参考:
http://blog.sciencenet.cn/blog-620659-579885.html
http://baike.baidu.com/link?url=HnHd3lU9mcVXwhKtTz78KucVBKXQTbiNHv1Mte4I7EZz0hqJbSIpmweqyIQLmpAVsNa9UgaD00d64Kr156WyJa