基金Supported by National Basic Research Program of China (973 Program) (2010CB731800), Key Project of Natural Science Fouudation of China (60934003), National Natural Science Foundation of China (61074065, 60974018), Natural Science Foundation of Hebei Province(F2012203119), and the Science Foundation of Yanshan University for the Excellent Ph. D. Students (201204) The authors thank Chen Cai-Lian of the Shanghai Jiao Tong University for her comments on English polishing and problem formulation.