1. Postdoctoral Fellow, Dept. of Aerospace and Mechanical Engineering, Univ. of Southern California, Los Angeles, CA 90089.
2. Professor, Dept. of Civil Engineering, Aerospace and Mechanical Engineering, Mathematics, and Information and Operations Management, Univ. of Southern California, 430K Olin Hall, Los Angeles, CA 90089-1453 (corresponding author).
3. Assistant Professor, Dept. of Mathematics, Univ. of Southern California, Los Angeles, CA 90089.