Spectral responses in granular compaction

Ling-Nan Zou
2010 Physical Review E  
The slow compaction of a gently tapped granular packing is reminiscent of the low-temperature dynamics of structural and spin glasses. Here, I probe the dynamical spectrum of granular compaction by measuring a complex (frequency-dependent) volumetric susceptibility χ̃_v. While the packing density ρ displays glass-like slow relaxations (aging) and history-dependence (memory) at low tapping amplitudes, the susceptibility χ̃_v displays very weak aging effects, and its spectrum shows no sign of a
more » ... pidly growing timescale. These features place χ̃_v in sharp contrast to its dielectric and magnetic counterparts in structural and spin glasses; instead, χ̃_v bears close similarities to the complex specific heat of spin glasses. This, I suggest, indicates the glass-like dynamics in granular compaction are governed by statistically rare relaxation processes that become increasingly separated in timescale from the typical relaxations of the system. Finally, I examine the effect of finite system size on the spectrum of compaction dynamics. Starting from the ansatz that low frequency processes correspond to large scale particle rearrangements, I suggest the observed finite size effects are consistent with the suppression of large-scale collective rearrangements in small systems.
doi:10.1103/physreve.81.031302 pmid:20365729 fatcat:wqpd25kbwzdhfj57jpdub5mt4u