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Wolfgang J. Bühler 《Environment international》1978,1(6):341-343
This paper re-proves and generalizes results by Hardin and Sweet on the time to absorption in certain Markov chains by using a theorem on the time to extinction in multitype branching processes. Renaming “absorption” as “death” and “state immediately before absorption” as “cause of death” makes possible an interpretation in terms of competing risks. This is of very limited value, however, due to the rather severe mathematical restrictions on the Markov chains at hand. 相似文献
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Wolfgang Kundt 《Die Naturwissenschaften》1977,64(10):493-498
A possible evolutionary history of neutron stars is delineated, ranging from star formation through supernova explosions, X-ray and pulsar stages to an eventual pulsar turnoff via spin alignment, or magnetic field decay. New is the emphasis that there should be two populations of pulsars, the slow and the fast one, according to their successive formation in a binary system. The two pulsar populations are related to two phenotypes of supernova remnants, of which Cas A and the Crab are the best known examples. 相似文献
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Spatial and temporal variability of water repellency in a sandy soil contaminated with tar oil and heavy metals 总被引:1,自引:0,他引:1
Water repellency can induce preferential flow and thus affect water flow and contaminant transport at hazardous waste sites. Since the spatial patterns of water repellency are mostly unknown, it is problematic to use numerical transport models to predict leachate composition. In this study, the spatial variability of soil water repellency was studied at an industrial site contaminated with tar oil, chromium, copper and arsenic. The persistence of water repellency was assessed by the water drop penetration time (WDPT), and the degree of water repellency was quantified by the ethanol percentage (EP) test. Measurements were made at the soil surface along 3.5-12.1 m long transects at different times between March and October 2002. The spatial variability of WDPT, EP, water content, and organic matter content was quantified by variogram analyses. Both the persistence and the degree of water repellency varied seasonally, with the highest water repellency during the summer months. The correlation lengths of WDPT values ranged between 16 and 406 cm, whereas EP values showed no spatial correlation. For field-moist samples, a critical soil water threshold, below which water repellency prevails, was estimated to be 2.5-4%. For oven dry samples, the WDPT values were dependent on the water content prior to drying. The wide range of correlation lengths and the temporal dynamics of spatial repellency patterns suggest that simulations of solute leaching must consider the spatial and temporal variability of soil hydrophobic properties. 相似文献