1. Department of Bioengineering, University of Pennsylvania, 210 S. 33rd Street, Room 240 Skirkanich Hall, Philadelphia, PA 19104
2. Injury Biomechanics Branch, Oak Ridge Institute for Science and Education, US Army Aeromedical Research Laboratory, Building 6901, Fort Rucker, AL 36362
3. Injury Biomechanics Branch, US Army Aeromedical Research Laboratory, Building 6901, Fort Rucker, AL 36362
4. Department of Bioengineering, University of Pennsylvania, 210 S. 33rd Street, Room 240 Skirkanich Hall, Philadelphia, PA 19104 e-mail: