Review of size effects in micro electrical discharge machining

Electrical discharge machining (EDM) is one of the most promising non-traditional micro-scale machining methods. Because several operating parameters that are insignificant in macro EDM cannot be neglected during micro EDM process, models derived from the macro EDM process may be inappropriate at the micro scale. This paper contains a comprehensive review of size effects in traditional micro-machining and characteristics specific to micro EDM compared to macro EDM techniques. The very concept of size effects in micro EDM is thoroughly defined and three categories of effects are presented: material microstructure, processing parameter and thermal conduction size effects. Future potential research directions on the subject are also summarized. We assert that careful research and precise attention must be given to size effects in micro EDM. Size effect information especially benefits the machining speed and machining precision of micro EDM.     

Simple size-controlled fabrication of Zn2SnO4 nanostructures and study of their behavior in dye sensitized solar cells

Zn₂SnO₄ nanostructures were obtained via facile and rapid co-precipitation approach in presence of amines with different long chain as a novel basic and capping agents. The effect of different amines such as NH₃, ethylenediamine, triethylenetetramine, tetraethylenepentamine on the size of Zn₂SnO₄ nanostructures were investigated. The results demonstrated that applying the appropriate amount of organic amine could be effective in particle size control. The obtained nanostructure products were specified by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectra, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX) and ultraviolet–visible (UV–vis) spectroscopy. Dye sensitized solar cells (DSSC) were created by the constructed electrodes as working electrode and then were studied by current density–voltage (J–V) curve. It was found that incorporating of TiO₂ nanoparticles to optimized Zn₂SnO₄ nanostructures has significant role on the constructed DSSCs photovoltaic properties.     

8位高速低功耗流水线型ADC的设计技术研究

采用7级子ADC流水线结构设计了一个8位80MS/s的低功耗模数转换电路。为减小整个ADC的芯片面积和功耗,改善其谐波失真和噪声特性,重点考虑了第一级子ADC中MDAC的设计,将整个ADC的采样保持电路集成在第一级子ADC的MDAC中,并且采用逐级缩放技术设计7级子ADC的电路结构,在版图设计中考虑每一级子ADC中的电容及放大器的对称性。采用0.18μm CMOS工艺,该ADC的信噪比（SNR）为53dB,有效位数（ENOB）为7.98位,该ADC的芯片面积只有0.56mm2,典型的功耗电流仅为22mA。整个ADC性能达到设计要求。     

12位逐次逼近模数转换器关键设计技术研究

采用逐次逼近方式设计了一个12位的超低功耗模数转换电路。为减小整个ADC的芯片面积、功耗和误差,提高有效位数,对整个ADC的采样保持电路结构进行了精确的设计,重点考虑了其中的高精度比较器电路结构;对以上两个模块的版图设计进行了精细的布局。采用0.18μmCMOS工艺,该ADC的信噪比（SNR）为72dB,有效位数（ENOB）为11.7位,该ADC的芯片面积只有0.36mm2,典型的功耗仅为40μW,微分非线性误差DNL小到0.6LSB、积分非线性误差INL只有0.63LSB。整个ADC性能达到设计要求。     

Bioanalytical and chemical assessment of the disinfection by-product formation potential: Role of organic matter

Disinfection by-products (DBP) formed from natural organic matter and disinfectants like chlorine and chloramine may cause adverse health effects. Here, we evaluate how the quantity and quality of natural organic matter and other precursors influence the formation of DBPs during chlorination and chloramination using a comprehensive approach including chemical analysis of regulated and emerging DBPs, total organic halogen quantification, organic matter characterisation and bioanalytical tools. In vitro bioassays allow us to assess the hazard potential of DBPs early in the chain of cellular events, when the DBPs react with their molecular target(s) and activate stress response and defence mechanisms. Given the reactive properties of known DBPs, a suite of bioassays targeting reactive modes of toxic action including genotoxicity and sensitive early warning endpoints such as protein damage and oxidative stress were evaluated in addition to cytotoxicity. Coagulated surface water was collected from three different drinking water treatment plants, along with reverse osmosis permeate from a desalination plant, and DBP formation potential was assessed after chlorination and chloramination. While effects were low or below the limit of detection before disinfection, the observed effects and DBP levels increased after disinfection and were generally higher after chlorination than after chloramination, indicating that chlorination forms higher concentrations of DBPs or more potent DBPs in the studied waters. Bacterial cytotoxicity, assessed using the bioluminescence inhibition assay, and induction of the oxidative stress response were the most sensitive endpoints, followed by genotoxicity. Source waters with higher dissolved organic carbon levels induced increased DBP formation and caused greater effects in the endpoints related to DNA damage repair, glutathione conjugation/protein damage and the Nrf2 oxidative stress response pathway after disinfection. Fractionation studies indicated that all molecular weight fractions of organic carbon contributed to the DBP formation potential, with the humic rich fractions forming the greatest amount of DBPs, while the low molecular weight fractions formed more brominated DBPs due to the high bromide to organic carbon ratio. The presence of higher bromide concentrations also led to a higher fraction of brominated DBPs as well as proportionally higher effects. This study demonstrates how a suite of analytical and bioanalytical tools can be used to effectively characterise the precursors and formation potential of DBPs.     

小户型设计研究

本文通过对中国小户型现状及政策背景的归纳分析,得出保障性住房供应结构将从以售为主向租售并举、以租为主转变,小户型将成为主流这一结论。文章在分析国内外小户型案例以及我国现存小户型不足之处的基础上,以国家政策与人的根本需求为指导,探索小户型设计的基本原则及处理手法。在保证结构无大变动的情况下,分别从平面以及空间两个方面进行设计,满足1代至3代人居住的不同需求。对细节设计及组合体设计进行深入研究,最终提出实现产业化、标准化、工业化、单元化的拼接,从根本上降低公租房成本,这一主要结论与观点。     

XK719数控铣床的结构尺寸优化

为了能够有效地提高数控铣床整机的静动态特性,以XK719数控铣床整机结构为研究对象,利用有限元分析方法对整机进行了建模、分析与优化。首先,对数控铣床的整机结构进行了谐响应分析,分析结果表明:该型号数控铣床的第1阶、第2阶固有频率分别为38和48 Hz,低阶频率偏低。其次,对整机各主要零部件的壁厚进行了灵敏度分析,找出对结构质量和第1、2阶固有频率影响较大的关键尺寸。然后,以质量和第1阶、第2阶固有频率为目标函数,以关键尺寸作为相应的设计变量进行尺寸优化。结果表明:在整机的质量基本不变的情况下,达到第1阶固有频率提高了11%,第2阶固有频率提高了12%的优化结果。该设计方法能够为整机的快速设计提供参考。     

Evaluation of Tensile and Fatigue Properties of Metals Using Small Specimens

Small specimens are increasingly being used in getting mechanical properties directly when there are limited materials to facilitate standard specimens, which play a great role in the rapid measurement of mechanical properties and residual life assessment of in-service reactor components. Although tensile and fatigue properties of the small specimens are investigated extensively, theoretical models for describing the mechanical properties of small specimens need to be established. Here, we conduct a systematic investigation of tensile and fatigue properties of pure Cu specimens with thicknesses ranging from 3 to 0.2 mm. The results show that the decrease in uniform elongation of the 0.2 mm-thick specimens is mainly due to the effects of grain boundary and free surface on the strain hardening rate. A modified theoretical model correlated with the ratio of the surface grain layer thickness to the grain size is proposed to predict variation in yield strength of the small specimens more accurately. Furthermore, the mechanism for the difference in fatigue life between the 0.2 mm-thick specimen and other thicker specimens is elucidated. The Basquin equation-based model is presented as a potential way to evaluate the fatigue life of metals using small specimens.