Affiliation: | aGraduate School of Engineering, Hokkaido University, N13W8 Kita-ku, Sapporo 060-8628, Japan bGraduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan cJoining and Welding Research Institute, Osaka University, 11-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan |