1. Department of Precision Mechanical Engineering, Kyungpook National University, Sangju 742-711, South Korea
2. Department of Mechanical Engineering, POSTECH, Pohang 790-784, South Korea
3. Division of Advanced Nuclear Engineering, POSTECH, Pohang 790-784, South Korea
4. Division of Mechanical System Engineering, Incheon National University, Incheon 406-772, South Korea