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From Chains to Chromophores: Tailored Thermal and Linear/Nonlinear Optical Features of Asymmetric Pyrimidine—Coumarin Systems
No full textInternational audienceEleven novel asymmetric pyrimidine derivatives were synthesized. The pyrimidine core was functionalized with a coumarin chromophore and a pro-mesogenic fragment bearing either chiral or linear alkyl chains of variable length and substitution patterns. The thermal properties were investigated using polarized optical microscopy, differential scanning calorimetry, and small-angle X-ray scattering, revealing that only selected derivatives exhibited liquid crystalline phases with ordered columnar or smectic organizations. Linear and nonlinear optical properties were characterized by UV–Vis absorption, fluorescence spectroscopy, two-photon absorption, and second-harmonic generation. Optical responses were found to be highly sensitive to the substitution pattern: derivatives functionalized at the 4 and 3,4,5 positions exhibited enhanced 2PA cross-sections and pronounced SHG signals, whereas variations in alkyl chain length exerted only a minor influence. Notably, compounds forming highly ordered non-centrosymmetric mesophases produced robust SHG-active thin films. Importantly, strong SHG responses were obtained without the need for a chiral center, as the inherent asymmetry of the linear alkyl chain derivatives was sufficient to drive self-organization into non-centrosymmetric materials. These results demonstrate that asymmetric pyrimidine-based architectures combining π-conjugation and controlled supramolecular organization are promising candidates for nonlinear optical applications such as photonic devices, multiphoton imaging, and optical data storage
Tailoring of mesostructured alumina properties by the one pot incorporation of fluorine
No full textInternational audienceIn this study, to modulate the properties of mesostructured alumina synthetized by combining the sol-gel process and the surfactant templating mechanism, the introduction of fluorine has been carried out through a one step process using ammonium fluoride as fluorinating agent.Small angle x-ray scattering, X-ray diffraction, 19 F, 27 Al NMR and manometry nitrogen adsorption-desorption analyses show that even after heating at 500 • C, amorphous mesostructured aluminum (hydr)oxyfluoride with an intrinsic mesoporosity are obtained for NH 4 F concentration in water lower than 112.5 g L -1 .With the increase in the fluorine content, the mesostructuration is lost. For materials recovered after removal of the porogen agent (Pluronic P123) by Soxhlet extraction, aluminum (hydr)oxyfluoride hydrate Al 2 (OH) 2.76 F 3.24 (H 2 O) and ammonium fluoroaluminates, are detected by XRD. When the extracted materials are calcined at 500 • C, ammonium fluoroaluminates are decomposed into AlF 3 and AlF 1.96 (OH) 1.04 is also detected. Because of the presence of the crystalline phases, the intrinsic porosity vanishes and the mesoporosity is mainly inter-aggregates.Adsorption of pyridine followed by infrared spectroscopy reveals that whatever the fluorine content, no Brønsted acid site is present. The concentration of the Lewis acid sites first increases to reach a maximum value around 0.8 μmol m -2 for a NH 4 F concentration in water of 112.5 g L -1 , then it reaches a plateau.</p
L’historien de l’Antiquité face aux collections et archives
No full textInternational audiencePubliques ou privées, les archives des anciens ont largement accompagné des logiques de sophistication du droit et des échanges. Publiques ou privées, elles ont bien sûr aussi concouru à la mémoire collective. Comment ont-elles été réutilisées sur le temps long
Donner voix aux récits invisibilisés. ONG, personnes migrantes et luttes symboliques dans les espaces publics
No full textInternational audienceIn a context of growing polarization in public discourse on migration and migrants (Thiéblemont-Dollet, 2003; Dalibert & Doytcheva, 2014; Boursier & Seoane, 2024), marked by the “rise of populism” (Wihtol de Wenden, 2018) and the normalization of xenophobic and racist rhetoric in political and media arenas, this paper examines how non-governmental organizations (NGOs) contribute to the production and circulation of contemporary narratives about migration. The aim is to understand how these narratives can make visible migratory trajectories that are often marginalized, while producing counter-discourses that challenge the stereotypical representations conveyed by traditional and social media (Barats, 2001; Israël Garzón, 2003; Nana Ketcha, 2019; Boursier & Seoane, 2024). The central issue concerns the processes of mediation and mediatization of migratory narratives implemented by NGOs to support the expression of migrants’ voices: what narrative formats are mobilized to enable migrants to speak for themselves? How do these communicative devices contribute to processes of recognition, collective memory, and empowerment? To address these questions, the analysis is based on ethnographic research conducted since 2017 within la Cimade, a French NGO dedicated to defending the rights of migrants. Three main types of narrative devices have been identified. First, educational interventions – including the screening of animated documentary films (Samè, 2023) and the classroom listening of oral testimonies delivered by migrants themselves (Samè, 2021) – follow a logic of sensitive and ethical mediation: these stories are not reported by intermediaries but told directly by those concerned, with the aim of fostering recognition and respectful transmission of their experiences to younger audiences. Second, the production of a podcast series, available on la Cimade’s website and major streaming platforms (Spotify, Amazon Music, Apple Podcasts), allows migrants to contribute to building a sonic memory of migratory experiences. Finally, in partnership with other collectives, la Cimade has supported the staging, in urban public spaces, of theatrical performances based on the testimonies of migrants themselves – the Parlement de rue, created in response to the 2024 Asylum and Immigration Act, thereby mobilizing their capacity for agency (Samè, 2025).Dans un contexte de polarisation croissante des discours sur les questions migratoires et les personnes en situation de migration (Thiéblemont-Dollet, 2003 ; Dalibert et Doytcheva, 2014 ; Boursier et Seoane, 2024), marqué par « la montée des populismes » (Wihtol de Wenden, 2018) et la banalisation des propos xénophobes et racistes qui s’érigent dans les espaces publics politiques et médiatiques, cette communication interroge la manière dont les organisations non gouvernementales (ONG) participent à la production et à la circulation des narrations contemporaines sur les migrations. L’objectif est ainsi de comprendre comment ces récits peuvent contribuer à rendre visibles des parcours migratoires souvent marginalisés, tout en produisant des contre-discours visant à contrer les représentations stéréotypées véhiculées dans les médias traditionnels et socionumériques (Barats, 2001 ; Israël Garzón, 2003 ; Nana Ketcha, 2019 ; Boursier et Seoane, 2024). La problématique centrale concerne les processus de médiation et de médiatisation des récits migratoires mis en œuvre par les ONG pour accompagner la prise de parole des personnes migrantes : quels formats narratifs sont mobilisés pour donner la parole aux personnes migrantes ? Comment ces dispositifs participent-ils à une dynamique de reconnaissance, de mémoire collective et d’empowerment ? Pour répondre à cette question, l’analyse repose sur une enquête ethnographique conduite depuis 2017 au sein de la Cimade, une ONG française de défense des droits des personnes migrantes. Trois grands types de dispositifs narratifs ont été identifiés. Premièrement, des interventions en milieu scolaire, incluant la diffusion de films d’animation documentaire (Samè, 2023) et l’écoute en classe de récits oraux énoncés par les personnes migrantes (Samè, 2021), s’inscrivent dans une logique de médiation sensible et éthique – ces récits ne sont pas rapportés par des tiers, mais énoncés directement par les personnes concernées, dans une perspective de reconnaissance et de transmission respectueuse de leurs expériences à un jeune public. Deuxièmement, la production d’une série de podcasts, disponibles sur le site web de la Cimade et diffusés sur les principales plateformes (Spotify, Amazon Music, Apple Podcasts), permet aux personnes étrangères de contribuer à la mise en place d’une mémoire sonore des parcours migratoires. Enfin, en partenariat avec d’autres collectifs, la Cimade a soutenu la mise en scène, dans l’espace public urbain, de témoignages théâtralisés portés par les personnes migrantes elles-mêmes ; le Parlement de rue, en réaction à la loi Asile et Immigration promulguée en 2024, mobilisant ainsi leur capacité d’agir (Samè, 2025)
Understanding the hard carbon's closed pore formation and Na-ion storage beyond the first charge/discharge cycle
No full textInternational audienceThe lack of accurate determination of hard carbon's (HC) open and closed pores, but also the systematic analysis of only the first charge/discharge cycle, in half-cells, impedes understanding of Na-ions storage. Therefore, a combined approach based on the adsorption of multiple gases (N 2 , O 2 , H 2 and CO 2 ) and He density is proposed to understand the HC's open porosity evolution and closed pores formation during pyrolysis. At 900 • C the pores are completely open, they partially close in the range of ~1100-1300 • C, and completely close starting from 1500 • C. The narrower pores (<0.7 nm) close firstly, with the formation of few larger open pores and plenty of closed pores, which increase with temperature. Examination of property-performance relationships from both 1st and 2nd cycles, revealed that the 1st cycle sloping capacity increases with open porosity, O-functional groups and defects, and is associated not only with reversible Na-storage but also with irreversible reactions (SEI formation).On the contrary, the 2nd cycle is only linked with reversible Na-storage, and an optimal property threshold was established. The plateau capacity was found to increase with the increase in graphitic domains and closed pores, no matter the cycle. These findings suggest an adsorption-insertion-filling mechanism
Photostimulus-responsive Non-covalent Interactions in Polymers: A Review
No full textInternational audienceThis study reviews light-responsive polymers in various applications, including drug delivery, information storage, sensor, self-healing material, antibacterial or anti-fouling, and environmental applications. Light-responsive polymers are a new material type being developed for various medical, electronics, engineering, and environmental applications. The working principle of light-responsive materials is based on metal-ligand interactions or non-covalent interactions between polymer functional groups, metal ions, and other filler functional groups. Light irradiation causes physical and mechanical changes in drug delivery and antibacterial systems, which results in the materials releasing more drugs or antibacterial substances. When materials in information storage devices and sensors are exposed to light, they can change color or glow. This has been applied for data storage to reveal QR codes under UV light. Additionally, this review discusses the thermodynamic aspects and computer modeling of light-responsive materials to emphasize the importance and development of these materials. Finally, light-responsive polymer development for various applications is presented
Adaptation de la réponse spectrale visible des métasurfaces de sol-gel VO 2 à changement de phase présentant un contraste de résistivité élevé
No full textInternational audienceVO 2 phase change material (PCM) was used to elaborate optical thin films and metasurfaces from sol-gel processing with performant switching ability in the visible. The initial formulation was developed from VO(acac) 2 precursor, reacting in a typical hydroalcoholic medium, and was deposited through liquid deposition before treatment at high temperature under vacuum. The crystalline switch between the monoclinic (M1) and tetragonal (rutile) has been well put in evidence around 53 °C, confirming the efficient metal-insulator transition (MIT), characteristics of the VO 2 PCM. We also highlight the major role of crystallite preferential orientation (texture) in the coating to achieve an efficient optical switching. This effect was attributed to thermodynamic and kinetic aspects governing the nucleation growth and the intrinsic high birefringence of the M1 phase. Under optimal conditions, the VO 2 PCM film with preferential M1(011) orientation exhibited an electrical resistance switching over two orders of magnitude and an optical contrast above 1 refractive index unit in the near infrared region. This optimal material was then deposited as a conformal layer above a dielectric SiO 2 metasurface composed of submicronic pillars organized into periodical square arrays of between 400 and 880 nm pitches. Upon thermal modulation, the composite dielectric/PCM metasurfaces exhibits an efficient reflective spectral switching (Δλ r up to 70 nm) located in the visible. Finally, the optimal material switching ability and high stability and reproducibility upon switching were investigated through in situ simultaneous XRD and sheet resistance analysis. The established synthesis-structure-property relationships of the proposed method provide a foundation for developing advanced optoelectronic devices and dynamically tunable photonic systems in the visible compatible with a rapid and simple sol-gel-based synthetic approach.</div
Usages et non-usages des IA génératives : premières pistes de réflexion sur le processus de réflexivité et sur l’appropriation des tâches de production de textes
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Éco-spiritualité versus religiosité : Quel moteur pour améliorer les pratiques de recyclage alimentaire dans les foyers ?
No full textInternational audienceGiven the environmental problems posed by food waste, recycling food leftovers in the home is a solution that should be encouraged. Within the framework of the theory of planned behaviour, this study examines the comparative effects of consumers' intrinsic religiosity and eco-spirituality on their intentions to recycle food leftovers in the home. The results of a survey of more than 500 consumers representative of the French population show that eco-spirituality is an important determinant of intentions and declared behaviour to recycle food scraps, via attitudes to the consumption of food scraps and the subjective norm. Contrary to expectations, intrinsic religiosity has no effect on attitude and subjective norm but exerts a slightly negative influence on intentions. Societal recommendations are drawn from these results.Face aux problèmes environnementaux posés par le gaspillage alimentaire, le recyclage des restes alimentaires dans le cadre du foyer est une solution à encourager. Dans le cadre de la théorie du comportement planifié, ce travail s’interroge sur les effets comparés de la religiosité intrinsèque et de l’éco-spiritualité des consommateurs sur les intentions de recyclage des restes alimentaires dans le foyer. Les résultats d’une enquête réalisée auprès de plus de 500 consommateurs représentatifs de la population française montrent que l’éco-spiritualité est undéterminant important des intentions et des comportements déclarés de recyclage des restes alimentaires par l’intermédiaire de l’attitude à l’égard de la consommation des restes alimentaires et de la norme subjective. Contrairement à ce qui était attendu, la religiosité intrinsèque n’a pas d’effet sur l’attitude et la norme subjective mais exerce une influence légèrement négative sur les intentions. Des préconisations sociétales sont tirées de ces résultats
Étude des propriétés physico-chimiques des charbons (biochars) issus de la pyrolyse de biomasse : Application à la catalyse pour la production de dihydrogène
No full textBiochar is a versatile material with applications in diverse fields such as soil conditioning and carbon sequestration. Its carbon-rich structure makes it a promising catalyst/support for catalysis, particularly in processes such as dry reforming of methane (DRM) and thermocatalytic decomposition of methane (TCD) to produce hydrogen. Various biochars were produced by fast pyrolysis of lignocellulosic biomass (oak, douglas, corn cobs) and non-lignocellulosic biomass (poultry droppings) by fast pyrolysis at 500°C and 800°C. These materials were characterized using various analytical techniques to study the effect of pyrolysis temperature and feedstock types on their physicochemical properties. Biochars produced at 800°C from douglas and corn cobs were physically activated using steam, CO2 and air, to improve their reactivity and porosity. Some activated biochars were subsequently impregnated with nickel nitrate. These materials, impregnated (Ni/AC) or not (AC), were used as catalysts for hydrogen production by TCD and DRM in a fixed-bed reactor. These catalysts were characterized before and after reactions, to highlight structure/activity relationships and identify possible causes of deactivation. This made it possible to evaluate the effect of several factors on hydrogen production, including nickel addition, use of CO₂, CH₄ concentration and catalysis temperature.Le biochar est un matériau polyvalent qui trouve des applications dans divers domaines tels que l'amendement des sols et la séquestration du carbone. Sa structure riche en carbone en fait un catalyseur/support prometteur pour la catalyse, en particulier dans des processus tels que le reformage à sec (DRM) et la décomposition thermocatalytique du méthane (TCD) pour produire de l'hydrogène. Différents biochars ont été produits par pyrolyse rapide de biomasses lignocellulosiques (chêne, douglas, rafles de maïs) et non-lignocellulosiques (fientes de volaille) par pyrolyse rapide à 500°C et 800°C. Ces matériaux ont été caractérisés par différentes techniques d’analyse afin d’étudier l’effet de la température de pyrolyse et de la nature de la biomasse sur leurs propriétés physicochimiques. Les biochars produits à 800°C à partir du douglas et des rafles de maïs ont été activés physiquement à la vapeur d’eau, au CO2 et à l’air, afin d’améliorer leur réactivité et leur porosité. Certains biochars activés ont été par la suite imprégnés avec du nitrate de nickel. Ces matériaux, imprégnés (Ni/AC) ou non (AC), ont été utilisés comme catalyseurs pour la production d’hydrogène par TCD et DRM dans un réacteur à lit fixe. Ces catalyseurs ont été caractérisés avant et après réactions afin de mettre en évidence des relations structure/activité et d’identifier les causes de désactivation possibles. Ceci a permis d’évaluer l’effet de plusieurs facteurs sur l’activité catalytique des catalyseurs, notamment l’ajout de Ni, la nature du catalyseur, l’utilisation de CO₂, la concentration en CH₄ et la température de catalyse