微积分中Fejér核的性质及应用

介绍微积分中Fejér核的概念,给出其性质,实例展示其在习题解答和定理证明中的具体应用,并分别给出Fejér定理与Weierstrass第二逼近定理的一种新证明.     

Dirichlet函数类的Fejér算子逼近

对Cn中的单位球Bn上的Dirichlet类Dp,得到与Hardy空间Hp的包含关系,并获得其精确的多项式逼近阶和以Hardy空间度量的Fejér算子逼近的一个上界估计.     

二维Hardy空间维林肯型系统的极大算子（英文）

本文研究二维Hardy空间维林肯型系统的极大算子的有界性.利用原子分解方法,我们证明二维极大算子T_αf:=sup₍2^-α≤n/m≤2^α)|f*P_n,m|是从鞅Hardy空间H^p到L^p有界的,其中0 *f=₍2^-α≤n/m≤2^α)|σ_n,mf|/([(n+1)(m+1)])^1/p-2的有界性证明.通过构造反例,我们证明二维极大算子■不是从鞅Hardr空间H^p到L^p有界的,其中0

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L~p空间中的Fejér和Hermite-Hadamard型不等式

给出了二阶导数属于Lp空间时Fejér和Hermite-Hadamard型不等式的推广,得到两个新结果.     

Fejér不等式加强形式的推广

通过建立积分恒等式,将一个关于4阶可微函数的Fejér不等式的加强形式推广到关于2n-1(n≥2)阶可微函数的Fejér型不等式.对此新推广的不等式还给出了若干误差估计.     

严格的Hermite-Hadamard型不等式和Fejér型不等式

已有文献引入与Hermite-Hadamard不等式和Fejér不等式有关的单调函数.考虑这些函数与其上界和下界的差,利用二阶导数,给出这些差的上下界,建立了一些新的严格的Hermite-Hadamard型不等式和Fejér型不等式.     

第III类非自共轭锥上的Gamma函数

本文将Gamma函数及Siegel积分推广到一般的第III类非自共轭锥上.作为其应用,显式给出了以这些锥为底的管状域(也称第一类Siegel域)的Cauchy-Szeg"o核和形式Poisson核.     

第I类非自共轭锥上的Gamma函数

本文将Ｇａｍｍａ函数及Ｓｉｅｇｅｌ积分推广到一般的第Ｉ类非自共轭锥上．作为其应用，显式给出了以这些锥为底的管状域（或第一类Ｓｉｅｇｅｌ域）的Ｃａｕｃｈｙ Ｓｚｅｇ¨ｏ核和形式Ｐｏｉｓｏｎ核．     

第Ⅲ类非自共轭锥上的Gamma函数

本文将Ｇａｍｍａ函数及Ｓｉｅｇｅｌ积分推广到一般的第Ⅲ类非自共轭锥上,作为其应用,显式给出了以这些锥为底的管状域（也称第一类Ｓｉｅｇｅｌ域）的Ｃａｕｃｈｙ－Ｓｚｅｇｏ核和形式Ｐｏｉｓｓｏｎ核。关键词     

正规实型对称空间上平方函数算子的弱1——1有界性

利用正规实型对称空间上热核的一个上界估计及非紧致Riemann对称空间上热核 的一个梯度估计,证明了正规实型对称空间上的Littlewood-Paley平方函数算子的弱1-1 有界性.     

Berezin kernels and analysis on Makarevich spaces

Following ideas of van Dijk and Hille we study the link which exists between maximal degenerate representations and Berezin kernels.We consider the conformal group Conf(V) of a simple real Jordan algebra V. The maximal degenerate representations π_s (s ε ℂ) we shall study are induced by a character of a maximal parabolic subgroup P¯ of Conf(V). These representations π_s can be realized on a space I_s of smooth functions on V. There is an invariant bilinear form ℬ_s on the space Is. The problem we consider is to diagonalize this bilinear form ℬ_s, with respect to the action of a symmetric subgroup G of the conformal group Conf(V). This bilinear form can be written as an integral involving the Berezin kernel B_v an invariant kernel on the Riemannian symmetric space G/K, which is a Makarevich symmetric space in the sense of Bertram. Then we can use results by van Dijk and Pevzner who computed the spherical Fourier transform of B_v. From these, one deduces that the Berezin kernel satisfies a remarkable Bernstein identity: D(_ν)B_ν=b(ν)B_ν+1, where D(_ν) is an invariant differential operator on G/K and b(ν) is a polynomial. By using this identity we compute a Hua type integral which gives the normalizing factor for an intertwining operator from I_−s to I_s. Furthermore, we obtain the diagonalization of the invariant bilinear form with respect to the action of the maximal compact group U of the conformal group Conf(V).     

Fourier analysis

Book Reviews

Fourier analysisT. W. Körner: Cambridge University Press, Cambridge, 1988, 591 pp. $95     

Fourier analysis on domains in compact groups

Let Ω be a measurable subset of a compact group G of positive Haar measure. Let be a non-negative function defined on the dual space and let L²(μ) be the corresponding Hilbert space which consists of elements (ξπ)_π∈suppμ satisfying , where ξπ is a linear operator on the representation space of π, and is equipped with the inner product: . We show that the Fourier transform gives an isometric isomorphism from L²(Ω) onto L²(μ) if and only if the restrictions to Ω of all matrix coordinate functions , π∈suppμ, constitute an orthonormal basis for L²(Ω). Finally compact connected Lie groups case is studied.     

On the divergence of Fourier series of functions in several variables

The paper deals with the problems of divergence of the series from absolute values of the Fourier coefficients of functions in several variables. It is proved that as the dimension of the space increases, the absolute convergence of Fourier series with respect to any complete orthnormal system (ONS) of functions with continuous partial derivatives becomes worse. For instance, for any ? ∈ (0, 2) there exists a function in variables $k > \frac{{2(2 - \varepsilon )}} {\varepsilon }$ having all the continuous partial derivatives, however the series of absolute values of its coefficients with respect to any complete orthnormal system diverges in power 2 ? ?.     

Fourier expansions of functions with bounded variation of several variables

In the first part of the paper we establish the pointwise convergence as for convolution operators under the assumptions that has integrable derivatives up to an order and that with . We also estimate the Hausdorff dimension of the set where divergence may occur. In particular, when the kernel is the Fourier transform of a bounded set in the plane, we recover a two-dimensional analog of the Dirichlet theorem on the convergence of Fourier series of functions with bounded variation. In the second part of the paper we prove an equiconvergence result between Fourier integrals on euclidean spaces and expansions in eigenfunctions of elliptic operators on manifolds, which allows us to transfer some of the results proved for Fourier integrals to eigenfunction expansions. Finally, we present some examples of different behaviors between Fourier integrals, Fourier series and spherical harmonic expansions.

     

On pointwise convergence of Fourier series of radial functions in several variables

We prove the pointwise convergence of the Fourier series for radial functions in several variables, which in the case is the Dirichlet-Jordan theorem itself. In our proof the method for the case of the indicator function of the ball is very useful.

     

Remarks on optimum kernels and optimum boundary kernels

Kernel smoothers belong to the most popular nonparametric functional estimates used for describing data structure. They can be applied to the fix design regression model as well as to the random design regression model. The main idea of this paper is to present a construction of the optimum kernel and optimum boundary kernel by means of the Gegenbauer and Legendre polynomials. This work is part of the research project “The Czech Economy in the Process of Integration and Globalization, and the Development of Agricultural Sector and the Sector of Service under the New Conditions of the Integrated European Market”.