Submitted by Maria Medeiros (maria.dilva1@ufcg.edu.br) on 2018-10-17T13:12:41Z No. of bitstreams: 1 VERILÂNEA NEYONARA FAUSTINO LISBOA - DISSERTAÇÃO (PPGEQ) 2017.pdf: 1445004 bytes, checksum: c2f80a5d04e632d9c74d55a966dca898 (MD5) / Made available in DSpace on 2018-10-17T13:12:41Z (GMT). No. of bitstreams: 1 VERILÂNEA NEYONARA FAUSTINO LISBOA - DISSERTAÇÃO (PPGEQ) 2017.pdf: 1445004 bytes, checksum: c2f80a5d04e632d9c74d55a966dca898 (MD5) Previous issue date: 2017-11-28 / CNPq / O quiabo é um vegetal presente o ano inteiro sendo bastante consumido em diversas partes do mundo. Contudo apresenta tempo de prateleira curto gerando perdas pós-colheita. Assim a secagem constitui uma alternativa para minimizar o desperdício. Dentro dessa linha o presente trabalho tem como objetivo avaliar o efeito da secagem em temperaturas distintas sobre o teor de compostos fenólicos, atividade antioxidante e características físico-químicas do quiabo. Foi usado o secador de leito fixo com as temperaturas de 43ºC e 65ºC e uma velocidade do ar de 0,85 m/s. Todas as análises feitas no quiabo in natura foram realizadas no quiabo desidratado. Os resultados obtidos mostraram que houve uma concentração de todos os nutrientes avaliados após o processo de secagem. A aplicação de modelos empíricos resultou que o modelo de Page foi o mais adequado (R2=99,95%, SSE= 0,002 e RMSE= 0,0007) para a temperatura de 43ºC e para a temperatura de 65ºC o modelo Logarítmico forneceu melhor ajuste (R2=99,6%, SSE=0,008 e RMSE=0,020). A aplicação do modelo fenomenológico forneceu um valor de Deff = 9,16x10-8 m2/s (R2=98,5%) para a temperatura de 43ºC e um Deff = 2,16x10-7 m2/s (R2=98,2%) para 65ºC. / The okra is a vegetable present the whole year being quite consumed in several parts of the world. However, it presents short shelf life generating post-harvest losses. Thus drying is an alternative to minimize waste. Within this line the objective of this work is to evaluate the effect of drying at different temperatures on the content of phenolic compounds, antioxidant activity and physical and chemical characteristics of okra. The fixed bed drier was used with temperatures of 43ºC and 65°C and an air velocity of 0.85 m/s. All the analyzes made on okra in natura were carried out on dehydrated okra. The results showed that there was a concentration of all nutrients evaluated after the drying process. The application of empirical models showed that the Page model was the most adequate (R2 = 99.95%, SSE = 0.002 and RMSE = 0.0007) for the temperature of 43 ° C and for the temperature of 65 ° C the logarithmic model provided the best fit (R2 = 99.6%, SSE = 0.008 and RMSE = 0.020). The application of the phenomenological model yielded a Deff = 9.16x10-8 m2 / s (R2 = 98.5%) for the temperature of 43ºC and a Deff = 2,16x10-7 m2 / s (R2 = 98.2 %) to 65 ° C.

Les fibres végétales utilisées comme renfort dans les matériaux composites présentent des propriétés mécaniques spécifiques concurrentielles par rapport à celles des fibres de verre. De plus, elles ont l'avantage d'être renouvelables et recyclables. Toutefois, leur principal inconvénient est leur sensibilité à l'humidité, ce qui a pour conséquence d'induire une baisse des propriétés mécaniques ainsi d'une décohésion de l'interface fibre/matrice. L'objectif principal de cette thèse est d'étudier l'influence de l'humidité sur le comportement hygro-mécanique de fibres de lin. La première partie de mes travaux a été consacrée à la caractérisation des propriétés hygroscopiques et mécaniques de la fibre et du composite. Dans la deuxième partie, deux modèles multi-échelles, l'un analytique et l'autre numérique, ont été développés pour l'estimation des propriétés hygro-mécaniques des fibres élémentaires de lin. Ils utilisent en partie pour données d'entrée, les propriétés identifiées dans la première partie. / Natural fibres used as reinforcement in composite materials present specific mechanical properties, which are comparable to glass fibres. In addition, they have the advantage of being renewable and recyclable. But, their main drawback is their inherent susceptibility to moisture expansion, which has the effect of inducing a decrease in mechanical properties, and of debonding and fracturing interface in the composite. The main aim of this thesis is to study the influence of humidity on hygro-mechanical behavior of flax fibres. The first part of my work was deal with the characterization of mechanical and hygroscopic properties of the fibre and the composite. The second part is dedicated to the development of two multiscale models, one analytical and one numerical. They have been developed for the estimation of hygro-mechanical properties of elementary flax fibres. Properties identified in the first part of the work are used as input data.

Orientador: Julio Cesar Hadler Neto / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-26T04:48:46Z (GMT). No. of bitstreams: 1 Pereira_LucasAntoniassi_M.pdf: 1401742 bytes, checksum: e450c67acc972690e5fca996ffceb006 (MD5) Previous issue date: 2014 / Resumo: A medida da atividade de radônio (222Rn) no ar ambiental tem sido feita intensamente nas últimas quatro décadas, pelo fato de ser este o contaminante natural mais importante a que o homem está sujeito. Sabe-se que os filhos do 222Rn são os verdadeiros contaminantes a serem considerados no caso da contaminação de ambientes internos por radônio, no entanto ainda não há uma metodologia robusta para a medida passiva da concentração de atividade dos filhos no ar. Resultados anteriores do Grupo de Cronologia da Unicamp apontam que a utilização de detectores CR-39 de tamanhos reduzidos se apresentam como possível alternativa na investigação da concentração dos produtos de decaimento do 222Rn no ar. Nesse sentido, conjuntos com detectores de traços nucleares CR-39 de diversos tamanhos foram expostos no interior de ambientes fechados e de pouca ventilação, longe de qualquer superfície material. As exposições ocorreram em duas etapas: conjuntos com 6 detectores foram expostos durante cerca de 7 meses em 14 ambientes, e conjuntos com 10 detectores foram novamente expostos durante aproximadamente 5 meses em 3 destes locais. Observou-se que a densidade de traços nos detectores foi tanto maior quanto menor o tamanho do detector. Dados de densidade de traços foram ajustados utilizando-se uma equação deduzida com base no pressuposto de que o comportamento dos átomos dos filhos do radônio no ar pode ser descrito pela Lei de Fick, ou seja, o principal mecanismo de transporte dessas partículas no ar é a difusão. Considerou-se também o fenômeno da deposição (plate-out) dos filhos do radônio (livres ou ligados em aerossóis) em superfícies dos ambientes, incluindo as dos detectores. A atividade de radônio no ar foi determinada de maneira independente pela técnica do monitor NRPB/SSI. A equação resultante para a densidade de traços nos detectores das montagens expostas nos vários ambientes foi ajustada aos resultados experimentais. Observou-se, de fato, que na maioria dos ambientes pouco ventilados vale a lei de Fick, o que significa que radônio e filhos estariam em equilíbrio de atividades. Este resultado, se confirmado com mais dados experimentais, é importante por duas razões: i) porque é raro se fazer medidas conjuntas de radônio e filhos em exposições longas, e ii) porque ambientes de convívio humano pouco ventilados são comumente usados. Porém, a quantificação destes ajustes precisa ser aprimorada, tanto no que diz respeito a testes estatísticos como simulação computacional / Abstract: Radon activity in indoor environments has been intensively studied in the last four decades, probably because it is the main natural contamination to which man is subjected. It is well known that radon daughters are in fact the true contaminants. However, there is not yet a robust and accepted methodology for measuring radon progeny activity in the air passively. Previous results obtained by the Chronology Group of Unicamp show that the use of CR-39 detectors in reduced sizes may be an alternative to investigate the radon progeny concentration in the air. In this sense, sets of CR-39 nuclear track detectors of different sizes were exposed in poor ventilated indoor environments, far from any material surfaces. The exposures occurred in two steps: sets with 6 detectors were exposed during 7 months in 14 environments, and sets with 10 detectors were again exposed during approximately 5 months in 3 of these same places. It was observed that track density was as greater as smaller was the detector¿s size. Alpha particle track densities were fitted against an equation deduced based on the assumption that the behavior of radon progeny in the air was described by Fick¿s Law, i.e., the main transport mechanism of these particles was diffusion. It was also considered the deposition phenomenon (plate-out) of radon progeny (free or attached to aerosols) on environmental surfaces, including the detector themselves. Radon activity in the air was determined independently by NRPB/SSI monitor technique. The resulting equation for the track density was fitted to the experimental track densities measured on each exposed set of detectors. It was observed, indeed, that in most of the poor ventilated environments the Fick¿s law was valid under ?2 test, which means that radon and its progeny would be in equilibrium of activities. If, confirmed with more experimental data, these results are important for two reasons: i) because results of simultaneous measures of radon and progeny for long term expositions are rare, and ii) because poorly ventilated indoor environments are commonly used all over the world. However, these fittings quantification needs improvement, both regarding statistical tests and computer simulations / Mestrado / Física / Mestre em Física

Volatile substances such as perfumes, insect pheromones and volatile corrosion inhibitors can be released into the atmosphere from polymer matrices. The release characteristics of the volatile substances depend on the original concentration of the substances, and also on the type and geometry of the matrix. The design of the matrix can be done with a trial and error process involving several iterations of tool making followed by testing of the release characteristics. However, this is a costly and time-consuming method. The objective of this study is to propose and evaluate a mathematical model based on Fick's second law of diffusion. The model can be used to predict the release profiles of volatile substances from polymer matrices based on the initial volatile concentration, matrix geometry and the coefficient of diffusion of the volatile through the polymer. The alcohols I-propanol, I-butanol, I-hexanol and I-octanol and the polymer ethylene-eo-vinyl acetate (EVA) were chosen as a model system for this study. The coefficients of diffusion of all the alcohols through the EVA were determined with the time lag test using a diffusion cell and polymer sheets. Several methods of making polymer sheets were evaluated. Injection moulded disks was the most suitable method for the system under consideration. Based on the results of the time lag tests, the proposed model was used to predict the release characteristics of the different alcohols from two EVA matrix designs. Injection moulded test pieces of both designs were prepared. All the test pieces contained ca. 10% of one of the alcohols. The test pieces were aged at ambient conditions and the release of the alcohols was monitored. It was found that the proposed model gave a good prediction of the residual mass of the dispensers, never diverging more than 10% from the experimental result. The experimental results tended to show faster release than predicted. This was expected since the model does not consider the effect of concentration on the coefficient of diffusion. It was concluded that the model gave accurate predictions of the release characteristics of the system investigated. It would be a useful tool in the design and development of polymer dispensers for volatile substances. The smaller number of tool modifications and release tests required will lead to cost and time savings in the development process. / Dissertation (M Eng (Chemical Engineering))--University of Pretoria, 2006. / Chemical Engineering / unrestricted

No description available.

Karst landscapes can serve as carbon sinks when carbon dioxide (CO2) reacts with water to form carbonic acid, which then weathers carbonate rocks. However, CO2 can also move through the subsurface via gas diffusion, a process that is not well-understood in karst systems. This study focused on quantifying CO2 diffusion within a karst sinkhole. The objectives of this study were to: 1) identify the depth of the zero-flux plane (i.e., depths of local maximum CO2 concentrations), analyze the distributions of concentration gradients, and investigate the validity of a uniform concentration gradient throughout the profile; and 2) assess the influences of vertical position and seasonality on CO2 fluxes within this sinkhole. The study site contained three locations within the sinkhole, including shoulder, backslope, and toeslope locations. Each location had three soil CO2 and three soil water content/temperature sensors placed at 20, 40, and 60 cm depths. Zero-flux planes were seldom detectable during the warm season (April-September) but were frequently found near the surface (20 or 40 cm) during the cool season (October-March). The common assumption of a uniform concentration gradient was often invalid based on relative concentrations between sensor pairs. As for the second objective, CO2 fluxes generally followed a trend of upward fluxes in warmer months that was partially offset by downward fluxes during the cooler months. These study results provide new insight into CO2 dynamics in a karst system, and suggest that subsurface processes such as chemical weathering and cave ventilation affect the direction and magnitude of CO2 fluxes. / Master of Science / Carbon dioxide (CO2) within soils is a larger pool of CO2 than atmospheric CO2. Therefore, the movement of CO2 within soils is important to understand, as soil CO2 may eventually diffuse through the soil and into the atmosphere. Soil CO2 movement is dependent on many factors such as soil water content, porosity, and temperature. Soil CO2 movement may vary between landscapes as well, due to chemical weathering processes being sinks of soil and atmospheric CO2. One type of important landscape is karst, which can be identified by easily soluble rocks, usually in the forms of limestone and dolomite rocks. In order to investigate the influences of karst landscapes on the movement of soil CO2, in this study I identified the depths of CO2 maximum concentrations and CO2 movement over time and by sinkhole slope position. The results from this study were that the depth of maximum CO2 concentration was deeper, > 40 cm, during the warmer months and often shallower, ≤ 40 cm, during the cooler months. The CO2 fluxes generally followed a trend of upward fluxes in warmer months that was partially offset by downward fluxes during the cooler months. The results from this study suggest that due to vertical differences in soil properties, temperature, chemical weathering of the karst rock, and cave ventilation the depth of the maximum CO2 concentration and the CO2 movement vary by season and sinkhole slope location. This study provides new insight to CO2 movement relative to karst landscapes while highlighting the importance of soil and geologic properties as influences that can alter the direction and magnitude of CO2 fluxes.

Technological advancement has thrust MEMS design and fabrication into the forefront of modern technologies. It has become sufficiently self-sustained to allow mass production. The limiting factor which is stalling commercialization of MEMS is the packaging and device reliability. The challenging issues with MEMS packaging are application specific. The function of the package is to give the MEMS device mechanical support, protection from the environment, and electrical connection to other devices in the system. The current state of the art in MEMS packaging transcends the various packaging techniques available in the integrated circuit (IC) industry. At present the packaging of MEMS includes hermetic ceramic packaging and metal packaging with hermetic seals. For example the ADXL202 accelerometer from the Analog Devices. Study of the packaging methods and costs show that both of these methods of packaging are expensive and not needed for majority of MEMS applications. Due to this the cost of current MEMS packaging is relatively high, as much as 90% of the finished product. Reducing the cost is therefore of the prime concern. This Thesis explores the possibility of an inexpensive plastic package for MEMS sensors like accelerometers, optical MEMS, blood pressure sensors etc. Due to their cost effective techniques, plastic packaging already dominates the IC industry. They cost less, weigh less, and their size is small. However, porous nature of molding materials allows penetration of moisture into the package. The Thesis includes an extensive study of the plastic packaging and characterization of three different plastic package samples. Polymeric materials warp upon absorbing moisture, generating hygroscopic stresses. Hygroscopic stresses in the package add to the thermal stress due to high reflow temperature. Despite this, hygroscopic characteristics of the plastic package have been largely ignored. To facilitate understanding of the moisture absorption, an analytical model is presented in this Thesis. Also, an empirical model presents, in this Thesis, the parameters affecting moisture ingress. This information is important to determine the moisture content at a specific time, which would help in assessing reliability of the package. Moisture absorption is modeled using the single phase absorption theory, which assumes that moisture diffusion occurs freely without any bonding with the resin. This theory is based on the Fick's Law of diffusion, which considers that the driving force of diffusion is the water concentration gradient. A finite difference simulation of one-dimensional moisture diffusion using the Crank-Nicolson implicit formula is presented. Moisture retention causes swelling of compounds which, in turn, leads to warpage. The warpage induces hygroscopic stresses. These stresses can further limit the performance of the MEMS sensors. This Thesis also presents a non invasive methodology to characterize a plastic package. The warpage deformations of the package are measured using Optoelectronic holography (OEH) methodology. The OEH methodology is noninvasive, remote, and provides results in full-field-of-view. Using the quantitative results of OEH measurements of deformations of a plastic package, pressure build up can be calculated and employed to assess the reliability of the package.

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

As estruturas de concreto armado são um dos tipos de estrutura mais utilizados no mundo e quando localizadas em ambientes não agressivos, respeitam a vida útil para a qual foram projetadas. Entretanto, a durabilidade dessas estruturas pode ser fortemente reduzida por processos de degradação de origens ambientais e/ou funcionais. Dentre esses processos, destacam-se aqueles que desencadeiam a corrosão das armaduras, sendo a difusão de cloretos um dos fatores de maior importância no desencadeamento do processo corrosivo. Apesar da robustez de diversos modelos propostos na literatura, abordagens determinísticas frequentemente falham ao prever o tempo de início da corrosão devido à enorme e à inerente aleatoriedade envolvida nesse processo. Neste contexto, a durabilidade pode ser mais realisticamente representada por meio de modelos probabilísticos. Este trabalho apresenta uma formulação numérica, baseada no Método dos Elementos Finitos (MEF), para a determinação de cenários de falha de vigas de concreto armado submetidas à penetração de cloretos. Nessa formulação, a não linearidade física do concreto é descrita pelo modelo de dano de Mazars e a variação da concentração de cloretos no interior do concreto é determinada por meio da segunda lei de Fick. Além disso, as leis de corrosão de Faraday são adotadas para a determinação da taxa de redução das áreas de aço ao longo do tempo. A partir das cargas de colapso calculadas pelo modelo mecânico, as probabilidades de falha são determinadas utilizando o algoritmo de confiabilidade FORM. Os resultados obtidos mostram a influência da corrosão na segurança estrutural de estruturas de concreto armado ao longo do tempo, assim como, seu impacto na durabilidade dessas estruturas. / Reinforced concrete structures are one of the most commonly used types of structures in the world and when these structures respects the structural life predicted when it is located in non-aggressive environments. However, the durability of these structures can be strongly reduced by degradation processes caused by environmental and/or functional origins. Among these processes, those related to reinforcement\'s corrosion are more outstanding, being the chloride diffusion one of most important factors that triggers the corrosion process. Despite the robustness of several models proposed in literature, deterministic approaches often fail to predict the time of corrosion initiation due to the huge inherent randomness involved in the process itself. In this context, the durability can be more realistically represented by probabilistic models. This work presents a numerical formulation based on the Finite Element Method (FEM) to determine the failure configuration of reinforced concrete beams subjected to chloride penetration. In this formulation, the non-linearity of the concrete is described by Mazars damage model and the variation of chloride concentration along concrete cover is determined by Fick\'s second law. Moreover, Faraday\'s law concerning corrosion is adopted in order to determine the reduction rate of steel areas over a period of time. The probabilities of failure are determined using the reliability algorithm FORM, which accounts the collapse Sloads calculated by the mechanical model. The results showed the influence of corrosion phenomenon on the structural safety of reinforced concrete along time as well as its impact on the structural durability.

O presente estudo trata do problema da corrosão de armaduras em estruturas de concreto armado submetidas à penetração de cloretos. É amplamente reconhecido nos meios técnico e científico que, dentre os diversos processos causadores de patologias nas estruturas de concreto armado, destacam-se aqueles que desencadeiam a corrosão das armaduras. O processo de corrosão é iniciado quando a concentração de cloretos na interface armadura/concreto atinge um valor limite, despassivando a camada química protetora ao redor da armadura. A utilização de uma abordagem probabilística é capaz de tratar o problema de forma mais consistente, uma vez que as variáveis envolvidas no fenômeno possuem um alto grau de aleatoriedade associado. A formulação utilizada para a análise não linear mecânica emprega o método dos elementos finitos, utilizando o modelo de dano de Mazars para descrever o comportamento do concreto e o modelo elastoplástico para descrever o comportamento do aço. A lei de Fick é empregada para descrever o mecanismo de difusão dos íons cloretos no interior dos elementos de concreto armado e leis empíricas são utilizadas para representar a penalização das áreas de aço das armaduras bem como a redução de sua tensão de escoamento. A formulação utilizada para a análise probabilística emprega o FORM (First Order Reliability Method), o método de superfície de resposta e a simulação de Monte Carlo. Enfoque especial é dado na análise de estruturas hiperestáticas, com o objetivo de determinar a probabilidade de falha do sistema, sendo esta uma das contribuições desse estudo. Os resultados obtidos indicam de que forma os efeitos corrosivos considerados contribuem para a redução da durabilidade estrutural. / This work deals with the problem of reinforcement corrosion of concrete structures subjected to chloride penetration. It is widely recognized in the technical and scientific communities that, among the different processes which cause pathologies in reinforced concrete structures, reinforcement corrosion is one of the most relevant. The corrosion process starts when chloride concentration at the reinforcement/concrete interface reaches a threshold value, causing depassivation of the protecting chemical layer surrounding the armor. A probabilistic approach is capable of dealing with the problem in a more consistent manner, since the variables involved in the phenomenon have a high degree of randomness. The formulation used in the mechanical non-linear analysis utilizes the finite element method, employing Mazars\' damage model to describe the concrete behavior and the elastoplastic model to describe the steel behavior. Fick\'s law is used to describe the diffusion mechanism of chloride ions inside the concrete elements and empirical laws are used to represent the steel area reduction as well as the reduction of steel yield stress. The formulation used for the probabilistic analysis employs the FORM (First Order Reliability Method), the response surface method and the Monte Carlo simulation. A contribution of this study concerns the analysis of hyper-static structures, in order to evaluate the failure probability of the system, giving special attention to this type of problem. The obtained results show how the considered corrosive effects influences the structural durability reduction.