In a domain having several cylindrical outlets to infinity, the stationary Maxwell system with perfectly conductive boundary conditions is studied. The dielectric permittivity and magnetic permeability are assumed to be arbitrary positive definite matrix-valued functions that slowly stabilize at infinity. The authors introduce the scattering matrix, establish the unique solvability of the problem with radiation conditions at infinity, and describe the asymptotics of solutions.
{"title":"The Maxwell system in nonhomogeneous anisotropic waveguides with slowly stabilizing characteristics of the filling medium","authors":"B. Plamenevskii, A. Poretskii","doi":"10.1090/spmj/1773","DOIUrl":"https://doi.org/10.1090/spmj/1773","url":null,"abstract":"In a domain having several cylindrical outlets to infinity, the stationary Maxwell system with perfectly conductive boundary conditions is studied. The dielectric permittivity and magnetic permeability are assumed to be arbitrary positive definite matrix-valued functions that slowly stabilize at infinity. The authors introduce the scattering matrix, establish the unique solvability of the problem with radiation conditions at infinity, and describe the asymptotics of solutions.","PeriodicalId":51162,"journal":{"name":"St Petersburg Mathematical Journal","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43624988","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Exponential polynomials satisfying a homogeneous equation of convolution type are called its elementary solutions. The article is devoted to convolution-type operators in the complex domain that generalize the well-known operators of q q -sided convolution and π pi -convolution. The properties of such operators are investigated and the general form of elementary solutions (general elementary solution) of a homogeneous equation of q q -sided convolution type is described.
满足卷积型齐次方程的指数多项式称为它的初等解。本文研究了复域上的卷积型算子,它推广了著名的q - q边卷积算子和π pi -卷积算子。研究了这类算子的性质,给出了一类q - q边卷积型齐次方程初等解的一般形式。
{"title":"General elementary solution of a 𝑞-sided convolution type homogeneous equation","authors":"Yuriy Saranchuk, A. Shishkin","doi":"10.1090/spmj/1774","DOIUrl":"https://doi.org/10.1090/spmj/1774","url":null,"abstract":"Exponential polynomials satisfying a homogeneous equation of convolution type are called its elementary solutions. The article is devoted to convolution-type operators in the complex domain that generalize the well-known operators of \u0000\u0000 \u0000 q\u0000 q\u0000 \u0000\u0000-sided convolution and \u0000\u0000 \u0000 π\u0000 pi\u0000 \u0000\u0000-convolution. The properties of such operators are investigated and the general form of elementary solutions (general elementary solution) of a homogeneous equation of \u0000\u0000 \u0000 q\u0000 q\u0000 \u0000\u0000-sided convolution type is described.","PeriodicalId":51162,"journal":{"name":"St Petersburg Mathematical Journal","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45564488","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
In the classical inverse theorems of constructive function theory, structural characteristics of an approximated function are estimated in terms of its best approximations. Most of the known proofs of the inverse theorems utilize Bernstein’s idea to expand the function in polynomials of its best approximation. In the present paper, Bernstein’s proof is modified by using integrals instead of sums. With this modification, it turns out that desired inequalities are based on identities similar to Frullani integrals. The considerations here are quite general, which allows one to obtain analogs of the inverse theorems for functionals in abstract Banach or even seminormed spaces. Then these abstract results are specified and inverse theorems in concrete spaces of functions are deduced, including weighted spaces, with explicit constants.
{"title":"On the constants in abstract inverse theorems of approximation theory","authors":"O. Vinogradov","doi":"10.1090/spmj/1770","DOIUrl":"https://doi.org/10.1090/spmj/1770","url":null,"abstract":"In the classical inverse theorems of constructive function theory, structural characteristics of an approximated function are estimated in terms of its best approximations. Most of the known proofs of the inverse theorems utilize Bernstein’s idea to expand the function in polynomials of its best approximation. In the present paper, Bernstein’s proof is modified by using integrals instead of sums. With this modification, it turns out that desired inequalities are based on identities similar to Frullani integrals. The considerations here are quite general, which allows one to obtain analogs of the inverse theorems for functionals in abstract Banach or even seminormed spaces. Then these abstract results are specified and inverse theorems in concrete spaces of functions are deduced, including weighted spaces, with explicit constants.","PeriodicalId":51162,"journal":{"name":"St Petersburg Mathematical Journal","volume":null,"pages":null},"PeriodicalIF":0.8,"publicationDate":"2023-07-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42336313","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}