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The study of focal shift in focused beams using unapodized apertures has been well documented. However, not much work has been done on apodized apertures. In this thesis we use a Fourier-Optic approach to analyze the field distribution of a focused beam around the region of geometrical focus. The analytical formulation developed is general in nature as it is valid for any arbitrary aperture functions. This is then applied to some specific cases. Two cases of interest that are considered are the unapodized and the Gaussian apodized annular apertures. In order to study the intensity distributions around the geometrical focus, simulation results are presented using closed form analytical expressions and approximate integral forms. Specific emphasis is placed on the focal shift in the two apertures and on the effect of changing various parameters. A prognosis for future work using a-Modulation on Gaussian apodized annular apertures is also presented. / Master of Science

To achieve high thermal efficiency in modern gas turbines, the turbine-inlet temperature has to be increased. In response to such requisites and to prevent thermal failure of the components exposed to hot gas streams, the use of different cooling techniques, including film cooling, is essential. Finding an optimum film cooling design has become a challenge as it is influenced by a large number of flow and geometrical parameters. This study is dedicated to some important aspects of film cooling of a turbine guide vane and consists of three parts. The first part is associated with an experimental investigation of the suction and pressure side cooling by means of a transient IR-Thermography technique under engine representative conditions. It is shown that the overall film cooling performance of the suction side can be improved by adding showerhead cooling if fan-shaped holes are used, while cylindrical holes may not necessarily benefit from a showerhead. According to the findings, investigation of an optimum cooling design for the suction side is not only a function of hole shape, blowing ratio, state of approaching flow, etc., but is also highly dependent on the presence/absence of showerhead cooling as well as the number of cooling rows. In this regard, it is also discussed that the combined effect of the adiabatic film effectiveness (AFE) and the heat transfer coefficient (HTC) should be considered in such study. As for the pressure side cooling, it is found that either the showerhead or a single row of cylindrical cooling holes can enhance the HTC substantially, whereas a combination of the two or using fan-shaped holes indicates considerably lower HTC. An important conclusion is that adding more than one cooling row will not augment the HTC and will even decrease it under certain circumstances. In the second part, computational fluid dynamics (CFD) investigations have shown that film cooling holes subjected to higher flow acceleration will maintain a higher level of AFE. Although this was found to be valid for both suction and pressure side, due to an overall lower acceleration for the pressure side, a lower AFE was achieved. Moreover, the CFD results indicate that fan-shaped holes with low area ratio (dictated by design constraints for medium-size gas turbines), suffer from cooling jet separation and hence reduction in AFE for blowing ratios above unity. Verification of these conclusions by experiments suggests that CFD can be used more extensively, e.g. for parametric studies. The last part deals with method development for deriving correlations based on experimental data to support engineers in the design stage. The proposed method and the ultimate correlation model could successfully correlate the laterally averaged AFE to the downstream distance, the blowing ratio and the local pressure coefficient representing the effect of approaching flow. The applicability of the method has been examined and the high level of predictability of the final model demonstrates its suitability to be used for design purposes in the future. / Turbo Power Program

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20907号 / 理博第4359号 / 新制||理||1625(附属図書館) / 京都大学大学院理学研究科物理学・宇宙物理学専攻 / (主査)准教授 國友 浩, 教授 高柳 匡, 教授 川合 光 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DFAM

This dissertation presents the results of testing to determine the load-slip characteristics of single-shear single lag screw connections subjected to monotonic lateral loading parallel to grain. Of particular importance was the comparison of experimental capacity and 5% offset yield load resistances to load resistances as predicted by the American Forest & Paper Association's (AF&PA) publication General Dowel Equations for Calculating Lateral Connection Values, Technical Report 12 (TR-12). Additionally some other tests were conducted, including fracture, tension strength perpendicular-to-grain, lag screw connection inking, dowel embedment, specific gravity and moisture content. The results for the testing program are presented. Four hundred and forty eight lateral tests were conducted on lag screw connections. Each connection was comprised of a 2 x 6 x 14 in. long wood main member, 1/4 in. thick steel side plate, and a single lag screw. The parameters of interest were specific gravity, lag screw diameter, and pilot hole diameter. Two species of wood, Douglas-fir and spruce-pine-fir, three lag screws diameters, and three pilot hole diameters for each species of wood were implemented. Models were developed to predict lag screw connection capacity and 5% offset yield and are contained herein. Models were based on results from connection and inking tests and mechanical analysis. Recommendation for ASD and LRFD design values were derived from connection test results for connections that used AF&PA's National Design Specification for Wood Construction (NDSb) specified pilot holes. Using fracture mechanics results, work was performed to determine the effective load required to crack and separate fracture surfaces of wood main members due to the installation of lag screws with varying pilot hole diameters. / Ph. D.

In a preamble, a quick summary of the line of thought from Noether's theorems to modern views on conserved charges in gauge theories is attempted. Most of the background material needed for the thesis is set out through a small survey of the literature. Emphasis is put on the concepts more than on the formalism, which is relegated to the appendices. The treatment of exact conservation laws in Lagrangian gauge theories constitutes the main axis of the first part of the thesis. The formalism is developed as a self-consistent theory but is inspired by earlier works, mainly by cohomological results, covariant phase space methods and by the Hamiltonian formalism. The thermodynamical properties of black holes, especially the first law, are studied in a general geometrical setting and are worked out for several black objects: black holes, strings and rings. Also, the geometrical and thermodynamical properties of a new family of black holes with closed timelike curves in three dimensions are described. The second part of the thesis is the natural generalization of the first part to asymptotic analyses. We start with a general construction of covariant phase spaces admitting asymptotically conserved charges. The representation of the asymptotic symmetry algebra by a covariant Poisson bracket among the conserved charges is then defined and is shown to admit generically central extensions. The asymptotic structures of three three-dimensional spacetimes are then studied in detail and the consequences for quantum gravity in three dimensions are discussed.

In this thesis we investigate selection effects in astrophysical observations. We demonstrate that the determination of the quasar black hole mass function and Eddington ratio distribution via observations are biased. By modelling the quasar selection function and the black hole mass measurement process we show that one is able to infer the true distribution of physical quantities from observations. We present the intrinsic accretion rates of AGN, the intrinsic accretion rates and the black hole mass function for optically selected quasars up to redshift of two. The results show that the Eddington limit continues to be a real physical limit to black hole accretion. We present a new upper limit of black hole masses from the inferred intrinsic black hole mass function and demonstrate the need of a mass dependent accretion rate in accordance with down sizing. Finally we investigate correlations between radio luminosity and observed black hole mass for optically selected quasars. We first show that mixing of fiat and steep spectrum quasars leads to results that are dependent on the observing frequency, and therefore should be treated with caution. We demonstrate that beaming of the radio core together with an orientation dependent optical selection effect can give rise to a bimodal distribution in the radio luminosities of optically selected quasars.

Following the financial turmoil in 2007/2008 liquidity black holes (LBH) has become arising topic often discussed among academics as well as portfolio managers all around the world. More recent view on liquidity risk covers those liquidity black holes which occur when the liquidity completely dries up in a particular market and the market becomes one-sided. There are basically 2 channels through which liquidity can be affected - Demand and Supply. In first case, the portfolios of investors lose the value and consequently the investors lose confidence in financial system. In the second case, banks hit their capital constraints, they tighten the terms of providing credits and loans to reduce the credit risk exposure and hence it becomes more difficult for firms to raise the funds. At this point dangerous spiral arises and the liquidity of financial system evaporates rapidly. The crucial point of this master thesis is to find the main determinants of Liquidity Black holes and find possible solutions to avoid their appearance.

O estudo de perturbações em buracos negros tem sido um campo de pesquisa ativo nas últimas décadas, levando a importantes contribuições para o entendimento da física de corpos compactos em geral. Para o caso de geometrias esféricas assintoticamente planas quadridimensionais, existe um panorama muito bem delineadi para a dinâmica de diversos campos de interesse. A introdução de uma constante cosmológica nas equações de Eisntein muda o caráter assintótico das soluções tipo buraco negro e neste caso, muito menos é conhecido. No trabalho desenvolvido nesta tese abordamos alguns aspectos da propagação de campos em geometrias esféricas assintoticamente de Sitter e anti-de Sitter, considerando inclusive geometrias com dimensão maios que quatro. No regime quase extremo a dinâmica é mais simples. Neste caso, são obtidas expressões analíticas para os potenciais efetivos e para os modos quase-normais, caracterizando completamente a dinâmica. Em geral, entretando, somos forçados a recorrer a métodos semi-analíticos e numéricos. Empregamos estes métodos para uma análise ampla da forma de decaimento dos diversos campos. Nossos resultados esboçam um quadro geral bastante coeso em uma grande gama de situações. / The study of pertubations in Black holes hás been na active Field of research in the last decades, leading to a better understanding of the physics of compact objects in general. In the case of asymptotically flat spherical geometries with four dimensions, there is a schematic Picture regarding the dynamics of many fields of interest. The introduction of a cosmological Constant in the Einstein equations changes the asymptotic character of the Black hole solutions, and in this case much less is known. In the work developed in this thesis we treat some aspects of the fiels propagation in spherically symmetric geometries which are asymptotically de Sitter and anti-de Sitter, considering also geometries with dimension greater than four. In the near extreme regime the dynamics is simpler. In this case, we obtain analytic expressions to the effective potentials and to the quasinormal modes, completely characterizing the dynamics. In general we are forced to use semi-analytics and numerical methods.These methods are employed in na extensive analysis of the decay modes of the fields cosidered. Our results sketch a general Picture in a wide sample of situations.