CONTINUOUS APPROXIMATION OF A RANDOM-WALK

We consider the problem of nucleation affected by pre-existing nuclei which can be treated as a one-step random process described by a nonli near master equation (ME). We construct a nontrivial time-dependent ex pression for the flux of nucleated particles and demonstrate that in t he sense of a specific criterion-the time lag of transient nucleation- this expression satisfies the ME with asymptotic accuracy. A Fokker-Pl anck approximation to the ME which describes correctly both nucleation and growth is also constructed.