Understanding the propagation of influence and the concept flow over a network in general has profound theoretical and practical implications. In this paper, we propose a novel approach to ranking individual members of a real-world communication network in terms of their roles in such propagation processes. We first improve the accuracy of the centrality measures by incorporating temporal attributes. Then, we integrate weighted PageRank and centrality scores to further improve the quality of these measures. We valid these ranking measures through a study of an email archive of a W3C working group against an independent list of experts. The results show that time-sensitive Degree, time-sensitive Betweenness and the integration of the weighted PageRank and these centrality measures yield the best ranking results. Our approach partially solves the rank sink problem of PageRank by adjusting flexible jumping probabilities with Betweenness centrality scores. Finally the text analysis based on Latent Semantic Indexing extracts key concepts distributed in different time frames and explores the evolution of the discussion topics in the social network. The overall study depicts an overview of the roles of the actors and conceptual evolution in the social network. These findings are important to understand the dynamics of the social networks.