Sistema de comando de vôo Fly-by-wire associados com o conceito de estabilidade relaxada vêm trazendo vantagens às aeronaves comerciais nas últimas décadas, e um procedimento de projeto de sistemas de aumento de estabilidade e controle utilizando técnicas modernas traz como vantagem a redução no custo e no tempo de desenvolvimento, que são os principais empecilhos para implementação de sistemas deste tipo. Este trabalho apresenta o projeto de leis de controle para um sistema de controle de vôo empregando ferramentas de controle robusto, tais como H-infinitivo, síntese um e transformações lineares fracionárias (LFTs). As incertezas em geral ocorrem no modelo dinâmico da aeronave, em função de parâmetros tais como massa e momentos de inércia da aeronave, posição do centro de gravidade e condição de vôo (velocidade e altitude) são consideradas no projeto. O objetivo é encontrar um controlador que atenda aos requisitos de projeto tanto no ponto nominal como no caso de incertezas e variações destes parâmetros, apresentando assim robustez de estabilidade e de desempenho. O projeto de realimentação é baseado no parâmetro C*, que é largamente empregado na indústria aeronáutica, e permite avaliações e especificações de desempenho de forma simples e bem conhecida. Outros critérios bastante conhecidos na literatura são também empregados para uma análise mais completa de qualidade de vôo.

This work presents the open-loop stability analysis and an active control strategy for an airbreathing hypersonic vehicle. The 14-XB, a bidimensional flow airframe derived from the Brazilian 14-X Aerospace Hypersonic Vehicle, is adopted as study platform. In order to perform such analyses, a simulation mathematical model of the airframe longitudinal forces and moments is obtained using perfect gas equations, after considering the relevance of the real gas hypotheses for the expected Mach number range and verifying that the simpler formulation is sufficient. An all-moving horizontal tail is designed in order to enable the aircraft trimming. The horizontal tail design considered simple constraints based on static analysis, and the same gas equations as those used for the airframe study. In order to analyze the aircraft';s dynamic behavior, a Six-Degree-of-Freedom set of equations of motion considering a spherical, rotating Earth is presented in detail, and the necessary conditions to have adequate longitudinal trimming in this scenario are discussed. The open-loop stability of the 14-XB with the designed horizontal tail is assessed through eigenvalue analysis and numerical flight simulations with the horizontal tail fixed at a trim position. Having observed that the aircraft presents unstable long-term natural modes, an active control strategy is suggested in order to stabilize the vehicle and track a desired flight path angle, assuming that thrust is constant and the control surface is an all-moving horizontal tail. The suggested control structure presents pitch stability augmentation system and flight path angle compensator. Optimal gains are calculated using linear quadratic design, along with a gain-scheduling strategy based on simultaneous control design, and the resulting controller presents proper results.

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Companies in the 21st century are exposed to a variety of pressures to respond to a plethora of environmental issues. Understanding how these issues impact companies over time is, therefore, important for corporate practitioners and policy makers alike. This thesis investigates the state and evolution of corporate environmental strategy with the help of a multi-study, longitudinal research design. Theoretically grounded in complexity theory, a conceptual framework is developed that portrays organisations as open systems within which agents interact and attempt to improve organisational fitness. By conceptualising the organisational metaphor of ‘rugged fitness landscapes’, firms are depicted as complex adaptive systems searching for peaks on a constantly changing fitness landscape in order to guarantee economic long-term profit and survival. While study one examines environmental responses among a stratified sample of UK companies through repeated interviews both in 2006 and 2008, the second study draws on KLD data from S&P500 corporations for the period 1991 to 2006 by distinguishing between changes at firm and at population level. The findings suggest that the state and evolution of corporate environmental strategy are effectively subordinated to contributing towards firms’ fitness, whereby firms mostly attempt to remain profitable and obtain social legitimacy. Even over longer periods of time this behaviour has not changed markedly, except that starting from around 2004 higher levels of oil prices and lower interest rates have spurred more proactive environmental changes among a number of firms. Equally, different motivations, individuals and contextual factors appear to influence the varying patterns of evolution. The thesis fills a gap in the existing literature with respect to the lack of conceptual and empirical contributions about the evolution of corporate environmental strategy by providing new insights into how firms are responding to environmental issues over time and by extending various strands of theory.

In longitudinal settings, modeling the covariance structure of repeated measure data is essential for proper analysis. The first paper in this three-paper dissertation presents a survey of four journals in the fields of Education and Psychology to identify the most commonly used methods for analyzing longitudinal data. It provides literature reviews and statistical details for each identified method. This paper also offers a summary table giving the benefits and drawbacks of all the surveyed methods in order to help researchers choose the optimal model according to the structure of their data. Finally, this paper highlights that even when scholars do use more advanced methods for analyzing repeated measure data, they very rarely report (or explore in their discussions) the covariance structure implemented in their choice of modeling. This suggests that, at least in some cases, researchers may not be taking advantage of the optimal covariance patterns. This paper identifies a gap in the standard statistical practices of the fields of Education and Psychology, namely that researchers are not modeling the covariance structure as an extension of fixed/random effects modeling. The second paper introduces the General Serial Covariance (GSC) approach, an extension of the Linear Mixed Modeling (LMM) or Hierarchical Linear Model (HLM) techniques that models the covariance structure using spatial correlation functions such as Gaussian, Exponential, and other patterns. These spatial correlations model the covariance structure in a continuous manner and therefore can deal with missingness and imbalanced data in a straightforward way. A simulation study in the second paper reveals that when data are consistent with the GSC model, using basic HLMs is not optimal for the estimation and testing of the fixed effects. The third paper is a tutorial that uses a real-world data set from a drug abuse prevention intervention to demonstrate the use of the GSC and basic HLM models in R programming language. This paper utilizes variograms (a visualization tool borrowed from geostatistics) among other exploratory tools to determine the covariance structure of the repeated measure data. This paper aims to introduce the GSC model and variogram plots to Education and Psychology, where, according to the survey in the first paper, they are not in use. This paper can also help scholars seeking guidance for interpreting the fixed effect-parameters.

IQ has been shown to predict life outcomes such as income and education, but to benefit men more than women. Parenthood is in turn known to be partly predicted by variables correlated with IQ, with more educated and well-paid subjects being more probable to become parents. Previous research has found evidence for a “fatherhood premium” for men and a “motherhood penalty” for women, with fathers tending to earn more than comparable non-fathers and mothers in turn earning less than childless women. This study used data from a longitudinal Swedish study to investigate the relationship between IQ, parenthood and income. Results showed that both men and women in the low IQ group had a lower probability of parenthood, men significantly so. A fatherhood premium was found, but it disappeared when controlling for working hours. A more consistent and significant motherhood penalty disfavoring women with children was found in the high IQ group, but this difference could not explain much of the much larger income difference between the genders. Whereas the average hourly wages of all groups of men were higher than those of all groups of women, all groups of women had a higher mean probability of parenthood than all groups of men.  Previous research has indicated that some groups seem to “have it all” in the sense of being uniformly well-adjusted, but in this sample it appears to be more of a trade-off with no group being consistently at an advantage on all indices of adjustment.

The correlation between locus of control and marital satisfaction is examined as part of a longitudinal study spanning 44 years and 3 time points. It is predicted that as locus of control has more of an external orientation marital satisfaction will be lower. Participants include high school juniors and seniors in the state of Washington from 1966 with follow-up surveys in 1980 and 2010. Using ordinary least squares regressions, marital satisfaction scores in 1980 or 2010 are predicted by locus of control scores from either 1966 or 1980 with control variables that include gender, income, educational attainment, occupational prestige, and military service. Partial support for the presented hypotheses is found and discussed. Locus of control as measured in middle adulthood predicted marital satisfaction measured contemporaneously. However, in contrast to previous reports, none of the control variables significantly predicted marital satisfaction. A primary limitation that is discussed regards the measurement of locus of control occurring in a manner without any established psychometric data to confirm reliability or validity. Understanding the relationship between locus of control and marital satisfaction may help improve case conceptualization and treatment for couples seeking treatment. Considerations for future research are explored.

This study examines how hopelessness impacts youth engagement in violent behavior over time. The data are from waves I and II of The National Longitudinal Study of Adolescent Health (Add Health). Poisson regression was used to analyze contributors to violence in just wave I, and then again across time in wave II using explanatory and control variables from wave I. Results indicate that hopelessness is positively associated with violent behavior. Furthermore, while hopelessness and most of the other explanatory variables predicted violent behavior in wave I, almost all the variables became non-significant or negative except hopelessness and a measure of community when predicting violence in wave II. This shows that hopelessness is a concept that needs to be explored more closely when studying violence among youth.

The foundation for osteoporosis risk is established during the time periods of childhood, adolescence, and young adulthood, periods of development when bone mass is being accrued rapidly. The relative quantity of bone mass accrued is influenced by both lifestyle and genetic factors. The purpose of this dissertation project was to discover single nucleotide polymorphisms (SNPs) associated with: (1) The rate of hip bone accrual (measured as bone mineral content or BMC) during the adolescent growth spurt, and (2) Total hip bone mass measured as BMC around the age of 19 when the amount of bone accrued is approximately at its peak. Additionally, SNP × longitudinal lifestyle factor (calcium intake per day, vitamin D intake per day, and minutes of moderate to vigorous physical activity (MVPA) per day) multiplicative interaction effects were assessed. Each cohort member’s vector of longitudinal physical activity measurements was summarized as belonging to one of a set of specific trajectory groups using finite mixture modeling. The same was then done for calcium intake and vitamin D intake. The source of the data utilized was the Iowa Bone Development Study (IBDS), which includes genetic and longitudinal bone measurement information. To discover SNPs, a genome-wide association study (GWAS) design was utilized. Females and males were analyzed separately and together. The association between SNPs and the rate of hip bone accrual during the adolescent growth spurt was assessed using linear mixed models controlling for body size, and the association between SNPs and peak hip bone mass was assessed using an ordinary linear regression model, also controlling for body size. Approximately 500,000 SNPs were tested in each GWA analysis; significance was assessed at a familywise error rate of 0.05, the individual test cutoff of which was determined by using SimpleM, a modified Šídák correction. No statistically significant SNPs were detected at the 0.05 familywise error rate threshold established by SimpleM (p < 1.76×10-7); however genes near suggestive SNPs (24 total) were assessed for biological relevance. Of most biological relevance were two suggestive SNPs (rs2051756 and rs2866908, p-values of 1.25×10-6 and 4.28×10-6, respectively) that were detected in an intron of the DKK2 gene through the GWA analysis exploring peak bone mass in females. The DKK2 gene is part of the Wnt signaling pathway and is associated with embryonic development; additionally, it is expressed more highly in osteoarthritic osteoblasts than in normal osteoblasts. No statistically significant results were found from the SNP × lifestyle factor multiplicative interaction effect tests. The potential importance of the DKK2 gene to peak hip bone mass accrual in females should be studied further in order to understand the pathophysiology of this suggested novel association identified during a discovery GWA analysis.

Interest in mediation analysis has increased over time, with particular excitement in the social and behavioral sciences. A mediator is defined as an intermediate in the causal sequence between an independent and dependent variable. Previous research has demonstrated that the cross-sectional form of mediation analysis is inherently flawed, evidenced by the inability of the cross-sectional mediation model to account for temporal precedence and estimation of the indirect effect being biased in nearly all situations. For these reasons, a longitudinal model is recommended. However, a method for determining the exact time points to measure the variables used in mediation analysis has not been adequately examined. In this study, we examined methods for determining an appropriate time lag when designing a mediation study. The methods implemented include correlation analysis, the quadratic and exponential forms of the lag as a moderator approach, and knot estimation using basis splines. The data for the study was simulated for three distinct trends generated using a linear piecewise model, a sigmoid model, and a sigmoid piecewise model. Additionally, two sampling approaches, an intense sampling approach and a three-measure approach, were examined as well as six sample sizes and three effect sizes for the total effect on the outcome. The estimation methods were additionally compared by considering different types of error structures used in data generation as well as by examining equal and unequal time lag lengths between the predictor and mediator, and the mediator and outcome. The intent of the study is to provide methods so that researchers can estimate the best time to evaluate mediator and outcome measurements that will be used in mediation analysis. The results from this study showed that the best estimation method varied depending on the lag being estimated, the sampling approach, and the length of the lag. However, the knot estimation approach worked reasonably well in most scenarios considered even with small sample sizes of 5 or 10 per group. The findings from this study have the potential to improve study design for research implementing longitudinal mediation analysis by reducing bias in the estimate of the indirect effect when adequate time points are used.