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Machine-Learning assisted characterization of defects in FeNiCr alloys induced by displacement cascades
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Comparative study of a new semi-empirical model of the proton exchange membrane fuel cell for online prognostics applications
No full textInternational audienceThe prognostic of the proton exchange membrane fuel cell is a current topic of research. Consequently, the complexity of its degradation mechanisms has led to the development of semi-empirical models to improve predictive analysis. The accurate estimation of parameters for these models is a challenging task due to their multivariate, nonlinear, and complex characteristics. This work proposes a new semi-empirical model of the proton exchange membrane fuel cell and compares it with a widely used model in the literature. Unlike other similar studies, this comparison not only focuses on minimizing the sum of squared errors in relation to the experimental data but also evaluates the variation in the solution set and the computational effort involved. For both models, the unknown parameters are estimated using the recent Pelican Optimization Algorithm. Four datasets are used to evaluate the development of the proposed model and the selected benchmark model. The first three datasets are open-access and well-recognized in academic literature, whereas the fourth dataset was obtained from a developed experimental test bench. The results show that the proposed model achieves high accuracy, with a mean absolute percentage error lower than 0.89% and the sum of squared errors below 0.9272 for all the studied scenarios. This model reduces parameter variation and decreases the relative standard deviation by over 12.7% compared to the utilized benchmark model for the first three datasets. Hence, the proposed model not only improves the precision of the estimated parameters without a notable increase in error but also reduces the computational load by at least 21.7% across all case studies
Understanding and Enhancing the Cycling Stability of Layered Double Hydroxides with Intercalated Ferrocene Anions for Energy Storage Application
No full textInternational audienceIn this work, the layered double hydroxide (LDH) Mg 2 Al(OH) 6 was intercalated with redox active ferrocene carboxylate anions in order to implement charge storage capability to the interlayer spaces of the LDH structure. Two sets of anions, namely mono‐ and dicarboxylic ferrocene, were intercalated to produce two different active materials: MgAl‐FcMono and MgAl‐FcDi. The electrochemical investigation of these two materials was performed in two model electrolytes: 1 M LiTFSI in H 2 O and Pyr 13 TFSI. In the aqueous electrolyte, the first charge reaches the full theoretic capacity of ca. 60 and 40 mAh g −1 for both materials. However, significantly less capacity is stored and delivered during subsequent cycles. In‐situ UV/vis experiments identified the loss as a release of charged ferrocene anions from the LDH during oxidation in the charging process, which is more severe for MgAl‐FcMono. It is possible to prevent this release of redox species by the use of the ionic liquid Pyr 13 TFSI as a high concentrated electrolyte. Subsequently, both materials cycled very steadily with high coulombic efficiency for 150 cycles. This better understanding of the capacity degradation of the LDH‐ferrocene active material is key to improving this new and promising concept of using modified LDHs as active material in energy storage application
A stateful protocol-based detection engine combining behavior use cases and system specifications
No full textInternational audienceFaced with the increasing need for network monitoring, many detection methods have been proposed. In the last few years, AI-based methods, especially Machine Learning, have been the most popular. However, these methods are not yet fully operational and detection methods based on signatures or on specifications still keep all their legitimacy. In this letter, we propose a technique that combines a detection method based on protocol specification with a learning method train on a dataset specific to a use case. This combination leads to the definition of the notion of protocol profile. Our solution is a continuation of a previous work which proposes an anomaly detection over-layer that are complementary to the pre-existing ones within a NIDS. The latter keeps its usual detection technique to which is added a stateful monitoring layer based on protocol specifications represented using Harel statecharts as well as our protocol profile layer. An algorithm has been proposed to automatically generate a protocol profile. It is based on event occurrence probabilities and an intermediate data format that we introduce: the Flow Graph Execution Log (FGEL). Other algorithms are also mentioned. A prototype has been realized and an experimentation with the POP3 protocol and simulated data sets has allowed to validate the concept.</div
Targeted and untargeted discovery of UV filters and emerging contaminants with environmental risk assessment on the Northwestern Mediterranean coast
No full textInternational audienceMarine ecosystems, particularly coastal areas, are becoming increasingly vulnerable to pollution from human activities. Persistent organic pollutants and contaminants of emerging concern (CECs) are recognized as significant threats to both human and environmental health. Our study aimed to identify the molecules present in the seawater of two bathing areas in the Western Mediterranean Sea. Polar Organic Chemical Integrative Samplers were employed for passive sampling of UV filters and other contaminants in the seawater. The concentrations of UV filters bemotrizinol (BEMT), benzophenone-3 (BP3), diethylamino hydroxybenzoyl hexyl benzoate (DHHB), octyl triazone (ET), and octocrylene (OC) were measured at these bathing sites during the summer of 2022. In addition, non-targeted chemical analysis was used to complement the list of pollutants in the sampling areas, leading to the identification of 53 contaminants and three natural products. Dodecyltrimethylammonium (DTA) and tetradecyltrimethylammonium (TTA) ions, 1,3-diphenylguanidine (DPG), N,N-diethyl-m-toluamide (DEET), and crystal violet (CV) were successfully quantified. Risk assessments showed that DEET, DPG, and BP3 present low environmental risks at the detected concentrations, while CV, DTA, and TTA pose medium to high risks, warranting further investigation. OC was found to pose a significant risk to marine biodiversity, as its environmental concentrations exceeded predicted no-effect concentration values. Overall, this study highlights the complexity of environmental pollution in coastal bathing areas and underscores the urgent need for comprehensive risk assessments to safeguard marine life and public health.</div
A simple criterion to exclude the risk of brittle fracture in the brittle-to-ductile transition temperature range
No full textInternational audienceThis paper presents the use of a simple threshold stress criterion to exclude the risk of brittle fracture in the brittle-to-ductile transition temperature range of carbon-manganese ferritic steel. In order to compare its predictions for laboratory specimens as well as for structures, fracture tests on CT specimens and three pipe structures representative of the in-service auxiliary piping system of French PWR, were analysed. In association with Finite Element analyses, this criterion allowed the authors to predict a lower bound of the non-fracture threshold
A comparison of eight weakly dispersive Boussinesq-type models for non-breaking long-wave propagation in variable water depth
No full textInternational audienceWeakly dispersive Boussinesq-type models are extensively used to model long-wave propagation in coastal areas and their interaction with coastal infrastructures. Many equations falling in this category have been formulated during the last decades, but few detailed comparisons between them can be found in the literature. In this work, we investigate theoretically and with computational experiments eight variants of the most popular models used by the coastal engineering community. Both weakly nonlinear and fully nonlinear models are considered, hoping to understand better when the additional complexity of the latter class of models is necessary or justified. We provide an overview and discuss the properties of these models, including the linear dispersion relation in uniform water depth, the second-order nonlinear coupling coefficient, the shoaling gradient, and the sensitivity to wave trough instabilities. The models are then numerically discretised using the same general strategy in a single numerical code, using fourth-order methods for time and space discretisation. Their capacity to simulate coastal wave propagation and their transformation when approaching the shore is assessed on three challenging one-dimensional benchmarks. It appears that fully nonlinear models are more consistent than their weakly nonlinear counterparts, which can occasionally perform better but show different behaviours depending on the case
On the use of a local to improve MCMC convergence diagnostic
No full textInternational audienceDiagnosing convergence of Markov chain Monte Carlo is crucial and remains an essentially unsolved problem. Among the most popular methods, the potential scale reduction factor, commonly named , is an indicator that monitors the convergence of output chains to a target distribution, based on a comparison of the between-and within-variances. Several improvements have been suggested since its introduction in the 90s. Here, we aim at better understanding the behaviour by proposing a localized version that focuses on quantiles of the target distribution. This new version relies on key theoretical properties of the associated population value. It naturally leads to proposing a new indicator , which is shown to allow both for localizing the Markov chain Monte Carlo convergence in different quantiles of the target distribution, and at the same time for handling some convergence issues not detected by other versions
Réflexions sur la puissance motrice du Soleil
No full textInternational audienceA quintessential source of heat, the Sun radiates toward the Earth a power ten thousand times greater than humanity's energy needs. Harnessing this energy bounty, however, requires capturing and converting sunlight. Today, this conversion can be achieved through several families of technologies at varying stages of maturity: photovoltaic solar, thermal, concentrated solar power, and more. While their applications differ, all these technologies must meet common fundamental constraints, and as Carnot proposed, one can 'consider in all its generality the principle of producing motion through heat' from the Sun. However, unlike traditional 'heat engines,' the coupling with the hot source here is radiative, introducing specific constraints that must be accounted for. In this presentation dedicated to radiative machines, you will encounter familiar terms as well as particular expressions that will provide the keys to understanding solar technologiesSource de chaleur par excellence, le Soleil rayonne vers la Terre une puissance dix mille fois supérieure aux besoins d'énergie de l'humanité. Tirer parti de cette manne énergétique nécessite cependant de parvenir à capter et à convertir la lumière. Cette conversion peut aujourd'hui être réalisée par plusieurs familles de technologies, à différents degrés de maturité : solaire photovoltaïque, thermique, à concentration… Si leurs applications sont différentes, toutes ces technologies doivent répondre à des contraintes fondamentales communes, et on peut comme Carnot « envisager dans toute sa généralité le principe de la production du mouvement par la chaleur » du Soleil. Mais contrairement aux « machines à feu », le couplage avec la source chaude est ici radiatif, ce qui ajoute des contraintes particulières dont il faut tenir compte. Dans cet exposé consacré aux machines radiatives, on retrouvera donc des termes familiers, mais aussi des expressions particulières qui donneront les clés de compréhension des technologies solaires
