Un composite époxy/fibre de verre élaboré à partir de matériaux simplifiés a été soumis en parallèle à du vieillissement artificiel (UV et thermohydrique) et à du vieillissement naturel (climat tropical humide). Une étude des matériaux (résine seule et composite) à travers un large panel de techniques de caractérisation physico-chimiques, mécaniques et de moyens d’observation (MEB, AFM) a permis d’identifier clairement la structure, la morphologie et les principales propriétés du réseau époxy-amine de l’état initial. Une caractérisation systématique des échantillons par couches de 20 microns d’épaisseur a permis, en particulier, d’identifier un gradient de structure et de propriétés dans les 200 premiers microns à la surface des plaques de résine et de composite. Ce gradient est attribué à l’évaporation du durcisseur amine lors de l’élaboration des matériaux. Dans les plaques de composites, le DMA ainsi que l’AFM ont permis de mettre en évidence une zone d’interphase autour des fibres pour laquelle le réseau époxy-amine présente des caractéristiques différentes de celles de la résine en masse.La même méthodologie a été adoptée pour suivre l’évolution de ces matériaux lors des vieillissements artificiels et naturels.Les études séparées des vieillissements UV et thermohydrique ont permis de mettre en évidence les altérations chimiques et physico-chimiques de la matrice seule d’une part, et des interphases fibres/matrice d’autre part. Le vieillissement photochimique se montre le plus dégradant pour la surface des plaques, alors que les effets du vieillissement thermohydrique sont principalement observés au niveau des interfaces fibres/matrice dans les composites. Dans les deux cas également, nous pouvons proposer des mécanismes simplifiés de dégradation de la résine époxy-amine.Enfin, les résultats de caractérisation après le vieillissement naturel nous permettent de faire des corrélations avec les vieillissements artificiels et de pointer les effets prépondérants des deux paramètres de vieillissement, ainsi que d’avancer un facteur d’accélération. / A simplified glass fiber/epoxy composite was exposed to artificial ageing conditions (UV and Hygrothermal) and natural ageing (humid tropical climate). A wide range of physicochemical, mechanical and observation techniques (SEM, AFM) were used to clearly identify the structure, morphology and the main properties of the epoxy-amine network of the resin alone and composite in the initial state. A gradient in structure and properties was shown up in the first 200 microns of resin and composite plates surfaces thanks to the systematic characterization of sample layers of 20 microns thickness. It is attributed to an amine deficit during the sample elaboration process. In composite plates, DMA and AFM measurements have highlighted the existence of an interphase area around the fibers with a higher molecular mobility and a lower stiffness than the epoxy-amine network in the bulk resinThe same methodology was used to follow the materials evolution during artificial and natural ageing.The effects of UV and hygrothermal ageing were analyzed independently on the resin and on the composite in order to identify the chemical and physicochemical alterations of the matrix on one hand and of fiber/matrix interphases on the other hand. Photochemical ageing effects are mainly localized on materials surfaces, while the hygrothermal ageing affects mainly fiber/matrix interfaces in composite. In both cases simplified degradation mechanisms of epoxy-amine network are proposed.Finally, the characterization results after natural exposure allow us to establish correlations with artificial ageing. Predominant effects are identified and an acceleration factor is proposed.

O objetivo deste estudo foi avaliar a estabilidade de cor e opacidade de cinco sistemas cerâmicos glazeados naturalmente e com pintura extrínseca, utilizando os espectrofotômetros Color Guide 45/0 (BYK-Gardner) e Easyshade (Vita), sob influência do envelhecimento artificial acelerado. Foram confeccionados 14 corpos de prova para cada grupo testado de cerâmica - metalocerâmica Ceramco 3 (Dentsply) (grupo 1), cerâmica pura Ceramco 3 (grupo 2), cerâmica pura EX -3 (Noritake) (grupo 3), Vitroceram (Angelus) recoberta com Allceram (Degudent) (grupo 4) e Vitroceram recoberta com Cerabien (Noritake) (grupo 5). Sete corpos de prova de cada grupo cerâmico foram glazeados naturalmente e sete foram submetidos à pintura extrínseca com pigmento Vita Chrom 712. Uma leitura inicial foi realizada em todos os corpos de prova utilizando o espectrofotômetro Color Guide, obtendo valores de opacidade e das coordenadas L*, a*, b* e E*; e utilizando o espectrofotômetro Easyshade, obtendo valores de L*, C*, h* e E*. Após o envelhecimento artificial de 500h, foram realizadas novas leituras nos espectrofotômetros. Os resultados encontrados foram submetidos à análise estatística e concluiu-se que os grupos 2, 3 e 4 foram influenciados estatisticamente pelo envelhecimento artificial acelerado quanto à opacidade; e que o grupo 5 foi o que obteve o pior desempenho de estabilidade de cor (E* = 3,32 - VTCE e E* = 2,68 = VTCEPE) para o espectrofotômetro Color Guide. Com o espectrofotômetro Easyshade os grupos 4 e 5 e as cerâmicas MC, CER, EX foram considerados ineficazes quanto à estabilidade de cor (p<0,05). / The aim of this study was to evaluate the color stability and opacity of five ceramic systems naturally glazed and with extrinsic porcelain colorant, under influence of accelerated aging, using two spectrophotometers Color Guide 45/0 (BYK-Gardner) and Easyshade (Vita) as a tool for color and opacity measurement. Fourteen samples were provided for each tested group of ceramics: metal-ceramic Ceramco3 (Dentsply) (Group 1), Ceramco3 (Group 2), EX3 (Noritake) (Group 3), Vitroceram (Angelus) with Allceram (Degudent) (Group 4) and Vitroceram with Cerabien (Noritake) (Group 5). Seven samples of each group were submitted to extrinsic colorant (Vita Chrom 712) and the other seven were naturally glazed. An initial measurement was performed and the values of opacity, L*, a*, b* and E* were obtained using the Color Guide spectrophotometer, and using Easyshade the values of L*, C*, h* and E* were obtained. After the process of 500h accelerated aging a new measurement was performed for all samples. The results were statistically analyzed and the conclusion was that the opacity of groups 2, 3 and 4 were statistically influenced by the accelerated aging and the group 5 had the worst assessment in color stability (E* = 3,32 - VTCE e E* = 2,68 - VTCEPE) with the Color Guide spectrophotometer. With Easyshade, groups 4 and 5 and MC, CER and EX ceramics were considered ineffective as for color stability (p<0,05).

A erosão é um fenômeno natural no modelado da superfície, no processo de remoção e de deposição de sedimentos, porém as atividades antrópicas, como o desmatamento, excedem os níveis naturais de perdas de solo. Para estimar a perda de solo anual em terrenos agricultáveis, existem modelos de predição, que relacionam elementos físicos da paisagem junto às atividades antrópicas existentes. Nessa temática, o objetivo deste trabalho é avaliar a perda de solos na Bacia Hidrográfica do Córrego Baguaçu, localizada no oeste do estado de São Paulo, considerada uma região de intensa erosão acelerada, resultado de solos provenientes de materiais arenosos e areno-argilosos de fácil erosão, isso aliado às pressões de uso agropecuário. A EUPS (Equação Universal de Perda de Solos) foi o modelo de predição utilizado para estimar a perda de solos superficiais nessa bacia. A EUPS permite avaliar o resultado dos produtos da erosividade da chuva, erodibilidade do solo, fator topográfico, cobertura do uso do solo, manejo e práticas conservacionistas. Utilizando o Sistema de Informação Geográfica (SIG), foi possível estimar espacialmente as áreas de maior vulnerabilidade a erosão, além de mapear feições lineares erosivas e apontar qual uso é mais responsável por grandes perdas de solos. Os resultados mostraram que grande parte da perda de solos na bacia concentra-se nas classes mais baixas (0 a 3 t/ha/ano), com predomínio das áreas ocupadas com pastagem e com cana-de-açúcar. / Erosion is a natural phenomenon in the modeled the surface removal process and sediment deposition, but human activities, such as deforestation, exceed natural levels of soil loss. To estimate the annual soil loss in arable land, there are models of prediction, which relate to physical elements of the landscape with anthropogenic activities. On this subject, the aim of this study is to evaluate the loss of soils in the watershed of Córrego Baguaçu, located in the west of the State of São Paulo, considered a region of intense accelerated erosion, result of soils from sandy and sandy-clay materials of easy erosion, that ally to the pressures of agricultural use. The USLE (Universal Soil loss Equation) was the prediction model used to estimate the loss of surface soils in this basin. The USLE allows you to evaluate the outcome of rainfall erosion index, soil erodibility, topographic factor, coverage of land use, management and conservation practices. Using the Geographical Information System (GIS), it was possible to estimate spatially the areas of greatest vulnerability to erosion, as well as linear features map changes and point out what is most responsible for heavy losses from soils. The results showed that much of the soil loss in the concentrates on lower classes (0 to 3 t/ha/yr), with predominance of the occupied areas with pasture and sugar cane.

O objetivo deste estudo foi avaliar a estabilidade de cor e opacidade de cinco sistemas cerâmicos glazeados naturalmente e com pintura extrínseca, utilizando os espectrofotômetros Color Guide 45/0 (BYK-Gardner) e Easyshade (Vita), sob influência do envelhecimento artificial acelerado. Foram confeccionados 14 corpos de prova para cada grupo testado de cerâmica - metalocerâmica Ceramco 3 (Dentsply) (grupo 1), cerâmica pura Ceramco 3 (grupo 2), cerâmica pura EX -3 (Noritake) (grupo 3), Vitroceram (Angelus) recoberta com Allceram (Degudent) (grupo 4) e Vitroceram recoberta com Cerabien (Noritake) (grupo 5). Sete corpos de prova de cada grupo cerâmico foram glazeados naturalmente e sete foram submetidos à pintura extrínseca com pigmento Vita Chrom 712. Uma leitura inicial foi realizada em todos os corpos de prova utilizando o espectrofotômetro Color Guide, obtendo valores de opacidade e das coordenadas L*, a*, b* e E*; e utilizando o espectrofotômetro Easyshade, obtendo valores de L*, C*, h* e E*. Após o envelhecimento artificial de 500h, foram realizadas novas leituras nos espectrofotômetros. Os resultados encontrados foram submetidos à análise estatística e concluiu-se que os grupos 2, 3 e 4 foram influenciados estatisticamente pelo envelhecimento artificial acelerado quanto à opacidade; e que o grupo 5 foi o que obteve o pior desempenho de estabilidade de cor (E* = 3,32 - VTCE e E* = 2,68 = VTCEPE) para o espectrofotômetro Color Guide. Com o espectrofotômetro Easyshade os grupos 4 e 5 e as cerâmicas MC, CER, EX foram considerados ineficazes quanto à estabilidade de cor (p<0,05). / The aim of this study was to evaluate the color stability and opacity of five ceramic systems naturally glazed and with extrinsic porcelain colorant, under influence of accelerated aging, using two spectrophotometers Color Guide 45/0 (BYK-Gardner) and Easyshade (Vita) as a tool for color and opacity measurement. Fourteen samples were provided for each tested group of ceramics: metal-ceramic Ceramco3 (Dentsply) (Group 1), Ceramco3 (Group 2), EX3 (Noritake) (Group 3), Vitroceram (Angelus) with Allceram (Degudent) (Group 4) and Vitroceram with Cerabien (Noritake) (Group 5). Seven samples of each group were submitted to extrinsic colorant (Vita Chrom 712) and the other seven were naturally glazed. An initial measurement was performed and the values of opacity, L*, a*, b* and E* were obtained using the Color Guide spectrophotometer, and using Easyshade the values of L*, C*, h* and E* were obtained. After the process of 500h accelerated aging a new measurement was performed for all samples. The results were statistically analyzed and the conclusion was that the opacity of groups 2, 3 and 4 were statistically influenced by the accelerated aging and the group 5 had the worst assessment in color stability (E* = 3,32 - VTCE e E* = 2,68 - VTCEPE) with the Color Guide spectrophotometer. With Easyshade, groups 4 and 5 and MC, CER and EX ceramics were considered ineffective as for color stability (p<0,05).

Os sistemas de medição são projetados para obter uma capabilidade de acordo com as exigências do cliente final ou especificações de engenharia. Esta capabilidade deve ser mantida através de manutenções preventivas e calibrações. Este estudo apresenta um procedimento, onde se determina a capabilidade do sistema de medição utilizando o MSA (Measurement System Analisys). Obtendo a capabilidade, a confiabilidade das medições obtidas do sistema de medição é estimada, considerando como falha a perda da capabilidade obtida. Os tempos estimados de falha são obtidos em testes de vida acelerados utilizando como sobrecarga o aumento da temperatura e extrapolando os tempos de falha para condição de uso através dos modelos de Arrhenius-exponencial, Arrenius-Weibull e Arrhenius-lognormal. O MTTF é calculado para estimação dos tempos de manutenção e calibração do sistema de medição. Uma aplicação do procedimento proposto é realizada em um equipamento protótipo de medição do número de Swirl desenvolvido com uma nova tecnologia de medição mais rápida e precisa em relação aos existentes no mercado. O estudo avalia a capabilidade do equipamento de medição de Swril e posteriormente estima tempos de falha para obter a confiabilidade das medições obtidas e o tempo necessário para sua manutenção. / The measuring systems are designed to achieve a capability according to the requirements from the end customer or engineering specifications. This capability must be maintained through preventive maintenance and calibration. This study presents a procedure, where the measurement system capability is determined using the MSA (Measurement System Analyzes). Obtaining the capability, the reliability of the measurements obtained from the measurement system is estimated, considering as failure the loss of the capability obtained. An estimated failure times are obtained in accelerated life tests using the temperature increase as an overloading and extrapolating the failure times to condition of use through the Arrhenius-exponential, Arrenius-Weibull and Arrhenius-lognormal models. The MTTF is calculated to estimate the maintenance and calibration times for the measurement system. An application of the proposed procedure is carried out on a prototype equipment to measure the Swirl number developed with a new measurement technology faster and more accurate than others available on the market. The study evaluates the capability of equipment to measure the Swirl number and then estimates failure times to obtain the reliability of measurements obtained and the time required for their maintenance.

O objetivo deste estudo é desenvolver um método para avaliar a confiabilidade de sistemas eletrônicos complexos. A análise proposta baseia-se na aplicação de ensaios de confiabilidade e de normas técnicas, bem como modelos matemáticos para estimação da vida operacional. Os ensaios de confiabilidade executados nesse estudo simulam condições operacionais mais severas que as usualmente enfrentadas pelo sistema, a fim de reduzir o tempo de execução dos ensaios. Ao longo destes, foram coletados os tempos até a falha de diversas amostras do sistema, os quais são submetidas a diferentes condições de operação. O planejamento das variáveis que aceleram os principais modos de falha de componentes eletrônicos e os perfis de solicitação empregados também são discutidos, sendo consideradas as mais importantes a temperatura e a umidade. Através da aplicação de modelos matemáticos para predição da vida nas condições normais de operação, dadas as ocorrências de falhas nas condições aceleradas, a confiabilidade e o tempo médio até a falha são determinados para a central telefônica estudada, tomada como exemplo na aplicação do método. Adicionalmente aos ensaios são desenvolvidas estimativas da confiabilidade da central telefônica através da norma militar US MIL-HDBK-217 F (1991). Os resultados destas estimativas são utilizados para comparação e confirmação dos resultados obtidos através dos ensaios. Destaca-se que os métodos descritos neste texto não são restritos a aplicação em centrais telefônicas analógicas, mas podem ser empregados a uma grande família de equipamentos eletrônicos de complexidade tecnológica semelhante. / This research aims to develop a method to evaluate the reliability of complex electronic systems. The analysis proposed is based on application of reliability laboratory tests, technical standards and mathematical models to estimate the system operational life. Reliability tests proposed simulate harder operational conditions than those usually faced by the system, aiming to reduce the time of execution. During the tests, time to failure of several samples are collected. Those samples are submitted to different environmental conditions. Selection of variables that accelerate the main failure modes of electronic components and the load profiles used are also analyzed, considering humidity and temperature the most important variables for failure acceleration. The proposed model is used to estimate the reliability and the mean time to failure of an analog PABX, those values being generated by the application of mathematical models for life prediction in the usage operation condition, given the accelerated reliability estimate. Additionally to the tests, a reliability estimation of the PABX central is done using US MIL-HDBK-217 F (1991). Results are used to compare and to validate the reliability value evaluated through the accelerated tests. It is important to emphasize that the application of the methods described in this present text is not restricted to analog PABX systems, being applied to a wide range of electronic equipments with similar technological complexity.

This research describes a proposed accelerated testing procedure for evaluating pavement patching materials under the simulation of traffic loading and environmental conditions such as freeze-thaw cycles. Potholes were constructed in concrete blocks with different tilt angles (13¢ª, 17¢ª and 22¢ª) to simulate normal and shear wheel surface stresses. Different patching materials, including hot mix, cold mix and commercial cold patch were tested. Various cyclic loads accompanied with cycles of freezing and thawing were applied to the patch. Patch performance is assessed by visual monitoring of the surface distresses and measuring surface elevation for rutting and shoving determination. Applied vertical loads varied between 2,250 and 4,500 pounds at a frequency of 2 Hz. Patch performance comparisons were made as a function of the patch mix, applied load, number of applied loads, frequency of loading, and applied freeze/thaw cycles. The new method of accelerated testing is successful in differentiating the performance of good and poor quality mixes. The proposed test could be used as a reliable method by state highway agencies for establishing acceptance criteria for selecting pothole patching mixtures.

The purpose of this thesis was to evaluate a method for testing the appropriateness of accelerated life model. This method is based upon a polynomial approximation. The parameters are estimated and used for testing the appropriateness of the model. An example illustrates the polynomial method. Real data are applied for this method. Comparison with another method demonstrates that the polynomial method is much simpler and has comparable accuracy.

Briefing for a clinical simulation in nursing school is an information session that sets the stage for a meaningful simulation activity. Improper or inadequate briefing practices can impact the quality of learning nursing students receive through clinical simulation experience. The purpose of this study, guided by the novice to expert and social cognitive theories, was to explore accelerated baccalaureate nursing (ABN) students' perceptions of their briefing experiences and how the briefing experiences influenced the acquisition of clinical skills and knowledge. Twelve ABN students from a school of nursing in one of the Northeastern states were interviewed through e-mail correspondence. Thematic coding was conducted on the data and the themes derived were inconsistencies in briefing practices, a sense of uncertainty, and inefficient acquisition of clinical skills and knowledge. The inconsistencies in the practice of briefing varied between courses and instructors and improper briefing generated a sense of uncertainty among participants and feelings of ineffective acquisition of clinical skills and knowledge from simulations. The results will enable nurse educators in the local setting to improve briefing protocols and adhere to the briefing standards to facilitate students' learning. The use of rigorous research designs involving a larger sample size from multiple research sites in different geographical regions is recommended for future research to examine if this problem is relevant to all nursing schools. The implications for positive social change include the potential impact of proper briefing practices in enabling ABN students to acquire clinical skills and knowledge effectively so that they can safely provide quality care to their patients.

Eustress, the positive response to stress, is a relatively understudied concept. Most of the research on eustress has been concentrated in the occupational and management setting. Empirical studies of eustress in adolescents are absent, even though youth experience unique sources and magnitudes of stress. Specifically, Advanced Placement (AP) and International Baccalaureate (IB) students report more stress than their general education peers but excel in their rigorous academic program. Eustress is related to a variety of positive psychological and physiological outcomes among adult samples, which makes it an important concept to explore in adolescent samples. Many constructs such as self-efficacy, hope, meaningfulness, flow, engagement and coping have correlated with eustress among samples of adults. This study investigated different aspects of eustress in a sample of 2379 AP and IB students (grades 9 – 12), and explored if its relationship with positive outcomes (among adults) holds true in this population. First, the psychometric properties of a modified self-report measure of eustress were examined. Results from this study supported a five-item eustress measure that had adequate reliability (α= .85) and construct validity based on a confirmatory factor analysis. Second, differences between the eustress measure in different subgroups, namely gender, grade level, and academic program were explored. Only a significant difference in eustress was found between grade levels, indicating that students in upper grade levels had higher levels of eustress. Third, relationships between eustress scores and a nomological network of theoretically similar constructs (potential correlates) and salient outcomes – indicators of students’ academic and emotional success— were examined. Consistent with previous literature, eustress had a significant positive relationship with task-focused coping, cognitive and affective engagement, self-efficacy, flow, and grit. Eustress had a negative relationship with distress and emotion-focused coping. Related to student outcomes, eustress was a significant predictor of higher levels of positive indicators of success—GPA and life satisfaction— lower levels of indicators of undesirable outcomes—school burnout and psychopathology. Implications for practitioners and future directions for research are discussed.