Self-healing polyurethane elastomer with thermally reversible alkoxyamines as crosslinkages

To provide self-healing ability to polyurethane elastomer, alkoxyamine-based diol was synthesized and reacted with tri-functional homopolymer of hexamethylene diisocyanate (tri-HDI) and polyethylene glycol (PEG). Because alkoxyamines acted as crosslinkers of the resultant polyurethane, the thermally reversible fission/recombination of C–ON bonds in alkoxyamine moieties enabled repeated crosslinking and de-crosslinking of polyurethane chains at certain temperature and hence crack healing. Both qualitative and quantitative characterizations demonstrated that the reversibly crosslinked polyurethane was capable of re-bonding ruptured parts and restoring mechanical strength. The remendability was a function of molecular structure and compositions of the components, which can be purposely tuned according to different application demands.     

Tetrakis‐(4‐thiyphenyl)methane: Origin of a Reversible 3D‐Homopolymer

The efficient syntheses of tetrakis(thiophenol)methane and of a new poly(disulfide) hyper‐crosslinked polymer based on the former monomer are described. Controlled de‐polymerization as well as surface post‐functionalization are successfully conducted on this novel material. Direct prove of post‐functionalization is obtained through solid‐state fluorescence emission spectroscopy, and the number of unreacted thiol‐functions on the surface of the polymeric material is indirectly quantified by de‐polymerization of the post‐functionalized material.     

星形阳离子聚丙烯酰胺在不同浆料体系中的应用

研究了星形阳离子聚丙烯酰胺(S-CPAM)对不同浆料体系的助留助滤作用。结果表明,S-CPAM对漂白针叶木浆的作用效果明显优于漂白废新闻纸浆。随着作用时间的延长、体系中剪切作用的增强及pH值的升高,纸料的留着率和滤水性能均呈降低的趋势,但S-CPAM分子的支化构型对吸附后的分子重构和电荷衰减有一定阻碍作用,其在中、碱性体系中仍具有较好的助留助滤作用。     

APPLICATION OF A SYSTEMATIC APPROACH FOR DETERMINING POSSIBLE REACTION MECHANISMS: METHANOL SYNTHESIS AND ANODIC OXIDATION OF ZINC

A systematic enumeration of possible reaction mechanisms consistent with a given set of chemical species and elementary steps is useful in guiding research in heterogeneous reaction systems which are encountered in catalysis and electrochemistry. In this paper, the synthesis of methanol by catalytic hydrogenation of carbon monoxide and the anoidic oxidation of zinc in alkaline solutions are presented as two examples of the usefulness of such an approach. The technique utilized to generate the reaction mechanisms is based upon combinatorial analysis, linear algebra and the principle of microscopic reversibility.

In the case of methanol synthesis, it is shown that in addition to the two currently proposed mechanisms, there exist two alternate reaction pathways each of which involves the hydrogenation of a formyl species to form a surface methoxide. One of these mechanisms has recently been proposed for a ZnO catalyst, however there remains an additional mechanism for consideration. For the case of anodic zinc oxidation, it is shown that mechanisms which involve cathodic elementary steps are also possible. To the authors knowledge, these mechanisms have not been previously discussed in the literature.     

Movement compatibility for rotary control and circular display--Computer Simulated Test and real Hardware Test

This experiment studied strength and reversibility of direction-of-motion stereotypes and response times for different configurations of circular displays and rotary knobs. The effect of pointer position, instruction of turn direction, and control plane on movement compatibility was analyzed with precise quantitative measures of strength and reversibility index of stereotype. A comparison of results was made between a Computer Simulated Test and a Hardware Test with real rotary controls. There was consensus in the results of the two tests that strong and significantly reversible clockwise-for-clockwise (CC) and anticlockwise-for-anticlockwise (AA) stereotypes were obtained at the 12 o'clock position. Subjects' response times were found to be generally longer when there were no clear movement stereotypes. Nevertheless, differences of results were observed that while the CC and AA preferences were found to be dominant and reversible at all the planes and pointer positions in the Hardware Test, there was variation in the strength and reversibility of the two stereotypes amongst different testing configurations in the Simulated Test. This phenomenon was explained by the operating of the clockwise-for-right and anticlockwise-for-left principles, as shown in the analysis of contributions of component principles to the overall stereotype. The differences of results from the two tests were discussed with regard to simulation fidelity and it was suggested that a real Hardware Test should be used whenever possible for determination of design parameters of control panels in consideration of movement compatibility. Based on the Hardware Test, a pointer is recommended to be positioned at 12 o'clock position for check reading or resetting purpose, and the frontal plane is the best plane for positioning a rotary control with circular display. The results of this study provided significant implications for the industrial design of control panels used in man-machine interfaces for improved human performance.     

自适应数字水印中的可反向性以及相关的欺骗和对策

为进一步加强当前数字水印的安全性,对得到广泛研究的自适应水印中的可反向性问题进行了探讨.首先对水印体制进行了分类和抽象.随后基于自适应水印对植入水印和调节因子的形成没有约束的前提,对存在的可反向性和半可反向性问题,以及由此引起的反向工程攻击和半反向工程攻击进行了定义、分析和实验,指出了它们对相关数字所有权验证的干扰甚至否定作用.最后得出了对植入水印和调节因子的形成都必须进行约束的结论,指出了一些自适应技术本身的不可反向性对安全性的增强作用.让植入水印和调节因子的形成单向依赖于原始媒体,并充分利用人类感知系统,使水印体制对上述攻击具备抵抗性,增强了数字所有权验证的可靠性.     

设计稳定和可逆的锂-空气电池阴极催化剂的研究进展

锂-空气电池具有极高的理论能量密度,成为下一代最有希望的电化学能量储存技术之一。锂-空气电池的性能主要取决于空气阴极表面发生的电化学反应,因此,合理设计具有高稳定性和可逆性的阴极是实现商业化可行的锂-空气电池的关键所在。然而,传统碳基电极的不稳定性导致的副反应会限制电池容量及其循环性能,因此,需要寻找能够替代碳基电极的新型电极。本文首先结合锂-空气电池的结构和阴极反应原理,提出了目前锂-空气电池面临的挑战,然后基于碳基阴极的不稳定性分析总结了设计稳定和可逆的锂-空气电池阴极的方法,最后提出了阴极催化剂的合理设计和催化机理的深入理解对锂-空气电池阴极的性能改善起着决定性作用的观点。     

随机动态规划中的可逆性及其证明

本文在详细分析随机动态规划递推方程中产生内插缘由的基础上,提出了水资源系统方程组的可逆性的一般概念,并进行了较严格的证明,从而把余留效益内插的问题转嫁到对随机入流分布函数曲线的分级上,这样,既提高了最优解的真实性和可靠性,又提高了计算精度,且在一定程度上减少了计算机时,保证了最优解的收敛性。     

Reversible Stacking of 2D ZnIn2S4 Atomic Layers for Enhanced Photocatalytic Hydrogen Evolution

It is technically challenging to reversibly tune the layer number of 2D materials in the solution. Herein, a facile concentration modulation strategy is demonstrated to reversibly tailor the aggregation state of 2D ZnIn₂S₄ (ZIS) atomic layers, and they are implemented for effective photocatalytic hydrogen (H₂) evolution. By adjusting the colloidal concentration of ZIS (ZIS-X, X = 0.09, 0.25, or 3.0 mg mL⁻¹), ZIS atomic layers exhibit the significant aggregation of (006) facet stacking in the solution, leading to the bandgap shift from 3.21 to 2.66 eV. The colloidal stacked layers are further assembled into hollow microsphere after freeze-drying the solution into solid powders, which can be redispersed into colloidal solution with reversibility. The photocatalytic hydrogen evolution of ZIS-X colloids is evaluated, and the slightly aggregated ZIS-0.25 displays the enhanced photocatalytic H₂ evolution rates (1.11 µmol m⁻² h⁻¹). The charge-transfer/recombination dynamics are characterized by time-resolved photoluminescence (TRPL) spectroscopy, and ZIS-0.25 displays the longest lifetime (5.55 µs), consistent with the best photocatalytic performance. This work provides a facile, consecutive, and reversible strategy for regulating the photo-electrochemical properties of 2D ZIS, which is beneficial for efficient solar energy conversion.