[1] Univ Fed Rio Grande do Norte, Int Inst Phys, Campus Univ Lagoa Nova, BR-59078970 Natal, RN, Brazil
[2] Univ Fed Rio Grande do Norte, Dept Theoret & Expt Phys, Campus Univ Lagoa Nova, BR-59078970 Natal, RN, Brazil
[3] Swansea Univ, Dept Phys, Swansea SA2 8PP, Wales
[4] Univ Oviedo, Dept Phys, Avda Federico Garcia Lorca S-N, Oviedo 33007, Spain
[5] Inst Univ Ciencias & Tecnol Espaciales Asturias IC, Calle Independencia 13, Oviedo 33004, Spain
[6] Univ Southampton, Sch Math Sci, Southampton SO17 1BJ, England