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Euclid Quick Data Release (Q1): Hunting for luminous z > 6 galaxies in the Euclid Deep Fields -- forecasts and first bright detections
No full textInternational audienceThe evolution of the rest-frame ultraviolet luminosity function (UV LF) is a powerful probe of early star formation and stellar mass build-up. At z > 6, its bright end (MUV 6 Lyman break galaxies (LBGs) and constrain the UV LF's bright end. With NIR coverage extending to 2um, Euclid can detect galaxies out to z = 13. We present forecasts for the number densities of z > 6 galaxies expected in the final EDF dataset. Using synthetic photometry from spectral energy distribution (SED) templates of z = 5--15 galaxies, z = 1--4 interlopers, and Milky Way MLT dwarfs, we explore optimal selection methods for high-z LBGs. A combination of S/N cuts with SED fitting (from optical to MIR) yields the highest-fidelity sample, recovering >76% of input z > 6 LBGs while keeping low-z contamination 10 sources. Based on empirical double power-law LF models, we expect >100,000 LBGs at z = 6-12 and >100 at z > 12 in the final Euclid release. In contrast, steeper Schechter models predict no z > 12 detections. We also present two ultra-luminous (MUV 9, highlighting Euclid's power to constrain the UV LF's bright end and identify the most luminous early galaxies for follow-up
Non-Hermitian topology in the quantum Hall effect of graphene
No full textQuantum Hall phases have recently emerged as a platform to investigate non-Hermitian topology in condensed-matter systems. This platform is particularly interesting due to its tunability, which allows to modify the properties and topology of the investigated non-Hermitian phases by tuning external parameters of the system such as the magnetic field. Here, we show the tunability of non-Hermitian topology chirality in a graphene heterostructure using a gate voltage. By changing the charge carrier density, we unveil some novel properties specific to different quantum Hall regimes. First, we find that the best quantization of the non-Hermitian topological invariant is interestingly obtained at very high filling factor rather than on well-quantized quantum Hall plateaus. This is of particular importance for the efficient operation of devices based on non-Hermitian topology. Moreover, we observe an additional non-Hermitian topological phase in the insulating nu=0 quantum Hall plateau, which survives at lower fields than the opening of the nu=0 gap, confirming a recent prediction of a disorder-induced trivial phase. Our results evidence graphene as a promising platform for the study of non-Hermitian physics and of emergent phases in such topological devices
Diode-pumped orange Sm:LiYF<sub>4</sub> lasers emitting at 605 nm
No full textInternational audienceWe report on the first visible orange samarium laser directly pumped by a blue 465-nm GaN semiconductor laser diode. The diode-pumped continuous-wave Sm:LiYF4 laser delivers 23.9 mW at 605 nm (4G5/2 → 6H7/2 transition) with a slope efficiency of 9.4%, a laser threshold of 385 mW and a linear polarization (π). We investigate the impact of pump beam quality on laser performance and revisit the polarized spectroscopic properties of Sm3+ ions in the LiYF4 crystal. The stimulated-emission cross-section σSE amounts to 1.27 × 10−20 cm2 at 604.8 nm for π-polarized light, and the luminescence lifetime of the 4G5/2 level is 4.02 ms for 1.1 at.% Sm-doping. Our work represents a proof-of-principle for compact low-threshold diode-pumped orange and red samarium lasers
Recommandations pour l'adoption des identifiants persistants dans l'enseignement supérieur et la recherche
No full textLe paysage actuel de la recherche produit un volume croissant de publications, de données et, plus largement, de résultats et objets scientifiques (numériques et/ou physiques) diversifiés. Dans ce contexte, la capacité à identifier de manière unique et fiable les différents éléments de l'écosystème scientifique – équipes de recherche, publications, ensembles de données, logiciels, etc. - à travers une multiplicité de systèmes d’information, est devenue un enjeu central pour la structuration et la valorisation de l’activité scientifique notamment pour permettre une traçabilité des objets scientifiques.Les identifiants persistants (PID – Persistent Identifiers) répondent à cet enjeu. Il s’agit de codes numériques ou alphanumériques, uniques et permanents, lisibles à la fois par l’homme et par la machine. Contrairement aux adresses URL, susceptibles de changer ou de devenir obsolètes, les PIDs sont conçus pour constituer des références durables, assurant la stabilité de l’accès à une entité (numérique ou non). Ils permettent ainsi son identification, sa découverte, sa traçabilité et sa citation normalisée, tout au long du cycle de la recherche.L’usage des PIDs participe directement à la mise en œuvre des principes FAIR (Findable, Accessible, Interoperable, Reusable), en rendant les objets numériques plus facilement repérables, accessibles, interopérables et réutilisables. Par ailleurs, ils favorisent l'automatisation des échanges de données entre systèmes d'information, contribuant à la simplification administrative, dans une logique de réutilisation et de non-duplication des informations ("Dites-le nous une fois"). À ce titre, les PIDs sont indispensables pour garantir la durabilité, la cohérence et l’interopérabilité des données dans les environnements numériques, notamment ceux de l’enseignement supérieur et de la recherche.La reconnaissance des PIDs comme instruments structurants de la science ouverte s’inscrit dans une dynamique internationale. Plusieurs initiatives convergent en ce sens, notamment la feuille de route pour la science ouverte du gouvernement fédéral canadien , les orientations de l’Office of Science and Technology Policy (OSTP) aux États-Unis , ou encore la politique PID développée dans le cadre de l’European Open Science Cloud (EOSC) . Le Royaume Uni et l’Australie ont mesuré les bénéfices de l’adoption des PIDs en termes de nombre de jours de travail administratif évités par les chercheurs . Ces pays, ainsi que la Finlande, le Canada, les Pays-Bas, l’Allemagne, la République tchèque, la Corée du Sud et la Nouvelle-Zélande se sont dotés de politiques ou de feuilles de route en la matière pour améliorer la qualité et l'efficacité de la recherche . Le Pacte pour la recherche du G7 (2021) engage également les pays membres à renforcer la disponibilité, la durabilité, l’interopérabilité et l’accessibilité des données, technologies et infrastructures scientifiques . Enfin, les PIDs sont explicitement mentionnés dans les recommandations de l’UNESCO sur la science ouverte, en tant qu’éléments fondamentaux pour une gouvernance ouverte, fiable et durable de la recherche .L’ensemble de ce document s’inscrit dans le cadre des travaux initiés en 2024 par le MESR autour de la feuille de route des « Données pour la simplification et le pilotage de la recherche », dont les principes directeurs visent à garantir la circulation et l’interopérabilité des données, tout en respectant le principe d’autonomie des établissements. Cette feuille de route repose sur un plan d’action élaboré collectivement par les parties prenantes et s’appuie sur le principe « dites-le-nous une fois », qui illustre la volonté d’alléger le fardeau administratif des équipes de recherche, en s’appuyant sur un ensemble de données qualifiées à partager entre les systèmes d’information, selon des standards et principes de qualité communs et une gouvernance collective. Les objectifs visés sont l’interopérabilité accrue entre systèmes, la consolidation et la fiabilité des données partagées, une meilleure coordination entre tutelles et la réduction des collectes et enquêtes répétitives. Dans ce contexte, les identifiants persistants jouent un rôle clé pour assurer l’interopérabilité des données des systèmes hétérogènes de l’ESR, en garantissant traçabilité, fiabilité et réutilisabilité des informations
Polymer conformation changes observed with the naked eye in a liquid crystal elastomer and their use to produce adjustable and multidirectional deformations
No full textThe monodomain nematic liquid crystal elastomer (LCE) is a nonporous material with one-dimension (1D) negative thermal expansion (NTE) along the direction of orientation. This stimuli-responsive size change is comparable with the contractile response of a muscle fibre. Recently, LCEs have become more and more popular and increasingly investigated as a full-fledged class of stimuli-responsive materials.However, the nematic LCE is limited to a single, unidirectional deformation unless complex hybrid architectures are made. We develop here a special LCE based on a liquid crystal polymer with an extraordinary phase transition sequence, "re-entrant nematic (NRe) -smectic A (SmA) -nematic (N) -isotropic (I) phase", along with "prolate -oblate -weakly oblate -spherical" chain conformation evolution. In the aligned LCE film, these conformational changes of polymer chain are observed with the naked eye through their macroscopic translations into a unique sequence of "contraction -expansion -second expansion" deformations. Notably, a switch from NTE to positive thermal expansion (PTE) occurs upon heating. Moreover, a bilayer actuator composed of aligned and non-aligned LCE layers can perform 2D to 3D shape transformation with "curling -uncurling -second uncurling" actuation sequence. This LCE capable of multiple deformations in response to a single stimulus paves the way to multimodal single-material actuators. It provides a new strategy for the development of advanced materials with adjustable and multidirectional deformations.</div
Édition numérique, inclusive et critique du fonds patrimonial de l’Association Valentin Haüy, en partenariat avec la Sorbonne et le CNRS
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Étude numérique de la transition laminaire-turbulent sur un engin hypersonique en conditions de vol et de soufflerie
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A Neural Network Approach for Online Reconstruction of Bremsstrahlung Spectra Produced by Electron Accelerator
No full textInternational audienceThe characterization of bremsstrahlung spectra generated by electron accelerators is becoming increasingly crucial, particularly in radiation processing applications such as sterilization of medical devices or food irradiation. The growing transition from isotopic to electric irradiators presents new challenges related to the control of beam properties. In this context, the technology resource center Aerial in collaboration with CEA/IRESNE and IPHC is looking to develop a tool and methodology enabling the online characterization of the bremsstrahlung spectra generated in its feerix[1] installation. This step is very important for their irradiation operations to ensure precise dose deposition in the sample and to precisely estimate the activation product when the photon energy exceeds the photonuclear reaction threshold. Information on the energy spectrum is also a key input for Monte Carlo simulations, which are increasingly used in radiation processing. However, conventional direct and indirect spectrometry methods are limited in meeting the challenges of Aerial’s high energy and high-power irradiation platform. In this study, we propose a new theoretical approach based on neural networks to solve an ill-posed inverse problem, enabling the reconstruction of bremsstrahlung spectra from depth-dose measurements. This approach is motivated by the limitations of previously discussed regularization methods and existing neural network approaches. We focus here on an analytical approach for generating realistic training and validation datasets, consisting of Bremsstrahlung spectra and their corresponding dose distributions in any medium. This neural network approach will also be compared with other methods reported in the literature.Key words: Electron accelerator / Bremsstrahlung spectra / Inverse method / Unfolding / Deep Learning / Neural Networ
Mitigating imaging systematics for DESI 2024 emission Line Galaxies and beyond
No full textInternational audienceEmission Line Galaxies (ELGs) are one of the main tracers that the Dark Energy Spectroscopic Instrument (DESI) uses to probe the universe. However, they are afflicted by strong spurious correlations between target density and observing conditions known as imaging systematics.In this paper, we present the imaging systematics mitigation applied to the DESI Data Release 1 (DR1) large-scale structure catalogs used in the DESI 2024 cosmological analyses. We also explore extensions of the fiducial treatment. This includes a combined approach, through forward image simulations (Obiwan) in conjunction with neural network-based regression, to obtain an angular selection function that mitigates the imaging systematics observed in the DESI DR1 ELGs target density.We further derive a line of sight selection function from the forward model that removes the strong redshift dependence between imaging systematics and low redshift ELGs. Combining both angular and redshift-dependent systematics, we construct a three-dimensional selection function and assess the impact of all selection functions on clustering statistics. We quantify differences between these extended treatments and the fiducial treatment in terms of the measured 2-point statistics. We find that the results are generally consistent with the fiducial treatment and conclude that the differences are far less than the imaging systematics uncertainty included in DESI 2024 full-shape measurements.We extend our investigation to the ELGs at 0.6 < z < 0.8, i.e., beyond the redshift range (0.8 < z < 1.6) adopted for the DESI clustering catalog, and demonstrate that determining the full three-dimensional selection function is necessary in this redshift range.Our tests showed that all changes are consistent with statistical noise for BAO analyses indicating they are robust to even severe imaging systematics. Specific tests for the full-shape analysis will be presented in a companion paper
Spectral phase control for optimized ionization injection in laser wakefield acceleration
No full textInternational audienceGenerating narrow energy spread beams from laser wakefield accelerators with minimal dark current is important for many applications. We present an automated experiment using Bayesian optimization to control the laser spectral phase and focal position, where beam quality was significantly enhanced. Starting from a broadband spectrum, the optimized configuration achieved low energy spread with negligible dark current above 20 MeV. Particle-in-cell simulations reveal that fine control over the laser spectral phase, particularly third-order dispersion, directly impacts the timing and localization of ionization injection due to its effect on the initial laser intensity envelope and its subsequent evolution. A positively skewed temporal profile enhances the plasma potential depth at the right location, enabling localized injection and reducing the energy spread and dark current. These findings highlight the impact of algorithmic optimization and the powerful, underutilized role of temporal shaping in beam quality control