1. Mechanics Laboratory, University of Douala, Douala, Cameroon
2. Laboratory of Mechanics and Adapted Materials, University of Douala, Douala, Cameroon
3. Laboratory of Industrial Systems and Environment, University of Dschang, Bandjoun, Cameroon
4. Laboratory of Photochemistry and Macromolecular Engineering, University of Haute-Alsace, Mulhouse, France