[1] China Univ Petr, Sch Econ & Management, Qingdao 266580, Peoples R China
[2] China Univ Petr, Inst Energy Econ & Policy, Qingdao 266580, Peoples R China
[3] Nanjing Univ Aeronaut & Astronaut, Coll Econ & Management, Nanjing 211106, Peoples R China