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151.
152.
IntroductionI.thasbeenpayingattentiontotheanomalousphenomenonbyseismologiststhattheearthquakeactivityoftenstrengthensinacertainspaceandduringacertaintimearoundthesourceareabeforeastrongearthquake.Mogi(1969)pointedoutthataringdistributiveareaofthestrengthenedearthquakeactivityoftenappearsaroundthesourcearea10to20yearsbeforegreatshock,whichcalledaringphenomenon(or"doughnut").Afterthat,otherscholarsreportedinsuccessionthatringdistributionofearthquakeactivityoccurredbeforeastrongertquakeorevenbefo… 相似文献
153.
V. Krishan 《Journal of Astrophysics and Astronomy》1988,9(4):231-236
The occurrence of superluminal motion in extragalactic radio sources is believed to be quite common. Among others, the geometrical
scattering of radio radiation can also cause superluminal expansion and or motion and halo formation, In this paper, the effectiveness
of the stimulated Raman scattering in producing these features is investigated. The scattering medium is a plasma whose position,
density and temperature decide the rate and angle of scattering. When the radiation from a stationary and constant source
gets scattered from a stationary plasma, a halo is formed around the source. However, the scattering of a rotating radiation
beam does produce superluminal motion of the virtual source. It is found that the plasma should have the characteristics of
the emission-line regions and the intercloud medium in order to Raman scatter the radiation. Since the scattering is polarization
dependent, it is possible to estimate the rotation of the electric vector along the direction of the apparent motion of a
radio source. 相似文献
154.
S. C.?Tarantino M.?ZemaEmail author M.?Pistorino M. C.?Domeneghetti 《Physics and Chemistry of Minerals》2003,30(10):590-598
Structural investigations at high temperature were carried out on natural columbite samples across the join Fe(Nb0.95Ta0.05)2O6–Mn(Nb0.95Ta0.05)2O6. The samples were preliminarily annealed to attain the complete cation-ordered state and avoid the superimposition of the effects of cation ordering during high-temperature studies. Unit-cell parameters of three columbites with different XFe content were measured at regular intervals in the temperature range 25–900 °C using single-crystal X-ray diffraction techniques. The crystal structures of completely ordered ferrocolumbite and manganocolumbite were also refined from intensity data collected at room temperature, 300 and 600 °C. Structural thermal expansion coefficients show positive, linear expansion of a, b, c lattice constants and cell volume. In general, slightly higher expansion occurs along a and c directions. However, anisotropy decreases sharply with decreasing Fe content. Reversibility of thermal expansion in the investigated temperature range was checked by high-temperature diffraction studies under heating-up and cooling-down conditions. Impurities do not play an important role in thermal expansion of columbites; expansion coefficients measured on two crystals of the same sample characterized by different Ti content are in fact almost identical. Structural changes with temperature essentially affect bond lengths: volumes of both A and B octahedral sites increase linearly with temperature, whereas interpolyhedral geometrical parameters do not vary significantly. 相似文献
155.
X射线荧光光谱分析检出限问题的探讨与建议 总被引:12,自引:5,他引:7
对有关X射线荧光光谱分析低含量元素的检出限问题进行了多方面的探讨。从检出限的定义及其定义下的相对标准偏差到各种不同测量、校准与校正方法的检出限及其相对应的相对标准偏差进行计算。提出了以定义检出限的相对标准偏差为基准,对各种测量方法计算出的检出限进行重新界定,从而确认一个具有可比性的、精度一致的检出限。同时还讨论了仪器与X光管固有杂质元素谱线对该元素检出限的影响;测量仪器、测量条件与测量时间对检出限的影响;不同岩性试样对检出限的影响;检出限与测定限等问题。 相似文献
156.
Webster Cash 《Experimental Astronomy》2003,16(2):91-136
For the astronomer, X-ray interferometry is the theory and practice of building dilute aperture telescopes for studying celestial X-ray sources. The short wavelengths and high surface brightness of X-ray sources will make the eventual scientific payoff very high, with direct imaging of the event horizons of black holes as the centerpiece. In this article, we review the history of X-ray interferometry and discuss the recent technical developments toward astronomical applications. We present several mission concepts and show they are achievable with todays technology. 相似文献
157.
YU Wen-fei 《天文研究与技术》2003,(1):12-15
最近对低质量X射线双星中的千赫兹准周期振动的研究表明 ,是辐射压力 ,而不是盘和磁球的相互作用以及处于盘内边界的广义相对论效应在短时标的盘切断机制上起作用。本文给出了一些研究结果及讨论。 相似文献
158.
遥感影像镶嵌时拼接缝的消除方法 总被引:29,自引:0,他引:29
对现有的影像并接缝消除方法的优缺点进行了分析,提出了拼接缝消除的强制改正方法,并用大量的实际图像进行了试验。结果表明:所提出的方法具有较好的拼接缝消除效果,且算法简单,易于实现,可以处理彩色和黑白等多种图像。 相似文献
159.
We constructed a grid of relativistic models for standard high-relative-luminosity accretion α-disks around supermassive Kerr black holes (BHs) and computed X-ray spectra for their hot, effectively optically thin inner parts by taking into account general-relativity effects. They are known to be heated to high (~106–109 K) temperatures and to cool down through the Comptonization of intrinsic thermal radiation. Their spectra are power laws with an exponential cutoff at high energies; i.e., they have the same shape as those observed in active galactic nuclei (AGNs). Fitting the observed X-ray spectra of AGNs with computed spectra allowed us to estimate the fundamental parameters of BHs (their mass and Kerr parameter) and accretion disks (luminosity and inclination to the line of sight) in 28 AGNs. We show that the Kerr parameter for BHs in AGNs is close to unity and that the disk inclination correlates with the Seyfert type of AGN, in accordance with the unification model of activity. The estimated BH masses Mx are compared with the masses Mrev determined by the reverberation mapping technique. For AGNs with luminosities close to the Eddington limit, these masses agree and the model under consideration may be valid for them. For low-relative-luminosity AGNs, the differences in masses increase with decreasing relative luminosity and their X-ray emission cannot be explained by this model. 相似文献
160.