1Applied Mechanics Group, Lawrence Livermore National Laboratory, Livermore, CA 94550, USA
2Orthopedic Biomechanics Institute, Department of Bioengineering, University of Utah, Salt Lake City, UT 84107, USA
3Livermore Software Technology Corporation, Livermore, CA 94550, USA
4Department of Civil Engineering, University of California, Berkeley, Berkeley, CA 94720, USA