1. Department of Mechanical Engineering, Rose-Hulman Institute of Technology, Terre Haute, IN 47803, USA;
2. Department of Civil Engineering, University of California at Berkeley, Berkeley, CA 94704, USA
3. Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana-Champaign, IL 61801, USA
4. Department of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332, USA