液晶盒双折射效应的测量与应用

介绍了测量液晶盒双折射效应的实验方法,并利用此方法推测了液晶盒的表面锚泊方向并测量了液晶盒的扭曲角,探讨了应用此方法校准偏振片起偏方向的可能性.     

X射线单晶衍射研究系列功能七元杂环桥联联苯构象

含有七元杂环桥联联苯的π-共轭聚合物是重要的宽禁带光电材料, 其发光性质决定于两苯环间扭曲角. 利用X射线单晶衍射仪确定了系列功能的七元杂环桥联联苯化合物的晶体结构, 比较了桥联原子, 6,6位取代基及分子间弱氢键对这类桥联联苯扭曲构象的影响. 桥联键是—CH2—O—CH2—和—CH2—S—CH2—的七元杂环桥联联苯两苯环间的扭曲角分别为39°和51°, 在6,6位上含有不同取代基的双氧桥联七元杂环桥联联苯的扭曲角存在5°的差异. 在双氧桥联的七元杂环桥联联苯的二聚物中, 桥联的氧原子与非桥联的苯亚基-苯亚基2,2’位置上的两个氢原子之间形成的氢键网络结构导致中心联苯呈现平面构象, 但氢键并没有改变桥联联苯的构象. 七元杂环桥联联苯的构象主要由桥联原子决定, 同时分子间相互作用亦能轻微调控这类桥联联苯的扭曲角.     

政府支出结构、扭曲性税收及内生贴现因子

在一个无穷期限模型中,假设经济主体具有完全理性,通过将常数贴现因子转换为关于效用水平的内生变量,利用跨期优化方法重新考虑了政府支出结构、扭曲性税收对宏观经济变量的影响.尤其关注这两种变量的长期和短期变化对资本积累路径的影响,理论模型表明,当贴现因子内生化后,政府支出结构和扭曲性税收对宏观经济的影响会更为复杂,尤其体现在生产性支出上.     

含扭曲并苯结构的线性聚合物合成及光电性能

将扭曲并苯分子单元引入到聚合物中能够有效减弱聚合物固相下聚集,为发展高荧光的有机显示材料提供新的思路,为此,通过经典Suzuki偶联反应,合成了四种新型的含有扭曲并苯分子的线性聚合物(P1-P4)。在四氢呋喃溶剂和固体薄膜下,聚合物在302-417 nm处有两个宽的吸收峰,峰形状类似, 发出蓝色荧光,且薄膜的发射波长红移。四种聚合物重量损失为5%时的温度都高于350℃,表明都具有良好的热稳定性。通过循环伏安法测定其电化学行为。     

浅析老龄经济中的税收政策

本文放宽人口结构平稳假设,将总人口增长率与劳动人口增长率之差定义为老龄化率,在此基础上构建老龄经济模型,分析税收政策对老龄经济的影响。基于一定假设,老龄经济存在鞍型收敛路径,平衡增长路径上的人均收入增长率取决于技术进步率与老龄化率之差,技术进步率在积极应对人口老龄化方面至关重要。从税收角度看,资产收入税与企业利润税对老龄经济的扭曲程度较高,而劳动收入税与消费税的扭曲程度相对较低。通过削减政府支出与调整税收结构,减税不仅可以提高均衡的资本水平,若能够激励经济主体积极创新,还将会提高平衡路径上人均收入的增长速度。一定条件下,老龄经济中将会存在正的最优税率。     

Coupled extension and thickness-twist vibrations of lateral field excited AT-cut quartz plates简

In this paper, the coupled extension and thickness- twist vibrations are studied for AT-cut quartz plates under Lateral Field Excitation （LFE） with variations along the x1- direction. Mindlin＇s two-dimensional equations are used for anisotropic crystal plates. Both free and electrically forced vibrations are considered. Important vibration characteristics are obtained, including dispersion relations, frequency spectra, and motional capacitances. It is shown that, to avoid the effects of the couplings between extension and thickness-twist vibrations, a series of discrete values of the length/thickness ratio of the crystal plate need to be excluded. The results are of fundamental significance for the design of LFE resonators and sensors.     

A corrected method of distorted printed circuit board image

This paper proposes a corrected method of distorted image based on adaptive control. First, the adaptive control relationship of pixel point positions between distorted image and its corrected image is given by using polynomial fitting, thus control point pairs between the distorted image and its corrected image are found. Secondly, the value of both image distortion centre and polynomial coefficient is obtained with least square method, thus the relationship of each control point pairs is deduced. In the course of distortion image processing, the gray value of the corrected image is changed into integer with bilinear interpolation. Finally, the experiments are performed to correct two distorted printed circuit board images. The results are perfect and the mean square errors of residual error are tiny.     

Local structure distortion and spin Hamiltonian parameters for Cr3＋-Vzn tetragonal defect centre in Cr3＋ doped KZnF3 crystal

The quantitative relationship between the spin Hamiltonian parameters (D, g_‖, Δg) and the crystal structure parameters for the Cr³⁺—V_Zn tetragonal defect centre in a Cr³⁺:KZnF₃ crystal is established by using the superposition model. On the above basis, the local structure distortion and the spin Hamiltonian parameter for the Cr³⁺—V_Zn tetragonal defect centre in the KZnF_3 crystal are systematically investigated using the complete diagonalization method. It is found that the V_Zn vacancy and the differences in mass, radius and charge between the Cr³⁺ and the Zn²⁺ ions induce the local lattice distortion of the Cr³⁺ centre ions in the KZnF₃ crystal. The local lattice distortion is shown to give rise to the tetragonal crystal field, which in turn results in the tetragonal zero-field splitting parameter D and the anisotropic g factor Δg. We find that the ligand F^- ion along [001] and the other five F^- ions move towards the central Cr³⁺ by distances of Δ₁ = 0.0121 nm and Δ₂ = 0.0026 nm, respectively. Our approach takes into account the spin—orbit interaction as well as the spin—spin, spin—other-orbit, and orbit—orbit interactions omitted in the previous studies. It is found that for the Cr³⁺ ions in the Cr³⁺:KZnF₃ crystal, although the spin—orbit mechanism is the most important one, the contribution to the spin Hamiltonian parameters from the other three mechanisms, including spin—spin, spin—other-orbit, and orbit—orbit magnetic interactions, is appreciable and should not be omitted, especially for the zero-field splitting (ZFS) parameter D.     

使用点弥散函数模型法校正扩散频谱影像內磁化率差异引致影像扭曲的效力评估(英文)

平面回波影像(EPI)常常在额叶、颞叶或脑干处出现严重的影像扭曲.目前已有数种方法可校正这种由磁化率差异造成的影像扭曲,该文提出一种简单有效的方法叫点弥散函数模型法.由纤维追踪的角度来探讨影像扭曲校正的有效性.评估的方法是将点弥散函数模型法应用于扩散频谱影像,并比较由扭曲影像与校正影像所得之扣带回纤维数目的多寡.定义了一个指标用来量化影像扭曲校正的有效性:r=( Nc-Nd)/( Nc+Nd),此值越大代表校正影像的纤维追踪结果越好.对于左扣带回与右扣带回,其r值分别为0 .424±0 .452(平均±标准差)及0 .343±0 .452 ,且在统计上皆显著大于零.结果显示,就左右扣带回而言,校正后的影像其纤维追踪的结果较扭曲影像更佳.因此,将点弥散函数模型法应用于校正扩散频谱影像的扭曲可增进左右扣带回的纤维追踪的结果.     

Vibrational Spectra of Distorted Structure Molecules by Using Lie Algebraic Techniques: an Application to Copper and Magnesium Octaethyl Porphyrin

Using a U （2） algebraic model the fundamental stretching vibrations of copper octaethyl porphyrin and magnesium octaethyl porphyrin are calculated for 24 vibrational bands. The locality parameter ξ confirms the highly local behavior of the stretching modes of these porphyrin molecules. The model Hamiltonian so constructed appears to describe the vibrational energy levels accurately.