1. Interdisciplinary and Fusion Technology Division, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 136-791, Republic of Korea
2. Department of Physics, Ewha Womans University, Seoul 120-750, Republic of Korea
3. Department of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-744, Republic of Korea
4. Department of Mechanical Engineering, Kyungpook National University, Deagu 702-701, Republic of Korea