1. Department of Physics and Mathematics, Aoyama Gakuin University, Sagamihara, Kanagawa 229-8558
2. Faculty of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8521
3. Venture Business Laboratory of Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8527