Dissertations / Theses on the topic 'Contans'
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Matheron, Michael E., and Martin Porchas. "Effectiveness of Contans and Serenade Within a Biologically Intensive Integrated Pest Management System for Sclerotinia Drop on Lettuce: 2005 Study." College of Agriculture and Life Sciences, University of Arizona (Tucson, AZ), 2005. http://hdl.handle.net/10150/215018.
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Sclerotinia drop of lettuce, caused by the pathogenic fungi Sclerotinia minor and S. sclerotiorum, is a serious disease in most regions where this crop is grown. Conventional fungicides, such as Rovral (iprodione) and Endura (boscalid), are usually applied after lettuce is thinned and once more 2 to 3 weeks later. Two biological products, Contans (Coniothyrium minitans) and Serenade (Bacillus subtilis), are also available. In earlier field trials conducted from 2001 to 2003 in the presence of S. sclerotiorum, the mean reduction in disease by Contans, Serenade and Endura was 69, 18 and 41%, respectively. The objective of the current study was to determine the efficacy of the biological products Contans and Serenade, applied alone or in combination with each other or the conventional fungicide Endura, within a biologically intensive integrated pest management system for Sclerotinia drop on lettuce. The study was conducted at The University of Arizona, Yuma Valley Agricultural Center. Sclerotia of Sclerotinia sclerotiorum were produced in the laboratory. Lettuce ‘Winterhaven’ was seeded and sclerotia were applied to the plots on November 8, 2004. Disease assessment was performed three times, including plant maturity (February 24), by recording the number of dead plants in each plot. Lettuce drop caused by Sclerotinia sclerotiorum was significantly reduced by the biofungicides Contans and Serenade as well as the conventional fungicide Endura. At plant maturity, the highest level of disease control among all treatments was provided by one or two applications of the biofungicide Contans as well as application of Contans at seeding following by either Serenade or Endura after thinning. Also, two applications of the other tested biofungicide, Serenade, controlled Sclerotinia drop as well as two applications of the conventional fungicide, Endura. The results of this study suggest that the biological products Contans and Serenade, used either alone or with the conventional fungicide Endura, can provide effective levels of control of lettuce drop caused by S. sclerotiorum. Although encouraging, the results from this initial field trial will need to be confirmed by additional studies. Funding for this research project was provided, in part, by the IR-4 project under a cooperative agreement with the U.S. Environmental Protection Agency.
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Arnatt, Matthew. "Contents, and criticisms as reflexes to content." Thesis, Goldsmiths College (University of London), 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.514226.
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Moraes, Marta Bueno de. "Estudo teórico de característica elétrica de contato schottky não íntimo metal-isolante amorfo e estrutura metal-isolante-metal." Universidade de São Paulo, 1989. http://www.teses.usp.br/teses/disponiveis/54/54132/tde-16012008-104334/.
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No presente trabalho foi desenvolvida uma teoria de característica elétrica da estrutura metal-isolante-metal considerando uma camada fina de óxido entre o metal e o isolante, sendo o óxido um outro isolante de banda de energia proibida mais larga. Foi considerada uma distribuição energética uniforme de estados de impurezas à interface óxido-isolante. Estudamos a distribuição real do potencial na região de carga espacial usando a equação de Poisson. Através desta distribuição obtemos a relação entre o potencial de contato e a carga positiva na região de depleção e assim a característica capacitância-voltagem da estrutura. Este tipo de característica é útil para se calcular as características corrente em função do potencial e corrente em função do tempo para um dado potencial e deste modo é importante para o entendimento das estruturas MIM e MOIM.In this work we have developed a theory of electric characteristic of the metal-oxide-insulator-metal structure, considering a thin film of oxide between metal and insulator; the oxide is another insulator of wider forbidden energy gap. A uniform energy distribution of impurity states at the oxide-insulator interface was considered. W e have studied the actual distribution of potential in the region of spatial charge using the Poisson equation. With this distribution we obtain the relation between the contact potential and the charge in the depletion region and then the characteristic potential - capacitance of t his structure. This type of characteristic is useful to calculate the characteristic current - potential, and current-time at a given potential . In this manner it is important to the understanding of MIM and MOIM structures.
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Benoit, Huet. "Étude de Contenus Multimédia: Apporter du Contexte au Contenu." Habilitation à diriger des recherches, Université de Nice Sophia-Antipolis, 2012. http://tel.archives-ouvertes.fr/tel-00744320.
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Parel, Kurien Stephen. "An analysis of contact stiffness and frictional receding contacts." Thesis, University of Oxford, 2017. http://ora.ox.ac.uk/objects/uuid:3c29863a-b0cf-4870-851d-261be72f457f.
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The tangential contact stiffness for ground Ti-6Al-4V surfaces is measured to linearly decrease with the application of tangential load. At the beginning of the application of tangential load, for ground surfaces, the ratio of the tangential contact stiffness to the normal contact stiffness is seen to be approximately half the Mindlin ratio. This is consistent with many other published experimental studies. Measurements of normal contact stiffness for ground surfaces conform to a model that posits a linear relationship between normal contact stiffness and normal load. An equivalent surface roughness parameter is defined for two surfaces in contact; and the normal contact stiffness for ground surfaces is observed to be inversely proportional to this parameter. Single asperity models were constructed to simulate the effect of different frictional laws and plasticity on the tangential displacement of an asperity contact. Further, multi-asperity modelling showed the effect of different normal load distributions on the tangential behaviour of interfaces. In addition, normal contact stiffness was modelled for a grid of asperities taking into account asperity interactions. A receding contact problem for which the required form of the distributed dislocations is bounded-bounded was solved. Then, a fundamental 2D frictional receding contact problem involving a homogeneous linear elastic infinite layer pressed by a line load onto a half-plane of the same material was analysed. This was done by the insertion of preformed distributed dislocations (or eigenstrains), which take into account the correct form of the separation of the interface at points away from the area of loading, along with corrective bounded-bounded distributions. The general method of solution was further refined and adapted to solve three other receding contact problems. The solutions demonstrated the robustness and applicability of this new procedure.
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Djerroud, Dalila. "Modélisation markovienne du séchage continu par contact avec agitation." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0111/document.
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Dans un procédé de séchage, l'évacuation de l'eau induit des modifications structurelles et physicochimiques qui engendrent des difficultés d'écoulement dans le séchoir. Cette étude a porté sur la modélisation du séchage continu par contact avec agitation. Nous avons développé un modèle markovien pour décrire les transferts de masse, de chaleur et l'écoulement dans un séchoir continu. Les paramètres d'entrée du modèle ont été déterminés expérimentalement sur un produit pâteux, tandis que d'autres paramètres ont été obtenus à partir de la littérature scientifique. L'étude de sensibilité de la teneur en eau et de la masse sèche retenue dans le séchoir a permis d'analyser et de hiérarchiser les effets des différentes variables opératoires. Enfin, nous avons étudié l'influence des variables opératoires sur le profil de teneur en eau, le temps de passage et les courbes de distribution de temps de séjours simulées. L'évolution structurelle du produit a été mise en évidence dans le modèleIn a drying process, the evacuation of water induced structural and physico-chemical modifications that generate difficulties of flow in the dryer. This study focused on the modeling of agitated indirect continuous dryer. We developed a Markov model to describe the mass transfer, heat transfer and flow in a continuous dryer. The input parameters of the model were determined experimentally on a pasty product, while other parameters were obtained from the scientific literature. The sensitivity study of the moisture content and dry mass retained in the dryer was used to analyze and treat on a hierarchical basis the effects of different operating variables. Finally, we studied the influence of variables operating on the profile of moisture content, the passage time and the simulated curves of residence time distribution. The structural evolution of the product was considered in the model
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Alshahrany, Shaya. "Rolling contact fatigue in heavily loaded gear transmission contacts." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/90422/.
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This thesis examines the influence of asperities such as found on the teeth of gears and discs, and failure mechanisms associated with rough surface Elastohydrodynamic Lubrication (EHL). The principal outcomes of the research provide a good insight into fatigue life, residual stress effects, damage prediction and surface contact failures. In particular, the study is intended to provide understanding into the residual stress distribution resulting from plastic deformation of surface asperities in the running in process. The residual stress is then added to the asperity elastic stress distribution and examined in detail to see the effects on fatigue damage and fatigue life. So, a theoretical model has been developed to assist design against the residual stress effect and surface contact fatigue, such as micropitting. The technique used in the study starts with developing an elastic plastic model of the rough surface by using the Abaqus Finite Element analysis software package. This is a nonlinear problem and ranges of applied loads have been applied to the as-manufactured surfaces causing the asperity features to experience varying degrees of plastic deformation. The pre and post running roughness profiles are studied in order to assess the level of plastic deformation actually occurring at significant surface asperity features by aligning the pre and post running profiles. This results in a new technique that has helped to identify the level of plastic deformation occurring in the practice, and also to make a comparison with FEA contact analysis for the same asperity features to identify the appropriate residual stress field. The residual stress field associated with the plastic deformation was extracted and evaluated. The extracted residual stress field was transferred to a form that facilitated IV inclusion in stress evaluation code to obtain the stress history for the material subject to loading in an EHL contact. The research carried out considers surface fatigue analysis with and without a residual stress field, so as to establish the influence of asperity plastic deformation on the fatigue properties of the surface. All the work is based on numerical simulation of surface fatigue failure in EHL situations and carried out numerically. The procedure can be applied quickly and gives the opportunity to apply several models and investigate the influence of all the model parameters on material deformation and fatigue life.
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Almeida, Fabio Cardoso. "Análise das forças de contato e comportamento dinâmico de rodeiro ferroviário." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3152/tde-05092006-113355/.
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Sistemas dinâmicos ferroviários são modelados levando-se em consideração as forças de contato roda trilho. As equações de movimento são fortemente influenciadas pela determinação dessas forças, o que requer o conhecimento da mecânica de contato, ferramenta imprescindível na previsão do comportamento de uma composição ferroviária. O rodeiro é responsável por receber as excitações na forma de irregularidades e imperfeições da via e transferi-la para a suspensão primária. A proposta dessa dissertação consiste em realizar simulações no domínio do tempo, da resposta do comportamento dinâmico do rodeiro ferroviário de 2 graus de liberdade. O modelo matemático equivalente é desenvolvido. A rigidez de contato e a conicidade são linearizados em torno de um ponto de operação, próximo ao centro da via. É apresentada a influência da velocidade na estabilidade para o modelo linearizado e para a conicidade variando de 0.1 a 1.0. Os respectivos modos de vibrar também são apresentados. Em seguida, o modelo matemático não linear do rodeiro ferroviário é gerado por software especializado na criação de sistemas de multicorpos, VAMPIRE, que permite a criação das equações de movimento através da topologia do sistema. O modelo é criado seguindo a proposta do benchmarck apresentada pela International Association of Vehicle System Dynamics (IAVSD). O rodeiro recebe uma força lateral crescente que se estabiliza em 20kN. O rodeiro é excitado com a aplicação de outra força lateral a uma taxa de 50kN/s até o descarrilamento. As forças longitudinais, laterais que aparecem no contato, o ângulo do plano de contato, ângulo de yaw e afastamento lateral são comparados com o benchmarck e outros autores.Railway dynamics systems are modeled regarding the creep forces between wheel-rail. The equations of movement are strongly influenced by these forces, what requests the knowledge of the theory in mechanical of contact, necessary tool to foresee the behavior of a railway vehicle. The wheelset is responsible by receiving the perturbations of irregularities and transfer them to the primary suspension. A railway vehicle is composed by primary and secondary suspensions. The proposal is based on performing simulations in the time domain, dynamic mresponse of a railway wheelset of two degrees of freedom. The mathematical model is developed. The stiffness of contact and conicity are linearized around an operation point, near to track center. The influence of speed is determined to linearized model and to a range of 0.1 to 1.0 in the conicity. The eigenvectors are presented. In the following, the non linear model of the wheelset is generated using a specialized package of multi body system, VAMPIRE. The package creates equations of movement after the generation of the topology. The non linear mathematical model are defined by the benchmark proposed by International Association of Vehicle System Dynamics (IAVSD). The wheelset is submitted to 20kN at the rail level. In a second case, the wheelset is submitted to a rate of 50kN/s of lateral force until derailing. The determined longitudinal and lateral forces on contact, yaw angle and displacement of the center of gravity of the wheelset, contact angle are compared with the benchmark results and other authors.
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Li, Sheng. "Lubrication And Contact Fatigue Models For Roller And Gear Contacts." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1234822355.
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Balcombe, Robbie. "A study of rolling contact fatigue cracks in lubricated contacts." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9848.
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A novel method for coupling fluid pressure and crack deformation for the purpose of analysing rolling contact fatigue (RCF) cracks in lubricated, hydrodynamic and elastohydrodynamic, contacts is presented. The model addresses some of the simplifying assumptions applied to existing models presented in the literature such as: (i) using an imposed fluid pressure gradient inside the crack, (ii) using an imposed fluid pressure at the crack mouth, and (iii) adopting a surface contact pressure, Hertzian or EHL, that does not account for the fluid flow in and out of the crack during loading. The model has been used to model the effect of lubricant/crack interaction in various RCF configurations as the rolling element passes over the pre-formed crack; which has direct application to bearings and rail/wheel contacts. The results of the simulations performed with the fully-coupled fluid/solid solver developed by the author suggest that the cracked component/lubricant interaction contributes significantly to accelerate the rate of surface breaking crack growth in rolling element bearings and wheel/rail type contacts. It is shown through simulations that the lubricant works as a catalyst inside the crack to convert the compressive contact load into a crack opening, tensile fatigue mechanism, through the effect of fluid pressurisation inside the crack. The results obtained using such a model suggest that the opening associated with the fluid action within the crack induces large mode I stress intensity factors. This has been shown to be the principal factor that promotes and influences the rate of rolling contact fatigue crack growth in lubricated contacts. In addition to the modelling work, an experimental method of analysing RCF cracks in real time has been developed. The technique is based on laser induced fluorescence that allows the penetration of the fluid within the crack to be observed. Though the method would require development to be used to provide results that could be used for quantitative comparisons with crack models, some encouraging preliminary results have been obtained: the technique has been shown to be suitable for measuring, at least qualitatively, the real time evolution of the film thickness in RCF cracks.
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Everitt, Carl-Magnus. "Initiation of rolling contact fatigue from asperities in elastohydrodynamic lubricated contacts." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222371.
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Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem. För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln. Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum.
QC 20180213
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Babori, Abdelghani. "Etude didactique et conception d'une plate-forme d'enseignement à distance d'un contenu en algorithmique. Implications pour la conception d'un MOOC en ingénierie." Thesis, Lille 3, 2019. http://www.theses.fr/2019LIL3H056.
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Le travail que nous présentons dans cette thèse s’inscrit dans une problématique générale d’étude et de conception des MOOCs (Massive Open Online Courses). Elle s’intéresse plus particulièrement à l’étude didactique d’un MOOC d’algorithmique conçu au profit des étudiants de premier cycle de l’université d’Hassan Premier au Maroc. Ce travail se situe dans une approche compréhensive et vise plus précisément à comprendre le processus d’élaboration du contenu d’algorithmique véhiculé par le dispositif MOOC et la manière dont les étudiants le construisent au sein et en relation avec ce dispositif. En considérant le MOOC comme un dispositif didactique, deux approches didactique et épistémologique des activités d’apprentissage en algorithmique ont été articulées. La notion de performance didactique est mobilisée pour examiner les stratégies d’apprentissage adoptées par les étudiants. En recourant aux forums de discussion et en mobilisant un questionnaire et des entretiens semi-directifs, les discours des étudiants ont été analysés en vue de caractériser les contenus construits, les performances didactiques et les difficultés rencontrées. La caractérisation de la conception du MOOC met en évidence deux étapes : 1) l’identification des concepts incontournables en algorithmique : variable, instructions de base, conditions, boucles et leur organisation en unités d’apprentissage 2) la scénarisation pédagogique décrivant les tâches d’apprentissage des unités pédagogiques et leur organisation ; le cours est par ailleurs adapté à la massification des audiences notamment en diminuant la charge horaire des semaines du MOOC et en exigeant peu de prérequis.L’analyse des pratiques identifiées montre que les étudiants ont construit deux types de contenus, d’une part, des savoirs conceptuels (condition et boucle) et d’autre part des savoirs procéduraux (démarche de résolution d’un problème, exécution d’un algorithme) ; que les étudiants ont manifesté plus de performances didactiques cognitives et techniques que sociales pour construire le contenu. Plus particulièrement, la démarche de construction du contenu consiste 1) en des stratégies cognitives d’élaboration telle que la mise en lien du contenu avec les connaissances antérieures et d’organisation à savoir l’utilisation des organigrammes pour construire pas à pas le savoir algorithmique ; 2) en des stratégies techniques en termes de mobilisations des vidéos du MOOC. Les résultats montrent également que même si les étudiants se sont avérés particulièrement performants dans l’analyse des problèmes (détermination des objets d’entrées et sorties), certaines difficultés subsistent, tels que le passage de la phase d’analyse d’un problème à celle d’élaboration de l’algorithme.Ce travail de thèse a l’ambition de proposer aux concepteurs pédagogiques des MOOCs des principes utiles pour l’élaboration d’un contenu, d’une part, et ouvrir une voie de recherche en didactiques, sur les dispositifs MOOCs, qui tient compte de la spécificité des contenus véhiculésThe work presented in this thesis is part of a broader issue of study and design of MOOCs (Massive Open Online Courses). It focuses more particularly on the didactic study of an algorithmic MOOC designed for undergraduate students at Hassan First University (Morocco). This work is part of a comprehensive approach and aims more specifically to understand the process of developing algorithmic content conveyed by the MOOC and how learners construct basic knowledge essential to the course. Considering MOOC as a didactic device, two approaches : didactic and epistemological of algorithmic have been articulated. The notion of didactic performance is mobilized to examine the learning strategies adopted by students. By using discussion forums and mobilizing a questionnaire and semi-structured interviews, the discourses of students were analysed in order to characterize the constructed content, the didactic performance and the difficulties encountered by students.The characterization of the design of the MOOC highlights two steps : 1) identification of the essential concepts in algorithmics :variable, basic instructions, conditions, loops and their organization into learning units 2) development of a pedagogical scenario by describing the learning tasks of the pedagogical units and their organisation, and, on the other hand, that the course is also adapted to the massification of audiences, in particular by decreasing the hourly workload and demanding few prerequisites.The results show that students constructed two types of content: conceptual knowledge (condition, loop and procedural knowledge (analysis of a problem, decomposition of a problem, etc.). Students showed more interest in cognitive and technical didactic performances to build, step by step, content. More specifically, students constructed algorithmic content by making greater use of these learning strategies 1) elaboration strategies (linking the content with previous knowledge) and organization strategies such as the use of flowcharts 2) technical strategies in terms of mobilizing MOOC videos. The results also show that although students have been particularly successful in analysing problems (determination of input and output objects), some difficulties remain, such as passing from analysing problems to elaborating algorithms.These results can not only provide MOOC instructional designers with the necessary elements for content development, but also improve didactic research on MOOCs by providing researchers with elements for the study of MOOCs, taking into account the specificity of their content
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MʾNasri, Hechmi. "Comportement d'un accumulateur au plomb associe a un convertisseur statique contine-continu." Paris 6, 1988. http://www.theses.fr/1988PA066422.
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Un accumulateur au plomb est soumis a des decharges hachees et continues sur un automate de mesure pilote par un micro-ordinateur. Les parametres des decharges hachees sont: le courant moyen, la frequence et le rapport cyclique. Un seul parametre variant a la fois, les capacites des decharges hachees sont comparees a celles des decharges continues. Les resultats sont proches. L'etude de la tension transitoire observee aux bornes de la cellule lors des commutations montre que l'impedance interne est comparable a celle d'un conducteur electrique de geometrie simple
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Carlier, Axel. "Compréhension de contenus visuels par analyse conjointe du contenu et des usages." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0085/document.
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Dans cette thèse, nous traitons de la compréhension de contenus visuels, qu’il s’agisse d’images, de vidéos ou encore de contenus 3D. On entend par compréhension la capacité à inférer des informations sémantiques sur le contenu visuel. L’objectif de ce travail est d’étudier des méthodes combinant deux approches : 1) l’analyse automatique des contenus et 2) l’analyse des interactions liées à l’utilisation de ces contenus (analyse des usages, en plus bref). Dans un premier temps, nous étudions l’état de l’art issu des communautés de la vision par ordinateur et du multimédia. Il y a 20 ans, l’approche dominante visait une compréhension complètement automatique des images. Cette approche laisse aujourd’hui plus de place à différentes formes d’interventions humaines. Ces dernières peuvent se traduire par la constitution d’une base d’apprentissage annotée, par la résolution interactive de problèmes (par exemple de détection ou de segmentation) ou encore par la collecte d’informations implicites issues des usages du contenu. Il existe des liens riches et complexes entre supervision humaine d’algorithmes automatiques et adaptation des contributions humaines via la mise en œuvre d’algorithmes automatiques. Ces liens sont à l’origine de questions de recherche modernes : comment motiver des intervenants humains ? Comment concevoir des scénarii interactifs pour lesquels les interactions contribuent à comprendre le contenu manipulé ? Comment vérifier la qualité des traces collectées ? Comment agréger les données d’usage ? Comment fusionner les données d’usage avec celles, plus classiques, issues d’une analyse automatique ? Notre revue de la littérature aborde ces questions et permet de positionner les contributions de cette thèse. Celles-ci s’articulent en deux grandes parties. La première partie de nos travaux revisite la détection de régions importantes ou saillantes au travers de retours implicites d’utilisateurs qui visualisent ou acquièrent des con- tenus visuels. En 2D d’abord, plusieurs interfaces de vidéos interactives (en particulier la vidéo zoomable) sont conçues pour coordonner des analyses basées sur le contenu avec celles basées sur l’usage. On généralise ces résultats en 3D avec l’introduction d’un nouveau détecteur de régions saillantes déduit de la capture simultanée de vidéos de la même performance artistique publique (spectacles de danse, de chant etc.) par de nombreux utilisateurs. La seconde contribution de notre travail vise une compréhension sémantique d’images fixes. Nous exploitons les données récoltées à travers un jeu, Ask’nSeek, que nous avons créé. Les interactions élémentaires (comme les clics) et les données textuelles saisies par les joueurs sont, comme précédemment, rapprochées d’analyses automatiques des images. Nous montrons en particulier l’intérêt d’interactions révélatrices des relations spatiales entre différents objets détectables dans une même scène. Après la détection des objets d’intérêt dans une scène, nous abordons aussi le problème, plus ambitieux, de la segmentationThis thesis focuses on the problem of understanding visual contents, which can be images, videos or 3D contents. Understanding means that we aim at inferring semantic information about the visual content. The goal of our work is to study methods that combine two types of approaches: 1) automatic content analysis and 2) an analysis of how humans interact with the content (in other words, usage analysis). We start by reviewing the state of the art from both Computer Vision and Multimedia communities. Twenty years ago, the main approach was aiming at a fully automatic understanding of images. This approach today gives way to different forms of human intervention, whether it is through the constitution of annotated datasets, or by solving problems interactively (e.g. detection or segmentation), or by the implicit collection of information gathered from content usages. These different types of human intervention are at the heart of modern research questions: how to motivate human contributors? How to design interactive scenarii that will generate interactions that contribute to content understanding? How to check or ensure the quality of human contributions? How to aggregate human contributions? How to fuse inputs obtained from usage analysis with traditional outputs from content analysis? Our literature review addresses these questions and allows us to position the contributions of this thesis. In our first set of contributions we revisit the detection of important (or salient) regions through implicit feedback from users that either consume or produce visual contents. In 2D, we develop several interfaces of interactive video (e.g. zoomable video) in order to coordinate content analysis and usage analysis. We also generalize these results to 3D by introducing a new detector of salient regions that builds upon simultaneous video recordings of the same public artistic performance (dance show, chant, etc.) by multiple users. The second contribution of our work aims at a semantic understanding of fixed images. With this goal in mind, we use data gathered through a game, Ask’nSeek, that we created. Elementary interactions (such as clicks) together with textual input data from players are, as before, mixed with automatic analysis of images. In particular, we show the usefulness of interactions that help revealing spatial relations between different objects in a scene. After studying the problem of detecting objects on a scene, we also adress the more ambitious problem of segmentation
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Almeida, Lia Ramadoss Ramesh. "Experimental and theoretical investigation of contact resistance and reliability of lateral contact type ohmic MEMS relays." Auburn, Ala., 2006. http://repo.lib.auburn.edu/2006%20Fall/Theses/ALMEIDA_LIA_13.pdf.
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McNeal, Cedric J. "Barrel wear reduction in rail guns : the effects of known and controlled rail spacing on low voltage electrical contact and the hard chrome plating of copper-tungsten rail and pure copper rails /." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Jun%5FMcNeal.pdf.
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Thesis (M.S. in Applied Physics)--Naval Postgraduate School, June 2003.Thesis advisor(s): William B. Maier II, Richard Harkins. Includes bibliographical references (p. 45-46). Also available online.
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Rajan, Naveen Mukund. "Experimental study of the effect of a contact conditioner on sliding electrical contacts." Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1546.
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This thesis documents research carried over the past two years, aimed at studying the tribology of sliding contacts subjected to high densities of current of the order is 422 --917A/mm2. The overall aim was the development of an experimental test bed for evaluating the effect of different solid lubricant conditioners on sliding electrical contacts. The experimental configuration consists of a flat ended copper tip pressed in contact with a flat copper disc. The copper plate is mounted on a spindle of a lathe which is operated at 550rpm, whereas the copper tip is mounted on a shaft which is instrumented with force sensing piezos to measure the forces during the test. A weak spring is used to compensate for wear of the tip during the experiment. The interface is subjected to high current densities of the order of 422 and 917A/mm2 to evaluate the effect of solid conditioner as contrast with the surface behavior when no interface lubrication was used. The key outputs of the experiments are a) Friction coefficient, b) Contact resistance, c) Amount of material transfer, d) number of passes to failure and e) Wear rate. Two types of tests, namely circular and spiral tests were carried out. The current density of 422A/mm2 would result in softening of the interface whereas current density of 917A/mm2 results in melting of the interface. In terms of contact voltages it is noted that Cu-Cu interface softens at 0.12V and melts at 0.43V. It has been noted that pre-application of SLIC leads to increase of contact resistance by approximately 20% when the interface is loaded statically. When the interface is tested for contact resistance, there is a significant effect of oxide layer on the surface of the plates. When contact resistance is measured these oxide layers contribute significantly, and increase the contact resistance substantially.Thesis (M.S)-- Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering
"December 2007."
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Rajan, Naveen Mukund Madhavan Viswanathan. "Experimental study of the effect of a contact conditioner on sliding electrical contacts /." Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1546.
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Anisetti, Anusha. "On the Thermal and Contact Fatigue Behavior of Gear Contacts under Tribo-dynamic Condition." Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright149363918488722.
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Praquin, Jérôme. "Étude des revêtements et des paramètres de fonctionnement électrique, climatique et mécanique sur la conduction et la commutation de faibles courants des contacts électriques de type membrane." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S094.
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L'objet de la présente étude est d'étudier, de comprendre et de maîtriser les différentes propriétés électriques de contacts électriques constitués de membranes souples en carbone, qui commutent sur des pistes métalliques d'un circuit imprimé. Ces contacts sont de plus en plus utilisés dans l'automobile car ils possèdent des propriétés mécaniques intéressantes vis-à-vis du ressenti de l'utilisateur, tout en permettant une bonne durée de vie. Dans un premier temps, les paramètres électriques et mécaniques de ces contacts sont caractérisés, les phénomènes de commutation sur divers type de charges sont étudiés et l'influence de contaminants et de la corrosion sur la conduction électrique sont examinés. L'évolution des résistances d'isolement en présence d'humidité est quantifiée. Dans un second temps, une approche de fiabilité est réalisée : l'évolution des paramètres électriques et mécaniques de ces contacts est étudiée lorsqu'ils sont soumis à des stress environnementaux, en particulier la chaleur humide. Les principaux modes d'endommagement sont étudiés. Nous montrons en particulier que les défaillances mécaniques proviennent essentiellement du polymère, et les défaillances électriques proviennent plutôt du circuit imprimé. L'influence d'un revêtement doré côté circuit imprimé, pour différentes épaisseurs, est également étudiée. Notre travail se poursuit par une étude un peu plus fondamentale sur les phénomènes de commutation en présence de matériaux en carbone. Au cours de ce travail novateur, les signatures optiques sont examinées lors de la coupure du courant. Un phénomène baptisé « glowing » est mis en évidence ; les limites en courant et en tension entre « glowing » et arcage électrique sont données, et les phénomènes comparés par rapport aux phénomènes de commutation dans les contacts de type métal – métal. L'étude se termine par un bilan synthétique concernant l'utilisation de contacts comprenant une pastille en carbone, avec leurs avantages et leurs limitationsThe purpose of this study is to explore, understand and master the different electrical properties of electrical contacts made of flexible carbon membranes, which switch on metal tracks on a printed circuit board. These contacts are increasingly used in the automobile because they have interesting mechanical properties for the user, while providing a good reliability. At first, the electrical and mechanical parameters of these contacts are characterized, the switching phenomena on various types of loads are studied and the influence of contaminants and corrosion on the electrical conduction is examined. The evolution of insulation resistance in the presence of moisture is quantified. In a second step, an approach to reliability is achieved: the evolution of electrical and mechanical parameters of these contacts is studied when subjected to environmental stresses, especially moist and heat. The main types of damage are considered. We show in particular that mechanical failures come mainly from polymer and electrical failures from the PCB. The influence of a gold-plated printed for different thicknesses system side, is also studied. Our work continues with a slightly more fundamental study on switching phenomena in the presence of carbon materials. In this pioneering work, the optical signatures are discussed at the current break. A phenomenon called "glowing" is highlighted; limits current and voltage between "glowing" and electrical arcing are given, and compared with respect to the phenomena switching phenomena in metal contacts - type metal. The study concludes with a summary review on the use of contacts comprising a carbon pill, with their advantages and limitations
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Neves, Julio Cesar Klein das. "Desenvolvimento de um equipamento para ensaio de fadiga de contato esfera sobre plano e sua aplicação na caracterização de ferros fundidos com matrizes de elevada dureza." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-11122006-131939/.
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Esse trabalho descreve o projeto e construção de um equipamento destinado ao estudo de fadiga de contato de rolamento e sua posterior aplicação na caracterização de ferros fundidos. O trabalho foi iniciado com a utilização de um equipamento previamente existente no Laboratório de Fenômenos de Superfície da EPUSP, a máquina I. Esse equipamento era baseado na substituição das pistas externas de um rolamento axial de esferas por corpos de prova na forma de arruelas. Ensaios preliminares mostraram que a máquina I apresentava limitações, a principal delas era não ser capaz de reproduzir integralmente o movimento de rolamento, havendo uma relação desconhecida rolamento/deslizamento no decorrer do ensaio. Com base nas dificuldades operacionais da máquina I, uma segunda máquina, também baseada em um rolamento axial, foi projetada e construída. Ensaios preliminares mostraram que o novo equipamento reproduzia mecanismos de falha por fadiga de contato de rolamento. A etapa seguinte então foi utilizar a máquina II no estudo de fadiga de contato de rolamento de dois tipos de ferro fundido com matrizes de levada dureza, um cinzento e um nodular, os quais foram testados em duas condições: com e sem pré-tensionamento e analisados segundo a estatística de Weibull. Um aço também foi ensaiado como referência. A pré-tensão foi aplicada com uma ferramenta bi-partida e modelada por elementos finitos. Foram realizados ensaios lubrificados, com a aplicação de uma pressão máxima de contato de 3,6 GPa e conduzidos até a falha dos materiais por lascamento da superfície de rolamento. Em todas as condições de ensaio o ferro fundido nodular se mostrou muito superior ao ferro cinzento. Enquanto esse último que apresentou resultados similares na condição com e sem pré-tensão, o ferro fundido nodular teve a sua curva de distribuição de falhas significativamente alterada pela aplicação de tensão externa. Uma heterogeneidade na distribuição do tamanho de nódulos de grafita fez com que as falhas ocorressem sempre na mesma região do corpo-deprova evidenciando a sensibilidade do ensaio a variáveis microestruturais.This work presents design and construction of an equipment for rolling contact fatigue studying and its use to cast irons analysis. Firstly it was used an equipment available at Surface Phenomena Laboratory, in São Paulo University, which was called machine I. The design of the system followed the well-known architecture where races of a thrust ball bearing are substituted by washers made with the material under investigation. Preliminary tests have shown that the first machine had severe limitations, but the most important was lack of ability to reproduce rolling contact fatigue mechanisms. An unknown sliding/rolling ratio always took place in its work. Then a second machine was designed and assembled. Sets up tests have shown typical mechanisms of rolling contact fatigue. The next step was to use the new machine to study two types of cast irons, a gray iron and a ductile iron, under two test conditions: with and without pre-stress. Also a steel specimen was tested as a reference. Results were subjected to Weibull analysis. A device was developed for pre-stress application, and the specimen/device system was modeled by finite elements analysis. Tests were carried out till failure, under lubrication, and with maximum contact pressure of 3.6 GPa. Ductile cast iron behavior was superior to gray iron in all tests. Gray iron specimens with and without pre-stress presented very similar results. On the other hand, ductile iron probability failure curve was strongly affected by pre-stress. An unexpected heterogeneity on graphite nodules size distribution promoted failures on just one region, which is an evidence of test sensitivity to micro structural changes.
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MARQUES, Danielle Medeiros. "Vigilância sobre os contatos de hanseníase no município de João Pessoa: soroprevalência anti-NDO-LID-1 e adesão ao Programa Nacional de Controle da Hanseníase." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/17987.
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CNPq
A hanseníase ainda representa um grave problema de Saúde Pública no Brasil, com número absoluto de casos novos atingindo em torno de 30.000/ano. O Programa Nacional de Controle da Hanseníase (PNCH), no sentido de aumentar a detecção e tratamento precoce da doença, preconiza a avaliação dermatoneurológica e a vacinação BCG em contatos intradomiciliares de hanseníase. Além desta avaliação clínica, estudos sorológicos utilizando antígenos específicos do M. leprae vêm demonstrando alta especificidade, sendo relatada a relação entre a positividade sorológica nos contatos e o maior risco de adoecimento. O presente estudo teve como objetivos estimar a soroprevalência anti-NDO-LID-1 em contatos de casos novos de hanseníase e avaliar a adesão dos mesmos ao PNCH, através de um estudo transversal e um estudo caso-controle, respectivamente. Metodologia: a população estudada foram os contatos de casos novos de hanseníase residentes na cidade de João Pessoa, Paraíba nos anos de 2012 e 2013 (na etapa transversal) e no ano de 2013 (na etapa caso-controle). Utilizou-se o teste sorológico rápido NDOLID- 1 para aferir a soroprevalência e a adesão ao PNCH foi aferida através da resposta a um questionário padronizado. Toda a coleta de dados foi domiciliar. Resultados da etapa transversal: foram identificados 135 casos novos de hanseníase, com 405 contatos estudados. A soroprevalência foi de 23% (93/405), sendo maior no sexo feminino (25,9%-58/224), com tempo médio de convívio entre cinco e 10 anos (44%- 22/50) e naqueles que dormiam no mesmo cômodo e na mesma cama (26,3%-31/118) do caso índice. Em menores de quinze anos, a soroprevalência alcançou 27,7% de positividade. Não houve associação da com variáveis biossociais (faixa etária e sexo), passado de tratamento pra hanseníase, vacinação BCG e variáveis relacionadas ao caso índice (grau de parentesco, frequência de contato e tempo de convívio). Resultados da etapa caso-controle: dentre os 231 contatos, apenas 31 (13,4%) haviam aderido ao PNCH, através da realização do exame dermatoneurológico. Não foi observada associação significativa da baixa adesão com as variáveis do contato como sexo, cor da pele, faixa etária, escolaridade, estado civil, renda familiar, tabagismo, etilismo, uso de drogas ilícitas e distância do posto de saúde. Observou-se maior adesão ao PNCH dos contatos de casos de hanseníase com maior idade média e naqueles relacionados às formas dimorfa e virchowiana. A maioria dos contatos que não aderiram ao Programa 8 Nacional de Controle da Hanseníase relataram como justificativa a desinformação sobre a necessidade de fazê-lo, fator este determinante para a não adesão ao programa (OR=0,04, p-valor=0,001). Conclusões: a população de contatos estudada apresentou uma elevada taxa de soroprevalência e uma baixa adesão ao exame dermatoneurológico, denotando haver um alta carga bacilar do M. leprae circulante e uma vigilância sobre os contatos ainda negligenciada.
Leprosy is a serious health public problem in Brazil, with new absolute cases ranging around 30,000 / year. The National Program of Leprosy Control (NPLC) recommends skin and nerves examination and BCG vaccination in all households leprosy contacts (HHC). Besides, serological studies using specific antigens of M. leprae had demonstrated correlation between seropositivity in contacts and increased risk of illness. This study aimed to assess positivity to anti- NDO-LID-1 test and to evaluate the adherence to NPLC among contacts of newly leprosy cases at João Pessoa, Paraíba, 2012 and 2013, using a cross-sectional and a case-control study. Methodology: the study population were contacts of new leprosy cases residents at João Pessoa, Paraíba in 2012 and 2013 (cross-sectional study) and 2013 (casecontrol study). The serological test used to assess seroprevalence was anti-NDOLID- 1 rapid test and the adherence to PNCH was measured by response to a standard questionnaire. All data collection was did at home.Cross-sectional results: there were identified 135 new cases of leprosy, with 405 contacts studied. Serological positivity to anti-NDO-LID-1 was 23% (93/405), higher in females (25.9% -58 / 224), with average living time between five and 10 years (44% - 22/50) and those who slept in the same room and the same bed (26.3% -31 / 118) of the index case. The seroprevalence among contacts under fifteen years reached 27.7% positivity. There was no association with biossocial variables (age and gender), past treatment for leprosy, BCG vaccination and variables related to the index case (degree of relationship, frequency of contact and interaction time). Case-control results: 13.4% (31/231) of the contacts had accomplished the skin and nerves examination, as recommended. There was no significant association with gender, age, ethnicity, instruction degree, marital status, family income, smoking, alcohol use, illicit drugs use and distance from the health center. There was better adherence in contacts of elderly index cases and from borderline and lepromatous forms. Misinformation about the need of doing the dermatologic exam was a determinant factor for non-adherence to the program (OR=0.04, p-value= 0.001). Conclusions: the seropositivity in leprosy contacts was high and adherence to NPLC was low, showing that surveillance needs to be improved.
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Bruel, Paulo Eduardo Nunes. "Abordagem analítica e caracterização de contato entre superfícies." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18149/tde-06122006-003830/.
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Pode-se definir o tato através da capacidade de um corpo sentir o contato, localizá-lo, reconhecer a forma e a rugosidade da superfície impactante. Normalmente, não se encontram estruturas analíticas adequadas para descrever o fenômeno. Neste trabalho, pretende-se determinar a localização dos pontos de contato entre dois corpos através da análise dos sinais resultantes das vibrações causadas pelo contato, além de estimar a geometria da superfície do objeto impactante. A descrição qualitativa do impacto é obtida através da análise de uma série de funções matemáticas que geram uma base ortogonal adequada para este tipo de evento. Assim, o contato não é considerado através de uma modelagem física tradicional, mas pela descrição das ondas geradas pelas tensões e deformações superficiais, incorporando a interação de múltiplos pontos vinculados e procedimentos de contagem estatística. Com a metodologia para estudo de impacto experimental, é efetuada a construção qualitativa do espectro de deslocamento de uma placa simplesmente apoiada sujeita à aplicação de esforços distribuídos.The tact may be defined as the capacity of a body to locate the contact on its surface, to recognize shape of the contacting surface as well as the superficial rugosity. Usually analytical models are not able to describe the phenomenon properly. This work, proposes an approach for the contact form location between two bodies using the resultant signals analysis of the vibrations caused for the contact. In this way it is determined the target surface geometry. The qualitative description of the impact is obtained through the analysis of mathematical series that generate orthogonal basis for this sort of event. Thus, the contact is not considered through a traditional physical modeling, but by the description of the waves generated for the superficial stress and strain, incorporating the interaction of multiple entailed points and procedures of counting statistics. With a methodology for study of theoretical impact, the quantitative construction of the specter of displacement of a subject plate to the application of distributed strains is effected.
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Silva, Alysson Alexander Naves. "Simulação numérica de escoamentos bidimensionais com superfícies livres e linhas de contato dinâmicas." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/55/55134/tde-22062010-145307/.
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Um método lagrangeano-euleriano arbitrário para a resolução de escoamentos dominados por tensão superficial é apresentado neste trabalho. Tais escoamentos são importantes em muitas aplicações, especialmente em canais capilares que frequentemente aparecem em escoamentos em microescala. A resolução deste tipo de escoamento apresenta vários desafios que são abordados neste trabalho. O escoamento é resolvido somente para a fase líquida, com condições de contorno apropriadas para a superfície livre que delimita o líquido e o gás, que é representada por arestas e vértices da malha computacional. Esta se move e se deforma, sendo que sua qualidade é mantida sob controle para não degradar a solução numérica. As equações de Navier-Stokes são discretizadas pelo método de elementos finitos em um referencial arbitrário. O método de incorporação dos efeitos de tensão superficial e linha de contato é explicado em detalhes. Validações comprovam a precisão do método proposto, com comparações através de soluções pseudo-analíticas para casos simples. Finalmente alguns resultados sobre escoamentos em capilares são apresentadosAn arbitrary lagrangian-eulerian finite element method to solve surface tension dominated flows is presented. Such flows are important in many applications, particularly in capillary channels, that appear in microscale flows. The resolution of such flows presents several challenges that are addressed in this work. The flow is solved only in the liquid phase, and proper boundary conditions are applied on the free-surface, bounding the liquid and gas, which is explicitly represented by vertices and edges of the computational mesh. The mesh is moved and deformed, but its quality is kept under control in order to control errors in the numerical solution. The Navier-Stokes equations are discretized by standard Galerkin finite element method in an arbitrary reference. Details of the computation of surface tension and contact line effects are presented. The methodology is validated for a number of simple test cases against known pseudo-analytical solutions, and numerical results are presented, showing the robustness and accuracy of the methodology. Finally, some results about surface-tension-driven flows in capillaries are presented
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Bélteky, Markus. "Emotion in video game audio : Can sound effects be perceived to contain positive emotional content?" Thesis, Luleå tekniska universitet, Medier, ljudteknik och teater, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-74148.
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Sound is an important part of almost all media. In games, sounds are used to evoke intense emotions in players. Studies has showed that music on its own can induce emotions. Soundeffects is another type of sounds that appear in games. However, do they contribute to the emotional experience? Understanding this will help sound designers enhance scenes in future video games. In this study, 23 participants were asked to conduct a test divided into two part. In the first part they were tasked to listen to four sound effects of fire and choose attributes from a predetermined list that they thought suited. Among these physical attributes were two emotional attributes. In the second part, the subjects were tasked with choosing one of the fours sound effects for a scenario with a positive emotion and motivate their choice. The results show that no sound had neither positive nor negative as an emotional attribute. Of the four sounds, two showed significance that emotion alone was an attribute for the sound. The results from the second part showed that the subjects were divided in what motivated them to choose a sound. More than a third of the subjects based their choice only on if the sound matched the emotion of the scenario presented while slightly less than a third based it only on to fit the location. The last third based it on both emotion and location.
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Ndiaye, Serigne Ndiaga. "Ultimate behavior of confined fluids under very high pressure and shear stress." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI104/document.
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L’étude du frottement dans les contacts lubrifiés fortement chargés est un sujet complexe. En effet, le frottement dépend fortement du comportement rhéologique du lubrifiant dans le centre du contact et, celui-ci n'est pas bien connu à pression et taux de cisaillement élevé. Diverses méthodes expérimentales ont été développées pour expliquer le comportement plateau dans les courbes de frottement, associé à l’existence d’une contrainte limite de cisaillement, mais aucune d'elles n'a fourni une image complète des mécanismes réels impliqués. Dans la continuité de ces efforts, des études sont présentées dans ce mémoire. Le premier défi dans ce travail est d'effectuer des mesures de frottement dans des conditions isothermes nominales, ce qui signifie que même si des effets thermiques doivent se produire dans toute mesure de frottement, il est possible de les minimiser et de rendre les résultats insensibles à une faible dissipation d'énergie dans le volume expérimental d'intérêt. La minimisation de l’échauffement du lubrifiant aide à se focaliser sur l’origine mécanique de la contrainte limite de cisaillement et de mieux caractériser sa dépendance à la pression et à la température. C'est pourquoi, tout d'abord, une série d'expériences a été réalisée sur deux lubrifiants, un diester pur (benzyl benzoate) et une huile minérale de turbine (Shell T9) avec des vitesses d'entraînement variables. Cela nous permet d'abord d'observer directement l'influence des effets thermiques sur les valeurs de la contrainte limite de cisaillement et ensuite, de déterminer les conditions expérimentales qui limitent ces effets tout en assurant un régime en film complet. Le deuxième objectif est de caractériser le comportement en frottement des lubrifiants sous conditions isothermes nominales et sur une large gamme de pression (jusqu'à 3 GPa) et de température (jusqu’à 80°C) afin d'établir un nouveau modèle découplé permettant de décrire la dépendance à la température et à la pression de la contrainte limite sous fortes charges. Enfin, l'étude se focalise sur la compréhension du comportement microscopique des lubrifiants dans des conditions extrêmes de cisaillement et de pression. Des mesures in situ de spectroscopie Raman et Brillouin ont été également effectuées sous conditions statiques, afin d'étudier le changement de phase du lubrifiantFriction in highly loaded lubricated contacts is a complex issue. Indeed, it highly depends on the lubricant rheological behaviour in the Hertzian region, which is not well known under such high pressure and high shear stress. Various experimental methods have been developed to explain the plateau-like behaviour in friction curves referred to as the limiting shear stress (LSS), but none of them provided a full picture of the real mechanisms involved. In a continuation of these efforts, some investigations are presented in this manuscript. The first challenge in this work is to carry out friction measurements under nominal isothermal conditions, meaning that even if thermal effects must occur in any friction measurement, it is possible to minimize them and to make the results almost insensitive to a weak energy dissipation within the experimental volume of interest. Minimizing shear heating of the lubricant help us to focus on the mechanical origin of the LSS and to better characterize its dependence to pressure and temperature. That’s why, first of all, a series of experiments was performed on two lubricants, a pure diester fluid (benzyl benzoate), and a commercial turbine mineral oil (Shell T9) with varying entrainment velocities. This allow us first to directly observe the influence of the lubricant shear heating on the LSS values and then to determine the experimental conditions which limit this thermal effect while ensuring a full film regime. The second objective is to characterize the frictional behavior of both lubricants under nominal isothermal conditions and over a wide range of pressure (up to 3 GPa) and temperature (up to 80°C) in order to establish a new uncoupled model to describe the temperature and pressure dependence of the limiting shear stress under highly loaded conditions. Finally, the study focuses on the understanding of the microscopic behavior of lubricants under extreme shear and pressure conditions. In situ Raman and Brillouin spectroscopy investigations were also conducted under static conditions, in order to study the lubricant phase changes under various pressure and temperature conditions
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Jeandot, Chrystel. "Ce que l'information en continu fait à l'information. Le cas de BFMTV." Thesis, Sorbonne Paris Cité, 2016. http://www.theses.fr/2016USPCA156.
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Si l’information en continu semble constituer un genre télévisuel aujourd’hui installé, le modèle d’information qu’elle propose fait l’objet de nombreuses questions concernant les effets de reprise de l’information et la nature même de celle-ci. Parce que la chaîne BFMTV cristallise ces questions critiques, il a semblé pertinent, au moment où elle a plus de dix ans d’existence, d’essayer de comprendre le type d’information dont il s’agit. D’autant qu’elle se présente dorénavant, dans un contexte de convergence médiatique, sur plusieurs supports évoluant au gré des pratiques et des possibilités techniques, qui poussent à se pencher sur le lien que la chaîne, via son dispositif, entretient avec ses usagers. Pensé selon une approche pragmatique, ce travail a ainsi pour ambition de mieux cerner les enjeux de l’information en continu mais aussi ses impacts sur l’information en généralIf 24-hour news channels today seem to constitute an established television genre, the type of information that they provide leaves many questions open concerning both the re-presentation of information and the latter’s very nature. Because the 24-hour news channel BFMTV incarnates those critical questions, it seems relevant, more than ten years after its creation, to examine the model of information that it provides. Moreover, in the context of media convergence, this channel is now transmitted on several platforms that evolve according to the user's practices and existing technical possibilities. This fact leads to a further examination of how the channel develops a relationship, through its technical possibilities, with its users. Deploying a pragmatic approach, this thesis aims to achieve a better understanding of what is at stake in continuous news cycles and also of the impact that the latter have on information in general
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Porras, Vazquez Alberto. "Lubricant starvation in elastohydrodynamic large-size spinning contacts." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI109.
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Cette thèse est dédiée à l'étude des contacts pivotants de grandes dimensions situés à l'interface entre l'extrémité du rouleau et le collet de la bague des roulement. L'objectif principal de l'étude est d'évaluer l'influence de la sous-alimentation sur la distribution d'épaisseur de film du contact et d'analyser comment le pivotement pourrait affecter ce mécanisme. En raison de son importance dans la fiabilité et la performance du roulement, l'accent est mis sur l'épaisseur de film minimale locale située dans la région de faible vitesse de la zone de contact. Pour résoudre ce problème, une double approche numérique-expérimentale est proposée. La distribution de l'épaisseur de film des contacts pivotants est étudiée numériquement à l’aide d'un modèle d'éléments finis préalablement validé par deux bancs d'essai dédiés: Jerotrib et Tribogyr. La simulation de différentes conditions opératoires, cinématiques, géométriques et de lubrification permet d'écrire une expression analytique pour prédire l'épaisseur critique du film précédent. En même temps, de nouvelles techniques pour induire et contrôler expérimentalement la sous-alimentation au contact sont mises en œuvre dans les deux bancs d'essai et leurs résultats sont comparés à ceux de la simulation. Il est démontré que les effets du pivotement et de la sous-alimentation s’additionnent, de sorte que la distribution de l’épaisseur de film du contact pivotant reste asymétrique mais tend à une distribution plus hertzienne, et donc plus mince, lors de la limitation de l’alimentation en huile en amont de l’entrée du contactThis thesis is dedicated to the study of large-size spinning contacts located at the interface between the roller-end and the flange in rolling-element bearings. The main goal of the study is to evaluate the influence of lubricant starvation on the film thickness distribution of the contact and analyze how spinning might affect this mechanism. Due to its importance in the reliability and performance of the bearing, the focus is set of the local minimum film thickness found at the low velocity region of the contact area. To tackle this problem, a dual numerical-experimental approach is proposed. The film thickness distribution of spinning contacts is investigated numerically by means of a finite element model previously validated by two dedicated test rigs: Jerotrib and Tribogyr. The simulation of different operating, kinematic, geometric and lubrication conditions enables to write an analytic expression for predicting the aforementioned critical film thickness. At the same time, novel techniques to experimentally induce and control starvation in the contact are implemented into both test rigs and their results are contrasted with those of the simulation. It is demonstrated that the effects of spinning and starvation add up, so that the film thickness distribution of the spinning contact remains asymmetric but tends to a more Hertzian, and therefore thinner, distribution when limiting the oil supply upstream of the contact’s inlet
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Votsios, Vasilis. "Contact mechanics and impact dynamics of non-conforming elastic and viscoelastic semi-infinite or thin bonded layered solids." Thesis, Loughborough University, 2003. https://dspace.lboro.ac.uk/2134/11815.
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The thesis is concerned with the contact mechanics behaviour of non-conforming solids. The geometry of the solids considered gives rise to various contact configurations, from concentrated contacts with circular and elliptical configuration to those of finite line nature, as well as those of less concentrated form such as circular flat punches. The radii of curvature of mating bodies in contact or impact give rise to these various nonconforming contact configurations and affect their contact characteristics, from those considered as semi-infinite solids in accord with the classical Hertzian theory to those that deviate from it. Furthermore, layered solids have been considered, some with higher elastic modulus than that of the substrate material (such as hard protective coatings) and some with low elastic moduli, often employed as tribological coatings (such as solid lubricants). Other bonded layered solids behave in viscoelastic manner, with creep relaxation behaviour under load, and are often used to dampen structural vibration upon impact. Analytic models have been developed for all these solids to predict their contact and impact behaviour and obtain pressure distribution, footprint shape and deformation under both elastostatic and transient dynamic conditions. Only few solutions for thin bonded layered elastic solids have been reported for elastostatic analysis. The analytical model developed in this thesis is in accord with those reported in the literature and is extended to the case of impact of balls, and employed for a number of practical applications. The elastostatic impact of a roller against a semi-infinite elastic half-space is also treated by analytic means, which has not been reported in literature. Two and three-dimensional finite element models have been developed and compared with all the derived analytic methods, and good agreement found in all cases. The finite element approach used has been made into a generic tool for all the contact configurations, elastic and viscoelastic. The physics of the contact mechanical problems is fully explained by analytic, numerical and supporting experimentation and agreement found between all these approaches to a high level of conformance. This level of agreement, the development of various analytical impact models for layered solids and finite line configuration, and the development of a multi-layered viscoelastic transducer with agreed numerical predictions account for the main contributions to knowledge. There are a significant number of findings within the thesis, but the major findings relate to the protective nature of hard coatings and high modulus bonded layered solids, and the verified viscoelastic behaviour of low elastic modulus compressible thin bonded layers. Most importantly, the thesis has created a rational framework for contact/impact of solids of low contact contiguity.
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Neto, Dorival Piedade. "Sobre estratégias de resolução numérica de problemas de contato." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-14072009-165646/.
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Os problemas de contato representam uma classe de problemas da mecânica dos sólidos para a qual a não-linearidade é introduzida pela alteração das condições de contorno, as quais só podem ser determinadas no decorrer do processo de resolução. O presente trabalho trata dos problemas de contato abordando aspectos de sua formulação e implementação numérica. Apresentam-se, em particular, as formulações de dois diferentes tipos de elemento de contato revendo-se, mais detalhadamente, o tratamento numérico das restrições decorrentes de contato. Algumas estratégias para resolução computacional desta classe de problemas, consistindo em técnicas de otimização, foram implementadas num programa computacional de elementos finitos e avaliadas comparativamente por meio de exemplos numéricos com diferentes graus de complexidade.Contact problems represent a class of solid mechanics problems for which the nonlinear behavior is caused by the change of the boundary conditions during the solution process. The present work treats contact problems observing aspects of its formulation and numerical implementation. Specifically, the formulation for two different contact elements is presented, analyzing, in details, the numerical formulation that results from the contact. Some strategies for the computational solution of this class of problems, given by optimization techniques, were implemented in a finite element computational program and were compared and evaluated by numerical examples with different levels of complexity.
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Tomanik, Antonio Eduardo Meirelles. "Modelamento do desgaste por deslizamento em anéis de pistão de motores de combustão interna." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/3/3132/tde-08122004-203125/.
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O desgaste de anéis de pistão e cilindro foi modelado através de um programa computacional que calcula as pressões hidrodinâmicas e de contato rugoso agindo nas superficies deslizantes de contato. Os valores previstos de desgaste são comparados com um ensaio em dinamometro de um motor diesel.The wear of piston rings and cylinder liner was modelled through a computer code that calculates the hydrodynamic and roughness contact pressures acting in the contact surfaces. The predicted wear is compared with a 750 hours dynamometer test of a medium duty diesel engine
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Caro, Anne-Sophie. "Formulation et résolution des problèmes de contact avec frottement et adhérence en grandes déformations." Aix-Marseille 2, 1999. http://www.theses.fr/1999AIX2A001.
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Sallais, Damien. "Contribution à l'étude de nouveaux matériaux élaborés par métallurgie des poudres pour les contacts électriques soumis aux arcs de coupure et de fermeture du courant continu." Rennes 1, 2007. http://www.theses.fr/2007REN1S162.
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Pour satisfaire la demande croissante en puissance électrique des automobiles modernes, l’actuel réseau sous 14 VDC ainsi que les systèmes de commande qui lui sont rattachés doivent évoluer. C’est le cas en particulier des dispositifs de coupure. Deux solutions envisageables pour répondre à ces besoins en puissance électrique ont tout d’abord été confrontées : l’augmentation du courant sous 14 VDC et le passage à une tension de 42 VDC. L’augmentation de la tension se révèle être l’option la plus intéressante mais exige le développement de nouveaux matériaux de contact. De nouveaux pseudo alliages AgMeO ainsi qu’un matériau composite très innovant ont donc été élaborés et testés électriquement. Ils représentent des solutions matériau très intéressantes en terme de réduction de la durée d’arc et du gap d’extinction. Parallèlement à ces études expérimentales, des calculs théoriques ont été menés afin de simuler l’érosion et le transfert de matière entre les contactsIn order to satisfy the increasing electrical power needs in modern cars, the actual 14 VDC battery and its command systems as switching devices, have to evolve. First, two present tendencies were evaluated: the increase of current levels under 14 VDC and the change of voltage from 14 VDC to 42 VDC. A new 42 VDC system seems to be the more interesting solution, it needs however the development of new electrical contact materials. New silver-oxide composites and an innovating contact material were also elaborated and tested. They exhibit strong improvements in term of arc duration and extinction gap minimization. In addition, a theoretical study using a finite element simulation was led to calculate erosion and material transfer between contacts
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Maouche, Nadir. "Modélisation des phénomènes d'endommagements dus aux contacts à faible amplitude de débattement." Phd thesis, Marne-la-vallée, ENPC, 1997. http://www.theses.fr/1997ENPC9732.
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La thèse a pour thème la modélisation numérique et la prédiction de l'endommagement (l'usure ou la fissuration) du au contact avec frottement avec petits débattements (fretin). Elle comporte deux parties. Dans la première partie, une nouvelle méthode de calcul éléments finis est développée pour les chargements cycliques. Contrairement aux algorithmes classiques incrémentaux, cette méthode est basée sur un algorithme original qui permet d'obtenir directement l'état stabilise mécanique éventuel. La méthode est itérative et consiste à chercher sur tout le cycle de chargement, en un premier temps des solutions statiquement et cinématiquement admissibles, et puis après des solutions plastiquement admissibles. À la fin de chaque itération, la condition de périodicité est imposée. Et ainsi, lorsque l'algorithme converge, on obtient des champs de contraintes et de déformations périodiques et vérifiant l'équilibre et la loi de comportement sur tout le cycle. La comparaison des temps de calculs par rapport à la méthode incrémentale a démontré la performance de cette méthode. Dans la deuxième partie, cette méthode est mise en œuvre dans le cas du chargement cyclique mobile de fretin. Ainsi des cartes d'adaptation et d'accommodation sont établies en fonction de divers paramètres. Les résultats de prédiction de l'initiation des fissures de fatigue faite par l'application du critère multiaxial de Dang van sont en très bon accord avec les résultats expérimentaux. L’usure est obtenue pour une réponse mécanique de type accommodation et elle donc est le résultat d'un mécanisme de fatigue oligocyclique.
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Oliveira, Sônia Paiva de. "Acessibilidade ao exame de contato de hanseníase na Estratégia de Saúde da Família em Cuiabá, Mato Grosso - Brasil." Dissertação apresentada ao Programa de Pós-Graduação do Instituto de Saúde Coletiva, como requisito parcial para a obtenção do título de mestre em Saúde Coletiva, 2013. http://www.repositorio.ufba.br/ri/handle/ri/13132.
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A hanseníase ainda é um sério problema de saúde pública em alguns países do mundo, entre eles o Brasil, que ocupa o segundo lugar em número de casos absolutos no mundo. O estado de Mato Grosso ocupou, em 2011, o primeiro lugar em número de casos novos detectados entre os 27 estados da federação, estando sua capital Cuiabá em situação de hiperendemicidade pelos parâmetros do Ministério da Saúde. O objetivo desse estudo foi analisar a acessibilidade ao exame de contato de hanseníase na Estratégia de Saúde da Família no município de Cuiabá/MT. Na primeira etapa do estudo foi realizada a avaliabilidade do PECH/MT, constatando-se que o mesmo encontra-se implantado adequadamente. Identificou-se que entre os aspectos deficientes na condução das ações do programa está a dificuldade em realizar exames de contatos dos pacientes com hanseníase, revelando a existência de problemas de acessibilidade aos serviços de saúde. A avaliação da acessibilidade foi conduzida através de estudo de caso em duas unidades de saúde da família, por meio de análise documental, observação sistemática e entrevistas semiestruturadas com informantes-chave. O Projeto foi aprovado pelo Comitê de Ética em Pesquisa (CEP) do Instituto de Saúde Coletiva - ISC/UFBA, e os entrevistados assinaram Termo de Consentimento Livre e Esclarecido. A análise da acessibilidade foi realizada em duas dimensões, no âmbito da organização do sistema e dos serviços de saúde. Na primeira dimensão, a avaliação demonstrou que o município encontra-se em situação insatisfatória, evidenciado pela inexistência de plano com ações e metas específicas para o desenvolvimento das ações, falta de garantia de acesso ao serviço de saúde e de insumos para o exame. Na segunda dimensão, observou-se que as unidades foram consideradas de situação intermediária (USF1) e insatisfatória (USF2), indicando a existência de dificuldades quanto à: centralização da realização do exame de baciloscopia, no LACEC; ausência de atividades educativas e falta de sistematização na marcação de consultas. Recomenda-se a composição de equipe de trabalho para coordenar as ações e a proposição de uma política de capacitação contínua de recursos humanos voltados para hanseníase. Deve atentar para a implantação do terceiro turno nas unidades de saúde para atender a demanda de trabalhadores e para o aumento do número de ACS, indispensáveis na busca ativa de casos novos, de contatos faltosos e ações educativas; bem como rever a normatização do MS quanto ao exame dos contatos, pois não está baseado em evidências científicas.
Salvador
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van, der Linden Franciscus [Verfasser]. "Gear contact modeling for system simulations and experimental investigation of gear contacts / Franciscus van der Linden." München : Verlag Dr. Hut, 2017. http://d-nb.info/1128467631/34.
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Brunetti, Jacopo. "Mechanical energy balance of frictional contacts : From surface to solid energy dissipation in contact dynamic instabilities." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0118/document.
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Chaque fois que se produit un mouvement relatif entre deux systèmes, avec une interface à contact sec, le contact frottant induit des vibrations. La dynamique locale au contact (ruptures et la génération d'ondes) se couple avec la dynamique du système, donnant origine à des vibrations et affectant le comportement frictionnel macroscopique du système. Dans cette thèse, afin de développer une approche globale pour l'investigation des phénomènes multi-physiques, l'énergie a été utilisée comme une caractéristique physique universelle du couplage. La formulation de un bilan énergétique mécanique est utilisé pour identifier deux termes dissipatifs différents, i.e. la dissipation par amortissement matériel/système et la dissipation au contact. Les flux d'énergie, provenant des surfaces en contact et dus aux vibrations induites par frottement, excitent la réponse dynamique du système et, vice versa, l'influence de la réponse dynamique du système sur la dissipation d'énergie locale à l'interface de contact affecte les phénomènes tribologiques connexes. Dans cette thèse, les vibrations induites par le frottement ont été analysées en utilisant: l'approche par éléments finis pour étudier, par l'analyse des flux d'énergie, le couplage entre le contact et la dynamique du système; l'approche expérimentale pour valider les résultats numériques et observer l'influence des phénomènes pas encore inclus dans les modèles numériques; une approche avec une modèle à paramètres concentrés pour évaluer rapidement les effets des paramètres du système. L'analyse numérique par le modèle éléments finis 2D permet une répartition de l’énergie introduite dans le système mécanique entre les deux termes dissipatifs (amortissement matériau et contact), au cours de la réponse transitoire aussi bien en conditions stables qu’instables. En particulier, les vibrations induites par frottement modifient la capacité globale du système à absorber et dissiper l’énergie; une estimation de la puissance dissipée au contact, sans prendre en compte le comportement dynamique du système (flux d’énergie par les vibrations induites par frottement) peut conduire à des erreurs significatives dans la quantification de l’énergie dissipée au contact, ce qui affecte directement plusieurs phénomènes tribologiques. Les mesures expérimentales de crissement montrent comment les mêmes modes instables sont reproduits soit expérimentalement soit numériquement, validant l’utilisation de la simulation 2D transitoires pour l’analyse des vibrations instables induites par le frottement. L’équilibre énergétique a été utilisé sur le modèle à paramétrés concentrés, pour approcher le problème de la surestimation d’instabilité, qui est caractéristique d’une analyse des valeurs propres complexes. Un nouvel indice d’instabilité (MAI) a été défini, par des considérations énergétiques, pour comparer les différents modes instables et pour sélectionner le mode qui devient effectivement instable pendant le crissementWhenever relative motion between two system components occurs, through a dry contact interface, vibrations are induced by the frictional contact. The local dynamics at the contact (ruptures and wave generation) couples with the system dynamics, giving origin to vibrations and affecting the macroscopic frictional behavior of the system. In this thesis, in order to develop an overall approach to the investigation of the multi-physic phenomenon, the energy has been pointed out as a coupling physical characteristic among the several phenomena at the different scales. The formulation of a mechanical energy balance is used for distinguishing between two different dissipative terms, i.e. the dissipation by material/system damping and the dissipation at the contact. The energy flows coming from the frictional surfaces, by friction induced vibrations, excites the dynamic response of the system, and vice versa the influence of the system dynamic response on the local energy dissipation at the contact interface affects the related tribological phenomena. The friction-induced vibrations have been analyzed using three different approaches: the finite element approach, to investigate the coupling between the contact and system dynamics by the analysis of the energy flows; the experimental approach to validate the numerical results and observe the influence of phenomena not still included into the numerical model; a lumped parameter model approach to quickly investigate the effects of the system parameters. The numerical analysis by the 2D finite element model allowed investigating the repartition of the energy introduced into the mechanical system between the two dissipative terms (material damping and contact) during both stable and unstable friction-induced vibrations. In particular, it has been shown how the friction-induced vibrations modify the overall capacity of the system to absorb and dissipate energy; an estimation of the power dissipated at the contact, without considering the dynamic behavior of the system (energy flows by friction induced vibrations) can lead to significant error in the quantification of the dissipated energy at the contact, which affects directly several tribological phenomena. The experimental squeal measurements show how the same unstable modes are recovered both experimentally and numerically, validating the use of the 2D transient simulations for the reproduction of the unstable friction-induced vibrations. Once the energy balance formulated, it has been used on the lumped model to approach the instability over-prediction issue characteristic of the complex eigenvalue analysis. By energy considerations, a newer instability index (MAI) has been defined to compare the different unstable modes and to select the mode that becomes effectively unstable during the transient response. The Modal Absorption Index allows quantifying the capability of each mode to exchange energy with the external environment
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Pleşca, Cezar. "Supervision de contenus multimédia : adaptation de contenu, politiques optimales de préchargement et coordination causale de flux." Toulouse, INPT, 2007. http://ethesis.inp-toulouse.fr/archive/00000499/.
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La qualité des systèmes d'informations distribués dépend de la réactivité du service, de la pertinence et de la cohérence des informations présentées vis-à-vis des centres d'intérêt de l'utilisateur. Dans un premier volet, nous améliorons la délivrance de contenus hypermédia et utilisons des modèles décisionnels markoviens 'PDM) pour dériver des politiques de préchargement agressives optimales intégrant les habitudes des utilisateurs et les ressources disponibles. Dans le deuxième volet, consacré aux contextes partiellement observables, nous montrons qu'une politique d'adapatation à des ressources limitées (modèle PDM) peut être nuancée selon l'intérêt des utilisateurs, en utilisant un PDM partiellement observable (PDMPO). Le troisième volet concerne le contexte des applications multimédia interactives réparties. Nous proposons un service de cohérence flexible capable de gérer plusieurs ordres partiels (fifo, causal, total) et montrons de meilleures performances par rapport à la causalité classique ou la [delta]-causalitéDistributed systems information quality depends on service responsiveness, data consistency and its relevance according to user interests. The first part of this study deals with hypermedia content delivery and uses Markov Decision Processes (MDP) to derive aggresive optimal prefetching policies integrating both users habits and ressource availability. The second part addresses the partial observable contexts. We show how a ressource-based policy adaptation (MDP model) can be modulated according to user interest, using partially observable MDP (POMDP). Finally, the third part is placed in distributed multimedia applications context. We propose a coordination-level middleware for supporting flexible consistency. Our simulations show that its ability to handle several partial orders (e. G. Fifo, causal, total) makes it better than classic or [delta)-causality
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Pleşca, Cezar Padiou Gérard Patriciu Victor. "Supervision de contenus multimédia adaptation de contenu, politiques optimales de préchargement et coordination causale de flux /." Toulouse : INP Toulouse, 2007. http://ethesis.inp-toulouse.fr/archive/00000499.
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Grégoire, Isaac. "Analyse du coefficient de frottement sur les contacts lubrifiés et impact sur le grippage : Application aux transmissions par engrenages aéronautiques." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI100.
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Le développement de nouvelles technologies permettant d’obtenir des procédés de fabrication novateurs, de même que l’utilisation de nouveaux matériaux et lubrifiants, ont rendu possible une amélioration globale de l’efficacité des systèmes mécaniques et la résolution de nombreuses défaillances. Néanmoins, certains types de détérioration comme le grippage restent difficiles à appréhender car ils résultent de nombreux paramètres connexes tels que le régime de lubrification, la température du contact et le coefficient de frottement. Le grippage est un phénomène qui apparait de manière brutale et qui se caractérise par des arrachements et des transferts de matières entre les surfaces en contact pouvant aller jusqu’à la destruction complète du système. Ce dernier est généralement associé à une mauvaise dissipation des calories entrainant des températures de contact élevées. De nombreux critères basés sur la dissipation d’énergie dans le contact ont été établis sans pour autant que l’un d’eux ne soit unanimement reconnu par la communauté scientifique. La première partie de cette étude a consisté à caractériser le comportement en frottement d’un couple matériau-lubrifiant grâce à l’utilisation d’une machine bi-disque. En parallèle, une modélisation thermique de ce banc d’essais a été réalisée en utilisant la méthode des réseaux thermiques. Les corrélations entre les formules analytiques et les mesures expérimentales ont permis d’aboutir à l’établissement d’une loi de frottement liant conditions de contact et température de masse des éprouvettes. Il a aussi pu être démontré que la température de masse des disques pouvait être considérablement différente de la température d’injection du lubrifiant en fonction des conditions opératoires. Ce résultat permet une analyse nouvelle des critères de grippage dont la plupart assimilent la température des éprouvettes à celle d’injection du lubrifiant. Malgré cela, les différents essais de grippage réalisés montrent que l’unique considération de la température de contact pour établir un critère de grippage s’avère insuffisanteThe development of new technologies, which allow innovative manufacturing processes, as well as the use of new materials and lubricants have led to an overall improvement of mechanical systems efficiency and reliability. However some failures, like scuffing, remain difficult to understand since they depend on many related parameters such as the lubrication regime, the contact temperature and the friction coefficient. Scuffing is a critical damage that appears suddenly and which is characterised by local welds and scratches between the sliding surfaces. It can lead to complete destruction of the mechanical system. This phenomenon is in general related to poor heat dissipation and overheating resulting in high contact temperature. Numerous studies were conducted in order to establish a scuffing criterion based on energetic approach. But none of them is unanimously recognized by the scientific community. The first part of this study consisted in characterizing the frictional behaviour of a given couple of lubricant and material thanks to the use of a twin-disc machine. In a second part, a thermal modelling of this test bench has been realised using the thermal network methodology. Correlations between analytical formulas and experimental measurements allowed to establish a friction law relating contact conditions and disc bulk temperature. It has also been demonstrated that the disc bulk temperature could be considerably different from the lubricant injection temperature depending on the operating conditions. This result allows a new interpretation of existing scuffing criteria, which for most of them consider the disc temperature to equal the oil temperature. Despite this analysis, the scuffing experiments performed reveal that accounting solely for the contact temperature is not sufficient to establish a reliable scuffing criterion
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Kounoudji, Komla Apelete. ""Intimité tribologique" des contacts d'un assemblage boulonné. Contrôle du serrage, du dévissage, ...des assemblages d'aéro-structures et conséquences sur leur conception." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI055/document.
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Depuis l'utilisation des boulons au XVème siècle pour assembler deux pièces, les assemblages boulonnés posent des questions quant à la compréhension de leur fonctionnement et de leurs défaillances, telles que la variation de la tension de serrage entrainant, le desserrage, le dévissage, la perte d'étanchéité, l'initialisation de fissures, ... Pour comprendre leur fonctionnement, une méthodologie d'analyse tribologique a été mise en place, permettant de démonter un assemblage boulonné sans le desserrer, afin de ne pas modifier les conditions de contact lors du desserrage. Ainsi, toutes les interfaces d'assemblages (‘‘filets’’ écrou/vis et ‘‘autres que filets’’) formant des triplets tribologiques, ont été étudiées durant les trois phases de leur cycle de vie (fabrication, serrage, service) par le biais de cas-tests de matériaux différents. Un dialogue interactif entre les expérimentations (corrélations d'images, expertises) et la simulation numérique (Eléments Finis, Eléments Discrets) a permis de dégager des interprétations, notamment concernant les trois phases. Lors de la fabrication, le roulage des vis engendre des transformations tribologiques superficielles au niveau des sous-surfaces des filets formés. Le cœur des vis (noyau) restant non-déformé, ce procédé crée ainsi une différence de microstructure au sein de ces vis, ce qui est une source d'altération de leurs propriétés en fatigue. Lors du serrage, il se forme à l'interface ‘‘filets’’ une mixture de troisièmes corps ‘‘sec-solide’’, accommodant la vitesse entre la vis et l'écrou. Cette mixture résulte d'une réactivité entre une graisse utilisée pour le serrage et des particules, détachées d'un revêtement appliqué sur les filets d'écrous et/ou de vis. En fin de serrage, une partie de la mixture reste piégée entre les filets, jouant le rôle de maintien de la tension de serrage. Dans ces conditions, il apparaît que le frottement varie en fonction de la rhéologie de la mixture, conditionnant la variation de la tension de serrage. En service, des instabilités de contact (glissement, décollement, ...) ont été identifiées au niveau des interfaces. Ces instabilités engendrent dans les interfaces ‘‘autres que filets’’ la formation d'un troisième corps oxydé. Ce dernier constitue un surplus de matière qui peut entrainer l'augmentation des contraintes mécaniques dans les assemblages. A l'interface ‘‘filets’’ écrou/vis, il a été constaté que si la mixture de troisièmes corps piégée en serrage n'est pas cohésive, elle est extrudée des contacts, initialisant la perte de la tension de serrage. A partir de ces interprétations, des interactions entre plusieurs circuits tribologiques conduisent à converger vers un scénario de fonctionnement des assemblages boulonnés, permettant de solutionner leurs défaillances par la re-conception (mise en place de gorge de décharge, ...)Since the use of bolts in the fifteenth century to assemble two parts, the bolted assemblies have the interrogations according to the understanding of their operating and failures occurring, such as the variation of the clamping force leading to, self-loosening, loss of sealing performance, cracks initialization, ... In order to understand their operating, a methodology focused on tribological approach was established, enabling to disassemble a bolted assembly without loosen its, allowing to not change the contact conditions during loosening. So, all the bolted assemblies interfaces (nut/screw ‘‘threads’’ and ‘‘others than threads’’) constituting tribological triplets, have been studied according to the three stages of their full life-cycle (manufacturing, tightening and service) using configurations of different materials. An interactive dialogue between the experiments (fields measuring by digital images correlation, tribological analysis) and the numerical simulation (Finite Element Method, Discrete Element Method) has led to interpretations about the three stages. During the manufacturing, the rolling of screws generates tribological superficial transformations in subsurfaces of machined threads. Contrariwise, inside the volume of these machined screws, there is no tribological transformation. So, this manufacturing process creates a difference of microstructure in these screws, that could be a source of their fatigue properties destruction. During the tightening, it produces at ‘‘threads’’ interface a ‘‘dry-solid’’ mixture of third bodies, accommodating the speed jump between the screw and the nut. This mixture is the result of a reactivity between a grease used for bolted tightening and the particles, detached by plastic flow from a coating initially applied on the threads of nuts and/or bolts. At the end of the process, a part of the mixture remains trapped in the threads, playing the role of maintaining the clamping force. In these conditions, it appears that the friction varies depending of the rheology of the mixture, conditioning the variation of the clamping force. In service, contact instabilities (slip, peeling off, ...) have been identified in the interfaces. These instabilities lead to the formation of an oxidized third body in ‘‘others than threads’’ interfaces. This oxidized third body represents a surplus of material and can increase mechanical stresses in the assemblies. In the nut/screw ‘‘threads’’ interface, it was found that if the mixture of third bodies trapped during the tightening stage is not cohesive, it is extruded, initializing the loss of clamping force. Based on the findings, the interactions between multiple tribological circuits lead to converge to a scenario of bolted assemblies operating, allowing to solve their failures by re-designing (create discharge grooves, ...)
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Ng, Sophia. "Five year tuberculosis risk in institutional contacts an evaluation from a territory wide mass contact screening program /." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B41711713.
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Morgan, Brent A. "The nature of the metal-semiconductor contact : evidence of spatially variant energy barriers in metal-semiconductor contacts /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952669.
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Marques, Débora Maria Mitter. "Estudo do contato entre sólidos metálicos por meio de simulações de dinâmica molecular." Universidade de São Paulo, 2011. http://www.teses.usp.br/teses/disponiveis/3/3151/tde-29062012-153859/.
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Neste trabalho, a relação entre a adesão e o grau de desordem de superfícies em contato é estudada por meio de simulações por dinâmica molecular. O sistema em estudo é composto por um indentador cilíndrico rígido e um bloco deformável. Um reservatório térmico é colocado logo abaixo do bloco, de forma a manter o sistema a temperatura ambiente. Os sólidos são feitos do mesmo material e são modelados por intermédio do potencial genérico de Lennard-Jones. A adesão entre as superfícies é variada gradualmente por meio da variação do raio de corte do potencial que descreve a interação entre as superfícies indentador-bloco. Cada simulação se inicia com um recozimento, após o qual são realizadas as simulações de contato propriamente ditas, até que ocorra penetração de 1,7 raios atômicos. A força normal, a energia potencial, a temperatura e a energia cinética são acompanhadas ao longo do processo. Os resultados reforçam a importância da adesão no jump-to-contact, estando este fenômeno relacionado à geração de defeitos cristalinos. Há indícios de que a distribuição da carga, bem como a dissipação de energia, seja influenciada pela adesão na interface. Mostra-se que a desordem apresentada pelos átomos do bloco é proporcional à contribuição da adesão.In this work, the relationship between adhesion and the degree of disorder of surfaces in contact is studied by means of molecular dynamics simulations. The system consists of a rigid cylindrical indenter and a deformable block. A heat reservoir is placed just below the block, in order to maintain the system at room temperature. Both solids are made of the same material and are modeled through the generic Lennard-Jones potential. Adhesion between the surfaces is gradually varied by varying the cut-off radius of the potential describing the interaction between the indenter surface and the block. Each contact simulation is preceeded by an annealing step, and is conducted until the penetration reaches 1.7 atomic radii. The normal force, the potential energy, kinetic energy and temperature are monitored throughout the process. The results reinforce the importance of adhesion in the phenomenon of jump-to-contact, which is also related to the generation of crystalline defects. The results indicate that the load distribution and power dissipation is influenced by the adhesion at the interface. It is shown that the disorder presented by the atoms of the block is proportional to the contribution of adhesion.
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Silva, Matheus Zegatti e. "Estudo da influência do desgaste na falha prematura de componentes de linhas de ancoragem." reponame:Repositório Institucional da UnB, 2016. http://repositorio.unb.br/handle/10482/22413.
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Dissertação (mestrado)—Universidade de Brasília, Faculdade de Tecnologia, Departamento de Engenharia Mecânica, 2016.Submitted by Camila Duarte (camiladias@bce.unb.br) on 2017-02-02T16:03:41Z No. of bitstreams: 1 2016_MatheusZegattieSilva.pdf: 9341825 bytes, checksum: 78f4c2e143358fcb5cba0f2ed0392bf4 (MD5)
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Neste trabalho é apresentado um estudo sobre a influência do desgaste na vida à fadiga de conectores e elos de linhas de ancoragem de plataformas petrolíferas offshore. O excessivo desgaste observado em componentes que falharam prematuramente levantou a suspeita do desgaste ser um dos fatores que possa estar causando uma diminuição na vida à fadiga. Por meio de uma simplificação do problema tridimensional, analisam-se duas configurações de contato bidimensionais presentes na interação entre elos e conectores. São realizados inicialmente estudos comparativos de resultados numéricos e analíticos com o intuito de validar a modelagem numérica inicial das configurações de contato. Para realizar essa análise utiliza-se a Teoria de Hertz de contato entre corpos elásticos, assim como o potencial de Muskhelishvili. Realiza-se também um estudo elasto-plástico de um deslocamento recíproco, onde importantes constatações são feitas em torno da máxima pressão de contato e do comprimento do semi-arco de contato. Nessa mesma análise verifica-se que o momento que antecede o escorregamento total dos corpos é o mais crítico, pois é onde são observadas as maiores tensões e deformações plásticas no corpo. Ao final desta análise verifica-se que o modelo de Archard utilizado para estimar o volume global de desgaste, revelou-se ser mais conservador do que o modelo da Energia Dissipada. Em outra análise, a retirada de material das superfícies é realizada por meio da implementação da subrotina UMESHMOTION no programa de análise de elementos finitos, Abaqus. Através dessa subrotina computa-se o desgaste local em cada nó da malha que experimenta uma pressão normal de contato e um deslizamento relativo. Devido à observação da diminuição nos valores das tensões e deformações à medida que um maior volume de material é retirado pelo desgaste, verifica-se um aumento na vida à fadiga prevista pelo modelo de Smith-Watson-Topper (SWT). Portanto, observa-se que para ambas as configurações de contato observadas no contato entre elos e conectores, a vida à fadiga, pelo menos inicialmente (primeiros 5000 ciclos), é afetada positivamente pelo desgaste. É possível que para um número maior de ciclos, ou seja, para um maior volume de material retirado pelo desgaste, a redução da secção transversal seja um fator determinante na previsão da vida.
This work presents a study about the influence of wear in the fatigue life of connectors and chain links employed in the mooring lines of offshore platforms. The high rates of wear observed in components that have failed prematurely, brought up the issue that wear could possibly be one of the factors that is reducing the fatigue life. Through a simplification of the 3D problem, two 2D contact configurations present in the interaction of chain links and connectors are analyzed. Initially a comparison of analytical and numerical results is carried out in order to validate the numerical modeling of both contact geometries. To compute the analytical results, both the Hertz theory for elastic bodies and the Muskhelishvili potential were used. Furthermore, an elasto-plastic analysis of a reciprocate displacement is also carried out, where interesting changes are noticed on the maximum normal contact pressure and in the contact half-width. In the same analysis is verified that the moment that precedes the slip between the bodies is the most critical because is where the highest stresses and equivalent plastic strains are observed. In the end of this analysis, a global wear volume estimation is made, where the Archard wear model showed to be more conservative than the Energy Dissipated model. In another analysis, the material removal is carried out by an subroutine implementation (UMESHMOTION) within the finite element analysis program Abaqus. By means of this subroutine, the local wear can be computed in each element nodal of the surfaces that experiences a normal contact pressure and a relative displacement. Due to the decrease observed in the values of stresses and strains as wear takes place, an increase in the fatigue life predicted by the Smith-Watson-Topper (SWT) model is verified. Therefore, is noticed that for both contact configurations present in the contact interaction of chain links and connectors, the fatigue life, at least initially (first 5000 cycles), is positively affected by the wear. It’s possible that for a higher number of cycles, in other words, a higher amount of material removal, the reduction in the cross sectional area turns to be a determinant factor in the life estimation.
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Strubel, Vincent. "Particle entrapment in EHD contacts - Aerospace applications." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI098/document.
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Une lubrification suffisante est essentielle au bon fonctionnement des mécanismes et/ou composants comme par exemple les paliers à roulement. Par contre, les lubrifiants contiennent souvent des débris d’usure ou des polluants extérieurs. Ces particules micrométriques peuvent pénétrer des contacts d’épaisseur inférieure au micromètre induisant des empruntes ou indents pouvant conduire à des endommagements irréversibles pour les surfaces en contact. L’objet de ce travail est l’étude du piégeage de polluants solides à l’aide de particules sphériques d’acier, d’un point de vue théorique, numérique et expérimental. Dans un premier temps, une étude phénoménologique a été proposée à l’aide d’une nouvelle méthode expérimentale basée sur la technique PIV combinée à un tribomètre bille/disque. Les trajectoires des polluants à l’entrée du contact ont pu ainsi être identifiées. En parallèle, un modèle numérique d’écoulement du lubrifiant a été développé pour permettre l’évaluation des conditions menant au piégeage ou non de particules. Finalement, des expériences sur une machine bi-disques en conditions de lubrification polluée contrôlée ont permis de valider les tendances observées pour le piégeage. Une première série de résultats a montré que le piégeage de contaminants est fortement dépendant du profil de vitesse du lubrifiant. Un taux de piégeage très hétérogène a été observé sur des contacts avec une ellipticité transverse à l’écoulement variable. De manière surprenante, malgré une augmentation de la largeur de contact, une forte diminution du nombre de particules piégées a été observée dans des contacts elliptiques. Il a été démontré que cette diminution pouvait être imputée à la présence d’importants reflux de lubrifiant dans les contacts elliptiques larges. L’étude de contacts hybrides, nitrure de silicium–acier, a montré une bonne résistance à l’indentation du nitrure de silicium. Il est à noter que les contacts hybrides présentent des niveaux de piégeage similaire à un contact tout acierContact lubrication is essential in a wide range of mechanical systems like rolling element bearings (REBs). A minimum quantity of clean lubricant all along the bearing life is necessary but difficult to ensure. In fact, lubricants contain inevitably wear debris or external particles, like dust. Carried by the lubricant in the vicinity of elastohydrodynamic (EHD) contacts, particles can be entrapped with disastrous consequences for contacting surfaces. Entrapment of micrometric particles in submicrometric contacting gaps means irreversible damages for the surfaces. Damages weaken the surfaces and reduce significantly the REBs lifetime. The goal of this work is to analyze the critical particle entrainments in the contact inlet. Entrapment of steel spherical particles was investigated from the numerical and experimental point of view. Firstly, the phenomenology of entrapment was explored with a new experimental method based on Particle Image Velocimetry (PIV) technique installed on a tribometer. It enabled the evaluation of velocity profiles in the contact inlet and the tracking of particles within EHD contacts. Secondly, a numerical modelling of the inlet flow for EHD contacts, including the particle tracking, was developed. Finally, tests on a twin-disc machine with a controlled level of well-defined contamination were conducted to validate previous conclusions. A first set of results showed that particle entrapment is highly dependent on the lubricant velocity profile. Depending on contact geometry, from point to wide elliptical contacts, different entrapment probability were revealed. Surprisingly, increasing contact width with wide elliptical contacts leads to a drop of entrapped particles. It was demonstrated that this phenomenon is due to backflows occurring upstream from these contacts. Introducing a hybrid pair of contacting materials (silicon nitride–steel), dents on the surfaces due to entrapped particles were explored. It has been confirmed that silicon nitride surface offers a real ability to resist to indentation. It was also noticed that the entrapment probability for silicon nitride–steel contacts is equivalent to a steel–steel one
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Ghezzi, Ilaria. "Tribological and vibro-acoustic behaviour of a lubricated contact subjected to the stick-slip phenomenon : The case of the spring-brake system." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI116.
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Les travaux de thèse proposent une approche complémentaire, combinant analyses dynamiques et tribologiques, au problème de stick-slip d’un contact graissé, dans un frein mécanique à ressort. L’instabilité de stick-slip est le résultat du couplage entre la réponse dynamique du système mécanique (frein) et la réponse locale du contact lubrifié à l’interface de freinage. La réponse locale du contact graissé a d’abord été caractérisée par des tests expérimentaux effectués sur tribomètre. Ensuite, les conditions qui conduisent à l'instabilité ont pu être investiguées en détail, à l’aide d’un modèle numérique a paramètres concentres du système complet. Ce modèle simule le comportement dynamique global du système de freinage mécanique. En entrées, il prend les paramètres propres au fonctionnement et à la conception du frein, ainsi que les courbes de frottement locales. En sortie, le poids de chacun des paramètres sur la génération du stick-slip a donc pu être analysé. Enfin, une étude expérimentale de l’influence des différents composants de la lubrification (DLC et graisse) sur le comportement du contact frottant lubrifié a été réalisée. Dépendante de l’épaississant, de l’huile et des additifs, la rhéologie complexe de la graisse est un point clé pour comprendre l'apparition du stick-slip. En effet si la lubrification est traditionnellement censée réduire les pertes par frottement, elle peut malgré tout participer à l’apparition d’instabilités. La compréhension des conditions pour lesquelles un système est prédisposé au phénomène de stick-slip peut permettre de prévenir l'apparition de telles instabilités et des nuisances qu’elles engendrent. Néanmoins, en présence de contacts lubrifiés, la littérature n’y consacre que peu de travaux. C’est dans ce contexte que l’analyse multi-approches présentée dans cette thèse permet de contribuer à la compréhension de l’apparition des instabilités de frottement dans les contacts lubrifiés avec graisse, en apportant également des éléments de solution dans le cas d’une application spécifiqueThe thesis works propose a complementary approach, combining dynamic and tribological analyzes, to the stick-slip problem of a greased contact, in a mechanical spring brake. Stick-slip instability is the result of the coupling between the dynamic response of the mechanical system (brake) and the local response of the lubricated contact at the brake interface. The local response of the greased contact was first characterized by experimental tests performed on a tribometer. Then, the conditions which lead to instability have been investigated in detail, using a numerical lumped model of the complete system. This model simulates the overall dynamic behavior of the mechanical braking system. As inputs, it takes the parameters specific to the operation and design of the brake, as well as the local frictional behavior obtained experimentally. At the output, the influence of each of the parameters on the generation of the stick-slip has been therefore analyzed. Finally, an experimental study of the influence of the different lubricant components (DLC and grease) on the behavior of the lubricated frictional contact has been carried out. Dependent on thickener, oil and additives, the complex rheology of grease is a key point for the understanding of the stick-slip appearance. Indeed, if lubrication is traditionally supposed to reduce friction losses, it can also participate in the appearance of instabilities. Understanding the conditions for which a system is predisposed to the stick-slip phenomenon can help prevent the appearance of such instabilities and the nuisance they cause. However, in the presence of lubricated contacts, the literature shows a lack of informations. It is in this context that the multi-approach analysis presented in this thesis makes it possible to contribute to the understanding of the appearance of friction instabilities in contacts lubricated with grease, by also providing elements of solution in the case of a specific application
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Silvestre, Marilene Chaves. "Avaliação da dermatite de contato alérgica ao níquel através da técnica de imuno-histoquímica." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/5/5133/tde-09082017-103915/.
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A dermatite de contato alérgica (DCA) ao íon níquel (Ni2+) é uma dermatose inflamatória frequente nos países industrializados. Envolve a ativação de células T específicas ao Ni2+, seguida da proliferação e indução de um perfil misto de citocinas, tanto pró-inflamatórias quanto reguladoras, sugerindo que vários subtipos de células T (helper - Th e citotóxica - Tc) estão envolvidos na resposta imune. Este estudo teve como objetivo a análise das citocinas TNF-alfa, INF-y, IL-2, IL-4, IL-10, IL-13, IL-17 e IL-23 pela técnica de imuno-histoquímica, para tentar identificar a prevalência de um ou mais subtipos de células T (Th/Tc), nos eczemas crônico e agudo de pacientes com DCA ao Ni2+. Avaliamos 20 pacientes (17 mulheres e 3 homens, com idade mediana de 46 anos) apresentando eczema crônico, pelo contato cotidiano do paciente com o Ni2+. Foram coletadas duas biópsias de pele em cada um dos 20 pacientes, a primeira no local do eczema crônico ao Ni2+, antes da aplicação do teste de contato (TC); e a segunda no local do eczema agudo, provocado pelo TC com o sulfato de níquel, 48 horas após sua fixação, nas leituras positivo forte (++) ou positivo muito forte (+++). Foram 160 amostras de eczema agudo e 160 de eczema crônico, perfazendo um total de 320 amostras. Apenas três amostras foram excluídas devido a algum tipo de falha técnica, como, por exemplo, o descolamento dos cortes de pele da lâmina. Para a análise dos dados utilizou-se o software estatístico STATA versão 13. As amostras coradas revelaram resultados positivos para as oito citocinas estudadas, e estas apresentaram valores heterogêneos. Esta heterogeneidade foi medida pelo coeficiente de variação, indicando a variabilidade do conjunto dos dados obtidos. O TNF-alfa, IFN-y, IL-4, IL-13 e IL-17 tiveram prevalência maior no eczema crônico do que no eczema agudo, a IL-2 e IL-23 apresentaram maior prevalência no eczema agudo, em comparação com o eczema crônico e a IL-10 apresentou prevalência similar tanto no eczema agudo quanto no crônico, porém, estas prevalências foram muito baixas, em ambos os eczemas. O TNF-alfa foi a citocina que mais prevaleceu no eczema crônico e a IL-2 foi a mais prevalente no eczema agudo. Porém, estas prevalências foram estatisticamente significantes apenas para a IL-4 e IL-13. Verificamos, nos eczemas crônico e agudo, a presença de um perfil misto de citocinas dos subtipos de células T (Th/Tc), sugerindo que as respostas imunes são expressas ao mesmo tempo. Entretanto, são necessários mais estudos para uma compreensão mais ampla sobre o perfil das citocinas na DCA ao Ni2+, o que poderia levar a novas abordagens terapêuticasAllergic contact dermatitis (ACD) to nickel (Ni+2) is a inflammatory dermatosis, common in industrialized countries. It involves the activation of nickel-specific T cells, followed by the proliferation and induction of a mixed profile of both proinflammatory and regulatory cytokines, suggesting that several T cell subtypes (helper - Th and cytotoxic - Tc) are involved in the immune response. This study aimed to analyze the cytokines TNF-alfa, INF-y, IL-2, IL-4, IL-10, IL-13, IL-17 and IL-23 using the immunohistochemistry technique in order to try to identify the prevalence of one or more T cell subtypes (Th/Tc) in the chronic and acute eczema of patients with ACD to Ni+2. We evaluated 20 patients (17 women and 3 men, median age of 46 years) with chronic eczema, by the patient\'s daily contact with Ni+2. Two skin biopsies were collected in each of the 20 patients, the first at the site of the chronic eczema to Ni+2, prior to the application of the contact test (CT); and the second at the site of acute eczema caused by CT with nickel sulphate, 48 hours after its fixation in the strong positive (++) or very strong positive (+++) readings. There were 160 samples of acute eczema and 160 of chronic eczema, a total of 320 samples. Only three samples were excluded due to some kind of technical failure, such as detachment of the skin cuts from the microscope slide. Statistical software STATA version 13 was used to analyze the data. The stained samples showed positive results for the eight cytokines studied, and these presented heterogeneous values. This heterogeneity was measured by the coefficient of variation, indicating the variability of the data set obtained. TNF-alfa, IFN-y, IL-4, IL-13 and IL-17 had a higher prevalence in chronic eczema than in acute eczema, IL-2 and IL-23 were more prevalent in acute eczema compared to chronic eczema and IL-10 presented similar prevalence in both acute and chronic eczema, however, a very low prevalence in both eczema. TNF-alfa was the most prevalent cytokine in chronic eczema and IL-2 was the most prevalent in acute eczema. However, these prevalences were statistically significant only for IL-4 and IL-13. In chronic and acute eczema, we observed the presence of a mixed cytokine profile of the T cell subtypes (Th/Tc), suggesting that immune responses are expressed at the same time. However, further studies are needed for a broader understanding of the cytokine profile in ACD to Ni+2, which could lead to new therapeutic approaches
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