PKU@TRECVID2009: Single-Actor and Pair-Activity Event Detection in surveillance Video. - Zhipeng Hu; Guangnan Ye; Guochen Jia; Xibin Chen; Kaihua Jiang; Yaowei Wang 001; Yonghong Tian 001; Xihong Wu; Wen Gao 001; Qiong Hu; Lei Qing (TRECVID, 2009)