1. School of Economics, Zhongnan University of Economics and Law, No. 182, Nanhu Avenue, Wuhan 430073, P. R. China
2. Institut Supérieur de Technologies Appliquées — TechnoLAB-ISTA, ACI-2000 BAMAKO Mali
3. College of Economics and Management, Nanjing Agricultural University, Nanjing 210095, P. R. China
4. School of Management and Economics, Beijing Institute of Technology, Beijing 100081, P. R. China