1. School of Computational Sciences, Korea Institute for Advanced Study, 207-43 Cheongnyangni 2-dong, Dongdaemun-gu, Seoul 130-012, Korea
2. Department of energy resources development, Jungwon University, 5 dongburi, Goesan-eup, Goesan-gun Chungbuk 367-805, Korea
3. Division of Liberal Arts, Chungju National University, Chungju 380-702, Korea
4. Department of Physics, Daejin University, Pocheon, Gyeonggi 487-711, Korea