


Volume 516, Nº 1 (2024)
MATHEMATICS
On reconstruction of Kolmogorov operators with discontinuous coefficients
Resumo
We obtain broad sufficient conditions for reconstructing the coefficients of a Kolmogorov operator by means of a solution to the Cauchy problem for the corresponding Fokker–Planck–Kolmogorov equation.



Exact estimates of functions in Sobolev spaces with uniform norm
Resumo
For functions from the Sobolev space and an arbitrary point , the best estimates are obtained in the inequality . The connection of these estimates with the best approximations of splines of a special kind by polynomials in and with the Peano kernel is established. Exact constants of embedding the space in are found.



On undecidability of subset theories of some unars
Resumo
This paper is dedicated to studying of the algorithmic properties of unars with an injective function. We prove that the theory of every such unar admits quantifier elimination if the language is extended by a countable amount of predicate symbols. Necessary and sufficient conditions are established for the quantifier elimination to be effective, and a criterion of decidability of theories of such unars is formulated. Using this criterion we build a unar such that its theory is decidable, but the theory of the unar of its subsets is undecidable.



Induced forests and trees in Erdös–Rényi random graph
Resumo
We prove concentration in the interval of size for the size of the maximum induced forest (of bounded and unbounded degree) in for for arbitrary fixed . We also show 2-point concentration of the size of the maximum induced forest (and tree) of bounded degree in the binomial random graph for



Generalized solution of a mixed problem for a wave equation with a non-smooth right-hand side
Resumo
Under minimal conditions on the right side of the wave equation, a generalized solution of the mixed problem is constructed. The solution is presented as a series from the Fourier method, its sum is found. The form of a generalized solution of a mixed problem for an inhomogeneous telegraphic equation is given.



On kernels of invariant Schrödinger operators with point interactions. Grinevich–Novikov problem
Resumo
According to Berezin and Faddeev, a Schrödinger operator with point interactions is any self-adjoint extension of the restriction of the Laplace operator to the subset of the Sobolev space . The present paper studies the extensions (realizations) invariant under the symmetry group of the vertex set of a regular m-gon. Such realizations HB are parametrized by special circulant matrices . We describe all such realizations with non-trivial kernels. А Grinevich–Novikov conjecture on simplicity of a zero eigenvalue of the realization HB with a scalar matrix and an even is proved. It is shown that for an odd m non-trivial kernels of all the realizations with scalar are two-dimensional. Besides, for arbitrary realizations the estimate is proved, and all the invariant realizations of the maximal dimension are described. One of them is the Krein realization, which is the minimal positive extension of the operator .



A joint logic of problems and propositions
Resumo
In a 1985 commentary to his collected works, Kolmogorov informed the reader that his 1932 paper On the interpretation of intuitionistic logic “was written in hope that with time, the logic of solution of problems [i.e., intuitionistic logic] will become a permanent part of a [standard] course of logic. A unified logical apparatus was intended to be created, which would deal with objects of two types – propositions and problems.” We construct such a formal system as well as its predicate version, QHC, which is a conservative extension of both the intuitionistic predicate calculus QH and the classical predicate calculus QC. The axioms of QHC are obtained as a result of a simultaneous formalization of two well-known alternative explanations of intiuitionistic logic: 1) Kolmogorov's problem interpretation (with familiar refinements by Heyting and Kreisel) and 2) the proof interpretation by Orlov and Heyting, as clarified and extended by Gödel.



Description of turbulent flows using a kinetic model
Resumo
In this paper, a closed system of equations for describing turbulent flows is obtained. Additional equations for cross pulsation moments are derived on the basis of a balanced kinetic equation, with the help of which a quasi gas-dynamic system of equations was previously obtained. The results of the calculation of the spatially two-dimensional problem of the mixing layer of two streams are presented.



Continued fractions in hyperelliptic fields with an arbitrarily large period length
Resumo
The article proves the following statement: in any hyperelliptic field L defined over the field of algebraic numbers K which having non-trivial units of the ring of integer elements of the field L, there is an element for which the period length of the continued fraction is greater any pre-given number.



Invariants of seventh-order homogeneous dynamical systems with dissipation
Resumo
New cases of integrable dynamical systems of the seventh order homogeneous in terms of variables are presented, in which a system on a tangent bundle to a three-dimensional manifold can be distinguished. In this case, the force field is divided into an internal (conservative) and an external one, which has a dissipation of a different sign. The external field is introduced using some unimodular transformation and generalizes the previously considered fields. Complete sets of both first integrals and invariant differential forms are given.



On an extremal problem for compactly supported positive definite functions
Resumo
This article considers an extremal problem for positive definite functions on with a fixed support and a fixed value at the origin (the class 𝔉 r (
)). It is required to find the least upper bound of a special form functional over 𝔉 r (
). This problem is a generalization of the Turán problem for functions with support in a ball. We have obtained a general solution to this problem for
. As a consequence, new sharp inequalities are obtained for derivatives of entire functions of exponential spherical type.









On the Boyarsky–Meyers estimate for the gradient of the solution to the Dirichlet problem for the second order elliptic equation with drift. The case the critical Sobolev exponen
Resumo
The increased integrability of the gradient of the solution to the Increased integrability of the gradient o the solution to the homogeneous Dirichlet problem for the Poisson equation with lower terms in a bounded Lipschitz domain is established. A proof of the unique solvability of this problem is also given.



Inversion problem for Radon transforms defined on pseudoconvex sets
Resumo
This paper is devoted to some questions of inversion for the classical and generalized integral Radon transform. The main question is to determine information about the integrand functions if the values of some integrals are known. A feature of the work of the authors of this message is an analysis of the case when the function is integrated according to hyperplanes in finite-dimensional Euclidean space, and the integrands depend not only on the variables of integration, but also on some of the variables characterizing the hyperplanes. At the same time, the number of independent variables describing known integrals are smaller than those of the unknown integrand. We consider discontinuous integrands defined specifically introduced pseudo-convex sets. A Stefan-type problem is posed about finding surfaces discontinuities of the integrand function. The work provides formulas based on the application special integro-differential operators to known data and allowing you to solve the assigned tasks.



Multi-vortices and lower bounds for the attractor dimension of 2d Navier-Stokes equations
Resumo
A new method for obtaining lower bounds for the dimension of attractors for the Navier–Stokes equations, which does not use Kolmogorov flows, is presented. Using this method, exact estimates of the dimension are obtained for the case of equations on a plane with Ekman damping. Similar estimates were previously known only for the case of periodic boundary conditions. In addition, similar lower bounds are obtained for the classical Navier–Stokes system in a two-dimensional bounded domain with Dirichlet boundary conditions.



COMPUTER SCIENCE
On ml methods for network powered by computing infrastructure
Resumo
The paper considers the application of machine learning methods for optimal resource management for Network Powered by Computing (NPC) – a new generation computing infrastructure. The relation between the proposed computing infrastructure and the GRID concept is considered. It is shown how machine learning methods applied to computing infrastructure management make it possible to solve the problems of computing infrastructure management that did not allow the GRID concept to be fully implemented. As an example, the application of multi-agent optimization methods with reinforcement learning for network resources management is considered. It is shown that the application of multi-agent machine learning methods makes it possible to increase the speed of distribution of transport flows and ensure optimal NPC network channel load according to the criterion of uniform load distribution, and that such management of network resources is more effective than a centralized approach.


