Paris West University Nanterre La Défense

About: Paris West University Nanterre La Défense is a education organization based out in Paris, France. It is known for research contribution in the topics: Computer science & Politics. The organization has 895 authors who have published 1430 publications receiving 21712 citations.

Electronic control of linear-to-circular polarization conversion using a reconfigurable metasurface

Abstract: A reflective metasurface enabling linear-to-circular polarization (LP-to-CP) conversion is proposed. The metasurface polarizer is composed of active unit cells incorporating voltage-controlled varactor diodes, where the dispersion responses of the cells can be tailored. When illuminated by an incident wave, the metasurface converts the LP wave from the source to a CP one. Moreover, in a single voltage configuration, two circular polarized waves with different handedness can be obtained at distinct frequencies. Such operation can be tuned in frequency by changing the applied voltage along the metasurface. Simulations are performed to verify the concept, and measurements done on a fabricated prototype validate the polarization conversion performances at microwave frequencies.

Approximation Methods for Supervised Learning

Abstract: Let ź be an unknown Borel measure defined on the space Z := X × Y with X ź źd and Y = [-M,M]. Given a set z of m samples zi =(xi,yi) drawn according to ź, the problem of estimating a regression function fź using these samples is considered. The main focus is to understand what is the rate of approximation, measured either in expectation or probability, that can be obtained under a given prior fź ź ź, i.e., under the assumption that fź is in the set ź, and what are possible algorithms for obtaining optimal or semioptimal (up to logarithms) results. The optimal rate of decay in terms of m is established for many priors given either in terms of smoothness of fź or its rate of approximation measured in one of several ways. This optimal rate is determined by two types of results. Upper bounds are established using various tools in approximation such as entropy, widths, and linear and nonlinear approximation. Lower bounds are proved using Kullback-Leibler information together with Fano inequalities and a certain type of entropy. A distinction is drawn between algorithms which employ knowledge of the prior in the construction of the estimator and those that do not. Algorithms of the second type which are universally optimal for a certain range of priors are given.

Functionally graded graphene reinforced porous nanocomposite curved beams: Bending and elastic stability using a higher-order model with thickness stretch effect

Abstract: Here, the investigation of thick functionally graded graphene platelets reinforced porous nanocomposite curved beams is carried out considering the static bending and elastic stability analyses based on a higher-order shear deformation theory accounting for through-thickness stretching effect. The formulation is general through which different theories can be realized for various structural applications of beam. The governing equations are developed using the Hamilton's principle and are solved by introducing the Navier's solutions. The formulation is firstly assessed considering problems for that results are available in the literature. The performance of various theories is compared here for the selected problems. The structural characteristics of curved beam, constituting of porous metal foam and graphene platelets as nanofillers for reinforcement, are evaluated considering different dispersion patterns for the graphene and porosity, shallowness of the curved beam, thickness ratio, and platelet geometry. The deflection and stress variations in the thickness direction of the beam are also examined.