26 February 2010
Micron-sized bacteria or algae operate at very small Reynolds numbers. In this regime, inertial effects are negligible and, hence, efficient swimming strategies have to be different from those employed by fish or bigger animals. Mathematically, this means that, in order to achieve locomotion, the swimming stroke of a microorganism must break the time-reversal symmetry of the Stokes equations. Large ensembles of bacteria or algae can exhibit rich collective dynamics (e.g., complex turbulent patterns, such as vortices or spirals), resulting from a combination of physical and chemical interactions. The spatial extent of these structures typically exceeds the size of a single organism by several orders of magnitude. One of our current projects in the Soft and Biological Matter Group aims at understanding how the collective macroscopic behavior of swimming microorganisms is related to their microscopic properties. I am going to outline theoretical and computational approaches, and would like to discuss technical challenges that arise when one tries to derive continuum equations for these systems from microscopic or mesoscopic models.
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