Sobolev Spaces with Zero Boundary Values on Metric Spaces

We generalize the definition of the first order Sobolev spaces with zero boundary values to an arbitrary metric space endowed with a Borel regular measure. We show that many classical results extend to the metric setting. These include completeness, lattice properties and removable sets.     

Invariant Subspaces for Compact-Friendly Operators in Sobolev Spaces

In this note we extend the concept of compact-friendlyness, defined in the literature for operators on a Banach lattice, to the case of operators on Sobolev spaces and derive the existence of invariant subspaces for compact-friendly operators of this type.     

Bases in Sobolev Spaces on Bounded Domains with Lipschitzian Boundary

In the Sobolev space , where is a bounded domain in ⁿ with a Lipschitzian boundary, for an arbitrarily given , we construct a basis such that the error of approximation of a function the Nth partial sum of its expansion with respect to this basis can be estimated in terms of the modulus of smoothness of order .     

On the Summing Property of the Sobolev Embedding Operators

We prove that the Sobolev embedding operator S _d,k,p : , where 1/s=1/p-k/d , is (v,1) -absolutely summing for appropriate v > 1 . The result is optimal for s 2 .     

Characterization of Smoothness of Multivariate Refinable Functions in Sobolev Spaces

Wavelets are generated from refinable functions by using multiresolution analysis. In this paper we investigate the smoothness properties of multivariate refinable functions in Sobolev spaces. We characterize the optimal smoothness of a multivariate refinable function in terms of the spectral radius of the corresponding transition operator restricted to a suitable finite dimensional invariant subspace. Several examples are provided to illustrate the general theory.

     

The Convergences of Bivariate Integral Jackson Interpolating Operators in Orlicz Spaces

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Subelliptic Sobolev Spaces for Manifolds with Symmetries

Given a group of symmetries on a (generally non-compact) differentiable manifold, we construct invariant locally subelliptic operators, prove Sobolev inequalities and verify existence of correspondent minimizers. The results apply, in particular, to a class of singular elliptic operators on domains in R^N with singularity on the boundary. Mathematics Subject Classifications (2000) 35H20, 35J20, 40A30, 22E30, 43A85.K. Tintarev: Research supported by a grant from Vetenskaprådet.     

Lower Estimates of the Norms of Extension Operators for Sobolev Spaces on the Halfline

It is proved that for an arbitrary extension operator its norm cannot be less than ε₀2^mm^—1/2p, ε₀ > 0. Previously only the upper estimates (≤ 8^m) for these norms were known.     

The Dirichlet Energy Integral and Variable Exponent Sobolev Spaces with Zero Boundary Values

We define and study variable exponent Sobolev spaces with zero boundary values. This allows us to prove that the Dirichlet energy integral has a minimizer in the variable exponent case. Our results are based on a Poincaré-type inequality, which we prove under a certain local jump condition for the variable exponent.     

新的齐型BMO, Lipschitz空间上的奇异积分算子

Let(X, d, μ) be a space of homogeneous type, BMO_A(X) and Lip_A(β,X) be the space of BMO type,lipschitz type associated with an approximation to the identity {A_t}_t0 and introduced by Duong,Yan and Tang, respectively. Assuming that T is a bounded linear operator on L~2(X), we find the sufficient condition on the kernel of T so that T is bounded from BMO(X) to BMO_A(X) and from Lip(β, X) to Lip_A(β, X). As an application, the boundedness of Calderón-Zygmund operators with nonsmooth kernels on BMO(R~n) and Lip(β, R~n) are also obtained.     

Weierstrass'' Theorem in Weighted Sobolev Spaces

We characterize the set of functions which can be approximated by polynomials with the following norm

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for a big class of weights w₀, w₁, …, w_k     

Operator Equations and Duality Mappings in Sobolev Spaces with Variable Exponents

After studying in a previous work the smoothness of the space UΓ0={u∈W1,p(·)(Ω);u=0 on Γ0 Γ=Ω},where dΓ-measΓ0>0,with p(·)∈C(Ω)and p(x)>1 for all x∈Ω,the authors study in this paper the strict and uniform convexity as well as some special properties of duality mappings defined on the same space.The results obtained in this direction are used for proving existence results for operator equations having the form Ju=Nfu,where J is a duality mapping on UΓ0 corresponding to the gauge function,and Nf is the Nemytskij operator generated by a Carath′eodory function f satisfying an appropriate growth condition ensuring that Nf may be viewed as acting from UΓ0 into its dual.     

Sobolev Spaces on Quasi-K\"ahler Complex Varieties

If $V$ is an irreducible quasi-K\"ahler complex variety and $E$ is a vector bundle over $\mathrm{reg}(V)$, the author proves that $W^{1,2}_{0}(\mathrm{reg}(V),E)=W^{1,2}(\mathrm{reg}(V),E)$, and that for $\dim_{\mathbb{C}}\mathrm{reg}(V)>1$, the natural inclusion $W^{1,2}(\mathrm{reg}(V),E)\hookrightarrow L^{2}(\mathrm{reg}(V),E)$ is compact, the natural inclusion $W^{1,2}(\mathrm{reg}(V),E)\hookrightarrow L^{\frac{2v}{v-1}}(\mathrm{reg}(V),E)$ is continuous.     

Non Integral Regularizing Operators on Lp- Spaces

We present bounded positivity preserving operators from L_p(?) to L_q (?), for 1 < p < ∞, 1/p-1/q < 1/2, which are not integral operators.     

Sobolev空间中多小波Bessel序列

Bessel sequence plays an important role in the study of frames for a Hilbert space with the convergence of a frame series, which has been widely studied in the literature. This paper addresses multi-wavelet Bessel sequences in Sobolev spaces setting, the result obtained is useful for the study of multi-wavelet frames in these spaces.     

Generalized Weighted Sobolev Spaces and Applications to Sobolev Orthogonal Polynomials I

In this paper we present a definition of Sobolev spaces with respect to general measures, prove some useful technical results, some of them generalizations of classical results with Lebesgue measure and find general conditions under which these spaces are complete. These results have important consequences in approximation theory. We also find conditions under which the evaluation operator is bounded.     

Convolution Operators on Discrete Hardy Spaces

We establish the connection between the boundedness of convolution operators on H^p(ℝ^N) and some related operators on H^p(ℤ^N). The results we obtain here extend the already known for L^p spaces with p > 1. We also study similar results for maximal operators given by convolution with the dilation of a fixed kernel. Our main tools are some known results about functions of exponential type already presented in [BC1] that, in particular, allow us to prove a sampling theorem for functions of exponential type belonging to Hardy spaces     

振荡超奇性Hilbert变换的Sobolev有界性

主要研究R~n上沿曲线Γ(t)=(t~(p_1),t~(p_2),…,t~(p_n))的振荡超奇性Hilbert变换H_(n,α,β)=∫_0~1 f(x-Γ(t))e~(it-β)t~(-1-α),在Sobolev空间上的有界性,其中0p_1P_2…P_n,αβ0.证明了对于0γ(nα)/((n+1))(p_1+α),当|1/p-1/2|(β-(n+1)[α-(β+p_1)γ])/(2β)时,H_(n,α,β)是从L_γ~2(R~n))到L~2(R~n)的有界算子.特别地,当β≥(α-γp_1)/(γ+1/(n+1))等时,H_(n,α,β)是从L_γ~2(R~n)到L~2(R~n)的有界算子·