Shell structures with "magic numbers" of spheres in a swirled dish

Molecular dynamic simulations of a low number N less than or equal to 54 of spheres in a swirled dish yield solidlike shell structures with stable rin gs. In contrast to known granular media, solidification occurs only at sing ular values of N: 7, 8, 12, 14, 19, 21, 30, 37, 40. Otherwise, we obtain in termittent switching of particles between rings - the average switching tim e scaling exponentially with a control parameter - or fluidlike disorder. S table shell structures can be classified by particular geometrical arrangem ents (one-centered hexagonal, one-centered ''quasicircular,'' three centere d, and four centered). [S1063-651X(99)08112-X].