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Phases topologiques avec des atomes froids et des photons
No full textWe propose theoretical models that support topological phases and which are relevant to current experiments on lattices hosting photonic modes or ultracold atoms. In the first part of this thesis, we introduce a topological phase on a Kagom ́e lattice whose degrees of freedom are photons. In that context, we discuss two protocols to access the local Berry curvature and the Chern number of Bloch bands from semiclassical dynamics of wavepackets. Secondly, we obtain the phase diagram for bosons at unit filling with repulsive on–site interactions whose kinetic term corresponds to a Chern insulator defined on the honeycomb lattice. In the second part, we turn to recently realized quasi one–dimensional lattices, and un- cover their phase diagrams, comprising low–dimensional Meissner phases, chiral Mott insulating phases as well as abelian fractional quantum Hall states.Dans cette thèse, nous proposons des modèles qui présentent des phases topologiques. Ces modèles sont réalisables expérimentalement dans des systèmes d’atomes froids et dans des systèmes de circuit d’éléctrodynamique quantique. Dans la première partie de cette thèse, nous introduisons une phase topologique sur un réseau Kagomé, dont les degrés de liberté sont des photons. Nous discutons deux méthodes pour mesurer la courbure de Berry et le nombre de Chern pour les bandes de Bloch. Ces deux protocoles se basent sur la dynamique semi–classique des paquets d’onde. Nous obtenons aussi le diagramme de phases pour des bosons avec une interaction répulsive de type Bose-Hubbard sur chaque site d’un réseau hexagonal propos ́e par F.D.M. Haldane. Nous découvrons un état isolant de Mott avec des courants locaux quand la densité moyenne est d’un boson par site. Les excitations de cet isolant de Mott ont des caractéristiques topologiques. Dans la deuxième partie de cette thèse, nous nous concentrons sur des réseaux quasi-uni-dimensionnels récemment réalisés dans des systèmes d’atomes froids. Nous étudions leurs diagrammes de phases, étant composés de phases Meissner, d’isolants de Mott chiraux, et d’états d’effet Hall quantique fractionnaire abélien
Ozone and aerosol tropospheric concentrations variability analyzed using the ADRIMED measurements and the WRF and CHIMERE models
No full textInternational audienceDuring the months of June and July 2013, over the Euro–Mediterranean area, the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region) project was dedicated to characterize the ozone and aerosol concentrations in the troposphere. It is first shown that this period was not highly polluted compared to previous summers in this region, with a moderate ozone production, no significant vegetation fire events and several precipitation periods scavenging the aerosol. The period is modeled with the WRF (Weather Research and Forecasting) and CHIMERE models, and their ability to quantify the observed pollution transport events is presented. The CHIMERE model simulating all kinds of sources (anthropogenic, biogenic, mineral dust, vegetation fires); the aerosol speciation, not available with the measurements, is presented: during the whole period, the aerosol was mainly constituted by mineral dust, sea salt and sulfates close to the surface and mainly by mineral dust in the troposphere. Compared to the AERONET (Aerosol Robotic Network) size distribution, it is shown that the model underestimates the coarse mode near mineral dust sources and overestimates the fine mode in the Mediterranean area, highlighting the need to improve the model representation of the aerosol size distribution both during emissions, long-range transport and deposition
Caractérisation des plasmas chauds et denses produits par interaction laser à ultra-haute intensité d'une cible solide
No full textIn the fields of stellar interiors and inertial confinement fusion, determination of dense and hot plasmas opacity is a major goal. Laboratory plasmas, close to both solid density and hundreds of electron-volt temprature are needed to improve theoretical and numerical models. This work is focused on the characterization of such plasmas formed by ultra-high-intensity laser interaction with solid matter. Experimental measurements on aluminium plasmas are presented. They highlight the complexity arising in the interpretation of K-shell x-ray emission spectra, typically used to infer the plasma density and temperature. To reproduce these experimental results, simulations using 3 codes were carried out (PIC code - CALDER, radiationhydrodynamics code - MULTI and atomic population code - SPECT3D). This work concludes on the need to account for many physical phenomena to further characterize the plasma: non-LTE equilibrium, hot electrons, time evolution and spatial gradients. All these issues are addressed and discussed. This kind of experiment opens bright perspectives in the study of very-high-density plasmas. Good temporal and spatial resolution is nevertheless necessary to ensure an accurate characterization of the plasma density and temperature.Les propriétés radiatives de plasmas denses et chauds conditionnent de nombreux phénomènes rencontrés dans les intérieurs stellaires et dans le cadre de la fusion par confinement inertielle. Afin d’améliorer les modèles dans un régime à la fois proche du solide (de l’ordre du g.cm-3) et de plusieurs centaines d’électron-Volts, des mesures en laboratoire sont aujourd’hui nécessaires. L’étude menée dans cette thèse consiste en lacaractérisation de tels plasmas formés par interaction laser à ultra-haute intensité. Dans le cas d’un plasma d’aluminium, les mesures expérimentales obtenues ont permis de mettre en évidence le caractère complexe de l’interprétation d’un spectre d’émission de couche K habituellement utilisé pour estimer la densité et la température du plasma. Pour restituer les résultats expérimentaux, une suite de simulations numériques utilisant plusieurs codes (codes PIC CALDER, hydro-radiatif MULTI et de physique atomique SPECT3D) a été menée. Ces simulations ont permis de conclure sur la nécessité de prendre en compte de nombreux phénomènes physiques pour caractériser au mieux le plasma : les conditions d’équilibre, la présence d’électrons chauds, l’évolution temporelle rapide et les gradients spatiaux. Ces points sont abordés et discutés dans ce travail. Ces études montrent que ce type d’expériences ouvre de vastes perspectives dans l’étude des plasmas à très haute densité. Une bonne résolution temporelle et spatialeest néanmoins nécessaire pour assurer une caractérisation précise de la densité et de la température du plasma produit
Estimating the Template in the Total Space with the Fréchet Mean on Quotient Spaces may have a Bias: a Case Study on Vector Spaces Quotiented by the Group of Translations
No full textInternational audienceWhen we have a deformation group acting on a vector space of observations, these data are not anymore elements of our space but rather orbits for the group action we consider. If the data are generated from an unknown template with noise, to estimate this template, one may want to minimize the variance in the quotient set. In this article we study statistics on a particular quotient space. We prove that the expected value of a random variable in our vector space mapped in the quotient space is different from the Fréchet mean in the quotient space when the observations are noisy
A Stochastic Model for Car-Sharing Systems
No full textVehicle-sharing systems are becoming important for urban transportation. In these systems, users arrive at a station, pick up a vehicle, use it for a while and then return it to another station of their choice. Depending on the type of system, there might be a possibility to book vehicles before picking-up and/or a parking space at the chosen arrival station. Each station has a finite capacity and cannot host more vehicles and reserved parking spaces than its capacity. We propose a stochastic model for an homogeneous car-sharing system with possibility to reserve a parking space at the arrival station when picking-up a car. We compute the performance of the system and the optimal fleet size according to a specific metric. It differs from a similar model for bike-sharing systems because of reservation that induces complexity, especially when traffic increases
Five-dimensional Janis–Newman algorithm
No full textInternational audienceThe Janis–Newman algorithm has been shown to be successful in finding new stationary solutions of four-dimensional gravity. Attempts for a generalization to higher dimensions have already been found for the restricted cases with only one angular momentum. In this paper we propose an extension of this algorithm to five-dimensions with two angular momenta—using the prescription of Giampieri—through two specific examples, that are the Myers–Perry and BMPV black holes. We also discuss possible enlargements of our prescriptions to other dimensions and maximal number of angular momenta, and show how dimensions higher than six appear to be much more challenging to treat within this framework. Nonetheless this general algorithm provides a unification of the formulation in of the Janis–Newman algorithm, from which several examples are exposed, including the BTZ black hole
Information Sets of Multiplicity Codes
No full textInternational audienceWe here provide a method for systematic encoding of the Multiplicity codes introduced by Kopparty, Saraf and Yekhanin in 2011. The construction is built on an idea of Kop-party. We properly define information sets for these codes and give detailed proofs of the validity of Kopparty's construction, that use generating functions. We also give a complexity estimate of the associated encoding algorithm
Multi-gigaelectronvolt acceleration of positrons in a self-loaded plasma wakefield
No full textInternational audienc
Synthesis, antimicrobial and antioxidant activities of imidazotriazoles and new multicomponent reaction toward 5-amino-1-phenyl[1,2,4]triazole derivatives
No full textInternational audienceThe Groebke-type multicomponent reaction between 5-amino-1,2,4-triazole derivatives, aromatic aldehydes and isocyanides has been studied from the viewpoint of convenient generation of combinatorial arrays of imidazo[2,1-c][1,2,4]triazoles. The reaction is considered to proceed via the formation of an iminium species followed by a [4 + 1] cyclo addition with the isocyanides using scandium triflate as a Lewis acid catalyst. The synthesized imidazo[2,1-c][1,2,4]triazole derivatives 4a, 4b, 4f and 4g were screened for antibacterial, antifungal and antioxidant activities. Among the tested compounds, 4b followed by 4f showed potent antibacterial and antifungal activities. All of these compounds were also screened in vitro for the antioxidant activity using DPPH assay. Most of them have shown very significant antioxidant activity
Physics of fully-loaded laser-plasma accelerators
No full textInternational audienceWhile large efforts have been devoted to improving the quality of electron beams from laser plasma accelerators, often to the detriment of the charge, many applications do not require very high quality but high-charge beams. Despite this need, the acceleration of largely charged beams has been barely studied.Here we explore both experimentally and numerically the physics of highly loaded wakefield acceleration. We find that the shape of the electron spectra is strikingly independent of the laser energy, due to the emergence of a saturation effect induced by beamloading. A transition from quasi-Maxwellian spectra at high plasma densities to flatter spectra at lower densities is also found, which is shown to be produced by the wakefield driven by the electron bunch itself after the laser depletion