Institution: | 1. Group of Analysis & Mathematic modeling, Departamento de Matemática, Universidad Técnica Federico Santa Maria, , Avenida Espa?a, Valparíso, Chile. This author was partially supported by programa Basal CMM, Universidad de Chile;2. Laboratoire de Mathématiques (UMR CNRS 6205), Université de Bretagne Occidentale, , 29238 Brest Cedex 3, France |