The Mullinsndash;Sekerka linear stability analysis of a perturbation on a growing interface is extended to take into account concentration effects. The concentration dependence is included by considering the surrounding particles as an effective medium in the form of a sink term lsqb;xminus;kgr;2crsqb; in the diffusion equation. This problem is analyzed without the effects of surface tension ford=2 andd=3 and with surface tension ford=3. The stability analysis is also applied to two particles in isolation as well asNparticles arranged in a regular planar polygon to study directly the competition for the diffusing species between theNgrowing spheres. We conclude that the Mullinsndash;Sekerka criterion for growth or decay of an instability is only valid for an isolated particle and that in the presence of an effective medium, the surrounding particles have the effect of increasing an otherwise negative growth rate to a positive value.
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