1. Contribution from the Institute of Industrial Science, University of Tokyo, Roppongi, Minato-ku, Tokyo, Japan, The Noguchi Institute, Kaga, Itabashi-ku, Tokyo, Japan, Ajinomoto Co., Kyobashi, Chuo-ku, Tokyo, Japan, and Teikyo University of Science and Technology, Yatsusawa, Uenohara, Yamanashi 409-0193, Japan