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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

Characterization of Forest Harvest Residue from the Great Lakes-St Lawrence Forests of South-eastern Ontario

Acquah, Gifty Ewurama 14 December 2010 (has links)
The use of fossil derived products and the environmental and economic problems associated with them have made a shift to abundant renewable resources such as forest biomass more attractive. However before forest biomass can be used as a resource, its properties must be known. This study determined the physical properties of heterogeneous biomass residues produced during harvesting on two operational forest sites within the Great Lakes-St Lawrence forest of south-eastern Ontario. Properties measured were moisture content, size distribution, bulk density, and wood-to-bark ratio; also thermo-chemical properties including elemental composition, thermal reactivity and energy content were measured. The effects of forest site and harvest type, storage and position in storage pile, on the properties of biomass were also investigated. Results of the study showed that the various heterogeneous forest harvest residues differed more physically than thermo-chemically for the different variables, and this affected biomass procurement more than the potential utilization options.
412

High Performance Steel for Percussive Drilling

Åkerlund, Elin, Havo, Rebecka, Jonsson Åberg, Jakob, Österberg, Patrik, Fredriksson, Mikael January 2017 (has links)
Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched.  The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.
413

High Performance Steel for Percussive Drilling

Åkerlund, Elin, Jonsson Åberg, Jakob, Österberg, Patrik, Havo, Rebecka, Fredriksson, Mikael January 2017 (has links)
Atlas Copco Secoroc AB are searching after new bulk materials for drill heads that are used in percussive drilling in order to improve their strength and durability. The aim of this project is to assist Atlas Copco in this search and provide them with further information regarding material properties, alloying elements, suppliers, etc. A literary study was carried out in order to identify materials that had UTS and KIC more than or equal to 1700 MPa and 70 MPa*m^1/2, respectively. Materials that fulfilled these criteria were T250 grade maraging steel, Cobalt free maraging steel, High cobalt maraging steel, 300 grade maraging steel, AerMet 100, AF1410, S53, M54, 300M, 4340M and PremoMet. These were categorized into maraging steels, high alloy secondary hardened steels, and low alloy steels, and were then further researched. The material with the highest combination of UTS and KIC was M54 followed by AerMet 100; while AF1410 had the highest KIC but a low UTS, and PremoMet had the highest UTS but a low KIC. Maraging steels and HASH steels have a similar price range, while low alloy steels are much cheaper.
414

Etude de la transparence de greffons cornéens humains : imagerie OCT, analyse par diffusion et modélisation électromagnétique / Study of transparency loss in human corneal grafts : OCT, light scattering measurement and electromagnetic modelling

Casadessus, Olivier 07 December 2012 (has links)
Prolongement central de la sclère, la cornée est la couche la plus externe de l'œil. Elle laisser pénétrer la lumière dans le globe oculaire grâce à sa propriété de transparence. Cette transparence repose sur une structure très organisée du tissu, maintenue en équilibre physiologique. Lorsque cet équilibre est rompu, notamment suite à une augmentation anormale de son taux d'hydratation et au développement d'un œdème, l'épaisseur du tissu augmente et il tend à s'opacifier. Lorsque l'œdème devient trop important, il est nécessaire de procéder à une greffe. Les cornées destinées à la greffe sont triées dans des banques de tissus, et sont en particulier soumises à une évaluation qualitative de leur transparence. Cette thèse s'inscrit dans le cadre d'un projet visant à étudier les propriétés de diffusion de greffons cornéens humains, afin d'améliorer l'évaluation quantitative de leur transparence en banque des tissus ou de mieux paramétrer les lasers de découpe lors des greffes de cornées, dont les performances sont altérées à cause du phénomène de diffusion. Le comportement diffusant de la cornée est mesuré dans l'espace réfléchi, afin d'évaluer à terme la possibilité d'une caractérisation in vivo. Conjointement à la mesure de diffusion, une imagerie du volume de la cornée est réalisée grâce à un dispositif de tomographie de cohérence optique apportant une caractérisation de la structure microscopique du tissu. L'œdème et son développement sont ainsi caractérisés par l'analyse de la diffusion du tissu, de sa transparence et des hétérogénéités à l'échelle du micron. / Along with the crystalline lens, the cornea is the unique tissue being transparent in the human body. With a transmission coefficient over 90% in the visible spectrum, the main function of the cornea is to transmit the light inside the eye. This property is due to an absence of blood vessels and a very regular organization of the corneal bulk. In the case of an edema development, the cornea swells because of an abnormally high hydration. This involves a disorganization of its internal structure and an increase of the light scattering, leading to cornea haziness. When the edema is too critical, a graft is then required. In tissue banks, several criteria, such as the evaluation of the transparency, are considered in order to choose only the tissues eligible for corneal transplantation. This thesis aims to study the scattering properties of human corneal grafts in order to improve transparency evaluation in tissue banks or to lead to a better calibration of laser cuts during surgery procedure. A characterization of the scattering properties of the tissues is performed in the reflective half-space. Indeed, backscattering characterization could be used in in-situ conditions. Moreover, 3D images of the bulk of the cornea are performed using a Optical Coherence Tomography set-up. Edema developement is studied through the analysis of the scattering behaviour and of the microscopic structure of the graft. Scattering properties and microstructure are linked together through the use of an electromagnetic modelling. Maxwell's equations are solved using Born approximation, and a numerical method was adapted to perform those calculations in the case of the cornea.
415

Operação de carga-rápida (bulk-loading) em métodos de acesso métricos / Bulk-loading Dynamic Metric Acess Methods

Vespa, Thiago Galbiatti 10 December 2007 (has links)
O grau de similaridade entre elementos de dados é o fator primordial para a recuperação de informações em Sistemas Gerenciadores de Bases de Dados que manipulam dados complexos, como seqüências genéticas, séries temporais e dados multimídia (imagens, áudios, vídeos, textos longos). Para responder a essas consultas em um tempo reduzido, faz-se necessário utilizar métodos que usam métricas para avaliar a similaridade entre os elementos. Esses métodos são conhecidos como Métodos de Acesso Métricos. Dentre os mais conhecidos na literatura estão a M-tree e a Slim-tree. Existem duas maneiras de executar as operações de construção de índices em qualquer método de acesso: inserindo elemento a elemento ou usando a operação de carga-rápida (bulk-loading). O primeiro tipo de construção é comum e necessário para todo tipo de método de indexação dinâmico. Já as operações de carga-rápida são utilizadas para conjuntos de dados maiores, como por exemplo, na recuperação de backups em bases de dados ou na criação posterior de índices. Nessas situações, a inserção individual tende a ser mais demorada. Realizar uma carga-rápida possibilita a construção de índices com melhor eficiência e em menor tempo, pois há a disponibilidade de todos os dados no instante da criação da estrutura de índices, possibilitando explorar as propriedades do conjunto como um todo. Os Sistemas Gerenciadores de Base de Dados oferecem operações de carga-rápida dos dados nos métodos tradicionais, as quais devem ser supridas também nos Métodos de Acesso Métricos. Neste trabalho, são apresentadas três abordagens, uma técnica para carga-rápida dos dados em Métodos de Acesso Métricos e foi desenvolvido um algoritmo baseado nessa técnica para construir uma Slim-tree. Este é o primeiro algoritmo de carga-rápida baseada em amostragem que sempre produz uma Slim-tree válida, portanto é o primeiro descrito na literatura que pode ser incluído em um Sistema Gerenciador de Base de Dados. Os experimentos descritos neste trabalho mostram que o algoritmo proposto mantém bom agrupamento dos dados e supera o desempenho dos métodos de inserção seqüencial levando em conta tanto o desempenho de construção quanto à eficiência para realizar consultas / The similarity degree between data elements is the primordial factor for information retrieval in databases that handle complex data, such as genetic sequences, time series and multimedia objects (long images, audio, videos, texts). To answer these queries in a reduced time, it is necessary methods that use metrics to evaluate the similarity between elements. These methods are known as Metric Access Methods. The most known Metric Access Methods in the literature are the M-tree and the Slim-tree. There are two ways to build index in any access method: inserting element one by one or using the bulk-load operation. The first build type is very common and required for all kinds of dynamic access methods. The bulk-load operations are used for bigger datasets, as for example, in the recovery of backups and re-creation of database indexes. In these situations, the individual insertion takes much time. The bulk-load operation makes it possible to construct indexes more efficiently and faster, because it has the availability of the whole data when the index structure are created, and thus, it is possible to explore the properties of the whole set. Database Management Systems offer bulk-load operations for the traditional methods, so it is important that they can be also supplied for Metric Access Methods. This work presents three bulk-loading approaches and it proposes a technique to bulk-load data into Metric Access Methods. An algorithm based on this technique was developed to construct a Slim-tree. This is the first bulk-load algorithm based on sampling that always produces a valid Slim-tree, therefore is the first one described in literature that can be enclosed in a Database Management System. The experiments show that this algorithm keeps good clustering of data and in such a way that it surpasses the performance of sequential insertion, taking into account the construction performance and the efficiency to perform queries
416

Análise térmica da influência do oxigênio na amorfização de ligas baseadas em Cu-Zr / Thermal analysis of oxygen influence on the amorphization of Cu-Zr-based alloys

Santa Maria, Felipe Henrique 19 February 2018 (has links)
Os vidros metálicos baseados em Cu-Zr representam uma classe bastante promissora para a categoria de materiais estruturais, tendo em vista suas interessantes propriedades resultantes da natureza amorfa. Sabe-se que o oxigênio tem grande influência na formação da estrutura amorfa e consequentemente nas propriedades dessa classe de materiais. No presente trabalho, ligas amorfas baseadas em Cu-Zr foram analisadas termicamente a fim de se observar o comportamento das mesmas frente à contaminação com oxigênio. As análises térmicas foram realizadas em um equipamento de calorimetria exploratória diferencial (DSC), e as temperaturas características como de transição vítrea, cristalização, fusão e líquidus foram determinadas. Concluiu-se que conforme a literatura apresenta, o processo de cristalização é favorecido pela presença de oxigênio, causando uma queda na energia de ativação dos processos de cristalização das ligas trabalhadas. Através de ensaios que simularam tratamentos térmicos, cristalizou-se controladamente as amostras amorfas baseadas em Cu-Zr a fim de formar compósitos entre cristais e vidros metálicos buscando diminuir a fragilidade das ligas. / Cu-Zr-based bulk metallic glasses represent a very promising class of structural materials with interesting properties resulting from the amorphous nature. It is known that oxygen has a great influence on the formation of the amorphous structure and consequently on the properties of these materials. In the present work, Cu-Zr-based amorphous alloys were thermally analyzed in order to observe their behavior against oxygen contamination. Thermal analyzis were performed on a differential scanning calorimetry (DSC) equipment, and characteristic temperatures as glass transition, crystallization, melting and liquidus were determined. It was concluded that, according to the literature, the crystallization process is favored by the presence of oxygen, causing a decrease in the activation energy of the crystallization processes of the worked alloys. Through tests that simulated heat treatments, the amorphous samples were crystallized in order to form composites between crystals and metallic glasses in order to reduce the brittleness of the alloys.
417

Detecção e contagem de Streptococcus agalactiae em leite bovino pela reação em cadeia da polimerase / Detection and counting of Streptococcus agalactiae in bovine milk by polymerase chain reaction

Carvalho, Nara Ladeira de 31 July 2013 (has links)
O objetivo do presente estudo foi: a) comparar dois métodos de detecção e contagem de S. agalactiae, (cultura microbiológica e qPCR) em leite de vacas e de tanques; b) determinar a sensibilidade analítica e a repetibilidade do diagnóstico por qPCR em relação à cultura microbiológica para detecção de S. agalactiae em amostras compostas de leite de vaca e de tanque. Foram utilizadas amostras de leite de vaca (n=31) e de tanque (n=150), as quais foram submetidas à cultura microbiológica e contagem de S. agalactiae por cultura de microbiologia convencional e qPCR. Para avaliar a sensibilidade analítica, foi construída uma curva padrão com amostras de leite desnatado reconstituído estéril contaminado artificialmente com S. agalactiae (ATCC 13813). Em apenas duas amostras não foi possível amplificação de DNA, o que indica que a qPCR foi capaz de detectar S. agalactiae, em 96% e 97%, do leite de vaca e de tanque, respectivamente. Embora a técnica qPCR tenha apresentado alta sensibilidade analítica, não houve equivalência de resultados de contagem S. agalactiae entre os dois métodos propostos. Os coeficientes de variação interensaio utilizados para avaliar a técnica qPCR foram < 5%, o que demonstra que a técnica possui repetibilidade adequada. Portanto, não houve equivalência entre a contagem de S. agalactiae por cultura microbiológica padrão e a técnica de qPCR, provavelmente pela alta sensibilidade da técnica qPCR em quantificar DNA de células inviáveis. No entanto, a qPCR apresentou-se como uma técnica sensível para identificação de S. agalactiae em amostras de leite de vaca e de taque. / The aim of this study was to: a) to compare two methods of detection and enumeration of S. agalactiae (microbiological culture and qPCR) in cow`s milk and bulk tank milks, b) to determine the analytical sensitivity and repeatability of the diagnosis by qPCR in relation to microbiological culture for detection of S. agalactiae on composite samples of cow\'s milk and bulk tank milk. Samples of cow\'s milk (n = 31) and bulk tank milk (n = 150), which were submitted to microbiological culture and enumeration of S. agalactiae by conventional microbiology culture and qPCR. To evaluate the analytical sensitivity, a standard curve was made with samples of sterile reconstituted skim milk artificially contaminated with S. agalactiae (ATCC - 13813). In two samples was not possible the amplification of DNA, indicating that qPCR was able to detect S. agalactiae, 96% and 97% cow\'s milk and bulk tank milk, respectively. Although the technique has presented qPCR high analytical sensitivity, there was no equivalent result of counting S. agalactiae between the two proposed methods. The interassay coefficients of variation technique used to evaluate the qPCR were <5%, which demonstrate that the technique has adequate repeatability. So there was no equivalence between the counts of S. agalactiae by standard microbiological culture and qPCR technique, probably due to the high sensitivity of qPCR technique to quantify DNA of unviable cells. However, the qPCR presented as a sensitive technique for identifying S. agalactiae in samples of cow\'s milk and bulk tank milk.
418

Influência do processo de secagem por pulverização mecânica (spray dryer) no tamanho de partícula e densidade aparente do café solúvel. / The influence of the mechanical spray drying process on particle size and bulk density of instant coffee.

Esteves, Bruno Neves 27 November 2006 (has links)
O Brasil é um grande produtor e consumidor de café. A bebida é a segunda mais consumida no país. O café solúvel é uma alternativa para o consumo diário visto que dispensa todo aparato de preparo da bebida, sendo necessária apenas água quente. O tamanho de partícula seca está diretamente ligado à densidade aparente do produto. Foram realizados testes de secagem de extrato de café em spray-dryer com atomização por disco rotativo e fluxo co-corrente variando-se a temperatura do ar de entrada (140 - 170 °C) e rotação do disco atomizador (27000 - 33000 rpm). A análise de tamanho de partícula mostrou tendência de partículas maiores quanto menor a temperatura de secagem (26 - 36 µm). Notou-se a influência tanto da temperatura quanto da rotação do disco atomizador na análise da atividade de água. A densidade aparente não se mostrou significativamente alterada pelos parâmetros estudados nos experimentos. / Brazil is a big producer and consumer of coffee. The drink is the second most consumed in the country. Instant coffee is an alternative for daily consumption since it dispenses with all the apparatuses for preparing the drink, being necessary only hot water. The dry particle size is directly related to the bulk density of the product. Coffee extract drying tests were made in a co-current flow spray-dryer with atomization by disc with a varying inlet air temperature (140 - 170 °C) and disc velocity (27000 - 33000 rpm). The particle size analysis has shown the tendency for bigger particles to form at lower drying temperatures (26 - 36 µm). The influence of inlet air temperature and the atomizer disc spin velocity were noted in water activity analysis. The bulk density was not significantly modified by the parameters studied in the experiments.
419

Análise da influência da massa específica de agregados graúdos provenientes de resíduos de construção e demolição no desempenho mecânico do concreto. / Analyses of the influence of construction and demolition waste coarse aggregate porosity on the mechanical performance of concrete.

Carrijo, Priscila Meireles 16 March 2005 (has links)
Em virtude de muitas dúvidas ainda existentes, referentes ao desempenho e durabilidade dos concretos com agregados de RCD reciclados, sua utilização até o momento é limitada, não chegando aos níveis desejáveis e necessários. Somam-se a essas, a falta de gestão, de ferramentas de controle de qualidade, de normalização e de melhoria nas operações unitárias de beneficiamento do RCD. Os agregados reciclados apresentam características físicas e comportamento bastante heterogêneo, o que dificulta sua utilização com confiabilidade, principalmente em situações que demandam um maior controle e responsabilidade por parte do material empregado, como no caso de concretos estruturais. A porosidade e absorção dos agregados reciclados influenciam, de maneira significativa, as propriedades do concreto fresco e endurecido. Mesmo que estes sejam separados por fases (concreto, argamassa e cerâmica), é possível encontrar porosidades variadas dentro de uma mesma fase. Portanto, não se pode afirmar que o comportamento de concretos com agregados de mesma fase será homogêneo. Por este motivo, para esta pesquisa os agregados reciclados vermelho (predominância visual de cerâmica vermelha) e cinza (predominância visual de materiais cimentícios) foram separados em quatro faixas de densidade (d<1,9; 1,9<d<2,2; 2,2<d<2,5; d>2,5 g/cm³). Foram analisados os resultados de resistência à compressão, módulo de elasticidade, absorção de água, índice de vazios, massa específica e consumo de cimento. Os resultados obtidos nos ensaios de avaliação das propriedades físicas e mecânicas dos concretos usando agregados vermelho e cinza e concretos com agregados convencionais foram analisados para quantificar a influência da porosidade dos agregados. Verificou-se que a influência da natureza mineralógica dos agregados (vermelho ou cinza) influenciou as propriedades de maneira menos intensa que sua porosidade. Além disso, os concretos produzidos com RCD de densidade inferior a 2,2 g/cm3 apresentaram menor resistência e módulo e maior absorção de água, tornando o concreto muito menos eficiente para aplicações estruturais. A separação dos agregados em faixas de densidade garantiu um comportamento bastante homogêneo dos concretos, quando se utilizou agregados da mesma faixa. Com isso, foi possível estabelecer uma correlação entre a porosidade dos agregados e o desempenho mecânico dos concretos. A separação por faixas de densidade se mostrou como um critério confiável de classificação e caracterização dos agregados para a fabricação de concretos, podendo ser utilizado em conjunto com a separação visual normalmente empregada. / Construction and Demolition Waste (CDW) aggregates have not yet been widely used in concrete applications due to the many doubts relating to its performance and durability. The lack of an appropriate CDW recycling management, standardization, an innovative process technology as well as faster, cheaper and accurate quality control techniques also limits the use of this material. The reliable use of recycled CDW aggregates, especially in major situations such as in structural concrete, is still difficult due to its heterogeneous physical characteristics and behavior. Fresh and hard concrete properties are significantly influenced by recycled aggregate porosity and water absorption. Even if aggregates are separated in phases by hand sorting (concrete, mortar and ceramics) it is possible to find different porosities within the same phase and, for that reason, concretes will also present heterogeneous behavior. In this direction, the two types of recycled aggregates used in this research – named red (mainly constituted of red ceramics) and grey (mainly constituted of cimenticious materials) – were separated in four density classes (d<1.9; 1.9<d<2.2; 2.2<d<2.5; d>2.5 g/cm³). The compressive strength, elastic modulus, water absorption, specific weight and cement consumption of concretes were analyzed. The mechanical and physical properties of concretes were studied in terms of the recycled aggregate porosity and comparisons of results obtained with concretes using red or grey recycled aggregates and with ordinary aggregates were carried out. It was verified that the concretes properties were mostly influenced by the aggregates porosity when compared to its phase. Recycled aggregates with bulk specific gravity under 2.2 g/cm3 provided a significant reduction of the compressive strength and the elastic modulus and an increase of water absorption, producing concretes less efficient for structural applications. The behaviour of concretes produced by aggregates within the same density class was found to be homogeneous. A relation between porosity of aggregates and mechanical performance of concrete was verified. The heavy media separation can be used, together with the hand sorting, as an efficient and reliable aggregate quality control method for the production of concretes.
420

Motivators and barriers of bulkfood store customers : An examination through the application of the Theory of Planned Behavior

Valerius, Julian, Wolf, Niklas January 2019 (has links)
The pollution of the oceans through plastics has received global wide media coverageover the last years. Also, micro-plastics in ground water and even in fish had beendetected, which leads to increased awareness of waste-reduction. Since the beginning ofthis decade, more bulk food stores open in Germany’s cities and provide an alternative toconventional, packaged products.Plastics and so-called micro-plastics have been found in the bodies of seabirds and in fish.There is an imminent danger of plastics ending up in the human bodies while it travels upthe food chain.In order to reduce their impact on the environment, an increasing number of customersengages in the zero-waste movement. To reduce single-use plastics, customers can shoptheir groceries in bulk-food stores, which allow shopping loose goods from largecontainers in contrast to individually packed items in regular supermarkets. Customerscan bring their own reusable packaging to buy mostly dry foods such as vegetables, pasta,nuts, grains but also some liquids such as oil, honey etc. The stores often also include anon-food section where additional consumable products can be bought.The paper identified a research gap in regards the store concept of bulk-stores which isan emerging trend in Germany since 2014.This thesis analyzes the motivators of bulk-food store shoppers in Germany based on anadapted version of the Theory of Planned Behavior by Izek Ajzen. The frameworkthereby builds upon research conducted by Maloney et al. (2014) who tested motivatorsof organic clothing customers.The research identified a significant positive influence of the Personal Norm and asignificant negative correlation between Perceived Expensiveness on the PurchaseIntention of the customers.The main barriers for bulk food shoppers were identified as the distance to the next store,the product portfolio and perceived high prices. Other issues have been discovered butwere – in comparison –only of secondary relevance.The paper contributes to closing the gap in literature between bulk foods and othersustainability-related topics, such as organic products and their production. Furthermore,it provides a foundation for future research on the topic.

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