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O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

O desemprego é um dos principais problemas enfrentados pelas economias capitalistas. Analisando a sua incidência sobre a força de trabalho, há evidências que alguns grupos de trabalhadores - como as mulheres, os jovens, os negros - sofrem sistematicamente com taxas de desemprego mais elevadas. Neste contexto, o objetivo desta dissertação é analisar a relação entre o desemprego e a heterogeneidade dos trabalhadores e como ela se apresentou no Brasil no período entre 1990 a 2013. A principal hipótese deste trabalho é de que as diferenças existentes entre os trabalhadores - como gênero, raça, idade, entre outras - também podem ser responsáveis, em interação com outros determinantes macroeconômicos, por níveis e dinâmicas diferenciadas de desemprego. A metodologia dessa pesquisa consiste em uma revisão bibliográfica de quatro abordagens macroeconômicas do desemprego e o modo como elas tratam a heterogeneidade da força de trabalho, além do uso de métodos quantitativos com base em dados sobre a economia brasileira. Com base na revisão bibliográfica e nos dados da economia brasileira, é utilizado um modelo econométrico de vetores de correção de erros (VECM) para verificar algumas hipóteses do desemprego e a sua relação com a heterogeneidade. Os resultados do trabalho indicam que, apesar das dificuldades nas teorias do desemprego em inserir a heterogeneidade dos trabalhadores em seus arcabouços teóricos, as visões marxista e pós-keynesiana oferecem importantes instrumentos teóricos e metodológicos para esse tipo de problema. Além disso, os resultados econométricos confirmam, parcialmente, que a demanda efetiva, seguindo a hipótese pós-keynesiana, e o conflito distributivo entre lucros e salários, argumento marxista, são fatores importantes para compreender o desemprego no Brasil. No que diz respeito à relação entre a heterogeneidade e o desemprego, os resultados apontam que um choque na taxa de desemprego incide de forma diferenciada entre os grupos que compõem a força de trabalho. Contudo, nem sempre o desemprego atinge de forma mais intensa os grupos que apresentam historicamente as maiores taxas de desocupação. / Unemployment is one of the main problems faced by capitalist economies. By analyzing its impact on the workforce, the research shows that there are evidences that some groups of workers – such as women, young people, blacks - systematically suffer from higher unemployment rates. In this context, the objective of this work is to analyze the relationship between unemployment and the heterogeneity of workers and how this relationship appears in Brazil from 1990 to 2013. The main hypothesis of this work is that the differences between the workers - such as gender, race, age, among others - may also be responsible, in interaction with other macroeconomic determinants, for the level and the dynamic of the different unemployment rates. The methodology of this research consists of a literature review of four macroeconomic approaches of the unemployment and how they treat the heterogeneity of the workforce, and also the use of quantitative methods using data for the Brazilian economy. Based on the bibliographic review and on the data of the Brazilian economy, an econometric model is used for vector error correction (VEC) to test some hypotheses regarding unemployment and its relationship with the heterogeneity. The results indicate that, despite the difficulties with the theories of unemployment regarding the heterogeneity of workers in their frameworks, the marxist and post keynesian theories provide important theoretical and methodological tools for this type of problem. In addition, the econometric results confirm, in part, that the effective demand, following the post keynesian hypothesis, and the distributive conflict between profits and wages, in terms of the marxist argument, are important factors to understand the unemployment in Brazil. Concerning the relationship between heterogeneity and unemployment, the results indicate that a shock in the unemployment rate has different impacts on the groups that make up the workforce. However, unemployment is not always more intense on the groups that historically have the highest rates of unemployment.

Resources that can optimize survival are distributed unevenly across landscapes. I assumed that the distribution of these resources is reflected by landscape heterogeneity and that selection for areas with relatively high heterogeneity reflects on selection for resources. I therefore hypothesized that landscape heterogeneity determines variability in elephant home range location and size. I evaluated home range sizes for elephants living in the Etosha National Park (n = 6), Khaudum Game Reserve (n = 6) and Ngamiland District 11 (n = 4) during two wet and two dry seasons. I used raster grid landscape maps, which were based on structural classes, to superimpose elephant home ranges and to generate randomly located ranges. I then used the FRAGSTATS programme to calculate five landscape metrics that measure aspects of heterogeneity within elephant and randomly located ranges. I compared landscape heterogeneity of the three study areas using the landscape metrics calculated for the randomly located ranges. Assuming that higher values of Patch density, Lanscape shape index and Shannon diversity index, and lower values of Largest patch index and Contagion implies selection for heterogeneity, I qualitatively compared the distribution and the mean of the landscape metric values for the elephant home ranges with those for the randomly located ranges. The influence of season on selection for the landscape metrics was also evaluated. I searched for relationships between home range size and landscape metrics for the three study areas and searched for a possible relationship between home range size and water point density for elephants in Etosha and Khaudum. Khaudum was consistently more heterogeneous than Etosha and NG11, while the latter was the least heterogeneous. Within these study areas, at least some of the landscape metrics may explain the location of elephant home ranges. The consistent apparent selection for areas with relatively higher values of Landscape shape index and Shannon diversity index and lower values of Largest patch index and Contagion across both wet and/or dry seasons by elephants in Etosha and NG11 suggests that landscape heterogeneity can explain landscape selection by elephants. This did not hold for elephants in Khaudum where elephants inconsistently selected for Largest patch index and Landscape shape index. This study further suggested that landscape heterogeneity did not determine home range size. However, water was a strong determinant of home range size and may therefore explain the lack of selection for heterogeneity in Khaudum. Heterogeneity is an inherent characteristic of landscapes and seems to reflect on the availability of resources that may subsequently influence the way elephants use space. My study supported the concept that increasing space, while promoting heterogeneity for elephants may enhance range expansion. The management of elephants should therefore be directed at optimising the availability of heterogeneous landscapes when setting land aside for their conservation. Management also should reconsider water distribution policies since the availability of water influences landscape use and conceivably potential impact on vegetation. / Dissertation (MSc)--University of Pretoria, 2008. / Zoology and Entomology / unrestricted

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Oscillations and rhythms are measured in the brain through large-scale measures like EEG (electroencephalogram) and LFP (Local Field Potential). Particularly, cortical gamma rhythms (30-90 Hz) found in different brain regions are correlated with different cognitive states. Despite vast differences in the range frequencies in gamma rhythms, the regions communicate to complete high-level tasks. One way in which this takes place is entrainment, where the postsynaptic group phase-lock to the rhythmic input from the presynaptic group (constant phase-shift). Mathematical models of the neurons and the neural networks are proposed to uncover the mechanisms behind experimentally observed phenomena. Most works have used homogeneous models of spiking networks. These simplified models provide a valuable understanding of neural dynamics. However, neural heterogeneity (variation in the neural or network parameters) has been experimentally observed and shown to have a non-trivial effect on many neural processes. Few studies have dealt with the role of different types of neural heterogeneity in the entrainment of a large network, and how it affects the frequency range the neural network entrains to. In this project, we aimed to show how different types of network heterogeneity affect the ability of the networks to entrain to gamma frequencies. We used the Pyramidal-Interneuronal Network Gamma (PING) model, a model consisting of excitatory pyramidal cells (E-cells) and inhibitory interneurons (I-cells) that are synaptically connected and generate gamma oscillations. We show that heterogeneity in the synaptic conductance from excitatory neurons to inhibitory neurons greatly increases the frequency range over which the network can entrain. The mechanism that allows this to happen requires the heterogeneity to 1. Create an I-cell excitability gradient; 2. Introduce input synchrony difference among the I-cells. The entrained I-cell subsets formed under these two conditions are necessary for well-enhanced entrainment as they support the entrainment of the whole network through feedback inhibition. This improvement is shown to be robust in large parameter space.

<p> Protein sequences display replacement rate heterogeneity across sites. In an earlier work, half of the causal site-wise variation in replacement rates was explained by a simple linear regression model consisting of terms for the solvent exposure of each residue, distance from the active site, and glycines in unusual main-chain conformations. Replacement rates vary not only across sites, they may also vary over time. In this study, we apply the linear regression model to phylogenies divided into subtrees to see if lineage-specific rate shifts have a structural basis that can be detected by the model. This approach is applied to two different data sets. The first set consists of phylogenies containing two representative structures, divided into subtrees such that one structure is present in each subtree. These structures have little or no obvious functional divergence between them. The model is tested with permutations of subtrees and structures from each subtree. While there is a slight effect of the specific structure on the fit of the model, the specific subtree has a greater effect. The second data set involves homologous structure pairs where the quaternary structure has changed at some point in the phylogeny. These pairs are examined to see how the change in constraint on the new interface sites affect the replacement rate, and its relationship with other structural factors. We find that the unique interfaces are as conserved as the shared ones, and they exhibit a different relationship between replacement rates and indicators of constraint than the shared interfaces or other protein sites. We also find that the unique interfaces display characteristic amino acid preferences that may identify interfaces which are still in the process of stabilizing. </p> / Thesis / Master of Science (MSc)

The corrosion-wear resistance tradeoff in conventional metals imposes a great challenge to their reliable long-term performance under extreme conditions where surface stress and corrosive environment coexist (i.e., tribocorrosion). In this work, strategies to introduce chemical and structural heterogeneity with controlled length-scale at nanometers were proposed and studied in three metallic systems (i.e., Zr-based, Al-based and Mg-based), in order to enhance their tribocorrosion resistance. In the first study, ZrCuNiAl thin film metallic glasses (TFMG) with either homogeneous or heterogeneous local composition were deposited by magnetron sputtering through controlling processing conditions (i.e., argon (Ar) pressure). It was found that the mechanical properties, wear, corrosion and tribocorrosion resistance of ZrCuNiAl TFMG were significantly affected by nanoscale chemical heterogeneity. As a result, nanoscale chemical heterogeneity promoted ductility but reduced hardness, which in turn weakened wear resistance. While, in the 0.6 M NaCl solution, the resistance to pitting corrosion and tribocorrosion was improved because the presence of nanoscale chemical heterogeneity facilitates to generate more protective passive layer with lower defect density and faster repassivated capability, compared to their homogenous counterparts. In the second study, nanoscale chemical and structural heterogeneity were introduced in Al by forming Al/X nanostructured metallic multilayers (NMMs), where X=Mg, Cu, and Ti. Compared to the respective monolithic films, the alternating nanolayer configuration not only increased strength due to the presence of abundant interfaces but also reduced surface activity and pitting susceptibility. The electrochemical performance was significantly affected by the interaction, i.e., galvanic effect, between Al layer and underlayer constituents, which in turn led to different tribocorrosion behaviors, Specifically, transmission electron microscopy revealed that the materials loss in Al/Mg and Al/Cu NMMs primarily resulted from corrosion, while Al/Ti was dominated by severe plastic deformation during tribocorrosion as a result of sustained surface passivity. Lastly, in the bulk biodegradable Mg alloys system, the surface was treated by femtosecond laser shock peening (fs-LSP) technique with ultra-low pulse energy to introduce structural heterogeneity. Treatment conditions (e.g., power density, direct ablation and confined ablation) significantly affected the ultimate peening effect and further surface performance. In this work, the optimized peening effect was obtained at 28 GW/cm2 laser power density in the confined ablation with the assistance of the adsorption layer and confining medium. Combined with transmission electron microscopy and finite element analysis, the improvement of surface performance was attributed to high dislocation density near the surface, rather than compressive residual stress. The existence of structural heterogeneity not only reduced corrosion kinetics but simultaneously improved the self-repassivation in the blood bank buffered saline solution at body temperature. / Doctor of Philosophy / In various industrial applications such as marine infrastructure, nuclear power plants, and biomedical devices, the synergistic effect of wear and corrosion, known as tribocorrosion, is an inevitable material degradation phenomenon. To resist such aggressive degradation and prolong the service life of metals in complex environments, it is crucial to simultaneously enhance the wear and corrosion resistance, i.e., tribocorrosion resistance of metals. Unfortunately, the corrosion-wear resistance tradeoff in conventional metals imposes a great challenge. For example, most precipitation-hardened Al alloys impart high strength and wear but exhibit low resistance against localized corrosion as a sacrifice owing to the micro-galvanic coupling between the matrix and precipitates. Several previous works pointed out that compositional and structural heterogeneity, even at the nanoscale, could simultaneously affect the mechanical properties and corrosion resistance of metals. However, few works have been performed to understand the effects of such heterogeneity and their length-scale during tribocorrosion of metals. In this dissertation, by combining materials processing, advanced characterization, and tribocorrosion testing, the effects of chemical and structural heterogeneity, as well as their length-scale, on the deformation and degradation mechanisms of metals were studied using model systems of Zr-, Al- and Mg-based alloys, where the chemical and/or structural heterogeneity were introduced by tuning the materials processing conditions. Firstly, the nanoscale chemical heterogeneity was introduced into ZrCuNiAl thin film metallic glasses (TFMG) by adjusting argon (Ar) pressure during magnetron sputtering. Compared with the homogeneous composition, heterogenous local composition in ZrCuNiAl TFMG improved ductility but sacrificed hardness and wear resistance. In 0.6 M NaCl solution, higher pitting corrosion and tribocorroison resistance can be observed due to the generation of low defect density protective passive film with low defect density and with fast repassivation rates in heterogeneous ZrCuNiAl TFMG. Secondly, the architecture of nanostructured metallic multilayer in Al-based with different constituents, from noble to active metals (e.g., Cu, Ti and Mg), were studied the effects of chemical and structural heterogeneity on wear, corrosion and tribocorrosion performance. The results showed that the deformation and corrosion behaviors significantly depended on the distinct interfaces and chemical modulation at the nanoscale, caused by different constituents, which ultimately resulted in various tribocorrosion resistance in 0.6 M NaCl solution at room temperature. Transmission electron microscopy of deformed and degraded sample surfaces showed characteristic different deformation and degradation modes of all samples, governed by the synergistic effects of the mechanical and corrosion properties of the constituting materials. Specifically, severe plastic deformation mainly led to material loss in Al/Ti NMMs owing to the noble surface reactivity, while corrosion was the dominant factor for material loss in Al/Mg and Al/Cu NMMs during tribocorroison. Lastly, the ultra-low pulse energy femtosecond laser shock peening technique was successfully applied to introduce structural heterogeneity in the bulk biodegradable Mg alloys since in some cases the deposition is not feasible for bulk metals. The optimizing peening effect was firstly investigated and was achieved at confined ablation conditions under 28 GW/cm2 laser power density. Results show that the high dislocation density near the surface was contributing to the surface strengthening effect, high corrosion and tribocorrosion resistance in a simulated body environment via transmission electron microscopy observation. The finite element analysis method investigated the compressive residual stress in current work that did not significantly affect the surface performance of Mg alloys. In summary, the study of this dissertation contributes to a good basis and design strategy of conventional metals for applications under complex environments.