Introduction of fluorin into PBO polymer chains: Toward higher thermal stability and lower dielectric constant

A series of novel fluorinated benzoxazole polymers (6FPBO's) with high thermal stability and low dielectric constant were synthesized by copolymerization of 1,3-diamino-4, 6-dihydroxybenzene dihy-drochloride (DAR), 1,4-benzenedicarboxylic acid (PTA) and various amount of 4'4- (hexafluoroisopro-pylidene) bis (benzoic acid) (BIS-B-AF) in the medium of polyphosphoric acid (PPA). 6FPBO fibers were then obtained via dry-jet wet-spinning technique and characterized by means of Fourier transform infrared (FTIR) spectra, thermogravimetric analysis (TGA), single fiber tensile testing machine and scanning electron microscopy (SEM). FTIR spectrum of 6FPBO fibers indicated that the fluorine groups had been incorporated into PBO molecular chains successfully. TGA curves revealed that 6FPBO fibers possessed high thermal stability just as pure PBO fibers. Moreover, dielectric constant spectrum of 6FPBO exhibited that the polymers had low dielectric constant, especially in the range of high- frequency.     

超声波合成羧甲基壳聚糖及表征

采用超声波辐射,以壳聚糖为原料、乙醇为分散介质、一氯乙酸为羧甲基化试剂合成了羧甲基壳聚糖,通过四因素三水平正交实验得出最优合成条件为：mNaOH/m壳聚糖为1．5;mclCH2COOH/m壳聚糖为1．5;反应时间2h;反应温度60℃;采用红外光谱仪、紫外-可见分光光度计、热重／差热分析仪、X射线衍射仪、扫描电镜对产物结构进行了表征．     

建设项目生命周期成本估价集成环境研究

分析了建设项目生命周期成本估价存在的困难,认为缺乏可靠的、有效的和一致的生命周期成本数据是当前生命周期成本估价理论应用的主要障碍.给出了建设项目生命周期成本数据搜集与处理的方法,在给出建设项目生命周期成本估价方法的基础上,对在不同的数据质量下估价方法的选择标准进行了论述.最后给出了建设项目生命周期成本估价的集成环境以及应用该环境计算生命周期成本的流程.     

区域对接的多目标决策模型研究

在系统目标分析的基础上,提出了系统的模型体系结构,确定了区域对接模型的目标、决策变量,及约束条件;根据模型要达到的不同日标,分别建立了3种发展方案.该模型可较好地反映局部与整体协调发展的制衡关系,为区域对接的定量研究提供了基础.     

互联电力系统未知机理低频振荡分析

近年来,我国互联电力系统多次发生低频振荡。针对南方互联电网"5.13"功率振荡,首先采用特征值分析法详细分析南方互联电网低频振荡特性,得出主要振荡模式以及发电机组参与因子和模态分布图。其次利用仿真软件PSS/E,对强相关机组的切机、三相短路故障以及原动机周期扰动分别进行时域仿真,并与实际振荡曲线进行对比。结果表明,南方电网此次功率振荡不是因为强相关机组电气侧故障,采用负阻尼机理也不能很好地解释,其产生原因可能是发电机组受原动机周期扰动有关。     

胆固醇氧化酶高产菌株的诱变选育及产酶条件优化

在对细脚拟青霉、玫烟色拟青霉、粉拟青霉、香菇、平菇、金针菇等胆固醇氧化酶产生菌初筛的基础上．选择以产酶较高的玫烟色拟青霉作为紫外诱变的出发菌株,筛选出一株相对高产突变菌株MFEC006,其酶活达到了0．5483U／mL,比出发菌株提高了154％,经8次传代培养,突变株性质稳定．对MFEC006菌株产酶条件进行优化,得出其最佳产酶条件为：pH为6．5,温度27℃,接种量10％,摇床转速180r／min．     

Fabrication of a gradient refractive index preform using laminar shear mixing

A gradient refractive index rod was successfully prepared by a new fabrication method using laminar shear mixing, and a graded index polymer optical fiber that satisfied IEEE1394b was obtained from the method. To fabricate the gradient refractive index rod, a liquid monomer mixture with a relatively low refractive index was placed in a prepared cylindrical glass reactor and a transparent polymer rod with a higher refractive index was introduced at the center of the reactor. The reactor and the polymer rod were then rotated concurrently with a small rotating speed difference to generate a Couette flow in the liquid phase. The centrifugal force generated by rotation and the polymer diffusion into the liquid monomer mixture developed a graded concentration profile in a radial direction. The Couette flow could reduce the concentration fluctuation in a tangential direction. In addition, the graded index profile could be controlled by the copolymer composition of the rod and its diameter. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 95: 1100–1104, 2005     

水性聚氨酯胶粘剂改性研究进展

简要介绍了水性聚氨酯胶粘剂的特点,综述了几种改性方法,指出了目前水性聚氨酯胶粘剂所存在的问题,并展望了其发展趋势。     

LTE-A网络端到端通信安全模型的研究与设计

以LET-A网络为基础的D2D通信,既能为吞吐量、能源消耗、交通卸载等提供便利,还能为象局域网广告等新商业服务.基于这些原因,D2D通信在学术与工业团体中已逐渐成为热门话题.然而,目前多数研究工作主要集中于结点发现、无线资源管理等应用方面,很少涉及安全方面.针对安全架构、相关威胁及需求,采用现存的安全机制,提出一种可行的解决方案.     

计算机网络安全漏洞及防范措施解析

计算机网络的运行中,安全漏洞成为系统遭遇恶意攻击的主要途径,加强对计算机网络安全漏洞及防范措施的研究是十分重要的.对计算机网络安全漏洞的种类、计算机网络安全漏洞的成因及计算机网络安全漏洞的防范措施进行了分析和探讨.