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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.
461

Alveolar Ridge Dimension Analysis Following Socket Preservation Using Clinical Assessment and Cone Beam Computed Tomography (CBCT).

Duggan, Sayward 12 May 2001 (has links)
AIM: Extraction of a tooth can lead to alveolar ridge resorption which can be minimized by socket preservation. The aim of this study is to analyze vertical and horizontal alveolar ridge dimensions clinically and by CBCT immediately following extraction and 3-4 months following socket preservation. METHODS: The preserved group (P) consisted of 20 patients with1-2 non-molar teeth requiring extraction with socket preservation, while the control group (C) consisted of 5 patients requiring extraction alone. An acrylic stent was fabricated presurgically in order to measure vertical and horizontal ridge dimensions clinically and radiographically immediately following extraction and 3-4 months following socket preservation. RESULTS: Overall, P sites gained ridge height and lost minimal ridge width over 3-4 months, while C sites lost both ridge height and width. Preserved sites in which the teeth were extracted due to caries had the most significant gain in the radiographic vertical occlusal dimension (RVO). Overall, high correlations were found between the clinical and radiographic measurements at the initial surgery and at the 3-4 month follow up. CONCLUSIONS: The preserved group had minimal ridge resorption and more socket bony fill when compared to the non-preserved group 3-4 months following tooth extraction, especially when the tooth was extracted due to caries. Additionally, the CBCT can be a useful diagnostic tool to evaluate socket preservation healing, as it compares well to clinical assessments of socket healing.
462

Evaluation of Maxillary Molar Furcations, Clinical Measurements versus Cone Beam Computed Tomography

Allen, Jessica 14 April 2014 (has links)
BACKGROUND: The use of three-dimensional imaging has shown to provide advantages to the clinician in assessing bone morphology. The aim of this study will be to compare the diagnostic efficacy of cone beam computed tomography (CBCT) versus diagnostic clinical measurements in patients presenting with furcation involved maxillary first molars. METHODS: The study population included 20 patients with 34 maxillary first molar teeth with furcation involvement. Clinical horizontal and vertical probing measurements were compared to CBCT measurements taken by two calibrated examiners. RESULTS: Horizontal measurements showed a significant difference between Glickman class II and class III. There were no statistical significant differences with the horizontal measurements between clinical probing, bone sounding and CBCT measurements. CBCT vertical measurements were statistically greater than clinical probing measurements. CONCLUSION: The CBCT can provide similar horizontal measurements to standard clinical horizontal probing measurements and will provide a greater vertical dimension of a furcation defect to standard vertical probing measurements.
463

50%-50% Beam Splitters Using Transparent Substrates Coated by Single- or Double-Layer Quarter-Wave Thin Films

Sudradjat, Faisal 22 May 2006 (has links)
A pair of light beams that have orthogonal polarizations and equal intensity can be generated through reflection and refraction of a monochromatic light at a dielectric surface. Sytematic procedures to design beam splitters which can produce such output light beams are described in this thesis. Two designs that are of particular interest are prismatic substrates coated by a single layer and a double layer of thin films. Specific examples of each beam splitter in the visible and infrared are included. The performance of each beam splitter as a function of incidence angle, film thickness, and wavelength is also discussed.
464

In-situ Scanning Electron Microscopy for Electron-beam Lithography and In-situ One Dimensional Nano Materials Characterization

Long, Renhai 15 May 2009 (has links)
In this thesis, we demonstrate in-situ scanning electron microscopy techniques for both electron beam lithography (EBL) and in-situ one dimensional nano materials electrical characterization. A precise voltage contrast image positioning for in-situ EBL to integrate nanowires into suspended structures for nanoswitch fabrication has been developed. The in-situ EBL eliminates the stage movement error and field stitching error by preventing any movements of the stage during the nanolithography process; hence, a high precision laser stage and alignment marks on the substrate are not needed, which simplifies the traditional EBL process. The ZnO piezoelectronics is also studied using nano-manipulators in scanning electron microscope. Methods to improve the contact have been demonstrated and the contacts between probe tips and the nanowires are found to have significant impact on the measurement results.
465

Estimating beam and diffuse solar irradiance components using multiple solar irradiance meters

Delibasic, Tarik January 2019 (has links)
In recent years, different renewable energy sources have been on the rise. Among these, solar power has shown great potential in both small and big scale. Since solar irradiance is the main input for solar power systems, it is of great importance to examine how much of the solar irradiance actually reaches a certain location, and how much of the total solar irradiance consists of direct (beam), diffuse and reflected irradiance. This is usually done with expensive measurement meters, such as pyranometers and pyrheliometers. In this thesis, incident solar irradiance data from a cheap sensor network is analyzed, a new proposed model for estimating beam and diffuse fraction is examined and the results are compared to another estimation model, namely Erbs model. The comparison between the two models shows high correlation for beam irradiance, regardless of weather conditions, whereas the correlation for diffuse irradiance shows a highly varying result, much dependent on the weather conditions. It is difficult to motivate how well the proposed model is performing on a broader scale, since the study is limited to a specific area during a short period of time.
466

Enriched elasto-plastic beam model / Modele de poutre elasto-platique enrichi

Corre, Grégoire 19 April 2018 (has links)
Ce travail s'inscrit dans le cadre d'un partenariat scientifique entre le Laboratoire Navier et la société STRAINS. Convaincue du besoin de renouveler les méthodes actuelles de calcul de structures, STRAINS développe un nouveau logiciel dédié à l'analyse des ouvrages d'art. Dans ce contexte, cette thèse propose de nouveaux outils pour l'analyse des structures élancées. Le modèle élastique de poutre d'ordre supérieur développé par cite{Ferradi2016} est d'abord adapté au cas des déformations imposées, permettant ainsi au modèle de représenter un grand nombre de phénomènes physiques tels que le fluage, la précontrainte ou les chargements thermiques. Différents exemples viennent souligner la précision numérique du modèle ainsi que ses performances en temps de calcul. Le modèle est également étendu au cadre de la théorie de la plasticité. Considérant les déformations plastiques comme des déformations imposées, les résultats précédemment obtenus sont utilisés pour développer une nouvelle cinématique d'ordre supérieur. Enfin, un nouvel élément de poutre élastoplastique pour le béton armé est proposé. Le béton est décrit grâce au modèle élastoplastique et les ferraillages sont modélisés par des éléments barres à une dimension. Cette méthode permet une description précise du comportement du béton et une représentation fidèle des renforcements. La validité des calculs est évaluée par des considérations de dissipation énergétique / This thesis work is presented in the framework of a scientific partnership between Laboratoire Navier and the french start-up STRAINS. Believing in the need for new methodologies in structural analysis, STRAINS is developing a new software dedicated to the structural analysis of bridges. In this context, this work suggests new tools for the analysis of slender structures.The higher-order elastic beam element developed by cite{Ferradi2016} is first extended to the case of eigenstrains, enabling the model to deal with various physical phenomena such as creep, prestress or thermal loads. An enriched kinematics is used to capture the local response of the structure. Different examples highlight the local accuracy of the model and its fast computational performances. The model is also extended to plasticity in small perturbations. Considering the plastic strains developing in the structure as eigenstrains, the previous works are used to derive a higher-order elastoplastic kinematics.Finally, a new elastoplastic beam element for reinforced concrete is suggested. The concrete material is described by using the elastoplastic beam model developed previously while steel rebars are modeled by one dimensional bar elements. This method enables a fine local description of the concrete behavior and an accurate representation of the reinforcement. The validity of computations is assessed thanks to energy considerations
467

Espectroscopia de alta resolução num feixe supersônico de sódio / Ultra-high resolution spectroscopy in a supersonic sodium beam

Marega Junior, Euclydes 26 February 1993 (has links)
Neste trabalho realizamos medidas espectroscópicas de alta resolução nas bandas vibracionais da transição A1∑+u→X1∑+g do dímero de Sódio, produzido a partir da expansão supersônica do vapor deste metal no vácuo. Para determinação das constantes moleculares utilizamos técnicas alternativas de espectroscopia óptica de alta-resolução, tais como: Fluorescência Ressonante, Raman Estimulado e Depopulação Óptica. As duas últimas técnicas utilizam dois campos de laser, por isso são também chamadas de técnicas de campo duplo e proporcionam a simplificação do espectro de Fluorescência Ressonante, ajudando no seu entendimento e no cálculo das constantes moleculares dos estados estudados. Desenvolvemos também um método de obtenção de padrões de interferência, baseado no método proposto por Ramsey, a partir da modulação espacial da população do estado fundamental de um sistema aberto de dois níveis quaisquer. Foi possível obter franjas de interferência na região visível, sem que haja necessariamente coerência entre estados atômicos, efeito este observado pela primeira vez na literatura. / This work reports measurements in the vibrational bands of the A1∑+u→X1∑+g transition for Sodium dimer, produced in a supersonic expansion of the metal vapor into the vacuum. For the determination of the molecular constants we used righ-resolution laser spectroscopy techniques: Resonance Fluorescence, Stimulated Raman and Optical Depletion. The two last techniques need two lasers fields and provide the simplification of the Resonance Fluorescence spectrum, suitable for the tine assignment. We have also developed a new method to obtain Ramsey-like fringes in the optical region, due to a spatial modulation of the ground state population of any open two-level system. Tbe fringes were obtained without any atomic coherence of the levels, which is an effect observed in the literature for the first time.
468

Análise teórica e experimental de vigas de concreto armado com armadura de confinamento / Theoretical and experimental analysis of reinforced concrete beams with confinement reinforcement

Delalibera, Rodrigo Gustavo 29 April 2002 (has links)
Este trabalho discute a utilização de armadura de confinamento em vigas superarmadas de concreto armado. Essa armadura é constituída de estribos quadrados colocados na região de compressão da seção transversal da viga, aumentando a ductilidade. Para a análise numérica, utilizou-se programa computacional baseado no Método dos Elementos Finitos e que leva em consideração o efeito do confinamento no concreto, possibilitando estudar criteriosamente a influência da armadura de confinamento em vigas superarmadas. Na etapa experimental foi investigada a influência da taxa volumétrica da armadura transversal de confinamento, sendo realizados ensaios de quatro vigas superarmadas -três detalhadas com estribos adicionais destinados ao confinamento e uma projetada sem armadura de confinamento. Todas as vigas tiveram deformações nas barras da armadura de tração próximas a 'épsilon' y e resistência média à compressão do concreto de 25MPa. Os resultados experimentais mostraram que o índice de ductilidade pós-pico é proporcional à taxa volumétrica da armadura transversal de confinamento. Isso não aconteceu para o índice de ductilidade pré-pico, que teve variação aleatória com a taxa volumétrica de armadura de confinamento. Observou-se também que a resistência à compressão do concreto confinado no núcleo de confinamento diminuiu na proximidade da linha neutra. Considerando os resultados numéricos e experimentais, foi desenvolvido um processo simplificado para o dimensionamento de vigas de concreto armado com armadura de confinamento, onde a resistência à compressão do concreto confinado é função da taxa volumétrica da armadura de confinamento e da resistência do concreto não confinado / This work discusses the use of confinement reinforcement in over designed reinforced concrete beam. This reinforcement is composed by square stirrup placed on the compression zone of the beam transversal section, which improves the ductility avoiding fragile collapse. A Finite Element program was used to make a parametric numerical study. This program considers the non-linearity of the material and the confinement effect, making possible an accuracy study of those beams. In the experimental part, the influence of volumetric confinement transversal reinforcement rate was investigated by the test of four over designed beam, where three had addiction stirrup for the confinement reinforcement and one was designed without this reinforcement. All the beams were composed by 25MPa concrete. The experimental results show that the pos-peak ductility index is proportional to the volumetric confinement transversal reinforcement rate, however it was not observed for the pre-peak ductility index. It was also observed that effect of the confinement is smaller closed to the neutral axis. A simplified design process for reinforced concrete beam with reinforcement confinement was developed based on the numerical study that was performed. In this method the concrete strength is function of the transversal reinforcement volumetric rate and the non-confined concrete strength
469

Desaceleração e manipulação de átomos neutros / Decelerating and manipulating neutral atoms

Leite, Carlos Alberto Faria 21 August 1992 (has links)
O trabalho trata da desaceleração de feixes de átomos neutros de Sódio, pela técnica de sintonia Zeeman. O processo de desaceleração é estudado em detalhes e demonstrado com a utilização de um único laser. É feito o estudo do seguimento adiabático do átomo em relação ao campo magnético e demonstrada sua importância no processo de produção de fluxos intensos de átomos lentos. A posição em que os átomos param foi modificada, através da mudança do perfil do campo magnético onde os átomos se movimentam, levando-os para uma região de fácil acesso. A forma peculiar da distribuição espacial dos átomos ao atingirem o repouso é explicada e, finalmente, é estudada a focalização dos átomos, através de um campo magnético hexapolar, e o aprisionamento de átomos em uma armadilha magnética / This work describes the deceleration a sodium atoms beam by means of the Zeeman tuning technique. The deceleration process is studied in details and its demonstration is made using a single laser. We have studied and present the adiabatic following of the atoms along the magnetic field and its relevance to produce slow, high density, flux of neutral atoms. The atoms\' stopping position was varied, by changing the magnetic field profile, in a way to produce slows atoms outside the solenoid. The peculiar shape of the atomic spatial distribution of atoms at rest is explained, the focusing of atoms though a hexapole magnetic field is studied and the trapping of atoms in a magnetic trap is demonstrated
470

Determinação da carga crítica de instabilidade lateral no regime linear elástico, em vigas de madeira laminada colada (MLC) / Determination of critical load of lateral instability in the linear elastic regime, on glued laminated wood beams

Abrantes, Celso Antonio 11 October 2012 (has links)
O crescente aumento do uso de madeira laminada colada (MLC) em peças estruturais exige dos meios acadêmicos a pesquisa e desenvolvimento de teorias e rotinas de cálculo, que proporcionem suporte teórico para projetos estruturais que empreguem tal material. Nesta pesquisa foi desenvolvido em laboratório de modelos estruturais, um programa para o cálculo estrutural de vigas de madeira laminada colada (MLC), por meio do método dos elementos finitos para material ortotrópico e material isotrópico. Foram rompidas, em uma prensa universal, vigas de Madeira Laminada Colada (MLC), em escala natural, com e sem emendas nas lâminas, com a finalidade de comparação dos resultados assim obtidos, com os obtidos em modelos de cálculo existentes para vigas maciças de material isotrópico, como o método de cálculo da NBR 7190/97 e o método de cálculo da Teoria da Elasticidade (Timoshenko). Tais resultados também foram comparados com os resultados obtidos pelo método dos Elementos Finitos para materiais isotrópicos e ortotrópicos, acima citados. Para comparação entre as propriedades da madeira maciça e da madeira laminada colada, foram retirados corpos de prova das partes intactas das vigas sacrificadas, para realização de ensaios de cisalhamento na linha de cola e nas lâminas coladas, bem como corpos de prova para ensaios de flexão nas lâminas maciças das vigas de MLC. Para obtenção da tensão de ruptura a compressão paralela às fibras e do módulo de elasticidade, foram rompidos corpos de prova de 5cm x 5 cm x 15 cm. A comparação e análise dos resultados obtidos pelos procedimentos acima, levou à conclusão de que a madeira laminada colada (MLC), quando fabricada com cola estrutural, comporta-se como madeira maciça. Também foi possível observar que os modelos de cálculo empregando elementos finitos, ortotrópicos ou isotrópicos, reproduzem o comportamento de uma viga de madeira laminada colada. O modelo de cálculo da NBR 7190/97, pode ser empregado, mas apresenta resultados conservadores, a favor da segurança. Assim como o modelo de cálculo da Teoria da Elasticidade não deve ser empregado sem adaptação à madeira, pois apresentou resultados muito discrepantes. Os módulos de elasticidade da madeira maciça obtidos por ensaios de flexão e a partir do ensaio de compressão paralela às fibra, não representa o módulo de elasticidade representativo de uma viga de MLC. Da mesma forma a existência ou não de emendas nas lâminas, não altera os resultados. / The increasing use of glued laminated timber in structural parts requires academic research and development of theories and calculation routines that provide theoretical support for structural designs employing such material. In this research was developed in the laboratory of structural models, a program for calculating structural glued laminated timber beams by the finite element method for orthotropic material and isotropic material. Were disrupted in a press universal beam of glued laminated wood in full scale with and without splices blades, for the purpose of comparison of the results thus obtained with those obtained in calculation models exist for solid beams material isotropic, as the method of calculating the NBR 7190/97 and the calculation method of the theory of elasticity (Timoshenko). These results were also compared with results obtained by the method of finite elements for isotropic and orthotropic materials, mentioned above. To compare the properties of solid wood and glued laminated timber, specimens were removed from intact parts of the broken beams for testing shear line glue and glued the layers, as well as specimens for bending tests blades massive beam. To obtain the tensile strength parallel to the compression of the fibers and elastic modulus were broken specimens with the dimensions 5 cm x 5 cm x 15 cm. The comparison and analysis of the results obtained by the above procedure led to the conclusion that the glued laminated wood when manufactured with structural adhesive, behaves as solid wood. It was also noted that the model calculations using finite elements, both isotropic and orthotropic represent the behavior of a beam of glued laminated wood. The calculation model of the NBR 7190/97, can be employed, but has conservative results, in favor of security. As the calculation model of the theory of elasticity should not be used without adjustment to the wood, because it showed very discrepant results. The modulus of elasticity of solid wood obtained by bending tests from test and compression parallel to the fiber, it is not the representative elastic modulus of a beam of glued laminated wood. Likewise, the presence or absence of amendments in the layers, does not change the results.

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