Effective and Green Synthesis of Methyl Pyrrole-1-carboxylate with Dimethyl Carbonate Over Solid Base

The methyl pyrrole-1-carboxylate (1-MPC) was synthesized by highly selective one-pot N-methoxycarbonylation of pyrrole with dimethyl carbonate (DMC). Solid bases were found to be effective catalysts and the formation of 1-MPC was closely related to their basicity. The in-situ FTIR indicated that the role of solid base catalysts was to activate pyrrole via the formation of O–H bond and the weakening of N–H bond, which was attributed to the interaction between pyrrole and surface oxygen anion of solid base. Furthermore, the reaction temperature and the reactants molar ratio were found to be the main factors for the improvement of pyrrole conversion.     

催化剂活性非均匀分布分析——(Ⅰ)无外扩散和幂指数动力学的情形

本文采用正态函数逼近分析的方法,讨论了活性分布宽度对球形催化剂有效因子的影响。对于具有幂指数型动力学的放热反应,活性组分集中在最佳位置处的无限薄层上可得到最大有效因子η_(max),然而,分布宽度的略微增加会使有效因子迅速降至最小有效因子η_(max)。随着β值的增加,这种现象更加显著。若活性组分以一定宽度存在于颗粒内部,那么,分布位置必须向的内侧偏移一定距离才会使催化剂有最佳有效因子。因此,为使真实催化剂具有最佳有效因子,就必须在附近对分布宽度和位置再次进行优化。     

基于铜-锡等温键合技术的圆片级气密封装

本文提出了一种新颖的基于铜-锡等温键合技术的圆片级气密封装方法。设计了多层焊环结构,并且根据理论计算和实验结果对焊料用量以及键合工艺参数进行了优化。验证实验证明该方法可以成功避免焊料层的氧化,空洞的生成以及贝壳状Cu6Sn5相的生成。利用金相分析、剪切强度和气密性检测对键合质量进行了分析,实验结果表明：优化后的Cu/Sn键合结构具有理想的键合效果,平均剪切力强度为19.5MPa,漏率约为1.9×10-9atm cc/s,达到了MIL-STD-883E表准的要求。     

Novel sulfonated polyimide ionomers by incorporating pyridine functional group in the polymer backbone

A series of sulfonated polyimides (SPIs) containing pyridine ring in the polymer backbone were synthesized by the polycondensation of 1,4,5,8‐naphthalene‐tetracarboxylic dianhydride (NTDA), 5‐(2,6‐bis(4‐aminophenyl)pyridin‐4‐yl)‐2‐methoxy benzene sulfonic acid (SDAM), and 4,4′‐diaminodiphenyl ether (ODA). Flexible, transparent, and tough membranes were obtained. Property study revealed that all the membranes displayed high thermal stability with the desulfonation and decomposition temperature higher than 290 and 540°C, respectively, as well as good mechanical property with Young's modulus larger than 1.0 GPa, maximum strength (MS) on a scale of 60–80 MPa, and elongation at break (EB) ranged from 41.79 to 75.17%. More importantly, the new materials exhibited small water uptake and excellent dimensional stability with the highest sulfonated SPI‐80 showing the maximum water uptake of 36.1%, and maximum swollen ratio of Δt = 0.038 and Δl = 0.026, respectively (Δt and Δl stands for the thickness and diameter change of the film, respectively). The high water stability exhibited by the SPI films is attributed to the formation of inner salts and/or ionic crosslinking between the sulfonic acid and pyridine functional groups, which suppresses the water uptake ability of sulfonic acid and strengthened the interpolymer chain interactions. Thus, the excellent water stability, good thermal and mechanical properties, and the technologically applicable conductivity of SPI‐80 render this material attractive for proton exchange membrane (PEM) application. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Hollow mesoporous silica sphere supported cobalt catalysts for F–T synthesis

High dispersion Co₃O₄ nano-particles supported on hollow mesoporous silica spheres (HMSS) with bimodal pore distribution were prepared by “two-solvent” technique. As-synthesized catalysts were characterized by XRD, N₂ adsorption–desorption, XPS, SEM, TEM, and H₂-TPR. The results showed that Co₃O₄ nano-particles were present inside the pore system of HMSS and the particles sizes increased with the increasing loaded cobalt content. The catalysts show good performance and high selectivity of C₅–C₁₈ hydrocarbon in F–T synthesis, which should attribute to the unique bimodal pore distribution facilitating reactants to access the active sites and to transport higher hydrocarbon products.     

纳米氧化锌微乳液制备方法研究进展

微乳液法具有操作简单、粒径可控、生成粒子的尺寸比较均匀等优点.采用微乳液法制备的纳米氧化锌具有普通氧化锌所无法比拟的光、电、磁等性能.结合国内外的研究进展,主要介绍了微乳液法制备纳米氧化锌的各反应条件的影响.表面活性剂的种类和用量、反应温度、反应物浓度比、后处理温度及时间对产物的形貌和粒径具有重要的影响,通过改变各反应参数可以实现产物从零维向一维方向的转变.     

一种简化SVPWM 控制的死区分析与补偿方法

为降低死区时间影响,提出一种简化的空间矢量脉冲宽度调制(space vector pulse width modulation,SVPWM)的电压型逆变器死区补偿方法。分析死区效应对输出电压和功率因数角的影响,通过坐标变换推导出参考向量在SVPWM各个扇区与相关向量的有效占空比,进而得到死区补偿方法,并采用DSP实验装置对补偿前后的电流波形进行对比分析。实验结果表明,该方法是正确、可行的。在高速时,补偿后的波形更接近标准波形;低速时,补偿后的波形更规则。     

超声波辅助冷冻对面团中小麦淀粉理化特性及分子结构的影响

本研究在面团冷冻的全过程和最大冰晶生成带分别施加超声波,探讨超声辅助冷冻对面团中小麦淀粉理化特性与分子结构的影响。结果显示:与未超声的冷冻对照样品相比,在最大冰晶生成带和全过程施加超声分别使得面团中小麦淀粉的峰值粘度降低了8.6%和14.5%,谷值粘度降低了17.1%和13.7%,终值粘度升高了11.3%和-3.6%;在面团的最大冰晶生成带和全过程施加超声均在一定程度上改变了小麦淀粉体系的稠度系数和抗剪切能力,分别使得淀粉的稠度系数降低了19.0%和23.3%,剪切结构恢复力提高了4.0%和7.2%。与未超声的冷冻样品相比,经过超声处理的面团中小麦淀粉相对结晶度降低,并在一定程度上降低了淀粉分子的短程有序化结构。综上,超声场的施加细化了冰晶,减缓了冷冻过程对面团中小麦淀粉内部结构的破坏,比较两种超声过程可看出,在面团冷冻的全过程施加超声的效果优于在最大冰晶生成带施加超声。     

双肽（IIb类）细菌素的结构特点及其与功能的关系

双肽（IIb类）细菌素通常是由革兰氏阳性菌产生的热稳定小分子（＜10 kDa）双组分抗菌肽,该类肽能够依靠特定模式基序介导肽-肽互作,形成具有跨膜能力的活性二聚体蛋白。大量研究表明,双肽细菌素具有可靠的安全性和理想的抑菌效果,在耐药菌控制方面有着巨大的应用潜力。因此,双肽细菌素发挥功能的结构特征与作用机制受到研究者们的广泛关注。本文按照双肽细菌素结构形成、肽-肽互作及肽-膜互作的逻辑梳理该类抗菌肽发挥抑菌作用的机制,同时综合现有研究阐述双肽细菌素的结构规律及影响其活性的结构要点,以期为双肽细菌素的相关研究提供新的思路。