ABSTRACT
Furthermore, one should point out that the identification of the ejected beads is delicate in the first stages of the ejection process, when they are not clearly detached from the bed. As a consequence, we were able to identify the ejected beads only if they reached a height, at least, greater than one bead diameter above the bed. It means that we did not took into account, in our analysis, the weakly energetic beads which have a vertical ejection speed smaller than
√ 2gd.
