1. Ph.D. Candidate, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, Rm. #1-290, 77 Massachusetts Ave., Cambridge, MA 02139 (corresponding author).
2. Professor, Mechanical Engineering and Information Sciences; and Brain and Cognitive Sciences; and Director, Nonlinear Systems Laboratory, Massachusetts Institute of Technology, Rm. #3-338, 77 Massachusetts Ave., Cambridge, MA 02139.
3. Professor, Civil and Environmental Engineering, Massachusetts Institute of Technology, Rm. #1-253, 77 Massachusetts Ave., Cambridge, MA 02139.