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1.
A new procedure to separate the instrumental and atmospheric components of stray light is presented. It is based on the dependence of the aureole's atmospheric component on the air mass and is applied to measurements taken with the Vacuum Newton Telescope (VNT) at the Observatorio del Teide (Tenerife). The resulting instrumental part is independent of the air mass.The variation of both components with wavelength is also studied. The instrumental component shows no dependence on wavelength, in contrast to the atmospheric one which is greater in the blue than in the red.It is concluded that observations with air masses larger than two will probably be strongly affected by stray light. 相似文献
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Roberto Mínguez Fernando Delgado Ignacio Escuder Manuel G. de Membrillera 《国际地质力学数值与分析法杂志》2006,30(10):1019-1037
Empirical criteria have been used successfully to design filters of most embankment large dam projects throughout the world. However, these empirical rules are only applicable to a particular range of soils tested in laboratory and do not take into account the variability of the base material and filter particle sizes. In addition, it is widely accepted that the safety of fill dams is mainly dependent on the reliability of their filter performance. The work herein presented consists in a new general method for assessing the probability of fulfilling any empirical filter design criteria accounting for base and filter heterogeneity by means of first‐order reliability methods (FORM), so that reliability indexes and probabilities of fulfilling any particular criteria are obtained. This method will allow engineers to estimate the safety of existing filters in terms of probability of fulfilling their design criteria and might also be used as a decision tool on sampling needs and material size tolerances during construction. In addition, sensitivity analysis makes possible to analyse how reliabilities are influenced by different sources of input data. Finally, in case of a portfolio risk assessment, this method will allow engineers to compare the safety of several existing dams in order to prioritize safety investments and it is expected to be a very useful tool to evaluate probabilities of failure due to internal erosion. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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We have calculated prominence thread models for different values of the center temperature and pressure. We have simultaneously solved the radiative transfer, statistical equilibrium and ionization equilibrium equations assuming a three-level atom plus continuum. We have also computed the energy balance equation including the hydrogen radiative losses from our calculations, plus other radiative losses and heat conduction. Some models have been calculated assuming possible variations in thermal conductivity and heating terms. We computed the lines and continua emitted by a number of threads, in order to compare with the observations and evaluate how the different values of the parameters affect the profiles and absolute intensities of L, L, H, and Ly continuum.Member of the Carrera del Investigador, CONICET, Argentina.c.c.67 Suc. 28 Buenos Aires 1428, Argentina. 相似文献
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F. Parello A. Aiuppa H. Calderon F. Calvi D. Cellura V. Martinez M. Militello K. Vammen D. Vinti 《Applied Geochemistry》2008
This paper reports new geochemical data on dissolved major and minor constituents in surface waters and ground waters collected in the Managua region (Nicaragua), and provides a preliminary characterization of the hydrogeochemical processes governing the natural water evolution in this area. The peculiar geological features of the study site, an active tectonic region (Nicaragua Depression) characterized by active volcanism and thermalism, combined with significant anthropogenic pressure, contribute to a complex evolution of water chemistry, which results from the simultaneous action of several geochemical processes such as evaporation, rock leaching, mixing with saline brines of natural or anthropogenic origin. The effect of active thermalism on both surface waters (e.g., saline volcanic lakes) and groundwaters, as a result of mixing with variable proportions of hyper-saline geothermal Na–Cl brines (e.g., Momotombo geothermal plant), accounts for the high salinities and high concentrations of many environmentally-relevant trace elements (As, B, Fe and Mn) in the waters. At the same time the active extensional tectonics of the Managua area favour the interaction with acidic, reduced thermal fluids, followed by extensive leaching of the host rock and the groundwater release of toxic metals (e.g., Ni, Cu). The significant pollution in the area, deriving principally from urban and industrial waste-water, probably also contributes to the aquatic cycling of many trace elements, which attain concentrations above the WHO recommended limits for the elements Ni (∼40 μg/l) and Cu (∼10 μg/l) limiting the potential utilisation of Lake Xolotlan for nearby Managua. 相似文献
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To establish when the presence of colloids can favour contaminant migration is a critical task for the performance assessment of a high level radioactive waste repository. In this study, the effects of the presence of bentonite colloids on the migration of highly sorbing elements, such as Eu and Pu, in a granite environment were investigated. Special efforts were made to quantify the filtration of bentonite colloids in this medium and to determine the experimental uncertainties that could bias the interpretation of the results. 相似文献
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