[1] Univ Catolica Santisima Concepcion, Dept Matemat & Fis Aplicadas, Alonso Ribera 2850, Concepcion, Chile
[2] Univ Wroc Aw, Inst Theoret Phys, Pl M Borna 9, PL-50204 Wroclaw, Poland
[3] Univ Adolfo Ibanez, Fac Artes Liberales, Dept Ciencias, Vina Del Mar, Chile