  We propose a mean-field model of intermittent particle transport, where a
particle may be in one of two phases: the first is an active (ballistic) phase,
when a particle runs with constant velocity in some direction, and the second
is a passive (diffusive) phase, when the particle diffuses freely. The particle
can instantly change the phase of motion. When the particle is in the active
phase the rate of transition to the passive phase depends, in general, on time
from the beginning of the run, so the distribution of the free path is not
exponential. When the particle is in the passive phase the transition rate is
constant, and diffusion is non-anomalous Brownian.
