Levich Institute Seminar Announcement, 04/07/2009
Tuesday, 04/07/2009
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Corey O'Hern
Yale University
Department of Mechanical Engineering and Physics

"Testing Ergodicity in Dense Granular Media"


Statistical mechanics descriptions, like the Edwards' entropy approach, have been successful in describing aspects of the structure and dynamics of dense, slowly driven granular media. However, these descriptions assume that all of the `microstates'---mechanically stable (MS) packings---at a given packing fraction are equally likely. We explicitly test this assumption using experiments and simulations of small granular systems undergoing vertical tapping and quasistatic shear flow. We find generically that MS packings do not occur with equal probabilities. In fact, the probabilities of frequent versus rare packings differ by many orders of magnitude. We speculate on reasons why Edwards' entropy descriptions of granular media are successful even though the equal-probability assumption is violated. Finally, we show that MS packings occur as distinct points in configuration space in frictionless granular systems, whereas MS packings occur as continuous geometric `families' in frictional systems, and emphasize that this distinction should be included in subsequent statistical descriptions of granular `microstates'.


  • B. S. Physics, Duke University, 1994
  • Ph.D. Theoretical Soft Condensed Matter Physics, University of Pennsylvania, 1999
  • Postdoctoral Research Associate, Physical Chemistry, UCLA, 1999-2002
  • Postdoctoral Research Associate, Physics, University of Chicago, 1999-2002
  • Assistant Professor of Mechanical Engineering and Physics, 2002-2006
  • Associate Professor of Mechanical Engineering and Physics, 2006-present


Granular media, jamming, glassy dynamics, structure and dynamics of proteins, protein folding