1. Graduate Student, Dept. of Civil and Environmental Engineering, Tufts Univ., Medford, MA 02155 (corresponding author).
2. Research Leader, Battelle, One Cranberry Hill, 750 Marrett Road, Lexington, MA 02421; formerly, Research Professor, Dept. of Civil and Environmental Engineering, Tufts Univ., Medford, MA 02155.
3. Professor, Dept. of Civil and Environmental Engineering, Tufts Univ., Medford, MA 02155.