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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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For the investigation of climatic history for the last 65 million years, several holes were drilled in 1990 on the Ontong Java Plateau by the drilling vessel Joides Resolution, under the auspices of the international Ocean Drilling Program. The Ontong Java Plateau is the largest basalt plateau on earth, and was formed in the Middle Cretaceous. From the core material, seismic reflectors from the overlying sediments can be associated with specific, climate-related oceanic events. For the cyclic sediments of the last 2 million years, high-resolution isotope curves were generated which depict the two dominant Milankovitch cycles with periods of 100 000 and 41000 years. 相似文献
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Monitoring of iodinated X-ray contrast media in surface water 总被引:1,自引:0,他引:1
A monitoring programme was carried out in order to determine iodinated X-ray contrast media (ICM) in the River Danube and to investigate the raw water quality for drinking water production at Langenau waterworks. The study revealed that the maximum concentrations of ICM (over 500 ng l(-1) for diatrizoic acid and iopamidol) were found in 2h-composite samples taken from the downstream of the Ulm/Neu-Ulm metropolitan area. By means of a concentration profile over one month the highest ICM concentrations were observed on weekdays. The extended data evaluation with principal component analysis shows that the upstream and downstream samples had different pattern of variations in ICM concentration and also demonstrates a clear change in ICM composition by the discharge of municipal wastewater. In addition to load profiles of ICM, time-dependent plots of principal component 1 exhibited peaks, indicating a short-term discharge of ICM between the two sampling sites. In conclusion, a point source for ICM contamination between the sampling sites in Ulm upstream and Leipheim downstream seems to be the reasonable explanation for peak ICM concentrations. Due to the observed high variations of ICM concentrations in river, the evaluation of natural waters by means of a single analysis is not representative. 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
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Tradescantia micronucleus test indicates genotoxic potential of traffic emissions in European cities
Klumpp A Ansel W Klumpp G Calatayud V Garrec JP He S Peñuelas J Ribas A Ro-Poulsen H Rasmussen S Sanz MJ Vergne P 《Environmental pollution (Barking, Essex : 1987)》2006,139(3):515-522
Urban atmospheres contain complex mixtures of air pollutants including mutagenic and carcinogenic substances such as benzene, diesel soot, heavy metals and polycyclic aromatic hydrocarbons. In the frame of a European network for the assessment of air quality by the use of bioindicator plants, the Tradescantia micronucleus (Trad-MCN) test was applied to examine the genotoxicity of urban air pollution. Cuttings of Tradescantia clone #4430 were exposed to ambient air at 65 monitoring sites in 10 conurbations employing a standardised methodology. The tests revealed an elevated genotoxic potential mainly at those urban sites which were exposed to severe car traffic emissions. This bioassay proved to be a suitable tool to detect local 'hot spots' of mutagenic air pollution in urban areas. For its use in routine monitoring programmes, however, further standardisation of cultivation and exposure techniques is recommended in order to reduce the variability of results due to varying environmental conditions. 相似文献
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