Competitive Clustering in a Bi-disperse Granular Gas
  A bi-disperse granular gas in a compartmentalized system is experimentally found to cluster competitively: Depending on the shaking strength, the clustering can be directed either towards the compartment initially containing mainly small particles, or to the one containing mainly large particles. The experimental observations are quantitatively explained within a flux model. 
Ren\'e Mikkelsen, Devaraj van der Meer, Ko van der Weele, and Detlef   Lohse