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The Evolution of Active Matter with Nematic Order

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Thursday, April 13, 2023 3pm to 4pm

Fashion by Marina Debris

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Thursday, April 13, 2023 3pm to 4pm

Maxwell Dworkin, G125
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Daniel Beller, Assistant Professor of Physics and Astronomy, Johns Hopkins University

The orientational order and topological defects that define the nematic liquid crystal phase also emerge in the far-from-equilibrium collective motions of a broad variety of systems: Biophysical examples of such “active nematics” include bacterial colonies, several types of cellular tissues, and biofilament suspensions. While steady-state chaotic flows are now well understood in terms of active production of nematic defects, this framework applies directly only to systems where the microscopic active forces share the nematic (apolar) symmetry of the emergent active phase.

In this seminar, I will present simulation results for the time-evolution of two other types of active nematics, where the active forces have polar or isotropic components, respectively. The first, a quasi-two-dimensional system of self-propelled filaments, models “gliding assay” experiments of microtubules and kinesin motors in vitro. Our findings suggest that the time-evolution of long-range order can undergo multiple stages, and an experimentally observed “active phase” could in fact be a long-lived transient. The second system is a growing colony of rod-shaped bacteria, for which we combine the perspectives of active matter and population genetics. Here, we propose that active mixing flows may have implications for the evolution (in the biological sense) of the microbial colony.

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