Stress and large-scale spatial structures in dense, driven granular flows.

We study the appearance of large-scale dynamical heterogeneities in a simplified model of a driven, dissipative granular system. Simulations of steady-state gravity-driven flows of inelastically colliding hard disks show the formation of large-scale linear structures of particles with a high collision frequency. These chains can be shown to carry much of the collisional stress in the system due to a dynamical correlation that develops between the momentum transfer and time between collisions in these frequently colliding particles. The lifetime of these dynamical stress heterogeneities is seen to grow as the flow velocity decreases toward jamming, leading to slowly decaying stress correlations reminiscent of the slow dynamics observed in supercooled liquids.