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61.
Historical optical data are combined on the BL Lac object OQ 530.Verifying the existence of correlations among the flux variations in different bands serves as an important tool to investigate emission processes.To examine the possible existence of a lag between variations in different optical bands from this source,a statistical analysis is performed through the discrete correlation function(DCF)method and the z-transformed discrete correlation function(ZDCF)method.Monte Carlo simulations called"flux redistribution/random subset selection"(FR/RSS)are performed to obtain statistically meaningful values for the cross-correlation time lags and their related uncertainties.The analysis confirms that the variations in different optical light curves are strongly correlated,with zero-lag within the errors.Long term variability of color indexes is also analyzed.The result suggests a strong correlation between color index and brightness.A clear bluer-when-brighter chromatism is found,in the sense that the spectrum steepens as the brightness decreases.  相似文献   
62.
恒星内部电荷屏蔽对电子俘获反应的影响   总被引:1,自引:0,他引:1  
本文分析了在恒星环境下,电荷强屏蔽对原子核电子俘获反应的影响,分析中忽略了电荷屏蔽对核跃迁矩阵元的影响.作为例子,分别讨论了电荷屏蔽对核素33S、30P和57Fe的电子俘获率的影响.结果表明:在较低温度和较高密度下,由于电荷屏蔽,其电子俘获率相对于无屏蔽情形有明显降低,这可能对恒星晚期演化和超新星爆发理论带来明显的影响.  相似文献   
63.
戴子高 《天文学报》1997,38(1):67-74
本文研究了广义相对论效应和量子力学效应对中子量γ射线辐射的影响.通过选择磁偶极矩以及观察者视线与磁轴之间的夹角这两个观测量作为参量,我们数值计算了从中子星表面发射的、传播方向沿着磁场的光子的逃逸能量.我们得到,在磁偶极矩较小时,量子力学效应不重要,而广义相对论效应使逃逸能量显著降低;当磁偶极矩很大时,两个效应几乎相抵消,光子的逃逸能量几乎不受它们的影响.我们讨论这些结果在脉冲星γ射线谱上的意义.  相似文献   
64.
Large dams and reservoirs alter not only the natural flow regimes of streams and rivers but also their flooding cycles and flood magnitudes. Although the effect of dams and reservoirs has been reported for some vulnerable locations, the understanding of the inner-basin variation with respect to the effects remains limited. In this study, we analyse the Three Gorges Dam (TGD) built on the Changjiang mainstream (Yangtze River) to investigate the dam effect variations in the system of interconnected water bodies located downstream. We investigated the effect of flow alterations along the downstream river network using discharge time series at different gauging stations. The river–lake interactions (referring to the interactions between the Changjiang mainstream and its tributary lakes i.e. the Dongting and Poyang lakes) and their roles in modifying the TGD effect intensity were also investigated in the large-scale river–lake system. The results show that the water storage of the tributary lakes decreased after the activation of the TGD. Severe droughts occurred in the lakes, weakening their ability to recharge the Changjiang mainstream. As a consequence, the effect of the TGD on the Changjiang flow increase during the dry season diminished quickly downstream of the dam, whereas its impact on the flow decrease during the wet season gradually exacerbated along the mainstream, especially at sites located downstream of the lake outlets. Therefore, when assessing dam-induced hydrological changes, special attention should be paid to the changes in the storage of tributary lakes and the associated effects in the mainstream. This is of high importance for managing the water resource trade-offs between different water bodies in dam-affected riverine systems.  相似文献   
65.
This study deals with the toxic effects of Zn2+, Cu2+, Cd2+ and NH3 on Chinese prawn (Penaeus orientalis). The median lethal concentrations of the toxic matters on Chinese prawn were determined. Cd2+>Cu2+>Zn2+>NH3-Nm is the toxic order of these chemicals to Chinese prawn. The toxic order of concentrated Zn2+ and Cd2+ in tissues and organs of Chinese prawn is in the order. gill>shell+appendage>viscera>muscle.  相似文献   
66.
Estimates of AGN Black Hole Mass and Minimum Variability Timescale   总被引:4,自引:0,他引:4  
Black hole mass is one of the fundamental physical parameters of active galactic nuclei (AGNs), for which many methods of estimation have been proposed. One set of methods assumes that the broad-line region (BLR) is gravitationally bound by the central black hole potential, so the black hole mass can be estimated from the orbital radius and the Doppler velocity. Another set of methods assumes the observed variability timescale is determined by the orbital timescale near the innermost stable orbit around the Schwarzschild black hole or the Kerr black hole, or by the characteristic timescale of the accretion disk. We collect a sample of 21 AGNs, for which the minimum variability timescales have been obtained and their black hole masses (Mσ) have been well estimated from the stellar velocity dispersion or the BLR size-luminosity relation. Using the minimum variability timescales we estimated the black hole masses for 21 objects by the three different methods, the results are denoted by Ms, Mk and Md, respectively. We compared each of them with Mσindividually and found that: (1) using the minimum variability timescale with the Kerr black hole theory leads to small differences between Mσand Mk, none exceeding one order of magnitude, and the mean difference between them is about 0.53 dex; (2) using the minimum variability timescale with the Schwarzschild black hole theory leads to somewhat larger difference between Mσand Ms: larger than one order of magnitude for 6 of the 21 sources, and the mean difference is 0.74 dex; (3) using the minimum variability timescale with the accretion disk theory leads to much larger differences between Mσand Md, for 13 of the 21 sources the differences are larger than two orders of magnitude; and the mean difference is as high as about 2.01 dex.  相似文献   
67.
辽南早元古宙辽河群变质岩系中的金矿床为变质热液成因金矿床,矿床的形成与吕梁期变质变形作用关系密切。金矿化带的展布与金矿体的产出受韧性剪切带控制。剪切带内岩石具有明显的动态性组构特征,直接赋矿围岩为辽河群盖县组糜棱岩化千枚岩、变砂岩及云母石英糜棱岩等。韧性剪切带为含矿流体的运移提供通道。作者定义这类金矿床为变质热液型含金剪切带金矿床。  相似文献   
68.
河南省华北陆块南缘富碱侵入岩与金矿床成矿关系主要表现在空间、热动力和衍生关系三方面,与碱性岩有关的金矿床主要分为三种类型:热液-淋滤富集型、含金剪切带型和熔结(爆发)角砾岩型。富碱岩石含金背景值总体较高,近矿围岩含金丰度低于远矿围岩,富碱侵入体中的部分金组分参与了成金作用。区域侵入体含金性,其一:沿着栾川—方城深大断裂带分布的富碱浅成侵入体的成矿作用主要表现为区域构造活动引发淋滤富集作用和含金剪切构造带成金作用;其二:位于成金基底源区出露的一些富碱侵入体的成矿作用主要表现为爆发角砾岩和热液蚀变。  相似文献   
69.
Small‐area patch merging is a common operation in land use data generalization. However, existing research on small‐area patch merging has mainly focused on local compatibility measures, which often lead to area imbalances among land use types from a global perspective. To address the shortcomings of previous studies by resolving local and global concerns simultaneously, this article proposes a merging method that considers both local constraints and the overall area balance. First, a local optimization model that considers three constraints—namely, the areas of neighboring patches, the lengths of shared arcs, and semantic similarity—is established. The areas of small patches are first pre‐allocated. Subsequently, in accordance with an area change threshold for individual land use types, land use types with area changes that exceed this threshold are identified. The patches corresponding to these land use types are subjected to iterative adjustments while considering the overall area balance. Based on their area splitting abilities, the split lines for small‐area patches are determined, and small‐area patches are merged. Finally, actual data from Guangdong Province are used for validation. The experimental results demonstrate that the proposed method is capable of preserving the local compatibility of patches while balancing the overall area associated with each land use type.  相似文献   
70.
本文报道了运用图像处理技术,分别计算河北省南皮县试区两个不同时相TM与SPOT图像的亮度指数和垂直植被指数,进而求算变化向量、自动输出变化分类图的试验研究结果。经实地对22块变化图斑进行检验,都准确无误,表明从不同时相的卫星图像提取土地利用变化信息,分析耕地消长及大宗作物种植面积波动是完全可能的,有广阔的应用前景。  相似文献   
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