1. Postdoctoral Research Fellow, Dept. of Civil and Environmental Engineering, Technological Institute, Northwestern Univ., 2145 Sheridan Rd., Tech A236, Evanston, IL 60208.
2. Professor, Dept. of Civil and Environmental Engineering, Univ. of Tennessee, Knoxville, TN 37996 (corresponding author).
3. Research Scientist, Advanced Photon Source, Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL 60439.