1. Department of Electromechanical Engineering, Centre for Aerospace Science and Technologies, UBI, University of Beira Interior, Calçada Fonte do Lameiro, 6201-001 Covilhã, Portugal
2. Scientific Area of Mathematics, ESTGV, Polytechnic Institute of Viseu, Campus Politécnico, 3504-510 Viseu, Portugal
3. Department of Mathematics and Applications, School of Sciences, Centre of Physics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal