Influence of aliphatic polycarbonate middle block on mechanical and microstructural behaviour of triblock copolymers based on poly(l‐lactide) and polycarbonate

Three different ABA‐type triblock copolymers each containing biodegradable aliphatic polycarbonate as the middle block and poly(l ‐lactide) as the outer blocks were synthesized and the influence of the methylene chain length of the aliphatic polycarbonate middle block on various properties of the triblock copolymers was evaluated. Differential scanning calorimetry and wide‐angle X‐ray diffraction studies revealed that the incorporation of the outer blocks reduced the crystallinity of the middle aliphatic polycarbonate block. Variation of methylene chain length of the middle block led to a change in morphology from spherical to cylindrical as evidenced from atomic force microscopy studies. In addition, the mechanical properties of the block copolymers showed semi‐ductile to quasi‐brittle behaviour depending upon the composition of the middle block which was also confirmed using scanning electron microscopy. Dynamic mechanical analysis of the triblock copolymers indicated that storage modulus increased with a decrease in methylene chain length. © 2018 Society of Chemical Industry     

柔性曲环吹塑型坯控制系统的研制

本文介绍了一种独立研发的柔性曲环径向壁厚控制系统，介绍了该系统的特点与研究试验情况。     

An Improved Identity-Based Ring Signcryption Scheme

Abstract

Biometrics can be defined as science by which an individual is identified through analyses of physical data and behavioral characteristics.¹ The measurement of an individual's characteristics quantifies his or her physical, behavioral characteristics. The physically unique characteristics include, but are not limited to, fingerprints, hand or palm geometry, retina or iris scans, voice or facial characteristics, keystroke patterns, and gait. These presumably unique characteristics are used, in turn, to recognize (identify), authenticate, deny, or grant access based on the individual's characteristics.     

Modal analysis of ultra-compact channel filters based on race-track photonic crystal ring resonators

A new channel drop filter (CDF) is proposed based on a race-track photonic crystal ring resonator composed of square-lattice cylindrical silicon rods in air. By using a two-dimensional finite-difference, time-domain numerical technique, the modal behavior of two representative CDFs, parallel and perpendicular, has been analyzed. The analyses include the impact of additional scatterer size, scatterer amount and their position on the performance of proposed CDFs, such as drop efficiency and quality factor (Q). For the parallel CDF, about 130 spectral Q and 99% drop efficiency can be optimally achieved at 1363?nm channel with 0.145 periodicity scatterer size, whereas for the perpendicular one, about 180 spectral Q and 99% drop efficiency can be optimally obtained at 1366?nm channel with 0.165 periodicity scatterer size. By increasing the number of scatterers, the efficiency of both configurations can be enhanced. No obvious variation is obtained by changing the scatterer position.     

Corrosion behaviour of banded microstructure within nugget of friction stir welds in AA2024-T351

Abstract

Corrosion behaviour of the banded structure known as ‘onion ring’ in the nugget of friction stir weld AA2024-T351 was investigated to find the relation to microstructure. A micro-electrochemical cell with a 50 μm diameter glass pipette tip was used for electrochemical measurements. It was found that onion rings consisted of two bands: ‘dark’ bands that contain fewer constituent particles but show extensive precipitation of S phase and ‘light’ bands that contain fewer S phase precipitates but greater numbers of constituent particles. Electrochemical results showed that the light band has more noble (less active) open circuit potential compared to the dark band. Microstructurally, this is due to the lower number of S precipitates and therefore the possibility of higher Cu solid solution within the band compared to that of the dark band.     

自动喷水灭火系统湿式报警阀组误报案例引发的思考

通过对一起自动喷水灭火系统湿式报警阀组误报案例的研究,分析了误报发生的原因,提出了防止误报应采取的措施,并对修改完善有关消防技术标准提出建议。     

带台阶的D形橡胶密封圈密封特性分析

使用有限元方法分析一种新型带台阶的D形橡胶密封圈在不同预压缩率、工质压力和结构参数下的密封特性,并将之与相同尺寸的普通D形密封圈进行对比。分析结果表明:与普通D形密封圈相比,带台阶D形密封圈在高预压缩率下能获得更好的密封效果,但使用寿命较短;在低工质压力下,带台阶D形密封圈的密封性能更优,且使用寿命较长;在高工质压力下,2种D形密封圈的密封效果基本一致,但带台阶D形密封圈的使用寿命较短;结构参数H_1/H_2(底座矩形高度与截面弧形高度比)是影响D形密封圈密封性能的重要参数,当H_1/H_2的比值为3∶1时,2种D形密封圈的综合密封性能最优。     

二阶镶拼圆管矢量接收换能器研究

文章介绍了一种二阶镶拼圆管矢量接收换能器的设计方法，获得了类偶极子指向性以及波束宽度更为锐化的类四极子指向性。利用理论计算以及有限元仿真分析了镶拼圆管的指向性以及接收灵敏度，并实际制作了二阶镶拼圆管矢量接收换能器。在消声水池的测试表明，灵敏度测试结果与有限元仿真计算结果吻合较好，镶拼圆管矢量接收换能器类偶极子指向性图-3 dB波束宽度在95°左右，类四极子指向性图-3 dB波束宽度在40°左右，二阶矢量指向性图波束宽度明显比一阶矢量指向性图波束宽度更加锐化。     

水环真空泵临界转速的计算和有限元分析

针对于水环真空泵转轴系统的临界转速问题,在综合传统算法的基础上,提出了一种新的有效的计算方法。该计算途径首先将阶梯轴通过当量直径来等效转换为等径轴,计算出其临界转速。同时将叶轮等效为均布载荷,利用叠加原理计算挠度,可计算出只有叶轮载荷下(不计轴重)的临界转速。最后运用邓克尔莱方程可计算出转轴系统的临界转速。同时运用ANSYS Workbench软件对转动机构进行模态分析,分析结果显示计算结果正确。该计算方法能很好地求解工程中阶梯轴转子系统的临界转速,特别是对于叶轮转子轴向长度较长而不宜采用集中载荷的实际情况。