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SUMMARY:Fluid entrainment by individual microswimmers. - Dr. Dmitri (Mitya
 ) Pushkin\, Rudolf Peierls Centre for Theoretical Physics\, University of 
 Oxford
DTSTART:20121003T120000Z
DTEND:20121003T130000Z
UID:TALK40635@talks.cam.ac.uk
CONTACT:Aurelia Honerkamp-Smith
DESCRIPTION:Stirring the surrounding fluid may be an evolutionary strategy
  of microscopic swimmers to ensuring continuous supply of nutrient and rem
 oval of waste products [1]. The possibility of a significant biogenic cont
 ribution to oceanic mixing is currently under intense debate [1]. However\
 , different biomixing mechanisms\, their effectiveness and universality re
 main poorly understood.\n\nIn this talk we focus on the Lagrangian transpo
 rt of the surrounding fluid by microswimmers [3]. Fluid particles advected
  by swimmers move in loops that are\, in general\, almost closed. This obs
 ervation is in apparent contradiction with the effectiveness of biomixing 
 observed in experiments. We set off by analyzing the fundamental reasons f
 or closedness of the fluid particle trajectories. Building on the gained i
 nsight and noting that non-closedness of loops is a natural requirement fo
 r an efficient mixing\, we propose a classification of possible mechanisms
  for biogenic mixing. \n\nIn the following we discuss the universal (commo
 n to all swimmers) and the swimmer-dependent features of the resulting flu
 id particle displacements and analyse the Darwin dift\, the total fluid vo
 lume displaced by a swimmer passing from and to infinity. We show that the
  Darwin drift is finite for force-free swimmers and can be decomposed into
  a universal and a swimmer-dependent part.\n\nResults of detailed numerica
 l simulations of Rhodobacter sphaeroides and simple models of microswimmer
 s corroborate our considerations.
LOCATION:MR11\,  Centre for Mathematical Sciences\, Wilberforce Road\, Cam
 bridge
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