Powders and grains 2009 : proceedings of the 6th International Conference on Micromechanics of Granular Media : Golden, Colorado : 13-17 July 2009 / editors, Masami Nakagawa, Stefan Luding ; sponsoring organizations, Association for the Study of the Micromechanics of Granular Media (AEMMG), Universiteit Twente (UT), Netherlands, [and] Colorado School of Mines (CSM), USA.