Studies of cognitive performance among persons with chronic fatigue syndrome (CFS) have yielded largely inconsistent results. The present study sought to contribute to findings in this area by examining intraindividual variability as well as level of performance in cognitive functioning. A battery of cognitive measures was administered to 14 CFS patients and 16 healthy individuals on 10 weekly occasions. Analyses comparing the two groups in terms of level of performance as defined by latency and accuracy scores revealed that the CFS patients were slower in their reaction speeds than healthy persons. Comparing the groups with respect to intraindividual variability (as measured by intraindividual standard deviations and coefficients of variation) revealed greater intraindividual variability within the CFS group, although the results varied by task and time frame used. Intraindividual variability was found to be fairly stable across time, and consistent across tasks on each testing occasion. The present findings support the proposition that intraindividual variability is a meaningful correlate of cognitive performance in CFS patients. / Graduate

Many daily activities and sporting events require an individual to perform brief periods of maximal exercise (i.e. < 10s) interrupted by limited periods of recovery. In the first study an intermittent maximal exercise test was used to examine the decline in power output with successive exercise periods and identify the changes in the metabolic environment associated with such exercise. The exercise protocol consisted of ten 6s maximal sprints with 30s recovery between each sprint on a cycle ergometer. The results suggest that phosphocreatine (PCr) and anaerobic glycolysis provided the majority of the energy to sustain an average power output (MPO) of 870.1 ±159.2W in the first sprint. In the final sprint, however, no change in lactate concentration was apparent, yet the average power output was still 73% of that in the initial sprint. It was suggested that the energy was derived from PCr degradation and oxidative metabolism.

As a consequence of metal fatigue, cracks can develop and grow in operational aircraft. Periodic inspections must be made in order to detect and repair them before they reach a dangerous length. Cracks which grow from holes are a significant problem for aircraft since the wings and fuselage can contain many thousands of fasteners, or rivets. Since it is impractical to remove them all, inspection must be made with them installed. Research into the application of eddy currents to this problem has led to the development of a scanning procedure in which a small coil is moved around the circumference of the fastener while its impedance is repeatedly measured at different positions. This set of data constitutes an image which can be analvsed using pattern recognition techniques to identify the presence of a crack. A self-contained automated instrument has been built on these principles. It incorporates a microprocessor which controls all aspects of the systems operation, including analysis and display of results. Tests show that it can detect the presence of simulated radial cracks as small as 0.2 mm long beneath the heads of fasteners. The natural extension of these ideas leads to the concept of eddy-current imaging in which a 3D picture of a defect is reconstructed from measurements of the surface magnetic field. The feasibility of implementing this, using techniques such as tomography, is discussed.

No description available.

Made available in DSpace on 2014-06-11T19:34:58Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-12-19Bitstream added on 2014-06-13T21:06:53Z : No. of bitstreams: 1 martins_ms_dr_guara.pdf: 6006771 bytes, checksum: 6cdfc9dd93c227e74bc70e676c33b600 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Atualmente, as montadoras de automóveis têm procurado reduzir o peso total da estrutura de seus veículos, além das peças e componentes produzidos em aços, por dois motivos principais: um focado nos aspectos de segurança para os passageiros e outro na necessidade em se diminuir as emissões de CO2, melhorando o consumo de combustível. Em linha a estes requisitos buscados, o presente trabalho tem por objetivo caracterizar em fadiga e impacto, uma nova classe de material desenvolvida pelas siderúrgicas, o aço de fases complexas (complex phase steel), de atuação estrutural, utilizado para a confecção da carroceria de veículos. Foram realizados ensaios metalográficos, onde as fases presentes em sua microestrutura foram analisadas e discutidas, e ensaios para avaliar suas propriedades mecânicas em situações de fadiga (ASTM E 466) e impacto (ASTM E 23), seguido de análises fractográficas das superfícies de fratura dos corpos-de-prova utilizados durante estes ensaios, utilizando para isto, um microscópio eletrônico de varredura (MEV). Desta forma, este trabalho mostra que seu potencial de utilização pode ser ampliado, em virtude dos resultados obtidos, que mostraram a homogeneidade de sua microestrutura, com um alto grau de refino, em comparação com outras duas especificações de aços estruturais utilizados convencionalmente pela indústria automotiva, indicando, assim, melhores resultados nos ensaios realizados / Currently, automakers have sought to reduce the total weight of the structure of their vehicles, and parts and components produced in steel, for two main reasons: one focused on aspects of safety for passengers and one in the necessity to reduce emissions CO2, improving fuel consumption. In line with these requirements, this study aims to characterize the fatigue and impact, a new class of materials developed, the steel complex phase, with structural actuation, used for making the body of vehicles. To evaluate the characteristics of this specification steel, metallographic tests were conducted, where the phases present in their microstructure was analyzed and discussed, and tests to assess their mechanical properties in situations of fatigue (ASTM E 466) and impact (ASTM E 23) followed by fractográficas analysis of fracture surfaces of the specimens used during these tests, with a SEM. This will show that their potential use could be extended, because the results obtained during tests, which the material was compared with two other specifications of conventional structural steels used in the automotive industry

L’objectif de ce travail est, d’une part, d’expliquer le mécanisme de formation d’extrusion-intrusion par fatigue oligocyclique à température ambiante à la surface d’un acier martensitique à 12% de chrome et, d’autre part, de définir le rôle des différentes interfaces de la microstructure sur la formation des extrusions et des intrusions. L'analyse en microscope à force atomique de la surface de l'échantillon après chaque interruption de l’essai de fatigue oligocyclique a révélé deux morphologies d'extrusions qui ont été appelées extrusions principales et extrusions secondaires. L’étude des évolutions microstructurales sous les marques de glissement à l’aide de la microscopie électronique à transmission a confirmé la localisation des extrusions principales à proximité des différentes interfaces de la structure martensitique ou des murs des cellules de dislocations, et prouvé la localisation des intrusions dans les interfaces elles-mêmes. Quant aux extrusions secondaires, leur localisation à l'intérieur des lattes a également été validée. L'ensemble des résultats confrontés au modèle de Polak a conduit à proposer un mécanisme de formation des extrusions et intrusions à la surface de l'acier martensitique hiérarchiquement organisé. Ainsi, les différents joints inhérents à la structure martensitique et les cellules de dislocation formées par fatigue jouent un rôle primordial dans la création des intrusions. / The objective of this work is to explain the mechanism of extrusion-intrusion pair formation in a 12%Cr martensitic steel during low cycle fatigue at room temperature in regards to the different interfaces creating the material complexity. The atomic force microscope analysis of the specimen surface after each interruption step of low cycle fatigue test revealed two different morphological types of extrusions that were named principal and secondary extrusions. The transmission electron microscope investigation of microstructural evolutions under the fatigue slip markings demonstrated the localization of principal extrusions in the vicinity of different martensitic boundaries as well as of fatigue dislocation cell walls, and the localization of intrusions in the boundaries or walls themselves. As for the secondary ones, their localization inside the laths was validated too. The ensemble of results together with the Polak’s model helped to propose the mechanism of formation of fatigue slip markings in the hierarchically organized martensitic steel. Thus, the existing different boundaries and the formed dislocation cells were found to play a definitive role in the creation of intrusions. As follows, the martensitic hierarchical interfaces and dislocation cell walls are considered to be a source of dislocations and at the same time a sink for vacancies.

abstract: Fatigue is a degradation process of materials that would lead to failure when materials are subjected to cyclic loadings. During past centuries, various of approaches have been proposed and utilized to help researchers understand the underlying theories of fatigue behavior of materials, as well as design engineering structures so that catastrophic disasters that arise from fatigue failure could be avoided. The stress-life approach is the most classical way that academia applies to analyze fatigue data, which correlates the fatigue lifetime with stress amplitudes during cyclic loadings. Fracture mechanics approach is another well-established way, by which people regard the cyclic stress intensity factor as the driving force during fatigue crack nucleation and propagation, and numerous models (such as the well-known Paris’ law) are developed by researchers. The significant drawback of currently widely-used fatigue analysis approaches, nevertheless, is that they are all cycle-based, limiting researchers from digging into sub-cycle regime and acquiring real-time fatigue behavior data. The missing of such data further impedes academia from validating hypotheses that are related to real-time observations of fatigue crack nucleation and growth, thus the existence of various phenomena, such as crack closure, remains controversial. In this thesis, both classical stress-life approach and fracture-mechanics-based approach are utilized to study the fatigue behavior of alloys. Distinctive material characterization instruments are harnessed to help collect and interpret key data during fatigue crack growth. Specifically, an investigation on the sub-cycle fatigue crack growth behavior is enabled by in-situ SEM mechanical testing, and a non-uniform growth mechanism within one loading cycle is confirmed by direct observation as well as image interpretation. Predictions based on proposed experimental procedure and observations show good match with cycle-based data from references, which indicates the credibility of proposed methodology and model, as well as their capability of being applied to a wide range of materials. / Dissertation/Thesis / Masters Thesis Materials Science and Engineering 2018

Orientador: Itamar Ferreira / Dissertação (mestrado profissional) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica, Faculdade de Engenharia Eletrica e de Computação e Instituição de Quimica / Made available in DSpace on 2018-08-14T20:41:02Z (GMT). No. of bitstreams: 1 Mattos_JoaoJoseIfarraguirrede_M.pdf: 6966915 bytes, checksum: 6a6ed6b801e5d2e44c4e448a4c71a74e (MD5) Previous issue date: 2009 / Resumo: O crescente uso das ligas alumínio-silício fundido na indústria automotiva deve-se principalmente a redução de peso, consumo de combustível e níveis de emissões. Isto inclui a liga de alumínio-silício EN AlSi7Mg0,6, equivalente a liga ASTM A357.0, que é empregada em cabeçotes de motores Diesel. É importante conhecer o impacto na integridade e confiabilidade deste componente na presença de defeitos intrínsecos dos processos de fundição convencional como a de molde permanente. Tais defeitos, como porosidades e filmes de óxidos, quando localizados na superfície, ou próxima a esta, são nucleadores de trincas de fadiga. Neste estudo é analisado o impacto na resistência à fadiga e nos micromecanismos de fratura pelo ensaio de corpos-de-prova fresados com dimensões de 7x14x60mm, retirados do cabeçote da linha de produção e submetidos a ensaio de flexão em três pontos. As superfícies de fratura dos espécimes foram analisadas em microscópio eletrônico de varredura (MEV) a fim de caracterizar os micromecanismos de fratura e o local de iniciação da trinca de fadiga. A resistência à fadiga média, para 1 milhão de ciclos, foi determinada como sendo ao redor de 140MPa. Foi observado na superfície de fratura dos espécimes testados, um claro contraste entre o micromecanismo da zona de fadiga (estrias) e zona final de fratura (alvéolos), sendo que o fator predominante para nuclear trincas de fadiga foram poros próximos da superfície. / Abstract: The increase usage of casting aluminum-silicon alloys in the automotive industry is due to reduce weight, fuel consumption, and emissions level. This includes the aluminum-silicon cast alloy EN AlSiMg0.6 (ASTM A357.0) which is used to make Diesel engine cylinder head. It is important to know the impact on the integrity and reliability of this component in the presence of intrinsical defects of conventional casting parts produced on permanent mold process. Such defects, as porosity and oxide film, when locate on the surface or subsurface of casting parts, could be a fatigue crack initiators. In this paper is analyzed the impact on the fatigue strength and micromechanisms of fracture, by using 7x14x60mm specimens machined from cylinder head drew from production assembly line, and submitted to three point bending tests. Fracture surface of the specimens were observed by SEM to characterize the micromechanisms and the initiation fracture local. The average fatigue strength, based on 1 million of cycles, is about 140MPa. It was observed on the fracture surface of fatigue test specimens, a clear contrast between the micromechanisms of fatigue zone (striations) and the final fracture zone (dimples) and fatigue crack initiation occurs at the porosities near the surface. / Mestrado / Materiais / Mestre em Engenharia Automobilistica

M.Phil. / This dissertation is a study of the importance of the awareness of a balanced life in accordance with the six life dimensions in order to preventing chronic fatigue. According to Hafen et al., specialists in psycho-physiological medicine estimate that possibly as much as 90 per cent of all the health problems can be traced, at least in part, to the influence of emotions. The fact that chronic fatigue is related to "disease" and is sometimes the forerunner of illnesses in the human body enhances the importance of life-force energy. We know that the cells of our bodies are fed by various nutrients derived from the food we eat as well as oxygen from the air we breathe. But our cells are also fed by a continuous stream of life-force energy. We possess a variety of specialised energy-distributing systems that also support the cells and organs of our bodies. These energy systems are affected by different factors that can enhance or inhibit the flow of life-force energy to the cells and organs of our bodies. Among those critical factors are our emotions, our relationships to others, our ability to give and to receive love, and even our relationship to God. While seemingly nebulous and difficult to define in terms of specific physiological effects, these emotional and spiritual factors are of great importance to the sustenance and support of the tissues and organs of our bodies.

L'objectif de ce travail est une contribution à la compréhension des mécanismes de déformation plastique monotone et cyclique d'un acier duplex (50% [Alpha]-50%[Gamma]) en utilisant la microscopie à force atomique comme technique d'investigation. Les analyses après sollicitation monotone valident le potentiel de la technique AFM et imposent une identification minutieuse des lignes de glissement en fonction de leurs morphologies et dimensions, dans les grains de ferrite et d'austénite. En fatigue oligocyclique à faible variation de déformation, en faisant varier la dureté de la ferrite, nous montrons que la réponse macroscopique à la sollicitation cyclique de l'acier duplex hypertrempé résulte de la contribution effective des deux phases, Alpha et Gamma, contrairement à ce qui est proposé dans la littérature. En réalisant des essais de fatigue à variation de déformation élevée et interrompus à différents pourcentages de la durée de vie, les mécanismes d'amorçage de fissure ont pu être proposés. En fonction de la morphologie des îlots d'austénite, de leur répartition et de leur cohérence cristallographique avec la matrice ferritique, certaines extrusions dans l'austénite peuvent générer des zones de haute rugosité dans la ferrite, à la frontière Alpha/Gamma, qui constituent les sites d'amorçage de fissure dans la phase ferritique. De plus, l'interactivité des deux phases est de nouveau démontrée dans le mécanisme de plasticité cyclique par le transfert progressif de la plasticité de la phase austénitique vers la phase ferritique. L'ensemble des résultats propose que la plasticité cyclique des aciers duplex est accommodée progressivement et de manière interactive par les deux phases Alpha et Gamma. De ce fait, la séparation du comportement en fatigue en régimes différents, concept mettant en avant une activité ou passivité de chaque phase selon la déformation imposée, semble être une approche simplifiée ne reflétant pas nécessairement le comportement réel de ce matériau biphasé. / In order to increase the understanding of monotonic and cyclic plastic deformation mechanisms in multiphase alloys, an intensive research task has been carried out on a Duplex Stainless Steels (DSS-50%α-50%γ) using Atomic Force Microscopy (AFM). After monotonic deformation, AFM investigations of the surface reveal that this technique is especially promising for the plasticity studies of DSS. It allows high detailed characterisation of different types of slip lines, depending of their morphology, dimensions and the analysed phase, austenite or ferrite. Concerning the Low Cycle Fatigue behaviour at low strain range, contrary to earlier works, the comparison of the surface topography between two alloys differing by their ferrite hardness (annealed and aged), suggests that the macroscopic cyclic behaviour of the annealed DSS is a consequence of the mutual contribution of the two phases. Performing interrupted fatigue tests at high strain range, High-Rugged (HR) areas were identified in ferritic grains and near the α/γ interfaces. The formation of HR areas is a consequence of the high surface activity (extrusions) in an austenitic neighbour grain, the relative crystallographic “compatibility” between α/γ grains and the phase distribution. In addition, the close interaction between the two phases was still evidenced, this time as a transfer of the plastic activity from austenite to ferrite. It turns out that, taking into account the whole results set obtained in this work, the cyclic plasticity of the duplex stainless steels could be explained like a progressive contribution of the activity in the two phases and their interactions. Therefore, the utilisation of different regimes depending of the deformation levels, supported by the individually activity or passivity of each phase, appears to be a simplified explanation that does not illustrate the real cyclic behaviour of this material.