1. Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 3-446, Cambridge, MA 02139 e-mail:
2. LUCID-ULG, University of Liège, Chemin des Chevreuils 1, bat. B52, Liège 4000, Belgium e-mail:
3. Mem. ASME Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 3-446, Cambridge, MA 02139 e-mail:
4. Fellow ASME Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, 3-449B, Cambridge, MA 02139 e-mail: