COALESCENCE OF SPHERES BY SURFACE DIFFUSION
The shape evolution of small heated metal particles is dominated by surface diffusion. When two spheres touch, they will thus merge into one, as they continually decrease their surface area. Focusing on the asymptotic behavior when the radius r of the neck joining the two spheres is still small, it is found that the metal does not stay simply connected, but encloses an intricate succession of toroidal voids. The temporal evolution of r exhibits a new type of self-similar behavior resulting from a discrete sequence of secondary singularities. [S0031-9007(98)05587-2]