Entropy and approximation numbers of limiting embeddings; an approach via Hardy inequalities and quadratic forms

This paper deals with entropy numbers and approximation numbers for compact embeddings of weighted Sobolev spaces into Lebesgue spaces in limiting situations. This work is based on related Hardy inequalities and the spectral theory of some degenerate elliptic operators.     

Yang-Mills theory and Tamagawa numbers: the fascination of unexpected links in mathematics

Atiyah and Bott used equivariant Morse theory applied to theYang–Mills functional to calculate the Betti numbers ofmoduli spaces of vector bundles over a Riemann surface, rederivinginductive formulae obtained from an arithmetic approach whichinvolved the Tamagawa number of SL_n. This article attempts tosurvey and extend our understanding of this link between Yang–Millstheory and Tamagawa numbers, and to explain how methods usedover the last three decades to study the singular cohomologyof moduli spaces of bundles on a smooth projective curve over can be adapted to the setting of ¹-homotopy theory to studythe motivic cohomology of these moduli spaces over an algebraicallyclosed field.     

Entropy numbers, s-numbers,and eigenvalue problems

We establish inequalities between entropy numbers and approximation numbers for operators acting between Banach spaces. Furthermore we derive inequalities between eigenvalues and entropy numbers for operators acting on a Banach space. The results are compared with the classical inequalities of Bernstein and Jackson.     

Embedding theorems of Besov and Triebel-Lizorkin spaces on spaces of homogeneous type

In this paper, the author establishes the embedding theorems for different metrics of inhomoge-neous Besov and Triebel-Lizorkin spaces on spaces of homogeneous type. As an application, the author obtains some estimates for the entropy numbers of the embeddings in the limiting cases between some Besov spaces and some logarithmic Lebesgue spaces.     

A GIT construction of moduli spaces of stable maps in positive characteristic

In a previous paper, the author and Swinarski constructed themoduli spaces of stable maps, _g,n(P^r, d) via geometric invariant theory (GIT). That paper requiredthe base field to be the complex numbers, a restriction thatthis paper removes: here the coarse moduli spaces of stablemaps are constructed via GIT over a more general base.     

Estimates for the entropy numbers of embedding operators of function spaces on sets with tree-like structure: Some limiting cases

In this paper we obtain order estimates for the entropy numbers of embedding operators of weighted Sobolev spaces into weighted Lebesgue spaces, as well as two-weighted summation operators on trees. Here, the parameters satisfy some critical conditions.     

Entropy Numbers of Diagonal Operators between Vector-Valued Sequence Spaces

Upper and lower bounds are established for the entropy numbersof certain diagonal operators between Banach sequence spaces.These diagonal operators are isomorphisms between the spacesconsidered in the paper and weighted sequence spaces consideredby Leopold so that the entropy numbers in question coincidewith those considered by Leopold. The results in the paper improvethe previous results in at least two ways. The estimates inthe paper are ‘almost’ sharp in the sense that theupper and lower estimates differ only by logarithmic factorsfor a much wider range of parameters. Moreover, all the upperestimates are improvements on the previous ones, the improvementbeing quite significant in some cases.     

Eigenvalues and Entropy Moduli of Operators in Interpolation Spaces

The paper approaches in an abstract way the spectral theory of operators in abstract interpolation spaces. We introduce entropy numbers and spectral moduli of operators, and prove a relationship between them and eigenvalues of operators. We also investigate interpolation variants of the moduli, and offer a contribution to the theory of eigenvalues of operators. Specifically, we prove an interpolation version of the celebrated Carl–Triebel eigenvalue inequality. Based on these results we are able to prove interpolation estimates for single eigenvalues as well as for geometric means of absolute values of the first n eigenvalues of operators. In particular, some of these estimates may be regarded as generalizations of the classical spectral radius formula. We give applications of our results to the study of interpolation estimates of entropy numbers as well as of the essential spectral radius of operators in interpolation spaces.     

Wavelet Frames,Sobolev Embeddings and Negative Spectrum of Schrödinger Operators on Manifolds with Bounded Geometry

We consider weighted function spaces of Sobolev-Besov type and Schrödinger type operators on noncompact Riemannian manifolds with bounded geometry. First we give characterization of the spaces in terms of wavelet frames. Then we describe the necessary and sufficient conditions for the compactness of Sobolev embeddings between the spaces. An asymptotic behavior of the corresponding entropy numbers is calculated. At the end we use the asymptotic behavior to estimate the number of negative eigenvalues of the Schrödinger type operators.     

Asymptotic estimates for the approximation and entropy numbers of a one-weight Riemann-Liouville operator

We obtain two-sided estimates for the asymptotic behavior of the approximation and entropy numbers of a one-weight Riemann-Liouville operator of an arbitrary integer order acting in Lebesgue spaces on the semiaxis.     

cut* 空间的拓扑性质

该文引入了 cut^*空间的概念,所谓的 cut^*空间是指去掉任意一点连通,去掉任意两点不连通的连通空间.通过对其性质的讨论,得到如下主要结论: 首先得到cut^*空间中每个点非开即闭,并且cut^*空间中有无限多个闭点;其次讨论了一类特殊的 cut^*空间,即去掉一点是COTS的 cut^* 空间.指出``$X$是 cut^*空间,任意 $x\inX,X\setminus\{x\}$是不可约cut空间'这样的空间类是不存在的.在文章的最后,讨论了去掉一点是LOTS的 cut^*空间的覆盖性质,得到这样的空间是紧空间或Lindel\"of空间的结论.     

Best m-Term Approximation and Sobolev–Besov Spaces of Dominating Mixed Smoothness—the Case of Compact Embeddings

We shall investigate the asymptotic behavior of the widths of best m-term approximation with respect to tensor products of Sobolev as well as Besov spaces in case of compact embeddings. Furthermore, we compare best m-term approximation with optimal linear approximation and entropy numbers.     

Entropy numbers and lattice arrangements in l∞ (Γ)

The Banach spaces l_∞(Γ) admit tilings by balls of equal size that are arranged along a lattice. We present classes of bounded sets in spaces l_∞(Γ) whose optimal packings and covers in the sense of inner and outer metric entropy numbers are realized by lattice arrangements. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Rn中区域上的加权Hardy定理

Ω С Rⁿ是一个区域时,该文给出了区域Ω上加权Hardy空间的定义,并得到该空间的原子分解,所得的定理在椭圆边界值问题的研究中有潜在的应用.     

Characterizations of Hardy-Orlicz spaces on strictly pseudoconvex domains of C<Superscript>n</Superscript>

In this paper, we characterize Hardy-Orlicz spaces on strictly pseudoconvex domains of Cⁿ using real variable methods. Concretely, we prove the basic properties for a boundary behavior of functions in Hardy-Orlicz spaces, an approximation of functions in Hardy-Orlicz spaces by some functions holomorphic up to a neighborhood of the boundary, and a boundedness of the Szegö projection.     

∑e1型Banach空间上C0半群稳定性的谱特征

讨论一类不可分解的∑_e¹型Banach空间上有界线性算子的谱的特殊性质;给出了∑_e¹型Banach空间上一致有界C₀半群稳定性的一个谱特征,并给出稳定性定理的一个应用.     

单位球上不同Hardy空间之间的乘法算子

作者研究了C^N 中单位球B上不同Hardy空间之间的乘法算子, 给出了有界的乘法算子M_g: H^p(B) → H^q(B)$的特征.     

Quantum lower bounds by entropy numbers

We use entropy numbers in combination with the polynomial method to derive a new general lower bound for the nth minimal error in the quantum setting of information-based complexity. As an application, we improve some lower bounds on quantum approximation of embeddings between finite dimensional L_p spaces and of Sobolev embeddings.     

Compact embeddings of Sobolev spaces with power weights perturbed by slowly varying functions

We study compact embeddings of weighted Sobolev spaces into Lebesgue spaces on the unit ball in . The weight is of slowly varyingly disturbed polynomial growth with a singularity at the origin. It extends 21 , 27 to a wider class of weights. Special attention is paid to the influence of the growth rate of the weight on the quality of compactness, measured in terms of entropy and approximation numbers. In case of Hilbert spaces, the results are related to the distribution of eigenvalues of some degenerate elliptic operators.