Adsorption Kinetic Characteristics of H2S on Activated Carbon

This study compared H₂S adsorption kinetic parameters in both grain adsorption and column adsorption systems. Results indicated that when the nondimensional mass transfer parameter for adsorption column design was included, the axial dispersion (Pe > 1, < 1) and external film resistance (B 1) could be neglected, the fluid viscosity effect was small (Sc = 0.76), and the adsorbate affinity was fine (). Surface and pore diffusion controlled the adsorbent and fluid mass transfer. In addition, spent activated carbon could be treated by a thermal process and then impregnated with NaOH. After the pretreatment, the spent activated carbon could be used for H₂S adsorption. Furthermore, we also propose that the H₂S adsorption reaction on the carbon is due to the formation of sulfur crystals.     

高能Zn离子注入CaF2基质形成ZnO纳米粒子的机制、构型及电子结构

将高能Zn2+注入到CaF2介电基质中,在CaF2的表面下注入Zn2+浓度呈近似高斯分布,通过氧气氛后经热退火形成ZnO量子点.采用MaterialsStudio和Gaussian98W程序,结合实验结果计算分析了CaF2基质中ZnO纳米粒子的电子结构和光学性质.选取由4个ZnO原胞组成的超晶胞模型计算了ZnO纳米粒子的吸收光谱,理论结果与实验结果相符.对ZnO纳米粒子电子结构的研究结果表明,ZnO纳米粒子与CaF2基质的相互作用主要是ZnO表面的O与基质中Ca之间的作用,这种作用使ZnO纳米晶体的Fermi能级变窄,带隙相应减小;ZnO纳米粒子表面构型的变化对其本征吸收光谱没有影响,理论计算结果与实验值一致.     

Stereoselective determination of R(-)- and S(+)-MK-571, a leukotriene D4 antagonist, in human plasma by chiral high-performance liquid chromatography.

A stereoselective high-performance liquid chromatographic method that utilizes fluorescence detection was developed for the selective and sensitive quantification of R(-)- and S(+)-enantiomers of MK-571 (1), a potent and specific leukotriene D4 antagonist, in human plasma. Racemic 1 was isolated from the acidified plasma using solid-phase extraction and the resulting residue was successfully reacted with isobutyl chloroformate and R(+)-1-(1-naphthyl)ethylamine in triethylamine-acetonitrile medium to form the diastereomer of each enantiomer. A structural analogue of 1 was used as internal standard. The derivatized sample was dissolved in 1,1,2-trichlorotrifluoroethane and an aliquot was chromatographed on a (R)-urea chiral column using a mobile phase containing 89% triethylamine-pentane (3:1000, v/v), 10% 2-propanol, and 1% acetonitrile at a flow-rate of 1.5 ml/min. The fluorescence response (excitation wavelength, 350 nm; emission wavelength, 410 nm) was linear (r2 greater than 0.999) for concentrations of enantiomers of 1 from 0.05 micrograms/ml, the lowest quantitation limit, up to 2.5 micrograms/ml. Intra-day coefficients of variation at 0.05 microgram/ml were 2.4% for the R(-)-isomer and 2.0% for S(+)-isomer. The corresponding inter-day coefficients of variation for R(-)- and S(+)-1 were 2.6 and 3.6%, respectively. The utility of the methodology was established by analysis of plasma samples from male volunteers receiving single intravenous and oral doses of racemic 1.     

Availability Analysis of Repairable <Emphasis Type="Italic">N</Emphasis>-Server <Emphasis Type="Italic">n</Emphasis><Subscript><Emphasis Type="Italic">i</Emphasis></Subscript>-Replicated Systems

We develop an exact closed-form expression for the steady-state availability of a repairable, N-server system in which the ith server contains n _i identical, reconfigurable, breakdown-prone units. Our approach, which follows from the Markov chain balance equations and the recursive properties of Hessenberg matrix determinants, is simpler than previously proposed matrix geometric approaches, and can readily be adapted to the availability analysis of more complicated structures. We illustrate this by computing the steady-state availability of a mixed parallel-serial gracefully degrading replicated system.     

Determination of surface charge properties of PC-12 cells by electrophoresis

The electrophoretic behavior of pheochromocytoma (PC-12) cells was investigated both experimentally and theoretically. Cell mobility in aqueous media at different pHs and ionic concentrations was measured, and a model, which assumed that the cell surface contains both acidic and basic functional groups, was proposed. As a result, it was revealed that the experimental data gathered can be described satisfactorily by assuming that the cell surface contains two types of monovalent acidic functional groups and one basic functional group. The values of the dissociation constants of the acidic and basic groups are found to be close to those of acidic amino acids, which indicates that the acidic amino acids may play an important role in the surface electrical properties of PC-12 cells.     

Dibromomethane as one-carbon source in organic synthesis: total synthesis of (±)-canadensolide

A diastereoselective total synthesis of (±)-canadensolide is described. The key step is to introduce the α-methylene group by the ozonolysis of mono-substituted alkenes followed by reaction with a preheated mixture of CH₂Br₂-Et₂NH.