A composite approach to Al2O3 based plasma-sprayed coatings

25-29 septembreInternational audienceThermally-sprayed ceramic coatings such as plasma-sprayed alumina show a composite microstructure actually due to the presence of defects such as pores, inter-lamellar and intralamellar cracks. These 2nd phase-typed features influence the mechanical behavior and electrical insulation of the coating dramatically. In this study, a composite approach to the microstructure of plasma-sprayed alumina was developed for the optimising of component properties such as electrical gaps used in the oil industry. This approach consisted of a Finite Element Analysis (FEA) of thermo-mechanical and electrical properties from simulated microstructures. Series of composite microstructures were tested, i.e that of air plasma-sprayed (APS) alumina basically plus those obtained by addition of glass or resin using co-spraying and impregnation respectively. Various degrees of porosity and cracks could be obtained from different spraying conditions and by subsequent laser surface remelting. Every composite microstructure was studied using quantitative image analysis of series of SEM cross-sections. Electrochemical Impedance Spectroscopy (EIS) in NaCl solution was also performed to characterize the level of connected pores and the resulting electrical insulating properties. From experiments, a Finite Element Model (FEM) based on the actual microstructure was developed. The latter was simulated with involving of all significant features, such as phase distribution, porosity and defects. This simulation was developed to optimize the composite microstructure to meet industrial applications

Computational models that matter during a global pandemic outbreak: A call to action

The COVID-19 pandemic is causing a dramatic loss of lives worldwide, challenging the sustainability of our health care systems, threatening economic meltdown, and putting pressure on the mental health of individuals (due to social distancing and lock-down measures). The pandemic is also posing severe challenges to the scientific community, with scholars under pressure to respond to policymakers’ demands for advice despite the absence of adequate, trusted data. Understanding the pandemic requires fine-grained data representing specific local conditions and the social reactions of individuals. While experts have built simulation models to estimate disease trajectories that may be enough to guide decision-makers to formulate policy measures to limit the epidemic, they do not cover the full behavioural and social complexity of societies under pandemic crisis. Modelling that has such a large potential impact upon people’s lives is a great responsibility. This paper calls on the scientific community to improve the transparency, access, and rigour of their models. It also calls on stakeholders to improve the rapidity with which data from trusted sources are released to the community (in a fully responsible manner). Responding to the pandemic is a stress test of our collaborative capacity and the social/economic value of research

Efficient Photonic Integration of Diamond Color Centers and Thin-Film Lithium Niobate

On-chip photonic quantum circuits with integrated quantum memories have the potential to radically progress hardware for quantum information processing. In particular, negatively charged group-IV color centers in diamond are promising candidates for quantum memories, as they combine long storage times with excellent optical emission properties and an optically-addressable spin state. However, as a material, diamond lacks many functionalities needed to realize scalable quantum systems. Thin-film lithium niobate (TFLN), in contrast, offers a number of useful photonic nonlinearities, including the electro-optic effect, piezoelectricity, and capabilities for periodically-poled quasi-phase matching. Here, we present highly efficient heterogeneous integration of diamond nanobeams containing negatively charged silicon-vacancy (SiV) centers with TFLN waveguides. We observe greater than 90\% transmission efficiency between the diamond nanobeam and TFLN waveguide on average across multiple measurements. By comparing saturation signal levels between confocal and integrated collection, we determine a $10$-fold increase in photon counts channeled into TFLN waveguides versus that into out-of-plane collection channels. Our results constitute a key step for creating scalable integrated quantum photonic circuits that leverage the advantages of both diamond and TFLN materials

Genetics of human hydrocephalus

Human hydrocephalus is a common medical condition that is characterized by abnormalities in the flow or resorption of cerebrospinal fluid (CSF), resulting in ventricular dilatation. Human hydrocephalus can be classified into two clinical forms, congenital and acquired. Hydrocephalus is one of the complex and multifactorial neurological disorders. A growing body of evidence indicates that genetic factors play a major role in the pathogenesis of hydrocephalus. An understanding of the genetic components and mechanism of this complex disorder may offer us significant insights into the molecular etiology of impaired brain development and an accumulation of the cerebrospinal fluid in cerebral compartments during the pathogenesis of hydrocephalus. Genetic studies in animal models have started to open the way for understanding the underlying pathology of hydrocephalus. At least 43 mutants/loci linked to hereditary hydrocephalus have been identified in animal models and humans. Up to date, 9 genes associated with hydrocephalus have been identified in animal models. In contrast, only one such gene has been identified in humans. Most of known hydrocephalus gene products are the important cytokines, growth factors or related molecules in the cellular signal pathways during early brain development. The current molecular genetic evidence from animal models indicate that in the early development stage, impaired and abnormal brain development caused by abnormal cellular signaling and functioning, all these cellular and developmental events would eventually lead to the congenital hydrocephalus. Owing to our very primitive knowledge of the genetics and molecular pathogenesis of human hydrocephalus, it is difficult to evaluate whether data gained from animal models can be extrapolated to humans. Initiation of a large population genetics study in humans will certainly provide invaluable information about the molecular and cellular etiology and the developmental mechanisms of human hydrocephalus. This review summarizes the recent findings on this issue among human and animal models, especially with reference to the molecular genetics, pathological, physiological and cellular studies, and identifies future research directions

Nouveau procédé d’outillage rapide par projection plasma de coques épaisses d’acier sur un modèle en résine élaboré par stéréolithographie

L’utilisation de la projection thermique présente un fort intérêt pour développer de nouvelles méthodes de fabrication rapide d’outils de production tels que les moules d’injection de polymères (méthodes d’outillage rapide). Comparée à l’une des méthodes actuelles les plus en pointe, qui fait appel à la projection à l’arc électrique ou à la flamme, la projection plasma permet une plus grande variété de matériaux et une meilleure maîtrise du procédé, donc d’élaborer des revêtements à propriétés très supérieures. Les travaux présentés portent sur la mise au point de la deuxième étape d’une méthode d’outillage rapide par stéréolithographie combinée à la projection plasma. Il s’agissait d’élaborer des coques épaisses d’acier AISI 316 sur des pièces prototypes en résine fabriquées par stéréolithographie. Pour cela, plusieurs difficultés étaient à vaincre : obtenir une adhérence modèle/dépôt suffisante, conserver les caractéristiques du modèle (forme, précision dimensionnelle, état de surface), éviter toute dégradation thermique du modèle durant la phase de projection, limiter les contraintes résiduelles inhérentes au procédé d’élaboration de dépôts par projection thermique, élaborer des dépôts d’acier compatibles avec les applications industrielles. Les solutions aux différents problèmes posés ont été apportées par le développement d’un procédé inédit de traitement de la surface du substrat et par la mise au point de conditions de projection particulières

Effect of substrate preparation on flattening of plasma sprayed aluminium bronze powders

International audiencePlasma spray coatings are produced by introducing powder particles of the material into a plasma plume, which melts and forwards them to the substrate. The flattening process of these individual molten droplets is one of the most critical factors as the coating quality strongly depends on the deposition of individual particles. Powders of aluminium bronze, a fine (−53 + 11 μ m) and a coarse one (−125 + 45 μm) were plasma sprayed onto stainless steel substrates (AISI 304L) under atmospheric condition with three different substrate temperatures (25, 165 and 270°C). Two different ranges of surface roughness Ra were used: mirror polished substrates with about 0·01-0·03 μm and grit blasted substrates with about 1·89-2·43 μm. A scanning electron microscopy equipped with energy dispersive spectrometry system and an electron probe microanalysis, were used in order to study the splat morphology and the chemical composition of the splats

Effect of substrate roughness and temperature on splat formation in plasma sprayed aluminium bronze

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