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SUMMARY:Crystallography on curved surfaces - David Nelson\, Lyman Laborato
 ry of Physics\, Harvard University
DTSTART:20111024T131500Z
DTEND:20111024T141500Z
UID:TALK32388@talks.cam.ac.uk
CONTACT:Dr G Moller
DESCRIPTION:The difficulty of constructing ordered states on spheres was r
 ecognized by J. J. Thomson\, who discovered the electron and then attempte
 d regular tilings of the sphere in an ill-fated attempt to explain the per
 iodic table. We discuss how protein packings in virus shells solve a relat
 ed “Thomson problem”\, and the remarkable modifications in the theory 
 necessary to account for grain boundary scars in colloidal particles packe
 d on spheres. We then apply related ideas to the folding strategies and sh
 apes of pollen grains during dehydration. The grain can be modeled as a pr
 essurized high-Young-modulus sphere with a weak sector and a nonzero spont
 aneous curvature. In the absence of such a weak sector\, these shells crum
 ple irreversibly under pressure via a strong first order phase transition.
  The weak sectors eliminate the hysteresis and allow easy re-hydration at 
 the pollination site\, somewhat like the collapse and subsequent reassembl
 y of a folding chair.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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