Affiliation: | 1. Department of Mathematics, Valahia University of Târgovişte, Bd. Unirii 18, Târgovişte 130082, Romania;2. Doctoral School of Faculty of Applied Sciences, University “Politehnica” of Bucharest, Splaiul Independentei 313, 060042 Bucharest, Romania;3. Academy of Romanian Scientists, Splaiul Independenţei 54, Bucharest 050094, Romania |