香港维多利亚港表层沉积物有机氯农药和PCBs的含量和分布

香港维多利亚港表层沉积物有机氯农药和ＰＣＢｓ的含量和分布张珞平，洪华生，庄峙厦（环境科学研究中心）自从１９８８年禁止使用ＤＤＴ以来，香港的ＤＤＴ用量逐渐减少．由于六氯苯被禁止使用，不仅做为农药，在工业中也使用六六六（ＨＣＨ）￣［１］．香港目前使用或存...     

基于TOPSIS法的电路板拆卸元器件加热方法评价

拆卸电路板上元器件所用的加热方法有热风加热、红外线加热、液体加热和激光加热.文章利用TOPSIS法比较了这几种加热方法,建立了指标评价体系和评价模型,运用三标度法确定评价指标权重,最后对这几种方案进行优先排序,结果为:液体加热>红外线加热>激光加热>空气加热.     

基于IBIS模型的仿真分析在高速服务器主板GSMB-1中的应用

阐述了基于IBIS模型的仿真分析在高速、复杂系统中的重要作用与实用性，简述了基于IBIS模型的信号完整性仿真分析的概念及其流程，并分析了一个基于IBIS模型的信号完整性仿真分析在高速服务器主板中成功应用的实例．     

PCB检测中的自动光学检测系统的设计

本文介绍了用自动光学系统检测PCB板的设计方法.主要包括AOI系统的功能,自动光学检测系统的组成及工作原理,通过自动检测来确定PCB板的质量,从而避免传统人工方式的繁琐,具有智能化的特点.     

GC-MS analysis of the PCB substitute Ugilec 141 and its occurrence in waste mineral oils

After the restrictions on production and use of PCBs, Ugilec 141, a technical mixture of dichlorobenzyldichlorotoluenes (DBDTs), has been used as a PCB substitute in hydraulic systems. In the Netherlands, the production, import and use of Ugilec 141 has been forbidden since 1988. A method has been developed for the analysis of Ugilec 141 in waste mineral oils to control waste oil import and processing. The method development was based on modification of procedures for the analysis of PCBs in oil and dioxins in fatty matrices and analysis was performed with gas chromatography with mass spectrometry. For sample clean-up, several combinations of column chromatography with activated carbon, alumina, and silica gel have been tested to obtain extracts free from matrix interferences. An internal standard of ¹³C-labeled DBDT was examined to check recoveries from the clean-up procedures. Quantification was performed by comparison with the six most abundant peaks of an external Ugilec 141 standard mixture. Validation experiments showed a linear range from 0.25 to 60 mg Ugilec 141 kg^?1 oil, a reproducibility of 3% and a limit of determination of 0.25 mg Ugilec 141 kg^?1 waste oil. The method was applied in a survey of 70 samples of waste mineral oils from producers all over the Netherlands; this revealed levels below the limit of determination and one positive sample with a concentration of 5.7±0.1 mg Ugilec 141 kg^?1 oil. In an inspection inquiry, one contaminated oil was found containing 116 ± 9 g Ugilec 141 kg^?1 oil.     

Applications of polydimethylsiloxane in analytical chemistry: A review

Silicones have innumerable applications in many areas of life. Polydimethylsiloxane (PDMS), which belongs to the class of silicones, has been extensively used in the field of analytical chemistry owing to its favourable physicochemical properties. The use of PDMS in analytical chemistry gained importance with its application as a stationary phase in gas chromatographic separations. Since then it has been used in many sample preparation techniques such as solid phase microextraction (SPME), stir bar sorptive extraction (SBSE), thin-film extraction, permeation passive sampling, etc. Further, it is gaining importance in the manufacturing of lab-on-a-chip devices, which have revolutionized bio-analysis. Applications of devices containing PDMS and used in the field of analytical chemistry are reviewed in this paper.     

基于多色集合的PCB组装优化建模方法研究

提出了一种基于多色集合理论的印制电路板(PCB)组装优化建模方法.基于多色集合(PS)的递阶结构,构建了包括PS集合层、逻辑层和数量层3个层次的集成模型框架.分别在集合层描述PCB、元件和设备的参数及其相互间的联系;在逻辑层描述各PCB组装任务的工序和设备组成;在数量层描述各PCB组装工序所组装的元件类型、数量和所需的组装时间.基于各层次模型及其相互间的映射关系,建立了多任务、多设备环境下PCB组装优化可计算模型,不仅描述了PCB组装优化问题中各种计算参数、工艺约束、资源约束等复杂的约束关系,还描述了组装过程中,元件短缺、设备故障、订单变化等不确定性影响因素,有利于实现复杂大规模PCB组装优化问题的高效求解.     

Degradation of PCB by Bacteria Isolated from Long-Time Contaminated Soil

Abstract

Four bacterial isolates belonging to the genera Pseudomonas and Alcaligenes were obtained by the enrichment method, using biphenyl as the sole carbon source, from the soil, which underwent long-time contamination with technical mixtures of PCB. Kinetics of PCB degradation by individual isolates was measured using n-hexane extraction of the cultivation media in proper time intervals and analysed by congener specific gas chromatography with electron capture detection. All isolates exhibit interesting biodegradative potential. Specific degradation of individual congeners with respect to the number and position of chlorine substituents is discussed. The influence of glucose, biphenyl and 3-chlorobenzoic acid on the PCB degradation has been assessed.     

Bioassay (CALUX) measurements of 2,3,7,8-TCDD and PCB 126: Interference effects

Interference effects in CALUX measurements were studied. 2,3,7,8-TCDD and PCB 126 solutions were added, according to an experimental design, to the genetically modified cells. CALUX responses were measured for pure solutions of each of these pollutants, for their mixtures and for successive additions where the first added pollutant is removed after 4 h and replaced by medium solution, the same pollutant or the other one. It appeared that in cases where the cells were exposed to TCDD and PCB 126 in series, additivity was obeyed. This was not the case when the pollutants were added to the cells simultaneously as these results show antagonistic effects.     

QFP结构中引脚焊缝界面端的奇异性热应力问题研究

由于引脚、印制电路板和焊接剂的热-机材料属性不同,在受到热载荷或机械载荷时,引脚焊接界面端会产生奇异性应力,有可能产生界面开裂.为了基于界面端奇异场来评价QFP结构引脚界面端力学行为,本文拟采用数值方法求解引脚焊缝任意角度尖劈界面端的应力强度系数.具体步骤为:首先,基于高次内插有限元特征分析法确定两相任意角度尖劈界面端的奇异性指数和应力角分布函数,并引入常数热应力项,获得热-机耦合奇异性应力场表达式;采用有限元分析技术和最小二乘拟合法来获得应力强度系数的数值解.文中考察了热-机材料属性对热载荷下焊接剂/印制电路板界面端应力强度系数的影响,并给出改善界面端热应力状态的建议.