Interactions among metastable pits on heterogeneous electrodes

A previously developed spatiotemporal model of the interactions among metastable pits on homogeneous electrodes is extended to heterogeneous surfaces with randomly distributed inclusion sites in an otherwise passive electrode. The inclusions are treated as favored sites for pit initiation events. The effect of the spatial density of inclusions on susceptibility to explosive growth in pitting corrosion is investigated. It is shown that there exist critical values of the pit density for the explosive growth of metastable pits that leads to a transition to pitting corrosion. Convective mass transport is shown to alter the density required for explosive growth. The effect of a limitation on the number of times that an inclusion can initiate a pit on the transition to the pitting corrosion is also considered.     

Study of the factors influencing the exfoliation of an organically modified montmorillonite in methyl methacrylate/poly(methyl methacrylate) mixtures

The factors that affect the dispersion of exfoliated organically modified montmorillonite in a solution of poly(methyl methacrylate) in methyl methacrylate are explored. Exfoliation of montmorillonite in the solution is achieved with the assistance of ultrasound, and rheological measurements indicate a very significant increase in the viscosity, a dramatic shear thinning behavior, and a finite yield stress, all of which are direct consequences of the exfoliated state of the clay platelets. A number of factors, including the sonication power, clay loading, use of a swelling agent, and moisture content of the modified montmorillonite, are found to influence the exfoliation process. The effect of addition of a range of titanate coupling agents (LICA‐01, 12, 38, 44, and 97) on the viscosity of the nanoclay dispersions was investigated. It was found that LICA‐44 had the effect of reducing the viscosity of the exfoliated montmorillonite dispersion without apparently influencing the extent of the exfoliation. Molecular modeling, UV–visible and Fourier transform infrared spectrometry were used to investigate the possible reasons for efficacy of this LICA. The LICA appears to act through a combination of steric effects and the presence of certain charges on the organic molecule. The magnitude of the negative charges on elements of the LICA appears to influence its ability to bind to the clay and also its ability to reduce the viscosity of the nanoclay. This article indicates how the apparently conflicting requirements of achieving a highly exfoliated state and also maintaining a viscosity low enough for processing can be effectively addressed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

基于CATIA的CAD/CAT系统集成方法研究

探讨CATIA V5与计算机辅助公差设计(CAT)系统的集成方法,最终实现零件定位特征的识别以及公差规范的自动标注。首先识别出用户所选几何要素的类型,提取各要素的几何信息并保存在Excel中,用CAT系统进行功能公差规范,然后在CATIA中实现了三维公差的自动标注,用实例验证了该方法的可行性。     

改性剂用量对MFIIR/NR性能的影响

以丁基橡胶(IIR)为原料,氢化钠(NaH)和马来酸酐(MAH)为改性剂,制备了多官能化丁基橡胶(MFIIR),并与NR进行了共混。研究了改性剂用量对并用胶硫化性能、力学性能和动态力学性能的影响。结果表明,采用NaH/MAH体系对IIR进行改性,在保留IIR原有分子链结构基础上引入了极性的羧基官能团和C-C不饱和双键结构,从而实现了IIR的官能化改性;且当NaH∶C=C为1∶1时,MFIIR/NR并用胶的力学性能及动态力学性能最佳。     

Scaling studies with the dual crystal spectrometer at the OMEGA-EP laser facility

The dual crystal spectrometer (DCS) is an approved diagnostic at the OMEGA and the OMEGA-EP laser facilities for the measurement of high energy x-rays in the 11-90 keV energy range, e.g., for verification of the x-ray spectrum of backlighter targets of point projection radiography experiments. DCS has two cylindrically bent transmission crystal channels with image plate detectors at distances behind the crystals close to the size of the respective Rowland circle diameters taking advantage of the focusing effect of the cylindrically bent geometry. DCS, with a source to crystal distance of 1.2 m, provides the required energy dispersion for simultaneous detection of x-rays in a low energy channel (11-45 keV) and a high-energy channel (19-90 keV). A scaling study is described for varied pulse length with unchanged laser conditions (energy, focusing). The study shows that the Kα line intensity is not strongly dependent on the length of the laser pulse.     

地理信息系统:设计未来

随着社会的高速发展,人类对环境的压迫日益严重,似乎已接近临界点,造成环境系统失衡、损失难以挽回.我们要首先意识到事态的严重性,提出可能的解决方案,并最终执行可行的补救措施.阐述了拯救环境的紧迫性并提出了一套通过被称为地理设计的框架的有效的大地系统管理手段.它从伊安·麦克哈格颇具影响的名著<与自然共设计>中取得理论灵感、从大地系统工程管理这样的综合学科中汲取实践经验.方法学上它得益于斯坦尼兹景观变化模型的支持.地理信息系统在描述过去和现时的状况中游刃有余,但我们还需要将其功能扩展,使其能够用于设计未来--即把设计因素引入地理信息系统框架,使其成为囊括一切的规划设计工具,让规划师、设计师用起来更加得心应手.已有一些早期试点地理设计软件付诸实施,如ArcSketch即代表了这样一种认真的探索.尽管地理和设计存在已久,但地理设计作为一种学科还相对较新.作者认为现在我们应刻不容缓地采用地理设计这一动议,协调一致、共同努力,以进一步防止环境恶化,使我们大家共享的、日益变化的地球一人为大地一更加健康和长寿.     

Preparation of La-Ni Based Alloys Used in Ni-Metal Hydride Bateries by Mechanical Alloying

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Study of failure and scale effects in rocks under uniaxial compression using 3D cellular automata

A numerical model for simulating the rock fracturing process has been developed and implemented in the three-dimensional code EPCA^3D, which is based on the earlier EPCA^2D (elasto-plastic cellular automaton). EPCA^3D has the ability to simulate the initiation, propagation and coalescence of cracks in the failure processes of rocks. Using this code, we studied the failure processes of simulated rock specimens with different sizes and shapes in three-dimensional space. It is concluded that the ‘scale effect’ is not directly related to the heterogeneity, if the rock specimens have the same homogeneity. If the platen-rock elastic mismatch effect in physical testing is not considered in the numerical simulations, there is almost no scale effect for rock specimens with different sizes and shapes. However, by considering the platen-rock interaction in the simulation of the rock failure process with the EPCA^3D code, the modeling results reproduced the well-known phenomenon of scale effects found in physical experiments.     

不同温度下碱-硅酸反应膨胀规律研究

参照砂浆棒快速法,调整试验温度,研究了温度对骨料碱-硅酸反应(ASR)膨胀的影响规律。采用化学反应速率常数描述温度对混凝土ASR膨胀的影响,探讨了ASR速率常数与养护温度之间的关系,验证了温度对碱-骨料反应的影响可以用Arrhenius方程来描述的设想。运用Arrhenius方程初步建立了ASR膨胀预测模型。     

GFRP用量及倒角半径影响约束素混凝土柱体的试验研究

为了研究玻璃纤维增强复合材料(GFRP)约束素混凝土柱体的力学性能,进行了13组试件的轴心受压试验。主要考虑GFRP用量、倒角半径对GFRP约束素混凝土柱体的力学性能的影响,通过试件的试验过程和最终破坏形态可知,GFRP约束素混凝土柱体的强度都有一定程度的提高,延性增大,破坏过程与没包裹GFRP试件相比缓慢;由于试件的棱角处存在应力集中现象,所以随着倒角半径的增加,GFRP约束的试件强度提高幅度逐渐增加,GFRP约束不同倒角半径(0、20、35、50)素混凝土方柱试件的强度提高幅度远不如圆形截面柱,较方形截面柱分别提高了6%、14%、16.9%、20.9%。