Flux from a vibrated granular medium

We have studied vertically vibrated granular media by measuring the flux through a hole in the container's bottom surface. We find that when fully fluidized, the flux is controlled by the peak velocity of the vibration, $v_{max}$, i.e., the flux is nearly independent of the frequency and acceleration amplitude for a given value of $v_{max}$. The flux decreases with increasing peak velocity and then becomes constant for the largest values of $v_{max}$. We demonstrate that the data at low peak velocity can be quantitatively described by a hydrodynamic model. By contrast, the nearly constant flux at larger peak velocity signals a crossover to a state in which the granular density near the bottom is insensitive to the energy input to the system. This research was supported by the NASA through grant NAG3-2384 and the NSF REU program through grant DMR 0305238.