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Probing methane in Uranus’ upper stratosphere using HST observations of the 1280 Å Raman feature
No full textInternational audienceWe analysed far-ultraviolet (FUV) spectra of Uranus obtained by the HST STIS and COS instruments in 2012 and 2014, respectively, to determine the brightness of Raman-scattered Lyman-alpha (Ly α ) emissions centred at 1280 Å (hereafter, the Raman feature). The Raman feature is unique among the Solar System’s giant planets and forms in Uranus’ atmosphere due to weak vertical mixing of hydrocarbons with H 2 , leading to efficient Rayleigh–Raman scattering. Methane is the dominant hydrocarbon species on Uranus, and since it absorbs FUV radiation, it affects the Rayleigh–Raman scattering of Ly α photons by H 2 and, eventually, the brightness of the Raman feature. We derive a brightness of 20 −6 +1 R from the STIS data, which is similar to the brightness measured by Voyager 2 UVS during the 1986 flyby of Uranus, when considering the suggested recalibration of UVS measurements by a factor of ∼0.5. Based on the observed brightness, we constrain the upper altitude (pressure) level for the abundance of methane in the upper atmosphere using radiative transfer simulations that include resonant scattering by H, Rayleigh–Raman scattering by H 2 , and absorption by CH 4 . We considered the solar Ly α flux as the source of Ly α radiation at Uranus. We find that resonant scattering by H significantly affects Rayleigh–Raman scattering by H 2 and thus the modelled brightness of the Raman feature. We derive methane profiles by obtaining the simultaneous fit to the observed Ly α , as well as the 1280 Å brightness of Uranus. Methane appears to be depleted (number density becomes less than 1 cm −3 ) above the altitude (pressure) range of ∼478–515 km (4 × 10 −3 –2.4 × 10 −3 mbar), while the Ly α absorption optical depth reaches unity for methane in the altitude (pressure) range of ∼237–257 km (2.54 × 10 −1 –1.65 × 10 −1 mbar). When neglecting resonant scattering by H, the methane depletion must be deeper in the atmosphere at an altitude (pressure) of ∼395 km (1.4 × 10 −2 mbar), similar to previous findings based on Voyager 2 observations of the feature. The analysis of the Raman feature provides independent CH 4 constraints in the upper atmosphere for detailed photochemistry modelling and highlights the importance of UV instruments for the future Uranus Orbiter and Probe (UOP) mission
70 years of spectroscopy of the photosphere and the solar chromosphere at the Pic du Midi Observatory (1956-2026)
No full textDocument d'histoire des sciences en astrophysique, écrit pour les70 ans de spectroscopie du soleil à l'observatoire du Pic du MidiObservations of the solar corona at the Pic du Midi began with Bernard Lyot and his spectro coronagraph installed on the multi-purpose equatorial mount of the Baillaud cupola. It was not until 1956 that domes and instruments specifically dedicated to observations of the photosphere and the solar chromosphere appeared. On the occasion of the International Geophysical Year, a solar spectroscopy laboratory was created to the west of the Pic du Midi, based on two spectrographs of 4 m and 9 m focal length. In 1961 the turret dome appeared to the east of the Pic, later equipped with an 8 m spectrograph. Around 1965, the Baillaud dome finally specialized in the corona with a new table and new spectrographs. At the same time, a revolution in infrastructure took place at the Pic in a few years, which we present as well as the solar spectrographs and their goal
Steerable Thin-Film Electrode Array for Cochlear Implantation: Design and Development for Future Atraumatic Insertion
No full textInternational audienceDuring cochlear implant surgery, standard electrode arrays are inserted into the scala tympani to stimulate the spiral ganglion cells and rehabilitate hearing in deaf patients. However, conventional electrode arrays' stiffness and passive nature lead to potential trauma or incomplete insertion during the procedure. To overcome these limitations, an original steerable thin film electrode array (TFEA) has been developed. First, the twenty gold electrodes, distributed over a 25 mm length, with an average surface area of 0.16 mm2, are significantly larger than those of existing TFEAs. These larger electrode surface areas enable safe neural stimulation within charge density limits below the Shannon threshold. By adjusting the material thicknesses, the proposed TFEA offers tunable stiffness, enabling safer and more flexible insertion. The microfabrication process, using SU-8 negative photoresist thin films, is both cost-effective and straightforward. In addition, the ability to dynamically adjust the curvature of the TFEA during insertion into a 3D printed cochlea model using low voltage conducting polymer based micro-actuator has been demonstrated. This marks the first instance of electrode array insertion with adaptive curvature, minimizing contact with cochlear walls. Successful insertion was achieved, with a curvature angle close to 360°. This active TFEA has the potential to improve insertion control and reduce the risk of trauma during cochlear implantation
Efficient computational methods for the estimation of ideal points in social sciences
No full textEstimation of ideological positions among voters, legislators and social media users is central to many subfields in the social sciences. To achieve this, a particular class of Item-Response theory (IRT) models, called ‘ideal points’ models, employs a range of collective choice data: roll call votes, co-sponsorship records, social media engagement data, or word occurrences in speech. Estimation challenges in such models include model identification, data volume and sparsity, while inference robustness against noise is unknown, and ideological position measurements inherently lack ground truth data. These have led to several estimation approaches, from Markov Chain Monte Carlo (MCMC), which is computationally costly in large settings, to fast, albeit less flexible, factor analysis approximations. We formulate a unifying framework for a large family of ideal point models across disciplines and examine their computational complexity and accuracy under noisy data. We examine several synthetic scenarios and first introduce, from signal processing, the Iterated Conditional Modes estimation method for IRT models. Finally, we illustrate the applicability of our framework in a multi-dimensional ideal points inference problem for nearly 20,000,000 X (previously Twitter) users in France, the UK, and the US, along several ideology and issue dimensions calibrated with survey data
Towards the Giant Radio Array for Neutrino Detection (GRAND): the GRANDProto300 and GRAND@Auger prototypes
No full textInternational audienceThe Giant Radio Array for Neutrino Detection (GRAND) is a proposed multi-messenger observatory of ultra-high-energy (UHE) particles of cosmic origin. Its main goal is to find the long-sought origin of UHE cosmic rays by detecting large numbers of them and the secondary particles created by their interaction -- gamma rays, and, especially, neutrinos. GRAND will do so using large arrays of radio antennas that look for the radio signals emitted by the air showers initiated by the interactions of the UHE particles in the atmosphere. Since 2023, three small-scale prototype GRAND arrays have been in operation: GRAND@Nançay in France, GRAND@Auger in Argentina, and GRANDProto300 in China. Together, their goal is to validate the detection principle of GRAND under prolonged field conditions, achieving efficient, autonomous radio-detection of air showers. We describe the hardware, software, layout, and operation of the GRAND prototypes and show the first radio spectra measured by them. Despite challenges, the successful operation of the prototypes confirms that the GRAND instrumentation is apt to address the goals of the experiment and lays the groundwork for its ensuing stages
Préface e-N TEXTE-]S—On[-iMAGE / hommage à Claude Rutault
No full textInternational audienceQuand nous avons imaginé cet ouvrage collectif poursuivant les différents points d’interrogations soulevés pendant le colloque TEXTE & IMAGE 6 — Pour un nouveau contrat social de l’errance : entre Art[S], Territoire[S], Blockchain[S] et Crypto- monnaie[S] — qui s’était déroulé à La Valette2 en 2021, nous pensions encore avoir le temps. Le temps de développer avec Claude Rutault une extension de sa Définition / Méthode 169 AMZ par rapport à la blockchain ; le temps de vous offrir avec cette extension que nous avions intitulée [AMZ] U-P — avec un petit smiley nous tirant la langue — comme un pied de nez offert à la postérité autour de l’œuvre de cet artiste majeur de la fin du XXe siècle..
Anomalous thermal broadening in the Shastry-Sutherland model and SrCuBO
No full text5 pages, 5 figuresInternational audienceIn the quantum magnet SrCu(BO), an anomalous thermal broadening of the triplon modes has been measured at relatively low temperatures compared to the triplon gap using both inelastic neutron scattering and Raman spectroscopy. Given how accurately a broad variety of physical phenomena inSrCu(BO) are captured by the spin Shastry-Sutherland model, it remains an open question whether the anomalous thermal broadening is also an intrinsic feature of this minimal model. However, few techniques are available for computing the finite-temperature dynamics of strongly interacting many-body systems. To address this problem, we have developed a broadly applicable numerical simulation method based on matrix-product states to simulate dynamical spectral functions at nonzero temperatures accurately, detailed in a companion paper [Phys. Rev. B 113, 024406 (2026)]. Using this technique, we demonstrate that the experimentally observed broadening is captured by the Shastry-Sutherland model. Perturbative calculations identify the origin of this phenomenon as singlet bound two-triplon states being thermally excited at an energy scale small compared to the gap to the single triplon excitations at the experimentally relevant model parameters
Contre l’évidence de la langue. Apprendre à interroger sa langue en formation initiale et continue
No full textInternational audienceThis paper reports on training content aimed at questioning the French language from both inter- and intralingual perspectives, and at challenging the taken-for-granted assumptions of the school tradition, which tends to conceive of it as uniform. In initial teacher education, we show how canonical texts necessarily invite us to move beyond a traditional syntactic approach, requiring teacher educators to address language in a plural way by articulating the different strands of linguistic analysis. In continuing professional development, comparison serves as the guiding thread: whether the comparison is internal (across different stages of the language) or external (between languages), the goal is to arrive at linguistic analyses that account for certain acquisition difficulties (in speaking, reading, and writing; in both reception and production), while fostering in trainee teachers an open, thoughtful, and reflective stance toward language.La contribution rend compte de contenus de formation visant à interroger la langue française, dans une perspective inter-et intralinguale, et à aller contre les évidences de la tradition scolaire qui la conçoit de manière uniforme. En formation initiale, nous montrons comment les textes patrimoniaux invitent nécessairement à dépasser l'approche syntaxique traditionnelle, ce qui impose au formateur d'aborder la langue de manière plurielle, en articulant les différents pans de l'analyse linguistique. En formation continue, c'est le comparatisme qui sert de fil conducteur : que la comparaison porte en interne (sur différents états de langue) ou en externe (entre les langues), l'objectif est d'aboutir à des analyses linguistiques qui expliquent certaines difficultés d'acquisition (dans le parler-lire-écrire ; en situation de réception et de production), tout en faisant adopter aux enseignants en formation une posture ouverte, réfléchie et réflexive sur la langue
ADRC-based dual-loop control and stability analysis of stacked interleaved DC–DC buck converter for hydrogen production using PEM electrolyzer
No full textInternational audienceHydrogen production via water electrolysis, particularly using Proton Exchange Membrane (PEM) electrolyzers, is a key technology for advancing renewable energy integration. Ensuring a stable and efficient supply requires DC–DC converters capable of precise regulation under disturbances. This paper proposes a dual-loop Active Disturbance Rejection Control (ADRC) strategy for a stacked interleaved DC–DC converter supplying a PEM electrolyzer. The proposed ADRC enhances robustness against disturbances and improves system stability under dynamic conditions typical of RES-based microgrids. Simulation results demonstrate that the approach significantly improves voltage regulation and overall performance—achieving a settling time of 10 ms and limiting overshoot to 20.06%—thereby ensuring a reliable and efficient power supply for PEM electrolyzers in renewable energy applications
Impact of charge transfer inefficiency on transit light curves: A correction strategy for PLATO
No full textInternational audienceContext. PLATO is designed to detect Earth-sized exoplanets orbiting solar-type stars and to measure their radii (relative to the star radii) with an accuracy better than 2% via the transit method. Charge transfer inefficiency (CTI), a by-product of radiation damage to charge-coupled devices (CCDs), can jeopardise this accuracy constraint and therefore must be corrected to reach scientific requirements.Aims. We assessed and quantified the impact of CTI on transit depth measurements. Our objective was to demonstrate the need for CTI correction and to develop a correction strategy that restores CTI-biased transit depths with an acceptable residual within the accuracy budget.Methods. Using a calibration dataset generated with PLATOSim to simulate a realistic stellar field, we modelled the parallel overscan signal as the sum of exponential decays and used least-squares fitting to infer the number of trap species and initial estimates for the release times (τr,k). Smearing was then modelled with an exponential-plus-constant function and removed on a column-wise basis. We modelled the spatial variation in the trap density with a quadratic polynomial function of the radial distance from the centre of the focal plane. The polynomial coefficients (ap,k) of this model, the well-fill power index (β), and the release times (τr,k) were subsequently adjusted via an iterative application of the extended pixel edge response method combined with a CTI correction algorithm. This yielded the final calibration model that underpins our correction strategy.Results. In the worst-case scenario (8-year mission, high CTI impact zone), we found that CTI induced a bias of approximately 4% in the measured transit depth. The polynomial coefficients from our trap density model were then used to correct the CTI-affected transit depths. Our correction reduced the bias to a residual of 0.06%, which is comfortably within PLATO’s accuracy requirements.Conclusions. We quantified the CTI-induced bias in transit depth measurements and implemented a calibration strategy that incorporates spatial variations in trap density. From the calibrated parameters, we derived a correction scheme that brought the photometric measurements within PLATO’s noise budget, ensuring that the mission’s precision requirements are met