二维Ising反铁磁-反铁磁超晶格的磁性

本文用有效场理论讨论二维反铁磁一反铁磁超晶格(AFAFs)在无外场时的临界温度与超晶格结构的依赖关系,并讨论了超晶格中每一层的磁化强度、磁化率与温度和超晶格结构的依赖关系,得到了由于超晶格结构导致的磁化率的异常峰的存在.并从超晶格的对称性出发讨论了反铁磁-反铁磁超晶格和铁磁-铁磁超晶格之间的异同.     

光晶格原子钟研究进展

经过近20年的发展,基于光频跃迁的光晶格原子钟展示了优异的频率稳定度和不确定度,是重定义时间单位“秒”的有力候选者之一。随着地面基准光晶格原子钟性能的提升,光晶格原子钟已经成功地走出了实验室,实现了可搬运晶格原子钟并正在研制可在太空中运行的空间光晶格原子钟。本文综述了影响光晶格原子钟稳定度和准确度的关键因素,以及抑制或者消除这些因素的主要技术;并结合国内外的研究成果,综述了地面基准光晶格原子钟、可搬运光晶格原子钟和空间光晶格原子钟的技术特点和研究进展。     

无衍射二维光学晶格的仿真方法

无衍射光学晶格主要采用函数传递的方式进行数值计算分析,数学模型抽象,程序构建复杂,难以灵活地分析不同光学元件及其缺陷和光路结构对光学晶格物理形成过程的影响。从光路仿真角度出发,提出了一种无衍射光学晶格的分析方法,实现了基础方晶格、最大对称组合基础方晶格、一级稀疏方晶格等典型光学晶格结构的仿真,并验证了光束的无衍射性,说明了该方法的可行性。将该方法应用于光路结构和光学元件特性与光学晶格结构之间的关联分析,有助于探索无衍射二维光学晶格的形成与调控方法,以及潜在应用效果的评估。     

改进型FCC晶格材料设计与吸能特性

基于金属微观晶体结构,设计了一种改进型面心立方(FCC)晶格材料。利用ABAQUS有限元软件,对体心立方(BCC)及FCC晶格材料进行了准静态与速度为10~100 m/s的动态加载数值模拟,定量分析了两种晶格材料的能量吸收性能,给出了动态加载下晶格材料压缩平台应力及塑性能量耗散的半经验公式。结果表明:在准静态压缩载荷下,相同相对密度的FCC晶格比BCC晶格具有更优异的能量吸收性能,当相对密度为10.5%~10.6%时,FCC晶格材料的归一化比吸能是BCC晶格材料的2.6倍。此外,与常见负泊松比材料及大部分桁架晶格材料相比,相同相对密度的FCC晶格材料具有更高的比刚度、能量吸收效率及压缩力效率。     

近共振三维光学晶格中铯原子温度的参数依赖

介绍了四光束三维近共振光学晶格的方案,在铯原子磁光阱和光学粘团的基础上搭建了近共振光学晶格的光路,实现了光学晶格中冷原子的装载.利用短程飞行时间吸收法测量了近共振光学晶格中冷原子的温度,通过改变晶格的光强和失谐等条件,对近共振光学晶格中铯原子的亚多普勒冷却的参数依赖关系作了实验研究,并与光学粘团作了比较.     

基于平面波展开法的二维光子晶体表面模式研究

采用平面波展开法研究了四种二维光子晶体结构(圆柱介质柱四方晶格、圆柱介质柱三角晶格、正方介质柱四方晶格、正方介质柱三角晶格)的带隙宽度随介质柱尺寸变化的关系.使用平面波展开法计算常规晶格和表面缺陷晶格的模式并进行结果叠加,研究了各结构的二维光子晶体在带隙宽度最大时的表面模式.结果表明,同种晶格的光子晶体带隙宽度随着介质柱的尺寸增大呈先增后减趋势,存在最大值.随着表面介质柱尺寸的增加,四种晶格表面模式曲线均呈下降趋势.四方晶格光子晶体与三角晶格相比,表面介质柱尺寸的变化范围更大,但能获取表面模式频率范围较小.     

基于~(87)Rb原子的大失谐光晶格的设计与操控

提出了一种基于~(87)Rb原子的大失谐光学晶格的设计方案,详细介绍了光晶格光束的校准、频率失谐的调整以及光强输出的控制方式.在磁光阱和偏振梯度冷却的基础上,研究了光学晶格的总光强和频率失谐等参数对原子装载的影响,实现了光晶格中冷原子的绝热装载与卸载.通过光强调制的方法,测量了光晶格的振动频率.光晶格的引入,使得温度降低为原有的1/3.涉及的系统设计和结论对其他碱金属原子光晶格的实验设计具有参考价值.     

极性补偿对LaMnO3/LaNiO3超晶格交换偏置场强度的影响

钙钛矿超晶格中蕴含着丰富的磁现象,特别是锰酸镧/镍酸镧超晶格中的异常磁交换偏置现象是一个研究热点.本文采用脉冲激光沉积技术,制备出不同取向的锰酸镧/镍酸镧超晶格,并对超晶格的电输运性能和交换偏置现象进行了系统的研究.实验发现,超晶格在不同取向的衬底上外延生长并保持晶格应力;超晶格的母体是Mott绝缘体并遵循二维Mott变程跃迁导电机理;不同取向的超晶格都表现出交换偏置现象;场冷和零场冷曲线表明在低温下超晶格中存在两种不同的磁性组元.对超晶格交换场强度的进一步分析发现,交换场强度与超晶格的取向以及超晶格与衬底界面处的极性补偿有关.在不同温度下都观察到,极性连续的超晶格的交换场强度都高于极性失配的超晶格.上述研究结果对进一步理解钙钛矿超晶格中的磁电输运性能有所帮助.     

不同结构光子晶体的带隙特性

基于平面波展开法研究光子晶体的带隙特性,数值模拟了横磁波和横电波在三角晶格和正方晶格构成的二维光子晶体中的带隙特性,得到了三角晶格较正方晶格更容易出现带隙,且三角晶格的横电波光子带隙较大.实验结果为光子晶体器件的设计提供理论依据.     

基于平面波展开法的二维光子晶体表面模式研究

采用平面波展开法研究了四种二维光子晶体结构(圆柱介质柱四方晶格、圆柱介质柱三角晶格、正方介质柱四方晶格、正方介质柱三角晶格)的带隙宽度随介质柱尺寸变化的关系.使用平面波展开法计算常规晶格和表面缺陷晶格的模式并进行结果叠加,研究了各结构的二维光子晶体在带隙宽度最大时的表面模式.结果表明,同种晶格的光子晶体带隙宽度随着介质柱的尺寸增大呈先增后减趋势,存在最大值.随着表面介质柱尺寸的增加,四种晶格表面模式曲线均呈下降趋势.四方晶格光子晶体与三角晶格相比,表面介质柱尺寸的变化范围更大,但能获取表面模式频率范围较小.     

Optical surface modes of lattice vibrations

Two simple methods, based on simple crystal models, for estimating the longitudinal optical surface vibration mode frequencies which lie in a LALO gap are examined. One method consists of deriving and solving a single-variable equation for the surface mode frequency, which depends only on the experimental bulk dispersion curves. The other method consists of fitting the known dispersion curves of a simple one-dimensional model, for which the optical surface mode frequency is given by a simple expression, to experimental bulk dispersion curves of more complex crystals. The results are compared with detailed theoretical surface mode calculations. The latter method is found to give better estimates.     

管靶X射线辐射输运初步研究Ⅰ简化模型数值模拟与分析

运用简化的X射线输运模型对管靶中的X射线输运进行初步的数值模拟与分析.介绍X射线输运的简化模型,给出相关参量,推导出视角因子的积分表达式,对视角因子进行数值计算,讨论了简化输运模型方程的数值解法.由数值计算结果得到辐射输运的定标公式,提出三种与辐射输运有关的自由程概念,使得辐射输运的定标公式具有明确的物理意义.     

On the role of the image potential in electron surface studies

Exchange and correlation contributions to the vacuum part of the effective electron potential of a semiinfinite crystal are modelled by a simple shifted image potential. Modifications, introduced by this potential, are studied for the cases of electron surface states and of the diffraction of low-energy electrons on a simple one-dimensional model.     

Generating Simple Random Graphs with Prescribed Degree Distribution

Let F be a probability distribution with support on the non-negative integers. Four methods for generating a simple undirected graph with (approximate) degree distribution F are described and compared. Two methods are based on the so called configuration model with modifications ensuring a simple graph, one method is an extension of the classical Erdös-Rényi graph where the edge probabilities are random variables, and the last method starts with a directed random graph which is then modified to a simple undirected graph. All methods are shown to give the correct distribution in the limit of large graph size, but under different assumptions on the degree distribution F and also using different order of operations.     

On Factorization of Coupled Channel Scattering S Matrices

We investigate the problem on how to factorize a coupled channel scattering S matrix into a product of simple S matrices. Simple S matrix solntions are found, respecting unitarity, analyticity and being real analytic. The phase shift and its physical meaning produced by these simple S matrices are discussed.     

Approximate treatment for semi-core states

The “semi-core” states which are not completely localized on a single atomic site are nonetheless simple enough in structure as not to require a full energy band calculation for their inclusion into the charge density. A simple approximate technique to accomplish this is presented.     

Series expansions of rotating two and three dimensional sound fields

The cylindrical and spherical harmonic expansions of oscillating sound fields rotating at a constant rate are derived. These expansions are a generalized form of the stationary sound field expansions. The derivations are based on the representation of interior and exterior sound fields using the simple source approach and determination of the simple source solutions with uniform rotation. Numerical simulations of rotating sound fields are presented to verify the theory.     

On neutrino and antineutrino scattering by electrons,and by partons

Assuming a non-derivative point interaction, and Born approximation, there are some simple relations between neutrino and antineutrino scattering on electrons or partons. They have been observed already, for some special cases, in the results of explicit calculations. Here they are obtained from simple general considerations.     

Angular distributions of neutrino and antineutrino scatterings by electrons and gauge models

Assuming a nonderivative point interaction, and Born approximation, the complete angular distributions for the scatterings of neutrinos and antineutrinos by electrons are obtained from only simple general considerations, without explicit calculation; the simple extension to parton targets is noted. Two pairs of simple constraints on the angular distributions can be violated only if the interaction has a helicity-flipping component; this can serve to disfavour the large class of models which are purely helicity-conserving. Comparison is made with some explicit calculations done for special cases of some of our results.