1. Department of Physics, Systems Engineering and Signal Theory, University of Alicante, 03690 Alicante, Spain
2. Department of Civil Engineering, University of Alicante, 03690 Alicante, Spain
3. Department of Mathematics, Universidade da Coruña, 15071 A Coruña, Spain
4. Department of Information Engineering and Computer Science, University of Trento, 38123 Trento, Italy