Reflet

Résumé

Un reflet est, en physique, l' virtuelle formée par la réflexion spéculaire d'un objet sur une surface. La nature spéculaire de la réflexion est liée aux caractéristiques du corps réfléchissant. Les formes les plus connues s'obtiennent par réflexion sur une surface métallique (miroir), le verre ou l'eau. L'image virtuelle est inversée et se trouve de manière symétrique à l'objet par rapport au plan de réflexion (lois de Descartes). Un reflet est aussi une nuance de lumière ou de couleur apparaissant sur un fond ou un motif. Sur la perle et les lèvres de La Jeune Fille à la perle, Johannes Vermeer peint des reflets. Par analogie avec la distinction des ombres propres et des ombres portées, on peut parler de reflet propre. Réflexion surface eau.jpg|[[Equus quagga|Zèbres]] se reflétant dans l'eau ([[Parc national d'Etosha|Etosha]]). Holdamoos Halde1.jpg|Reflet dans un lac de montagne. Flickr - Tour d'Afrique - Sunileyes. By Adam Birkin (2).jpg|Sur une paire de [[lunettes]]. Institut

Source officielle

https://fr.wikipedia.org/wiki/Reflet

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L'objectif de ce cours est de fournir les connaissances et le moyen de comprendre, au niveau moléculaire, le fonctionnement des réactions chimiques organiques. Pendant le cours, l'étudiant réfléchira et résoudra de nouveaux problèmes.

Ce cours met en relation les différents niveaux de structuration de la matière avec les propriétés mécaniques, thermiques, électriques, magnétiques et optiques des matériaux. Des travaux pratiques en laboratoire et un projet de groupe permettent d'apréhender le métier d'ingénieur en matériaux.

This course aims to teach essential notions of the structure of matter, chemical equilibria and reactivity. Classes and exercises provide the means to analyze and solve, by reasoning and calculation, novel problems of geeneral chemistry.

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Séances de cours associées (31)

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A Data-Driven Fault Location Algorithm Based on the Electromagnetic Time Reversal in Mismatched Media

Zhe Chen, Mario Paolone, Zhaoyang Wang

The classical electromagnetic time reversal (EMTR) fault location method in power systems can be time consuming, especially when a high location accuracy is desired. To cope with this issue, the concept of EMTR in mismatched media has recently been introduced, substantially improving the fault location efficiency. In this paper, we present a theoretical study and rigorous demonstration of the mismatched-media-based mirrored minimum energy property. Firstly, we infer a direct-reversed-time transfer function and present a theorem according to which, at the fault switching frequency and its odd harmonics, the mirror-image point of the fault location with respect to the line center corresponds to a local minimum of the squared modulus of the transfer function. Next, it is proved that the mirrored minimum energy property is a corollary of this theorem. Based on these theoretical findings, we propose an algorithm that uses the reversed-time voltage energy as a fault location metric in the frequency domain, instead of the original time-domain approach. We further propose applying a data-driven strategy to maximize the computation efficiency of the algorithm. The applicability and robustness of the frequency-domain fault location metric, together with the computational efficiency of the accelerating algorithm, are numerically and experimentally validated.

2021

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Discrete metal nanoparticles with plasmonic chirality

Jijun He

From a geometrical perspective, a chiral object does not have mirror planes or inversion symmetry. It exhibits the same physical properties as its mirror image (enantiomer), except for the chiroptical activity, which is often the opposite. Recent advancements have identified particularly interesting implications of chirality on the optical properties of metal nanoparticles, which are intimately related to localized surface plasmon resonance phenomena. Although such resonances are usually independent of the circular polarization of light, specific strategies have been applied to induce chirality, both in assemblies and at the single-particle level. In this tutorial review, we discuss the origin of plasmonic chirality, as well as theoretical models that have been proposed to explain it. We then summarise recent developments in the synthesis of discrete nanoparticles with plasmonic chirality by means of wet-chemistry methods. We conclude with a discussion of promising applications for discrete chiral nanoparticles. We expect this tutorial review to be of interest to researchers from a wide variety of disciplines where chiral plasmonics can be exploited at the nanoparticle level, such as chemical sensing, photocatalysis, photodynamic or photothermal therapies, etc.

ROYAL SOC CHEMISTRY2021

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An Isotropic Auxetic Structural Network with Limited Shear Stiffness

Alessandro Spadoni

The chiral lattice is a unique structural network not symmetric to its mirror image, and with a negative Poisson’s ratio. Previous investigations have considered this structural network for the design of superior structural components with sandwich construction, but these were limited by the in-plane Poisson’s ratio predicted to be exactly -1. This paper presents estimates of the mechanical properties of the chiral lattice obtained from a multi-cell finite-element model. It is shown that the chiral lattice has a shear stiffness bound by that of the triangular lattice and it is very compliant to direct stresses. The minimum in-plane poisson’s ratio is estimated to be approximately -0.94.

ASME2011

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