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1.
A new extraction method for ginsenosides from ginseng roots, ginseng leaves and ginseng drug preparations by Sep-Pak C18 cartridges has been studied. Ginsenoside extraction by Sep-Pak cartridges is a rapid, efficient, reproducible method. In addition, the extracts were analyzed by high performance thin layer chromatography (HPTLC) and reverse phase high performance liquid chromatography (HPLC). The major components of ginseng saponins were effectively separated using an ODS-120T column. 相似文献
2.
Gas chromatography using flameless sulfur chemiluminescence detection was applied to the analysis of sulfur compounds in air. A trap employing the solid adsorbent Tenax GR was used to enrich ambient levels of volatile sulfur compounds. The sulfur gases were then thermally released according to programmed temperature from the adsorbent trap and re-collected in a column cooled with liquid nitrogen. The sulfur compounds were revolatilized and directly transferred to the system of PLOT-column gas chromatograph/flameless sulfur chemiluminescence detector for analysis. The PTV injector has been used as a thermal resorption chamber for analysis of sulfur compounds. The sulfur gaseous compounds known to cause nuisance odors in the air from sewerage treatment works were determined. 相似文献
3.
We have evaluated an analytical method for the determination of polycyclic aromatic hydrocarbons (PAHs) and sulfur compounds in air by means of adsorption/temperature-programmed thermal desorption (ATPTD) with small bed volume (0.08g) Tenax-TA cartridges, followed by a cryogenic trap in a precolumn with liquid nitrogen as an appropriate concentration method before capillary gas chromatography is described. The enriched components from the adsorption cartridges are transferred to the capillary column with a valveless switching system. Recoveries were determined for the complete ATPTD method. Desorption recoveries near 100% were found for various of polycyclic aromatic hydrocarbons and sulfur compounds. The sulfur compounds known to cause nuisance odors in the atmosphere near sulfur recovery and sewerage treatment works were also determined. 相似文献
4.
A series of alumina-supported alkaline earth metal oxide catalysts were prepared by incipient-wetness impregnation. These
catalysts were characterized by nitrogen-sorption to determine their surface areas and pore size distributions. The basicities
of these catalysts were characterized by temperature-programmed desorption of carbon dioxide. The TPD results demonstrate
that all of the catalysts have one-peak profiles. The basicity increases with increasing atomic number of the alkaline earth
metal. The alumina-supported alkaline earth oxides exhibit the same basic properties as bulk metal oxides. However, the presence
of alumina can increase the mechanical strength of the catalyst, since the alkaline earth oxides have a weak mechanical strength.
The basic properties of the catalysts are strongly influenced by the calcination temperature. 相似文献
5.
For the generalized statistical mechanics based on the Tsallis entropy, a variational perturbation approximation method with the principle of minimal sensitivity is developed by calculating the generalized free energy up to the third order in variational perturbation expansion. The approximation up to the first order amounts to a variational approach which covers the variational method developed by E.K. Lenzi, L.C. Malacarne, R.S. Mendes [Phys. Rev. Lett. 80 (1998) 218] and the approximations up to higher orders can systematically improve variational results. As an illustrated example, the generalized free energy for a classical harmonic oscillator (considered in the Lenzi's joint work) are calculated up to the third order, and the resultant approximations up to the first, second, and third orders are numerically compared with the exact result. 相似文献
6.
Wen-Pin Wang Sheng-Rui Jian Jenh-Yih Juang Yi-Shao Lai Wen-Fa Wu Chang-Pin Chou 《Applied Surface Science》2007,253(23):9248-9253
The effects of H2 plasma pretreatment on the growth of vertically aligned carbon nanotubes (CNTs) by varying the flow rate of the precursor gas mixture during microwave plasma chemical vapor deposition (MPCVD) have been investigated in this study. Gas mixture of H2 and CH4 with a ratio of 9:1 was used as the precursor for synthesizing CNTs on Ni-coated TiN/Si(1 0 0) substrates. The structure and composition of Ni catalyst nanoparticles were investigated by using scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (XTEM). Results indicated that, by manipulating the morphology and density of the Ni catalyst nanoparticles via changing the flow rate of the precursor gas mixture, the vertically aligned CNTs could be effectively controlled. The Raman results also indicated that the intensity ratio of the G and D bands (ID/IG) is decreased with increasing gas flow rate. TEM results suggest H2 plasma pretreatment can effectively reduce the amorphous carbon and carbonaceous particles and, thus, is playing a crucial role in modifying the obtained CNTs structures. 相似文献
7.
热效应仍是限制激光放大器向高功率、高光束质量进一步发展的瓶颈问题, 高效的热管理是抑制热效应的重要技术途径. 研究了基于激光二极管抽运氦气冷却的钕玻璃叠片激光放大器的热效应. 利用有限元数值模拟的方法, 分析了钕玻璃的温度、应力应变和应力双折射分布, 并计算了热致波前畸变和退偏损耗, 与实验结果符合得较好, 在热沉积为0.7 W/cm3的条件下, 6片钕玻璃总的热致波前畸变为6.77λ , 最大退偏量大于90%. 相似文献
8.
9.
Through the calculation of the effective potential and the excited state energies for the sinh-Gordon and the sine-Gordon models in (D + 1) dimensions, we show that the variational technique of Bogoliu bov transformations is equivalent to the Gaussian wave-functional approach. 相似文献
10.
具有激素活性的Schiff碱化合物的研究(Ⅰ)──苯氧乙酸类Schiff碱的合成及其生物活性汪焱钢,叶文法,尹大学,黄君珉,陆爱红(华中师范大学化学系,武汉,430070)关键词Schiff碱,氨基苯氧乙酸,植物激素活性芳胺的Schiff碱类化合物,... 相似文献