Comparative analysis on homogeneity of Pb and Cd in epoxy molding compounds

Reference materials for quantitative determination of regulated heavy metals, such as Pb and Cd in electronic components, were designed and investigated in terms of stability and homogeneity. Reference materials with two concentration levels of heavy metals were prepared by spiking Pb and Cd compounds to epoxy molding compounds made by mixing silica powders and epoxy resin. The concentration changes of the reference materials during stability test for 1 a were not observed. In the homogeneity assessment, the as-prepared reference materials were studied by using three different analytical tools, inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray fluoroescence spectrometry (XRF) and laser ablation ICP mass. The results show different homogeneities by the characteristics of analytical tools and the materials.     

永磁磁共振成像装置主磁体设计方法研究

针对小动物磁共振成像分析仪,进行双柱型永磁小磁体的设计,要求静磁场强度为0.5 T,磁场不均匀度小于25×10-6.考虑磁路漏磁情况及磁阻现象,采用磁路设计中常用的磁路方法,进行永磁磁体结构的初始设计;利用有限元方法对初始的模型进行磁场数值分析;改变匀场环的形状和尺寸,观察空隙中磁力线的走向改变,分析匀场环的改变对成像区磁场均匀度的影响.利用Ansys有限元软件对匀场环的尺寸进行了优化计算,当匀场环内径大约为外径的1/3时,成像区不均匀度提高一个数量级.结果表明永磁磁体的磁路设计方法和有限元数值计算合理,可以满足成像要求.     

以生态学的观念看经济全球化

分析了经济全球化中的同质性和异质性 ,用生态学的观点阐述了同质性存在的问题 ,并提出了在经济全球化的大环境中如何保持异质性、保护经济安全的方法     

Cathodoluminescence in transmission electron microscopy

We describe a cathodoluminescence spectrometer that is attached to an analytical transmission electron microscope. After a brief consideration of the set‐up and the peculiarities of recording spectra and of mapping defect distributions in panchromatic and monochromatic cathodoluminescence, we discuss two examples of applications. Emphasis is placed on the potential for obtaining novel information about materials and processes on a microscopic and a nanoscopic scale by combining cathodoluminescence with the structural and chemical information for the same site of the specimen. We select an example concerning the role of In distribution in light emission from InGa/GaN quantum wells and a second one concerning the analysis of the initial electron radiation damage of Cu(In,Ga)Se₂ photovoltaic films.     

Transient Characteristics of Thermal Conduction in Dispersed Composites

The effective thermal conductivity of dispersed composites with a hot-melt-adhesive matrix, measured using the steady-state method, is compared with the apparent thermal conductivity calculated from the average heat capacity and from the thermal diffusivity measured by the laser-flash method. The transient effect has been observed obviously at higher volume percentages for various dispersed particle sizes and ratios of the thermal conductivity values of dispersed and continuous phases. All of the experimental results are compared with those calculated by existing models and by the finite element method (FEM). An attempt has been made to show how the criterion for the homogeneity of dispersed composites under transient conditions is affected by the percentages of dispersed phase, dispersed particle size, and ratio of the thermal conductivity values of dispersed and continuous phases.     

Homogeneity of member personality and its effect on group problem-solving.

The capacity to solve problems was studied in 2 groups, one composed of Ss with similar personalities (as measured by the Guilford-Zimmerman Tempermant Survey), the "homogenous" group, and a "nonhomogenous" group. Several aspects of the solution were studied with the result that "The degree of homogeneity of personality of the members of the groups used in this study was seen to have a direct bearing on the effectiveness of the groups in producing solutions to problems," and "The results imply that a multiplicity of perceptions of a problem are productive of creative solutions." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

原子荧光法检验小白菜中砷制样均匀性不确定度的评定

为探索食品检验制样均匀性对检测结果分散性的影响,以原子荧光法检测小白菜中砷为例,采集了一组四分取样过程中取舍的样品并测得其数据,用单因素方差分析法检验出样品间的均匀性存在差异,算得其相对不确定度为10-2量级,此量级与常占主要地位的曲线拟合浓度的不确定度、回收率及方法偏差不确定度的量级相当。表明制样均匀性不确定度是非均匀性食品样品测量不确定度的主要来源之一,在评估非均匀性食品样品测量不确定度时不可忽视制样环节均匀性的影响。     

Tailoring the chemical heterogeneity of Mn-modified 0.75BiFeO3-0.25BaTiO3 ceramics for piezoelectric sensor applications

The Mn-modified 0.75BiFeO₃-0.25BaTiO₃ (75BFBTMn) piezoelectric ceramic possesses a high depolarization temperature of 500 °C and a large piezoelectric coefficient of 110 pC/N, showing the potential for high temperature piezoelectric sensors. However, 75BFBTMn ceramic usually suffers dielectric degradation and abrupt drop of piezoelectric coefficient in the range of 300 °C to 500 °C. Combined the high-energy synchrotron X-ray diffraction analysis with Backscatter-SEM results, it is demonstrated that the electrical thermal instability is owing to the existence of chemical inhomogeneity. The Air-annealing treatment is able to decrease the volume fraction of pseudo-cubic phase and the lattice distortion, removes the chemical inhomogeneity in the grain and free Bi₂O₃ at grain boundary, and then eliminates dielectric anomalies and piezoelectric degradation with temperature. These results indicate that air-annealing is a simple but effective method to eliminate the chemical inhomogeneity in 75BFBTMn ceramics, thereby improving the property thermal stability for high temperature piezoelectric sensor applications.     

Mechanics-aided digital image correlation for the investigation of piezoelectric and ferroelectric behaviour of a soft PZT

The strain response of a polarised PZT was characterised using Digital Image Correlation (DIC). The DIC algorithm is based on a global approach and regularises the displacement field using the balance equations of solid mechanics. The measurement error is reduced by correcting the displacements that are mechanically not admissible. A ferroelectric test showed that the standard deviations of strain fields remain mostly under 1.2 × 10^?4 for an element size of 64 px. The standard deviation on the average value is 3 × 10^?6. The strain field is homogeneous and its average value is consistent with the strain obtained from a CCD laser measurement device. The longitudinal strain, transverse strain and polarisation response of the PZT were measured for bipolar and unipolar loadings ranging from 50 to 5000 V/mm. Material properties were extracted from these measurements. This work shows the advantages of a novel 2D-DIC algorithm for piezoelectric strain characterisation.     

On simple scheme of finite/fixed-time control design*

ABSTRACT

Control laws are designed for stabilisation of a chain of integrators of arbitrary degree in finite and fixed time. Presented control laws are obtained with use of Lyapunov function method and homogeneity concept. The present analysis is based on use of explicitly defined Lyapunov function that is the hallmark with respect to similar works. This analysis allows to get simple procedure of parameters tuning and obtain new estimates for settling-time function. The theoretical results are supported by numerical examples.