[1
]Mathematics Department, University of Oviedo, c/Federico García Lorca 18, 33007 Oviedo,
Spain
[2
]Department of Information Engineering, Electronics and Telecommunications (DIET),
Sapienza University of Rome, Via Eudossiana 18, 00184 Rome, Italy
[3
]Department of Risk Assessment and Industrial Safety, Central Mining Institute, Plac
Gwarków 1, 40166 Katowice, Poland