纳米银对水中三价砷的催化氧化研究

纳米银由于具有优良的杀菌性能,越来越多地用到饮用水消毒等领域.其作为杀菌剂主要针对饮用水中细菌超标以及水处理膜组件中存在的膜污染（菌污染）等问题.然而,由于AgNPs具有良好的光催化活性,可能会影响水处理系统中共存无机砷[As（Ⅲ）和As（V）]的形态转化.本研究采用液相色谱-电感耦合等离子质谱联用技术（HPLC-ICP/MS）测定As（Ⅲ）和As（V）,系统考察了水相中AgNPs对As（Ⅲ）和As（V）的吸附性能,体系pH值、NOM及共存离子（以Ca²⁺为例）等环境因素以及AgNPs的粒径和包覆剂等对As（Ⅲ）形态变化的影响.结果表明,AgNPs对As（Ⅲ）不存在物理吸附,但对As（Ⅲ）的氧化具有明显的催化作用.体系pH大于7.0时,AgNPs开始呈现对As（Ⅲ）氧化的显著催化作用,NOM、Ca²⁺、光照等环境因素均在一定程度上促进As（Ⅲ）的形态转化.此外,该过程与AgNPs本身的性质密切相关,粒径越小其催化性越好,PVP/CTS包覆AgNPs对As（Ⅲ）的催化氧化反应速率常数（k＝15.82×10^－2 h^－1）为柠檬酸包覆AgNPs的2倍.最后,在实际环境水样中验证了AgNPs对As（Ⅲ）的催化氧化.以上研究结果表明,水处理系统中的AgNPs在杀菌抑菌的同时,还能够促使As（Ⅲ）向低毒As（V）的转化,为As污染的去除提供了新的思路.     

城市部分环境监测因子中铅含量的测定及与人体健康潜在关系的探讨

应用石墨炉原子吸收法测定了饮用水、地表水、酸雨、总悬浮颗粒物中铅的含量,并比较了饮用水源中可溶性铅与总铅的含量差别,探讨了以上各环境监因子中不同浓度水平的铅与人体健康的潜在关系。     

Analysis of dimensionally stable copolyimide with a low‐level residual stress

Copolyimide thin film, which has low‐level stress and stress relaxation induced by water sorption, was characterized for potential applications as an encapsulant, a stress‐relief buffer, and in interlayer dielectrics. The polyimides examined were poly(p‐phenylene pyromellitimide) (PMDA‐PDA) and poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA) as well as their random copolyimides with various compositions. These copolyimide films exhibited good combinations of physical and mechanical properties with low thermal expansion coefficients, residual stress, and moisture‐induced stress–relaxation behavior by appropriately selecting the ratios of the dianhydride component. For these polyimides, the residual stress increased in the range of −8.1–7.5 MPa, whereas stress relaxation induced by water uptake decreased in the range of 10.3–4.7 MPa with increasing BPDA contents, respectively. The major factor in determining the magnitude of the stress behavior induced by both the thermal mismatch and water uptake in films should be the morphological factors such as chain rigidity, chain orientation, crystallinity, and microvoids. Their morphological structures were examined by wide angle X‐ray diffraction and a prism coupler, and the thermal properties were measured using a dynamic mechanical thermal analyzer as well as thermomechanical analysis. Overall, the candidate for the low level stress buffer application from the PMDA/BPDA‐PDA copolyimide was the 30/70 (= PMDA/BPDA in molar ratio) copolyimide. This copolyimide showed no residual stress after curing at 400 °C and relatively insensitive stress relaxation to ambient humidity. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 796–810, 2001     

北京市固体废弃物产生的需求驱动因素研究——基于投入产出模型

基于引入废弃物产生的投入产出模型,从最终需求视角对2007、2010和2012年北京市典型固体废弃物产生的驱动因素进行实证分析.结果表明:秸秆产生的驱动因素由市内消费转变为调出,调出驱动产生的秸秆由2007年的20%增加到2012年的70%;一般工业固体废弃物产生的驱动因素主要是调出,产生的废弃物由2007年的36%增加到2012年的81%;建筑垃圾产生的驱动因素主要是投资,产生的建筑垃圾居高不下,2007年和2012年均达总量的91%;生活垃圾产生的驱动因素主要是调出和消费,其中调出驱动产生的生活垃圾由2007年的38%增加到2012年的49%,市内消费驱动产生的生活垃圾稳定在30%左右.     

单位圆周上多解析函数的Riemann边值问题(英文)

本文研究了单位圆周上具不同回子的Riemann边值问题的可解性.利用转化法,得到了可解条件和解的表达式,将现有的相同冈了的情况作为特例.     

Efficiency assessment of primary care providers: A conditional nonparametric approach

This paper uses a fully nonparametric approach to estimate efficiency measures for primary care units incorporating the effect of (exogenous) environmental factors. This methodology allows us to account for different types of variables (continuous and discrete) describing the main characteristics of patients served by those providers. In addition, we use an extension of this nonparametric approach to deal with the presence of undesirable outputs in data, represented by the rates of hospitalization for ambulatory care sensitive condition (ACSC). The empirical results show that all the exogenous variables considered have a significant and negative effect on efficiency estimates.     

关于概率论学习障碍的分析与对策

对大学生学习概率论的障碍因素进行分析,得出影响概率论学习的障碍因素包含三方面:直观能力,概率思维品质,心理因素及情感,并分析了这几方面因素,给出克服这些障碍的相应对策,以期能从根本上改进传统教学方法,更新传统教学理念.     

一维六方准晶中带三条不对称裂纹的圆形孔口问题的解析解

利用复变函数方法,通过构造保角映射,研究了一维六方准晶中带不对称三裂纹的圆形孔口的反平面剪切问题,给出了Ⅲ型裂纹问题的应力强度因子,在极限情形下,不仅可以还原为已有的结果,而且求得一维六方准晶中L裂纹问题在裂纹尖端的应力强度因子.     

1‐Factor and Cycle Covers of Cubic Graphs

Let G be a bridgeless cubic graph. Consider a list of k 1‐factors of G. Let be the set of edges contained in precisely i members of the k 1‐factors. Let be the smallest over all lists of k 1‐factors of G. Any list of three 1‐factors induces a core of a cubic graph. We use results on the structure of cores to prove sufficient conditions for Berge‐covers and for the existence of three 1‐factors with empty intersection. Furthermore, if , then is an upper bound for the girth of G. We also prove some new upper bounds for the length of shortest cycle covers of bridgeless cubic graphs. Cubic graphs with have a 4‐cycle cover of length and a 5‐cycle double cover. These graphs also satisfy two conjectures of Zhang 18 . We also give a negative answer to a problem stated in 18 .