New solutions for charge distribution on conductor surface

In the paper, a problem of electrostatics for charge distribution on a conductor surface is analytically solved for three new particular cases of conducting surfaces with complicated shape and specified value of electrostatic potential. The exact analytical expressions for surface charge density for the bodies are obtained. All the solutions are represented in a clear view of 3D graphs. It is shown that the proposed method of electrostatic problem for conductors allows to obtain infinitely many numerical solutions for the problem but only several special cases can be solved analytically.     

Anisotropic compressive behavior of rigid PVC foam at strain rates up to 200 s−1

The elevated strain rate compressive response of closed-cell polyvinyl chloride (PVC) foam at various densities is investigated. Two loading directions, (i.e., parallel and perpendicular to foam rise direction) were considered to investigate structural anisotropy. The elevated strain rates tests (up to 200 s⁻¹) were performed using a customized drop tower device. Engineering stress/strain behavior, energy dissipation, and maximum stress capacity were obtained for each density and compared against each other. Except for the lowest density of 45 kg/m³, strain rate effects were clearly observed through increased compressive strength and plateau stress when loading in the foam rise direction. The strain rate effect is more evident at higher densities. However, no significant strain rate effect was observed when loading perpendicular to the foam rise direction. Scanning electron microscopy (SEM) analysis showed that plastic hinges are the primary deformation mechanism for PVC foam cells. An analytical model has been calibrated using the experimental results and successfully predicted the mechanical response of the foam. Shape anisotropy has been measured employing the SEM images. The analytical approach was also able to predict the foam's anisotropic mechanical response.     

北京大学分析化学系列小班阅读讨论课的教学实践

简介了北京大学化学与分子工程学院分析化学系列基础课(定量分析化学、仪器分析、中级分析化学)开展小班阅读讨论课教学的实践。     

An overview of emerging pollutants in air: Method of analysis and potential public health concern from human environmental exposure

Air pollutants are perhaps the largest cause of diseases and death in the world today. Increasing urbanization and industrialization have caused an increase in number of diverse forms and types of new pollutants, which are difficult to detect and characterize due to their stench behaviour and complex sources of production. Such pollutants have been called emerging pollutants (EPs) and their list is ever increasing. Therefore, the understanding of the method of analysis and health implication of (EPs) in air is critical to providing a more robust understanding of exposure routes, regulations and mitigation. EPs in air discussed in this study are not in any way exhaustive but limited to emerging VOCs (including acrylonitrile, 1−3-butadiene, chloroform, dichloromethane, ethylene oxides, formaldehyde, toluene, trichloroethylene, 1,4-Dioxane) and metals (arsenic, manganese, and vanadium), ultrafine particles, micro- and nano- plastics, engineered nanoparticles, diesel/black carbon and bioaerosols. Occurrence, detection and health implications of these EPs in air are still unfolding due to limited monitoring studies, lack of standard methodology and regulations. To address this knowledge gap, authors conducted an in-depth review of available information. Their spatial distribution, analytical methods and health implications are discussed including the novel coronavirus (COVID-19) as a potential EP in air. The study concluded with highlights of gaps in knowledge and suggestions to key areas for future research. This information is of general interest to environmental scientists and of specific interest to both health and sanitation workers and policymakers at private, government and international organizations.     

Analytical theory for ion transfer–electron transfer coupled reactions at redox layer–modified/thick film–modified electrodes

Electrodes modified by liquid films or plasticized polymeric membranes containing a redox species offer valuable alternatives for the study of ion transfers and bimolecular electron transfers at liquid–liquid interfaces with conventional electrode arrangements and stable interfaces. The ion-to-electron (or electron-to-electron) transducer affects the electrochemical signal, complicating the accurate analysis of experimental data. This can be reduced through the use of an electrode surface-attached redox species of well-defined electrochemical behaviour. As will be demonstrated, the voltammetry of these systems show significant deviations with respect to individual charge transfers, which must be considered for appropriate diagnosis and quantitative analysis. For this, a simple analytical theory is presented here, deducing mathematical expressions for the current–potential response, as well as for the potential difference at the two polarized interfaces, the surface excess of the redox species and the ion interfacial concentrations.     

Analytical method development and validation of anticancer agent, 5-fluorouracil,and its metabolites in biological matrices: An updated review

Abstract

5-fluorouracil (5-FU) refers to a fluorinated pyrimidine analogue that has been widely used as an anticancer agent for colon, head, and neck cancers. Detection of 5-FU and its metabolites; 5-fluorouridine and 5-fluoro-2-deoxyuridine in biological samples allows optimization of pharmacotherapy and encourages fundamental investigations of this medication. The development of accurate and reliable sample preparation, as well as analytical methods, is critical to isolate targeted analytes from complex matrices, apart from increasing detection sensitivity of analytes. With that, this paper presents a review of prior studies pertaining to chromatographic and electrophoretic methods that focused on the analysis of 5-FU and its metabolites in biological matrices such as plasma and urine. This paper concentrates on HPLC, GC and CE systems, which are the most commonly used strategies for analytical separation of 5-FU and its metabolites from samples. Detection of these antineoplastic agents at trace level demands highly sensitive and selective analytical methodologies. Application of these analytical techniques to biological matrices is reviewed with a focus on method development strategies, including types of mobile phases and background electrolytes employed in LC and CE systems.     

Theoretical investigation on submicron particle penetration through circular tubes inside a porous medium

The analytical infinite series solution of submicron particle transport in a circular tube bounded by a porous wall, such as a pinhole, is determined under the slip velocity boundary condition, and the solution is verified by using the experimental data in the previous studies for the specific cases. The results show that particle penetration rate increases with the increase of the porous parameter, the axial pressure drop, and the pinhole radius, whereas it decreases with increasing the pinhole length. The penetration rate of nano-particles are more sensitive to the variation of these parameters. However, the differences between the penetrations of particles ranging from 0.3 μm to 1 μm are not evident because the diffusion becomes weak gradually in this size range. In addition, a further comparison is performed between the analytical solution and the existing studies, and approximate expressions are presented for accurate calculation of particle penetration rate through pinholes appearing in porous materials including filter devices and masks.     

高功率半导体激光端面泵浦方形掺Nd3+离子激光晶体热形变研究

为了解决高功率半导体激光器端面泵浦激光晶体引起的热效应问题,激光晶体泵浦端面的热形变必须进行准确的计算.通过对于全固态激光器中激光晶体的工作特点分析,建立了矩形截面激光晶体热分析模型.基于热传导方程,提出了泊松方程的一种新解,并获得了矩形截面激光晶体端面热形变分布的一般解析表达式.同时讨论了半导体激光器偏心泵浦激光晶体给端面热形变带来的影响.与有限元分析方法以及其他数值分析方法相比,解析分析方法不会给计算引入任何的误差.热形变的解析分析为解决激光晶体的热效应问题以及提高激光器的性能提供了理论的依据.     

对光谱快速定量分析的探讨

通过固定光谱校准曲线,压缩光谱谱带间隙,可降低测试成本,工作效率提高1.5倍,分析质量准确可靠.     

A note on the spheroidal modes vibration of an elastic sphere in linear viscoelastic fluid

Vibration characteristics of elastic nanostructures embedded in fluid medium have been used for biological and mechanical sensing, and also to investigate materials mechanical properties. An analytical approach based on the exact theory has been developed in this paper, to establish a new accurate and simple generalized frequency equation to predict spheroidal vibration of an elastic nanosphere, in a compressible viscoelastic fluid using linear Maxwell fluid model. To demonstrate the accuracy of the present approach, a comparison is made with the published theoretical results in the literature in some particular cases, which shows a very good agreement. Thus, the obtained frequency equation can be very useful to interpret the experimental measurements of vibrational dynamics of nanospheres and can serve as benchmark solution in design of liquid sensors.