1. Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, Pennsylvania 19104
2. School of Mechanical and Aerospace Engineering, Sunchon National University, 315 Maegok-dong, Sunchon, Jeonnam 540-742, South Korea
3. School of Mechanical Engineering Inha University 253 Younghyun-dong, Nam-gu, Incheon 402-751 South Korea