pdf dblp BUPT_PRIS at TREC 2012 Crowdsourcing Track 1 Chuang Zhang | Minjie Zeng | Xiaokang Sang | Kailai Zhang | Houfu Kang Proceedings of The Twenty-First Text REtrieval Conference, TREC 2012, Gaithersburg, Maryland, USA, November 6-9, 2012