1. Department of Mathematics, Donghua University, Shanghai 201620, P. R. China
2. National Laboratory of Scientific Computing LNCC, 25651-076 Petrópolis, RJ, Brazil
3. Department of Mathematics, University of Bío-Bío, Concepción 4051381, Chile
4. Department of Mathematics, University of Brasília, 70910-900 Brasília, DF, Brazil