Experimental study of segregation patterns in binary granular mixtures under vertical vibration

We report the experimental observations of the segregation patterns in initially well mixed copper and glass spheres subjected to a vertical sinusoidal vibration at different values of acceleration Gamma and frequency f. A segregation phase diagram is obtained, which includes Brazil nut (BN), Reversed-BN (RBN) and "sandwich" segregation patterns at different Gamma and f. The stable RBN segregation is experimentally found for the first time, in which large heavy particles move down to the bottom and form the lower-layer while small particles rise to the top and form an upper-layer. The boundary values (Gamma, f), which separate regions of different patterns, depend on system's initial condition, i.e. hysteresis exists.