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Evidence for Methylaluminoxane (MAO) Molecular Structure and Reactivity from Ultra-High Magnetic Field 27Al MAS NMR Spectroscopy Combined with DFT Calculations.
No full textInternational audienceThe structure and reactivity of methylaluminoxane (MAO), a reagent of major interest for olefin polymerization, both industrially and academically, has been probed using ultrahigh magnetic field solid-state NMR (28.2 T, 1200 MHz for 1H Larmor frequency). High resolution methods combined with density functional calculations allowed for the identification and quantification of five major aluminum sites, providing precise information on the structure of MAO at the molecular level. Based on reactivity studies with THF and [ZrCp2Me2], the main reactive centers are identified as bismethyl aluminum species stabilized via a bridging methyl group from a neighboring Al center, featuring both high chemical shift and quadrupolar coupling constants (162 ppm and 27.4 MHz, respectively). This approach demonstrates the ability to monitor the chemistry of MAO with unprecedented precision, enabling a state-of-the-art understanding of its structure and reactivity
Champagne et placement de produit : une alliance effervescente dans Emily in Paris
No full textInternational audienceCette recherche traite des enjeux sous-jacents d’un placement de produit narratif ausein d’une série télévisée. Il s’agit d’identifier et de comprendre les enjeux mutuels, pour lesmarques et les scénaristes, de la mise en avant du champagne dans Emily in Paris à traversplusieurs approches méthodologiques : l’analyse lexicale d’un corpus presse de 14 392 mots ;l’identification par visionnage des formes de placement du champagne mobilisées dans la série etl’analyse de leurs critères d’efficacité ; l’analyse thématique de 20 entretiens individuels semi-directifs réalisés auprès de spectateurs de la série. Les résultats préliminaires confirment que lestechniques liées au placement de produit dans les séries télévisées sont similaires à cellesidentifiées dans les films. En revanche, leurs effets sur l’identification et la mémorisation desmarques semblent incertains. Enfin, nous confirmons qu’une marque ou catégorie de produitspeut jouer un rôle diégétique dans la construction des personnages et de l’univers d’une série
Un problème, neuf approches !
No full textInternational audienceDe la différenciation pédagogique dans l'enseignement des mathématiques au collège et au lycé
Why we should review research software
No full texthttps://blog.khinsen.net/At the recent SciCodes Symposium, I brought up the question of reviewing research software during the panel discussion. One panelist then raised the question of why we should review research software. I found this question surprising at first, but I do agree that it deserves an answer. Here is mine
Enhanced Numerical Solutions for Fractional PDEs Using Monte Carlo PINNs Coupled with Cuckoo Search Optimization
No full textInternational audienceIn this study, we introduce an innovative approach for addressing fractional partial differential equations (fPDEs) by combining Monte Carlo-based physics-informed neural networks (PINNs) with the cuckoo search (CS) optimization algorithm, termed PINN-CS. There is a further enhancement in the application of quasi-Monte Carlo assessment that comes with high efficiency and computational solutions to estimates of fractional derivatives. By employing structured sampling nodes comparable to techniques used in finite difference approaches on staggered or irregular grids, the proposed PINN-CS minimizes storage and computation costs while maintaining high precision in estimating solutions. This is supported by numerous numerical simulations to analyze various high-dimensional phenomena in various environments, comprising two-dimensional space-fractional Poisson equations, two-dimensional time-space fractional diffusion equations, and three-dimensional fractional Bloch–Torrey equations. The results demonstrate that PINN-CS achieves superior numerical accuracy and computational efficiency compared to traditional fPINN and Monte Carlo fPINN methods. Furthermore, the extended use to problem areas with irregular geometries and difficult-to-define boundary conditions makes the method immensely practical. This research thus lays a foundation for more adaptive and accurate use of hybrid techniques in the development of the fractional differential equations and in computing science and engineering
Organics in the stratosphere: new insights from weather balloon flights conducted in France
No full textInternational audienceAtmospheric aerosols significantly influence the Earth’s climate, yet they remain a major source of uncertainty in climate projections. Here, we present a set of unique offline analysis of organics collected from the ground to the stratosphere with ultimate sensitivity using a new balloon-borne sampling technique deployed on simple weather balloons. Activated and functionalized carbon fabrics were used to target chemical compounds in the gaseous and aerosol forms during three flights over France. Ultra-high-resolution mass spectrometry, enabling the detection of thousands of organic compounds, and highlighted high-carbon-number organics, indicating oligomerization in long-lived tropical stratospheric air masses. Our measurements suggest that large stratospheric sulfate aerosols from volcanic eruptions could play a role in the formation of secondary aerosols in internally mixed particles and may explain the presence of organics with higher carbon numbers. These measurements revealed a drop in the number of unsaturated carbons at higher altitudes
Les conséquences du CEP à Tahiti : jalons d'une histoire environnementale de l'agglomération de Pape'ete
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Real-Time Object and Human Detection using YOLO for Autonomous Robot Navigation in Healthcare Workspaces
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Low temperature oxidation of neo-pentanal – Detailed speciation and kinetic modelling
No full textInternational audienceNeo-pentanal (2,2-Dimethylpropanal) is a highly branched C5 aldehyde, which has not been studied before for its oxidation kinetics. This study provides a detailed speciation of neo-pentanal oxidation between 600 and 1200 K. The experiments were done in a jet-stirred reactor at a constant residence time of 0.7 s and at 10 atm. A fuel-lean (ϕ = 0.5), a stoichiometric and a fuel-rich mixture (ϕ = 2) with an initial fuel mole fraction of 0.1% were tested. A fourth mixture with an initial fuel mole fraction of 0.3% was also tested at a higher residence time of 1.5 s. The former experimental conditions are the same as in our previous studies on n-pentanal and 2- and 3-methybutanal, while the latter condition is chosen in order to trigger reactivity at lower temperatures
Marches aléatoires transcientes sur l'espace des réseaux.
No full textGiven , we construct a Zariski-dense random walk on the space of lattices SLSL that exhibits escape of mass. This negates the suggestion of recurrence made by Benoist [Ben14] (ICM 2014) and by Bénard-de Saxcé [BS22] (also asked in [BQ12]). For any , we also construct such a random walk with finite -moment which shows that the moment assumption in [BS22] is sharp