Max Planck Institute for Dynamics and Self-Organization, Goettingen


Publication list of the Laboratory for Fluid Dynamics, Pattern Formation and Biocomplexity


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Eidi, Z., Mohammad-Rafiee, F., Khorrami, M. and Gholami, A., "Modelling of Dictyostelium discoideum movement in a linear gradient of chemoattractant", October 2017
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},
  month = {October},
  year = {2017},
  url = {http://pubs.rsc.org/en/content/articlehtml/2017/sm/c7sm01568b},
  doi = {10.1039/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},
  url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.148101},
  doi = {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},
  url = {https://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.2.103502},
  doi = {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},
  url = {https://arxiv.org/abs/1706.02530},
  doi = {10.1063/1.4986153}
}
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},
  url = {https://www.ncbi.nlm.nih.gov/pubmed/28935937},
  doi = {10.1038/s41598-017-12348-w}
}
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},
  url = {https://link.springer.com/article/10.1007/s00348-017-2428-5},
  doi = {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},
  url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.128701},
  doi = {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},
  url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.134502},
  doi = {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},
  url = {https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561252/},
  doi = {10.1038/s41598-017-09092-6}
}
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},
  url = {http://aip.scitation.org/doi/10.1063/1.4999473},
  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},
  url = {http://www.biochemsoctrans.org/content/45/4/999},
  doi = {10.1042/BST20170163}
}
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},
  url = {http://www.pnas.org/content/114/37/E7727.short},
  doi = {10.1073/pnas.1616600114}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0010465517301911},
  doi = {10.1016/j.cpc.2017.06.009}
}
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},
  url = {https://link.springer.com/article/10.1007/s00526-017-1187-8},
  doi = {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},
  url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.95.052218},
  doi = {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},
  url = {https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.114503},
  doi = {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},
  url = {http://link.springer.com/article/10.1007%2Fs10955-017-1739-5},
  doi = {10.1007/s10955-017-1739-5}
}
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},
  url = {https://journals.aps.org/pre/abstract/10.1103/PhysRevE.95.022215},
  doi = {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},
  url = {http://www.pnas.org/content/114/6/1281.short},
  doi = {10.1073/pnas.1611475114}
}
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},
  url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/mean-flow-structure-in-horizontal-convection/759294BE5E272703205AF21D228F5D95},
  doi = {10.1017/jfm.2016.866}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0032591016303539},
  doi = {10.1016/j.powtec.2016.06.015}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0377027316303547},
  doi = {10.1016/j.jvolgeores.2016.09.009}
}
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)},
  url = {http://journals.aps.org/prfluids/abstract/10.1103/PhysRevFluids.1.062301},
  doi = {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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.117.148102},
  doi = {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},
  url = {https://www.cambridge.org/core/journals/journal-of-fluid-mechanics/article/small-scale-anisotropy-in-turbulent-boundary-layers/099DC1792A7D0021DFDC2D0764F1FC70#},
  doi = {10.1017/jfm.2016.529}
}
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},
  url = {http://science.sciencemag.org/content/353/6295/176},
  doi = {10.1126/science.aae0450}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0997754615304027},
  doi = {10.1016/j.euromechflu.2016.07.006}
}
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},
  url = {http://iopscience.iop.org/article/10.1088/1367-2630/18/6/065007/pdf},
  doi = {10.1088/1367-2630/18/6/065007}
}
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)},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.050201},
  doi = {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)},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.051102},
  doi = {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},
  url = {http://scitation.aip.org/content/aip/journal/pof2/28/4/10.1063/1.4944685},
  doi = {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},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.042701},
  doi = {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},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.043102},
  doi = {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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.124502},
  doi = {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},
  url = {http://www.sciencedirect.com/science/article/pii/S0017931015307304},
  doi = {10.1016/j.ijheatmasstransfer.2015.11.012}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=10193782&fulltextType=RA&fileId=S0022112016000562},
  doi = {10.1017/jfm.2016.56}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/2015GL067003/full},
  doi = {10.1002/2015GL067003}
}
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},
  url = {http://journals.cambridge.org/download.php?file=%2FFLM%2FFLM790%2FS0022112016000550a.pdf&code=36e97ccd95fa88ecd990e75cf703ee45},
  doi = {10.1017/jfm.2016.55}
}
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},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.93.012414#fulltext#fulltext},
  doi = {10.1103/PhysRevE.93.012414}
}
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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.024302},
  doi = {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},
  url = {http://link.springer.com/article/10.1007/s11433-015-5736-x},
  doi = {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},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.92.062510},
  doi = {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},
  url = {http://www.sciencemag.org/content/350/6256/40.summary?sid=cb42e5f4-2ef2-44b5-96ba-c78ad569f4d9},
  doi = {10.1126/science.aad1386}
}
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},
  url = {http://iopscience.iop.org/article/10.1088/1367-2630/17/10/103015},
  doi = {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},
  url = {http://iopscience.iop.org/article/10.1088/1367-2630/17/9/093040/meta},
  doi = {10.1088/1367-2630/17/9/093040}
}
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},
  url = {http://link.springer.com/article/10.1007/s00348-015-2050-3},
  doi = {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},
  url = {http://iopscience.iop.org/article/10.1209/0295-5075/111/50005/meta},
  doi = {10.1209/0295-5075/111/50005}
}
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},
  url = {http://www.atmos-meas-tech-discuss.net/8/541/2015/amtd-8-541-2015.html},
  doi = {10.5194/amtd-8-541-2015}
}
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},
  url = {http://www.atmos-meas-tech.net/8/3219/2015/amt-8-3219-2015.html},
  doi = {10.5194/amt-8-3219-2015}
}
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},
  url = {http://www.tandfonline.com/doi/abs/10.1080/14685248.2014.948628},
  doi = {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},
  url = {http://scitation.aip.org/content/aip/journal/pof2/27/6/10.1063/1.4922241#},
  doi = {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},
  url = {http://iopscience.iop.org/1367-2630/17/6/063007/article},
  doi = {10.1088/1367-2630/17/6/063007}
}
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 $10^11lesssim Ralesssim 2times 10^14$ 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 $Ralt Ra_1^*simeq 2times 10^13$ 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 $zeta simeq 0.33$ by GL (Grossmann and Lohse 2004 Phys. Fluids 16 4462) for ReV. At $Ra=Ra_2^*simeq 7times 10^13$ the dependence of ReV on Ra changed, and for larger Ra $Re_Vsim Ra^0.50pm 0.02$, 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},
  url = {http://iopscience.iop.org/1367-2630/17/6/063028/},
  doi = {10.1088/1367-2630/17/6/063028}
}
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},
  url = {http://rsob.royalsocietypublishing.org/content/5/6/150038.abstract?ijkey=1VhwXRIwbtlK84d&keytype=ref},
  doi = {10.1098/rsob.150038}
}
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},
  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},
  doi = {10.1063/1.4921879}
}
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},
  url = {http://link.springer.com/article/10.1007/s00348-015-1980-0},
  doi = {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},
  url = {http://link.springer.com/article/10.1007/s00348-015-1975-x},
  doi = {10.1007/s00348-015-1975-x}
}
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},
  url = {http://arxiv.org/abs/1411.5826},
  doi = {10.1103/PhysRevLett.114.114302}
}
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},
  url = {http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0118443},
  doi = {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},
  url = {http://iopscience.iop.org/0004-637X/799/2/227},
  doi = {10.1088/0004-637X/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},
  url = {http://arxiv.org/abs/1410.7285}
}
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},
  url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-6-26&vt=f&tpn=0&bpn=searchResult},
  doi = {10.3762/bjnano.6.26}
}
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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.018103},
  doi = {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},
  url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-6-21&vt=f&tpn=0&bpn=searchResult},
  doi = {10.3762/bjnano.6.21}
}
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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.034501},
  doi = {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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9449002&fileId=S0022112014006521},
  doi = {10.1017/jfm.2014.652}
}
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},
  url = {http://www.cell.com/biophysj/abstract/S0006-3495(14)01105-9},
  doi = {10.1016/j.bpj.2014.10.027}
}
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},
  url = {http://www.beilstein-journals.org/bjnano/single/articleFullText.htm?publicId=2190-4286-5-257},
  doi = {10.3762/bjnano.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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9464672&fileId=S002211201400665X},
  doi = {10.1017/jfm.2014.665}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9377080&fileId=S0022112014005436},
  doi = {10.1017/jfm.2014.543}
}
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},
  url = {http://scitation.aip.org/content/aip/journal/pof2/26/11/10.1063/1.4900848},
  doi = {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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9395167&fileId=S0022112014006028},
  doi = {10.1017/jfm.2014.602}
}
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},
  url = {https://journals.aps.org/prx/abstract/10.1103/PhysRevX.4.041006},
  doi = {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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9338307&fileId=S002211201400456X},
  doi = {10.1017/jfm.2014.456}
}
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},
  url = {http://scitation.aip.org/content/aip/journal/rsi/85/9/10.1063/1.4896138},
  doi = {10.1063/1.4896138}
}
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},
  url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0106574},
  doi = {10.1371/journal.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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9302687&fulltextType=RA&fileId=S0022112014003255},
  doi = {10.1017/jfm.2014.325}
}
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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.113.054501},
  doi = {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},
  url = {http://iopscience.iop.org/1478-3975/11/4/046002/article?fromSearchPage=true},
  doi = {10.1088/1478-3975/11/4/046002}
}
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},
  url = {http://www.nonlin-processes-geophys.net/21/645/2014/npg-21-645-2014.html},
  doi = {10.5194/npg-21-645-2014}
}
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 $(z,r)$ 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 $Ra = 1.60^13$ and $1.10^15$ and for a Prandtl number $Pr simeq 0.8$ 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 $0.1$ $(z,r)$ 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 $f0$ less than or similar to $0.2$, had the form $P(f0) = P_0 (f0)^-1$ with $P_0 =0.208 pm 0.008$ a universal constant. Here $0 = 2R$ where $R$ is the radius of curvature of the temperature autocorrelation function $C($ at $tau = 0$. For $z/L simeq 0.5$ the measurements yielded $P(f0) sim (f0)^-alpha$ with $ 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},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.112.174501},
  doi = {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 &#8804; 1/Ro &#8804; 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},
  url = {http://scitation.aip.org/content/aip/journal/pof2/26/5/10.1063/1.4878669},
  doi = {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},
  url = {http://journals.aps.org/pre/abstract/10.1103/PhysRevE.89.052507},
  doi = {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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=9270846&fileId=S0022112014002596},
  doi = {10.1017/jfm.2014.259}
}
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},
  url = {http://www.pnas.org/content/111/21/7558.short},
  doi = {10.1073/pnas.1321682111}
}
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},
  url = {http://iopscience.iop.org/1367-2630/16/4/043030},
  doi = {10.1088/1367-2630/16/4/043030}
}
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},
  url = {http://iopscience.iop.org/1367-2630/16/3/033012},
  doi = {10.1088/1367-2630/16/3/033012}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v112/i5/e054101},
  doi = {10.1103/PhysRevLett.112.054101}
}
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},
  url = {http://link.springer.com/chapter/10.1007/978-3-642-40371-2_7},
  doi = {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},
  url = {http://arxiv.org/abs/1303.0650},
  doi = {10.1103/PhysRevLett.111.174501}
}
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},
  url = {http://iopscience.iop.org/1367-2630/15/8/083051/pdf/1367-2630_15_8_083051.pdf},
  doi = {10.1088/1367-2630/15/8/083051}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/grl.50759/abstract},
  doi = {10.1002/grl.50759}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v111/i2/e024501},
  doi = {10.1103/PhysRevLett.111.024501}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v110/i19/e199401},
  doi = {10.1103/PhysRevLett.110.199401}
}
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},
  url = {http://www.landesbioscience.com/journals/cib/article/23894/?show_full_text=true&#},
  doi = {10.1371/journal.pone.0054172}
}
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},
  url = {http://iopscience.iop.org/1367-2630/15/5/055015/},
  doi = {10.1088/1367-2630/15/5/055015}
}
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},
  url = {http://pof.aip.org/resource/1/phfle6/v25/i3/p035101_s1?isAuthorized=no},
  doi = {10.1063/1.4795547}
}
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},
  url = {http://www.pnas.org/content/110/10/3853.short},
  doi = {10.1073/pnas.1216629110}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8838091&fileId=S1633476058000223},
  doi = {10.1051/eas/1258022}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v110/i6/e064501},
  doi = {10.1103/PhysRevLett.110.064501}
}
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},
  url = {http://iopscience.iop.org/0957-0233/24/2/024006/},
  doi = {10.1088/0957-0233/24/2/024006}
}
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},
  url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0054172},
  doi = {10.1371/journal.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},
  url = {http://link.springer.com/article/10.1007%2Fs00348-012-1392-3},
  doi = {10.1007/s00348-012-1392-3}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/smll.201200853/abstract},
  doi = {10.1002/smll.201200853}
}
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},
  url = {http://iopscience.iop.org/1367-2630/14/11/115002/},
  doi = {10.1088/1367-2630/14/11/115002}
}
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},
  url = {http://arc.aiaa.org/doi/abs/10.2514/1.J051491},
  doi = {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},
  url = {http://iopscience.iop.org/1367-2630/14/10/103012/},
  doi = {10.1088/1367-2630/14/10/103012}
}
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},
  url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0046745},
  doi = {10.1371/journal.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},
  url = {http://iopscience.iop.org/0295-5075/100/1/16001/},
  doi = {10.1209/0295-5075/100/16001}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs00332-012-9126-5},
  doi = {10.1007/s00332-012-9126-5}
}
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},
  url = {http://iopscience.iop.org/1367-2630/14/10/105030/},
  doi = {10.1088/1367-2630/14/10/105030}
}
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},
  url = {http://iopscience.iop.org/1367-2630/14/10/105031/},
  doi = {10.1088/1367-2630/14/10/105031}
}
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},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.114501},
  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},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.109.108103},
  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},
  url = {http://arxiv.org/abs/1209.4335},
  doi = {10.1088/0031-8949/2013/T155/014055}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v109/i11/e118106},
  doi = {10.1103/PhysRevLett.109.118106}
}
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},
  url = {http://iopscience.iop.org/2041-8205/757/1/L18/},
  doi = {10.1088/2041-8205/757/1/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 à ? 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 à = 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},
  url = {http://iopscience.iop.org/1367-2630/14/9/095004?fromSearchPage=true},
  doi = {10.1088/1367-2630/14/9/095004}
}
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},
  url = {http://pre.aps.org/abstract/PRE/v86/i3/e036209},
  doi = {10.1103/PhysRevE.86.036209}
}
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.
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},
  url = {http://circres.ahajournals.org/content/111/4/402},
  doi = {10.1161/CIRCRESAHA.112.274530}
}
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},
  url = {http://pof.aip.org/resource/1/phfle6/v24/i5/p055102_s1},
  doi = {10.1063/1.4711397}
}
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},
  url = {http://pof.aip.org/resource/1/phfle6/v24/i6/p061702_s1},
  doi = {10.1063/1.4726077}
}
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},
  url = {http://iopscience.iop.org/1367-2630/14/6/063030/},
  doi = {10.1088/1367-2630/14/6/063030}
}
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},
  url = {http://www.worldscientific.com/doi/abs/10.1142/S0218127412501325},
  doi = {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},
  url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0037213},
  doi = {10.1371/journal.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 was observed to increase significantly with particle inertia for identical flow conditions. We show that this increase is related to a preferential alignment between these dynamical quantities. With increasing particle density the probability for those two vectors to be collinear was observed to grow. We show that these results are consistent with the preferential sampling of strain-dominated regions by inertial particles.
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8539092},
  doi = {10.1017/jfm.2012.72}
}
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},
  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},
  doi = {10.5772/34671}
}
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},
  url = {http://iopscience.iop.org/1367-2630/14/5/053010/pdf/1367-2630_14_5_053010.pdf},
  doi = {10.1088/1367-2630/14/5/053010}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0010482511000618},
  doi = {10.1016/j.compbiomed.2011.03.017}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8478322},
  doi = {10.1017/jfm.2011.529}
}
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},
  url = {http://pre.aps.org/abstract/PRE/v85/i1/e015301},
  doi = {10.1103/PhysRevE.85.015301}
}
Chang, K., "Explorations into the Inertial and Integral Scalse of Homogeneous Axisymmetric Turbulence", January 2012
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},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.108.024502},
  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},
  url = {http://www.sciencedirect.com/science/article/pii/S0167488911002151},
  doi = {10.1016/j.bbamcr.2011.07.016}
}
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},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.107.254101},
  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},
  url = {http://link.springer.com/article/10.1007%2Fs10509-011-0600-6},
  doi = {10.1007/s10509-011-0600-6}
}
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},
  url = {http://iopscience.iop.org/1367-2630/13/11/113020/},
  doi = {10.1088/1367-2630/13/11/113020}
}
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},
  url = {http://link.aps.org/doi/10.1103/PhysRevE.84.056405},
  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},
  url = {http://pre.aps.org/abstract/PRE/v84/i5/e056214},
  doi = {10.1103/PhysRevE.84.056214}
}
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},
  url = {http://rmp.aps.org/abstract/RMP/v83/i4/p1323_1},
  doi = {10.1103/RevModPhys.83.1323}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0171933511001038},
  doi = {10.1016/j.ejcb.2011.05.006}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs10955-011-0323-7},
  doi = {10.1007/s10955-011-0323-7}
}
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},
  url = {http://chaos.aip.org/resource/1/chaoeh/v21/i3/p033104_s1},
  doi = {10.1063/1.3613921}
}
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},
  url = {http://pubs.acs.org/doi/abs/10.1021/tx200115q},
  doi = {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},
  url = {http://www.nature.com/nphys/journal/v7/n9/full/nphys2010.html},
  doi = {10.1038/nphys2010}
}
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},
  url = {http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0024333},
  doi = {10.1371/journal.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.
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},
  url = {http://www.nature.com/nature/journal/v475/n7355/full/nature10216.html},
  doi = {10.1038/nature10216}
}
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},
  url = {http://iopscience.iop.org/1751-8121/44/28/285209/},
  doi = {10.1088/1751-8113/44/28/285209}
}
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$},
  journal = {13th European Turbulence Conference (etc13): Convection, Rotation, Stratification and Buoyancy Effects},
  month = {June},
  year = {2011},
  volume = {318},
  pages = {082001},
  url = {http://iopscience.iop.org/1742-6596/318/8/082001/},
  doi = {10.1088/1742-6596/318/8/082001}
}
Parlitz, U., Schlemmer, A. and Luther, S., "Synchronization patterns in transient spiral wave dynamics", Phys. Rev. E, May 2011, Vol. 83(5), 057201 pp.
Abstract: Transient dynamics of spiral waves in a two-dimensional Barkley model is shown to be governed by pattern formation processes resulting in regions of synchronized activity separated by moving interfaces. During the transient the number of internally synchronized regions decreases as synchronization fronts move to the boundary of the simulated area. This spatiotemporal transient dynamics in an excitable medium is detected and visualized by means of an analysis of the local periodicity and by evaluation of prediction errors across the spatial domain. During the (long) transient both analyses show patterns that must not be misinterpreted as any information about (spatial) structure of the underlying (completely homogeneous) system.
BibTeX:
@article{Parlitz.Schlemmer.ea2011,
  author = {Parlitz, U. and Schlemmer, A. and Luther, S.},
  title = {Synchronization patterns in transient spiral wave dynamics},
  journal = {Phys. Rev. E},
  month = {May},
  year = {2011},
  volume = {83},
  number = {5},
  pages = {057201},
  url = {http://pre.aps.org/abstract/PRE/v83/i5/e057201},
  doi = {10.1103/PhysRevE.83.057201}
}
Ahlers, G., Funfschilling, D. and Bodenschatz, E., "Transitions in heat transport by turbulent convection at Rayleigh numbers up to 10$^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},
  url = {http://iopscience.iop.org/1367-2630/13/4/049401/pdf/1367-2630_13_4_049401.pdf},
  doi = {10.1088/1367-2630/13/4/049401}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs00348-010-0948-3},
  doi = {10.1007/s00348-010-0948-3}
}
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},
  url = {http://iopscience.iop.org/1367-2630/13/4/043011/},
  doi = {10.1088/1367-2630/13/4/043011}
}
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},
  url = {http://iopscience.iop.org/1742-6596/333/1/011001?fromSearchPage=true},
  doi = {10.1088/1742-6596/333/1/011001}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/mame.201000339/abstract;jsessionid=E33D7B5F89A07C2D8918F4F64F80BD18.d02t02},
  doi = {10.1002/mame.201000339}
}
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},
  url = {http://iopscience.iop.org/article/10.1088/0169-5983/43/2/025505/meta},
  doi = {10.1088/0169-5983/43/2/025505}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/smll.201001955/abstract;jsessionid=47D3864DC27C6F80BC839166BB16120F.d01t04},
  doi = {10.1002/smll.201001955}
}
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},
  url = {http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2010.04957.x/abstract},
  doi = {10.1111/j.1365-294X.2010.04957.x}
}
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},
  url = {http://pra.aps.org/abstract/PRA/v83/i2/e023804},
  doi = {10.1103/PhysRevA.83.023804}
}
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},
  url = {http://circres.ahajournals.org/content/108/3/294},
  doi = {10.1161/CIRCRESAHA.110.228312}
}
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},
  url = {http://iopscience.iop.org/1367-2630/13/1/013036/},
  doi = {10.1088/1367-2630/13/1/013036}
}
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},
  url = {http://link.springer.com/chapter/10.1007%2F978-3-642-14139-3_33},
  doi = {10.1007/978-3-642-14139-3_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},
  url = {http://www.pnas.org/content/107/44/E165},
  doi = {10.1073/pnas.1011900107}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs10514-010-9199-7},
  doi = {10.1007/s10514-010-9199-7}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs10439-010-0071-x},
  doi = {10.1007/s10439-010-0071-x}
}
Nobach, H., "Reduktion des Fehlers durch Intensit?ts?nderung 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 Intensit?ts?nderung 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},
  url = {http://iopscience.iop.org/0295-5075/91/3/36003/},
  doi = {10.1209/0295-5075/91/36003}
}
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},
  url = {http://link.springer.com/article/10.1007/s00348-010-0948-3},
  doi = {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},
  url = {http://www.sciencedirect.com/science/article/pii/S0167278910000989},
  doi = {10.1016/j.physd.2010.03.004}
}
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},
  url = {http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2907310/},
  doi = {10.1186/1757-5036-3-12}
}
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},
  url = {http://iopscience.iop.org/0295-5075/90/6/64005/},
  doi = {10.1209/0295-5075/90/64005}
}
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},
  url = {http://rsta.royalsocietypublishing.org/content/368/1918/2221},
  doi = {10.1098/rsta.2010.0038}
}
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},
  url = {http://rsi.aip.org/resource/1/rsinak/v81/i5/p055112_s1},
  doi = {10.1063/1.3428738}
}
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},
  url = {http://iopscience.iop.org/0295-5075/90/2/28005/},
  doi = {10.1209/0295-5075/90/28005}
}
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},
  url = {http://link.springer.com/article/10.1186/1757-5036-3-9},
  doi = {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},
  url = {http://pre.aps.org/abstract/PRE/v81/i3/e036317},
  doi = {10.1103/PhysRevE.81.036317}
}
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},
  url = {http://www.sciencemag.org/content/327/5968/970},
  doi = {10.1126/science.1185138}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs00220-009-0916-z},
  doi = {10.1007/s00220-009-0916-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},
  url = {http://pre.aps.org/abstract/PRE/v81/i1/e010901},
  doi = {10.1103/PhysRevE.81.010901}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=6837836},
  doi = {10.1017/S0022112009991959}
}
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},
  url = {http://iopscience.iop.org/1367-2630/11/12/123001/},
  doi = {10.1088/1367-2630/11/12/123001}
}
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},
  url = {http://chaos.aip.org/resource/1/chaoeh/v19/i4/p041102_s1},
  doi = {10.1063/1.3176902}
}
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},
  url = {http://www.sciencedirect.com/science/article/pii/S0011227508001793},
  doi = {10.1016/j.cryogenics.2008.10.018}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs10909-009-9903-1},
  doi = {10.1007/s10909-009-9903-1}
}
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},
  url = {http://link.springer.com/chapter/10.1007/978-3-642-03085-7_42},
  doi = {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},
  url = {http://www.annualreviews.org/doi/abs/10.1146/annurev.fluid.010908.165210},
  doi = {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},
  url = {http://circ.ahajournals.org/content/120/6/467},
  doi = {10.1161/CIRCULATIONAHA.108.825091}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v103/i1/e014503},
  doi = {10.1103/PhysRevLett.103.014503}
}
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},
  url = {http://link.springer.com/article/10.1007%2Fs00348-009-0627-4},
  doi = {10.1007/s00348-009-0627-4}
}
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},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=5832344},
  doi = {10.1017/S0022112009006697}
}
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},
  url = {http://pubs.rsc.org/en/Content/ArticleLanding/2009/LC/b905521e},
  doi = {10.1039/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},
  url = {http://www.unesco.de/infothek/publikationen/publikationsverzeichnis/handbuch-open-access.html},
  doi = {10.2777/93994}
}
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},
  url = {http://iopscience.iop.org/1367-2630/10/12/123015/},
  doi = {10.1088/1367-2630/10/12/123015}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v101/i25/e254102},
  doi = {10.1103/PhysRevLett.101.254102}
}
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},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.101.214503},
  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},
  url = {http://iopscience.iop.org/1367-2630/10/10/103012/},
  doi = {10.1088/1367-2630/10/10/103012}
}
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},
  url = {http://prl.aps.org/abstract/PRL/v101/i14/e144501},
  doi = {10.1103/PhysRevLett.101.144501}
}
Zimmermann, R., "The Lagrangian Exploration Module, Generation of homogeneous and isotropic turbulence with little mean flow for Lagrangian experiments", October 2008
BibTeX:
@mastersthesis{Zimmermann2008,
  author = {Zimmermann, R.},
  title = {The Lagrangian Exploration Module, Generation of homogeneous and isotropic turbulence with little mean flow for Lagrangian experiments},
  month = {October},
  year = {2008},
  url = {http://www.lfpn.ds.mpg.de/turbulence/documents/Zimmermann_diploma_2008.pdf}
}
Enculescu, M., Gholami, A. and Falcke, M., "Dynamic regimes and bifurcations in a model of actin-based motility", Phys. Rev. E, September 2008, Vol. 78(3), 031915 pp.
Abstract: Propulsion by actin polymerization is widely used in cell motility. Here, we investigate a model of the brush range of an actin gel close to a propelled object, describing the force generation and the dynamics of the propagation velocity. We find transitions between stable steady states and relaxation oscillations when the attachment rate of actin filaments to the obstacle is varied. The oscillations set in at small values of the attachment rate via a homoclinic bifurcation. A second transition from a stable steady state to relaxation oscillations, found for higher values of the attachment rate, occurs via a supercritical Hopf bifurcation. The behavior of the model near the second transition is similar that of a system undergoing a canard explosion. Consequently, we observe excitable dynamics also. The model further exhibits bistability between stationary states or stationary states and limit cycles. Therefore, the brush of actin filament ends appears to have a much richer dynamics than was assumed until now.
BibTeX:
@article{Enculescu.Gholami.ea2008,
  author = {Enculescu, M. and Gholami, A. and Falcke, M.},
  title = {Dynamic regimes and bifurcations in a model of actin-based motility},
  journal = {Phys. Rev. E},
  month = {September},
  year = {2008},
  volume = {78},
  number = {3},
  pages = {031915},
  url = {http://pre.aps.org/abstract/PRE/v78/i3/e031915},
  doi = {10.1103/PhysRevE.78.031915}
}
Beta, C., Amselem, G. and Bodenschatz, E., "A bistable mechanism for directional sensing", New J. Phys., August 2008, Vol. 10, 083015 pp.
Abstract: We present a generic mechanism for directional sensing in eukaryotic cells that is based on bistable dynamics. As the key feature of this modeling approach, the velocity of trigger waves in the bistable sensing system changes its sign across cells that are exposed to an external chemoattractant gradient. This is achieved by combining a two-component activator/inhibitor system with a bistable switch that induces an identical symmetry breaking for arbitrary gradient input signals. A simple kinetic example is designed to illustrate the dynamics of a bistable directional sensing mechanism in numerical simulations.
BibTeX:
@article{Beta.Amselem.ea2008,
  author = {Beta, C. and Amselem, G. and Bodenschatz, E.},
  title = {A bistable mechanism for directional sensing},
  journal = {New J. Phys.},
  month = {August},
  year = {2008},
  volume = {10},
  pages = {083015},
  url = {http://iopscience.iop.org/1367-2630/10/8/083015/},
  doi = {10.1088/1367-2630/10/8/083015}
}
Xu, H. and Bodenschatz, E., "Motion of inertial particles with size larger than Kolmogorov scale in turbulent flows", Physica D, August 2008, Vol. 237(14-17), 2095 pp.
Abstract: We report experimental results on the motion of tracer and non-tracer particles in intense turbulent water flows between counter-rotating disks measured by three-dimensional Lagrangian particle tracking. The sizes of the non-tracer particles were in the range of eta
BibTeX:
@article{Xu.Bodenschatz2008,
  author = {Xu, H. and Bodenschatz, E.},
  title = {Motion of inertial particles with size larger than Kolmogorov scale in turbulent flows},
  journal = {Physica D},
  month = {August},
  year = {2008},
  volume = {237},
  number = {14-17},
  pages = {2095},
  url = {http://www.sciencedirect.com/science/article/pii/S0167278908001863},
  doi = {10.1016/j.physd.2008.04.022}
}
Arneodo, A., Benzi, R., Berg, J., Biferale, L., Bodenschatz, E., Busse, A., Calzavarini, E., Castaing, B., Cencini, M., Chevillard, L., Fisher, R. T., Grauer, R., Homann, H., Lamb, D., Lanotte, A. S., Leveque, E., Luethi, B., Mann, J., Mordant, N., Mueller, W.-C., Ott, S., Ouellette, N. T., Pinton, J.-F., Pope, S. B., Roux, S. G., Toschi, F., Xu, H. and Yeung, P. K., "Universal intermittent properties of particle trajectories in highly turbulent flows", Phys. Rev. Lett., June 2008, Vol. 100(25), 254504 pp.
Abstract: We present a collection of eight data sets from state-of-the-art experiments and numerical simulations on turbulent velocity statistics along particle trajectories obtained in different flows with Reynolds numbers in the range R-lambda is an element of [120740]. Lagrangian structure functions from all data sets are found to collapse onto each other on a wide range of time lags, pointing towards the existence of a universal behavior, within present statistical convergence, and calling for a unified theoretical description. Parisi-Frisch multifractal theory, suitably extended to the dissipative scales and to the Lagrangian domain, is found to capture the intermittency of velocity statistics over the whole three decades of temporal scales investigated here.
BibTeX:
@article{Arneodo.Benzi.ea2008,
  author = {Arneodo, A. and Benzi, R. and Berg, J. and Biferale, L. and Bodenschatz, E. and Busse, A. and Calzavarini, E. and Castaing, B. and Cencini, M. and Chevillard, L. and Fisher, R. T. and Grauer, R. and Homann, H. and Lamb, D. and Lanotte, A. S. and Leveque, E. and Luethi, B. and Mann, J. and Mordant, N. and Mueller, W.-C. and Ott, S. and Ouellette, N. T. and Pinton, J.-F. and Pope, S. B. and Roux, S. G. and Toschi, F. and Xu, H. and Yeung, P. K.},
  title = {Universal intermittent properties of particle trajectories in highly turbulent flows},
  journal = {Phys. Rev. Lett.},
  month = {June},
  year = {2008},
  volume = {100},
  number = {25},
  pages = {254504},
  url = {http://prl.aps.org/abstract/PRL/v100/i25/e254504},
  doi = {10.1103/PhysRevLett.100.254504}
}
Biferale, L., Bodenschatz, E., Cencini, M., Lanotte, A. S., Ouellette, N. T., Toschi, F. and Xu, H., "Lagrangian structure functions in turbulence: A quantitative comparison between experiment and direct numerical simulation", Phys. Fluids, June 2008, Vol. 20(6), 065103 pp.
Abstract: A detailed comparison between data from experimental measurements and numerical simulations of Lagrangian velocity structure functions in turbulence is presented. Experimental data, at Reynolds number ranging from R(lambda)=350 to R(lambda)=815, are obtained in a swirling water flow between counter-rotating baffled disks. Direct numerical simulations (DNS) data, up to R(lambda)=284, are obtained from a statistically homogeneous and isotropic turbulent flow. By integrating information from experiments and numerics, a quantitative understanding of the velocity scaling properties over a wide range of time scales and Reynolds numbers is achieved. To this purpose, we discuss in detail the importance of statistical errors, anisotropy effects, and finite volume and filter effects, finite trajectory lengths. The local scaling properties of the Lagrangian velocity increments in the two data sets are in good quantitative agreement for all time lags, showing a degree of intermittency that changes if measured close to the Kolmogorov time scales or at larger time lags. This systematic study resolves apparent disagreement between observed experimental and numerical scaling properties. (C) 2008 American Institute of Physics.
BibTeX:
@article{Biferale.Bodenschatz.ea2008,
  author = {Biferale, L. and Bodenschatz, E. and Cencini, M. and Lanotte, A. S. and Ouellette, N. T. and Toschi, F. and Xu, H.},
  title = {Lagrangian structure functions in turbulence: A quantitative comparison between experiment and direct numerical simulation},
  journal = {Phys. Fluids},
  month = {June},
  year = {2008},
  volume = {20},
  number = {6},
  pages = {065103},
  url = {http://pof.aip.org/resource/1/phfle6/v20/i6/p065103_s1},
  doi = {10.1063/1.2930672}
}
Xu, H., "Tracking Lagrangian trajectories in position-velocity space", Meas. Sci. Technol., June 2008, Vol. 19(7), 075105 pp.
Abstract: Lagrangian particle-tracking algorithms are susceptible to intermittent loss of particle images on the sensors. The measured trajectories are often interrupted into short segments and the long-time Lagrangian statistics are difficult to obtain. We present an algorithm to connect the segments of Lagrangian trajectories from common particle-tracking algorithms. Our algorithm tracks trajectory segments in the six-dimensional position and velocity space. We describe the approach to determine parameters in the algorithm and demonstrate the validity of the algorithm with data from numerical simulations and the improvement of long-time Lagrangian statistics on experimental data. The algorithm has important applications in measurements with high particle seeding density and in obtaining multi-particle Lagrangian statistics.
BibTeX:
@article{Xu2008,
  author = {Xu, H.},
  title = {Tracking Lagrangian trajectories in position-velocity space},
  journal = {Meas. Sci. Technol.},
  month = {June},
  year = {2008},
  volume = {19},
  number = {7},
  pages = {075105},
  url = {http://iopscience.iop.org/0957-0233/19/7/075105/},
  doi = {10.1088/0957-0233/19/7/075105}
}
Beta, C., Froehlich, T., Bödeker, H. U. and Bodenschatz, E., "Chemotaxis in microfluidic devices - a study of flow effects", Lab Chip, May 2008, Vol. 8(7), 1087 pp.
Abstract: The use of microfluidic devices has become increasingly popular in the study of chemotaxis due to the exceptional control of flow properties and concentration profiles on the length scale of individual cells. In these applications, it is often neglected that cells, attached to the inner surfaces of the microfluidic chamber, are three-dimensional objects that perturb and distort the flow field in their vicinity. Depending on the interplay of flow speed and geometry with the diffusive time scale of the chemoattractant in the flow, the concentration distribution across the cell membrane may differ strongly from the optimal gradient in a perfectly smooth channel. We analyze the underlying physics in a two-dimensional approximation and perform systematic numerical finite element simulations to characterize the three-dimensional case and to identify optimal flow conditions.
BibTeX:
@article{Beta.Froehlich.ea2008,
  author = {Beta, C. and Froehlich, T. and Bödeker, H. U. and Bodenschatz, E.},
  title = {Chemotaxis in microfluidic devices - a study of flow effects},
  journal = {Lab Chip},
  month = {May},
  year = {2008},
  volume = {8},
  number = {7},
  pages = {1087},
  url = {http://pubs.rsc.org/en/content/articlepdf/2008/lc/b801331d},
  doi = {10.1039/b801331d}
}
Bodenschatz, E., "A Rising Star", Physik Journal, May 2008, Vol. 7(5)
BibTeX:
@standard{Bodenschatz2008,
  author = {Bodenschatz, E.},
  title = {A Rising Star},
  journal = {Physik Journal},
  month = {May},
  year = {2008},
  volume = {7},
  number = {5},
  url = {http://www.dpg-physik.de/veroeffentlichung/njp/njp_10Jahre_Artikel_Bodenschatz.pdf}
}
Daniels, K. E., Brausch, O., Pesch, W. and Bodenschatz, E., "Competition and bistability of ordered undulations and undulation chaos in inclined layer convection", J. Fluid Mech., February 2008, Vol. 597, 261 pp.
Abstract: Experimental and theoretical investigations of undulation patterns in high-pressure inclined layer gas convection at a Prandtl number near unity are reported. Particular focus is given to the competition between the spatiotemporal chaotic state of undulation chaos and stationary patterns of ordered undulations. In experiments, a competition and bistability between the two states is observed, with ordered undulations most prevalent at higher Rayleigh number. The spectral pattern entropy, spatial correlation lengths and defect statistics are used to characterize the competing states. The experiments are complemented by a theoretical analysis of the Oberbeck-Boussinesq equations. The stability region of the ordered undulations as a function of their wave vectors and the Rayleigh number is obtained with Galerkin techniques. In addition, direct numerical simulations are used to investigate the spatiotemporal dynamics. In the simulations, both ordered undulations and undulation chaos were observed dependent on initial conditions. Experiment and theory are found to agree well.
BibTeX:
@article{Daniels.Brausch.ea2007,
  author = {Daniels, K. E. and Brausch, O. and Pesch, W. and Bodenschatz, E.},
  title = {Competition and bistability of ordered undulations and undulation chaos in inclined layer convection},
  journal = {J. Fluid Mech.},
  month = {February},
  year = {2008},
  volume = {597},
  pages = {261},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=1691952},
  doi = {10.1017/S0022112007009615}
}
Stich, M., Punckt, C., Beta, C. and Rotermund, H. H., "Control of spatiotemporal chaos in catalytic CO oxidation by laser-induced pacemakers", Phil. Trans. R. Soc. A, February 2008, Vol. 366(1864), 419 pp.
BibTeX:
@article{Stich.Punckt.ea2008,
  author = {Stich, M. and Punckt, C. and Beta, C. and Rotermund, H. H.},
  title = {Control of spatiotemporal chaos in catalytic CO oxidation by laser-induced pacemakers},
  journal = {Phil. Trans. R. Soc. A},
  month = {February},
  year = {2008},
  volume = {366},
  number = {1864},
  pages = {419},
  url = {http://rsta.royalsocietypublishing.org/content/366/1864/419.short},
  doi = {10.1098/rsta.2007.2099}
}
Bodenschatz, E. and Wolf, F., "Focus on Heart and Mind", New J. Phys., January 2008, Vol. 10, 015002 pp.
Abstract: Among the organs of our body, the function of heart and brain are unique in that their operation emerges from the collective dynamics of millions of strongly interacting cells well organized in their geometrical structure and connectivity. In the heart muscle the propagation of a nonlinear wave pulse, the cardiac action potential, controls the contraction. Usually the propagation is well-organized both in space and time and the heart functions as an efficient biological pump. Instabilities triggered by diseased tissue but also by dynamical heterogeneities, may, however, induce cardiac arrhythmia and fibrillation, where the pacemaker looses control to dynamically generated, high-frequency self-excitation of the muscle. In this state the coherence of contraction is lost and may lead within minutes to death.
The appearance of arrhythmias can be associated with topological singularities, the so called spiral or scroll waves, and how the occurrence of this malfunctioning pattern-formation process can be understood is a dominant subject of current research. This is all the more important as cardiac arrhythmias and fibrillation are the main cause of premature death in the developed world. Similarly, in the brain the propagation of a nonlinear wave pulse, namely the neural action potential, is at the basis of the computational and memory power of the brain, i.e. what determines the workings of our 'minds'. Here, however, due to the high degree of interconnectivity and topological complexity of the neuronal network, the coordinated activity of millions of interacting nerve cells is more complex, although the basic principles of action potential generation at the level of each cell are quite similar. The currently emerging field of network dynamical systems is largely driven by the mathematical challenge and the steady stream of novel dynamical phenomena that results from the interplay of local nonlinear dynamics and complex network structure in models of biological neuronal networks. The brain, however, would be only incompletely understood when just viewed as a complex dynamical system. Understanding the operation of the mind also requires describing and analyzing its emergent information processing functions. To achieve this, many aspects of neural computation have been successfully formulated as problems of statistical inference and optimal decision making, phrasing them in the mathematical language of statistical physics. Both subjects, heart and mind, are thus united through the similarity of current models for the emergence of collective capabilities. They rely conceptually and technically essentially on the paradigms and tools of statistical physics and nonlinear dynamics. In general, none of the functions and processes of the heart or mind can be appropriately understood without a thorough analysis of the collective dynamics of the underlying biological networks and nonlinear media. Approaching any of these problems with necessity requires a coordinated interdisciplinary effort utilizing approaches from nonlinear dynamics and pattern formation to genetics, molecular biology and biological imaging. Because of their thorough understanding and advanced methodology for dissecting nonlinear and collective phenomena, physicists are playing an increasingly important role in unravelling the dynamical principles governing the operation as well as the malfunction of heart and mind.
Current research in the physics of heart and mind spans a wide spectrum of theoretical, experimental, and computational approaches. Many are guided by the aim for a transparent picture of systems function that links the biophysics of individual cells to the operation of the entire organ or information processing system. Theoretical work thus often centres on the construction and analysis of models that contain sufficient biophysical detail to represent reliably all cellular mechanisms of importance, but that are still theoretically sufficiently transparent and tractable to support a comprehensive analysis of functional performance at the systems level. Analogously, experimental work increasingly probes the system dynamics simultaneously at multiple levels from cell to whole organ. Here an invaluable contribution of physics to the experimental characterization of large scale activity in cardiac and neuronal tissues is the currently emerging high level of quantitative precision and control. Long-term high precision recording of large scale activity patterns of neural and cardiac tissues increasingly supports the formulation of quantitative phenomenological theories of complex dynamical states as well the realization of algorithms for manipulating and controlling them. Both quantitative phenomenology and control are not only essential for bridging theory and experiment in complex systems; they are also indispensable for turning scientific insight into diagnostic progress and improved treatment for the affected heart and mind.
The present Focus Issue in New Journal of Physics reflects well the richness and excitement of this currently rapidly evolving field. It combines theoretical and experimental approaches and covers analyses ranging from the organ level over investigations of model systems to the biophysics of individual cells. The articles below represent the first contributions to this collection and further additions will appear in the near future.
BibTeX:
@article{Bodenschatz.Wolf2008,
  author = {Bodenschatz, E. and Wolf, F.},
  title = {Focus on Heart and Mind},
  journal = {New J. Phys.},
  month = {January},
  year = {2008},
  volume = {10},
  pages = {015002},
  url = {http://iopscience.iop.org/1367-2630/10/1/015002?fromSearchPage=true},
  doi = {10.1088/1367-2630/10/1/015002}
}
Xu, H., Ouellette, N. T. and Bodenschatz, E., "Evolution of geometric structures in intense turbulence", New J. Phys., January 2008, Vol. 10, 013012 pp.
Abstract: We report measurements of the evolution of lines, planes and volumes in an intensely turbulent laboratory flow using high-speed particle tracking. We find that the classical characteristic timescale of an eddy at the initial scale of the object considered is the natural timescale for the subsequent evolution. The initial separation may only be neglected if this timescale is much smaller than the largest turbulence timescale, implying extremely high turbulence levels.
BibTeX:
@article{Xu.Ouellette.ea2008,
  author = {Xu, H. and Ouellette, N. T. and Bodenschatz, E.},
  title = {Evolution of geometric structures in intense turbulence},
  journal = {New J. Phys.},
  month = {January},
  year = {2008},
  volume = {10},
  pages = {013012},
  url = {http://iopscience.iop.org/1367-2630/10/1/013012/},
  doi = {10.1088/1367-2630/10/1/013012}
}
Chang, K., Ouellette, N. T., Xu, H. and Bodenschatz, E., "Lagrangian particle tracking in high Reynolds number turbulence", Particle-Laden Flow: From Geophysical to Kolmogorov Scales, 2007, Vol. 11, European Mech Soc; Univ Technol Delft pp.
Abstract: We describe a Lagrangian particle tracking technique that can be applied to high Reynolds number turbulent flows. This technique produces three-dimensional Lagrangian trajectories of multiple particles, from which both Lagrangian and Eulerian statistics can be obtained. We illustrate the application of this technique with measurements performed in a von Karman swirling flow generated in a vertical cylindrical tank between two counter-rotating baffled disks. The Taylor microscale Reynolds number investigated runs from 200 to 815. The Kolmogorov time scale of the flow was resolved and both the turbulent velocity and acceleration were obtained and their probability density functions measured. Measurements of the Eulerian and Lagrangian velocity structure functions are presented. The average energy dissipation rates are determined from the Eulerian velocity structure functions.
BibTeX:
@inproceedings{Chang.Ouellette.ea2007,
  author = {Chang, K. and Ouellette, N. T. and Xu, H. and Bodenschatz, E.},
  title = {Lagrangian particle tracking in high Reynolds number turbulence},
  journal = {Particle-Laden Flow: From Geophysical to Kolmogorov Scales},
  year = {2007},
  volume = {11},
  pages = {European Mech Soc; Univ Technol Delft},
  url = {http://link.springer.com/chapter/10.1007%2F978-1-4020-6218-6_24?LI=true#page-1},
  doi = {10.1007/978-1-4020-6218-6_24}
}
Nobach, H., Tropea, C., Cordier, L., Bonnet, J.-P., Delville, J., Lewalle, J., Farge, M., Schneider, K. and Adrian, R., "Handbook of Experimental Fluid Dynamics", 2007, 1337 pp.
Abstract: This chapter is devoted to reviewing some fundamental transforms and analysis procedures commonly used for both signal and data processing in fluid mechanics measurements. The chapter begins with a brief review of the Fourier transform and its digital counterpart the discrete Fourier transform. In particular its use for estimating power spectral density is discussed in detail. This is followed by an introduction of the correlation function and its relation to the Fourier transform. The Hilbert transform completes the introductory topics. The chapter then turns to a rigorous presentation of the proper orthogonal decomposition (POD) in the context of the approximation theory and as an application of singular value decomposition (SVD). The relationship between POD and SVD is discussed and POD is described in a statistical setting using an averaging operation for use with turbulent flows. The different POD approaches are briefly introduced, whereby the main differences between the classical POD and the snapshot POD are highlighted. This section closes with a presentation of the POD as a generalization of the classical Fourier analysis to inhomogeneous directions. The chapter continues with a discussion of conditional averages and stochastic estimation as a means of studying coherent structures in turbulent flows before moving in a final section to a comprehensive discussion of wavelets as a combination of data processing in time and frequency domain. After first introducing the continuous wavelet transform and orthogonal wavelet transform their application in experimental fluid mechanics is illustrated through numerous examples.
BibTeX:
@inbook{Nobach.Tropea.ea2007,
  author = {H Nobach and C Tropea and L Cordier and J-P Bonnet and J Delville and J Lewalle and M Farge and K Schneider and R Adrian},
  title = {Handbook of Experimental Fluid Dynamics},
  year = {2007},
  pages = {1337},
  url = {http://link.springer.com/referenceworkentry/10.1007%2F978-3-540-30299-5_22},
  doi = {10.1007/978-3-540-30299-5_22}
}
Nobach, H. and Tropea, C., "Handbook of Experimental Fluid Dynamics", 2007, 1399 pp.
Abstract: In this chapter the fundamentals of statistical parameter estimation are reviewed for applications typical in experimental fluid mechanics. The chapter begins with a review of the probability density function and its moments and continues with common estimators for the mean and variance of stationary random processes. A brief introduction to signal noise is given as a prelude to a rigorous discussion of the Cramér-Rao Lower Bound (CRLB). The CRLB represents the lower bound of variance of unbiased estimators of a parameter. This concept is deepened using illustrations from the laser Doppler, phase Doppler and PIV measurement techniques. The chapter closes with a short discussion about the propagation of errors in a measurement chain.
BibTeX:
@inbook{Nobach.Tropea2007,
  author = {H Nobach and C Tropea},
  title = {Handbook of Experimental Fluid Dynamics},
  year = {2007},
  pages = {1399},
  url = {http://link.springer.com/referenceworkentry/10.1007/978-3-540-30299-5_23},
  doi = {10.1007/978-3-540-30299-5_23}
}
Vincenzi, D., Jin, S., Vaithianathan, T., Collins, L. R. and Bodenschatz, E., "Statistical closures for homogeneous shear flow turbulence of dilute polymer solutions", Progress in Turbulence II, 2007, Vol. 109, 261 pp.
BibTeX:
@inproceedings{Vincenzi.Jin.ea2007b,
  author = {Vincenzi, D. and Jin, S. and Vaithianathan, T. and Collins, L. R. and Bodenschatz, E.},
  title = {Statistical closures for homogeneous shear flow turbulence of dilute polymer solutions},
  journal = {Progress in Turbulence II},
  year = {2007},
  volume = {109},
  pages = {261},
  url = {http://link.springer.com/chapter/10.1007%2F978-3-540-32603-8_53?LI=true},
  doi = {10.1007/978-3-540-32603-8_53}
}
Xu, H., Ouellette, N. T., Nobach, H. and Bodenschatz, E., "Experimental measurements of Lagrangian statistics in intense turbulence", Advances In Turbulence, 2007, Vol. 117, 1 pp.
Abstract: We report Lagrangian laboratory measurements of fluid turbulence at high Reynolds numbers. First, the experimental techniques that have made Lagrangian measurements possible, including both optical and acoustic particle tracking, are reviewed. Then some of the laboratory flows used in Lagrangian measurements are described and a selection of new experimental results are presented.
BibTeX:
@proceedings{Xu.Ouellette.ea2007,
  author = {Xu, H. and Ouellette, N. T. and Nobach, H. and Bodenschatz, E.},
  title = {Experimental measurements of Lagrangian statistics in intense turbulence},
  journal = {Advances In Turbulence},
  year = {2007},
  volume = {117},
  pages = {1},
  url = {http://link.springer.com/book/10.1007/978-3-540-72604-3/page/1},
  doi = {10.1007/978-3-540-72604-3_1}
}
Xu, H., Ouellette, N. T. and Bodenschatz, E., "Multi-particle statistics - lines, shapes, and volumes in high Reynolds number turbulence", Proceedings of the 5th International Conference On Nonlinear Mechanics, 2007
Abstract: We present experimental measurements of multi-particle Lagrangian statistics in high Reynolds number turbulence. We find that initial separations play an important role in the evolution of particle separation and the area or volume enclosed by multiple fluid particles. A time scale associated with the initial separation appears to be a natural time scale for characterizing the evolution. The existence of any universal scaling law for the evolution of particle clusters is possible only if this time scale is much smaller than the turbulence integral scale, the largest time scale of a turbulent flow, requiring very intense flows with large Reynolds numbers.
BibTeX:
@proceedings{Xu.Ouellette.ea2007g,
  author = {Xu, H. and Ouellette, N. T. and Bodenschatz, E.},
  title = {Multi-particle statistics - lines, shapes, and volumes in high Reynolds number turbulence},
  journal = {Proceedings of the 5th International Conference On Nonlinear Mechanics},
  year = {2007}
}
Pumir, A., Nikolski, V., Hoerning, M., Isomura, A., Agladze, K., Yoshikawa, K., Gilmour, R., Bodenschatz, E. and Krinsky, V., "Wave emission from heterogeneities opens a way to controlling chaos in the heart", Phys. Rev. Lett., November 2007, Vol. 99(20), 208101 pp.
Abstract: The effectiveness of chaos control in large systems increases with the number of control sites. We find that electric field induced wave emission from heterogeneities (WEH) in the heart gives a unique opportunity to have as many control sites as needed. The number of pacing sites grows with the amplitude of the electric field. We demonstrate that WEH has important advantages over methods used in clinics, and opens a new way to manipulate vortices in experiments, and potentially to radically improve the clinical methods of chaos control in the heart.
BibTeX:
@article{Pumir.Nikolski.ea2007,
  author = {Pumir, A. and Nikolski, V. and Hoerning, M. and Isomura, A. and Agladze, K. and Yoshikawa, K. and Gilmour, R. and Bodenschatz, E. and Krinsky, V.},
  title = {Wave emission from heterogeneities opens a way to controlling chaos in the heart},
  journal = {Phys. Rev. Lett.},
  month = {November},
  year = {2007},
  volume = {99},
  number = {20},
  pages = {208101},
  url = {http://prl.aps.org/abstract/PRL/v99/i20/e208101},
  doi = {10.1103/PhysRevLett.99.208101}
}
Xu, H., Ouellette, N. T., Vincenzi, D. and Bodenschatz, E., "Acceleration correlations and pressure structure functions in high-Reynolds number turbulence", Phys. Rev. Lett., November 2007, Vol. 99(20), 204501 pp.
Abstract: We present measurements of fluid particle accelerations in turbulent water flow between counterrotating disks using three-dimensional Lagrangian particle tracking. By simultaneously following multiple particles with sub-Kolmogorov-time-scale temporal resolution, we measured the spatial correlation of fluid particle acceleration at Taylor microscale Reynolds numbers between 200 and 690. We also obtained indirect, nonintrusive measurements of the Eulerian pressure structure functions by integrating the acceleration correlations. Our measurements are in good agreement with the theoretical predictions of the acceleration correlations and the pressure structure function in isotropic high-Reynolds number turbulence by Obukhov and Yaglom in 1951 [Prikl. Mat. Mekh. 15, 3 (1951)]. The measured pressure structure functions display K41 scaling in the inertial range.
BibTeX:
@article{Xu.Ouellette.ea2007b,
  author = {Xu, H. and Ouellette, N. T. and Vincenzi, D. and Bodenschatz, E.},
  title = {Acceleration correlations and pressure structure functions in high-Reynolds number turbulence},
  journal = {Phys. Rev. Lett.},
  month = {November},
  year = {2007},
  volume = {99},
  number = {20},
  pages = {204501},
  url = {http://prl.aps.org/abstract/PRL/v99/i20/e204501},
  doi = {10.1103/PhysRevLett.99.204501}
}
Nobach, H. and Bodenschatz, E., "Grenzen von PIV durch individuelle Intensit?tsänderung von Streuteilchen", September 2007
Abstract: Durch die Anwendung von adäquaten Interpolationsalgorithmen ist die PIV-Bildauswertung deutlich genauer als die nominelle Pixelauflösung der verwendeten Kameras. Während in Simulationen Genauigkeiten von besser als 0.01 Pixel gefunden werden, bleiben die Ergebnisse mit experimentellen Bildern normaler Weise deutlich dahinter zur?ck, wo die erreichbare Genauigkeit bei etwa 0.1 Pixel liegt. Eine Ursache f?r die Begrenzung der Genauigkeit könnte in der individuellen Änderung der Intensität der Streuteilchen zwischen den Aufnahmen liegen. Diese Schwankungen treten in realen PIV-Messungen üblicher Weise auf, während sie in Computersimulationen oft nicht berücksichtigt werden. Es wird gezeigt, wie die individuellen Intensitätsänderungen der Streuteilchen entstehen und wie dadurch die erreichbare Genauigkeit bei der Auswertung von PIV-Aufnahmen begrenzt wird. Dabei werden sowohl Einschrittverfahren als auch iterative Verfahren mit Fensterverschiebung und -deformation untersucht.
BibTeX:
@proceedings{Nobach.Bodenschatz2007,
  author = {Nobach, H. and Bodenschatz, E.},
  title = {Grenzen von PIV durch individuelle Intensit?tsänderung von Streuteilchen},
  month = {September},
  year = {2007},
  url = {http://www.gala-ev.org/images/Beitraege/Beitraege%202007/pdf/11.pdf}
}
Shirai, K., Bayer, C., Nobach, H., Klaucke, C., Voigt, A., B?ttner, L. and Czarske, J., "Application of laser Doppler Velocity Profile Sensor to Turbulent Flows: Measurement of Water Channel Flow and Two-Point Correlation", September 2007
BibTeX:
@conference{Shirai.Bayer.ea2007,
  author = {Shirai, K. and Bayer, C. and Nobach, H. and Klaucke, C. and Voigt, A. and B?ttner, L. and Czarske, J.},
  title = {Application of laser Doppler Velocity Profile Sensor to Turbulent Flows: Measurement of Water Channel Flow and Two-Point Correlation},
  month = {September},
  year = {2007}
}
Beta, C., Wyatt, D., Rappel, W. and Bodenschatz, E., "Flow photolysis for spatiotemporal stimulation of single cells", Anal. Chem., May 2007, Vol. 79(10), 3940 pp.
Abstract: d Quantitative studies of cellular systems require experimental techniques that can expose single cells to well-controlled chemical stimuli with high spatiotemporal resolution. Here, we combine microfluidic techniques with the photochemical release of caged signaling molecules to generate tailored stimuli on the length scale of individual cells with subsecond switching times. We exemplify this flexible approach by initiating membrane translocation of fluorescent fusion proteins in chemotactic Dictyostelium discoideum cells.
BibTeX:
@article{Beta.Wyatt.ea2007,
  author = {Beta, C. and Wyatt, D. and Rappel, W.J. and Bodenschatz, E.},
  title = {Flow photolysis for spatiotemporal stimulation of single cells},
  journal = {Anal. Chem.},
  month = {May},
  year = {2007},
  volume = {79},
  number = {10},
  pages = {3940},
  url = {http://pubs.acs.org/doi/abs/10.1021/ac070033y},
  doi = {10.1021/ac070033y}
}
Bodega, P. S., Kaira, P., Beta, C., Krefting, D., Bauer, D., Mirwald-Schulz, B., Punckt, C. and Rotermund, H. H., "High frequency periodic forcing of the oscillatory catalytic CO oxidation on Pt (110)", New J. Phys., March 2007, Vol. 9
Abstract: Resonant periodic forcing is applied to catalytic CO oxidation on platinum (110) in the oscillatory regime. The external parameters are chosen such that the unperturbed system spontaneously develops chemical turbulence. By periodically modulating the CO partial pressure, changes in the spatiotemporal behaviour of the system can be induced: the turbulent behaviour is suppressed and frequency locked patterns with sub-harmonic entrainment develop. A novel gas-driving compressor has been implemented to perform the experimental work.
BibTeX:
@article{Bodega.Kaira.ea2007,
  author = {Bodega, P. S. and Kaira, P. and Beta, C. and Krefting, D. and Bauer, D. and Mirwald-Schulz, B. and Punckt, C. and Rotermund, H. H.},
  title = {High frequency periodic forcing of the oscillatory catalytic CO oxidation on Pt (110)},
  journal = {New J. Phys.},
  month = {March},
  year = {2007},
  volume = {9},
  url = {http://iopscience.iop.org/1367-2630/9/3/061/},
  doi = {10.1088/1367-2630/9/3/061}
}
Xu, H., Ouellette, N. T. and Bodenschatz, E., "Curvature of Lagrangian trajectories in turbulence", Phys. Rev. Lett., February 2007, Vol. 98(5), 050201 pp.
Abstract: We report measurements of the curvature of Lagrangian trajectories in an intensely turbulent laboratory water flow measured with a high-speed particle-tracking system. The probability density function (PDF) of the instantaneous curvature is shown to have robust power-law tails. We propose a model for the instantaneous curvature PDF, assuming that the acceleration and velocity are uncorrelated Gaussian random variables, and show that our model reproduces the tails of our measured PDFs. We also predict the scaling of the most probable vorticity magnitude in turbulence, assuming Heisenberg-Yaglom scaling. Finally, we average the curvature along trajectories and show that, by removing the effects of large-scale flow reversals, the filtered curvature reveals the turbulent features.
BibTeX:
@article{Xu.Ouellette.ea2007e,
  author = {Xu, H. and Ouellette, N. T. and Bodenschatz, E.},
  title = {Curvature of Lagrangian trajectories in turbulence},
  journal = {Phys. Rev. Lett.},
  month = {February},
  year = {2007},
  volume = {98},
  number = {5},
  pages = {050201},
  url = {http://prl.aps.org/abstract/PRL/v98/i5/e050201},
  doi = {10.1103/PhysRevLett.98.050201}
}
Vincenzi, D., Jin, S., Bodenschatz, E. and Collins, L. R., "Stretching of polymers in isotropic turbulence: A statistical closure", Phys. Rev. Lett., January 2007, Vol. 98(2), 024503 pp.
Abstract: We present a new closure for the mean rate of stretching of a dissolved polymer by homogeneous isotropic turbulence. The polymer is modeled by a bead-spring-type model (e.g., Oldroyd B, FENE-P, Giesekus) and the analytical closure is obtained assuming the Lagrangian velocity gradient can be modeled as a Gaussian, white-noise stochastic process. The resulting closure for the mean stretching depends upon the ratio of the correlation time for strain and rotation. Additionally, we derived a second-order expression for circumstances when strain and rotation have a finite correlation time. Finally, the base level closure is shown to reproduce results from direct numerical simulations by simply modifying the coefficients.
BibTeX:
@article{Vincenzi.Jin.ea2007,
  author = {Vincenzi, D. and Jin, S. and Bodenschatz, E. and Collins, L. R.},
  title = {Stretching of polymers in isotropic turbulence: A statistical closure},
  journal = {Phys. Rev. Lett.},
  month = {January},
  year = {2007},
  volume = {98},
  number = {2},
  pages = {024503},
  url = {http://prl.aps.org/abstract/PRL/v98/i2/e024503},
  doi = {10.1103/PhysRevLett.98.024503}
}
Bodenschatz, E. and Pöschl, U., "Qualitätssicherung bei Open Access", 2006
BibTeX:
@openaccess{Bodenschatz.Poschl2006,
  author = {Bodenschatz, E. and Pöschl, U.},
  title = {Qualitätssicherung bei Open Access},
  year = {2006},
  url = {http://www.lfpn.ds.mpg.de/Docs/Qualitaetssicherung-bei-Open-Access-de.pdf}
}
Celani, A., Mazzino, A. and Vincenzi, D., "Magnetic field transport and kinematic dynamo effect: a Lagrangian interpretation", Proc. R. Soc. A, November 2006, Vol. 462(2065), 137 pp.
Abstract: The growth of magnetic fluctuations in the inertial range of turbulence is investigated in terms of fluid particle dynamics. The existence of dynamo effect is related to the time behaviour of the correlations between tangent vectors evolving along Lagrangian trajectories. In the presence of dynamo effect, the correlations between tangent vectors grow exponentially in time; in the absence of dynamo effect they decay as power laws. The above behaviours are intimately related to statistical conservation laws for the Lagrangian dynamics.
BibTeX:
@article{Celani.Mazzino.ea2006,
  author = {Celani, A. and Mazzino, A. and Vincenzi, D.},
  title = {Magnetic field transport and kinematic dynamo effect: a Lagrangian interpretation},
  journal = {Proc. R. Soc. A},
  month = {November},
  year = {2006},
  volume = {462},
  number = {2065},
  pages = {137},
  url = {http://rspa.royalsocietypublishing.org/content/462/2065/137.short},
  doi = {10.1098/rspa.2005.1561}
}
Ayyalasomayajula, S., Gylfason, A., Collins, L. R., Bodenschatz, E. and Warhaft, Z., "Lagrangian measurements of inertial particle accelerations in grid generated wind tunnel turbulence", Phys. Rev. Lett., October 2006, Vol. 97(14), 144507 pp.
Abstract: We describe Lagrangian measurements of water droplets in grid generated wind tunnel turbulence at a Taylor Reynolds number of R-lambda=250 and an average Stokes number (< St >) of approximately 0.1. The inertial particles are tracked by a high speed camera moving along the side of the tunnel at the mean flow speed. The standardized acceleration probability density functions of the particles have spread exponential tails that are narrower than those of a fluid particles (St approximate to 0) and there is a decrease in the acceleration variance with increasing Stokes number. A simple vortex model shows that the inertial particles selectively sample the fluid field and are less likely to experience regions of the fluid undergoing the largest accelerations. Recent direct numerical simulations compare favorably with these first measurements of Lagrangian statistics of inertial particles in highly turbulent flows.
BibTeX:
@article{Ayyalasomayajula.Gylfason.ea2006,
  author = {Ayyalasomayajula, S. and Gylfason, A. and Collins, L. R. and Bodenschatz, E. and Warhaft, Z.},
  title = {Lagrangian measurements of inertial particle accelerations in grid generated wind tunnel turbulence},
  journal = {Phys. Rev. Lett.},
  month = {October},
  year = {2006},
  volume = {97},
  number = {14},
  pages = {144507},
  url = {http://prl.aps.org/abstract/PRL/v97/i14/e144507},
  doi = {10.1103/PhysRevLett.97.144507}
}
Beta, C., Mikhailov, A. S., Rotermund, H. H. and Ertl, G., "Defect-mediated turbulence in a catalytic surface reaction", EPL, September 2006, Vol. 75(6), 868 pp.
Abstract: We analyze the statistical properties of topological defects in an experimental reaction-diffusion system—the catalytic CO oxidation on Pt(110). Based on the gain and loss rates of defects, a probabilistic description of defect-mediated turbulence in this system is derived. We observe deviations from theoretical predictions for the statistics of topological defects that can be explained by the presence of short-range correlations between defects and underline the importance of correlations for defect dynamics in such systems.
BibTeX:
@article{Beta.Mikhailov.ea2006,
  author = {Beta,C. and Mikhailov,A. S. and Rotermund, H. H. and Ertl, G.},
  title = {Defect-mediated turbulence in a catalytic surface reaction},
  journal = {EPL},
  month = {September},
  year = {2006},
  volume = {75},
  number = {6},
  pages = {868},
  url = {http://iopscience.iop.org/0295-5075/75/6/868/},
  doi = {10.1209/epl/i2006-10215-5}
}
Celani, A., Puliafito, A. and Vincenzi, D., "Dynamical Slowdown of Polymers in Laminar and Random Flows", Phys. Rev. Lett., September 2006, Vol. 97(11-15), 118301 pp.
Abstract: The influence of an external flow on the relaxation dynamics of a single polymer is investigated theoretically and numerically. We show that a pronounced dynamical slowdown occurs in the vicinity of the coil-stretch transition, especially when the dependence on polymer conformation of the drag is accounted for. For the elongational flow, relaxation times are exceedingly larger than the Zimm relaxation time, resulting in the observation of conformation hysteresis. For random smooth flows, hysteresis is not present. Yet, relaxation dynamics is significantly slowed down because of the large variety of accessible polymer configurations. The implications of these results for the modeling of dilute polymer solutions in turbulent flows are addressed.
BibTeX:
@article{Celani.Puliafito.ea2006,
  author = {Celani, A. and Puliafito, A. and Vincenzi, D.},
  title = {Dynamical Slowdown of Polymers in Laminar and Random Flows},
  journal = {Phys. Rev. Lett.},
  month = {September},
  year = {2006},
  volume = {97},
  number = {11-15},
  pages = {118301},
  url = {http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.97.118301},
  doi = {10.1103/PhysRevLett.97.118301}
}
Kinzel, M., Nobach, H., Tropea, C. and Bodenschatz, E., "MESSUNG LAGRANGE’SCHER BESCHLEUNIGUNGEN MITTELS LASER-DOPPLER-ANEMOMETRIE", September 2006
Abstract: Dieser Beitrag behandelt die M?glichkeit, mit der Laser-Doppler-Technik, zus?tzlich zu der Geschwindigkeiten auch die Lagrange’sche Beschleunigung von Streuteilchen zu messen. Zun?chst wird auf den optischen Aufbau und die Signalverarbeitung eingegangen. Danach wird ein Verfahren zur ?berpr?fung der Genauigkeit des optischen Aufbaus vorgestellt. Zum Schluss werden die durchgef?hrten Validierungsmessungen erl?utert und ihre Ergebnisse diskutiert.
BibTeX:
@proceedings{Kinzel.Nobach.ea2006,
  author = {Kinzel, M. and Nobach, H. and Tropea, C. and Bodenschatz, E.},
  title = {MESSUNG LAGRANGE’SCHER BESCHLEUNIGUNGEN MITTELS LASER-DOPPLER-ANEMOMETRIE},
  month = {September},
  year = {2006},
  url = {http://www.gala-ev.org/images/Beitraege/Beitraege%202006/pdf/1.pdf}
}
Nobach, H. and Bodenschatz, E., "Neue Aufl?sungsgrenzen von PIV", September 2006
Abstract: Die Particle Image Velocimetry (PIV) erlaubt prinzipiell eine fl?chige Bestimmung eines momentanen Geschwindigkeitsfeldes mit einer bestimmten r?umlichen Aufl?sung. Weiterentwicklungen der Auswertungsprozeduren betreffen haupts?chlich die Verbesserung hinsichtlich der erreichbaren Genauigkeit und der r?umlichen Aufl?sung. In diesem Beitrag werden M?glichkeiten und Grenzen der r?umlichen Aufl?sung diskutiert.
BibTeX:
@proceedings{Nobach.Bodenschatz2006,
  author = {Nobach, H. and Bodenschatz, E.},
  title = {Neue Aufl?sungsgrenzen von PIV},
  month = {September},
  year = {2006},
  url = {http://www.gala-ev.org/images/Beitraege/Beitraege%202006/pdf/4.pdf}
}
Song, L., Nadkarni, S. M., Bödeker, H. U., Beta, C., Bae, A., Franck, C., Rappel, W., Loomis, W. F. and Bodenschatz, E., "Dicyostelium discoideum chemotaxis: Threshold for directed motion", Eur. J. Cell Biol., September 2006, Vol. 85(9-10), 981 pp.
Abstract: The chemotactic response of Dictyostelium discoideum cells to stationary, linear gradients of cyclic adenosine 3',5'-monophosphate (cAMP) was studied using microfluidic devices. In shallow gradients of less than 10(-3) nM/mu m, the cells showed no directional response and exhibited a constant basal motility. In steeper gradients, cells moved up the gradient on average. The chemotactic speed and the motility increased with increasing steepness up to a plateau at around 10(-1) nM/mu m. In very steep gradients, above 10 nM/mu m, the cells lost directionality and the motility returned to the sub-threshold level. In the regime of optimal response the difference in receptor occupancy at the front and back of the cell is estimated to be only about 100 molecules. (c) 2006 Elsevier GmbH. All rights reserved.
BibTeX:
@article{Song.Nadkarni.ea2006,
  author = {Song, L. and Nadkarni, S. M. and Bödeker, H. U. and Beta, C. and Bae, A. and Franck, C. and Rappel, W. and Loomis, W. F. and Bodenschatz, E.},
  title = {Dicyostelium discoideum chemotaxis: Threshold for directed motion},
  journal = {Eur. J. Cell Biol.},
  month = {September},
  year = {2006},
  volume = {85},
  number = {9-10},
  pages = {981},
  url = {http://www.sciencedirect.com/science/article/pii/S0171933506000264},
  doi = {10.1016/j.ejcb.2006.01.012}
}
Vincenzi, D. and Bodenschatz, E., "Single polymer dynamics in elongational flow and the confluent Heun equation", J. Phys. A, August 2006, Vol. 39(34), 10691 pp.
Abstract: We investigate the non-equilibrium dynamics of an isolated polymer in a stationary elongational flow. We compute the relaxation time to the steady-state configuration as a function of the Weissenberg number. A strong increase of the relaxation time is found around the coil-stretch transition, which is attributed to the large number of polymer configurations. The relaxation dynamics of the polymer is solved analytically in terms of a central two-point connection problem for the singly confluent Heun equation.
BibTeX:
@article{Vincenzi.Bodenschatz2006,
  author = {Vincenzi, D. and Bodenschatz, E.},
  title = {Single polymer dynamics in elongational flow and the confluent Heun equation},
  journal = {J. Phys. A},
  month = {August},
  year = {2006},
  volume = {39},
  number = {34},
  pages = {10691},
  url = {http://iopscience.iop.org/0305-4470/39/34/007/},
  doi = {10.1088/0305-4470/39/34/007}
}
Nobach, H. and Bodenschatz, E., "New Resolution limits in PIV image processing", June 2006
BibTeX:
@proceedings{Nobach.Bodenschatz2006a,
  author = {Nobach, H. and Bodenschatz, E.},
  title = {New Resolution limits in PIV image processing},
  month = {June},
  year = {2006},
  url = {http://ltces.dem.ist.utl.pt/LXLASER/lxlaser2006/downloads/papers/26_2.pdf}
}
Nobach, H., Kinzel, M., Tropea, C. and Bodenschatz, E., "Measurement of Lagrangian Acceleration in turbulent flows using the laser Doppler technique", Optical Methods of Flow Investigation, June 2006, Vol. 6262
Abstract: The use of the laser Doppler technique for measuring Lagrangian acceleration with a high spatial resolution is introduced. The requirements in system alignment and accuracy of signal processing is estimated. Specifications of the optical design and the signal processing are given.
BibTeX:
@proceedings{Nobach.Kinzel.ea2006,
  author = {Nobach, H. and Kinzel, M. and Tropea, C. and Bodenschatz, E.},
  title = {Measurement of Lagrangian Acceleration in turbulent flows using the laser Doppler technique},
  journal = {Optical Methods of Flow Investigation},
  month = {June},
  year = {2006},
  volume = {6262},
  url = {http://proceedings.spiedigitallibrary.org/proceeding.aspx?articleid=1287806},
  doi = {10.1117/12.682916}
}
Ouellette, N. T., Xu, H. T., Bourgoin, M. and Bodenschatz, E., "An experimental study of turbulent relative dispersion models", New J. Phys., June 2006, Vol. 8, 109 pp.
Abstract: We report measurements of the spreading rate of pairs of tracer particles in an intensely turbulent laboratory water flow. We compare our measurements of this turbulent relative dispersion with the longstanding work of Richardson and Batchelor, and find excellent agreement with Batchelor's predictions. The distance neighbour function, the probability density function of the relative dispersion, is measured and compared with existing models. We also investigate the recently proposed exit time analysis of relative dispersion.
BibTeX:
@article{Ouellette.Xu.ea2006a,
  author = {Ouellette, N. T. and Xu, H. T. and Bourgoin, M. and Bodenschatz, E.},
  title = {An experimental study of turbulent relative dispersion models},
  journal = {New J. Phys.},
  month = {June},
  year = {2006},
  volume = {8},
  pages = {109},
  url = {http://iopscience.iop.org/1367-2630/8/6/109/},
  doi = {10.1088/1367-2630/8/6/109}
}
Ouellette, N. T., Xu, H. T., Bourgoin, M. and Bodenschatz, E., "Small-scale anisotropy in Lagrangian turbulence", New J. Phys., June 2006, Vol. 8, 102 pp.
Abstract: We report measurements of the second-order Lagrangian structure function and the Lagrangian velocity spectrum in an intensely turbulent laboratory flow. We find that the asymmetries of the large-scale flow are reflected in the small-scale statistics. In addition, we present new measurements of the Lagrangian structure function scaling constant C-0, which is of central importance to stochastic turbulence models as well as to the understanding of turbulent pair dispersion and scalar mixing. The scaling of C-0 with the turbulence level is also investigated, and found to be in agreement with an existing model.
BibTeX:
@article{Ouellette.Xu.ea2006b,
  author = {Ouellette, N. T. and Xu, H. T. and Bourgoin, M. and Bodenschatz, E.},
  title = {Small-scale anisotropy in Lagrangian turbulence},
  journal = {New J. Phys.},
  month = {June},
  year = {2006},
  volume = {8},
  pages = {102},
  url = {http://iopscience.iop.org/1367-2630/8/6/102/},
  doi = {10.1088/1367-2630/8/6/102}
}
Xu, H. T., Ouellette, N. T. and Bodenschatz, E., "Multifractal dimension of Lagrangian turbulence", Phys. Rev. Lett., March 2006, Vol. 96(11), 114503 pp.
Abstract: We report experimental measurements of the Lagrangian multifractal dimension spectrum in an intensely turbulent laboratory water flow by the optical tracking of tracer particles. The Legendre transform of the measured spectrum is compared with measurements of the scaling exponents of the Lagrangian velocity structure functions, and excellent agreement between the two measurements is found, in support of the multifractal picture of turbulence. These measurements are compared with three model dimension spectra. When the nonexistence of structure functions of order less than -1 is accounted for, the models are shown to agree well with the measured spectrum.
BibTeX:
@article{Xu.Ouellette.ea2006a,
  author = {Xu, H. T. and Ouellette, N. T. and Bodenschatz, E.},
  title = {Multifractal dimension of Lagrangian turbulence},
  journal = {Phys. Rev. Lett.},
  month = {March},
  year = {2006},
  volume = {96},
  number = {11},
  pages = {114503},
  url = {http://prl.aps.org/abstract/PRL/v96/i11/e114503},
  doi = {10.1103/PhysRevLett.96.114503}
}
Bourgoin, M., Ouellette, N. T., Xu, H. T., Berg, J. and Bodenschatz, E., "The role of pair dispersion in turbulent flow", Science, February 2006, Vol. 311(5762), 835 pp.
Abstract: Mixing and transport in turbulent flows - which have strong local concentration fluctuations - essential in many natural and industrial systems including reactions in chemical mixers, combustion in engines and burners, droplet formation in warm clouds, and biological odor detection and chemotaxis. Local concentration fluctuations, in turn, are intimately tied to the problem of the separation of pairs of fluid elements. We have measured this separation rate in an intensely turbulent laboratory flow and have found, in quantitative agreement with the seminal predictions of Batchelor, that the initial separation of the pair plays an important rote in the subsequent spreading of the fluid elements. These results have surprising consequences for the decay of concentration fluctuations and have applications to biological and chemical systems.
BibTeX:
@article{Bourgoin.Ouellette.ea2006,
  author = {Bourgoin, M. and Ouellette, N. T. and Xu, H. T. and Berg, J. and Bodenschatz, E.},
  title = {The role of pair dispersion in turbulent flow},
  journal = {Science},
  month = {February},
  year = {2006},
  volume = {311},
  number = {5762},
  pages = {835},
  url = {http://www.sciencemag.org/content/311/5762/835},
  doi = {10.1126/science.1121726}
}
Ouellette, N. T., Xu, H. T. and Bodenschatz, E., "A quantitative study of three-dimensional Lagrangian particle tracking algorithms", Exp. Fluids, February 2006, Vol. 40(2), 301 pp.
Abstract: A neural network particle finding algorithm and a new four-frame predictive tracking algorithm are proposed for three-dimensional Lagrangian particle tracking (LPT). A quantitative comparison of these and other algorithms commonly used in three-dimensional LPT is presented. Weighted averaging, one-dimensional and two-dimensional Gaussian fitting, and the neural network scheme are considered for determining particle centers in digital camera images. When the signal to noise ratio is high, the one-dimensional Gaussian estimation scheme is shown to achieve a good combination of accuracy and efficiency, while the neural network approach provides greater accuracy when the images are noisy. The effect of camera placement on both the yield and accuracy of three-dimensional particle positions is investigated, and it is shown that at least one camera must be positioned at a large angle with respect to the other cameras to minimize errors. Finally, the problem of tracking particles in time is studied. The nearest neighbor algorithm is compared with a three-frame predictive algorithm and two four-frame algorithms. These four algorithms are applied to particle tracks generated by direct numerical simulation both with and without a method to resolve tracking conflicts. The new four-frame predictive algorithm with no conflict resolution is shown to give the best performance. Finally, the best algorithms are verified to work in a real experimental environment.
BibTeX:
@article{Ouellette.Xu.ea2006,
  author = {Ouellette, N. T. and Xu, H. T. and Bodenschatz, E.},
  title = {A quantitative study of three-dimensional Lagrangian particle tracking algorithms},
  journal = {Exp. Fluids},
  month = {February},
  year = {2006},
  volume = {40},
  number = {2},
  pages = {301},
  url = {http://link.springer.com/article/10.1007%2Fs00348-005-0068-7},
  doi = {10.1007/s00348-005-0068-7}
}
Xu, H., Bourgoin, M., Ouellette, N. T. and Bodenschatz, E., "High order Lagrangian velocity statistics in turbulence", Phys. Rev. Lett., January 2006, Vol. 96(2), 024503 pp.
Abstract: We report measurements of the Lagrangian velocity structure functions of orders 1 through 10 in a high Reynolds number (Taylor microscale Reynolds numbers of up to R(lambda)=815) turbulence experiment. Passive tracer particles are tracked optically in three dimensions and in time, and velocities are calculated from the particle tracks. The structure function anomalous scaling exponents are measured both directly and using extended self-similarity and are found to be more intermittent than their Eulerian counterparts. Classical Kolmogorov inertial range scaling is also found for all structure function orders at times that trend downward as the order increases. The temporal shift of this classical scaling behavior is observed to saturate as the structure function order increases at times shorter than the Kolmogorov time scale.
BibTeX:
@article{Xu.Bourgoin.ea2006,
  author = {Xu, H. and Bourgoin, M. and Ouellette, N. T. and Bodenschatz, E.},
  title = {High order Lagrangian velocity statistics in turbulence},
  journal = {Phys. Rev. Lett.},
  month = {January},
  year = {2006},
  volume = {96},
  number = {2},
  pages = {024503},
  url = {http://prl.aps.org/abstract/PRL/v96/i2/e024503},
  doi = {10.1103/PhysRevLett.96.024503}
}
Rhoads, D. S., Nadkarni, S., Song, L., Voeltz, C., Bodenschatz, E. and Guan, J., "Using microfluidic channel networks to generate gradients for studying cell migration", Methods Mol. Biol., 2005, Vol. 294, 347-357 pp.
Abstract: In this chapter, we will discuss a method for the generation of gradients that can be quantitatively used for studying directional cell migration. Microfluidic networks, which serially split and remix small volumes of solutions under laminar flow conditions to generate a series of microchannels of increasing protein concentration. At a juncture of these microchannels, where a single broad channel is formed, a protein concentration gradient can be easily achieved. This method is highly useful because of the ability with which we can control, manipulate and analyze chemical gradients and cells’ chemotactic behavior in a quantitative manner.
BibTeX:
@incollection{Rhoads.Nadkarni.ea2004,
  author = {Rhoads, D. S. and Nadkarni, S.M. and Song, L. and Voeltz, C. and Bodenschatz, E.. and Guan, J.},
  title = {Using microfluidic channel networks to generate gradients for studying cell migration},
  journal = {Methods Mol. Biol.},
  year = {2005},
  volume = {294},
  pages = {347--357},
  url = {http://link.springer.com/protocol/10.1385/1-59259-860-9:347/fulltext.html},
  doi = {10.1385/1-59259-860-9:347}
}
Katz, R. F. and Bodenschatz, E., "Taking wax for a spin: microplates in an analog model of plate tectonics", Europhysics News, September 2005, Vol. 36(5), 155 pp.
BibTeX:
@article{Katz.Bodenschatz2005,
  author = {Katz, R. F. and Bodenschatz, E.},
  title = {Taking wax for a spin: microplates in an analog model of plate tectonics},
  journal = {Europhysics News},
  month = {September},
  year = {2005},
  volume = {36},
  number = {5},
  pages = {155},
  url = {http://www.europhysicsnews.org/index.php?option=com_article&access=doi&doi=10.1051/epn:2005503&Itemid=129},
  doi = {10.1051/epn:2005503}
}
Martins Afonso, M. and Vincenzi, D., "Nonlinear elastic polymers in random flow", J. Fluid Mech., September 2005, Vol. 540, 99 pp.
Abstract: Polymer stretching in random smooth flows is investigated within the framework of the FENE dumbbell model. The advecting flow is Gaussian and short-correlated in time. The stationary probability density function of polymer extension is derived exactly. The characteristic time needed for the system to attain the stationary regime is computed as a function of the Weissenberg number and the maximum length of polymers. The transient relaxation to the stationary regime is predicted to be exceptionally slow in the proximity of the coil–stretch transition.
BibTeX:
@article{MartinsAfonso.Vincenzi2005,
  author = {Martins Afonso, M. and Vincenzi, D.},
  title = {Nonlinear elastic polymers in random flow},
  journal = {J. Fluid Mech.},
  month = {September},
  year = {2005},
  volume = {540},
  pages = {99},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=340432&fileId=S0022112005005951},
  doi = {10.1017/S0022112005005951}
}
Nobach, H., Ouellette, N. T., Bodenschatz, E. and Tropea, C., "Full-field correlation-based image processing for PIV", September 2005
Abstract: Due to its high robustness, correlation-based particle image velocimetry (PIV) has become the prime choice for processing image-based flow measurements in fluid dynamics experiments. However, in recent years, whole-field techniques like optical flow methods have been successfully applied to these kind of images. To avoid the dependence of optical flow methods on intensity variations and to combine the robustness of the correlationbased PIV technique with the whole-field flow description of the optical flow method, a hybrid estimation procedure has been developed. It is an iterative method, optimizing a dense, hypothetical velocity field with respect to vanishing residual displacements, obtained by image correlation.
BibTeX:
@proceedings{Nobach.Ouellette.ea2005,
  author = {Nobach, H. and Ouellette, N. T. and Bodenschatz, E. and Tropea, C},
  title = {Full-field correlation-based image processing for PIV},
  month = {September},
  year = {2005},
  url = {http://nambis.bplaced.de/download/text/piv05.pdf}
}
Utter, B. and Bodenschatz, E., "Double dendrite growth in solidification", Phys. Rev. E, July 2005, Vol. 72(1), 011601 pp.
Abstract: We present experiments on the doublon growth morphology in directional solidification. Samples used are succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as the solute. Doublons, or symmetry-broken dendrites, are generic diffusion-limited growth structures expected at large undercooling and low anisotropy. Low anisotropy growth is achieved by selecting a grain near the 111 plane leading to either seaweed (dense branching morphology) or doublon growth depending on experimental parameters. We find selection of doublons to be strongly dependent on solute concentration and sample orientation. Doublons are selected at low concentrations (low solutal undercooling) in contrast to the prediction of doublons at large thermal undercooling in pure materials. Doublons also exhibit preferred growth directions and changing the orientation of a specific doublonic grain changes the character and stability of the doublons. We observe transitions between seaweed and doublon growth with changes in concentration and sample orientation.
BibTeX:
@article{Utter.Bodenschatz2005,
  author = {Utter, B. and Bodenschatz, E.},
  title = {Double dendrite growth in solidification},
  journal = {Phys. Rev. E},
  month = {July},
  year = {2005},
  volume = {72},
  number = {1},
  pages = {011601},
  url = {http://pre.aps.org/abstract/PRE/v72/i1/e011601},
  doi = {10.1103/PhysRevE.72.011601}
}
Katz, R. F., Ragnarsson, R. and Bodenschatz, E., "Tectonic microplates in a wax model of sea-floor spreading", New J. Phys., February 2005, Vol. 7, 37 pp.
Abstract: Rotating, growing microplates are observed in a wax analogue model of sea-floor spreading. Wax microplates are kinematically similar to sea-floor tectonic microplates in terms of spreading rate and growth rate. Furthermore, their spiral pseudofault geometry is quantitatively consistent with Schouten's oceanic microplate model. These results suggest that Schouten's edge-driven microplate model captures the kinematics of tectonic microplate evolution on Earth. Based on the wax observations, a theory for the nucleation of overlapping spreading centres, the precursors of tectonic microplates, is developed.
BibTeX:
@article{Katz.Ragnarsson.ea2005,
  author = {Katz, R. F. and Ragnarsson, R. and Bodenschatz, E.},
  title = {Tectonic microplates in a wax model of sea-floor spreading},
  journal = {New J. Phys.},
  month = {February},
  year = {2005},
  volume = {7},
  pages = {37},
  url = {http://iopscience.iop.org/1367-2630/7/1/037/},
  doi = {10.1088/1367-2630/7/1/037}
}
Reynolds, A. M., Mordant, N., Crawford, A. M. and Bodenschatz, E., "On the distribution of Lagrangian accelerations in turbulent flows", New J. Phys., February 2005, Vol. 7, 58 pp.
Abstract: Superstatistical Lagrangian stochastic models are shown to predict accurately the distribution of the magnitude of the acceleration vector in three-dimensional high Reynolds-number turbulence. Distributions are closely log-normal having high tails that are nearly coincident with measured distributions of enstrophy. The findings support the view that the dominant contribution to extreme accelerations comes from centripetal accelerations induced by vortex filaments.
BibTeX:
@article{Reynolds.Mordant.ea2005,
  author = {Reynolds, A. M. and Mordant, N. and Crawford, A. M. and Bodenschatz, E.},
  title = {On the distribution of Lagrangian accelerations in turbulent flows},
  journal = {New J. Phys.},
  month = {February},
  year = {2005},
  volume = {7},
  pages = {58},
  url = {http://iopscience.iop.org/1367-2630/7/1/058/},
  doi = {10.1088/1367-2630/7/1/058}
}
Crawford, A. M., Mordant, N. and Bodenschatz, E., "Joint statistics of the Lagrangian acceleration and velocity in fully developed turbulence", Phys. Rev. Lett., January 2005, Vol. 94(2), 024501 pp.
Abstract: We report experimental results on the joint statistics of the Lagrangian acceleration and velocity in highly turbulent flows. The acceleration was measured up to a microscale Reynolds number R-lambda=690 using high speed silicon strip detectors from high energy physics. The acceleration variance was observed to be strongly dependent on the velocity, following a Heisenberg-Yaglom-like u(9/2) increase. However, the shape of the probability density functions of the acceleration component conditioned on the same component of the velocity when normalized by the acceleration variance was observed to be independent of velocity and to coincide with the unconditional probability density function of the acceleration components. This observation imposes a strong mathematical constraint on the possible functional form of the acceleration probability distribution function.
BibTeX:
@article{Crawford.Mordant.ea2005,
  author = {Crawford, A. M. and Mordant, N. and Bodenschatz, E.},
  title = {Joint statistics of the Lagrangian acceleration and velocity in fully developed turbulence},
  journal = {Phys. Rev. Lett.},
  month = {January},
  year = {2005},
  volume = {94},
  number = {2},
  pages = {024501},
  url = {http://prl.aps.org/abstract/PRL/v94/i2/e024501},
  doi = {10.1103/PhysRevLett.94.024501}
}
Utter, B., Ragnarsson, R. and Bodenschatz, E., "Experimental apparatus and sample preparation techniques for directional solidification", Rev. Sci. Instrum., January 2005, Vol. 76(1), 013906 pp.
Abstract: We describe a directional solidification stage which allows the controlled solidification of transparent organic alloys. We present two variations of the experiment. In one, large aspect ratio sample cells can be rotated with respect to the temperature gradient between runs, allowing full 360degrees control over in-plane sample orientation. In the other, thin-walled capillaries are pulled through an oil-filled channel which is optimized for high speed solidification studies (Vapproximate to5 mm/s). The use of large aspect ratio cells (approximate to11 cm diameter rotatable) and long capillary cells (approximate to38 cm) allows solidification for significant times even at rapid solidification rates. We describe in detail material purification, cell construction, and vacuum filling procedures which allow high quality sample preparation completely under inert atmosphere. Succinonitrile is purified using a sublimation apparatus and samples are filled directly from the sublimation chamber. Vacuum-filling epoxied cells produces long-lasting degassed samples. The techniques presented are also suitable for similar materials such as liquid crystals, CBr4, and pivalic acid. Additional features of the experiment include a linear stepper motor and linear temperature gradient (3-150 K/cm). (C) 2005 American Institute of Physics.
BibTeX:
@article{Utter.Ragnarsson.ea2005,
  author = {Utter, B. and Ragnarsson, R. and Bodenschatz, E.},
  title = {Experimental apparatus and sample preparation techniques for directional solidification},
  journal = {Rev. Sci. Instrum.},
  month = {January},
  year = {2005},
  volume = {76},
  number = {1},
  pages = {013906},
  url = {http://rsi.aip.org/resource/1/rsinak/v76/i1/p013906_s1},
  doi = {10.1063/1.1807592}
}
Rhoads, D. S., Nadkarni, S. M., Song, L., Voeltz, C., Bodenschatz, E. and Guan, J., "Using microfluidic channel networks to generate gradients for studying cell migration", 2004, Vol. 294, 347 pp.
Abstract: In this chapter, we will discuss a method for the generation of gradients that can be quantitatively used for studying directional cell migration. Microfluidic networks, which serially split and remix small volumes of solutions under laminar flow conditions to generate a series of microchannels of increasing protein concentration. At a juncture of these microchannels, where a single broad channel is formed, a protein concentration gradient can be easily achieved. This method is highly useful because of the ability with which we can control, manipulate and analyze chemical gradients and cells’ chemotactic behavior in a quantitative manner.
BibTeX:
@inbook{Rhoads.Nadkarni.ea2004a,
  author = {Rhoads, D. S. and Nadkarni, S. M. and Song, L. and Voeltz, C. and Bodenschatz, E. and Guan, J.},
  title = {Using microfluidic channel networks to generate gradients for studying cell migration},
  year = {2004},
  volume = {294},
  pages = {347},
  url = {http://link.springer.com/protocol/10.1385%2F1-59259-860-9%3A347?LI=true},
  doi = {10.1385/1-59259-860-9:347}
}
Voeltz, C. and Bodenschatz, E., "Experiments with Dictyostelium Discoidium Amoebae in Different Geometries", 2004, 373 pp.
BibTeX:
@inbook{Voeltz.Bodenschatz2004,
  author = {Voeltz, C. and Bodenschatz, E.},
  title = {Experiments with Dictyostelium Discoidium Amoebae in Different Geometries},
  year = {2004},
  pages = {373},
  url = {https://books.google.de/books?hl=de&lr=&id=CTx2hHTa2gUC&oi=fnd&pg=PA373&dq=Experiments+with+Dictyostelium+Discoidium+Amoebae+in+Different+Geometries&ots=J1Mg1f2G5I&sig=ccnTmp4uTDV8U5620_iCif7adoc#v=onepage&q=Experiments%20with%20Dictyostelium%20Discoidium%20Amoebae%20in%20Different%20Geometries&f=false}
}
Mordant, N., Crawford, A. M. and Bodenschatz, E., "Three-dimensional structure of the Lagrangian acceleration in turbulent flows", Phys. Rev. Lett., November 2004, Vol. 93(21), 214501 pp.
Abstract: We report experimental results on the three-dimensional Lagrangian acceleration in highly turbulent flows. Tracer particles are tracked optically using four silicon strip detectors from high energy physics that provide high temporal and spatial resolution. The components of the acceleration are shown to be statistically dependent. The probability density function of the acceleration magnitude is comparable to a log-normal distribution. Assuming isotropy, a log-normal distribution of the magnitude can account for the observed dependency of the components. The time dynamics of the acceleration components is found to be typical of the dissipation scales, whereas the magnitude evolves over longer times, possibly close to the integral time scale.
BibTeX:
@article{Mordant.Crawford.ea2004a,
  author = {Mordant, N. and Crawford, A. M. and Bodenschatz, E.},
  title = {Three-dimensional structure of the Lagrangian acceleration in turbulent flows},
  journal = {Phys. Rev. Lett.},
  month = {November},
  year = {2004},
  volume = {93},
  number = {21},
  pages = {214501},
  url = {http://prl.aps.org/abstract/PRL/v93/i21/e214501},
  doi = {10.1103/PhysRevLett.93.214501}
}
Variano, E. A., Bodenschatz, E. and Cowen, E. A., "A random synthetic jet array driven turbulence tank", Exp. Fluids, October 2004, Vol. 37(4), 613 pp.
Abstract: We measure the flow above an array of randomly driven, upward-facing synthetic jets used to generate turbulence beneath a free surface. Compared to grid stirred tanks (GSTs), this system offers smaller mean flows at equivalent turbulent Reynolds numbers with fewer moving parts.
BibTeX:
@article{Variano.Bodenschatz.ea2004,
  author = {Variano, E. A. and Bodenschatz, E. and Cowen, E. A.},
  title = {A random synthetic jet array driven turbulence tank},
  journal = {Exp. Fluids},
  month = {October},
  year = {2004},
  volume = {37},
  number = {4},
  pages = {613},
  url = {http://link.springer.com/article/10.1007%2Fs00348-004-0833-z},
  doi = {10.1007/s00348-004-0833-z}
}
Huepe, C., Riecke, H., Daniels, K. E. and Bodenschatz, E., "Statistics of defect trajectories in spatio-temporal chaos in inclined layer convection and the complex Ginzburg-Landau equation", Chaos, September 2004, Vol. 14(3), 864 pp.
Abstract: For spatio-temporal chaos observed in numerical simulations of the complex Ginzburg-Landau equation (CGL) and in experiments on inclined-layer convection (ILC) we report numerical and experimental data on the statistics of defects and of defect loops. These loops consist of defect trajectories in space-time that are connected to each other through the pairwise annihilation or creation of the associated defects. While most such loops are small and contain only a few defects, the loop distribution functions decay only slowly with the quantities associated with the loop size, consistent with power-law behavior. For the CGL, two of the three power-law exponents are found to agree, within our computational precision, with those from previous investigations of a simple lattice model. In certain parameter regimes of the CGL and ILC, our results for the single-defect statistics show significant deviations from the previously reported findings that the defect dynamics are consistent with those of random walkers that are created with fixed probability and annihilated through random collisions. (C) 2004 American Institute of Physics.
BibTeX:
@article{Huepe.Riecke.ea2004,
  author = {Huepe, C. and Riecke, H. and Daniels, K. E. and Bodenschatz, E.},
  title = {Statistics of defect trajectories in spatio-temporal chaos in inclined layer convection and the complex Ginzburg-Landau equation},
  journal = {Chaos},
  month = {September},
  year = {2004},
  volume = {14},
  number = {3},
  pages = {864},
  url = {http://chaos.aip.org/resource/1/chaoeh/v14/i3/p864_s1},
  doi = {10.1063/1.1778495}
}
Walter, T., Pesch, W. and Bodenschatz, E., "Dislocation dynamics in Rayleigh-Bénard convection", Chaos, September 2004, Vol. 14(3), 933 pp.
Abstract: Theoretical results on the dynamics of dislocations in Rayleigh-Bénard convection are reported both for a Swift-Hohenberg model and the Oberbeck-Boussinesq equations. For intermediate Prandtl numbers the motion of dislocations is found to be driven by the superposition of two independent contributions: (i) the Peach-Koehler force and (ii) an advection force on the dislocation core by its self-generated mean flow. Their competition allows to explain the experimentally observed bound dislocation pairs. (C) 2004 American Institute of Physics.
BibTeX:
@article{Walter.Pesch.ea2004,
  author = {Walter, T. and Pesch, W. and Bodenschatz, E.},
  title = {Dislocation dynamics in Rayleigh-Bénard convection},
  journal = {Chaos},
  month = {September},
  year = {2004},
  volume = {14},
  number = {3},
  pages = {933},
  url = {http://adsabs.harvard.edu/abs/2001APS..MARX15008B},
  doi = {10.1063/1.1772231}
}
Daniels, K. E., Beck, C. and Bodenschatz, E., "Defect turbulence and generalized statistical mechanics", Physica D, June 2004, Vol. 193(1-4), 208 pp.
Abstract: We present experimental evidence that the motion of point defects in thermal convection patterns in an inclined fluid layer is well described by Tsallis statistics with an entropic index q approximate to 1.5. The dynamical properties of the defects (anomalous diffusion, shape of velocity distributions, power-law decay of correlations) are in good agreement with typical predictions of nonextensive models, over a range of driving parameters. (C) 2004 Elsevier B.V. All rights reserved.
BibTeX:
@article{Daniels.Beck.ea2004,
  author = {Daniels, K. E. and Beck, C. and Bodenschatz, E.},
  title = {Defect turbulence and generalized statistical mechanics},
  journal = {Physica D},
  month = {June},
  year = {2004},
  volume = {193},
  number = {1-4},
  pages = {208},
  url = {http://www.sciencedirect.com/science/article/pii/S016727890400034X},
  doi = {10.1016/j.physd.2004.01.033}
}
Mordant, N., Crawford, A. M. and Bodenschatz, E., "Experimental Lagrangian acceleration probability density function measurement", Physica D, June 2004, Vol. 193(1-4), 245 pp.
Abstract: We report experimental results on the acceleration component probability distribution function at R-lambda = 690 to probabilities of less than 10(-7). This is an improvement of more than an order of magnitude over past measurements and allows us to conclude that the fourth moment converges and the flatness is approximately 55. We compare our probability distribution to those predicted by several models inspired by non-extensive statistical mechanics. We also look at acceleration component probability distributions conditioned on a velocity component for conditioning velocities as high as three times the standard deviation and find them to be highly non-Gaussian. (C) 2004 Published by Elsevier B.V.
BibTeX:
@article{Mordant.Crawford.ea2004,
  author = {Mordant, N. and Crawford, A. M. and Bodenschatz, E.},
  title = {Experimental Lagrangian acceleration probability density function measurement},
  journal = {Physica D},
  month = {June},
  year = {2004},
  volume = {193},
  number = {1-4},
  pages = {245},
  url = {http://www.sciencedirect.com/science/article/pii/S0167278904000417},
  doi = {10.1016/j.physd.2004.01.041}
}
Song, L., Nadkarni, S. and Bodenschatz, E., "Microfluidic channels with well-defined spatial and temporal chemical gradients to study chemotaxis in dictyostelium discoideum", Biophys. J., January 2004, Vol. 86(1), 482A pp.
BibTeX:
@article{Song.Nadkarni.ea2004,
  author = {Song, L. and Nadkarni, S. and Bodenschatz, E.},
  title = {Microfluidic channels with well-defined spatial and temporal chemical gradients to study chemotaxis in dictyostelium discoideum},
  journal = {Biophys. J.},
  month = {January},
  year = {2004},
  volume = {86},
  number = {1},
  pages = {482A}
}
Sawford, B. L., Yeung, P. K., Borgas, M. S., Vedula, P., La Porta, A., Crawford, A. M. and Bodenschatz, E., "Conditional and unconditional acceleration statistics in turbulence", Phys. Fluids, November 2003, Vol. 15(11), 3478 pp.
Abstract: In this paper we study acceleration statistics from laboratory measurements and direct numerical simulations in three-dimensional turbulence at Taylor-scale Reynolds numbers ranging from 38 to 1000. Using existing data, we show that at present it is not possible to infer the precise behavior of the unconditional acceleration variance in the large Reynolds number limit, since empirical functions satisfying both the Kolmogorov and refined Kolmogorov theories appear to fit the data equally well. We also present entirely new data for the acceleration covariance conditioned on the velocity, showing that these conditional statistics are strong functions of velocity, but that when scaled by the unconditional variance they are only weakly dependent on Reynolds number. For large values of the magnitude u of the conditioning velocity we speculate that the conditional covariance behaves like u(6) and show that this is qualitatively consistent with the stretched exponential tails of the unconditional acceleration probability density function (pdf). The conditional pdf is almost identical in shape to the unconditional pdf. From these conditional covariance data, we are able to calculate the conditional mean rate of change of the acceleration, and show that it is consistent with the drift term in second-order Lagrangian stochastic models of turbulent transport. We also calculate the correlation between the square of the acceleration and the square of the velocity, showing that it is small but not negligible. (C) 2003 American Institute of Physics.
BibTeX:
@article{Sawford.Yeung.ea2003,
  author = {Sawford, B. L. and Yeung, P. K. and Borgas, M. S. and Vedula, P. and La Porta, A. and Crawford, A. M. and Bodenschatz, E.},
  title = {Conditional and unconditional acceleration statistics in turbulence},
  journal = {Phys. Fluids},
  month = {November},
  year = {2003},
  volume = {15},
  number = {11},
  pages = {3478},
  url = {http://pof.aip.org/resource/1/phfle6/v15/i11/p3478_s1},
  doi = {10.1063/1.1613647}
}
Daniels, K. E., Wiener, R. J. and Bodenschatz, E., "Localized transverse bursts in inclined layer convection", Phys. Rev. Lett., September 2003, Vol. 91(11), 114501 pp.
Abstract: We investigate a novel bursting state in inclined layer thermal convection in which convection rolls exhibit intermittent, localized, transverse bursts. With increasing temperature difference, the bursts increase in duration and number while exhibiting a characteristic wave number, magnitude, and size. We propose a mechanism which describes the duration of the observed bursting intervals and compare our results to bursting processes in other systems.
BibTeX:
@article{Daniels.Wiener.ea2003,
  author = {Daniels, K. E. and Wiener, R. J. and Bodenschatz, E.},
  title = {Localized transverse bursts in inclined layer convection},
  journal = {Phys. Rev. Lett.},
  month = {September},
  year = {2003},
  volume = {91},
  number = {11},
  pages = {114501},
  url = {http://prl.aps.org/abstract/PRL/v91/i11/e114501},
  doi = {10.1103/PhysRevLett.91.114501}
}
Bodenschatz, E., Imbihl, R. and Rehberg, I., "Focus on Pattern Formation", New J. Phys., June 2003, Vol. 5
Abstract: Pattern formation is a subfield of nonlinear dynamics in spatially extended systems. Although the latter term is often used narrowly to describe nonlinear systems with not too many degrees of freedom, in general it may be applied to describe more or less everything that happens in the Universe. Thus this statement can hardly be used as a definition. More precisely, the field of pattern formation focuses on systems where the nonlinearities conspire to form spatial patterns that sometimes are stationary, travelling or disordered in space and time. The latter is often referred to as spatio-temporal chaos.
The past two decades have provided major progress in the field of pattern formation. We now have a well-developed theoretical framework for understanding weakly nonlinear patterns that can be described by Ginzburg-Landau-type theories. Close to the onset of instability, our understanding of time-independent or simple time-dependent patterns is quite advanced. Phase field models for the investigation of interfacial instabilities are leading to a breakthrough. Nonlinear phase diffusion equations that are derived from first principles allow the investigation of the `elastic' properties of pattern dynamics even in the fully nonlinear region.
Rapid progress continues to be made possible by a close collaboration of experiment and theory. Advances in computational power are enabling the study of complex spatio-temporal patterns in systems of large spatial extent. In experiment, the increase in computational power combined with novel imaging technology allows the analysis of millions of high-resolution digital images. For instance, novel visualization and data analysis techniques have yielded progress in identifying and studying the nonequilibrium dynamics of extended systems in terms of the spatial and temporal evolution of defect structures that are found in many spatio-temporal chaotic systems. Numerical simulations based on first principles or on general higher-order equations can now be conducted in large systems under realistic boundary conditions.
Pattern formation is a truly interdisciplinary science. The similarity in fundamental mechanisms and the accompanying mathematics brings together scientists from many disciplines, such as biology, chemistry, fluid dynamics, material science, mathematics, medicine, geophysics, ecology, physics and surface science. We believe that the articles collected here provide an overview of the widespread activities within this field.
We feel that New Journal of Physics, as a purely electronic journal, is particularly useful for our field of research: if a picture says a thousand words, a movie can say many more about the spatio-temporal dynamics of a pattern. We would like to thank all of the authors for their contributions and, in many cases, for bearing the additional burden of including moving pictures for the undoubted benefit of readers.
BibTeX:
@article{Bodenschatz.Imbihl.ea2003,
  author = {Bodenschatz, E. and Imbihl, R. and Rehberg, I.},
  title = {Focus on Pattern Formation},
  journal = {New J. Phys.},
  month = {June},
  year = {2003},
  volume = {5},
  url = {http://iopscience.iop.org/1367-2630/5/1/003?fromSearchPage=true},
  doi = {10.1088/1367-2630/5/1/003}
}
Daniels, K. E. and Bodenschatz, E., "Statistics of defect motion in spatiotemporal chaos in inclined layer convection", Chaos, March 2003, Vol. 13(1), 55 pp.
Abstract: We report experiments on defect-tracking in the state of undulation chaos observed in thermal convection of an inclined fluid layer. We characterize the ensemble of defect trajectories according to their velocities, relative positions, diffusion, and gain and loss rates. In particular, the defects exhibit incidents of rapid transverse motion which result in power law distributions for a number of quantitative measures. We examine connections between this behavior and Levy flights and anomalous diffusion. In addition, we describe time-reversal and system size invariance for defect creation and annihilation rates. (C) 2003 American Institute of Physics.
BibTeX:
@article{Daniels.Bodenschatz2003,
  author = {Daniels, K. E. and Bodenschatz, E.},
  title = {Statistics of defect motion in spatiotemporal chaos in inclined layer convection},
  journal = {Chaos},
  month = {March},
  year = {2003},
  volume = {13},
  number = {1},
  pages = {55},
  url = {http://chaos.aip.org/resource/1/chaoeh/v13/i1/p55_s1},
  doi = {10.1063/1.1536330}
}
Fox, J. J., Gilmour, R. F. and Bodenschatz, E., "Conduction block in one-dimensional heart fibers", Phys. Rev. Lett., November 2002, Vol. 89(19), 198101 pp.
Abstract: We present a nonlinear dynamical systems analysis of the transition to conduction block in one-dimensional cardiac fibers. We study a simple model of wave propagation in heart tissue that depends only on the recovery of action potential duration and conduction velocity. If the recovery function has slope greater than or equal to 1 and the velocity recovery function is nonconstant, rapid activation causes dynamical heterogeneity and finally conduction block away from the activation site. This dynamical mechanism may play a role in the initiation and breakup of spiral waves in excitable media.
BibTeX:
@article{Fox.Gilmour.ea2002a,
  author = {Fox, J. J. and Gilmour, R. F. and Bodenschatz, E.},
  title = {Conduction block in one-dimensional heart fibers},
  journal = {Phys. Rev. Lett.},
  month = {November},
  year = {2002},
  volume = {89},
  number = {19},
  pages = {198101},
  url = {http://prl.aps.org/abstract/PRL/v89/i19/e198101},
  doi = {10.1103/PhysRevLett.89.198101}
}
Utter, B. and Bodenschatz, E., "Dynamics of low anisotropy morphologies in directional solidification", Phys. Rev. E, November 2002, Vol. 66(5), 051604 pp.
Abstract: We report experimental results on quasi-two-dimensional diffusion limited growth in directionally solidified succinonitrile with small amounts of poly(ethylene oxide), acetone, or camphor as a solute. Seaweed growth, or dense branching morphology, is selected by growing grains close to the 111 plane, where the in-plane surface tension is nearly isotropic. The observed growth morphologies are very sensitive to small anisotropies in surface tension caused by misorientations from the 111 plane. Different seaweed morphologies are found, including the degenerate, the stabilized, and the strongly tilted seaweeds. The degenerate seaweeds show a limited fractal scaling range and, with increased undercooling, suggests a transition from "fractal" to "compact" seaweed. Strongly tilted seaweeds demonstrate a significant twofold anisotropy. In addition, seaweed-dendrite transitions are observed in low anisotropy growth.
BibTeX:
@article{Utter.Bodenschatz2002,
  author = {Utter, B. and Bodenschatz, E.},
  title = {Dynamics of low anisotropy morphologies in directional solidification},
  journal = {Phys. Rev. E},
  month = {November},
  year = {2002},
  volume = {66},
  number = {5},
  pages = {051604},
  url = {http://pre.aps.org/abstract/PRE/v66/i5/e051604},
  doi = {10.1103/PhysRevE.66.051604}
}
Voth, G. A., La Porta, A., Crawford, A. M., Alexander, J. and Bodenschatz, E., "Measurement of particle accelerations in fully developed turbulence", J. Fluid Mech., October 2002, Vol. 469, 121 pp.
Abstract: We use silicon strip detectors (originally developed for the CLEO III high-energy particle physics experiment) to measure fluid particle trajectories in turbulence with temporal resolution of up to 70 000 frames per second. This high frame rate allows the Kolmogorov time scale of a turbulent water flow to be fully resolved for 140 greater than or equal to R-lambda greater than or equal to 970. Particle trajectories exhibiting accelerations up to 16 000 m s(-2) (40 times the r.m.s. value) are routinely observed. The probability density function of the acceleration is found to have Reynolds-number-dependent stretched exponential tails. The moments of the acceleration distribution are calculated. The scaling of the acceleration component variance with the energy dissipation is found to be consistent with the results for low-Reynolds-number direct numerical simulations, and with the K41-based Heisenberg-Yaglom prediction for R-lambda greater than or equal to 500. The acceleration flatness is found to increase with Reynolds number, and to exceed 60 at R-lambda = 970. The coupling of the acceleration to the large-scale anisotropy is found to be large at low Reynolds number and to decrease as the Reynolds number increases, but to persist at all Reynolds numbers measured. The dependence of the acceleration variance on the size and density of the tracer particles is measured. The autocorrelation function of an acceleration component is measured, and is found to scale with the Kolmogorov time tau(eta).
BibTeX:
@article{Voth.LaPorta.ea2002,
  author = {Voth, G. A. and La Porta, A. and Crawford, A. M. and Alexander, J. and Bodenschatz, E.},
  title = {Measurement of particle accelerations in fully developed turbulence},
  journal = {J. Fluid Mech.},
  month = {October},
  year = {2002},
  volume = {469},
  pages = {121},
  url = {http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=124817},
  doi = {10.1017/S0022112002001842}
}
Fox, J. J., Bodenschatz, E. and Gilmour, R. F., "Period-doubling instability and memory in cardiac tissue", Phys. Rev. Lett., September 2002, Vol. 89(13), 138101 pp.
Abstract: Theoretical studies have indicated that alternans (period-doubling instability) of action potential duration is associated with a restitution relation with a slope greater than or equal to1. However, recent experimental findings suggest that the slope of the restitution relation is not necessarily predictive of alternans. Here, we compared a return map memory model to action potential data from an ionic model and found that the memory model reproduced dynamics that could not be explained by a unidimensional restitution relation. Using linear stability analysis, we determined the onset of the alternans in the memory model and confirmed that the slope of the restitution curve was not predictive.
BibTeX:
@article{Fox.Bodenschatz.ea2002,
  author = {Fox, J. J. and Bodenschatz, E. and Gilmour, R. F.},
  title = {Period-doubling instability and memory in cardiac tissue},
  journal = {Phys. Rev. Lett.},
  month = {September},
  year = {2002},
  volume = {89},
  number = {13},
  pages = {138101},
  url = {http://prl.aps.org/abstract/PRL/v89/i13/e138101},
  doi = {10.1103/PhysRevLett.89.138101}
}
Fox, J. J., Riccio, M. L., Hua, F., Bodenschatz, E. and Gilmour, R. F., "Spatiotemporal transition to conduction block in canine ventricle", Circ. Res., February 2002, Vol. 90(3), 289 pp.
Abstract: Interruption of periodic wave propagation by the nucleation and subsequent disintegration of spiral waves is thought to mediate the transition from normal sinus rhythm to ventricular fibrillation. This sequence of events may be precipitated by a period doubling bifurcation, manifest as a beat-to-beat alternation, or alternans, of cardiac action potential duration and conduction velocity. How alternans causes the local conduction block required for initiation of spiral wave reentry remains unclear, however. In the present study, a mechanism for conduction block was derived from experimental studies in linear strands of cardiac tissue and from computer simulations in ionic and coupled maps models of homogeneous one-dimensional fibers. In both the experiments and the computer models, rapid periodic pacing induced marked spatiotemporal heterogeneity of cellular electrical properties, culminating in paroxysmal conduction block. These behaviors resulted from a nonuniform distribution of action potential duration alternans, secondary to alternans of conduction velocity. This link between period doubling bifurcations of cellular electrical properties and conduction block may provide a generic mechanism for the onset of tachycardia and fibrillation.
BibTeX:
@article{Fox.Riccio.ea2002a,
  author = {Fox, J. J. and Riccio, M. L. and Hua, F. and Bodenschatz, E. and Gilmour, R. F.},
  title = {Spatiotemporal transition to conduction block in canine ventricle},
  journal = {Circ. Res.},
  month = {February},
  year = {2002},
  volume = {90},
  number = {3},
  pages = {289},
  url = {http://circres.ahajournals.org/content/90/3/289},
  doi = {10.1161/hh0302.104723}
}
Daniels, K. E. and Bodenschatz, E., "Defect turbulence in inclined layer convection", Phys. Rev. Lett., January 2002, Vol. 88(3), 034501 pp.
Abstract: We report experimental results on the defect turbulent state of undulation chaos in inclined layer convection of a fluid with Prandtl number approximate to1. By measuring defect density and undulation wave number, we find that the onset of undulation chaos coincides with the theoretically predicted onset for stable, stationary undulations. At stronger driving, we observe a competition between ordered undulations and undulation chaos, suggesting bistability between a fixed-point attractor and spatiotemporal chaos. In the defect turbulent regime, we measured the defect creation, annihilation, entering, leaving, and rates. We derive a universal probability distribution function which agrees with the experimental findings.
BibTeX:
@article{Daniels.Bodenschatz2002,
  author = {Daniels, K. E. and Bodenschatz, E.},
  title = {Defect turbulence in inclined layer convection},
  journal = {Phys. Rev. Lett.},
  month = {January},
  year = {2002},
  volume = {88},
  number = {3},
  pages = {034501},
  url = {http://prl.aps.org/abstract/PRL/v88/i3/e034501},
  doi = {10.1103/PhysRevLett.88.034501}
}
Voth, G. A., Porta, A. L., Crawford, A. M., Bodenschatz, E., Ward, C. and Alexander, J., "A silicon strip detector system for high resolution particle tracking in turbulence", Rev. Sci. Instrum., December 2001, Vol. 72(12), 4348 pp.
Abstract: We describe a high speed imaging system that is used to track tracer particles in highly turbulent flows. The system uses silicon strip detectors designed for high energy physics experiments and is capable of reading two detectors at a frame rate of 70 kHz. Each detector contains 512 strips and measures a one-dimensional projection of the light striking it. The position measurements from this system have a dynamic range of 6400:1. Extensions to higher frame rates and more detectors are possible. We describe the detectors, readout system, supporting systems, and give an evaluation of the measurement accuracy. (C) 2001 American Institute of Physics.
BibTeX:
@article{Voth.Porta.ea2001,
  author = {Voth, G. A. and Porta, A. L. and Crawford, A. M. and Bodenschatz, E. and Ward, C. and Alexander, J.},
  title = {A silicon strip detector system for high resolution particle tracking in turbulence},
  journal = {Rev. Sci. Instrum.},
  month = {December},
  year = {2001},
  volume = {72},
  number = {12},
  pages = {4348},
  url = {http://rsi.aip.org/resource/1/rsinak/v72/i12/p4348_s1},
  doi = {10.1063/1.1416112}
}
Utter, B., Ragnarsson, R. and Bodenschatz, E., "Alternating tip splitting in directional solidification", Phys. Rev. Lett., May 2001, Vol. 86(20), 4604 pp.
Abstract: We report experimental results on the tip splitting dynamics of seaweed growth in directional solidification of succinonitrile alloys. Despite the random appearance of the growth, a tip splitting morphology was observed in which the tip alternately splits to the left and to the right. The tip splitting frequency f was found to be related to the growth velocity V as a power law f proportional to V-1.5. This finding is consistent with the predictions of a tip splitting model that is also presented. Small anisotropies are shown to lead to different kinds of seaweed morphologies.
BibTeX:
@article{Utter.Ragnarsson.ea2001,
  author = {Utter, B. and Ragnarsson, R. and Bodenschatz, E.},
  title = {Alternating tip splitting in directional solidification},
  journal = {Phys. Rev. Lett.},
  month = {May},
  year = {2001},
  volume = {86},
  number = {20},
  pages = {4604},
  url = {http://prl.aps.org/abstract/PRL/v86/i20/p4604_1},
  doi = {10.1103/PhysRevLett.86.4604}
}
La Porta, A., Voth, G. A., Crawford, A. M., Alexander, J. and Bodenschatz, E., "Fluid particle accelerations in fully developed turbulence", Nature, February 2001, Vol. 409(6823), 1017 pp.
Abstract: The motion of fluid particles as they are pushed along erratic trajectories by fluctuating pressure gradients is fundamental to transport and mixing in turbulence. It is essential in cloud formation and atmospheric transport(1,2), processes in stirred chemical reactors and combustion systems(3), and in the industrial production of nanoparticles(4). The concept of particle trajectories has been used successfully to describe mixing and transport in turbulence(3,5), but issues of fundamental importance remain unresolved. One such issue is the Heisenberg-Yaglom prediction of fluid particle accelerations(6,7), based on the 1941 scaling theory of Kolmogorov(8,9). Here we report acceleration measurements using a detector adapted from high-energy physics to track particles in a laboratory water flow at Reynolds numbers up to 63,000. We find that, within experimental errors, Kolmogorov scaling of the acceleration variance is attained at high Reynolds numbers. Our data indicate that the acceleration is an extremely intermittent variable-particles are observed with accelerations of up to 1,500 times the acceleration of gravity (equivalent to 40 times the root mean square acceleration). We find that the acceleration data reflect the anisotropy of the large-scale flow at all Reynolds numbers studied.
BibTeX:
@article{LaPorta.Voth.ea2001,
  author = {La Porta, A. and Voth, G. A. and Crawford, A. M. and Alexander, J. and Bodenschatz, E.},
  title = {Fluid particle accelerations in fully developed turbulence},
  journal = {Nature},
  month = {February},
  year = {2001},
  volume = {409},
  number = {6823},
  pages = {1017},
  url = {http://www.nature.com/nature/journal/v409/n6823/full/4091017a0.html},
  doi = {10.1038/35059027}
}
Melnikov, I. V., Egolf, D. A., Jeanjean, S., Plapp, B. B. and Bodenschatz, E., "Invasion of spiral defect chaos into straight rolls in Rayleigh-Bénard convection", AIP Conf. Proc., 2000, Vol. 501(501), 36 pp.
Abstract: For Rayleigh-Bénard convection of a fluid with Prandtl number sigmaap1, we report experimental results of the competition between two stable attractors-ideal straight rolls (ISR) and spiral defect chaos (SDC). For convection cells containing regions of both ISR and SDC, we show that the SDC region invades the ISR region with a time-independent front speed v(E), where E is the reduced Rayleigh number (R-R c)/R c
BibTeX:
@proceedings{Melnikov.Egolf.ea2000,
  author = {Melnikov, I. V. and Egolf, D. A. and Jeanjean, S. and Plapp, B. B. and Bodenschatz, E.},
  title = {Invasion of spiral defect chaos into straight rolls in Rayleigh-Bénard convection},
  journal = {AIP Conf. Proc.},
  year = {2000},
  volume = {501},
  number = {501},
  pages = {36},
  url = {http://proceedings.aip.org/resource/2/apcpcs/501/1/36_1},
  doi = {10.1063/1.59948}
}
Daniels, K. E., Plapp, B. B. and Bodenschatz, E., "Pattern formation in inclined layer convection", Phys. Rev. Lett., June 2000, Vol. 84(23), 5320 pp.
Abstract: We report experiments on thermally driven convection in an inclined layer of large aspect ratio in a fluid of Prandtl number sigma approximate to 1. We observed a number of new nonlinear, mostly spatiotemporally chaotic, states. At small angles of inclination we found longitudinal rolls, subharmonic oscillations, Busse oscillations, undulation chaos, and crawling rolls. At larger angles, in the vicinity of the transition from buoyancy- to shear-driven instability, we observed drifting transverse rolls, localized bursts, and drifting bimodals. For angles past vertical, when heated from above, we found drifting transverse rolls and switching diamond panes.
BibTeX:
@article{Daniels.Plapp.ea2000,
  author = {Daniels, K. E. and Plapp, B. B. and Bodenschatz, E.},
  title = {Pattern formation in inclined layer convection},
  journal = {Phys. Rev. Lett.},
  month = {June},
  year = {2000},
  volume = {84},
  number = {23},
  pages = {5320},
  url = {http://prl.aps.org/abstract/PRL/v84/i23/p5320_1},
  doi = {10.1103/PhysRevLett.84.5320}
}
La Porta, A., Voth, G. A., Moisy, F. and Bodenschatz, E., "Using cavitation to measure statistics of low-pressure events in large-Reynolds-number turbulence", Phys. Fluids, June 2000, Vol. 12(6), 1485 pp.
Abstract: The structure of the pressure field of a turbulent water flow between counter-rotating disks is studied using cavitation. The flow is seeded with microscopic gas bubbles and the hydrostatic pressure is reduced until large negative pressure fluctuations trigger cavitation. Cavitation is detected via light scattering from cavitating bubbles. The spatial structure of the low-pressure events are visualized using a high-speed video system. A fast photo detector is used to measure the scaling of the cavitation statistics with the pressure. This data is used to determine the shape of the tail of the probability density function for the pressure. The tail is found to be exponential and scales more rapidly with Reynolds number than the standard deviation of the pressure. This may indicate the influence of internal intermittency. (C) 2000 American Institute of Physics. [S1070-6631(00)01106-5].
BibTeX:
@article{LaPorta.Voth.ea2000,
  author = {La Porta, A. and Voth, G. A. and Moisy, F. and Bodenschatz, E.},
  title = {Using cavitation to measure statistics of low-pressure events in large-Reynolds-number turbulence},
  journal = {Phys. Fluids},
  month = {June},
  year = {2000},
  volume = {12},
  number = {6},
  pages = {1485},
  url = {http://pof.aip.org/resource/1/phfle6/v12/i6/p1485_s1},
  doi = {10.1063/1.870397}
}
Harrison, C., Chaikin, P. M., Huse, D. A., Register, R. A., Adamson, D. H., Daniel, A., Huang, E., Mansky, P., Russell, T. P., Hawker, C. J., Egolf, D. A., Melnikov, I. V. and Bodenschatz, E., "Reducing substrate pinning of block copolymer microdomains with a buffer layer of polymer brushes", Macromolecules, February 2000, Vol. 33(3), 857 pp.
Abstract: We study the range of orientational order of a single layer of cylindrical block copolymer microdomains annealed on several types of substrate. The orientational persistence length or nematic correlation length (xi) is evaluated using recently developed imaging and analysis methods to measure the grain size of the block copolymer microdomains. We show that the substrate can lower xi for block copolymers with a majority component that interacts strongly with the substrate, but this can be mitigated by attaching a buffer layer of polystyrene brushes to the substrate. In addition, we show that, for a block copolymer where the block that strongly interacts with the substrate is the minority component, the microdomain correlation length does not increase when substrates are treated with this buffer layer. We suggest that in this case the brushes do not increase xi not only because of the lower volume fraction of the strongly interacting component but also because there are block copolymer wetting layers at the free and substrate interfaces that decouple the microdomains from the substrate in a similar manner as the polystyrene brushes.
BibTeX:
@article{Harrison.Chaikin.ea2000,
  author = {Harrison, C. and Chaikin, P. M. and Huse, D. A. and Register, R. A. and Adamson, D. H. and Daniel, A. and Huang, E. and Mansky, P. and Russell, T. P. and Hawker, C. J. and Egolf, D. A. and Melnikov, I. V. and Bodenschatz, E.},
  title = {Reducing substrate pinning of block copolymer microdomains with a buffer layer of polymer brushes},
  journal = {Macromolecules},
  month = {February},
  year = {2000},
  volume = {33},
  number = {3},
  pages = {857},
  url = {http://pubs.acs.org/doi/abs/10.1021/ma991551g},
  doi = {10.1021/ma991551g}
}
Bodenschatz, E., Pesch, W. and Ahlers, G., "Recent developments in Rayleigh-Bénard convection", Annu. Rev. Fluid Mech., January 2000, Vol. 32, 709 pp.
Abstract: This review summarizes results for Rayleigh-Bénard convection that have been obtained over the past decade or so. It concentrates on convection in compressed gases and gas mixtures with Prandtl numbers near one and smaller. In addition to the classical problem of a horizontal stationary fluid layer heated from below, it also briefly covers convection in such a layer with rotation about a vertical axis, with inclination, and with modulation of the vertical acceleration.
BibTeX:
@article{Bodenschatz.Pesch.ea2000,
  author = {Bodenschatz, E. and Pesch, W. and Ahlers, G.},
  title = {Recent developments in Rayleigh-Bénard convection},
  journal = {Annu. Rev. Fluid Mech.},
  month = {January},
  year = {2000},
  volume = {32},
  pages = {709},
  url = {http://www.annualreviews.org/doi/abs/10.1146/annurev.fluid.32.1.709},
  doi = {10.1146/annurev.fluid.32.1.709}
}
Moisy, F., la Porta, A., Voth, G. and Bodenschatz, E., "Using cavitation as a probe of low-pressure filaments in turbulence", Vortex Structure and Dynamics, January 2000, Vol. 555, 263 pp.
Abstract: We report new observations of low-pressure filaments in a turbulent flow between counter-rotating disks. Cavitation from microscopic gas bubbles seeding the water is used to probe the structure of the pressure field. The spatial structure of the low-pressure events, mainly vertical filaments standing along the disks axis, are visualized using a high speed video system. The negative tail of the probability density functions of pressure is determined from light scattering measurements performed with a fast photo detector, and is found to be exponential. These observations highlight the importance of the large scales on the pressure fluctuations
BibTeX:
@book{Moisy.Porta.ea2000,
  author = {Moisy, F. and la Porta, A. and Voth, G. and Bodenschatz, E.},
  title = {Using cavitation as a probe of low-pressure filaments in turbulence},
  journal = {Vortex Structure and Dynamics},
  month = {January},
  year = {2000},
  volume = {555},
  pages = {263},
  url = {http://www.fast.u-psud.fr/~moisy/papers/moisylpvb_lnp00.pdf},
  doi = {10.1007/3-540-44535-8_17}
}
Berry, M. V. and Bodenschatz, E., "Caustics, multiply reconstructed by Talbot interference", J. Mod. Opt., February 1999, Vol. 46(2), 349 pp.
Abstract: In planar geometrical optics, the rays normal to a periodically undulating wavefront curve W generate caustic lines that begin with cusps and recede to infinity in pairs; therefore these caustics are not periodic in the propagation distance z. On the other hand, in paraxial wave optics the phase diffraction grating corresponding to W gives a pattern that is periodic in z, the period for wavelength lambda and grating period a being the Talbot distance, z(T) = a(2)/lambda, that becomes infinite in the geometrical limit. A model where W is sinusoidal gives a one-parameter family of diffraction fields, which we explore with numerical simulations, and analytically, to see how this clash of limits (that wave optics is periodic but ray optics is not) is resolved. The geometrical cusps are reconstructed by interference, not only at integer multiples of z(T) but also, according to the fractional Talbot effect, at rational multiples of z = z(T)p/q, in groups of q cusps within each grating period, down to a resolution scale set by lambda. In addition to caustics, the patterns show dark lanes, explained in detail by an averaging argument involving interference.
BibTeX:
@article{Berry.Bodenschatz1999,
  author = {Berry, M. V. and Bodenschatz, E.},
  title = {Caustics, multiply reconstructed by Talbot interference},
  journal = {J. Mod. Opt.},
  month = {February},
  year = {1999},
  volume = {46},
  number = {2},
  pages = {349},
  url = {http://www.tandfonline.com/doi/abs/10.1080/09500349908231276},
  doi = {10.1080/09500349908231276}
}
Ragnarsson, R., Utter, B. and Bodenschatz, E., "Superdendrites in directional solidification of polymer-solvent mixtures", Phase Transformations and Systems Driven Far From Equilibrium, 1998, Vol. 481, 65 pp.
Abstract: The directional solidification of the transparent binary alloy succinonitrile-poly(ethylene oxide) was studied in an experiment in which solidification speeds of about 2 mm/sec could be reached without loss of the linear temperature gradient. The low diffusivity of the polymer solute allowed the study of the dynamics of rapid solidification using an optical microscope. For both normal and doublonic dendrites we observed a transition to large triangular "superdendrites" above a certain solidification speed and we report measurements of the primary and secondary spacing as a function of the pulling speed. Our measurements suggest that the observed triangular shape is due to a decoupling of primary and secondary growth at large undercooling.
BibTeX:
@inproceedings{Ragnarsson.Utter.ea1998,
  author = {Ragnarsson, R. and Utter, B. and Bodenschatz, E.},
  title = {Superdendrites in directional solidification of polymer-solvent mixtures},
  journal = {Phase Transformations and Systems Driven Far From Equilibrium},
  year = {1998},
  volume = {481},
  pages = {65},
  url = {http://journals.cambridge.org/article_S1946427400243583},
  doi = {10.1557/PROC-481-65}
}
Plapp, B. B., Egolf, D. A. and Bodenschatz, E., "Dynamics and selection of giant spirals in Rayleigh-Bénard convection", Phys. Rev. Lett., December 1998, Vol. 81(24), 5334 pp.
Abstract: For Rayleigh-Bénard convection of a fluid with Prandtl number sigma = 1.4, we report experimental and theoretical results on a pattern selection mechanism for cell-filling, giant, rotating spirals. We show that the pattern selection in a certain limit can be explained quantitatively by a phase-diffusion mechanism. This mechanism for pattern selection is very different from that for spirals in excitable media.
BibTeX:
@article{Plapp.Egolf.ea1998,
  author = {Plapp, B. B. and Egolf, D. A. and Bodenschatz, E.},
  title = {Dynamics and selection of giant spirals in Rayleigh-Bénard convection},
  journal = {Phys. Rev. Lett.},
  month = {December},
  year = {1998},
  volume = {81},
  number = {24},
  pages = {5334},
  url = {http://prl.aps.org/abstract/PRL/v81/i24/p5334_1},
  doi = {10.1103/PhysRevLett.81.5334}
}
Voth, G. A., Satyanarayan, K. and Bodenschatz, E., "Lagrangian acceleration measurements at large Reynolds numbers", Phys. Fluids, September 1998, Vol. 10(9), 2268 pp.
Abstract: We report experimental measurements of Lagrangian accelerations in a turbulent water flow between counter-rotating disks for Taylor-Reynolds numbers 900 < R-lambda < 2000. Particle tracks were recorded by imaging tracer particles onto a position sensitive photodiode, and Lagrangian information was obtained from fits to the position versus lime data. Several challenges associated with extracting Lagrangian statistical quantities from particle tracks are addressed. The acceleration variance is obtained as a function of Reynolds number and shows good agreement with Kolmogorov (1941) scaling. The Kolmogorov constant for the acceleration variance is found to be a(0) = 7 +/- 3. (C) 1998 American institute of Physics.
BibTeX:
@article{Voth.Satyanarayan.ea1998,
  author = {Voth, G. A. and Satyanarayan, K. and Bodenschatz, E.},
  title = {Lagrangian acceleration measurements at large Reynolds numbers},
  journal = {Phys. Fluids},
  month = {September},
  year = {1998},
  volume = {10},
  number = {9},
  pages = {2268},
  url = {http://pof.aip.org/resource/1/phfle6/v10/i9/p2268_s1},
  doi = {10.1063/1.869748}
}
Egolf, D. A., Melnikov, I. V. and Bodenschatz, E., "Importance of local pattern properties in spiral defect chaos", Phys. Rev. Lett., April 1998, Vol. 80(15), 3228 pp.
Abstract: analyze experimental data from Rayleigh-Bénard convection in a large aspect ratio cell using a new, efficient method applicable to disordered striped patterns from biological, chemical, optical, and fluid systems. We present statistics of various local pattern properties such as the local wave-vector magnitude, local pattern orientation, and defect densities. Using these statistics, we provide quantitative evidence demonstrating that the stability boundaries derived for infinite systems are applicable to local patches within disordered patterns. We also present the first experimental observation of multiple length scales within spiral defect chaos.
BibTeX:
@article{Egolf.Melnikov.ea1998,
  author = {Egolf, D. A. and Melnikov, I. V. and Bodenschatz, E.},
  title = {Importance of local pattern properties in spiral defect chaos},
  journal = {Phys. Rev. Lett.},
  month = {April},
  year = {1998},
  volume = {80},
  number = {15},
  pages = {3228},
  url = {http://prl.aps.org/abstract/PRL/v80/i15/p3228_1},
  doi = {10.1103/PhysRevLett.80.3228}
}
Cakmur, R. V., Egolf, D. A., Plapp, B. B. and Bodenschatz, E., "Bistability and competition of spatiotemporal chaotic and fixed point attractors in Rayleigh-Bénard convection", Phys. Rev. Lett., September 1997, Vol. 79(10), 1853 pp.
Abstract: For Rayleigh-Bénard convection in a square cell with a fluid of Prandtl number sigma approximate to 1, we report experimental results on the bistability of the spatiotemporal chaotic state of spiral defect chaos (SDC) and a stationary state of ideal straight rolls (ISR). We present the first large aspect ratio experimental confirmation of the theoretical prediction of stable ISR in the parameter regime where typical initial conditions lead to SDC. As a function of the control parameter and for typical experimental initial conditions, we also find a transition in the selection between SDC and ISR which is mediated by front propagation. We characterize the transition with two measures, the spatial correlation length and the spectral pattern entropy, and find that the transition shows similarities to equilibrium phase transitions.
BibTeX:
@article{Cakmur.Egolf.ea1997,
  author = {Cakmur, R. V. and Egolf, D. A. and Plapp, B. B. and Bodenschatz, E.},
  title = {Bistability and competition of spatiotemporal chaotic and fixed point attractors in Rayleigh-Bénard convection},
  journal = {Phys. Rev. Lett.},
  month = {September},
  year = {1997},
  volume = {79},
  number = {10},
  pages = {1853},
  url = {http://prl.aps.org/abstract/PRL/v79/i10/p1853_1},
  doi = {10.1103/PhysRevLett.79.1853}
}
Roberts, B. W., Bodenschatz, E. and Sethna, J. P., "A bound on the decay of defect-defect correlation functions in two-dimensional complex order parameter equations", Physica D, December 1996, Vol. 99(2-3), 252 pp.
Abstract: Motivated by generic scale invariance, we examine the behavior of topological defect-defect correlation functions in two-dimensional systems driven out of equilibrium to regimes where they exhibit ''defect chaos''. Using the topological nature of the defects, we show that these defect-defect correlations cannot decay as slowly as predicted by generic scale invariance. We also provide numerical calculations that yield defect-defect correlation functions in the defect turbulence regime of the two-dimensional, anisotropic complex Ginzburg-Landau equation. These numerical results, which test the specific regime of broken square symmetry, do not appear to decay as slowly as predicted by the ideas of generic scale invariance. These results are in agreement with the analytical predictions.
BibTeX:
@article{Roberts.Bodenschatz.ea1996,
  author = {Roberts, B. W. and Bodenschatz, E. and Sethna, J. P.},
  title = {A bound on the decay of defect-defect correlation functions in two-dimensional complex order parameter equations},
  journal = {Physica D},
  month = {December},
  year = {1996},
  volume = {99},
  number = {2-3},
  pages = {252},
  url = {http://www.sciencedirect.com/science/article/pii/S0167278996001273},
  doi = {10.1016/S0167-2789(96)00127-3}
}
Morris, S. W., Bodenschatz, E., Cannell, D. S. and Ahlers, G., "The spatio-temporal structure of spiral-defect chaos", Physica D, October 1996, Vol. 97(1-3), 164 pp.
Abstract: We present a study of the recently discovered spatially extended chaotic state known as spiral-defect chaos, which occurs in low-Prandtl number, large-aspect ratio Rayleigh-Bénard convection. We employ the modulus squared of the space-time Fourier transform of time series of two-dimensional shadowgraph images to construct the structure factor S(k, omega). This analysis is used to characterize the average spatial and temporal scales of the chaotic state. We find that the correlation length and time can be described by power law dependences on the reduced Rayleigh number epsilon. These power laws have as yet no theoretical explanation.
BibTeX:
@article{Morris.Bodenschatz.ea1996,
  author = {Morris, S. W. and Bodenschatz, E. and Cannell, D. S. and Ahlers, G.},
  title = {The spatio-temporal structure of spiral-defect chaos},
  journal = {Physica D},
  month = {October},
  year = {1996},
  volume = {97},
  number = {1-3},
  pages = {164},
  url = {http://www.sciencedirect.com/science/article/pii/0167278996000966#},
  doi = {10.1016/0167-2789(96)00096-6}
}
deBruyn null, J. R., Bodenschatz, E., Morris, S. W., Trainoff, S. P., Hu, Y. C., Cannell, D. S. and Ahlers, G., "Apparatus for the study of Rayleigh-Bénard convection in gases under pressure", Rev. Sci. Instrum., June 1996, Vol. 67(6), 2043 pp.
Abstract: We review the history of experimental work on Rayleigh-Benard convection in gases, and then describe a modern apparatus that has been used in our experiments on gas convection. This system allows for the study of patterns in a cell with an aspect ratio (cell radius/fluid layer depth) as large as 100, with the cell thickness uniform to a fraction of a mu m, and with the pressure controlled at the level of one part in 10(5). This level of control can yield a stability of the critical temperature difference for the convective onset of better than one part in 10(4). The convection patterns are visualized and the temperature field can be inferred using the shadowgraph technique. We describe the flow visualization and image processing necessary for this. Some interesting results obtained with the system are briefly summarized. (C) 1996 American Institute of Physics.
BibTeX:
@article{.Bodenschatz.ea1996,
  author = {deBruyn, J. R. and Bodenschatz, E. and Morris, S. W. and Trainoff, S. P. and Hu, Y. C. and Cannell, D. S. and Ahlers, G.},
  title = {Apparatus for the study of Rayleigh-Bénard convection in gases under pressure},
  journal = {Rev. Sci. Instrum.},
  month = {June},
  year = {1996},
  volume = {67},
  number = {6},
  pages = {2043},
  url = {http://rsi.aip.org/resource/1/rsinak/v67/i6/p2043_s1},
  doi = {10.1063/1.1147511}
}
Plapp, B. B. and Bodenschatz, E., "Core dynamics of multi-armed spirals in Rayleigh-Bénard convection", Phys. Scr., April 1996, Vol. T67, 111 pp.
Abstract: We report experimental observations of the core dynamics of multi-armed, rotating spirals in Rayleigh-Bénard convection for a fluid with Prandtl number near one. In addition to the large-scale rotation of the spirals, we found a cyclic core motion within a central area of radius r congruent to n lambda/2, where n is the number of spiral arms ending in the core and lambda is the wavelength of the pattern. The dynamics of the core was much faster than the large-scale spiral rotation. We observed multiarmed spirals for which the two periods were commensurate and others for which they were incommensurate.
BibTeX:
@article{Plapp.Bodenschatz1996,
  author = {Plapp, B. B. and Bodenschatz, E.},
  title = {Core dynamics of multi-armed spirals in Rayleigh-Bénard convection},
  journal = {Phys. Scr.},
  month = {April},
  year = {1996},
  volume = {T67},
  pages = {111},
  url = {http://iopscience.iop.org/1402-4896/1996/T67/022/pdf/1402-4896_1996_T67_022.pdf},
  doi = {10.1088/0031-8949/1996/T67/022}
}
Ragnarsson, R., Ford, J. L., Santangelo, C. D. and Bodenschatz, E., "Rifts in spreading wax layers", Phys. Rev. Lett., April 1996, Vol. 76(18), 3456 pp.
Abstract: We report results on the rift formation between two freezing wax plates floating on molten wax which are pulled apart with constant velocity. Several distinct patterns were observed for increasing spreading rates; a stable straight rift, a spiky rift with fracture zones almost parallel to the spreading direction, and a regular zigzag pattern characterized by an angle dependent on the spreading rate. The characteristic angles of the zigzag pattern agree with a simple geometrical model. The coarsening of the pattern over time and the three-dimensional structure of the crust are also discussed.
BibTeX:
@article{Ragnarsson.Ford.ea1996a,
  author = {Ragnarsson, R. and Ford, J. L. and Santangelo, C. D. and Bodenschatz, E.},
  title = {Rifts in spreading wax layers},
  journal = {Phys. Rev. Lett.},
  month = {April},
  year = {1996},
  volume = {76},
  number = {18},
  pages = {3456},
  url = {http://prl.aps.org/abstract/PRL/v76/i18/p3456_1},
  doi = {10.1103/PhysRevLett.76.3456}
}
Bodenschatz, E., "Rayleigh-Bénard-Konvektion in Gasen: Hexagone, Spiralen und raumzeitliches Chaos", Physikalische Blätter, June 1994, Vol. 50(6), 527 pp.
BibTeX:
@article{Mueller.Bodenschatz.ea1994,
  author = {Bodenschatz, E.},
  title = {Rayleigh-Bénard-Konvektion in Gasen: Hexagone, Spiralen und raumzeitliches Chaos},
  journal = {Physikalische Blätter},
  month = {June},
  year = {1994},
  volume = {50},
  number = {6},
  pages = {527},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/phbl.19940500606/abstract},
  doi = {10.1002/phbl.19940500606}
}
Morris, S. W., Bodenschatz, E., Cannell, D. S. and Ahlers, G., "Spiral Defect Chaos In Large Aspect Ratio Rayleigh-Bénard Convection", Phys. Rev. Lett., September 1993, Vol. 71(13), 2026 pp.
Abstract: We report experiments on convection patterns in a cylindrical cell with a large aspect ratio. The fluid had a Prandtl number sigma almost-equal-to 1. We observed a chaotic pattern consisting of many rotating spirals and other defects in the parameter range where theory predicts that steady straight rolls should be stable. The correlation length of the pattern decreased rapidly with increasing control parameter so that the size of a correlated area became much smaller than the area of the cell. This suggests that the chaotic behavior is intrinsic to large aspect ratio geometries.
BibTeX:
@article{MORRIS.BODENSCHATZ.ea1993,
  author = {Morris, S. W. and Bodenschatz, E. and Cannell, D. S. and Ahlers, G.},
  title = {Spiral Defect Chaos In Large Aspect Ratio Rayleigh-Bénard Convection},
  journal = {Phys. Rev. Lett.},
  month = {September},
  year = {1993},
  volume = {71},
  number = {13},
  pages = {2026},
  url = {http://prl.aps.org/abstract/PRL/v71/i13/p2026_1},
  doi = {10.1103/PhysRevLett.71.2026}
}
Lerman, K., Bodenschatz, E., Cannell, D. S. and Ahlers, G., "Transient localized states In 2D binary liquid convection", Phys. Rev. Lett., June 1993, Vol. 70(23), 3572 pp.
Abstract: We report an experimental study of the onset of convection in ethanol/water mixtures confined in a circular cell of radial aspect ratio of 11.6. The initial bifurcation was to radial traveling waves; however, the linear state typically gave way to a nonlinear one in which convection alternately focused along one cell diameter and then another roughly perpendicular to the first. After a number of cycles, this state frequently contracted radially to a localized pulse of traveling-wave convection very similar to those observed in 1 D geometries. The pulses we observed either decayed back to pure conduction or grew to fill or nearly fill the cell.
BibTeX:
@article{LERMAN.BODENSCHATZ.ea1993,
  author = {Lerman, K. and Bodenschatz, E. and Cannell, D. S. and Ahlers, G.},
  title = {Transient localized states In 2D binary liquid convection},
  journal = {Phys. Rev. Lett.},
  month = {June},
  year = {1993},
  volume = {70},
  number = {23},
  pages = {3572},
  url = {http://prl.aps.org/abstract/PRL/v70/i23/p3572_1},
  doi = {10.1103/PhysRevLett.70.3572}
}
Bodenschatz, E., Cannell, D. S., Debruyn, J. R., Ecke, R., Hu, Y. C., Lerman, K. and Ahlers, G., "Experiments on three systems with non-variational aspects", Physica D, December 1992, Vol. 61(1-4), 77 pp.
Abstract: We present recent experimental results for three pattern-forming systems in which non-variational effects play an important role. The first is thermal convection in a shallow horizontal layer of fluid with temperature-dependent properties. In this system, a hexagonal lattice of convection cells forms at onset. This lattice becomes unstable to rolls when the temperature difference is increased sufficiently. In the ''roll'' state, the rolls are curved and the system forms stable rotating spirals. The rotating spiral states are associated with non-variational effects. Secondly, we discuss the formation of localized pulses in binary-mixture convection near onset. These pulses would not exist in a potential system. In narrow channels, they have been observed as stable states. In systems which are spatially extended in two dimensions they can form spontaneously, and can be long-lived. The third topic which we discuss is the Kuppers-Lortz instability in a thin horizontal layer of a Boussinesq fluid heated from below and rotated about a vertical axis. In this case, the pattern which forms immediately above the onset of convection is non-periodically time dependent even though the amplitude grows continuously from zero as the temperature difference is increased. The dominant mechanism of the instability is found to involve the motion of boundaries between coherent regions of convection rolls of a given orientation. The time dependence could not occur in a variational system. Since it occurs for arbitrarily small amplitudes, one might hope that it is amenable to theoretical analysis.
BibTeX:
@article{BODENSCHATZ.CANNELL.ea1992,
  author = {Bodenschatz, E. and Cannell, D. S. and Debruyn, J. R. and Ecke, R. and Hu, Y. C. and Lerman, K. and Ahlers, G.},
  title = {Experiments on three systems with non-variational aspects},
  journal = {Physica D},
  month = {December},
  year = {1992},
  volume = {61},
  number = {1-4},
  pages = {77},
  url = {http://www.sciencedirect.com/science/article/pii/016727899290150L},
  doi = {10.1016/0167-2789(92)90150-L}
}
Kaiser, M., Pesch, W. and Bodenschatz, E., "Mean flow effects in the electro-hydrodynamic convection in nematic liquid crystals", Physica D, November 1992, Vol. 59(4), 320 pp.
Abstract: On the basis of the weakly nonlinear analysis a set of two coupled amplitude equations is derived, which lead to a better understanding of the electro-hydrodynamic instability in nematic liquid crystals near onset. It is shown that the normal convective patterns are very sensitive against large scale flow (mean flow) modes, which are systematically included. Simulation of the equations shows typically a complex spatio-temporal behavior ("defect turbulence") very similar to the situation often observed in experiments.
BibTeX:
@article{KAISER.PESCH.ea1992,
  author = {Kaiser, M. and Pesch, W. and Bodenschatz, E.},
  title = {Mean flow effects in the electro-hydrodynamic convection in nematic liquid crystals},
  journal = {Physica D},
  month = {November},
  year = {1992},
  volume = {59},
  number = {4},
  pages = {320},
  url = {http://www.sciencedirect.com/science/article/pii/016727899290073V},
  doi = {10.1016/0167-2789(92)90073-V}
}
Bodenschatz, E., Debruyn, J. R., Ahlers, G. and Cannell, D. S., "Transitions between patterns in thermal convection", Phys. Rev. Lett., November 1991, Vol. 67(22), 3078 pp.
Abstract: We present experimental studies of the transitions between conduction, hexagons, and rolls in non-Boussinesq convection of gaseous CO2 in a cylindrical cell of radius-to-height ratio 86. Except for the transition from conduction to hexagons, transitions occur when the two states involved have nearly the same value of a generalized potential rather than at the stability limits. Conduction gives way to hexagons via the propagation of a front connecting the two states, while the transitions between hexagons and rolls are facilitated at the cell walls which appear to nucleate the minority state.
BibTeX:
@article{BODENSCHATZ.DEBRUYN.ea1991,
  author = {Bodenschatz, E. and Debruyn, J. R. and Ahlers, G. and Cannell, D. S.},
  title = {Transitions between patterns in thermal convection},
  journal = {Phys. Rev. Lett.},
  month = {November},
  year = {1991},
  volume = {67},
  number = {22},
  pages = {3078},
  url = {http://link.aps.org/doi/10.1103/PhysRevLett.67.3078},
  doi = {10.1103/PhysRevLett.67.3078}
}
Bodenschatz, E., Weber, A. and Kramer, L., "Interaction and dynamics of defects in convective roll patterns of anisotropic fluids", J. Stat. Phys., September 1991, Vol. 64(5-6), 1007 pp.
Abstract: We present an overview of the dynamics and interaction of defects in roll patterns of electroconvection in nematic liquid crystals (EHC). For the decay of an Eckhaus-unstable pattern we distinguish three regimes, depending on the width of the system perpendicular to the wavenumber mismatch. Motivated by recent experiments, we examine the annihilation process of defects in patterns with wavenumber near to band center, where the motion of the defects is dominated by the interaction. The comparison with the experiments shows that this process can be described even quantitatively within the framework of Ginzburg-Landau theory.
BibTeX:
@article{BODENSCHATZ.WEBER.ea1991,
  author = {Bodenschatz, E. and Weber, A. and Kramer, L.},
  title = {Interaction and dynamics of defects in convective roll patterns of anisotropic fluids},
  journal = {J. Stat. Phys.},
  month = {September},
  year = {1991},
  volume = {64},
  number = {5-6},
  pages = {1007},
  url = {http://link.springer.com/article/10.1007%2FBF01048810},
  doi = {10.1007/BF01048810}
}
Weber, A., Bodenschatz, E. and Kramer, L., "Defects In Continuous Media", Adv. Mater., April 1991, Vol. 3(4), 191 pp.
Abstract: Review: Defects often determine the mechanical and other properties of materials to a large extent. An understanding of these ordering imperfections would therefore facilitate the design of improved materials. Using nematic liquid crystals as an example, the various theoretical approaches to the description of defects are described and a correlation with the information obtained through experiment allows the success of the methods to be assessed.
BibTeX:
@article{WEBER.BODENSCHATZ.ea1991,
  author = {Weber, A. and Bodenschatz, E. and Kramer, L.},
  title = {Defects In Continuous Media},
  journal = {Adv. Mater.},
  month = {April},
  year = {1991},
  volume = {3},
  number = {4},
  pages = {191},
  url = {http://onlinelibrary.wiley.com/doi/10.1002/adma.19910030405/abstract;jsessionid=38F624AA2B00D4EDDCF3EC18379F2041.d01t02},
  doi = {10.1002/adma.19910030405}
}
Kramer, L., Bodenschatz, E. and Pesch, W., "Interaction and Dynamics of Defects In Anisotropic Pattern-forming Systems", Phys. Rev. Lett., May 1990, Vol. 64(21), 2588 pp.
BibTeX:
@article{KRAMER.BODENSCHATZ.ea1990,
  author = {Kramer, L. and Bodenschatz, E. and Pesch, W.},
  title = {Interaction and Dynamics of Defects In Anisotropic Pattern-forming Systems},
  journal = {Phys. Rev. Lett.},
  month = {May},
  year = {1990},
  volume = {64},
  number = {21},
  pages = {2588},
  url = {http://prl.aps.org/abstract/PRL/v64/i21/p2588_1},
  doi = {10.1103/PhysRevLett.64.2588}
}
Kramer, L., Bodenschatz, E., Pesch, W., Thom, W. and Zimmermann, W., "New Results On the Electrohydrodynamic Instability In Nematics - Invited Lecture", Liq. Cryst., 1989, Vol. 5(2), 699 pp.
Abstract: We present theoretical results on the threshold and near-threshold behaviour of electrohydrodynamic convection of planarly aligned nematics under D.C. and A.C. driving. We use the general three dimensional description and include the flexoelectric effect. The experimentally established threshold behaviour is captured in many cases quantitatively, an exception being the extended travelling patterns. Slightly above threshold the observed undulated rolls pose some problems. Defectmediated turbulence can presumably be explained by mean-flow effects.
BibTeX:
@article{KRAMER.BODENSCHATZ.ea1989,
  author = {Kramer, L. and Bodenschatz, E. and Pesch, W. and Thom, W. and Zimmermann, W.},
  title = {New Results On the Electrohydrodynamic Instability In Nematics - Invited Lecture},
  journal = {Liq. Cryst.},
  year = {1989},
  volume = {5},
  number = {2},
  pages = {699},
  url = {http://www.tandfonline.com/doi/abs/10.1080/02678298908045420},
  doi = {10.1080/02678298908045420}
}
Bodenschatz, E., Zimmermann, W. and Kramer, L., "On electrically driven pattern-forming instabilities in planar nematics", J. Phys. France, November 1988, Vol. 49(11), 1875 pp.
Abstract: The theoretical description of the threshold and near-threshold behavior of electrohydrodynamic convection in nematic liquid crystals in the (low-frequency) conduction regime is reconsidered. We present essentially the full three-dimensional linear stability analysis of the basic state and a major part of the weakly-nonlinear theory of the convective state. Boundary conditions at the upper and lower plates as well as the time dependence are treated rigorously but the flexoelectric effect is neglected. Related transitions like the periodic splay-twist instability, which is relevant in polymer materials with positive dielectric anisotropy, are also considered. We give criteria for finding the oblique-roll state and for the competition between different instabilities. Comparison with experiments is made wherever possible. Good qualitative and sometimes quantitative agreement is found.
BibTeX:
@article{BODENSCHATZ.ZIMMERMANN.ea1988,
  author = {Bodenschatz, E. and Zimmermann, W. and Kramer, L.},
  title = {On electrically driven pattern-forming instabilities in planar nematics},
  journal = {J. Phys. France},
  month = {November},
  year = {1988},
  volume = {49},
  number = {11},
  pages = {1875},
  url = {http://jphys.journaldephysique.org/index.php?option=com_article&access=doi&doi=10.1051/jphys:0198800490110187500&Itemid=129},
  doi = {10.1051/jphys:0198800490110187500}
}
Bodenschatz, E., Pesch, W. and Kramer, L., "Structure and dynamics of dislocations in anisotropic pattern-forming systems", Physica D, August 1988, Vol. 32(1), 135 pp.
Abstract: The motion of dislocations in convective roll patterns provides an important wavevector selection mechanism. In this work the structure and velocity of dislocations is calculated near threshold using amplitude equations appropriate for systems with an axial anisotropy. The fact that then the roll pattern has a preferred direction leads to characteristic differences to isotropic systems like Rayleigh-B?nard convection in simple fluids. Furthermore the nucleation process of dislocation pairs is discussed by analyzing the threshold solution that describes the nucleation barrier.
BibTeX:
@article{BODENSCHATZ.PESCH.ea1988,
  author = {Bodenschatz, E. and Pesch, W. and Kramer, L.},
  title = {Structure and dynamics of dislocations in anisotropic pattern-forming systems},
  journal = {Physica D},
  month = {August},
  year = {1988},
  volume = {32},
  number = {1},
  pages = {135},
  url = {http://www.sciencedirect.com/science/article/pii/0167278988900905},
  doi = {10.1016/0167-2789(88)90090-5}
}
Bodenschatz, E. and Kramer, L., "Influence of lateral boundaries on the Eckhaus instability in anisotropic pattern-forming systems", Physica D, July 1987, Vol. 27(1-2), 249 pp.
Abstract: Motivated by recent experiments on convective instabilities in nematic liquid crystals we examine near threshold the existence and stability of roll-type solutions in anisotropic pattern forming systems with boundaries perpendicular to the roll axis which reduce the amplitude. For half-infinite systems the wavenumber bands for existence and stability of solutions are unchanged, but the modulation wavenumber of the fastest-growing mode in the unstable region is increased. For finite width small deviations from the “universal Eckhaus ratio” View the MathML source are found, which vanish in the one-dimensional limit. Some parameters for quantitative comparison with experiments on the electrohydrodynamic instability are given for the standard nematic material MBBA.
BibTeX:
@article{BODENSCHATZ.KRAMER1987,
  author = {Bodenschatz, E. and Kramer, L.},
  title = {Influence of lateral boundaries on the Eckhaus instability in anisotropic pattern-forming systems},
  journal = {Physica D},
  month = {July},
  year = {1987},
  volume = {27},
  number = {1-2},
  pages = {249},
  url = {http://www.sciencedirect.com/science/article/pii/0167278987900169},
  doi = {10.1016/0167-2789(87)90016-9}
}
Rehberg, I., Bodenschatz, E., Winkler, B. and Busse, F. H., "Forced phase diffusion in a convection experiment", Phys. Rev. Lett., July 1987, Vol. 59(3), 282 pp.
Abstract: In a thermal-convection box the boundaries parallel to the convection rolls are replaced by ramps, i.e., smooth variations in the Rayleigh number from supercritical to subcritical values. Such a geometry selects a small wavelength band. The wavelength selected by the left and right ramps are not necessarily the same—resulting in a wavelength gradient. This gradient leads to forced phase diffusion: The convection pattern drifts from the short-wavelength end to the ramp selecting the longer wavelength. An experimental observation of this phenomenon is presented.
BibTeX:
@article{REHBERG.BODENSCHATZ.ea1987,
  author = {Rehberg, I. and Bodenschatz, E. and Winkler, B. and Busse, F. H.},
  title = {Forced phase diffusion in a convection experiment},
  journal = {Phys. Rev. Lett.},
  month = {July},
  year = {1987},
  volume = {59},
  number = {3},
  pages = {282},
  url = {http://prl.aps.org/abstract/PRL/v59/i3/p282_1},
  doi = {10.1103/PhysRevLett.59.282}
}