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Savoirs, contre-récits et silences de l’archive : écrire l’histoire des diasporas africaines aujourd’hui
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Articulation entre Espaces de travail mathématique (ETM) et algorithmique (ETA) : une séquence de programmation en mathématiques au secondaire au Québec
No full textInternational audienceAlthough computer programming is not part of the mathematics curriculum in Quebec, some teachers have begun integrating it into their lessons. Based on a case study conducted in a Quebec City high school classroom, we analyze how one teacher attempts to use Mathematical Workspace (MWS) and Algorithmic Workspace (AWS) to facilitate algebraic generalization. Our analysis of five episodes reveals the challenges of setting up a fibered workspace in which objects can move seamlessly between mathematics and informatics. We also discuss the difficulties of introducing algorithms to develop or initiate mathematical concepts, particularly generalization.Bien que la programmation informatique ne figure pas dans les programmes de mathématiques au Québec, certains enseignants l’intègre dans leur enseignement. À partir d’une étude de cas menée dans une classe de secondaire à Québec, nous analysons la manière dont une enseignante tente d’articuler Espace de Travail Mathématique (ETM) et Espace de Travail Algorithmique (ETA) pour soutenir la construction de premières formes de généralisations algébriques. L’analyse de cinq épisodes révèle les difficultés à installer un espace de travail fibré dans lequel les objets circulent de façon fluide entre les deux espaces mathématiques et informatique. Nous mettons en évidence les défis didactiques liés à l’introduction de l’algorithmique pour construire ou initier des concepts mathématiques, en particulier lorsqu’il s’agit d’introduire les prémices de la généralisation
Space oddity: How context matters in waste-sorting behavior
No full textInternational audienceThe circular economy gives a prominent role to recycling, entailing the general implementation of waste sorting in private, semi-public, and public locations. Previous literature has extensively explored the psychological and contextual antecedents of waste-sorting behavior, but mainly with a focus on one specific setting, without considering how the sorting location might moderate the influence of these antecedents. To investigate this research question, we develop a dual-route model of waste-sorting behavior based on an integrated TPB-NAM framework. To test this model, we used a survey based on self-reported data considering three successive locations (i.e., home, university and on the way to university) from the same 296 French college students and analyzed it using structural equation modeling with partial least squares (PLS-SEM). Although both psychological and contextual routes influence waste sorting, we show that their relative importance differs across locations. Furthermore, at university and on the way to university, the contextual route influences the psychological one. These results highlight why individuals' self-reported waste-sorting behavior may vary across locations and call on academics to replicate pro-environmental behavior models across all relevant contexts before recommending public policies to promote them
HALO I: Photometric continuum reverberation mapping of Fairall 9
No full textInternational audienceWe investigate the origin of inter-band continuum time delays in active galactic nuclei (AGNs) to study the structure and properties of their accretion disks. We aim to measure the inter-band continuum time delays through photometric monitoring of Seyfert galaxy Fairall 9 to construct the lag-spectrum. Additionally, we explain the observed features in the Fairall 9 lag-spectrum and discuss the potential drivers behind them, based on our newly collected data from the Obserwatorium Cerro Murphy (OCM) telescope. We initiated a long-term, continuous AGN photometric monitoring program in 2024, titled 'Hubble constant constraints through AGN Light curve Observations' (HALO) using intermediate and broad band filters. Here, we present the first results from HALO, focusing on photometric light curves and continuum time-delay measurements for Fairall 9. To complement these observations and extend the wavelength coverage of the lag-spectrum, we also reanalyzed archival Swift light curves and spectroscopic data available in the literature. Using HALO and Swift light curves, we measured inter-band continuum delays to construct the lag-spectrum of Fairall 9. Excess lags appear in the and bands (Balmer continuum contamination) and in the band (Paschen jump/dust emission from the torus). Overall, the lag-spectrum deviates significantly from standard disk model predictions. We find that inter-band delays deviate from the power-law, due to BLR scattering, reprocessing, and dust contributions at longer wavelengths. Power-law fits are therefore not well suited for characterizing the nature of the time delays
Recommender system in X inadvertently profiles ideological positions of users
No full textStudies on recommendations in social media have mainly analyzed the quality of recommended items (e.g., their diversity or biases) and the impact of recommendation policies (e.g., in comparison with purely chronological policies). We use a data donation program, collecting more than 2.5 million friend recommendations made to 682 volunteers on X over a year, to study instead how real-world recommenders learn, represent and process political and social attributes of users inside the so-called black boxes of AI systems. Using publicly available knowledge on the architecture of the recommender, we inferred the positions of recommended users in its embedding space. Leveraging ideology scaling calibrated with political survey data, we analyzed the political position of users in our study (N=26,509 among volunteers and recommended contacts) among several attributes, including age and gender. Our results show that the platform's recommender system produces a spatial ordering of users that is highly correlated with their Left-Right positions (Pearson rho=0.887, p-value < 0.0001), and that cannot be explained by socio-demographic attributes. These results open new possibilities for studying the interaction between human and AI systems. They also raise important questions linked to the legal definition of algorithmic profiling in data privacy regulation by blurring the line between active and passive profiling. We explore new constrained recommendation methods enabled by our results, limiting the political information in the recommender as a potential tool for privacy compliance capable of preserving recommendation relevance
Sediment routing and palaeogeographic evolution of the Western Alpine Foreland Basin during the early collisional stage
No full textInternational audienceIn the Western Alpine Foreland Basin (WAFB), Late Eocene and Miocene periods were characterized by longitudinal sediment routing systems: The first one was situated within the turbidite basin during the underfilled phase and exhibited a northward orientation toward the Swiss Basin, whereas the second was located in the Rhône Valley during the overfilled phase and was directed southward toward the Mediterranean Sea. The transition between these two periods occurred during the Oligocene, which corresponds to both the underfilled/ overfilled transition and the early overfilled period. In this study, we provide new fieldwork observations, seismic and well data interpretations, biostratigraphic analyses and a literature synthesis to reconstruct the palaeogeographic and source-to-sink evolution of the WAFB from Priabonian to Aquitanian. The aim is to discuss this reorganisation of sediment routing in relation to the evolution of the Alpine orogenic wedge, as well as the structural inheritance and the suite of geodynamic events that affected southeastern France during the mid-Cenozoic. We divided the WAFB sedimentary formations into four depositional sequences (S1 to S4). During the deposition of the first two sequences (Priabonian to early late Rupelian; ~37.4-28.8 Ma), the WAFB routing system was influenced by the end of the Pyrenean-Provençal orogeny, the European Cenozoic Rifting System (controlling the Rhône Valley s.l.) and the Alpine orogenic wedge (controlling the Alpine foredeep). The very first connection between the Alpine domain and the Rhône Valley is established at ~30 Ma, during the late Rupelian (S2 highstand), controlled by E-W inherited Pyrenean-Provençal structures implying a 'broken foreland'. In the meanwhile, from the Dévoluy Basin and northward, the orogenic wedge controlled a classical, although thin, foreland basin characterized by a northward sediment routing connected to the Northern Alpine Foreland Basin. Most of the S3 sequence (Latest Rupelian to middle Chattian; ~28.8-23.25 Ma) corresponds to a decrease of clastic Alpine inputs throughout SE France caused by a reorganisation of the drainage network related with the exhumation of the southern External Crystalline Massifs. S3 highstand and S4 sequence (late Chattian to Aquitanian; from ~23.25 Ma) correspond to the establishment of a longitudinal sediment routing system in the Rhône Valley, with material flowing southwards toward the Gulf of Lion, and supplied by the Palaeo-Isère to the north and potentially by the Palaeo-Durance to the south. This final stage in the reorganisation of the drainage network is clearly associated with the post-rift phase of the Gulf of Lion, which facilitated the opening of a new sink and the ultimate southward migration of the sedimentary area
Euclid Quick Data Release (Q1). Extending the quest for little red dots to z<4
No full textInternational audienceRecent James Webb Space Telescope (JWST) observations have revealed a population of sources with a compact morphology and a `v-shaped' continuum, namely blue at rest-frame A and red at longer wavelengths. The nature of these sources, called `little red dots' (LRDs), is still debated, since it is unclear if they host active galactic nuclei (AGN) and their number seems to drastically drop at z<4. We utilise the 63 covered by the quick Euclid Quick Data Release (Q1) to extend the search for LRDs to brighter magnitudes and to lower z than what has been possible with JWST to have a broader view of the evolution of this peculiar galaxy population. The selection is done by fitting the available photometric data (Euclid, Spitzer/IRAC, and ground-based griz data) with two power laws, to retrieve the rest-frame optical and UV slopes consistently over a large redshift range (i.e, z<7.6). We exclude extended objects and possible line emitters, and perform a visual inspection to remove imaging artefacts. The final selection includes 3341 LRD candidates from z=0.33 to z=3.6, with 29 detected in IRAC. Their rest-frame UV luminosity function, in contrast with previous JWST studies, shows that the number density of LRD candidates increases from high-z down to z=1.5-2.5 and decreases at even lower z. Less evolution is apparent focusing on the subsample of more robust LRD candidates having IRAC detections, which is affected by low statistics and limited by the IRAC resolution. The comparison with previous quasar UV luminosity functions shows that LRDs are not the dominant AGN population at z<4. Follow-up studies of these LRD candidates are key to confirm their nature, probe their physical properties and check for their compatibility with JWST sources, since the different spatial resolution and wavelength coverage of Euclid and JWST could select different samples of compact sources
Ultramafic float rocks at Jezero crater (Mars): excavation of lower crustal rocks or mantle peridotites by impact cratering?
No full textInternational audienceBased on observation and data from meteorites and in situ scientific missions, experiments as well as models, the Martian mantle is assumed to share some compositional and mineralogical affinity with the terrestrial mantle. However, there might be subtle differences like the Martian mantle being more ferroan. Yet, we do not have any direct analysis of a Martian mantle rock to confirm this assumption. NASA’s Perseverance rover found olivine-rich boulder-sized float rocks on the upper Jezero fan (Mars). These boulders have an ultramafic composition and their mineralogy is dominantly composed of Fo73±3 olivine with high-Mg orthopyroxene, Cr-rich Ti-Fe oxides and minor plagioclase and high-Ca pyroxene. Microtextural and petrological analysis reveals that these minerals crystallized at equilibrium. In addition, these boulders are different from all the bedrocks analyzed by Perseverance along its traverse which are crustal igneous rocks and sediments. Comparing our data to Martian meteorites and available Mars bulk silicate models (BSM), we discuss that these boulders could represent primitive melts and/or lower crustal material, and we specifically hypothesize that they could be mantle peridotites. We propose that these putative mantle rocks could have been excavated by the succession of impacts from the shallow mantle or lower crust in the Isidis region where Jezero crater is located. These olivine-rich boulders could thereby constitute the first direct analysis of a Martian mantle rock
How to Achieve the Best Trade-off Between Robustness and Performance
No full textThe work presents an innovative approach to addressing the trade-off between robustness and performance, known as the optimality criterion. Moreover, the procedure relies on well-established methods that effectively support the search for the best trade-off, namely multi-criteria optimization problem. Thus, by separating the robustness and performance problems, it becomes possible to achieve the best trade-off between these two criteria. In this search for a trade-off, two complementary approaches are combined: robust control for the closed-loop system by minimizing Hinf-norm, and performance optimization in open-loop by minimizing l2-norm. This combination is made possible by the Youla-Kučera parameterization. However, to implement this parameterization in the presence of model errors, a new approach is used: estimating the Youla-Kučera parameterization.</div
