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981.
982.
Polydimethylsiloxane-based permeation passive air sampler. Part II: Effect of temperature and humidity on the calibration constants 总被引:1,自引:0,他引:1
Polydimethylsiloxane (PDMS) has low permeability towards water vapour and low energy of activation of permeation towards volatile organic compounds (VOCs) when compared to many other polymers. Suitability of the material for use in permeation-type passive air samplers was tested as it theoretically should reduce uptake rate variations due to temperature changes and eliminate or reduce complications arising from sorbent saturation by water vapour. The calibration constants of a simple autosampler vial-based permeation passive sampler equipped with a PDMS membrane (Waterloo Membrane Sampler®) were determined for various analytes at different temperatures. From the data, the activation energy of permeation for PDMS towards the analytes was determined. The analytes studied belonged to various classes of compounds with wide ranging polarities, including n-alkanes, aromatic hydrocarbons, esters and alcohols. The results confirmed Arrhenius-type relationship between temperature and calibration constant and the energy of activation of permeation for PDMS ranged from −5 kJ/mole for butylbenzene to −17 kJ/mole for sec-butylacetate. Calibration constants of the samplers towards n-alkanes and aromatic hydrocarbons determined at humidities between 30% and 91% indicated no statistically significant variations in the uptake rate with changes in humidity for 9 of the 11 analytes studied. The results confirmed the suitability of the sampler for deployment in high humidity areas and under varying temperature conditions. 相似文献
983.
The introduction of genetically modified (GM) crops into the market has raised a general alertness relating to the control and safety of foods. The applicability of protein separation hyphenated to mass spectrometry to identify the bacterial enolpyruvylshikimate-3-phosphate synthase (CP4 EPSPS) protein expressed in GM crops has been previously reported [M.F. Ocana, P.D. Fraser, R.K.P. Patel, J.M. Halket, P.M. Bramley, Rapid Commun. Mass Spectrom. 21 (2007) 319.]. Herein, we investigate the suitability of two strategies that employ heavy stable isotopes, i.e. AQUA and iTRAQ, to quantify different levels of CP4 EPSPS in up to four GM preparations. Both quantification strategies showed potential to determine whether the presence of GM material is above the limits established by the European Union. The AQUA quantification procedure involved protein solubilisation/fractionation and subsequent separation using SDS-PAGE. A segment of the gel in which the protein of interest was located was excised, the stable isotope labeled peptide added at a known concentration and proteolytic digestion initiated. Following recovery of the peptides, on-line separation and detection using LC-MS was carried out. A similar approach was used for the iTRAQ workflow with the exception that proteins were digested in solution and generated tryptic peptides were chemically tagged. Both procedures demonstrated the potential for quantitative detection at 0.5% (w/w) GM soya which is a level below the current European Union's threshold for food-labelling. In this context, a comparison between the two procedures is provided within the present study. 相似文献
984.
Possible roles of passive sampling within the context of the European REACH legislation are discussed. Passive samplers can provide information on environmental concentrations, fate and behaviour of substances of concern. They can potentially replace biota in the assessment of bioavailability, having advantages including lower cost and variability, and greater repeatability and acceptability on ethical grounds. Where remedial actions (e.g., product withdrawal, replacement or redesign) may be required, wrong decisions are potentially very costly. Against this background it may be possible to develop strategies based on passive sampling that will protect the environment from potential damage whilst minimising operational costs. 相似文献
985.
基于构件的软件复用的前提之一是存在并能够找到大量可复用的构件,软件构件库是对软件构件进行管理的基础设施,其作用是对大量构件进行管理,并辅助软件开发者找到合适的构件.在构件库中,基于构件标签的分类管理是一种新型的构件信息分类管理方法,该方法使用构件标签(Tag)对构件进行管理,并支持用户通过选择标签进行构件检索,该方法能够更直接的反应构件的特性,并能够有效提高检索效率.然而,由于构件库中许多构件没有构件标签,而通过人工的方法为构件库中存在的构件资源添加标签需要耗费大量的时间和人力资源,特别是当构件数量较大时,通过人工方式为构件添加标签是难以实现的.因此本文提出了一种基于分类的构件标签自动提取方法,该方法能够根据构件描述信息自动提取构件标签.本文对基于该方法的构件标签自动提取工具的实现进行了论述,并通过实验验证了该工具的有效性. 相似文献
986.
987.
模型和视点相关性的多分辨率模型的渲染 总被引:1,自引:1,他引:0
介绍了一种基于视点相关和模型相关的混合LOD模型渲染方法.以二叉树为基本存储结构,通过变换了的长方体视景体对可视区域内场景重要部分md3模型进行裁剪,通过人物模型tag对手上的工具模型进行层次选择,同时对场景其他部分利用视点与模型距离进行模型的选择.最后解决了模型带来的"龟裂"问题.试验表明,该方法保持了场景实时绘制的逼真性和流畅性,有效地突出了场景的目的性和重要性. 相似文献
988.
Jonghun Chun Seunghak Rhee Gwangwon Kang Yongseon Moon Jongan Park 《International Journal of Communication Systems》2009,22(11):1341-1354
In this paper, we have designed an RFID reader receiver system for improving the performance of the passive Tag‐based 908.5–914 MHz RFID reader, and analyzed the system performance vis‐à‐vis frequency, reader, and tag properties. The commercial receiver system causes a loss in sensitivity because of its 24 capacitors and six inductors. To improve the overall sensitivity of the receiver, we have designed a system using a circulator, low noise amplifier (LNA) and a SAW filter. The experimental results show that the use of a circulator to separate the Tx/Rx paths eliminates interference, the LNA improves the sensitivity of the Rx module and SAW filter eliminates the noise and spurious components in the received signal. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
989.
三相交流电源供电的较大功率变频空调日益得到广泛应用,带来了三相整流器的功率校F问题。在简要分析三相单开关部分有源PFC的基础上,根据三相三线制、三相四线制供电方式的不同,提出了两种结合有源PFC技术和无源PFC技术的Buck型混合三相有源部分PFC方案,在对其工作原理进行简要分析和仿真分析的基础上,进行了实验研究,所得结果验证了所提出的三相部分PFC具有电压与电流应力小、效率高、功率因数高、直流平均电压较高的特点,各种负载下交流输入侧的各次谐波电流均满足IEC61000-3-2标准,中等负载以上时输入功率因数高达0.98。 相似文献
990.
We experimentally investigated the performance degradation due to broadband light source (BLS) polarization in wavelength-division multiplexing-passive optical network systems based on a wavelength-locked Fabry-Perot laser diode. The results showed that the BLS polarization difference between two polarization states should be less than 3 dB, and its injection power should be greater than −18 dBm for a received-power penalty of less than 1 dB. 相似文献