Relationship between Dispersive Surface Tension and Density and Molecular Weight of Solvents and Polymers

The surface and interfacial properties of polymers are important for their applications. Generally, the surface property is quantitatively characterized by the surface tension or surface tension component parameters, which are obtained with the contact angle technique. However, the contact angle technique has an inherent problem, contact angle hysteresis phenomenon, which will result in many incredible surface tension data. In order to find a simple and easy method to estimate the rationality of a surface tension result, the relationship between dispersive surface tension component and density and molecular weight is researched in this work. It is found that for 30 organic solvents, there is a good relationship between the dispersive surface tension r^d and the parameter . In addition, for 12 polymers, when the molecular weight is replaced with the molecular weight of the repeat unit, there is still the same relationship as for small liquids. However, because it is difficult to judge the accuracy of the published dispersive data of the polymers, the found experiential relationship needs further confirmation, requiring more reliable published data.     

Influence of the blend compatibility on the morphology of thin polymer blend films

Thin films of incompatible polymer blends can form a variety of structures on preparation. For the polymer blend system consisting of two poly(styrene-co-para-bromo-styrene)s at different degrees of bromination, PBr_xS/PBr_yS, the compatibility can be tuned through a variation of the difference in the degree of bromination. Within this blend system, two series of samples with different compatibilities were investigated at various blend compositions. The surface morphology of the thin films was investigated by atomic force microscopy (AFM) measurements, while diffuse X-ray scattering provided additional depth sensitivity at a comparable lateral resolution. The results are indicative for phase separation lateral, as well as perpendicular, to the sample surface.     

Simulation of pedestrian counter flow through bottlenecks by using an agent-based model

Considerable research has been conducted on the topic of unidirectional evacuations from exits. However, few studies aim at simulating counter flow through a bottleneck with complex conflict. This paper proposes an agent-based model to investigate bidirectional flow evacuation. Pedestrian speed is determined by the speed of the leading agent and the surrounding agents. The moving direction of pedestrian originates from four forces, namely, gradient force, repulsive force, resistance force, and random force. These four forces dominate the main stream of the pedestrian moving trajectory, the interaction between pedestrians and their local environment, the resistance or disinclination to movement, and the random variations and chaotic nature of pedestrian dynamics. The novelty of this research is in the agent-based model that combines the agent and forces while providing insights for the simulation of the pedestrian dynamic on the cognitive level. The experiment results show that the behavior that arises from this model is consistent with the observations from Guangzhou Metro and that this model could help capture the essence of pedestrian behavior near egresses.     

对颗粒物质运动的一致性进行控制的随机力场

在颗粒流的研究中引入了一个正态分布的随机力场, 并通过计算机模拟研究了该力场对均匀颗粒流的影响. 结果发现: 随机力场基本上不改变均匀颗粒流的平均密度和速度, 对颗粒流密度的涨落也影响很小. 随机力场对均匀颗粒流的影响主要体现在它可提高速度的涨落, 它与颗粒体系的耗散性质相抗衡, 使颗粒流维持一定的波动能量. 研究结果还显示: 通过随机力场所获得的波动能量并没有均匀分布到各个自由度上, 由于颗粒体系的耗散性质颗粒体系难以达到能均分状态. 关键词： 颗粒物质 随机力 分子动力学模拟     

Force-field dependence of the conformational properties of α,ω-dimethoxypolyethylene glycol

A molecular dynamics (MD) study of α,ω-dimethoxypolyethylene glycol has been carried out under various conditions with respect to solvent composition, ionic strength, chain length, force field and temperature. A previous MD study on a 15-mer of polyethyleneglycol (PEG) suggested a helical equilibrium structure that was stabilised by hydrogen bonding and bridging water molecules. Experiments show that PEG is highly soluble in water, and indicate that clustering is not favoured. In the present study using different force fields, the GROMOS force fields 45A3 and 53A6, a variation on the latter 53A6_OE, and a force field by Smith et al. produced different results. For the GROMOS force fields 45A3 and 53A6 no helical structure was found, but formation of more or less compact random coils in aqueous solution due to hydrophobic interactions was observed. For the other two force fields used, α,ω-dimethoxypolyethylene glycol stayed flexible and more or less elongated in aqueous solution, more in agreement with experimental observations and the previous MD study.     

Surface modification of platinum by laser-produced X-rays

Laser-induced plasma is used as an X-ray source for the growth of hillocks like nanostructures on platinum surface. To generate X-rays, plasma is produced by Nd:YAG laser, which is operated at second harmonics (λ?=?532?nm, E?=?400?mJ). Analytical grade 5?N pure Al, Cu and W are used as laser targets for X-rays production. X-rays produced from Al, Cu and W plasmas are used to irradiate three analytical grade (5?N pure) platinum substrates, respectively, under the vacuum ～10^?4 torr. XRD analysis shows considerable structural changes in the exposed platinum. The decrement in reflection intensities, increment in dislocation line density, change in d-spacing and disturbance in the periodicity of planes evidently prove these structural changes. Atomic force microscope AFM topographic analysis of the platinum exposed to X-rays emitted from Al, Cu and W targets showed that nanometer-size hillocks are produced on the platinum surface irrespective of the source. It has also been observed that due to these hillocks, the roughness of the surface has increased. Conductivity of hillocks produced from X-rays produced by Al, Cu and W targets is compared and it is shown that the hillocks produced by Al target X-rays have better conductivity compared to the hillocks produced by X-rays from Cu and W targets.     

GPS/SINS伪距(伪距变化率)组合导航系统实验研究

基于挠性捷联惯性测量系统和ＧＰＳ接收机ＯＥＭ板，以伪距（（伪距变化率）残差作为观测信息，实现了ＧＰＳ／ＳＩＮＳ伪距组合导航系统的软硬件设计，并先后在实验室和高速公路上对样机的导航定位、测速以及姿态性能和精度进行了静态考核和动态车载试验。试验结果表明，系统伪距组合滤波器的设计和参数选择正确，样机取得了较好的精度。