Funding The author(s) disclosed receipt of the following financial support for the research, authorship, or publication of this article: The National Natural Science Foundation of China (71102097, 40971292), the Chinese Department of Education (08JA840012), the Guangdong Social Science Foundation (07YH01), the Guangzhou Social Science Foundation (07Q6), and Sun Yat-Sen University (14000-3181304). The supporting organizations intend to promote academic research.