Dynamics of Torsional Vibration Damper (TVD) pulley, implementation of a rubber elastomeric behavior, simulations and experiments

International audienceIn this work, the Torsional Vibration Damper (TVD) rubber ring viscoelastic-material properties are determined based on Dynamical Mechanical Analysis (DMA) measurements and master curves reconstructions using thermo-simplicity principle. The elastomeric constitutive behavior is then implemented in the torsional vibration damper's equation of motion and the frequency response is simulated so that enhanced physical representation of the TVD dynamics can be achieved. Major differences in the TVD frequency response are highlighted and analyzed whether or not the viscoelastic material properties (elasticity modulus and damping) are considered constant or frequency and temperature dependent

Contrôle modal autoadaptatif de vibrations de structures évolutives

L allègement des structures imposé par les réductions de coût se traduit par des structures de plus en plus souples qui les rendent de plus en plus sensibles aux vibrations. Le contrôle des vibrations devient donc un enjeu majeur dans de nombreuses applications industrielles et les limites des matériaux imposent maintenant un recours au contrôle actif de plus en plus fréquent. L évolution des structures au cours du temps (viellisement, conditions aux limites, architecture, ) pose le problème de la robustesse du contrôle. Par ailleurs, l actionnement de plus en plus présent dans le domaine mécanique constitue à la fois une source supplémentaire de vibrations, mais aussi de contrôle et d évolution d architecture des structures. La thèse s intéresse au contrôle actif autoadaptatif des vibrations permettant de maintenir automatiquement la performance et la stabilité des structures évolutives. Il s agit donc de s affranchir de la connaissance des causes et des informations sur les évolutions. La méthode proposée s appuie sur un développement modal permettant de limiter le nombre de composants de contrôle et de cibler les modes à contrôler en limitant l énergie de contrôle. Ainsi, il est nécessaire de reconstruire les caractéristiques du modèle modal indispensables pour réactualiser le contrôle en figeant seulement une structure de modèle. S affranchissant à la fois des causes d évolution de la structure et utilisant seulement une structure de modèle, la méthode est généralisable à toute application en mécanique des structures. La méthode proposée, basée sur l utilisation d un identificateur exploitant à la fois excitation et réponse de la structure, prend en compte les limites imposées par le contrôleur. Le modèle constitue le lien qui doit être établi entre identificateur et contrôle pour permettre la réactualisation. Par ailleurs, un compromis entre l objectif d atténuation des vibrations et les performances de l identification est alors nécessaire du fait du couplage identification/contrôle apparaissant dans la boucle fermée. Ce compromis est également conditionné par le matériel utilisé. La méthode proposée est exploitée sur une structure discrète mettant en évidence une inversion de formes modales au cours de son évolution qui déstabilise un contrôle figé. Le choix opéré pour répondre aux différents compromis cités ci dessus a conduit à l utilisation d un contrôleur classique (LQG) et un identificateur basé sur la méthode des sous-espaces (N4SID). Cette application sur une structure simple a permis de caractériser un certain nombre de limites physiques : la bande passante, densité modale, vitesse d évolution, Le contrôle modal autoadaptatif proposé s avère robuste en performance et efficace lorsque la réactualisation est systématique. Une variante conditionnelle, toujours basée sur l analyse de la réponse de la structure, est enfin proposée pour optimiser le processus de réactualisation afin de suivre plus efficacement les évolutions.The lightness of structure due to the reduction of cost results in some structures which are more and more flexible. This flexibility makes these structures more sensitive to vibrations. The vibration control becomes an important issue in lots of industrial applications, and now the limitation of materials imposes a requirement of active control more and more frequently.The change of time-varying structure(ageing effect, boundaries conditions, architecture of structure etc)brings the robust problem of control.Further more,the action of device which emerges more and more frequently in mechanical fields introduces not only an additional cause of vibrations,but also a source of control and a source for changing the architecture of structures.The thesis focuses on self-adaptive active control of vibration which permits to keep up automatically the performance and stability of the time-varying structures.So it needs to overcome the knowing about cause and information on the changes.The proposed method relies on a development of modal technology which permits to limit the amount of component in control system and to target on the modes which need to be controlled.So the energy of control is limited. Further more,it needs to reconstruct the characteristics of modal model which are indispensable for updating the control.In this case, only the structure of model is fixed.Overcoming the knowing about cause of change in the structure and using only the structure of model, this method can be generalized for all applications in mechanical structures.The proposed method is based on the utilization of an identifier which uses both the excitation and response of the structure.And this method considers the limitations induced by the controller.The model forms le link which should be established between the identifier and the controller for allowing the updating. Further more, a compromise between the objective of reducing vibrations and the performance of identification is necessary due to the coupling effect of identification/control which appears in the closed-loop. This compromise is also conditioned by the used equipments.The proposed method is carried out on a discrete time-varying structure for showing an inversion of mode shape during its change. This inversion of mode shape destabilises a fixed control system. The operated choices for responding the different previous quoted compromise lead to a classic controller (LQG) and an identifier based on the subspace method (N4SID).This application on a simple structure permitted to characterise some physical limitation: the bandwidth, the modal density and the velocity of change The proposed self-adaptive modal control is proved to be robust in terms of performance and be efficient when the updating is systematical. Always based on the analysis of the response of the structure, a conditional variant is finally proposed for optimizing the process of updating in order to follow the change more efficiently.VILLEURBANNE-DOC'INSA LYON (692662301) / SudocVILLEURBANNE-DOC'INSA-Bib. elec. (692669901) / SudocSudocFranceF

Dairy products and inflammation: a review of the clinical evidence

Inflammation is a major biological process regulating the interaction between organisms and the environment, including the diet. Because of the increase in chronic inflammatory diseases, and in light of the immune-regulatory properties of breastfeeding, the ability of dairy products to modulate inflammatory processes in humans is an important but unresolved issue. Here, we report a systematic review of 52 clinical trials investigating inflammatory markers in relation to the consumption of dairy products. An inflammatory score (IS) was defined to quantitatively evaluate this interaction. The IS was significantly positive for the entire data set, indicating an anti-inflammatory activity in humans. When the subjects were stratified according to their health status, the IS was strongly indicative of an anti-inflammatory activity in subjects with metabolic disorders and of a pro-inflammatory activity in subjects allergic to bovine milk. Stratifying the data by product categories associated both low-fat and high-fat products, as well as fermented products, with an anti-inflammatory activity. Remarkably, the literature is characterized by a large gap in knowledge on bioavailability of bioactive nutrients. Future research should thus better combine food and nutritional sciences to adequately follow the fate of these nutrients along the gastrointestinal and metabolic axes.info:eu-repo/semantics/publishedVersio

Identification of a time-varying mechanical system using the Akaike information criterion

Cet article démontre l'intérêt du critère d'information d'Akaike pour les méthodes d'identification contenant une étape de projection de signaux de mesure sur des bases spécifiques. On s'intéresse particulièrement au problème d'identification de paramètres mécaniques variant dans le temps. La méthode est testée expérimentalement avec succès sur un système à un degré de liberté, constitué d'une inertie et d'une poutre à longueur variable travaillant en torsion. Les variations de cette longueur rendent les paramètres du système dynamique changeant. Une approche par moindre carré combinée à une projection des signaux mesuré sur une base polynomiale permet de reconstruire aisément les fluctuations des paramètres mécaniques. Cependant le choix de l'ordre de troncature de la base de projection est toujours un problème clef dans ce genre de méthode inverse et reste bien souvent une question ouverte. On propose ici d'utiliser le critère d'information Akaike permettant ainsi une sélection robuste et automatique de cet ordre de troncature. L'étude présentée ici ainsi que l'expérimentation montrent la pertinence et l'intérêt de ce type de critère associé aux méthodes d'identification

A randomised cross-over trial in healthy adults indicating improved absorption of omega-3 fatty acids by pre-emulsification

BACKGROUND: The health benefits of increased intakes of omega-3 fatty acids are well established but palatability often presents a problem. The process of emulsification is used in the food industry to provide a wider spectrum of use, often with the result of increased consumption. Moreover, as emulsification is an important step in the digestion and absorption of fats, the pre-emulsification process may enhance digestion and absorption. In this study the levels of plasma fatty acid and triacylglycerol (TAG) following the ingestion of either an oil mixture or an emulsified oil mixture have been compared. METHODS: In this randomised cross-over study, 13 volunteers received the oil mixture and 11 received the oil emulsion as part of an otherwise fat free meal. Blood samples were collected at 0, 1.5, 3, 4.5, 6, 7.5 and 9 hours after ingestion of oil, separated and stored at -20°C. Plasma triacylglycerols were assessed spectrophotometrically and fatty acids were determined by gas chromatography. Following a washout period of twenty days the procedure was repeated with the assignments reversed. RESULTS: The postprandial plasma TAG and the C18:3 (n-6), C18:3(n-3), C20:5(n-3) and C22:6 (n-3) polyunsaturated fatty acid (PUFA) levels for the emulsified oil group were increased significantly (P = 0.0182; P = 0.0493; P = 0.0137; P < 0.0001; P = 0.0355 respectively) compared with the non-emulsified oil group. The C16:0 and C18:0 saturated fatty acids, the C18:1 (n-9) monounsaturated fatty acid and the C18:2 PUFA were not significantly different for the oil and emulsified oil groups. CONCLUSION: Pre-emulsification of an oil mixture prior to ingestion increases the absorption of longer chain more highly unsaturated fatty acids (especially eicosapentaenoic acid and docosahexaenoic acid) but does not affect absorption of shorter chain less saturated fatty acids, suggesting that pre-emulsification of fish oils may be a useful means of boosting absorption of these beneficial fatty acids. Trial registration: Current Controlled Trials ISRCTN4320260

Conservation of the links between gene transcription and chromosomal organization in the highly reduced genome of Buchnera aphidicola

<p>Abstract</p> <p>Background</p> <p>Genomic studies on bacteria have clearly shown the existence of chromosomal organization as regards, for example, to gene localization, order and orientation. Moreover, transcriptomic analyses have demonstrated that, in free-living bacteria, gene transcription levels and chromosomal organization are mutually influenced. We have explored the possible conservation of relationships between mRNA abundances and chromosomal organization in the highly reduced genome of <it>Buchnera aphidicola</it>, the primary endosymbiont of the aphids, and a close relative to <it>Escherichia coli</it>.</p> <p>Results</p> <p>Using an oligonucleotide-based microarray, we normalized the transcriptomic data by genomic DNA signals in order to have access to inter-gene comparison data. Our analysis showed that mRNA abundances, gene organization (operon) and gene essentiality are correlated in <it>Buchnera </it>(i.e., the most expressed genes are essential genes organized in operons) whereas no link between mRNA abundances and gene strand bias was found. The effect of <it>Buchnera </it>genome evolution on gene expression levels has also been analysed in order to assess the constraints imposed by the obligate symbiosis with aphids, underlining the importance of some gene sets for the survival of the two partners. Finally, our results show the existence of spatial periodic transcriptional patterns in the genome of <it>Buchnera</it>.</p> <p>Conclusion</p> <p>Despite an important reduction in its genome size and an apparent decay of its capacity for regulating transcription, this work reveals a significant correlation between mRNA abundances and chromosomal organization of the aphid-symbiont <it>Buchnera</it>.</p

TRANSVERSE VIBRATION INSTABILITIES IN MULTIRIBBED BELT TRANSMISSION SUBJECTED TO MULTI-FREQUENCY EXCITATIONS: MODELLING AND EXPERIMENTS

ABSTRACT This paper experimentally investigates the parametric in

An electromagnetic-mechanical modeling of an induction motor and rotor shaft coupled to angular approach

Ce papier présente un modèle électromécanique pour simuler le comportement dynamique d'une machine asynchrone / arbre du rotor. Le modèle décrit dans ce travail combine un modèle de réseau de perméances d'un moteur à induction à cage d'écureuil et un modèle dynamique simple de son arbre de rotor. Un échantillonnage angulaire est utilisé pour permettre d'investiguer les variations de vitesse angulaire instantanée et de couple. Le système rotatif est décrit en se référant à la position angulaire de l'arbre. La méthodologie de couplage électromécanique est bien détaillée. En se basant sur un certain nombre de simulations, on montre l'influence des variations de couple provenant de la machine à 'induction sur le comportement dynamique du système mécanique

A dietary supplementation with leucine and antioxidants is capable to accelerate muscle mass recovery after immobilization in adult rats

Prolonged inactivity induces muscle loss due to an activation of proteolysis and decreased protein synthesis; the latter is also involved in the recovery of muscle mass. The aim of the present work was to explore the evolution of muscle mass and protein metabolism during immobilization and recovery and assess the effect of a nutritional strategy for counteracting muscle loss and facilitating recovery. Adult rats (6-8 months) were subjected to unilateral hindlimb casting for 8 days (10-18) and then permitted to recover for 10 to 40 days (R10-R40). They were fed a Control or Experimental diet supplemented with antioxidants/polyphenols (AOX) (10 to 18), AOX and leucine (AOX + LEU) (18 to R15) and LEU alone (R15 to R40). Muscle mass, absolute protein synthesis rate and proteasome activities were measured in gastrocnemius muscle in casted and non-casted legs in post prandial (PP) and post absorptive (PA) states at each time point. Immobilized gastrocnemius protein content was similarly reduced (-37%) in both diets compared to the non-casted leg. Muscle mass recovery was accelerated by the AOX and LEU supplementation (+6% AOX+LEU vs. Control, P<0.05 at R40) due to a higher protein synthesis both in PA and PP states (+23% and 31% respectively, Experimental vs. Control diets, P<0.05, R40) without difference in trypsin-and chymotrypsin-like activities between diets. Thus, this nutritional supplementation accelerated the recovery of muscle mass via a stimulation of protein synthesis throughout the entire day (in the PP and PA states) and could be a promising strategy to be tested during recovery from bed rest in humans

En situation de catabolisme musculaire, les protéines de lactosérum permettent bien de restaurer un anabolisme musculaire post prandial mais d’une durée très transitoire probablement insuffisante pour limiter la fonte musculaire

En situation de catabolisme musculaire, les protéines de lactosérum permettent bien de restaurer un anabolisme musculaire post prandial mais d’une durée très transitoire probablement insuffisante pour limiter la fonte musculair