1. Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208 e-mail:
2. Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail:
3. Department of Mechanical Engineering, Oregon State University, Corvallis, OR 97331 e-mail:
4. Research and Advanced Engineering, Ford Motor Company, Dearborn, MI 48126 e-mail: