1. College of Science and Technology, Nihon University, Funabashi Campus, 24-1, Narashinodai 7-Chome, Funabashi-Shi, Chiba 274–8501, Japan
2. Department of Applied Mathematics, Faculty of Engineering, Yokohama National University, 79-5 Tokiwadai, Hodogaya-Ku, Yokohama 240–8501, Japan