G. Feng, T. Liu, Y. Wang, Y. Bao, Z. Ma, X. Zhang, and W. Ma. Proceedings of the 29th annual international ACM SIGIR conference on Research and development in information retrieval - SIGIR \textquotesingle06, ACM Press, (2006)
J. Teevan, C. Alvarado, M. Ackerman, and D. Karger. Proceedings of the SIGCHI Conference on Human Factors in Computing Systems, page 415--422. New York, NY, USA, ACM, (2004)