Title: Testing the equal-probability assumption for jammed particle packings

Author (Talk): Guo-Jie Gao, Yale University

Abstract:

The Edwards\' and similar statistical descriptions for athermal particulate systems assume that all jammed configurations at a given volume fraction $\\phi$ are equally likely. Although recent numerical simulations and experiments have provided indirect evidence that the Edwards\' equal probability assumption is valid, there have been no direct tests. In our work, we focus on small systems in two dimensions and are thus able to generate nearly all mechanically stable disk packings and obtain the probabilities with which these packings occur. We have studied two experimentally relevant packing generation protocols, a compression/decompression scheme and quasi-static shear flow at zero pressure, to assess how the packing probabilities depend on protocol. We find that the mechanically stable packings are not equally likely for either protocol. Our results suggest that the equal probability assumption for granular and particulate systems is suspect and should be investigated in more detail.