Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session N11: Biological Active Matter IVFocus
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Sponsoring Units: DBIO Chair: Suraj Shankar, Harvard University Room: Room 203 |
Wednesday, March 8, 2023 11:30AM - 12:06PM |
N11.00001: Cytoskeletal dynamics generate active liquid-liquid phase separation.Alexandra Tayar, Weizmann Institute of Science Invited Speaker: Alexandra Tayar
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Wednesday, March 8, 2023 12:06PM - 12:18PM |
N11.00002: Self-organization and hydrodynamics of active rods on fluid membranes Arijit Mahapatra, Wenzheng Shi, Ehssan Nazockdast The transport and self-organization of active self-propelled rod-like proteins and biopolymers on the cell membrane is a key component of many cellular processes and functions. Such systems are shown to exhibit a complex range of collective behavior, including aggregation, self-organization, and complex defect dynamics. Here we use a combination of continuum modeling and particle simulations based on slender-body theory to study the collective dynamics of a suspension of pusher and puller rods in a fluid membrane submerged in bulk fluid, as a simplified model for the assembly of cytoskeletal biopolymers on the cell membrane. Specifically, we explore the effect of the ratio of the membrane to bulk fluid viscosities and the aspect ratio of the rods on the generated flows and the orientation and concentration fields of the active rods. |
Wednesday, March 8, 2023 12:18PM - 12:30PM |
N11.00003: Defect dynamics in viscoelastic passive and active nematics Michael M Norton, Moumita Das Passive and active nematics are most often modeled as ordered fluids. However, in biopolymeric systems, elastic stresses can play an important role in shaping the evolution of the nematic field and material flows. Here, we explore a hydrodynamic model of nematics that includes a single relaxation time through linear stability analysis and simulation. We find that stress build-up during defect motion impacts their annihilation dynamics. Results are discussed in the context of experimental work on microtubule-based active nematics and passive biomolecular condensates. |
Wednesday, March 8, 2023 12:30PM - 12:42PM |
N11.00004: Motility induced patterning in range expansions Suraj Shankar, Julien Tailleur, David R Nelson Range expansions, i.e., the invasion and colonization of space by growing populations of organisms, play a key role in the spread of genetic diversity in spatially extended environments. While most studies of microbial range expansions focus on nondirected diffusive transport as the primary mode of dispersal, microorganisms such as flagellated bacteria are capable of active modes of transport through directed swimming, quorum sensing, chemotaxis etc. How does active motility, which tends to produce radial as opposed to azimthual genotype segregation, affect the frontier expansion of a colony of dividing cells? What are the genetic consequences of active patterning on spatial range expansions when motility is strong? By using numerical simulations and analysis of a continuum model, we demonstrate activity induces finite wavelength patterns that can strongly affect colony expansion for both pulled and pushed waves. We also explore the genetic consequences of these phenomena in populations of antagonistically competing strains and highlight the competition between a genetic line tension and active forces in deciding the evolutionary fate of such mixtures. |
Wednesday, March 8, 2023 12:42PM - 12:54PM |
N11.00005: Self-organization and control in acoustically coupled active matter Alexander Ziepke, Ivan Maryshev, Igor Aranson, Erwin Frey In active matter systems, interactions and self-propulsion of agents lead to the formation of structures that exceed the size of individual units by orders of magnitude. The resulting collective structures exhibit emergent properties and functionalities that are not realizable by the individual constituent units. Recently, it has been shown that chemical communication with active decision making at the level of individual agents enables a rapid collectively controlled multi-scale organization process resulting in functional self-assembled structures [1]. |
Wednesday, March 8, 2023 12:54PM - 1:06PM |
N11.00006: Spontaneous flow transition in confined active nematic droplets Salman Alam, Bibi Najma, Jeremy Laprade, Peter J Foster, Guillaume Duclos Active matter collectively organizes mesoscale active stresses that drive a variety of emergent phenomena at the macroscopic scale including spontaneous large-scale, self-driven flows in active nematics. The underlying dynamics of the flows generated in 3D active nematics are thought to be governed by the ratio of nematic elasticity and active stress which sets the active length scale. We find that confining active nematics below a critical length scale stabilizes the dynamics and suppresses flows. This transition between a quiescent and a flowing state is reminiscent of the Fréedericksz transition in equilibrium systems. In this work, we present an analog of the active Fréedericksz transition and probe independently how the interplay between confinement, active stress, and nematic elasticity controls the flow to no-flow transition and investigate the rate of energy consumption in the observed states. |
Wednesday, March 8, 2023 1:06PM - 1:18PM |
N11.00007: Pair interactions of bacterial active droplets in nematic liquid crystals Hend M Baza, Mojtaba Rajabi, Sergij V Shiyanovskii, Oleg D Lavrentovich Self-propulsion of water-based droplets with a large number of suspended bacteria is enabled by the asymmetric structure (Hyperbolic Hedgehog) forms around them in a nematic liquid crystal environment [1]. Here, we report on the interaction of two active droplets moving: (1) in the same direction, (2) in opposite directions. We also discuss the speeds of the pairs after the interaction comparing to that of the individual droplets. |
Wednesday, March 8, 2023 1:18PM - 1:30PM |
N11.00008: E. coli through obstacles: fluxes, entropy production and extractable work in active matter Satyam Anand, Xiaolei Ma, Shuo Guo, Stefano Martiniani, Xiang Cheng Relating entropy production to underlying thermodynamic fluxes and extractable work for systems arbitrarily far from equilibrium remains a challenging problem. For systems in a non-equilibrium steady state, entropy production rate (EPR) has been studied based on the statistical irreversibility between time-forward and time-reversed trajectories of observed degrees of freedom (DOFs), both globally and, more recently, locally. Here, we explore the relation between local EPR, fluxes, and extractable work for an active matter system consisting of swimming E. coli rectified by funnel-shaped obstacles using theory, simulations, and experiments. We propose a minimal mechanical model to quantitatively capture experimentally measured local fluxes at funnel tips. We then measure irreversibility in different DOFs such as position and momentum, and show how they are related to the corresponding fluxes. Finally, we measure the local work extracted by an optically trapped colloid at a funnel tip that is weakly coupled to bacterial motion and characterize its relation to fluxes and EPR. Our work sheds light on the intrinsic relation between fluxes, irreversibility, and work in active systems far away from equilibrium. |
Wednesday, March 8, 2023 1:30PM - 1:42PM |
N11.00009: Spontaneous flow created by active topological defects Louis Brezin, Thomas Risler, Jean-François Joanny Topological defects are at the root of the large-scale organization of liquid crystals. In two-dimensional active nematics, two classes of topological defects of charges ±1/2 are known to play a major role due to active stresses. Despite this importance, few analytical results have been obtained on the flow-field and active-stress patterns around active topological defects. Using the generic hydrodynamic theory of active systems, we investigate the flow and stress patterns around these topological defects in unbounded, two-dimensional active nematics. Under generic assumptions, we derive analytically the spontaneous velocity and stall force of self-advected defects in the presence of both shear and rotational viscosities. Applying our formalism to the dynamics of monolayers of elongated cells at confluence, we show that the non-conservation of cell number generically increases the self-advection velocity and could provide an explanation for their observed role in cellular extrusion and multilayering. |
Wednesday, March 8, 2023 1:42PM - 1:54PM |
N11.00010: Chiral Symmetry Breaking and Vortical States in Bacterial Biofilm Livio Nicola Carenza, Mustafa Basaran, Tevfik Can Yüce, Luca Giomi, Askin Kocabas Bacterial biofilms are one of the most primordial forms of collective interaction leading to complex coordinated functional communities. Biofilms are observed across the whole bacterial kingdom and play a central role in many biological processes with many repercussions on human life. |
Wednesday, March 8, 2023 1:54PM - 2:06PM |
N11.00011: Novel critical phenomena in compressible polar active fluids: A functional renormalization group approach Patrick Jentsch, Chiu Fan Lee Polar active fluids (PAFs) describe the large-scale collective behavior of aligning self-propelling particles, such as birds, fish, or bacteria through hydrodynamic equations of motion. As for passive fluids, one can identify a phase diagram revealing either ordered flocking motion, disordered motion, different states of phase separation, and critical points. Generically, these critical points can be systematically categorized into universality classes (UCs), using renormalization group (RG) methods. Indeed, dynamic RG, together with the perturbative ε-expansion method, has uncovered both novel UCs as well as attributed known UCs to some of the critical points in PAFs in both the incompressible as well as the infinitely compressible limits. Similar studies on the more general compressible PAFs have been hindered by technical difficulties, except for rare cases. |
Wednesday, March 8, 2023 2:06PM - 2:18PM |
N11.00012: Structural states and conservation laws in a system of two-dimensional active swimmers Naomi Oppenheimer, Yuval Shoham Ensembles of motile microswimmers display complex collective dynamics. Nonetheless, when confined to two dimensions, we show they can be expressed using a unifying formalism. A system of swimming particles such as algae or bacteria in a thin film can be described by a many-body Hamiltonian. When simulating a random arrangement of micro-swimmers, we find they evolve into sharp lines at a particular tilt. We call these states "escalators" as particles circulate along these canted conveyor belts. We argue that the conservation of the Hamiltonian and its symmetry germinate the self-assembly of the observed steady-state arrangements. The Hamiltonian is scale-invariant and depends strictly on the angles between the swimmers and their swimming orientation, thereby restricting their available phase space. Stability analysis predicts that an initial alignment at either a low or a high angle is unstable and that the ensemble of swimmers will break into the observed escalators. |
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