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SUMMARY:Understanding liquids and glass transition on the basis of elastic
   interactions - Dr Kostya Trachenko (University of Cambridge)
DTSTART:20090515T150000Z
DTEND:20090515T160000Z
UID:TALK17839@talks.cam.ac.uk
CONTACT:Dr Jonathan Keeling
DESCRIPTION:Existing textbook expressions for the energy and heat capacity
  of gases \nand solids are widely taught in physics courses. However\, no 
 such \nexpression exists for a liquid. Based on the old idea of Frenkel\, 
 I \nformulate this problem in the language of phonons\, and calculate liqu
 id \nenergy and heat capacity for both the classical and quantum cases.\n\
 nI subsequently address the old and very controversial problem of glass \n
 transition\, and propose the solution that is based on elastic \ninteracti
 ons in a liquid. Central to this discussion is the range of \npropagation 
 of high-frequency elastic waves in a liquid\, which I call \n"liquid elast
 icity length d". d measures the range over which local \nrelaxation events
  in a liquid elastically interact with each other via \nthe elastic waves 
 they induce. d is small at high temperature\, and \nincreases on lowering 
 the temperature. This sets the cooperativity of \nmolecular relaxation in 
 a liquid\, and gives the famous \nVogel-Fulcher-Tammann law. In this pictu
 re\, I also discuss other central \nproperties of glass transition: the ab
 sence of divergence at a finite \ntemperature\, the origins of two dynamic
  crossovers and the origin of \nliquid "fragility" (Angell plot).\n
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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