1. Institute of Advanced Machinery and Design; Seoul National University; 599 Gwanak-ro Gwanak-gu, Seoul 151-744 Korea
2. Department of Mechanical Engineering; Seoul National University of Science and Technology; 172 Gongreung-2-dong Nowon-gu, Seoul 139-743 Korea
3. School of Mechanical and Aerospace Engineering; College of Engineering, Seoul National University; 599 Gwanak-ro Gwanak-gu, Seoul 151-744 Korea