1. E. L. Ginzton Laboratory, Stanford University, Stanford, CA 94305, USA.
2. National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430, Japan.
3. Department of Mathematical Informatics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
4. Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan.
5. NTT Basic Research Laboratories, 3-1 Morinosato, Wakamiya, Atsugi, Kanagawa 243-0198, Japan.
6. ImPACT Program, Japan Science and Technology Agency, Gobancho 7, Chiyoda-ku, Tokyo 102-0076, Japan.