Editorial: Powders & Grains 2021 9th International Conference on Micromechanics of Granular Media María Alejandra Aguirre, Stefan Luding, Luis A. Pugnaloni and Rodrigo Soto EPJ Web Conf., 249 (2021) 00001 Published online: 07 June 2021 DOI: 10.1051/epjconf/202124900001