Arching in tapped deposits of hard disks
  We simulate the tapping of a bed of hard disks in a rectangular box by using a pseudo dynamic algorithm. In these simulations, arches are unambiguously defined and we can analyze their properties as a function of the tapping amplitud. We find that an order--disorder transition occurs within a narrow range of tapping amplitudes as it has been seen by others. Arches are always present in the system althought they exhibit regular shapes in the ordered regime. Interestingly, an increase in the number of arches does not always correspond to a reduction in the packing fraction. This is in contrast with what is found in three-dimensional systems. 
Luis A. Pugnaloni, Marcos G. Valluzzi and Lucas G. Valluzzi