火焰原子吸收光谱法测定鱼腥草、西洋参和茯苓中的铜含量

用硝酸-高氯酸混合酸(4∶1)消化鱼腥草、西洋参和茯苓,在波长324.8nm处,利用火焰原子吸收光谱法测定鱼腥草、西洋参和茯苓中铜的含量。线性回归方程为A=0.1708C 0.0004,相关系数r=0.9997,线性范围为0—5μg/mL,检出限为0.0035μg/mL,测定结果的相对标准偏差为0.09%,加标回收率为98.0%—104.2%。     

Forced oscillation of second order linear and half-linear difference equations

Oscillation properties of solutions of the forced second order linear difference equation

are investigated. The authors show that if the forcing term does not oscillate, in some sense, too rapidly, then the oscillation of the unforced equation implies oscillation of the forced equation. Some results illustrating this statement and extensions to the more general half-linear equation

1, \end{displaymath}">

are also given.

     

Thin-layer chromatography--the forgotten alternative for the quantitative determination of steroids

We have developed a high performance thin layer chromatography (HPTLC) system for quantitative determination of androgens, corticosteroids, mineralocorticoids and gestagens on silicagel KG-60 HPTLC-plates with different solvent systems. A complete separation of androgens, gestagens and metabolites was achieved with dichlormethane/cyclohexane/acetone (70:25:5). Corticosteroids, mineralocorticoids and their derivatives were completely separated with diethylether/isooctane/isopropanol (70:25:5). The quantitative in situ fluorescence determination was carried out after post-chromatographic derivatization with cinnamic aldehyde, 4-dimethylaminobenzaldehyde and sulfuric acid. The sensitivity of detection was found between 500 pg and 1 ng per spot. The steroid metabolism as catalysed by rat liver microsomal oxidoreductases was measured by these procedures, and was compared with determination of steroids by gas chromatography (GC). According to HPTLC, steroids were reduced by NADPH-5 alpha-reductase (EC 1.3.1.4) in the order progesterone greater than testosterone greater than aldosterone greater than cortisol greater than corticosterone. The enzyme activities as measured by HPTLC agree well with those obtained by GC (r = 0.94). When turnover of enzyme assays, speed of determination, detection limit, application to labile steroids and costs of steroid determination are considered, all points speak in favour of HPTLC.     

Copolymerization of propylene with higher α‐olefins in the presence of the syndiospecific catalyst i‐Pr(Cp)(9‐Flu)ZrCl2/MAO

The catalyst system i‐Pr(Cp)(9‐Flu)ZrCl₂/methylaluminoxane was used for the synthesis of random syndiotactic copolymers of propylene with 1‐hexene, 1‐dodecene, and 1‐octadecene as comonomers. An investigation of the microstructure by ¹³C NMR spectroscopy revealed that the stereoregularity of the copolymers decreased because of an increase in skipped insertions in the presence of the higher 1‐olefin. The melting temperature of the copolymers, as measured by differential scanning calorimetry (DSC), decreased linearly with increasing comonomer content independently of the comonomer nature. During the DSC heating cycle, an exothermic peak indicating a crystallization process was observed. The decrease in the crystallization temperature with higher 1‐olefin content, measured by crystallization analysis fractionation, indicated a small but significant dependence on the nature of the comonomer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 128–140, 2002     

信息管理与信息资源管理及知识管理的关系

分别对IM(信息管理)、IRM(信息资源管理)、KM(知识管理)的概念及内涵进行了阐述，比较了三者的联系与区别，进而就三者的关系进行了探讨。     

The digital microscopy classroom.

This paper describes the implementation and functionality of a base-band network for the remote control of scientific instruments, in particular scanning and transmission electron microscopes. The base-band network is a hard-wired connection between keyboard and pointing devices from the remote computers to the CPU of the instrument computer; the video signal is then routed back to the remote user and to a high resolution projection system. The system is independent of software and hardware platform, and is highly reliable.     

Existence, multiplicity, and dependence on a parameter for a periodic boundary value problem

The authors consider the boundary value problem

     

Symmetric positive solutions of nonlinear boundary value problems

We study the nonlinear boundary value problem

     

A simple method for measuring surface strains around cracks

A simple system has been developed to measure surface strains that occur during in situ deformation of mechanical test specimens. The system uses photolithographically deposited displacement markers and computer image recognition routines to determine in-plane displacements and strains from digital images. The strain calculating routines are integrated into a simple mouse-driven software package that facilitates the transformation from digital images to useful strain field information. Additional routines have been developed to determine crack tip stress fields and J integrals. Crack tip stress intensities have been calculated from strain maps obtained for traction-free cracks in stainless steel. The J integrals were found to be independent of contour and consistent with applied stress intensities. Crack tip stress intensities were calculated for bridged cracks in lamellar TiAl. The toughening effect of the bridging zones was determined by including the bridged region in the contours. Resistance curves generated from strain maps were consistent with those measured during mechanical testing.     

三原西郊水库抽水试验及降水模型研究

根据三原西郊水库水文地质和工程地质情况,确定了现场单井抽水试验的抽水量测设备,设计了抽水井与观测井的布置、井的结构和成井工艺,确定了抽水试验要求,建立了降水数学模型并确定了水文地质参数。