1. Department of Mechanical and Materials Engineering, College of Engineering and Applied Science, University of Cincinnati, 2600 Clifton Avenue, Cincinnati, OH 45221
2. Division of Solid and Fluid Mechanics, Center for Devices and Radiological Health, U. S. Food and Drug Administration, 10903 New Hampshire Avenue, Silver Spring, MD 20993
3. Department of Mechanical and Materials Engineering, College of Engineering and Applied Science, University of Cincinnati, 598 Rhodes Hall, P.O. Box 210072, Cincinnati, OH 45221 e-mail: