T. Yang, R. Jin, Y. Chi, and S. Zhu. Proceedings of the 15th ACM SIGKDD international conference on Knowledge discovery and data mining, page 927--936. ACM, (2009)
S. Fortunato, and C. Castellano. (2007)cite arxiv:0712.2716Comment: 42 pages, 13 figures. Chapter of Springer's Encyclopedia of Complexity and System Science.