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Segregation of hydrogen on screw dislocations in tungsten and its impact on dislocation mobility
No full textInternational audienceWe investigate the interaction between hydrogen atoms and 1/2 screw dislocations in tungsten combining density functional theory (DFT) calculations and molecular dynamics (MD) simulations using a newly developed machine learning (ML) potential trained on ab initio data. Our study reveals two distinct hydrogen-decorated dislocation core structures: the previously known hard core configuration and a newly characterized easy core configuration. DFT calculations indicate comparable dislocation-hydrogen interaction energies for both cores, suggesting a potential competition between these configurations. Ising models, parameterized on DFT data are employed to predict hydrogen segregation profiles for both core configurations, and the results are corroborated by MD simulations. Free energy analyses and finite-temperature MD simulations indicate that the hydrogen-decorated hard core is thermodynamically favored over a wide range of temperatures and hydrogen concentrations. The mobility of this stable hydrogen-decorated hard core structure is assessed by evaluating energy barriers through DFT calculations and performing MD simulations under applied stress. Both approaches consistently show that hydrogen segregation on the hard core structure significantly reduces dislocation mobility, leading to a locking of screw dislocations
A new beam monitor at NFS/SPIRAL2 based on position-sensitive PPACs detecting fission fragments from <math altimg="si2.svg" display="inline" id="d1e235"><msup><mrow/><mrow><mn>238</mn></mrow></msup></math>U<math altimg="si3.svg" display="inline" id="d1e243"><mrow><mo>(</mo><mi>n</mi><mo>,</mo><mi>f</mi><mo>)</mo></mrow></math>
No full textInternational audienceA new experimental setup has been installed at the Time-Of-Flight area of the Neutrons For Science facility (NFS) at GANIL/SPIRAL2 for neutron beam monitoring. This setup consists of an array of Position-Sensitive Parallel-Plate Avalanche Counters (PS-PPACs) that detects both fission fragments in coincidence from secondary neutron-induced fission reactions in several 238U targets. The neutron energy is determined on an event-by-event basis using the Time-of-Flight method, and the reaction point within the U targets is reconstructed, enabling the measurement of the neutron beam flux and beam profile. The high transparency of the setup allows it to operate in parallel with other experiments running at NFS, thus providing an in-beam monitor of the neutron intensity. In this work, we report on the characteristics of this new setup, its operating principle, and the first results obtained using the high-intensity white-spectrum neutron beam at NFS. This beam is produced via reactions between a primary 40-MeV deuteron beam, accelerated in the SPIRAL2 LINAC, and a 8 mm-thick rotating beryllium converter target
StripesCounter: A new image software for increment measurement in paleoclimate archives
No full textInternational audienceMost natural paleoclimate archives are accretionary material presenting periodic structures that bear environmental and/or chronological information. Here we present StripesCounter, an open access Python software designed for automated banding detection and measurement. As a study case, 16-year long profiles of daily growth increment measurements were conducted on a modern shell of the giant clam Tridacna gigas. High resolution images of shell thin sections were obtained using a confocal laser scanning microscopy and processed using StripesCounter. We demonstrate that StripesCounter provides highly reproducible and accurate results. The long time series of daily increments indicate that Tridacna gigas growth is strongly modulated by seasonal oceanographic variations, reflecting changes in sea surface temperature, precipitation, and salinity. Notably, growth profiles reveal semi-annual variations related to semi-annual variations in environmental factors, potentially linked to ENSO events. This automated growth increment analysis can be extended to other archives with cyclic structures, including tree rings, corals, and other biogenic or abiotic laminated materials. StripesCounter offers a powerful and accessible tool for generating long high-resolution, temporally explicit datasets, opening new perspectives for investigating rapid environmental changes across diverse ecosystems and geological timescales
Weak Scale Triggers in the SMEFT
No full textInternational audienceThere are no weak scale triggers in the SMEFT up to dimension six that can solve the hierarchy problem far above the weak scale. Our arguments can be used to show that the same is true at dimension eight. Weak scale triggers are local operators sensitive to the Higgs mass squared and they are needed in a large number of qualitatively different cosmological solutions to the hierarchy problem. These solutions have little in common besides the use of a trigger operator. We argue that focusing on the signatures of the three already-known trigger operators can lead to discover or exclude this class of solutions to the hierarchy problem
Kinematic lensing with high-resolution spectroscopic surveys. A unique opportunity for transformative cosmology at high redshifts in the 2040s
No full textInternational audienceWe present a science case to perform high-redshift cosmic shear surveys for cosmology with next-generation spectroscopic instruments, such as the proposed MegaMapper and Wide-field Spectroscopic Telescope. We argue that by using the novel technique called 'kinematic lensing' (KL) it will be possible to obtain shear catalogues at redshifts between 2 and 5. We show that the signal-to-noise ratio of KL at such high redshifts is on average twice as much that expected from current weak lensing (WL) surveys such as Euclid or LSST, and several times that of the previous generation of WL surveys like DES and KiDS, even with very conservative assumptions about the fraction of spectroscopically-detected sources for which KL shear estimates will be available. This will allow cosmologists to perform joint galaxy clustering-cosmic shear analyses over unprecedented cosmic volumes and to probe the growth of structures deep in the matter-dominated era and across the onset of dark-energy domination, offering a unique opportunity to unveil the mystery of cosmic acceleration
Metrological concepts applied to Total Alkalinity measurements in seawater: reference materials, inter-laboratory comparison and uncertainty budget
No full textInternational audienceAbstract. Total alkalinity (TA) measurements in seawater are crucial for characterizing and monitoring the oceanic carbonate system. While international best practices and guidelines exist, the field still lacks widely available traceable reference materials and a well-established uncertainty budget of the measurement method. In this study, we applied key metrological principles – development of reference materials, inter-laboratory comparison and uncertainty quantification – to TA measurements. We developed two reference materials, including an artificial material with a rigorously characterized reference value and an associated uncertainty budget, being traceable to the International System of units (SI). These materials were tested in an inter-laboratory comparison involving five laboratories and demonstrated the applicability of the reference materials developed for quality control. Additionally, we established an uncertainty budget for the TA measurement method using two metrological approaches. The resulting expanded uncertainty was 5 µmol kg−1 (with a coverage factor k=2) in TA, approaching the 4 µmol kg−1 target set by the Global Ocean Acidification Observing Network for climate monitoring. These findings mark a significant step toward improving the quality and comparability of TA measurements, thereby strengthening long-term ocean carbonate system monitoring
Impact of finite-range spin-orbit and tensor terms in Gogny EDF on structure and fission properties
No full textInternational audienceEnergy Density Functionals are of major interest for the study of the atomic nucleus as, coupled with mean-field and beyond N-body approaches, they are applicable to the whole nuclear chart, including superheavy elements. On the one hand, the growing need for nuclear data and, on the other hand, the large amount of experimental data on exotic nuclei explain the work carried out on these phenomenological forms of the nucleon-nucleon interaction to analyze the richness of the nuclear phenomena. In this paper, we propose a fully finite-range extension of the Gogny EDF, including a short-range spin-orbit term and a long-range tensor term. The original fitting protocol of the Gogny interaction has been adapted to include both finite range spin-orbit and tensor terms, adding new constraints and filters linked to relevant data. Nuclear matter, spectroscopic and fission properties are discussed, highlighting ways of improving EDFs when all spin and isospin exchanges are introduced with finite-range terms
Measurements of the proton-induced reaction 155Gd(p,n)155Tb at energies between 7 and 26 MeV with highly-enriched 155Gd targets
No full textInternational audienceBackground The need for new medical radionuclides continues to grow as treatments become more personalised. Terbium-155, a gamma emitter, is an appealing isotope that could be used for Single Photon Emission Computed Tomography (SPECT). Since it belongs to the Terbium quadruplet, it could be coupled with other Tb isotopes to form a theranostic pair. However, it is currently not accessible in sufficient quantities with an acceptable radionuclidic purity. An investigation of the excitation function of the nuclear reaction 155Gd(p,n) over an energy range accessible to most medical cyclotrons is relevant for optimizing 155Tb production. For the first time, we report the measurements of this reaction with highly enriched (> 99.0%) 155Gd targets. Methods Pure 155Gd targets, with isotopic enrichment better than 99%, have been produced using the highperformance electromagnetic separator SIDONIE at IJClab, Orsay, France. Proton activation measurements have been performed using two different cyclotrons and a linear accelerator (linac). Results The full excitation function of 155Gd(p,n)155Tb has been obtained over the 7-26 MeV range. All 18 measured cross-sections are consistent with each other, without the need of any renormalization. All the obtained data were compared with already published results and clearly show a maximum production at 11 MeV, with a cross section of 500 mb. Conclusion Experimental data indicates excitation function maximum around 11 MeV for the studied energy range, and cross sections are greater when target purity in 155Gd is higher
An adaptive quasi-neutrality solver for full-F flux-driven gyrokinetic simulations of tokamak plasmas in presence of poloidal asymmetries
No full textInternational audienceGyrokinetic codes are used to simulate transport in tokamak plasmas. In these codes, the distribution functions evolve self consistently with an electromagnetic field. To compute the temporal evolution of the electrostatic potential, a quasi-neutrality equation is solved. In some gyrokinetic codes, the quasi-neutrality solver assumes that the background densities and temperatures are constant in time and on flux surfaces. This assumption, which implicitly uses the so-called δF approach, can break up, in particular at the edge of the plasma which can display large and time evolving poloidal asymmetries.In this paper, a numerical solver of the quasi-neutrality equation accounting for time evolving poloidal asymmetries is presented. This solver is compatible with all electron models (adiabatic, kinetic or hybrid) and written for the long wavelength or the Padé approximations for the polarisation term. The impact of such an improvement is carefully reported on different types of simulations, illustrating when the δF approach forquasi-neutrality is valid and when it fails. A procedure to limit the numerical cost of updating the background profiles in the quasi-neutrality solver is also presented
Constraining primordial non-Gaussianity from DESI DR1 quasars and Planck PR4 CMB Lensing
No full textInternational audienceWe present the first measurement of local-type primordial non-Gaussianity from the cross-correlation between million spectroscopically confirmed quasars from the first data release (DR1) of the Dark Energy Spectroscopic Instrument (DESI) and the Planck PR4 CMB lensing reconstructions. The analysis is performed in three tomographic redshift bins covering , covering a sky fraction of . We adopt a catalog-based pseudo- estimator and apply linear imaging weights validated on noiseless mocks. Compared to previous analyses using photometric quasar samples, our results benefit from the high purity of the DESI spectroscopic sample, the reduced noise of PR4 lensing, and the absence of excess large-scale power in the spectroscopic quasar auto-correlation. Fitting simultaneously for the non-Gaussianity parameter and the linear bias amplitude in each redshift bin, we obtain for a response parameter , and for . These results improve the constraints on by compared to the previous analysis based on the Legacy Imaging Survey DR9. Our results demonstrate the statistical power of DESI quasars for probing inflationary physics, and highlight the promise of future DESI data releases