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21.
J. T. Graham R. G. Alamo L. Mandelkern 《Journal of Polymer Science.Polymer Physics》1997,35(2):213-223
Nominal stress-strain curves of a series of random ethylene-hexene copolymers having narrow composition and most probable molecular weight distributions were investigated. A series of such molecular weight copolymers with a constant concentration of branches were crystallized under a variety of conditions. In each molecular weight series the level of crystallinity was approximately constant. Particular attention was focused on the yield region and the nature of the yielding process. It was found, quite surprisingly, that the yield stress was not solely dependent on the crystallinity level. Moreover, the shape of the force-elongation curve in the yield region was very dependent on the molecular weight and the crystallization mode. These changes in yielding correlated quite well with the overall crystallite structure that was characterized by thin section transmission electron microscopy. The orthorhombic unit cell of polyethylene was maintained in all the samples despite the changes that occurred in the overall crystallite structure. © 1997 John Wiley & Sons, Inc. 相似文献
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By chemically modifying the FeO(1 1 1) thin film on Pt(1 1 1), we show that it is possible to unambiguously correlate its STM morphology with its underlying structure without recourse to STM simulations. Partial reduction of the oxide surface leads to the formation of triangularly-shaped oxygen vacancy dislocation loops at specific sites in the moiré structure of the film. Their presence allows unambiguous identification of the high-symmetry domains of the moiré structure, whose differing chemical properties govern the templating effect on adsorbed metal atoms, clusters and molecules. 相似文献
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采用具有"同步增长,同步断撑和原位缩合"特性的超分子构筑调控逐步偶联和聚合方法,合成了高规整的反应性梯形聚乙烯基倍半硅氧烷Vi-LPSQ.该反应性乙烯基可进一步功能化,是制备功能高分子材料的重要前驱体.29Si-NMR是表征梯形聚合物规整性最有效的方法,Vi-LPSQ的重复结构单元共振吸收峰的化学位移δ=-21.6,且峰宽Δca.1,说明其规整性很高.它的XRD谱图上存在两个明显的衍射峰,分别对应于梯形的宽度(d1=0.74 nm)和厚度(d2=0.40 nm),这证实了Vi-LPSQ以典型的梯形结构存在.另外,Vi-LPSQ的玻璃化转变温度Tg高达191.3℃,表明Vi-LPSQ分子具有很高的刚性和规整性. 相似文献
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In recent years, a number of researchers have applied various computational methods to study the wave and tsunami forcing on bridge superstructure problems. Usually, these computational analyses have relied upon application of computational fluid dynamic (CFD) codes. While CFD models provide accurate results, their disadvantage is that they tend to be computationally expensive. Thus, it may be difficult to apply these techniques during risk assessment analyses. During this study, an alternative computational method was explored in which a previously-developed diffraction model was combined with a previously-developed trapped air model under worst-case wave loading conditions (i.e., when the water surface was at the same elevation as the bottom bridge chord elevation). The governing equations were solved using a finite difference algorithm for the case where the bridge was attacked by a single wave in two dimensions. Resultant water forces were computed using results from the diffraction/trapped air computations, and water force values were compared with data from three datasets. In general, excellent agreement between the diffraction/trapped air model and data was observed. The computational time associated with the model was only approximately one hour per bridge configuration, which would appear to be an improvement when compared with other computational techniques. 相似文献
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船体上层建筑有效性分析的简化模型 总被引:1,自引:0,他引:1
钱仍 《上海交通大学学报》1996,(10)
提出了一种估计上层建筑有效性的简化模型,把船体的三维结构简化为二维模型,使上层建筑和主甲板结构间的相互作用得到较好的模拟,从而对上层建筑参加船体总纵弯曲程度的计算得以简化,并得到满意的结果. 相似文献
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以某传统"五大片"式客车车身上部结构为基础,设计一种新型整体式"U"型梁客车车身上部结构.根据ECE R66法规要求,建立了2种车身上部结构方案的整车侧翻有限元模型.对客车车身局部骨架刚度试验进行模拟分析,检验了模拟计算的可靠性.采用显式非线性有限元求解器LS_DYNA对客车侧翻过程进行模拟分析.利用ADAMS软件计算出客车侧翻撞击地面时的线速度和角速度,作为侧翻模拟分析的初始条件.研究结果表明,两种车身上部结构方案的客车都能满足ECE R66法规关于乘员生存空间的要求;与传统"五大片"式客车相比,整体式"U"型梁客车车身上部结构将更多的碰撞能量传递给顶盖骨架和非碰撞侧侧围骨架,使得碰撞侧侧围骨架吸能减少,侧窗立柱的变形量减小,提高了客车的侧翻安全性. 相似文献
30.
R. V. Panin N. R. Khasanova A. M. Abakumov W. Schnelle J. Hadermann E. V. Antipov 《Russian Chemical Bulletin》2006,55(10):1717-1722
Sodium ruthenium(III,IV) oxide Na1−x
Ru2O4 was synthesized by the solid state reaction of Na2CO3 and RuO2 in inert atmosphere and characterized by X-ray powder diffraction, electron diffraction, and high-resolution transmission
electron microscopy. The compound crystallizes in the CaFe2O4-type structure (space group Pnma, Z = 4, a = 9.2641(7) Å, b = 2.8249(3) Å, c = 11.1496(7) Å). Double rutile-like chains of the RuO6 octahedra form a three-dimensional framework, whose tunnels contain sodium cations. The structure contains two crystallographically
independent sites of ruthenium atoms randomly occupied by the RuIII and RuIV cations. The superstructure with the doubled b parameter found for one of the samples under study using electron diffraction is caused, probably, by ordering of the Ru
cations in the rutile-like chains. The Na1− x
Ru2O4 compound exhibits temperature-independent paramagnetism with χ0 = 1.9·10−4 cm3 (mole of Ru−1).
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1655–1660, October, 2006. 相似文献