Vol 57, No 2 (2016)
- Year: 2016
- Articles: 19
- URL: https://journals.rcsi.science/0037-4466/issue/view/10360
Article
Finite groups with generalized subnormal embedding of Sylow subgroups
Abstract
Given a set π of primes and a hereditary saturated formation F, we study the properties of the class of groups G for which the identity subgroup and all Sylow p-subgroups are F-subnormal (K-F-subnormal) in G for each p in π. We show that such a class is a hereditary saturated formation and find its maximal inner local screen. Some criteria are obtained for the membership of a group in a hereditary saturated formation in terms of its formation subnormal Sylow subgroups.
Multielement equations for analytic functions in the plane with cuts
Abstract
We consider linear equations for analytic functions in the complex plane with cuts along a half of the boundary of a quadrangle. We propose a regularization method that reduces the equations to an equation with summary-difference kernels. Some applications are given to the moment problem for entire functions of exponential type.
Sharp quadrature formulas and inequalities between various metrics for rational functions
Abstract
We obtain the sharp quadrature formulas for integrals of complex rational functions over circles, segments of the real axis, and the real axis itself. Among them there are formulas for calculating the L2-norms of rational functions. Using the quadrature formulas for rational functions, in particular, for simple partial fractions and polynomials, we derive some sharp inequalities between various metrics (Nikol’skiĭ-type inequalities).
Perturbations of vectorial coverings and systems of equations in metric spaces
Abstract
E. R. Avakov, A. V. Arutyunov, S. E. Zhukovskiĭ, and E. S. Zhukovskiĭ studied the problem of Lipschitz perturbations of conditional coverings of metric spaces. Here we propose some extension of the concept of conditional covering to vector-valued mappings; i.e., the mappings acting in products of metric spaces. The idea is that, to describe a mapping, we replace the covering constant by the matrix of covering coefficients of the components of the vector-valued mapping with respect to the corresponding arguments. We obtain a statement on the preservation of the property of conditional and unconditional vectorial coverings under Lipschitz perturbations; the main assumption is that the spectral radius of the product of the covering matrix and the Lipschitz matrix is less than one. In the scalar case this assumption is equivalent to the traditional requirement that the covering constant be greater than the Lipschitz constant. The statement can be used to study various simultaneous equations. As applications we consider: some statements on the solvability of simultaneous operator equations of a particular form arising in the problems on n-fold coincidence points and n-fold fixed points; as well as some conditions for the existence of periodic solutions to a concrete implicit difference equation.
The real analog of the Jacobi inversion problem on a Riemann surface with boundary, its generalizations, and applications
Abstract
Given a finite Riemann surface of genus h ≥ 1 with boundary composed of m+1 connected components we consider a system of m+h real congruences analogous to the classical Jacobi inversion problem. We provide a solution to this system and its applications to boundary value problems.
On hereditary superradical formations
Abstract
A formation F is superradical provided that: (1) F is a normally hereditary formation; (2) each group G = AB, where A and B are F-subnormal F-subgroups in G, belongs to F. We give an example of a hereditary superradical formation that is not soluble saturated. This gives a negative answer to Problem 14.99(b) in The Kourovka Notebook.
New metric characteristics of nonrectifiable curves and their applications
Abstract
We introduce new metric characteristics for nonrectifiable curves. They admit applications to the theory of boundary value problems for analytic functions. Using these characteristics, we in particular obtain some sharper conditions than those available for the solvability of the jump problem and the Riemann problem in domains with nonrectifiable boundaries.
The portion of matrices with real spectrum in the real orthogonal Lie algebra
Abstract
The portion of matrices with real spectrum in a matrix Lie algebra is the ratio of the volume of the set of matrices with real spectrum in a ball centered at the zero of the algebra to the volume of the whole ball. We calculate the portion for the real orthogonal Lie algebra.
Finding ein components in the moduli spaces of stable rank 2 bundles on the projective 3-space
Abstract
Some method is proposed for finding Ein components in moduli spaces of stable rank 2 vector bundles with first Chern class c1 = 0 on the projective 3-space. We formulate and illustrate a conjecture on the growth rate of the number of Ein components in dependence on the numbers of the second Chern class. We present a method for calculating the spectra of the above bundles, a recurrent formula, and an explicit formula for computing the number of the spectra of these bundles.
Dirac flow on the 3-sphere
Abstract
We illustrate some well-known facts about the evolution of the 3-sphere (S3, g) generated by the Ricci flow. We define the Dirac flow and study the properties of the metric \(\bar g = dt^2 + g(t)\), where g(t) is a solution of the Dirac flow. In the case of a metric g conformally equivalent to the round metric on S3 the metric \(\bar g\) is of constant curvature. We study the properties of solutions in the case when g depends on two functional parameters. The flow on differential 1-forms whose solution generates the Eguchi–Hanson metric was written down. In particular cases we study the singularities developed by these flows.
Best approximation methods and widths for some classes of functions in Hq,ρ, 1 ≤ q ≤ ∞, 0 < ρ ≤ 1
Abstract
We compute the exact values of widths for various widths for the classes Wq,a(r)(Φ, μ), μ ≥ 1, of analytic functions in the disk belonging to the Hardy space Hq, q ≥ 1, whose averaged moduli of continuity of the boundary values of the derivatives with respect to the argument fa(r), r ∈ N, are dominated by a given function Φ. For calculating the linear and Gelfand n-widths, we use best linear approximation for these functions.