Otimização de antenas lineares e planares para aplicações em sistemas de banda larga

O objetivo deste trabalho é a otimização da largura de banda de antenas linear e planar para aplicações em sistemas de banda larga. Nesse sentido, foi feito um estudo das técnicas de análise, aumento da largura de banda e otimização adequadas para o problema em questão. Como técnica de análise, foi utilizado o método dos momentos, o qual está apresentado no capítulo II. Para aumentar a largura de banda, foram utilizadas as técnicas de colocação de elementos parasitas e construção de fendas no radiador, descritos sucintamente no capítulo III. Como algoritmo de otimização, foi utilizado o algoritmo genético, descrito sucintamente no capítulo II. Neste trabalho, são apresentadas duas propostas de antenas, uma antena dipolo linear combinada com quatros espiras parasitas, capítulo IV, e uma antena planar do tipo espira, capítulo V. No primeiro caso, foram utilizados elementos parasitas e o algoritmo genético para aumentar a largura de banda e, no segundo, foram empregadas fendas no radiador e a otimização paramétrica para este objetivo.

L'efficienza degli indici azionari: un'analisi empirica

La studio dell’efficienza di un indice azionario ha accresciuto la propria importanza nell’industria dell’asset management a seguito della diffusione dell’utilizzo di benchmark e investimenti indicizzati. Il presente lavoro valuta il livello di efficienza dei principali indici del mercato azionario statunitense, dell’Area Euro e italiano. Lo studio empirico ricorre a quattro misure di efficienza: il GRS, un test small-sample multivariato fondato sul CAPM; il test large sample di Wald, implementato tramite una simulazione bootstrap; il test GMM, che è stato applicato in una cornice non-gaussiana attraverso una simulazione block bootstrap; la misura di efficienza relativa di Kandel e Stambaugh. I risultati empirici forniscono una prova evidente della superiore efficienza degli indici equiponderati. Questa conclusione è interpretata sulla base della letteratura scientifica esistente, analizzando le diverse cause di ordine teorico ed empirico che sono state proposte.

Estimating Particle Shape and Orientation Using Volume Tensors

We develop statistical procedures for estimating shape and orientation of arbitrary three-dimensional particles. We focus on the case where particles cannot be observed directly, but only via sections. Volume tensors are used for describing particle shape and orientation, and we derive stereological estimators of the tensors. These estimators are combined to provide consistent estimators of the moments of the so-called particle cover density. The covariance structure associated with the particle cover density depends on the orientation and shape of the particles. For instance, if the distribution of the typical particle is invariant under rotations, then the covariance matrix is proportional to the identity matrix. We develop a non-parametric test for such isotropy. A flexible Lévy-based particle model is proposed, which may be analysed using a generalized method of moments in which the volume tensors enter. The developed methods are used to study the cell organization in the human brain cortex.

GMM Based Inference with Standard Stratified Samples when the Aggregate Shares are Known

We show how to do efficient moment based inference using the generalized method of moments (GMM) when data is collected by standard stratified sampling and the maintained assumption is that the aggregate shares are known.

How has financial deepening affected poverty reduction in India? : empirical analysis using state-level panel data

This paper examines empirically whether financial deepening has contributed to poverty reduction in India. Using unbalanced panel data for 28 states and union territories between 1973 and 2004, we estimate models in which the poverty ratio is explained by financial deepening, controlling for international openness, inflation rate, and economic growth. From the dynamic generalised method of moments (GMM) estimation, we find that financial deepening and economic growth alleviate poverty, while international openness and the inflation rate have the opposite effect. These results are robust to changes in the poverty ratios in rural areas, urban areas, and the whole economy.

Simulating heterogeneous multinational firms

This paper develops a micro-simulation framework for multinational entry and sales activities across countries. The model is based on Eaton, Kortum, and Kramarz's (2010) quantitative trade model adapted towards multinational production. Using micro data on Japanese manufacturing firms, we first stylize the empirical regularities of multinational entry and sales activity and estimate the model's structural parameters with simulated method of moments. We then demonstrate that our adapted model is able to replicate important dimensions of the in-sample moments conditioned in our estimation strategy. Importantly, it is able to replicate activity under an economic period with a far different level of FDI barriers than was conditioned upon in our estimation sample. Overall, our research highlights the richness of the simulation framework for performing counterfactual analysis of various FDI policies.

Different approaches to grounding resistance. Calculation for thin wire structures at low frequency energization

The present paper deals with the calculation of grounding resistance of an electrode composed of thin wires, that we consider here as perfect electric conductors (PEC) e.g. with null internal resistance, when buried in a soil of uniform resistivity. The potential profile at the ground surface is also calculated when the electrode is energized with low frequency current. The classic treatment by using leakage currents, called Charge Simulated Method (CSM), is compared with that using a set of steady currents along the axis of the wires, here called the Longitudinal Currents Method (LCM), to solve the Maxwell equations. The method of moments is applied to obtain a numerical approximation of the solution by using rectangular basis functions. Both methods are applied to two types of electrodes and the results are also compared with those obtained using a thirth approach, the Average Potential Method (APM), later described in the text. From the analysis performed, we can estimate a value of the error in the determination of grounding resistance as a function of the number of segments in which the electrodes are divided.

Electromagnetic fields inside a lossy, multilayered spherical head phantom excited by MRI coils: models and methods

The precise evaluation of electromagnetic field (EMF) distributions inside biological samples is becoming an increasingly important design requirement for high field MRI systems. In evaluating the induced fields caused by magnetic field gradients and RF transmitter coils, a multilayered dielectric spherical head model is proposed to provide a better understanding of electromagnetic interactions when compared to a traditional homogeneous head phantom. This paper presents Debye potential (DP) and Dyadic Green's function (DGF)-based solutions of the EMFs inside a head-sized, stratified sphere with similar radial conductivity and permittivity profiles as a human head. The DP approach is formulated for the symmetric case in which the source is a circular loop carrying a harmonic-formed current over a wide frequency range. The DGF method is developed for generic cases in which the source may be any kind of RF coil whose current distribution can be evaluated using the method of moments. The calculated EMFs can then be used to deduce MRI imaging parameters. The proposed methods, while not representing the full complexity of a head model, offer advantages in rapid prototyping as the computation times are much lower than a full finite difference time domain calculation using a complex head model. Test examples demonstrate the capability of the proposed models/methods. It is anticipated that this model will be of particular value for high field MRI applications, especially the rapid evaluation of RF resonator (surface and volume coils) and high performance gradient set designs.

Executive remuneration, financial performance and corporate governance in UK and Spanish listed firms

This study examines the relationship between executive directors’ remuneration and the financial performance and corporate governance arrangements of the UK and Spanish listed firms. These countries’ corporate governance framework has been shaped by differences in legal origin, culture and backgrounds. For example, the UK legal arrangements can be defined as to be constituted in common-law, whereas for Spanish firms, the legal arrangement is based on civil law. We estimate both static and dynamic regression models to test our hypotheses and we estimate our regression using Ordinary Least Squares (OLS) and the Generalised Method of Moments (GMM). Estimated results for both countries show that directors’ remuneration levels are positively related with measures of firm value and financial performance. This means that remuneration levels do not lead to a point whereby firm value is reduced due to excessive remuneration. These results hold for our long-run estimates. That is, estimates based on panel cointegration and panel error correction. Measures of corporate governance also impacts on the level of executive pay. Our results have important implications for existing corporate governance arrangements and how the interests of stakeholders are protected. For example, long-run results suggest that directors’ remuneration adjusts in a way to capture variation in financial performance

Dinâmica industrial, emprego e pobreza no Brasil, uma abordagem alternativa

Between 2003 and 2014 Brazil has increased exports by 52%, increased the formal employment and paid employment by 19% and reduced multidimensional poverty by 42%. The purpose of this work is to test the hypothesis that there is a Brazilian Growth Virtuous Circle where these three variables would be connected in order to increase exports and reduce poverty through the salaries transfer of funds. The construction of the hypothesis is made for Export Industry through ideas Verdoorn, Kaldor and Thirlwall presenting the export industry as an engine of economic growth. To present employment acting directly on economic growth is used Wage Led Rowthorn approach. The Capability Approach of Amartya Sen is used to understand the Multidimensional Poverty. The hypothesis was tested using data from the National Household Survey and Aliceweb between 2003 and 2014 with the use of the Generalized Method of Moments and the generation of elasticities between export and employment, employment and poverty, and export and poverty.

Efeitos da internacionalização no desvio da estrutura de capital alvo e na velocidade de ajuste

This dissertation investigates the effects of internationalization in two gaps related to the capital structure that have not been discussed by the Brazilian literature yet. To this, were developed two independent sections. The first examined what the effects of internationalization on the deviation from the target capital structure. The second examined what the effects of internationalization on speed of adjustment (SOA) of the capital structure. It used data from Brazil, multinational and domestic companies, from 2006 to 2014. The results of the first analysis indicate that internationalization helps reduce the difference between the target and the current debt. That is, to the extent that the level of internationalization increases; whether only export or a combination of export, assets and employees abroad, the gap between the current structure and the target structure decreases. This reduction is given as a function of internationalization as a consequence of the upstream effect of the upstream-downstream hypothesis. Thus, as the Market Timing theory, it can be seen as an opportunity for adjustment of the capital structure, and with the reduction of deviation, there is also a reduction in the cost of capital of the firm. The result of the second analysis indicates that internationalization is able to significantly increase the speed adjustment, ensuring for the multinational a faster adjustment of its capital structure. Exports increase the SOA in 9 to 23%. And when also kept active assets and employees abroad the increase is 8 to 20%. In terms of time, while domestic company takes more than three years to reduce half of the deviation that has, while multinacional companies take on average one and a half year to reduce the same proportion of the deviation. The validity of the upstream-downstream hypothesis for the effect of internationalization in SOA was confirmed by comparing the results for US companies. Thus, the phenomenon of internationalization increases SOA when companies are from less stable markets, such as Brazil; and it has a less significcative effect when companies are derived from more stable markets, because they already have a high speed of adjustmennt. In addition, the adequacy analysis of the estimators also showed the model pooled OLS (Ordinary Least Squares) presents the highest quality in predicting the SOA than the system GMM (Generalized Method of Moments). For future studies it is suggested to analyze the effect of international event, by itself, and to validate the hypothesis using samples of different markets and the use of other estimators.

Three Essays on Taxation, Growth and Consumption

The purpose of this dissertation is to examine three distributional issues in macroeconomics. First I explore the effects fiscal federalism on economic growth across regions in China. Using the comprehensive official data set of China for 31 regions from 1952 until 1999, I investigate a number of indicators used by the literature to measure federalism and find robust support for only one such measure: the ratio of local total revenue to local tax revenue. Using a difference-in-difference approach and exploiting the two-year gap in the implementation of a tax reform across different regions of China, I also identify a positive relationship between fiscal federalism and regional economic growth. The second paper hypothesizes that an inequitable distribution of income negatively affects the rule of law in resource-rich economies and provides robust evidence in support of this hypothesis. By investigating a data set that contains 193 countries and using econometric methodologies such as the fixed effects estimator and the generalized method of moments estimator, I find that resource-abundance improves the quality of institutions, as long as income and wealth disparity remains below a certain threshold. When inequality moves beyond this threshold, the positive effects of the resource-abundance level on institutions diminish quickly and turn negative eventually. This paper, thus, provides robust evidence about the endogeneity of institutions and the role income and wealth inequality plays in the determination of long-run growth rates. The third paper sets up a dynamic general equilibrium model with heterogeneous agents to investigate the causal channels which run from a concern for international status to long-run economic growth. The simulation results show that the initial distribution of income and wealth play an important role in whether agents gain or lose from globalization.

Multivariate Appoximations to Portfolio Return Distribution

This article proposes a three-step procedure to estimate portfolio return distributions under the multivariate Gram-Charlier (MGC) distribution. The method combines quasi maximum likelihood (QML) estimation for conditional means and variances and the method of moments (MM) estimation for the rest of the density parameters, including the correlation coefficients. The procedure involves consistent estimates even under density misspecification and solves the so-called ‘curse of dimensionality’ of multivariate modelling. Furthermore, the use of a MGC distribution represents a flexible and general approximation to the true distribution of portfolio returns and accounts for all its empirical regularities. An application of such procedure is performed for a portfolio composed of three European indices as an illustration. The MM estimation of the MGC (MGC-MM) is compared with the traditional maximum likelihood of both the MGC and multivariate Student’s t (benchmark) densities. A simulation on Value-at-Risk (VaR) performance for an equally weighted portfolio at 1% and 5% confidence indicates that the MGC-MM method provides reasonable approximations to the true empirical VaR. Therefore, the procedure seems to be a useful tool for risk managers and practitioners.

Um modelo matemático baseado em wavelets para análise do método térmico de recuperação de óleo pesado aplicando irradiação eletromagnética

This work proposes a model to investigate the use of a cylindrical antenna used in the thermal method of recovering through electromagnetic radiation of high-viscosity oil. The antenna has a simple geometry, adapted dipole type, and it can be modelled by using Maxwell s equation. The wavelet transforms are used as basis functions and applied in conjunction with the method of moments to obtain the current distribution in the antenna. The electric field, power and temperature distribution are carefully calculated for the analysis of the antenna as electromagnetic heating. The energy performance is analyzed based on thermo-fluid dynamic simulations at field scale, and through the adaptation in the Steam Thermal and Advanced Processes Reservoir Simulator (STARS) by Computer Modelling Group (CMG). The model proposed and the numerical results obtained are stable and presented good agreement with the results reported in the specialized literature