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。     

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.     

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.     

碱性燃料电池Co-N/C复合催化剂的电化学性能

碳黑经过酸处理后再加入醋酸钴经氨气900 ℃热处理后, 以其制备的气体扩散电极在6 mol•L^―1 KOH溶液中对氧还原反应(ORR)的电催化性能得到大大提高. XRD物相分析表明: 碳粉中加入醋酸钴经氨气热处理生成了氮化钴(Co_5.47N). 通过极化曲线和交流阻抗方法对制备的气体扩散电极在空气中的性能进行了研究. 室温时在－0.2 V (vs. Hg/HgO)电位下, 未经处理的碳电极对氧还原基本没有电流产生; 用酸处理后的碳电极在空气中的电流密度提高到57 mA•cm^―2; 而Co-N/C复合电极在同样条件下电流密度可达170 mA•cm^―2, 交流阻抗显示氮化物的生成减小了氧还原反应的阻抗, 增强了对氧还原反应的电催化作用.     

Thermally stimulated depolarization current of novolac resin

A novolac phenol-formaldehyde resin was investigated via the thermally stimulated depolarization current, using integral and partial measurements in the temperature range from 137 to 270 K. Tow broadened peaks, assigned as Β₁, and Β₂, appeared at about 160 and 190 K. The influence of water and ¯M_n was investigated. The activation energy E_a vs. T relationship was analysed, and a search was made for compensation phenomena. The distribution of the relaxing dipolesN vs. E_a was approximated. Three different relaxation ranges were distinguished. All the motions were attributed to the rotation of the phenyl rings. The differences found are due to the heterogeneity in the resin. Contamination with water increases the polarizability, decreases the structure differences and relieves the motions in the resin. A resin with a smaller ¯M_n exhibits a higher polarizability and a decreases in structure variety.     

基于流动池的电化学二氧化碳还原研究进展

采用电化学方法将二氧化碳（CO₂）还原转化为基础化学品或碳基燃料是目前极具前景的碳资源利用新方式. 考虑到该技术未来的发展方向和大规模应用需求,人们亟需开发具有高转化效率和高稳定性的电解设备. 在本文中,作者详细介绍了现阶段发展的两种流动池的结构特点及性能优势,阐述了每种反应体系的内在局限性, 深入分析了整个反应体系所用组件（电解池、气体扩散电极、离子交换膜）对于性能的影响. 最后,针对目前该领域存在的挑战及未来发展趋势进行了总结与展望.     

He 2++ molecular ion in a strong time-dependent magnetic field: a current-density functional study

The He molecular ion exposed to a strong ultrashort time‐dependent (TD) magnetic field of the order of 10⁹ G is investigated through a quantum fluid dynamics (QFD) and current‐density functional theory (CDFT) based approach using vector exchange‐correlation (XC) potential and energy density functional that depend not only on the electronic charge‐density but also on the current density. The TD‐QFD‐CDFT computations are performed in a parallel internuclear‐axis and magnetic field‐axis configuration at the field‐free equilibrium internuclear separation R = 1.3 au with the field‐strength varying between 0 and 10¹¹ G. The TD behavior of the exchange‐ and correlation energy of the He is analyzed and compared with that obtained using a [B‐TD‐QFD‐density functional theory (DFT)] approach based on the conventional TD‐DFT under similar computational constraints but using only scalar XC potential and energy density functional dependent on the electronic charge‐density alone. The CDFT based approach yields TD exchange‐ and correlation energy and TD electronic charge‐density significantly different from that obtained using the conventional TD‐DFT based approach, particularly, at typical magnetic field strengths and during a typical time period of the TD field. This peculiar behavior of the CDFT‐based approach is traced to the TD current‐density dependent vector XC potential, which can induce nonadiabatic effects causing retardation of the oscillating electronic charge density. Such dissipative electron dynamics of the He molecular ion is elucidated by treating electronic charge density as an electron‐“fluid” in the terminology of QFD. © 2011 Wiley Periodicals, Inc. J Comput Chem, 2011