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Element (chemie)

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Finite element models (FEMs) are widely used to understand the dynamic behaviour of various systems. FEM updating allows FEMs to be tuned better to reflect measured data and may be conducted using two different statistical frameworks: the maximum likelihood approach and Bayesian approaches. Finite Element Model Updating Using Computational Intelligence Techniques applies both strategies to the field of structural mechanics, an area vital for aerospace, civil and mechanical engineering. Vibration data is used for the updating process. Following an introduction a number of computational intelligence techniques to facilitate the updating process are proposed; they include: ¢ multi-layer perceptron neural networks for real-time FEM updating; ¢ particle swarm and genetic-algorithm-based optimization methods to accommodate the demands of global versus local optimization models; ¢ simulated annealing to put the methodologies into a sound statistical basis; and ¢ response surface methods and expectation maximization algorithms to demonstrate how FEM updating can be performed in a cost-effective manner; and to help manage computational complexity. Based on these methods, the most appropriate updated FEM is selected using the Bayesian approach, a problem that traditional FEM updating has not addressed. This is found to incorporate engineering judgment into finite elements systematically through the formulations of prior distributions. Throughout the text, case studies, specifically designed to demonstrate the special principles are included. These serve to test the viability of the new approaches in FEM updating. Finite Element Model Updating Using Computational Intelligence Techniques analyses the state of the art in FEM updating critically and based on these findings, identifies new research directions, making it of interest to researchers in strucural dynamics and practising engineers using FEMs. Graduate students of mechanical, aerospace and civil engineering will also find the text instructive.

Mathematical analysis --- Engineering sciences. Technology --- finite element method --- eindige elementen

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This is an introduction to the mathematical basis of finite element analysis as applied to vibrating systems. Finite element analysis is a technique that is very important in modeling the response of structures to dynamic loads. Although this book assumes no previous knowledge of finite element methods, those who do have knowledge will still find the book to be useful. It can be utilised by aeronautical, civil, mechanical, and structural engineers as well as naval architects. This second edition includes information on the many developments that have taken place over the last twenty years. Existing chapters have been expanded where necessary, and three new chapters have been included that discuss the vibration of shells and multi-layered elements and provide an introduction to the hierarchical finite element method.

Vibration. --- Finite element method. --- Vibració. --- Elements finits, Mètode dels.

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Introduction. Obesity and related-metabolic disorders are a major problem of public health. In Western diet, fried foods represent an important part of the excessive caloric intake. Frying oils (thermal treatment at high temperature) – and more particularly vegetables oils riche in polyunsaturated fatty acids – deteriorate them. Degradation products (namely oxidized lipid) appear and accumulate in oils and fried foods. The main objective of this dissertation is the evaluation of the effect of these degradation products on obesity and metabolic disorders in a mouse model of nutritional obesity.
Experimental methods. Mice C57Bl6J (8 per group) were fed with four different diets with different levels of peroxides: either a control diet (CT) of a high-fat diet supplemented with 5% control soybean oil (HF) or a high-fat diet supplemented with 5% thermally treated soybean oil (Px, which increased peroxide level in the diet) of a Px diet supplemented with 1% coenzyme Q10H2 (CoQ, supplementation with antioxidant properties that counteract the increase in peroxide level).
Results. HF mice show a significant increase of body weight gain, associated with a significant increase in adipose tissues weights. In the plasma, non-esterified fatty acids (NEFA) and cholesterol are significantly increased in HF mice. Px mice do not lead to any further inflammatory or oxidative stress in the analysed tissues (liver, jejunum, colon and adipose tissue). Px diet increases relative liver weight, which could be associated with and accumulation of glycogen in the liver. Px diet also modifies lipid metabolism compared to HF diet: in the plasma, total cholesterol and LDL cholesterol are increased and triglycerides and NEFA are decreased; while in the liver, free cholesterol and triglycerides are decreased. These changes could be associated with an activation of LXR pathway following Px treatment. However, the reduced levels of peroxide in the CoQ diet do not induce any modification of lipid metabolism.
Discussion – Conclusion. Chronic ingestion of a diet supplemented with thermally oxidized oil is associated with modification of lipid metabolism. These perturbations are probably linked to the activation of LXR pathways. Those modifications of lipid metabolism seem to be independent of the peroxide level in the diet, as shown by the use of the antioxidant CoQ10H2. The main perspective is the identification of the other degradation products present in the diet and which can be associated with the observed modification of lipid metabolism Introduction. L’obésité et les désordres métaboliques associés constituent actuellement un problème majeur de santé publique. Dans l’alimentation occidentale, les produits cuits par friture représentent une part importante de l’apport calorique excédentaire. Les huiles de friture se dégradent à haute température, surtout les huiles végétales. Des produits issus de l’oxydation lipidique apparaissent alors et s’accumulent à la fois dans l’huile et dans les aliments frits. L’objectif principal de ce mémoire est d’évaluer l’influence de ces composés sur l’obésité et les désordres métaboliques dans un modèle murin d’obésité nutritionnelle. Pour ce faire, la mise au point d’un régime hyperlipidique enrichi de manière contrôlée en produits de dégradation issus de la peroxydation lipidique a été nécessaire.
Matériel & Méthodes. Quatre groupes de souris C57Bl6J ont été nourries avec des diètes présentant des taux variables de peroxydes : une diète standard pauvre en lipides (contrôle) ; une diète hyperlipidique enrichie de 5% d’huile de soja (HF) ; une diète hyperlipidique enrichie de 5% d’huile de soja thermo-oxydée (Px) ; une diète Px enrichie d’1% de coenzyme Q10 (CoQ, ajout d’un antioxydant pour réduire la teneur en peroxydes).
Résultats. L’ingestion de la diète HF provoque un gain de poids corporel important ainsi qu’une augmentation des acides gras libres et du cholestérol sériques. Les animaux ayant reçu la diète Px ne présentent ni un état inflammatoire, ni un état de stress oxydatif dans les différents organes étudiés. Par contre, ils présentent une augmentation du poids du foie associée à une tendance vers une accumulation de glycogène. Cette diète Px est également responsable de modifications du métabolisme lipidique par rapport à la diète HF : on observe une augmentation du cholestérol total et du LDL cholestérol mais une diminution des acides gras libres et des triglycérides au niveau sérique, et une diminution des triglycérides au niveau hépatique. Une activation de la voie LXR, récepteur nucléaire aux oxystérols, est mise en évidence dans le groupe PX ; cette voie étant associée à une augmentation du catabolisme et de la sécrétion du cholestérol. Par contre, la diminution de la teneur en peroxydes de la diète par l’ajout de CoQ10H2 ne contre aucun des effets de la diète Px sur le métabolisme lipidique.
Discussion – Conclusion. L’ingestion chronique d’une diète enrichie en huile thermo-oxydée induit des modifications du métabolisme lipidique via notamment l’activation de la voie LXR. Ces changements métaboliques semblent se produire indépendamment de la teneur en peroxydes dans la diète. La perspective principale de ce mémoire est la détermination des produits de dégradation de la diète pouvant être associés aux modifications du métabolisme lipidique observées (entre autres les oxystérols).

Obesity --- Disease --- Sterol Regulatory Element Binding Proteins --- Lipid Metabolism Disorders --- Lipid Peroxides --- Chylomicrons --- liver X receptor

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Applied Metal Forming: Including FEM Analysis describes metal forming theory and how experimental techniques can be used to study any metal forming operation with great accuracy. For each primary class of processes, such as forging, rolling, extrusion, wiredrawing, and sheet-metal forming, it explains how FEA (Finite Element Analysis) can be applied with great precision to characterize the forming condition and in this way optimize the processes. FEA has made it possible to build very realistic FEM-models of any metal forming process, including complex three-dimensional forming operations, in which complex products are shaped by complex dies. Thus, using FEA it is now possible to visualize any metal forming process and to study strain, stresses, and other forming conditions inside the parts being manufactured as they develop throughout the process.

Metal-work --- Metal products --- Metal stamping --- Finite element method. --- Mathematics. --- Mathematical models.