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991.
The air-sea exchange is one of the main mechanisms maintaining the abundances of trace gases in the atmosphere. Some of these,
such as carbon dioxide and dimethyl sulphide (DMS), will have a bearing on the atmospheric heat budget. While the former facilitates
the trapping of radiation (greenhouse effect) the latter works in the opposite direction through reflectance of radiation
back into space by sulphate aerosols that form from oxidation of DMS in atmosphere. Here we report on the first measurements
made on DMS in the Bay of Bengal and the factors regulating its abundance in seawater. Phytoplankton alone does not seem to
control the extent of DMS concentrations. We find that changes in salinity could effectively regulate the extent of DMSP production
by marine phytoplankton. In addition, we provide the first ever evidence to the occurrence of DMS precursor, DMSP, in marine
aerosols collected in the boundary layer. This suggests that the marine aerosol transport of DMSP will supplement DMS gaseous
evasion in maintaining the atmospheric non-sea salt sulphur budget. 相似文献
992.
Natural polysaccharides such as starch, dextrin, guar gum, cellulose and their derivatives are promising non-toxic organic depressants. Although generally perceived as non-selective, these polymers have found use in commercial processes or have been tested in laboratories in practically all flotation systems involving every type of minerals. In this communication, the adsorption mechanisms of natural polysaccharides are reviewed, with the objective of promoting the wider applications of the polymers. While it seems generally accepted that natural polysaccharides interact with minerals via surface metal-hydroxylated species, an acid/base interaction model between the natural polysaccharides and mineral surfaces is proposed to explain many observed adsorption and flotation phenomena. 相似文献
993.
994.
医学图像三维表面模型重建 总被引:10,自引:0,他引:10
三维表面模型重建是医学图像处理的重要内容,是将CT和MRI等医疗影像设备获得的二维图像重建成三维立体表面显示图像的过程.本文重点研究了其重建算法的具体实现:(1)在建模上采用了基于体素的三维物体体积重建;(2)在显示上提出了基于Ray-Casting的三维物体二维直接显示技术.所以,和传统采用三角面拟合的方法相比,具有图像重建过程无需生成中间数据、无需进行3D物体的边界检测等优点,同时该算法并行性好,易于采用硬件方法实现加速.因此,本研究为医学图像三维表面模型重建应用软件的开发打下了理论基础. 相似文献
995.
996.
997.
楚雄盆地云龙凹陷尖山油苗油源对比 总被引:3,自引:0,他引:3
对楚雄盆地云龙凹陷泥盆系尖山油苗的有机地化特征进行了分析,并通过生物标记物12个参数多因素油源对比,认为该油苗主要为油苗之下的华二段油页岩附近的灰质泥岩为其烃源岩;同时,泥盆系灰岩对油苗的形成具有一定的贡献作用。 相似文献
998.
The passage of subtropical cold fronts through central Australia produces the only significant mesoscale meteorological features in the region. The interaction of these cold fronts with the surface energy balance strongly affects the local weather and climate. The surface energy balance was measured at a semi-arid site in Alice Springs, central Australia, to determine how it was influenced by the passage of subtropical cold fronts. Both Bowen ratio and eddy correlation methods were used. The daytime energy balance of the site showed high net radiation that was partitioned into 75% sensible heat flux and 25% soil heat flux with little or no latent heat flux. At night there was a large net radiative loss that was balanced primarily by a loss of heat from the soil. The cold fronts predominately passed through Alice Springs at night and showed a strong surface signature. The fronts brought moister air resulting in higher water vapour pressures during their passage. The nocturnal boundary layer was often disturbed as the front passed, resulting in warm, moist air being mixed down toward the land surface. Mixing decreased the soil heat flux and increased latent heat fluxes toward the surface. Moisture that accumulated at the surface at these times was often evaporated after a return to drier conditions. During the daytime, surface signatures in soil and sensible heat fluxes were less distinct due to the strong convective mixing. Latent heat fluxes followed a similar trend to the nocturnal case. 相似文献
999.
We present an improved crossover adjustment procedure to determine mean sea surface height using TOPEX, 35-day repeat phase ERS-1, Geosat, and 168-day repeat phase ERS-1 satellite altimeter data. The mean sea surface frame defined by the TOPEX data is imposed as certain constraints in our crossover adjustment procedure rather than held fixed as in some other procedures. The new procedure is discussed in detail. Equations are developed to incorporate the a priori information of Topex data as well as other satellite altimeter data. The numerical computation result shows that the rms crossover discrepancies are reduced by an order of 1 cm when the Topex data is not fixed. Furthermore, the computed mean sea surface is less noisy and more realistic than that computed by the traditional procedure. 相似文献
1000.
根据 1 994年 9月 1 8— 30日南沙群岛海域渚碧礁的近海面大气湍流观测实验资料 ,分别计算了该海域光滑海面和粗糙海面上的空气动力粗糙度 (z0 )、中性曳力系数 (CDN)。利用Brutsaert的假定 ,推导了一组求取标量粗糙度 (zT,zQ)、整体输送系数 (感热交换系数CHN、水汽交换系数CEN)的公式。在此基础上分别计算和分析了该海域近海面光滑海面和粗糙海面上z0 ,zT,zQ,CDN,CHN,CEN 及它们关于水平风速u分量的分布 ,并得到了一些有意义的结论。 相似文献