Orientador: Nelson de Jesus Parada / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-23T17:50:02Z (GMT). No. of bitstreams: 1 Brescansin_LuizMarco_M.pdf: 1642543 bytes, checksum: a83d33a8bab288a7875e2d40e80bdb08 (MD5) Previous issue date: 1972 / Resumo: Neste trabalho foram calculadas as faixas de energia eletrônicas do AlSb pelo método APW-K.P. Inicialmente, pelo método APW não relativistico foram calculadas nove faixas de energia no ponto G que, juntamente com as correspondentes autofunções da Hamiltoniana foram utilizadas para obter os elementos de matriz do operador momento P entre estados em G. Estes, por sua vez, foram utilizados na expansão K.P para se obterem as energias e autofunções nos eixos de simetria 2p/a(l ,0,0) , 3p/2a(1,1,0) e p/a(1,1,1 ). Posteriormente foi verificado como as correções relativisticas afetam os resultados no ponto G: com as correções de Darwin e massa-velocidade, novas energias e funções de onda foram calculadas nesse ponto e finalmente introduziu-se a correção do termo spin-órbita, quando é necessário levar em conta o spin nas funções de onda, que são construidas a partir das autofunções da Hamiltoniana não relativistica. Os elementos de matriz relativistico entre estas funções de onda foram calculadas numericamente e a matriz Hamiltoniana resultante foi diagonalizada, dando os níveis de energia relativisticos do AlSb no ponto G. Os resultados obtidos deixam antever a necessidade de correções à forma do potencial "muffin-tin", bem como a necessidade de um cálculo de faixas de energia auto-consistente, para uma tentativa de interpretar corretamente os dados experimentais disponiveis deste material / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Orientador: Nelson de Jesus Parada / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-23T17:23:07Z (GMT). No. of bitstreams: 1 Meneses_GildaDalcanale_M.pdf: 2389543 bytes, checksum: 23c0cfa094ad60087ef5081f4faf18a9 (MD5) Previous issue date: 1972 / Resumo: Neste trabalho é feito um estudo dos níveis de energia eletrônicos no centro da zona de Brillouin, da liga CdxHg1-x Te para as composições x = 0, 0.1, 1.2, 0.3, 0.5, 0.6, 0.8 e 1.0, incluindo, portanto, os cristais componentes do sistema HgTe. Foram utilizados os valores de 6,43 Å e 6,477 Å para o parâmetro de rede, e 0.6715 Ry e 0.633 Ry para Vc, o potencial constante fora das esferas no modelo "Muffin - tin". O Método empregado é o APW ( Augmented Plane Wave ) não relativístico. O potencial cristalino da liga foi aproximado pelo potencial virtual. Curvas que dão a evolução das energias E( G ), Gj = Gl, G2 , G12, G15, G25 em função da composição x foram determinadas, tendo sido feita uma estimativa da variação do 'gap" com a composicão. Para HgTe e CdTe, foi obtida a a variação do "gap" de energia, com o único parâmetro ajustável do cálculo, o potencial constante Vc fora das esferas. Foi calculada, ainda, a função de onda correspondente a cada. nível de energia. Os resultados quantitativos encontrados indicam serem necessárias correções relativisticas e do potencial cristalino da liga / Abstract: Not informed. / Mestrado / Física / Mestre em Física

Orientadores: Aurea Rosas Vasconcellos, Roberto Luzzi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica "Gleb Wataghin" / Made available in DSpace on 2018-07-27T20:50:03Z (GMT). No. of bitstreams: 1 Rodrigues_ClovesGoncalves_D.pdf: 12304170 bytes, checksum: 0e856f16c9444a08a4bd1bd417c5ffc5 (MD5) Previous issue date: 2001 / Resumo: Apresentamos um estudo extenso e detalhado do estado termodinâmico de não-equilíbrio, e de propriedades ópticas e de transporte de semicondutores polares de gap direto na presença de campos elétricos moderados e intensos. Para tal fim recorremos à teoria cinética quântica não-linear, que é baseada num atual e poderoso formalismo mecânico estatístico de ensembles para sistemas abertos longe do equilíbrio. Particular atenção foi dada ao caso de semicondutores polares de gap largo, especialmentes aos nitretos dos elementos da coluna III ( III-N, como GaN, InN, AlN ). Foram deduzidas as equações de evolução temporal para: o momento dos portadores, a energia dos portadores, a energia dos fônons ópticos longitudinais e trânsversais e dos fônons acústicos. Cálculos numéricos foram realizados considerando o caso particular do plasma fotocriado no semicondutor polar polar de gap direto GaN, na forma zincblenda ( cúbico ) e wurtzita ( hexagonal ), nas condições iniciais estabelecidas em um experimento de espectroscopia óptica de resolução temporal ultra-rápida. Analizamos tanto o estado transiente quanto o estacionário. Foi estudado também o caso dos semicondutores dopados tipo n, em particular: n-AlN, n-GaN e n-InN, todos na forma wurtzita. Comparações com outros resultados teóricos foram feitos para o Arseneto de Gálio e Nitreto de Gálio. Comparações com resultados experimentais no estado estacionário foram realizados para o Arseneto de Gálio e para o GaN, porém a campos baixos; até o presente há inexistência de experimentos em materiais III-N em campos intensos. Além das propriedades de transporte, estudamos também propriedades ópticas ( luminescência e absorção ) analizando o efeito de campo elétrico sobre os espectros / Abstract: It is presented a somewhat extented and detailed study of the nonequilibrium thermodynamic state, as well as transport and optical properties of direct-gap polar semicondutors when under the action of moderate to intense electric fields. For that purpose we resort to a nonlinear quantum kinetic theory which is based on a nowadays existent powerful and physically sounded mechanical statistic ensemble formalism for far-from-equilibrium open systems. Particular attention was given to the case of large-gap polar semicondutors, mainly the III-Nitrides ( like GaN, InN, AlN ). The equations of evolution - in the nonequilibium ( dissipative ) thermodynamic state of the system - for the enerfy and the linear momentum of the carrier, the energy of the optical ( LO and TO ) as well as acoustical phonons, are derived. Specific numerical calculations have been performed considering the particular case of the photoinjected plasma in GaN in both the wurtzite ( hexagonal ) and zincblende ( cubic ) crystalline structures, in conditions akin to those present in a typical pump-probe experiment in ultrafast time-resolved optical spectroscopy. The transient and the steady state are analized. It has also beeb considered the case of doped GaN, AlN, and InN in the wurtzite ( hexagonal ) structure. Are also presented comparisons with other theoretical calculations and with some experimental results. This is done far GaN and also GaAs, once for the latter there exists a good amount of experimental data. This is not the case for III-N in high fields when up to present experimental reports are not available; we have only make comparison whith meansurements of mobility in GaN ( cubic ) at low fields. Besides the study of Transport properties it has also been studied optical properties, particularly absorption and luminescence, analyzing the effect of the electric field on the corresponding spectra / Doutorado / Física / Doutor em Ciências

Orientador: Carlos Henrique de Brito Cruz / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-28T23:15:56Z (GMT). No. of bitstreams: 1 Andrade_LeandroHostalacioFreirede_D.pdf: 8621992 bytes, checksum: 26619c5e02d7a1718428c54694a54e97 (MD5) Previous issue date: 1999 / Resumo: Estudamos a dinâmica de portadores em escala de tempo de femtossegundos em filmes de AlxGa1-xAs para composições de Al nas quais a liga se encontra próxima à transição gap direto-gap indireto. A técnica utilizada foi a espectros copia de excitação e prova, na qual o pulso de teste se trata de um contínuo cujo espectro cobre o gap das ligas estudadas e possui tipicamente 30 fs de duração. A transmissão diferencial para altas densidades de portadores fotoinjetados na banda de condução adquire considerável complexidade e resulta de um delicado equilíbrio entre o enchimento de estados na banda e efeitos de blindagem e muitos- corpos tais como blindagem pelo plasma foto excitado e renormalização do gap. Nós observamos urna correlação entre a dinâmica dos portadores na banda de condução ( dinâmica intrabanda ) e a renormalização do gap da liga. Esta correlação relaciona-se à dinâmica ultra-rápida de redistribuição de portadores fotoexcitados entre os vales G, X e L da banda de condução / Abstract: We have studied the femtosecond carrier dynamics in AlxGa1-xAs thin films in the composition range near the G-x crossover. We carried pump and probe spectroscopy using 2 eV, 150 fs-250 fs pumping pulses derived from a copper vapor amplified colliding pulse mode-locked dye laser (CPM), and white light probing, tipically with 30 fs pulses which cover in energie the band gap of the a1loys. The results of the differential transmission for high density of photoinjected carriers in the alloy conduction band can not be interpreted in terms of occupation effects alone and results from a delicate balance between occupation effects, like band filling and screening and many-particle effects like band gap renonnalization and plasma screening of the electron-hole interaction. Also we have observed a correlation between the intraband carrier dynamics and the renormalization of the alloy direct energy gap. This correlation is related to the ultrafast redistribution of the photoinjected carriers between the G and X, L valleys of the alloy conduction band / Doutorado / Física / Doutor em Ciências

Whereas the effect of motherhood on women’s earnings has been well documented, little research has been done in Canada exploring the impact of fatherhood on men’s earnings. Although international research has shown that, unlike women, men who have a child increase their earnings, a growing body of research suggests that this benefit may be mediated by whether or not the father takes a parental leave. Using the 2011 General Social Survey (GSS) on family issues and employing ordinary least squares regression I investigate whether fathers receive an earnings bonus compared to childless men and whether fathers who take paternity/ parental leave earn less than fathers who do not. Our findings show that after controlling for personal and work related characteristics fathers earn significantly more than childless men and fathers who took paternity/parental leave earn significantly less than fathers who did not. Potential explanations for these earnings gaps are discussed.

The connexins are a family of 21 proteins that represent the structural units of intercellular gap junctions and single membrane hemichannels. These channels provide a means for cells to exchange small metabolites and signaling molecules with adjacent cells and the extracellular space, respectively. Compelling evidence implicates connexins, and the more recently discovered pannexins, in the control of neural progenitor cell proliferation, survival and migration. Moreover, connexin and pannexin dysregulation following central nervous system injuries such as cerebral ischemia, spinal cord injury, and epilepsy contributes to the secondary expansion of lesions days and weeks after the initial insult. While these data suggest that connexins and pannexins represent novel therapeutic targets to both reduce the extent of neural injury and promote neural repair and regeneration, we currently lack the necessary repertoire of therapeutically useful connexin- and pannexin-specific compounds to test these hypotheses. In this thesis, I conducted targeted screening of a large, ethnobotanically-derived library to address my overarching objective of identifying compounds that selectively alter connexin and/or pannexin channel function. To accomplish this, I characterized the repertoire of connexins and pannexins expressed by neural progenitor cell-like NT2/D1 cells, quantified the intercellular flux of calcein through connexin gap junctions, and measured the uptake of lucifer yellow and propidium iodide through pannexin hemichannels. Collectively, these screens identified several promising lead compounds and ethanolic plant extracts that selectively alter connexin and pannexin channel activity.

Thick-section austenitic stainless steels have widespread industrial applications, especially in nuclear power plants. The joining methods used in the nuclear industry are primarily based on arc welding processes. However, it has recently been shown that the Narrow Gap Laser Welding (NGLW) technique can be used to join materials with thicknesses that are well beyond the capabilities of single pass autogenous laser welding. The heat input for NGLW is much lower than that of arc welding, as are the expected levels of residual stress and distortion. The multi-pass laser welding technique, based on the narrow gap approach, is an emerging welding technology which can be applied to thick-section welds using a relatively low-power laser, but the process is more complicated than autogenous laser welding, since it is necessary to introduce filler wire to narrow gap weld configurations. Despite this complexity, the technique is very promising for improving the penetration capabilities of the laser welding process. However a limited amount of research has been conducted on the development of the NGLW technique; the control and optimization of weld bead quality inside the narrow gap is still an area of weakness. The research described in this thesis involves investigations on NGLW of AISI grade 316L austenitic stainless steel, and the performance of the resulting welds. Design-of-experiments and statistical modelling techniques were employed to understand and optimize the welding process. A statistical model was used in order to understand the significant process parameters and their interactions, allowing improved control of the weld quality in ultra-narrow gap (1.5 mm gap width) welds. The results show a significant improvement in weld quality can be achieved through the use of statistical modelling and multi-variable optimisation. The microstructure characteristics and mechanical properties (e.g. tensile strengths, fatigue, bending strength and fracture toughness) of the NGLW samples were examined and compared with those of other welding techniques - autogenous laser welding and gas-tungsten arc welding (GTAW). The work shows that NGLW of 316L steel sheets up to 20 mm thickness have generally better or comparable mechanical properties than those of GTAW but with much higher welding productivity. The results of detailed investigations of the 2D residual stress distributions, material distortions, and plastic strain characteristics of the NGLW technique are described. The contour method was employed for residual stress evaluation of the NGLW technique, and the results were validated using X-Ray and neutron diffraction measurements. The results were compared with those obtained with GTAW. The results suggest that the longitudinal tensile residual stresses in NGLW joints are 30-40% lower than those for GTAW joints. The influence of the laser power and number of passes for the NGLW technique, on the developed residual stress and plastic strain has been investigated, and the influence of welding strategy and the use of restraint during welding were also investigated. To understand the thermal history in NGLW and its effect on residual stress, finite element analysis was carried out using ABAQUS to numerically model the behaviour of residual stress across the multipass NGLW weld joints. The model has been validated with the experiments using temperature measurements and in terms of residual stresses the model is compared with neutron diffraction and the contour method. There is a very good correlation between the model and experimental results. The influence of both the laser power and welding speed on the induced residual stress during the NGLW process was also investigated using the model. The aqueous, pitting and stress corrosion cracking behaviour of the NGLW joints were investigated, and the results compared to those for GTAW joints under the same conditions. The results show that NGLW joints have better resistance to pitting corrosion than the GTA welds. Preliminary results also suggest that NGLW has better resistance to stress corrosion cracking.

Orientador: Roberto Luzzi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin / Made available in DSpace on 2018-07-15T08:48:19Z (GMT). No. of bitstreams: 1 Sampaio_AntonioJosedaCosta_D.pdf: 2605293 bytes, checksum: 1a6b273715fb19378c33c661469f64dd (MD5) Previous issue date: 1983 / Resumo: Sérias dificuldades surgem quando estudamos sistemas que se encontram longe do equilíbrio termodinâmico, principalmente porque sabemos ser completamente inaplicáveis às Teorias Lineares (Resposta Linear de Kubo, etc.). Nós discutimos neste trabalho a reação de um plasma fotoexcitado num semicondutor polar de Gap direto e, conjuntamente, fazemos uma análise completa sobre a cinética de relaxação deste sistema, isto é, como o sistema evolui para o equilíbrio termodinâmico. Usamos o método estatístico de não-equilíbrio proposto por Zubarev para a matriz densidade r(t). A partir deste construímos a função Resposta dada em termos de funções de Green Termodinâmicas, cujas soluções estão acopladas ao conjunto de equações de Transporte não-lineares que descrevem a evolução do fenômeno irreversível que ocorre no sistema. Os resultados teóricos são comparados com os dados fornecidos pela experiência, obtidas com a espectroscopia ótica ultra-rápida com resolução temporal para o CdSe e o GaAs e os resultados da comparação estão em excelente arranjo. Discutimos o espectro que determina um plasma no CdSe e também discutimos os vários canais de relaxação relevante para o GaAs. Mostramos que o estudo teórico e numérico proporciona uma boa descrição dos mecanismos de perda de energia que são considerados para esta espécie de sistemas / Abstract: Not informed. / Doutorado / Física / Doutor em Ciências

Developing countries, such as Namibia, need to bridge the existing infrastructure gap to improve the country's comparative advantage, economic growth and competitiveness, quality of life and the welfare of its citizens. As traditional sources of finance dwindle, Pension Fund savings need to be pooled to complement traditional sources of funding, such as government budgetary allocations, borrowing and user fees. Although infrastructure's economic and financial characteristics are a match to Pension Fund liabilities, Namibia's Pension Fund investment in infrastructure lags behind world-class benchmarks. This study investigated the factors that hinder Pension Fund investment in infrastructure in Namibia. The study employed a mixed-method research method and convergent parallel data collection processes. The study obtained a representative sample to participate in the survey from a population of NAMFISA registered Pension Fund and investment managers using a combination of the stratified random and simple random sampling techniques as part of primary data collection. The financial characteristics that make infrastructure assets attractive such as; long term, low sensitivity to economic swings, a low correlation with other assets and long term and inflation hedged returns makes them suitable for Pension Fund investments. The study confirms findings of previous studies by Beeferman, (2008); Ehlers, (2014); Inderst & Della Croce, (2013); Sy, (2017) and Thierie & Moor (2016), amongst others, revealed factors such as; a lack of a project pipeline, a lack of expertise by Pension Funds in infrastructure investments, Pension Fund regulation and a lack of financial instruments and assets that match Pension Funds are barriers to Pension Fund investment in infrastructure. The lack of a project pipeline is further attributable to issues such as infrastructure projects that are not sufficiently developed or viable on their own without some form of government support, inefficiencies in public procurement and public-private partnership policies and a lack of project preparation funding. The study recommends the following initiatives by policymakers and key stakeholders towards increasing Pension Fund investment in infrastructure: firstly, government and state-owned institutions responsible for public services should implement policies that will increase the pipeline of bankable and implementable projects. The National Development Plans (NDP5), the Harambee Prosperity plans and the Vision 2030 already identify projects; however, institutionstasked with infrastructure development need to develop implementation modelsthat are viable and bankable. The development plans need to be coordinated across the various levels iii of government and state-owned enterprises for effective implementation. Secondly, it is recommended that policymakers create the necessary conditions for Public Procurement and Public Private Partnership Policies to gain confidence amongst investors. Rooting out corruption and ensuring processes are transparent and fair to all stakeholders can have the effect of creating investor confidence in the two policies. The financial institutions, especially with a developmental angle, should support the public institutions with project preparation funding and technical assistance during project planning/development. Thirdly, the government, through the regulators, NAMFISA, are advised to continue with the implementation of policies aimed at increasing the limit on assets held with unlisted investment managers to allow increased Pension Fund investment in infrastructure without compromising the performance (return) and risk exposure. The financial regulators, NAMFISA and the Bank of Namibia should encourage the growth of the local financial sector to increase the quality and quantity of financial instruments available to investors and increase the depth of the financial sector to absorb local funding capacity. Lastly, the government is recommended to explore the options of partial listing infrastructure SOEs,such as NamPower, NamWater, Road Fund Administrator (RFA), NamPort, TransNamib, among others, to facilitate Pension Fund investment into infrastructure and reduce transaction cost and risks. The study identifies the need for future research opportunities with the aim of understanding issues that affect the project pipeline in the Namibian context in greater detail.

Since the failure of the Scan Line Corrector (SLC) instrument on Landsat 7, observable gaps occur in the acquired Landsat 7 imagery, impacting the spatial continuity of observed imagery. Due to the highly geometric and radiometric accuracy provided by Landsat 7, a number of approaches have been proposed to fill the gaps. However, all proposed approaches have evident constraints for universal application. The main issues in gap-filling are an inability to describe the continuity features such as meandering streams or roads, or maintaining the shape of small objects when filling gaps in heterogeneous areas. The aim of the study is to validate the feasibility of using the Direct Sampling multiple-point geostatistical method, which has been shown to reconstruct complicated geological structures satisfactorily, to fill Landsat 7 gaps. The Direct Sampling method uses a conditional stochastic resampling of known locations within a target image to fill gaps and can generate multiple reconstructions for one simulation case. The Direct Sampling method was examined across a range of land cover types including deserts, sparse rural areas, dense farmlands, urban areas, braided rivers and coastal areas to demonstrate its capacity to recover gaps accurately for various land cover types. The prediction accuracy of the Direct Sampling method was also compared with other gap-filling approaches, which have been previously demonstrated to offer satisfactory results, under both homogeneous area and heterogeneous area situations. Studies have shown that the Direct Sampling method provides sufficiently accurate prediction results for a variety of land cover types from homogeneous areas to heterogeneous land cover types. Likewise, it exhibits superior performances when used to fill gaps in heterogeneous land cover types without input image or with an input image that is temporally far from the target image in comparison with other gap-filling approaches.