  A Monte Carlo model of radiative transfer in multi-phase dusty media is
applied to the situation of stars and clumpy dust in a sphere or a disk. The
distribution of escaping and absorbed photons are shown for various filling
factors and densities. Analytical methods of approximating the escaping
fraction of radiation, based on the Mega-Grains approach, are discussed.
Comparison with the Monte Carlo results shows that the escape probability
formulae provide a reasonable approximation of the escaping/absorbed fractions,
for a wide range of parameters characterizing a clumpy dusty medium. A possibly
more realistic model of the interstellar medium is one in which clouds have a
self-similar hierarchical structure of denser and denser clumps within clumps,
resulting in a fractal distribution of gas and dust. Monte Carlo simulations of
radiative transfer in such multi-phase fractal media are compared with the
two-phase clumpy case.
