Search results for " Geometry"

Assouad Type Dimensions in Geometric Analysis

2021

We consider applications of the dual pair of the (upper) Assouad dimension and the lower (Assouad) dimension in analysis. We relate these notions to other dimensional conditions such as a Hausdorff content density condition and an integrability condition for the distance function. The latter condition leads to a characterization of the Muckenhoupt Ap properties of distance functions in terms of the (upper) Assouad dimension. It is also possible to give natural formulations for the validity of Hardy–Sobolev inequalities using these dual Assouad dimensions, and this helps to understand the previously observed dual nature of certain cases of these inequalities. peerReviewed

Spectral multipliers and wave equation for sub-Laplacians: lower regularity bounds of Euclidean type

2018

Let $\mathscr{L}$ be a smooth second-order real differential operator in divergence form on a manifold of dimension $n$. Under a bracket-generating condition, we show that the ranges of validity of spectral multiplier estimates of Mihlin--H\"ormander type and wave propagator estimates of Miyachi--Peral type for $\mathscr{L}$ cannot be wider than the corresponding ranges for the Laplace operator on $\mathbb{R}^n$. The result applies to all sub-Laplacians on Carnot groups and more general sub-Riemannian manifolds, without restrictions on the step. The proof hinges on a Fourier integral representation for the wave propagator associated with $\mathscr{L}$ and nondegeneracy properties of the sub…

On the role of virtual work in Levi-Civita’s parallel transport

2015

A Complete, Exact and Efficient Implementation for Computing the Edge-Adjacency Graph of an Arrangement of Quadrics

2011

International audience; We present a complete, exact and efficient implementation to compute the edge-adjacency graph of an arrangement of quadrics, i.e. surfaces of algebraic degree 2. This is a major step towards the computation of the full 3D arrangement. We enhanced an implementation for an exact parameterization of the intersection curves of two quadrics, such that we can compute the exact parameter value for intersection points and from that the edge-adjacency graph of the arrangement. Our implementation is complete in the sense that it can handle all kinds of inputs including all degenerate ones, i.e. singularities or tangential intersection points. It is exact in that it always comp…

Modéliser un demi-cercle et autres questions de poids nuls

2018

National audience; Les courbes de Bézier rationnelles avec des points pondérés peinent à prendre en compte certaines situations élémentaires comme la modélisation d'un demi-cercle avec une courbe de degré 2. Dans cet article nous mon-trons comment l'utilisation de courbes de Bézier rationnelles avec des points massiques résout ce problème. Plus largement, nous montrons aussi que la formulation usuelle de Bézier rationnelles n'est pas complète.

Introduction à la modélisation de l'écriture manuscrite par des courbes Bézier Rationnelles massiques

2019

National audience; L’article est une introduction à la modélisation de l’écriture manuscrite. La représentation de l’écriture cursive in- terfère, selon l’approche hors ligne ou en ligne, sur la robustesse des algorithmes de reconnaissance des caractères manuscrits, de l’identification des auteurs et de leur signature. Les caractéristiques de base de l’écriture cursive que sont les traits et leur inclinaisons, les boucles, les pleins et déliés peuvent être modélisés par des courbes. Des méthodes existent. Elles reposent sur les B-splines et leur points de contrôle. Dans un premier temps, des traits, les auteurs proposent une modélisation, rebroussements, boucles, arrondis, pleins et déliés.…

Some remarks on Hilbert's (Weak) Nullstellensatz

2011

Certain remarks are provided related to weak nullstellensatz exploiting some problems proposed in Fulton’s book entitled “An Introduction to Algebraic Geometry” and elementary notions of Functional Analysis.

Quasiconformal Jordan Domains

2020

We extend the classical Carath\'eodory extension theorem to quasiconformal Jordan domains $( Y, d_{Y} )$. We say that a metric space $( Y, d_{Y} )$ is a quasiconformal Jordan domain if the completion $\overline{Y}$ of $( Y, d_{Y} )$ has finite Hausdorff $2$-measure, the boundary $\partial Y = \overline{Y} \setminus Y$ is homeomorphic to $\mathbb{S}^{1}$, and there exists a homeomorphism $\phi \colon \mathbb{D} \rightarrow ( Y, d_{Y} )$ that is quasiconformal in the geometric sense. We show that $\phi$ has a continuous, monotone, and surjective extension $\Phi \colon \overline{ \mathbb{D} } \rightarrow \overline{ Y }$. This result is best possible in this generality. In addition, we find a n…

Lenses on very curved zones of a singular line field of ${\mathbb C}^2$ or of a singular plane field of ${\mathbb C}^3$

2020

We renormalize, using suitable lenses, small domains of a singular holomorphic line field of ${\mathbb C}^2$ or plane field of ${\mathbb C}^3$ where the curvature of a plane-field is concentrated. At a proper scale the field is almost invariant by translations. When the field is integrable, the leaves are locally almost translates of a surface that we will call {\it profile}. When the singular rays of the tangent cone (a generalization to a plane-field of the tangent cone of a singular surface is defined) are isolated, we obtain more precise results. We also generalize a result of Merle (\cite{Me}) concerning the contact order of generic polar curves with the singular level $f=0$ when $\ome…

FROM THE DESCRIPTIVE GEOMETRY TO THE INFORMATICS LANGUAGE.

2010

This study is centred in the environment of the research into solutions of the problems of graphic representation, expressing theoretical considerations which allow the carrying out of geometric-descriptive procedures decoded in informatics language, for implementing CAD commands. The solution of these problems requires a reliable command of stereometry and descriptive geometry and it can extend remarkably the level of external geometric competences. The implementation of the means of ICT has brought a higher effectiveness of graphing mapping processes. In the informatics field, the advent of software dedicated to computerized representation has increased the possibilities of investigation …