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We have investigated a simple model for the effects of a central pulsar on the expansion of supernova shells. Some numerical results relevant to the Crab Nebula are also reported. 相似文献
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Over the last four centuries several botanists have analysed the Colosseum flora, and by using modern ecological and biogeographical approaches to these same floras, we have observed similar trends with respect to the climatic phenomena as those of the historic Torre Calandrelli Observatory and by other older historical records. The elements of which can be summarised as follows: 1) a substantial reduction of all the biogeographical components taken as indicators of cooler and damper habitats, such as the Euro-Asiatic and Boreal areas starting from the 17th Century in particular; 2) a decrease in numbers of all the species more dependent on water (independent of their chorology); 3) similar clear-cut increases in the species belonging to phytosociological classes typical to Mediterranean climatic conditions, to the detriment of those typical to Middle-European temperate bioclimates. All of which can be interpreted as clear indicators of non-negligible climatic changes towards hotter and drier conditions independent of local variations due to urbanisation. 相似文献
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Urbanization impact on metals mobility in riverine suspended sediment: Role of metal oxides 总被引：2，自引：2，他引：0
C. Priadi S. Ayrauk S. Pacini P. Bonte 《International Journal of Environmental Science and Technology》2011,8(1):1-18
Spatial and temporal fractionation of trace metals and major elements in suspended particulate matter in the Seine River was investigated to study the impact of the increasing urbanization in the Greater Paris Region. Suspended sediments in the Seine River were collected between December 2008 to August 2009 upstream and downstream of Paris. They were subjected to total digestion and sequential extraction procedure certified by the Bureau Communautaire de Référence and trace metals along with major elements were analyzed with inductively coupled plasma mass spectroscopy. Metal enrichment factors increased up to eight folds after the Seine River downstream of the Greater Paris Region showing a significant contribution of urbanization. Enrichment of copper, lead and zinc downstream of Paris are followed by the increase of their reducible fraction of at least 10% implicating an increase in metals associated with iron oxides. The exchangeable fraction, which includes the carbonate-associated metals, is only significant for cadmium, nickel and zinc (more than 2 %) while the oxidisable fraction accounts for less than 20 % for the anthropogenic metals downstream except for copper. The metals can be divided to (a) “reducible” group including cadmium, lead, and zinc, associated with more than 60 % of the total Bureau Communautaire de Référence extractable metals to the reducible fraction containing mostly iron oxide phases for the downstream sites. (b) A “distributed” group including chromium, copper, and nickel that are associated to at least 3 different phase-groups: (1) oxides, (2) organic matter and sulphides and (3) mineral phases. 相似文献
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Raulin Jean Pierre Makhmutov Vladimir S. Kaufmann Pierre Pacini Alessandra Abe Lüthi Thomas Hudson Hugh S. Gary Dale E. 《Solar physics》2004,223(1-2):181-199
We present a report on the strong X5.3 solar flare which occurred on 25 August 2001, producing high-level γ-ray activity, nuclear lines and a dramatic long-duration white-light continuum. The bulk of millimeter radio fluxes reached a peak of ∼100 000 solar flux units at 89.4 GHz, and a few thousands of solar flux units were detected in the submillimeter range during the impulsive phase. In this paper we focus on and discuss (i) the implications inferred from high frequency radio observations during the impulsive phase; (ii) the dynamics of the low corona active region during the impulsive phase. In particular we found that 4–5 × 1036 accelerated (>20 keV) electrons s−1 radiating in a 1000–1100 G region, are needed to explain the millimeter to submillimeter-wave emissions. We present evidence that the magnetic field in the active region was very dynamic, and that strong non-thermal processes were triggered by the appearance of new, compact, low-lying (few thousand kilometers) loop systems, suggesting the acceleration site(s) were also located in the low solar atmosphere. 相似文献
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A.-P. Leppänen A.A. Pacini I.G. Usoskin A. Aldahan E. Echer H. Evangelista S. Klemola G.A. Kovaltsov K. Mursula G. Possnert 《Journal of Atmospheric and Solar》2010,72(13):1036-1043
The long-time series of 7Be activity in surface air have been studied with the wavelet analysis technique in order to find coherence between 7Be activity, theoretical production in the troposphere and climatic indices. The 7Be activity were obtained from five different locations, Angra in the tropics in Brazil, Skåne in mid-latitudes in Southern Sweden, Kiruna in Polar region in Northern Sweden, Loviisa in Southern Finland and Rovaniemi in polar region in Northern Finland. The 7Be data from the Northern hemisphere sites where tested for coherence with theoretical production of the isotope in troposphere and with the North Atlantic Oscillation index. In the Southern hemisphere separate theoretical production was calculated in order to describe local production and Southern Annular Mode was used as the climatic index. Consistent and significant coherence were found with theoretical production at Skåne, Kiruna and Loviisa at time-scales of four years or longer. At Angra and Rovaniemi sites, no coherence was detected between 7Be theoretical tropospheric production and measured activity at ground level. The coherence between 7Be data from Skåne and Angra and climatic indices is insignificant while data from Northern and Eastern Scandinavia show clear coherence with climatic indices at time-scales of four years or longer. Additionally, significant coherence was found between the cosmic ray induced production and NAO at the time band of 8–12 years whereas the coherence between cosmic ray induced production and SAM was insignificant. This feature implies that the ground level 7Be activity contain mixed information on both production and transport. This conclusion means that further evaluation through models which enable accurate realistic models that will be investigated in future studies. 相似文献
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