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Disertaciniame darbe aprašyti autoriaus sudaryti geometriškai netiesinių tamprių plastinių statybinių strypinių konstrukcijų skaičiavimo ir optimizavimo uždavinių, ribojant konstrukcijos poslinkius, matematiniai modeliai. Sukurtas geometriškai netiesinių erdvinių strypinių konstrukcijų optimizavimo, ribojant poslinkius, uždavinio sprendimo originalus algoritmas. Disertaciją sudaro įvadas, trys skyriai, rezultatų apibendrinimas, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai bei 8 priedai. Įvadiniame skyriuje aptariama tiriamoji problema, aprašomas tyrimų objektas ir metodai, formuluojamas darbo tikslas bei uždaviniai, aprašomas darbo mokslinis naujumas bei aktualumas, darbo rezultatų praktinė reikšmė. Įvado pabaigoje pristatomos disertacijos tema autoriaus paskelbtos publikacijos ir pranešimai konferencijose bei disertacijos struktūra. Pirmajame skyriuje analizuojamos projektavimo ir konstrukcijų optimizavimo uždavinių sąsajos, pateikiama trumpa konstrukcijų optimizavimo metodų analitinė apžvalga. Nagrinėjama netamprių geometriškai netiesinių plieninių rėminių konstrukcijų optimizavimo ribojant poslinkius problematika. Aprašomos pasirinktos pagrindinės prielaidos ir fizinės priklausomybės bei dydžiai, apibrėžiantys konstrukcijos įtemptąjį-deformuotąjį būvį (ĮDB). Pateikiamas konstrukcijų optimizavimo uždavinio matematinis modelis. Pasiūlomas algoritmas šiam uždaviniui spręsti. Apžvelgiamos optimizavimo uždavinio skaitinės realizacijos galimybės... [toliau žr. visą tekstą] / The optimization mathematical models of geometrically nonlinear elastic plastic frameworks structures optimization under displacement constraints are created in the thesis. Original solution algorithm was created for the optimization of geometrically nonlinear elastic-plastic frameworks structures under displacement constraints. The dissertation consists of introduction, 3 chapters, conclusions, references and 8 annexes. The introduction reveals the investigated problem, the object of research and describes the purpose and tasks of the thesis, research methodology, scientific novelty, the practical significance of results examined in the thesis. The introduction ends in presenting the author’s publications on the subject of the defended dissertation, offering the material of made presentations in conferences and defining the structure of the dissertation. Construction design and structures optimization problems correlation is describing in chapter 1. Short historical review of optimization methods and structures optimization analytical analysis are presented. Reviewing problematic of non-elastic geometrically nonlinear steel frame structures optimization under displacements constraints. Describing basic accepted assumptions and physical dependences and values describing structures real stress-strain state (SSS). Structure optimization problem mathematical model is presented. Algorithm for such optimization problem solution is suggested. Optimization problem numerical... [to full text]

This thesis consists of four manuscripts in the area of nonlinear time series econometrics on topics of testing, modeling and forecasting nonlinear common features. The aim of this thesis is to develop new econometric contributions for hypothesis testing and forecasting in these area. Both stationary and nonstationary time series are concerned. A definition of common features is proposed in an appropriate way to each class. Based on the definition, a vector nonlinear time series model with common features is set up for testing for common features. The proposed models are available for forecasting as well after being well specified. The first paper addresses a testing procedure on nonstationary time series. A class of nonlinear cointegration, smooth-transition (ST) cointegration, is examined. The ST cointegration nests the previously developed linear and threshold cointegration. An Ftypetest for examining the ST cointegration is derived when stationary transition variables are imposed rather than nonstationary variables. Later ones drive the test standard, while the former ones make the test nonstandard. This has important implications for empirical work. It is crucial to distinguish between the cases with stationary and nonstationary transition variables so that the correct test can be used. The second and the fourth papers develop testing approaches for stationary time series. In particular, the vector ST autoregressive (VSTAR) model is extended to allow for common nonlinear features (CNFs). These two papers propose a modeling procedure and derive tests for the presence of CNFs. Including model specification using the testing contributions above, the third paper considers forecasting with vector nonlinear time series models and extends the procedures available for univariate nonlinear models. The VSTAR model with CNFs and the ST cointegration model in the previous papers are exemplified in detail,and thereafter illustrated within two corresponding macroeconomic data sets.

The thesis concentrates on property of linearity in time series models, its definitions and possibilities of testing. Presented tests focus mainly on the time domain; these are based on various statistical methods such as regression, neural networks and random fields. Their implementation in R software is described. Advantages and disadvantages for tests, which are implemented in more than one package, are discussed. Second topic of the thesis is additivity in nonlinear models. The definition is introduced as well as tests developed for testing its presence. Several test (both linearity and additivity) have been implemented in R for purposes of simulations. The last chapter deals with application of tests to real data. 1

The Asian summer monsoon (ASM) is a high-dimensional and highly complex phenomenon affecting more than one fifth of the world population. The intraseasonal component of the ASM undergoes periods of active and break phases associated respectively with enhanced and reduced rainfall over the Indian subcontinent and surroundings. In this thesis the nonlinear nature of the intraseasonal monsoon variability is investigated using the leading Empirical Orthogonal Functions of ERA-40 sea level pressure reanalyses field over the ASM region. The probability density function is then computed in spherical coordinates using the Epaneshnikov kernel method. Three significant modes are identified. They represent respectively (i) the East - West mode with above normal sea level pressure over East China sea and below normal pressure over Himalayas, (ii) the mode with above normal sea level pressure over East China sea (without compensating centre of opposite sign as in (i)) and (iii) the mode with below normal sea level pressure over East China sea (same as (ii) but with opposite sign). The relationship with large-scale forcing is also investigated by stratifying the PCs according to representing indices. The regimes derived from spherical PDFs appear to be opposite under opposite large-scale conditions. EOF technique with...

The aim of this thesis is to analyze the performance of nonlinear threshold models in forecasting the exchange rate of Czech koruna against EUR. Data for this study were obtained from Statistical Data Warehouse of European Central Bank (ECB) website, from Czech National Bank (CNB) Board decisions minutes and from the press releases of Governing Council of ECB. The data set was split into two periods - from 1999 until November, 2013 when CNB started to use interventions and from November, 2013 until April, 2016. Models used in the thesis are Self-Exciting Threshold Auto Regressive (SETAR) models with one and two thresholds and two Threshold Auto Regres- sive (TAR) models with different threshold variables - meetings of CNB Board as dummy variable and average volatility over recent periods. The forecasting results indicate that SETAR models did not outperform Random Walk in any period. TAR models offered promising results in the period before interventions and surprisingly failed in the period during interventions. This study supports the general belief of exchange rates being difficult to forecast and that it holds in case of Czech koruna as well. JEL Classification F12, F21, F23 H25, H71, H87 Keywords forecasting, exchange rate, time series, nonlin- earity, SETAR, TAR Author's e-mail zaka.one@gmail.com...

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Este estudo tem como principal objetivo a compreensão de dois dos principais métodos de otimização topológica disponíveis na literatura: o método SIMP e ESO. Estes métodos foram implementados computacionalmente utilizando a linguagem de programação FORTRAN 90. Utiliza-se o Método dos Elementos Finitos (MEF) como parâmetro de solução mecânica neste trabalho, adotando-se a formulação baseada em deslocamentos para elasticidade linear. Ademais, visando avaliar o efeito da não linearidade geométrica na topologia ótima obtida, utiliza-se também o MEF posicional, o qual baseia-se nas posições nodais para solução do sistema não linear. Em conjunto com este método, adota-se a lei constitutiva de Saint-Venant-Kirchhoff, visando considerar os efeitos não lineares. Desta maneira, avalia-se a eficiência dos resultados obtidos por meio da aplicação de exemplos presentes na literatura. Conforme esperado, conclui-se que para exemplos cuja resposta apresenta pequenos deslocamentos, ambas as soluções se sobrepõem. No entanto, em se tratando de problemas em que a não linearidade geométrica tem influência, como estruturas constituídas de baixa densidade, a técnica do MEF posicional apresenta relevância na solução ótima. / This study has as main objective the understanding of two main topology optimization methods available in the literature: the methods SIMP and ESO. These methods were implemented computationally using the FORTRAN 90 programming language. The finite element method (FEM) is used as the mechanical solution parameter in this work, adopting the displacement-based formulation for linear elasticity. In addition, in order to evaluate the effect of geometric non-linearity in the optimal topology obtained, the FEM positional-based formulation is used, which uses the nodal positions for solution of the non-linear system. In conjunction with this method, the constitutive law adopted is the Saint-Venant-Kirchhoff in order to consider the nonlinearity. Hence, benchmarks presented in the literature are used to evaluate the efficiency of the obtained results. As expected, we conclude that the examples subjected to small displacements have similar solutions for both linear and nonlinear behavior. However, when problems that undergo geometrically nonlinear behavior, such as the ones modelled with soft materials, the FEM positional-based formulation has significant influence in the optimal solution.

<p>In this thesis, we analyze the performance of a loop-back built-in-self-test for a RF transceiver front-end. The tests aim at spot defects in a transceiver front-end and they make use of RF specifications such as NF (Noise Figure), G (power gain) and IIP3 (third order Intercept point). To enhance fault detectability, RF signal path sensitization is introduced. We use a functional RF transceiver model that is implemented in MatLab™ to verify this analysis.</p>

<p>In this thesis, a new way of using predisortion for linearization of power amplifiers is evaluated. In order to achieve an adequate power level for the jamming signal, power amplifiers are used in military jamming systems. Due to the nonlinear characteristic of the power amplifier, distortion will be present at the output. As a consequence, unwanted frequencies are subject to jamming. To decrease the distortion, linearization of the power amplifier is necessary. </p><p>In the system of interest, a portion of the distorted power amplifier output signal is fed back. Using this measurement, a predistortion signal is synthesized to allow suppression of the unwanted frequency components. The predistortion signal is updated a number of times in order to achieve a good outcome. Simulations are carried out in Matlab for testing of the algorithm. </p><p>The evaluation of the new linearization technique shows promising results and that good suppression of distortion components is achieved. Furthermore, new predistortion features are possible to implement, such as predistorsion in selected frequency bands. However, real hardware testing needs to be carried out to confirm the results.</p>