非对称脉冲超强激光产生的尾场空泡区和超空泡区中的正电子加速

在震荡中心哈密顿原理的(oscillation-center Hamiltonian)框架下,讨论了用非对称圆极化的强激光脉冲激发的尾场和在超空泡区中加速正电子的相关问题.研究内容包括:在超强激光所激发的空泡后区中的尾场正电子加速方法和在超空泡区中的雪梨(snow-plow)正电子加速方法.通过理论分析和数值模拟方法定性地比较了2种正电子加速方法的有效加速性能.结果显示,尾场加速的效果比雪梨加速好,2种加速方法中激光脉冲振幅与被加速正电子的能量之间分别存在着指数关系和线性关系.文中还分析了正电子最大尾场和雪梨加速能量与等离子体密度之间的关系     

Molecular Dynamics Simulation of 4-N-Hexyl-4'-Cyanobiphenyl Adsorbed at the Air-Water Interface

The interfacial behavior of 4-n-hexyl-4'-cyanobiphenyl(6CB) molecules at the air-water interface is investigated by full atomistic molecular dynamics simulations. To understand the morphology and the structure of adsorbed 6CB molecules in detail, the snapshots and mass density profiles of the simulation system are generated. The average tilt angles between the interface normal and various vectors defined in the rigid and alkyl parts of 6CB are in good agreement with the experimental data available. The interfacial thickness and monolayer width are obtained from the mass density profiles of water and 6CB phase, respectively. The second and fourth rank orientational order parameters of cyanobiphenyl core are found to be larger than those of an elastic alkyl chain.Bond order parameters for 6CB are also calculated. The calculated oxygen-oxygen radial distribution function and hydrogen bonding statistics for bulk water are compared with those for the interfacial region. The surface tensions of the systems are calculated. All simulation results are compared with the available literature data.     

Theoretical Studies on Electronic Structures and Spectroscopy of Fluorescent Arylamino Fumaronitrile

设计了一系列发荧光的芳胺氰化物, 并用密度泛函方法在B3LYP/6-31G*水平上进行几何构型优化．在优化构型基础上,分别用INDO/CIS、AM1、CIS-ZINDO TD和B3LYP/6-31G*方法计算了芳胺氰化物的电子光谱、红外光谱、荧光光谱及核磁共振碳谱．结果表明,与母体相比,由于萘环较大的立体效应使氰化物的能隙变宽,荧光光谱及电子光谱的主要吸收峰发生蓝移．而由于电子被分散到萘环上,氰化物的主要红外频率发生红移．相反,羟基的存在改善了分子的对称性,扩展了共轭体系,使能隙变窄,荧光光谱及电子光谱的主要吸收峰发生红移．同时由于羟基的供电效应,C-H伸缩振动发生蓝移．     

A new strategy for the stereoselective synthesis of 2,3-dideoxy-3-fluoro-D-ribofuranose derivatives

The important intermediate for syntheses of various anti-HIV nucleoside analogues, methyl 2,3-dideoxy-3-fluoro-6-O-(p-methylbenzoyl)-a-D-ribofuranoside, was synthesized starting from 2-deoxy-D-ribose in 5 steps with an overall yield of 24%. This strategy can be also used for synthesizing other analogues with various substitutions at 3-C position.     

Stress Analysis And Geometrical Configuration Selection for Multilayer Piezoelectric Displacement Actuator

Multilayer piezoelectric ceramic displacement actuators are susceptible to cracking in the region near the edge of the internal electrode, which may cause system damage or failure. In this paper, the stress distribution of a multilayer piezoelectric composite is investigated in a working environment and the optimized geometrical con?guration of the piezoelectric layer is obtained. The stress distribution in the structure and the stress concentration near the edge of th…     

钢筋混凝土梁的受压区高度计算的统一公式

本文将单筋矩形截面钢筋混凝土梁的受压区高度计算公式进行了推广，使之可以用于双筋或Ｔ形截面．     

TIME PERIODIC SOLUTIONS TO THE EVOLUTIONARY OSEEN MODEL FOR A GENERALIZED NEWTONIAN INCOMPRESSIBLE FLUID

In this paper we study a nonstationary Oseen model for a generalized Newtonian incompressible fluid with a time periodic condition and a multivalued, nonmonotone friction law. First, a variational formulation of the model is obtained; that is a nonlinear boundary hemivariational inequality of parabolic type for the velocity field. Then, an abstract first-order evolutionary hemivariational inequality in the framework of an evolution triple of spaces is investigated. Under mild assumptions, the no...     

Ultrabright γ-ray emission from the interaction of an intense laser pulse with a near-critical-density plasma

An efficient scheme for generating ultrabright γ-rays from the interaction of an intense laser pulse with a near-critical-density plasma is studied by using the two-dimensional particle-in-cell simulation including quantum electrodynamic effects. We investigate the effects of target shape on γ-ray generation efficiency using three configurations of the solid foils attached behind the near-critical-density plasma: a flat foil without a channel (target 1), a flat foil with a channel (target 2), and a convex foil with a channel (target 3). When an intense laser propagates in a near-critical-density plasma, a large number of electrons are trapped and accelerated to GeV energy, and emit γ-rays via nonlinear betatron oscillation in the first stage. In the second stage, the accelerated electrons collide with the laser pulse reflected from the foil and emit high-energy, high-density γ-rays via nonlinear Compton scattering. The simulation results show that compared with the other two targets, target 3 affords better focusing of the laser field and electrons, which decreases the divergence angle of γ-photons. Consequently, denser and brighter γ-rays are emitted when target 3 is used. Specifically, a dense γ-ray pulse with a peak brightness of 4.6×10²⁶ photons/s/mm²/mrad²/0.1%BW (at 100 MeV) and 1.8×10²³ photons/s/mm²/mrad²/0.1%BW (at 2 GeV) are obtained at a laser intensity of 8.5×10²² W/cm² when the plasma density is equal to the critical plasma density n_c. In addition, for target 3, the effects of plasma channel length, foil curvature radius, laser polarization, and laser intensity on the γ-ray emission are discussed, and optimal values based on a series of simulations are proposed.     

扰动角关联在表面研究中的应用

扰动角关联方法,作为一种超精细相互作用技术,具有高的微观灵敏度,可研究局部范围的表面性质.其在表面研究中的应用已涉及表面现象的各个方面,揭示了一系列感兴趣的现象.通过测量作用在探核上的电场梯度,可辨认探针在表面的不同位置,研究杂质与探针相互作用及扩散过程.利用扰动角关联技术已经观察到探核从表面吸附位置经与台阶有关的位置到达表面最上层晶格点阵替位的微扩散过程.本文综述扰动角关联在表面物理研究中的应用以及Ni 单晶表面和超薄Ni 膜磁性质研究的最新结果. Recently,the perturbed angular correlation (PAC) technique with the microscopicsensitivity to study local surface properties has been applied to study surface phenomena.The electricfield gradient acting at the probe nuclei can serve as a fingerprint to elucidate different probe sites atthe surface,impurity-probe configurations and diffusion of impurities.The microscopic diffusion ofPAC-probes from adatomic sites via step sites to substitutional terrace sites has been observed withPAC...