10 research outputs found

    On the Sensitivity of Massive Star Nucleosynthesis and Evolution to Solar Abundances and to Uncertainties in Helium Burning Reaction Rates

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    We explore the dependence of pre-supernova evolution and supernova nucleosynthesis yields on the uncertainties in helium burning reaction rates. Using the revised solar abundances of Lodders (2003) for the initial stellar composition, instead of those of Anders & Grevesse (1989), changes the supernova yields and limits the constraints that those yields place on the 12C(a,g)16O reaction rate. The production factors of medium-weight elements (A = 16-40) were found to be in reasonable agreement with observed solar ratios within the current experimental uncertainties in the triple alpha reaction rate. Simultaneous variations by the same amount in both reaction rates or in either of them separately, however, can induce significant changes in the central 12C abundance at core carbon ignition and in the mass of the supernova remnant. It therefore remains important to have experimental determinations of the helium burning rates so that their ratio and absolute values are known with an accuracy of 10% or better.Comment: Accepted for publication by the Astrophysical Journa

    Dependence of S-Process Nucleosynthesis in Massive Stars on Triple-Alpha and 12C(a,g)16O Reaction Rate Uncertainties

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    We have studied the sensitivity of s-process nucleosynthesis in massive stars to +/- 2 sigma variations in the rates of the triple alpha and 12C(a,g)16O reactions. We simulated the evolution of massive stars from H-burning through Fe-core collapse, followed by a supernova explosion. We found that: the production factors of s-process nuclides between 58Fe and 96Zr change strongly with changes in the He burning reaction rates; using the Lodders (2003) solar abundances rather than those of Anders and Grevesse (1989) reduces s-process nucleosynthesis; later burning phases beyond core He burning and the shell C burning have a significant effect on post-explosive production factors. We also discuss the implications of the uncertainties in the helium burning rates for evidence of a new primary neutron capture process (LEPP) in massive stars.Comment: Submitted to the Astrophysical Journa

    Estudo clínico aberto multicêntrico da efetividade e tolerabilidade do gel de adapaleno a 0,1%* em pacientes com acne vulgar Multicentric open clinical study of the efficacy and tolerability of adapalene 0.1% gel* in patients with acne vulgaris

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    FUNDAMENTOS: O adapaleno é um derivado do ácido naftóico, com propriedades biológicas similares às do ácido retinóico e utilizado no tratamento da acne vulgar. OBJETIVOS: Avaliar a eficácia e a tolerabilidade do adapaleno 0,1% gel no tratamento da acne vulgar leve à moderada, em pacientes residentes no Brasil. MATERIAIS E MÉTODOS: Os pacientes aplicaram o gel à noite, durante 12 semanas, e foram avaliados quanto à efetividade pelo número de lesões em cada visita e quanto à tolerabilidade ao produto nas consultas da segunda e da décima segunda semana. RESULTADOS: Dos 125 pacientes, 81,6% completaram as 12 semanas de tratamento, e 10,4% dos casos terminaram o estudo antes do período estabelecido por estarem livres de lesões. Os resultados permitem confirmar a marcante atividade antiinflamatória, antiproliferativa e na diferenciação celular dos ceratinócitos. Houve diminuição dos comedões e das lesões inflamatórias, com resposta satisfatória no eritema, no ressecamento e na descamação da pele. Efeitos adversos pouco graves foram relatados em apenas 9,6% dos pacientes. CONCLUSÕES: O adapaleno, neste estudo e nos vários que o antecederam, vem-se mostrando uma das melhores opções de tratamento tópico para os casos leves a moderados de acne vulgar.<br>BACKGROUND: Adapalene, a naftoic acid derivative with biological properties similar to those of the retinoic acid, is indicated in the treatment of acne vulgaris. OBJECTIVES: The present study was carried out to evaluate the therapeutic action of adapalene 0.1% gel and its tolerability in the treatment of mild to moderate acne vulgaris in patients living in Brazil. MATERIAL AND METHODS: Patients applied the gel at night for 12 weeks; and were evaluated regarding the efficacy and tolerability of the product according to the number of lesions observed at each of the 2-week and 12-week visits. RESULTS: Out of 125 patients, 81.6% completed 12 weeks of therapy and 10.4% of the cases left the study before week 12 because they were found to be lesion-free. Results allow us to confirm its effect upon keratinocyte cellular differentiation with antiinflammatory and antiproliferative properties. Adapalene induces a marked decrease in comedos and inflammatory lesions. Mild adverse events were reported in less than 10% of patients. CONCLUSION: Adapalene has been shown to be one of the best topical therapies for mild or moderate acne both in the present study and in previous studies

    Massive stars and their supernovae

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    Stars more massive than about 8-10 solar masses evolve differently from their lower-mass counterparts: nuclear energy liberation is possible at higher temperatures and densities, due to gravitational contraction caused by such high masses, until forming an iron core that ends this stellar evolution. The star collapses thereafter, as insufficient pressure support exists when energy release stops due to Fe/Ni possessing the highest nuclear binding per nucleon, and this implosion turns into either a supernova explosion or a compact black hole remnant object. Neutron stars are the likely compact-star remnants after supernova explosions for a certain stellar mass range. In this chapter, we discuss this late-phase evolution of massive stars and their core collapse, including the nuclear reactions and nucleosynthesis products. We also include in this discussion more exotic outcomes, such as magnetic jet supernovae, hypernovae, gamma-ray bursts and neutron star mergers. In all cases we emphasize the viewpoint with respect to the role of radioactivities