Institution: | 1. College of Science, University of Shanghai for Science and Technology, Shanghai, 200093 China;2. Department of Mathematics, Pusan National University, Busan, 46241 Republic of Korea;3. College of Mathematics and Information Science, Henan Normal University, Xinxiang, 453007 China;4. Department of Mathematics, University of Florida, 358 Little Hall, PO Box 118105, Gainesville, 32611-8105 FL, USA |