Noboru Kanedera, Tetsuo Funada, Seiichi Nakagawa. Lecture subtopic retrieval by retrieval keyword expansion using subordinate concept. In Takao Kobayashi, Keikichi Hirose, Satoshi Nakamura, editors, INTERSPEECH 2010, 11th Annual Conference of the International Speech Communication Association, Makuhari, Chiba, Japan, September 26-30, 2010. pages 1281-1284, ISCA, 2010. [doi]