Portail HAL Ensta
Not a member yet
11080 research outputs found
Sort by
Experimental investigation of the effect of infill parameters on dynamic compressive performance of 3D-Printed carbon fiber reinforced polyethylene terephthalate glycol composites
No full textInternational audienceThe current investigation evaluates the compressive response of 3D-printed carbon fiber-reinforced PETG thermoplastics to optimize different infill parameters when loaded at high impact pressures (strain rates). The selected parameters for the 3D printing of different samples are the filling pattern (rectilinear and honeycomb) and the filling density (25%, 50%, and 75%). Compression-split Hopkinson pressure bars (SHPBs) combined with a high-speed camera were used to monitor the evolution of the mechanical behavior and damage kinetics of 3D-printed samples in real-time with the variation in strain rate. The results revealed a significant improvement in compressive strength and compressive modulus when the filling density was increased from 20% to 75% for both patterns. However, the combination of a honeycomb pattern with 75% filling presented the best compressive strength, stiffness and damage resistance, irrespective of impact pressure. In particular, the highest compressive strengths, ranging from 35.5 to 56.16 MPa for impact pressures of 1.4 to 2.4 bar, respectively, were obtained with this configuration (75% honeycomb pattern). This represents a substantial difference of 25 to 38% compared with the 75% rectilinear pattern, which showed values below 35 MPa. Another significant result was observed for the compressive modulus, which reached 2787.8 MPa for the honeycomb-filled samples, whereas this value remained below 2000 MPa for the rectilinear pattern
Beyond the Fermat optimality rules
No full textThis work proposes a general framework for analyzing the behavior at its extrema of an extended real-valued function assumed neither convex nor differentiable and for which the classical Fermat rules of optimality do not apply. The tools used for building this frame are the notions of sup-subdifferential, recently introduced by two of the authors together with A. Kruger, and partial sup-subdifferentials. The sup-subdifferential is always a \textit{nonempty} enlargement of the Moreau-Rockafellar subdifferential from convex optimization. It satisfies most of the fundamental properties of the Moreau-Rockafellar subdifferential and enjoys certain calculus rules. The partial sup-subdifferentials are obtained by breaking down the sup-subdifferential into one-dimensional components through basis elements and play the same role as the partial derivatives in the Fermat optimality rules
Relaxed-inertial proximal point type algorithms for problems involving strongly quasiconvex functions
No full textInternational audienceIntroduced in the 1970's by Martinet for minimizing convex functions and extended shortly afterwards by Rockafellar towards monotone inclusion problems, the proximal point algorithm turned out to be a viable computational method for solving various classes of optimization problems even beyond the convex framework. In this talk we propose a relaxed-inertial proximal point type algorithm for solving optimization problems consisting in minimizing strongly quasiconvex functions whose variables lie in finitely dimensional linear subspaces. The method is then extended for equilibrium functions involving strongly quasiconvex functions. Computational results confirm the theoretical advances
Characterization of auto-inducing molecules from bacterial quorum sensing using Paternò-Büchi reaction and tandem mass spectrometry
No full textInternational audienceThe quorum sensing is a chemical language allowing bacteria to interact [1], through the excretion of a set of molecules called auto-inducers. From a threshold population density, and thus a threshold concentration of auto-inducing molecules, their detection by an intracellular receptor regulates bacterial gene expression, including resistance or virulence genes.Our study focuses on the auto-inducing N-acyl-homoserine lactones (AHL) [2] of Gram-negative bacteria from the Burkholderia and Paraburkholderia genus as some of these bacteria species are described as opportunistic pathogens for humans [2]. The AHL differ in their acyl-chain length (generally from C4 to C18) and may be modified by a 3-oxo or 3-hydroxy substituent, a terminal methyl branch, or various degrees of unsaturations [3]. As the bacterial signal specificity depends on all of those, including the instauration’s position on the acyl chain, it is essential to obtain a complete structural charaterization of AHL to better understand the population regulation and virulence phenomenon.Although several mass spectrometry (MS) methods have been developed to study AHL [4], only NMR analyses requiring the purification of a large amount of product enable the localization of the double bonds on the acyl chain. Thus, this study aims to develop a new method that will significantly reduce the amount of biological material needed. This method is based on LC-MS/MS or/and SFC-MS/MS analyses of extracts derived by a Paternò-Büchi reaction in solution or post-column [5]. In parallel, in situ characterization will be performed by the deposition of a photoreactive matrix on the bacterial cultures followed by imaging MS analyses. References1. J. Baltenneck, S. Reverchon, F. Hommais, Microorganisms, 9, 239 (2021)2. L. Eberl, Int. J. Med. Microbiol., 296, 103-110 (2006)3. M. Churchill, L. Chen, Chem. Rev., 111, 68-85 (2011)4. N. Patel, J. Moore, H. Blackwell, D. Amador-Noguez, PloS One, 11, e0163469 (2020)5. T. Xu, Z. Pi, F. Song, S. Liu, Z. Liu, Anal. Chim. Acta, 1028, 32-44 (2018
Structural characterization of N-acyl-homoserine lactones involved in bacterial quorum sensing using LC-MS/MS or SFC-MS/MS after in-solution Paternò-Büchi derivatization
No full textInternational audienceThe quorum sensing is a chemical language allowing bacteria to interact through the excretion of molecules called auto-inducers. Those molecules regulate bacterial gene expression, including resistance or virulence ones.Our study focuses on the auto-inducing N-acyl-homoserine lactones (AHLs) of Gram-negative bacteria from the Burkholderia and Paraburkholderia genus. The AHLs dier in their acylchain length and may be modied by a 3-oxo or 3-hydroxy substituent, or various degrees of unsaturation (1). As the bacterial signal specicity depends on all of these features, including the unsaturation position, it is mandatory to determine their complete structuralcharacterization to better understand the population regulation and virulence phenomenon. Therefore, this study aimed to develop a method enabling the localization of the C=C double bond while using signicantly low amount of biological material. Our method is based on LC-MS/MS or/and SFC-MS/MS analyses of bacterial extracts after in-solution derivatization by a Paterno-Buchi reaction which is a photochemical (2+2) addition of a ketone on a C=C double bond leading to the formation of an oxetane ring (2).To optimize the in-solution derivatization of AHLs, the influence of various parameters (UV wavelength, solvent, Paterno-Buchi reagent, AHL/reagent ratio, reaction time) was studied with a design of experiments on 12.5 pmol of an AHL standard per LC-MS/MS analysis. The best results were obtained after a 15-minute derivatization at 254 nm, in acetonitrile, and with 2-acetylpyridine at AHL/reagent ratio of 1/100. MS/MS of Paterno-Buchi products enabled the localization of the C=C double bond due to the specic fragmentation of the oxetane ring. As a proof of concept, LC-MS/MS and SFC-MS/MS analyses were performed on bacterial extracts after in-solution derivatization.Finally, the implementation of the Paterno-Buchi reaction post-column is currently under investigation.(1) Churchill et al., Chem. Rev., 2011, 111 (1), 68-85(2) Xu et al., Anal. Chim. Acta, 2018, 1028, 32-4
Étude théorique et expérimentale du réarrangement de Hock
No full textThe Hock rearrangement is a Brønsted or Lewis acid catalyzed reaction involving the heterolytic cleavage of a Cα-Cβ bond adjacent to a peroxide group, which leads to the 1,2 migration of the β carbon to the closest oxygen of the peroxide group. Despite its significant industrial applications such as the cumene process, there is still a lack of understanding of this reaction. The aim of this thesis was thus to shed light on the physico-chemistry and potential applications of this reaction through an approach combining synthesis and modeling. Herein, we present the first mechanistic study of the Hock reaction using DFT, we explore the development of new tandem reactions involving this rearrangement and provide insights into its selectivity. DFT studies have allowed to elucidate the underlying mechanism of the InCl3-catalyzed Hock reaction. The presence of a metastable Wheland intermediate was established, providing insight on the impact of substituents on the activation barrier of the Hock rearrangement through the use of interpretative methods of quantum chemistry such as NBO and IBO. The active structure of InCl3 was investigated, revealing the existence of a monomer which exists only in a coordinated form in the reaction media. A novel tandem reaction involving the Hock cleavage and the Hosomi-Sakurai allylation has been developed. This reaction allowed the access to biologically interesting products such as allylated chroman rings from substituted indanyl hydroperoxide substrates. In particular, branched allylsilanes have been shown to be effective nucleophiles in trapping the reaction intermediates. Then, the reaction was adapted to work with substituted phenylcyclobutyl peroxide substrates to study the sp2/sp3 selectivity of the rearrangement. An inversion of chemoselectivity on these substrates was predicted by modeling and confirmed experimentally. Particularly, incorporating π-donor substituents in the ortho and para positions of the aromatic ring enabled to promote the migration of the sp2 carbon rather than the sp3, leading to an extension of the cyclobutane ring to form tetrahydrofuran. To conclude, this study fills a gap in the understanding of this crucial reaction, it also enabled to expand its application scope with potential implications for drug development and fine chemistry.Le réarrangement de Hock est une réaction impliquant la rupture hétérolytique d’une liaison Cα-Cβ adjacente à une fonction peroxyde sous catalyse acide de Brønsted ou de Lewis. Elle entraine la migration 1,2 du carbone β vers l’oxygène le plus proche du groupement peroxyde. Bien que certaines applications industrielles importantes existent, comme le procédé au cumène, un manque de connaissances concernant cette réaction est manifeste. L’objectif de cette thèse était donc, par une démarche couplant expériences de synthèse et modélisations, d’apporter un nouvel éclairage sur la physico-chimie et les applications potentielles de cette réaction. Ce manuscrit présente ainsi la première étude mécanistique de la réaction de Hock basée sur la DFT, le développement de nouvelles réactions tandem impliquant ce réarrangement ainsi que des éclaircissements sur sa sélectivité. Les études DFT ont permis de fournir une compréhension claire du mécanisme de la réaction de Hock catalysée par InCl3. Un intermédiaire de Wheland métastable a été mis en évidence, permettant d’expliquer, grâce à l’utilisation de méthodes interprétatives de la chimie quantique comme NBO et IBO, l’influence électronique des substituants sur la barrière d’activation du réarrangement de Hock. La structure active du catalyseur InCl3 a également été investiguée, mettant en évidence que, dans le milieu réactionnel, sa forme monomérique n’existe que lorsqu’il est coordiné. Concernant les applications de ce réarrangement, une nouvelle réaction tandem combinant le clivage de Hock et l’allylation de Hosomi-Sakurai a été développée. Cette réaction a permis d’accéder à des produits d’intérêt biologique tels que des cycles chromanes allylés à partir d’hydroperoxydes d’indan-1-yl substitués. Des nucléophiles de type allylsilane ramifiés se sont notamment révélés efficaces pour piéger les intermédiaires de réaction. Enfin, cette réaction a été adaptée pour travailler avec des substrats peroxyde de 1-phenylcyclobutyle substitués afin d’étudier la sélectivité sp2/sp3 du réarrangement. Une inversion de la chimiosélectivité sur ces substrats a été prédite par modélisation et confirmée expérimentalement. En effet, l’ajout de substituants π-donneurs en position ortho et para du cycle aromatique favorise la migration du carbone sp2 plutôt que la migration du carbone sp3, conduisant à l'extension du cycle cyclobutane pour former un tétrahydrofurane. En conclusion, ces travaux comblent une lacune dans la compréhension de cette réaction importante, élargissent son champ d’application et pourraient ainsi avoir un impact significatif sur le développement de médicaments et la chimie fine
Beam current from downramp injection in electron-driven plasma wakefields
No full textInternational audienceWe study the stability of plasma wake wave and the properties of density-downramp injection in an electron-driven plasma accelerator. In this accelerator type, a short high-current electron bunch (generated by a conventional accelerator or a laser-wakefield acceleration stage) drives a strongly nonlinear plasma wake wave (blowout), and accelerated electrons are injected into it using a sharp density transition which leads to the elongation of the wake. The accelerating structure remains highly stable until the moment some electrons of the driver reach almost zero energy, which corresponds to the best interaction length for optimal driver-to-plasma energy transfer efficiency. For a particular driver, this efficiency can be optimised by choosing appropriate plasma density. Studying the dependence of the current of the injected bunch on driver and plasma parameters, we show that it does not depend on the density downramp length as long as the condition for trapping is satisfied. Most importantly, we find that the current of the injected bunch primarily depends on just one parameter which combines both the properties of the driver (its current and duration) and the plasma density
Domain generalization of 3D semantic segmentation in autonomous driving
No full textInternational audienc
