1.School of Science, Qingdao Technological University, Qingdao, Shandong 266033, China
2.School of Computer Science and Technology, Shandong Jianzhu University, Jinan 250101, China
3.Department of Power Grid Maintenance Training, State Grid of China Technology College, Jinan 250002, China
4.Basic Courses Department, Shandong University of Science and Technolagy, Tai’an, Shandong 271021, China