1. Department of Mathematics, City University of Hong Kong, Tat Chee Avenue, Kowloon Tong, Kowloon, Hong Kong
2. Departamento de Matemática Aplicada II, E.T.S. de Ingeniería, Universidad de Sevilla, Camino de los Descubrimientos s/n, 41092 Sevilla, Spain
3. Laboratory of Renewable Energy and Dynamic of Systems, University Hassan II of Casablanca, Casablanca, Morocco