1. Department of Mathematics , Federal University of St. Catarina , 88040-900 Florianópolis SC , Brazil
2. Department of Mathematics ; and Department of Chemical Engineering , Federal University of St. Catarina , 88040-900 Florianópolis SC , Brazil
3. Department of Mathematics , Federal University of St. Catarina , 88040-900 Florianópolis SC; and Department of Mathematics, Federal University of Piaui, 64049-550, Teresina PI , Brazil