Francis G. Woodhouse, Raymond E. Goldstein
Many active fluid systems encountered in biology are set in total geometric confinement. Cytoplasmic streaming in plant cells is a prominent and ubiquitous example, in which cargo-carrying molecular motors move along polymer filaments and generate coherent cell-scale flow. When filaments are not fixed to the cell periphery, a situation found both in vivo and in vitro, we observe that the basic dynamics of streaming are closely related to those of a dipolar microswimmer suspension. This paradigm is used to demonstrate that confinement brings about a qualitative change in behavior; a linear stability analysis and numerical studies show that there is an activity threshold for spontaneous auto-circulation. Analysis of the long-time behavior reveals a phenomenon akin to defect separation in nematic liquid crystals, and a high-activity bifurcation to an oscillatory regime.
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http://arxiv.org/abs/1207.5349
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