Many inhomogeneous systems involve domains of well-de?ned phases se- rated by a distinct
interface. If they are driven out of equilibrium one phase will grow at the cost of the other.
Examples are phase separation by sp- odal decomposition or nucleation and subsequent growth of
the nucleus in the nourishing phase [139]. Another example which has often been discussed as a
paradigmatic problem is that of dendritic solidi?cation [29 64 79 199]. The phenomenological
description of these phenomena involves the de?- tion of a precisely located interfacial
surface on which boundary conditions are imposed. One of those boundary conditions typically
yields a normal - locity at which the interface is moving. This is the so-calledsharp interface
approach adopted both in analytical and numerical studies for a variety of contexts involving
a moving boundary. The origin of such a description is - ten transparent being obtained by
symmetry arguments and common sense.
