1. Department of Biomedical Engineering, University of Florida, P.O. Box 116131, Gainesville, Florida 32611, Department of Mechanical and Aerospace Engineering, University of Florida, P.O. Box 116250, Gainesville, Florida 32611, Department of Molecular Genetics and Microbiology, University of Florida, P.O. Box 100266, Gainesville, Florida 32610, and Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, California 94551