Copolymerization of styrene and norbornene with β‐diketiminato nickel/methylaluminoxane catalytic system

Styrene–norbornene (S‐N) copolymerizations were carried out using β‐diketiminato nickel complexes CH{C(CF₃)NAr}₂NiBr (Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; Ar = 2,6‐Me₂C₆H₃, 2 ) in the presence of methylaluminoxane. The influence of the comonomer feed content and polymerization temperature on the conversion and composition of the copolymers with the catalytic system was investigated. An increase in the feed ratio of S/N led to an increase in the incorporated styrene content of the resulting copolymer. NMR characterization of the copolymers generated with the catalytic systems showed that the random S‐N copolymers are produced. Differential scanning calorimetric determination of the copolymers shows higher T_g values than polystyrene, and gel permeation chromatographic measurements have shown that the copolymers possess rather narrow molecular weight distributions, suggesting that the copolymerization take place at a single active site. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and characterization of phenol‐based biaryl proton conducting polymers

Biaryl hydroxy polymers with orthogonal disposition of proton transporting ? OH moieties have been synthesized via conventional free radical polymerization. The polymers are characterized for their thermal stability and proton conductivity, and the results are compared with the corresponding styrenic hydroxy polymers. The orthogonal disposition of ? OH moieties in biaryl polymers does result in lower E_a for proton transport. However, the lower E_a values in biaryl polymers did not translate into a net increase in proton conductivity. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Application of alkoxide in catalytic transfer hydrogenation of unsaturated nitrogen compounds

Alcoholate was utilized in catalytic transfer hydrogenation of unsaturated nitrogen compounds. In the reduction of nitro compounds, oximes and imines, alkoxide was used as the promoter, with alcohol as the hydrogen source, while in the reduction of nitriles, alkoxide was used as the hydrogen source.     

Discontinuous crack-bridging model for fracture toughness analysis of nacre

Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis.     

界面态电荷对n沟6H-SiC MOSFET场效应迁移率的影响

针对界面态密度在禁带中的不均匀分布，分析了界面态电荷对n沟6H碳化硅MOSFET场效应迁移率的影响.分析结果显示，界面态电荷使n沟碳化硅器件的场效应迁移率明显降低.并给出了实验测定的场效应迁移率和反型层载流子迁移率的比值与界面态密度之间关系. 关键词： 碳化硅 界面态 反型层迁移率 场效应迁移率     

一种线性模型的精确转换方法

基于广义范德蒙矩阵的逆矩阵的计算方法,导出线性系统的连续时间模型和离散时间模型在含有重极点时的严格的直接换算关系,其结果可以直接表示为两者的分子多项式系数之间的关系,并且,对不同的调制器具有统一的转换形式.     

有机激光染料-1,4-双[5’-(2’-苯基恶唑基)]苯及其2’-(3”-取代苯基)衍生物的光性能研究(Ⅱ)

本文报导了1,4-双[5’-(2’-苯基恶唑基)]苯及其2’-(3”-取代苯基)衍生物共八个化合物,其中除母体化合物外,其余化合物至今尚未见报导。测定了它们的红外光谱、质谱、紫外光谱、荧光光谱、荧光量子产率和激光转换效率。     

神龙一号电子束质心运动测量研究

 在强流直线感应加速器中,电子束质心位置的控制是一项重要技术,要达到较好的控制效果,前提是对电子束质心位置进行准确的测量和定位。针对具有时间分辨的电子束质心位置的测量和确定,介绍了测量实验系统的建立和数据处理两个方面的研究工作。该处理方法在实际应用时能够将电子束质心位置的误差控制在1～2个像素内。用高速分幅相机以10 ns的时间间隔、3 ns的曝光时间获得了神龙一号加速器在漂移段出口处的电子束质心运动情况。结果表明：束的质心主要在半径为0.5 mm的区域内运动,束斑直径dFWHM值分别为8.4,8.8,8.5,9.3和7.6 mm,测量结果可以为束的调控提供准确参数。     

圆形复合式磁控溅射阴极设计及其放电特性模拟研究

基于二维有限元算法使用COMSOL软件对圆形复合式磁控溅射阴极的磁场进行了计算,结合Matlab优化工具箱分别采用遗传算法和模拟退火算法对圆形复合式磁控溅射阴极的结构进行优化,得到靶材利用率达到最大的最优结构.对得到的最优化磁控阴极,基于自洽粒子模拟方法,使用VSim软件对不同工况下的放电特性进行了模拟.研究发现随着磁场非平衡度的增加,阴极表面电势降落最大的位置和等离子体聚集的位置,沿着阴极表面外沿不断向阴极中心移动,阴极表面磁场的强度不断减小.随着磁场非平衡度的增加,等离子体密度先增加后减小,鞘层厚度先减小后增加,等离子体的密度和鞘层厚度不仅与磁场非平衡度有关,而且与磁场强度有关.最后根据粒子模拟的结果,对复合式磁控阴极的靶材刻蚀深度进行了研究.研究发现,在优化前后靶材的刻蚀范围从60 mm扩展至整个靶面,极大地提高了靶材利用率.