1. Division of Applied Mathematics, Brown University, Providence, RI 02912 e-mail:
2. Division of Applied Mathematics, Brown University, Providence, RI 02912
3. Department of Mechanical Engineering, University of Connecticut, Storrs, CT 06269;
4. Department of Biomedical Engineering, University of Connecticut, Storrs, CT 06269
5. Fellow ASME Division of Applied Mathematics, Brown University, Providence, RI 02912 e-mail: