Selectivity of Crystal Growth Direction in Layered Double Hydroxides

Investigation of selectivity of crystal growth direction in layered double hydroxides is helpful to control their particle sizes in different directions. Mg-AI layered double hydroxides (LDHs) were synthesized using a coprecipitation method. The influences of aging temperature, aging time, and Mg/AI molar ratio on the crystal structure, the LDHs particle size, and the selectivity of crystal growth in different directions wereinvestigated. The results show that the size of the crystallites in the a direction is larger than that in the c direction for all experimental conditions, indicating faster crystal growth in the a direction than in the c direction. The crystallite sizes in the a and c directions both increase with decreasing Mg/AI molar ratio but with less difference between the sizes in the two directions. Therefore, the crystal growth rate in the c direction increases more than that in the a direction as the Mg/AI molar ratio decreases. The influence of the aging time, aging temperature, and Mg/AI molar ratio on the selectivity of the crystal growth direction can be used to prepare LDHs with selected sizes in the a and c directions.     

Structure, flame retarding and smoke suppressing properties of Zn-Mg-Al-CO3 layered double hydroxides

Zn-Mg-Al-CO3 layered double hydroxides (LDHs) have been synthesized by a new method involving separate nucleation and aging steps. The Zn-Mg-Al-CO3 LDHs were characterized by XRD, FT-IR, ICP and TG-DTA. The limiting oxygen index and smoke density of composites of the LDHs with EVA-28 were determined. Incorporation of Zn^2 in the layers of the LDHs was found promoting material charring and smoke suppression. The mechanism of flame retardation and smoke suppression is discussed. The results show that Zn-Mg-Al-CO3 LDHs have better flam eretarding and smoke suppressing effects than Mg-Al-CO3 LDHs.     

不同热处理条件下的Ag/Ni超晶格薄膜层状结构的X射线衍射研究

用Ｘ射线衍射法,对经不同条件热处理后的Ａｇ／Ｎｉ超晶格薄膜的结构进行研究．结果表明,未经热处理的超晶格膜显示良好的人工双元素层调制周期性,且存在［１１１］晶向垂直于膜面的织构．升温时的应变弛豫使超晶格膜的晶格沿垂直于膜面方向发生轻微收缩,直至达平衡态．热处理形成新晶粒,其取向不再严格有序,减弱了薄膜的［１１１］织构．加热所激发的原子长程扩散导致一些元素层厚度减小并趋于消失,而另外的元素层厚度增大,从而使人工调制周期性逐渐被破坏;原始态超晶格膜元素层的厚度越大,则周期结构的热稳定性相应也越高,这部分归因于原子扩散长度与元素层厚度成正比关系     

TFEL of Ce3+ in zine sulpho-oxide

A new TFEL material ZnS_xO_1−x: Ce³⁺ is prepared. The EL brightness of ZnS_xO_1−x: Ce³⁺ is at least one order higher than that of ZnS: Ce³⁺ at the same doping concentration of Ce³⁺. The EL emission wavelength of ZnS_xO_1−x: Ce³⁺ (X = 0.5) ranges from 400 to 600 nm. The emission of ZnS_xO_1−x: Ce³⁺ may be used as the blue part of white TFEL.     

多面体类零件三维模型自动生成的研究

在对零件二维工程图特征进行分析的基础上，提出了一个不同于前人的重构方法——层构法．从二维环出发，逐步得到零件各个截面的轮廓，最终形成零件的三维实体模型．该方法思想独特、效果良好，具有效率高、速度快的优点．算法以多面体为研究对象，实现的结果令人满意     

层状半空间场地对地震波的放大作用

应用Haskell-Thomson方法求解加速度问题,并采用入射波幅值为基准来研究不同土层性质场地对地震波的放大作用,比认为土层下为刚性基岩且基岩处位移(加速度)已知的方法更符合实际。研究了天津市和平区和南开区两场地对加速度地震波的放大作用:分析了不同刚度土层的排列次序对场地整体放大作用的影响,对规范中场地特征周期的取值范围进行了探讨;还提出了由一种场地地震波记录计算另一种场地记录的方法     

利用超声回波识别分层介质结构

研究了利用ＢＰ神经网络进行分层介质结构超声识别的方法。应用理论模型分析了不同分层介质结构的回波，研究了用ＢＰ神经网络进行介质结构识别的算法与性能，结果表明它具有良好的识别效果，实际分层介质结构的正确识别率在９０％以上。     

分层正交各向异性板壳非线性有限元分析

采用三维退化等参中厚壳元和分层模型，建立了分析弹塑性和几何非线性各向异性板壳的有限单元法，为克服退化壳元出现剪切和薄膜自锁问题，采用９节点Ｈｅｔｅｒｏｓｉｓ单元并采用选择积分方法，文末算例表明所编程序的可靠性和通用性。     

考虑土体、基础和上部结构共同工作时的箱形基础的优化设计

本文建议用子结构法凝聚上部结构的荷载和刚度,同时用有限分层地基模型确定土体的刚度和基底反力,并计及基础自身的刚度影响,进而对箱基进行较全面的内力分析。 在此基础上,选择板、壁的厚度和钢筋用量作为设计变量,并采用可变容差法对箱基进行优化设计。利用本文编制的程序BFOD—88进行计算,所得结果比现行设计方法算得的数值降低造价13％以上。     

大学生分层教育中实训教学方法的研究

我国高等教育已经历史性地进入了国际公认的大众化教育阶段,大力发展分层教育将是一种有益的探索,但在教育分层中实训教学质量且主要瓶颈,因此提高实训教学质量是完善分层教育,促进人才培养与社会需求的良性互动一条很好的途径。本文拟从实训教学的概念、我国实训教学存在的主要问题进行论述,并在此基础上创造性地提出实训教学的三个结合和四大创新思路。