Convection and crystallization in vertically vibrated granular'' capillary'' systems
受振颗粒"毛细"系统中的对流与有序化

The packing structure of identical spheres poured into a narrow cylindrical container will be influenced by the curvature of the container wall. This has been known as the wall effect. Our experiments reveal that under the action of vertical vibration, the wall effect can be enhanced, that the spheres, initially in a random packed state, can be organized through convection into a stable ordered packing consisting of a concentric array of cylindrical "shells" of spheres. In each shell the spheres are hexagonally arrayed. During such a structure transition, the packing density distribution, initially with a damped oscillatory variation along the radial direction, turns into an undamped one. The effects of interstitial air and inhomogeneity in the packing on the convection of particles, and thereby on the dynamics for the formation of "shell" structure, are analyzed. In addition, some discussions on the stability of the "shell" structure are made.