Bulletin of the American Physical Society
2007 APS March Meeting
Volume 52, Number 1
Monday–Friday, March 5–9, 2007; Denver, Colorado
Session Y2: Collective Motions of Living and Nonliving Self-Propelled Particles |
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Sponsoring Units: DBP Chair: Frank Moss, University of Missouri-St. Louis Room: Colorado Convention Center Four Seasons 4 |
Friday, March 9, 2007 11:15AM - 11:51AM |
Y2.00001: Swarming by Nature and by Design Invited Speaker: The cohesive movement of a biological population is a commonly observed natural phenomenon. With the advent of platforms of unmanned vehicles, this occurrence is attracting renewed interest from the engineering community. This talk will review recent research results on modeling and analysis of biological swarms with some connection to the design ideas for efficient algorithms to control groups of autonomous agents. For biological models we consider two kinds of systems: driven particle systems based on force laws and continuum models based on kinematic and dynamic rules. Both models involve long-rage social attraction and short range dispersal and yield patterns involving clumping, mill vortices, and surface-tension-like effects. [Preview Abstract] |
Friday, March 9, 2007 11:51AM - 12:27PM |
Y2.00002: Direct and Indirect Mechanisms for Collective Behavior in the Spatial Dynamics of Plankton Invited Speaker: Plankton are the dark matter of life in the sea. Though they are poorly understood and usually unseen, plankton dominate the biological dynamics that ultimately determine characteristics important to humans ranging from sustainable fish harvests to rates of carbon sequestration. Through a variety of social, sensory and biophysical mechanisms, plankton display collective behaviors that profoundly alter ecological systems. These collective behaviors include formation of large, coherent social groups (e.g. swarms and schools); alteration of water's mechanical properties (e.g. viscosity) and motion (e.g. bioconvection); and induction of self-organized spatial heterogeneity. In this talk, I will describe recent individual-level observations of collective plankton behaviors. I will develop mathematical descriptions that link some of these behaviors to spatio-temporal patterns in plankton populations. Finally, I will outline some important unsolved problems in plankton ecology that can be addressed using analytical and computational approaches. [Preview Abstract] |
Friday, March 9, 2007 12:27PM - 1:03PM |
Y2.00003: Predicting the growth of fractal particle agglomeration networks with graph theoretical methods. Invited Speaker: We study an electromechanical system [J. Jun, A. Hubler, \textit{PNAS} \textbf{102}, 536 (2005); J. Jun, Ph.D. thesis, UIUC (2004)], where conducting particles self-organize into dendritic patterns under the influence of an electric field for the purpose of collecting and transporting charge. The system forms stable open-loop networks with many reproducible statistical quantities, such as the number of termini and the number of branch points, but the final topology of the network is sensitive to the initial conditions of the particles. Small differences in the initial configuration may lead to very different stationary states. We present robust and reliable ensemble prediction algorithms for the growth of such fractal charge transportation networks. These predictors may lead to the discovery of common properties and serve a prototype to predict fractal growth in other areas, including neural systems; blood vessel systems, river networks, and dielectric break through. [Preview Abstract] |
Friday, March 9, 2007 1:03PM - 1:39PM |
Y2.00004: Swarming Behavior of Particle-Like Waves in Excitable Media Invited Speaker: Unstable waves in the photosensitive Belousov-Zhabotinsky reaction are stabilized by global feedback, and the motion of these waves is controlled by imposing excitability gradients that are regulated by a secondary feedback loop. We describe studies of these particle-like waves interacting with one another via realistic excitability potentials. Simulations and experiments with increasing numbers of mutually coupled waves have demonstrated very complex swarming behavior. Measures for characterizing the behavior, such as the average velocity and group size, will be discussed. We will also describe experiments and simulations of stabilized waves navigating excitability landscapes. Of particular interest is the interaction of a swarm with various obstacles as it navigates through the medium. [E. Mihaliuk, T. Sakurai, F. Chirila, and K. Showalter, Phys. Rev. E 65, 65602 (2002); T. Sakurai, E. Mihaliuk, F. Chirila, and K. Showalter, Science 296, 2009-2012 (2002); V. S. Zykov and K. Showalter, Phys. Rev. Lett. 94, 068302 (2005).] [Preview Abstract] |
Friday, March 9, 2007 1:39PM - 2:15PM |
Y2.00005: Chemically Powered Nanomotors Invited Speaker: Molecular motors play important roles in transport in biological systems. These molecular machines are powered by chemical energy and operate in the regime of low Reynolds number hydrodynamics. Recently a class of simple inorganic molecular motors has been constructed and studied experimentally [1,2]. These motors are bimetallic rods, one end of which is chemically active. The talk will describe simple mesoscopic models for the motion of such nanomotors. The motor consists of two linked spheres, one of which catalyzes the conversion between two chemical species. The chemical species interact differently with the the two spheres in the dimer. The nano-dimer motor is solvated by a molecules treated at a mesoscopic level whose evolution is governed by multi-particle collision dynamics. The dynamics conserves mass, momentum and energy so that coupling between the nanomotor and the hydrodynamic modes of the solvent is treated correctly. The simulations allow one to explore the mechanisms of the chemically powered motion and the effects of fluctuations on the motor dynamics. \newline \newline [1] W. F. Paxton, et al., ``Catalytic Nanomotors: Autonomous Movement of Striped Nanorods,'' J. Am. Chem. Soc. (JACS), 126 (41), 13424 (2004). \newline [2] S. Fournier-Bidoz, et al. ``Synthetic Self-Propelled Nanorotors,'' Chem. Commun., (4), 441 (2005). [Preview Abstract] |
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