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DY: Fachverband Dynamik und Statistische Physik
DY 15: Active Matter II (joint session BP/CPP/DY)
DY 15.12: Talk
Tuesday, March 19, 2024, 12:30–12:45, H 1028
Flow Localization on Active Ordered Surfaces — •Rushikesh Shinde1, Raphael Voituriez2, and Andrew Callan-Jones1 — 1Laboratoire de Matière et Systèmes Complexes, Université de Paris Cité and CNRS, Paris, France — 2Laboratoire de Physique Théorique de la Matière Condensée, Sorbonne Université and CNRS, Paris, France
During morphogenetic processes, active flows occur in the plane of curved tissues. Tissues often exhibit orientational order, and topological defects arise during tissue development. We have studied the behavior of a +1 defect in a film of active ordered fluid on a curved axi-symmetric surface. We find strikingly different physics compared with the flat-space variant of the problem, in which extensile activity causes vortex-like or aster-like integer defects to undergo spiral ordering and rotational motion. We focus in particular on the influence of extrinsic curvature in the elastic free energy, usually neglected in theories of ordered fluids on curved surfaces. We consider two biologically-relevant surfaces: a capped-tube-like rigid surface, similar to epithelial tubes; and a bump on an otherwise flat plane. In the first case, we find that the activity threshold for instability becomes independent of system size, and spontaneous rotational flows become localized. In the latter case, we find that an aster can be passively unstable towards a spiral state, and as a result, contractility-driven active flows are thresholdless and localized. High contractility extinguishes the flow and restores the aster. Surprisingly, for high enough saddle curvature, the spiral to aster transition shifts from continuous to discontinuous.