CRITICAL VOLUME IN DIFFUSION THROUGH RANDOM-MEDIA

It has been found, very generally, that there is a critical volume of the diffusion space, c, for a class of diffusions in random media, characterized by V(r) with a zero mean. If the size of the diffusion space is bigger than c, the total population increases with time. Otherwise, the total population decreases with time and will eventually vanish. An estimation of c is obtained by a variation method. © 1990 The American Physical Society.