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Euclid Quick Data Release (Q1). Active galactic nuclei identification using diffusion-based inpainting of Euclid VIS images
No full textInternational audienceLight emission from galaxies exhibit diverse brightness profiles, influenced by factors such as galaxy type, structural features and interactions with other galaxies. Elliptical galaxies feature more uniform light distributions, while spiral and irregular galaxies have complex, varied light profiles due to their structural heterogeneity and star-forming activity. In addition, galaxies with an active galactic nucleus (AGN) feature intense, concentrated emission from gas accretion around supermassive black holes, superimposed on regular galactic light, while quasi-stellar objects (QSO) are the extreme case of the AGN emission dominating the galaxy. The challenge of identifying AGN and QSO has been discussed many times in the literature, often requiring multi-wavelength observations. This paper introduces a novel approach to identify AGN and QSO from a single image. Diffusion models have been recently developed in the machine-learning literature to generate realistic-looking images of everyday objects. Utilising the spatial resolving power of the Euclid VIS images, we created a diffusion model trained on one million sources, without using any source pre-selection or labels. The model learns to reconstruct light distributions of normal galaxies, since the population is dominated by them. We condition the prediction of the central light distribution by masking the central few pixels of each source and reconstruct the light according to the diffusion model. We further use this prediction to identify sources that deviate from this profile by examining the reconstruction error of the few central pixels regenerated in each source's core. Our approach, solely using VIS imaging, features high completeness compared to traditional methods of AGN and QSO selection, including optical, near-infrared, mid-infrared, and X-rays
Proof assistants for undergraduate mathematics education: elements of an a priori analysis
No full textInternational audienceThis paper presents an a priori analysis of the use of six different interactive proof assistants for education, based on the resolution of a typical undergraduate exercise on abstract functions. It proposes to analyze these tools according to three main categories of aspects: language and interaction mode, automation and user assistance, and proof structure and visualization. We argue that this analysis may help formulate and clarify further research questions on the possible impact of such tools on the development of reasoning and proving skills
The effects of the spin and quadrupole moment of SgrA* on the orbits of S stars
No full textInternational audienceMeasuring the astrometric and spectroscopic data of stars orbiting the central black hole in our galaxy (Sgr A*) offers a promising way to measure relativistic effects. In principle, the "no-hair" theorem can be tested at the Galactic Center by monitoring the orbital precession of S-stars due to the angular momentum (spin) and quadrupole moment of Sgr A*. Closer-in stars, more strongly affected by the black hole's rotation, may be required. GRAVITY+ could detect such stars that are currently too faint for GRAVITY. We aim to analytically and numerically characterize orbital reorientations induced by spin-related effects of Sgr A* up to the second post-Newtonian (2PN) order. We use the two-timescale method to derive the 2PN analytical expressions of the secular evolution of the orbital parameters that are related to the observer. To study the interaction between the orbital and spin orientations, we introduce observer-independent quantities that offer insight into the Kerr geometry. We also use the post-Newtonian code OOGRE to simulate hypothetical stars orbiting closer to Sgr A*, where spin and quadrupole effects are stronger. This enables comparison with our analytical predictions. We exhibit three orbital-timescale precession rates that encode the in-plane pericenter shift and the out-of-plane redirection of the osculating ellipse. We provide the 2PN expressions of these precession rates and express the orbit-integrated associated angular shifts of the pericenter and of the ellipse axes. We relate these orbital-timescale precession rates to the secular-timescale precession of the orbital angular momentum around the black hole spin axis. We consider that the theoretical insight we provide in this article will be useful in constraining the spin effect of Sgr A* with GRAVITY+ observations
Metabolomic analysis of macromycetes from French Guiana revueals chemodiversity in Xylariales order
No full textInternational audienceAn original approach was undertaken to explore the metabolomic variability of macroscopic fungi collected in French Guiana. Extracts from 160 specimens, representing 13 fungal orders, were analyzed using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The resulting metabolomic profiles enabled the construction of chemotaxonomic dendrograms, which successfully grouped most samples assigned to the order Xylariales and highlighted chemodiversity at both the genus and species levels within this lineage. Principal Component Analysis based on molecular family presence/absence revealed 35 discriminant clusters, including specific markers distinguishing Thamnomyces chordalis and Phylacia sp. Five previously undescribed natural products were isolated and structurally characterized: four polyketides-prochordapyrone (1) and chordapyrones A-C (2-4)-and one terpenoid, chordapyranone (5). Structural elucidation was accomplished through a combination of nuclear magnetic resonance (NMR) spectroscopy, circular dichroism and single-crystal X-ray diffraction. Based on structural and mechanistic considerations, a putative biosynthetic pathway was proposed for the formation of the polyketide compounds
Metaphor, Translation and Human Rights: The Arab Charter as a Case Study
No full textInternational audienceAbstract Metaphors are deeply embedded in their cultural contexts, making their translation a complex task, as it is often difficult to find an equivalent that preserves the metaphor’s original meaning and cultural resonance. Although metaphor translation has been extensively explored in many fields, it remains understudied in human rights discourse. This study addresses this gap through a comparative analysis of the 2004 Arab Charter on Human Rights and its United Nations English translation, drawing on Lakoff and Johnson’s Conceptual Metaphor Theory (Metaphors we live by. Chicago: The University of Chicago Press, 1980) and Lindqvist’s (Högt och lågt i skönlitterär översättning till Svenska, Hallgren och Fallgren, Uppsala, 2005) taxonomy of metaphor translation strategies. The Arabic and English texts are analyzed qualitatively and quantitatively to identify the translation strategies and investigate the underlying conceptualizations of human rights within the interplay between universality and cultural specificity. This analysis is guided by the following research questions: (1) How are the metaphors identified in the Arab Charter rendered in the English translations? (2) To what extent do the employed strategies preserve or modify the conceptual and cultural framework of the metaphors? (3) How do these strategies affect the universality of human rights? The findings reveal that image transfer was the most frequent strategy, mainly preserving personification-based metaphors, while the remaining metaphors were adapted through the strategies of substitution, reduction to sense, and omission. The prevalence of image transfer may universalize human rights’ metaphors, yet these adaptations produce conceptual shifts that may obscure the source culture and potentially impede intercultural understanding
Photographier l'absence. La violence invisible de la disparition forcée en Colombie depuis 1990
No full textIn its final report published in 2022, the Colombian Truth Commission documented 121,768 cases of enforced disappearance in the country between 1985 and 2016, with statistical estimation models suggesting over 210,000 cases. The signing of definitive peace agreements with the country’s oldest guerrilla group (FARC-EP) in 2017 may have marked an official end to the armed conflict, yet the issue of enforced disappearances remains highly relevant: not only because disappearances continue to occur today, but also because the country faces memorial debt toward its thousands of missing persons and their families.Enforced disappearance is commonly described as an “invisible” crime, deprived of possible images. Indeed, this form of violence aims both at ensuring the impunity of its perpetrators and at the radical erasure—both physical and identity-based—of its victims, leaving their relatives in a state of uncertainty and terror. In this sense, it constitutes a form of violence devoid of visibility, one that seeks to undermine language and representation. Nevertheless, photography plays a particular role in the lives of relatives of the disappeared, both within private mourning rituals and in contexts where such mourning becomes politicized as a form of protest. When photographers engage with these images with an awareness of their uses, they do more than simply reproduce them or evoke absence, violence, or the disappeared and their families. In these recursive processes, the photographic medium speaks of itself, illustrating photography as a vernacular and everyday practice that actively contributes to the construction of individual narratives, memory, and identity.This study intersects the history of violence and conflict, the development of memorial discourse, and photographic representations of enforced disappearance. Given the centrality of enforced disappearance to the construction of historical memory in Colombia—and, more broadly, its place within contemporary national and continental culture—it was essential to compile a contemporary photographic corpus on absence. The aim is to understand the position of these photographs within a given visual culture, and what they contribute more broadly to a visual discourse on disappearance, the Colombian armed conflict, and, more generally, on violence as a social phenomenon.The study is organized into four parts. The first two sections primarily aim to elucidate the historical and theoretical framework of the research, while the third examines the ethical positions and photographic strategies of the works analyzed. References to the corpus, initially occasional or indirect, become progressively more frequent and detailed, culminating in the fourth and final section: an in-depth iconographic analysis of the motifs and techniques used to represent absence through photography.Dans son rapport final publié en 2022, la Commission de la vérité colombienne recense dans le pays 121.768 disparitions forcées entre 1985 et 2016, pour plus de 210.000 selon les modèles d’estimation statistique. La signature d’accords de paix définitifs avec la plus ancienne guérilla du pays (FARC-EP), en 2017, a peut-être mis un point final au conflit armé comme tel, mais la problématique des disparitions forcées reste d’actualité : non seulement car les disparitions continuent encore aujourd’hui de se produire, mais parce que le pays est désormais aux prises avec une dette mémorielle envers ses milliers d’absent·e·s et leurs proches.A propos de la disparition forcée de personnes, il est commun de parler d’un crime “invisible”, parce qu’il est “sans images”. En effet, cette forme de violence vise autant à l’impunité des auteurs qu’à l’effacement radical (identitaire et physique) de ses victimes, en enfermant ses proches dans l’incertitude et la terreur ; en cela, c’est une violence sans visibilité, qui veut mettre en échec le langage et les représentations. Pourtant, la photographie joue dans la vie des proches de disparu·e·s un rôle particulier, dans le cadre de rituels de deuil privé et dans un contexte de politisation de ce deuil comme mode de contestation. Lorsque les photographes s’emparent de ces images en connaissance de leurs usages, ils ne font pas que les rediffuser, évoquer l’absence, la violence, les disparu·e·s ou leurs proches. Dans ces mises en abîme, le médium photographique nous parle de lui-même, de la photographie comme pratique vernaculaire et quotidienne qui participe activement à la construction de nos récits individuels, de la mémoire et de l’identité. Ce travail fait coïncider l’histoire de la violence et du conflit, l’élaboration du discours mémoriel et les représentations photographiques de la disparition forcée. Au vu du rôle que tient la disparition forcée dans la construction de la mémoire historique en Colombie, et même plus largement la place qu’elle occupe dans la culture nationale et continentale contemporaine, il était essentiel de réunir un corpus photographique contemporain sur l’absence. L’enjeu sera de comprendre où se situent ces photographies au sein d’une culture visuelle donnée, et ce qu’elles apportent, plus largement, à un discours visuel sur la disparition, sur le conflit armé colombien, et, au-delà, sur la violence dans son ensemble.Ce travail est structuré en quatre parties. Les deux premières ont pour objectif principal d’éclairer le cadre historique et théorique de notre étude, tandis que la troisième interroge les positionnements éthiques et les dispositifs photographiques des œuvres étudiées. Les références au corpus, d’abord ponctuelles ou indirectes, se feront de plus en plus fréquentes et détaillées, et culminent dans la quatrième et dernière partie : celle-ci consiste en une analyse iconographique approfondie des motifs et moyens de représenter l’absence par l’image photographique
Enantiopurity‐Dependent Peptide Coacervates and Asymmetric Organocatalysis
No full textInternational audienceABSTRACT Membraneless compartmentalization via liquid–liquid phase separation (LLPS) has emerged as a powerful strategy to organize biochemical reactions. Recently, peptide‐based coacervates demonstrated the potential to function as microreactors by enhancing reaction kinetics through increased local concentrations and altered microenvironments. Here, we introduce an O‐methylated diphenylalanine‐based tripeptide LLL PFF‐OCH 3 containing an N‐terminal proline, designed to undergo LLPS, and simultaneously function as an enantioselective organocatalyst. Comprehensive characterization via confocal microscopy, fluorescence recovery after photobleaching (FRAP), micro‐Raman and attenuated total reflection infrared (ATR‐IR) spectroscopy, diffusion‐surface plasmon resonance ( D ‐SPR), and molecular dynamics (MD) simulations revealed the formation of stable liquid droplets. In contrast, a racemic mixture of LLL PFF‐OCH 3 and DDD PFF‐OCH 3 failed to form liquid droplets and instead formed a solid precipitate, unveiling a critical role of enantiopurity in LLPS. Proof‐of‐concept catalytic studies proved enantioselective organocatalytic activity of the LLL PFF‐OCH 3 liquid coacervates. Beyond catalysis these results may have broader implications in understanding prebiotic chemistry and neurodegeneration
Evidence of mutually exclusive outflow forms from a black hole X-ray binary
No full textInternational audienceAccretion onto black holes often leads to the launch of outflows that significantly influence their surrounding environments. The two primary forms of these outflows are X-ray disk winds-hot, ionized gases ejected from the accretion disk-and relativistic jets, which are collimated streams of particles often expelled along the rotational axis of the black hole. While previous studies have revealed a general association between spectral states and different types of outflows, the physical mechanisms governing wind and jet formation remain debated. Here, using coordinated NICER and MeerKAT observations of the recurrent black hole X-ray binary 4U 1630-472, we identify a clear anti-correlation between X-ray disk winds and jets: during three recent outbursts, only one type of outflow is detected at a time. Notably, this apparent exclusivity occurs even as the overall accretion luminosity remains within the range expected for a standard thin disk, characteristic of the canonical soft state. These results suggest a competition between outflow channels that may depend on how the accretion energy is partitioned between the disk and the corona. Our findings provide new observational constraints on jet and wind formation in X-ray binaries and offer a fresh perspective on the interplay between different modes of accretion-driven feedback
Arbor-TVB: a novel multi-scale co-simulation framework with a case study on neural-level seizure generation and whole-brain propagation
No full textInternational audienceComputational neuroscience has traditionally focused on isolated scales, limiting understanding of brain function across multiple levels. While microscopic models capture biophysical details of neurons, macroscopic models describe large-scale network dynamics. Integrating these scales, however, remains a significant challenge. In this study, we present a novel co-simulation framework that bridges these levels by integrating the neural simulator Arbor with The Virtual Brain (TVB) platform. Arbor enables detailed simulations from single-compartment neurons to populations of such cells, while TVB models whole-brain dynamics based on anatomical features and the mean neural activity of a brain region. By linking these simulators for the first time, we provide an example of how to model and investigate the onset of seizures in specific areas and their propagation to the whole brain. This framework employs an MPI intercommunicator for real-time bidirectional interaction, translating between discrete spikes from Arbor and continuous TVB activity. Its fully modular design enables independent model selection for each scale, requiring minimal effort to translate activity across simulators. The novel Arbor-TVB co-simulator allows replacement of TVB nodes with biologically realistic neuron populations, offering insights into seizure propagation and potential intervention strategies. The integration of Arbor and TVB marks a significant advancement in multi-scale modeling, providing a comprehensive computational framework for studying neural disorders and optimizing treatments
Le pluriel de l’identité des enseignantes et enseignants de géographie
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