“…This early work firmly established the nonlinear flavor of the problem: Nesterenko showed that under appropriate assumptions, among them the slow spatial variation of the displacements of the particles, the equations of motion for granular particles could in most cases be approximated by a continuous nonlinear partial differential equation that admits a soliton solution (later shown to actually be a solitary wave solution [2,3]) for a propagating perturbation in the chain. The recent revival of interest in the subject [2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] has been triggered in part by a concern with important technological applications such as the design of efficient shock absorbers [14], the detection of buried objects [5,6,7,8], and the fragmentation of granular chains [9]. The revival has involved advances in the modeling, simulation, and solution of the equations associated with important features of granular materials such as their discreteness [2,3,10,14], dimensionality [14], disorder [7,11,14], and loading provided by gravitational forces [4,7,13,14,17,18].…”