1. Division of Sustainable Resources Engineering, Graduate School of Engineering, Hokkaido University, Hokkaido, Japan
2. Center for Regional Revitalization in Research and Education, Akita University, Akita, Japan
3. Rock Tools Group, Sales Division, MMC RYOTEC, Tokyo, Japan
4. Graduate School of International Resource Sciences, Department of Earth Resource Engineering and Environmental Science, Akita University, Akita, Japan