Figure 1: (a) The number of news and (b) the number of comments as the functions of time. In this figure, we find abnormal busty phenomena during some days marked by shadow. With further analysis of the data, we find that these phenomena may result from exogenous factors. For example, there are two major natural disasters happened on April 14, 2010 and August 7, 2010, which are Qinghai earthquake and Zhouqu mudslide, respectively.