水中高压放电的二次放电现象

通过测量水中铜丝电爆炸的电流、电压波形发现水中高压放电存在着二次放电现象.利用高速摄影拍摄了二次放电过程的高速阴影和高速扫描照片.直观的图象证实了这一奇特的放电现象的存在.比较了二次放电与一次放电的不同并简要分析了原因 关键词： 高压放电 等离子体 高速摄影     

虎杖中白藜芦醇和白藜芦醇甙的高速逆流色谱分离提纯及其分析

采用高速逆流色谱技术分离提纯中药虎杖中的活性多酚成分白藜芦醇和白藜芦醇甙。确定了样品前处理方法,选择了逆流色谱流动相体系,经高效液相色谱检验纯度,＾１ＨＮＭＲ及质谱判定结构,证实所得样品为白藜芦醇和白藜芦甙,得率分别为２．１８％和１．０７％。     

Partial Molar and Excess Volumes and Adiabatic Compressibilities of Binary Mixtures of Ethanolamines with Water

Speed of sound and densities of solutions of mixtures of seven ethanolamineswith water were measured over the full range of composition at 25, 35, and 45°C.Results of these measurements were used to calculate adiabatic compressibilities,excess volumes, partial molar and apparent molar volumes, and apparent molarcompressibilities. Knowledge of the above properties of these mixtures are abasis for understanding some of the molecular interactions in these systems. Fromthe analysis of the results, the type of interactions between the ethanolaminesand water are discussed in terms of the number and size of the alkyl groupsattached to the nitrogen atom of ethanolamine.     

A device to regulate rotational speed using a rotating regulator with electrorheological fluid

The authors propose a device consisting of a rotating regulator within an electrorheological fluid (ERF), in which the rotational speed of the rotating body can be regulated by supplying an electric field. This new type of device with ERF is relevant to engineering applications and can play a role in braking as well as in rotation regulation. The ERF used here consists of a colloidal suspension of smectite particles in a solvent. The experimental conditions are fixed in a range of comparatively small rotational speed. The authors clarified the hydrodynamic and electrical effects of the shape of the rotating disk, the kind of solvent contained in the ERF, the temperature, the electrode gap and the electric field strength on the steady characteristics of the torque, the electric current density and the electric power to a rotational speed. From the torque and rotational speed data, empirical equations were derived using nondimensional parameters for the purpose of convenient engineering design. The authors also clarified the correlation between the hydrodynamic and steady electric characteristics of the device and the transient characteristics of torque, the electric current and the rotational speed.     

Hopf分岔的代数判据及其在车辆动力学中的应用

利用Hurwitz行列式,给出平衡点失稳而发生Hopf分岔的代数判定准则和计算方法,这一方法将Hopf分岔点的求解转化为一个非线性方程的求解问题,从而克服了以前方法在计算Hopf分岔点时,对于参数的每一次变化通过求特征根并判定特征根的实部是否为零的庞大工作量。应用这一方法,我们进行了非线性车辆系统蛇行运动稳定性的研究,得到了轮对系统发生蛇行运动的临界速度的解析表达式。     

RUPTURE OF THIN METAL TUBES BY NORMAL AND OBLIQUE IMPACT OF BLUNT CONICALNOSED MISSILES: EXPERIMENTS

Impact tests at both normal and oblique angles of incidence were conducted on thin mild tubes using a moderate size of 90° conical-nosed missiles. The minimum impact speed that generated cracks through the thickness of the wall, termed the speed for rupture, was measured, and various modes of rupture were identified. For a thin tube hit by a missile at a normal angle of obliquity at the speed for rupture, the contact region spreads across the nose of the missile, and the transverse shear deformation is predominant in the final failure process. If the angle of obliquity is 30°, the missile pierces a hole through the wall of the tube. At the speed for rupture, the kinetic energy of the missile for oblique angle 30° is only about 45% that required for plugging at a normal angle of obliquity. The project sponsored by National Natural Science Foundation of China(No. 19842001, 19872048) and Scientific Research Foundation for Returned Overseas Chinese Scholars of State Education Commission and Shanxi Province of China.     

基于光谱和改进极限学习机的土壤含盐量分析

研究盐碱地的性质、组成,对于生态环境具有重要意义。传统的含盐量测定方法大多基于化学分析,因其成本高、效率低的缺点使得应用于大面积土地的可行性很低。极限学习机（ELM）作为一种基于前馈神经网络构建的机器学习系统,在许多研究中作为一种光谱处理方法被成功运用。为了改进传统的盐碱地含盐量检测方法,采用光谱学结合改进的极限学习机（ELM）模型的方法对盐碱地进行研究。根据镇赉县采集得到的62个土壤表层样本得到对应的光谱反射率和含盐量数据,提出了基于随机值改进粒子群优化算法（RVIPSO-MELM）优化的多层极限学习机模型。首先使用主成分分析提取光谱数据特征,并使用ELM算法对光谱数据建立分类模型,引入改进的粒子群优化算法以提高精度和速度。该模型结合了具有随机值的多层ELM（RV-MELM）和改进PSO算法的多层ELM（IPSO-MELM）二者的优点,在运用启发式算法搜索最优值的同时还具有随机性,提高了模型优化速度,同时以提高模型性能为目的对隐含层之间参数进行优化和选择。并且该模型可以推广到多层,对隐含层之间的参数的两种选择方法,根据经验公式计算和使用改进的启发式算法搜索,进行了提高模型性能和优化时间的讨论,实践结果表明,选择第一层参数使用改进粒子群优化算法,确定随后的隐含层之间参数选择,使用经验公式进行计算得到一种更具现实意义的方法模型。模型在进行启发式搜索最优值之前,利用蒙特卡罗方法确定一个较好的初值,使得模型能保持较高准确率的条件下,优化速度进一步提高。相比于传统方法,这种光谱分析结合ELM的模型节省时间和经济成本,有一定推广意义。     

Orthogonality catastrophe and the speed of quantum evolution in a qubit-spin-bath system

The orthogonality catastrophe (OC) of quantum many-body systems is an important phenomenon in condensed matter physics. Recently, an interesting relationship between the OC and the quantum speed limit (QSL) was shown (Fogarty 2020 Phys. Rev. Lett. 124 110601). Inspired by the remarkable feature, we provide a quantitative version of the quantum average speed as another different method to investigate the measure of how it is close to the OC dynamics. We analyze the properties of an impurity qubit embedded into an isotropic Lipkin-Meshkov-Glick spin model, and show that the OC dynamics can also be characterized by the average speed of the evolution state. Furthermore, a similar behavior of the actual speed of quantum evolution and the theoretical maximal rate is shown which can provide an alternative speed-up protocol allowing us to understand some universal properties characterized by the QSL.     

Isolation and purification of arctigenin from Fructus Arctii by enzymatic hydrolysis combined with high‐speed counter‐current chromatography

Enzymatic hydrolysis pretreatment combined with high‐speed counter‐current chromatography for the transformation and isolation of arctigenin from Fructus Arctii was successfully developed. In the first step, the extract solution of Fructus Arctii was enzymatic hydrolyzed by β‐glucosidase. The optimal hydrolysis conditions were 40°C, pH 5.0, 24 h of hydrolysis time, and 1.25 mg/mL β‐glucosidase concentration. Under these conditions, the content of arctigenin was transformed from 2.60 to 12.59 mg/g. In the second step, arctigenin in the hydrolysis products was separated and purified by high‐speed counter‐current chromatography with a two‐phase solvent system composed of petroleum ether/ethyl acetate/methanol/water (10:25:15:20, v/v), and the fraction was analyzed by HPLC, ESI‐MS, and ¹H NMR spectroscopy. Finally, 102 mg of arctigenin with a purity of 98.9% was obtained in a one‐step separation from 200 mg of hydrolyzed sample.     

Ultrafiltration liquid chromatography combined with high‐speed countercurrent chromatography for screening and isolating potential α‐glucosidase and xanthine oxidase inhibitors from Cortex Phellodendri

Cortex Phellodendri is a typical Chinese herb with a large number of alkaloids existing in all parts of it. The most common methods for screening and isolating alkaloids are mostly labor intensive and time consuming. In this study, a new assay based upon ultrafiltration liquid chromatography was developed for the rapid screening of ligands for α‐glucosidase and xanthine oxidase. The C. Phellodendri extract was found to contain two alkaloids with both α‐glucosidase‐ and xanthine oxidase binding activities and one lactone with α‐glucosidase‐binding activity. Subsequently, with the help of high‐speed countercurrent chromatography, the specific binding ligands including palmatine, berberine, and obaculactone with purities of 97.38, 96.12, and 96.08%, respectively, were successfully separated. An optimized low‐toxicity two‐phase solvent system composed of ethyl acetate/n‐butanol/ethanol/water (3.5:1.7:0.5:5, v/v/v/v) was used to isolate the three compounds mentioned above from C. Phellodendri. The targeted compounds were identified by liquid chromatography coupled with mass spectrometry and NMR spectroscopy. Therefore, ultrafiltration liquid chromatography combined with high‐speed countercurrent chromatography is not only a powerful tool for screening and isolating α‐glucosidase and xanthine oxidase inhibitors in complex samples but is also a useful platform for discovering bioactive compounds for the prevention and treatment of diabetes mellitus and gout.