Properties of Dense Fluid Hydrogen and Helium in Giant Gas Planets

Equilibrium properties of hydrogen-helium mixtures under thermodynamic conditions found in the interior of giant gas planets are studied by means of density functional theory molecular dynamics simulations. Special emphasis is placed on the molecular-to-atomic transition in the fluid phase of hydrogen in the presence of helium. Helium has a substantial influence on the stability of hydrogen molecules. The molecular bond is strengthened and its length is shortened as a result of the increased localization of the electron charge around the helium atoms, which leads to more stable hydrogen molecules compared to pure hydrogen for the same thermodynamic conditions. The {\it ab initio} treatment of the mixture enables us to investigate the structure of the liquid and to discuss hydrogen-hydrogen, helium-helium, and hydrogen-helium correlations on the basis of pair correlation functions.Comment: 6 pages, 3 figures, 1 table, proceedings PNP1

Phase separation in hydrogen-helium mixtures at Mbar pressures

The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a given pressure, when helium becomes insoluble in dense metallic hydrogen. These results are directly relevant to models of the interior structure and evolution of Jovian planets. We find that the temperatures for the demixing of helium and hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures around 5 Mbar; helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter.Comment: 6 pages, 7 figures. Published in "Proceedings of the National Academy of Sciences USA

Modelagem de processos usando equações diferenciais parciais fracionárias

Orientador : Prof. Dr. Marcelo Kaminski LenziCoorientador: Prof. Dr. David Alexander MitchelDissertação (mestrado) - Universidade Federal do Paraná, Setor de Tecnologia, Programa de Pós-Graduação em Engenharia Química. Defesa: Curitiba, 30/04/2010Bibliografia: fls. 56-60Resumo: O emprego de técnicas de modelagem de processos químicos é de fundamental importância para descrição matemática dos mesmos e a aplicação de técnicas de controle de processo que venham garantir sua operação segura e competitiva. Neste trabalho, aplicou-se o ferramental baseado em equações diferenciais de ordem fracionárias para a modelagem de sistemas de engenharia química. Mais especificamente, foram estudadas e aplicadas técnicas numéricas para problemas não reportados na literatura, concernentes à sistemas com geometria radial. Em uma segunda etapa, foram analisadas a mistura de sólidos e a dispersão axial sob a ótica de equações diferenciais fracionárias. A partir de dados experimentais previamente reportados na literatura, foram estimados parâmetros de modelos representados por equações diferenciais de ordem fracionária tipo parcial. Considerando a técnica heurística de algoritmos genéticos, foram estimados parâmetros do modelo de ordem fracionária e de ordem inteira para comparação. Em ambos os estudos, mistura de sólidos e dispersão axial, o modelo fracionário levou à menores valores da função objetivo usada para estimação de parâmetros. Para mistura de sólidos o modelo fracionário obteve FOBJ = 0,0480 e o modelo inteiro obteve FOBJ = 0,0501. Para dispersão axial, o modelo fracionário obteve FOBJ = 0,0593 e o modelo inteiro obteve FOBJ = 0,0766. Desta forma, o ajuste dos pontos experimentais mostrou-se melhor pelo modelo fracionário, o que pode ser comprovado pela inspeção visual dos gráficos comparativos, o que comprava a viabilidade do uso de equações diferenciais fracionárias para a modelagem de sistemas de engenharia química.Abstract: The use of process modeling techniques plays a key role for mathematical description of chemical processes and the consequent use of process control techniques which allow a safer and competitive operation. In this work, fractional differential equations were used to model chemical engineering systems. More specifically, numerical techniques were studied applied to solve equations not reported in the literature, mainly concerning radial systems. In a second step, solid mixture and axial dispersion were considered for modeling purposes using fractional differential equations. From experimental data previously reported in the literature, parameters were estimated in order to obtain a fractional partial differential equation based model to adequately describe the data. The heuristic technique of genetic algorithms was considered for parameter estimation and as benchmark of comparison integer order models were also obtained. In both studies, i.e., solid mixing and axial dispersion, the fractional based model lead to lower values of the objective function used for parameter estimation. For solid mixing studies, the fractional model lead to FOBJ = 0,0480, while the integer model lead to FOBJ = 0,0501. For axial dispersion, the fractional model lead to FOBJ = 0,0593 and the integer model lead to FOBJ = 0,0766. Consequently, the fractional model provided a better experimental data fit, which can also be proved by visual inspection of comparative plots. Therefore, fractional differential equations can be successfully used for chemical engineering systems modeling

Forecasting the price of wheat and other commodities

The long term behaviour of primary product prices has been a central issue underlying projections of commodity price series. Against the background of the Prebisch Singer Hypothesis, the presence, magnitude and direction of a secular trend in commodity price series have themselves become the subject of a long standing debate. This study uses the individual commodity price series underlying the Grilli and Yang data set and, where possible, extends these data series up to 1998. Deflating primary commodity prices by the MUV index, the question of trend components in the time series is studied considering evidence from univariate models and allowing for trend stationary or integrated data series with drift. In this context the impact of serial correlation in finite samples and the impact of wrongly modelling a data series as integrated are considered in detail. Further evidence from a trend test developed by Vogelsang (1998) is also taken into account. In selecting forecast models, the usefulness of unit root pre-testing is assessed allowing for interdependence between the inferred order of integration and the significance of the trend or drift coefficient estimate obtained. Projections from univariate models are obtained for a ten year horizon and Beveridge-Nelson trend cycle decompositions are computed to assess the importance of volatility surrounding the forecasts. It is found that with regards to the past behaviour of primary commodities as well as for the forecasts obtained, the trajectory of primary commodity prices relative to the price of developed country manufactures exports is not generally characterised by a downwards trend

Comparative Evolution of Jupiter and Saturn

We present evolutionary sequences for Jupiter and Saturn, based on new nongray model atmospheres, which take into account the evolution of the solar luminosity and partitioning of dense components to deeper layers. The results are used to set limits on the extent to which possible interior phase separation of hydrogen and helium may have progressed in the two planets. When combined with static models constrained by the gravity field, our evolutionary calculations constrain the helium mass fraction in Jupiter to be between 0.20 and 0.27, relative to total hydrogen and helium. This is in agreement with the Galileo determination. The helium mass fraction in Saturn's atmosphere lies between 0.11 and 0.25, higher than the Voyager determination. Based on the discrepancy between the Galileo and Voyager results for Jupiter, and our models, we predict that Cassini measurements will yield a higher atmospheric helium mass fraction for Saturn relative to the Voyager value.Comment: 18 pages, LaTeX, 4 figures. submitted to ``Planetary and Space Science.'

Sistema Web para Contratação de Serviços

TCC(graduação) - Universidade Federal de Santa Catarina. Centro Tecnológico. Sistemas de Informação.Este trabalho relata o desenvolvimento de uma aplicação web para contratação de serviços online, em que é possível encontrar prestadores de serviço, visualizar as avaliações e outras informações relevantes sobre o prestador, e contratar o serviço pela plataforma, garantindo assim uma maior confiabilidade, segurança e transparência ao contratar um serviço.This paper reports on the development of a web application for online service contracting, where it is possible to find service providers, view evaluations and other relevant information about the provider, and contract the service through the platform, thus ensuring greater reliability, security and reliability. transparency when hiring a service

EXTRACTION OF SOLAR CELLS FROM UAV-BASED THERMAL IMAGE SEQUENCES

This paper discusses the automatic generation of thermal infrared ortho image mosaics and the extraction of solar cells from these ortho image mosaics. Image sequences are recorded by a thermal infrared (TIR) camera mounted on a remotely piloted aerial system (RPAS). The image block is relatively oriented doing a bundle block adjustment and transferred to a local coordinate system using ground control points. The resulting ortho image mosaic is searched for solar cells. A library of templates of solar cells from thermal images is used to learn an implicit shape model. The extraction of the single solar cells is done by estimating corners and centre points of cells using these shape models in a Markov-Chain-Monte-Carlo algorithm by combining four corners and a centre point. As for the limited geometric resolution and radiometric contrast, most of the cells are not directly detected. An iterative process based on the knowledge of the regular grid structure of a solar cell installation is used to predict further cells and verify their existence by repeating the corner extraction and grammar combination. Results show that this work flow is able to detect most of the solar cells under the condition that the cells have a more or less common radiometric behaviour and no reflections i.e. from the sun occur. The cells need a rectangular shape and have the same orientation so that the model of the grammar is applicable to the solar cells