State Key Laboratory of Plateau Ecology and Agriculture Department of Computer Technology and Applications Qinghai University Xining 810016 China;
Department of Computer Science and Technology Tsinghua University Beijing 100084 China;
State Key Laboratory of Plateau Ecology and Agriculture Department of Computer Technology and Applications Qinghai University Xining 810016 ChinaJianqiang Huang Department of Computer Science and Technology Tsinghua University Beijing 100084 China;