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Constraints on effective field theories via quadruple-differential angular decay rates from -channel single-top-quark production at TeV with the ATLAS detector
No full textInternational audienceEvents with -channel single top quarks are used to probe effective field theory operators in TeV proton-proton collision data corresponding to 140 fb recorded by the ATLAS detector at the Large Hadron Collider. An analysis method leveraging Fourier techniques applied to quadruple-differential decay rates based on observables containing angular information about the decays of the top quarks is used to achieve high sensitivity. The relevant effective field theory operators are those sensitive to top-quark decay and -channel production vertices. Their Wilson coefficients are tightly constrained, with results compatible with Standard Model predictions
Constraining the TeV gamma-ray emission of SN 2024bch, a possible type IIn-L from a red supergiant progenitor - Multiwavelength observations and analysis of the progenitor
No full textInternational audienceWe present very high-energy optical photometry and spectroscopic observations of SN 2024bch in the nearby galaxy NGC 3206 (∼20 Mpc). We used gamma-ray observations performed with the first Large-Sized Telescope (LST-1) of the Cherenkov Telescope Array Observatory (CTAO) and optical observations with the Liverpool Telescope (LT) combined with data from public repositories to evaluate the general properties of the event and the progenitor star. No significant emission above the LST-1 energy threshold for this observation (∼100 GeV) was detected in the direction of SN 2024bch, and we computed an integral upper limit on the photon flux of Fγ(> 100 GeV)≤3.61 × 10−12 cm−2 s−1 based on six nonconsecutive nights of observations with the LST-1, between 16 and 38 days after the explosion. Employing a general model for the gamma-ray flux emission, we found an upper limit on the mass-loss-rate to wind-velocity ratio of Ṁ/uw ≤ 10−4 M⊙/ yr s/km, although gamma-gamma absorption could potentially have skewed this estimation, effectively weakening our constraint. From spectro-photometric observations we found progenitor parameters of Mpr = 11 – 20 M⊙ and Rpr = 531 ± 125 R⊙. Finally, using archival images from the Hubble Space Telescope, we constrained the luminosity of the progenitor star to log (Lpr/L⊙) ≤ 4.82 and its effective temperature to Tpr ≤ 4000 K. Our results suggest that SN 2024bch is a type IIn-L supernova that originated from a progenitor star consistent with a red supergiant. We show how the correct estimation of the mass-loss history of a supernova will play a major role in future multiwavelength observations.Key words: supernovae: general / supernovae: individual: SN 2024bch / gamma rays: genera
Radiation screens and their impact on air temperature measurement: a review
No full textInternational audienceOutdoor air temperature measurements are essential to be applied to agriculture, meteorology, hydrology, and urban planning. Precise measurements are particularly needed in the lower troposphere where the existence of large temperature gradients is prevalent. Urban temperature observation has been an area of research concern in recent years, particularly to study the urban heat island effect, local overheat, and heat reduction measures. Temperature readings most often employ sensors housed in protective shields. Low thermal inertia and fastresponding thermocouples and platinum probes, though less accurate, are two sensor types that are common. Shielding is used to minimize error by protecting sensors from precipitation and direct sunlight and allowing ventilation. Poor shielding can generate large temperature differences, over +4°C. Different shielding designs, such as Stevenson screens, Gill shields, and aspirated shelters, are investigated. Shielding efficiency depends upon their optical property, ventilation, and design. Correction methods like empirical corrections, numerical models including CFD, and neural network are also being considered to maximize data accuracy over urban areas. This paper offers an overview of studies that investigate radiation shields used for the measurement of external air temperatures and compare their performance in terms of various attributes. The methodology for selecting studies is presented first, encompassing field measurements, laboratory experiments, and numerical models. An inter-comparison of literature is then conducted, distinguishing commercially manufactured and home-made shields, ventilated and non-ventilated designs, and other significant features such as shape, size, optical properties, and materials. Errors in measurements, their reasons, and the procedures for correcting them are treated with special care
Legacy of snow cover on alpine landscapes
No full textInternational audienceOver the past four decades, seasonal snow cover has declined rapidly in temperate alpine regions. However, the fine-scale dynamics of snowmelt preceding the ongoing warming period remain largely unknown, limiting our understanding of the long-term influence of past snow cover on alpine ecosystems. Here we rely upon the spatial similarities in melt-out patterns and a temperature-based model of fractional snow cover area, to reconstruct fine-scale snow cover changes over the past 250 years in instrumented catchments of the southwestern Alps. We provide evidence that, until the 1980s, prolonged snow cover in many late-lying snowfields delayed ecosystem development and explain why current vegetation cover, soil organic matter content, and mineral weathering are significantly lower in these areas than in surrounding ecosystems. These findings highlight the long-term legacy of snow cover on alpine landscapes and underscore the need to re-evaluate its effects on ecosystem structure, functioning, and responsiveness to ongoing changes
Climate, not land-use, drives a recent acceleration of larch expansion at the forest-grassland ecotone in the southern French alps
No full textInternational audienceIn recent decades significant forest expansion into treeless alpine zones has been observed across global mountain ranges, including the Alps, driven by a complex interplay of global warming and land-use changes. The upward shift of treelines has far-reaching implications for ecosystem functioning, biodiversity, and biogeochemical cycles. However, climate variables alone account for only a fraction of treeline dynamics, highlighting substantial research gaps concerning the influence of non-climatic factors. This study addresses these gaps by combining dendrochronological methods, high-resolution bioclimatic data, and historical land-use records to investigate treeline dynamics in the southern French Alps. Our results reveal a marked acceleration in tree establishment, starting in the early 2000s, attributable primarily to climate change rather than the pastoral abandonment of the 19th century. We demonstrate that historical land-use changes created predisposing conditions for tree establishment, while recent climate change has increasingly acted as an accelerator for this dynamic. While key climatic factors, such as thermal indicators and growing season length, are identified as significant contributors to treeline shifts, our study highlights the need for further research to disentangle the specific drivers of tree recruitment and survival in the context of ongoing climate change
Histoire du développement des activités agro-pastorales depuis 5500 ans sur le territoire du Haut-Giffre Auteurs
No full textInternational audienceLes paysages de montagne aujourd'hui sont le fruit d'une longue histoire d'interactions entre l'homme, le climat et le milieu. Quelle est le déroulé de cette histoire dans le vallon de Sales et plus largement à l'échelle du Haut Giffre ? Pour répondre de manière la plus exhaustive possible à cette question, nous avons développé une approche interdisciplinaire croisant données paléoenvironementales provenant de l'étude de sédiments lacustres, données archéologiques et données historiques. La trajectoire à long terme de l'agroécosystème développé sur cet espace est en accord avec celle documentée à l'échelle des Alpes du Nord-Ouest. L'analyse plus détaillée, notamment du Moyen Âge jusqu'à aujourd'hui, considérant 1) les variations à plus haute résolution temporelle et spatiale, 2) la nature précise des activités (intégrant des données de pollen, d'ADN sédimentaire lacustre, d'archéozoologie et d'archéologie) et 3) la structure et l'organisation du bâti (archéologie et documents historiques), suggère aussi l'existence d'une diversité de trajectoires des agroécosystèmes de montagne. Cette diversité de trajectoires est probablement le fruit d'une complexité des interactions entre climat, environnement, dynamique des populations humaines, et contingences socio-économiques
Exploring continual learning strategies in artificial neural networks through graph-based analysis of connectivity: insights from a brain-inspired perspective
No full textInternational audienceArtificial Neural Networks (ANNs) aim at mimicking information processing in biological networks. In cognitive neuroscience, graph modeling is a powerful framework widely used to study brain structural and functional connectivity. Yet, the extension of graph modeling to ANNs has been poorly explored especially in term of functional connectivity (i.e. the contextual change of the activity's units in networks). From the perspective of designing more robust and interpretable ANNs, we study how a brain-inspired graph-based approach can be extended and used to investigate their properties and behaviors. We focus our study on different continual learning strategies inspired by the human brain and modeled with ANNs. We show that graph modeling offers a simple and elegant framework to deeply investigate ANNs, compare their performances and explore deleterious behaviors such as catastrophic forgetting
Chapter 22 - Unveiling the hemispheric specialization of language: Organization and neuroplasticity
No full textInternational audienceThe advancements in understanding hemispheric specialization of language (HSL) have been following two primary avenues: the development of neuroimaging techniques and the study of its reorganizations in patients with various neuropathologic conditions. Hence, the objectives of this chapter are twofold. First, to provide an overview of the key neuroimaging techniques employed to investigate HSL, along with the notable findings derived from them in the healthy population. Second, it focuses on the reorganization of HSL in physiologic (healthy aging) and pathologic (poststroke aphasia and temporal lobe epilepsy) conditions. The chapter emphasizes the importance of employing multimodal methodologies to comprehend the complex relationship between underlying HSL mechanisms affected by disease and resulting language impairments. Combining the neuroimaging techniques can help us understand how different characteristics of language networks combine into general mechanisms that support their plasticity. Nevertheless, it highlights the need for standardized HSL metrics, as the absence of such metrics poses challenges in synthesizing findings across studies. Additionally, while HSL findings are being accumulated, albeit multimodal, there is a lack of integration within a robust theoretical framework. In conclusion, there is a need for novel models acknowledging multimodal aspects of HSL while positioning it within the context of other cognitive functions
The i-FSC proxy for predicting inter-event and spatial variation of topographic site effects
No full textInternational audienceOur study focuses on predicting topographic amplification of ground motion in the nearsource region, where seismic rays reach the free-surface at varying incidence angles. We rely on data from previous 3D numerical simulations conducted on a topographic relief with a homogeneous medium. First, using neural networks, we identify which key parameters, describing the geometric characteristics of the relief relative to the seismic source position, control ground motion amplification. Then, we determine the functional form that relates these parameters to the simulated amplifications. Subsequently, we conduct a regression study to develop a model of topographic amplification, referred to as the i-FSC proxy (Illuminated Frequency-Scaled Curvature). Our estimator depends on the frequency-scaled (1) curvature, a parameter that accounts for the occurrence of amplifications over convex topographies and de-amplification over concave ones; (2) normalized illumination angle, a newly defined parameter that quantifies the slope exposure to the incoming wavefield, accounting for high amplification on slopes oriented opposite to the seismic source. The illumination parameter reduces the uncertainties of the proxy by a factor of 2 compared to estimators that rely solely on curvature. The proxy does not require high computational resources. It uses a digital elevation map and a seismic source position to predict amplification factors (without lithological effects) for an S-wave at any site on the surface topography. It allows exploration of variations in topographic amplification near seismic sources, representing a significant breakthrough as areas closest to the fault typically sustain the highest damages. A MATLAB script performing the i-FSC calculations is provided