1. School of Science, Xi’an Polytechnic University, Xi’an, Shaanxi 710048, CHINA
2. Departamento de Análise Matemática, Facultade de Matemáticas, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, SPAIN
3. Faculty of Science, King Abdulaziz University, P.O. Box 80203, 21589 Jeddah, SAUDI ARABIA