Hygroresponsive Torsional Yarns and Actuators Based on Cascade Amplification of the Deformation

Fiber-based hygroresponsive torsional actuators provide desirable merits, such as light weight and shapeability, for developing smart systems to harvest energy from moisture which is a ubiquitous natural resource. A key challenge in this development is to realize moisture-triggered actuation combining large actuation and rapid responses. Here, a multiscale design strategy is explored to create high-performance hygroresponsive torsional actuators consisting of chitosan and multiwalled carbon nanotubes (MWCNTs). The superior actuation performance arises from the synergism of contributing factors at different scales, including 1) MWNCTs accelerate the water transport in primary twisted fibers (PTFs), fostering the rotation of PTFs upon moisture stimuli; 2) in situ-formed hierarchically-assembled twists realize cascade amplification of moisture-triggered actuation. Specifically, PTFs are self-twisted to generate secondary helical yarns, that are subsequently over-twisted to yield tertiary coiled yarn. The resultant yarn actuator can reach a maximum rotation speed of 11 400 rpm in 5 s, output gravitational potential energy of 2.4 J kg⁻¹ and gravitational potential power of 0.053 W kg⁻¹ during contraction. This work represents the first design of fiber-based actuators by virtue of moisture-triggered in situ formation of yarns. The established principles of multiscale design will enable high-performance fiber-based hygroresponsive actuators toward advanced intelligent textile and soft robotics.     

液膜法分离富集,测定水中微量锶

用乳状液膜体系对锶进行分离富集，该体系包括协同流动载体（ＰＭＢＰ，ＴＢＰ），表面活性剂（ＳＰＡＮ８０）增强剂（丙三醇）溶剂（正己烷）和内相（１．２ｍｏｌ／Ｌ的盐酸溶液），实验表明，在适宜的条件下，锶的富集效率可达９９．５％以上，而在此条件下许多共存离子，如Ｆｅ＾３＋，Ａｌ＾３＋，Ｃａ＾２＋，Ｍｇ＾２＋，Ｂａ＾２＋，Ｃｒ＾３＋，ＣＯ＾２＋，Ｎｉ＾２＋，Ｚｒ＾４＋，Ｃｕ＾２＋，Ｚｎ＾２＋，Ｐｂ＾２＋和     

Simulation studies on the fuel electrode of a H2---O2 polymer electrolyte fuel cell

The macro-homogeneous porous electrode theory is used to develop a model which describes the catalyst layer of the hydrogen electrode formed by catalyst particles that are bonded to the membrane. The water transport in the catalyst layer and polymer electrolyte membrane is considered. The effects of catalyst layer structure parameters such as polymer volume fraction, catalyst layer thickness, platinum loading and reactant gas humidity as well as CO poison on the hydrogen electrode behavior are examined. The results show that the catalyst layer thickness has a significant effect on the electrode performance. A thicker catalyst layer will result in a larger ohmic voltage loss and higher catalyst cost. The optimal polymer volume fraction and catalyst layer thickness are 0.5 and 1.5–4 μm, respectively, for this electrode. An optimal platinum surface coverage on carbon need not exceed 20% (20 wt% Pt/C). Larger platinum coverage will increase the cost, but only slightly enhance the electrode performance.     

延长大型露天矿铁路运输服务年限的浅见

大型露天矿在由山坡型转入深凹型开采后,随着运输条件的恶化,将单一的准轨铁路运输,改变为铁路—汽车联合运输,以延长铁路运输的服务年限,为此,需要解决提高电力机车运输性能、改造运输线路系统等问题。     

气刀操作条件对聚丙烯密相脉冲气力输送行为的影响

在一管线水平长１９ｍ、垂直长１１ｍ、内径５０ｍｍ的密相脉冲气力输送实验台上进行了气刀操作条件对管道输送行为影响的实验研究．结果表明：气刀操作条件对管道输送气速、输送能力、固气比、能耗等均有明显影响．确定最佳的气刀操作条件需综合考虑发送压力、输送结构、物料物性等因素．     

Investigation of transport phenomena in a hybrid ion exchange-electrodialysis system for the removal of copper ions

Hybrid ion exchange electrodialysis processes allow the removal of metal ions from dilute waste liquids and the recovery of more concentrated solutions. The work reported here was aimed at investigating the two steps in the treatment process, namely, adsorption of metal ions onto the packed bed of resin and electromigration (i.e., the transport of these ions in the complex system under the applied electrical field). The case of copper sulfate was investigated. Dowex resins with a cross-linking degree of 2 and 8% were used. The flux of copper through the resin bed and the current efficiency for ion transfer to the cathode compartment were determined as a function of potential gradient and copper ionic fraction in the bed. Apparent diffusion coefficients of Cu²⁺ in the overall system were deduced from the experimental data.     

Determination of the vapor pressures of select polychlorinated dibenzo-p-dioxins and dibenzofurans at 75-275 °C

Vapor pressures were determined for several polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) at 75-275 °C, extending the available literature data to more relevant temperature regions and providing the first experimental data for 2,3,7-trichlorodibenzo-p-dioxin (2,3,7-TriCD). A modification of the effusion technique, based upon controlling the diffusion of the target compound and subsequent high resolution gas chromatography/low resolution mass spectrometry (HRGC/LRMS) analysis, was proven comparable to other accepted methods for determining the vapor pressures of semi-volatile organic compounds (SVOCs). Vapor pressures for octachlorodibenzo-p-dioxin (OCDD) and octachlorodibenzofuran (OCDF) were in excellent agreement with those reported in literature. The application of the current method for the vapor pressure determinations of eight polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDDs/PCDFs) in the extended temperature range (up to 275 °C) is reported. The extension of the vapor pressures to such temperatures, unprecedented for the PCDDs/Fs, is important for vapor-particle partitioning modeling in regions relevant to PCDD/F formation and control. Estimates for the melting temperatures and enthalpies of sublimation and vaporization are also reported, the latter for which no experimentally determined values have been found in the literature. The use of the method to deliver reproducible, trace concentrations (ppt-ppb) of targets was applied to the calibration of the jet-REMPI/TOFMS as an online detector for low chlorinated PCDDs/Fs.     

大潮差河口闸下水流的流动特性分析

福建数座河口水闸发生剧烈淘刷,闸上游和下游的最大冲刷深度达到闸室高度的0.5~1.2倍,且屡修屡毁。有的水闸经多次除险加固后,不得不再花巨资重建。通过数学模型和物理模型揭示了河口水闸下游水位因受东海大潮差海潮影响发生剧烈波动时的变化规律,发现了水闸泄流过程中的间歇性淹没及非常工况甚至出现逆流的独特流动现象,给出了典型日孔流及堰流泄流能力动态变化过程线,分析了消能工变化对闸址水流结构的显著影响,并对水闸水毁修复前后闸下冲刷进行了预测。结果表明:水闸修复前闸下涨急最高水位4.53 m,修复后下降0.67 m,水闸修复后逆流现象减弱。修复后首次水跃位置往上游移动了35 m,平均水跃高度下降47.46%,闸后及二级池末端最大流速2.27 m/s和0.08 m/s,较修复前分别下降了40.58%和96.48%。常遇泄流条件下,水闸的淹没度和泄流能力呈现不断变化的动态过程。当西溪水闸62#先启孔全开,上游保持正常高水位3.2 m,下游为最低潮位-0.72 m时,修复后最大冲刷深度减少64.48%,消能防冲效果十分明显。研究成果对河口水闸安全运行具有一定的参考价值。     

Selective gas transport in miscible PPO-PS blends

The permeation rates of He, CO₂ and CH₄ though miscible blends of polystyrene and poly(phenylene oxide) at 35°C are reported as a function of pressure. Sorption isotherms for CO₂ and CH₄ are also presented. By using ratios of the permeabilities of the pure gases the separation factors for the gas pairs He---CH₄ and CO₂---CH₄ can be estimated. For both pairs the estimated separation factor goes through a prominent maximum, thus indicating that these blends are more permselective than expected from the behaviour of polystyrene and poly(phenylene oxide). This stems from mobility considerations rather than solubility effects and a qualitative free volume argument is proposed as an explanation. The sorption and transport data have been interpreted and correlated using the dual sorption-mobility models developed previously for glassy polymers. Since the commercial polystyrene used contained a small amount of mineral oil to improve flow behaviour, the effect of this additive on polystyrene properties was explored in some detail.