1. Faculty of System Science and Technology, Akita Prefectural University, 84-4 Ebinokuchi, Tsuchiya-aza,
Yurihonjyo-shi, Akita 015-0055, Japan, and International College of Arts and Sciences, Yokohama City University,
22-2 Seto, Kanazawa-ku, Yokohama 236-0027, Japan