A. O. Gel'fond's method in the theory of transcendental numbers

Obtained in this work, with the help of a method of A. O. Gel'fond, are several results on algebraic independence of the values of an exponential function at nonalgebraic points.Translated from Matematicheskie Zametki, Vol. 10, No. 4, pp. 415–426, October, 1971.     

A decomposition theory for matroids. I. General results

A new matroid decomposition with several attractive properties leads to a new theorem of alternatives for matroids. A strengthened version of this theorem for binary matroids says roughly that to any binary matroid at least one of the following statements must apply: (1) the matroid is decomposable, (2) several elements can be removed (in any order) without destroying 3-connectivity, (3) the matroid belongs to one of 2 well-specified classes or has 10 elements or less. The latter theorem is easily specialized to graphic matroids. These theorems seem particularly useful for the determination of minimal violation matroids, a subject discussed in part II.     

A new version of the ergodic method of Yu. V. Linnik in number theory

A new version of a known method of analytic number theory is developed. This version is demonstrated with a very simple model example — the problem on the asymptotically uniform distribution of integer points of a sphere with respect to a given modulus.This paper is a reworking of §5 of survey [6].Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 50, pp. 179–186, 1975.     

A contribution to the theory of Maxwell fluids. II

The local classical unique solvability of the periodic initial-boundary problem and of the cauchy problem is proved for the nonstationary quasilinear system describing the motion of Maxwell fluids.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 131, pp. 106–113, 1983.     

A result of L. N. Bol'shev from the theory of the statistical testing of hypotheses

One gives a proof of L. N. Bol'shev's result on the existence of an optimal statistical test for the problem of the testing of two simple hypotheses under the condition that there exists the possibility to decline the taking of a decision.Translated from Zapiski Nauchnykh Seminarov Leningradskogo Otdeleniya Matematicheskogo Instituta im. V. A. Steklova AN SSSR, Vol. 153, pp. 129–137, 1986.     

On the monadic theory ofω 1 without A.C.

Buchi inLecture Notes in Mathematics, Decidable Theories II (1973) by using A.C. characterized the theoriesMT[β, <] forβ<ω ₁ and showed thatMT[ω ₁, <] is decidable. We extend Buchi’s results to a larger class of models of ZF (without A.C.) by proving the following under ZF only: (1) There is a choice function which chooses a “good” run of an automaton on countable input (Lemma 5.1). It follows that Buchi’s results cocerning countable ordinals are provable within ZF. (2) Let U.D. be the assertion that there exists a uniform denumeration ofω ₁ (i.e. a functionf: ω ₁ → ω ₁ ^ω such that for everyα<ω ₁,f(α) is a function fromω ontoα). We show that U.D. can be stated as a monadic sentence, and thereforeω ₁ is characterizable by a sentence. (3) LetF be the filter of the cofinal closed subsets ofω ₁. We show that if U.D. holds thenMT[ω ₁, <] is recursive in the first order theory of the boolean algebraP (ω ₁)/F. (We can effectively translate each monadic sentence Σ to a boolean sentenceσ such that [ω ₁, <] ⊨ Σ iffP(ω ₁)/F⊨σ). (4) As every complete boolean algebra theory is recursive we have that in every model of ZF+U.D.,MT[ω ₁, <] is recursive. All our proofs are within ZF. Buchi’s work is often referred to. Following Buchi, the main tool is finite automata. We don’t deal withMT[ω ₁, <] forω ₁ which doesn’t satisfy U.D. The results in this paper appeared in the author’s M.Sc. thesis, which was prepared at the Hebrew University under the supervision of Professor M. Rabin.     

A theory of PWD-structures

A general study is undertaken of product-wedge-diagonal (=PWD) structures on a space. In part this concept may be viewed as arising from G.W. Whitehead's fat-wedge characterization of Lusternik-Schnirelmann category. From another viewpoint PWD-structures occupy a distinguished position among those structures that provide data allowing Hopf invariants to be defined. Indeed the Hopf invariant associated with a PWD-structure is a crucial component of the structure. Our overall theme addresses the basic question of existence of compatible structures on X and Y with regard to a map X→Y. A principal result of the paper uses Hopf invariants to formulate a Berstein-Hilton type result when the space involved is a double mapping cylinder (or homotopy pushout). A decomposition formula for the Hopf invariant (extending previous work of Marcum) is provided in case the space is a topological join U*V that has PWD-structure defined canonically via the join structure in terms of diagonal maps on U and V.     

A continuum theory of superconductivity

Abstract. A continuum theory of superconductivity is formulated for a mixture consisting of three species: a superelectron fluid, a conducting fluid, and a conducting elastic solid. Each one of the three species is subject to their own electro-magnetic (E-M) fields and motions. Irreversible thermodynamics are used to obtain constitutive equations. Field equations, boundary and initial conditions are given. A special case is obtained, suitable for mathematical analysis and applications. The Pippard theory of superconductivity is shown to be a special case of the present theory.     

A note on the theory of immanants

General properties of immanants are derived with special emphasis on practical methods of computing them. A general theorem on the structure of the immanants of a skew-symmetric matrix of odd order is proven.     

Problems of the theory of bitopological spaces. 2

This paper is the second part of a survey of recent results and new problems in the theory of bitopological spaces. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 208, 1993, pp. 5–67. Translated by A. A. Ivanov.     

A dynamic theory of the credit union

A topic of recent interest in the retail financial sector has been the growth of credit unions or “pure cooperatives”. Past credit union researchers built mathematical models of credit union operations. These models identified important operating characteristics but were modeled under assumptions of static operating environments. The model presented in this paper departs from the traditional static models and examines dynamic operation for a United States credit union. Its inter-temporal structure clarifies a number of issues—such as optimal equity retention and inter-temporal rate policy—not addressed by earlier studies. Given initial conditions, the model specifies equity retention and inter-temporal deposit and loan rate policies until an equilibrium state is reached.     

A generalization of D. A. Grave's method for plane boundary-value problems in harmonic potential theory

The article describes and proves D. A. Grave's method that solves classical plane boundary-value problems for the Green's function of the Laplace equation in regions whose boundaries are smooth analytical curves defined by finite-order irreducible polynomials. The proposed method has certain advantages compared with the method that constructs the Green's function by conformally mapping the original region onto the unit disk. A class of regions are identified for which Grave's methods produces an explicit analytical solution in convergent-series form. This is a natural generalization of the conformal mapping method for simplest regions. Translated from Prikladnaya Matematika i Informatika, No. 1, pp. 5–19, 1999.     

A contribution to the statistical theory of linear graduation

Moving (weighted) average techniques provide a flexible tool for the graduation (smoothing) of vital rates. As is shown in the present paper, one may construct linear graduation methods which are superior with respect to some formal evaluation criteria, but such ‘improved’ methods lack an important robustness property which the moving average graduation techniques possess and which is a main motivation for their use.A linear graduation technique is an estimation method, and an important consideration in the evaluation of its properties is the class for which it is unbiased, i.e., the class of functions which it reproduces unchanged. A classical test usually said to be a chi-square test of the goodness-of-fit of a graduation is revealed to be a test of the hypothesis that the graduation method is indeed unbiased for the set of theoretical rates actually estimated, and its properties are investigated along with those of alternative chi-square tests.     

A variant of the theory of local strains

A variant of the theory of local strains giving the stress tensor as a function of a given strain tensor is formulated. The stresses in an orthogonal coordinate system are established by means of a functional that averages the local stresses expressed by the local stress function. This function is determined by the given strain program. It is shown that in certain practical problems these relations are more convenient than those previously proposed.Mekhanika Polimerov, Vol. 3, No. 5, pp. 800–802, 1967     

A technique in the classification theory of point-line geometries

A general technique is presented to generate from local subspaces (determined by the residue at a point) global subspaces which are needed to recognize a point-line goemetry.The author is supported by the N.F.W.O. (National grant for scientific research of Belgium).     

A new method in the scattering theory

A new method allowing one to establish the existence of wave operators is demonstrated on the example of the well-known Friedrichs’ model.     

A problem in the theory of mixing layers

The classical problem of the free steady mixing layer which is formed as the result of the interaction between two parallel homogeneous flows which move with different velocities and come into contact in a certain section is considered. Subject to the additional condition that the first derivative of the solution in a class of self-similar functions is positive, a boundary-value problem is studied, for values of the self-similarity index m > 0, which describes the mixing of two viscous streams of the same fluid for m = 1 [1] and for m = 2 [2]. The method of investigation used [3–5] enables the third-order non-linear equation to be reduced to a first-order equation and enables the corresponding solutions (Gz) to be constructed in a parametric form as a function of the values of m. A knowledge of the behaviour of the velocity profile of the main stream can be used to investigate the flow stability. The results obtained form the basis of the subsequent construction of the solution of Lock's problem [6] and the investigation of the uniqueness of the solutions obtained.     

A representation theory for the impulse control of jump processes

A state space representation theory for the impulse control of a quite general class of non-Markov jump processes is developed. Control decisions are based upon observations of past histories of an input jump process and observations of the current state of the corresponding controlled output. A verification theorem establishes that a solution of a system of quasi variational inequalities gives rise naturally to an optimal impulse policy. The proof of optimality relies upon an extended version of the well-known Dynkin formula for Markov processes.     

A functional calculus of closed operators on Banach space. III. certain topics of perturbation theory

The present paper is a continuation of research of A. A. Atvinovskii and of the author in the area of functional calculus of closed operators on Banach spaces based on Markov and related functions as symbols. The following topics in the perturbation theory are considered: Estimates of bounded perturbations of operator functions with respect to general operator ideal norms, Lipschitz property, moment inequality, Fréchet differentiability, analyticity of operator functions under consideration with respect to the perturbation parameter, spectral shift function, and Lifshits–Krein trace formula.     

On ergodic theory of A. Schmidt's complex continued fractions over Gaussian field

We construct a natural extension transformation associated with A. Schmidt's complex continued fractions. The transformation is defined on a subset of geodesics over a three dimensional hyperbolic space and an invariant measure for it is naturally induced from the hyperbolic measure. We discuss some applications of it to the metrical theory of continued fractions.