Salt effect on molecular orientation at air/liquid methanol interface

The salt effects on molecular orientation at air/liquid methanol interface were investigated by the polarization-dependent sum frequency generation vibrational spectroscopy(SFG-VS). We clarified that the average tilting angle of the methyl group to be u = 308 58 at the air/pure methanol surface assuming a d-function orientational distribution. Upon the addition of 3 mol/L Na I, the methyl group tilts further away from the surface normal with a new u = 418 38. This orientational change does not explain the enhancement of the SFG-VS intensities when adding Na I, implying the number density of the methanol molecules with a net polar ordering in the surface region also changed with the Na I concentrations. These spectroscopic findings shed new light on the salt effects on the surfaces structures of the polar organic solutions. It was also shown that the accurate determination of the bulk refractive indices and Raman depolarization ratios for different salt concentrations is crucial to quantitatively interpret the SFG-VS data.     

Surface of room temperature ionic liquid [bmim][PF6] studied by polarization- and experimental configuration-dependent sum frequency generation vibrational spectroscopy

Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface.     

Chemical equilibrium controlled synthesis of polyoxymethylene dimethyl ethers over sulfated titania

The chemical equilibrium and reaction kinetic behavior in the synthesis of polyoxymethylene dimethyl ethers(DMMn) were investigated over sulfated titania in order to reveal the decisive factor controlling the reaction. The results showed that the molar ratio of adjacent DMMn products in equilibrium solution had the same value, which depended absolutely on the reaction temperature. Meanwhile, the reactions had the same DMMn products distributions under varied reaction conditions. The equilibrium constants of the related step-wise reactions for DMMn formation were equal, which were calculated based on the bulk compositions of the reaction solution. And thus, the selectivity to DMMn was mainly controlled by the chemical equilibrium, i.e., thermodynamic control. In brief, the present results provide some guidance for future synthesis of DMMn.     

Direct synthesis of propylene carbonate from propylene and carbon dioxide catalyzed by quaternary ammonium heteropolyphosphatotungstate–TBAB system

In this paper,we have developed a highly efficient method for the direct preparation of propylene carbonate from propylene and carbon dioxide(CO2) using quaternary ammonium heteropolyphosphatotungstate–quaternary ammonium halide catalytic system with anhydrous hydrogen peroxide as an oxidant through one-pot two-step process.The effects of the amount of tetrabutylammonium bromide(TBAB),the concentration of hydrogen peroxide and other reaction conditions were investigated.The catalyst system gave an optimum propylene oxide yield(91%) at75°C in oxidation step and the highest propylene carbonate yield(99%) at 140°C and 3.0 MPa in cycloaddition step.Based on the results,a reaction mechanism has been proposed.     

EFFECTS OF FINELY DISPERSED METALLIC PALLADIUM ON MICROSTRUCTURE AND PROPERTIES OF NANOCOMPOSITES PRODUCED BY SOL-GEL TECHNIQUE

Nanosized palladium particles were incorporated into mesoporous silica matrix to obtain nanocomposites using the sol-gel technique. Effects of the finely dispersed metallic palladium on the microstructure and properties of the nanocomposites were investigated. By means of X-ray diffraction and optical absorption, it was found that palladium particles were 5-9 nm in diameter and their uniform dispersion in the mesoporous silica depended on both the content of the palladium and the structural features of the silica matrix. The results showed that the mixing method of preparation led to wider size distribution of the nanosized particles as compared to the immersion method, but dispersed degree was reduced. Although the incorporation of nanosized palladium particles could not substantially induce significant structural changes of the matrix, the apparent red-shifted optical absorptions for the nanocomposites were observed as compared to the parent monolithic silica, particularly with increase in palladium loading and calcination temperature.     

基于拓扑描述函数的连续体结构拓扑优化方法

提出了一种利用拓扑描述函数(TDF)作为拓扑设计变量求解连续体结构拓扑优化问题 的新方法. 优化问题的目标函数是结构的整体柔顺性，约束条件为对于可利用材料的体积限 制. 这种方法不仅可以消除拓扑优化中经常出现的棋盘格式等数值不稳定现象，而且能够有 效地抑制传统算法处理此类优化问题时所引发的边界扩散效应. 与其它的基于水平集描述函 数的拓扑优化方法相比，所提出的算法不仅无需求解控制水平集函数演化的双曲守恒方 程，而且合理地考虑了目标函数的拓扑导数信息，因而使得算法的计算效率有了显著的提高.     

SYNTHESIS AND CHARACTERIZATION OF SURFACE-HYPERBRANCHED MAGNETITE NANOPARTICLE FOR BOVINE SERUM ALBUMIN IMMOBILIZATION

A hyperbranched polyamidoamine polymer was synthesized on the surface of magnetite nanoparticles to enhance bovine serum albumin (BSA) immobilization efficiency. The amount of immobilized bovine serum albumin (BSA) on the surface-hyperbranched magnetite nanoparticle was up to 2.5 times as much as that of magnetite nanoparticle modified with only amino silane.     

坡面流及土壤侵蚀动力学（II）——————土壤侵蚀

介绍了坡面土壤侵蚀的基本特征和主要类型, 综述了坡面土壤侵蚀动力学过程和预报模型等方面的研究进展, 包括土壤表层结皮、雨滴溅蚀、片流侵蚀、细沟侵蚀、坡面流输沙、土壤侵蚀界限坡度, 以及土壤侵蚀预报模型等. 并简要讨论了土壤侵蚀动力学研究的发展趋势.     

双周期圆截面纤维复合材料平面问题的解析法

结合双准周期Riemann边值问题理论与Eshelby等效夹杂原理，为双周期圆截面纤维复合材 料平面问题发展了一个实用有效的解析方法，获得了问题的全场级数解并与有限元结果进行 了比较. 该方法为非均匀材料的力学性质分析和复合材料等新材料的微结构设计提供了 一个有效的计算工具，也可用来评估有限元等数值与近似方法的精度.     

冲击速度和磨粒粒度对FeCrAl/WC复合涂层冲蚀性能的影响

采用粉芯丝材作为原料,利用高速电弧喷涂技术制备了具有良好抗高温冲蚀磨损性能的FeCrAl/WC复合涂层;考察了650℃下冲击速度和磨粒粒度对复合涂层高温冲蚀磨损性能的影响.结果表明,复合涂层和20G锅炉钢的耐高温冲蚀磨损能力随着磨粒粒度的增加而有所提高;30°攻角下冲蚀率随磨粒粒度的变化速率比90°攻角下的小;同20G锅炉钢相比,复合涂层对速更加敏感,速度越低,FeCrAl/WC复合涂层的抗冲蚀磨损性能越好.