GRANULAR CONVECTION OBSERVED BY MAGNETIC-RESONANCE-IMAGING

Vibrations in a granular material can spontaneously produce convection rolls reminiscent of those seen in fluids. Magnetic resonance imaging provides a sensitive and noninvasive probe for the detection of these convection currents, which have otherwise been difficult to observe. A magnetic resonance imaging study of convection in a column of poppy seeds yielded data about the detailed shape of the convection rolls an d the depth dependence of the convection velocity. The velocity was fo und to decrease exponentially with depth; a simple model for this beha vior is presented here.