1. NTT Device Technology Laboratories, NTT Corporation, 3-1 Morinosato,
Wakamiya, Atsugi 243-0198, Kanagawa, Japan
2. Bio-Medical and Informatics Research Center, NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato, Wakamiya, Atsugi 243-0198, Kanagawa, Japan