Institution: | 1. Mathematical Sciences & Technology Research Laboratories, Advanced Technology Research Laboratories, Nippon Steel & Sumitomo Metal Corporation, , Futsu 293‐8511, Japan;2. Department of Mathematics, Inha University, , Incheon 402‐751, South Korea;3. Department of Mathematics, Hokkaido University, , Sapporo 060‐0810, Japan;4. Department of Mathematics, Southeast University, , Nanjing 210096, China |