1. Computational Science Research Laboratory, Fujitsu Limited, Ota-ku, Tokyo 144, Japan
2. Department of Applied Physics, Faculty of Engineering, Fukui University, Fukui 910, Japan
3. Department of Physics, Hiroshima University, Higashi-Hiroshima 724, Japan
4. Faculty of Education, Yamagata University, Yamagata, Japan
5. IPS, ETH-Zrich, CH-8092 Zūrich, Switzerland
6. Konrad-Zuse-Zentrum für Informationstechnik Berlin, Berlin 31, Germany
7. FEST, Schmeilweg 5, 69118 Heidelberg, Germany
8. Institut für Theoretische Physik, Universität Heidelberg, 6900 Heidelberg, Germany