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71.
Dmitri Nikolaevich Severov Valentina Pshennikov Alexsandr Vasilievich Remeslo 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Fronts and thermohaline structure of the Brazil–Malvinas Confluence System (BMCS) are studied from climatic data, “Marathon Exp. Leg.8, 1984” data, and Sea surface temperature (SST) data base “ds277-Reynolds” (1981–2000). The South Atlantic Central Water (SACW) is divided in two main types: tropical (TW) and subtropical water (ST). Water masses, Fronts, Inter-Frontal and Frontal Zones are analysed and classified: (a) the water masses: Tropical Low-Salinity Water, Tropical Surface Water, Tropical Tropospheric Water, Subtropical Low-Salinity Water, Subtropical Surface Water, Subtropical Tropospheric Water. T,S characteristics of intermediate, deep and bottom water defined by different authors are confirmed and completed; (b) the Inter-Frontal Zones: Tropical/Brazil Current Zone, Subtropical Zone and Subantarctic Zone; (c) the Frontal Zones: Subtropical, Subantarctic and Polar, and (d) the Fronts: Subtropical Front of the Brazil Current, Principal Subtropical Front, North Subtropical Front, Subtropical Surface Front, South Subtropical Front, Subantarctic Surface Front, Subantarctic Front and Polar Front. Several stable T–S relationships are found below the friction layer and at the Fronts. The maximum gradient of the oceanographic characteristics occurs at the Brazil Current Front, which can be any of the subtropical Fronts, depending on season. Minimum mean depth of the pycnocline coincides with the Fronts of the BMCS, indicating the paths of low-salinity shelf waters into the open ocean. In the work it is shown how to recover the horizontal and vertical thermohaline structure of waters from satellite data RSMAS SST. 相似文献
72.
Deuterium fractionations in cometary ices provide important clues to the origin and evolution of comets. Mass spectrometers
aboard spaceprobe Giotto revealed the first accurate D/H ratios in the water of Comet 1P/Halley. Ground-based observations
of HDO in Comets C/1996 B2 (Hyakutake) and C/1995 O1 (Hale-Bopp), the detection of DCN in Comet Hale-Bopp, and upper limits
for several other D-bearing molecules complement our limited sample of D/H measurements. On the basis of this data set all
Oort cloud comets seem to exhibit a similar
ratio in H2O, enriched by about a factor of two relative to terrestrial water and approximately one order of magnitude relative to the
protosolar value. Oort cloud comets, and by inference also classical short-period comets derived from the Kuiper Belt cannot
be the only source for the Earth's oceans. The cometary O/C ratio and dynamical reasons make it difficult to defend an early
influx of icy planetesimals from the Jupiter zone to the early Earth. D/H measurements of OH groups in phyllosilicate rich
meteorites suggest a mixture of cometary water and water adsorbed from the nebula by the rocky grains that formed the bulk
of the Earth may be responsible for the terrestrial D/H. The D/H ratio in cometary HCN is 7 times higher than the value in
cometary H2O. Species-dependent D-fractionations occur at low temperatures and low gas densities via ion-molecule or grain-surface reactions and cannot be explained by a pure solar nebula chemistry. It is plausible that cometary
volatiles preserved the interstellar D fractionation. The observed D abundances set a lower limit to the formation temperature
of (30 ± 10) K. Similar numbers can be derived from the ortho-to-para ratio in cometary water, from the absence of neon in
cometary ices and the presence of S2. Noble gases on Earth and Mars, and the relative abundance of cometary hydrocarbons place the comet formation temperature
near 50 K. So far all cometary D/H measurements refer to bulk compositions, and it is conceivable that significant departures
from the mean value could occur at the grain-size level. Strong isotope effects as a result of coma chemistry can be excluded
for molecules H2O and HCN. A comparison of the cometary
ratio with values found in the atmospheres of the outer planets is consistent with the long-held idea that the gas planets
formed around icy cores with a high cometary D/H ratio and subsequently accumulated significant amounts of H2 from the solar nebula with a low protosolar D/H.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
73.
74.
采用射频CVD法制备出连续SiC(W)纤维,利用XPS分析手段研究了纤维的元素组成及形态与强度的关系,结果表明,纤维中的杂质特别是自由Si的存在对纤维抗拉强度有很大影响。 相似文献
75.
Tomographic determination of the spatial distribution of water vapor using GPS observations 总被引:1,自引:0,他引:1
M. Troller A. Geiger E. Brockmann J.-M. Bettems B. Bürki H.-G. Kahle 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2006,37(12):2211-II
With the advent of the GPS navigation system, a promising ground based technique has been introduced which makes it possible to estimate the amount of water vapor in the troposphere from operational GPS networks at relatively low additional costs. While the estimation of the integrated amount is currently well established, the determination of the spatial water vapor distribution and its temporal variation are still a major challenge. To account for the vertical resolution, several tomographic approaches were pursued. We developed the software package AWATOS (atmospheric water vapor tomography software) which is based on the assimilation of double differenced GPS observations. Applying a least-squares inversion, the inhomogeneous spatial distribution of water vapor is determined. An extensive investigation has been carried out in Switzerland. GPS measurements are performed by the dense permanent Swiss national GPS network AGNES of the Swiss Federal Office of Topography (swisstopo). A total of 40 equally distributed water vapor profiles have been estimated on an hourly basis. For the purpose of validation, 22 radiosonde profiles were used at the GPS and meteorological station Payerne. Furthermore, data of the numerical weather model aLMo (alpine model in Switzerland, MeteoSwiss) were compared with the tomographic results. An overall good agreement of the three methods with an rms of better than 1.6 g/m3 absolute humidity was achieved. The results show that AGNES can be used as a dedicated network for the purpose of GPS-tomography, using a horizontal resolution of approximately 50 km and height layers of 300–500 m thickness in the lower troposphere. 相似文献
76.
77.
针对高温风洞中扩压器前段壁面防热问题,提出对高温气流外缘喷水降温的方法。通过在收集器入口与喷管出口间安装喷水环,利用液态水汽化吸热对高温气流进行降温,使扩压器壁面形成低温保护层。为了解该方法降温效果,本文利用DPM、组分输运等模型的耦合建立了超声速两相流CFD模型,对向超声速热气流喷水进行降温的过程进行了数值计算,计算结果表明,扩压器启动后有显著的降温保护效果。同时,为探索风洞排气背压和喷水量对风洞流场和壁面降温效果的影响,通过计算得出了变排气背压、变喷水量与降温效果之间的关系,为高温风洞收集口喷水降温装置的优化设计提供了参考。 相似文献
78.
79.
通过在氰酸酯树脂中添加不同低含量环氧树脂AG80和催化剂苄基二甲胺(BDMA),分析了低含量环氧树脂改性氰酸酯树脂的微观结构、固化热效应、真空逸气特性、力学性能、吸水率和热失重。实验结果表明,在催化剂BDMA的作用下,当环氧树脂AG80的质量分数为5%和8%时,可以有效促进氰酸酯的固化程度,减少未固化小分子数量,进而改善氰酸酯材料的真空逸气性能。其中BADCy-1的真空逸气性能和耐湿性能达到最优,总质量损失(TML)和可凝挥发物(CVCM)分别为0.41%和0.03%,吸水率降低15%。BADCy-2的力学性能达到最优,拉伸强度和弯曲强度改善效果显著,分别提高23%和20%。同时随着环氧树脂含量的增加,材料的耐热性能有所下降。 相似文献
80.