1. Center for Computational Sciences, University of Tsukuba; 1-1-1 Tennodai Tsukuba Ibaraki 305-8577 Japan
2. Department of Biomedical Information Sciences; Graduate School of Information Sciences, Hiroshima City University; 3-4-1 Ozuka-Higashi, Asa-Minami-Ku Hiroshima 731-3194 Japan