1. Graduate School of Computer Science and Systems Engineering, Okayama Prefectural University, Soja, Okayama 719-1197, Japan
2. Department of Materials Physics, Nagoya University, Nagoya 464-8603, Japan
3. Department of Information and Communication Engineering, Okayama Prefectural University, Soja, Okayama 719-1197, Japan
4. Nanostructures Research Laboratory, Japan Fine Ceramics Center, Nagoya 456-8587, Japan