1. Department of Precision Machinery and Precision Instrumentation University of Science and Technology of China Hefei 230026 P. R. China
2. Department of Biomedical Engineering The Ohio State University Columbus 43210 USA
3. Department of Nutritional Sciences and Toxicology University of California Berkeley Berkeley 94720 USA
4. Department of Mechanical and Aerospace Engineering The Ohio State University Columbus 43210 USA
5. Department of Modern Mechanics University of Science and Technology of China Hefei 230026 P. R. China