1. School of Materials Science and Engineering, Seoul National University, Shillim-dong, Seoul 151-744, Republic of Korea
2. First Systems Development Centre, Agency for Defence Development, P.O. Box 35-1, Yuseong, Daejeon 305-600, Republic of Korea
3. Department of Materials Science and Engineering, Yonsei University, Shinchon-dong, Seoul 120-749, Republic of Korea