Effective temperature of an aging powder
  The aging dynamics and the fluctuation-dissipation relation between the spontaneous diffusion induced by a random noise and the drift motion induced by a small stirring force are numerically investigated in a 3D schematic model of compacting powder: a gravity-driven lattice-gas with kinetic constraints. The compaction dynamics is characterized by a super-aging behaviour and, in analogy with glasses, exhibits a purely dynamical time-scale dependent effective temperature. A simple experiment to measure this quantity is suggested. 
M. Sellitto