Affiliation: | (1) Department of Applied Mathematics, Faculty of Science, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo 162, Japan;(2) Department of Mathematics, College of Natural Sciences, Kyungpook National University, Taegu 702-701, Korea;(3) Department of Mathematics, University of North Carolina at Charlotte, UNCC Station Charlotte, NC 28223, USA |