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Microstructure and (De)lithiation Front in a 400 µm Thick 3D‐Printed LiFePO 4 Electrode
No full textInternational audienceThe progress towards more sustainable practices for the manufacturing of lithium‐ion batteries has lagged behind the faster evolution in the Li‐insertion materials and electrolyte formulations. 3D printing is a potential alternative coating method that can enable the preparation of high‐loading electrodes with a good control over the microstructural details and spatial distribution of the electrode components. Herein, a high loading LiFePO 4 electrode with an areal loading of 30 mg cm −2 is reported. This is achieved by 3D printing of an aqueous ink with an optimal formulation including carbon microfiber and carbon black as conductive additives and carboxymethyl cellulose and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate as binders. The electrodes are characterized for the electronic and ionic percolation to substantiate the superior performance of the 3D‐printed electrodes compared to their conventionally doctor‐blade coated counterparts. The in situ µ‐x‐ray diffraction (XRD) imaging of the electrodes is performed to visualize the in‐ and through‐plane solid‐state Li concentration profiles within the 400 µm thick 3D‐printed electrodes during cycling at C/5 and 1C. The concentration‐gradient maps, once analyzed together with the tortuosity data, and physics‐based simulations, identify the synergistic effect of an enhanced ionic transport and higher active surface‐area of the 3D‐printed electrodes to be the cause of their superior performance
Modification of the stress corrosion cracking behavior of a zinc aluminosilicate glass with crystallization
No full textNational audienc
Wind Task 51 and PVPS task 16: How large-scale weather pattern influence short-term solar forecast error?
No full textInternational audienceAccurate intraday solar forecasts are crucial for electricity trading and microgrid management. While satellitebased methods outperform numerical weather prediction (NWP) models for short-term horizons, their accuracy depends heavily on stable weather conditions, performing poorly during convection, fog, or large depressions. This study investigates the impact of various North Atlantic weather regimes-Atlantic Ridge, Scandinavian Blocking, NAO+, and NAO--on the reliability of satellite-based forecasts.We conducted an 8-year backtest using forecasts generated four hours ahead with a 15-minute time step and validated them against pyranometer data. Our analysis shows that forecast errors vary significantly with the prevailing weather regime. The difference in relative RMSE between the Scandinavian Blocking and Atlantic Ridge regimes was 10-12% in summer (2016-2020) and approximately 10% after 2020. In winter, this difference was around 20% before 2020 and 15% after 2020. These findings demonstrate that large-scale atmospheric patterns significantly influence forecast reliability. Given that weather regimes can be predicted in advance, this analysis provides valuable insights for anticipating forecast error, which can help optimize PV integration and serve as a useful input for machine-learning-based forecast algorithms. These variations in weather regime frequencies directly impact forecast errors, emphasizing the importance of large-scale atmospheric patterns in solar energy forecast reliability. As weather regimes can be predicted several days in advance, this analysis provides useful information to anticipate the magnitude of forecast error and therefore adapt suitable decisions for optimizing PV integration management and electricity trading and provide important insights to develop deep learning forecast algorithms
Constraining the nature of the most extreme Galactic particle accelerator. H.E.S.S. observations of the microquasar V4641 Sgr
No full textInternational audienceMicroquasars have emerged as promising candidates to explain the cosmic-ray flux at petaelectronvolt energies. LHAASO observations revealed V4641~Sgr as the most extreme example so far. Using 100~h of H.E.S.S. data, we performed a spectro-morphological study of the gamma-ray emission around V4641~Sgr. We employed HI and dedicated CO observations of the region to infer the target material for cosmic-ray interactions. We detected multi-TeV emission around V4641~Sgr with a high significance. The emission region is elongated. We found a power-law spectrum with an index 1.8, and together with results from other gamma-ray instruments, this reveals a spectral energy distribution that peaks at energies of 100~TeV for the first time. We found indications (3) of a two-component morphology, with indistinguishable spectral properties. The position of V4641~Sgr is inconsistent with the best-fit position of the single-component model and with the dip between the two components. We found no significant evidence of an energy-dependent morphology. No dense gas was found at any distance towards V4641~Sgr. The peak of the SED at 100~TeV identifies V4641~Sgr as a candidate cosmic-ray accelerator beyond the so-called knee. The absence of dense target gas places stringent energetic constraints on hadronic interpretations, however. The H.E.S.S. measurement requires an unusually hard () spectral index for the protons. A leptonic scenario faces fewer obstacles if the particle transport is fast enough to avoid losses and to reproduce the observed energy-independent morphology. The absence of bright \xray emission across the gamma-ray emission region requires a magnetic field strength ~G, however. Our findings favour a leptonic origin of the gamma-ray emission. This conclusion does not exclude hadron acceleration in the V4641~Sgr system
Explaining higher-order correlations between elliptic and triangular flow
No full textInternational audienceThe ALICE Collaboration has analyzed a number of cumulants mixing elliptic flow () and triangular flow (), involving up to particles, in Pb+Pb collisions at the LHC. We unravel an unexpected simplicity in these complex mathematical quantities for collisions at fixed impact parameter. We show that as one increases the order in , for a given order in , the changes in the cumulants are solely determined by the mean elliptic flow in the reaction plane, which originates from the almond-shaped geometry of the overlap area between the colliding nuclei. We derive simple analytic relations between cumulants of different orders on this basis. Some of these relations are in reasonable agreement with existing data. We postulate that agreement will be much improved if the analysis is repeated with a finer centrality binning and a larger pseudorapidity acceptance
Characterization of multifractality in oscillatory dynamics
No full textNeuronal oscillations exhibit large variability that has been hypothesized to reflect critical brain dynamics arising from the brains operating at a phase transition between disorder and order. A hallmark observable of such critical dynamics is scale-invariance that is typically quantified as long-range temporal correlations (LRTCs) in oscillation amplitude fluctuations. In this work, we extend the conventional scale-invariance-analysis framework for brain oscillations from selfsimilarity to multifractality. Using the new approach, we performed a multifractal analysis on the brain oscillation dynamics in different frequency bands of resting-state MEG recordings of 75 healthy human subjects. We estimated multifractal exponents from oscillation envelopes in frequencies from 5 to 96 Hz and assessed their anatomical and spectral patterns. To evaluate the statistical significance of multifractality estimates, we advance here two surrogate data generation methods. We found multifractality to be significant across the studied frequency range and to be most prevalent in the alpha-(8-14 Hz) and beta-(15-30 Hz) frequency bands. Moreover, we found self-similarity and multifractality estimates to be correlated and showed using the Principal Component Analysis that was explained by a correlation between the leading principal component and the multifractal estimates. Finally, we found the aggregate multifractal estimates to be highly consistent between sensor space and source-reconstructed MEG data
Théorie des séquences adaptée à la vérification des programmes
No full textThe choices of semantic models for a programming language have a significant effect on the efficiency of the verification of programs in that language. Indeed, many verification techniques generate mathematical formulas using those models. The mathematical theories used in these formulas and their shape have a direct impact on their solvability by the used solver. The modelization of memory and data structures often uses the SMT (Satisfiablity Modulo Theories) theory of arrays which is well established and used in SMT solvers. In this theory, arrays associate values with indices, both of which can be of any type. The theory also allows for operations that enable the writing and reading of the stored data. However, in the concrete programs from which the formulas that need to be solved are produced, memory and data structures are usually limited. For example, arrays in programming languages are usually indexed from 0 to a constant n. Although it is possible to encode finite arrays in the SMT theory of arrays, that would not always be a satisfying solution, one reason being that extensional equality on a finite array from 0 to n cannot be directly modelized using the extensional equality on infinite arrays which considers all integers. An SMT theory of finite sequences, in which the sequences are collections of values indexed over a set of contiguous integers, would simplify the solving of formulas that modelize such data structures. Moreover, finite sequences with concatenation and extraction operators can also be used to express particular specification languages such as separation logic. One difficulty is to choose the set of operations on the sequences to support, since the decidability of the theory depends on them. On the other hand, complete decidability is not always required since the formulas obtained from program verification can have specific shapes or uses of the operations.The goal of the thesis is to study which the- ory of sequences is suitable for program ver- ification. The thesis focuses particularly on the case of n-indexed sequences, which are se- quences that can start at any index n and end at any index m. These sequence appear in the Ada programming language, but since they are a generalization of 0-indexed sequences, they should also make it possible to represent and reason about the latter. In this thesis, a the- ory of n-indexed sequences is proposed, and dif- ferent ways of reasoning about this theory are explored, whether through axiomatizations, by using existing theories, or by developing vari- ous calculi dedicated to this theory. The evalua- tion of these reasoning approaches is carried out through OCaml implementations in the Colibri2 CP (Constraint Programming) solver. Various details of these implementations are presented, as well as additional contributions to arithmetic reasoning.Les choix de modèles sémantiques d'un langage de programmation ont un effet important sur l'efficacité de la vérification des programmes dans ce langage. En effet, de nombreuses techniques de vérification génèrent des formules mathématiques en utilisant ces modèles. Les théories mathématiques utilisées dans ces formules et leur forme ont un impact direct sur leur solvabilité par le solveur utilisé. La modélisation de la mémoire et des structures de données utilise souvent la théorie SMT (Satisfiabilité Modulo Théories) des tableaux qui est bien établie et utilisée dans le domaine des solveurs SMT. Dans cette théorie, les tableaux permettent d'associer des valeurs à des indices, quel que soit le type des indices ou des valeurs. La théorie permet également des opérations permettant d'écrire et de lire le contenu des tableaux. Cependant, dans les programmes concrets d'où viennent les formules à prouver, la mémoire et les structures de données sont généralement limitées. Par exemple, les tableaux dans les langages de programmation sont généralement indexés de 0 à une constante n. Bien qu'il soit envisageable d'encoder les tableaux finis dans la théorie SMT des tableaux, cela n'est pas toujours une solution satisfaisante, une raison étant que l'égalité extensionnelle sur un tableau fini de 0 à n, ne peut pas être directement modélisée en utilisant l'égalité extensionnelle sur des tableaux infinis qui considère tous les entiers. Une théorie SMT des séquences finies, dans laquelle les séquences sont des collections de valeurs indexées sur un ensemble contigu d'entiers, simplifierait la résolution des formules qui modélisent de telles structures de données. De plus, les séquences finies avec des opérateurs de concaténation et d'extraction peuvent également être utilisées pour exprimer des langages de spécification particuliers tels que la logique de séparation. Une difficulté est de choisir l'ensemble des opérations sur les séquences à supporter, puisque la décidabilité de la théorie en dépend. D'un autre côté, la décidabilité complète n'est pas toujours requise, car les formules obtenues par la vérification de programmes peuvent avoir une forme ou une utilisation spécifique des opérations. L'objectif de la thèse est d'étudier quelle théorie des séquences est appropriée pour la vérification de programmes. La thèse s'intéresse notamment au cas des séquences n-indexées, qui sont des séquences qui peuvent commencer à n'importe quel indice n et se terminer à n'importe quel indice m. Ces séquences sont no- tamment présentes dans le langage de program- mation Ada, mais étant une généralisation des séquences 0-indexées, elles devraient permettre de représenter et de raisonner sur ces dernières également. Dans cette thèse, une théorie des séquences n-indexées est proposée, et différentes façons de raisonner sur cette théorie sont ex- plorées, que ce soit à travers des axiomatisa- tions, en utilisant des théories existantes ou en développant différents calculi dédiés à cette théorie. L'évaluation de ces approches de raisonnement est effectuée à travers des implé- mentations en OCaml dans le solveur de con- traintes Colibri2. Divers détails de ces implé- mentations sont présentés, ainsi que des con- tributions supplémentaires apportées au raison- nement arithmétique
A diffusion model for light scattering in ejecta
No full textInternational audienceWe derive a diffusion equation for light scattering from ejecta produced by extreme shocks on metallic samples. This model is easier to handle than a more conventional model based on the Radiative Transfer Equation (RTE) and is a relevant tool to analyze spectrograms obtained from Photon Doppler Velocimetry measurements in the deep multiple scattering regime. We also determine the limits of validity of the diffusive model compared to the RTE, based on a detailed analysis of various ejecta properties in configurations with increasing complexity
Electrochemical Wiring of Sugars onto Proteins and Living Cells
No full textInternational audienceIn the present study, we employed N-methylluminol (NML), a highly selective tyrosine-anchoring group upon one-electron oxidation, for the electro-bioconjugation of cell surfaces from viruses, live bacteria, and eukaryotic cells . The click-electrochemistry strategy was successfully applied to therapeutic adeno-associated viruses (AAV2), E. coli (Gram-negative), S. epidermidis (Gram-positive), and various eukaryotic cell lines. Within minutes, biologically relevant carbohydrates were grafted onto cell surfaces, offering a versatile and rapid alternative to metabolic engineering for targeted biotherapies and the exploration of cell surface glycans
Cloud and haze parameterization in atmospheric retrievals: Insights from Titan's Cassini data and JWST observations of hot Jupiters
No full textInternational audienceContext. Before JWST, telescope observations were not sensitive enough to constrain the nature of clouds in exo-atmospheres. Recent observations, however, have inferred cloud signatures as well as haze-enhanced scattering slopes motivating the need for modern inversion techniques and a deeper understanding of the JWST information content. Aims. We aim to investigate the information content of JWST exoplanet spectra. We particularly focus on designing an inversion technique able to handle a wide range of cloud and hazes. Methods. We built a flexible aerosol parameterization within the TAUREX framework, enabling us to conduct atmospheric retrievals of planetary atmospheres. The method is evaluated on available Cassini occultations of Titan. We then use the model to interpret the recent JWST data for the prototypical hot Jupiters HAT-P-18 b, WASP-39 b, WASP-96 b, and WASP-107 b. In parallel, we performed complementary simulations on controlled scenarios to further understand the information content of JWST data and provide parameterization guidelines. Results. Our results use free and kinetic chemistry retrievals to extract the main atmospheric properties of key JWST exoplanets, including their main molecular abundances (and elemental ratios), thermal structures, and aerosol properties. In our investigations, we show the need for a wide wavelength coverage to robustly characterize clouds and hazes - which is necessary to mitigate biases arising from our lack of priors on their composition - and break degeneracies with atmospheric chemical composition. With JWST, the characterization of clouds and hazes might be difficult, due to the lack of simultaneous wavelength coverage from visible to mid-infrared by a single instrument and the likely presence of temporal variability between visits (from e.g., observing conditions, instrument systematics, stellar host variability, or planetary weather)