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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.
31

Estudo das etapas de fabricação de dispositivos eletro-termo-ópticos utilizando o interferômetro Mach-Zehnder. / Study of the fabrication steps of an electro-thermo-optical device using Mach-Zehnder interferometer.

Alexandre Martin Mina 29 July 2008 (has links)
Neste trabalho é realizado o estudo das etapas de fabricação de um dispositivo eletro-termo-óptico. O dispositivo baseia-se em um interferômetro Mach-Zehnder (IMZ) onde um micro-resistor é colocado em um dos braços do IMZ. Este interferômetro foi construído usando guias de onda ARROW (Anti-Resonant Reflecting Optical Waveguide) onde filmes de oxinitreto de silício e carbeto de silício amorfo hidrogenado foram utilizados como materiais constituintes. Estes materiais foram depositados pela técnica de PECVD (Plasma Enhanced Chemical Vapor Deposition) a baixas temperaturas (~300°C) usando silano (SiH4), nitrogênio (N2), hidrogênio (H2), oxido nitroso (N2O) e metano (CH4) como gases precursores. Para isolar termicamente a região de aquecimento do dispositivo, parte do braço sensor do IMZ foi suspenso através da corrosão superficial do substrato de silício em solução de hidróxido de potássio (KOH). Basicamente o dispositivo termo-eletroóptico utiliza para seu funcionamento o efeito termo-óptico dos materiais constituintes. Neste caso, com a aplicação de uma corrente elétrica no micro-resistor localizado em uma pequena região de um dos braços do IMZ é produzido uma variação na temperatura e no índice de refração dos filmes próximos ao microresistor. Com isto, o aparecimento de uma diferença de fase entre as ondas propagantes dos dois braços do IMZ é ocasionado e, como conseqüência, uma interferência eletromagnética dependente da diferença de fase das ondas propagantes causada pela variação de temperatura é originado. Dessa maneira, é possível fabricar um dispositivo termo-eletro-óptico onde uma variação da corrente aplicada no micro-resistor produz uma alteração da potência óptica na saída do interferômetro. / In this work, a study of the steps to fabricate an electro-thermo-optical device is realized. This device is based in a Mach-Zehnder interferometer (IMZ) where a micro-resistor is placed in one of the IMZ arms. The Mach-Zehnder interferometer was fabricated using Anti-Resonant Reflecting Optical Waveguide (ARROW) where oxinytride and amorphous hydrogenated silicon carbide films were used as constituent materials. These materials were deposited by PECVD (Plasma Enhanced Chemical Vapor Deposition) technique at low temperatures (~300°C) using silane (SiH4), nitrogen (N2), hydrogen (H2), nitrous oxide (N2O) and methane (CH4) as precursor gases. In order to isolate thermally the heating region of the structure, part of the IMZ sensor arm was suspended by the surface etching of the silicon substrate in KOH solution. Basically, the electro-thermo-optical device is based in the Thermo- Optic Effect of the constituent materials. In this case, with the application of an electrical current in the micro-resistor located in a small region of the sensor arm of the IMZ, a change in the temperature and in the refractive index of the films close to the micro-resistor is produced. So, a phase difference between the electromagnetic waves that travel by the two arms of the IMZ is produced and, as consequence, an electromagnetic interference dependent of the temperature variation is originated. In this way, it is possible fabricate an electro-thermo-optical device where the optical power output depends of the electrical current applied to a micro-resistor.
32

Aplicação do interferômetro de Gires-Tournois em linearização de moduladores eletroópticos de intensidade.

Braulio Fernando Ribeiro Sakamoto 17 November 2006 (has links)
Este trabalho apresenta um estudo analítico da aplicação do Interferômetro de Gires-Tournois (GTI, Gires-Tournois Interferometer) em linearização de moduladores eletroópticos de intensidade. Os dispositivos abordados consistem, basicamente, em Moduladores Interferométricos do tipo Mach-Zehnder (Mach-Zehnder Modulator, MZM) ou equivalentes, em cujas estruturas foram adicionadas os GTI, como técnica de linearização de sua característica de transmissão. Os moduladores assim obtidos apresentam configurações tais que utilizam estruturas de microondas a parâmetros concentrados, sendo os conceitos apresentados através do ponto de vista de óptica volumétrica. Serão abordados inicialmente os fundamentos de modulação eletroóptica, com ênfase no efeito eletroóptico, conhecimentos esses necessários ao entendimento do processo de modulação eletroóptica. Os moduladores de fase de parâmetros concentrados e parâmetros distribuídos são apresentados. Aborda-se também o modulador eletroóptico tipo Mach-Zehnder, convencionalmente empregado na maioria dos enlaces ópticos atuais e que servirá de referência na avaliação dos modulares com características de baixa distorção. Abordam-se as cavidades GTI em sua estrutura original, derivada do interferômetro de Fabry-Perot, para em seguida analisar seu emprego como modulador eletroóptico de fase, na situação em que a cavidade óptica é preenchida com material eletroopticamente ativo. O modulador linearizado de intensidade, empregando apenas uma célula GTI em versão birrefringente, é apresentada e analisada. Por fim, quantiza-se a distorção desta última configuração, através da determinação de sua faixa dinâmica livre de distorção, SFDR (Spur-Free Dynamic Range) e compara-se com o caso convencional empregando o MZM. Finalmente, são apresentadas as conclusões obtidas ao longo desta tese, bem como algumas sugestões de continuidade dos trabalhos nesta linha de pesquisa.
33

Flowfield Characterization of the Boeing/AFOSR Mach-6 Quiet Tunnel

Kathryn A. Gray (5930645) 03 January 2019 (has links)
<div>The quiet-flow capabilities of the Boeing/AFOSR Mach-6 Quiet Tunnel have been well established in the last decade, but a full characterization of the nozzle flow is an ongoing project. Pitot probes outtted with Kulite pressure transducers were used to further the investigation of the tunnel's flowfield. Noise levels were calculated by integrating the power spectral densities of the measured pitot pressure fluctuations, and experiments were performed to investigate several aspects of the flow.</div><div><br></div><div><div>First, the temperature distribution along the nozzle was varied to determine if heating had an effect on the stability of the laminar nozzle-wall boundary layer. Runs made with initial stagnation pressures slightly above the maximum quiet pressure determined that additional nozzle-wall heating did not have an effect on the amount of runtime which experienced quiet flow. In addition, pitot-probe measurements were taken at various locations to better determine the axial dependence of the noise levels. Experiments were also performed using pitot probes of varying forward-facing diameters to determine the effects of probe geometry on the measured fluctuations. The results were found to differ signicantly from simulations and from a previous set of experimental data, but a likely cause of the discrepancies was not found. A pitot probe mounted on the base of a cone confirmed that the aft end of a model does experience quiet flow. Finally, characterization of the flowfield was attempted when the tunnel is run using helium. The measured pressures for these experiments have a signicant level of uncertainty because the sensor calibration changes as helium diffuses across the diaphragm. Nevertheless, the measurements suggest that there may be periods of uniform flow, although these periods remain unstable and unsteady.</div></div><div><br></div><div><br></div>
34

The design and implementation of a load distribution facility on Mach.

January 1997 (has links)
by Hsieh Shing Leung Arthur. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1997. / Includes bibliographical references (leaves 78-81). / List of Figures --- p.viii / List of Tables --- p.ix / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Background and Related Work --- p.4 / Chapter 2.1 --- Load Distribution --- p.4 / Chapter 2.1.1 --- Load Index --- p.5 / Chapter 2.1.2 --- Task Transfer Mechanism --- p.5 / Chapter 2.1.3 --- Load Distribution Facility --- p.6 / Chapter 2.2 --- Load Distribution Algorithm --- p.6 / Chapter 2.2.1 --- Classification --- p.6 / Chapter 2.2.2 --- Components --- p.7 / Chapter 2.2.3 --- Stability and Effectiveness --- p.9 / Chapter 2.3 --- The Mach Operating System --- p.10 / Chapter 2.3.1 --- Mach kernel abstractions --- p.10 / Chapter 2.3.2 --- Mach kernel features --- p.11 / Chapter 2.4 --- Related Work --- p.12 / Chapter 3 --- The Design of Distributed Scheduling Framework --- p.16 / Chapter 3.1 --- System Model --- p.16 / Chapter 3.2 --- Design Objectives and Decisions --- p.17 / Chapter 3.3 --- An Overview of DSF Architecture --- p.17 / Chapter 3.4 --- The DSF server --- p.18 / Chapter 3.4.1 --- Load Information Module --- p.19 / Chapter 3.4.2 --- Movement Module --- p.22 / Chapter 3.4.3 --- Decision Module --- p.25 / Chapter 3.5 --- LD library --- p.28 / Chapter 3.6 --- User-Agent --- p.29 / Chapter 4 --- The System Implementation --- p.33 / Chapter 4.1 --- Shared data structure --- p.33 / Chapter 4.2 --- Synchronization --- p.37 / Chapter 4.3 --- Reentrant library --- p.39 / Chapter 4.4 --- Interprocess communication (IPC) --- p.42 / Chapter 4.4.1 --- Mach IPC --- p.42 / Chapter 4.4.2 --- Socket IPC --- p.43 / Chapter 5 --- Experimental Studies --- p.47 / Chapter 5.1 --- Load Distribution algorithms --- p.47 / Chapter 5.2 --- Experimental environment --- p.49 / Chapter 5.3 --- Experimental results --- p.50 / Chapter 5.3.1 --- Performance of LD algorithms --- p.50 / Chapter 5.3.2 --- Degree of task transfer --- p.54 / Chapter 5.3.3 --- Effect of threshold value --- p.55 / Chapter 6 --- Conclusion and Future Work --- p.57 / Chapter 6.1 --- Summary and Conclusion --- p.57 / Chapter 6.2 --- Future Work --- p.58 / Chapter A --- LD Library --- p.60 / Chapter B --- Sample Implementation of LD algorithms --- p.65 / Chapter B.l --- LOWEST --- p.65 / Chapter B.2 --- THRHLD --- p.67 / Chapter C --- Installation Guide --- p.71 / Chapter C.1 --- Software Requirement --- p.71 / Chapter C.2 --- Installation Steps --- p.72 / Chapter C.3 --- Configuration --- p.73 / Chapter D --- User's Guide --- p.74 / Chapter D.1 --- The DSF server --- p.74 / Chapter D.2 --- The User Agent --- p.74 / Chapter D.3 --- LD experiment --- p.77 / Bibliography --- p.78
35

A study of transonic normal shock wave-turbulent boundary layer interactions in axisymmetric internal flow /

Om, Deepak. January 1982 (has links)
Thesis (Ph. D.)--University of Washington, 1982. / Vita. Includes bibliographical references.
36

Design and Fabrication of Straight and Curve Optical Waveguides and Ring Cavity Wavelength Filter

Lin, Cheng-Nan 30 July 2007 (has links)
The goal of the thesis is to fabricate the integrated asymmetric Mach-Zehnder Interferometer and optical waveguide ring resonator with simple fabrication process. 1.41£gm and 1.49£gm symmetric quantum well InGaAlAs epitaxial wafer is used to fabricate the devices. In the asymmetric Mach-Zehnder Interferometer , we design asymmetric straight waveguides with difference optical path differences £GL=480£gm, 970£gm, and 1900£gm. And asymmetric bend waveguides with curvature radius differences £GR=260£gm, 200£gm, 160£gm, and 100£gm. By this design, we can observe the interference variation of output light. In optical waveguide ring resonator design, we reduce the length of original K=0.15 Multi-Mode Interference (MMI) by stepped-width waveguide. By three-stepped width waveguide MMI design, it can be reduced 33.2% length. We obtain different transmission spectrum by adjusting the splitting ratio of MMI couplers (K=0.85, 0.5, and 0.15) and cascading doudle rings. We use a series of two ring resonators by MMI (K0=0.5,K1=0.15,K2=0.5) to get the FSR=50GHz. In fabrication process, we combined dry etching method with RIE-ICP and wet etching to get smooth sidewall and highly vertical waveguide. In measure , we get the FSR= 41.25 GHZ in throughput port in double ring filters . No signal in drop port was obserred due to material absorption, bending loss, and waveguide loss.
37

Bifurcating Mach Shock Reflections with Application to Detonation Structure

Mach, Philip 26 August 2011 (has links)
Numerical simulations of Mach shock reflections have shown that the Mach stem can bifurcate as a result of the slip line jetting forward. Numerical simulations were conducted in this study which determined that these bifurcations occur when the Mach number is high, the ramp angle is high, and specific heat ratio is low. It was clarified that the bifurcation is a result of a sufficiently large velocity difference across the slip line which drives the jet. This bifurcation phenomenon has also been observed after triple point collisions in detonation simulations. A triple point reflection was modelled as an inert shock reflecting off a wedge, and the accuracy of the model at early times after reflection indicates that bifurcations in detonations are a result of the shock reflection process. Further investigations revealed that bifurcations likely contribute to the irregular structure observed in certain detonations.
38

Amplification of solitary waves along a vertical wall

Li, Wenwen 16 November 2012 (has links)
Reflection of an obliquely incident solitary wave at a vertical wall is studied experimentally in the laboratory wave tank. Precision measurements of water-surface variations are achieved with the aid of laser-induced fluorescent (LIF) technique and detailed temporal and spatial features of the Mach reflection are captured. During the development stage of the reflection process, the stem wave is formed with the wave crest perpendicular to the wall; this stem wave is not in the form of a Korteweg-de Vries (KdV) soliton but a forced wave, trailing by a continuously broadening depression wave. Evolution of stem-wave amplification is in good agreement with the Kadomtsev-Petviashvili (KP) theory. The asymptotic characteristics and behaviors are also in agreement with the theory of Miles (1977b) except those in the neighborhood of the transition between the Mach reflection and the regular reflection. The maximum fourfold amplification of the stem wave at the transition predicted by Miles is not realized in the laboratory environment: the maximum amplification measured in the laboratory is 2.92, which is however in excellent agreement with the numerical results of Tanaka (1993). The present laboratory study is the first to sensibly analyze validation of the theory; note that substantial discrepancies exist from previous (both numerical and laboratory) experimental studies. Agreement between experiments and theory can be partially attributed to the large-distance measurements that the precision laboratory apparatus is capable of. More important, to compare the laboratory results with theory, the corrected interaction parameter is derived from proper interpretation of the theory in consideration of the finite incident wave angle. Our laboratory data indicate that the maximum stem wave can reach higher than the maximum solitary wave height. The wave breaking along the wall results in the substantial increase in wave height and slope away from the wall. Extending the foregoing study on the reflection of a single solitary wave at a vertical wall, laboratory and numerical experiments are performed on two co-propagating obliquely incident solitary waves with different amplitudes that are reflected at the wall. The larger wave catches up with the smaller wave; hence the two waves collide with the strong interaction. The resulting wave pattern near the wall is complex due to the interaction among the two incident solitons and the two reflected solitons. The numerical predictions of the KP theory are in good agreement with the experimental results. Another comparison of the KP theory with laboratory experiments is demonstrated for one of the exact soliton solutions of the KP equation by Chakravarty and Kodama (2009). This solution is called the T-type solution by Kodama. The theoretically predicted formation of the 'box'-shape wave pattern in the vicinity of two-soliton intersection is realized in the laboratory tank. The agreement between the laboratory observation and the KP theory is found better for the cases with the larger wave amplitude a and smaller oblique angle ψ (i.e. tan ψ/(√3a cos ψ) < 0.6). Subtle and unavoidable differences among the analytical KP solution, the setup of numerical calculation, and the laboratory condition are discussed. / Graduation date: 2013
39

Numerical Determination Of The Transition Boundary Between Regular and Mach Reflection For Planar Shocks Striking Wedges and Cones in Air

Michalagas, Dean Andrew 15 February 2010 (has links)
A numerical investigation of the interaction of a planar shock wave with a rigid wedge and cone in an air-filled shock tube is performed by computing the unsteady flow field of the interaction process. The Euler and Navier-Stokes equations are solved in two dimensions to produce flow solutions for regular and Mach reflections with and without the viscous and thermal boundary layer on the inclined surface. The transition boundary between these two patterns is determined by changing both the shock strength and the angle of the inclined surface so that the simulations are perpendicular to the theoretical transition boundary. The numerically determined boundaries are compared to the theoretical boundaries predicted by two- and three- shock theories and with results obtained from experiments. The results show that the transition boundary between regular and Mach reflection is different not only for wedges and cones but also for inviscid and viscous numerical solutions.
40

Numerical Determination Of The Transition Boundary Between Regular and Mach Reflection For Planar Shocks Striking Wedges and Cones in Air

Michalagas, Dean Andrew 15 February 2010 (has links)
A numerical investigation of the interaction of a planar shock wave with a rigid wedge and cone in an air-filled shock tube is performed by computing the unsteady flow field of the interaction process. The Euler and Navier-Stokes equations are solved in two dimensions to produce flow solutions for regular and Mach reflections with and without the viscous and thermal boundary layer on the inclined surface. The transition boundary between these two patterns is determined by changing both the shock strength and the angle of the inclined surface so that the simulations are perpendicular to the theoretical transition boundary. The numerically determined boundaries are compared to the theoretical boundaries predicted by two- and three- shock theories and with results obtained from experiments. The results show that the transition boundary between regular and Mach reflection is different not only for wedges and cones but also for inviscid and viscous numerical solutions.

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