1. Research Fellow, Dept. of Physics and Earth Sciences, Univ. of Ferrara, Via Saragat 1, Building B-206, 44122 Ferrara, Italy (corresponding author).
2. Associate Professor, School of Civil and Environmental Engineering and School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr. N.W., Atlanta, GA 30332-0250.
3. Associate Professor, Dept. of Physics and Earth Sciences, Univ. of Ferrara, Via Saragat 1, Building B-206, 44122 Ferrara, Italy.
4. Ken Byers Professor, School of Electrical and Computer Engineering, Georgia Institute of Technology, 777 Atlantic Dr. N.W., Atlanta, GA 30332-0250.
5. Professor and Associate Chair for Finance and Administration, School of Civil and Environmental Engineering, Georgia Institute of Technology, 790 Atlantic Dr., Atlanta, GA 30332-0355.