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231.
黑洞X射线暂现源的迷你爆发是一类峰值光度较低、持续时间较短的爆发.由于观测数据较少,其物理机制仍不清楚.利用RXTE (Rossi X-ray Timing Explorer)卫星从2001年1月28日到3月14日的数据,研究了黑洞X射线暂现源XTE J1550–564 2001年迷你爆发的X射线能谱特性.发现在本次迷你爆发中, XTE J1550–564的X射线能谱可以用幂律谱很好地拟合.整个爆发的硬度强度图不是标准的q型,而是一直保持在最右侧.此外,还分析了此次爆发谱指数Γ与未吸收的2–10 keV能段的X射线流量F_(2–10 keV)的相关性,发现Γ-F_(2–10 keV)呈反相关关系,且谱指数Γ∈[1.35, 1.72].上述结果表明2001年这次爆发一直处于低/硬态,它的X射线辐射主要来自于辐射低效的吸积模式,如ADAF(Advection-Dominated Accretion Flow). 相似文献
232.
H. Knutsen 《Astronomische Nachrichten》1988,309(4):263-265
We report here the results of our examination of the physical properties of Vaidya-Tikekar's model for a relativistic star. Full details will be published elsewhere. The analysis yields a strong indication that the model is stable with respect to infinitesimal radial oscillations. We find that the adiabatic speed of sound is smaller than the speed of light everywhere inside the fluid sphere if the radius of the sphere is larger than 1.46 times its Schwarzschild radius. We also find that the fluid must necessarily be supraluminal somewhere if the speed of sound is decreasing outwards close to the center. We further find that the strong energy condition is fulfilled everywhere if it is fulfilled at the center. Since the ratio of the pressure p and the density ⋅ is decreasing outwards, this indicates that the temperature gradient is negative. We also find that the relativistic adiabatic index is larger than two. Demanding the fluid to be causal, and taking the pressure and the density to be somewhere given by 7.4 ⋅ 1033 dynes/cm3 and 5.1 ⋅ 1014 g/cm3, we calculate the maximum mass of the fluid sphere to be 3 solar masses. 相似文献
233.
N. Sali 《Astronomische Nachrichten》1988,309(4):303-305
By a general relativistic fluctuation theory developed recently following ideas by LANDAU and LIFSHITZ, hydrodynamical fluctuations in a simple model of a contracting star are considered. It can be shown that there are always regions in which the fluctuations and mean square values of basic physical quantities are increasing. 相似文献
234.
本文介绍一种最近由作者在美国研制的,由计算机产生等距离区域分界线的程序及其数据结构,同时给出初步的试验结果。 相似文献
235.
本文利用不同地物在同一波段或相同地物在不同波段具有不同色调的变化规律,来目视判读7幅l∶l0万的TM黑白和彩色合成图像。通过细致地分析、对比,在富顺─南溪地区判读不同泥沙含量、不同深浅的水体,了解河床中深槽、浅滩地貌,准确勾绘所有大于像元的水体涯线,确定沟谷的宽度和相对深度,查明沟谷成因,划分漫滩和河谷阶地,圈定丘陵和山地的,分布,研究它们的形态和成因,为区域开发奠定科学的基础。 相似文献
236.
Pavlos S. Kanaroglou 《The Professional geographer》1994,46(3):359-368
Samples used to estimate discrete choice models in geography and regional science are typically assumed to be simple random samples. This assumption is not always met with existing samples. Furthermore, data collection is usually less costly if a stratified sampling strategy is adopted. Existing sampling theory suggests that stratified sampling can affect the consistency of parameter estimates. This paper reviews the salient points of this theory and relates theory to practice by means of a simple example on housing choice by elderly. 相似文献
237.
1 INTRODUCTIONThe mixing length theory (MLT) for stellar convection originally developed by Vitense(1953, 1958) has been the most popularly used local convection theory in the studies of stellarstructure and evolution. The theory was later modified and revised by many investigators,who suggested some different expressions. In fact, MLT is not a real hydrodynamic theory,rather, it is a simple "ballistic" theory which traces the motion of imaginary convective elements. In reality j stell… 相似文献
238.
In this paper, a simple scenario and probabilistic approach is used to assess the potential groundwater risk due to proposed
overdraft remedial actions in cone of depression, Jining City, China. Focusing on the concentrations of Chloride ions (Cl−) and total hardness (TH), the impact of artificial recharge and reduced pumping on groundwater quality and quantity is analysed
by using the three-dimensional finite difference groundwater flow and transport model, Visual MODFLOW, to simulate groundwater
flow and transport within the study area based on scenarios, and utilizes SURFER software to map risk levels. Although 5,
10 or 15% reduced pumping with artificial recharge leads to more decrease in Cl− and TH concentrations than the 25%, less volume increase is achieved for the remediation of land subsidence and other environmental
problems in the cone of depression. The Cl− concentrations in recovered groundwater are within the desired concentration of 200 mg/l; however, TH in some cases are above
the maximum permissible limit of 500 mg/l, with an exceedence probability of about 0.67 for recharge and recharge with reduced
pumping at 25%. The presence of fractures and hydrogeological complexity greatly determines impacts of remediation, and the
22% reduced pumping with artificial recharge offers an optimum strategy for overdraft remediation in the Jining cone of depression. 相似文献
239.
240.
Chris Koen 《Monthly notices of the Royal Astronomical Society》2001,322(1):97-99
The amplitude spectra of the light curves of RR Lyrae Blazhko stars can often be typified by symmetrical triplets. It is shown that the same applies to V473 Lyr. Furthermore, the star is probably a radial pulsator – as is thought to be the case for the RR Lyrae stars – thus ruling out rotational splitting of a purely non-radial mode. 相似文献