{"title":"Trigonometric Polynomials with Frequencies in the Set of Cubes","authors":"M. R. Gabdullin, S. V. Konyagin","doi":"10.1134/s0001434624030052","DOIUrl":"https://doi.org/10.1134/s0001434624030052","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> We prove that for any <span>(varepsilon>0)</span> and any trigonometric polynomial <span>(f)</span> with frequencies in the set <span>({n^3: N leq nleq N+N^{2/3-varepsilon}})</span> one has </p><span>$$|f|_4 ll varepsilon^{-1/4}|f|_2$$</span><p> with implied constant being absolute. We also show that the set <span>({n^3: Nleq nleq N+(0.5N)^{1/2}})</span> is a Sidon set. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"36 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573361","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}
{"title":"On Angles between Linear Subspaces in $$mathbb R^4$$ and the Singularity","authors":"A. O. Chebotarenko","doi":"10.1134/s0001434624030131","DOIUrl":"https://doi.org/10.1134/s0001434624030131","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> We generalize the Khinchin singularity phenomenon for the problem in which, for a given irrational linear subspace, rational subspaces forming the least angle with the given subspace are sought. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"17 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573483","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}
{"title":"On the Boundedness of the Fractional Maximal Operator, the Riesz Potential, and Their Commutators in Orlicz Spaces","authors":"A. R. Aliev, R. A. Aliev","doi":"10.1134/s0001434624030180","DOIUrl":"https://doi.org/10.1134/s0001434624030180","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> In this paper, conditions are found for the boundedness of the fractional maximal operator, the Riesz potential, and their commutators in Orlicz spaces. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"36 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573484","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}
{"title":"Convergence of the Fourier Series in Meixner–Sobolev Polynomials and Approximation Properties of Its Partial Sums","authors":"R. M. Gadzhimirzaev","doi":"10.1134/s0001434624030027","DOIUrl":"https://doi.org/10.1134/s0001434624030027","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> We study the convergence of Fourier series in the polynomial system <span>({m_{n,N}^{alpha,r}(x)})</span> orthonormal in the sense of Sobolev and generated by the system of modified Meixner polynomials. In particular, we show that the Fourier series of <span>(fin W^r_{l^p_{rho_N}(Omega_delta)})</span> in this system converges to <span>(f)</span> pointwise on the grid <span>(Omega_delta)</span> as <span>(pge2)</span>. In addition, we study the approximation properties of partial sums of Fourier series in the system <span>({m_{n,N}^{0,r}(x)})</span>. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"1 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141577929","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}
{"title":"Approximation by Refinement Masks","authors":"E. A. Lebedeva","doi":"10.1134/s0001434624030076","DOIUrl":"https://doi.org/10.1134/s0001434624030076","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> We construct a Parseval wavelet frame with compact support for an arbitrary continuous <span>(2pi)</span>-periodic function <span>(f)</span>, <span>(f(0)=1)</span>, satisfying the inequality <span>(|f(x)|^2+|f(x+pi)|^2le 1)</span>. The frame refinement mask uniformly approximates <span>(f)</span>. The refining function has stable integer shifts. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"28 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573363","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}
{"title":"On Locally Chebyshev Sets","authors":"K. S. Shklyaev","doi":"10.1134/s0001434624030362","DOIUrl":"https://doi.org/10.1134/s0001434624030362","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> It is proved that every connected boundedly compact locally Chebyshev set in a normed space is a Chebyshev set. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"30 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573500","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}
{"title":"$$n$$ -Dimensional Generalizations of a Thébault Conjecture","authors":"Q. H. Tran, B. Herrera","doi":"10.1134/s0001434624030337","DOIUrl":"https://doi.org/10.1134/s0001434624030337","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> This paper presents some generalizations of a Thébault conjecture, provides an analog of the Thébault conjecture for the <span>(n)</span>-simplex, and also solves a conjecture in a 2022 paper by the authors by using linear algebra. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"32 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573501","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}
{"title":"Approximation Numbers of the Two-Dimensional Rectangular Hardy Operator","authors":"V. D. Stepanov, E. P. Ushakova","doi":"10.1134/s0001434624030118","DOIUrl":"https://doi.org/10.1134/s0001434624030118","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> Upper and lower bounds are obtained for the approximation numbers of the two-dimensional rectangular Hardy operator on weighted Lebesgue spaces on <span>(mathbb{R}_+^2)</span>. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"9 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573479","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}
I. A. Aleksandrova, S. E. Stepanov, I. I. Tsyganok
{"title":"Lichnerowicz Laplacian from the Point of View of the Bochner Technique","authors":"I. A. Aleksandrova, S. E. Stepanov, I. I. Tsyganok","doi":"10.1134/s0001434624030179","DOIUrl":"https://doi.org/10.1134/s0001434624030179","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> Vanishing theorems for the kernels of Lichnerowicz and Hodge Laplacians on a complete Riemannian manifold are proved, and the eigenvalues of a Lichnerowicz Laplacian on a closed Riemannian manifold are estimated. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"42 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573487","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}
{"title":"Common Fixed Point Theorems for Contractive Mappings of Integral Type in $$b$$ -Metric Spaces","authors":"Hongyan Guan, Jinze Gou","doi":"10.1134/s0001434624030258","DOIUrl":"https://doi.org/10.1134/s0001434624030258","url":null,"abstract":"<h3 data-test=\"abstract-sub-heading\">Abstract</h3><p> This paper is the first to introduce a fixed point problem of integral type in a <span>(b)</span>-metric space. We study sufficient conditions for the existence and uniqueness of a common fixed point of contractive mappings of integral type. We also give two examples to support our results. </p>","PeriodicalId":18294,"journal":{"name":"Mathematical Notes","volume":"11 1","pages":""},"PeriodicalIF":0.6,"publicationDate":"2024-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141573491","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}