Submitted by Haroudo Xavier Filho (haroudo.xavierfo@ufpe.br) on 2016-02-23T17:50:58Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_wanessa_cd.pdf: 804330 bytes, checksum: c0fbb3cc28dd1681f8de342fc6d5bfc8 (MD5) / Made available in DSpace on 2016-02-23T17:50:58Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Dissertação_wanessa_cd.pdf: 804330 bytes, checksum: c0fbb3cc28dd1681f8de342fc6d5bfc8 (MD5) Previous issue date: 2015-07-09 / FACEPE / O modelo linear de regressão é amplamente utilizado em aplicações práticas. Duas suposições que são comumente violadas são as de homoscedasticidade e não autocorrelação. Vários autores avaliaram os desempenhos de testes que usam erros-padrão consistentes quando há heteroscedasticidade de forma desconhecida. Na presente dissertação nós avaliamos os desempenhos de tais testes quando adicionalmente há correlação serial nos erros. Várias simulações de Monte Carlo foram realizadas em que os desempenhos de diferentes testes são avaliados tanto sob a hipótese nula quanto sob a hipótese alternativa. Uma aplicação prática é apresentada e discutida. / The linear regression model is commonly used by practitioners. Two assumptions are commonly violated, namely: homoskedasticity and no autocorrelation. Several authors have investigated the finite sample behavior of tests that use heteroskedasticity-consistent standard errors. In this thesis, we numerically evaluate the finite sample behavior of such tests under heteroskedasticity and autocorrelation. Monte Carlo simulation results under both the null and alternative hipotheses are presented. We also present and discuss an empirical application.

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The main focus of the thesis is the issue of determining jurisdiction in matters of tort, delict or quasi-delict with regard to the internet. The author finds that the general rules of determining jurisdiction are suitable for use even in disputes arising with connection to the internet. However, strict application of the aforementioned rules would lead to undesirable results. Therefore it is necessary to construe the general rules in such a way that takes into account the unique characteristics of the internet environment. Given the fact that courts are mainly responsible for the interpretation and application of the general rules, significant decisions of European and American courts are thoroughly analyzed. Even though the main focus of the thesis are the decisions of the courts, recent findings of jurisprudence and recommendations of the international bodies are taken into account as well. In the opening chapters, the unique characteristics of the internet and basic rules for determining the special jurisdiction are presented. Although the issue of determining jurisdiction in contracts is also mentioned in chapter 3, this topic exceeds the scope of this work and is discussed mainly in connection with the "targeting" criterion, which is also significant for out of contract issues. Chapters 4 and...

Ce travail a pour but d'étudier la tolérance à l'impact de 3 stratifiés carbone/époxy soumis simultanément à différents types de chargements hygrothermiques et mécaniques. Ces stratifications présentant des caractéristiques mécaniques globales particulières d'isotropie, il s'agit ici de déterminer l'influence de la séquence d'empilement sur le développement de l'endommagement lors d'un impact. Dans un premier temps, la cinétique de vieillissement hygrothermique des trois stratifications est étudiée et analysée. Ensuite, leur tolérance à un unique impact ainsi qu'à des impacts répétés est évaluée. L'endommagement résultant de ces impacts est analysé par contrôle ultrasonore. La morphologie générale et l'amplitude de l'endommagement dans la profondeur des matériaux sont mises en relation avec les propriétés mécaniques et la séquence d'empilement spécifique à chaque stratifié. Dans un deuxième temps, l'influence combinée de plusieurs sollicitations est étudiée. Différents scénarii associant un vieillissement hygrothermique ainsi qu'un ou deux impacts sont mis en oeuvre. L'endommagement résultant est mis en rapport avec les temps relatifs de vieillissement et la position des impact durant le cycle de vieillissement. Ensuite, l'influence d'une précharge de traction sur la tolérance à l'impact est mise en évidence. Un montage spécifique a été conçu et fabriqué pour réaliser ces tests. Enfin, l'association d'un vieilllissement hygrothermique et d'une précharge de traction est abordée afin d'identifier la sollicitation la plus pénalisant en terme de tolérance et d'impact / This study examines impact damage processes in three types of CFRP composite materials simultaneously subjected to different hygrothermal and mechanical loading conditions. The composite structures tested are chosen for having particular global isotropic responses when loaded, the aim being to ascertain the exact influence of lay-up sequence on impact damage propagation. The work is presented in four main sections. Firstly by establishing hygrothermal ageing dynamics for the three composite structure types and their behaviour when impacted once or several times ; impact damage is measured and analysed using ultrasonic method. The extent and general morphology of the damage through the material thickness is correlated with mechanical properties and lay-up sequence specific to each material. Secondly the influence of simultaneous load combinations is examined. These include different durations of hygrothermal ageing associated with single or double impacts.The resulting damage incurred is analysed with respect to overall ageing time and time during the ageing cycle when the impact was applied. Thirdly the effect of tensile loading during impact on damage within the material was studied. This was achieved using a specially designed test apparatus that allows loading and impacting conditions to be independently modified. By associating a high-speed digital camera to film specimen impacts it is possible to evaluate a relationship between overall composite specimen stiffness and the impact damage. Finally, in order to identify the most unfavourable situation with regard to impact damage resistance an association between hygrothermal ageing and an applied tensile load is examined

Approved for public release; distribution is unlimited. / The major driver for broadband wireless communications has been reliable, high-data rate services. In wireless communication, the multipath fading constitutes a bottleneck for increasing data rates and causes performance degradation. To combat fading, we can use diversity. Wireless systems with multiple antennas at the transmitter and receiver have much larger capacity in fading channels than standard wireless systems. The objective of this thesis is to investigate the transmission scheme provided by matrix A and B in the 802.16 standard and show how it can be implemented. The research focuses on using maximal-ratio combining (MRC) to demodulate the transmitted symbols. Modifications to the existing matrix by using more frequency bands were introduced; this reduces the number of transmitting antennas and uses fewer time slots to transmit the same number of symbols. The modulator and demodulator design is also discussed. The performance of orthogonal and non-orthogonal space time codes (STC) are evaluated. / Civilian

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Quasi-hom-Lie algebras (qhl-algebras) were introduced by Larsson and Silvestrov (2004) as a generalisation of hom-Lie algebras, which are a deformation of Lie algebras. Lie algebras are defined by an operation called bracket, [·,·], and a three-term Jacobi identity. By the theorem from Hartwig, Larsson, and Silvestrov (2003), this bracket and the three-term Jacobi identity are deformed into a new bracket operation, <·,·>, and a six-term Jacobi identity, making it a quasi-hom-Lie algebra. Throughout this thesis we deform the Lie algebra sl2(F), where F is a field of characteristic 0. We examine the quasi-deformed relations and six-term Jacobi identities of the following polynomial algebras: F[t], F[t]/(t2), F[t]/(t3), F[t]/(t4), F[t]/(t5), F[t]/(tn), where n is a positive integer ≥2, and F[t]/((t-t0)3). Larsson and Silvestrov (2005) and Larsson, Sigurdsson, and Silvestrov (2008) have already examined some of these cases, which we repeat for the reader's convenience. We further investigate the following σ-twisted derivations, and how they act in the different cases of mentioned polynomial algebras: the ordinary differential operator, the shifted difference operator, the Jackson q-derivation operator, the continuous q-difference operator, the Eulerian operator, the divided difference operator, and the nilpotent imaginary derivative operator. We also introduce a new, general, σ-twisted derivation operator, which is σ(t) as a polynomial of degree k.

It is well known that light can carry two different kind of angular momentum that together form the total angular momentum of photons. These two forms are the spin orbital angular momentum, associated with the circular polarisation of light, and the orbital angular momentum of light associated with a wavefront tilted with respect to the propagation axis. Any tilted wavefront generates an orbital component of the angular momentum but there are some special cases in which this property becomes particularly interesting. It is the case of optical vortices which form when the waveform is continuously and uniformly tilted to the propagation axis forming a spiral structure.

This work investigates some aspects of the dynamics of non-invertible quasi-periodic circle maps, from the point of view of rotation numbers and their structure in parameter space.Circle maps and quasi-periodically forced circle maps have been widely used asa model for a broad range of physical phenomena. From the mathematical point of view they have also received considerable attention because of the many interesting features they exhibit.The system used is given by the maps: x_n = [ x_n-1 + a + b/(2pi) sin( 2pi x_n-1) + c sin( 2pi theta_n-1) ] mod 1, and, theta_n = theta_n-1 + omega.Where a, b and c are real constants. In addition, b and omega are restricted, respectively, to values larger than one and irrational.A fundamental part of this thesis consists of numerical approximations of rotation intervals using and adapting of the work of Boyland (1986) to the quasi-periodic case.Particular emphasis was given to the case of large coupling strength in quasi-periodicforcing.Examination of the computed rotation numbers for the large coupling case, together with previous claims suggesting that for large coupling strength the b-term could be neglected (see Ding (1989)), led to the formulation of an ergodic argument which is statistically supported. This argument indicates that, for this case, the qualitative behavior of rotation number depends linearly on a. It is also shown that the length of the rotation interval, when the transition from a trivial rotation interval (invertible case) to a non-trivial rotation interval occurs, it develops locally as a universal unfolding.A different map, piecewise monotone, and structurally similar to the maps defined to calculate the edges of rotation intervals in Boyland (1986), is studied to illustrate how the rotation number grows. The edges of rotation intervals are analytically calculated and matched with numerical observations.

With the projected growth of wind energy in the United States expected to account for 20% of the energy portfolio by 2030, it can be expected that wind turbines will not only increase in number, but also in size. This increase in size implies that internal components, such as the gearbox, will also increase to handle the higher loads. And given the high failure rates for gearbox components already in existence, one could expect more failure if nothing is done to improve reliability. It is well known that wind loading is not constant, rather it is random and ultimately causes fatigue loading. This thesis is concerned with studying what the effects of dynamic loading are on a smaller gear system. It is assumed the findings of this study can be scaled to a larger wind turbine system. A simple spur gear pair is first simulated at constant loading to establish a baseline and then run with a sinusoidal input with differing amplitudes and frequencies. The hypothesis is that by varying the amplitude and frequency, the responses for gear contact force and input and output shaft torques will also vary. And if these variations are noted, then conclusions may be drawn as how the frequency and amplitude influence the system. After which, it may then be correlated to a wind turbine system. Knowing what affects the frequency and amplitude have on a smaller system may help to establish guidelines. For this model, mechanical simulation software is used to build a multibody dynamics model of a spur gear system with flexible shafts. Using known wind data obtained near Amarillo, TX, a matrix of possible frequencies and amplitudes for a sinusoidal input are implemented and the solutions compared to those at constant loading. It was found that the system responded similarly regardless of input, showing RMS values for accelerations of approximately 50 m/s2, gear contact forces of 520 N, input shaft torques of 42 Nm, and output shaft torques of 78 Nm. This behavior is not expected is most likely due to insufficiencies in the assumptions made to construct the model.