Portail HAL ENSCP
Not a member yet
9647 research outputs found
Sort by
Understanding Polymerized Ionic Liquids as Solid Polymer Electrolytes for Sodium Batteries
No full textInternational audienc
The ornamentation steps of the Bull Rotunda of the Lascaux cave give new insights into the Upper Palaeolithic natural life cycle
No full textInternational audienceAlthough the ornamentation of the Lascaux cave seems relatively homogeneous in style, the analysis by scanning and transmission electron microscopy of 32 microsamples from the figures of the Hall of the Bulls (Bull Rotunda) and one desquamated sample from the soil highlighted different paint pots. The black and red paint matters with their associated mineralogical phases were extensively characterized. Considering previous stylistic and superimposition studies, we were eventually able to confirm five creation steps of monothematic figures (‘assemblages’) based on the chemical and mineralogical characteristics. Further interpretations in terms of the rhythm and temporal framework of the Hall of the Bulls (Bull Rotunda) of the Lascaux cave could be reinforced. Some particular representations such as the black cave bear and one of the cross‐shaped signs were shown to be likely added at later moments by different hands because their paint pots were different from those of the Bull Rotunda and similar to that of other representations in deeper rooms of the Lascaux cave. We also found that the paint matter of the Bull Rotunda was different than those of other Palaeolithic cave sites on a more regional scale indicating a very local sourcing
Optical properties and coloration of lead silicate glasses
No full textInternational audienceThis chapter reviews the physical bases of the main optical properties, with an emphasis on color. Then it presents an overview of the optical properties and applications of transparent SiO2-PbO-M2O (M, alkaline) glasses that are often said to take a yellow color. Further on it discusses the color of lead glasses colored by transition ions, case of “colored transparent glazes”. The colors of these glasses differ from those of alkaline glasses colored by the same ions, and hypotheses are proposed to understand the origin. This chapter does not cover opacification and coloration by lead-based pigments (lead antimonates, arsenates or stannates), which can be added to alkaline glasses and also to lead glasses, considering that it involves an opacification and coloration whose origin is external to the lead glass, properly speaking. Moreover, the opacification of lead glasses and their possible coloration by semiconductor or metallic particles will not be covered either, as they involve the same agents and mechanisms as the silicate glasses in general, lead oxide not modifying the phenomena except for the increase in the refractive index of the glass and the role that it can play in redox equilibriums
Synthèse d'une nouvelle famille de bioconjugués peptide-polymère
No full textThe use of peptides for therapeutic purposes has fascinated researchers for over a century. Indeed, these biomolecules are characterized by their bioactivity, high specificity and essential physiological functions. However, their low metabolic and physical stability limits their direct use as drugs. Peptide-polymer bioconjugates constitute is presented as an alternative to overcome these limitations. In this thesis, we explore a new method for bioconjugate synthesis using anionic ring-opening polymerization. This simple to implement approach enables rapid production of bioconjugates without the need to pre-functionalize peptides. γ-thiolactones play a central role in this work, being used both as co-initiators for anionic ring-opening polymerization of episulfides and as co-monomers in the synthesis of poly(thioether-alt-ester). The materials obtained display interesting physicochemical properties, including oxidation sensitivity and low cytotoxicity, paving the way for potential applications in the biomedical field.L'utilisation des peptides à des fins thérapeutiques passionne les chercheurs depuis plus d'un siècle. En effet, ces biomolécules se distinguent par leur bioactivité, leur grande spécificité et leurs fonctions physiologiques essentielles. Cependant, leur faible stabilité métabolique et physique limite leur emploi direct en tant que médicaments. Les bioconjugués peptide-polymère se sont révélés être une solution prometteuse pour surmonter ces limitations. Dans cette thèse, nous explorons une nouvelle méthode de synthèse de bioconjugués en utilisant la polymérisation anionique par ouverture de cycle. Cette approche, simple à mettre en oeuvre, permet de produire rapidement des bioconjugués sans avoir besoin de pré-fonctionnaliser les peptides. Les γ-thiolactones jouent un rôle central dans ce travail, étant utilisées à la fois comme co-amorceurs pour la polymérisation anionique par ouverture de cycle d'épisulfures et comme co-monomères dans la synthèse de poly(thioéther-alt-ester). Les matériaux obtenus présentent des propriétés physicochimiques intéressantes, notamment une sensibilité à l'oxydation et une faible cytotoxicité, ce qui ouvre la voie à des applications potentielles dans le domaine biomédical
Dynamic Kinetic Resolution of β-Cyano α-Ketoesters via Asymmetric Transfer Hydrogenation
No full textInternational audienceAn efficient rhodium-catalyzed asymmetric transfer hydrogenation of β-cyano α-ketoesters via dynamic kinetic resolution has been developed. Despite the challenge posed by multiple functional groups, the reaction proceeded smoothly under mild conditions, generating versatile synthons with two adjacent stereocenters in high yields with excellent enantio- and diastereoselectivities. Furthermore, the power of this strategy is highlighted by the scale-up reaction and the follow-up synthesis of cytoxazone and paclitaxel intermediates
Rhodium-Catalyzed Asymmetric Hydrogenation and Transfer Hydrogenation of α-Nitro Ketones
No full textInternational audienceA catalytic protocol for the enantioselective hydro- genation and transfer hydrogenation of α-nitro ketones was developed, providing a wide range of β-nitro-α-phenylethanols with high yields and excellent enantioselectivities (up to 98% yield and up to >99.9% ee). Compatibility with a wide range of solvents and bases demonstrates the robustness of this reaction. The synthetic potential of the protocol was demonstrated by the highTON experiment as well as the application in the synthesis of key intermediates of mirabegron (S/C = 10,000, 95% yield, 99% ee)
Analysis of Monitoring Strategies for Photovoltaic Water Pumping Systems in Low-Income Remote Areas
No full textInternational audiencePhotovoltaic water pumping systems (PVWPS) can greatly enhance access to clean water in rural and low-income regions of sub-Saharan Africa, thereby contributing to improved health and well-being. PVWPS monitoring can significantly help for effective operation and performance, with continuous monitoring providing comprehensive data. However, there is a lack of detailed feedback on the long-term effects of continuous monitoring. This article addresses this gap by presenting a five-year case study of continuous monitoring on a PVWPS in Gogma, Burkina Faso, and by analyzing the benefits and challenges associated with such extended monitoring. We also detail the technical decisions involved in designing a robust data acquisition system (DAS) and highlight the academic contributions enabled by the five-year dataset obtained, including the development of machine learning algorithms for detecting module cleaning. Despite the clear benefits in terms of scientific research, significant challenges associated with continuous long-term monitoring have been identified, including logistical difficulties, financial constraints, and maintenance issues of DAS in remote areas. To mitigate these challenges, we suggest implementing a periodic monitoring approach, with annual or bi-annual site visits by trained technicians. This method is aimed at local practitioners, retaining the benefits of data collection while reducing costs and logistical burdens, making it suitable for practical (non-research) applications in resource-constrained environment
Hexaphyrin-Cyclodextrin Hybrids: Switching between Möbius and Hückel Aromatic Systems in Chiral Environment
No full textInternational audienc
Conception et élaboration d'alliages de titane antibactériens pour l'implantologie dentaire
No full textTitanium alloys such as Ti grade 4 and TA6V are preferred in dental implantology because of their corrosion resistance, good mechanical properties and biocompatibility. However, bacterial infections around implants remain a source of complications. To remedy this, the addition of silver, an antibacterial element, to the composition of titanium alloys is being explored to create intrinsically biocidal materials. The aim of this thesis work is to develop thermomechanical processes to obtain controlled microstructures to optimize both biological and mechanical properties. The study of the Ti-7Ag alloy revealed slow precipitation kinetics resulting in microstructures different from thermodynamic predictions. By applying a recrystallization treatment after deformation steps, a homogeneous distribution of nanometric precipitates is obtained, facilitated by the accelerated diffusion of silver along the dislocations. This optimized structure improves the mechanical properties, making them comparable to those of grade 4 titanium. A similar thermomechanical process was then developed for an innovative alloy designed in the laboratory, Ti-4.5Zr-0.6O, after adding silver to its composition. The work showed that it was difficult to chemically homogenize the microstructure due to the low diffusion rate of zirconium, which reduces the efficiency of precipitation. The mechanical properties show low ductility but much higher mechanical strength than TA6V, making further study of the alloy promising with a view to a new antibacterial material for dental implantology.Les alliages de titane, comme le Ti grade 4 et le TA6V, sont privilégiés en implantologie dentaire pour leur résistance à la corrosion, leurs bonnes propriétés mécaniques et leur biocompatibilité. Cependant, des infections bactériennes autour des implants restent une source de complications. Pour y remédier, l'ajout d'argent, un élément antibactérien, dans la composition des alliages de titane est exploré dans cette thèse pour créer des matériaux intrinsèquement biocides. Ce travail vise à développer des procédés thermomécaniques permettant d'obtenir des microstructures contrôlées, afin d'optimiser leurs propriétés biologiques et mécaniques. L'étude de l'alliage Ti-7Ag a révélé une cinétique de précipitation lente, aboutissant à des microstructures différentes des prévisions thermodynamiques. En appliquant un traitement de recristallisation après des étapes de déformation, on obtient une distribution homogène de précipités nanométriques, facilitée par la diffusion accélérée de l'argent le long des dislocations. Cette structure optimisée améliore les propriétés mécaniques, les rendant comparables à celles du titane grade 4. Un procédé thermomécanique similaire est ensuite développé pour un alliage innovant conçu au laboratoire, Ti-4,5Zr-0,6O, après avoir ajouté de l'argent dans sa composition. Les travaux ont montré une difficulté à homogénéiser chimiquement la microstructure à cause de la faible vitesse de diffusion du zirconium, ce qui réduit l'efficacité de la précipitation. Les propriétés mécaniques montrent une faible ductilité, mais une résistance mécanique bien supérieures à celle du TA6V, ce qui rend la poursuite de l'étude de l'alliage prometteuse, dans l'optique d'un nouveau matériau antibactérien pour l'implantologie dentaire
