O objetivo deste trabalho é realizar um estudo comparativo da recristalização de dois aços rápidos, AISI M2 (Werkstoffnummer 1.3343) e ABC III (Werkstoffnummer 1.3333), após o encruamento resultante do processo de laminação a frio de chapas planas utilizadas para a confecção de serras fitas. Estudar a recristalização estática nesta classe de aços é relevante, pois eles freqüentemente são laminados a frio e recozidos na etapa final de processamento, antes da confecção da peça ou componente. Inicialmente, foi realizada a caracterização das amostras no estado como recebido, ou seja \'\'laminado a quente\'\'. A caracterização envolveu análise química, ensaios mecânicos, microscopia óptica, microscopia eletrônica de varredura, medidas de dureza e dilatometria. Em seguida, as amostras sofreram deformação a frio da ordem de até 50% de redução em espessura para determinação das curvas de endurecimento por deformação. Amostras com 25% de redução foram recozidas entre 100ºC e 750ºC, durante 1 hora e os resultados de dureza foram utilizadas para determinar as curvas isócronas de amolecimento. Amostras com 25% redução foram recozidas entre 600ºC e 750ºC, entre 15 e 480 minutos para cada uma das temperaturas, para determinação curvas isotérmicas de amolecimento. Resultados da análise microestrutural mostraram que o aço rápido AISI M2 apresenta uma distribuição mais homogênea de carbonetos. Esses carbonetos são mais finos em relação aos do aço ABC III, que apresenta uma distribuição mais heterogênea. Os dois aços apresentaram curvas muito similares de endurecimento por deformação. Após recozimento das amostras encruadas, foi verificado que o aço AISI M2 apresenta recuperação e recristalização levemente mais rápidas quando comparado com o ABC III. Ainda na etapa de recuperação e antes da recristalização, notou-se nos dois aços um pequeno aumento de dureza, principalmente entre 30 e 60 minutos de recozimento, na faixa de 650 ºC e 700ºC. Utilizando-se análises por difração de elétrons retroespalhados (microtextura e mesotextura) observou-se que o aço ABC III apresenta maior resistência para a recristalização se completar que o aço AISI M2. / This work aims at the comparative study of the recrystallization of two high-speed steels, namely AISI M2 (Werkstoffnummer 1.3343) and ABC III (Werkstoffnummer 1.3333), hardened by cold rolling of sheets employed in the production of band saws. Studying static recrystallization in this class of steels is relevant, since frequently they are cold rolled and annealed in their final processing stage, prior to the actual work piece manufacturing. Initially, samples have been characterized in the as-received condition, i.e. hot rolled. Characterization involved chemical analysis, tensile testing, optical metallography, scanning electron microscopy, hardness measurements and dilatometry. Following, samples have been cold worked with a 50% thickness reduction in order to evaluate the cold work hardening curves. Samples with 25% reduction have been annealed at temperatures in the 100oC to 750oC range, for one hour and hardness results have been used to determine the isochronous softening curves. Samples with 25% reduction have been annealed between 600 oC and 750oC for 15 to 480 minutes, for each one of the temperatures, to determine the isothermal softening curves. The microstructural analysis has shown that the AISI M2 steel presents a homogeneous carbide distribution. These carbides were fine when compared to those of the ABCIII steel that presented a heterogeneous distribution. Both steels presented similar work-hardening curves. After annealing the cold worked samples, it has been observed that the AISI M2 steel presented a slightly faster recovery and recrystallization than the ABCIII steel. Still in the recovery stage, prior to recrystallization, both steels showed a small hardness increase, mainly on annealing during 30 to 60 minutes in the 650oC to 700oC temperature range. Using electron backscattered diffraction analysis (microtexture and mesotexture) it has been observed that the ABCIII steel presented higher resistance to complete recrystallization than the AISI M2 steel.

The middle ear plays an integral role in the normal hearing process by transforming sound energy from the air inside the ear canal into vibrations of the inner-ear fluid, and a malfunction in any middle-ear component can lead to significant hearing loss. Despite decades of research on the Tympanic Membrane (TM or eardrum), the transformation of sound energy into ossicular mechanical vibrations is not yet well understood. Part of this is because the available clinical and research tools provide insufficient data to understand the complexities of this transformation. The data insufficiency arises due to methodological, technological, and physiological limitations such as required nanometer and microsecond spatio-temporal resolutions of the sound-induced TM motions. Although holographic methods provide nondestructive non-contact measuring capabilities that satisfy most of the constraints for TM measurements, the influence of large submillimeter scale physiological motions in live samples produced by heartbeat and breathing can result in near complete saturation of TM holograms. In this Dissertation, a new high-speed correlation interferometry holographic method is proposed that can compensate for the effects of physiological noise using an open-loop control configuration. Preliminary animal measurements with the proposed method demonstrate the necessary accuracy and precision to measure the motion of the entire TM produced by short- duration (≥1 kHz) transient stimuli. Such rapid measurements reduce the effect of the longer and slower environmental and physiologic noises, and enable clinical applications. In the second part of this Dissertation, a novel multiple wavelength high-speed holographic interferometric shape measurement method is incorporated into the high-speed displacement measurements. The method uses the imaging optics of the displacement measurement system to perform shape and orientation measurements. Displacement and shape measurements can be made in less than 200 msec and allow computation of true surface-normal displacements. The surface-normal measurements are independent of the direction of observation, which helps comparisons of measurements made after changes in TM orientation or location. The results enable accurate and precise shape and displacement measurements for use in applications such as modal and finite element analyses, additive manufacturing of prosthetic TM grafts, clinical diagnosis, hearing rehabilitation, as well as optimization of hearing devices. In addition, measured shape parameters such as curvature, depth of cone etc., can help us understand TM mechanics and contribute to quantitative diagnostic assessments.

Quality-of-service (QoS) requirements for the timely delivery of real-time multimedia raise new challenges for the networking world. A key component of QoS is QoS routing which allows the selection of network routes with sufficient resources for requested QoS parameters. Several techniques have been proposed in the literature to compute QoS routes, most of which require dynamic update of link-state information across the Internet. Given the growing size of the Internet, it is becoming increasingly difficult to gather up-to-date state information in a dynamic environment. We propose a new technique to compute QoS routes on the Internet in a fast and efficient manner without any need for dynamic updates. Our method, known as Selective Flooding, checks the state of the links on a set of pre-computed routes from the source to the destination in parallel and based on this information computes the best route and then reserves resources. We implemented Selective Flooding on a QoS routing simulator and evaluated the performance of Selective Flooding compared to source routing for a variety of network parameters. We find Selective Flooding consistently outperforms source routing in terms of call-blocking rate and outperforms source routing in terms of network overhead for some network conditions. The contributions of this thesis include the design of a new QoS routing algorithm, Selective Flooding, extensive evaluation of Selective Flooding under a variety of network conditions and a working simulation model for future research.

"On-off control of hydraulic circuits enables significant improvements in efficiency compared with throttling valve control. A key enabling technology to on-off control is an efficient high speed on-off valve. This project aims to design an on-off hydraulic valve that minimizes input power requirements and increases operating frequency over existing technology by utilizing a continuously rotating valve design. This is accomplished through use of spinning port discs which chop the flow into pulses, with the relative phase between these discs determining the pulse duration. A mathematical model for determining system efficiency is developed with a focus on the throttling, leakage, compressibility, and viscous friction power losses of the valve. Parameters affecting these losses were optimized to produce the most efficient design under the chosen disc-style architecture. Using these optimum parameter values, a first generation prototype valve was developed and experimental data collected. The experimental valve matched predicted output pressure and flows well, but suffered from larger than expected torque requirements and leakage, resulting in a maximum efficiency of 38% at 1.0 duty ratio. Also, due to motor limitations, the valve was only able to achieve a 64Hz switching frequency versus the designed 100Hz frequency. Future design iterations will need to focus on controlling leakage, hydrodynamically balancing the spinning port disc axially to reduce torque requirements, developing a computational fluid dynamics model to gain further insight into the workings of the valve, and creating a control methodology for single and multiple high speed valves."

"3D shape measurements are critical in a range of fields, from manufacturing for quality measurements to art conservation for the everlasting archival of ancient sculptures. The most important factor is to gather quantitative 3D information from measurement devices. Currently, there are limitations of existing systems. Many of the techniques are contact methods, proving to be time consuming and invasive to materials. While non-contact methods provide opportunities, many of the current systems are limited in versatility. This project focuses on the development of a fringe projection based system for 3D shape measurements. The critical advantage of the fringe projection optical technique is the ability to provide full field-of-view (FOV) information on the order from several square millimeters to several square meters. In the past, limitations in speed and difficulties achieving sinusoidal projection patterns have restricted the development of this particular type of system and limited its potential applications. For this reason, direct coding techniques have been incorporated to the developed system that modulate the intensity of each pixel to form a sinusoidal pattern using a 624 nm wavelength MEMS based spatial light modulator. Recovered phase data containing shape information is obtained using varying algorithms that range from a single image FFT analysis to a sixteen image, phase stepping algorithm. Reconstruction of 3D information is achievable through several image unwrapping techniques. The first is a spatial unwrapping technique for high speed applications. Additionally, the system uses an optimized Temporal Phase Unwrapping (TPU) algorithm that utilizes varying fringe frequencies ranging from 4 to 512 pixels per fringe to recover shape information in the time domain. This algorithm was chosen based on its robustness and accuracy for high resolution applications [Burke et al., 2002]. Also, unwrapping errors are minimized by approximately 90% as the number of images used is increased from the minimum to maximum fringe density. Cxoontrary to other systems, the 3D shape measurement system developed in the CHSLT laboratories has unprecedented versatility to accommodate a variety of applications with the z-depth resolution of up to 25.4 µm (0.001 inches) and speeds close to 200 frames per second. Hardware systems are integrated into user-friendly software that has been customized for fringe projection. The system has been tested in two extreme environments. The first is for quantification of cracks and potholes in the surface of roads under dynamic conditions. The second application was digitization of an art sculpture under static conditions. The system shows promising results and the potential for high quality images via algorithm optimization. Most importantly, there is potential to present real time 3D information at video speeds."

This work presents information obtained from high-speed video and electrical monitoring of electrical breakdown (discharge) events during plasma electrolytic oxidation (PEO) of aluminium alloy substrates. Discharges were found to occur in extended sequences termed "cascades" at particular locations. This was a feature common to all the substrates and processing frequencies investigated. As the coating thickness increases, the characteristics remained broadly similar, although discharges become more energetic and longer-lived. Short PEO treatments were applied to existing PEO coatings in order to investigate the microstructural effects of discharge cascades. It was found that cascades persist at particular locations due to the residual deep pore channel left by previous discharges in the cascade. Observations were made of the way the coating was restructured around a cascade location. Samples were illuminated with very high intensity flashes during PEO processing, revealing that relatively large (1 mm diameter) bubbles form where a discharge emerges from the surface of a coating. Analysis of the overall energy consumption, as well as the energetic processes occurring within an individual discharge, indicate that the bubble growth occurs due to rapid volatilisation of water originating from the electrolyte. It is postulated that the growth of this bubble causes the electrical resistance to rise and is responsible for the termination of the discharge current. Investigations of high frequency (2,500 Hz) processing lead to the discovery of discharges occurring during the cathodic half-cycle, after a certain coating thickness had been achieved. Cathodic discharges were more energetic than anodic discharges, and created large craters in the coatings. Gas evolution was found to exceed the electrochemical Faraday yield, and was similar at low and high frequency initially. Once cathodic discharges began, the gas evolution rate increased and the coating mass gain levelled off.

This thesis presents a combined numerical and experimental study on the response of kidney cells to shock waves. The motivation was to develop a mechanistic model of cell deformation in order to improve the clinical use of shock waves, by either enhancing their therapeutic action against target cells or minimising their impact on healthy cells. An ultra-high speed camera was used to visualise individual cells, embedded in tissue-mimicking gel, in order to measure their deformation when subject to a shock wave from a clinical shock wave source. Advanced image processing was employed to extract the contour of the cell from the images. The evolution of the observed cell contour revealed a relatively small deformation during the compressional phase and a much larger deformation during the tensile phases of a shock wave. The experimental observations were captured by a numerical model which describes the volumetric cell response with a bilinear Equation of State and the deviatoric cell response with a viscoelastic framework. Experiments using human kidney cancer cells (CAKI-2) and noncancerous kidney cells (HRE and HK-2) were compared to the model in order to determine their mechanical properties. The differences between cancerous and noncancerous cells were exploited to demonstrate a design process by which shock waves may be able to improve the specificity on targeted cancer cells while having minimal effect on normal cells. The cell response to shock waves was studied in a more biophysically realistic environment to include influence of cell size, shape and orientation, and the presence of neighbouring cells. The most significant difference was predicted when cells were in a cluster in which case the presence of neighbouring cells resulted in a four-fold increase on the von Mises stress and the membrane strain. Finally the numerical model was extended to capture the effect of cell damage using one of two paradigms. In the first paradigm the model captured microdamage during one shock wave but then assumed that the cell recovered by the time the next shock wave arrived. The second model allowed microdamage to accumulate with increasing number of shock waves. These models may be able to explain the strong effect that shock wave loading rate has on tissue damage. In conclusion a validated numerical model has been developed which provides a mechanistic understanding of how cells respond to shock waves. The model has application in suggesting improved strategies for current uses of shock waves, e.g., lithotripsy, as well as opening up new indications such as cancer treatment.

Lo, Ming Gai Stanley. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 131-135). / Abstracts in English and Chinese. / Title Page --- p.i / Abstract --- p.ii / Acknowledgements --- p.v / Table of Contents --- p.vii / List of Figures --- p.ix / List of Tabic --- p.xiv / Chapter Chapter 1: --- Introduction --- p.1 / Chapter 1.1 --- Photonic Integrated Circuits --- p.1 / Chapter 1.2 --- Silicon Photonics --- p.7 / Chapter 1.3 --- Optical Modulators --- p.15 / Chapter 1.4 --- Modulation Mechanisms in Silicon --- p.19 / Chapter 1.5 --- Motivation --- p.27 / Chapter 1.6 --- Thesis Outline --- p.28 / Chapter Chapter 2: --- Use of Silicon-bascd Modulators in Radio-over-fiber Optical Links --- p.29 / Chapter 2.1 --- Modeling of Linearity of Silicon Carrier Depletion-based Modulators --- p.31 / Chapter 2.2 --- Modeling of Dependence of Linearity on Various Diode Structures --- p.45 / Chapter 2.3 --- Experiment of Radio-over-Fiber Signal Transmission by a Carrier-Injection Silicon Microring Modulator --- p.52 / Chapter 2.3.1 --- Device Fabrication --- p.53 / Chapter 2.3.2 --- Experimental Setups --- p.59 / Chapter 2.3.3 --- Experimental Results --- p.61 / Chapter 2.4 --- Summary --- p.66 / Chapter Chapter 3: --- Novel Diode Structures and T-Rail Travelling-Wave Electrodes to Enhance the Performance of Depletion-based Modulators --- p.67 / Chapter 3.1 --- Requirements of Diode Design for Depletion-based Optical Modulators --- p.70 / Chapter 3.2 --- Diode Design Principle --- p.72 / Chapter 3.3 --- Modeling Results of Vertical-Junction p-n Diodes --- p.79 / Chapter 3.4 --- Fabrication Process of the Silicon Modulator --- p.88 / Chapter 3.5 --- Experimental Results of the Fabricated Devices --- p.92 / Chapter 3.6 --- T-Rail Travelling-Wave Electrodes --- p.102 / Chapter 3.6.1 --- The Limiting Factors to the Speed of Depletion-based Modulators --- p.102 / Chapter 3.6.2 --- The Design Principle of T-Rail Travelling-Wave Electrodes --- p.104 / Chapter 3.6.3 --- The Fabricated Devices --- p.111 / Chapter 3.7 --- Summary --- p.112 / Chapter Chapter 4: --- Conclusion and Future Work --- p.113 / Chapter 4.1 --- Conclusion --- p.113 / Chapter 4.1.1 --- Use of Silicon-based Modulators in Radio-over-fiber Optical Links --- p.113 / Chapter 4.1.2 --- Novel Diode Structures and T-Rail Travelling-Wave Electrodes to Enhance the Performance of Depletion-based Modulators --- p.114 / Chapter 4.2 --- Future Work --- p.116 / Chapter Appcndix-A --- List of Symbols --- p.118 / Chapter Appcndix-B --- List of Abbreviations --- p.120 / Chapter Appcndix-C --- Principles of Various Optical Structures of Modulators --- p.123 / Chapter Appcndix-D --- Modeling of Refractive Index Change by Free-Carrier Plasma Dispersion Effcct --- p.127 / Reference --- p.131 / Publication List --- p.136

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Li-Moon Wann. / M.S.

No presente trabalho foi investigada a nitretação a plasma do aço rápido ASTM M2 utilizando diferentes configurações, envolvendo as técnicas convencional e com tela ativa. Na técnica convencional, o material a ser nitretado atua como o cátodo do sistema, sendo coberto diretamente pela bainha da descarga luminescente. Nos tratamentos conduzidos com a técnica de tela ativa, uma estrutura de tela em formato cilíndrico atua como cátodo e o material a ser nitretado é posicionado no seu interior. Neste novo processo, como não há potencial elétrico externo aplicado aos substratos, a descarga luminescente se desenvolve apenas na estrutura da tela, evitando problemas intrínsecos do método convencional de nitretação a plasma. Todos os tratamentos investigados foram executados com os seguintes parâmetros: Temperatura de 500 °C, mistura gasosa composta 76% de volume de gás nitrogênio e 24% de volume de gás hidrogênio e pressão de 3 milibar. Para os tratamentos com tela ativa, os substratos foram mantidos eletricamente isolados. Os resultados foram comparados observando a diferença de método de nitretação (com e sem o uso de tela ativa) e a influência do tempo de tratamento (variando sua duração em 1, 4 e 8 horas) Todos os experimentos foram realizados utilizando uma fonte de potência de tensão retificada aplicada na tela ou nas amostras, dependendo da configuração. Adicionalmente, para o tempo de nitretação de 4 horas uma fonte de potência com tensão pulsada também foi aplicada. As amostras nitretadas foram caracterizadas por ensaios de rugosidade, ensaios de dureza e microdureza, microscopia ótica, microscopia eletrônica de varredura e difração de raios-X. Ensaios tribológicos para avaliação da resistência ao desgaste das diferentes condições de tratamento foram conduzidos. Dentre os principais resultados foi observada uma clara diferença na profundidade de camada nitretada, que foi sempre mais profunda nos tratamentos convencionais. Apesar de formadas camadas menos profundas, as amostras nitretadas oriundas dos tratamentos com tela ativa demonstraram melhor desempenho nos ensaios tribológicos, resultando em taxas de desgaste até sete vezes inferior do que as amostras do nitretadas convencionalmente, este resultado foi atribuído a não formação da zona de compostos nas amostras nitretadas com tela ativa. / In the present work an investigation on the plasma nitriding of ASTM M2 High-Speed Steel using different configurations was carried out, involving traditional and active screen techniques. In the traditional technique, the material to be nitrided act as the system cathode, being directly covered by the glow discharge sheath. In the active screen treatments, a cylindrical mesh structure (screen) plays the role of the cathode and the material to be nitrided is positioned in its interior. In this new process, as there is no external electric potential applied to the specimens, the glow discharge develops only in the screen structure, avoiding intrinsic problems from the conventional plasma nitriding method. All the studied treatments were carried out with the following parameters: temperature of 500 °C, gas mixture of 76 vol.-% N2 and 24 vol.-% H2 and pressure of 3 millibar. For the active screen treatments, the samples were kept electrically insulated. The results were compared observing the differences in the nitriding method (with and without the use of active screen) and the nitriding time influence (varying its duration in 1, 4 and 8 hours) All experiments were carried using a rectified voltage power supply applied to the screen or to the samples, depending on the configuration. Additionally, for the nitriding time of 4 hours a pulsed voltage power supply was also employed. The nitrided samples were characterized by roughness tests, hardness and microhardness tests, optical microscopy and scanning electron microscopy, X-ray diffraction. Tribological tests to evaluate the wear resistance of the different treatment conditions were also carried out. Among the main results a clear difference in the case layer depth was noticed, which was always deeper in the conventional treatments. Although forming shallower case depths, the active screen nitrided specimens presented better performance in the tribological tests, resulting in wear rates up to seven times lower than the wear rate for conventionally plasma nitrided samples, this result was assigned due to the non-formation of compound layer in the active screen plasma nitrided samples.