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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.
251

Operating correction factor of PV system : Effects of temperature, angle of incidence and invertor in PV system performance

Lopez Ramirez, Izar January 2017 (has links)
In this project, the correction factor of different solar panels of the laboratory of the University of Gävle, located in Sweden, is going to evaluated. The solar modules’working conditions are different from the ones used to test them in the laboratory. In the laboratory. the output energy of the modules is less than in working conditions,and therefore a correction factor is going to be calculated from the data collected, inorder to describe the factors that affect the performance of the solar modules.Also, the obtained correction factor validity for different PV systems it is going to be examined, determining which system has a better correction factor and the energy losses due to temperature, angle of incidence and micro invertor.
252

Premelting Study of Nickel Nanorod Arrays

Alrashid, Ebtihaj, Jr. 01 May 2013 (has links)
In this study, samples of nanoscale structures of nickel (Ni) nanorods were prepared using the glancing angle deposition (GLAD) technique. Annealing was done using a split- top tube furnace at high vacuum chamber pressure. The pre-melting of the nanorods was maintained at 500 °C for 30 minutes in all the samples. Using the samples with 90 minutes of GLAD time, the annealing behavior of the nanorods was studied at 300 °C, 400 °C, 500 °C and 600 °C. The nanorods were then imaged using scanning electron microscopy. Using X-ray diffraction, the crystalline microstructures of the nanorods were studied. It was found that with increasing annealing temperatures, the intensity of peaks for both Ni (111) and Ni (200) increased, which indicates that better crystals were formed. The results indicate that re-crystallization occurs after annealing, leading to the formation of larger grain sizes compared to as-deposited grain sizes. Annealing substantially changed the structure of the nanorods, leading to different smoother, more connected crystal structures for the annealed nanorods compared to as-deposited ones.
253

CAPILLARITY AND TWO-PHASE FLUID TRANSPORT IN MEDIA WITH FIBERS OF DISSIMILAR PROPERTIES

Bucher, Thomas M, Jr. 01 January 2014 (has links)
Capillarity is a physical phenomenon that acts as a driving force in the displacement of one fluid by another within a porous medium. This mechanism operates on the micro and nanoscale, and is responsible for countless observable events. This can include applications such as absorption in various hygiene products, self-cleaning surfaces such as water beading up and rolling off a specially-coated windshield, anti-icing, and water management in fuel cells, among many others. The most significant research into capillarity has occurred within the last century or so. Traditional formulations for fluid absorption include the Lucas–Washburn model for porous media, which is a 1-D model that reduces a porous medium to a series of capillary tubes of some educated equivalent radius. The Richards equation allows for modeling fluid saturation as a function of time and space, but requires additional information on capillary pressure as a function of saturation (pc(S)) in order to solve for absorption. In both approaches, the surface can only possess one fluid affinity. This thesis focuses on developing capillary models necessary for predicting fluid absorption and repulsion in fibrous media. Some of the work entails utilizing approximations based on pore space available to the fluid, which allows for capillary pressure simulation in media with arbitrary fiber orientation. This thesis also presents models for tracking the fluid interface in fibrous media and coatings with simpler geometries such as horizontally and vertically aligned fibers and orthogonal fiber layers. This method hinges on solving for the true fluid interface shape between the fibers based on the balance of forces across it, ensuring the accurate location and total content of fluid in the medium, and therefore accurate pc(S). Using this approach also allows, for the first time, fibers of different fluid affinities to exist in the same structure, to examine their combined influence on fluid behavior. The models in this thesis focus mainly on absorbent fabrics and superhydrophobic coatings, but can be easily expanded for use in other applications such as water filtration from fuel, fluid transport and storage in microchannels, polymer impregnation in fiber-reinforced composite materials, among countless others.
254

DEVELOPMENT OF MAGNETIC FABRICS WITH TUNABLE HYDROPHOBICITY

Ho, Thu 27 July 2012 (has links)
Polystyrene (PS) fiber mats incorporating iron (Fe) particles were fabricated by electrospinning and the hydrophobicity of the resulting magnetic fabrics was investigated with and without an applied magnetic field. The results show that the hydrophobicity (as measured using water droplet contact angle) increases in the presence of a magnetic field and the hysterisis in the advancing/receding contact angle (a measure of the stickiness of the surface) decreases in the presence of a magnetic field. It is also shown that the contact angle and hysterises increase with decreasing fiber diameter and mat thickness.
255

Stable tearing characterization of three materials with three methods

Johnston, Elizabeth Nicole January 1900 (has links)
Master of Science / Department of Mechanical and Nuclear Engineering / Kevin Lease / Over the past several years the crack tip opening angle (CTOA) has been identified as one of the key fracture parameters to characterize low constraint stable tearing and instability in structural metallic alloys. This document presents the results of experimental stable tearing characterizations. Characterization methods include optical microscopy and marker band measurements of crack front tunneling. Specific attention is given to the measurement methods used, and also the correlation between CTOA and Delta-5. The effect of tunneling and comparisons with computational results are discussed, and the effect of material and measurement method on CTOA is observed and a clear relationship is seen. Preliminary work on future studies into internal features and behavior is also presented.
256

Durability of Superhydrophobic Coatings - Sand Abrasion Test

Holmberg, Max, Harlin, Hugo January 2016 (has links)
The interest in superhydrophobic coatings have increased exponentially in the recentdecades due to their potential and versatility in their applications. The use forsuperhydrophobic surfaces range from water repellent fabric, to self cleaning surfacesand numerous applications in industry. In this project the durability of 6 differentsuperhydrophobic coatings have been examined. The durability was tested bydropping sand on the surfaces from a set hight of 10 cm and a flow of 40 g/min. Thesurfaces were mounted on a 45° angle. The surfaces were abraded for 30 seconds ata time and the static, receding, and advancing contact angles along with the roll-ofangle was measured. Five of the surfaces were built up with nano particles and onewas sand blasted and anodized to create a superhydrophobic structure. The surfacesthat withstood the most abrasion was the surface that had been calcined to improveadhesion and the surface that had been sand blasted and anodized. Measurementsshowed that the roll-off angle and the receding contact angle were the two bestindicators of the deterioration of a surface, while the static contact angle and theadvancing contact angle varied little with abrasion. The project was done at thecompany Technical Research Institute of Sweden (SP) at their chemistry, surfaces andmaterials department in Stockholm. All coatings and equipment was supplied by SP.
257

Avaliação da posição condilar e disfunção temporomandibular em pacientes com má oclusão de classe II submetidos a protusão mandibular ortopédica

Conti, Ana Claudia de Castro Ferreira 25 May 2004 (has links)
O objetivo deste trabalho foi avaliar a articipação da protrusão mandibular ortopédica e da posição condilar na prevalência de sinais e sintomas de disfunção temporomandibular (DTM). A amostra foi composta por 60 indivíduos divididos proporcionalmente em três grupos. O grupo I foi constituído por jovens indicados para tratamento da má oclusão de Classe II, com o aparelho Bionator, e o grupo II foi composto por jovens avaliados durante o tratamento com o aparelho Bionator. Pacientes já submetidos à terapia com o mesmo tipo de aparelho formaram o grupo III. Um questionário relativo aos principais sintomas de DTM permitiu a elaboração de um índice anamnésico, objetivando classificar a amostra de acordo com a presença e severidade dessas disfunções. Foi realizado exame de palpação dos músculos mastigatórios e cervicais, e da articulação temporomandibular (ATM), além de detecção de ruídos articulares e análise da movimentação mandibular. Radiografias transcranianas padronizadas das ATMs direita e esquerda foram executadas com a boca fechada e abertura máxima. Os espaços articulares anterior e posterior foram mensurados nas radiografias digitalizadas, para obtenção do grau de concentricidade condilar. ANOVA a um critério, teste de Kruskal-Wallis e qui-quadrado foram utilizados para análise dos dados. De acordo com os resultados do questionário anamnésico, 66,67% da amostra foram classificados com ausência de DTM, 30% com DTM leve e apenas 3,33% com DTM moderada, sem diferença entre os grupos estudados (p> 0,05). Quanto à concentricidade condilar, o grupo II apresentou os valores de menor concentricidade (côndilos mais anteriorizados), com diferença estatisticamente significante em relação ao grupo I (p< 0,05). Uma associação entre a concentricidade condilar e a prevalência de DTM, no entanto, não foi encontrada. Concluiu-se que a protrusão ortopédica, apesar de alterar a posição dos côndilos, não aumentou a prevalência de DTM na população estudada. / The aim of this study was to evaluate the possible effects of orthopedic mandibular protrusion and condyle position in the prevalence and severity of Temporomandibular Disorders (TMD). The sample was composed of 60 individuals with Angle class II malocclusion divided into three groups depending upon the accomplishment of functional orthopedic treatment (prior, during and after therapy with the bionator appliance). An anamnestic questionnaire, composed of questions regarding most frequent symptoms was used to classify the sample according to the TMD presence and severity. A clinical examination, including temporomandibular joint (TMJ) and muscle palpation, mandibular range of motion and joint noises analysis was also performed. Serial standard right and left TMJ transcranial images were taken with the teeth in intercuspal position, digitalized and condyle concentricity was determined. One-way ANOVA, Kruskal-Wallis and Chi- square accounted for data analysis. Based on the anamnestic questionnaire, 30% was considered as having mild TMD, while 3.33% had moderate TMD, with no difference between groups (p> 0.05). Group II (during therapy) has shown significant anterior condyle positioning (p< 0.05) when compared to group I, although no association was found between this variable and TMD presence or severity (p> 0.05). Authors concluded that mandibular orthopedic protrusion was not a risk factor for TMD in the sample studied.
258

Efeitos cefalométricos do aparelho extrabucal conjugado (splint maxilar) e do bionator, no tratamento da má oclusão de classe II, 1ª divisão / Comparative study of the maxillary splint and bionator appliances in the treatment of Class II, division 1 malocclusion

Pedrin, Renata Rodrigues de Almeida 23 September 2003 (has links)
Este estudo cefalométrico objetivou avaliar as alterações dentárias, esqueléticas e tegumentares, em jovens com má oclusão de Classe II, 1a divisão, tratados com o aparelho extrabucal conjugado (splint maxilar) e com o Bionator. Estes dois grupos experimentais foram comparados a um grupo de jovens portadores da mesma má oclusão que não receberam tratamento, pareados pelo gênero, idade, tempo de observação e grandezas cefalométricas iniciais. A amostra constou de 180 telerradiografias em norma lateral de 90 jovens, divididos em três grupos de 30, sendo 15 do gênero masculino e 15 do feminino. Os jovens do grupo 1 foram mantidos como controle e apresentaram uma idade inicial média de 10,02 anos e foram observados pelo período médio de 1,49 anos. O grupo 2, foi submetido ao tratamento utilizando o aparelho extrabucal conjugado (splint maxilar), com idade inicial média de 10,02 anos e tempo de observação de 1,78 anos. O grupo 3, foi tratado com o Bionator por um tempo médio de 1,52 anos e os jovens apresentavam idade inicial média de 10,35 anos. A comparação entre as variáveis cefalométricas iniciais evidenciou grande similaridade entre os três grupos possibilitando comparações diretas entre eles. A análise dos resultados mostrou que o tratamento da má oclusão de Classe II, 1a divisão com o AEB conjugado e com o Bionator resultou de efeitos específicos e inerentes a cada aparelho. Os resultados patentearam que o deslocamento anterior da maxila foi restringido significantemente pelo tratamento com o AEB conjugado. O Bionator promoveu um aumento significante na protrusão mandibular, enquanto que o AEB conjugado mostrou efeitos esqueléticos menos evidentes. No entanto, ambos os aparelhos estudados produziram um aumento nos comprimentos efetivo e do corpo da mandíbula, com valores maiores para o grupo 2. A relação maxilomandibular melhorou significantemente nos grupos tratados em comparação ao grupo controle. A análise do padrão de crescimento craniofacial e das alturas faciais não revelou alteração significante entre os grupos. Em relação às alterações dentoalveolares ambos aparelhos provocaram inclinação para lingual e retrusão dos incisivos superiores, porém os efeitos do AEB conjugado foram significantemente mais intensos. Os incisivos inferiores foram afetados de maneira distinta pelos aparelhos. No grupo tratado com o AEB conjugado, os incisivos lingualizaram e retruíram enquanto que o grupo tratado com o Bionator apresentou inclinação para vestibular e protrusão destes dentes. Os molares inferiores apresentaram um maior desenvolvimento vertical e horizontal nos grupos 2 e 3. Os primeiros molares superiores distalizaram no grupo tratado com o AEB conjugado enquanto nos grupos 3 (Bionator) e controle houve mesialização. Em relação ao perfil tegumentar constatou-se que o ângulo nasolabial não foi afetado pelo tratamento. Os referidos aparelhos promoveram uma retrusão do lábio superior. Observou-se uma protrusão do lábio inferior no grupo tratado com o Bionator e retrusão desta estrutura com o emprego do AEB conjugado. Deste modo, verificou-se que ambos os protocolos de tratamento propiciaram alterações esqueléticas, dentárias e tegumentares, distintas e clinicamente relevantes para a correção da má oclusão de Classe II, 1a divisão. / The purpose of this investigation was to evaluate and compare the cephalometric changes of maxillary splint and bionator appliances on individuals with Class II, division 1 malocclusion. Lateral cephalograms were available for 90 patients of both sex, divided in three groups of 30 each one. The first group served as a control group, with initial mean age of 10.02 years. The second group was treated with maxillary splint appliance with initial mean age of 10.02 years. The group 3 was treated with bionator appliance with initial mean age of 10.35 years. The lateral cephalometric headfilms were taken of each patient at the beginning and the end of treatment, in a total of 180 headfilms. The cephalometric variables were analyzed with statistical tests. The results showed that only maxillary splint influenced changes in forward growth of the maxilla and bionator appliances provides a statistically significant increase in mandibular protrusion. However, it was observed that both appliances provides an increase in total mandibular and body length, with greater values in group 2, but these results do not showed statistically differences. This study indicated that both appliances provide an improvement in the maxillomandibular relationship, compared to the control group. In addition, there were no statistically significant differences in the craniofacial growth pattern among the three groups nor in the facial heights. It was observed that both appliances produced lingual inclination and retrusion of the upper incisors. Maxillary splint provided lingual tipping of the lower incisors while bionator produced labial tipping and protrusion of these teeth. The lower molars showed a greater vertical development and extrusion in experimental groups. The maxillary splint produced distal movement of the first upper molars and bionator showed mesial inclination. This investigation indicated that both treated groups produced a retrusion in the upper lips with greater intensity in group 2. Maxillary splint produced a retrusion in the lower lip while bionator provided lower lip protrusion.
259

Estudo da molhabilidade em madeiras tropicais ou de reflorestamento por medidas de ângulo de contato e de permeabilidade / Study of wettability in tropical or reforestation timber by contact angle technique and permeability measures.

Brisolari, André 25 April 2008 (has links)
Este trabalho tem por objetivo estudar a molhabilidade e a permeabilidade para quatro espécies de madeiras tropicais (Pinus elliottii, Araucaria angustifolia, Eucalyptus grandis e Eucalyptus citriodora). A molhabilidade é um parâmetro importante para a caracterização de diferentes espécies de madeira e, portanto, depende de fatores como o estado de limpeza da superfície da madeira, orientação das fibras, tipo de amostra (alburno ou cerne), secagem, tratamentos térmicos e químicos, rugosidade superficial, etc. Primeiramente, investigamos a molhabilidade para as quatro espécies tropicais por medida de ângulo de contato aparente para diferentes solventes na superfície da madeira As amostras foram tratadas termicamente no intervalo 100 200º C, por 8h e foi utilizado o método da gota séssil e um goniômeto. Os valores dos ângulos de contato foram maiores para as amostras submetidas aos tratamentos térmicos, indicando um aumento no caráter hidrofóbico da madeira. A técnica de ângulo de contato não foi eficiente para tratamentos térmicos superiores a 200º C, devido a sua degradação. No experimento de permeabilidade foi utilizado um fluxo de ar através das amostras com poros fechados e abertos. Foi verificado um acréscimo de 82 % na vazão para as situações de poros abertos no Eucalyptus citriodora. Nossos resultados permitem detectar mudanças consideráveis na molhabilidade e permeabilidade da madeira, sendo informações valiosas para a conservação e utilização destas madeiras. / This work aims to study wettability and permeability for tropical wood species (Pinus elliotti, Araucaria angustifolia, Eucalyptus grandis and Eucalyptus citriodora).The adhesive wettability is an important parameter for characterizing different wood species and depends on factors such as cleaning state of the wood surface, orientation of the wood fibers, type of sample (sapwood or heartwood), drying, thermal and chemical treatments, surface roughness, etc. First, we investigated the wettability of the four tropical wood species by measuring the apparent contact angles of different solvents on the wood surfaces. The samples were heat treated from 100 to 200 °C for 8 h, and the contact angles measured by the sessile drop method with a home-made goniometer. For samples heat-treated below 200 °C, higher values of contact angles were obtained, indicating a hydrophobic character for thermal treated woods. After this temperature, the wood degradation took place. For permeability experiments, a flow of air was used for wood samples with closed and open pores. An increase of 82% in flow was verified for open pores woods such as Eucalyptus citriodora. Our results allowed us to detect considerable changes on wood wettability and permeability and that are powerful information for conservation and use of these woods.
260

Avaliação do grau de eficiência do tratamento da Classe II realizado sem extrações e com extrações de dois pré-molares superiores

Barros, Sérgio Estelita Cavalcante 01 December 2004 (has links)
O objetivo deste trabalho foi comparar o grau de eficiência do tratamento da má oclusão de Classe II completa, realizado sem extrações e com extrações de dois pré-molares superiores. Para tanto, selecionou-se, a partir de todas as 3592 documentações do arquivo da disciplina de ortodontia da Faculdade de Odontologia de Bauru, uma amostra composta pelas documentações de 112 pacientes com má oclusão de Classe II completa. Em seguida, dividiu-se esta amostra em dois grupos, apresentando as seguintes características: Grupo 1, constituído por 43 pacientes, tratados sem extrações e com idade inicial média de 12,63 ± 1,45 anos (idade mínima de 9,39 e máxima de 16,03) e Grupo 2 composto por 69 pacientes, tratados com extrações de dois pré-molares superiores e com idade inicial média de 13,91 ± 2,71 anos (idade mínima de 9,42 e máxima de 27,08). Para comparar o grau de eficiência do protocolo de tratamento aplicado a cada grupo, os resultados oclusais do tratamento foram avaliados em modelos de gesso por meio dos índices oclusais IPT e PAR, enquanto o tempo despendido no tratamento de cada grupo foi calculado a partir das anotações clínicas presentes nos prontuários. O grau de eficiência foi calculado pela porcentagem de melhora oclusal, avaliada pelo IPT ou PAR, dividida pelo tempo de tratamento. Os índices oclusais finais, o tempo de tratamento e o grau de eficiência dos protocolos de tratamento dos grupos foram comparados por meio do teste t. Os resultados demonstraram que o protocolo de tratamento com extrações de dois pré-molares superiores apresentou melhores resultados oclusais, num menor tempo de tratamento e, portanto um maior grau de eficiência, do que o protocolo sem extrações, da má oclusão de Classe II completa. / This study compared the efficiency of complete Class II malocclusion treatment with and without extraction of two maxillary premolars. A sample of 112 records from patients with complete Class II malocclusion was obtained from the files of the Orthodontic Department at Bauru Dental School, which comprises a total of 3,592 records. This sample was divided into two groups with the following characteristics: Group 1, comprising 43 patients treated without extractions and an initial mean age of 12.63 ± 1.45 years (ranging from 9.39 to 16.03 years); and Group 2, comprising 69 patients treated with extraction of two maxillary premolars and an initial mean age of 13.91 ± 2.71 years (ranging from 9.42 to 27.08 years). To compare the efficiency of each treatment protocol, the occlusal outcomes were evaluated on dental casts with the TPI and the PAR occlusal indexes, and the treatment time of each group was calculated on the clinical charts. The treatment efficiency degree was calculated as the ratio between the percentages of occlusal improvement, evaluated through the TPI or PAR, by the treatment time. The occlusal indexes, the treatment time and the treatment protocols efficiency degree of the groups were compared by means of the t test. Results demonstrated that the two maxillary premolar extraction protocol provided better occlusal outcomes, in less time, and therefore a greater treatment efficiency than the non-extraction treatment protocol of complete Class II malocclusion.

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