We present an experimental study of the dispersion of tracer particles
close to the center, during the gravity flow of monodisperse granular
material in a flat silo. We obtained the mean and the mean-square dis
placement of the tracer position as a function of time. The local velo
city along the vertical direction shows a clear dependence on the heig
ht, which is due to the shape of the silo and the material friction pr
operties. (C) 1998 Published by Elsevier Science B.V.