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SUMMARY:Waltzing Worms: the dynamics of plant-animal collective vortex str
 uctures - George Fortune\, University of Cambridge\, UK
DTSTART:20210514T150000Z
DTEND:20210514T160000Z
UID:TALK160471@talks.cam.ac.uk
CONTACT:virginia mullins
DESCRIPTION:Circular milling\, a stunning manifestation of collective moti
 on\, is found across the natural world\, from fish shoals to army ants. It
  has been observed recently that the plant-animal worm Symsagittifera rosc
 offensis exhibits circular milling behaviour\, both in shallow pools at th
 e beach and in Petri dishes in the laboratory. Here in this talk\, we inve
 stigate this phenomenon\, through experiment and theory\, from a fluid dyn
 amical viewpoint\, focusing on the effect that an established circular mil
 l has on the surrounding fluid. Unlike systems such as confined bacterial 
 suspensions and collections of molecular motors and filaments that exhibit
  spontaneous circulatory behaviour\, and which are modelled as force dipol
 es\, the front-back symmetry of individual worms precludes a stresslet con
 tribution. Instead\, singularities such as source dipoles and Stokes quadr
 upoles are expected to dominate. A series of theoretical models is present
 ed to understand the contributions of these singularities to the azimuthal
  flow fields generated by a mill\, in light of the particular boundary con
 ditions that hold for flow in a Petri dish. A model that treats a circular
  mill as a rigid rotating disc that generates a Stokes flow is shown to ca
 pture basic experimental results well\, and gives insights into the emerge
 nce and stability of multiple mill systems. 
LOCATION:GKB 100 Fluid Mechanics Webinar Series
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