  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).
