1. Mechanical and Aerospace Engineering, Arizona State University, Tempe, AZ 85287 e-mail:
2. Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 e-mail:
3. Department of Mechanical Engineering, Stanford University, Stanford, CA 94305 e-mail:
4. George W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30313 e-mail:
5. Department of Psychology, Texas A&M University, College Station, TX 77843 e-mail:
6. Department of Mechanical Engineering, The University of Texas at El Paso, El Paso, TX 79902 e-mail: