171Yb核的核磁共振研究

测定了 1 71 Yb2 的静态和 MAS- NMR波谱 ,获得了 NMR基本参数 :化学位移 (δ)、屏蔽张量(δave-,δ∥ ,δ⊥ ) ,自旋晶格弛豫时间 (T1 ,T∥1 ,T⊥1 ) ,根据谱宽获得了自旋 -自旋弛豫时间 (T2 ) ,根据波谱形状 ,获得了中心离子局域对称性的信息。     

12种简单有机分子中四极核弛豫的动态同位素取代效应

首次研究了四极核弛豫速率的动态同位素效应,测定了12种简单有机分子及相应18种~2D同位素取代物中四极核~(17)O和~(14)N的弛豫速率R_1,并计算了这些分子的转动惯量张量的主值。结果表明,刚性小分子R_1的动态同位素效应与I的稳态同位素效应之间存在着必然的相关性。文中在核磁弛豫的理论中首次引入了碰撞频率和分子运动的平动-转动耦合的概念,从而对实验结果提出了合理的理论解释。     

Biomimetic Synthesis of CdSe Quantum Dots through Emulsion Liquid Membrane System of Gas-Liquid Transport

The cadmium selenide quantum dots (QD) have been synthesized by template-control in an emulsion fiquid membrane system. The system consisted of kerosene as solvent, L152 (dialkylene succinimide) as surfactant,N7301 (trialiphatic amine, R3N, R=C8-C10) as carrier, 0.1mol/L CdCl2 solution as internal-aqueous phase and H2Se gas as external phase. Additive organic template agent in internal-aqueous phase was necessary to form CdSe QD. The influence of the nature of template and its concentration on sizes of the formed CdSe QD has also been studied. Transmission electron microscopy showed that the sizes of the products could be controlled down to 3-4nm. X-ray diffraction analysis revealed that the crystals had cubic structure. The formation process and the optical properties of CdSe QD have also been presented.     

Mg-Zn-Al三金属类水滑石的合成及其复合氧化物的催化性能

水滑石（[Mg_６Al_２（OH）_(１６)[CO_３·４H_２O）是一种类似于水镁石结构的层状阴离子黏土，其骨架为阳离子，层间为阴离子。如改变骨架中的金属阳离子或在层间引入不同的阴离子，就可形成各种新组成的类水滑石。水滑石对有机分子反应具有较高的催化活性和选择性，且可以作为复合氧化物催化剂的前体，应用广泛。它作为碱催化剂，可用于醇醛缩合；作为氧化还原催化剂，用于水煤气转化、NO的还原、甲烷氧化反应等犤１，２犦。作为一种具有特殊结构的化合物，各种双金属组分的水滑石或类水滑石的合成、性质与应用已受到广泛的重视犤３…     

20-W sealed-off CuBr vapour laser excited with modified Blumlein circuit

A sealed-off CuBr vapour laser with the maximal average output laser power of 20 W was fabricated and investigated.The corresponding efficiency is 1.2% and the specific average output laser power is 123 mW/cm~3 in an active volume of 163 cm~3.The lifetime of the laser is more than 300 hours operating at 12-15W.     

排列组合与其它知识的交汇

<正>普通高中数学课程标准(实验)指出,要"体现相关内容的联系","提高对数学的整体认识",在此标准的引导下,近几年的高考卷中频频出现相关知识有机整合的新题型,本文以排列组合为例,来聚焦一下高考卷中排列组合与其它知识交汇的例子.     

三角形中的一个定理及应用

1．定理及推论 定理 如图1，在△PAB中，M是边AB上任意一点，Q是PM上的任意一点，过点Q任作一条直线交边PA，PB于A′，B′，若PA=xPA,PB=yPB,     

2005年中考数学中的网格问题

新的《数学课程标准》较大幅度地降低了对繁杂的数字运算、代数式运算、几何证明的要求.“网格”具有特有的优势,利用网格的特征,能得出线段间的平行、垂直等位置关系和线段间的数量关系,减少了不必要的繁杂的计算和繁难的证明,杜绝了简单记忆、生搬硬套和机械计算,因此,以网格     

Phase Control of Few-Cycle Coherent Terahertz Radiation Pulses

We report a method to control the carrier-envelope phase shift in nearly single-cycle coherent terahertz (THz) radiation pulses, in which we used Kerr effect and two-photon absorption in the generated crystals due to the pump beam peak intensity. Dependence of relative carrier-envelope phase shift of THz pulses on the pump beam intensity in the ZnTe crystal was measured experimentally. Under our experimental condition, we measured that maximum relative phase shift is 0.29 radians.