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How MeV-range Ions and high β will shape the core plasma dynamics of fusion power plants
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Unraveling Hydrogen-Induced Phase Transitions in Palladium Nanoparticles via In Situ BCDI
No full textInternational audienceThe advent of 4th-generation X-ray light sources offers transformative opportunities for in situ and operando studies of nanoparticle dynamics in reactive environments [1]. In this work, we employed Bragg Coherent X-ray Diffraction Imaging (BCDI) [2-3] to probe the structural evolution of a single palladium (Pd) nanoparticle during hydrogen absorption at 30°C. Measurements performed at the ID01 beamline (ESRF) reveal an α-to-β phase transition initiating near 40 mbar of hydrogen partial pressure, with β-phase nucleation occurring at specific corner site, and propagating inward. This transformation induces significant lattice strain and expansion, consistent with hydrogen incorporation and redistribution within the crystal [4]. Our results provide direct nanoscale insight into hybrid nucleation, strain evolution, and phase propagation, demonstrating the power of BCDI to visualize structural dynamics in reactive gas environments and to advance understanding of Pd-based materials for energy applications [5]
Anthropogenic climate change has increased severity of mid-latitude storms and impacted airport operations
No full textInternational audienceThe impact of extreme weather events, particularly those associated with tropical and extra-tropical cyclones (TC and ETC), on aviation can rise serious concerns in the context of the ongoing climate change. These events often lead to significant disruptions, including flight cancellations, delays, re-routing, and impacts on airport infrastructure resilience to adverse weather conditions. This study conducts an analysis of the influence of anthropogenic climate change on four recent major storm events that occurred over Europe, the USA, and East Asia, with an in-depth analysis on the Storm Eunice, a powerful ETC that affected the UK and Ireland. Using climate reanalysis data we assess the dynamics of these extreme storms and their implications for aviation operations, particularly during critical phases such as takeoff and landing. Our research underscores the growing intensity of extreme storms, particularly stronger winds, driven by human-induced climate change, and stresses the need for taking into account growing climate hazards to optimize planes and airport operations
Contribution du mésozooplancton et des pelotes fécales à l’export de carbone : une approche par traits fonctionnels
No full textMarine mesozooplankton refers to marine animals measuring between 0.2 and 20 mm that are unable to fight against currents. They support the world's fisheries and play a key role in the biological carbon pump (PCB), exporting organic carbon to the interior of the ocean. This transfer is based in particular on the production of particles (faecal pellets, moults, carcasses) that form part of the marine snow that sediments. Fecal pellets make up most of this. In addition, some mesozooplankton species migrate vertically on a daily or seasonal basis, amplifying the intensity of the PCB. Recent methods, such as imaging and metabarcoding, complement traditional methods (plankton nets and binocular magnifying glasses for mesozooplankton, sediment traps for particles) and make it possible to study ecosystems using a functional trait approach. These are measurable individual characteristics that influence the selective value of organisms (ability to survive, grow and reproduce). They can be associated with ecological functions at ecosystem level, such as carbon export. In addition, models can be used to produce balances on the scale of the global ocean, based on information (e.g. parameters) obtained from data. In this context, the goal of this thesis is to study the role of mesozooplankton and the particles they produce in carbon export, using various analytical methods.In Chapter 1, I analyse imaging and metabarcoding data from mesozooplankton samples collected at the Bermuda Atlantic Time-series Study (BATS) site. I identify groups of highly correlated taxa (“modules”) formed by organisms that are more or less transparent. These variations in transparency can be attributed to physiological or ecological functions. The modules appear in different ecosystem dynamics (e.g. productive period, oligotrophic period) and their relative abundances vary according to the intensity of carbon export. A morphological space highlights size and transparency as traits influencing this export. In Chapter 2, I focus on the identification of cylindrical faecal pellets, typical of those produced by Arctic mesozooplankton, among the non-living particles imaged in situ in Baffin Bay (Arctic Ocean), during a period of high productivity, using the Underwater Vision Profiler. The 50,771 particles identified by their morphology probably correspond to pellets produced by the large copepods Calanus hyperboreus, amphipods or euphausiids, according to a comparison with reference data. This work highlights the relevance of in situ imaging approaches for quantifying the carbon fluxes associated with the production of faecal pellets in productive ecosystems. Finally, in Chapter 3, I review the role of faecal pellets in carbon export, based on a meta-analysis gathering 197 scientific articles. The abundance, biomass and contribution of faecal pellets to carbon fluxes are closely linked to ecosystem productivity. The sedimentation rate of faecal pellets is strongly correlated with their morphology but appears to be independent of depth. There is a need to better characterise the types of pellet studied and to measure several variables on the same sample in order to better understand their dynamics and propose more realistic parameter values. This thesis opens up perspectives for the joint analysis of imagery and metabarcoding data, in particular via co-occurrence networks, and proposes a characterisation of marine snow particles involved in carbon export using imagery.Le mésozooplancton marin désigne les animaux marins mesurant entre 0,2 et 20 mm ne pouvant lutter contre les courants, il soutient les pêcheries mondiales et joue un rôle clé dans la pompe à carbone biologique (PCB), en exportant du carbone organique vers l'intérieur de l'océan. Ce transfert repose notamment sur la production de particules (pelotes fécales, mues, carcasses) formant une partie de la neige marine qui sédimente. Les pelotes fécales en constituent la majeure partie. Par ailleurs, certaines espèces du mésozooplancton effectuent des migrations verticales, quotidiennes ou saisonnières, amplifiant l'intensité de la PCB. De récentes méthodes, telles que l'imagerie ou le métabarcoding, complètent les méthodes traditionnelles (filets à plancton et loupe binoculaire pour le mésozooplancton, pièges à sédiments pour les particules) et permettent d'aborder l'étude des écosystèmes à travers une approche par traits fonctionnels. Ce sont des caractéristiques individuelles mesurables influençant la valeur sélective des organismes (capacité à survivre, croître et se reproduire). Ils peuvent être associés à des fonctions écologiques à l'échelle de l'écosystème, telles que l'export de carbone. En complément, l'utilisation de modèles permet de réaliser des bilans à l'échelle de l'océan global, en se basant sur des informations (e.g., paramètres) obtenues depuis les données. Dans ce contexte, l'objectif de cette thèse est d'étudier le rôle du mésozooplancton et des particules qu'il produit dans l'export de carbone, en mobilisant diverses méthodes d'analyses. Dans le Chapitre 1, j'analyse des données d'imagerie et de métabarcoding issues d'échantillons de mésozooplancton collectés sur le site de Bermuda Atlantic Time-serie Study (BATS). J'identifie des groupes de taxons fortement corrélés (“modules”) constitués d'organismes plus ou moins transparents. Ces variations de transparence peuvent être attribuées à des fonctions physiologiques ou écologiques. Les modules apparaissent dans des dynamiques d'écosystème différentes (e.g., période productive, période oligotrophe) et leurs abondances relatives varient selon l'intensité de l'export de carbone. Un espace morphologique met en évidence la taille et la transparence comme traits influençant cet export. Dans le Chapitre 2, je m'intéresse à l'identification de pelotes fécales cylindriques, typiques de celles produites par le mésozooplancton arctique, parmi les particules non-vivantes imagées in situ dans la Baie de Baffin (Océan Arctique), en période de forte productivité, grâce à l'Underwater Vision Profiler. Les 50 771 particules identifiées par leur morphologie correspondent probablement à des pelotes produites par les grands copépodes Calanus hyperboreus, les amphipodes ou les euphausiacés, selon une comparaison avec des données de référence. Ce travail met en lumière la pertinence des approches d'imagerie in situ pour quantifier les flux de carbone associés à la production de pelotes fécales dans les écosystèmes productifs. Enfin, dans le Chapitre 3, je dresse un état des lieux du rôle des pelotes fécales dans l'export de carbone, à partir d'une méta-analyse rassemblant 197 articles scientifiques. Ainsi, l'abondance, la biomasse et la contribution des pelotes fécales dans les flux de carbone sont étroitement liées à la productivité des écosystèmes. La vitesse de sédimentation des pelotes fécales est fortement corrélée à leur morphologie mais semble être indépendante de la profondeur. Il est nécessaire de mieux caractériser les types de pelotes étudiés et de mesurer plusieurs variables sur un même échantillon pour mieux comprendre leur dynamique et proposer des valeurs de paramètres plus réalistes. Cette thèse ouvre des perspectives pour l'analyse croisée des données d'imagerie et de métabarcoding, notamment via les réseaux de co-occurrence, et propose une caractérisation des particules de neige marine impliquées dans l'export de carbone grâce à l'imagerie
LMC+: Large-scale mapping of [CII] and [OIII] in the LMC molecular ridge, I. Dataset and line ratio analyses
No full textInternational audienceThe fundamental process of star formation in galaxies involves the interplay between the fueling of star formation via molecular gas and the feedback from recently formed massive stars. This process, by which galaxies evolve, is also closely connected to the intrinsic properties of the interstellar medium (ISM). To study the role that different molecular and atomic phases of the ISM play in star formation, and to characterize their physical conditions, we zoom into our nearest neighboring galaxy, the Large Magellanic Cloud (LMC; 50 kpc). The LMC offers a view of the ISM and star formation conditions in a low metallicity environment similar to, in that regard, the epoch of the peak of star formation in the earlier universe. We present an unprecedentedly detailed analysis of a well-known star-forming regions (SFRs) at a spatial resolution of a few pc. We mapped a 610pcx260pc region in the LMC molecular ridge in [CII] and the [OIII] using the FIFI-LS instrument on the SOFIA telescope. We compare the data with the distribution of the CO (2-1) emission from ALMA, the modeled TIR luminosity as well as Spitzer/MIPS continuum and Halpha. We also provide a detailed description of the observing strategy and the data reduction. We find that [CII] and [OIII] emission is associated with the SFRs in the molecular ridge, but also extends throughout the mapped region, not obviously associated with ongoing star formation. The CO emission is clumpier than the [CII] emission and we find plentiful [CII] present where there is little CO emission, possibly holding important implications for CO-dark gas. We find a clear trend of the [CII]/TIR ratio decreasing with increasing TIR. This suggests a strong link between the [CII]-deficit and the local physical conditions instead of global properties
Minimizing sensor-sample distances in scanning nitrogen-vacancy magnetometry
No full textInternational audienceScanning magnetometry with nitrogen-vacancy (NV) centers in diamond has led to significant advances in the sensitive imaging of magnetic systems. The spatial resolution of the technique, however, remains limited to tens to hundreds of nanometers, even for probes where NV centers are engineered within 10 nm from the tip apex. Here, we present a correlated investigation of the crucial parameters that determine the spatial resolution: the mechanical and magnetic stand-off distances, as well as the sub-surface NV center depth in diamond. We study their contributions using mechanical approach curves, photoluminescence measurements, magnetometry scans, and nuclear magnetic resonance (NMR) spectroscopy of surface adsorbates.We first show that the stand-off distance is mainly limited by features on the surface of the diamond tip, hindering mechanical access. Next, we demonstrate that frequency-modulated atomic force microscopy (FM-AFM) feedback partially overcomes this issue, leading to closer and more consistent magnetic stand-off distances (26 -87 nm) compared to the more common amplitude-modulated (AM-AFM) feedback (43 -128 nm). FM operation thus permits improved magnetic imaging of sub-100-nm spin textures, shown for the spin cycloid in BiFeO 3 and domain walls in a CoFeB synthetic antiferromagnet. Finally, by examining 1 H and 19 F NMR signals in soft contact with a polytetrafluoroethylene surface, we demonstrate a minimum NV-to-sample distance of 7.9±0.4 nm
Structural and functional characterization of the cardiac mitochondria-associated reticular membranes in the ob/ob mouse model
No full textInternational audienceType 2 diabetes (T2D) and obesity strongly lead to diabetic cardiomyopathy (DCM). The involvement of mitochondria-associated reticular membranes (MAMs), a signaling hub in the cardiomyocyte, starts to be demonstrated in T2D-related metabolic disorders. We recently discovered a cardiac MAM Ca2+ uncoupling in a high-fat high-sucrose diet (HFHSD)-induced mouse model of DCM. To better determine the role of MAMs in the progression of DCM, we here aimed to characterize the proteomic composition and function of the cardiac MAMs of another obesogenic T2D mouse model, the leptin-deficient ob/ob mouse. 12-week old male C57Bl6-N ob/ob mice displayed strain rate dysfunction and concentric remodeling, while no change was observed in fractional shortening or diastolic function. Increased lipid deposition but no fibrosis was measured in the ob/ob heart compared to WT. Electron microscopy analysis revealed that cardiac MAM length and width were similar between both groups. A trend towards an increased MAM protein content was measured in the ob/ob heart. MAM proteome analyses showed mainly increased processes in ob/ob hearts: cellular response to stress, lipid metabolism, ion transport and membrane organization. Functionally, MAM-driven Ca2+ fluxes were unchanged but hypoxic stress induced a cell death increase in the ob/ob cardiomyocyte. Mitochondrial respiration, cardiomyocyte shortening, ATP and ROS content were similar between groups. To conclude, at that age, while being strongly hyperglycemic and insulin-resistant, the ob/ob mouse model rather displays a modest DCM without strong changes in MAMs: preserved structural and functional MAM Ca2+ coupling but increased response to stress
Evaluation of synthetic mRNA with selected UTR sequences and alternative Poly(A) tail, in vitro and in vivo
No full textInternational audienceMessenger RNA (mRNA) has emerged as an attractive new technology of drugs. The efficacy of mRNA technology depends on both the efficiency of mRNA delivery and translation. Untranslated regions (UTRs) and the poly(A) tail play a crucial role in regulating mRNA intracellular kinetics. Intending to improve the therapeutic potential of synthetic mRNA, we evaluated various UTRs and tail designs, using Pfizer-BioNTech COVID-19 vaccine sequences as a reference. First, we screened six 5' UTRs (cap-dependent/independent), evaluated nine 5' UTR-3' UTR combinations, and a novel heterologous A/G tail in cell models, and in vivo using luciferase as a reporter gene. Then, to decipher the translation mechanism of selected UTRs, we correlated mRNA expression with ribosome load, mRNA half-life, mRNA immunogenicity, and UTR structures. Our results showed that the heterologous tail we introduced is as potent as the Pfizer-BioNTech tail and confirmed the high potency of the human α-globin 5' UTR. They also revealed the potential of the VP6 and SOD 3' UTRs. We validated our results using mRNA encoding the SARS-CoV-2 spike protein formulated as lipid nanoparticles (LNPs) for mouse immunization. Overall, the selected 3’ UTRs and heterologous A/G tail have great potential as new elements for therapeutic mRNA design
Beyond the Nyquist frequency: Asteroseismic catalog of undersampled Kepler late subgiants and early red giants
No full textInternational audienceSubgiants and early red giants are crucial for studying the first dredge-up, a key evolutionary phase in which the convective envelope deepens, mixing previously interior-processed material and bringing it to the surface. Yet, very few have been seismically characterized with Kepler because their oscillation frequencies are close to the 30 minute sampling frequency of the mission. We developed a new method as part of the new PyA2Z code of identifying super-Nyquist oscillators and inferring their global seismic parameters, νmax and large separation, Δν.Applying PyA2Z to 2065 Kepler targets, we seismically characterize 285 super-Nyquist and 168 close-to-Nyquist stars with masses from 0.8 to 1.6 M⊙. In combination with APOGEE spectroscopy, Gaia spectrophotometry, and stellar models, we derive stellar ages for the sample. There is good agreement between the predicted and actual positions of stars on the HR diagram (luminosity vs. effective temperature) as a function of mass and composition. While the timing of dredge-up is consistent with predictions, the magnitude and mass dependence show discrepancies with models, possibly due to uncertainties in model physics or calibration issues in observed abundance scales
Nanosecond intense relativistic electron beam propagation in gas and preformed plasma
No full textInternational audienceAn experimental and numerical study on the propagation of a typical flash radiography electron beam in helium gas and a preformed plasma is presented, in the context of a plasma lens applicability for such beams. The experiments consist of measuring the beam profile at the exit of an interaction chamber as a function of time, for various gas pressure and plasma densities. The plasma is produced before the beam’s arrival in the gas at ≈1×10−3mbar by a seeded, pulsed inductive discharge. The plasma density reaches a peak value of (1.2 ± 0.4)×1012cm−3 then decreases exponentially over several tens of microseconds. This allows probing the propagation in different plasma densities by varying the delay between the plasma discharge and the electron beam. The influence of the preformed plasma on the beam propagation is experimentally demonstrated, as well as an evolution of the propagation at the tens of nanoseconds time scale. Simulations are carried out in the regime where the plasma density ( 2×1010cm−3 or less) is lower than the beam density, using a full kinetic description with a particle-in-cell (PIC)/Monte-Carlo code. The simulations reproduce the main features of the observations, and show that after the effect of the fast plasma electron response (at the nanosecond time scale), the evolution of the propagation at the tens of nanoseconds time scale is mainly due to the plasma ion redistribution driven by the beam space charg