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TZID:Europe/Paris
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BEGIN:VEVENT
UID:1-156@lptms.universite-paris-saclay.fr
DTSTART:20130917T110000Z
DTEND:20130917T120000Z
DTSTAMP:20130902T183718Z
URL:https://www.lptms.universite-paris-saclay.fr/seminars/seminaire-du-lpt
 ms-tom-witten/
SUMMARY:Séminaire du LPTMS: Tom Witten - LPTMS\, salle 201\, 2ème étage\
 , Bât 100\, Campus d'Orsay - 17 Sep 13 11:00
DESCRIPTION:A colloidal dance: synchronizing motion of brownian particles\n
 Thomas A. Witten\, University of Chicago\nWatch a small flake of plastic g
 radually sink in a glass of water. The asymmetric flake pivots into a pref
 erred orientation and then rotates steadily as it sinks. The reason for th
 is rotational response to gravity is independent of length scale\; thus it
  applies to microscopic colloidal objects as well. Analogous responses occ
 ur under other forces\, eg from electric fields. The response is governed 
 by a 3x3 matrix called the twist matrix that depends on the object's shape
  and its mass distribution. The twist matrix controls the motion in much t
 he same way as the (symmetric) inertia tensor controls the free tumbling m
 otion of a body. However\, the twist matrix gives a richer response becaus
 e it is not symmetric. In this talk we explore ways to use this rotational
  response to organize a sample of objects so that they all rotate in uniso
 n\, with the same orientation. This complete orientation can be achieved w
 ithout using interaction between the particles\; instead we exploit the tr
 ansient pivoting response before the object settles into a fixed rotationa
 l axis. We demonstrate two types of programmed\, time-dependent forcing th
 at bring a set of randomly oriented particles into a common orientation. T
 he first is a simple alternating rocking motion. The second is a rotating 
 force analogous to the rotating magnetic field in an NMR device. Once orie
 nted\, the objects must respond identically to further forcing\; they tran
 slate and rotate in unison.\n
LOCATION:LPTMS\, salle 201\, 2ème étage\, Bât 100\, Campus d'Orsay\, 15 
 Rue Georges Clemenceau\, Orsay\, 91405\, France
GEO:48.698185;2.181768
X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=15 Rue Georges Clemenceau\,
  Orsay\, 91405\, France;X-APPLE-RADIUS=100;X-TITLE=LPTMS\, salle 201\, 2è
 me étage\, Bât 100\, Campus d'Orsay:geo:48.698185,2.181768
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