用于脉冲功率装置测量的混合式高压分压器

为准确测量脉冲放电电压,提出了固液混合式高压分压器的原理与结构,并进行了标定和实验测试。用简化模型分析了分压器系统的理想响应条件,讨论了两级分压的衰减特性,提出了控制误差的方法。通过负载标定,得到分压器脉冲电压频率响应大于2.9 MHz,最长脉冲宽度40 s,分压比(或衰减系数)为2.60 kV/V,测量误差小于5%。该高压分压器具有造价低、制作易,同时适于ns到s级脉冲电压的测量等优点,可以在实验室中得到应用。     

Impurity substitution effects in BiFeO3 thin films—From a viewpoint of FeRAM applications

Impurity substitution effects in BiFeO₃ thin films are reviewed from a viewpoint of FeRAM (ferroelectric random access memory) applications, in which such characteristics as a large remanent polarization, a low coercive voltage, and excellent fatigue endurance are most important. First, it is described that substitution experiments for Bi and Fe atoms in the films have already been conducted using almost all rare earth and transition metal elements. A list of the published paper is given in a form of the periodic table of elements. Then, two typical cases, La substitution for the Bi site and Mn substitution for the Fe site, are reviewed in detail. Particular attention is paid to the role of these impurity atoms by which the ferroelectric and insulating properties of BiFeO₃ films are significantly improved. Finally, impurity effects due to substitution or co-substitution of other elements are reviewed.     

450A接触电流测试仪测试网络和数据采集的设计

本文介绍了450A接触电流测试仪关键技术内容。     

安徽电信宽带骨干传输网构建方案介绍

随着IP业务的超常规发展，传输瓶颈日渐显现出来；以安微电信骨干传输网的发展规划为例，介绍安微电信宽带骨干传输网的构建方案。     

电涡流传感器所受电磁力研究

本文研究电涡流传感器的探测线圈与电涡流之间的电磁作用力。理论计算与测量结果表明,对于某些应用电涡流传感器的灵敏装置而言,这个力的影响是不能忽略的。     

Effects of applied anodic potential and pH on the repassivation kinetics of pure aluminium in aqueous alkaline solution

The repassivation kinetics of pure aluminium have been explored in aqueous alkaline solutions as functions of applied anodic potential and pH by using an abrading electrode technique and a rotating disc electrode. The repassivation rate of the abraded bare surface of pure aluminium increased with increasing applied anodic potential in aqueous alkaline solutions, while it decreased with increasing pH. These results revealed that the growth rate of the passivating oxide film is enhanced by an applied electric field, but it is lowered due to the chemical attack by hydroxyl ions. A potentiostatic anodic current decay transient obtained from the abraded electrode surface showed a constant repassivation rate in neutral and weakly alkaline solutions. In contrast, in concentrated alkaline solutions it was observed to consist of three stages: a high repassivation rate in the initial stage due to a high formation rate of the oxide film on the abraded bare surface; a zero value of the repassivation rate in the second stage due to the dissolution of the oxide film by the attack of OH⁻; a high repassivation rate in the third stage due to a lowered dissolution rate of the oxide film. The dissolution rate of the passivating oxide film was observed to depend on the removal rate of aluminate ions from the oxide/solution interface. Received: 1 April 1998 / Accepted: 3 July 1998     

Preparative isolation of pseudolaric acids A and B,and their glucosides from the root bark of Pseudolarix kaempferi using high‐speed counter‐current chromatography

In order to provide the chemical markers for the quality control of herbal medicines, four diterpenoids, pseudolaric acids A and B (PAA and PAB), and their glucosides were isolated from the methanol extract of the Chinese herb Pseudolarix kaempferi using high‐speed counter‐current chromatography (HSCCC). The diphase solvent system was n‐hexane/EtOAc/MeOH/H₂O which was used at two ratios (5:5:5:5 and 1:9:4:6 by volume) in the separation of pseudolaric acids and their glycosides, respectively. As a result, PAA (14 mg), PAB (129 mg), PAA‐O‐β‐D ‐glucopyranoside (8 mg, PAAG), and PAB‐O‐β‐D ‐glucopyranoside (42 mg, PABG) were obtained from 0.5 g of the crude extract. Their purities were determined to be above 97% by HPLC analysis. Their chemical structures were confirmed by ¹H and ¹³C NMR analysis or HPLC comparison with the reference compounds.     

Recent progress in separation prediction of counter‐current chromatography

As a liquid‐liquid partition chromatography, counter‐current chromatography has advantages in large sample loading capacity without irreversible adsorption, which has been widely applied in separation and purification fields. The main factors, including partition coefficient, two‐phase solvent systems, apparatus, and operating parameters greatly affect the separation process of counter‐current chromatography. To promote the applications of counter‐current chromatography, it is essential to develop theoretical research to master the principles of counter‐current chromatographic separations so as to achieve predictions before laborious trials. In this article, recent progress about separation prediction methods are reviewed from a point of the steady and unsteady state of the mass transfer process of counter‐current chromatography and its mass transfer characteristics, and then it is divided into three aspects: prediction of partition coefficient, modeling the thermodynamic process of counter‐current chromatography, and modeling the dynamic process of counter‐current chromatography.     

金属有机框架(MOFs)材料在锂离子电池及锂金属电池电解液中的应用

总结了金属有机框架(MOFs)材料在锂离子电池电解液中的研究进展.通过归纳锂离子电池长期存在的一些缺陷,随后将MOFs材料作为离子筛、人造负极保护层、准固态电解质以及用来调节电解液构型,使得锂离子电池的性能得到显著提升.最后,基于MOFs材料本身的特性,还对MOFs材料在电化学储能领域中的后续应用进行了合理地前瞻性展望...     

Preparative isolation and purification of atractylon and atractylenolide III from the Chinese medicinal plant atractylodes macrocephala by high-speed counter-current chromatography

The medicinal plant Atractylodes macrocephala (Baizhu in Chinese) has been widely used in traditional Chinese medicine for energy and stomach complaints, treatment of dyspepsia and anorexia, anti-inflammation, anticancer and for increasing assimilation. A high-speed counter-current chromatography (HSCCC) method was developed for the preparative separation and purification of two main bioactive components, namely, atractylon and atractylenolide III from A. macrocephala by using light petroleum (60-90 degrees C)-ethyl acetate-ethanol-water (4:1:4:1 v/v) as the two-phase solvent system in dual-mode elution. Compared with the separation using the normal-mode elution, the dual-mode HSCCC can be achieved with shorter elution time. Atractylenolide III (32.1 mg) at 99.0% purity and 319.6 mg atractylon at 97.8% purity could be obtained from 1000 mg crude sample in a single run. The recoveries of atractylenolide III and atractylon were 95.4 and 92.6%, respectively.