Anisotropy of hole structures in oriented polycarbonate probed by two-dimensional angular correlation of annihilation radiation

Two-dimensional angular correlation of annihilation radiation (2D-ACAR) experiments have been performed on an uniaxially oriented polymer, bisphenol-A polycarbonate. The two-dimensional hole structures of unoriented and oriented polymers, determined from the momentum distributions, are found to be spherical and ellipsoidal, respectively. The average hole radii are determined to be 2.9 Å in the unoriented sample and between 2.3 and 3.8 Å in the oriented sample. Applications of the 2D-ACAR method to image the three-dimensional hole structures of polymeric materials are discussed. © 1996 John Wiley & Sons, Inc.     

Pressure drop effects on selectivity and resolution in packed column supercritical fluid chromatography

The influence of pressure drop on retention, selectivity, plate height and resolution was investigated systematically in packed supercritical fluid chromatography (SFC) using pure carbon dioxide as the mobile phase. Numerical methods developed previously which enabled the prediction of pressure gradients, diffusivities, capacity factors, plate heights and resolutions along the length of the column were used for the model calculations. The effects of inlet pressure and supercritical fluid flow rate on selectivity and resolution are studied. In packed column SFC with pure carbon dioxide as the mobile phase, the pressure drop can have a significant effect on resolution. The flow rate is shown to have a larger effect than generally realized. The calculated data are shown to be in good agreement with the experimental results. Finally, the variation of the chromatographic parameters along a 5.5 meter long model SFC column is illustrated. The possibilities and limitations of using long packed columns in SFC are discussed. It is demonstrated that long columns with large plate numbers do not necessarily yield better separations.     

PPLT倍频宽线宽掺镱双包层光纤放大激光

分别通过理论和实验研究了周期性极化的钽酸锂（PPLT）倍频宽线宽准连续掺镱双包层光纤放大激光.PPLT样品长为40 mm,极化周期为7.67 μm.基频光的中心波长为1064 nm,线宽约为6 nm.从基频光的光谱特性出发,利用超晶格倍频理论,解释了实验中获得的倍频温度与二次谐波功率之间的关系.在基频光的功率为2.2 W时,获得的宽线宽光纤激光倍频效率为1.8%.     

环境监测实验室管理系统的开发与应用

基于2005版《计量认证/审查认可(验收)评审准则》要求,为满足环境监测实验室业务流程而设计开发了信息管理系统。该系统主要用于环境监测实验室的资源管理和日常自动化办公。系统采用B/S架构,实现全球化办公运作,能对监测样品的受理、分发、分析、原始记录、监测报告、数据三级审核、报告签发实现全程自动流转,并运用工作流和智能表单设计实现实验室程序文件中各类程序和日常办公事务流程的执行;原始记录和监测报告全部实现自动归档及智能查询;同时根据2005版准则中的要求,对人员、设备、材料、环境要素、记录、质量控制等所有要素全面实施网络化管理。     

具有生物活性的有机磷化合物的研究V.α—[（取代）芳氧基乙酰氧基]烷基膦酸

通过取代苯氧乙酰氯和α－羟基烷基膦酸酯的缩合反应合成了８种标题化合物，用元素分析，红外，核磁及质谱作了表征，测定了它们的除草活性和植物生长调节活性。     

Extraction of formic and acetic acids from aqueous solution by dynamic headspace-needle trap extraction temperature and pH optimization

A combined method of dynamic headspace-needle trap sample preparation and gas chromatography for the determination of formic and acetic acids in aqueous solution was developed in this study. A needle extraction device coupled with a gas aspirating pump was intended to perform sampling and preconcentration of target compounds from aqueous sample before gas chromatographic analysis. The needle trap extraction (NTE) technique allows for the successful sampling of short chain fatty acids under dynamic conditions while keeping the headspace (HS) volume constant. Two important parameters, including extraction temperature and effect of acidification, have been optimized and evaluated using the needle trap device. The method detection limits for the compounds estimated were 87.2microg/L for acetic acid and 234.8microg/L for formic acid in spite of the low flame ionization detection response for formic acid and its low Henry's law constant in aqueous solution. Precision was determined based on the two real samples and ranged between 4.7 and 10.7%. The validated headspace-needle trap extraction method was also successfully applied to several environmental samples.     

金属空气电池阴极氧还原催化剂研究进展

随着能源危机加剧和生态环境恶化, 可持续发展能源受到更大的重视. 金属空气电池作为一种绿色能源是具有很大发展潜力的新一代电池. 与传统电池相比, 此类电池有着更高的理论能量密度, 尤其是锂空电池, 能量密度可达3505 Wh/kg, 然而阴极缓慢的氧还原反应成为制约其发展的关键因素之一. 在简要介绍氧还原反应机理基础上, 着重介绍了近年来氧还原催化剂如贵金属及其合金、过渡金属氧化物/硫化物、功能化碳材料和金属氮化物的研究进展, 并根据目前所存在问题指出未来研究方向, 包括深入研究氧还原反应机理, 明确催化剂活性位; 研究催化剂结构等对催化活性的影响, 优化制备条件, 以提高催化活性和稳定性; 根据氧还原机理设计开发新型氧还原催化剂.     

载体表面氧化程度对Ni/SiC甲烷化催化剂性能的影响

采用等体积浸渍法制备了Ni/SiC甲烷化催化剂, 研究了SiC载体表面氧化程度对催化剂低温活性和高温稳定性的影响, 并采用热重-差示扫描量热、N₂物理吸附、傅立叶变换红外光谱、氨程序升温脱附、X射线衍射、氢程序升温还原和氢化学吸附技术对样品进行了表征. 结果表明, 随着载体氧化温度的提高, 催化剂的比表面积和镍分散度降低, 但还原性和反应稳定性提高. 未氧化载体所负载催化剂的高温稳定性最差, 其原因在于载体对镍粒子的固定作用最弱. 负载于500和700℃处理的SiC载体上的催化剂具有较好的低温活性和高温稳定性, 这是因为适度氧化后的载体能较好地分散并固定镍粒子. 900℃处理的载体因过度氧化形成了低活性的氧化层, 使负载的镍粒子变大, 因而催化剂的低温活性最差.