Berlin 2024 – wissenschaftliches Programm

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BP: Fachverband Biologische Physik

BP 20: Poster IIIa

BP 20.15: Poster

Mittwoch, 20. März 2024, 11:00–14:30, Poster B

Radius-Dependent Dynamics of Active Spot — •Arghavan Partovifard and Holger Stark — Institut für Theoretische Physik, Technische Universität Berlin, Berlin, Germany

Active nematics exhibit distinctive behavior for a spatially varying activity [1,2]. Utilizing the Doi-Edwards theory supplemented by an active stress tensor [1], we investicate an active nematics solely confined to a circular spot by switching off activity outside of the spot. Depending on the spot radius, we observe different emerging dynamics. At very small radii, two +1/2 defects form a spiral and rotate synchronously, while the velocity field displays a single vortex. As the radius of the activity spot increases, the two +1/2 defects gradually separate from each other, while circling around each other. When the +1/2 defects approach the border of the spot, a third +1/2 defect forms. Subsequently, one of the original +1/2 defects leaves the spot, and the two remaining +1/2 In this regime, the velocity field exhibits two or three vortices moving within the spot. With further increase of the spot radius, pairs of ± 1/2 defects are constantly generated and they annihilate with other defects. The corresponding velocity field consists of many vortices moving chaotically, similar to what is observed in active turbulence. We thoroughly investigate and classify the occuring dynamics.

[1] Partovifard et al., submitted (2023).

[2] Rønning et al., R. Soc. Open Sci. 10, 221229 (2023).

Keywords: active turbulence; active paranematics; active nematics; active fluid