1. Department of Physics, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku, Tokyo 1628601, Japan
2. Department of Integrated Science and Technology, Faculty of Science and Technology, Oita University, Dannoharu, 700, Oita City 870-1192, Japan
3. Tokyo Diatomology Lab, 2-3-2 Nukuikitamachi, Koganei, Tokyo 184-0015, Japan