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碳水化合物的组合合成是一项新兴技术，该技术可以在短时间内合成大量用于进行生物活性筛选的寡糖及拟糖物。液相与固相合成技术可以极大地加快药物研究与开发进程。作者针对该技术在碳水化合物合成方面的研究进展情况进行讨论。 相似文献
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I.A. Eltayeb 《Physics of the Earth and Planetary Interiors》1981,24(4):259-271
Recent developments in the study of linear wave motions in rotating magnetic systems are reviewed. Particular attention is paid to the relationship between motions in diffusionless and diffusive systems. The influence of the geometry of the system is also stressed. 相似文献
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Mohamed A. H. Eltayeb Jasna Injuk Willy Maenhaut René E. Van Grieken 《Journal of Atmospheric Chemistry》2001,40(3):247-273
Eighteen soil samples from central Sudan were fractionated by dry sieving ina size fraction from <45 m to >300 m while aerosols generatedfrom these soils were fractionated in the particle size range from 0.25 mto >16 m. The elemental concentrations of soil samples were determinedby energy-dispersive X-ray fluorescence, while the elemental concentrationsof generated aerosols were analysed by particle-induced X-ray emission. Theelements Al, K and Rb show a slight positive fractionation with decreasingparticle size throughout the particle size range studied. The concentrationsof Ca, Mn, Fe, Sr and Y are maximum in the small soil size fraction (<45m) and decrease for the coarse soil size fractions, while in the mineralaerosol particle sizes (0.25– > 16 m) the concentrations remainmore or less constant. The size distributions for Cr, Ti and Zr show a maximumin the particle size range 45–100 m and the concentrations of theseelements decrease sharply in the aerosol fraction down to 16 m to remainconstant in the smaller aerosol fractions.Enrichment factors for the elements were calculated relative to five referencematerials: average crustal rock, average soil, the investigated Sahara bulksoil, the finest fraction of this soil and the aerosol generated from thissoil, and using four reference elements: Al, Si, Ti and Fe. The enrichmentfactors were found to vary significantly depending on the choice of thereference material or the reference element. The enrichment factors for theSudan mineral aerosol were almost identical to those for Khartoum atmosphericaerosol but different from those for Namib mineral aerosol and Israelatmospheric aerosol following dust storms. Multivariate display methods(cluster analysis, principal component analysis and linear discriminantanalysis) were applied to the element ratios in the mineral aerosol from theSahara and Namib and this showed that these mineral aerosol can bedifferentiated into different groups. An attempt was also made to relate themineral aerosol to its parent soil through the use of these multivariatetechniques and the elemental ratios in both the mineral aerosols and the bulksoils (Namib and Sahara). It was also possible using the elemental ratios andthe multivariate display methods to associate the crustal component to themineral aerosol generated from the Sahara. 相似文献
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高原地区的强对流天气突发性强、易多发、强度大、影响重、预报难,但针对高原地区强对流天气及其短临预报系统的总结还较少。由于高原特殊的地理环境及显著的热力作用和动力作用的影响,高原强对流天气具有不同于东部平原地区的独特特征,其研究进展概括具有重要指导意义。概括了青藏高原地区尤其是西藏地区强对流天气研究的进展,包括高原地区强对流天气气候特征,高原强对流天气的环流背景及影响系统,强对流天气的预报技术、相关短临预报系统等,为进一步的研究工作和短临预报系统建设提供研究背景。 相似文献
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It is shown that the discontinuous jump in the vertical wave energy flux of slow hydromagnetic-gravity waves, occurring at a critical level, which is accompanied by wave absorption, and the existence of a reflection point imply that slow waves are trapped in the solar atmosphere. Thus such a system behaves as a leaky wave guide. 相似文献
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This article provides a partial answer to the question “What is the relation between excess hydraulic head and volume flux of water in a conduit within a porous matrix?”, focusing on the case that the forcing is steady. The conduit is modelled as a horizontal circular cylinder, imbedded within a porous matrix of rectangular cross section, having constant head prescribed on the sidewalls and being confined top and bottom. Laminar flow in the matrix is assumed to obey Darcy's law, while turbulent flow in the conduit is quantified using the Darcy–Weisbach equation. Analysis of the latter equation shows that the length scale of variations in the direction of the conduit is large compared with the scale of lateral and vertical variations. This permits separation of the full three-dimensional non-linear problem into a two-dimensional linear problem for head within the matrix and a one-dimensional non-linear problem for head within the conduit. Analytic solutions are obtained for the distribution of head in the matrix and in a conduit of either infinite or finite length. In both cases, the volume flux of water is proportional to the excess head to the 2/3 power, the conduit radius to the 5/3 power, the matrix permeability to the 1/3 power and gravity to the 1/3 power. The scale of variation of head along the conduit is proportional to the excess head to the ?1/3 power, the conduit radius to the 5/3 power, the matrix permeability to the ?2/3 power and gravity to the 1/3 power. 相似文献