神奇的原子——原子随笔之三

人类虽然在2000多年前就预言了原子的存在，然而可以断言，世界上还没有一个人——无论这个人智商有多高，无论这个人的想象力有多强，能够预言原子的种种神奇．因为在原子的世界里不仅不同于我们熟悉的任何东西，也不同于所能想象的任何事情．物理学家费曼曾说：“它显得又古怪，又神秘．”     

排列形状及阵列数目对纳米导线阵列场发射性能的影响

为了进一步研究纳米导线阵列的排列形状以及阵列数目对其场发射行为的影响，利用镜像悬浮球模型对正方形以及六边形排列的纳米导线阵列的场发射行为进行计算与模拟，近似的得到纳米导线阵列的场发射增强因子满足如下的变化趋势：β=h/ρ(1/1+W)+1/2(1/1+W)²+3,其中h为纳米导线的高度，ρ为纳米导线的半径，W是以R为自变量的函数，R为纳米导线阵列的间距.结果显示纳米导线阵列的排列形状对其场发射性能的影响较小，而阵列间距则是影响场发射性能的关键因素：当R<R₀时，场发射增强因子随着阵列间距的减小而急剧减小；当R>R₀时，场发射增强因子基本不变，其中R₀为导线阵列场发射的最佳间距.进一步研究表明改变纳米导线阵列的数目基本不会改变阵列的场发射性能随间距的变化趋势，但是随着阵列数目的增加，R₀会有一定程度的减小，场发射增强因子也会降低. 关键词： 纳米导线 场发射 增强因子 阵列数目     

非晶钛酸铋的晶化过程

利用差热分析、X射线衍射和透射电子显微镜等技术对溶胶-凝胶法合成的凝胶的晶化过程进行了分析，实验结果表明，Bi₄Ti₃O₁₂非晶凝胶晶化过程经历了四个过程：首先在433℃先形成了Bi₂O₃和TiO₂亚稳相，然后在488℃时TiO₂亚稳相与Bi₂O₃反应形成Bi，Ti复合氧化物亚稳相Bi₂T 关键词： 钛酸铋 铁电材料 溶胶凝胶 非晶 晶化过程     

圆外区域求解Helmholtz方程

1引言许多科学和工程计算问题都可以归结为无界区域上的偏微分方程边值问题．而求解椭圆方程边值问题的常用技术是有限元方法,可是对于无界区域,在用有限元方法求解时,往往遇到困难．最简单的办法显然是直接略去区域的无界部分求解,但这样做或者导致过低的计算精度,或者要付出很高的计算代价．边界归化,即将求解偏微分方程边值问题转化为边界积分方程,是求解某些无界区域问题的强有力的手段．自70年代以来,有限元和     

Photochemistry of dibenzo-1,4-dioxins: intramolecular rearrangement-reduction through observable 2,2′-biphenylquinones

The photochemistry of dibenzo-1,4-dioxin (7) and 2,3,7,8-tetramethyldibenzo-1,4-dioxin (15) — both of which have the parent ring system of the well-known enrimental contaminant dioxin— has been studied in aqueous solution and in selected organic solvents. It is shown that a novel intramolecular photorearrangement is the major mode of reaction for 7 and the exclusive reaction for 15, giving rise to observable (by UV—Vis spectrophotometry) intermediate 2,2′-biphenylquinones. Subsequent reduction by the organic co-solvent gives rise to 2,2′-biphenols as major or exclusive product. Thus, photolysis of these compounds generates oxidizing agents in the biphenylquinones. Photolysis in the presence of added N_aBH₄ resulted is greatly enhanced yields of biphenols along with more than 90% material balance. These findings have relevance to dioxin photodecomposition, which can be used as a method for its destruction.     

Chemical Speciation of Amphoteric Ions on Semi‐Dry Scrubber Residue and Bag‐House Ash from MSWI

Two series of size‐fractionated combusted residues, a bag‐house ash and a scrubber residue, from a municipal solid waste incinerator (MSWI) were prepared and extracted by means of sequential chemical extraction (SCE) procedures proposed by Tessier. Concentrations of water‐soluble phase, exchangeable phase, carbonated phase, Fe/Mn oxide phase, organic matter phase, and residual phase bound amphoteric metals (Pb and Zn) were obtained, and have been compared with those of single batch extraction of toxic characteristic leaching procedure (TCLP). In each size fraction of baghouse ash or scrubber residue, lead or zinc shows a common phenomena that the TCLP value is always lower than the content of the water‐soluble fraction. For lead, baghouse ash has a significant size‐dependent distribution on the water‐soluble phase to perform a size‐dependent test of lead in the TCLP test. The zinc TCLP data having less size dependence might be due to that neither the baghouse ash nor the scrubber residue has a size‐dependent distribution on the water‐soluble zinc phase.     

Aggregation Properties of an Amphiphilic Methanofullerene Derivative in THFH_2O Solvent Mixtures

Water-soluble fullerenes not only have a number of important applications in biological chemistry1, but also form ordered aggregate structures that can be utilized in materials science2. There are reports that some water-soluble fullerene derivatives can form ordered structures in water, such as vesicle, nanorod and nanoparticle2-5. However, relatively few reports on the aggregation process have been reported. Knowledge of factors that affect the cluster formation in solution is of consider…     

一种新型有机电致微腔结构的双模发射

采用结构Glass／DBR／ITO／NPB／NPB：Alq／Alq／Al制作了有机微腔电致发光器件。将空穴传输材料与发光材料以一定比例混合作为发光层，为了便于对比，在不改变有机层的膜厚的情况下同时制作了传统的异质结微腔器件，发现两种器件的发光光谱有很大不同，器件的复合效率与传统的异质结器件相比也得到了很大提高，这是因为将两种有机材料混合能消除界面势垒，提高器件的复合效率，从而提高了器件的发光性能，实现了微腔双模发射，且两个模式的半峰全宽分别为8nm和12nm。通过进一步优化器件结构可以实现微腔白光发射。     

单个波长到多个波长的变换实验

报道一种波长变换的新方法.采用此方法不需要任何泵浦光便能够直接将信号光变换成在特定谱宽内的任意多个任意波长的变换光,这对于将来的波分复用光网络提供了较大的方便.此波长变换的原理是利用色散位移光纤的非线性效应产生超连续光谱(SC)信号,由于这种SC信号携带有变换光信号,对这种连续谱进行滤波便能够得到所需要的任意频率的变换信号.此变换方式具有变换频带宽,偏振不敏感的优点。