Masataka Imai, Toru Kouyama, National Institute of Advanced Industrial Science and Technology (AIST), Japan; Junichi Kurihara, Hokkaido University, Japan; Toshinori Kuwahara, Shinya Fujita, Yuji Sakamoto, Tohoku University, Japan; Sei-Ichi Saitoh, Takafumi Hirata, Yukihiro Takahashi, Hokkaido University, Japan