Let $ℒ=$ -div $\left(A\right(x\left)\nabla \right)$ be a second order elliptic operator with real, symmetric, bounded measurable coefficients on ${ℝ}^n$ or on a bounded Lipschitz domain subject to Dirichlet boundary condition. For any fixed $p\>2$, a necessary and sufficient condition is obtained for the boundedness of the Riesz transform $\nabla {\left(ℒ\right)}^{-1/2}$ on the $L^p$ space. As an application, for $1\<p\<3+ϵ$, we establish the $L^p$ boundedness of Riesz transforms on Lipschitz domains for operators with $VMO$ coefficients. The range of $p$ is sharp. The closely related boundedness of ...

The aim of the present paper is to obtain an inequality of Brézis-Gallouët-Wainger type for Besov-Morrey spaces. We investigate these spaces in a self-contained manner. Also, we verify that our result is sharp.

A typical wavelet system constitutes an unconditional basis for various function spaces -Lebesgue, Besov, Triebel-Lizorkin, Hardy, BMO. One of the main reasons is the frequency localization of an element from such a basis. In this paper we study a wavelet-type system, called a brushlet system. In [3] it was noticed that brushlets constitute unconditional bases for classical function spaces such as the Triebel-Lizorkin and Besov spaces. In this paper we study brushlet expansions of functions in the...

Dans cet article, on considère les opérateurs différentiels $T=b\left(x\right)D\left(a\right(x\left)D\right)$, où $a\left(x\right)$ et $b\left(x\right)$ sont deux fonctions mesurables, bornées et accrétives, et $D=-i\frac{d}{dx}$. Les résultats principaux portent sur les propriétés fonctionnelles de $T$, de sa racine carrée, avec applications à l’équation elliptique ${\partial }_t^{2}u-Tu=0$ sur $ℝ\times [0,+\infty [$. On démontre que $T^{1/2}{D}^{-1}$ est un opérateur de Calderón-Zygmund qui dépend analytiquement du couple $(a,b)$. Les estimations ponctuelles optimales sur le noyau du semi-groupe $\exp (-t{L}^{1/2})$ et le calcul fonctionnel permettent de développer une théorie...

The paper presents the proof of the fact that the discrete Calderón condition characterizes the completeness of an orthonormal wavelet basis.

In this paper we use the Calderón-Zygmund operator theory to prove a Calderón type reproducing formula associated with a para-accretive function. Using our Calderón-type reproducing formula we introduce a new class of the Besov and Triebel-Lizorkin spaces and prove a Tb theorem for these new spaces.

We study Calderón-Zygmund operators acting on generalized Carleson measure spaces $CM{O}_r^{\alpha ,q}$ and show a necessary and sufficient condition for their boundedness. The spaces $CM{O}_r^{\alpha ,q}$ are a generalization of BMO, and can be regarded as the duals of homogeneous Triebel-Lizorkin spaces as well.

We study sufficient conditions on the weight w, in terms of membership in the $A_p$ classes, for the spline wavelet systems to be unconditional bases of the weighted space $H^p\left(w\right)$. The main tool to obtain these results is a very simple theory of regular Calderón-Zygmund operators.