Institution: | (1) Instituto de Física Gleb Wataghin , Universidade Estadual de Campinas, Unicamp, 13083-970 Campinas, São Paulo, Brasil;(2) Physics Department, State University of Maringá, 87020-900 Maringá, PR, Brazil;(3) Present address: Department of Applied Mathematics, IMECC, State University of Campinas, 13081-970 Campinas, SP, Brazil |