1. Information Media Center, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8521, Japan
2. General Education, Ube National College of Technology, Ube, Yamaguchi 755-8555, Japan
3. Department of Physics, Kyungpook National University, Daegu 702-701, Korea
4. A. Razmadze Mathematical Institute of Georgian Academy of Sciences, M. Alexidze Str. 1, 380093 Tbilisi, Georgia