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Dynamical Symmetries of the 2D Newtonian Free Fall Problem Revisited
No full textInternational audienceAmong the few exactly solvable problems in theoretical physics, the 2D (two-dimensional) Newtonian free fall problem in Euclidean space is perhaps the least known as compared to the harmonic oscillator or the Kepler–Coulomb problems. The aim of this article is to revisit this problem at the classical level as well as the quantum level, with a focus on its dynamical symmetries. We show how these dynamical symmetries arise as a special limit of the dynamical symmetries of the Kepler–Coulomb problem, and how a connection to the quartic anharmonic oscillator problem, a long-standing unsolved problem in quantum mechanics, can be established. To this end, we construct the Hilbert space of states with free boundary conditions as a space of square integrable functions that have a special functional integral representation. In this functional space, the free fall dynamical symmetry algebra is shown to be isomorphic to the so-called Klink’s algebra of the quantum quartic anharmonic oscillator problem. Furthermore, this connection entails a remarkable integral identity for the quantum quartic anharmonic oscillator eigenfunctions, which implies that these eigenfunctions are in fact zonal functions of an underlying symmetry group representation. Thus, an appropriate representation theory for the 2D Newtonian free fall quantum symmetry group may potentially open the way to exactly solving the difficult quantization problem of the quartic anharmonic oscillator. Finally, the initial value problem of the acoustic Klein–Gordon equation for wave propagation in a sound duct with a varying circular section is solved as an illustration of the techniques developed here
Modèles de molécules biologiques sondés vibrationnellement et électroniquement en phase gazeuse
No full textPhoto-induced processes are largely involved in the biological world due to the intrinsic properties of the molecules that compose them, like the UV/Vis aromatic chromophores residues of the proteins, the heme of hemoglobin protein or the chlorophylls. The goal of this thesis was in part to document in details the electronic relaxation processes that follow the UV/Vis absorption by these molecules. The interest was focused on the formation of triplet states formation in these systems that are still poorly known despite their major importance. Indeed, the biradical character of the triplet states and their long lifetimes made them efficient intermediate states involved in photochemical deactivation channels, potentially harmful to their biological function. Furthermore, because these properties can be influenced by the molecules conformation, when they are flexible like proteins, the second part of this work was devoted to the structure characterization. The chosen approach, the vibrational or electronic pump-probe spectroscopy in gas phase, aims to obtain detailed spectroscopic information intrinsic to the molecule, allowing an easier comparison with theoretical modelisation, in particular with quantum chemistry. However, a precise control of the system, its conformation and its temperature in gas phase require the study of model molecules, a fraction of the targeted biological molecule, relevant for the studied process, isolating them either in a supersonic expansion or in helium droplets. Three approaches have been investigated. On the structural and thermodynamical sides, the side chain tautomerism of the histidine aminoacid was studied on the 4(5)-methylimidazole molecule. The IR spectroscopy in helium droplets allowed quantifying the molecules' tautomerization thermodynamics. Moreover small peptide chains that contain the phenylalanine residue, used as peptide chain models when probing triplet states, have been characterized in a supersonic expansion by double IR/UV resonance spectroscopy in the spectral domain of the NH stretch modes. These studies have both been supported by quantum chemistry calculations at the DFT-D level. Both triplet state formation and characterization induced by the photo-excitation of peptide chains containing phenylalanine amino acid have been studied in the framework of the protein photo-degradation after UV photo-excitation. Although the phenyl ring is known for its high intersystem crossing quantum yield after the first singlet state excitation, it is still not well know for protein chains. The triplet state formation for a series of model molecules protein chains containing the phenylalanine residue has been probed with a pump-probe method. With the help of quantum chemistry calculation, these studies have shown that the relaxation of the excited phenylalanine that follows the triplet states formation depends on the side chain and of the presence of peptide bonds (-CO-NH-) in its environment. A relaxation schema have been proposed, suggesting the competition between the formation of long lived triplets states ( µs) and at least one alternative channel leading to undetected dark states. Finally, triplet states of two copper porphyrins, heme models, have been detected in pump-probe experiments. Their detection allowed to first uncovering absorption properties of these molecules and then to characterize the relaxation modes leading to the ground state after the absorption of an UV photon.Les processus photo-induits sont partout présents dans le monde biologique de par les propriétés intrinsèques des molécules qui les constituent, telles que les chromophores UV/Vis des résidus aromatiques des protéines, l’hème dans l’hémoglobine ou bien la chlorophylle. L’objectif de cette thèse a en partie été de documenter en détail les processus de relaxation électronique qui suivent l’absorption de la lumière visible ou UV par ces molécules. L’intérêt s’est porté sur la formation d’états triplets dans ces systèmes, qui restent mal connus malgré leur importance cruciale. En effet, le caractère bi-radicalaire des états triplets et leur longue durée de vie en font des intermédiaires efficaces vers des voies de désexcitation photochimiques, potentiellement dommageables à la fonction biologique de ces molécules. En outre, dans la mesure où ces propriétés peuvent être influencées par la conformation de ces molécules lorsqu’elles sont flexibles, comme les protéines, une autre part du travail a consisté à caractériser ces conformations. L’approche choisie, la spectroscopie pompe-sonde en phase gazeuse vibrationnelle ou électronique, vise à obtenir les informations spectroscopiques détaillées et intrinsèques à la molécule, permettant une comparaison facilitée avec la modélisation théorique, notamment par chimie quantique. Cependant, un contrôle précis du système, de sa conformation et sa température en phase gazeuse nécessite d’étudier des molécules modèles, fragments des molécules biologiques visées, pertinents pour l’étude du processus visé, en les isolant soit dans une détente supersonique, soit dans des gouttelettes d’hélium. Trois actions principales ont ainsi été menées. Du point de vue structurel et thermodynamique, la tautomérie de la chaine latérale de l’acide aminé histidine a été étudiée sur la molécule de 4(5)-méthylimidazole. La spectroscopie IR en gouttelettes d’hélium a notamment permis de quantifier la thermodynamique de la tautomérisation de ces molécules. Par ailleurs des petites chaînes peptidiques contenant le résidu phénylalanine, utilisées comme modèles de chaines peptidiques dans les études de sonde d'états triplets, ont été caractérisées en détente supersonique par spectroscopie de double résonance IR/UV dans le domaine spectral des élongations NH. Ces études ont toutes deux été appuyées par des calculs de chimie quantique au niveau DFT-D. La formation et la caractérisation d’états triplets issus de la photo-excitation de chaînes peptides contenant l’acide aminé phénylalanine ont été étudiées, dans le cadre de la problématique de la photo-dégradation des protéines après photo-excitation UV. Bien que le cycle phényle soit connu pour son fort rendement quantique de croisement intersystème après excitation du premier état singulet, ce point restait mal connu pour les chaines de protéines. Le passage à l’état triplet pour une série de molécules modèles de chaînes de protéines comportant l’acide aminé phénylalanine a donc été sondé par une méthode de type pompe-sonde nanoseconde, utilisant une sonde par photoionisation à 193 nm. Ces études, en conjonction avec des calculs de chimie quantique, ont montré, qu’après passage à l’état triplet, la relaxation de la phénylalanine excitée dépend notamment de la taille de la chaine latérale et de la présence de liaisons peptidiques (-CO-NH-) dans son environnement. Un schéma de relaxation a été proposé, suggérant la compétition entre formations d’états triplets à longue durée de vie (~µs) et au moins une voie alternative vers des états « noirs » non détectés. Enfin, les états triplets de deux porphyrines de cuivre, modèles de l’hème, ont également été détectés dans des expériences pompe-sonde. La détection de l’état triplet a dans un premier temps permis de remonter aux propriétés d’absorption de ces molécules puis de caractériser les modes de relaxation vers l’état fondamental après absorption d’un photon UV
MATISSE, the VLTI mid-infrared imaging spectro-interferometer
No full textInternational audienceContext. Optical interferometry is at a key development stage. The Very Large Telescope Interferometer (VLTI) has established a stable, robust infrastructure for long-baseline interferometry that is usable by general astronomical observers. The present second-generation instruments offer a wide wavelength coverage and improved performance. Their sensitivity and measurement accuracy lead to data and images of high reliability.Aims. We have developed the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE) to access, for the first time, high resolution imaging in a wide spectral domain. Many front-line topics are explored with this new equipment, including: stellar activity and mass loss; planet formation and evolution in the gas and dust disks around young stars; and environment interaction and accretion processes around super massive black holes in active galactic nuclei.Methods. The instrument is a spectro-interferometric imager in the transmission windows called L, M, and N, from 2.8 to 13.0 microns, combining four optical beams from the VLTI’s unit or auxiliary telescopes. Its concept, related observing procedure, data reduction, and calibration approach, is the product of 30 years of instrumental research and has benefitted from the expertise developed in the frame of the VLTI’s first generation instruments. The instrument utilises a multi-axial beam combination that delivers spectrally dispersed fringes. The signal provides the following quantities at several spectral resolutions: photometric flux, coherent fluxes, visibilities, closure phases, wavelength differential visibilities and phases, and aperture-synthesis imaging.Results. This article provides an overview of the physical principle of the instrument and its functionalities. The motivation of the choice of the instrumental concept and the characteristics of the delivered signal are detailed with a description of the observing modes and of their performance limit. MATISSE offers four spectral resolutions in L&M bands, namely 30, 500, 1000 and 3400, and 30 and 220 in the N band, and it provides an angular resolution down to 3 mas for the shortest wavelengths. The MATISSE stand-alone sensitivity limits are 60 mJy in L and 300 mJy in N. The paper gives details of the sensitivity limits for the different measurables and their related precision criteria, considering telescope configurations and spectral resolutions. We also discuss the gain provided with the GRA4MAT fringe tracker. An ensemble of data and reconstructed images illustrate the first acquired key observations.Conclusions. The instrument has been in operation at Cerro Paranal, ESO, Chile, since 2018, and has been open for science use by the international community since April 2019. The first scientific results are being published now
Methods and devices for calculating a level of "clinical relevance" for abnormal small bowel findings captured by capsule endoscopy video
No full textMultidimensional analyses of the noise impacts of COVID-19 lockdown
No full textInternational audienceAs part of the Agence Nationale de Recherche Caractérisation des ENvironnements SonorEs urbains (Characterization of urban sound environments) project, a questionnaire was sent in January 2019 to households in a 1 km2 study area in the city of Lorient, France, to which about 318 responded. The main objective of this questionnaire was to collect information about the inhabitants' perception of the sound environments in their neighborhoods, streets, and dwellings. In the same study area, starting mid-2019, about 70 sensors were continuously positioned, and 15 of them were selected for testing sound source recognition models. The French lockdown due to the COVID-19 crisis occurred during the project, and the opportunity was taken to send a second questionnaire during April 2020. About 31 of the first 318 first survey respondents answered this second questionnaire. This unique longitudinal dataset, both physical and perceptual, allows the undertaking of an analysis from different perspectives of such a period. The analysis reveals the importance of integrating source recognition tools, soundscape observation protocol, in addition to physical level analysis, to accurately describe the changes in the sound environmen
Polémique, objection, rhétorique : trois débats et leurs effets sur la diffusion de la psychocinétique de Jean Le Boulch
No full textInternational audienc
Droit des étrangers et de la nationalité
No full textInternational audiencedécembre 2020 – décembre 202
Learnable Triangulation for Deep Learning-based 3D Reconstruction of Objects of Arbitrary Topology from Single RGB Images
No full textWe propose a novel deep reinforcement learning-based approach for 3D object reconstruction from monocular images. Prior works that use mesh representations are template based. Thus, they are limited to the reconstruction of objects that have the same topology as the template. Methods that use volumetric grids as intermediate representations are computationally expensive, which limits their application in real-time scenarios. In this paper, we propose a novel end-to-end method that reconstructs 3D objects of arbitrary topology from a monocular image. It is composed of of (1) a Vertex Generation Network (VGN), which predicts the initial 3D locations of the object's vertices from an input RGB image, (2) a differentiable triangulation layer, which learns in a non-supervised manner, using a novel reinforcement learning algorithm, the best triangulation of the object's vertices, and finally, (3) a hierarchical mesh refinement network that uses graph convolutions to refine the initial mesh. Our key contribution is the learnable triangulation process, which recovers in an unsupervised manner the topology of the input shape. Our experiments on ShapeNet and Pix3D benchmarks show that the proposed method outperforms the state-of-the-art in terms of visual quality, reconstruction accuracy, and computational time