1. Faculty of Computer Science and System Engineering, Okayama Prefectural University, Soja, Okayama 719-1197, Japan
2. Center for Energy and Environmental Science, Shinshu University, Matsumoto, Nagano 390-8621, Japan
3. Institute of Laser Engineering, Osaka University, Suita, Osaka 565-0871, Japan
4. Advanced Technology R&D Center, Mitsubishi Electric Corporation, Amagasaki, Hyogo 661-8661, Japan