1. Graduate Student, Division of Engineering, Colorado School of Mines, Golden, CO 80401 (corresponding author).
2. Professor, Division of Engineering, Colorado School of Mines, Golden, CO 80401.
3. Assistant Professor, Institute of Mathematics, Univ. of Zurich, 8057 Zurich, Switzerland; formerly, Assistant Professor, Dept. of Mathematical and Computer Sciences, Colorado School of Mines, Golden, CO 80401.