Bulletin of the American Physical Society
2005 APS March Meeting
Monday–Friday, March 21–25, 2005; Los Angeles, CA
Session A23: Focus Session: Biological Hydrodynamics I |
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Sponsoring Units: DFD DBP GSNP Chair: Peter Lenz, Universitaet Marburg Room: LACC 410 |
Monday, March 21, 2005 8:00AM - 8:12AM |
A23.00001: Overview: Biological Hydrodynamics Peter Lenz A short overview will be given at the beginning of the focus session 'Biological Hydrodynamics'. [Preview Abstract] |
Monday, March 21, 2005 8:12AM - 8:24AM |
A23.00002: Vortex formation in Daphnia swarms J\"{u}rgen Vollmer, Bruno Eckhardt, Christoph Lange, Attila G. Vegh We propose a self-propelled particle model for the swarming of Daphnia, which takes into account propulsion of the particles, mutual avoidance of close encounters and attraction to a center. Various key parameters are identified in order to arrive at a phase diagram for qualitatively different steady-state motions. We find that a vertex is formed only in a finite range of propulsions, and analyze its transitions to other states. Hydrodynamic interaction between the particles can stabilize the vortex and change its velocity profile. [Preview Abstract] |
Monday, March 21, 2005 8:24AM - 8:36AM |
A23.00003: The effect of shear flow on ordered suspensions of active particles Sudipto Muhuri, Madan Rao, Sriram Ramaswamy We explore the stability of orientationally ordered phases of a suspension of active particles, such as bacteria or motor- microtubule extracts, using a set of coarse grained hydrodynamic equations. While the orientationally ordered phase is linearly unstable, we show that it can be stabilised by the imposition of an external shear. We study the nonlinear response including shear banding in such active suspensions when subjected to steady or oscillating shear. [Preview Abstract] |
Monday, March 21, 2005 8:36AM - 8:48AM |
A23.00004: Effects of the changes in the wall shear stresses (WSS) acting on endothelial cells (EC) during the enlargement of Abdominal Aortic Aneurysms (AAA) Anne-Virginie Salsac, Steven Sparks, Juan C. Lasheras, Jean-Marc Chomaz The changes in the spatial and temporal distribution of the WSS and gradients of WSS during the enlargement of AAAs are important to understand the etiology and progression of this vascular disease, since they affect the wall structural integrity, primarily via the changes induced on the shape, functions and metabolism of the endothelial cells. PIV measurements were performed in aneurysm models, while changing systematically their size and geometry. Two regions with distinct patterns of WSS were identified. The region of flow detachment extends over the proximal half and is characterized by oscillatory WSS of very low mean. The region of flow reattachment, located distally, is dominated by large, negative WSS and sustained gradients of WSS that result from the impact of the vortex ring on the wall. Cultured EC were subjected to these two types of stimuli in vitro. The permeability of the endothelium was found to be largely increased in the flow detachment region. Endothelium cell-cell adhesion, proliferation and apoptosis were also affected by the high gradients of WSS. [Preview Abstract] |
Monday, March 21, 2005 8:48AM - 9:00AM |
A23.00005: Model Cilia - Experiments with Biomimetic Actuable Structures and Surfaces R. Lloyd Carroll, Dan Blum, Ben Evans, Rich Superfine The use of cilia to drive fluid flow is a common motif in living organisms, and in the tissues of higher organisms. By understanding the ways that cilia function (or do not function), potential therapies to treat human diseases (such as cystic fibrosis) may be devised. The complex hydrodynamics of flow in beating ciliary tissues (such as lung epithelial tissues) are challenging to study in cultured tissues, suggesting the need for model systems that will mimic the morphology and beat patterns of living systems. To reach this goal, we have fabricated high aspect ratio cilia-like structures with dimensions similar to those of a lung epithelial cilium (0.2 to 2.0 $\mu $m diameter by $\sim $6 to 10 $\mu $m long). The structures and surfaces are composed of a magneto-elastomeric nanocomposite, allowing the actuation of artificial cilia by magnetic fields. We have studied the flexibility of the materials under conditions of flow (in microfluidics channels), and will present theoretical and experimental data from various efforts at actuation. We will discuss details of the fabrication of the ciliated structures and present results of mechanical characterization. The impact of this work on the understanding of fluid flow above ciliated cells and tissues and potential applications of such model systems will also be described. [Preview Abstract] |
Monday, March 21, 2005 9:00AM - 9:36AM |
A23.00006: Quorum polarity and the dynamics of the zooming bionematic phase Invited Speaker: John O. Kessler Many species of bacteria are peritrichously flagellated, i.e. the long, helical, rapidly rotating flagella that propel them emerge out of motors that appear randomly distributed over the body of the bacterial cell. The organism considered here is {\it Bacillus subtilis}. The cell body is a rod approximately 4 $\mu$m long, 0.7$\mu$m in diameter; flagella are 3 or 4 times longer than the body. Swimming cells are pushed by the flagella, bundled into a braid of rotating helices. When the bacteria self concentrate into an approximately close-packed assemblage, rapidly moving (zooming) domains of aligned bacterial rods continually form and break apart. PIV measurements show that correlation times are seconds, lengths are hundreds of micrometers, transport of passive tracers is superdiffusive.Below a threshold concentration there is no collective dynamic. A theory of this zooming bionematic phase will be presented, together with measurements and video sequences. The theory considers hydrodynamic cell-cell and collective interactions, the collectively generated flow of the suspending water relative to the cells, and the dynamics of helix bundle flipping, yielding quorum polarity within a given zooming domain. Quorum sensing of signalling molecules and molecular transport generally are pertinent microbiological applications. [Preview Abstract] |
Monday, March 21, 2005 9:36AM - 9:48AM |
A23.00007: Rheology and dynamics of active motor-filament mixtures M. Cristina Marchetti, Aphrodite Ahmadi, Tanniemola B. Liverpool We have developed a hydrodynamic description of both the isotropic and polarized phases of mixtures of polar filaments and molecular motors taking into account the fluctuations in both the motor and the filament densities. The various couplings in the hydrodynamic equations are related to microscopic parameters by comparing continuum equations written down on the basis of symmetry considerations to those obtained from a microscopic model of motor-filament interaction. Due to the anisotropy of filament diffusion, motors are capable of generating net filament motion relative to the solvent, resulting in filament convection along the direction of local alignment. The effect of this new term on traveling wave in the polarized phase is analyzed by numerical solutions of the nonlinear hydrodynamic equations. The equations are also used to study the linear rheology of active solutions (stress generated due to an imposed shear flow). [Preview Abstract] |
Monday, March 21, 2005 9:48AM - 10:00AM |
A23.00008: Two Dimensional State Transition of a Swarming Model Yao-li Chuang, Daniel Marthaler, Maria D`Orsogna, Lincoln Chayes, Andrea Bertozzi A rotating mill is widely seen in swarming patterns of various species, such as ants, fishes, or daphnia. Levine et al. (2000) proposed an individual based model which produces a pair of co- existing clockwise and counter-clockwise mills on top of each other while a unified rotating mill can be achieved by switching the formula of the self-propulsion to an ensemble average. Without changing its fundamental concepts, we modify the model to include a Rayleigh-type self-driving mechanism, which has a cleaner connection to its continuum limit, i.e., macroscopic description, where analysis can be more efficiently done. By varying parameter values, we find that the modified model goes through a three-stage transition from the co-existing state to the unified state. We also compare the numerical results of the model and of its continuum counterpart. [Preview Abstract] |
Monday, March 21, 2005 10:00AM - 10:12AM |
A23.00009: Dynamics of the Chemotactic Boycott Effect Luis Cisneros, Chris Dombrowski, John Kessler, Raymond Goldstein, Charles Wolgemuth, Idan Tuval Aerobic bacteria often live in thin fluid layers on irregular surfaces, near solid-air-water contact lines where the interplay between fluid interface geometry, nutrient transport, and chemotaxis is central to the micro-ecology. To elucidate these processes, we use the simplified geometry of a sessile drop and provide direct experimental evidence for the ``chemotactic Boycott effect" in suspensions of {\it B. subtilis}: upward oxygentaxis toward the drop surface leads to accumulation of cells in a thin layer, which flows down to the contact line and produces there a persistent vortex which traps cells near the meniscus. These phenomena are explained quantitatively with a mathematical model consisting of coupled oxygen diffusion and consumption, chemotaxis, and viscous fluid dynamics; they are shown to be associated with a singularity in the chemotactic dynamics at the contact line. [Preview Abstract] |
Monday, March 21, 2005 10:12AM - 10:24AM |
A23.00010: A new parameter identification method to obtain change in smooth musclecontraction state due to mechanical skin irritation Daniela Bauer, Reinhard Grebe, Alain Ehrlacher A light scratch with a needle induces histamine and neuropetide release on the line of stroke and in the surrounding tissue. Histamine and neuropeptides are vasodilaters. They create vasodilation by changing the contraction state of the vascular smooth muscles and hence vessel compliance. Smooth muscle contraction state is very difficult to measure. We propose an identification procedure that determines change in compliance. The procedure is based on numerical and experimental results. Blood flow is measured by Laser Doppler Velocimetry. Numerical data is obtained by a continuous model of hierarchically arranged porous media of the vascular network [1]. We show that compliance increases after the stroke in the entire tissue. Then, compliance decreases in the surrounding tissue, while it keeps increasing on the line of stroke. Hence, blood is transported from the surrounding tissue to the line of stroke. Thus, higher blood volume on the line of stroke is obtained. [1] Bauer, D., Grebe, R. Ehrlacher, A., 2004. A three layer continuous model of porous media to describe the first phase of skin irritation. J. Theoret. Bio. in press [Preview Abstract] |
Monday, March 21, 2005 10:24AM - 10:36AM |
A23.00011: Bacteriophage-mediated indirect competition in B.bronchiseptica:Experiment and Theory Jaewook Joo, Reka Albert, Eric Harvill We demonstrate empirical evidence of bacteriophage-mediated indirect competition in microbiological populations. The bacteriophage-mediated competition acts between two genetically identical bacterial strains that differ only in that one is the carrier of a temperate lysogenic phage and the other is susceptible to the phage. We observe that in spite of the absence of direct competition the strain with lysogenic phage successfully invades and outcompetes the resident strain susceptible and more vulnerable to the phage. The amount of indirect competition is dependent on the susceptibility and the phage-induced mortality of the resident bacterial strain. We develope mathematical models of the phage-mediated competition and reproduce its dependence on mortality. [Preview Abstract] |
Monday, March 21, 2005 10:36AM - 10:48AM |
A23.00012: Collective motion, superdiffusion, and non-thermal noise in active bacterial baths Daniel T.N. Chen, L.A. Hough, M.F. Islam, A.W.C. Lau, T.C. Lubensky, A.G. Yodh We present experimental studies of the dynamics of concentrated bacterial colonies in three-dimensions. The bacteria we use is e. coli at varying densities. By analyzing the trajectories of colloidal spheres embedded in these bacterial bath suspensions, we extract one- and two-point mean square displacements which exhibit superdiffusion crossing over to a diffusive regime. When combined with independent measurements of the response function of the suspension, the data enable us to extract the noise spectrum of the bath. This work was supported by NSF DMR02-03378 and NASA NAG3-2172 [Preview Abstract] |
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