995 research outputs found

    Variational Principles for Stellar Structure

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    The four equations of stellar structure are reformulated as two alternate pairs of variational principles. Different thermodynamic representations lead to the same hydromechanical equations, but the thermal equations require, not the entropy, but the temperature as the thermal field variable. Our treatment emphasizes the hydrostatic energy and the entropy production rate of luminosity produced and transported. The conceptual and calculational advantages of integral over differential formulations of stellar structure are discussed along with the difficulties in describing stellar chemical evolution by variational principles.Comment: 28 pages, LaTeX, requires AASTeX, 1 PostScript figure, revisions: erratum; accepted by Astrophysical Journa

    Information theory in the study of anisotropic radiation

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    Information theory is used to perform a thermodynamic study of non equilibrium anisotropic radiation. We limit our analysis to a second-order truncation of the moments, obtaining a distribution function which leads to a natural closure of the hierarchy of radiative transfer equations in the so-called variable Eddington factor scheme. Some Eddington factors appearing in the literature can be recovered as particular cases of our two-parameter Eddington factor. We focus our attention in the study of the thermodynamic properties of such systems and relate it to recent nonequilibrium thermodynamic theories. Finally we comment the possibility of introducing a nonequilibrium chemical potential for photons.Comment: 1 eps figure upon request by e-mail, to appear in Journal of Physics

    Idle hands are the devil’s tools: The geopolitics and geoeconomics of hunger

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    In current geopolitical and geoeconomic discourses, hunger is understood as both a threat to be contained, resulting in an often severe social and spatial localization of food insecurity, and a humanitarian problem to be solved through diffuse global flows of food and other aid. The resulting scalar tensions demonstrate the potentially contradictory alignment of geopolitics and geoeconomics within processes of globalization and neoliberalization. This article examines the geopolitical and geoeconomic place of hunger and the hungry through a critical analysis of the food-for-work (FFW) approach to combating hunger. FFW programs distribute food aid in exchange for labor, and have long been used to plan and deliver food aid. While debate continues as to whether and under what conditions FFW programs are socially and economically just, governments, international institutions, and NGOs tout them as a flexible and efficient way to deliver targeted aid, promote community development, and improve long-term prospects for economic development and food security. In the post-9/11 period, FFW programs are also cited as effective deterrents to terrorist recruitment strategies, while development and food security more broadly have been incorporated into national security strategies, especially but not only in the United States. The food-for-work approach attempts to resolve the scalar contradictions of hunger through the imposition of a labor requirement that disciplines the threat of the hungry while enforcing global connection. Case studies of FFW programs in Bangladesh, Ethiopia, and Indonesia illustrate this contradiction, and highlight the development and possible future of approaches to hunger under neoliberal geopolitics

    Baboon-to-human liver transplantation

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    Our ability to control both the cellular and humoral components of xenograft rejection in laboratory experiments, together with an organ shortage that has placed limits on clinical transplantation services, prompted us to undertake a liver transplantation from a baboon to a 35-year-old man with B virus-associated chronic active hepatitis and human immunodeficiency virus infection. Liver replacement was performed according to conventional surgical techniques. Immunosuppression was with the FK 506-prednisone-prostaglandin regimen used routinely for hepatic allotransplantation, to which a daily non-myelotoxic dose of cyclophosphamide was added. During 70 days of survival, there was little evidence of hepatic rejection by biochemical monitoring or histopathological examination. Products of hepatic synthesis, including clotting factors, became those of the baboon liver with no obvious adverse effects. Death followed a cerebral and subarachnoid haemorrhage that was caused by an angioinvasive aspergillus infection. However, the underlying cause of death was widespread biliary sludge that formed in the biliary tree despite a seemingly satisfactory choledochojejunostomy. During life and in necropsy samples, there was evidence of the chimerism that we believe is integral to the acceptance of both xenografts and allografts. Our experience has shown the feasibility of controlling the rejection of the baboon liver xenograft in a human recipient. The biliary stasis that was the beginning of lethal infectious complications may be correctable by modifications of surgical technique. In further trials, the error of over-immunosuppression should be avoidable. © 1993
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