Packing grains by thermally cycling
  One of the oldest and most intriguing problems in the handling of materials is how a collection of solid grains packs together. While granular packing is normally determined by how grains are poured or shaken, we find that a systematic and controllable increase in packing is induced by simply raising and lowering the temperature, e.g., without the input of mechanical energy. The results demonstrate that thermal processing provides a largely unexplored mechanism of grain dynamics, as well as an important practical consideration in the handling and storage of granular materials. 
K. Chen, J. Cole, C. Conger, J. Draskovic, M. Lohr, K. Klein, T.   Scheidemantel, and P. Schiffer