1. Thayer School of Engineering, Dartmouth College, Hanover, NH 03755 e-mail:
2. Department of Acute Care Solutions, Philips Research, Cambridge, MA 02141 e-mail:
3. Department of Mechanical Engineering, Columbia University, New York, NY 10027 e-mail:
4. Department of Civil Engineering and Engineering Mechanics, Columbia University, New York, NY 10027 e-mail: