1. Department of Electromechanical Engineering Technology, College of Engineering, California State Polytechnic University, Pomona, CA, 93740 USA
2. Department of Mechanical Engineering, the University of British Columbia, Vancouver, BC V6T 1Z4, Canada
3. Department of Mechanical and Aerospace Engineering, Brunel University London, Uxbridge UB8 3PH, UK
4. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 USA