1. Center of Mathematical Morphology, Ecole des Mines de Paris77305 Fontainebleau Cedex, France
2. Department of Mechanical Engineering, McGill UniversityMontreal, QC, Canada H3A 2T5
3. Department of Mechanical Science and Engineering, Institute for Condensed Matter Theory, University of Illinois at Urbana-ChampaignUrbana, IL 61801, USA