1. SYSTEC, Faculty of Engineering, Porto University, Institute for Systems and Robotics Rua Dr. Roberto Frias s/n, 4200–465 Porto, Portugal
2. Department of Mathematics and Informatics, Faculty of Sciences, Lucian Blaga University of Sibiu, I.Raţiu, Street, No.5–7, 550012, Sibiu, Romania
3. Department of Hospitality Services, Babeş-Bolyai University, Horea street, no 7, 400174, Cluj-Napoca, Romania