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SUMMARY:Active motion: under external fields and collective dynamics - Sta
 rk\, H (Technische Universitt Berlin)
DTSTART:20130624T100000Z
DTEND:20130624T104500Z
UID:TALK45869@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:Active motion of microorganisms or artificial microswimmers\, 
 such as active colloids\, is an appealing subject which has attracted much
  attention recently. Since these swimmers move constantly in non-equilibri
 um\, they give rise to novel phenomena which\, in particular\, occur when 
 external fields are applied or when they move collectively.\n\nThe talk re
 views our recent work on how active Brownian particles behave in external 
 fields and in confinement. For example\, they develop orientational order 
 in a gravitational field [1] and exhibit an interesting instability in den
 se suspensions when they are bottom-heavy. They also create active fluid p
 umps in a harmonic trap. Finally\, under Poiseuille flow they show nonline
 ar dynamics reminiscent of the nonlinear pendulum where the bounding walls
  introduce "dissipation" [2].\n\nWe also study the collective motion of so
 -called squirmers in a quasi 2D geometry by means of multi-particle collis
 ion dynamics. We observe dynamical clustering\, phase separation\, and act
 ive jamming which is strongly influenced by hydrodynamic near-field intera
 ctions. In dense suspensions rotational diffusion is greatly enhanced and 
 the critical volume fraction for crystallisation is different for pushers 
 and pullers.\n\n[1] M. Enculescu and H. Stark\, Phys. Rev. Lett. 106\, 208
 103 (2011). [2] A. Zoettl and H. Stark\, Phys. Rev. Lett. 108\, 218104 (20
 12).\n\nCo-authors: Marc Hennes (Institute of Theoretical Physics\, Techni
 sche Universitt Berlin)\, Katrin Wolff (Institute of Theoretical Physics\,
  Technische Universitt Berlin)\, Andreas Zoettl (Institute of Theoretical 
 Physics\, Technische Universitt Berlin)\n\n\n\n\n\n
LOCATION:Seminar Room 1\, Newton Institute
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