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Probing the Redox Reactivity of a Reduced Nontronite: A Quick XAS Operando Study
No full textInternational audienceFe-bearing clay minerals contain structural iron that can be redox-active and can participate in electron transfer reactions with aqueous species. Although these redox properties have been studied extensively in the past decade, questions remain about the respective roles of kinetic and thermodynamic constraints in establishing steady-state redox conditions. In this study, the reduction kinetics of aqueous Cr(VI) to Cr(III) by Fe(II) contained in the structure of reduced ferruginous clay samples (reference Nontronite NAu-1) was monitored with quick-XAS (X-ray absorption spectroscopy). These measurements revealed the occurrence of at least two reaction processes with contrasting fast and slow kinetic rates. According to mass and electron balance calculations, Fe(II) located at the edge of the clay mineral particles alone cannot account for the fast reactivity of the samples, pointing out the presence of electron transfer from the inner part of the clay mineral layer structure to the reactive sites. The Fe(II)/Fe(III) ratio in the clay structure quickly reached a steady state after each Cr(VI) addition to the solution. These steady-state conditions were consistent with either a complete depletion of the Cr(VI) reactant for the first spikes of Cr(VI) or a thermodynamic equilibrium between the redox couples, i.e., between structural Fe(III)/Fe(II) and aqueous Cr(VI)/Cr(III), after the pool of fast-reacting Fe(II) was depleted. These results highlight the need to consider kinetic and thermodynamic controls of clay structural iron redox reactivity to predict the fate of redox-sensitive contaminants in the environment
Multiple late Holocene glacier advances on the sub-Antarctic Kerguelen (49°S) islands: Evidence from a 1200 yr sediment core from a glacial threshold basin
No full textInternational audienceUnderstanding the transient dynamics of interlinked social–ecological systems (SES) is imperative for assessing sustainability in the Anthropocene. However, how to identify critical transitions in real-world SES remains a formidable challenge. In this study, we present an evolutionary framework to characterize these dynamics over an extended historical timeline. Our approach leverages multidecadal rates of change in socioeconomic data, paleoenvironmental, and cutting-edge sedimentary ancient DNA records from China’s Yangtze River Delta, one of the most densely populated and intensively modified landscapes on Earth. Our analysis reveals two significant social–ecological transitions characterized by contrasting interactions and feedback spanning several centuries. Initially, the regional SES exhibited a loosely connected and ecologically sustainable regime. Nevertheless, starting in the 1950s, an increasingly interconnected regime emerged, ultimately resulting in the crossing of tipping points and an unprecedented acceleration in soil erosion, water eutrophication, and ecosystem degradation. Remarkably, the second transition occurring around the 2000s, featured a notable decoupling of socioeconomic development from ecoenvironmental degradation. This decoupling phenomenon signifies a more desirable reconfiguration of the regional SES, furnishing essential insights not only for the Yangtze River Basin but also for regions worldwide grappling with similar sustainability challenges. Our extensive multidecadal empirical investigation underscores the value of coevolutionary approaches in understanding and addressing social–ecological system dynamics
Sorption kinetics of metallic and organic contaminants on micro-and nanoplastics: remarkable dependence of the intraparticulate contaminant diffusion coefficient on the particle size and potential role of polymer crystallinity
No full textInternational audienceWe developed a mechanistic diffusion model to describe the sorption kinetics of metallic and organic contaminants on nano- and micro-plastics. The framework implements bulk depletion processes, transient fluxes, and fully adaptable particle/water boundary conditions, i.e. not only the typically assumed simple linear Henry regime, which is not applicable to many contaminant-particle situations. Thus, our model represents a flexible and comprehensive theory for the analysis of contaminant sorption kinetics, which goes well beyond the traditional empirical pseudo first or second order kinetic equations. We applied the model to the analysis of a large body of literature data on the equilibrium and kinetic features of sorption of a wide range of contaminants by diverse types and sizes of plastic particles. Results establish the paramount importance of sorption boundary conditions (Henry, Langmuir, or Langmuir–Freundlich) and reveal interesting and often overlooked sorption features that depend on the plastic particle size and the extent to which the target compound is depleted in the bulk medium. The greater degree of polymer crystallinity reported for smaller particles may underlie our findings that the intraparticulate contaminant diffusion coefficient decreases with a decreasing particle size. We establish a universal law to predict the sorption kinetics and diffusion of any compound within any plastic phase, which has far reaching importance across many domains relevant to the environment and human health
The Leavitt law of Milky Way Cepheids from Gaia DR2 static companion parallaxes
No full textInternational audienceClassical Cepheids (CCs) are at the heart of the empirical extragalactic distance ladder. Milky Way CCs are the only stars of this class accessible to trigonometric parallax measurements. Until recently, the most accurate trigonometric parallaxes of Milky Way CCs were the HST/FGS measurements collected by Benedict et al. (2002, 2007). Unfortunately, the second Gaia data release (GDR2) has not yet delivered reliable parallaxes for Galactic CCs, failing to replace the HST/FGS sample as the foundation of all Galactic calibrations of the Leavitt law. We aim at calibrating independently the Leavitt law of Milky Way CCs based on the GDR2 catalog of trigonometric parallaxes. As a proxy for the parallaxes of a sample of 23 Galactic CCs, we adopt the GDR2 parallaxes of their spatially resolved companions. As the latter are unsaturated, photometrically stable stars, this novel approach allows us to bypass the GDR2 bias on the parallax of the CCs that is induced by saturation and variability. We present new Galactic calibrations of the Leavitt law in the J, H, K, V, Wesenheit WH and Wesenheit WVK bands based on the GDR2 parallaxes of the CC companions. We show that the adopted value of the zero point of the GDR2 parallaxes, within a reasonable range, has a limited impact on our Leavitt law calibration. However, we find a significant difference with respect to the calibration based on the HST/FGS parallaxes, that corresponds to an FGS parallax zero point offset of approx. +0.2 mas. The discrepancy that we observe between the GDR2 and HST/FGS parallaxes has important consequences on the existing Galactic calibrations of the Leavitt law. We note that our results translate into a Hubble constant of 68.43 +/- 2.08 km/s/Mpc and 69.30 +/- 2.08 km/s/Mpc for a GDR2 parallax offset of 0.029 mas and 0.046 mas, respectively
Multidisciplinary approach to characterize biofabricated and natural lipid-based nanoparticles
No full textInternational audienceINTRODUCTION. Mesenchymal stem cells (MSCs) secrete extracellular vesicles (EVs), which are particles bounded by a lipid bilayer similar to the plasma membrane and whose contents are complex (proteins, nucleic acids, etc.). Nanoscale EVs produced by MSCs have a higher potential for tissue regeneration than MSCs, without the disadvantages associated with the use of cells (absence of nucleus, ability to cross the extracellular matrix [ECM]). They are promising vectors for future developments of innovative acellular therapies [1]. An alternative strategy to target biological tissues is the use of nanoparticles biofabricated with lipids such as nanoliposomes (NLPs), where lipids derived from plant coproducts. NLPs are also promising vectorization systems due to their ease of production and their structure close to the cell membrane or EV membrane. They are synthetic vesicles with intrinsic anti-inflammatory properties whose nanometric dimensions can promote their ability to cross tissue ECM. NLPs are candidates of interest for vectorizing biomolecules into cells and thus promote tissue regeneration [2]. However, NLPs deliver fewer messages than EVs and can be phagocytized by immune cells. Creating a hybrid vesicle combining the properties of both EVs and NLPs would facilitate the encapsulation of target molecules in an innovative vector, while benefiting from a portion of the EV membrane to be transported into the body without being detected as a foreign element. Here we used a physicochemical, morphological and biological approach to characterize EVs derived from MSCs and NLPs biofabricated from colza coproducts as a steppingstone toward the design of more complex hybrid vectors [3].METHODS. NLP synthesis and EV isolation were followed by physicochemical analyses with zeta potential measurement and nanoparticle tracking analysis (NTA) to study the behaviour of these nanoparticles in a solution. Morphological analyses were performed with transmission electron microscopy (TEM) and cryoelectron microscopy (cryoEM) to ensure the vesicular nature of our nanoparticles. Biological EV markers were estimated by flow cytometry/nanoflow and western blot. The vesicular nature of EVs and NLPs was also evaluated with lipophilic dyes to stain the nanoparticles. A potency test to verify cell penetration of the stained vesicles was performed with spinning disk microscopy.RESULTS. Zeta potential showed that the nanoparticles had a negatively charged surface with a decent stability for both suspensions. NTA displayed that the production yield of synthetic vesicles was higher than natural ones, and that the mean hydrodynamic diameter was almost doubled for EVs compared to NLPs. This was confirmed by TEM and cryoEM. Furthermore, the content of EVs appears denser, which is consistent since NLPs were formulated empty. Biological analyses evidenced that EVs carry specific vesicular markers, such as CD9. The imaging of stained vesicles confirmed nanoparticle penetration in cells.CONCLUSION. Our multidisciplinary approach demonstrated good nanoparticle characterization and preservation with enough quantities for a combinate use to design hybrid vectors. The EV/NLP ratio required for hybrid vesicle formation remains to be determined in future experiments
A linear model of separation for western boundary currents with bathymetry
No full textThis paper is devoted to the asymptotic analysis of strongly rotating and stratified fluids, under a -plane approximation, and within a three-dimensional spatial domain with strong topography.Our purpose is to propose a linear idealized model, which is able to capture one of the key features of western boundary currents, in spite of its simplicity: the separation of the currents from the coast.Our simplified framework allows us to perform explicit computations, and to highlight the intricate links between rotation, stratification and bathymetry.In fact, we are able to construct approximate solutions at any order for our system, and to justify their validity.Each term in the asymptotic expansion is the sum of an interior part and of two boundary layer parts: a ``Munk'' type boundary layer, which is quasi-geostrophic, and an ``Ekman part'', which is not.Even though the Munk part of the approximation bears some similarity with previously studied 2D models, the analysis of the Ekman part is completely new, and several of its properties differ strongly from the ones of classical Ekman layers.Our theoretical analysis is supplemented with numerical illustrations, which exhibit the desired separation behavior
Les logiques spatiales de l’installation des Océaniens en France hexagonale
No full textInternational audienceUsing a mixed quantitative and qualitative approach, based on the analysis of individual-level data from the 2020 French population census (INSEE) and on thirty semi-structured interviews, this article offers an original examination of the spatial distribution of French nationals of Oceanian origin (New Caledonia, French Polynesia, and Wallis and Futuna) residing in metropolitan France. Conducted at both departmental level and IRIS scale, the analysis culminates in a detailed case study of the Toulon area, which hosts the highest concentration of Oceanian populations in metropolitan FranceEsta investigación propone un estudio inédito sobre la distribución espacial y la residencia de las poblaciones de nacionalidad francesa procedentes de las islas del Pacífico (Nueva Caledonia, Polinesia Francesa y Wallis y Futuna) en la Francia continental. Combina la investigación cuantitativa y cualitativa trabajando los microdatos por individuo del censo de población de 2020 del INSEE para la Francia continental y, por otra parte, realizando una treintena de entrevistas semiestructuradas. El estudio, a escala departamental, se ha desarrollado a partir de las unidades estadísticas IRIS y se ha focalizado en el área de Toulon, que es la zona con mayor concentración de residentes procedente de las islas del Pacífico en la Francia continental.À partir d’une approche quantitative et qualitative, fondée d’une part sur le traitement des données individuelles du recensement de la population de 2020 de l’INSEE dans l’Hexagone, et, d’autre part, sur l’analyse d’une trentaine d’entretiens semi-directifs, nous proposons une étude inédite de la répartition spatiale des populations de nationalité française et d’origine océanienne (Nouvelle-Calédonie, Polynésie française et Wallis-et-Futuna) résidant dans l’Hexagone. Notre analyse, à l’échelle départementale et au niveau des IRIS, débouche sur l’étude de l’aire toulonnaise, lieu de la plus forte concentration d’Océaniens dans l’Hexagone
pseudo trans-dimensional 3d geometrical inversion: a proof of concept using gravity data
No full textInternational audienceWe present and apply a pseudo trans-dimensional inversion method for 3D geometrical gravity inversion, in which the number of rock units, their geometry, and their density can vary during sampling. The method is designed for efficient exploration of the model space and to infer the presence and properties of units not directly observable but detectable with geophysical data. Sampling relies on a non-reversible Metropolis-Hastings algorithm, during which rock units can be added or removed from the model, interface geometries are perturbed using random fields, and densities are sampled from distributions informed by prior information. To visualise the space of sampled models and to aid interpretation, a workflow is proposed that combines dimensionality reduction with the clustering of models in families. The capabilities of the inversion method are evaluated using two synthetic cases. The first is a motivating example aimed at recovering an intrusion missing from the prior model. It features a horizontal layer-cake where fixed-dimensional inversion fails to adequately fit the data and sample models close to the true model, while the proposed pseudo trans-dimensional approach is much more successful. The second case investigates the recovery of two missing units and the capability to overcome prior model biases. Results show the potential of our method to infer the presence of unseen geological features such as intrusions. However, they suggest that with biased prior geological modelling, it may be challenging to infer with certainty the presence of more than two previously unknown rock units at depth
DESI-DR1 -pt analysis: consistent cosmology across weak lensing surveys
No full textInternational audienceWe present a joint cosmological analysis of projected galaxy clustering observations from the Dark Energy Spectroscopic Instrument Data Release 1 (DESI-DR1), and overlapping weak gravitational lensing observations from three datasets: the Kilo-Degree Survey (KiDS-1000), the Dark Energy Survey (DES-Y3), and the Hyper-Suprime-Cam Survey (HSC-Y3). This combination of large-scale structure probes allows us to measure a set of -pt correlation functions, breaking the degeneracies between parameters in cosmological fits to individual observables. We obtain mutually-consistent constraints on the parameter from the combination of DESI-DR1 and DES-Y3, from KiDS-1000, and from HSC-Y3. These parameter determinations are consistent with fits to the Planck Cosmic Microwave Background dataset, albeit with lower values in the plane. We perform our analysis with a unified pipeline tailored to the requirements of each cosmic shear survey, which self-consistently determines cosmological and astrophysical parameters. We generate an analytical covariance matrix for the correlation data including all cross-covariances between probes, and we design a new blinding procedure to safeguard our analysis against confirmation bias, whilst leaving goodness-of-fit statistics unchanged. Our study is part of a suite of papers that present joint cosmological analyses of DESI-DR1 and weak gravitational lensing datasets
Extraction d'information cosmologique de l'Univers tardif : amas de galaxies et structures à grande échelle
No full textThe main goal of observational cosmology is to find a model that can fit all of our observations with a single set of cosmological parameters. The current standard model of cosmology, the ΛCDM model, is quite successful, but some tensions still remain between observations of the early Universe through the CMB and observations of the late-time Universe. One of these tensions is the so-called S₈ tension, i.e. the fact that the large-scale structures we observe in our late-time Universe do not match the extrapolation one can make with the ΛCDM model from measurements of the CMB anisotropies. In this thesis, we focus on two specific probes of the late-time Universe matter distribution: weak-lensing (WL) surveys and galaxy cluster surveys.Weak-lensing surveys probe the total matter density field by detecting the subtle distortions its gravitational potential causes in the images of background galaxies. The detection of the signal is complex because of the small, percent-level magnitude of the effect, but its analysis is also challenging due to the non-linear evolution of the density field. Because of this, the smaller scales probed by WL surveys contain non-Gaussian information that cannot be extracted by conventional two-point correlation methods. This issue will be even stronger for next-generation surveys that will probe much smaller scales than the current ones. This has led to the development of new techniques capable of extracting non-Gaussian information, such as deep-learning-based approaches. While they are very promising, their 'black box' aspect is preventing their widespread adoption. In the first study presented in this thesis, we focus on the interpretability of deep-learning methods applied to WL surveys. We propose a method to evaluate the relative importance in the inference process of specific features in the WL maps, using various data degradations. We find the convolutional neural network's constraining performance is strongest when provided with both Gaussian and non-Gaussian information. Structures at the limit between linear and non-linear regimes, around 8 to 12 Mpc/h, and peaks in the matter distribution are particularly important in its inference process.Galaxy clusters are another way to probe the matter density field. As the largest peaks in the matter distribution, their abundance as a function of mass and redshift is very sensitive to the underlying cosmology. Currently, the limiting factor of cluster survey constraining power is the mass calibration. To compare observations with theoretical predictions, a precise knowledge of the cluster masses at the population level is needed. In the second study presented in this thesis, we update the mass calibration of Planck clusters with new calibration samples, and derive tighter, but coherent constraints with the original analysis of the same cluster sample. In the third study, we again focus on the mass calibration of Planck clusters, this time implementing an internal mass calibration using wide-field WL data, preparing the sample for the upcoming Stage IV WL surveys. We find coherent constraints with the previous study and the original analysis. Lastly, in the fourth study, we focus on the comparison of our results with the analyses of two other cluster samples, from the South Pole Telescope and eROSITA. We translate the differences in cosmological parameters into predicted galaxy cluster-related observables, such as number counts, hydrostatic mass biases, and Sunyaev-Zeldovich power spectrum. We find that obtaining the eROSITA cosmology with our Planck analysis pipeline would require 2.5 times more clusters in the sample. Overall, the constraints we derive with the Planck clusters in this thesis are in line with most late-time probes, finding S₈≃0.79 (depending on the various considered scenarios), lower than the S₈=0.830 ±0.013 value from the Planck CMB analysis.L'objectif principal de la cosmologie observationnelle est de trouver un modèle capable de prédire toutes nos observations à l'aide d'un seul ensemble de paramètres cosmologiques. L'actuel modèle standard de la cosmologie, le modèle ΛCDM, est très performant, mais certaines tensions subsistent entre les observations de l'Univers primitif à travers le CMB et les observations de l'Univers tardif. L'une de ces tensions, la tension S₈, est due au fait que les structures à grande échelle que nous observons dans notre Univers tardif ne correspondent pas à l'extrapolation faite avec le modèle ΛCDM à partir des mesures du CMB. Dans cette thèse, nous nous concentrons sur deux sondes de la distribution de la matière dans l'Univers tardif : les relevés de lentille gravitationnelle faible (LG) et les relevés d'amas de galaxies.Les relevés de LG sondent le champ de densité de la matière en détectant les faibles distorsions que son potentiel gravitationnel provoque dans les images des galaxies d'arrière-plan. La détection du signal est complexe en raison de la faible ampleur de l'effet, de l'ordre du pourcentage, mais son analyse est également difficile en raison de l'évolution non-linéaire du champ de densité. Les échelles plus petites sondées par les relevés WL contiennent des informations non-Gaussiennes qui ne peuvent être extraites par les méthodes de corrélation à deux points. Ce problème sera exacerbé avec les relevés de nouvelle génération qui sonderont des échelles plus petites que les études actuelles. Cela a conduit au développement de méthodes capables d'extraire des informations non-Gaussiennes, comme les approches basées sur le deep-learning. Bien qu'elles soient prometteuses, leur aspect "boîte noire" empêche leur adoption à grande échelle. Dans la première étude présentée dans cette thèse, nous nous concentrons sur l'interprétabilité de ces méthodes de deep-learning. Nous proposons une méthode pour évaluer l'importance relative dans le processus d'inférence de certaines structures, en utilisant diverses dégradations de données. Nous trouvons que les performances du réseau neuronal convolutif sont les meilleures lorsqu'il a accès à la fois à des informations Gaussiennes et non-Gaussiennes. Les structures à la limite entre les régimes linéaires et non linéaires, autour de 8 à 12 Mpc/h, et les pics dans la distribution de la matière sont particulièrement importants dans son processus d'inférence.Les amas de galaxies sont un autre moyen d'étudier le champ de densité. En tant que pics les plus importants dans la distribution de matière, leur abondance en fonction de la masse et du redshift est sensible à la cosmologie sous-jacente. Actuellement, la calibration de masse est le facteur limitant des relevés d'amas. Dans la deuxième étude présentée dans cette thèse, nous actualisons la calibration de masse des amas Planck à l'aide de nouveaux échantillons de calibration, et nous dérivons des contraintes plus strictes, mais cohérentes avec l'analyse originale. Dans la troisième étude, nous proposons une calibration interne de la masse des amas Planck avec des données de LG à grand champ, afin de préparer l'échantillon pour les prochaines relevés de LG de phase IV. Nous trouvons des contraintes cohérentes avec l'étude précédente et l'analyse originale. Enfin, dans la quatrième étude, nous comparons nos résultats avec les analyses de deux autres échantillons d'amas, du South Pole Telescope et d'eROSITA. Nous traduisons les différences entre les paramètres cosmologiques en observables liés aux amas de galaxies. Nous trouvons que l'obtention de la cosmologie eROSITA avec notre pipeline d'analyse Planck nécessiterait 2.5 fois plus d'amas dans l'échantillon. Dans l'ensemble, les contraintes obtenues avec les amas Planck dans cette thèse sont cohérentes avec la plupart des sondes de l'Univers tardif, donnant S₈≃0.79, ce qui est inférieur à la valeur S₈=0.830 ±0.013 obtenue avec le CMB Planck