Дисертації з теми "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.
Повний текст джерелаArnatt, 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.
Повний текст джерелаMoraes, 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/.
Повний текст джерелаIn 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.
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.
Повний текст джерелаParel, 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.
Повний текст джерелаDjerroud, Dalila. "Modélisation markovienne du séchage continu par contact avec agitation." Thesis, Toulouse, INPT, 2010. http://www.theses.fr/2010INPT0111/document.
Повний текст джерелаIn 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
Alshahrany, Shaya. "Rolling contact fatigue in heavily loaded gear transmission contacts." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/90422/.
Повний текст джерелаAlmeida, 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/.
Повний текст джерелаRailway 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.
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.
Повний текст джерелаBalcombe, Robbie. "A study of rolling contact fatigue cracks in lubricated contacts." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9848.
Повний текст джерелаEveritt, 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.
Повний текст джерелаRullande 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
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.
Повний текст джерелаThe 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
MʾNasri, Hechmi. "Comportement d'un accumulateur au plomb associe a un convertisseur statique contine-continu." Paris 6, 1988. http://www.theses.fr/1988PA066422.
Повний текст джерелаCarlier, Axel. "Compréhension de contenus visuels par analyse conjointe du contenu et des usages." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0085/document.
Повний текст джерелаThis 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
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.
Повний текст джерелаMcNeal, 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.
Повний текст джерелаThesis advisor(s): William B. Maier II, Richard Harkins. Includes bibliographical references (p. 45-46). Also available online.
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.
Повний текст джерелаThesis (M.S)-- Wichita State University, College of Engineering, Dept. of Industrial and Manufacturing Engineering
"December 2007."
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.
Повний текст джерелаAnisetti, 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.
Повний текст джерелаPraquin, 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.
Повний текст джерелаThe 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
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/.
Повний текст джерелаThis 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.
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.
Повний текст джерелаMade available in DSpace on 2016-10-14T13:03:49Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) DANIELLE_MEDEIROS_MARQUES_TESE_BC_UFPE_2016[1] 18ago.pdf: 1939643 bytes, checksum: e745bb62b8c1fd6f324e774f998313d0 (MD5) Previous issue date: 2016-02-29
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.
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/.
Повний текст джерелаThe 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.
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/.
Повний текст джерелаAn 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
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.
Повний текст джерелаNdiaye, Serigne Ndiaga. "Ultimate behavior of confined fluids under very high pressure and shear stress." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI104/document.
Повний текст джерелаFriction 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
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.
Повний текст джерелаIf 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
Porras, Vazquez Alberto. "Lubricant starvation in elastohydrodynamic large-size spinning contacts." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI109.
Повний текст джерелаThis 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
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.
Повний текст джерелаNeto, 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/.
Повний текст джерелаContact 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.
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/.
Повний текст джерелаThe 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
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.
Повний текст джерелаSallais, 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.
Повний текст джерелаIn 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
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.
Повний текст джерелаOliveira, 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
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.
Повний текст джерелаBrunetti, 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.
Повний текст джерелаWhenever 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
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/.
Повний текст джерелаDistributed 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
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.
Повний текст джерелаGrégoire, 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.
Повний текст джерелаThe 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
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.
Повний текст джерелаSince 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, ...)
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.
Повний текст джерелаMorgan, 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.
Повний текст джерелаMarques, 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/.
Повний текст джерелаIn 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.
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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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.
Strubel, Vincent. "Particle entrapment in EHD contacts - Aerospace applications." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEI098/document.
Повний текст джерелаContact 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
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.
Повний текст джерелаThe 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
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/.
Повний текст джерелаAllergic 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
Dahlberg, Johan. "A numerical and experimental investigation on surface and sub-surface initiation of contact fatigue cracks at cylindrical contacts /." Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3887.
Повний текст джерела楊貴永 and Kwai-wing Yeung. "Elastic-plastic analysis of rolling elliptical contacts and the effects of axial superimposed stresses on rolling contact fatiguefailure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31231032.
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