1. a Nagaoka University of Technology, 1603-1 Kamitomioka-machi, Nagaoka-shi, Niigata 940-2188, Japan;, Email: chowarit@stn.nagaokaut.ac.jp
2. b Nagaoka University of Technology, 1603-1 Kamitomioka-machi, Nagaoka-shi, Niigata 940-2188, Japan
3. c Kagawa National College of Technology, 355 Chokushi-cho, Takamatsu, Kagawa 761-8058, Japan
4. d Keio University, 3-14-1 Hiyoshi, Kouhoku-Ku, Yokohama, Kanagawa 223-8522, Japan