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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.
81

Multi-rigid-body contact dynamics and haptic interaction for fixture loading planning. / CUHK electronic theses & dissertations collection

January 2005 (has links)
Dynamics Simulation Engine is the foundation of the whole system. The engine maintains a realistic dynamics scene in either automatic planning or haptic guided planning. It serves as an off-line verification of the planned motion so that the generated scheme can be 'played' with the engine. In this thesis, we developed a three-dimensional dynamics simulation engine based on an extension of the explicit time-stepping scheme and an application of the differential inclusion process introduced by J. J. Moreau. In the engine, we developed the contact propagation method for a general three-dimensional rigid-body system with multiple unilateral contacts without any bilateral constraints. / In our approach, a sequence of applied forces on the mass center of the workpiece is planned. The applied forces will push the workpiece to get in contact with all the locators. For this purpose, we developed a system with two engines, Motion Planning Engine and Dynamics Simulation Engine. / The goal of Motion Planning Engine is to make the workpiece in contact with all the six locators. Here, the workpiece is initially at an arbitrary place with not contact with any locator. The planning follows a simple scheme of monotonously increase the number of contacts with locators. Here we use a two-step scheme. First, finding the velocity of the workpiece that can approach the new locator while maintaining contacts with old locators. This can be formulated as a linear programming problem. Second, finding the applied force to realize such motion. This step is a central issue in the planning because for the rigid-body model, the solution to multiple frictional contacts is generally indeterministic. One possibility is jamming, that is, the applied force cannot move the workpiece even with less than six contacts. In this thesis, we will give criteria to determine whether the jamming will happen, and we will also derive an algorithm to generate the non-jamming applied force. / The thesis presents an approach to the fixture loading planning problem. That is, to plan the applied forces on the workpiece in order for it to be loaded into a manufacturing fixture. / Liu Tong. / "June 2005." / Adviser: Michael Yu Wang. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4067. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 115-124). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.
82

Estudo das propriedades mecânicas do concreto com adição de látex para aplicação em pavimento / Study of the mechanical properties of concrete with addition of latex for pavement application

Ferreira, Lucilene dos Reis Barros [UNESP] 31 January 2017 (has links)
Submitted by LUCILENE DOS REIS BARROS null (lureisbarros@ibest.com.br) on 2017-03-24T11:46:17Z No. of bitstreams: 1 Dissertação mestrado Lucilene Ferreira.pdf: 2177054 bytes, checksum: 8673fd6a85a2ca423d1533a6021c69f1 (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-03-24T16:36:32Z (GMT) No. of bitstreams: 1 ferreira_lrb_me_ilha.pdf: 2177054 bytes, checksum: 8673fd6a85a2ca423d1533a6021c69f1 (MD5) / Made available in DSpace on 2017-03-24T16:36:32Z (GMT). No. of bitstreams: 1 ferreira_lrb_me_ilha.pdf: 2177054 bytes, checksum: 8673fd6a85a2ca423d1533a6021c69f1 (MD5) Previous issue date: 2017-01-31 / Esta dissertação trata-se de uma pesquisa, com acréscimo de látex natural e látex sintético SBR (estireno butadieno) na massa do concreto para aplicação em pavimento e análise de seu comportamento, tanto no estado fresco quanto endurecido. A proposta visa analisar o comportamento do látex sintético SBR e do látex coletado diretamente do seringal, apenas com adição de amônia. Sendo que o látex sintético já é usado para ser acrescido na argamassa. Os ensaios realizados foram de: Resistência à compressão axial, Resistência à tração na flexão e Módulo de Elasticidade para as idades de 7, 28 e 50 dias. Em uma segunda etapa, foram realizados novos ensaios, mas com o látex sem a amônia, apenas com o látex puro, apenas para analisar a influência da amônia. Nessa nova etapa foi realizado, somente ensaio de resistência à compressão. Os resultados mostraram que o látex com a amônia diminuíram as resistências à compressão e à tração na flexão para as idades de 7 e 28 dias e para 50 dias essa tendência desaparece. O módulo de elasticidade também apresentou queda, para o concreto com látex com amônia, entretanto isto é positivo para o concreto aplicado em pavimento, pois indica um aumento na capacidade de deformação para a mesma carga, ou seja, o material apresentou maior capacidade de deformação elástica. O módulo de elasticidade para o concreto com látex sintético foi maior que o de referência, para todas as idades. O Látex sem a amônia apresentou queda para o ensaio de resistência à compressão, confirmando que o aditivo aplicado para não deixar o látex coagular, não influência nas propriedades do concreto. / This dissertation is about a research, with addition of natural latex and synthetic latex SBR (styrene butadiene) in the concrete mass for application in pavement and analysis of its behavior, in both the fresh and hardened state. The purpose is analyze the behavior of synthetic latex SBR (styrene butadiene) and latex collected directly from the rubber tree, being that the synthetic latex is already used to be added in concrete. The tests were: axial compression strength, flexural tensile strength and modulus of elasticity for the ages of 7, 28 and 50 days. In a second step, new tests were performed, but with latex without ammonia, only with pure latex to analyze the influence of ammonia. In this new step, only the compressive strength test was performed. The results showed that latex with ammonia decreased the compressive and flexural tensile strengths at the ages of 7 and 28 days and for 50 days this tendency disappears. The modulus of elasticity also showed a drop, for latex concrete with ammonia, however this is positive for the concrete applied in pavement, since it indicates an increase in the capacity of deformation for the same load, that is, it indicates that the material is more ductile. The modulus of elasticity for concrete with synthetic latex was higher than the reference, for all ages. Latex without ammonia showed a drop for the compressive strength test, confirming that the additive applied not to allow the latex to stiffen does not influence the properties of the concrete.
83

Estudo das propriedades mecânicas do concreto com adição de látex para aplicação em pavimento /

Ferreira, Lucilene dos Reis Barros January 2017 (has links)
Orientador: Maria da Consolação Fonseca de Albuquerque / Resumo: Esta dissertação trata-se de uma pesquisa, com acréscimo de látex natural e látex sintético SBR (estireno butadieno) na massa do concreto para aplicação em pavimento e análise de seu comportamento, tanto no estado fresco quanto endurecido. A proposta visa analisar o comportamento do látex sintético SBR e do látex coletado diretamente do seringal, apenas com adição de amônia. Sendo que o látex sintético já é usado para ser acrescido na argamassa. Os ensaios realizados foram de: Resistência à compressão axial, Resistência à tração na flexão e Módulo de Elasticidade para as idades de 7, 28 e 50 dias. Em uma segunda etapa, foram realizados novos ensaios, mas com o látex sem a amônia, apenas com o látex puro, apenas para analisar a influência da amônia. Nessa nova etapa foi realizado, somente ensaio de resistência à compressão. Os resultados mostraram que o látex com a amônia diminuíram as resistências à compressão e à tração na flexão para as idades de 7 e 28 dias e para 50 dias essa tendência desaparece. O módulo de elasticidade também apresentou queda, para o concreto com látex com amônia, entretanto isto é positivo para o concreto aplicado em pavimento, pois indica um aumento na capacidade de deformação para a mesma carga, ou seja, o material apresentou maior capacidade de deformação elástica. O módulo de elasticidade para o concreto com látex sintético foi maior que o de referência, para todas as idades. O Látex sem a amônia apresentou queda para o ensaio de resistência à com... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: This dissertation is about a research, with addition of natural latex and synthetic latex SBR (styrene butadiene) in the concrete mass for application in pavement and analysis of its behavior, in both the fresh and hardened state. The purpose is analyze the behavior of synthetic latex SBR (styrene butadiene) and latex collected directly from the rubber tree, being that the synthetic latex is already used to be added in concrete. The tests were: axial compression strength, flexural tensile strength and modulus of elasticity for the ages of 7, 28 and 50 days. In a second step, new tests were performed, but with latex without ammonia, only with pure latex to analyze the influence of ammonia. In this new step, only the compressive strength test was performed. The results showed that latex with ammonia decreased the compressive and flexural tensile strengths at the ages of 7 and 28 days and for 50 days this tendency disappears. The modulus of elasticity also showed a drop, for latex concrete with ammonia, however this is positive for the concrete applied in pavement, since it indicates an increase in the capacity of deformation for the same load, that is, it indicates that the material is more ductile. The modulus of elasticity for concrete with synthetic latex was higher than the reference, for all ages. Latex without ammonia showed a drop for the compressive strength test, confirming that the additive applied not to allow the latex to stiffen does not influence the properties o... (Complete abstract click electronic access below) / Mestre
84

Non-rigid image registration evaluation using common evaluation databases

Wei, Ying 01 December 2009 (has links)
Evaluating non-rigid image registration performance is a difficult problem since there is rarely a “gold standard” (i.e., ground truth) correspondence between two images. The Non-rigid Image Registration Evaluation Project (NIREP) was started to develop a standardized set of common databases, evaluation statistics and a software tool for performance evaluation of non-rigid image registration algorithms. The goal of the work in this thesis is to build up common image databases for rigorous testing of non-rigid image registration algorithms, and compare their performance by a diverse set of evaluation statistics on our multiple well documented image databases. The well documented databases as well as new evaluation statistics have been and will be released to public research community. The performance of five non-rigid registration algorithms (Affine, AIR, Demons, SLE and SICLE) was evaluated using 22 images from two NIREP evaluation databases. Six evaluation statistics (Relative Overlap, Intensity Variance, Normalized ROI overlap, alignment of calcarine sulci, Inverse Consistency Error and Transitivity Error) were used to evaluate and compare registration performance. This thesis provides a complete and accurate reporting of evaluation tests so that others are able to get access to these results and make a comparison of registration algorithms they concerned in their specific use. Moreover, this work followed the recommendations of the Standards for Reporting of Diagnostic Accuracy (STARD) initiative to disclose all relevant information for each non-rigid registration validation test.
85

Properties of Rigid Foams for Application as Materials for Light Weight Structures in Space

Chi, Huichen 01 May 1993 (has links)
The mechanical and mesoscopic structural properties of rigid cellular foam made of polystyrene have been investigated. Basic properties (e.g., density, total and available porosity, permeability, surface area, isotropicity, and cell size and cell wall thickness distributions) were measured. In most cases, alternative methods were used to determine which methods were most appropriate for the type of samples we studied. Standard compression and deflection mechanical tests were performed. The stress-strain curves and related mechanical properties were found to agree with standard cellular structural models of open-cell foams. We investigated the effects of small (~<5 atm) hydrostatic stress applied to foam samples for long periods of time (~one day). We observed large changes (up to a factor of three) in the stress-strain diagrams, Young's modulus, elastic collapse stress, ultimate strength, resilience, Poisson's ratio, permeability, penetration depth, and available porosity. Effects were most pronounced above 2 atm applied pressure differential, but were observed even for 1 atm loads. Short-term exposure to loads up to ten times as large did not cause comparable changes. These changes were interpreted as resulting from observed changes in the mesoscopic structure occurring near the surface using standard cellular structural models. This work was originally motivated by applications of foam as an inflating agent and structural component of fiber-epoxy composite tubular struts to be used in innovative space structures. The key recommendations of this study, regarding such applications, are to closely monitor the effects on the mechanical properties of polystyrene foam of: (1) cell structure and density inhomogeneities, and (2) pressure differentials which may be encountered during deployment and curing.
86

Simulering av mjuka kroppar för spel

Johannesson, Roger January 2006 (has links)
<p>I dagens spelindustri baseras nästan samtliga 3D-spel på fysiksimuleringar med stela kroppar (rigid bodies). Examensarbetet undersöker vilka alternativa modeller som finns för att simulera mjuka deformerbara objekt, deformerbara i det avseendet att de kan ändra form och inte nödvändigtvis att de kan gå sönder i flera bitar. Rapporten inleds med en undersökande del som tar upp några existerande metoder för att hantera dynamiken inom ett mjukt objekt för att sedan beskriva en metod i detalj som dessutom implementeras i ett kodbibliotek. Ett deformerbart objekt är inte så spännande om det inte finns något sätt att deformera det på, därför undersöks även hur kollisionshantering kan gå till. Även här har rapporten först en undersökande del för att sedan beskriva en specifik metod i detalj som implementeras i kodbiblioteket. Examensarbetet resulterar i slutändan i en grundläggande interaktiv simuleringsmiljö för mjuka deformerbara objekt i form av ett kodbibliotek.</p>
87

Komfortskillnad mellan sfäriska och asfäriska stabila linser vid initial tillpassning

Johansson, Maja January 2013 (has links)
Syfte: Syftet med denna studie var att jämföra den initiala komforten mellan sfäriska och asfäriska stabila linser då uppfattningen har varit att asfäriska linser (med sin mer följsamma passform) borde vara bekvämare. Metoder: Studien omfattade 30 deltagare med en medelålder på 26 år. Med hjälp av topografens (Topcon CA-100) kontaktlinstillpassningsprogramvara valdes en sfärisk A- design lins (från Nordiska Lins) och en asfärisk A90 lins (från Expert Optik, Sverige) ut med passande parametrar. Linserna sattes i vardera öga utan att försökspersonen visste vilken lins som var vilken. Efter 5 respektive 15 minuter fick patienten, med hjälp av en modifierad VAS-skala, avgöra hur linserna kändes både i höger och vänster öga. Resultat: Ingen signifikant skillnad i komforten mellan de asfäriska och sfäriska linserna varken observerades efter 5 (p=0,78) eller 15 (p=0,84) minuter. Överlag ökade komforten både för de asfäriska och för de sfäriska linserna efter att de suttit i en stund; komforten ökade med 0,9 enheter för de asfäriska respektive 1,1 enheter för de sfäriska linserna mellan 5 och 15 minuters bärtid. Det fanns en signifikant skillnad i komfort för den enskilda asfäriska linsen mellan första och andra graderingstillfället (p=0,015) och samma gällde de sfäriska (p=0,0001). Slutsats: Resultatet visar ingen markant skillnad i initial komfort på stabila linser med dessa olika typer av designer; en multikurvig asfärisk samt en trekurvig sfärisk lins. Med detta i åtanke behöver man inte, ur ett komfortmässigt perspektiv, ta hänsyn till den specifika designen vid tillpassning med moderna stabila linser.
88

Quantifying the Frequency and Orientation of Mitoses in Embryonic Epithelia

Siva, Parthipan January 2007 (has links)
The miraculous birth of a new life starts by the formation of an embryo. The process by which an embryo is formed, embryogenesis, has been studied and shown to consist of three types of processes: mitosis, cell differentiation and morphogenetic movements. Scientists and medical doctors are still at a loss to explain the fundamental forces driving embryo development and the causes of birth defects remain largely unknown. Recent efforts by the Embryo Biomechanics Lab at the University of Waterloo have shown a relationship between morphogenetic movements that occur during embryo formation and the frequency and orientation of mitosis. To further study this relationship a means of automatically identifying the frequency and orientation of mitosis on time-lapse images of embryo epithelia is needed. Past efforts at identifying mitosis have been limited to the study of cell cultures and stained tissue segments. Two methods for identifying mitosis in contiguous sheets of cells are developed. The first method is based on local motion analysis and the second method is based on intensity analysis. These algorithms were tested on images of early and late stage embryos of the axolotl (Ambystoma mexicanum), a type of amphibian. The performance of the algorithms were measured using the F-Measure. The F-Measure determines the performance of the algorithm as the true mitosis detection rate penalized by the false mitosis detection rate. The motion based algorithm had performance rates of 68.2% on an early stage image set and 66.7% on a late stage image set, whereas the intensity based algorithm had a performance rates of 73.9% on early stage image set and 90.0% on late stage image set. The mitosis orientation errors for the motion based algorithm were 27.3 degrees average error with a standard deviation (std.) of 19.8 degrees for early stage set and 34.8 degrees average error with a std. of 23.5 degrees for the late stage set. For the intensity based algorithm the orientation errors were 39.8 degrees average with std. of 28.9 degrees for the early stage image set and 15.7 degrees average with std. of 18.9 degrees for the late stage image set. The intensity based algorithm had the best performance of the two algorithms presented, and the intensity based algorithm performs best on high-magnification images. Its performance is limited by mitoses in adjacent cells and by the presence of natural cell pigment variations. The algorithms presented here offer a powerful new set of tools for evaluating the role of mitoses in embryo morphogenesis.
89

Registering a Non-Rigid Multi-Sensor Ensemble of Images

Kim, Hwa Young January 2009 (has links)
Image registration is the task of aligning two or more images into the same reference frame to compare or distinguish the images. The majority of registration methods deal with registering only two images at a time. Recently, a clustering method that concurrently registers more than two multi-sensor images was proposed, dubbed ensemble clustering. In this thesis, we apply the ensemble clustering method to deformable registration scenario for the first time. Non-rigid deformation is implemented by a FFD model based on B-splines. A regularization term is added to the cost function of the method to limit the topology and degree of the allowable deformations. However, the increased degrees of freedom in the transformations caused the Newton-type optimization process to become ill-conditioned. This made the registration process unstable. We solved this problem by using the matrix approximation afforded by the singular value decomposition (SVD). Experiments showed that the method is successfully applied to non-rigid multi-sensor ensembles and overall yields better registration results than methods that register only 2 images at a time. In addition, we parallelized the ensemble clustering method to accelerate the performance of the method. The parallelization was implemented on GPUs using CUDA (Compute Unified Device Architecture) programming model. The GPU implementation greatly reduced the running time of the method.
90

Quantifying the Frequency and Orientation of Mitoses in Embryonic Epithelia

Siva, Parthipan January 2007 (has links)
The miraculous birth of a new life starts by the formation of an embryo. The process by which an embryo is formed, embryogenesis, has been studied and shown to consist of three types of processes: mitosis, cell differentiation and morphogenetic movements. Scientists and medical doctors are still at a loss to explain the fundamental forces driving embryo development and the causes of birth defects remain largely unknown. Recent efforts by the Embryo Biomechanics Lab at the University of Waterloo have shown a relationship between morphogenetic movements that occur during embryo formation and the frequency and orientation of mitosis. To further study this relationship a means of automatically identifying the frequency and orientation of mitosis on time-lapse images of embryo epithelia is needed. Past efforts at identifying mitosis have been limited to the study of cell cultures and stained tissue segments. Two methods for identifying mitosis in contiguous sheets of cells are developed. The first method is based on local motion analysis and the second method is based on intensity analysis. These algorithms were tested on images of early and late stage embryos of the axolotl (Ambystoma mexicanum), a type of amphibian. The performance of the algorithms were measured using the F-Measure. The F-Measure determines the performance of the algorithm as the true mitosis detection rate penalized by the false mitosis detection rate. The motion based algorithm had performance rates of 68.2% on an early stage image set and 66.7% on a late stage image set, whereas the intensity based algorithm had a performance rates of 73.9% on early stage image set and 90.0% on late stage image set. The mitosis orientation errors for the motion based algorithm were 27.3 degrees average error with a standard deviation (std.) of 19.8 degrees for early stage set and 34.8 degrees average error with a std. of 23.5 degrees for the late stage set. For the intensity based algorithm the orientation errors were 39.8 degrees average with std. of 28.9 degrees for the early stage image set and 15.7 degrees average with std. of 18.9 degrees for the late stage image set. The intensity based algorithm had the best performance of the two algorithms presented, and the intensity based algorithm performs best on high-magnification images. Its performance is limited by mitoses in adjacent cells and by the presence of natural cell pigment variations. The algorithms presented here offer a powerful new set of tools for evaluating the role of mitoses in embryo morphogenesis.

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