1. School of Electrical Engineering, Chongqing University, Chongqing, China
2. School of Economics and Business Administration, Chongqing University, Chongqing, China
3. School of Resources and Safety Engineering, Chongqing University, Chongqing, China
4. Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences, Langfang, China