1. Department of Mechanical Engineering, Applied Biotechnology and Engineering Laboratory, Higher Technical Teacher's Training College (ENSET) Ebolowa, University of Yaounde I, Yaoundé, Cameroon
2. Department of Mathematics, School of Digital Technologies, Tallinn University, Tallinn, Estonia
3. Departamento de Matemáticas y Física, Universidad Autónoma de Aguascalientes, Aguascalientes, Mexico