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Abstract

Pattern formation in out-of-equilibrium systems is diverse. Examining the nature of hydrodynamic patterns in active nematics has been a topic of interest for the past couple of years. Sokolov et al. investigate the dynamics of circularly aligned swimming bacteria. They show that in an active matter system the interplay of activity, elasticity and geometry leads to a wellcontrolled pattern formation and finer control of dynamic structures and transport phenomena. They report the emergence of bend stripes, an activityinduced undulations of the liquid crystal director field, in areas of high local curvature. Parameters such as velocity, relaxation rate and vorticity are compared for two experimental geometries; a pendant drop attached to a glass slide and in a thin free-standing film suspended between filaments. Hydrodynamic simulations are used to explain the origin of bend stripes. The effect of adding an extensile active stress on the hydrodynamic flows and its implications on the time evolution of the director field and the local curvature are compared. The instability patterns are seen to introduce a strong anisotropy to the angular distribution of emerging topological defects.