First-Principles Study on the Electronic Structures for Y^3＋：PbWO4 Crystals

The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （GULP）. The calculated results indicate that in the lightly doped Y^3＋ ：PWO crystal, the main compensating mechanism is [2Ypb^＋ ＋ VPb^2-], and in the heavily doped Y^3＋ ：PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^＋, forming defect clusters of [2Ypb^＋ ＋Oi^2-] in the crystal. The electronic structures of Y3＋ ：PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.     

Chebyshev spectral variational integrator and applications

The Chebyshev spectral variational integrator(CSVI) is presented in this paper. Spectral methods have aroused great interest in approximating numerically a smooth problem for their attractive geometric convergence rates. The geometric numerical methods are praised for their excellent long-time geometric structure-preserving properties.According to the generalized Galerkin framework, we combine two methods together to construct a variational integrator, which captures the merits of both methods. Since the interpolating points of the variational integrator are chosen as the Chebyshev points,the integration of Lagrangian can be approximated by the Clenshaw-Curtis quadrature rule, and the barycentric Lagrange interpolation is presented to substitute for the classic Lagrange interpolation in the approximation of configuration variables and the corresponding derivatives. The numerical float errors of the first-order spectral differentiation matrix can be alleviated by using a trigonometric identity especially when the number of Chebyshev points is large. Furthermore, the spectral variational integrator(SVI) constructed by the Gauss-Legendre quadrature rule and the multi-interval spectral method are carried out to compare with the CSVI, and the interesting kink phenomena for the Clenshaw-Curtis quadrature rule are discovered. The numerical results reveal that the CSVI has an advantage on the computing time over the whole progress and a higher accuracy than the SVI before the kink position. The effectiveness of the proposed method is demonstrated and verified perfectly through the numerical simulations for several classical mechanics examples and the orbital propagation for the planet systems and the Solar system.     

pH-Dependent Slipping and Exfoliation of Layered Covalent Organic Framework

Layered/two-dimensional covalent organic frameworks (2D COF) are crystalline porous materials composed of light elements linked by strong covalent bonds. Interlayer force is one of the main factors directing the formation of a stacked layer structure, which plays a vital role in the stability, crystallinity, and porosity of layered COFs. The as-developed new way to modulate the interlayer force of imine-linked 2D TAPB-PDA-COF (TAPB = 1,3,5-tris(4-aminophenyl)benzene, PDA = terephthaldehyde) by only adjusting the pH of the solution. At alkaline and neutral pH, the pore size of the COF decreases from 34 Å due to the turbostratic effect. Under highly acidic conditions (pH 1), TAPB-PDA-COF shows a faster and stronger turbostratic effect, thus causing the 2D structure to exfoliate. This yields bulk quantities of an exfoliated few/single-layer 2D COF, which was well dispersed and displayed a clear Tyndall effect (TE). Furthermore, nanopipette-based electrochemical testing also confirms the slipping of layers with increase towards acidic pH. A model of pH-dependent layer slipping of TAPB-PDA-COF was proposed. This controllable pH-dependent change in the layer structure may open a new door for potential applications in controlled gas adsorption/desorption and drug loading/releasing.     

氟锆酸盐玻璃光纤的研制

本文介绍聚全氟乙丙烯包皮的氟锆酸盐(ZrF_4-BaF_2-LaF_3-AlF_3-NaF)玻璃光纤的制备方法.研究了各种工艺因素对氟锆酸盐玻璃和光纤散射损耗的影响.结果表明,选择适当的熔化温度和均化时间,玻璃熔化和光纤拉制时环境中低的水含量是制得的损耗氟锆酸盐玻璃光纤的关键;配合料中引入适量NH_4HF_2,选用温度结构合理的拉丝炉及拉丝工艺也有助于降低光纤的损耗.在此工作基础上,获得了波长2.32μm处损耗为0.24dB/m的氟锆酸盐玻璃光纤.     

无源空心波导谐振腔横模模式的竞争与转换

本文提出并采用非对角化的分析法研究无源空心波导谐振腔横模模式间的竞争与转换。从计算EH_(1m)类波导本征模在腔内的转换矩阵中发现:在模式的传输过程中,存在着横模模式间的相互转换,而且其互换的能量不相等。在一定的腔设计条件下,会出现高阶横模向低阶横模的能量净流动,这有利于谐振腔横模模式的选择和基模输出功率的提高。     

非线性偏置条件下隧道二极管中的触发振荡

本文提出了一类在非线性偏置条件下,由N-型负阻器件构成的具有三个奇点(其中有两个奇点在负阻区)的触发振荡电路。借助于点变换方法研究了该电路的工作特性。分析表明,所提出的电路具有足够宽的触发振荡工作区。用隧道二极管进行了实验,实验结果与理论有较好的符合。     

Lattice Boltzmann Simulations of Particle-Particle Interaction in Steady Poiseuille Flow

The moving behaviour of two- and three-particles in a pressure-driven flow is studied by the lattice Boltzmann simulation in two dimensions. The time-dependent values, including particles＇ radial positions, translational velocities, angular velocities, and the x-directional distance between the particles are analysed extensively. The effect of flow Reynolds number on particle motion is also investigated numerically. The simulation results show that the leading particle equilibrium position is closer to the channel centre while the trailing particle equilibrium position is closer to the channel wall. If Reynolds number Re is less than 85.30, the larger flow Reynolds number results in the smaller x-directional equilibrium distance, otherwise the x-directional distance increases almost linearly with the increase of time and the particles separate finally. The simulation results are helpful to understand the particle-particle interaction in suspensions with swarms of particles.     

关于单位圆内解析系数的二阶线性微分方程的复振荡

对二阶线性微分方程f" A1(z)f' A0(z)f=F(z)的复振荡进行了研究,其中系数Ai(z)(i=0,1)和F(z)是单位圆Δ={z|z|＜1}内的解析函数,获得解的超级和超零点收敛指数的估计,也得到了一些关于解的不动点的结果.     

J-TEXT 扰动场交流电源峰值反馈系统设计

在J-TEXT 装置上设计了一种基于现场可编程逻辑门阵列(FPGA)的数字式峰值检测电路,该电路先对负载电流进行模数(AD)转换,再经有限冲激响应(FIR)滤波器进行数字滤波,然后用峰值算法获取电流峰值,最后经数模转换器(DA)输出电流峰值。在此基础上,完成了扰动场交流电源负载电流峰值反馈系统的设计,实验结果表明系统动态性能好、检测精度高,能很好满足交流电源负载电流反馈控制的需要。     

The Level-split of the Two-level Entangled Atom in an Optical Field

The behavior of a two-level entangled atom in an optical field with circular polarization is studied in this paper. The interaction of an optical field and one of the entangled atoms is analyzed in detail. A general solution of the SchrAo¨Gdinger equation about the motion of the entangled atom is obtained. The properties of the action are dependent on the initial state of the atom. By detecting the entangled atom out of the field, we can obtain the state of the other atom moving in the field. It is shown that the state of the atom out of the field will influence the energies of the split-levels of the atom in the field.