PCB图像检测中阈值化分割的研究

研究了3种目前常用的阈值选取方法对PCB图像进行了分割,并且利用最终测量精度对3种分割结果进行了评判.对PCB检测这种比较注重特征值测量的情况提出了一种能比较好的确定阈值的思路,并且做了实验研究.     

An inter-laboratory comparison study for the determination of copper and lead from the wastewater of printed circuit board manufacturing industry in Pakistan

This inter-laboratory comparison study was arranged for 28 laboratories from different public and private sector organizations in Pakistan having wastewater testing capabilities aimed at improving the quality and comparability of test results. This national inter-laboratory study was started in December 2003 and completed in July 2004. Laboratories were invited to analyze the wastewater collected from printed circuit board (PCB) industry for lead and copper contamination. The samples fulfill the criteria for homogeneity and stability as done by the reference laboratory. The results obtained from participating laboratories were analyzed in terms of Hampel Test for outliers, while the performance evaluation of the participating laboratories was done on the basis of Z-score. An assigned value derived from the participant's results was compared with a reference value provided by a reference laboratory. Overall >50% of the participating laboratories have shown good performance in this PT-program     

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.     

Gas chromatographic separation of polychlorinated biphenyls on a new apolar capillary column

Eighty one polychlorinated biphenyls (PCBs) and nineteen chlorinated pesticide standards have been analyzed on a newly developed apolar high resolution gas chromatography (HRGC) column. Emphasis was placed on the determination of PCB indicator congeners which are part of national regulations, and of toxic coplanar PCB congeners. The new column enables almost unambiguous quantification of the PCB indicator congeners (PCB 138 can be separated from both PCB 163 and PCB 164; PCB 28 and PCB 31 were also separated and no coelution was observed for PCB 52, PCB 118, and PCB 180). The new column furnished better results than CP-Sil 8 for the analysis of PCB indicator congeners in a sample of seal blubber.     

Compound-specific stable isotope analysis of organic contaminants in natural environments: a critical review of the state of the art,prospects, and future challenges

Compound-specific stable isotope analysis (CSIA) using gas chromatography-isotope ratio mass spectrometry (GC/IRMS) has developed into a mature analytical method in many application areas over the last decade. This is in particular true for carbon isotope analysis, whereas measurements of the other elements amenable to CSIA (hydrogen, nitrogen, oxygen) are much less routine. In environmental sciences, successful applications to date include (i) the allocation of contaminant sources on a local, regional, and global scale, (ii) the identification and quantification of (bio)transformation reactions on scales ranging from batch experiments to contaminated field sites, and (iii) the characterization of elementary reaction mechanisms that govern product formation. These three application areas are discussed in detail. The investigated spectrum of compounds comprises mainly n-alkanes, monoaromatics such as benzene and toluene, methyl tert-butyl ether (MTBE), polycyclic aromatic hydrocarbons (PAHs), and chlorinated hydrocarbons such as tetrachloromethane, trichloroethylene, and polychlorinated biphenyls (PCBs). Future research directions are primarily set by the state of the art in analytical instrumentation and method development. Approaches to utilize HPLC separation in CSIA, the enhancement of sensitivity of CSIA to allow field investigations in the µg L^–1 range, and the development of methods for CSIA of other elements are reviewed. Furthermore, an alternative scheme to evaluate isotope data is outlined that would enable estimates of position-specific kinetic isotope effects and, thus, allow one to extract mechanistic chemical and biochemical information.Abbreviations BTEX benzene, toluene, ethylbenzene, xylenes - MTBE methyl tert-butyl ether - PAHs polycyclic aromatic hydrocarbons - VOCs volatile compounds - PCBs polychlorinated biphenyls - CSIA compound-specific (stable) isotope (ratio) analysis - GC-IRMS, GC/IRMS or GCIRMS gas chromatography-isotope ratio mass spectrometry - GC-C-IRMS, GC/C/IRMS or GCC-IRMS gas chromatography-combustion-isotope ratio mass spectrometry - irmGC/MS isotope ratio monitoring gas chromatograph-mass spectrometry - GC/P/IRMS gas chromatography-pyrolysis-isotope ratio mass spectrometry (used for D/H) - KIE kinetic isotope effect - PSIA position-specific isotope analysis (for intramolecular isotope distribution) - SNIF-NMR site-specific natural isotopic fractionation by nuclear magnetic resonance spectroscopy     

Improvement of analytical performances of a disposable electrochemical immunosensor by using magnetic beads

A comparison of two electrochemical immunosensing strategies for PCBs detection, based on the use of two different solid phases, is here discussed. In both cases, carbon-based screen-printed electrodes (SPEs) are used as transducers in a direct competitive immunoassay scheme, where PCBs in solution compete with the tracer PCB28-alkaline phosphatase (AP) labeled for antibodies immobilized onto the solid-phase.In the standard format (called EI strategy), SPEs are both the solid-phase for immunoassay and electrochemical transducers: in this case the immunochemical reaction occurs onto the working electrode. Finally, the enzymatic substrate is added and an electroactive product is generated and detected by electrochemical measurement. In order to improve the performances of the system, a new approach (called EMI strategy) is developed by using functionalized magnetic beads as solid phase for the competitive assay; only after the immunosensing step they are captured by a magnet onto the working surface of the SPE for the electrochemical detection.Experimental results evidenced that the configuration based on the use of separate surfaces for immunoassay and for electrochemical detection gave the best results in terms of sensitivity and speed of the analysis. The improvement of analytical performances of the immunosensor based on EMI strategy was also demonstrated by the analysis of some spiked samples.     

现代电子系统的电磁兼容性设计

现代电子技术的高速发展，使电子系统广泛地应用于各个领域，而电子系统在自身对外界产生电磁干扰的同时也在受到外部电磁环境的干扰，所以电子系统的电磁兼容性的研究就显得尤为重要了，文章针对现代电子系统中存在的各种电磁干扰，分析了其产生的途径和原因，电子系统最终要形成印刷电路板(PCB)才是一个实用的系统。所以PCB设计中的电磁兼容性会对整个系统的可靠性产生很大的影响，文章对电子系统的PCB设计也提出了电磁兼容性的设计原则。     

电脑的音频系统设计

简要介绍AC‘97音频系统,对音频系统的元件选择作了详细的介绍,指出电脑音频设计的常见错误,并提出了提高音频系统音质的设计方法和途径.     

溴化环氧树脂印刷线路板热解产物的分析

在固定床反应器中惰性气氛条件下应用程序加热方法对典型的溴化环氧树脂基板进行热解试验，用气相色谱／质谱和傅里叶变换红外光谱等方法分析所收集的高沸点液体和气体产物的性质．结果表明，环氧树脂中非溴化树脂结构在热分解过程中发生O-CH2，C-C，C-N键断裂，生成苯酚，且芳香／脂肪醚．环氧树脂溴化部分的热分解中产生1或2溴苯酚，且脂肪链上包含1或2个溴原子的芳香／脂肪醚，证明了C-Br，C-C，N-CH2，O-CH2键的断裂．     

贴片机贴装印刷电路板中供料器的分配问题

供料器分配问题是贴片机贴装印刷电路板(PCB)中的一个关键问题，它直接影响贴片机生产效率的高低．针对该问题提出其优化模型，规定一种元器件只能装在一个供料器上，将各个取贴循环中的元器件集合看成一个整体，追求贴片头沿着供料槽从供料器上吸取元器件的移动时间最短．同时基于该模型给出了一种启发式的解决方法，首先将元器件分配组合成各个取贴循环的元器件集合，然后根据这些集合里元器件的贴装位置来分配供料器的位置，使贴片头同时取料的次数尽可能的多，在一台4头贴片机上的相关实验表明，该模型和方法能大幅度地降低生产时间。