Publications

The effects of side wall movement on granular packings were investigated. The studies showed that the resultant structure of the pack did not depend strongly on the magnitude of the wall movement, as long as the packing was moved for an equivalent distance. The main effect of wall movement was to drive the particle-wall and particle-particle contacts to the Coulomb criterion. This forced the packing in the high wall velocity case to obey the Janssen form, which took the Coulomb criterion as one of its main assumptions.

Abstract not provided.

We have computed the low energy quantum states and low frequency dynamical susceptibility of complex quantum spin systems in the limit of strong interactions, obtaining exact results for system sizes enormously larger than accessible previously. The ground state is a complex superposition of a substantial fraction of all the classical ground states, and yet the dynamical susceptibility exhibits sharp resonances reminiscent of the behavior of single spins. These results show that strongly interacting quantum systems can organize to generate coherent excitations and shed light on recent experiments demonstrating that coherent excitations are present in a disordered spin liquid. The dependence of the energy spectra on system size differs qualitatively from that of the energy spectra of random undirected bipartite graphs with similar statistics, implying that strong interactions are giving rise to these unusual spectral properties.