A batch of approximately 200,000 beads is poured into a cylindrical container forming an initial packing in a random configuration with a volume fraction ? ranging from 57% to 63%. The packing is then shaken intensely for few seconds, to the point of fluidization, where a fast compaction is observed. The resulting global packing density reaches 70.5%.
 DOI: http://dx.doi.org/10.1103/PhysRevLett.111.148001
 DOI: http://dx.doi.org/10.1103/PhysRevLett.113.148001