HAL Université de Toulouse, et Toulouse INP
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The affine geometry of meromorphic connections with irregular singularities
No full textA meromorphic connection on the tangent bundle of a Riemann surface induces a complex affine structure on the complement of the poles. Local models for Fuchsian singularities are already known. In this paper, we introduce a complete set of local invariants for a meromorphic connection and provide local models for a complex affine structure in a punctured neighborhood of an irregular singularity. Generalizing a construction attributed to Veech, we introduce the Delaunay decomposition of a compact Riemann surface endowed with a meromorphic connection with irregular singularities. In particular, we give upper bounds on the complexity of the decomposition
Minimization of Chemical Kinetic Reaction Set for System-Level Study of Non-Thermal Plasma NOx Abatement Process
No full textInternational audienceA system-level study of a NOx abatement process by means of non-thermal plasma (NTP) generated with dielectric barrier discharges (DBDs) is the framework of this article. With the goal of system improvement, the kinetic reaction simulation software ZdPlaskin is considered to select the most favorable operating conditions in order to optimize NOx abatement (deNOx). A parametric exploration of the performance, through variations in operating conditions (temperature, power injection pattern, and input gas mixture composition), requires highly numerous simulations; thus, the shortest possible computation times with robust results are of significant interest. As such, an analysis and filtering method is proposed and detailed to build a minimized chemical kinetic reaction set, allowing us to reliably analyze the impact of the selected operating conditions for the DBD reactor on treatment performance
Experimental analysis and modeling of an acrylic thermoplastic resin polymerization: Influence of reactive mixture composition on temperature dependent kinetics
No full textInternational audienceManaging the in-situ polymerization of reactive thermoplastic mixtures represents a key challenge for themanufacture of thick composite parts. In particular, the highly exothermic free-radical polymerization of methylmethacrylate (MMA) exhibits complex kinetic phenomena, including the Trommsdorff effect, which arises fromdiffusional limitations. In this work, the reaction kinetics of Elium® C195E reactive mixtures were investigatedby differential scanning calorimetry (DSC) under various isothermal and non-isothermal conditions. Power-compensated DSC and low-mass samples ensured minimal temperature rise caused by the exothermic natureof the reaction, thus enabling the polymerization to be analyzed from a purely kinetic angle. By varying thenature and initial quantity of peroxide initiators, the influence of the available active chain amount on theoccurrence and intensity of the various polymerization phases could be highlighted. With a view to processingoptimization, a time and temperature dependent kinetic model was then developed to simulate the reaction rateof this acrylic resin initiated by 3 different organic peroxides. Based on the reaction scheme, this semi-empiricalmodeling approach yields highly accurate predicting results and enables to account for the occurring phenomenaduring MMA polymerization in isothermal ([343–383] K) and dynamic conditions ([1–20] K. min 1). This modeltherefore provides valuable support for the manufacture of Elium® matrix composites and thus limits issuesresulting from medium overheating
Euclid preparation. Predicting star-forming galaxy scaling relations with the spectral stacking code SpectraPyle
No full textInternational audienceWe introduce SpectraPyle, a versatile spectral stacking pipeline developed for the Euclid mission's NISP spectroscopic surveys, aimed at extracting faint emission lines and spectral features from large galaxy samples in the Wide and Deep Surveys. Designed for computational efficiency and flexible configuration, SpectraPyle supports the processing of extensive datasets critical to Euclid's non-cosmological science goals. We validate the pipeline using simulated spectra processed to match Euclid's expected final data quality. Stacking enables robust recovery of key emission lines, including Halpha, Hbeta, [O III], and [N II], below individual detection limits. However, the measurement of galaxy properties such as star formation rate, dust attenuation, and gas-phase metallicity are biased at stellar mass below log10(M*/Msol) ~ 9 due to the flux-limited nature of Euclid spectroscopic samples, which cannot be overcome by stacking. The SFR-stellar mass relation of the parent sample is recovered reliably only in the Deep survey for log10(M*/Msol) > 10, whereas the metallicity-mass relation is recovered more accurately over a wider mass range. These limitations are caused by the increased fraction of redshift measurement errors at lower masses and fluxes. We examine the impact of residual redshift contaminants that arises from misidentified emission lines and noise spikes, on stacked spectra. Even after stringent quality selections, low-level contamination (< 6%) has minimal impact on line fluxes due to the systematically weaker emission of contaminants. Percentile-based analysis of stacked spectra provides a sensitive diagnostic for detecting contamination via coherent spurious features at characteristic wavelengths. While our simulations include most instrumental effects, real Euclid data will require further refinement of contamination mitigation strategies
Solar and Stellar Activity
No full textInternational audienceThis chapter provides an overview of the magnetic activity of the Sun and stars, discussing its underlying physical origin, manifestations, and fundamental role in exoplanet studies. It begins with a summary of the Sun's magnetic activity from the surface towards the outer atmospheric layers, highlighting features such as sunspots, faculae, chromospheric structures, and their temporal modulation known as the activity cycle. These phenomena are sustained throughout the lifetime of the Sun by the magnetic dynamo, which is driven by differential rotation and convective flows. Furthermore, extending these concepts to other stars, the chapter examines the diagnostics that are typically employed to track and quantify the magnetic activity level of stars, and it reviews spectropolarimetry, an observational technique with which to characterise stellar magnetic fields. We finally outline results from both observations and theoretical modelling of stellar activity across distinct spectral types, and we describe the variety of methods used to search for stellar activity cycles, underscoring the multi-wavelength nature of this field of research
Stable magnetic fields and changing starspots on Vega: An ultra-deep decadal survey at Pic du Midi and OHP
No full textInternational audienceAims. Monitoring magnetic and activity variations in A and B stars with ultra-weak magnetic fields is essential to our understanding of the origin and evolution of these fields in this domain of the Hertzsprung-Russell (HR) diagram. Vega is a prototype star of its type and its long-term monitoring offers the most promising opportunity to study these properties.Methods. High-resolution spectrocopic and spectropolarimetric data were gathered with SOPHIE/OHP in 2018 and NARVAL/NEO-NARVAL/TBL in 2018, 2023, and 2024. A total of 13 108 individual spectra of Vega were obtained, which are the basis for the analysis carried out in this work. Magnetic field maps were reconstructed with the Zeeman-Doppler imaging (ZDI) method, while activity maps were reconstructed with an innovative code built for this purpose. These maps were compared to previous results.Results. The rotation period of Vega was confirmed to be very close to the former reference period of 0.678 d. The average magnetic field confirms a negative spot of radial field on the pole with stable strength, while the magnetic maps confirm the long-term stability of an oblique dipole, as well as smaller magnetic features showing up consistently throughout our three observing epochs. However, brightness maps show strong variations of the spot location over a timescale of years (and possibly even shorter). The spot contrast is shown to be very similar in the observations from 2012, 2018, 2023, and 2024, with a normalised spectral amplitude of 0.0003. A direct correlation between the magnetic field and brightness patches could not be revealed in the simultaneous SOPHIE and NARVAL 2018 dataset.Conclusions. Vega’s so-called magnetic mystery has gained complexity since indications point towards the presence of a fossil magnetic field, but also to the presence of a dynamo-generated field, most likely concentrated on equatorial regions
Embedding peer assessment in MCQs has improved immediate performance but increased task duration without enhancing transfer
No full textInternational audienceIntroduction: Multiple-choice questions are widely used in higher education and online training because of their scalability. This study examines whether incorporating peer assessment, such as evaluating written explanations accompanying students’ answers, can increase students’ cognitive engagement and improve learning outcomes in asynchronous settings.Methods: One hundred undergraduate science students were randomly assigned to three groups and completed a series of conceptual questions on an online platform. Group A responded to standard multiple-choice questions. Group B additionally evaluated fictional peer explanations using agreement ratings. Group C additionally provided written feedback. All participants completed four experimental questions followed by five transfer questions. Completion time and performance at each phase were recorded.Results: Students in both peer assessment groups demonstrated significant gains between initial and revised answers. A linear regression revealed a significant effect of the peer assessment type on immediate performance, with written feedback benefiting low-performing students more markedly. However, no group outperformed the control in the transfer questions. Task duration increased significantly with peer assessment, particularly for the group providing written comments.Discussion: Embedding peer assessment appears to enhance immediate MCQ performance, especially when students are required to articulate written feedback; however, it did not improve transfer performance and significantly increased task duration. The absence of measurable gains in conceptual learning raises questions about the cost–benefit ratio of such interventions in time-constrained educational settings. Further research is warranted to delineate the conditions under which such interventions yield long-term benefits
Agir sur la génétique de l’hôte pour moduler la composition du microbiote : exemple chez le porc
No full textInternational audienceLes populations de microorganismes qui forment le microbiote sont caractérisée par leur diversité, les abondances relatives des genres bactériens ou leur assemblage en écosystèmes. Le rôle du microbiote, en particulier le microbiote intestinal, sur les performances de l’hôte est de mieux en mieux documenté chez les animaux d’élevage. Comprendre l’influence des caractéristiques de l’hôte et analyser les interactions hôte-microbiote est encore un vaste champ d’étude. En prenant comme exemple le porc, des résultats expérimentaux montrent les voies possibles de l’utilisation de leviers génétiques pour influencer la composition du microbiote. L’objectif, à terme, est d’élaborer des stratégies de sélection des populations animales en prenant en compte le microbiote pour mieux comprendre, prédire et piloter les phénotypes de l’hôte
Study on EM Interferences Due to LED Lighting Sources and Their Impacts on the Railway Telecommunication System in Ukraine
No full textInternational audienceThis article reports a significant malfunction that occurred following the installation of light-emitting diode lighting fixtures in railway communication stations in Ukraine. Severe disturbances on railway automatics and telecommunications were observed, linked to the poor quality of the light-emitting diode lighting fixtures, which induce disturbances of several types, either on the electrical network by producing harmonics or through electromagnetic radiation emissions, which can result either directly impacting the telecommunications devices or indirectly affecting electronic circuits or communication lines near the two devices. Investigations are currently underway; this article is a first approach presenting a range of disturbances that can be caused by LED luminaires that do not comply with electromagnetic interference standards, as well as the determination and calculation of the technical characteristics of EM shielding to overcome these problems