Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session M33: Kinetic Theory and Its Applications in the Physical, Biological and Social SciencesFocus

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Sponsoring Units: DSOFT GSNP Room: 505 
Wednesday, March 4, 2020 11:15AM  11:51AM 
M33.00001: Kinetic theory of defect dynamics in active nematics Invited Speaker: M Cristina Marchetti Active nematics are fluids of elongated active agents that exhibit selfsustained flows and liquid crystalline order. Realizations include suspensions of cytoskeletal filaments and motor proteins, epithelial tissue, and vibrated layers of granular rods. At high activity, active nematics exhibit spatiotemporal chaotic, turbulentlike flows with proliferation of topological defects. In this talk I will show that, focusing on the defects as the relevant quasiparticles driving the nonequilibrium dynamics, we can formulate a kinetic theory of the active defect gas and describe the onset of active turbulence as activitydriven defect unbinding. By coarsegraining the kinetic theory, we obtain a hydrodynamic description of the active defect gas. 
Wednesday, March 4, 2020 11:51AM  12:27PM 
M33.00002: Kinetic theory for financial Brownian motion: a microscopic model based on forex data analysis and its meanfield theory Invited Speaker: Kiyoshi Kanazawa Kinetic theory is a powerful mathematical framework in statistical physics and has been applied to understand physical Brownian motions from their microscopic setups. In light of this success, it is an interesting attempt to extend kinetic theory for various social phenomena beyond physics. In particular, we have focused on its application to financial markets since they exhibit random motions quite similar to physical Brownian motion. In this presentation, we will show our recent kinetic approach (K. Kanazawa et al., PRL 2018; PRE 2018) to financial Brownian motion in the context of highfrequency data analyses. First, we have analyzed trading log data of individual traders, to identify the microscopic dynamics in a forex market. The proposed microscopic model of the financial market is then solved systematically via the kinetic theory: we derive the Liouville equation, the BogoliubovBornGreenKirkwoodYvon hierarchy, the Boltzmann equation, and the Langevin equation for the financial market as a parallel mathematical program to conventional kinetic theory. Our work highlights the potential power of kinetic theory to understand social phenomena from their microscopic dynamics. 
Wednesday, March 4, 2020 12:27PM  12:39PM 
M33.00003: A generalization of the GlansdorffPrigogine criterion for stability based on information geometry and thermodynamic uncertainty relationships Sosuke Ito To consider the relationship between the excess entropy production and the Fisher information of time, we have generalized the GlansdorffPrigogine criterion for stability. In information geometry, the Fisher information of time is the speed of a statistical manifold, and then our generalized criterion can be interpreted as a criterion by acceleration (deceleration) of this speed. If this speed is accelerated (decelerated), dynamics is unstable (stable). 
Wednesday, March 4, 2020 12:39PM  12:51PM 
M33.00004: Pattern Selection of Shallow Suspensions of Shrimp Andrea Welsh, Krishma Singal, Divya Velivela, Ellie Finch, Michael Barnhill, Flavio H Fenton Swarming, a selforganization phenomenon which occurs in many biological systems, can emerge spontaneously, arising without any sort of centralized control or leadership. Many crustaceans, such as brine shrimp, produce swarms, in which individuals cluster together rather than spreading out uniformly in their environment. The motion of these crustaceans is also affected by light due to their phototactic nature. The size and distribution of these swarms are governed by local interactions between individuals but are also affected by the boundaries of the container. We discuss the threedimensional patterns that can be observed in brine shrimp swarms, specifically of the Great Salt Lake strain of Artemia franciscana, at high concentration . We experimentally test the effects of average concentration, temperature, and container size on the basic length and times scales of the patterns, the type patterns selected, and the stability of those patterns. We then discuss the physical mechanism behind the formation and selection of these patterns. 
Wednesday, March 4, 2020 12:51PM  1:03PM 
M33.00005: Hydrodynamics of Active Lévy Matter Andrea Cairoli, Chiu Fan Lee Collective ordered motion is often modeled within the framework of active fluids, where hydrodynamic descriptions typically rely on microscopic models of active selfpropelled particles subjected to alignment interactions and reorientational dynamics. However, singleparticle superdiffusion is also widespread in biology as it can represent an optimal search strategy for living organisms. Nevertheless, the collective properties of interacting systems exhibiting such anomalous diffusive dynamics  denoted here as active Lévy matter  cannot be captured by current active fluid theories. Here, we formulate the hydrodynamic description of active Lévy matter by coarsegraining a microscopic model of alignment interacting active particles performing superdiffusion manifest as Lévy flights. This theory predicts characteristic disordered and ordered phases. Linear stability analysis suggests that the phase transition can be critical. This analysis highlights the need for more realistic models of active matter integrating both anomalous diffusive motility and interparticle interactions and suggests that these models can shed new light on the universal properties of active systems. 
Wednesday, March 4, 2020 1:03PM  1:15PM 
M33.00006: Towards a statistical mechanics of chiral active gases Ming Han, Michel Fruchart, Colin Scheibner, Suriyanarayanan Vaikuntanathan, William Thomas Mark Irvine, Juan De Pablo, Vincenzo Vitelli Statistical mechanics allows to describe materials near equilibrium using just a few thermodynamic variables. Extending this approach farfromequilibrium is tempting but often unfeasible. In this talk, we present the footprints of a statistical mechanical treatment of chiral active fluids composed of selfspinning particles. The nature of selfspinning breaks timereversal symmetry and detailed balance. Nevertheless, such active fluids converge to a nonequilibrium steady state exhibiting Boltzmann statistics with a universal effective temperature determined by the active torques. Beyond exhibiting analogues of common thermodynamic properties, the chiral active gas also displays a dissipationless odd viscosity in addition to the shear viscosity. Both transport coefficients satisfy a Kubo relation in terms of our effective temperature. We show that the stochastic dynamics of this many body system can be represented as a chiral Brownian motion in shearstress space. Using this assumption, we derive analytically the full frequency dependence of the viscosities in agreement with simulations. 
Wednesday, March 4, 2020 1:15PM  1:27PM 
M33.00007: Hydrodynamic memory and driven microparticle transport: hedging against fluctuating sources of energy Sean Seyler, Steve Pressé In a viscous fluid, the motion of an accelerating particle is retained as an imprint on the vorticity field, giving rise to the famous t^{3/2} decay of the velocity autocorrelation. For nonuniform particle motion at low Reynolds number, this hydrodynamic memory effect is captured by the BassetBoussinesqOseen (BBO) equation, which can be derived from various physical perspectives, including (fluctuating) hydrodynamics and kinetic theory. Moreover, finitetemperature dynamics can be modeled by using fluctuationdissipation to reincorporate (correlated) thermal noise, turning BBO into a generalized Langevin equation. In this work, we numerically solve the BBO equation to simulate driven microparticles and show that hydrodynamic memory generally reduces transport friction, particularly when driving forces do not vary smoothly. Remarkably, this enables coasting over uneven potentials that otherwise trap particles modeled by pure Stokes drag. Our results are germane to questions surrounding intracellular transport efficiency and, more generally, provide direct physical insight into the role of particlefluid coupling in microparticle transport. 
Wednesday, March 4, 2020 1:27PM  1:39PM 
M33.00008: Cargo transport by dissipative solitonsdirector bullets in nematics Bingxiang Li, RuiLin Xiao, Sergij V Shiyanovskii, Oleg D Lavrentovich An alternating current (AC) electric field applied to a uniformly aligned nematic liquid crystal is capable to excite and drive particlelike threedimensional dissipative solitons, the socalled director bullets [1, 2]. The bullets represent regions of a distorted molecular orientation of broken leftright or headtail symmetry that propagate perpendicularly to the driving field. Here, we demonstrate that the bullets can be generated around colloidal spheres with both tangential and radial anchoring, dispersed in the nematic. The effect represents a solitonmediated liquid crystalenabled electrophoresis, in which the electric field first breaks the quadrupolar symmetry of the director field around the sphere and then drives oscillations of this asymmetric director field to power a directional motion of the sphere dressed in the soliton. The effect can be used to transport microscopic cargo when modes of liquid crystalenabled elecrtokinetics based on static asymmetry are ineffective, which is the case of tangentially anchored inclusions. 
Wednesday, March 4, 2020 1:39PM  1:51PM 
M33.00009: Brownian motion in confinement Maxime Lavaud, Pierre Soulard, Vincent Bertin, David Dean, Raphael Sarfati, Elie Raphael, Yann Louyer, Thomas Salez, yacine Amarouchene Brownian motion in confinement is a paradigm for numerous biological situations. Here, we study the diffusion of micrometersized beads in water confined between two walls that are separated by a micrometric distance. Using holographic microscopy, we track the particles in three dimensions with a precision approaching the nanometric range. From statistical analysis performed on the individual trajectories, we extract the local diffusion coefficient as a function of the position of the bead in the microcavity. The experimental results are in good agreement with the numerical and analytical predictions — which paves the way towards the study of other situations of confinement, such as soft boundaries. 
Wednesday, March 4, 2020 1:51PM  2:03PM 
M33.00010: Superdiffusion and diffusion in active matter using a stochastic field theory Patrick Underhill, Peter R Kramer One important impact of the outofequilibrium nature of active matter is the enhanced fluctuations in the system and the mixing of passive tracers. Interesting properties arise in both small and large concentrations of the active objects. Agent based models can incorporate fluctuations and interactions, but are limited to smaller systems. It can also more difficult to extract physical insight from the results. One of the most successful alternative approaches has been a mean field theory. However, in some situations the mean field theory makes predictions that differ significantly from experiments and direct (agent or particle based) simulations. There are also some quantities that cannot be calculated by the mean field theory. In this talk, we will describe our new approach which uses a stochastic field to overcome the limitations of the mean field assumption. The characteristic superdiffusion observed for passive tracers can be computed along with the longtime diffusivity. We will describe how this enhanced diffusion depends on the characteristics of the active particles and their hydrodynamic interactions. 

M33.00011: Disordered hyperuniform state of circularly swimming algae Mingji Huang, Wensi Hu, Siyuan Yang, QuanXing Liu, Hepeng Zhang Active matter comprises of individual units that convert locally stored energy into mechanical motion. Interactions between active units can lead to a wide range of collective phenomena, which do not exist in equilibrium systems. Here we show that density fluctuations in active system can be greatly suppressed. Our experiments are carried out with marine algae (Symbiodinium voratum). Cells swim in circles at interface and longranged nature of hydrodynamic interactions suppresses density fluctuations; disordered hyperuniform state is observed over a wide range of conditions. Emergence of hyperuniformity can be quantitatively reproduced in a numerical model whose main ingredients are hydrodynamic interactions and uncorrelated random cell motion. Our results demonstrate a new form of collective state in active matter and suggest the possibility to use hydrodynamic flow to assemble active matter into hyperuniform states. 
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