Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session R25: Active Matter |
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Sponsoring Units: GSNP DSOFT Chair: Yuhai Tu, IBM TJ Watson Research Center Room: 402 |
Thursday, March 5, 2020 8:00AM - 8:12AM |
R25.00001: Propagating Activity Fronts in Columns fo Fire Ants Caleb Anderson, Alberto Fernandez-Nieves, Guillermo Goldsztein For the past three decades, the study of active matter has revealed rich physics and universal behaviors, such as collective motion, across a wide variety of biological and synthetic systems with seemingly disparate particle interactions. Here we present our surprise observation and measurements of stable activity fronts propagating through two-dimensional columns of thousands of fire ants. We then propose both computational and analytical models to explain the origin of these macroscopic non-linear fronts from simplified pairwise interactions between ants. Finally, we finish by comparing these fronts to other instances of collective motion observed in active systems. |
Thursday, March 5, 2020 8:12AM - 8:24AM |
R25.00002: Self- and air-driven fluidization of black soldier fly larvae Olga Shishkov, David Hu, Daniel I Goldman Active systems can be driven via internal activity of individual elements or via external mechanical forcing. Here we study a living system in which both internal and external activity can be varied. In laboratory experiments, we confine thousands of ~10 mm long black soldier fly larvae in an air fluidized bed (~4 larva lengths in diameter, 10 in height ) and study the collective and individual dynamics. When larvae are not externally fluidized, due to their internal activity they self-pack and the height of the column of larvae decreases over time to a steady state value. In steady state, larval motion is distributed heterogeneously and transiently, with regions of motion and clustering appearing and disappearing throughout the bed volume. These dynamics can be altered by gentle flow of air to the bed: like fluidized beds of inactive (non-living) particles, steady-state larval collective volume (column height) increases with increasing air flow, and the persistence of the transient regions change. Further, external fluidization has the same effect as the addition of food, where activity also causes large-scale mixing. |
Thursday, March 5, 2020 8:24AM - 8:36AM |
R25.00003: Stochastic thermodynamics for self-propelled particles Grzegorz Szamel We present a generalization of stochastic thermodynamics to systems of active particles, which move under the combined influence of stochastic internal self-propulsions (activity) and a heat bath. The generalization relies upon a formal similarity of an active system and a system consisting of two subsystems interacting with different heat reservoirs and coupled by a non-symmetric interaction. The resulting thermodynamic description closely follows the standard stochastic thermodynamics. In particular, total entropy production, Δstot, can be decomposed into housekeeping, Δshk, and excess, Δsex, parts. Both Δstot and Δshk satisfy fluctuation theorems. The average rate of the steady-state housekeeping entropy production can be related to the violation of the fluctuation-dissipation theorem via a Harada-Sasa relation. The excess entropy production enters into a Hatano-Sasa-like relation, which leads to a generalized Clausius inequality involving the change of the system's entropy and the excess entropy production. |
Thursday, March 5, 2020 8:36AM - 8:48AM |
R25.00004: Odd viscosity in active materials: microscopic origin and 3D effects Tomer Markovich, Tom Lubensky Active materials are composed of many components that convert energy from the environment into directed mechanical motion, thus locally breaking time reversal symmetry (TRS). Examples of active materials go beyond living systems such as bacteria and is also realized in e.g. colloidal rollers. A striking phenomenon of breaking TRS is the possible appearance of odd viscosity. Onsager reciprocal relations require that when TRS holds the viscosity tensor is symmetric for exchanging its first and last pair of indices. However, when TRS is broken, Onsager relations predict an odd viscosity that is both odd under TRS and under the change of indices. Such odd viscosity is non-dissipative and should thus be derivable from a Hamiltonian theory. Active materials innately break TRS, which led to recent studies of odd viscosity in 2D active materials. In this talk I will present a novel microscopic Hamiltonian theory for odd viscosity, valid also in 3D. Our theory give rise to intriguing 3D effects such as generalization of Bernoulli’s principle, propagation of bulk waves, and a few types of unidirectional surface waves. We further predict that odd viscosity should emerge in actomyosin gels and bacterial suspensions. |
Thursday, March 5, 2020 8:48AM - 9:00AM |
R25.00005: Quincke Oscillation of Colloids at Planar Electrodes Zhengyan Zhang, Yong Dou, Kyle Bishop Dielectric particles immersed in a weakly conducting liquid are known to exhibit spontaneous rotational motion under uniform DC electric fields above a critical magnitude. So-called Quincke rotation near a planar substrate leads to particle translation and provides a useful experimental model for studying the collective dynamics of active colloids. Here, we show that individual Quincke rollers at planar electrodes can also exhibit oscillatory dynamics, whereby particles move back and forth about a stationary location. The transition from steady rolling to oscillatory motion occurs at a critical field three times larger than that required for rolling. In contrast to previous reports of oscillatory Quincke dynamics based on inertial effects, our observations of micron-scale particles are characterized by low Reynolds numbers (Re ~ 0.01) and therefore negligible inertia.We propose a plausible explanation for Quincke oscillations using the leaky-dielectric model and accounting for electric (and hydrodynamic) interactions of the particle with the conductive substrate. |
Thursday, March 5, 2020 9:00AM - 9:12AM |
R25.00006: Capturing the local entropy production of an active Brownian particles system by compression Buming Guo, Stefano Martiniani, Paul M Chaikin, Dov Levine The entropy production of a stationary process is known to be the Kullback-Leibler divergence (KLD), or relative entropy, between the probability of observing a trajectory with time running forward and its time reversal, which quantitatively characterizes the time-reversal asymmetry and features the nonequilibrium nature of the system. Here we use a compression based Ziv-Merhav method and other techniques to estimate KLD and time reversal symmetry to define a natural spatial decomposition of entropy production by applying the algorithms on discrete time series of state evolution in local block regions. As an example, we will discuss how local entropy production is captured with this method in a phase-separated system of active Brownian particles. |
Thursday, March 5, 2020 9:12AM - 9:24AM |
R25.00007: Superdiffusion and hydrodynamic phase separation in a uniaxial active suspension Lokrshi Dadhichi, K Vijay Kumar, J K Bhattacharjee, Sriram Ramaswamy We examine, analytically and to some extent numerically, the dynamics of the concentration |
Thursday, March 5, 2020 9:24AM - 9:36AM |
R25.00008: Chemistry-Induced Mobility in Catalytic Chemical Reactions Huan Wang, Myeonggon Park, Tsvi Tlusty, Steve Granick With a standard pulse-field gradient nuclear magnetic resonance based diffusion ordered spectroscopy (DOSY), we measure chemical-shift specific molecular diffusivity simultaneously with reaction kinetics in situ as reaction progresses. In simple exothermic, catalysed chemical reactions, we observe unexpected solvent enhanced diffusion, both in water and in organic solvents, to be tightly correlated with molecular catalytic cycles. Scaling analysis suggests the critical role of hydrodynamic coupling at nanoscale among “force-dipole-like” chemical reaction centers. The observation of chemistry-induced mobility challenges the simple “passive” picture of chemical reaction, suggesting rich energy dissipation pathways that eventually lead to collective consequences, for example, a counterintuitive antichemotaxis flux, revealed from a gradient microfluidic chip measurement. |
Thursday, March 5, 2020 9:36AM - 9:48AM |
R25.00009: Spontaneous locomotion of nano-catalysed BZ droplets D Jaya Prasanna Kumar, KABEER JASUJA, Pratyush Dayal The motion in living systems by chemo-mechanical transduction has inspired the scientists to design and develop self-moving biomimetic systems. Here, we harness self-oscillating Belousov-Zhabotinsky (BZ) reaction, synergized by graphene-based catalytic mats to demonstrate the spontaneous motion of the BZ reaction droplet in oil-surfactant medium. Specifically, we synthesize graphene-based catalytic mats by decorating Ru nanoparticles (NP) on graphene nanosheets, thereby creating 0D-2D heterostructures; subsequently, use these mats to catalyze BZ reaction within a droplet. Our results demonstrate spontaneous locomotion of BZ droplets due to Marangoni flow facilitated by the interaction between BZ reaction intermediates and the surfactant in the surrounding oil. We further show that the velocity of droplet motion depends upon the conductivity of the catalytic mats. In particular, we observe highest droplet velocities when RuNP decorated graphene sheets are used to catalyze the BZ reaction. In addition, we witnessed some interesting behaviours when multiple BZ droplets interact within the oil-surfactant medium. Our findings can be used to design self-moving synthetic systems to control their behavior through the use of 0D-2D hybrid nanomaterials. |
Thursday, March 5, 2020 9:48AM - 10:00AM |
R25.00010: Topological Mixing in the Vicsek Model of Active Matter Nguyen T Nguyen, Spencer Smith A general feature of active matter systems is that they consume energy on the small scale and coherent flows emerge on the large scale. Whether the units comprising these systems are bacteria, birds, or the microtubules of active nematics, coherence arises due to local interactions. In a now classic model, the Vicsek model, coherence, as measured by an order parameter, undergoes a phase transition with the changing importance of local interactions. We revisit this result from the perspective of mixing and fluid advection. In particular, we use a measure of dynamic disorder, the topological entropy, which captures the complexity of how the trajectories of these active agents wind about one another. We are able to calculate this mixing measure, and probe the thermodynamic limit of larger ensembles of agents, thanks to a new algorithm, which combines ideas from low dimensional topology and computational geometry. We will show some interesting results in how this disorder parameter behaves as we change the importance of local interactions. |
Thursday, March 5, 2020 10:00AM - 10:12AM |
R25.00011: Anomalous topological active matter Kazuki Sone, Yuto Ashida Systems with topologically nontrivial band structures, which are at the center of the modern condensed matter physics, exhibit unidirectional modes that propagate along the edge of a sample and are immune to disorder. Here, we show that the topological edge modes can ubiquitously emerge in active matter, the collection of self-propelled particles, under influences of spatially periodic structures [1]. Topological edge modes have been found in some active systems by constructing the counterparts of quantum Hall effect. However, to realize the effective external magnetic field, they introduce intricate structures, which can be the bottleneck for an experimental realization. We conclude that, without those intricate structures, it is hard to construct an active-matter counterpart of quantum Hall effect. Instead, by constructing the analogy with quantum anomalous Hall effect, our theoretical proposal eliminates the bottleneck for realizing topological active matter and broadens its applicability. We also discuss its relevance to ongoing experiments in biological systems. |
Thursday, March 5, 2020 10:12AM - 10:24AM |
R25.00012: Homotopy analysis method for Non-Markovian processes in active matter Leonardo Apaza Pilco, Mario Sandoval-Espinoza We solve the Fokker-Planck (FP) equation for active non-Markovian and quasi-Markovian processes using the homotopy analysis method, and provide analytical expressions for classic mean values as a series in time. For non-Markovian processes we show that the solution is equivalent to a Dyson series in the Fokker-Planck operator. As an example, the active particles case with color noise in an arbitrary potential is solved. Our analytical results were compared to Brownian dynamics simulations showing a good agreement. |
Thursday, March 5, 2020 10:24AM - 10:36AM |
R25.00013: Computational study of autonomous mechanical oscillations in a colloidal network crosslinked via clock proteins Lauren Melcher, Elisabeth Rennert, Jennifer L Ross, Michael Rust, Rae M Robertson-Anderson, Moumita Das We investigate a colloidal network as a model system that can dynamically switch between crosslinked and unlinked states when connected via crosslinkers made of clock proteins such as the bacterial circadian oscillator proteins KaiABC. We study this system using Brownian Dynamics simulations and obtain collective properties, such as the degree of order in the system, size of connected clusters, and the mechanical rigidity of the system as a function of time for different volume fractions of colloids, interaction strengths, and crosslinking kinetics. Using experimental parameters for polystyrene spheres and biotinylated KaiABC crosslinkers, we predict the behavior of real systems. Our results can provide insights into the design of self-sustaining soft materials that can autonomously transition between solid-like and fluid-like states, and how the properties of such materials can be tuned. |
Thursday, March 5, 2020 10:36AM - 10:48AM |
R25.00014: Scalar activity induced phase separation and liquid–solid transition in a Lennard-Jones system Chandan Dasgupta, S Siva Nasarayya Chari, Prabal K Maiti Molecular dynamics simulations are used to investigate the effects of scalar activity in a three-dimensional system of Lennard-Jones particles at state points spanning from the gas to the liquid regime. Scalar activity is introduced by increasing the temperature of half of the particles (labeled 'hot') while keeping the temperature of the other half (labeled 'cold') constant at a low value. The ratio of the temperatures of the two subsystems is considered to be a measure of scalar activity. We observe that the two species tend to phase separate at sufficiently high temperature ratio. The degree of phase separation is quantified by a suitably defined order parameter and the entropy production in the process of phase separation is determined by employing the two-phase thermodynamics (2PT) method. We observe that the degree of phase separation and the entropy production increase with the density of the system. The mean number of clusters and the mean size of the largest cluster are determined as functions of the density and the temperature ratio. A calculation of bond orientation order parameters reveals that the largest cluster develops solid-like order consisting of both FCC and HCP packings. |
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