[1] Nankai Univ, TEDA Appl Phys Inst, Tianjin, Peoples R China
[2] Nankai Univ, Sch Phys, Tianjin, Peoples R China
[3] Univ Crete, Dept Appl Math, Iraklion, Greece
[4] Univ Quebec, INRS EMT, Quebec City, PQ, Canada
[5] San Francisco State Univ, Dept Phys & Astron, San Francisco, CA 94132 USA