V.G. Shadrov - Ph.D. (Phys.-Math.), Leading Research Scientist, Scientific-Practical Materials Research Centre (Belarus) L.V. Nemtsevich - Research Scientist, Scientific-Practical Materials Research Centre (Belarus) A.V. Boltushkin - Ph.D. (Phys.-Math.), Senior Research Scientist, Scientific-Practical Materials Research Centre (Belarus). E-mail: nemtsevich@ifttp.bas-net.by