1. Faculty of Electrical Engineering, University POLITEHNICA of Bucharest, Splaiul Independenţei no. 313, sector 1, 060042 Bucharest, Romania Romania
2. “Gh. Mihoc - C. Iacob” Institute of Statistical Mathematics and Applied Mathematics, The Romanian Academy, Romania
3. Faculty of Electrical Engineering, University POLITEHNICA of Bucharest, Splaiul Independenţei no. 313, sector 1, 060042 Bucharest, Romania