Astrophysical thermonuclear functions

As theoretical knowledge and experimental verification of nuclear cross sections increases it becomes possible to refine analytic representations for nuclear reaction rates. In this paper mathematical/statistical techniques for deriving closed-form representations of thermonuclear functions are summarized and numerical results for them are given.The purpose of the paper is also to compare numerical results for approximate and closed-form representations of thermonuclear functions.Comment: 17 pages in LaTeX, 8 figures available on request from [email protected]

Extension of thermonuclear functions through the pathway model including Maxwell-Boltzmann and Tsallis distributions

The Maxwell-Boltzmannian approach to nuclear reaction rate theory is extended to cover Tsallis statistics (Tsallis, 1988) and more general cases of distribution functions. An analytical study of respective thermonuclear functions is being conducted with the help of statistical techniques. The pathway model, recently introduced by Mathai (2005), is utilized for thermonuclear functions and closed-form representations are obtained in terms of H-functions and G-functions. Maxwell-Boltzmannian thermonuclear functions become particular cases of the extended thermonuclear functions. A brief review on the development of the theory of analytic representations of nuclear reaction rates is given.Comment: 16 pages, LaTe

Stellar structure and compact objects before 1940: Towards relativistic astrophysics

Since the mid-1920s, different strands of research used stars as "physics laboratories" for investigating the nature of matter under extreme densities and pressures, impossible to realize on Earth. To trace this process this paper is following the evolution of the concept of a dense core in stars, which was important both for an understanding of stellar evolution and as a testing ground for the fast-evolving field of nuclear physics. In spite of the divide between physicists and astrophysicists, some key actors working in the cross-fertilized soil of overlapping but different scientific cultures formulated models and tentative theories that gradually evolved into more realistic and structured astrophysical objects. These investigations culminated in the first contact with general relativity in 1939, when J. Robert Oppenheimer and his students George Volkoff and Hartland Snyder systematically applied the theory to the dense core of a collapsing neutron star. This pioneering application of Einstein's theory to an astrophysical compact object can be regarded as a milestone in the path eventually leading to the emergence of relativistic astrophysics in the early 1960s.Comment: 83 pages, 4 figures, submitted to the European Physical Journal

Coeficientes médios da equação de Angström-Prescott, radiação solar e evapotranspiração de referência em Brasília Angström-Prescott equation mean coefficients, solar radiation and reference crop evapotranspiration in Brasília

O objetivo deste trabalho foi estimar os coeficientes médios a e b da equação de Angström-Prescott, em Brasília, e seus efeitos sobre o cálculo da radiação solar global (Rs) e da evapotranspiração de referência (ETo). Foram utilizados dados da estação meteorológica da Embrapa Hortaliças, do período de 1978 a 2003. Os coeficientes médios foram determinados por análise de regressão linear, no período todo e em períodos mensais e anuais. Utilizando-se o coeficiente calculado e os propostos pela FAO (0,25 e 0,50) estimaram-se Rs e ETo, e avaliaram-se os seus desempenhos. Os coeficientes médios mensais a variaram de 0,241 a 0,345, e b de 0,430 a 0,515. Os coeficientes médios anuais a e b foram 0,278 e 0,498, e os do período geral foram 0,282 e 0,490, respectivamente. A performance entre esses coeficientes na estimativa da radiação não diferiu. No mês de julho, foram verificados as piores estimativas e os piores desempenhos. Com as estimativas de Rs e os coeficientes médios calculados, as estimativas de ETo não diferiram dos observados, tendo-se constatado um ótimo desempenho, independentemente do coeficiente utilizado. Dependendo do tipo de aplicação final dos dados, recomenda-se utilizar, por sua simplicidade, os coeficientes médios obtidos para o período geral.<br>The objective of this work was to estimate Angström-Prescott equation mean coefficients in Brasília, DF, Brazil, and their effects on the calculations of global radiation (Rs) and reference crop evapotranspiration (ETo). It was used meteorological data from Embrapa Hortaliças weather station, from 1978 to 2003. The mean coefficients were determined by linear regression analysis considering monthly, annual and total periods. Using the calculated coefficients for different periods and those provided by FAO (0.25 and 0.50), Rs and ETo were estimated and their performances were evaluated. Monthly mean coefficient a varied from 0.241 to 0.345, and b from 0.430 to 0.515. Annual mean coefficients a and b were 0.278 and 0.498, and total means were 0.282 and 0.490, respectively. These coefficients did not differ from each other on radiation estimates. The month of July provided the worse estimates and performance. When using calculated Rs estimates with monthly, annual, total and FAO coefficients, estimated values of ETo did not differ from observed ones, providing excellent performance, despite the mean coefficient used. Depending on the final application, it is suggested the use of total mean coefficients due to their easiness to estimate the shortwave radiation

Efeito de sistemas de criação no conforto térmico ambiente e no desempenho produtivo de suínos na primavera Effect of different raising systems on the thermal environment comfort and swine productive performance under spring conditions

Esta pesquisa foi realizada com o objetivo de avaliar os sistemas de criação em camas sobrepostas de maravalha ou de casca de arroz e o sistema tradicional de piso de concreto e sua influência no ambiente térmico (ITGU e temperatura superficial do piso e cama) e no desempenho animal de suínos dos 25 aos 120 kg. Foram utilizados 216 animais (Landrace <FONT FACE=Symbol>&acute;</FONT> Large White), 72 por sistema de criação (18 suínos/ baia). Para comparação, os animais foram avaliados por fases: 1 - 64 a 98 dias (25 a 50 kg); 2 - 99 a 126 dias (50 a 75 kg); 3 - 127 a 162 dias (75 a 105 kg); e 4 - 163 a 186 dias (105 a 120 kg). Para avaliação do ambiente térmico, foi utilizado o delineamento em bloco casualizado, com três sistemas de criação, em que as repetições foram os dias de duração de cada fase. O desempenho animal foi avaliado em delineamento inteiramente casualizado, com quatro repetições (baias). Nas duas primeiras fases, os valores de ITGU obtidos nos sistemas de criação com cama sobreposta foram superiores aos observados no piso de concreto. Em todas as fases, os maiores valores de temperatura superficial de cama ou piso foram observados nos sistemas de criação com cama sobreposta. O desempenho animal foi similar entre todos os sistemas de criação nas duas primeiras fases, mas, na terceira fase, foi maior no sistema de criação com piso de concreto e, na quarta fase, foi superior em ambos os sistemas de criação com cama. O desempenho animal final não foi influenciado pelos sistemas de criação. Na fase de 25 a 75 kg, o sistema de criação com cama sobreposta mostrou-se satisfatório como alternativa ao sistema tradicional de piso de concreto.<br>This research was carried out with the objective to evaluate the raising systems in deep-bedding (wood shavings and rice husk) and the traditional system of concrete floor, and its influence in the thermal environment (BGTHI [Black Globe Temperature and Humidity Index] and surface temperature of both floor and bed), and swine animal performance from 25 kg to 120 kg. Two hundred sixteen animals were used (Landrace x Large White), 72 per raising system (18 pigs/pen). For comparison, the animals were evaluated per phases: 1 - from 64 to 98 days (25-50 kg); 2 - 99 to 126 days (50-75 kg); 3 - 127 to 162 days (75-105 kg); and phase 4 - 163 to 186 days (105-120 kg). For the evaluation of thermal environment, a randomized block experimental design was used, with three raising system, being the repetitions the period of days of each phase. A completely randomized design with four replicates (pens) were used for the evaluation of animals performance. At the first two phases, BGTHI values observed in the raising system with deep-bedding were higher to that observed in the concrete floor. In all phases, the highest values for surface temperature of the bed or floor were observed in the deep-bedding systems. The animal performance was similar among all the raisingsystems, in the two first phases, but, in the third phase, it was bigger in the raising system with concrete floor and, in the fourth phase, it was superior in both the raising systems with bed. The final animal performance was not influenced by the raisaing systems. In the phase from 25 to 75 kg, the raising system deep-bedding revealed to be satisfactory as alternative to the traditional system of concrete floor