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Approximating sub-Riemannian structures by Riemannian metrics and spectral convergence
No full textWe construct an approximating sequence of Riemannian metrics tailored to a given sub-Riemannian structure. We prove that the sequence of associated Riemannian volumes converge to Popp's volume and we then proceed to study the spectral convergence of the associated Laplace operators
Unveiling anionic migration mechanisms governed by mixed-anion chemistry in melilite oxyfluorides
No full textInternational audienceMixed-anion compounds provide a chemically flexible platform for tuning the anion sublattice configurations and defect landscapes, making them promising platforms for the design of novel anionic conductors. However, understanding how specific anionic configurations influence ionic migration remains a critical challenge. In this study, we report La1+xSr1-xGa3O7+0.5(x-δ)Fδ melilite oxyfluoride synthesis via topotactic fluorination of oxide precursors. Combined diffraction, impedance spectroscopy, solid-state nuclear magnetic resonance, and density functional theory calculations indicate that defect-level fluorine preferentially occupies interstitial voids within pentagonal rings rather than framework oxygen sites. However, this site-specific incorporation of fluorine appeared immobile, which disrupts the intrinsic oxide-ion migration pathway in melilite structures through impeding the site exchange between interstitial and framework oxygen atoms, thereby suppressing the oxide-ion transport and highlighting the unfavorable hetero-anionic site exchange and the importance of homoanionic site exchange for anionic conduction in the mixed-anion compounds. Our results highlight that anion site selectivity and configuration play a dominant role in governing anionic migration in mixed-anion compounds, offering valuable guidance for the future rational design of advanced mixed-anion ionic conductors
Transparent perovskite-based nanoceramics elaborated from full glass crystallization
No full textInternational audienceAll-inorganic perovskite nanocrystals are considered promising candidates for applications in optoelectronics including light-emitting diodes (LEDs), phosphors, solar cells and photodetectors, etc. However, all-inorganic perovskite nanocrystals mainly exist in the form of powders and single crystals. The former often suffers from limited chemical stability and large dependence on matrix materials, while the latter typically involves long-term and complex preparation processes. In this paper, we report the successful synthesis of a transparent GdAlO3 (GdAP)-based perovskite nanocrystalline ceramic for the first time using a low-temperature (1000°C) glass crystallization of 74 mol% Al2O3-26 mol% Gd2O3 bulk glass. The resulting ceramics exhibit a biphasic nanostructure composed of GdAP main phase (76.9 wt%) and Al2O3 secondary phase (23.1 wt%). The fully dense GdAP-Al2O3 nanoceramics demonstrate a good transmittance of 77%@780 nm and an excellent mechanical property (hardness is 24 GPa). When doped with Tb 3+ , the transparent Tb:GdAP-Al2O3 perovskite nanocrystalline ceramics can be efficiently excited under ultraviolet radiation at 369 nm to emit green fluorescence at 544 nm. Moreover, XEL spectra show that the luminous intensity of transparent 7%Tb:GdAP-Al2O3 perovskite nanocrystalline ceramic is approximately 4.5 times higher than that of the commercial BGO single crystal. Additionally, the light yield of transparent 7%Tb:GdAP-Al2O3 perovskite nanocrystalline ceramics is calculated to be approximately 45,000 ph/MeV. Therefore, the transparent GdAP-Al2O3 perovskite nanocrystalline ceramics presented in this paper exhibit good transmittance, excellent mechanical properties, and promising X-ray detection performance, demonstrating wide potential applications in a wide range of optical fields, including optical windows, lenses, scintillators, X-ray detection imaging, and phosphors
Starting a Non-Farm Enterprise to Escape Energy Poverty: Household Level Evidence from Rural West Africa
No full textInternational audienceThe choice of cooking fuel is a critical economic and health decision for rural households, with significant implications for well-being and environmental sustainability. This paper examines whether rural non-farm entrepreneurship promotes the adoption of cleaner cooking fuels, specifically liquefied petroleum gas (LPG). Using large, nationally representative data from eight WAEMU countries – Benin, Burkina Faso, Côte d’Ivoire, Guinea-Bissau, Mali, Niger, Senegal, and Togo – we apply econometric techniques to address endogeneity and selection bias. Our findings show that households engaged in non-farm entrepreneurial activities are significantly more likely to adopt LPG. We further show that non-farm entrepreneurship enhances financial inclusion by improving access to microfinance, mobile banking, and informal savings groups (ROSCAs), thereby easing liquidity constraints that limit investments in clean energy. These results suggest that promoting rural non-farm enterprises, along with expanding financial services and infrastructure, can effectively reduce energy poverty and improve health outcomes in sub-Saharan Africa
L'argent monnayé en Occident méditerranéen (Italie, Gaules, Hispanies, v. 150 a.C.‐14 p.C.). Procédés techniques, trajectoires économiques et stratégies d'approvisionnement
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A local generalisation of frame bundles
No full textFrame bundles equipped with a principal connection have their local structure characterised by a 1-form, called the Cartan connection 1-form, which gathers the principal connection form and the soldering form. We introduce generalised frame bundles as a smooth manifold equipped with a coframe with value in a suitable Lie algebra and which furthermore satisfies a weakened version of the Maurer-Cartan equation. From this structure it is possible to construct a Lie algebra action on the manifold. We study the question of whether it is possible to construct a Lie group action and build a base manifold over which the initial manifold is a frame bundle. We find that generalised frame bundles can have singular underlying manifolds
Les feedback de l'enseignant(e) d'EPS : perception et différences suivant le sexe des élèves
No full textThis research, at the crossroads of education and social sciences, looks to a better understanding of the possible stereotyped sexual differences as regards the feedbacks delivered by the PE teacher, namely the number and the type of feedbacks. Indeed stereotypical beliefs and their impacts often remain through the times and have obvious influences. The results we obtained from the observations on the field enabled us to highlight those phenomena whose analysis led us to determine a clear objective: figuring out why and how our lessons may be subjected to various culturally preconceived ideas. This work paves the way to a new and complex pattern of thought which is multi factorial and leads us to consider a new set of cumulative factors. The latter impacts the teacher's interactions toward his pupils and how they perceive those interactions. This accumulation of factors, whether incomplete or complete and more or less important, brings about possible differences as regards teaching processes. It positively and negatively affects the pupils' opportunities of success according to their sexes. As we become aware of those stereotypes, in themselves subjective or even unconscious, we urge the teaching staff to question their practices in order to overcome those various shortcomings.Ce travail de recherches qui croise sciences de l’éducation et sciences sociales, cherche à cerner davantage les phénomènes liés aux possibles différences stéréotypées sexuées en matière de nombre et de nature de feedback prodigués par l’enseignant-e d’EPS. En effet, très souvent, les croyances stéréotypées et leurs influences persistent malgré les changements d’époque. À travers la mise en exergue d’une analyse de ces phénomènes par le biais de résultats obtenus lors d’observations sur le terrain, l’objectif est évident : comprendre en quoi et comment nos enseignements peuvent être soumis à diverses idées culturellement préconçues. En ce sens, ces travaux de recherches ouvrent un prisme multi-factoriels complexe qui amène à réfléchir sur un nouveau continuum d’éléments impactant les interactions de l’enseignant-e envers ses élèves et les perceptions que ces derniers en ont. Ces influences partielles ou complètes, parfois plus ou moins importantes, créent, dès lors, de potentielles divergences dans les procédés éducatifs induisant les chances de réussite des élèves selon leur sexe. De ce fait, par l’entremise d’une prise de conscience de ces manifestations subjectives, voire inconscientes, que sont les stéréotypes, nous exhortons les enseignants et personnels d’éducation à s’interroger quant à leur pratique pour pallier ces multiples anomalies
Etude expérimentale de la distribution du soufre entre l'apatite et les liquides silicatés : application au dégazage volcanique
No full textMagmatic degassing is a universal process that shapes our atmosphere as well as those of other planets, and also causes many mineral concentrations of economic interest. Sulphur is a volatile element that fundamentally influences magmatic degassing. Among the minerals capable of recording the activity of volatile elements in magmas, apatite is certainly one of the most promising: although scarce, this mineral is ubiquitous in magmatic rocks. This experimental thesis studies the behaviour of sulphur in two main aspects. The first is the solubility of sulphur in basanites, a composition that has been little studied, with a focus on the La Palma 2021 eruption. The experiments were conducted at fixed temperature and pressure (1040°C-200MPa) and oxygen fugacity between NNO -0.47 and NNO+4.10. In the second approach, the distribution of sulphur between apatite and silicate melt was studied in relation to the fugacity of sulphur species. A study was carried out on various compositions at 200MPa, with temperatures between 1000 and 1040°C and oxygen fugacity between NNO-0.82 and NNO+4.17. The results showed that the solubility of sulphur in the silicate melt is primarily driven by oxygen fugacity. A positive correlation was found between the S content in the melt and in apatite, strongly influenced by oxygen fugacity. A detailed study on the fugacity of sulphur species allowed for the identification of a positive trend between the sulphur content and the sum of the fugacities. From this pattern, it was possible to create models, both for general compositions, to reconstruct the sulphur content in apatites from the fugacities of sulphur species and vice versa.Le dégazage magmatique est un processus universel qui façonne notre atmosphère ainsi que celles des autres planètes, et il provoque également de nombreuses concentrations minérales d'intérêt économique. Le soufre est un élément volatil qui influence de manière fondamentale le dégazage magmatique. Parmi les minéraux capables d'enregistrer l'activité des éléments volatils dans les magmas, l'apatite est certainement l'un des plus prometteurs : bien que rare, ce minéral est omniprésent dans les roches magmatiques. Cette thèse expérimentale étudie le comportement du soufre sous deux aspects principaux. Le premier est la solubilité du soufre dans les basanites, une composition peu étudiée, avec un focus sur l'éruption de La Palma 2021. Les expériences ont été réalisées à température et pression fixes (1040°C-200MPa) et fugacité d'oxygène entre NNO -0.47 et NNO+4.10. Dans la deuxième approche, la distribution du soufre entre l'apatite et le verre silicaté a été étudiée en relation avec la fugacité des espèces du soufre. Une étude a été réalisée sur différentes compositions à 200MPa, température entre 1000 et 1040°C et fugacité d'oxygène entre NNO-0.82 et NNO+4.17. Les résultats ont montré que la solubilité du soufre dans le verre silicaté est principalement guidée par la fugacité de l'oxygène. Une corrélation positive a été trouvée entre le contenu en S dans le verre silicaté et dans l'apatite, fortement influencée par la fugacité de l'oxygène. Une étude détaillée sur la fugacité des espèces du soufre a permis d'identifier une tendance positive entre le contenu en soufre et la somme des fugacités. À partir de ce modèle, il a été possible de créer des modèles, à la fois pour des compositions générales, pour reconstruire le contenu en soufre dans les apatites à partir des fugacités des espèces du soufre et vice versa
