155 research outputs found
Caractérisation de films durs multicouches élaborés par pulvérisation magnétron. Influence des conditions d'élaboration sur leurs propriétés.
No full textdate de rédaction: 30/07/2010The objective of this work was to develop and characterize a new generation of multilayer nitride coatings, based on chromium, and understanding the mechanisms of degradation, both from a physicochemical and a tribological standpoint, to define rules for producing optimized coatings later. Because of the conditions under which they operate; these deposits must have special characteristics. Given their potential application in the field of machining, we must first consider optimizing the hardness, tribological, and thermal properties of the coatings. In addition, they must have good resistance to high temperature oxidation, due to the concomitant temperature rise from friction. We have developed and characterized multilayers coating systems : CrAlN/CrN and CrAlN/CrN/Cr. We have optimized the conditions for achieving multilayer coatings. Subsequently, the films produced under these conditions are studied and characterized. We are especially interested in their morphologies, their physicochemical and mechanical characteristics (hardness, residual stress, adhesion and tribological properties). The results found in this study contribute to the understanding of the complex damage mechanisms in multilayer coatings.L'objectif de ce travail était de développer et caractériser une nouvelle génération de revêtements multicouches de type nitrures dont le métal constituant la base est le chrome, et de comprendre les mécanismes de dégradation, tant d'un point de vue physico-chimique que tribologique, afin de définir des règles d'élaboration optimisées ultérieurement. En raison des conditions auxquelles ils sont soumis, ces dépôts doivent présenter des caractéristiques particulières. Dureté, propriétés tribologiques et thermiques optimisées sont les premières à considérer, compte tenu de leur application potentielle dans le domaine de l'usinage. En outre, ils doivent présenter une bonne tenue à l'oxydation à chaud en raison de l'élévation de température concomitante au frottement. Nous avons développé et caractérisé ainsi des revêtements multicouches (CrN/CrAlN et Cr/CrN/CrAlN) en faisant varier les conditions d'élaboration des monocouches, nous avons déterminé les conditions optimales de réalisation des multicouches. Par la suite, les films élaborés dans ces conditions optimales ont été étudiés et caractérisés. Nous nous sommes intéressés en particulier à leurs morphologies, leurs propriétés physico-chimiques et leurs caractéristiques mécaniques (dureté, contraintes résiduelles, adhérence et propriétés tribologiques). Les résultats obtenus dans cette étude apportent une contribution à la compréhension des mécanismes complexes d'endommagement des revêtements multicouches
Caractérisation de films durs multicouches élaborés par pulvérisation magnétron. Influence des conditions d'élaboration sur leurs propriétés.
No full textdate de rédaction: 30/07/2010The objective of this work was to develop and characterize a new generation of multilayer nitride coatings, based on chromium, and understanding the mechanisms of degradation, both from a physicochemical and a tribological standpoint, to define rules for producing optimized coatings later. Because of the conditions under which they operate; these deposits must have special characteristics. Given their potential application in the field of machining, we must first consider optimizing the hardness, tribological, and thermal properties of the coatings. In addition, they must have good resistance to high temperature oxidation, due to the concomitant temperature rise from friction. We have developed and characterized multilayers coating systems : CrAlN/CrN and CrAlN/CrN/Cr. We have optimized the conditions for achieving multilayer coatings. Subsequently, the films produced under these conditions are studied and characterized. We are especially interested in their morphologies, their physicochemical and mechanical characteristics (hardness, residual stress, adhesion and tribological properties). The results found in this study contribute to the understanding of the complex damage mechanisms in multilayer coatings.L'objectif de ce travail était de développer et caractériser une nouvelle génération de revêtements multicouches de type nitrures dont le métal constituant la base est le chrome, et de comprendre les mécanismes de dégradation, tant d'un point de vue physico-chimique que tribologique, afin de définir des règles d'élaboration optimisées ultérieurement. En raison des conditions auxquelles ils sont soumis, ces dépôts doivent présenter des caractéristiques particulières. Dureté, propriétés tribologiques et thermiques optimisées sont les premières à considérer, compte tenu de leur application potentielle dans le domaine de l'usinage. En outre, ils doivent présenter une bonne tenue à l'oxydation à chaud en raison de l'élévation de température concomitante au frottement. Nous avons développé et caractérisé ainsi des revêtements multicouches (CrN/CrAlN et Cr/CrN/CrAlN) en faisant varier les conditions d'élaboration des monocouches, nous avons déterminé les conditions optimales de réalisation des multicouches. Par la suite, les films élaborés dans ces conditions optimales ont été étudiés et caractérisés. Nous nous sommes intéressés en particulier à leurs morphologies, leurs propriétés physico-chimiques et leurs caractéristiques mécaniques (dureté, contraintes résiduelles, adhérence et propriétés tribologiques). Les résultats obtenus dans cette étude apportent une contribution à la compréhension des mécanismes complexes d'endommagement des revêtements multicouches
Identification et commande des systèmes non linéaires : Utilisation des modèles de type NARMA
No full textThis work deals with the identification and predictive control of non linear systems. The Non linear Auto Regressive Moving Average (NARMA) model is used to characterize the non linear process. To identify nonlinear complex systems, using the NARMA type model, we propose two new approaches allowing the determination of the significant terms in the expression of NARMA model as well as the estimate of the corresponding coefficients. The first one exploits the Binary Genetic Algorithm, whereas the second uses a procedure based on a single layer neural network with polynomial activation function which is optimised with a real-coded genetic algorithm. We propose, also, the extension of the second method to identify the multivariable nonlinear systems. Both a simulation examples and a laboratory physical process are applied to identify a NARMA type models. The results confirmed the effectiveness of the proposed methods. Indeed, NARMA models characterized by an acceptable precision and a reasonable complexity were given. A derivative-free constrained predictive controller of nonlinear systems is then proposed. The NARMA model is used to characterize the behavior of the system. The control law is obtained by minimizing a non convex criterion. The optimization problem is solved by two methods using the Nelder-Mead and the Rosenbrock algorithms. These local and deterministic algorithms, which does not require the calculation of the criterion, combined with the penalty function and the CFON and multi-initialization aproches can converge towards the global minimum.Dans ce travail, nous nous sommes intéressés à l'identification et la commande prédictive des systèmes non linéaires monovariables et multivariables en exploitant les modèles NARMA. Pour l'identification des modèles de type NARMA, nous avons proposé deux nouvelles méthodes heuristiques. La première méthode est basée sur les algorithmes génétiques binaires et la deuxième méthode constitue une combinaison entre le réseau de neurones artificiels à fonction d'activation polynomiale et l'algorithme génétique sous sa représentation réelle. Cette dernière méthode a été également développée pour la modélisation des systèmes multivariables. Les résultats trouvés, pratiques ou en simulations, ont confirmé l'efficacité et la robustesse des méthodes proposées. En effet, les modèles NARMA déterminés caractérisent avec une précision acceptable et avec une complexité raisonnable le comportement des systèmes étudiés. Par la suite nous avons proposé un contrôleur prédictif des systèmes non linéaires sous contraintes, qui exploite les modèles de type NARMA. La loi de commande est obtenue en minimisant un critère quadratique non convexe. Le problème d'optimisation est résolu par deux méthodes utilisant les algorithmes de Nelder-Mead et de Rosenbrock qui ne nécessitent pas le calcul de la dérivée du critère. Ces méthodes, combinées avec la fonction de pénalité, l'approche CFON ainsi que l'utilisation de la notion de multi initialisation, permettent une meilleure convergence vers le minimum global
A multiscale modelling of bone ultrastructure elastic properties using finite elements simulation and neural network method
No full textBone is a living material with a complex hierarchical structure which entails exceptional mechanical properties, including high fracture toughness, specific stiffness and strength. Bone tissue is essentially composed by two phases distributed in approximately 30 70%: an organic phase (mainly type I collagen and cells) and an inorganic phase (hydroxyapatite-HA-and water). The nanostructure of bone can be represented throughout three scale levels where different repetitive structural units or building blocks are found: at the first level, col-lagen molecules are arranged in a pentameric structure where mineral crystals grow in specific sites. This primary bone structure constitutes the mineralized collagen microfibril. A struc-tural organization of inter-digitating microfibrils forms the mineralized collagen fibril which represents the second scale level. The third scale level corresponds to the mineralized col-lagen fibre which is composed by the binding of fibrils. The hierarchical nature of the bone tissue is largely responsible of their significant mechanical properties; consequently, this is a current outstanding research topic. Scarce works in literature correlates the elastic prop-erties in the three scale levels at the bone nanoscale. The main goal of this work is to estimate the elastic properties of the bone tissue in a multiscale approach including a sensitivity analy-sis of the elastic behaviour at each length scale. This proposal is achieved by means of a novel hybrid multiscale modelling that involves neural network (NN) computations and finite elements method (FEM) analysis. The elastic properties are estimated using a neural network simulation that previously has been trained with the database results of the finite element models. In the results of this work, parametric analysis and averaged elastic constants for each length scale are provided. Likewise, the influence of the elastic constants of the tissue constituents is also depicted. Results highlight that intelligent numerical methods are pow-erful and accurate procedures to deal with the complex multiscale problem in the bone tissue with results in agreement with values found in literature for specific scale levels.Barkaoui, A.; Tlili, B.; Vercher Martínez, A.; Hambli, R. (2016). A multiscale modelling of bone ultrastructure elastic properties using finite elements simulation and neural network method. Computer Methods and Programs in Biomedicine. 134:69-78. doi:10.1016/j.cmpb.2016.07.005S697813
Le travail informel : retour sur une notion floue. Remarques à partir du cas des entreprises françaises délocalisées au Maroc
No full textBased on the critical literature as well as on observations collected by the author for the preparation of his Ph. D. thesis, the article addresses the definition and the characterization of the main types of informal employment, the status of work in Morocco, and examines in more detail some atypical forms of work and employment which are related to the operation of French enterprises located in this country (the “ chaouch”, the maid, the …).L’article interroge la définition et les formes du travail informel dans le contexte sociétal marocain à partir de la littérature critique et des observations recueillies dans le cadre d’une thèse de doctorat en Sociologie. A la lumière des données collectées, on développe quelques remarques sur le statut du travail dans la société marocaine et on examine de façon plus précise la problématique du maintien de certaines figures atypiques en relation avec les entreprises françaises délocalisées au Maroc («chaouch » , bonne, porteur).Labari Brahim. Le travail informel : retour sur une notion floue. Remarques à partir du cas des entreprises françaises délocalisées au Maroc. In: Cahiers de sociologie économique et culturelle, n°41-42, 2004. pp. 71-93
Mesenchymal hamartoma of the liver incidentally discovered in a 4 year old girl: Management and treatment
No full textMesenchymal hamartomas of the liver is considered a benign tumour, although it provides significant challenges in the diagnosis and operative management. Clinical features, laboratory results and radiographic imaging are often non-specific and inconclusive. Thus, it is still difficult to differentiate from malignant lesion without pathological examination. While this tumour is usually diagnosed in the first 2 years of life, few cases in older children have been reported and most of them are case reports. In this article, we want to report our clinical evaluation, results of image diagnosis, surgical procedure and the follow-up simultaneously we discuss the possible differential diagnosis of such a case at this age
Isotomurus maculatus
No full text50. Isotomurus maculatus (Schäffer, 1896) (Fig. 10) Citation from Edough: Hamra-Kroua (2016: 86); Zoughailech (2017: 137). Not cited from Algeria outside Edough. Distribution: Distribution unclear, requires revision (Fjellberg 2007). The color pattern is slightly different from the specimens from Norway figured by this author and from Italy figured by Carapelli et al. (1995).Published as part of Brahim-Bounab, Hayette, Bendjaballah, Mohamed, Hamra-Kroua, Salah, Lachi, Noureddine, Bedos, Anne & Deharveng, Louis, 2020, Checklist of the springtails (Hexapoda: Collembola) of the Edough massif northeastern Algeria, pp. 51-78 in Zootaxa 4853 (1) on page 68, DOI: 10.11646/zootaxa.4853.1.3, http://zenodo.org/record/441036
Real-Time Fault Detection and Identification for MMC Using 1-D Convolutional Neural Networks
No full textAutomated early detection and identification of switch faults are essential in high-voltage applications. Modular multilevel converter (MMC) is a new and promising topology for such applications. MMC is composed of many identical controlled voltage sources called modules or cells. Each cell may have one or more switches and a switch failure may occur in anyone of these cells. The steady-state normal and fault behavior of a cell voltage will also significantly vary according to the changes in the load current and the fault timing. This makes it a challenging problem to detect and identify such faults as soon as they occur. In this paper, we propose a real-time and highly accurate MMC circuit monitoring system for early fault detection and identification using adaptive one-dimensional convolutional neural networks. The proposed approach is directly applicable to the raw voltage and current data and thus eliminates the need for any feature extraction algorithm, resulting in a highly efficient and reliable system. Simulation results obtained using a four-cell, eight-switch MMC topology demonstrate that the proposed system has a high reliability to avoid any false alarm and achieves a detection probability of 0.989, and average identification probability of 0.997 in less than 100 ms. - 2018 IEEE.Manuscript received October 23, 2017; revised February 11, 2018 and March 27, 2018; accepted April 16, 2018. Date of publication May 3, 2018; date of current version June 28, 2019. This work was supported by the National Priorities Research Program award (NPRP10-1203-160008) from the Qatar National Research Fund, a member of the Qatar Foundation. (Corresponding author: Serkan Kiranyaz.) S. Kiranyaz, A. Gastli, L. Ben-Brahim, and N. Al-Emadi are with the Department of Electrical Engineering, Qatar University, Doha 2713, Qatar (e-mail: [email protected]; [email protected]; [email protected]; [email protected]).Scopu
Experimental characterization and fatigue behavior of thermally and mechanically treated 316L stainless steel MIG-welded joints
No full text- …
