1. Theoretical and Applied Mechanics Graduate Program; Northwestern University; Evanston 60208 IL U.S.A.
2. Department of Civil and Environmental Engineering; Northwestern University, Evanston; 60208 IL U.S.A.
3. Department of Mechanical Engineering; State University of New York at Binghamton; Binghamton 13902 NY U.S.A.
4. ES3; 550 West C St. San Diego 92101 CA U.S.A