1. School of Economics and Management, North China Electric Power University, Hui Long Guan, Chang Ping District, Beijing 102206, China
2. Faculty of Arts and Social Sciences, University of Singapore, 21 Lower Kent Ridge Rd, Singapore 119077, Singapore
3. School of Economics and Management, North China Electric Power University, No. 689 Hua Dian Road, Baoding 071003, China
4. Energy and Economic Development & Philosophy and Social Science Research Base of Hebei Province (North China Electric Power University), No. 689 Hua Dian Road, Baoding 071003, China