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961.
Under Rayleigh equilibrium condition, stable isotopic ratio in residual water increases with the decrease of the residual water proportion f exponentially, and the fractionation rate of stable isotopes is inversely proportional to temperature. However, under kinetic evaporation condition, the fractionation of stable isotopes is not only related to the phase temperature but also influenced by the atmospheric humidity and the mass exchange between liquid and vapor phases. The ratio δ in residual water will not change with f after undergoing evaporation of a long time for great relative humidity. The rate that the evaporating water body reaches isotopic steady state is mainly dependent on the relative humidity in atmosphere. The analysis shows that the actual mean linear variety rates, about -30.0, of the δ18O in residual water versus the residual water proportion at Nagqu and Amdo stations are consistent with the simulated process under temperature of 20 oC and relative humidity of 50%. The distillation line simulated under Rayleigh equilibrium condition is analogous to the global meteoric water line (MWL) as the temperature is about 20 oC. Under non-equilibrium condition, the slope and constant values of distillation line are directly proportional to temperature and relative humidity. According to the basic data, the simulated distillation line is very consistent with the actual distillation line of Qinghai Lake. 相似文献
962.
M. V. Gyulzadyan J. A. Stepanian A. R. Petrosian D. Kunth B. McLean G. Comte 《Astrophysics》2003,46(2):131-143
The Second Byurakan Survey (SBS) is a well known combined survey, which uses the presence of UV-excess radiation in the continuum, or the presence of emission-lines in the spectra for the identification of active and star-forming galaxies. This paper reports on a comparative study of 77 galaxies identified with UV-excess, and 34 galaxies identified via emission-line techniques in the fields of the SBS. The spectroscopic parameters used for the comparison are the [OII]3727/H and [OIII]5007/H emission-lines ratios, the equivalent widths of [OII]3727, [OIII]5007 and H emission-lines, and the C
[OII]-C
H index. Spectroscopic parameters as well as new redshifts were determined from the spectra obtained with the 6m telescope of the Special Astrophysical Observatory (Russia). The main results are: 1) Galaxies discovered via UV-excess technique are preferably more active. 2) Galaxies discovered via emission-line technique are preferably high-excitation low-luminosity star-forming galaxies. 3) UV-excess galaxies with faintest UV-excess radiation are likely candidates to be LINER or Sy2 type objects. 相似文献
963.
在不同的天气条件下,由于气溶胶对光波的散射作用,通过成像系统获得的图像都会有一定程度的退化。利用图像的退化模型可以获取与天气现象相关的参量,从而达到识别天气的目的。对不同天气条件下得到的同一场景图进行研究,运用多垂线检测法,检测出不同天气条件下直线模糊边缘上的灰度值,采用signloid函数拟合出刃边函数,进而求出线扩散函数。通过分析线扩散函数的变化规律,总结出其与天气现象之间的紧密联系。测试结果表明,应用该方法对于晴天、薄雾、雨、霾、沙尘暴等天气现象具有一定的判别效果。 相似文献
964.
随着现代科学技术的发展,遥感影像为区域风沙地貌形态的研究提供了可靠的资料。近年来,有地貌学者提出了沙丘地貌格局分析法,通过在遥感影像上绘制沙丘脊线,量测和计算得到沙丘地貌格局表征参数,分析沙丘概率分布和空间变化规律、影响因素及形成时间。本文选取腾格里沙漠典型横向沙丘区域为研究对象,发展基于MATLAB平台的遥感影像沙丘脊线提取方法,利用沙丘迎风坡与落沙坡在遥感影像中成像的灰度差异, 对沙丘的沙脊线进行提取, 继而获得沙丘脊线长度、沙丘间距、走向、缺陷密度等沙丘地貌格局表征参数。结果表明,该方法快捷、可靠,为沙丘脊线的绘制提供了一种新方法。 相似文献
965.
M. D. Still † D. Steeghs V. S. Dhillon D. A. H. Buckley 《Monthly notices of the Royal Astronomical Society》1999,310(1):39-42
We present a small sample of time-resolved optical spectroscopy of the dwarf nova HL CMa during an outburst state. By combining radial velocity measurements with published data we show that the previously quoted value is not the only candidate for the orbital period of this system. We reduce the significance of daily aliasing but cannot distinguish between two periods at 0.2146±0.0004 and 0.2212±0.0005 d. We show that the low-excitation emission lines are composites from an accretion disc and the companion star, and that high-excitation emission originates in the disc or outflowing material associated with the accreting white dwarf. 相似文献
966.
This paper systematically presents the state-of-the-art of preparedness and reduction of earthquake disasters in China. It contains abundant information on the goal, policy, working links, administrative organizations, and main scientific and technological approaches for earthquake disaster reduction in this country. The focus is placed on "taking science and technology as the foundation" and "management based on legal system." 相似文献
967.
968.
969.
90年代世界贸易发展及空间格局变化的新特点 总被引:3,自引:0,他引:3
在世界贸易组织、日趋强烈的开放的区域主义倾向、跨国公司强劲的直接投资影响下,世界贸易正在经历着巨大变化,处在一个新的转换时期。本文从影响当今世界贸易发展的多重因素分析,揭示90年代世界贸易增长、内容结构以及空间格局发展变化的新特征,并展望世界贸易的未来发展。 相似文献
970.
ENVIRONMENTAL SUSTAINABILITY AND SCENARIOS OF URBANIZATION IN ARID AREA——A Case Study in Wuwei City of Gansu Province 总被引:1,自引:0,他引:1
YOUFei LIYu DONGSuo-cheng 《中国地理科学(英文版)》2005,15(2):120-130
1IN T R O D U C T IO N The western China isfacinggrowing problems of eco- logicaland economic development. The disparitiebse- tween the socio-economy of the western and eastern China were enlarging, and the major ecologicalprob- lems stilelvolve as past(H… 相似文献