rich in not yet fully explained interactions. We review preliminary investigations that include observing the vortex lattice in rotating helium, vortex reconnection in quantized vortex turbulence, and vortex ring decay. These data illustrate the basic mechanisms of dissipation in superfluid turbulence. (C) 2008 Elsevier Ltd. All rights reserved. |
BibTeX:
@article{Bewley2009, author = {Bewley, G. P.}, title = {The generation of particles to observe quantized vortex dynamics in superfluid helium}, journal = {Cryogenics}, month = {October}, year = {2009}, volume = {49}, number = {10}, pages = {549}, doi = {10.1016/j.cryogenics.2008.10.018},, url = {http://www.sciencedirect.com/science/article/pii/S0011227508001793} } |
Bewley, G. P. and Sreenivasan, K. R., "The Decay of a Quantized Vortex Ring and the Influence of Tracer Particles", J. Low Temp. Phys., September 2009, Vol. 156(3-6), 84 pp. |
Abstract: We capture the decay of a quantized vortex ring in superfluid helium-4 by imaging particles trapped on the vortex core. The ring shrinks in time, providing direct evidence for the dissipation of energy in the superfluid. The ring with trapped particles collapses more slowly than predicted by an available theory, but the collapse rate can be predicted correctly if the trapping of the particles on the core is taken into account. We theoretically explore the conditions under which particles may be considered passive tracers of quantized vortices and estimate, in particular, that their dynamics on the large-scale is largely unaffected by the burden of trapped particles if the latter are spaced by more than ten particle diameters along the vortex core, at temperatures between 1.5 K and 2.1 K. |
BibTeX:
@article{Bewley.Sreenivasan2009, author = {Bewley, G. P. and Sreenivasan, K. R.}, title = {The Decay of a Quantized Vortex Ring and the Influence of Tracer Particles}, journal = {J. Low Temp. Phys.}, month = {September}, year = {2009}, volume = {156}, number = {3-6}, pages = {84}, doi = {10.1007/s10909-009-9903-1},, url = {http://link.springer.com/article/10.1007%2Fs10909-009-9903-1} } |
Bodenschatz, E., Funfschilling, D. and Ahlers, G., "Search for the ``ultimate state'' in turbulent Rayleigh-Bénard convection", Advances In Turbulence Xii - Proceedings of the 12th Euromech European Turbulence Conference, September 2009, Vol. 132, 167 pp. |
BibTeX:
@inproceedings{Bodenschatz.Funfschilling.ea2009, author = {Bodenschatz, E. and Funfschilling, D. and Ahlers, G.}, title = {Search for the ``ultimate state'' in turbulent Rayleigh-Bénard convection}, journal = {Advances In Turbulence Xii - Proceedings of the 12th Euromech European Turbulence Conference}, month = {September}, year = {2009}, volume = {132}, pages = {167}, doi = {10.1007/978-3-642-03085-7_42},, url = {http://link.springer.com/chapter/10.1007/978-3-642-03085-7_42} } |
Theves, M., "Quantitative Study of Eukaryotic Chemotaxis with Microfluidic Devices", September 2009 |
BibTeX:
@mastersthesis{Theves2009, author = {Theves, M.}, title = {Quantitative Study of Eukaryotic Chemotaxis with Microfluidic Devices}, month = {September}, year = {2009},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/Theves_Diplomarbeit_2009.pdf} } |
Toschi, F. and Bodenschatz, E., "Lagrangian Properties of Particles in Turbulence", Annu. Rev. Fluid Mech., September 2009, Vol. 41, 375 pp. |
Abstract: The Lagrangian description of turbulence is characterized by a unique conceptual simplicity, and by an immediate connection with the physics of dispersion and mixing. In this article, we report some motivations behind the Lagrangian description of turbulence and focus on the statistical properties of particles when advected by fully developed turbulent flows. By means of a detailed comparison between experimental and numerical results, we review the physics of particle acceleration, Lagrangian velocity structure functions, and pairs and shapes evolution. Recent results for nonideal particles are discussed, providing an outlook on future directions. |
BibTeX:
@article{Toschi.Bodenschatz2009, author = {Toschi, F. and Bodenschatz, E.}, title = {Lagrangian Properties of Particles in Turbulence}, journal = {Annu. Rev. Fluid Mech.}, month = {September}, year = {2009}, volume = {41}, pages = {375}, doi = {10.1146/annurev.fluid.010908.165210},, url = {http://www.annualreviews.org/doi/abs/10.1146/annurev.fluid.010908.165210} } |
Fenton, F. H., Luther, S., Cherry, E. M., Otani, N. F., Krinsky, V., Pumir, A., Bodenschatz, E. and Gilmour R. F., J., "Termination of Atrial Fibrillation Using Pulsed Low-Energy Far-Field Stimulation", Circulation, August 2009, Vol. 120(6), 467 pp. |
Abstract: Background-Electrically based therapies for terminating atrial fibrillation (AF) currently fall into 2 categories: antitachycardia pacing and cardioversion. Antitachycardia pacing uses low-intensity pacing stimuli delivered via a single electrode and is effective for terminating slower tachycardias but is less effective for treating AF. In contrast, cardioversion uses a single high-voltage shock to terminate AF reliably, but the voltages required produce undesirable side effects, including tissue damage and pain. We propose a new method to terminate AF called far-field antifibrillation pacing, which delivers a short train of low-intensity electric pulses at the frequency of antitachycardia pacing but from field electrodes. Prior theoretical work has suggested that this approach can create a large number of activation sites ("virtual" electrodes) that emit propagating waves within the tissue without implanting physical electrodes and thereby may be more effective than point-source stimulation. Methods and Results-Using optical mapping in isolated perfused canine atrial preparations, we show that a series of pulses at low field strength (0.9 to 1.4 V/cm) is sufficient to entrain and subsequently extinguish AF with a success rate of 93% (69 of 74 trials in 8 preparations). We further demonstrate that the mechanism behind far-field antifibrillation pacing success is the generation of wave emission sites within the tissue by the applied electric field, which entrains the tissue as the field is pulsed. Conclusions-AF in our model can be terminated by far-field antifibrillation pacing with only 13% of the energy required for cardioversion. Further studies are needed to determine whether this marked reduction in energy can increase the effectiveness and safety of terminating atrial tachyarrhythmias clinically. (Circulation. 2009;120:467-476.) |
BibTeX:
@article{Fenton.Luther.ea2009, author = {Fenton, F. H. and Luther, S. and Cherry, E. M. and Otani, N. F. and Krinsky, V. and Pumir, A. and Bodenschatz, E. and Gilmour, R. F., Jr.}, title = {Termination of Atrial Fibrillation Using Pulsed Low-Energy Far-Field Stimulation}, journal = {Circulation}, month = {August}, year = {2009}, volume = {120}, number = {6}, pages = {467}, doi = {10.1161/CIRCULATIONAHA.108.825091},, url = {http://circ.ahajournals.org/content/120/6/467} } |
Funfschilling, D., Bodenschatz, E. and Ahlers, G., "Search for the ``Ultimate State'' in Turbulent Rayleigh-Bénard Convection", Phys. Rev. Lett., July 2009, Vol. 103(1), 014503 pp. |
Abstract: Measurements of the Nusselt number Nu and of temperature variations Delta T(b) in the bulk fluid are reported for turbulent Rayleigh-Beacutenard convection of a cylindrical sample. They cover the Rayleigh-number range 10(9)less than or similar to Ra less than or similar to 3x10(14) using He (Prandtl number Pr=0.67), N(2) (Pr=0.72) and SF(6) (Pr=0.79 to 0.84) at pressures up to 15 bars and near-ambient temperatures. The sample had a height L=2.24 m and diameter D=1.12 m and was located in a new High-Pressure Convection Facility (HPCF) at the Max Planck Institute for Dynamics and Self-Organization in Goumlttingen, Germany. The data do not show the transition to an "ultimate regime" reported by Chavanne et al. and are consistent with the measurements of Niemela et al. |
BibTeX:
@article{Funfschilling.Bodenschatz.ea2009, author = {Funfschilling, D. and Bodenschatz, E. and Ahlers, G.}, title = {Search for the ``Ultimate State'' in Turbulent Rayleigh-Bénard Convection}, journal = {Phys. Rev. Lett.}, month = {July}, year = {2009}, volume = {103}, number = {1}, pages = {014503}, doi = {10.1103/PhysRevLett.103.014503},, url = {http://prl.aps.org/abstract/PRL/v103/i1/e014503} } |
Nobach, H. and Bodenschatz, E., "Limitations of accuracy in PIV due to individual variations of particle image intensities", Exp. Fluids, July 2009, Vol. 47(1), 27 pp. |
Abstract: The effect of independent variations of the intensity of individual tracer particles between consecutive images on the accuracy of common displacement estimation methods in particle image velocimetry (PIV) is investigated. Such variations can be observed, e.g., in flows with components perpendicular to the illumination sheet, leading to out-of-plane displacements of the tracer particles. The achievable accuracy of PIV measurements is shown to be limited by this effect alone to be of the order of 0.1 pixel, yielding a basic limitation of the PIV technique. |
BibTeX:
@article{Nobach.Bodenschatz2009, author = {Nobach, H. and Bodenschatz, E.}, title = {Limitations of accuracy in PIV due to individual variations of particle image intensities}, journal = {Exp. Fluids}, month = {July}, year = {2009}, volume = {47}, number = {1}, pages = {27}, doi = {10.1007/s00348-009-0627-4},, url = {http://link.springer.com/article/10.1007%2Fs00348-009-0627-4} } |
Sandmann, R., "Microfluidic Study of Eukaryotic Chemotaxis: periodic stimulation and intracellular response", July 2009 |
BibTeX:
@mastersthesis{Sandmann2009, author = {Sandmann, R.}, title = {Microfluidic Study of Eukaryotic Chemotaxis: periodic stimulation and intracellular response}, month = {July}, year = {2009},, url = {http://www.lfpn.ds.mpg.de/biophysics/documents/Sandmann_Bachelorarbeit_2009.pdf} } |
Ouellette, N. T., Xu, H. and Bodenschatz, E., "Bulk turbulence in dilute polymer solutions", J. Fluid Mech., June 2009, Vol. 629, 375 pp. |
Abstract: By tracking small particles in the bulk of an intensely turbulent laboratory flow, we study the effect of long-chain polymers on the Eulerian structure functions. We find that the structure functions are modified over a wide range or length scales even for very small polymer concentrations. Their behaviour can be captured by defining a length scale that depends on the solvent viscosity, the polymer relaxation time and the Weissenberg number. This result is not captured by Current models. Additionally, the effects we observe depend strongly on the concentration. While the dissipation-range statistics change smoothly as a function of polymer concentration, we find that the inertial-range values of the structure functions are modified only when the concentration exceeds a threshold of approximately 5 parts per million (p.p.m.) by weight for the 18 X 10(6) atomic mass unit (a.m.u.) molecular weight polyacrylamide used in the experiment. |
BibTeX:
@article{Ouellette.Xu.ea2009, author = {Ouellette, N. T. and Xu, H. and Bodenschatz, E.}, title = {Bulk turbulence in dilute polymer solutions}, journal = {J. Fluid Mech.}, month = {June}, year = {2009}, volume = {629}, pages = {375}, doi = {10.1017/S0022112009006697},, url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=5832344} } |
Bae, A. J., Beta, C. and Bodenschatz, E., "Rapid switching of chemical signals in microfluidic devices", Lab Chip, March 2009, Vol. 9(21), 3059 pp. |
Abstract: We present an analysis of concentration switching times in microfluidic devices. The limits of rapid switching are analyzed based on the theory of dispersion by Taylor and Aris and compared to both experiments and numerical simulations. We focus on switching times obtained by photo-activation of caged compounds in a micro-flow (flow photolysis). The performance of flow photolysis is compared to other switching techniques. A flow chart is provided to facilitate the application of our theoretical analysis to microfluidic switching devices. |
BibTeX:
@article{Bae.Beta.ea2009, author = {Bae, A. J. and Beta, C. and Bodenschatz, E.}, title = {Rapid switching of chemical signals in microfluidic devices}, journal = {Lab Chip}, month = {March}, year = {2009}, volume = {9}, number = {21}, pages = {3059}, doi = {10.1039/b905521e},, url = {http://pubs.rsc.org/en/Content/ArticleLanding/2009/LC/b905521e} } |
Krinski, V., Luther, S. and Bodenschatz, E., "Multisite heart pacing with adjustable number of pacing sites for terminating high frequency cardiac arrhythmias", Patent, March 2009(US20090062877 A1) |
Abstract: A multisite heart pacing with adjustable number of pacing sites is realized by using only one lead directly connected to the heart. The number and locations of pacing sites is regulated by increasing the amplitude of pacing pulses delivered by the electric field, and by changing orientation of the electric field.
Improved termination of high frequency cardiac arrhythmias and AF is achieved by - regulating the number of pacing sites by choosing the pulse energy in the range 1/400-½ DE, where DE is energy of conventional cardioversion/defibrillation. - protection against inducing VF by choosing the direction and amplitude of the electric field, and by a proper synchronization with R wave of the ECG. - selection of the pacing frequency and amplitude based on the frequency spectrum of a high frequency cardiac arrhythmia. |
BibTeX:
@article{Krinski.Luther.ea2009, author = {Krinski, V. and Luther, S. and Bodenschatz, E.}, title = {Multisite heart pacing with adjustable number of pacing sites for terminating high frequency cardiac arrhythmias}, journal = {Patent}, month = {March}, year = {2009}, number = {US20090062877 A1},, url = {http://www.google.com/patents/US20090062877} } |
Bodenschatz, E. e. a., "Open Access - Opportunities and challenges", 2008 |
BibTeX:
@book{Bodenschatz2008a, author = {Bodenschatz, E. et al.}, title = {Open Access - Opportunities and challenges}, year = {2008}, doi = {10.2777/93994},, url = {http://www.unesco.de/infothek/publikationen/publikationsverzeichnis/handbuch-open-access.html} } |
Nobach, H., "Messung von Teilchenbeschleunigungen mit dem Laser-Doppler-Anemometer", 2008 |
Abstract: Die Erweiterung des Laser-Doppler-Messverfahrens zur Bestimmung von Teilchenbeschleunigungen stellt bekannter Ma?en hohe Anforderungen an die optischen Teile und die Signalverarbeitung. Dieser Beitrag stellt die erforderlichen Komponenten f?r eine erfolgreiche Realisierung mit einem kommerziellen Laser-Doppler-System zusammen. Referenzexperimente und Methoden zur Bestimmung von systematischen und zuf?lligen Fehlern werden vorgestellt. Die Aufl?sungsgrenze des realisierten Messaufbaus wird bestimmt. |
BibTeX:
@proceedings{Nobach2008, author = {Nobach, H.}, title = {Messung von Teilchenbeschleunigungen mit dem Laser-Doppler-Anemometer}, year = {2008},, url = {http://nambis.bplaced.de/download/text/ahmt08.pdf} } |
Crawford, A. M., Mordant, N., Xu, H. and Bodenschatz, E., "Fluid acceleration in the bulk of turbulent dilute polymer solutions", New J. Phys., December 2008, Vol. 10, 123015 pp. |
Abstract: We studied the effects of long-chain polymers on the small scales of turbulence by experimental measurements of Lagrangian accelerations in the bulk of turbulent flows of dilute polymer solutions. Lagrangian accelerations were measured by following tracer particles with a high-speed optical tracking system. We observed a significant decrease in the acceleration variance in dilute polymer solutions as compared with in pure water. The shape of the normalized acceleration probability density functions, however, remained the same as in Newtonian water flows. We also observed an increase in the turbulent Lagrangian acceleration autocorrelation time with polymer concentration. The decrease of acceleration variance and the increase of acceleration autocorrelation time are consistent with a suppression of viscous dissipation, and cannot be explained by a mere increase of effective viscosity due to the polymers. |
BibTeX:
@article{Crawford.Mordant.ea2008, author = {Crawford, A. M. and Mordant, N. and Xu, H. and Bodenschatz, E.}, title = {Fluid acceleration in the bulk of turbulent dilute polymer solutions}, journal = {New J. Phys.}, month = {December}, year = {2008}, volume = {10}, pages = {123015}, doi = {10.1088/1367-2630/10/12/123015},, url = {http://iopscience.iop.org/1367-2630/10/12/123015/} } |
McCoy, J. H., Brunner, W., Pesch, W. and Bodenschatz, E., "Self-Organization of Topological Defects due to Applied Constraints", Phys. Rev. Lett., December 2008, Vol. 101(25), 254102 pp. |
Abstract: While topological defects are essential to our understanding of self-organizing periodic systems, little is known about how these systems respond when their defects are subjected to geometrical constraints. In an experiment on spatially modulated thermal convection patterns, we observe that applied geometrical constraints bind topological defects into robust self-localized structures that evolve through aggregation, annihilation, and self-replication. We demonstrate that this unexpected cooperative response to the modulation is a natural consequence of three generic elements: phase locking, symmetry breaking, and spatial resonance. Our work provides new insights into the interplay between order, chaos, and control in self-organizing systems. |
BibTeX:
@article{McCoy.Brunner.ea2008, author = {McCoy, J. H. and Brunner, W. and Pesch, W. and Bodenschatz, E.}, title = {Self-Organization of Topological Defects due to Applied Constraints}, journal = {Phys. Rev. Lett.}, month = {December}, year = {2008}, volume = {101}, number = {25}, pages = {254102}, doi = {10.1103/PhysRevLett.101.254102},, url = {http://prl.aps.org/abstract/PRL/v101/i25/e254102} } |
Seiden, G., Weiss, S., McCoy, J. H., Pesch, W. and Bodenschatz, E., "Pattern Forming System in the Presence of Different Symmetry-Breaking Mechanisms", Phys. Rev. Lett., November 2008, Vol. 101(21), 214503 pp. |
Abstract: We report experiments on spatially forced inclined layer convection, where the combined effect of the intrinsic symmetry breaking due to a gravity-induced shear flow and spatially periodic 1D forcing is studied. We observed pattern selection processes resulting in stabilization of spatiotemporal chaos and the emergence of novel two-dimensional states. Phase diagrams depicting the different observed states for typical forcing scenarios are presented. Convection in the weakly nonlinear regime is compared with theory, and a good agreement is found. |
BibTeX:
@article{Seiden.Weiss.ea2008, author = {Seiden, G. and Weiss, S. and McCoy, J. H. and Pesch, W. and Bodenschatz, E.}, title = {Pattern Forming System in the Presence of Different Symmetry-Breaking Mechanisms}, journal = {Phys. Rev. Lett.}, month = {November}, year = {2008}, volume = {101}, number = {21}, pages = {214503}, doi = {10.1103/PhysRevLett.101.214503},, url = {http://link.aps.org/doi/10.1103/PhysRevLett.101.214503} } |
Bittihn, P., Luther, G., Bodenschatz, E., Krinsky, V., Parlitz, U. and Luther, S., "Far field pacing supersedes anti-tachycardia pacing in a generic model of excitable media", New J. Phys., October 2008, Vol. 10, 103012 pp. |
Abstract: Removing anchored spirals from obstacles is an important step in terminating cardiac arrhythmia. Conventional anti-tachycardia pacing (ATP) has this ability, but only under very restrictive conditions. In a generic model of excitable media, we demonstrate that for unpinning spiral waves from obstacles this profound limitation of ATP can be overcome by far field pacing (FFP). More specifically, an argument is presented for why FFP includes and thus can only extend the capabilities of ATP in the configurations considered. By numerical simulations, we show that in the model there exists a parameter region in which unpinning is possible by FFP but not by ATP. The relevance of this result regarding clinical applications is discussed. |
BibTeX:
@article{Bittihn.Luther.ea2008, author = {Bittihn, P. and Luther, G. and Bodenschatz, E. and Krinsky, V. and Parlitz, U. and Luther, S.}, title = {Far field pacing supersedes anti-tachycardia pacing in a generic model of excitable media}, journal = {New J. Phys.}, month = {October}, year = {2008}, volume = {10}, pages = {103012}, doi = {10.1088/1367-2630/10/10/103012},, url = {http://iopscience.iop.org/1367-2630/10/10/103012/} } |
Frisch, U., Kurien, S., Pandit, R., Pauls, W., Ray, S. S., Wirth, A. and Zhu, J., "Hyperviscosity, Galerkin truncation, and bottlenecks in turbulence", Phys. Rev. Lett., October 2008, Vol. 101(14), 144501 pp. |
Abstract: It is shown that the use of a high power alpha of the Laplacian in the dissipative term of hydrodynamical equations leads asymptotically to truncated inviscid conservative dynamics with a finite range of spatial Fourier modes. Those at large wave numbers thermalize, whereas modes at small wave numbers obey ordinary viscous dynamics [C. Cichowlas et al., Phys. Rev. Lett. 95, 264502 (2005)]. The energy bottleneck observed for finite alpha may be interpreted as incomplete thermalization. Artifacts arising from models with alpha > 1 are discussed. |
BibTeX:
@article{Frisch.Kurien.ea2008, author = {Frisch, U. and Kurien, S. and Pandit, R. and Pauls, W. and Ray, S. S. and Wirth, A. and Zhu, J.}, title = {Hyperviscosity, Galerkin truncation, and bottlenecks in turbulence}, journal = {Phys. Rev. Lett.}, month = {October}, year = {2008}, volume = {101}, number = {14}, pages = {144501}, doi = {10.1103/PhysRevLett.101.144501},, url = {http://prl.aps.org/abstract/PRL/v101/i14/e144501} } |