Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session B49: Active Matter: Recent Theoretical AdvancesInvited
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Sponsoring Units: DBIO GSNP GSOFT Chair: Yuhai Tu, IBM T. J. Watson Research Center Room: 396 |
Monday, March 13, 2017 11:15AM - 11:51AM |
B49.00001: From MIPS to Vicsek: A comprehensive phase diagram for self-propelled rods Invited Speaker: Xiaqing Shi Self-propelled rods interacting by volume exclusion is one of the simplest active matter systems. Despite years of effort, no comprehensive picture of their phase diagram is available. Furthermore, results on explicit rods are so far largely disconnected from those obtained on the relatively better understood cases of motility induced phase separation (MIPS) of (usually) isotropic active particles, and from our current knowledge of Vicsek-style aligning point particles. In this talk, I will present a complete phase diagram of a generic model of self-propelled rods and show how it is connected to both MIPS and Vicsek worlds. [Preview Abstract] |
Monday, March 13, 2017 11:51AM - 12:27PM |
B49.00002: The world of Vicsek-like models and related experiments Invited Speaker: Hugues Chate TBD [Preview Abstract] |
Monday, March 13, 2017 12:27PM - 1:03PM |
B49.00003: Phenomenological higher-order PDE models for active suspensions Invited Speaker: Jorn Dunkel A common characteristic of many active fluids, from bacterial suspensions to ATP-driven microtubule networks, is the emergence of turbulent flow structures that exhibit a preferred vortex scale. Although the biophysical origins of this self-organized length scale selection are not yet well understood, the existence of a dominant wavelength suggests that these systems can be efficiently described through phenomenological higher-order PDE models. In this talk, I will first outline how one can derive such PDEs from stochastic micro-swimmer models. Subsequently, we will consider two specific examples: a fourth-order Q-tensor model for active microtubule bundles (New J Phys 18: 093006, 2016), and a generalized Navier-Stokes model for the solvent flow in active suspensions (arXiv:1608.01757 and 1611.08075). Our discussion will focus on the comparison with recent experiments and on specific model predictions, such as the possibility of a helicity-driven inverse cascade in 3D active fluids. [Preview Abstract] |
Monday, March 13, 2017 1:03PM - 1:39PM |
B49.00004: Mechanical Pressure of self-propelled particles Invited Speaker: Julien Tailleur Pressure is the mechanical force per unit area that a confined system exerts on its container. For macroscopic equilibrium systems, the pressure depends only on bulk properties (density, temperature, etc.) through an equation of state. For active systems containing self-propelled particles (e.g. migrating cells or molecular motors) the pressure instead generically depends on the precise interactions between the particles and the confining walls. The mechanical pressure of an active system is therefore generically not given by an equation of state. I will show how one is nevertheless recovered in certain limiting cases. More generally, I will discuss the various interesting properties of the pressure of active fluids. [Preview Abstract] |
Monday, March 13, 2017 1:39PM - 2:15PM |
B49.00005: Birds, magnets, soap, and sandblasting: surprising connections in the theory of incompressible flocks Invited Speaker: John Toner In this talk I’ll describe the hydrodynamic theory of the motion of incompressible flocks: that is, collections of self-propelled entities (“birds”) that are packed so tightly together that their density cannot change as they move. In two dimensions, this problem can be mapped onto an equilibrium magnet with a peculiar constraint. This problem, in turn, can be shown to be equivalent to a 2d smectic (“soap”), with the flow lines of the flock playing the role of the smectic layers. Finally, this smectic problem can be mapped onto the 1+1 dimensional KPZ equation, which describes the growth or corrosion (“sandblasting”) of a one dimensional interface. The scaling properties of this last system, which have been known exactly for a long time, can thereby be used to determine those of incompressible 2d flocks. One important implication of the resulting scaling laws is that such flocks can exhibit long-ranged order in two dimensions, unlike their equilibrium counterparts. [Preview Abstract] |
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