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VertiGO : Development and electrical characterization of fully-vertical GaN-on-GaN trench-MOSFETs for power applications
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Angular structure of many-body correlations in atomic nuclei: From nuclear deformations to diffractive vector meson production in collisions
No full textInternational audienceThere is growing evidence that high-energy scattering processes involving nuclei can offer unique insights into the many-body correlations present in nuclear ground states, in particular those of deformed nuclei. These processes involve, for instance, the collective anisotropic flows in heavy-ion collisions, or the diffractive production of vector mesons in photo-nuclear () interactions. In this paper, we use a classical approximation and simple analytical models in order to exhibit characteristic and universal features of ground-state correlation functions that result from the presence of a deformed intrinsic state. In the case of a small axial quadrupole deformation, we show that the random rotation of the intrinsic density of the nucleus leads to a specific quadrupole modulation of the lab-frame two-body density as a function of the relative azimuthal angle. As a phenomenological, albeit academic application, we analyze the diffractive production of vector mesons in high-energy Be collisions. This demonstrates with the simplest deformed nucleus how the two-body correlations impact the dependence of the incoherent cross sections
Atomistic modeling of long-range ordering in FCC Ni-Cr-Fe alloys
No full textInternational audienceThis study examines the thermodynamics and kinetics of the face-centered cubic Ni-Cr-Fe system, focusing on the order-disorder phase transformation in Ni0.67(1−x)Cr0.33(1−x)Fex (x = 0 – 0.1) alloys. A pair interaction model (PIM) is developed, with a significant portion based on density functional theory (DFT) calculations and CALPHAD models for binary Ni-Cr and Ni-Fe alloys and further adjusted using experimental order-disorder transformation temperatures and diffusion data. Monte Carlo simulations using this PIM yield detailed phase diagrams and kinetic insights into the ordering process. The simulations reveal that adding up to 10 at.% Fe extends the incubation time by slowing down the atomic diffusion, while slight deviations in Ni-Cr ratio have minimal impact on the ordering kinetics. Although additional experimental data would be required—especially at low temperature and high Fe content—for further validation of the model, our results match reasonably well with the available experimental data on ordering incubation times, capturing the alloy’s key characteristics
Teichoic acids in the periplasm and cell envelope of Streptococcus pneumoniae
No full textInternational audienceTeichoic acids (TA) are linear phospho-saccharidic polymers and important constituents of the cell envelope of Gram-positive bacteria, either bound to the peptidoglycan as wall teichoic acids (WTA) or to the membrane as lipoteichoic acids (LTA). The composition of TA varies greatly but the presence of both WTA and LTA is highly conserved, hinting at an underlying fundamental function that is distinct from their specific roles in diverse organisms. We report the observation of a periplasmic space in Streptococcus pneumoniae by cryo-electron microscopy of vitreous sections. The thickness and appearance of this region change upon deletion of genes involved in the attachment of TA, supporting their role in the maintenance of a periplasmic space in Gram-positive bacteria as a possible universal function. Consequences of these mutations were further examined by super-resolved microscopy, following metabolic labeling and fluorophore coupling by click chemistry. This novel labeling method also enabled in-gel analysis of cell fractions. With this approach, we were able to titrate the actual amount of TA per cell and to determine the ratio of WTA to LTA. In addition, we followed the change of TA length during growth phases, and discovered that a mutant devoid of LTA accumulates the membrane-bound polymerized TA precursor
Experimental study of thermocline behavior under high propagation velocities in a water based thermal energy storage
No full textInternational audienceThis experimental study investigates the development of the thermocline under varied operating conditions and particularly at high propagation velocities ranging from 0.5 mm.s -1 up to 8 mm.s -1 and temperature differences (ΔT) of 10 • C, 30 • C and 65 • C. For this purpose, a new experimental setup, designed to investigate thermocline formation, propagation, and withdrawal is implemented. The setup meets essential requirements for acquiring controlled validation data for CFD models and enables the collection of novel high-velocity flow data. The storage system features extensive instrumentation, including temperature measurements at curved tank bottoms and radial positions. Dynamic experiments validated literature findings, demonstrating stronger stratification with slower axial propagation velocities and larger temperature differences. High propagation velocities remain feasible with adequate ΔT, i.e. with a Richardson number based on the penetration height of the inlet fluid, Ri 0,hi ≥ 0.25 ensuring a thin thermocline for this test section. Variation of the extraction distribution system revealed the influence of fluid withdrawal on thermocline thickness, underscoring the need to consider outlet dynamics in distributor design. These findings establish the relevance of Ri 0,hi for predictive performance correlations and provide a foundation for optimizing thermal energy storage systems through refined distributor designs. Finally, an original definition of thermocline thickness was introduced, based on the slope of the thermocline, offering an alternative to the classical boundary-temperature approach and limiting the dependence on temperature limits
Seeing inside Individual Palladium Hydride Nanoparticles with In Situ Synchrotron X-rays
No full textInternational audienceThe advent of the new 4th generation x-ray light sources provides an unprecedented opportunity to conduct in situ and operando studies on the structural evolution of nanoparticles in reactive liquid and gas environments. In this study, we employ Bragg coherent x-ray diffraction imaging (BCDI) [1-4] to investigate the strain, lattice deformation, and defect dynamics inside palladium (Pd) nanocrystals during electrochemical and gas-phase reactions. Palladium is widely used in water electrolysis, catalysis, hydrogen storage, and sensing technologies due to its ability to absorb hydrogen. Open questions remain regarding the maximal H uptake in a Pd nanocrystallite, the mechanism and kinetics of hydride (PdHx) nucleation (whether it occurs at preferential sites or homogeneously across the surface) and growth dynamics of the α/β phase transition (α/β sharp transition or two-phase coexistence). Using in situ BCDI, we map the strain and lattice parameter distributions across electrochemical potentials associated with hydrogen ad-, ab- and desorption, while minimizing undesired “beam effects”. We reveal a reversible strain inversion during the α-to-β phase transition. Through strain and reciprocal space analysis, and molecular simulations, we propose a model for the α-to-β phase transition which includes a hydrogen-saturated subsurface shell, hydrogen depletion from the α phase during β-phase nucleation, and propagation of the β phase in a spherical-cap fashion.We further investigate hydrogen absorption kinetics in individual Pd nanoparticles using time-resolved x-ray nano-diffraction. By comparing absorption kinetics in a gas-phase reactor and an electrochemical cell, we assess how different environments influence the process. Chronoamperometry measurements provide complementary insights, enabling a comparison between the kinetics of Pd nanoparticle ensembles and at the single-nanoparticle level. In the electrochemical system, absorption slows as the electrochemical potential is lowered, a phenomenon directly linked to increased hydrogen uptake. Additionally, we observe differences in absorption times, normalized by absorbed quantity, between hydrogen and deuterium absorbates.Finally, we examine the kinetics of individual Pd nanoparticles during the α-to-β phase transition in the gas phase. Our measurements capture the evolution speed of the α-to-β phase front, providing direct insight into the dynamics of this transformation.By resolving the structure in complex environments, we can provide new insights into the fundamental mechanisms of hydrogen absorption and phase transitions in Pd-based systems.We acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme under grant agreement CARINE No. 818823 and HERMES No. 952184.[1]I. Robinson and R. Harder, Coherent X-Ray Diffraction Imaging of Strain at the Nanoscale, Nat. Mater. 8, 291 (2009).[2]C. Atlan et al., Imaging the Strain Evolution of a Platinum Nanoparticle under Electrochemical Control, Nat. Mater. 22, 6 (2023).[3]M. L. Frisch et al., Unraveling the Synergistic Effects of Cu-Ag Tandem Catalysts during Electrochemical CO2 Reduction Using Nanofocused X-Ray Probes, Nat. Commun. 14, 1 (2023).[4] C. Atlan et al., Probing Strain in Individual Palladium Nanocrystals during Electrochemically-induced Phase Transition. submitted (2025)
Crystallinity in niobium oxides: A pathway to mitigate two-level-system defects in niobium three-dimensional resonators for quantum applications
No full textInternational audienceMaterials imperfections in Nb-based superconducting quantum circuits-in particular, two-levelsystem (TLS) defects-are a major source of decoherence, ultimately limiting the performance of quantum computation and sensing. Thus, identifying and understanding the microscopic origin of possible TLS defects in these devices will help develop strategies that eliminate them, which are key to superconducting qubit performance improvement. In this paper, we demonstrate an order-of-magnitude reduction in two-level system losses in three-dimensional superconducting radio frequency (SRF) niobium resonators by a 10-h high vacuum (HV) heat treatment at 650 °C, even after exposure to air and high-pressure rinsing (HPR). X-ray photoelectron spectroscopy (XPS) and high-resolution scanning transmission electron microscopy (STEM) reveal an alteration of the native oxide composition regrown after air exposure and HPR and the creation of nanoscale crystalline oxide regions, which correlates with the measured tenfold quality factor enhancement at low fields of the 1.3 GHz niobium resonator. Tunneling spectroscopy measurements show a pronounced proximity effect that further confirms the presence of metallic layers on the niobium surface
Rapport de conjoncture de la Section 17 "SYSTÈME SOLAIRE ET UNIVERS LOINTAIN" du Comité National de la Recherche Scientifique - Mandature 2021-2025
No full textCe rapport s'adresse à un lectorat non expert de la discipline Astrophysique, souhaitant avoir un aperçu de l'évolution de notre communauté de recherche au sein de CNRS INSU (Institut National des Sciences de l'Univers, également appelé CNRS Terre & Univers) sur la période 2022-2024. Il présente un résumé thématique et méthodologique de nos activités, un panorama de la structuration actuelle de notre communauté, ainsi qu'un bilan des recrutements et des promotions. Il est fondé sur le travail de la section 17, lequel comprend les concours de recrutement, les recrutements contractuels RQTH, la carrière (évaluation, promotion, éméritat, demande de rattachement à la section ou de détachement de celle-ci, changement d'affectation et RIPEC C3) des personnels de recherche rattachés à la section 17 ; l'évaluation des structures rattachées à la section 17 ; les propositions pour les médailles d'argent et de bronze du CNRS ; les demandes d'accueil en délégation au CNRS ; les écoles thématiques
Predictors of alcohol use disorder risk in young adults: Direct and indirect psychological paths through binge drinking
No full textInternational audienceAlcohol-use disorders (AUD) risk is highly prevalent in university students, and is associated with both intraindividual (e.g., metacognitions, personality traits) and interindividual (e.g., social motives, drinking identity, drinking norms) psychological factors. Binge drinking (BD) also constitutes a widespread drinking pattern in youth, distinct from AUD risk and mainly predicted by interindividual factors. As BD is itself a risk factor for AUD, we tested a dual psychological path model to AUD risk, combining a direct path (including intra/interindividual factors independent from BD) with an indirect path (where interindividual factors increase AUD risk through BD). We assessed a large range of psychological factors predicting BD and AUD risk in an online survey among 2026 university students (Mage = 20.46; SD = 2.82; 67.42% of women). We tested the direct and indirect (via BD) effects of these psychological factors on three subdimensions of AUDIT (alcohol intake, dependence symptoms, and alcohol-related problems) through a multivariate mediation model using percentile bootstrapped estimates. Support for the dual-path model to risk of AUD emerged from the results, comprising a direct path mainly influenced by intra-individual factors unrelated to BD (e.g., coping motives, depression symptoms, and uncontrollability beliefs), and an indirect BD-mediated path mainly influenced by inter-individual factors (e.g., social motives, enhancement motives, drinking norms) through BD. This new dual-path conceptualization combining direct/intra-individual and indirect/inter-individual risk factors identifies key psychological determinants of AUD risk in youth and offers new prevention avenues for AUD risk
3000 yr-old patterns of mobile pastoralism revealed by multiple isotopes and radiocarbon dating of ancient horses from the Mongolian Altai
No full textInternational audiencePastoral nomadism is of great cultural and economic importance in several regions of the world today. However, documenting ancient patterns of mobility in societies where pastoralism was central is challenging and requires tailored approaches and methodologies.Here we use strontium, oxygen and carbon isotopic analyses of dental enamel, together with a local strontium isoscape, to reconstruct the mobility patterns of seven domestic horses deposited in a Late Bronze Age grave from western Mongolia. Radiocarbon indicates that the animals were deposited within a short period of time, 3000 years ago. The isotope time series obtained from tooth enamel shows that four of the seven horses exhibited a common pattern characterized by a high frequency of mobility, suggesting that in this area (1) cyclical nomadic mobility dates back at least to the Late Bronze Age and (2) the animals belonged to the same herding family, implying that only a small community was involved in the funerary rite of this structure. The data show that the other three horse individuals had a distinct mobility pattern and that one was not from the local area, pointing to flexibility in mobility patterns over time or circulation of animals between herding groups. These results illustrate the power of the isotopic approach to reconstruct animal biographies and effectively address the archaeology of pastoral nomadism and mobility