Affiliation: | 1. Depto. de Matemática, ICE, Universidade Federal de Juiz de Fora, MG, Brazil;2. Yerevan State University, 1 Alex Manoogian St., Yerevan 0025, Armenia;3. Laboratory of Mathematical Physics, Tomsk Polytechnic University, 634050 Tomsk, Lenin Ave. 30, Russian Federation |