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1.
在文献」1「4 基础上,根据近年文选址实践中提出的问题,先进一步讨论了大气相干直径和时间的的物理和意义,然后强调了自由大气湍流的天文成像效应及选址中进行研究和测量的重要性。最后对差分像运动方法测量视宁度的定标和系统误差等问题作了分析。 相似文献
2.
Qiang Wang Derek A. Wyman Jifeng Xu Yusheng Wan Chaofeng Li Feng Zi Ziqi Jiang Huaning Qiu Zhuyin Chu Zhenhua Zhao Yanhui Dong 《Contributions to Mineralogy and Petrology》2008,155(4):473-490
New chronological, geochemical, and isotopic data are reported for Triassic (219–236 Ma) adakite-magnesian andesite-Nb-enriched
basaltic rock associations from the Tuotuohe area, central Qiangtang terrane. The adakites and magnesian andesites are characterized
by high Sr/Y (25–45), La/Yb (14–42) and Na2O/K2O (12–49) ratios, high Al2O3 (15.34–18.28 wt%) and moderate to high Sr concentrations (220–498 ppm) and εND (t) (+0.86 to +1.21) values. Low enrichments of Th, Rb relative to Nb, and subequal normalized Nb and La contents, and enrichments
of light rare earth elements combine to distinguish a group of Nb-enriched basaltic rocks (NEBs). They have positive εND (t) (+2.57 to +5.16) values. Positive correlations between Th, La and Nb and an absence of negative Nb anomalies on mantle
normalized plots indicate the NEBs are products of a mantle source metasomatized by a slab melt rather than by hydrous fluids.
A continuous compositional variation between adakites and magnesian andesites confirms slab melt interaction with mantle peridotite.
The spatial association of the NEBs with adakites and magnesian andesites define an “adakitic metasomatic volcanic series”
recognized in many demonstrably subduction-related environments (e.g., Mindanao arc, Philippines; Kamchatka arc, Russia; and
southern Baja California arc, Mexico). The age of the Touhuohe suite, and its correlation with Triassic NEB to the north indicates
that volcanism derived from subduction-modified mantle was abundant prior to 220 Ma in the central Qiangtang terrane. 相似文献
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4.
Qiu Dahong 《中国海洋工程》1992,(2)
Based on the 1st order cnoidal wave theory, the nonlinear wave diffraction around a circular cylinder in shallow water is studied in this paper. The equation of the wave surface around the cylinder is formulated and by using this formula the wave surface elevation on the cylinder surface can be obtained. In this paper, the formula for calculating the cnoidal wave force on a circular cylinder is also derived. For the wave conditions which are often encountered in practical engineering designs, the ratios of the nonlinear wave forces to the linear wave forces are calculated, and the results are plotted in this paper for design purposes. In order to verify the theoretical results, model tests are conducted. After comparing the test results with the theoretical ones, it is concluded that, in shallow water, for the case of T g / d~(1/2) > 8-10 and H / d > 0.3, the cnoidal wave theory should be used to calculate the wave action on a cylindrical pier. 相似文献
5.
Frequency-selective attenuation of sound propagaion and reverberation in shallow waterTXFrequency-selectiveattenuationofsoundp... 相似文献
6.
In this paper, the irregular wave force on a cylindrical pier group is calculated by the method of spectrum analysis, and the coefficients of the group effect of piers in the pier group are given here. The calculated results, using P-M and Bretshneider's. (B's) spectra, are obtained for the cases of 2 piers, 3 piers and 4 piers. To compare these results with those obtained for regular waves, we can come to some significant conclusions. Under the action of the irregular wave, when the distance between the piers in the pier group increases, the coefficient of the group effect decreases and tends rapidly to the case of a single pier. In general, when the ratio of the distance between the piers to the diameter of the pier is greater than 4, the group effect can be neglected. 相似文献
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南海西沙西南海域表层沉积物特征 总被引:3,自引:1,他引:3
西沙西南海域表层沉积物样品矿物成分,地球化学,微体古生物分析测试结果表明:沉积物可分为7种类型,沉积环境主要是陆坡,部分为深海平原,海洋生物,海洋化学以及火山物质的沉积起到了积极的作用,陆源物质的影响较小,它们主要来源于北部大陆和南部岛礁等物源区。 相似文献
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10.
M.K Vollmer R.F WeissR.T Williams K.K FalknerX Qiu E.A RalphV.V Romanovsky 《Geochimica et cosmochimica acta》2002,66(24):4235-4246
The relationships between electrical conductivity, temperature, salinity, and density are studied for brackish Lake Issyk-Kul. These studies are based on a newly determined major ion composition, which for the open lake shows a mean absolute salinity of 6.06 g kg−1. The conductivity-temperature relationship of the lake water was determined experimentally showing that the lake water is about 1.25 times less conductive than seawater diluted to the same absolute salinity as that of the lake water. Based on these results, an algorithm is presented to calculate salinity from in-situ conductivity measurements. Applied to the field data, this shows small but important vertical salinity variations in the lake with a salinity maximum at 200 m and a freshening of the surface water with increasing proximity to the shores. The algorithm we adopt to calculate density agrees well with earlier measurements and shows that at 20°C and 1 atm Lake Issyk-Kul water is about 530 g m−3 denser than seawater at the same salinity. The temperature of maximum density at 1 atm is about 0.15°C lower than that for seawater diluted to the same salinity. Despite its small variations, salinity plays an important role, together with temperature changes, in the static stability and in the production of deep-water in this lake. Changes in salinity may have had important consequences on the mixing regime and the fate of inflowing river water over geological time. Uncharged silicic acid is negligible for the stability of the water column except near an ∼15 m thick nepheloid layer observed at the bottom of the deep basin. 相似文献