1. Department of Industrial Engineering, School of Mechanical Engineering, Northwestern Polytechnical University, Xi’an, Shaanxi 710072, P. R. China
2. School of Mathematical Science, Ocean University of China, Qingdao 266100, P. R. China
3. Department of Management Science and Engineering, School of Economics and Management, Xidian University, Xi’an, Shaanxi 710126, P. R. China