Hong-Fang Ji1, Liang Shen2. 1. Shandong Provincial Research Center for Bioinformatic Engineering and Technique, Shandong University of Technology, Zibo 255049, P.R. China. Electronic address: jhf@sdut.edu.cn. 2. Shandong Provincial Research Center for Bioinformatic Engineering and Technique, Shandong University of Technology, Zibo 255049, P.R. China. Electronic address: shen@sdut.edu.cn.