Universal Laurent series in finitely connected domains

Universal Laurent series where the universal approximation is valid on the boundary of the multiple connected open Ω appears for the first time in [2]. We show that it is possible to demand universal approximation only to a part of the boundary while on the remaining part the universal function can be smooth. Received: 29 May 2007     

Universal boundary value problem for equations of mathematical physics

A new statement of a boundary value problem for partial differential equations is discussed. An arbitrary solution to a linear elliptic, hyperbolic, or parabolic second-order differential equation is considered in a given domain of Euclidean space without any constraints imposed on the boundary values of the solution or its derivatives. The following question is studied: What conditions should hold for the boundary values of a function and its normal derivative if this function is a solution to the linear differential equation under consideration? A linear integral equation is defined for the boundary values of a solution and its normal derivative; this equation is called a universal boundary value equation. A universal boundary value problem is a linear differential equation together with a universal boundary value equation. In this paper, the universal boundary value problem is studied for equations of mathematical physics such as the Laplace equation, wave equation, and heat equation. Applications of the analysis of the universal boundary value problem to problems of cosmology and quantum mechanics are pointed out.     

Einige laminare Grenzschichtströmungen,berechnet mittels einer neuen Reihenmethode

Summary A new and formally exact series solution of the general laminar boundary layer problem for arbitrary outer pressure distribution [1] is discussed briefly. The main part of the paper is concerned with the application of this solution to the numerical evaluation of instructive examples of boundary layer flows. Application of this new and rigorous series method requires only a short and simple numerical calculation, involving the application of tables of certain universal functions.      

Numerical implementation of iteration processes applied in the study of nonlinear boundary value problems of the theory of elasticity and filtration

Nonlinear elastic problems for hardening media are solved by applying the universal iteration process proposed by A.I. Koshelev in his works on the regularity of solutions to quasilinear elliptic and parabolic systems. This requires numerically solving a linear elliptic system at each step of the iteration procedure. The method is numerically implemented in the MATLAB environment by using its PDE Toolbox. A modification of the finite-element procedure is suggested in order to solve a linear algebraic system at each iteration step. The computer model is tested on simple examples. The same nonlinear problems are also solved by the method of elastic solutions, which consists in replacing the Laplace operator in the universal iteration process by the Lamé operator of linear elasticity. As is known, this iteration process converges to a weak solution of the nonlinear problem, provided that the displacements are fixed on the boundary. The method is tested on examples with stresses on the boundary. The third part of the paper is devoted to the nonlinear filtration problem. General properties of the iteration process for nonlinear parabolic systems have been studied by A.I. Koshelev and V.M. Chistyakov. The numerical implementation is based on slightly modified PDE Toolbox procedures. The program is tested on simple examples.     

Friction law for turbulent boundary layers on a flat plate with suction

A universal friction law for turbulent boundary layers on a flat plate with suction is established. Experimental skin-friction distributions obtained for various suction factors and Reynolds numbers are described in similarity variables by a single universal curve. The law is valid for the entire range of suction velocities from zero one till the limiting values corresponding to asymptotic-suction boundary layers. The analysis is not based on any particular turbulence model. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Quasiminimal crystals with a volume constraint and uniform rectifiability

We establish here, in a quite general context, uniform rectifiability properties for quasiminimal crystals with a volume constraint. Namely we prove that to any quasiminimal crystal with a volume constraint corresponds a unique equivalent open set whose boundary is Ahlfors-regular and which satisfies the so-called condition B. Moreover implicit bounds in these properties, which imply the uniform rectifiability of the boundary, can be chosen universal. As a consequence we give a universal upper bound for the number of connected components of reduced quasiminimizers and we also prove that quasiminimal crystals with a volume constraint actually satisfy, in some universal way, an apparently stronger quasiminimality condition where admissible perturbations are not required to be volume-preserving anymore.     

Interval optimal control problem in a Hilbert space

An optimal control problem for a system involving an interval parameter is considered. The concepts of a universal optimal state and a universal optimal control are introduced. The existence and uniqueness of a universal solution to the interval optimal control problem is proved, and an algorithm for its determination is presented. The interval optimal control problem for a system described by the boundary value problem for a second-order ordinary differential equation is solved as an example.     

ON CAUCHY－POMPEIU FORMULA FOR FUNCTIONS WITH VALUES IN A UNIVERSAL CLIFFORD ALGEBRA

This paper obtains the Cauchy-Pompeiu formaula on certain distinguished boundary for functions with values in a unviersal Clifford algebra ,This formulas is Just an extension of the Cauchy‘s integral formula obtained in [11].     

Asymptotics of solutions for a basic case of fluid–structure interaction

We consider the Navier–Stokes equations in a half-plane with a drift term parallel to the boundary and a small source term of compact support. We provide detailed information on the behavior of the velocity and the vorticity at infinity in terms of an asymptotic expansion at large distances from the boundary. The expansion is universal in the sense that it only depends on the source term through some constants. The expansion also applies to the problem of an exterior flow past a small body moving at constant velocity parallel to the boundary, and can be used as an artificial boundary condition on the edges of truncated domains for numerical simulations.     

Invariant boundary distributions for finite graphs

Let Γ be the fundamental group of a finite connected graph G. Let M be an abelian group. A distribution on the boundary ∂Δ of the universal covering tree Δ is an M-valued measure defined on clopen sets. If M has no χ(G)-torsion, then the group of Γ-invariant distributions on ∂Δ is isomorphic to H₁(G,M).     

泛Clifford分析中无界域上的Cauchy积分公式和Cauchy-Pompeiu公式

本文研究了泛Clifford分析中的Cauchy积分公式和Cauchy-Pompeiu公式.通过引入修正的Cauchy核,得出了取值在泛Clifford代数上的两公式在无界域上的表达式.此两公式是有界域上的相应结果的推广,并为研究无界域上的边值问题打下了基础.     

A Cauchy's Integral Formula for Functions with Values in a Universal Clifford Algebra and its Applications

In this paper, we obtain Cauchy's integral formula on certain distinguished boundary for functions with values in a universal Clifford algebra, which is similar to the classical Cauchy's integral formula on the distinguished boundary of polycylinder for several complex variables. By using it, both the mean value theorem and the maximum modulus theorem are given.     

Robin-type wall functions and their numerical implementation

The paper is devoted to numerical implementation of the wall functions of Robin-type for modeling near-wall turbulent flows. The wall functions are based on the transfer of a boundary condition from a wall to some intermediate boundary near the wall. The boundary conditions on the intermediate boundary are of Robin-type and represented in a differential form. The wall functions are formulated in an analytical easy-to-implement form, can take into account the source terms, and do not include free parameters. The relation between the wall functions of Robin type and the theory of Calderon–Ryaben'kii's potentials is demonstrated. A universal robust approach to the implementation of the Robin-type wall functions in finite-volume codes is provided. The example of an impinging jet is considered.     

Distortion and topology

For a self mapping f: D→D of the unit disk in C which has finite distortion, we give a separation condition on the components of the set where the distortion is very large - say greater than a given constant - which implies that f still extends homeomorphically and quasisymmetrically to the boundary S = ?D. Thus f shares its boundary values with a quasiconformal mapping whose distortion we explicitly estimate in terms of the data. This condition, uniformly separated in modulus, allows the set where the distortion is large to accumulate on the entire boundary S, but it does not allow a component to run out to the boundary - a necessary restriction. The lift of a Jordan domain in a Riemann surface to its universal cover D is always uniformly separated in modulus, and this allows us to apply these results in the theory of Riemann surfaces to identify an interesting link between the support of the high distortion of a map between surfaces and their geometry - again with explicit estimates. As part of our investigations, we study mappings ?: S → S which are the germs of a conformal mapping and give good bounds on the distortion of a quasiconformal extension of ? to the disk D. We then extend these results to the germs of quasisymmetric mappings. These appear of independent interest and identify new geometric invariants.     

Universality in the 2D Ising model and conformal invariance of fermionic observables

It is widely believed that the celebrated 2D Ising model at criticality has a universal and conformally invariant scaling limit, which is used in deriving many of its properties. However, no mathematical proof has ever been given, and even physics arguments support (a priori weaker) M?bius invariance. We introduce discrete holomorphic fermions for the 2D Ising model at criticality on a large family of planar graphs. We show that on bounded domains with appropriate boundary conditions, those have universal and conformally invariant scaling limits, thus proving the universality and conformal invariance conjectures.     

On Boundary Behavior of the Cauchy Type Integrals with Values in a Universal Clifford Algebra

In this paper, we discuss boundary behavior for the Cauchy type integrals with values in a universal Clifford algebra for certain distinguished boundary and obtain some Sochocki–Plemelj formulae and Privalov–Muskhelishvili theorems.     

泛Clifford分析中的Laurent展式和留数定理

该文由泛Clifford分析中在特异边界上的Cauchy积分式得出了具有孤立奇点的LR正则函数在其相应的Laurent域上的Laurent展式，并由此给出了留数的定义，得出了类似于经典函数理论的留数定理。     

Ordered Involutive Operator Spaces

This is a companion to recent papers of the authors; here we construct the ‘noncommutative Shilov boundary’ of a (possibly nonunital) selfadjoint ordered space of Hilbert space operators. The morphisms in the universal property of the boundary preserve order. As an application, we consider ‘maximal’ and ‘minimal’ unitizations of such ordered operator spaces.     

Moduli of roots of line bundles on curves

We treat the problem of completing the moduli space for roots of line bundles on curves. Special attention is devoted to higher spin curves within the universal Picard scheme. Two new different constructions, both using line bundles on nodal curves as boundary points, are carried out and compared with pre-existing ones.

     

Cloaking via impedance boundary condition for the 2-D Helmholtz equation

We consider control problems for the 2-D Helmholtz equation in an unbounded domain with partially coated boundary. Dirichlet boundary condition is given on one part of the boundary and the impedance boundary condition is imposed on another its part. The role of control in control problem under study is played by boundary impedance. Quadratic tracking–type functionals for the field play the role of cost functionals. Solvability of control problems is proved. The uniqueness and stability of optimal solutions with respect to certain perturbations of both cost functional and incident field are established.