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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.
1

Rapid cryogenic fixation of biological specimens for electron microscopy

Ryan, Keith Patrick January 1991 (has links)
This thesis describes investigations into cryofixation by the plunge-cooling technique, at ambient pressure. The objective was to characterise coolants which are commonly used for cryofixation, so that the structure and chemistry of biological specimens may be preserved in a more life-like state. The work began with the design of a suitable cooling device. This was developed further into a large test-bed apparatus which was used in both biological and methodological experiments. The large cooling apparatus demonstrated for the first time that ethane was a superior coolant under forced convection, compared to propane or Freon 22, for bare thermocouples, for exposed hydrated specimens and for metal-sandwiched hydrated specimens. Ice crystal formation was monitored in sandwiched specimens and found to correspond closely to modelling predictions. A biological application was the X-ray microanalysis of body fluids in "indicator" species of Chaetognaths, where results obtained from cryoscanning electron microscopy revealed ecophysiological differences. The use of low thermal mass supports demonstrated that good freezing can occur in the centre of specimens. A new cryomounting method was developed to load well-frozen specimens into the microscope. The effect of post-freeze processing temperature was investigated by monitoring ice crystals in red blood cells. Exposure to 213 K (-60°C) over a 48 hour period did not induce crystal growth and exposure to 233 K (-40°C) for 8 days showed minimal ice crystal damage. The progress of cryosubstitution was monitored over 48 h at 193 K ( -80°C), this showed that uranium ingressed to a depth of 320 µm which could be doubled when shrinkage was allowed for. The conclusion was that observed ice crystal damage originated during the initial freezing and not during subsequent cryoprocessing.
2

Modeling and LQR Control of a Two-Dimensional Airfoil

Olds, Shana D. 21 April 1997 (has links)
In this paper we develop a mathematical model of a two-dimensional aeroelastic airfoil. This model is used to design a flutter suppression controller. Flutter is a vibration in a wing caused by airstream energy being absorbed by the lifting surface. Flutter increases with increasing speed. For simplicity, we consider a flat plate in a two-dimensional flow. The model is developed in the frequency domain and then transformed into the time domain. The uncontrolled model is numerically simulated using MATLAB. Linear Quadratic Regulator (LQR) theory is used to design a state feedback controller. The LQR control scheme consists of using a full state feedback controller of the form u=-Kx, where K is a control gain matrix. The goal is to use LQR theory to supress flutter and to maintain stability of the closed loop system. / Master of Science
3

Thermo-electric temperature measurements in friction stir welding : Towards feedback control of temperature

Magalhães, Ana January 2016 (has links)
Friction Stir Welding has seen a fast uptake in many industry segments. Mechanical properties superior to fusion welding, the ability to weld "unweldable" aluminium alloys and low distortion are often described as the main reasons for the fast industrial implementation of FSW. Most existing applications consist of long straight welding joints. Applications with complex weld geometries, however, are rarely produced by FSW. These geometries can induce thermal variations during the welding process, thus making it challenging to maintain a consistent weld quality. In-process adaptation of weld parameters to respond to geometrical variations and other environmental variants allow new design opportunities for FSW. Weld quality has been shown to be reliant on the welding temperature. However, the optimal methodology to control the temperature is still under development.The research work presented in this thesis focuses on some steps to take in order to reach the improvement of the FSW temperature controller, thus reach a better and consistent weld quality. In the present work different temperature methods were evaluated. Temperature measurements acquired by the tool-workpiece thermocouple (TWT) method were accurate and fast, and thereby enhanced suitable for the controller. Different environmental conditions influencing the material heat dissipation were imposed in order to verify the controller effect on the joint quality. In comparison with no controlled weld, the use of the controller enabled a fast optimization of welding parameters for the different conditions, leading to an improvement of the mechanical properties of the joint.For short weld lengths, such as stitch welds, the initial plunge and dwell stages occupy a large part of the total process time. In this work temperature control was applied during these stages. This approach makes the plunge and dwell stages more robust by preventing local material overheating, which could lead to a tool meltdown. The TWT method was demonstrated to allow a good process control during plunging and continuous welding. The approach proposed for control offers weld quality consistency and improvement. Also, it allows a reduction of the time required for the development of optimal parameters, providing a fast adaptation to disturbances during welding and, by decreasing the plunge time, provides a significant decrease on the process time for short welds.
4

Separation and Vorticity Transport in Massively-Unsteady Low Reynolds Number Flows

Webb, Charles 17 June 2009 (has links)
No description available.
5

Numerical simulation of the hydraulic performances and flow pattern of swallow-tailed flip bucket

Zhang, L., Zhang, J., Guo, Yakun, Peng, Y. 20 April 2020 (has links)
Yes / In this study, the evolution process of the swallow-tailed flip bucket water nappe entering into the plunge pool is simulated by using the standard 𝑘-𝜀 turbulence model and the volume of fluid method. The effects of the upstream opening width ratio and downstream bucket angle on the flow pattern, the unit discharge distribution and the impact pressure distribution are studied. Based on the numerical results, the inner and outer jet trajectories are proposed by using the data. Results show that the longitudinal stretching length decreases with the increase of the upstream opening width ratio, and increases with the increase of the downstream bucket angle. The water nappe enters the plunge pool in a long strip shape. Thus, the unit discharge distribution of water nappe entry is consistent with the pressure distribution at the plunge pool bottom. The upstream opening width ratio and downstream bucket angle should be chosen as their intermediate values in order to have a uniform discharge distribution and to reduce the pressure peak at the plunge pool floor, which is effectively to avoid instability and destruction of plunge pool floor. / National Science Fund for Distinguished Young Scholars (No. 51625901) and National Nature Science Foundation of China (No: 51579165).
6

The Giant-con Gold Deposit: A Once-linked Archean Lode-gold System

Siddorn, James P. 31 August 2011 (has links)
The Giant and Con deposits, Yellowknife, Northwest Territories, represent a classic Archean lode-gold deposit now offset by a major Proterozoic fault (West Bay Fault). The link between the Giant and Con deposits is supported by their similarities. However, there are distinct differences between the two deposits in terms of the offset of stratigraphy, response to D2 deformation, geometry, gold mineralization styles, and depth of gold mineralization. Gold mineralization in the Giant-Con system formed over a protracted history of deformation and hydrothermal activity. Early D1 extension resulted in offset and excision of stratigraphy and the formation of refractory gold mineralization within strongly deformed schistose zones and quartz-carbonate veins. The main D2 deformation in the district resulted in the strong overprint of D1 refractory gold mineralization and was associated with the northwest-southeast flattening of the Giant deposit and progressive reverse-dextral shear of the Con deposit. Free-milling gold mineralization is associated with the D2 event, forming deeper in the Giant-Con system, creating a vertical zonation of free-milling quartz-carbonate veins overprinting earlier refractory gold mineralization that formed higher in the system. Ore plunge in the Giant deposit is controlled by the interaction of the original geometry of D1 deformation zones with the effects of D2 flattening. Ore plunge in the Con deposit is controlled by the orientation of F2 fold and B2 boudin axes in auriferous quartz-carbonate veins. D3 reactivation of the deformation zones (probably related to the end of the D2 compressive event) caused local reactivation of structures and is not associated with gold mineralization. D4 Proterozoic faulting offset and segmented the two deposits, including the major offset by the West Bay Fault. A new reconstruction of the West Bay Fault shows that the Con deformation zone is the down dip extension of the Giant deposit and not the Campbell deformation zone as previously thought.
7

Pleasure and utility : domestic bathrooms in Britain, 1660-1815

Graham, Elizabeth Ann January 2013 (has links)
The insertion of the bathroom into the floor plan of the traditional gentry house at the end of the seventeenth century disrupted the established sequence of rooms and the social order embodied in it. The gradual and uncoordinated trend towards bathroom ownership partook of the evolution of ideas about privacy, comfort and the specialisation of rooms in the grand house, and culminated in the compact bathroom. The revival of bathing took place against the backdrop of the Scientific Revolution, and was initiated by physicians. At first, the benefits of different methods of bathing were hotly contested. However, by the end of the century, physicians were beginning to believe that cleanliness, rather than cold water, was the key to good health. Although the rich often continued to build large plunge baths, this shift paved the way for the eventual dominance of the compact bathroom. At the beginning of the eighteenth century, a specialised bathing room within the house was out of reach for people of ordinary means. Changes to the plumbing trade were intertwined with developments that were to bring bathroom ownership within reach. In eighteenth-century Scotland, increasing numbers of bathroom projects might have been expected to expand the work of plumbers, but technological, commercial and legislative change—in particular the separation of design from construction—undermined their monopoly on their craft. Goods that had been manufactured on site and with local materials at the beginning of the eighteenth century were, by the beginning of the nineteenth, designed by a new breed of entrepreneur–inventor, manufactured by less skilled workers, and could be purchased in a shop and installed by a handyman with no particular trade identity. However, knowledge about the health benefits of bathing and technical advances are, in themselves, inadequate to account for the growing importance of bathrooms. The explanation lies in social, not technological or scientific change. Visiting public bathhouses exposed bathers to physical, moral and social pollution, at a time when failure to comply with the dictates of bodily cleanliness could provoke the disgust of one’s peers. Disgust constructed and policed the boundaries between social groups. Private bathing facilities met the requirements of bodily propriety without the risk of contamination. Moreover, a privately owned bathhouse in the grounds provided a focus for tourists or a site for intimate sociability. Bathhouses were a means of displaying wealth, taste and the fruits of the Grand Tour. Visitors could identify themselves with owners through the consumption of culture, improve their aesthetic skills through writing and drawing, and make claims to gentility through their appreciation of what they saw. As owners began to withdraw from the ever-increasing numbers of tourists, and from the formal sociability of the country seat, their bathhouses became a place for sociability in retirement which offered all kinds of entertainments, from boating and fishing, to cards and music.
8

Comparação entre os métodos convencional e com bocal modificado de aplicação de fluido de corte no processo de retificação cilíndrica interna /

Biscioni, Ricardo Pio Barakat. January 2010 (has links)
Resumo: Um processo muito utilizado na indústria metal-mecânica em geral para fabricação de componentes de responsabilidade é a operação de retificação cilíndrica interna de precisão, este processo é utilizado, por exemplo, na fabricação de anéis de rolamento e outros componentes. Atualmente a evolução das máquinas permitiu o aprimoramento deste processo no que diz respeito ao posicionamento e à rigidez do sistema máquina-peça-ferramenta, porém ainda são enfrentados grandes problemas quanto à lubrificação e refrigeração, principalmente no que diz respeito à utilização de fluidos de corte. Este trabalho visa o estudo do comportamento da operação de retificação cilíndrica interna de mergulho a alta velocidade, no processo de acabamento de um aço endurecido SAE 52100, utilizando-se um rebolo convencional e dois métodos de refrigeração: o método de refrigeração convencional e com um bocal modificado. O motivo para o emprego de um bocal modificado reside no fato de se encontrar uma alternativa viável para uma possível substituição do método convencional que consome grande quantidade de fluido, já que estes têm se tornando nas últimas décadas um grande problema para as indústrias, devido aos enormes dados ambientais e humanos que causam. Para efetivar a comparação entre os métodos de refrigeração foram analisados os dados a respeito da rugosidade, erros de circularidade e desgaste diametral do rebolo, além de análise de microdureza e MEV das amostras retificadas para os métodos de refrigeração citados anteriormente. Analisando os resultados a quebra de barreira aerodinâmica e a melhor eficiência da penetração do fluido de corte na região de contato entre o rebolo e a peça foi maior quando se utilizou o bocal modificado com vazão de 21 1/min (25 m/s); os resultados de rugosidade, erro de circularidade e desgaste do rebolo foram sempre... (Resumo completo, clicar acesso eletrÔnico abaixo) / Abstract: Precision internal plunge grinding is a process much used in the mechanical industry in general / Orientador: Eduardo Carlos Bianchi / Coorientador: Paulo Roberto de Aguiar / Banca: Carlos Elias da Silva Junior / Banca: Carlos Alberto Soufen / Mestre
9

Método prático para otimização do ciclo de retificação transversal de precisão / Practical way to optimization the cycle of precision plunge grinding

Rossi, Moacir Aparecido 13 March 2009 (has links)
Este trabalho descreve uma forma prática para planejamento do ciclo de operação de retificação por mergulho, em função da especificação dimensional da peça e da rigidez da máquina. Essa otimização é estendida além do ciclo, envolve produzir lotes de peças com dispersão das dimensões dentro de limites especificados. O tempo de set-up, que normalmente não está incluído no tempo de processo, aqui é incluído e considerado. A primeira atividade de laboratório teve como objetivo confirmar a relação entre a quantidade de material removido em função do tempo de spark-out. A segunda atividade comprovou a existência de uma relação linear entre a velocidade de avanço radial do rebolo e o diâmetro final da peça. A terceira atividade confirmou a existência de uma relação entre a velocidade de avanço radial e o índice de capabilidade especificado para o processo. Ainda, foi sugerida a inclusão deste processo proposto num programa CNC da máquina, de forma a se obter automaticamente o set-up. Concluiu-se que o método aqui apresentado reduziu significativamente o tempo de set-up da máquina conferindo um incremento de produtividade aos processos que fizerem uso deste princípio. / This work shows a practical way to design the cycle of a plunge grinding process as a function of workpiece dimensional specification and the machine stiffness. This optimization is extended beyond the cycle, it\'s included make batch of parts with dispersion within the specification limits. The set-up time, that usually isn\'t in the process time, here it was included and focused. The first activity of laboratory had an objective to confirm the relation of the amount of material removed as a function of spark out time. The second activity has been confirmed the linear relationship between the infeed velocity of the grinding wheel and the final diameter of the workpiece. The third activity has been confirmed the relation of the infeed velocity and the capability of the process. Yet, it was suggested to include this procedure in a CNC set of the machine to allow a faster and automatic set up. So, this work shows a conclusion that the set up time can be reduced a lot, allowing higher productivity for who use this procedure.
10

Método prático para otimização do ciclo de retificação transversal de precisão / Practical way to optimization the cycle of precision plunge grinding

Moacir Aparecido Rossi 13 March 2009 (has links)
Este trabalho descreve uma forma prática para planejamento do ciclo de operação de retificação por mergulho, em função da especificação dimensional da peça e da rigidez da máquina. Essa otimização é estendida além do ciclo, envolve produzir lotes de peças com dispersão das dimensões dentro de limites especificados. O tempo de set-up, que normalmente não está incluído no tempo de processo, aqui é incluído e considerado. A primeira atividade de laboratório teve como objetivo confirmar a relação entre a quantidade de material removido em função do tempo de spark-out. A segunda atividade comprovou a existência de uma relação linear entre a velocidade de avanço radial do rebolo e o diâmetro final da peça. A terceira atividade confirmou a existência de uma relação entre a velocidade de avanço radial e o índice de capabilidade especificado para o processo. Ainda, foi sugerida a inclusão deste processo proposto num programa CNC da máquina, de forma a se obter automaticamente o set-up. Concluiu-se que o método aqui apresentado reduziu significativamente o tempo de set-up da máquina conferindo um incremento de produtividade aos processos que fizerem uso deste princípio. / This work shows a practical way to design the cycle of a plunge grinding process as a function of workpiece dimensional specification and the machine stiffness. This optimization is extended beyond the cycle, it\'s included make batch of parts with dispersion within the specification limits. The set-up time, that usually isn\'t in the process time, here it was included and focused. The first activity of laboratory had an objective to confirm the relation of the amount of material removed as a function of spark out time. The second activity has been confirmed the linear relationship between the infeed velocity of the grinding wheel and the final diameter of the workpiece. The third activity has been confirmed the relation of the infeed velocity and the capability of the process. Yet, it was suggested to include this procedure in a CNC set of the machine to allow a faster and automatic set up. So, this work shows a conclusion that the set up time can be reduced a lot, allowing higher productivity for who use this procedure.

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