<p dir="ltr">Fretting wear occurs when two contacting bodies under load are subjected to small amplitude oscillatory motion. Depending on the applied normal load, displacement amplitude, coefficient of friction and resulting shear force, two types of fretting wear regimes exist – (i) partial slip and (ii) gross slip. At displacement amplitudes higher than gross slip condition, sliding wear regime prevails. Fretting wear becomes dominant in machine components subject to vibrations such as bearings, dovetail joints, etc. whereas sliding wear is observed in brakes, piston-ring applications, etc. The work in this dissertation primarily focuses on characterizing the material response of various machine components subjected to fretting and sliding wear regimes.</p><p dir="ltr">At first, the friction and fretting wear behavior of inlet ring and spring clip components used in land-based gas turbines was investigated at elevated (<a href="" target="_blank">500°C</a>) temperature. In order to achieve this objective, a novel high-temperature fretting wear apparatus was designed and developed to simulate the conditions existing in a gas turbine. The test apparatus was used to investigate fretting wear of atmospheric plasma sprayed (APS) Cr₃C₂-NiCr (25% wt.), high-velocity oxy-fuel (HVOF) sprayed Cr₃C₂-NiCr (25% wt.), HVOF sprayed T-800 and APS sprayed PS400 coated inlet rings against HVOF-sprayed Cr₃C₂-NiCr (25% wt.) coated spring clip. The PS400 coated inlet rings demonstrated a significant reduction in friction and wear. A finite element (FE) framework was also developed to simulate fretting wear in HVOF-sprayed Cr₃C₂-NiCr composite cermet coating. The material microstructure was modelled using Voronoi tessellations with a log-normal distribution of grain size. Moreover, the individual material phases in the coating were randomly assigned to resemble the microstructure from an actual SEM micrograph. A damage mechanics based cohesive zone model with grain deletion algorithm was used to simulate debonding of the ceramic carbide phase from the matrix and resulting degradation from repeated fretting cycles. The specific wear rate obtained from the model for the existing material microstructure was benchmarked against experiments. Novel material microstructures were also modeled and demonstrated to show less scatter in wear rate.</p><p dir="ltr">Following, a three-dimensional (3D) continuum damage mechanics (CDM) FE model was developed to investigate the effects of fretting wear on rolling contact fatigue (RCF) of bearing steels. In order to determine the fretting scar geometry, a 3D arbitrary Lagrangian-Eulerian (ALE) adaptive mesh (AM) FE model was developed to simulate fretting wear between two elastic bodies for different initially pristine fretting pressures (0.5, 0.75 and 1 GPa) and friction coefficients (0.15, 0.175 and 0.25) resulting in stick zone to contact width ratios, c/a = 0.35, 0.55 and 0.75. The resulting wear profiles were subjected to various initially pristine RCF pressures (1, 2.2 and 3.4 GPa). The pressure profiles for RCF were determined by moving the contact over the fretted wear profiles in 21 steps. These pressure profiles were then used in the CDM-FE model to predict the RCF life of fretted surfaces. The results indicate that increased fretting pressure leads to more wear on the surface, thereby reducing RCF life. As the RCF pressure increases (P_RCF ≥ 2.2 GPa), the effect of fretting on RCF life decreases for all fretting pressures and c/a values, indicating that life is primarily governed by the RCF pressure. The results from CDM-FE model were used to develop a life equation for evaluating the L₁₀ life of fretted M-50 bearing steel for the range of tested conditions.</p><p dir="ltr">Lastly, the sliding wear characteristics of pitch and poly-acrylonitrile based carbon-carbon (C/C) composites were investigated in air and nitrogen environment by designing and developing a disc brake test rig. It was found that the temperature of the disc, the surrounding environment, the supplied energy flux as well as the type of composite play a critical role in determining whether C/C composites operate in normal wear or dusting wear regime. Further analysis of wear mechanisms revealed interface and matrix cracking with fiber breakage from tests in air environment, whereas in nitrogen environment, particulate and layered debris played a prominent role.</p>

This paper addresses the problem of a failing net debt approach; deposited funds rarely compensate the cost of debt. Venturing into operational credit facilities, the study evaluates the efficiency and feasibility of transitioning into fully cash-free liquidity management. The study takes a holistic approach and evaluates the research questions from the perspective of management through case studies on four smaller Swedish industrial firms. The study finds that there is substantial potential to free up capital; return on equity could have been boosted by an annual 5-10 percent including substantial one-off distributions. The study also concludes that Agency reasons are strong reasons for why firms are carrying material cash reserves. Through qualitative interviews, the study identifies several additional, but not less important, obstacles in the way of a full out cash-free transition. Most significantly, the financial system is not offering fully committed long term operational credit facilities and operating across different jurisdictions complicates the consolidation of liquidity. The study concludes that the matter would not have vast negative implications on real business activities, although further research would be required in regard to an extended debt overhang problem. / Uppsatsen kretsar kring den fallerande logiken med begreppet nettoskuld; tillgodohavanden på bank genererar sällan upp för kostnaden relaterad till motsvarande skuld. Med utgångspunkt i operationella kreditstrukturer utvärderas möjliga effektivitetsvinster och genomförbarheten av en fullständig övergång till kassa-fri likviditetshantering. Studien har ett holistiskt angreppssätt och utvärderar frågeställningarna från ett management-perspektiv genom fallstudier på fyra mindre svenska industriella bolag. Studien finner betydande möjligheter att frigöra kapital; årliga avkastningen på eget kapital hade kunnat öka med 5–10 procent och betydande engångsutdelningar hade varit möjliga. Studien finner vidare att agentteorin är en stark anledning till att bolag bär betydande kassapositioner. Genom kvalitativa intervjuer identifierar studien ytterligare, men ej desto mindre betydande, hinder för en kassa-fri övergång. Mest betydelsefullt, är att nuvarande finansiella system inte erbjuder för syftet fullgoda kreditstrukturer, samt det faktum att företag med verksamhet över olika jurisdiktioner upplever juridiska svårigheter med att konsolidera likviditet. Studien drar slutsatsen att en övergång inte skulle medföra betydande negativa konsekvenser för den operativa affärsverksamheten, men identifierar samtidigt att ytterligare studier skulle vara nödvändiga framförallt kring hur finansiella incitament kopplade till agent-teorins ’debt overhang’ skulle förändras vill en övergång till en fullt garanterad operationell kreditstruktur.

L’analyse visuelle du rythme cardiaque fœtal (RCF) est une excellente méthode de dépistage de l’hypoxie fœtale. Cette analyse visuelle est d’autre part sujette à une variabilité inter- et intra-individuelle importante. L’hypoxie fœtale au cours du travail s’exprime par des anomalies du RCF. La sous-évaluation de la gravité d’un RCF entraine une prise de risque indue pour le fœtus avec une augmentation de sa morbi-mortalité et sa surévaluation entraine un interventionnisme obstétrical inutile avec une augmentation du taux de césariennes. Ce dernier point pose par ailleurs en France un problème de santé publique.L’analyse automatisée du signal RCF permet de diminuer la variabilité inter- et intra-individuelle et d’accéder à d’autres paramètres calculés visant à augmenter la valeur diagnostique. Les critères d’analyse morphologiques du RCF (ligne de base, nombre d’accélérations, nombre et typage des ralentissements, variabilité à long terme (VLT)) ont été décrits ainsi que d’autres tels que les surfaces des ralentissements, les indices de variabilité à court terme (VCT) et les analyses fréquentielles. Il n’en demeure pas moins que la définition de la ligne de base, à partir de laquelle sont repérés les accélérations et les ralentissements reste, dans certains cas, difficile à établir.L’objectif principal de la thèse est d’établir un modèle prédictif de l’acidose fœtale à partir d’une analyse automatisée du RCF. L’objectif secondaire est de déterminer la pertinence des différents paramètres élémentaires classiques (CNGOF 2007) (fréquence de base, variabilité, accélérations, ralentissements) et celle d’autres paramètres inaccessible à l’œil (indices de variabilité à court terme, surfaces des ralentissements, analyse fréquentielle…). Par la suite, nous voulons identifier des critères de décision qui aideront à la prise en charge obstétricale.Nous proposons d’aborder l’analyse automatisée du RCF pendant le travail par l’intermédiaire d’une étude cas-témoins ; les cas étant des tracés RCF de nouveau-nés en acidose néonatale (pH artériel au cordon inférieur ou égal à 7,15) et les témoins, des tracés RCF de nouveau-nés sans acidose (pH artériel au cordon supérieur ou égal à 7,25). Il s’agit d’une étude monocentrique à la maternité de l’hôpital Saint Vincent de Paul, GHICL – Lille, sur notre base de données « Bien Naitre » (archivage numérique des tracés RCF depuis 2011), comptant un un nombre suffisant de cas sur ce seul centre. La maternité Saint Vincent de Paul (GHICL) présente depuis 2011 environ 70 cas par an d’acidose néonatale (pHa ≤ 7,10) (3,41%). Le logiciel R sera utilisé pour l’analyse statistique / Visual analysis of the fetal heart rate FHR is a good method for screening for fetal hypoxia but is not sufficiently specific. The visual morphological analysis of the FHR during labor is subject to inter- and intra-observer variability – particularly when the FHR is abnormal. Underestimating the severity of an FHR leads to undue risk-taking for the fetus with an increase in morbidity and mortality and overvaluation leads to unnecessary obstetric intervention with an increased rate of caesarean section. This last point also induces a French public health problem.FHR automated analysis reduces inter and intra-individual variability and accesses other calculated parameters aimed at increasing the diagnostic value. The FHR morphological analysis parameters (baseline, number of accelerations, number and typing of decelerations, long-term variability (LTV)) were described as well as others such as the decelerations surfaces, short-term variability (STV) and frequency analyzes. Nevertheless, when attempting to analyze the FHR automatically, the main problem is computation of the baseline against which all the other parameters are determined.Automatic analysis provides information on parameters that cannot be derived in a visual analysis and that are likely to improve screening for fetal acidosis during labor.The main objective of the thesis is to establish a predictive model of fetal acidosis from a FHR automated analysis. The secondary objective is to determine the relevance of the classical basic parameters (CNGOF 2007) (baseline, variability, accelerations, decelerations) and that of other parameters inaccessible to the eye (indices of short-term variability, surfaces of decelerations, frequency analysis ...). Later, we want to identify decision criteria that will help in the obstetric care management.We propose to validate FHR automated analysis during labor through a case-control study; cases were FHR recordings of neonatal acidosis (arterial cord pH less than or equal to 7.15) and controls, FHR recordings of neonatal without acidosis (arterial cord pH upper than or equal to 7.25). This is a monocentric study at the maternity hospital of Saint Vincent de Paul Hospital, GHICL - Lille, on our « Well Born » database (digital archiving of RCF plots since 2011), with a sufficient number of cases on this only center. Since 2011, the Saint Vincent de Paul hospital (GHICL) has had about 70 cases per year of neonatal acidosis (pHa less than or equal to 7.10) (3.41%). The R software will be used for statistical analysis.

Made available in DSpace on 2016-08-18T18:19:25Z (GMT). No. of bitstreams: 1 Josberg Silva Rodrigues.pdf: 647762 bytes, checksum: 76e44a5c4743594c8862ff4d8b22704c (MD5) Previous issue date: 2009-04-30 / FUNDAÇÃO DE AMPARO À PESQUISA E AO DESENVOLVIMENTO CIENTIFICO E TECNOLÓGICO DO MARANHÃO / In this work we study the effects of the spontaneous breaking of Lorentz symmetry on black body radiation phenomenon in the context of the Maxwell-Caroll-Field-Jackiw (MCFJ) model. The MCFJ model is the electromagnetic CPT-odd sector of the standard model extension and, it presents for a purely space-like background a positive-definite hamiltonian. Firstly, we study the Maxwell electrodynamics by analyzing its hamiltonian structure following the Dirac s procedure for constrained systems. Then, we calculate the partition function via the path integrals formalism and consequently we obtain its thermodynamic properties such as: energy density, radiation pressure and the entropy. Afterwards, we apply the same procedure to find the partition function of the MCFJ model and we observe how the spectrum of black body changes due to the breaking of the CPT and Lorentz symmetries. We show that if the cosmic microwave background (CMB) radiation is described by this model, it shows an angular anisotropy in the energy density distribution. We also give, at leading order in the Lorentz violating parameter, the contributions of the Lorentz breaking for the Planck s radiation and the Stefan-Boltzmann laws. The Lorentz-violating (LV) corrections for the Planck s law is non-linear in the frequency and for the Stefan-Boltzmann law is quadratic in the temperature. Using our results, we set upper limits for the LV parameter by analyzing the Stefan-Boltmann law and the CMB anisotropy but it is shown that they are much less stringents that those obtained by birefringence or polarization analysis of light. / Esta dissertação aborda os efeitos da quebra espontânea da simetria de Lorentz sob a radiação do corpo negro no contexto da eletrodinâmica de Maxwell-Carroll-Field-Jackiw (MCFJ). O modelo MCFJ advém do setor CPT-ìmpar do modelo padrão estendido e apresenta uma hamiltoniana positiva-definida somente para um campo de fundo puramente tipo-espaço. O estudo começa pela eletrodinâmica de Maxwell realizando uma análise de sua estrutura hamiltoniana através do procedimento de Dirac para sistemas vinculados. Após essa análise, calcula-se a função de partição via o formalismo de integração funcional e obtendo consequentemente suas propriedades termodinâmicas relevantes como: densidade de energia, pressão de radiação e a entropia do sistema. Na segunda parte, seguindo um procedimento similar encontramos a função de partição do modelo MCFJ. Observa-se que o espectro de energia do corpo negro sofre alteração devido à quebra da invariância de Lorentz e da simetria CPT. Mostramos que se a radiação cósmica de fundo (RCF) for descrita por esse modelo desponta uma anisotropia na distribuição de densidade de energia. Também, mostramos que a lei de radiação de Planck e a lei de Stefan Boltzmann são afetadas pela introdução do campo externo responsável pela quebra de Lorentz. Tais modificações no caso da lei de Planck são não-lineares na frequência e na lei de Stefan-Boltzmann são quadráticas na temperatura. Usando esses resultados e os dados experimentais da constante de Stefan-Boltzmann e os dados referentes a anisotropia da radiação cósmica de fundo, estipulamos limites superiores para a magnitude do parâmetro da VL. Contudo, os limites obtidos são menos restritivos que os obtidos pela análise do fenômeno da birrefrigência.

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