Shape of convective cell in Faraday experiment with fine granular materials

The shape of convective cell at the onset of heap formation in the Faraday experiment with fine granular materials is studied in a simple experiment. The motion of fine grains are found to be confined in a single thin conical cell instead of a pair of convective cells as considered previously. The subsequent pattern-selection is strongly affected by the shape and size of the grains as well as the presence of ambient air.