Self-diffusion of particles in gas-driven granular layers with periodic flow modulation

We study particles self-diffusion in gas-driven granular layers by high-speed fluorescent video-microscopy. We show that periodic flow modulation results in an enhancement of the particle's diffusion. The diffusion enhancement, which in turn is an indication of more efficient fluidization of the granular layer, is associated with the onset of disordered sub-harmonic patterns. Our measurements provide a sensitive characterization method of the fluidization properties of particulate/gas systems.