1. Region of Electrical and Electronic Systems Engineering, Ibaraki University, 4-12-1 Nakanarusawa-cho, Hitachi, Ibaraki 316-8511, Japan
2. Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, (ISC-CNR) c/o Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino 10129, Italy
3. Department of Computer Science, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan