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SUMMARY:Hydrodynamic coordination of bacterial motions: from bundles to bi
 omixing - Graham\, M (University of Wisconsin-Madison)
DTSTART:20130625T104500Z
DTEND:20130625T113000Z
UID:TALK45909@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Many bacteria propel themselves though their fluid environment
  by means of multiple rotating flagella that self-assemble to form bundles
 . At a larger scale\, the fluid motion generated by an individual microbe 
 as it swims affects the motions of its neighbors. Experimental observation
 s indicate the presence of long-range order and enhanced transport in susp
 ensions of bacteria -- these phenomena may be important in many aspects of
  bacterial dynamics including chemotaxis and development of biofilms. This
  talk focuses on the role of fluid dynamics in the bundling of flagella an
 d the interactions between swimming organisms. \n\nWe first describe theor
 y and simulations of hydrodynamically interacting microorganisms\, using v
 ery simple models of the individual organisms. In the dilute limit\, simpl
 e arguments reveal the dependence of swimmer and tracer velocities and dif
 fusivities on concentration. As concentration increases\, we show that cas
 es exist in which the swimming motion generates large-scale flows and dram
 atically enhanced transport in the fluid. A physical argument supported by
  a mean field theory sheds light on the origin of these effects. \n\nThe s
 econd part of the talk focuses on the dynamics of the flagellar bundling p
 rocess\, using a mathematical model that incorporates the fluid motion gen
 erated by each flagellum as well as the finite flexibility of the flagella
 . The initial stage of bundling is driven purely by hydrodynamics\, while 
 the final state of the bundle is determined by a nontrivial and delicate b
 alance between hydrodynamics and elasticity. As the flexibility of the fla
 gella increases a regime is found where\, depending on initial conditions\
 , one finds bundles that are either tight\, with the flagella in mechanica
 l contact\, or loose\, with the flagella intertwined but not touching. Tha
 t is\, multiple coexisting states of bundling are found. The parameter reg
 ime at which this multiplicity occurs is comparable to the parameters for 
 a number of bacteria. \n
LOCATION:Seminar Room 1\, Newton Institute
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