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High resolution air quality simulation in the Himalayan valleys, a case study in Bhutan
No full textInternational audienceAbstract. Our study focuses on Bhutan, a highly mountainous country where government authorities are strengthening air pollution monitoring efforts. To support further analysis and the monitoring strategy, we present the first high-resolution air quality simulations with the chemistry transport model WRF-CHIMERE over the western region of Bhutan at a spatial resolution of roughly 1 km. Increasing the horizontal resolution of the model improves its performance and reduces potential errors caused by excessive spatial averaging of meteorological and emission data with high spatial variability. However, the air pollutant emissions must be improved at a fine scale with better proxy, particularly for industries where improvements are still required. For the first time, we propose high resolution maps of air pollution (concentrations and deposition fields). Our simulations confirm that Bhutan valleys also suffer from air pollution mainly due to PM2.5 (concentrations exceeding 20 µg m−3) dominated by carbonaceous species, largely above the World Health Organization guidelines. Wildfires and anthropogenic activities release large amount of carbonaceous species and can also impact the glaciers by atmospheric fallout. Wildfires can locally contribute to 20 % of the total PM2.5 concentrations over a 15 d period, and theoretically, black carbon can be transported up to the highest peaks. Ecosystems are at risks with deposition fluxes of sulfur and nitrogen species comparable with other locations at risk in the world
MIRANDA: short signatures from a leakage-free full-domain-hash scheme
No full textWe present , the first family of full-domain-hash signatures based on matrix codes. This signature scheme fulfils the paradigm of Gentry, Peikert and Vaikuntanathan (), which gives strong security guarantees. Our trapdoor is very simple and generic: if we propose it with matrix codes, it can actually be instantiated in many other ways since it only involves a subcode of a decodable code (or lattice) in a unique decoding regime of parameters. Though signing algorithm relies on a decoding task where there is exactly one solution, there are many possible signatures given a message to sign and we ensure that signatures are not leaking information on their underlying trapdoor by means of a very simple procedure involving the drawing of a small number of uniform bits. In particular does not use a rejection sampling procedure which makes its implementation a very simple task contrary to other -like signatures schemes such as or even . We instantiate with the famous family of Gabidulin codes represented as spaces of matrices and we study thoroughly its security (in the EUF-CMA security model). For~ bits of classical security, the signature sizes are as low as~ bytes and the public key sizes are in the order of~ megabytes
Estimation of extreme quantile from heavy tailed distributions with neural networks
No full textInternational audienceWe propose new parameterizations for neural networks in order to estimate extreme risk measures, such as conditional tail moments or extreme quantiles, in heavy-tailed settings. The proposed neural network estimator is able to extrapolate in the distribution tails thanks to an extension of the usual extreme-value second-order condition to an arbitrary order. The convergence rate of the uniform error between the log-conditional tail moment and its neural network approximation is established. The finite sample performance of the neural network estimator is compared to bias-reduced extreme-value competitors on simulated data. It is shown that our method outperforms them in difficult heavy-tailed situations where other estimators almost all fail
Hausses caniculaires en zones sahéliennes camerounaises : indice de survie de la biodiversité, normes requises du couvert végétal en milieux habités et capacités de résilience communautaire
No full textInternational audienceLes récentes vagues de chaleur extrême dans le Sahel, avec des maxima dépassant 45 °C, exposent la biodiversité, les habitants et les systèmes agricoles à des stress thermiques sévères. Cet article propose une synthèse des preuves climatiques récentes montrant l’intensification des canicules dans la région. Un protocole méthodologique combinant observations in situ, télédétection et modélisation pour estimer un Indice de Survie de la Biodiversité (ISB) face à des scénarii 35–45 °C. Les résultats montrent que des normes opérationnelles de couvert végétal pour milieux habités (seuils minimaux et cibles souhaitables) permettent de réduire l’îlot de chaleur et d’améliorer la résilience Des recommandations pratiques et politiques pour renforcer la résilience communautaire (agroforesterie, gestion de l’eau, aménagements urbains et systèmes d’alerte). Les preuves montrent que l’intensité et la fréquence des épisodes chauds récents ne seraient pas survenues sans le forçage climatique anthropique, et que des gains substantiels en atténuation locale de la chaleur peuvent être obtenus par des stratégies basées sur la végétation et la gouvernance locale
Efficient Monte-Carlo sampling of metastable systems using non-local collective variable updates
No full textMonte-Carlo simulations are widely used to simulate complex molecular systems, but standard approaches suffer from metastability. Lately, the use of non-local proposal updates in a collective-variable (CV) space has been proposed in several works. Here, we generalize these approaches and explicitly spell out an algorithm for non-linear CVs and underdamped Langevin dynamics. We prove reversibility of the resulting scheme and demonstrate its performance on several numerical examples, observing a substantial performance increase compared to methods based on overdamped Langevin dynamics as considered previously. Advances in generative machine-learning-based proposal samplers now enable efficient sampling in CV spaces of intermediate dimensionality (tens to hundreds of variables), and our results extend their applicability toward more realistic molecular systems
Measurement of Z production in proton-proton collisions at = 13.6 TeV and constraints on neutral triple gauge couplings
No full textInternational audienceA measurement of the Z production cross section in proton-proton collisions at a center-of-mass energy of 13.6 TeV is presented. Data corresponding to an integrated luminosity of 34.8 fb, collected by the CMS experiment at the LHC in 2022 are used. Events with an oppositely charged pair of muons or electrons, with an invariant mass corresponding to a Z boson, together with an isolated photon are selected. The measured fiducial cross section for the combined electron and muon channels is 1.896 0.033 (stat) 0.05 (syst) 0.006 (theo) pb, in agreement with the standard model prediction of 1.922 0.094 pb. Constraints on neutral triple gauge couplings generated by dimension-8 operators in a recently proposed effective field theory framework are determined for the first time
Measurement of the branching fractions and longitudinal polarisations of decays
No full textInternational audienceA time- and flavour-integrated amplitude analysis of and decays to the final state in the region is presented, using collision data recorded with the LHCb detector in 2011--2018, corresponding to an integrated luminosity of . The branching fractions of the and decays are measured relative to the and modes, respectively. The corresponding longitudinal polarisation fractions are found to be and , where the uncertainties are statistical and systematic, respectively. The theory-motivated observable is found to be , where the uncertainties are statistical, systematic, due to uncertainty of external mass and lifetime measurements, and due to knowledge of the fragmentation fraction ratio, respectively. This confirms the previously reported tension between experimental determinations and theoretical predictions of longitudinal polarisation in decays
Méthodes assistées par ordinateur pour des modèles de diffusion en dynamique des populations : diffusion croisée, réactions non-locales, et stabilité
No full textThe analysis of nonlinear cross-diffusion systems is a major challenge for understanding complex physical or biological phenomena. Computer-assisted methods provide powerful tools to deliver precise and rigorous answers to theoretical questions such as the existence and stability of steady states, or the search for eigenvalues in concrete situations.This thesis proposes the application and adaptation of these methods in the context of cross-diffusion and nonlocal or nonhomogeneous reaction-diffusion models. A first study concerns a chemotaxis model incorporating a nonlinearity in the diffusion term. We develop a specific tool to handle this nonlinearity, allowing us to establish the existence of multiple steady states using a fixed point theorem whose assumptions are verified by computer.A second study focuses on a nonlocal reaction-diffusion model, where we study the stability of a steady state as a function of the intensity of nonlocality. This study is a first step towards the analysis of stability for cross-diffusion systems. We propose a computer-assisted approach for the study of the spectrum of a compact resolvent operator, using a Gershgorin theorem for infinite matrices. We then analyze the dependence of the first eigenvalue with respect to the nonlocality parameter in order to determine the existence and uniqueness of a stability threshold.Finally, a last study on nonlinear models, which include cross-diffusion models, allows us to propose a general methodology to study the existence and stability of steady states. This methodology is inspired by an analogy with the Lyapunov stability theorem for systems of ordinary differential equations. We build a positive definite self-adjoint operator, whose properties are verified by a computer, thus obtaining a quadratic Lyapunov functional.L’analyse des systèmes de diffusion croisée non linéaire constitue un enjeu majeur pour la compréhension de phénomènes physiques ou biologiques complexes. Les méthodes assistées par ordinateur offrent des outils puissants pour apporter des réponses précises et rigoureuses à des questions théoriques telles que l’existence et la stabilité des états stationnaires, ou la recherche de valeurs propres dans des situations concrètes.Cette thèse propose l’application et l’adaptation de ces méthodes dans le cadre des modèles de diffusion croisée et de réaction-diffusion non locale ou non homogène. Une première étude concerne un modèle de chimiotaxie intégrant une non-linéarité dans le terme de diffusion. Nous y développons un outil spécifique pour traiter cette non-linéarité, permettant d’établir l’existence de plusieurs états stationnaires grâce à un théorème du point fixe dont les hypothèses sont vérifiées par ordinateur.Une seconde étude porte sur un modèle de réaction-diffusion non local, où nous étudions la stabilité d’un état stationnaire en fonction de l’intensité de la non-localité. Cette étude constitue une première étape vers l’analyse de la stabilité pour les systèmes de diffusion croisée. Nous proposons une approche assistée par ordinateur pour l’étude du spectre d’un opérateur à résolvante compacte, en utlisant un théorème de Gershgorin pour des matrices infinies. Nous analysons ensuite la dépendance de la première valeur propre par rapport au paramètre de non-localité afin de déterminer l’existence et l’unicité d’un seuil de stabilité.Enfin, une dernière étude sur des modèles non linéaires qui incluent les modèles de diffusion croisée, nous permet de proposer une méthodologie générale pour étudier l’existence et la stabilité des états stationnaires. Cette méthodologie s’inspire d’une analogie avec le théorème de stabilité de Lyapunov pour les systèmes d’équations différentielles ordinaires. Nous construisons un opérateur auto-adjoint défini positif, dont les propriétés sont vérifiées par ordinateur, permettant ainsi d’obtenir une fonctionnelle de Lyapunov quadratique
Multiclass Method to Analyze Banned Veterinary Drugs in Casings by LC-MS/MS: A Validation Study According to Regulation (EU) 2021/808
No full textInternational audienceFollowing the new (EU) regulation 2022/2292 with regard to requirements for the entry into the Union of consignments of food-producing animals and certain goods intended for human consumption, a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been optimized to identify and quantify 17 banned veterinary drugs in dry or brined casings from different species. Casings are used to manufacture various meat specialties (sausages,···) in Europe, and it is important to take into account the risk of contamination of these manufactured casings entering the European Union. The metabolites of seven nitrofurans, seven nitroimidazoles, chloramphenicol, and dapsone were simultaneously identified and quantified by the developed standard operating procedure, which was successfully validated according to the criteria of the Commission Implementing Regulation (EU) 2021/808, using the regulatory limits or levels of interest in force in Europe. The reliability of the method has been demonstrated by the analysis of proficiency testing reference materials. Additional data on a challenged nitrofuran marker residue are discussed
