Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session B20: DSOFT Prize Session: Emergent Mechanics of Active, Robotic, and Living Materials IFocus Prize/Award Recordings Available
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Sponsoring Units: DSOFT GSNP Chair: Corentin Coulais, University of Amsterdam Room: McCormick Place W-185BC |
Monday, March 14, 2022 11:30AM - 12:06PM |
B20.00001: Soft Matter Award (2022): Topics on the emergent mechanics of active, robotic, and living materials. Invited Speaker: Nikta Fakhri TBD |
Monday, March 14, 2022 12:06PM - 12:18PM |
B20.00002: Emergence, dynamics and control of topological defects in odd robotic matter Jonas Veenstra Active systems are not constrained by the principle of energy conservation, allowing for a wide variety of wave phenomena not accessible to ordinary passive matter. By implementing local energy non-conserving interactions between particles within a network, complex collective behaviour can result, providing new avenues in material design. |
Monday, March 14, 2022 12:18PM - 12:30PM |
B20.00003: Elasticity- and consensus-based mechanisms for self-organization in active systems Amir Shee, Cristián Huepe Self-organization is often observed in active systems such as cell colonies, developing tissue, insect swarms, bird flocks, and groups of autonomous robots. In recent years, several minimal models have been introduced to understand the underlying mechanisms that can lead to the emergence of collective coordinated motion in such systems for different types of individual interactions. |
Monday, March 14, 2022 12:30PM - 12:42PM |
B20.00004: Topological defects in non-reciprocal active solids with odd elasticity Colin R Scheibner, Lara Braverman, Bryan VanSaders, Vincenzo Vitelli We study topological defects in active solids that violate Maxwell-Betti reciprocity (MBR). A solid violates MBR whenever its microscopic forces are nonconservative, i.e. they are not the gradient of a potential energy. In the continuum, broken MBR generically yields an asymmetric (or odd) elastic modulus tensor. We show that such a tensor modifies the strain and interaction between topological defects, for example reversing the stability of otherwise bound dislocation pairs. Such odd elastic moduli can also arise in systems with conservative microscopic forces if stress is present prior to deformation. Evading continuum theories, isolated dislocations can also become motile due to microscopic work cycles active at dislocation cores that compete with conventional Peach-Koehler forces caused, for example, by an ambient torque density. We perform molecular dynamics simulations isolating active plastic processes and discuss their experimental relevance to solids composed of spinning particles and robotic metamaterials. |
Monday, March 14, 2022 12:42PM - 12:54PM |
B20.00005: Handed motor interactions create active chiral cytoskeletal networks. Sebastian Fuerthauer, Aleksandra Z Plochocka, Michael J Shelley Cells, the building blocks of life, move deform and perform mechanical work |
Monday, March 14, 2022 12:54PM - 1:06PM |
B20.00006: Non-Reciprocity in Metric and Topological Models of Flocking Charles R Packard, Daniel M Sussman Hydrodynamic models based on the symmetries (or lack thereof) of self-propelling agents have been a powerful tool in studying the large-scale collective motion of organisms such as flocks of birds. Recently, there has been an interest in understanding systems where, due to the level of description chosen, violations of the action-reaction symmetry of Newton's third law can be found. In this work we study the non-reciprocity embedded in the many-body interactions of the classic Vicsek model of flocking. We propose coarse-graining the non-reciprocal interactions into hydrodynamic couplings between density and velocity fields that would be normally forbidden in equilibrium systems, and explore the role of these "non-reciprocal" coupling constants on inhomogeneous pattern formation in the model. Our results suggest that the qualitative role of these couplings depend sensitively on whether interacting neighbors are chosen based on metric or topological considerations. |
Monday, March 14, 2022 1:06PM - 1:18PM |
B20.00007: Mechanical ReLU Spring Networks as a Physical Computing Resource Philip Buskohl, Andrew Gillman, Daniel Nelson, Benjamin Grossmann, Timothy J Vincent, Amanda Criner Nonlinear dynamics are a pervasive phenomena in natural and synthetic mechanical systems, which can be leveraged for novel control of vibrations and elastic wave propagation. The nonlinearity produces complex mappings between the input and output dynamics that have the potential to operate as a mechanical computing resource. To explore this concept, we numerically investigated the computing capacity of 2D nonlinear spring networks using a reservoir computing approach. Reservoir computing is a class of recurrent neural networks that trains only a readout layer of the network dynamics in contrast to tuning all the internal parameters of the network. We introduce a mechanical analog for the rectified linear unit (ReLU) activation function from the neural network community and benchmark the memory capacity, nonlinearity, and output tasks of mechanical ReLU networks sampled from a distribution of spring properties. Preliminary results indicate that the stiffness ratio of the ReLU spring (ie. ratio of the bilinear slopes) is a key driver of the nonlinearity score of the network, even more so than the incidence of activating the spring nonlinearity. In addition, spring networks with a mixture of linear and ReLU springs exhibit a marked loss in memory capacity even at low ReLU spring fractions. Collectively, the results highlight the potential to harness dynamics, and relatively simple mechanical nonlinearities, to perform physical computations to augment the computing capacity of mechanical systems. |
Monday, March 14, 2022 1:18PM - 1:30PM |
B20.00008: Nano-particles carried by multiple dynein motors: A self-regulating nano-machine Rony Granek, Anne Bernheim-Groswasser, Itay Fayer, Gal Halbi Native cargos demonstrate efficient intra-cellular active transport. Here we investigate the motion of spherical nanoparticles (NPs) grafted with flexible polymers, each ending with a nuclear localization signal peptide, thereby allowing recruitment of mammalian cytoplasmic dynein. Bead-motility assays, incorporating surface adsorbed microtubules (MTs), show several unique motility features, depending on the number of NP-ligated motors. To elucidate how motor-motor coupling influences these behaviors, we simulate a theoretical model that builds on single mammalian dynein properties, generalized to include motor-motor elastic and excluded-volume interactions. We find, both experimentally and by model simulations, that long-time trajectories exhibit both left-handed and right-handed helical motion, in which the plus-end directed and right-handed motions are correlated. Run-times and run-lengths are enhanced and mean velocities are somewhat suppressed when the number of NP-ligated motors is increased. The number of motors that bind to the MT and participate in the transport is stochastic along trajectories. It is distributed mainly between one to three motors, with the mean growing as the number of NP-ligated motors increases, but not surpassing two. We propose that this self-regulation and stochastic alternations between one, two, and three transporting motors allow our synthetic NP to achieve both persistent motion and obstacle bypassing, which is beneficial for native cargos in the crowded cellular environment. |
Monday, March 14, 2022 1:30PM - 1:42PM |
B20.00009: Harnessing stigmergy for emergent adaptive control, in soft modular systems. mannus schomaker, Johannes B Overvelde, Sergio Picella Generally, the field of autonomous control achieves versatility by increasing the complexity of centralized controllers. In contrast, the current study takes a decentralized and modular approach where adaptive control emerges from local interactions with the environment. Inspired by collective intelligence in nature (e.g., bird flocking behavior, termite mound construction), we aim to design robust system-level behavior while reducing the complexity of the individual modules to a minimum. With both experiments and simulations, we present a system comprised of light-seeking immobile units physically linked by soft connectors in lattice configurations. Each unit independently senses, actuates, and computes. In arrangements of multiple linked units, the expansion and contraction of the soft connections between the units facilitate the system's mobility as a whole. We demonstrate that the implicit communication imposed by the physical connection between the units is enough to achieve robust system-wide coordination, irrespective of the system's configuration and without prior knowledge of the system. As a result, we pave the way to more general and adaptive control solutions that thrive in unknown environments. |
Monday, March 14, 2022 1:42PM - 1:54PM |
B20.00010: Selective and Collective Actuation in Active Solids Paul Baconnier, Dor Shohat, Claudio Hernandèz, Corentin Coulais, Vincent Démery, Gustavo Düring, Olivier Dauchot Active solids consist of elastically coupled out-of-equilibrium units performing work. They are central to autonomous processes, such as locomotion, self-oscillations and rectification, in biological systems, designer materials and robotics. Yet, the feedback mechanism between elastic and active forces, and the possible emergence of collective behaviours in a mechanically stable elastic solid remains elusive. Making use of centimetric self-propelled particles, we construct the first experimental model system of active elastic material, and study its emerging behaviors in various mechanical conditions. We find that active units acting at the nodes of an elastic structure spontaneously organize and actuate selectively a few modes of the structure. Crucially, they are not necessarily the lowest energy ones. Combining experiments with the numerical and theoretical analysis of an agents model, we unveil the bifurcation scenario and the selection mechanism by which the collective actuation takes place. Our findings may provide a new mechanism for oscillatory dynamics in biological tissues, and opens the path toward the design of meta-materials with bona fide autonomy. |
Monday, March 14, 2022 1:54PM - 2:06PM |
B20.00011: When soft crystals defy Newton's third law: Non-reciprocal mechanics and dislocation motility Alexis Poncet, Denis Bartolo The effective interactions between the constituents of driven and active soft matter are able to bypass the constraints imposed by Newton's third law. This phenomenon is exemplified by the hydrodynamic interactions between units moving in a fluid medium: sedimenting particles, driven emulsions in shallow channels, spinning particles and microswimmers all interact by pairwise forces that are not equal and opposite and/or feature a transverse component. |
Monday, March 14, 2022 2:06PM - 2:18PM |
B20.00012: The usefulness of quantum concepts in soft matter: quasiparticles, flat bands, and the melting of hydrodynamic crystals Tsvi Tlusty, Hyuk Kyu Pak, Imran Saeed The concept of quasiparticles---long-lived low-energy particle-like excitations---has become a keystone of condensed quantum matter, where it explains a variety of emergent many-body phenomena, such as superfluidity and superconductivity. Here, we will use quasiparticles to examine the collective behavior of a classical system of hydrodynamically interacting particles in two dimensions. In the disordered phase of this matter, measurements show a sub-population of long-lived particle pairs. Modeling and simulation of the ordered crystalline phase identify the pairs as effective quasiparticles, emerging at the Dirac cones of the spectrum and inducing the melting of the crystal. When the intrinsic threefold symmetry of the hydrodynamic interaction matches that of the crystal, the cones connect to a multicritical, monkey-saddle van Hove singularity, forming a nearly-flat band of slow low-frequency excitations whose divergent density drives a sharper melting transition. Altogether, these findings demonstrate the usefulness of concepts from quantum matter theory in understanding many-body physics in classical dissipative settings. |
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