Potential Energy in a Three-Dimensional Vibrated Granular Medium   Measured by NMR Imaging
  Fast NMR imaging was used to measure the density profile of a three-dimensional granular medium fluidized by vertical vibrations of the container. For container acceleration much larger than gravity, the rise in center of mass of the granular medium is found to scale as (v0^alpha)/(N^beta) with alpha = 1.0 +/-0.2 and beta = 0.5 +/- 0.1, where v0 is the vibration velocity and N is the number of grains in the container. This value for alpha is significantly less than found previously for experiments and simulations in one dimension (alpha = 2) and two dimensions (alpha = 1.3-1.5). 
Xiaoyu Yang and D. Candela