1. The Academy of Applied Technical and Preschool Studies, Department Vranje, Niš, Serbia
2. Department of Physics, Faculty of Sciences and Mathematics, University of Niš, Serbia
3. Facultad de Ciencias Físico Matemáticas Departamento, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
4. Elementary School „Vuk Stefanović Karadžić“, Kragujevac, Serbia