Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2004. / Includes bibliographical references (p. 95-99).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains x, 140 p. Includes bibliographical references (p. 137-140). Available online via OhioLINK's ETD Center

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 114-119).

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 112-115).

Thesis (PhD) -- Stellenbosch University, 2014. / ENGLISH ABSTRACT: This work considers the efficient numerical analysis of large, aperiodic finite antenna arrays. A Method of Moments (MoM) based domain decomposition technique called the Domain Green's Function Method (DGFM) is formulated to address a wide range of array problems in a memory and runtime efficient manner. The DGFM is a perturbation approach that builds on work initially conducted by Skrivervik and Mosig for disjoint arrays on multi-layered substrates, a detailed review of which will be provided in this thesis. Novel extensions considered for the DGFM are as follows: a formulation on a higher block matrix factorisation level that allows for the treatment of a wider range of applications, and is essentially independent of the elemental basis functions used for the MoM matrix formulation of the problem. As an example of this, both conventional Rao-Wilton-Glisson elements and also hierarchical higher order basis functions were used to model large array structures. Acceleration techniques have been developed for calculating the impedance matrix for large arrays including one based on using the Adaptive Cross Approximation (ACA) algorithm. Accuracy improvements that extend the initial perturbation assumption on which the method is based have also been formulated. Finally, the DGFM is applied to array geometries in complex environments, such as that in the presence of finite ground planes, by using the Numerical Green's Function (NGF) method in the hybrid NGF-DGFM formulation. In addition to the above, the DGFM is combined with the existing domain decomposition method, viz., the Characteristic Basis Function Method (CBFM), to be used for the analysis of very large arrays consisting of sub-array tiles, such as the Low-Frequency Array (LOFAR) for radio astronomy. Finally, interesting numerical applications for the DGFM are presented, in particular their usefulness for the electromagnetic analysis of large, aperiodic sparse arrays. For this part, the accuracy improvements of the DGFM are used to calculate quantities such as embedded element patterns, which is a major extension from its original formulation. The DGFM has been integrated as part of an efficient array analysis tool in the commercial computational electromagnetics software package, FEKO. / AFRIKAANSE OPSOMMING: In hierdie werkstuk word die doeltre ende analise van eindige, aperiodiese antenna samestellings behandel. Eindige gebied benaderings wat op die Moment Metode (MoM) berus, word as vetrekpunt gebruik. `n Tegniek genaamd die Gebied Green's Funksie Metode (GGFM) word voorgestel en is geskik vir die analise van `n verskeidenheid van ontkoppelde samestellings. Die e ektiewe gebruik van rekenaargeheue en looptyd is onderliggend in die implementasie daarvan. Die GGFM is 'n perturbasie metode wat op die oorspronklike werk van Skrivervik en Mosig berus. Laasgenoemde is hoofsaaklik ontwikkel vir die analise van ontkoppelde antenna samestellings op multilaag di elektrikums. `n Deeglike oorsig van voorafgaande word in die tesis verskaf. In hierdie tesis is die bogenoemde werk op `n unieke wyse uitgebrei: `n ho er blok matriks vlak formulering is ontwikkel wat dit moontlik maak vir die analise van `n verskeidenheid strukture en wat onafhanklik is van die onderliggende basis funksies. Beide lae-vlak Rao-Wilton-Glisson (RWG) basis funksies, asook ho er orde hierargiese basis funksies word gebruik vir die modellering van groot antenna samestellings. Die oorspronklike perturbasie aanname is uitgebrei deur akkuraatheidsverbeteringe vir die tegniek voor te stel. Die Aanpasbare Kruis Benaderings (AKB) tegniek is onder andere gebruik om spoed verbeteringe vir die GGFM te bewerkstellig. Die GGFM is verder uitgebrei vir die analise van antenna samestellings in `n komplekse omgewing, bv. `n antenna samestelling bo `n eindige grondplaat. Die Numeriese Green's Funksie (NGF) metode is hiervoor ingespan en die hibriede NGF-GGFM is ontwikkel. Die GGFM is verder met die Karakteristieke Basis Funksie Metode (KBFM) gekombineer. Die analise van groot skikkings wat bestaan uit sub-skikkings, soos die wat tans by die \Low- Frequency Array (LOFAR) " vir radio astronomie in Nederland gebruik word, kan hiermee gedoen word. In die werkstuk word die GGFM ook toegepas op `n reeks interessante numeriese voorbeelde, veral die toepaslike EM analise van groot aperiodiese samestellings. Die akkuraatheidsverbeteringe vir die GGFM maak die berekening van elementpatrone vir skikkings moontlik. Die GGFM is by the sagteware pakket FEKO geintegreer.

Thesis (MScIng)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: A complete mixed-potential integral equation formulation for the analysis of arbitrarily shaped scatterers in a planarly layered medium is presented. The integral equation is able to solve for simultaneous electric and magnetic surface currents using a Method of Moments (MoM) procedure. The MoM formulation which was developed uses vector-valued basis functions defined over a triangular mesh and are used to model electric currents on conducting scatterers and magnetic currents on slotline structures. The Green’s functions employed in the analysis were developed for a stratified medium using a Sommerfeld plane wave formulation. The scheme used for filling the method of moments matrix was designed to simultaneously solve multiple problems that are stacked and separated by an infinite conducting ground plane. The filling algorithm also efficiently packs partially symmetric matrices, which are present when solving problems that support a combination of electric and magnetic currents. Several examples are presented to illustrate and validate the analysis method. Numerical predictions of the scattering parameters (both magnitude and phase) show good correspondence with results from literature and measured data. / AFRIKAANSE OPSOMMING: ’n Volledige gemengde potensiaal integraalvergelyking formulering vir die analise van stralers van arbitrˆere vorm binne gelaagde strukture word aangebied. Die integraalvergelyking kan gelyktydige elektriese en magnetiese oppervlakstrome oplos deur die Metode van Momente (MoM) te gebruik. Die MoM formulering gebruik vektor basis funksies wat oor ’n driehoekige diskretisering gedefinieer word om elektriese strome op geleidende stralers en magnetiese strome op gleuflyn strukture te modelleer. Die Green’s funksies wat in die analise gebruik word, is ontwikkel vir gelaagde media deur gebruik te maak van Sommerfeld se platvlakgolf formulering. Die metode wat gebruik word om the moment matriks te vul, is ontwerp om meervoudige gestapelde probleme wat deur oneindig geleidende grondvlakke geskei word, gelyktydig op te los. Gedeeltelik simmetriese matrikse word ook effektief gevul. Hierdie matrikse kom voor wanneer probleme ’n kombinasie van elektriese en magnetiese strome ondersteun. Verskeie voorbeelde word gebruik om die analise metode te verifieer. Numeriese voorspellings van strooiparameters (beide grootte en hoek) vergelyk baie goed met resultate en gemete data wat in die literatuur gevind is. iv

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 114-118).

Orientadores: Rodrigo Lanna Franco da Silveira, Celio Hiratuka / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Economia / Made available in DSpace on 2018-08-27T14:59:01Z (GMT). No. of bitstreams: 1 Fonseca_CamilaVeneoCampos_M.pdf: 2187150 bytes, checksum: 17c287ca376b037d1783e582e37cb3ab (MD5) Previous issue date: 2015 / Resumo: O reduzido acesso ao financiamento externo, particularmente o de longo prazo, é um dos principais problemas do ambiente corporativo brasileiro. Os conflitos de agência e a existência de informação assimétrica nas transações efetivadas no mercado financeiro resultam em um maior custo de capital e no racionamento do crédito, sendo estes proporcionais ao grau de desconfiança dos investidores. A adoção de melhores práticas de governança corporativa pelas empresas, como o comprometimento com a transparência das informações divulgadas e a vigência de sistemas mais eficientes de proteção aos acionistas minoritários e credores, ao implicar redução do custo de capital, amplia o papel exercido pelo mercado na captação de recursos para o investimento, mitigando o problema do financiamento empresarial. O objetivo deste trabalho é verificar a possível influência da adesão aos níveis diferenciados de governança corporativa da Bolsa de Valores, Mercadorias e Futuros (BM&FBOVESPA) sobre o montante e o perfil do endividamento das empresas brasileiras de capital aberto no período entre 2000 e 2013. Para atingir o objetivo acima exposto, o estudo fez uso de técnicas econométricas baseadas em dados em painel. Os parâmetros do modelo empírico foram estimados pelo Método dos Momentos Generalizado Sistêmico (GMM-Sis). Os resultados do teste econométrico corroboram as hipóteses da pesquisa, ou seja, a governança corporativa é relevante na determinação do nível de endividamento das empresas brasileiras, exercendo um efeito positivo sobre o acesso aos recursos de terceiros. Além disso, empresas reconhecidas pela adoção de melhores práticas de governança têm alterado o perfil do seu endividamento, sendo privilegiadas na captação de recursos de longo prazo. Conclui-se que a governança corporativa é um fator chave no debate sobre os determinantes da estrutura de capital no Brasil uma vez que modifica não somente o montante, mas o perfil de endividamento das empresas comprometidas com a implementação de melhores práticas / Abstract: The reduced access to finance, particularly the long-term one, is one of the main problems of the Brazilian corporate environment. Agency conflicts and the existence of asymmetric information in financial markets results in higher cost of capital and credit rationing, which are proportional to the degree of investors distrust. The adoption of best practices of corporate governance by enterprises - such as better disclosure and efficient systems of investor protection -, results in a reduced cost of capital, expands the role played by the market in raising funds for investment, and mitigates the problem of business financing. The objective of this study is to verify the possible influence of adherence to different levels of corporate governance on the amount and profile of the debt contract by Brazilian public companies during 2000-2013 period. The study adopts econometric methods based on panel data models to explore the impact of corporate governance on corporate capital structure of Brazilian companies. The parameters of the models were estimated using a Systemic Generalized Method of Moments (GMM-Sys). The results of the econometric tests corroborate the hypotheses of the research - corporate governance is relevant in determining the level of indebtedness of Brazilian companies. ln addition, companies recognized by the adoption of best corporate governance practices have changed the profile of its debt, being privileged in the long-term fundraising. ln conclusion, corporate governance is a key factor in the debate about the determinants of capital structure in Brazil since it modifies not only the amount, but also the profile of indebtedness of companies committed to implementing best practices / Mestrado / Ciências Economicas / Mestra em Ciências Econômicas

In this dissertation, a Method of Moments (MoM) Volume Integral Equation (VIE)-based modeling approach suitable for a patch or slot antenna on a thin finite dielectric substrate is developed and validated. Two new key features of this method are the use of proper dielectric basis functions and proper VIE conditioning, close to the metal surface, where the surface boundary condition of the zero tangential-component must be extended into adjacent tetrahedra. The extended boundary condition is the exact result for the piecewise-constant dielectric basis functions. The latter operation allows one to achieve a good accuracy with one layer of tetrahedra for a thin dielectric substrate and thereby greatly reduces computational cost. The use of low-order basis functions also implies the use of low-order integration schemes and faster filling of the impedance matrix. For some common patch/slot antennas, the VIE-based modeling approach is found to give an error of about 1% or less in the resonant frequency for one-layer tetrahedral meshes with a relatively small number of unknowns. This error is obtained by comparison with fine finite- element method (FEM) simulations, or with measurements, or with the analytical mode matching approach. Hence it is competitive with both the method of moments surface integral equation approach and with the FEM approach for the printed antennas on thin dielectric substrates. Along with the MoM development, the dissertation also presents the models and design procedures for a number of practical antenna configurations. They in particular include: i. a compact linearly polarized broadband planar inverted-F antenna (PIFA); ii. a circularly polarized turnstile bowtie antenna. Both the antennas are designed to operate in the low UHF band and used for indoor positioning/indoor geolocation.

Various error estimation and adaptive refinement techniques for the solution of electromagnetic integral equations were developed. Residual based error estimators and h-refinement implementations were done for the Method of Moments (MoM) solution of electromagnetic integral equations for a number of different problems. Due to high computational cost associated with the MoM, a cheaper solution technique known as the Locally-Corrected Nyström (LCN) method was explored. Several explicit and implicit techniques for error estimation in the LCN solution of electromagnetic integral equations were proposed and implemented for different geometries to successfully identify high-error regions. A simple p-refinement algorithm was developed and implemented for a number of prototype problems using the proposed estimators. Numerical error was found to significantly reduce in the high-error regions after the refinement. A simple computational cost analysis was also presented for the proposed error estimation schemes. Various cost-accuracy trade-offs and problem-specific limitations of different techniques for error estimation were discussed. Finally, a very important problem of slope-mismatch in the global error rates of the solution and the residual was identified. A few methods to compensate for that mismatch using scale factors based on matrix norms were developed.