Surface flows of granular mixtures

We discuss theoretically the filling of a (two dimensional) silo when a mixture of particles is poured at the center. Our basic tool is a coupled set of equations (for the local density of rolling species, aid for the profile) proposed by Bouchaud et al. We extend this to a pair of species. We obtain predictions for the steady state profile and for the concentration distribution. At the bottom side of the slope, we generally expect to have complete purification. Near this point, the concentrations should show unusual power laws.