1. Department
of Mathematics, University of California, Irvine, California 92697-3875, United States
2. CEA, LETI, Minatec Campus, F-38054 Grenoble, France
3. CASC,
Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom
4. Department
of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272, United States