Search

In this paper, we consider the operator sheaf $$ -\Delta +V+\varepsilon {\mathrm{\mathcal{L}}}_{\varepsilon}\left(\lambda \right)+{\lambda}^2 $$ in the space L2(ℝ2), where the real-valued potential V depends only on the first variable x1, e is a small positive parameter, λ is the spectral parameter, $$ {\mathrm{\mathcal{L}}}_{\varepsilon}\left(\lambda \right) $$ is a localized operator bounded with respect to the Laplacian −Δ, and the essential spectrum of this operator is independent of e and contains certain critical points defined as isolated eigenvalues of the operator $$ -\frac{d^2}{dx_1^2}+V\left({x}_1\right) $$ in L2(ℝ). The basic result obtained in this paper states that for small values of e, in neighborhoods of critical points mentioned, isolated eigenvalues of the sheaf considered arise. Sufficient conditions for the existence or absence of such eigenvalues are obtained. The number of arising eigenvalues is determined, and in the case where they exist, the first terms of their asymptotic expansions are found.

In this paper, we prove the integrability of certain classes of dynamical systems on the tangent bundles of four-dimensional manifolds (systems with four degrees of freedom). The force field considered possessed so-called variable dissipation; they are generalizations of fields studied earlier. This paper continues earlier works of the author devoted to systems on the tangent bundles of two- and three-dimensional manifolds.

We show that the phase tropical pair-of-pants is (ambient) isotopic to the complex pair-of-pants. This paper can serve as an addendum to the author's joint paper with Ruddat arXiv:2001.08267 where an isotopy between complex and ober-tropical pairs-of-pants was shown. Thus all three versions are isotopic., 10 pages, 8 figures. arXiv admin note: text overlap with arXiv:2001.08267

A very short proof of an unpublished result due to O. Gabber is given. More exactly, let R be a regular local ring containing a finite field k. Let G be a simply-connected reductive group scheme over k. It is proved that a principal G-bundle over R is trivial if it is trivial over the fraction field of R. This is the mentioned unpublished result due to O. Gabber. In this paper, this result is derived from a purely geometric one, proved in another paper of the author and stated in the Introduction.

The aim of this (mostly expository) article is to show a connection between the finiteness conditions arising in twisted K-theory. There are two different conditions arising naturally in two main approaches to the problem of computing the index of the appropriate family of elliptic operators (the approach of Nistor and Troitsky and the approach of Mathai, Melrose, and Singer). These conditions are formulated absolutely differently, but in some sense they should be close to each other. In this paper, we find this connection and prove the corresponding formal statement. Thereby it is shown that these conditions map to each other. This opens a possibility to synthesize these approaches. It is also shown that the finiteness condition arising in the paper of Nistor and Troitsky is a special case of the finiteness condition that appears in the paper of Emerson and Meyer, where the theorem of Nistor and Troitsky is proved not only for the case of a bundle of Lie groups, but also for the case of a general groupoid.

In this paper, we study questions related to the theory of stochastic processes on Lie nilpotent groups. In particular, we consider the stochastic process on the Heisenberg group H3(ℝ) whose trajectories satisfy the horizontal conditions in the stochastic sense relative to the standard contact structure on H3 (ℝ). It is shown that this process is a homogeneous Markov process relative to the Heisenberg group operation. There was found a representation in the form of a Wiener integral for a one-parameter linear semigroup of operators for which the Heisenberg sublaplacian generated by basis vector fields of the corresponding Lie algebra L(H3) is producing. The main method of solving the problem in this paper is using the path integrals technique, which indicates the common direction of further development of the results.

The paper is devoted to one open extremal problem in the geometric function theory of complex variables associated with estimates of a functional defined on the systems of non-overlapping domains. We consider the problem of the maximum of a product of inner radii of n non-overlapping domains containing points of a unit circle and the power γ of the inner radius of a domain containing the origin. The problem was formulated in 1994 in Dubinin’s paper in the journal “Russian Mathematical Surveys” in the list of unsolved problems and then repeated in his monograph in 2014. Currently, it is not solved in general. In this paper, we obtained a solution of the problem for five simply connected domains and power γ ∈ (1; 2:57] and generalized this result to the case of multidimensional complex space.

The paper presents a general duality theory for vector measure spaces taking its origin in the author's papers written in the 1960s. The main result establishes a direct correspondence between the geometry of a measure in a vector space and the properties of the space of measurable linear functionals on this space regarded as closed subspaces of an abstract space of measurable functions. An example of useful new features of this theory is the notion of a free measure and its applications., Comment: 20 pp.23 Ref

The existing notion of the Kostrikin radical as a radical in the Kurosh–Amitsur sense on classes of Mal’tsev algebras over rings with 1/6 is not completely justified. More precisely, to the fullest extent it is true for classes of Lie algebras over fields of characteristic zero and, as shown in the given paper, classes of algebraic Lie algebras of degree not greater than n over rings with 1/n! at all n ≥ 1. Similar conclusions are obtained in the paper also for the Jordan, regular, and extremal radicals constructed analogously to the Kostrikin radical.

The CMV matrix is the five-diagonal matrix that represents the operator of multiplication by the independent variable in a special basis formed of Laurent polynomials orthogonal on the unit circle C. The article by Cantero, Moral, and Velazquez, published in 2003 and describing this matrix, has attracted much attention because it implies that the conventional orthogonal polynomials on C can be interpreted as the characteristic polynomials of the leading principal submatrices of a certain five-diagonal matrix. The present paper recalls that finite-dimensional sections of the CMV matrix appeared in papers on the unitary eigenvalue problem long before the article by Cantero et al. was published. Moreover, band forms were also found for a number of other situations in the normal eigenvalue problem.

In the paper, a family of representations of maximal solvable subgroups of the simple Lie groups O(p, q), U(p, q), and Sp(p, q), where 1 ≤ p ≤ q, is introduced. These subgroups are called the Iwasawa subgroups of the corresponding simple groups. The main property of these representations is the existence of nontrivial 1-cohomology with values in the representations. For groups of rank 1, the representations from this family are unitary; for ranks greater than 1, they are nonunitary. The paper continues a series of our previous papers and serves as an introduction to the theory of nonunitary current groups.

A characterization of the prime radical of loops as the set of strongly Engel elements was given in our earlier paper. In this paper, some properties of the prime radical of loops are considered. Also a connection between the prime radical of the loop of units of an alternative ring and the prime radical of this ring is given.

This paper is a direct continuation of [26], where we proved that every normal lattice isomorphism of supersolvable Lie ring is induced at the isomorphism. In the present paper,we generalize this theorem for rational Lie rings.

In the present paper we consider local minimal and extremal networks in normed spaces. It is well known that in the case of the Euclidean space these two classes coincide and the length of a local minimal network can be found by using only the coordinates of boundary vertices and the directions of boundary edges (the Maxwell formula). Moreover, as was shown by Ivanov and Tuzhilin [15], the length of a local minimal network in the Euclidean space can be found by using the coordinates of boundary vertices and the structure of the network. In the case of an arbitrary norm there are local minimal networks that are not extremal networks, and an analogue of the formula mentioned above is only true for extremal networks; this is the main result of the paper. Moreover, we generalize the Maxwell formula for the case of extremal networks in normed spaces and give an explicit construction of norming functionals used in the formula for several normed spaces.

In the present paper, we construct an invariant of knots in the thickened sphere with g handles dependent on 2g + 3 variables. In the construction of the invariant we use the Wirtinger presentation of the knot group and the concept of parity introduced by Manturov [9]. In the present paper, we also consider examples of knots in the thickened torus considered in [2] such that their nonequivalence is proved by using the constructed polynomial.

The paper contains both known and new results on automorphism-invariant modules, automorphism-coinvariant modules and modules which are invariant or coinvariant with respect to idempotent endomorphisms of its hull and its cover, respectively. The main results are given with proofs.

In this paper, we describe the technique of extremely monotonic functions in the theory of computable linear orders. The basic definitions of extremely monotonic functions and their generalizations are given, and a number of their basic properties and applications are presented.

The categoricity spectrum of a computable structure S is the set of all Turing degrees capable of computing isomorphisms among arbitrary computable presentations of S. The degree of categoricity of S is the least degree in the categoricity spectrum of S. This paper is a survey of results on categoricity spectra and degrees of categoricity for computable structures. We focus on the results about degrees of categoricity for linear orders and Boolean algebras. We construct a new series of examples of degrees of categoricity for linear orders.

In this paper, the length of the group algebra of a dihedral group in the modular case is computed under the assumption that the order of the group is a power of two. Various methods for studying the length of a group algebra in the modular case are considered. It is proved that the length of the group algebra of a dihedral group of order 2k+1 over an arbitrary field of characteristic 2 is equal to 2k.

We study the Gnedin–Kingman graph, which corresponds to Pieri’s rule for the monomial basis {Mλ} in the algebra QSym of quasisymmetric functions. The paper contains a detailed announcement of results concerning the classification of indecomposable semifinite harmonic functions on the Gnedin–Kingman graph. For these functions, we also establish a multiplicativity property, which is an analog of the Vershik–Kerov ring theorem.

Let R be a discrete valuation ring with infinite residue field and X a smooth projective curve over R. Let G be a simple simply-connected group scheme over R and E a principal G-bundle over X. It is proved that E is trivial locally for the Zariski topology on X providing E is trivial over the generic point of X. The main aim of the present paper is to develop a method rather than to get a very strong concrete result.

This paper deals with studying some properties of a monogenic function defined on a vector space with values in the Clifford algebra generated by the space. We provide some expansions of a monogenic function and consider its application to study solutions of second-order partial differential equations.

Certain Hardy inequalities in domains of Euclidean space contain sharp but unreachable constants. V. G. Maz’ya and other authors used this fact to improve the corresponding inequalities by adding new integral terms. In this paper, a survey of results in this direction initiated by H. Brezis and M. Marcus is presented. Also, we give some generalizations of Brezis–Marcus-type inequalities to the case of Rellich-type inequalities with weights that are powers of the distance from a point to the boundary of the domain. Generalizations to the case of conformally invariant integral inequalities in simply connected and doubly connected planar hyperbolic domains are discussed.

The paper is a review of the latest results of I. R. Kayumov and S. Ponnusamy on the Bohr inequality. An exact estimate in the strong Bohr inequality is obtained and the Bohr–Rogosinski radius for a certain class of subordinations is examined. All results are exact.

In this paper, we examine the problem on the description in terms of the Laplace transform of functionals from the conjugate space for the Hilbert space of entire functions of n variables constructed by a convex function in ℂn, which depends on the modules of variables and grows at infinity faster than a‖z‖ for any a > 0.

In this paper, we study spectral decompositions with respect to a system of generalized eigenvectors of second-order differential operators on an interval whose resolvents possess convolution representations. We obtain the convolution representation of resolvents of second-order differential operators on an interval with integral boundary conditions. Then, using the convolution generated by the initial differential operator, we construct the Fourier transform. A connection between the convolution operation in the original functional space and the multiplication operation in the space of Fourier transforms is established. Finally, the problem on the convergence of spectral expansions generated by the original differential operator is studied. Examples of convolutions generated by operators are also presented.

In this paper, weight subspaces of the space of analytic functions on a bounded convex domain of the complex plane are considered. Descriptions of spaces that are strongly dual to the inductive and projective limits of uniformly weight spaces of analytic functions in a bounded convex domain D ⊂ ℂ are obtained in terms of the Fourier–Laplace transform. For each normed, uniformly weight space H(D, u), we construct the minimal vector space ℋi(D, u) containing H(D, u) and invariant under differentiation and the maximal vector space ℋp(D, u) contained in H(D, u) and invariant under differentiation. We introduce natural locally convex topologies on these spaces and describe strongly dual spaces in terms of the Fourier–Laplace transform. The existence of representing exponential systems in the space ℋi(D, u) is proved.

We consider examples of operator Lipschitz functions f for which the operator Lipschitz seminorm ‖f‖OL(ℝ) coincides with the Lipschitz seminorm ‖f‖Lip(ℝ). In particular, we consider the operator Lipschitz functions f such that |f ' (0)| = ‖f‖OL(ℝ). It is well known that f has this property if its derivative f′ is positive definite. It is proved in this paper that there are other functions having this property. It is also shown that the identity |f ' (t0)| = ‖f‖OL(ℝ) implies the continuity of f at t0. In fact, a more general statement is established concerning commutator Lipschitz functions on a closed subset of the complex plane.

In this paper, we state and examine the eigenvalue problem for symmetric tensor-block matrices of arbitrary even rank and arbitrary size m × m, m ≥ 1. We present certain definitions and theorems of the theory of tensor-block matrices. We obtain formulas that express classical invariants (that are involved in the characteristic equation) of a tensor-block matrix of arbitrary even rank and size 2×2 through the first invariants of powers of the same tensor-block matrix and also inverse formulas. A complete orthonormal system of tensor eigencolumns for a tensor-block matrix of arbitrary even rank and size 2 × 2 is constructed. The generalized eigenvalue problem for a tensor-block matrix is stated. As a particular case, the tensor-block matrix of tensors of elastic moduli is considered. We also present canonical representations of the specific energy of deformation and defining relations. We propose a classification of anisotropic micropolar linearly elastic media that do not possess a symmetry center.

In this paper, we review results related to the existence of the energy function for discrete dynamical systems. Also, we consider the technique of constructing such functions for various classes of Ω-stable and structurally stable diffeomorphisms on manifolds of dimension 2 and 3.

The famous Banach contraction principle holds in complete metric spaces, but completeness is not a necessary condition: there are incomplete metric spaces on which every contraction has a fixed point. The aim of this paper is to present various circumstances in which fixed point results imply completeness. For metric spaces, this is the case of Ekeland’s variational principle and of its equivalent, Caristi’s fixed point theorem. Other fixed point results having this property will also be presented in metric spaces, in quasi-metric spaces, and in partial metric spaces. A discussion on topology and order and on fixed points in ordered structures and their completeness properties is included as well.

A finite computational process using arithmetic operations only is called a rational algorithm. Matrices A and F are said to be Hermitian congruent if F = Q∗AQ for a nonsingular matrix Q. The paper is a survey of the necessary conditions for Hermitian congruences that are verifiable by rational algorithms. Bibliography: 7 titles.

The paper discusses the possibility of reducing a square complex matrix A to a direct sum of smaller matrices by using ∗-congruence transformations. It turns out that this possibility is related to appropriate partitions of the spectrum of the cosquare of A. This makes it possible to associate the direct summands of the sum with subsets of the latter spectrum.

The paper describes the nonsingular matrices U such that for every Hankel matrix A of the same order, the matrix U−1AU also is a Hankel matrix. Bibliography: 4 titles.

The paper considers some subclasses of the class of nonsingular H-matrices whose definitions involve matrix sparsity pattern. For matrices A in these subclasses, upper bounds for ‖A−1‖∞ are derived and shown to be sharper than the corresponding bounds ignoring matrix sparsity. Bibliography: 26 titles.

The problem of finding (−1, 1)-matrices with vanishing permanent was posed by Edward Wang in 1974. This paper states and proves bounds on the number of negative entries in a matrix with zero permanent and minimal number of negative entries among all matrices of the same equivalence class. Then representatives of every equivalence class of matrices with zero permanent are found for n ≤ 5. Bibliography: 20 titles.

In this paper, we introduce a geometric technique of working with skew-framed manifolds. It allows us to study stable homotopy groups of some Thom spaces by geometric means. We schematically describe how our results (which are also of independent interest) can be applied to obtain a proof of the Baum–Browder theorem stating nonimmersibility of ℝP10 to ℝ15.

In this paper, we have found necessary and sufficient conditions under which two Abel equations with coefficients depending on a control parameter are locally equivalent with respect to the same pseudogroup of feedback transformations. These conditions are formulated in terms of differential invariants.

In this paper, we solve the question, posed by A. M. Vershik, about the asymptotic behavior of the entropies of a given sequence of partitions of the infinite-dimensional cube satisfying the invariance and exhaustibility properties. On the one hand, it is proved that the entropy sequence increases faster than a linear function. On the other hand, we construct a series of examples that show that the estimate is sharp: for any given sequence increasing faster than a linear function, the entropy of a sequence of partitions can increase slower than the given sequence.

In the papers by V. I. Arnold and his successors based upon the ideas of H. Poincare and F. Klein, it was the Klein sail associated with an operator in ℝn that they considered to play the role of a multidimensional continued fraction, and in these terms generalizations of Lagrange’s theorem on continued fractions were formulated. A different approach to generalization of the notion of continued fraction was based upon modifications of Euclid’s algorithm for constructing, given an irrational vector, an approximating sequence of rational vectors. We suggest a modification of the Klein sail that is constructed directly from a vector, without any operator. We introduce a numeric characteristic of a Klein sail, its asymptotic anisotropy associated with a one-parameter transformation semigroup of the lattice generating the sail and of its Voronoi cell. In terms of this anisotropy, we hope to give a geometric characterization of irrational vectors worst approximated by rational ones. In the three-dimensional space, we suggest a vector (related to the smallest Pisot–Vijayaraghavan number) that is a candidate for this role. This vector may be called an analog of the golden number, which is the real number worst approximated by rationals in the classical theory of Diophantine approximations.

It is well known that the decomposition of injective modules over Noether rings and the decomposition of projective modules over Artinian rings are some of the most beautiful and important results in commutative algebra. The goal of the paper is to prove similar results for graded rings; this is important to understand the structure of modules over graded rings. The obtained results include structural theorems for gr-injective modules over gr-Noetherian G-graded commutative rings and for gr-finitely generated gr-projective modules over gr-Artinian G-graded commutative rings. Bibliography: 13 titles.

We describe the Hochschild cohomology ring for a family of self-injective algebras of tree class $E_6$ in terms of generators and relations. Together with the results of the previous paper, this gives a complete description of the Hochschild cohomology ring for a self-injective algebras of tree class $E_6$., part II of arXiv:1311.4756

The monograph consists of three parts. Part I is presented here. In this monograph, we develop a new approach (mainly based on papers of the author). Many results are published for the first time here. Chapter 1 is introductory. It provides the necessary background from functional analysis (for completeness). In this monograph, we mostly use weighted HOlder spaces; they are considered in Chap. 2. Chapter 3 plays the key role: in weighted HOlder spaces, we consider estimates of integral operators with homogeneous difference kernels, covering potential-type integrals and singular integrals as well as Cauchy-type integrals and double layer potentials. In Chap. 4, similar estimates in weighted Lebesgue spaces are proved. Integrals with homogeneous difference kernels will play an important role in Part III of the monograph, which will be devoted to elliptic boundary-value problems. They naturally arise in integral representations of solutions of first-order elliptic systems in terms of fundamental matrices or their parametrices. The investigation of boundary-value problems for second-order and higher-order elliptic equations or systems is reduced to first-order elliptic systems.

This paper is a review of results of studies of affine transformations in generalized spaces over real linear algebras over the past 15-20 years.

This paper is devoted to Young diagrams and $$ {L}_n^1 $$-equivariant projections of tensor spaces. We present the theory of representations of finite groups developed according to works of H. Weyl and H. Boerner.

This paper is a review of some directions in the study of special classes of metric affince spaces, i.e., spaces endowed with a (pseudo)Riemannian metric and a linear connection.

In this paper, we discuss almost complex structures on the sphere S6 and on the products of spheres S3 × S3, S1 × S5, and S2 × S4. We prove that all almost complex Cayley structures that naturally appear from their embeddings into the Cayley octave algebra ℂa are nonintegrable. We obtain expressions for the Nijenhuis tensor and the fundamental form 𝜔 for each gauge of the space ℂa and prove the nondegeneracy of the form d𝜔. We show that through each point of a fiber of the twistor bundle over S6, a one-parameter family of Cayley structures passes. We describe the set of U(2) ×U(2)- invariant Hermitian metrics on S3 × S3 and find estimates of the sectional sectional curvature. We consider the space of left-invariant, almost complex structures on S3 × S3 = SU(2) × SU(2) and prove the properties of left-invariant structures that yield the maximal value of the norm of the Nijenhuis tensor on the set of left-invariant, orthogonal, almost complex structures.

In this paper, we examine topological spaces that can be effectively defined over factor sets modulo equivalences on the set of natural numbers. We formulate a criterion of computable (effective) separability of topological spaces in terms of the approximability of the corresponding algebras by negative (uniformly effectively separated) algebras. We compare negative and positive algebra representations from the standpoint of the structure of the corresponding effective spaces. For effective infinite topological spaces, we prove the existence of their infinite effective compact extensions.

In this paper, we obtain formulas for residues and prove analogs of the argument principle and Rouche theorems for A(z)-analytic functions.

In this paper, we examine categorical and cardinal properties of hyperspaces with finite number of components. We prove that the functor Cn : Comp → Comp is not normal, i.e., it does not preserve epimorphisms of continuous mappings. We also discuss the density, the caliber, and the Shanin number of the space Cn(X).