Su un teorema di R. H. Martin Jr.
Compensation couples and isoperimetric estimates for vector fields
How to get rid of one of the weights in a two-weight Poincaré inequality?
We prove that if a Poincaré inequality with two different weights holds on every ball, then a Poincaré inequality with the same weight on both sides holds as well.
Hölder regularity theorem for a class of linear nonuniformly elliptic operators with measurable coefficients
Some Remarks on Vector Potentials for Maxwell's Equations in Space-Time Carnot Groups
In this paper we prove a -convergence result for time-depending variational functionals in a space-time Carnot group arising in the study of Maxwell's equations in the group. Indeed, a Carnot groups (a connected simply connected nilpotent stratified Lie group) can be endowed with a complex of ``intrinsic'' differential forms that provide the natural setting for a class of ``intrinsic'' Maxwell's equations. Our main results states precisely that a the vector potentials of a solution of Maxwell's...
De Giorgi’s Theorem, for a Class of Strongly Degenerate Elliptic Equations
In questa Nota enunciamo, per una classe di equazioni ellittiche del secondo ordine «fortemente degeneri» a coefficienti misurabili, un teorema di hölderianità delle soluzioni deboli che estende il ben noto risultato di De Giorgi e Nash. Tale risuJtato discende dalle proprietà geometriche di opportune famiglie di sfere associate agli operatori.
De Giorgi’s Theorem, for a Class of Strongly Degenerate Elliptic Equations
In questa Nota enunciamo, per una classe di equazioni ellittiche del secondo ordine «fortemente degeneri» a coefficienti misurabili, un teorema di hölderianità delle soluzioni deboli che estende il ben noto risultato di De Giorgi e Nash. Tale risuJtato discende dalle proprietà geometriche di opportune famiglie di sfere associate agli operatori.
Straightening of a noncylindrical region and evolution equations
Gehring's lemma for metrics and higher integrability of the gradient for minimizers of noncoercive variational functionals
We prove a higher integrability result - similar to Gehring's lemma - for the metric space associated with a family of Lipschitz continuous vector fields by means of sub-unit curves. Applications are given to show the higher integrability of the gradient of minimizers of some noncoercive variational functionals.
Definitions of Sobolev classes on metric spaces
There have been recent attempts to develop the theory of Sobolev spaces on metric spaces that do not admit any differentiable structure. We prove that certain definitions are equivalent. We also define the spaces in the limiting case .
Existence and properties of the Green function for a class of degenerate parabolic equations.
It is known that degenerate parabolic equations exhibit somehow different phenomena when we compare them with their elliptic counterparts. Thus, the problem of existence and properties of the Green function for degenerate parabolic boundary value problems is not completely solved, even after the contributions of [GN] and [GW4], in the sense that the existence problem is still open, even if the a priori estimates proved in [GN] will be crucial in our approach (...).
Esistenza e unicità degli stati fondamentali per equazioni ellittiche quasilineari
In this paper we describe some existence and uniqueness theorems for radial ground states of a class of quasilinear elliptic equations. In particular, the mean curvature operator and the degenerate Laplace operator are considered.
Courbure et sous-ensembles de courbes rectifiables dans le groupe de Heisenberg
Nous présentons une condition suffisante pour qu’un compact dans le groupe de Heisenberg (muni de sa structure de Carnot-Carathéodory) soit contenu dans une courbe rectifiable. Cette condition est aussi nécessaire dans le cas de courbes régulières (en particulier, des géodésiques) et elle est inspirée du lemme géométrique faible du à Peter Jones dans le cas euclidien. Cette note repose sur l’exposé fait par le troisième auteur (au Séminaire X-EDP) et décrit les principaux résultats de l’article...
Elliptic Equations Containing the Term in a Half Space
In questa Nota si considerano, in opportuni spazi con peso, problemi al contorno in un semispazio per operatori del tipo dove è un operatore ellittico e è un parametro complesso.
An Elliptic Boundary Value Problem with Unbounded Coefficients in a Half Space
In questa nota diamo alcuni risultati su di una classe di problemi al contorno per equazioni ellittiche a coefficienti polinomiali in un semispazio. Si stabilisce 1'esistenza di una parametrice destra e di una parametrice sinistra del problema; si stabiliscono inoltre stime a priori del problema e di quello aggiunto.
Esistenza e unicità degli stati fondamentali per equazioni ellittiche quasilineari
In this paper we describe some existence and uniqueness theorems for radial ground states of a class of quasilinear elliptic equations. In particular, the mean curvature operator and the degenerate Laplace operator are considered.
spaces and rectifiability for Carnot-Carathéodory metrics: an introduction
This paper is meant as a (short and partial) introduction to the study of the geometry of Carnot groups and, more generally, of Carnot-Carathéodory spaces associated with a family of Lipschitz continuous vector fields. My personal interest in this field goes back to a series of joint papers with E. Lanconelli, where this notion was exploited for the study of pointwise regularity of weak solutions to degenerate elliptic partial differential equations. As stated in the title, here we are mainly concerned...
Differentiability and Approximate Differentiability for Intrinsic Lipschitz Functions in Carnot Groups and a Rademacher Theorem
A Carnot group G is a connected, simply connected, nilpotent Lie group with stratified Lie algebra. We study intrinsic Lipschitz graphs and intrinsic differentiable graphs within Carnot groups. Both seem to be the natural analogues inside Carnot groups of the corresponding Euclidean notions. Here ‘natural’ is meant to stress that the intrinsic notions depend only on the structure of the algebra of G. We prove that one codimensional intrinsic Lipschitz graphs are sets with locally finite G-perimeter....
Representation formulas and weighted Poincaré inequalities for Hörmander vector fields
We derive weighted Poincaré inequalities for vector fields which satisfy the Hörmander condition, including new results in the unweighted case. We also derive a new integral representation formula for a function in terms of the vector fields applied to the function. As a corollary of the versions of Poincaré’s inequality, we obtain relative isoperimetric inequalities.
Two-weight Sobolev-Poincaré inequalities and Harnack inequality for a class of degenerate elliptic operators
In this Note we prove a two-weight Sobolev-Poincaré inequality for the function spaces associated with a Grushin type operator. Conditions on the weights are formulated in terms of a strong weight with respect to the metric associated with the operator. Roughly speaking, the strong condition provides relationships between line and solid integrals of the weight. Then, this result is applied in order to prove Harnack's inequality for positive weak solutions of some degenerate elliptic equations....
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