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Measuring Clear‐Air Vertical Motions From Space
No full textInternational audienceAbstract Measuring vertical velocity in the atmosphere has long been a challenge due to its small magnitude. Taking advantage of the modulation of free tropospheric relative humidity by vertical motions, we derive analytical relationships that allow us to retrieve vertical motions in clear air from geostationary measurements of brightness temperature in the infrared absorption band of water vapor. The new observations have a resolution of 1 hr and 2 km in time and space, respectively. They capture the variability of mesoscale and large‐scale vertical velocity measured during field campaigns. In the mid‐troposphere, clear‐sky vertical motions are mostly subsiding but highly heterogeneous in space and time. Around organized deep convective systems, strong subsidence (>500 hPa·day −1 ) is observed within a distance of a few hundred kilometers. In contrast, transient upward motions of up to 100 hPa·day −1 can occur at the mesoscale. Vertical motions in the clear‐sky atmosphere appear to be primarily associated with buoyancy and gravity waves at the mesoscale, and with radiative cooling and equatorial waves at larger spatial scales. This new retrieval reveals a rich range of dynamical features that were previously invisible, thus shedding new light on tropical meteorology
Linear response and resonances in adiabatic time-dependent density functional theory
No full textWe consider the electrons of a molecule in the adiabatic time-dependent density functional theory approximation. We establish the well-posedness of the time evolution and its linear response close to a non-degenerate ground state, and prove the appearance of resonances at relevant frequencies. The main mathematical difficulty is due to the structure of the linearized equations, which are not complex-linear. We bypass this difficulty by reformulating the linearized problem as a real Hamiltonian system, whose stability is ensured by the second-order optimality conditions on the energy
Random generation of subgroups of the modular group with a fixed isomorphism type
No full textInternational audienceWe show how to efficiently count and generate uniformly at random finitely generated subgroups of the modular group PSL 2 (Z) of a given isomorphism type. The method to achieve these results relies on a natural map of independent interest, which associates with any finitely generated subgroup of PSL 2 (Z) a graph which we call its silhouette, and which can be interpreted as a conjugacy class of free finite index subgroups of PSL 2 (Z)
A re-analysis of the circulation in the “transition region” of Venus atmosphere (90-130 km) with the Venus PCM
No full textInternational audienceIn this study we use the most recent version of the ground-to-thermosphere VPCM [1] that includes an ionosphere model, ambipolar diffusion and nitrogen chemistry [2]. This tool allows us to investigate and identify in 3D potential mechanisms responsible for the observed variability in Venus's atmosphere, in the region between 90 km and 130 km altitude. NO and O 2 (Δg) airglows, are commonly used to shed light on the global dynamics and circulation patterns above 90 km. Their characteristics are a combination of horizontal, vertical transport and chemical net reactions [3,4].We performed sensitivity tests of unconstrained parameters (e.g. gravity waves drag and eddy diffusion vertical profile) to evaluate the impact on the dynamical structures, O densities, temperature and O 2 (Δg) nightglow characteristics. These results depict possible scenarios useful to interpret future EnVision observations of trace compounds in those mesosphere layers currently poorly constrained, and not fully explained by current 3D models
Harmonized disposable income dataset for Europe at subnational level
No full textInternational audienceIn recent decades, detailed country-level estimates of income and wealth have become widely available and inform us about the evolution of inequality between and within countries. But a substantial portion of these available datasets lack sub-national geographical information, precluding the exploration of the spatial distribution and evolution of inequalities within countries. We present here a new dataset of disposable income for Europe at the subnational level. It has been compiled from existing income data (gross income, gross earnings, equivalised income, etc.) published by national statistical institutes at different geographical levels. We used linear regressions and numerical operations to estimate disposable income from other available socio-economic statistics (e.g. household size, tax rates). We developed a harmonization and adjustment procedures to ensure of the consistency of statistical units, income indicators, costs of living and inflation. The dataset covers 42 European countries distributed over more than 120,000 geographical entities on the 1995 to 2021 period (most of the data being available for the 2010–2020 decade). This new dataset opens avenues for investigating the links between income inequality and other socio-economic or ecological processes
: Flex-Mediation
No full textInternational audienceComprendre les médiations entre productions variables et utilisations évolutives de l'électricité. Présentation du projet de recherche en sciences humaines et sociales 2023-2028 en 5 axes : - Nouveaux arrangements organisationnels entre production et consommation et leur mode de valorisation des ressources- Influence des modes d’émergence et de fonctionnement des communautés énergétiques sur le juste partage des coûts et bénéfices- Influence des intermédiaires sur la perception de la variabilité des ENR et les pratiques des consommateurs- Conception des politiques publiques et de la régulation relative à la flexibilité : nouvelles formes de services (fournisseurs, agrégateurs, communautés) et intégration dans les mécanismes de marchés, comparaison internationale- Traduction légale de la flexibilité et questions de justice énergétique : comparaison européenne, analyse contractuelle multi-échelles, innovations en droits spécifiques pour les acteurs concerné
Global characterization of the Martian global dust optical depth with 2.7 μm observations by OMEGA/MEx
No full textInternational audienceDust is a key parameter of the Martian atmosphere, controlling its heating through direct absorption of solar radiation. The quality of dust is not constant in time and space, and dust storms explain part of this variability. Local dust storms, occurring at scales below 1.6 × 10 6 km 2 , have been suggested to develop into vertical dust transport movements that reach high altitudes, such as rocket dust storms [1,2]. Local dust storms can also coalesce and develop into regional dust storms [3,4,5,6]. Dust storms, notably regional dust storms larger than 1.6×10 6 km 2 have been frequently investigated by visible observations from orbiters [6,7]. However, spectroscopic observations of dust storms, notably local dust storms, are more limited, and no statistical studies have been conducted on such datasets yet. We successfully retrieved dust optical depth and statistically detected local dust storms using observation data from the Mars Express during Martian years (MY) 27-29, which was equipped with the high-resolution Near-Infrared Spectrometer OMEGA. We then conducted a statistical analysis of local dust storms over three Martian years, including MY28 when a global dust storm occurred, investigating their occurrence locations and frequencies.Method: In this analysis, we developed a new method to retrieve the dust optical depth using the atmospheric 2.77 μm CO2 absorption band. Typically, this band saturates during nadir observations when surface pressures is greater than approximately 400 Pa in the Martian environments, resulting in almost zero observed radiance under low dust conditions. However, when the aerosols are lifted into the atmosphere, reflected sunlight by aerosols can be detected in nadirobservations. We utilized this technique to retrieve dust optical depth in the atmosphere using the L-channel of OMEGA at 2.77 μm used here. For the retrievals of the dust optical depth, we employed a Look-up-table method [8,9] that calculates many synthetic spectra at 2.77 μm in advance for tabulated grid values of physical parameters (such as dust opacity, observing geometry, atmospheric temperature, etc) by DISORT radiative transfer module [10] implemented in the ARS code [11]. With this method, an instantaneous retrieval of dust optical depth is possible by comparing them with observed spectra
Constructive approaches to concentration inequalities with independent random variables
No full textConcentration inequalities, a major tool in probability theory, quantify how much a random variable deviates from a certain quantity. This paper proposes a systematic convex optimization approach to studying and generating concentration inequalities with independent random variables. Specifically, we extend the generalized problem of moments to independent random variables. We first introduce a variational approach that extends classical moment-generating functions, focusing particularly on first-order moment conditions. Second, we develop a polynomial approach, based on a hierarchy of sum-of-square approximations, to extend these techniques to higher-moment conditions. Building on these advancements, we refine Hoeffding's, Bennett's and Bernstein's inequalities, providing improved worst-case guarantees compared to existing results
Sociologie du commerce
No full textInternational audienceMalgré la place qu’occupe la consommation dans la vie des individus et le temps passé dans les lieux marchands, la sociologie n’a pas fait du commerce de détail un domaine de recherche délimité. Les enquêtes ne sont toutefois pas inexistantes mais le commerce ne figure bien souvent qu’à l’arrière-plan d’analyses consacrées au travail, à l’emploi, à la ville.À la fois activité et lieu, il présente cependant un intérêt scientifique propre. Ce secteur est un poste d’observation pertinent pour scruter la diffusion des marchandises, les innovations techniques sur lesquelles celle-ci repose, mais aussi la manière dont il prescrit, autant qu’il révèle, des normes de consommation. Son importance est donc à la fois économique, technique et socio-culturelle. Premier du genre, cet état des lieux des connaissances élaborées sur ce domaine considère le commerce comme le produit de relations entre divers éléments : les innovations apportées à l’intermédiation marchande, les cultures de consommation, les relations sociales, l’activité organisée, les réglementations et l’action publique, le territoire.Ce découpage permet de montrer comment la sociologie peut se saisir de cet objet en puisant dans des domaines divers (le travail, les techniques, la consommation, la ville, le droit) mais aussi dans d’autres sciences sociales comme l’histoire, l’anthropologie et la géographie. En regroupant des savoirs éparpillés, cette synthèse vise à constituer un champ de recherche consacré à cette activité ancienne, centrale dans l’existence des sociétés et de leur économie, et en profonde mutation sous l’effet de la transition numérique et de la crise climatique
Dust and Clouds on Mars: The View from Mars Express
No full textInternational audienceEuropean Space Agency’s Mars Express (MEX) has been orbiting Mars for 20 years and its instruments have provided a plethora of observations of atmospheric dust and clouds. These observations have been analysed to produce many unique views of the processes leading to dust lifting and cloud formation, and a full picture of the climatologies of dust and clouds has emerged. Moreover, the orbit of MEX enables viewing the planet at many local times, giving a unique access to the diurnal variations of the atmosphere. This article provides an overview of the observations of dust and clouds on Mars by MEX, complemented by the Trace Gas Orbiter that has been accompanying MEX on orbit for some years