supported by the National Natural Science Foundation of China(21006081,20976043);Natural Science Foundation of Hu-nan Province(11JJ3024,09JJ8002);Scientific Research Fund of Hunan Provincial Education Department(11B122);Scientificand Technological Plan Projec tof Hunan Province(2010JT4051);Program for New Century Excellent Talents in University(NCET-10-0168)~~