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Conservative models and numerical methods for pyrolysis-thermal coupling of heat shield degradation and deformations
No full textInternational audienc
A kHz laser desorption setup adapted to ultrafast gas-phase measurements of biomolecules
No full textInternational audienceWe have developed a new laser desorption scheme coupled to a supersonic expansion able to operate at several kHz rates. We demonstrate that it can be used to perform cold spectroscopy of flexible or fragile molecules. We also demonstrate its ability to study non-covalent complexes, such as hydrated molecules, which can be formed in the beam
Fast switching of various ions from 11 to 23 MeV/u for space applications at GANIL
No full textInternational audienceIn recent years, the demand for radiation hardness testing of electronic components for space applications has grown significantly across Europe. In response, the Grand Accélérateur National d’Ions Lourds (GANIL) is developing a dedicated test beamline downstream of the Cyclotron for Ions of Medium Energy (CIME), optimized for delivering fast-switchable heavy-ion cocktail beams suitable for irradiation in both air and vacuum environments. These beams include ions ranging from carbon to xenon, covering energies from 11 to 23 MeV/u. They span Linear Energy Transfers (LET) at the surface up to 50 MeV mg−1 cm2, with ranges in silicon up to 530 μm. The intensities of the various beams produced from the Electron Cyclotron Resonance (ECR) ion source can be adjusted from 102 to 105 particles⋅s−1⋅cm−2, ensuring uniform irradiation over a 6 cm2 area. Thanks to mass-to-charge (m/q) selection of the cyclotron and fast magnetic tuning, about ten ion species can be delivered successively in a single session, with switching times under 10 min. These capabilities enhance European heavy-ion Single Event Effect (SEE) testing capacity and complement other cyclotron-based infrastructures
High-throughput analysis of dislocation loops in irradiated metals using Mask R-CNN
No full textInternational audienceAdvances in transmission electron microscopy under extreme conditions have enabled in situ experiments to capture vast amounts of data on defect evolution. On the other hand, computer vision models such as Mask R-CNN have become popular in the last few years, enabling fast and accurate segmentation of images of different natures. In the present work, we propose a workflow to label, segment, and analyze irradiation-induced defects in TEM images using Mask R-CNN. The work focuses on interpreting bright-field (BF) videos recorded during the irradiation of three different metallic materials. After establishing a baseline dataset based on austenitic stainless steel 316L, we tested small and large models as the backbone of Mask R-CNN and different hyperparameters for training them. Our best model predicts the areal density of defects in 316L with 83.6 % accuracy, measured by a custom metric which assesses cumulative defect area using an ellipsoidal approximation. We tested the generalization limits of the trained model to ensure accurate estimations of key physical metrics, including the foreground fraction occupied by defects, the number of detected particles, and their relative sizes -all of which exhibit relative errors below 5%. At last, the model helps interpret videos concerning two similar irradiation experiments: one with the 16Cr-37Fe-13Mn-34Ni (at. %) alloy, and another with pure Cr. The model's segmentation clearly captures the different nature of defect evolution between different materials, as expected. Moreover, the proposed workflow not only enables consistent, real-time analysis of small defect loops during in situ TEM experiments but also generates the quantitative data needed to refine mesoscale models
Understanding the correlation between elliptic and triangular flow
No full textInternational audienceThe relative correlation between the magnitudes of elliptic flow () and triangular flow () has been accurately measured in nucleus-nucleus collisions at the LHC collider. As a function of the centrality of the collision, it changes sign and varies non-monotonically. We show that this is naturally explained by two combined effects. The first effect is a skewness in initial-state fluctuations, which is quantified by the correlation between the geometry-driven elliptic deformation in the reaction plane and the fluctuation-driven triangularity . We introduce an intensive measure of this skewness, which is generically of order unity and depends weakly on the system size and centrality. We evaluate its magnitude using Monte Carlo simulations of the initial state, which show that it is sensitive to the nucleon width. The second effect is the fluctuation of impact parameter relative to centrality classifiers used by experiment. The ATLAS collaboration uses two different centrality classifiers, the multiplicity and the transverse energy . We fit both sets of results for Pb+Pb collisions up to centrality with a single parameter, the intensive mixed skewness. Its value inferred from experiment agrees with theoretical expectations
Fusion of C+Si at deep sub-barrier energies
No full textInternational audienceThe existence of fusion hindrance is not well established in light heavy-ion systems. Studying slightly heavier cases allows extrapolating the trend to light systems of astrophysical interest. Fusion of 12C + 28Si has been measured down to deep sub-barrier energies, using 28Si beams from the XTU Tandem accelerator of LNL on thin 12C targets. The fusion-evaporation residues were detected by a detector telescope following an electrostatic beam separator, and coincidences between the gamma-ray array AGATA and segmented silicon detectors DSSD were performed, where the evaporated light charged particles were identified by pulse shape analysis. Fusion cross sections have been obtained in the wide range 150 mb-42 nb. Coupled-channel (CC) calculations using a Woods-Saxon potential reproduce the data above 0.1 mb. Below that, hindrance shows up and the CC results overestimate the cross sections which get close to the one-dimensional potential tunnelling limit. This suggests that the coupling strengths gradually vanish, as predicted by the adiabatic model. The hindrance threshold follows a recently updated phenomenological systematics
LiteBIRD Science Goals and Forecasts. -mode Anomalies
No full textInternational audienceVarious so-called anomalies have been found in both the WMAP and Planck cosmic microwave background (CMB) temperature data that exert a mild tension against the highly successful best-fit 6 parameter cosmological model, potentially providing hints of new physics to be explored. That these are real features on the sky is uncontested. However, given their modest significance, whether they are indicative of true departures from the standard cosmology or simply statistical excursions, due to a mildly unusual configuration of temperature anisotropies on the sky which we refer to as the "fluke hypothesis", cannot be addressed further without new information. No theoretical model of primordial perturbations has to date been constructed that can explain all of the temperature anomalies. Therefore, we focus in this paper on testing the fluke hypothesis, based on the partial correlation between the temperature and -mode CMB polarisation signal. In particular, we compare the properties of specific statistics in polarisation, built from unconstrained realisations of the CDM cosmological model as might be observed by the LiteBIRD satellite, with those determined from constrained simulations, where the part of the -mode anisotropy correlated with temperature is constrained by observations of the latter. Specifically, we use inpainted Planck 2018 SMICA temperature data to constrain the -mode realisations. Subsequent analysis makes use of masks defined to minimise the impact of the inpainting procedure on the -mode map statistics. We find that statistical assessments of the -mode data alone do not provide any evidence for or against the fluke hypothesis. However, tests based on cross-statistical measures determined from temperature and modes can allow this hypothesis to be rejected with a moderate level of probability
SPHINGOLIPIDS AND Δ8-SPHINGOLIPID DESATURASE FROM THE PICOALGA OSTREOCOCCUS TAURI AND INVOLVEMENT IN TEMPERATURE ACCLIMATION
No full textAlternative title : SPHINGOLIPID‐8 DESATURASE CONTROLS THE UNSATURATION OF ACIDIC GLYCOSYLCERAMIDES AND IS INVOLVED IN TEMPERATURE ACCLIMATION IN THE MINIMAL GREEN ALGA OSTROCOCCUS TAURISphingolipids are crucial components of cell membranes. Sphingolipid Δ8-unsaturation is more specific to plants and is involved in the regulation of stress responses. The structure and functions of sphingolipids in microalgae are still poorly understood. Ostreococus tauri is a minimal microalga at the base of the green lineage, and is therefore a key organism for understanding lipid evolution. The present work reports the characterisation as well as the temperature regulation of sphingolipids and Δ8-sphingolipid desaturase from O. tauri . Complex sphingolipids are glycosylceramides with unique glycosyl moieties encompassing hexuronic acid residues, reminiscent of bacterial glucuronosylceramides, with up to three additional hexose residues. In contrast, the ceramide backbones show limited variety, with dihydroxylated C18/C18:1 EΔ8 sphingoid bases and C16:0 fatty-acyl chain being the main compounds. The sphingolipid Δ8-desaturase from O. tauri , although phylogenetically related to plant homologues has a substrate preference similar to the diatom homologue. Both sphingolipid Δ8-desaturase transcripts and sphingolipid Δ8-unsaturation are regulated in a temperature- dependent manner being higher at 14°C than 24°C. Overexpressing the sphingolipid Δ8- desaturase in O. tauri at 24°C results in higher sphingolipid unsaturation and impairs the increase in cell size, structure and chlorophyll. In particular, the cell-size defect is not detected in cells acclimated to 14°C and is furthermore suppressed upon transfer from 24°C to 14°C. Our work provides the first functional evidence for the involvement of sphingolipid Δ8-unsaturation for temperature acclimation in microalgae, suggesting that this function is an ancestral feature in the green lineage
Measuring short-range correlations and quasi-elastic cross sections in A(e,e') at x>1 and modest Q
No full textInternational audienceWe present results from the Jefferson Lab E08-014 experiment, investigating short-range correlations (SRC) through measurements of absolute inclusive quasi-elastic cross sections and their ratios. This study utilized 3.356 GeV electrons scattered off targets including H, He, He, C, Ca, and Ca, at modest momentum transfers () did not yield a clear plateau; instead, the data diverged from the predicted 3N-SRC behavior as momentum transfer increased. However, when analyzed in terms of the struck nucleon's light-cone momentum, the data exhibited the opposite trend, progressively approaching the predicted 3N-SRC plateau. These observations suggest that future measurements at higher energies may facilitate a definitive isolation and identification of 3N-SRCs