1. Department of Mathematics and Science, School of Science and Engineering, Kokushikan University,
4-28-1, Setagaya, Setagaya-Ku, Tokyo 154-8515, Japan
2. Department of Electronics and Information Engineering, Hokkai-Gakuen University, Sapporo 062-8605,
Japan
3. Division of Mathematics and Physics, Faculty of Engineering, Shinshu University, Wakasato, Nagano
380-8553, Japan