[1] Univ Beira Interior, Management & Econ Dept, Rua Marques dAvila & Bolama, P-6201001 Covilha, Portugal
[2] Univ Beira Interior, NECE UBI, Covilha, Portugal
[3] Beijing Inst Technol, Sch Management & Econ, Beijing, Peoples R China
[4] Beijing Inst Technol, Ctr Energy & Environm Policy Res, Beijing 100081, Peoples R China