1. Material Science and Engineering Program, University of California, San Diego, La Jolla, California 92093, USA
2. Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, California 92093, USA
3. Department of Structural Engineering, University of California, San Diego, La Jolla, California 92093, USA
4. Fracture and Shock Physics, SMF Group, Department of Physics, Cavendish Laboratory, Cambridge CB3 0HE, United Kingdom