基金Project supported by the National Outstanding Youth ScienceFoundation of China (Grant No. 50425206), the National NaturalScience Foundation of China (Grant No. 10647132), the NaturalScience Foundation of Hunan Provincial Education Department(Grant No. 06C652), and the Natural Science Foundation of HunanProvincial Education Department (Grant No. 06C653).
基金This work was supported by the Natural Science Foundation of Hu＇nan Province （Grant No. 00JJY2072） the Foundation of Educational Committee of Hu＇nan Province （Grant No. 01B019）.
