Granular packings: nonlinear elasticity, sound propagation, and collective relaxation dynamics.
Makse HA, Gland N, Johnson DL, Schwartz L. Granular packings: nonlinear elasticity, sound propagation, and collective relaxation dynamics. Phys Rev E Stat Nonlin Soft Matter Phys. 2004 Dec; 70(6 Pt 1):061302.