1. Mechanical Engineering Department, University of California, Berkeley, Berkeley, CA, 94720
2. Departement des Mate´riaux, Ecole Polytechnique Fe´de´rale de Lausanne, 1015 Lausanne, Switzerland
3. Mechanical Technology, Sulzer-Innotec, 8401 Winterthur, Switzerland
4. Lawrence Livermore National Laboratory, Livermore, CA 94550