Gas separation performance of 6FDA-based polyimides with different chemical structures

This work reports the gas separation performance of several 6FDA-based polyimides with different chemical structures, to correlate chemical structure with gas transport properties with a special focus on CO₂ and CH₄ transport and plasticization stability of the polyimides membranes relevant to natural gas purification. The consideration of the other gases (He, O₂ and N₂) provided additional insights regarding effects of backbone structure on detailed penetrant properties. The polyimides studied include 6FDA-DAM, 6FDA-mPDA, 6FDA-DABA, 6FDA-DAM:DABA (3:2), 6FDA-DAM:mPDA (3:2) and 6FDA-mPDA:DABA (3:2). Both pure and binary gas permeation were investigated. The packing density, which is tunable by adjusting monomer type and composition of the various samples, correlated with transport permeability and selectivity. The separation performance of the polyimides for various gas pairs were also plotted for comparison to the upper bound curves, and it was found that this family of materials shows attractive performance. The CO₂ plasticization responses for the un-cross-linked polyimides showed good plasticization resistance to CO₂/CH₄ mixed gas with 10% CO₂; however, only the cross-linked polyimides showed good plasticization resistance under aggressive gas feed conditions (CO₂/CH₄ mixed gas with 50% CO₂ or pure CO₂). For future work, asymmetric hollow fibers and carbon molecular sieve membranes based on the most attractive members of the family will be considered.     

离聚物及其用于聚合物改性的研究进展

介绍了离聚物的定义、分类及其制备方法,阐述了离聚物聚集态结构与性能的关系,并综述了离聚物在聚合物改性中发挥热稳定剂、结晶成核剂和增容剂等作用.     

动态硫化EPDM/PP热塑性弹性体的制备

研究了三元惭丙橡胶／聚丙烯（ＥＰＤＭ／ＰＰ）共混型热塑性体的配方组成,探讨了其制备工艺,测定了其力学性能和加工流动性,并研究了其对ＰＰ的增韧作用效果,结果表明,所制备的ＥＰＤＭ／ＰＰ性能与国外产品相当,且其对ＰＰ的增韧效果优于传统的ＥＰＤＭ／ＰＰ母料。     

CO2激光加热局域热固定LiNbO3光折变全息的温度影响

利用 CO2 激光加热铌酸锂 ( L i Nb O3)光折变晶体可局域固定体全息 ,但形成的温度场空间上是不均匀的。在对固定显影后空间电荷场幅度 Esc 与固定温度 Tf 的关系进行理论分析的基础上 ,通过定义局域性系数和平均空间电荷场幅度两个判据 ,来评价不同的激光加热温度场的固定效果。这种方法也适用于对其他各类边界条件的 CO2 激光加热温度场局域热固定进行分析。     

连续油管缺陷综合检测传感器的磁路设计

为了在现场能同时检测连续油管金属截面损耗缺陷 (LMA)和连续油管局部缺陷 (LF)两类磁特性完全不同的缺陷 ,做了连续油管缺陷综合检测传感器的磁路设计。传感器的励磁源选择具有较高性价比的钕铁硼永磁体NdFeB ,选用多回路励磁方式。为了获得较好的缺陷检测信号的信噪比 ,经过对磁路的理论计算和磁化曲线的分析 ,提出连续油管检测时磁场强度应选在磁化曲线的近饱和区。磁路尺寸参数设计时 ,磁轭和极靴的尺寸应尽量小 ,但又不能进入饱和区     

分子生物学的发展和相关科学仪器的进展

在基因工程,人类基因组计划,核酸测序,基因诊断,基因体外扩增技术和基因芯片等分子生物学领域中发展起来的一些科学仪器,文章描述了科学仪器与学科发展之间的关系。     

星间光通信中的APT技术及其控制系统

APT（Acquisition Pointing and Tracking）技术是星间光通信的关键技术。介绍了该技术中的扫描、捕获、指向、跟踪过程及其控制系统,重点论述了实现跟踪的困难性,相应地介绍了一种有效的扰动抑制控制系统。     

立构三嵌段聚丁二烯的合成及其加氢产物的性能

用α -甲基萘锂作为双官能团引发剂 ,通过丁二烯在环己烷中进行负离子聚合 ,达到一定转化率后 ,加入极性改性剂 ,继续聚合至结束 ,合成了不同嵌段比的 1,2 - 1,4 - 1,2立构三嵌段聚丁二烯 ,并用三异丁基铝及 2 -乙基己酸钴作为加氢催化剂 ,制备了氢化立构嵌段聚丁二烯。考察了不同极性改性剂及其用量和聚合温度对聚丁二烯微结构的影响 ,分析表征了立构嵌段聚丁二烯及氢化物。结果表明 ,当引发剂用量一定时 ,极性改性剂 /引发剂的摩尔比越大 ,1,2 -链节摩尔分数越高 ;当加入极性改性剂时 ,1,2 -链节摩尔分数随聚合温度的降低而增加 ,1,2 -嵌段的生成宜控制在 0℃ ;立构三嵌段聚丁二烯的相对分子质量分布很窄 ,且存在 2个玻璃化转变温度。氢化物的结晶度为 30 % ,为 (1-丁烯 -乙烯 - 1-丁烯 )三嵌段共聚物 ,呈现热塑性弹性体的行为 ;当其特性黏数大于 2 0dL·g-1,且聚1-丁烯的质量分数为 2 0 %～ 6 0 %时 ,其力学性能较好。     

矩形截面对称配筋钢筋混凝土偏心受压构件的四系数设计计算方法

对常用的矩形截面对称配筋的钢筋混凝土偏心受压构件 ,提出了四系数设计法 ,利用该法建立的一张设计表格可适用不同等级的钢筋和各种强度等级的混凝土 ,且可同时适用于大小偏心两种状况。从而该表格设计法是目前最简化的方法。     

Performance of ATM traffic in optical CDMA

An ATM transit switch is proposed based on direct sequence optical code division multiple access technique. No buffering is necessary to facilitate the switching. Code conversion is used instead to emulate the switching function. The switch not only provides asynchronous access to the users but also has a limited capability of dynamic bandwidth allocation. It is free from timing jitters and switching delay is significantly reduced. A look‐up table is employed in the switching and updated through network management functions. The switch provides a new approach to asynchronous cross‐connection in the ATM core network. The performance of the new switch is evaluated by a set of prime codes and modified prime codes. Copyright © 2001 John Wiley & Sons, Ltd.