Hausdorff Operators on Compact Abelian Groups

A compact universal differentiability set with Hausdorff dimension one

We give a short proof that any non-zero Euclidean space has a compact subset of Hausdorff dimension one that contains a differentiability point of every real-valued Lipschitz function defined on the space.

Some Fibonacci sequence spaces of non-absolute type derived from $\ell_{p} $ with $(1 \leq p \leq \infty)$ and Hausdorff measure of non-compactness of composition operators

The aim of the paper is to introduce the spaces $\ell_{\infty}^λ(\widehat{F})$ and $\ell_{p}^λ(\widehat{F})$ derived by the composition of the two infinite matrices $Λ=(λ_{nk})$ and $\widehat{F}=\left( f_{nk} \right),$ which are the $BK$-spaces of non-absolute type and also derive some inclusion relations. Further, we determine the $α$-, $β$-, $γ$-duals of those spaces and also construct the basis for $\ell_{p}^λ(\widehat{F}).$ Additionally, we characterize some matrix classes on the spaces $\ell_{\infty}^λ(\widehat{F})$ and $\ell_{p}^λ(\widehat{F}).$ We also investigate some geometric propert…

A Compactness Theorem for The Dual Gromov-Hausdorff Propinquity

We prove a compactness theorem for the dual Gromov-Hausdorff propinquity as a noncommutative analogue of the Gromov compactness theorem for the Gromov-Hausdorff distance. Our theorem is valid for subclasses of quasi-Leibniz compact quantum metric spaces of the closure of finite dimensional quasi-Leibniz compact quantum metric spaces for the dual propinquity. While finding characterizations of this class proves delicate, we show that all nuclear, quasi-diagonal quasi-Leibniz compact quantum metric spaces are limits of finite dimensional quasi-Leibniz compact quantum metric spaces. This result i…

德布拉恩斯空间和帕莱-维纳空间上的豪斯多尔夫算子

Hausdorff Operators on de Branges Spaces and Paley-Wiener spaces

研究了德布拉恩斯空间中豪斯多尔夫算子的有界性和紧性条件，并将其转化为经典积分算子问题，得出了在帕莱-维纳空间中算子的有界性、紧性和核性条件，以及属于希尔伯特-施密特类的条件。

The approximate fixed point property in Hausdorff topological vector spaces and applications

We establish an approximate fixed point result for self-maps on compact convex subsets of Hausdorff topological vector spaces where continuity is not a necessary condition.

Infinitary logic and basically disconnected compact Hausdorff spaces

We extend Łukasiewicz logic obtaining the infinitary logic $\mathcal{IR}Ł$ whose models are algebras $C(X,[0,1])$, where $X$ is a basically disconnected compact Hausdorff space. Equivalently, our models are unit intervals in $σ$-complete Riesz spaces with strong unit. The Lindenbaum-Tarski algebra of $\mathcal{IR}Ł$ is, up to isomorphism, an algebra of $[0,1]$-valued Borel functions. Finally, our system enjoys standard completeness with respect to the real interval $[0,1]$.

The structure of normal Hausdorff operators on Lebesgue spaces

We consider a generalization of Hausdorff operator and introduce the notion of the symbol of such an operator. Using this notion we describe the structure and investigate important properties (such as invertibility, spectrum, norm, and compactness) of normal generalized Hausdorff operators on Lebesgue spaces over $\mathbb{R}^n.$ The examples of Cesàro operators are considered.

Vector-valued Hausdorff-Young inequality on compact groups

The main purpose of this paper is to study the validity of the Hausdorff-Young inequality for vector-valued functions defined on a non-commutative compact group. The natural context for this research is that of operator spaces. This leads us to formulate a whole new theory of Fourier type and cotype for the category of operator spaces. The present paper is the first step in this program, where the basic theory is presented, the main examples are analyzed and some questions are posed.

Hardy-Littlewood, Hausdorff-Young-Paley inequalities, and Lp-Lq Fourier multipliers on compact homogeneous manifolds

In this paper we prove new inequalities describing the relationship between the "size" of a function on a compact homogeneous manifold and the "size" of its Fourier coefficients. These inequalities can be viewed as noncommutative versions of the Hardy-Littlewood inequalities obtained by Hardy and Littlewood on the circle. For the example case of the group SU(2) we show that the obtained Hardy-Littlewood inequalities are sharp, yielding a criterion for a function to be in $L^p$ on SU(2) in terms of its Fourier coefficients. We also establish Paley and Hausdorff-Young-Paley inequalities on gener…

Ultrametric subsets with large Hausdorff dimension

It is shown that for every $\e\in (0,1)$, every compact metric space $(X,d)$ has a compact subset $S\subseteq X$ that embeds into an ultrametric space with distortion $O(1/\e)$, and $$\dim_H(S)\ge (1-\e)\dim_H(X),$$ where $\dim_H(\cdot)$ denotes Hausdorff dimension. The above $O(1/\e)$ distortion estimate is shown to be sharp via a construction based on sequences of expander graphs.

Recovering a compact Hausdorff space $X$ from the compatibility ordering on $C(X)$

Let $f$ and $g$ be scalar-valued, continuous functions on some topological space. We say that $g$ dominates $f$ in the compatibility ordering if $g$ coincides with $f$ on the support of $f$. We prove that two compact Hausdorff spaces are homeomorphic if and only if there exists a compatibility isomorphism between their families of scalar-valued, continuous functions. We derive the classical theorems of Gelfand-Kolmogorov, Milgram and Kaplansky as easy corollaries to our result as well as a theorem of Jarosz [Bull. Canad. Math. Soc. 1990] thereby building~a common roof for these theorems. Sharp…

局部紧Hausdor夫紧致拓扑群中正规概率测度的正则性

Regularity of the Semigroup of Regular Probability Measures on Locally Compact Hausdorff Topological Groups in which every element is of finite order

研究局部紧Hausdor夫群中正规概率测度的正则性，发现对于紧致群和局部紧群，某些子半群中代数正则元素的特征仍成立，并在群为可数或不可数且每个真子群可数时给出完整描述。

Quantum Metric Spaces and the Gromov-Hausdorff Propinquity

We present a survey of the dual Gromov-Hausdorff propinquity, a noncommutative analogue of the Gromov-Hausdorff distance which we introduced to provide a framework for the study of the noncommutative metric properties of C*-algebras. We first review the notions of quantum locally compact metric spaces, and present various examples of such structures. We then explain the construction of the dual Gromov-Hausdorff propinquity, first in the context of quasi-Leibniz quantum compact metric spaces, and then in the context of pointed quantum proper metric spaces. We include a few new result concerning…