磁场对异质界面上D-中心的影响

势阱中的类氢杂质的能级问题一直为学术界所长期关注。讨论了异质界面上中性施主D⁰和负施主离子D^-的能量随垂直于界面的磁场的变化情况,同时将磁场和势阱结合起来考虑其对类氢杂质的影响。研究发现随磁场的增大,其对D⁰基态能的影响越来越大,对其束缚能的影响逐渐变小,而对D^-中心,磁场的作用使得D^-由非束缚态转变为束缚态。计算中分别选取了两种不同的波函数,分析了这两种波函数的适用范围,利用变分的方法得到此结构中D⁰中心的基态能量和束缚能与D^-中心角动量L=-1自旋三重态的本征能量和束缚能随磁场的变化关系,找到了此三重态由非束缚态转变到束缚态对应磁场的阈值。     

CVD法制备碳纳米管的TG-DTA研究--温度对CVD法制备碳纳米管的影响

基于碳纳米管粗产品中无定形碳和不同直径碳纳米管对氧的反应活性的差异 ,通过差热 -热重 (TG DTA)方法 ,结合透射电镜 (TEM)和X射线衍射 (XRD)的测试结果 ,研究了合成温度对以乙炔气体为碳源 ,用CVD法制备碳纳米管的石墨化程度、碳纳米管直径以及直径分布的影响 .结果表明 :反应中 ,由于催化剂Co/SiO2中活性组分 (Co)微晶随合成温度的升高而增大 ,导致所制备的碳纳米管的直径增大 ,从 2 0～ 30nm (6 5 0℃ )增加到 30～ 5 0nm (75 0℃ ) .碳纳米管的石墨化程度随着反应温度的升高而增加 .XRD实验结果还表明 ,当合成温度从 6 5 0℃增加到 85 0℃时 ,2θ值从 2 5 .8°增加到 2 6 .8°,(0 0 2 )晶面的层间距从 3.45 减小到 3.32 ,即随着合成温度的升高 ,碳纳米管 (0 0 2 )晶面的层间距减小 .通过DTA放热峰的峰温和半峰宽的分析得出 ,无定形碳的放热峰峰温Tp<380℃ ,其含量随着温度的升高而减小 .碳纳米管的DTA放热峰的峰温Tp 随着碳纳米管的直径和石墨化的程度的增加而升高 ,半峰宽随着碳纳米管的直径的分布范围增大而增宽 .低温 (6 5 0℃ )有利于生成直径小且均匀的多层碳纳米管 (2 0～ 30nm) ,而高温 (大于 75 0℃ )则有利于生成直径大的多层碳纳米管 (大于 30～5 0nm) .     

Analysis of Alaskan crude oils by glass capillary gas chromatography/mass spectrometry

Glass capillary gas chromatography/mass spectrometry is used to profile Alaskan crude oil for purposes of origin verification. Alaskan oil, sampled at Valdez, Alaska, and transshipped to the U.S. East Coast, is compared with 21 samples of foreign crude oil using GC/MS techniques in which original data is reconstructed at selected parent and fragment ions to generate a series of chromatographic profiles. Comparison of selected profiles and compositional parameters derived from peak ratios allows distinction of Alaskan oil from many foreign crudes and may be applied to the examination of crude mixtures.     

The distribution and potential toxic effects of TBT in UK estuaries during 1986

The concentrations of butyltin compounds in seawater were measured at nine sites in the UK during 1986. In popular yachting centres concentrations of tributyltin (TBT) ranged from less than detectable ( < 1 ng dm^?3) in the winter, up to 1500 ng dm^?3 in marinas in the summer. Measurements of wastewater generated by high-pressure hosing of yachts demonstrated that even higher environmental concentrations of TBT resulted from the procedure. The results of the monitoring programme are discssed in relation to the toxicity of TBT and recent government legislative actions.     

火灾致因数据的模糊聚类分析

利用一种成熟的模糊聚类分析方法，对火灾危险源的前期数据进行分析和处理。为火灾危险源灾变的知识表征模型提供数据准备。得到火灾危险源识别的重要信息。     

反向场位形下的引导中心哈密顿函数

本文给出了反向场位形中场反向处引导中心哈密顿函数。在零级磁场线性近似下给出粒子运动及引导中心位置的精确解,分析了解的特性。小磁场注向分量对引导中心哈密顿函数的贡献由李变换方法求取。最后讨论了该哈密顿函数的性质并和数值结果作了比较。该理论可以用来研究带电粒子在行星际空间电流片、磁尾中性片以及实验室中反向场箍缩中的运动特性。     

Periodic solutions of rigid body–viscous flow interaction

This paper describes the work on extending the finite element method to cover interactions between a viscous flow and a moving body. The problem configuration of interest is that of an arbitrarily shaped body undergoing a simple harmonic motion in an otherwise undisturbed incompressible fluid. The finite element modelling is based on a primitive variables representation of the Navier-Stokes equations using curved isoparametric elements. The non-linear boundary conditions on the moving body are obtained using Taylor series expansion to approximate the velocities at the fixed finite element grid points. The method of averaging is used to analyse the resulting periodic motion of the fluid. The stability of the periodic solutions is studied by introducing small perturbations and applying Floquet theory. Numerical results are obtained for several example body shapes and compared with published experimental results. Good agreement is obtained for the basic non-linear phenomenon of steady streaming.     

Environmental aspects of tributyltin

The tributyltin species, the active ingredient in some antifouling paint formulations, is perhaps the most acutely toxic chemical to aquatic organisms ever deliberately introduced to water. It has been demonstrated to have an adverse effect on shellfish in France and England, and as a consequence the use of tributyltin-containing antifouling paints has been restricted in these countries. Other countries have banned the use of tributyltin-containing antifouling paints or are contemplating restrictions. This article reviews such environmental aspects of tributyltin as methods of analysis, toxicity, environmental occurrence, persistence and fate. Tributyltin concentrations in many locations may be high enough to cause chronic toxicity or harmful effects in some aquatic organisms, and in some locations the tributyltin concentrations may be high enough to be acutely toxic to some organisms. Biological degradation of tributyltin in water and sediment appears to be the most important factor limiting the persistence of tributyltin in aquatic environments. To some degree, then, the persistence of tributyltin in aquatic environments depends upon the nature of the ecosystem. Tributyltin exhibits low-to-medium persistence in water and moderate persistence in sediment. A summary is given of the regulatory status of tributyltin in some countries, and recommendations are made for further research.     

用超球坐标方法研究在弱磁场中的二维D-中心

将超球坐标数值计算近似方法引入半导体中的低维量子系统，求解了二维D^-中心在弱磁场中的薛定谔方程，得到了二维D^-中心的基态和低激发态的体系能，计算得到的基态能与变分法得到的结果及实验结果均获得较好的一致。