1. Institute of Engineering, Shinshu University, Nagano 380-8553, Japan
2. Seiko Epson Corporation, 3-3-5 Owa, Suwa, Nagano 392-8502, Japan
3. Faculty of Engineering, Information and Systems, University of Tsukuba and RIKEN AIP, 1-1-1 Tennodai, Tsukuba 305-8573, Japan