稀土元素在硅表面的化学吸附

本文对几种稀土元素(铈、钐、镱)在硅表面的化学吸附进行了理论计算。用定域密度泛函-离散变分方法(LDF-DVM)对顶位和三度开位两种集团模型进行了自洽计算,包括总结合能的计算,给出了吸附位能曲线,从而确定出最佳吸附构型和位置。讨论了电荷转移情况、吸附能的大小等,与一些实验结果进行了比较。并给出了三种元素在硅表面稳定吸附时的态密度图,分析讨论了其电子结构的差异和特点。 关键词：     

电负反馈半导体激光器半经典理论

本文建立了电负反馈半导体激光器的半经典速率方程模型,导出此类激光器的FM噪声功率谱密度,从而证明电负反馈技术可压窄激光器线宽。在反馈带宽之内激光器的频偏功率比(CPR)减小(1+H)倍,而带宽以外则不受影响,因此这类激光器可用作直接调制FSK相干传输系统光源。由于激光器直接频率调制时相位延迟的限制,l/f型FM噪声是限制谱线压缩的主要因素。 关键词：     

单脉冲BOXCARS技术在瞬态燃烧场测温中的应用

 用单脉冲交叉相干反斯托克斯喇曼散射技术测量了两种不同固体燃剂的瞬态燃烧场的温度。对燃烧场进行了优化，给出了在燃烧场中取得的部分典型单脉冲CARS光谱及其理论拟合结果，得到了燃烧场的温度及其随高度的分布；稳定燃烧时两种燃剂燃烧场的温度基本保持不变，平均值分别为2 260，2 090K；测量了实验的纵向空间分辨率。结果表明，BOXCARS技术能较好地完成复杂的瞬态燃烧场温度的测量工作。     

H MAS and H[Na] double resonance NMR studies on the modification of surface hydroxyl groups of γ-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na₂CO₃-γ-Al₂O₃ catalysts was investigated as a function of both the Na₂CO₃ loading and the calcination temperature by means of ¹H magic angle spinning (MAS) and ¹H[²³Na] spin-echo double resonance NMR techniques. The ¹H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 °C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na₂CO₃ coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the ¹H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the ¹H[²³Na] MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 °C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 °C. This is attributed to the formation of the coordinated species which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the ¹H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.     

固体酪氨酸^13C化学位移屏蔽张量研究中的氢键作用

应用规范不变原子轨道方法，考虑分子间的氢键作用，对固体酪氨酸＾１３Ｃ化学位移屏蔽张量进行了理论模拟，并对本文结果和以前的计算结果与实验值进行了比较。结果表明：对羧基碳，其理论值和实验值的方均根偏差（不考虑氢键作用）为３３．４ｐｐｍ；而考虑氢键作用，其相应的方均根偏差为２３ｐｐｍ，这表明在氨基酸羧基碳的化学屏蔽研究中考虑分子间的氢键作用是很重要的，特别是δ２２分量，对氢键作用非常敏感，这和ＭｃＤｅｒ     

低温氮化硅薄膜的介电性能研究

研究了微波电子回旋共振等离子体化学汽相沉积低温氮化硅薄膜在5—10⁶Hz频率范围内的介电性能．由于低温氮化硅薄膜为具有分形结构的纳米非晶薄膜，致使氮化硅薄膜的介电谱、损耗谱在低频区和高频区具有两种不同的分布规律．在低频区介电谱具有ε′∝ω^n－1₁的关系，ｎ₁在0.82—0.88之间，是电子跳跃导电的结果；在高频区介电谱具有ε′∝ω^n-1₂的关系，n₂在0 关键词：     

Uniqueness and Stability of Solution for Semi-liner Heat-conduction Equationin Higher Dimension

This paper deals with the uniqueness of solution to a class of semi-linear heat-conduction equation in higher dimension on the basis of references [1] and [2]. The main results in this paper are as follows: the solution of problem (A) is unique and stable if it exists.     

选择性激发技术在偶合常数精确测量中的应用

采用基于简单Gaussian软脉冲的选择性激发技术来获得自旋系统的一维反相磁化分裂峰,并结合J-Doubling方法来精确测量该分裂峰的J偶合常数,对于重叠分裂峰或者线宽大、偶合分裂小的谱峰的J偶合常数的精确测量,该方法尤其适合.     

Quantum Ising Criticality in Dimerized XY Spin-1/2 Chain

In the present paper we propose a spin-1/2 chain which provides an exactly solvable example to studythe Ising criticality with the central charge c = 1/2. We performthe diagonalization of this model in the presence ofmagnetic field. From the full energy spectrum, the central charge and the scaling dimensions are given at the criticalpoint. The results show evidently that the quantum Ising criticality exists in such a system.     

一种对中子相对不灵敏的大动态脉冲γ辐射探测器

使用CeF₃闪烁体配以CHT3,CHT5型大线性电流光电倍增管,组合成光电探测器.实验测量表明:CeF₃光电探测器对⁶⁰Coγ灵敏度约为常规塑料闪烁体ST401探测器的0.5—0.6倍,而对于脉冲DT中子,CeF₃探测器灵敏度相对于同尺寸闪烁体ST401探测器的灵敏度低约1个量级,探测器线性电流大于1.5A,暗流小于10nA,是一种对中子相对不灵敏的大动态脉冲γ辐射探测器.