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The equations of stationary fluid motion are solved for the case of spherical accretion onto non-magnetic, non-rotating neutron star. The X-ray radiation flux is calculated in two different ways: An approximate solution of the moment equations coupled to the gas fluid equations and numerical Monte-Carlo simulation of the photon random walk. We show that the spectrum of the X-ray radiation in the outer parts of the inflowing envelope has a characteristic power-law behaviour. We suggest that some of the properties of the X-ray sources in the globular clusters can be explained with this model. 相似文献
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We follow the accretion of hydrogen-rich matter onto the surface of a white dwarf in a close binary system. Two phases of accretion are assumed. First—slow accretion from the interstellar clouds, second—fast accretion from the companion.Hydrogen is ignited at the interface between the fast and slowly accreted layers. After a short runaway burning continues in the form of quasistationary deflagration front propagating inwards. The features of this front are discussed. A possibility of mass loss is indicated. 相似文献
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The accretion of hydrogen rich matter onto the surface of a white dwarf, assuming that the accreted matter keeps a small part of its gravitational falling energy, is investigated. The influence of this energy excess on the hydrogen ignition and the thermal instability that follows is described and discussed. 相似文献
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Shane C. Lishawa KathiJo Jankowski Pamela Geddes Daniel J. Larkin Andrew M. Monks Nancy C. Tuchman 《Aquatic Sciences - Research Across Boundaries》2014,76(4):483-495
Wetland ecosystems maintain and improve water quality through the process of denitrification, an increasingly important ecosystem service due to global N pollution. Invasive plants have the potential to disrupt denitrification by altering the environmental conditions that facilitate this process. Great Lakes coastal wetlands are experiencing widespread invasion by highly productive hybrid cattail with largely uncertain biogeochemical effects. Through field and controlled mesocosm studies, we sought to determine the effects of cattail invasion through time on denitrification rates and associated environmental factors in a Great Lakes coastal wetland. In the field, we found that cattail density correlated with increased denitrification and a suite of environmental and plant community characteristics and denitrification rates were positively correlated with NH4 +, sediment organic matter, reduced water levels, and cattail stand age. Through our controlled mesocosm study, we documented conditions 1- and 5-year following invasion and found that denitrification rates and soil organic matter increased in year 5, and cattail and year-since-invasion altered plant communities and soil NH4 +. Only a weak correlation between denitrification rates and cattail treatments was noted, however, owing to high replicate variability. Our results indicate that with increasing cattail residence time, one ecosystem service, biodiversity, was negatively impacted, while two other services, denitrification and sediment carbon accumulation, were enhanced. Thus, this highly invaded wetland still provides valuable services to aquatic ecosystems and to society. A holistic perspective is therefore critical when evaluating invasive species impacts in which negative impacts are weighed against other ecosystem services, which may be stimulated. 相似文献
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