Issue 5, 2024

Anisotropic run-and-tumble-turn dynamics

Abstract

Run-and-tumble processes successfully model several living systems. While studies have typically focused on particles with isotropic tumbles, recent examples exhibit “tumble-turns”, in which particles undergo 90° tumbles and so possess explicitly anisotropic dynamics. We study the consequences of such tumble-turn anisotropicity at both short and long-time scales. We model run-and-tumble-turn particles as self-propelled particles subjected to an angular potential that favors directions of movement parallel to Cartesian axes. Using agent-based simulations, we study the effects of the interplay between rotational diffusion and an aligning potential on the particles' trajectories, which leads to the right-angled turns. We demonstrate that the long-time effect is to alter the tumble-turn time, which governs the long-time dynamics. In particular, when normalized by this timescale, trajectories become independent of the underlying details of the potential. As such, we develop a simplified continuum theory, which quantitatively agrees with agent-based simulations. We find that the purely diffusive hydrodynamic limit still exhibits anisotropic features at intermediate times and conclude that the transition to diffusive dynamics precedes the transition to isotropic dynamics. By considering short-range repulsive and alignment particle–particle interactions, we show how the anisotropic features of a single particle are inherited by the global order of the system. We hope this work will shed light on how active systems can extend local anisotropic properties to macroscopic scales, which might be important in biological processes occurring in anisotropic environments.

Graphical abstract: Anisotropic run-and-tumble-turn dynamics

Supplementary files

Article information

Article type
Paper
Submitted
05 Mai 2023
Accepted
12 Dez 2023
First published
14 Dez 2023
This article is Open Access
Creative Commons BY license

Soft Matter, 2024,20, 1133-1150

Anisotropic run-and-tumble-turn dynamics

B. Loewe, T. Kozhukhov and T. N. Shendruk, Soft Matter, 2024, 20, 1133 DOI: 10.1039/D3SM00589E

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