10,498 research outputs found

    Gyroscopic polynomials

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    Gyroscopic alignment of a fluid occurs when flow structures align with the rotation axis. This often gives rise to highly spatially anisotropic columnar structures that in combination with complex domain boundaries pose challenges for efficient numerical discretizations and computations. We define gyroscopic polynomials to be three-dimensional polynomials expressed in a coordinate system that conforms to rotational alignment. We remap the original domain with radius-dependent boundaries onto a right cylindrical or annular domain to create the computational domain in this coordinate system. We find the volume element expressed in gyroscopic coordinates leads naturally to a hierarchy of orthonormal bases. We build the bases out of Jacobi polynomials in the vertical and generalized Jacobi polynomials in the radial. Because these coordinates explicitly conform to flow structures found in rapidly rotating systems the bases represent fields with a relatively small number of modes. We develop the operator structure for one-dimensional semi-classical orthogonal polynomials as a building block for differential operators in the full three-dimensional cylindrical and annular domains. The differential operators of generalized Jacobi polynomials generate a sparse linear system for discretization of differential operators acting on the gyroscopic bases. This enables efficient simulation of systems with strong gyroscopic alignment

    Essays on financial markets in Africa

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    Doutoramento em EconomiaEconomic growth in a modern economy hinges on an efficient financial sector that pools domestic savings and mobilizes foreign capital for productive investments. Absent an effective set of financial institutions, productive projects will remain unexploited. Inefficient financial institutions will have the effect of taxing productive investment and thus reducing scope for increasing the stock equipment needed to compete globally. The effect is to substantially cut growth from what would have been possible given appropriate policies and market structures. In this context, this thesis focuses on three essays analyzing the impact of financial markets in development and income inequality. First, we assessed the impact of stock market development on growth in Africa. The study uses annual data from a panel of nine countries in Africa over the period 1992–2017. Panel Vector Autoregressive econometrics technique is used in data analysis. Our main findings are that stock market development has a positive effect on economic growth. The paper also finds that when using the impulse response function, economic growth reacts to the stock market for a period of eight years and then returns to the initial level. The second essay presents evidence about the relationship between private credit, stock market indicators, income inequality and poverty, using the annual data that ranges from 1992 to 2018 on nine African economies. We applied the estimation method of Autoregressive Distributed Lag (ARDL) to model the long-run effect. In Addition, we used Dumitrescu and Hurlin Panel causality to check the direction of causality. The results of long‐run estimates show that the stock market indicators have a significant positive impact on income inequalities, but have a negative and significant impact on poverty. Further, our findings show that private credit adversely reduces income inequalities. The results also establish significant short‐run causalities among stock market indicators, private credit, income inequalities, and poverty. Lastly, we examine the relationship between financial development and economic growth in Angola for the period of Q12002 to Q42018. The results show that there is evidence of a long-run relationship between financial development and real GDP per capita, when using the Bound test approach for cointegration. Furthermore, the results of the Error Correction Model (ECM) indicate that financial development has a negative impact on GDP growth when considering credit to private and broad money as proxies for financial development. On the other hand, the degree of intermediation has a positive impact on GDP growth. The Toda–Yamamoto causality test was carried out, which indicates a unidirectional causality relationship, running from real GDP per capita to a purely financial development proxy, which shows demand-following responses. Consequently, policymakers should adopt policies that sustain the benefits of financial developments for economic growth.O crescimento económico numa economia moderna depende de um sector financeiro eficiente que reúna a poupança doméstica e mobilize capital estrangeiro para investimentos produtivos. Sem um conjunto efetivo de instituições financeiras, os projetos produtivos permanecerão inexplorados. Instituições financeiras ineficientes terão o efeito de tributar o investimento produtivo e, assim, reduzir a margem para aumentar o estoque de equipamentos necessários para competir globalmente. O efeito é reduzir substancialmente o crescimento do que seria possível com políticas e estruturas de mercado apropriadas. Nesse contexto, esta tese se concentra em três artigos que analisam o impacto dos mercados financeiros no desenvolvimento e na desigualdade de renda em África. Em primeiro lugar, avaliámos o impacto do desenvolvimento do mercado bolsista no crescimento económico em África. O estudo usa dados anuais de um painel de nove países da África durante o período de 1992 a 2017. Para a análise dos dados foi usada a técnica de econometria autorregressiva de vetor de painel. Nossas principais conclusões são que o desenvolvimento do mercado de ações tem um efeito positivo sobre o crescimento económico. O artigo também constata que, ao usar a função de impulso resposta, o crescimento económico reage ao mercado de ações por um período de oito anos e depois retorna ao nível inicial. O segundo artigo apresenta evidências sobre a relação entre crédito privado, indicadores do mercado de ações, desigualdade de renda e pobreza, usando os dados anuais que variam de 1992 a 2018 em nove economias africanas. Aplicamos o método de estimação de Autoregressive Distributed Lag (ARDL) para modelar o efeito de longo prazo. Além disso, usamos a causalidade do Painel de Dumitrescu e Hurlin para verificar a direção da causalidade. Os resultados das estimativas de longo prazo mostram que os indicadores do mercado de ações têm um impacto positivo e significativo nas desigualdades de renda, mas têm um impacto negativo e significativo na pobreza. Além disso, nossos resultados mostram que o crédito privado reduz negativamente as desigualdades de renda. Os resultados também estabelecem causalidades significativas de curto prazo entre indicadores do mercado de ações, crédito privado, desigualdades de renda e pobreza. Por último, examinamos a relação entre o desenvolvimento financeiro e o crescimento económico em Angola para o período de T12002 a T42018. Os resultados mostram que há evidências de uma relação de longo prazo entre o desenvolvimento financeiro e o PIB real per capita, quando se utiliza a abordagem do teste Bound para cointegração. Além disso, os resultados do Error Correction Model (ECM) indicam que o desenvolvimento financeiro tem um impacto negativo no crescimento do PIB quando se considera o crédito ao privado e a moeda ampla como proxies do desenvolvimento financeiro. Por outro lado, o grau de intermediação tem um impacto positivo no crescimento do PIB. Foi realizado o teste de causalidade Toda–Yamamoto, que indica uma relação de causalidade unidirecional, indo do PIB real per capita a uma proxy de desenvolvimento puramente financeiro, que mostra respostas de acompanhamento da procura. Consequentemente, os formuladores de políticas devem adotar políticas que sustentem os benefícios dos desenvolvimentos financeiros para o crescimento econômico.info:eu-repo/semantics/publishedVersio

    Design considerations of non-axisymmetric exhausts for large civil aero-engines

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    In order to reduce fuel consumption, the next generation of aero-engines are expected to operate with higher bypass ratios and lower fan pressure ratios. This will improve the propulsive efficiency of the power plant and reduce specific fuel consumption. Higher bypass ratios will be mostly accommodated with larger fan diameters. However, this will increase the size and mass of the powerplant, which could penalise the overall aircraft drag and erode some of the aero-engine cycle benefits. In addition, future configurations may require more close-coupled installations with the airframe due to structural and ground clearance requirements. This tendency may further exacerbate the adverse aerodynamic installation effects. A better integration of UHBR aero-engines with the airframe could be achieved with non-axisymmetric separate-jet exhausts. Non-axisymmetric configurations of the bypass nozzle can improve the performance of the aircraft by mitigating some of the penalising aerodynamic effects induced by the installation of the power plant. In this context, three-dimensional configurations of exhaust systems are parametrised and integrated with the propulsion system through a refined control of the geometry. The power plant is installed on the NASA Common Research Model and assessed with CFD. The design of non-axisymmetric exhausts is embedded in a relatively low-cost optimisation process. The method is based on response surface models and targets the optimisation of the aircraft net vehicle force for different design concepts of non-axisymmetric exhaust systems and several installation configuration. It is concluded that the optimisation of installed non-axisymmetric exhausts can benefit the overall aircraft net vehicle force between 0.5-0.9% of the engine nominal thrust, depending on the installation position.Rolls-Royce pl

    Bayesian Forecasting in Economics and Finance: A Modern Review

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    The Bayesian statistical paradigm provides a principled and coherent approach to probabilistic forecasting. Uncertainty about all unknowns that characterize any forecasting problem -- model, parameters, latent states -- is able to be quantified explicitly, and factored into the forecast distribution via the process of integration or averaging. Allied with the elegance of the method, Bayesian forecasting is now underpinned by the burgeoning field of Bayesian computation, which enables Bayesian forecasts to be produced for virtually any problem, no matter how large, or complex. The current state of play in Bayesian forecasting in economics and finance is the subject of this review. The aim is to provide the reader with an overview of modern approaches to the field, set in some historical context; and with sufficient computational detail given to assist the reader with implementation.Comment: The paper is now published online at: https://doi.org/10.1016/j.ijforecast.2023.05.00

    Simulating substrate binding sites in the S. aureus Type II NADH Dehydrogenase

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    "Type II NADH Oxidoreductase (NDH-2) from Staphylococcus aureus was established as a therapeutic target against the virulency of this bacterium and an alternative to treat Complex I-derived diseases. To accurately model interactions of NDH-2 with its substrates such as menaquinones and NADH, Coarse-Grain (CG) simulations were employed. "N/

    Meso-scale FDM material layout design strategies under manufacturability constraints and fracture conditions

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    In the manufacturability-driven design (MDD) perspective, manufacturability of the product or system is the most important of the design requirements. In addition to being able to ensure that complex designs (e.g., topology optimization) are manufacturable with a given process or process family, MDD also helps mechanical designers to take advantage of unique process-material effects generated during manufacturing. One of the most recognizable examples of this comes from the scanning-type family of additive manufacturing (AM) processes; the most notable and familiar member of this family is the fused deposition modeling (FDM) or fused filament fabrication (FFF) process. This process works by selectively depositing uniform, approximately isotropic beads or elements of molten thermoplastic material (typically structural engineering plastics) in a series of pre-specified traces to build each layer of the part. There are many interesting 2-D and 3-D mechanical design problems that can be explored by designing the layout of these elements. The resulting structured, hierarchical material (which is both manufacturable and customized layer-by-layer within the limits of the process and material) can be defined as a manufacturing process-driven structured material (MPDSM). This dissertation explores several practical methods for designing these element layouts for 2-D and 3-D meso-scale mechanical problems, focusing ultimately on design-for-fracture. Three different fracture conditions are explored: (1) cases where a crack must be prevented or stopped, (2) cases where the crack must be encouraged or accelerated, and (3) cases where cracks must grow in a simple pre-determined pattern. Several new design tools, including a mapping method for the FDM manufacturability constraints, three major literature reviews, the collection, organization, and analysis of several large (qualitative and quantitative) multi-scale datasets on the fracture behavior of FDM-processed materials, some new experimental equipment, and the refinement of a fast and simple g-code generator based on commercially-available software, were developed and refined to support the design of MPDSMs under fracture conditions. The refined design method and rules were experimentally validated using a series of case studies (involving both design and physical testing of the designs) at the end of the dissertation. Finally, a simple design guide for practicing engineers who are not experts in advanced solid mechanics nor process-tailored materials was developed from the results of this project.U of I OnlyAuthor's request

    Process intensification of oxidative coupling of methane

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    Modified Theories of Gravity and Cosmological Applications

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    This reprint focuses on recent aspects of gravitational theory and cosmology. It contains subjects of particular interest for modified gravity theories and applications to cosmology, special attention is given to Einstein–Gauss–Bonnet, f(R)-gravity, anisotropic inflation, extra dimension theories of gravity, black holes, dark energy, Palatini gravity, anisotropic spacetime, Einstein–Finsler gravity, off-diagonal cosmological solutions, Hawking-temperature and scalar-tensor-vector theories

    A family of total Lagrangian Petrov-Galerkin Cosserat rod finite element formulations

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    The standard in rod finite element formulations is the Bubnov-Galerkin projection method, where the test functions arise from a consistent variation of the ansatz functions. This approach becomes increasingly complex when highly nonlinear ansatz functions are chosen to approximate the rod's centerline and cross-section orientations. Using a Petrov-Galerkin projection method, we propose a whole family of rod finite element formulations where the nodal generalized virtual displacements and generalized velocities are interpolated instead of using the consistent variations and time derivatives of the ansatz functions. This approach leads to a significant simplification of the expressions in the discrete virtual work functionals. In addition, independent strategies can be chosen for interpolating the nodal centerline points and cross-section orientations. We discuss three objective interpolation strategies and give an in-depth analysis concerning locking and convergence behavior for the whole family of rod finite element formulations.Comment: arXiv admin note: text overlap with arXiv:2301.0559
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