Tsuyoshi Shirai1, Tohru Terada2. 1. Department of Computer Bioscience, Nagahama Institute of Bio-Science and Technology, 1266 Tamura, Nagahama, Shiga, 526-0829, Japan. t_shirai@nagahama-i-bio.ac.jp. 2. Interfaculty Initiative in Information Studies, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan.