Investigation of a cylindrical chemosorptive denuder for sampling and phase separation of toluene diisocyanate aerosols

A cylindrical chemosorptive denuder in series with a glass fibre filter has been evaluated for sampling toluene diisocyanate (TDI) aerosols. The sampler is designed for measuring personal exposure to diisocyanates. Several denuder coatings and derivatising reagents were investigated. Dimethylpolysiloxane (SE-30) and 5% phenyl dimethylpolysiloxane (SE-54) with either dibutylamine (DBA) or dipentylamine (DPeA) as derivatising reagents yielded the lowest vapour breakthrough (the amount (%) of the vapour that passes through the denuder), close to values predicted by theory. Immobilisation of the SE-30 denuder coating by in-situ cross-linking yielded comparable results. With an SE-30/DBA-coated denuder operating within an airflow range of 100–500 mL min^–1, the phase separation was shown to be consistent with theoretical predictions derived by use of the Gormley–Kennedy equation. This provides a means of calculating the vapour breakthrough and correcting experimentally obtained values with regard to vapour–particulate phase distribution, suggesting that the denuder can provide accurate phase-distribution measurements. The SE-30/DBA denuder can be used over a concentration range spanning nearly six orders of magnitude. Its capacity is sufficient to perform 15-min exposure measurements of a TDI aerosol with air concentrations as high as 1,700 g m^–3, 40 times higher than the Swedish occupational exposure limit (OEL). At the other end of the range, the estimated limit of detection (LOD) was less than 2 ng m^–3 for both the vapour and the aerosol phases when LC–ESI–MS–MS was used for chemical analysis.Electronic Supplementary Material Supplementary material for this article is available at     

SPME-GC-MSD for Determination of Nine Phenyl Compounds in Snow Water in Beijing China

Solid phase microextraction (SPME) then capillary gas chromatography with mass spectrometric detection have been used for determination of nine phenyl compounds in snow water in Beijing City. Headspace extraction with a fiber coated with 100 µm PDMS was used to extract the compounds. Extraction and desorption times were optimized at 8 and 2 min, respectively. Relative standard deviation (RSD) of the analytical method was found to be less than 5%. The linear range was wide and limits of detection were less than 5 ng mL⁻¹ for the nine target analytes. Several phenyl compounds at ng mL⁻¹ levels were detected in snow samples in Beijing, indicating the corresponding air pollution.     

关于Young-Laplace公式的吉布斯自由能证明

对于为论证球形液滴附加压强的Young-Laplace公式而设计的一个理想实验,有文献试图借助吉布斯自由能函数进行证明,本文给出符合这一条件的证明方法.     

基于分层采样粒子滤波的麦克风阵列说话人跟踪方法

针对噪声与混响环境下的说话人跟踪问题,本文提出了一种基于粒子滤波的麦克风阵列声源定位与跟踪方法.该方法在粒子滤波框架下,将无混响影响的语音建立信号作为观测信息,通过计算麦克风阵列波束形成器的输出能量来构建似然函数,同时考虑语音信号不同频率成分在声源定位中的作用,利用分层采样方法提高粒子的采样效率.实验结果表明,本文方法提高了说话人声源跟踪系统的抗噪声与抗混响能力.     

50GHz宽带采样电路的SPICE仿真建模

本文首先提出了一个在NTN(Nose-to-Nose)校准中实际应用的50GHz宽带采样电路的SPICE默认仿真模型;然后通过设计采样电路的模型参数,使仿真的NTN冲击响应与实际测量重构的50GHz宽带采样示波器冲击相应波形基本相似.当仿真结果和测量结果近似时,可以通过仿真试验估计出采样电路对相位误差的影响,这和实际的物理采样电路对相位误差的影响是相同的,而该误差的影响却无法用实际测量实验确定;最后研究其收敛特性从而确定正确的仿真条件,目的是确保在较宽的元件参数取值范围内,该SPICE仿真模型对参数研究具有足够的鲁棒性.     

数字音频功放处理芯片设计与实现

介绍了一种数字音频功率放大器数字信号处理的基本原理与实现方法.对整个数字音频功放的数字信号处理器的设计进行了详细介绍,并通过Xilinx FPGA工具进行了验证,利用Synopsys工具进行了完整的电路设计、仿真和版图设计.流片采用Chartered 0.35μm工艺.     

新型螯合树脂在线预富集测定海水中痕量Cd

将新型螯合树脂(XAD-H2Dz)应用于微柱现场在线采样(MFS)新技术中,实现了海水样中痕量Cd的在线原位预富集和实验室中流动注射-火焰原子吸收(FI-FAAS)系统的联机测定。采样体积为5 mL和50 mL时,检出限(3σ)分别为68和6.7 ng/L;相对标准偏差(n=7)分别为2.0%和2.6%。对国家海水微量元素标准物质GBW(E)080040和实际样品(大连老虎滩区域海水以及连云港黄海水域)中镉进行分析,均获得了满意的结果。     

基于单比特采样的IR-UWB系统采样抖动性能分析

研究了基于单比特采样接收的IR—UWB系统中采样抖动对性能的影响。论文给出了采样抖动的简化分析模型,推导了AWGN信道下全精度采样系统和单比特采样系统的误码率理论解。论文通过仿真实验验证了理论分析的正确性,并分析比较了全精度采样系统、单比特采样系统在AWCN信道与多径衰落信道下的抗采样抖动性能及其原因。     

基于马尔可夫随机场的降质光学图像预处理

文本图像等统计规律比较强的图像中存在模糊、笔划不完整等降质问题,基于文本图像在结构和统计规律等方面的特点,建立相应的马尔可夫随机场模型对其进行预处理,以进一步提高后续处理的正确率并减轻后续工作难度.该方法首先通过样本训练建立观测模型以对先验概率进行学习,然后采用模拟退火算法对模型参数优化计算,最后利用前两阶段所得模型进行未知图像处理.实验结果表明,该方法简单有效,可以取得较好的预处理效果.     

CCD类成像器件的噪声研究

CCD图像传感器的输出信号是空间采样的离散模拟信号,其中夹杂着各种噪声和干扰。对CCD信号进行处理的目的就是在不损失图像细节的前提下,尽可能地消除噪声和干扰,以提高信噪比,获取高质量的图像。为此,必须对CCD的噪声种类和特性有所了解,并针对各种噪声进行相应的去噪处理。所以对CCD成像器件噪声部分的研究,有利于提高CCD成像器件的分辨率,也能提高探测微弱光的能力。