Filling a silo with a mixture of grains: Friction-induced segregation
  We study the filling process of a two-dimensional silo with inelastic particles by simulation of a granular media lattice gas (GMLG) model. We calculate the surface shape and flow profiles for a monodisperse system and we introduce a novel generalization of the GMLG model for a binary mixture of particles of different friction properties where, for the first time, we measure the segregation process on the surface. The results are in good agreement with a recent theory, and we explain the observed small deviations by the nonuniform velocity profile. 
Antal K\'arolyi, J\'anos Kert\'esz, Shlomo Havlin, Hern\'an A. Makse   and H. Eugene Stanley