1. Department of Physics, Žilina University, Univerzitná 1, 010 26 Žilina, Slovakia
2. Institute of Scientific and Industrial Research, Osaka University, CREST, Japan Science and Technology Agency, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
3. School of Computer Science, Tokyo University of Technology, 1404-1, Katakura, Hachioji, Tokyo 192-0982, Japan