1. Deptartment of Mechanical Engineering, University of Washington, Seattle, WA 98195 e-mail:
2. Deptartment of Mechanical and Biomedical Engineering, National University of Ireland, Galway, Ireland e-mail:
3. Adjunct in Bioengineering, Deptartment of Mechanical Engineering, University of Washington, Seattle, WA 98195 e-mail: