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TZID:Europe/Paris
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UID:0-674@lptms.universite-paris-saclay.fr
DTSTART:20190925T140000Z
DTEND:20190925T150000Z
DTSTAMP:20190919T061256Z
URL:http://www.lptms.universite-paris-saclay.fr/seminars/physics-biology-i
 nterface-seminar-carine-douarche/
SUMMARY:Physics-Biology interface seminar: Carine Douarche - Salle des sém
 inaires du FAST et du LPTMS\, bâtiment Pascal n°530 - 25 Sep 19 14:00
DESCRIPTION:Collective motion in bacterial suspensions\nCarine Douarche (Un
 iversité Paris-Sud)\nWarning: special seminar time.\nSuspending highly mo
 tile Escherichia coli in a liquid lowers the viscosity of the solution at 
 low shear rate. At higher cell concentrations\, a regime of near zero visc
 osity can be reached. In this work\, we investigate the system-size depend
 ence of the rheological response of an E. coli suspension as a function of
  shear rate and bacteria concentration using a low-shear Couette rheometer
 . Additionally\, we image the suspensions in a cone-plate rheo-imaging set
 up allowing direct visualisation of the collective organisation under shea
 r. We find the flow becomes banded and viscosity decreases to near zero at
  a bacterial concentration close to where collective motion appears in abs
 ence of flow.\nIndeed\, dense suspensions of swimming bacteria display rem
 arkable collective motion\, i.e. local bacterial ordering associated with 
 a characteristic correlation length\, reminiscent of turbulent flow behavi
 our. Using video microscopy over large fields of view (up to 3 mm x 4 mm)\
 , and particle image velocimetry\, we calculate the spatial correlation of
  the velocity vectors and extract a characteristic length scale. At suffic
 iently high bacterial concentrations\, we find this length to be proportio
 nal to the smallest system size. However\, the absence of saturation towar
 ds large system-sizes suggests there is no intrinsic length-scale in these
  dense populations of such ‘pusher-like’ swimmers.
CATEGORIES:physbio,seminars
LOCATION:Salle des séminaires du FAST et du LPTMS\, bâtiment Pascal n°53
 0\, rue André Riviere\, Orsay\, 91405\, France
X-APPLE-STRUCTURED-LOCATION;VALUE=URI;X-ADDRESS=rue André Riviere\, Orsay\
 , 91405\, France;X-APPLE-RADIUS=100;X-TITLE=Salle des séminaires du FAST 
 et du LPTMS\, bâtiment Pascal n°530:geo:0,0
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