supported by the National Natural Science Foundation of China(30100015,30560020);China Postdoctoral Science Foundation(2005037111);Program for New Century Excellent Talents in University(NCET-07-0220);the Provincial Foundation for Excellent Youth in Science and Technology Field of Guizhou(20050520);Specialized Research Fund for the Doctoral Program of Higher Education(20060657001);the Nomarch Foundation for Excellent Talents in Science;Technology and Education Field of Guizhou(2005357)