Vol 230, No 1 (2018)

In the class of models of some theory in a countable first order language, we consider relationships between isomorphism, elementary embeddability, and elementary equivalence.

We consider a class of quasielliptic operators in Rⁿ and establish the isomorphism property in special weighted Sobolev spaces. In more general weighted spaces, we obtain the unique solvability conditions for quasielliptic equations and prove estimates for solutions. Based on the obtained results, we study the solvability of the initial problem for equations that are not solvable with respect to the higher order derivative.

We construct a discretization of the phase portrait of a 3-dimensional dynamical system of biochemical kinetics with piecewise linear right-hand sides. We describe geometry of the phase portrait and construct an invariant piecewise linear surface bounded by a stable cycle of this system composed of eight linear segments.

We establish the solubility of a group with Sylow 2-subgroup of the least order in the centralizer of an almost regular involution. We also study the structure of a group G with an almost perfect and almost regular involution a.

We consider multiplicative functions and Prym differentials on variable tori. We prove counterparts of the theorem on the total sum of residues for Prym differentials of any integer order on tori. As a consequence, reciprocity laws are proved. We construct elementary Prym differentials of all kinds with any integer order which holomorphically depend on the moduli of tori and characters. We derive an analogue of the Appell decomposition formula for functions with characters. We also study vector bundles of Prym differentials of any integer order over the product of Teichmueller spaces for a torus and a group of characters.

We obtain bounds for the distribution of the number of crossings of a strip by random walk paths.

We introduce the notions of n-algebraic complete algebras and n-algebraic completeness, which makes it possible to find algebraic closures of subsets of universal algebras. We clarify how the n-algebraic completeness of an algebra is connected with the pseudodirect product of algebras.

We establish the unique solvability of the equilibrium problem for a two-layer body. One layer contains a crack, whereas the second one is glued along its edge to the first layer in such a way that to cover one of the crack ends. In the case, where the second layer is a rigid plate, we show that the problem with a rigid patch is the limit of problems with elastic patches as the rigidity parameter tends to infinity. We also study the optimal control problem with the exterior forces acting on both layers taken for the control function.

We consider model pseudodifferential equations in canonical multidimensional domains with boundary singularities presented by the union of cones or a cone of lower dimension. We study the solvability of these equations by using the wave factorization concept.