1. Assistant Professor, Dept. of Civil, Construction, and Environmental Engineering, Iowa State Univ., Ames, IA 50011 (corresponding author).
2. Physicist Scientist, Applied Condensed-Matter Physics, Institute of Physics and Astronomy, Univ. of Potsdam, D-14476 Potsdam, Germany.
3. Professor, Dept. of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139.
4. Post Doc. Group Leader, Applied Condensed-Matter Physics, Institute of Physics and Astronomy, Univ. of Potsdam, D-14476 Potsdam, Germany.