1. Gas Hydrate Laboratory; Meiji University; 2-4-1, Sarugakucho, Chiyoda-ku Tokyo 101-0064 Japan
2. Tohoku University Museum; 6-3, Aoba, Aramaki, Aoba-ku Sendai 980-8578 Japan
3. Gas Hydrate Laboratory; Meiji University, Organization for the Strategic Coordination of Research and Intellectual Property; 1-1, Kanda, Surugadai, Chiyoda-ku Tokyo 101-8301 Japan
4. Graduate School of Science and Technology; Kumamoto University; 2-39-1, Kurokami, Chuoku Kumamoto 860-8555 Japan