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71.
5-Thio-D-galactopyranose has been synthesized from diacetone galactofuranose in nine steps and 13.4% overall yield. The key step involved a successful conversion of furanosyl 5,6-epoxide with an L-altrose configuration into the corresponding 5,6-thiirane D-galactose derivative, which was hydrolyzed to the target compound. 相似文献
72.
ABSTRACT Convenient regio- and stereoselective syntheses of rhamnose-containing oligosaccharides via sugar-sugar orthoester formation and rearrangement are described. 1→3 Linked rhamno di- and trisaccharides were synthesized effectively using unprotected rhamnose residue as the glycosyl acceptor by this methodology. 相似文献
73.
Impacts of air pressure on the evolution of nanosecond pulse discharge products 总被引:1,自引:0,他引:1 下载免费PDF全文
Based on the nonequilibrium plasma dynamics of air discharge, a dynamic model of zero-dimensional plasma is established by combining the component density equation, the Boltzmann equation, and the energy transfer equation. The evolution properties of nanosecond pulse discharge (NPD) plasma under different air pressures are calculated. The results show that the air pressure has significant impacts on the NPD products and the peak values of particle number density for particles such as O atoms, O3 molecules, N2(A3) molecules in excited states, and NO molecules. It increases at first and then decreases with the increase of air pressure. On the other hand, the peak values of particle number density for N2(B3) and N2(C3) molecules in excited states are only slightly affected by the air pressure. 相似文献
74.
75.
采用平面波赝势方法对菱铁矿FeCO3高压下的晶体结构, 电子构型和电子结构进行了第一性原理计算研究. 研究过程中考虑了菱铁矿FeCO3真实的反铁磁(AFM) 自旋有序态, 模拟静水压环境, 从零压逐步加压到500 GPa. 在40---50 GPa压力范围内, FeCO3发生了从高自旋(HS) AFM态到低自旋(LS) 非磁性(NM) 态的磁性相变, 伴随着晶胞体积坍塌10.5%. FeCO3在相变前后均是绝缘体, 但是相变后的LS-NM态的Fe2+ 离子的3d电子局域化程度更强, 能隙随着压力的进一步增大而逐步增大, 离化程度更高, 直到500 GPa没有发生金属绝缘体相变. 相似文献
76.
文章研究了小尺寸的(ZnSe)n团簇(n=2-16)的结构和电子性质.通过手工搭建得到团簇结构,用DMol软件包进行结构优化和能量计算,最后分析计算结果 .研究结果表明,对于n=2-4,平面环状结构的能量最低;对于n=5,非平面环状结构的能量最低;对于n=6-12,空心笼状结构的能量最低;对于n=13,核-壳笼状结构的能量最低;对于n=14-16,依旧是空心笼状结构的能量最低.通过分析(ZnSe)_n团簇(n=2-16)的电子性质,我们可以得到,(ZnSe)_9团簇、(ZnSe)_(12)团簇具有很好的稳定性. 相似文献
77.
A palladium-based catalyst (Fe3O4/SiO2/HPG–OPPh2–PNP) supported on chlorodiphenylphosphine-functionalized magnetic nanoparticles was successfully prepared from Fe3O4/SiO2 with sequential attachment of glycerol and chlorodiphenylphosphine, followed by treatment of an ethanolic solution of palladium chloride with hydrazine. The as-prepared catalyst was characterized by ICP-AES, FTIR, XRD, SEM, and TEM. The Fe3O4/SiO2/HPG–OPPh2–PNP was found as a magnetically separable and highly active catalyst for Suzuki coupling reactions of aryl iodides, bromides, and chlorides as well as Heck reactions of aryl iodides and bromides. Under appropriate conditions, all reactions afforded the desired products in moderate to excellent yields. Moreover, this catalyst can be easily recovered by using a magnetic field and directly reused for at least six cycles without significant loss of its activity. 相似文献
78.
79.
A method for characterizing and identifying firing patterns of neural spike trains is presented. Three characteristic variables defined at sequential moments, including two formal derivatives and the integration of the counting process, are introduced to reflect the temporal patterns of a spike train. This paper also examines how noise interacts with encoding mechanisms of neuronal stimulus in a cold receptor. From ISI series and bifurcation diagrams it is shown that there are considerable differences in interval distributions and impulse patterns caused by purely deterministic simulations and noisy simulations. The ISI-distance can be used as an effective and powerful way to measure the noise effects on spike trains quantitatively. It is found that spike trains observed in cold receptors can be more strongly affected by noise for low temperatures than for high temperatures in some aspects; meanwhile, spike train has greater variability with the noise intensity increasing. 相似文献
80.