Department of Mathematics;
Nanjing University of Information Science and Technology;
Nanjing 210044;
China;
School of Mathematics and System Sciences;
Shandong University;
Jinan 250100;
China;
Laboratório Nacional de Computacao Científica;
MCT;
Avenida Getúlio Vargas 333;
25651-075 Petrópolis;
PJ;
Brazil;
Department of Mathematics;
East China Normal University;
Shanghai 200062;
China;