不同晶体取向下纳米压痕的多尺度模拟

采用准连续介质多尺度方法模拟面心立方金属铝单晶薄膜的纳米压痕变形过程.对薄膜分别采用三种不同的晶体取向(分别为x［1 1 1］,y［1 1 0］,z［1 1 2］; x［1 1 2］,y［1 1 1］,z［1 1 0］;x［1 1 0］,y［0 0 1］,x［1 1 0］),得到载荷-位移响应曲线.加载过程中,对晶体内部变形比较剧烈的部分画出原子图,并从微观角度分析产生剧烈变形的原 关键词： 纳米压痕 准连续介质方法 晶体取向 位错成核     

噪声环境下基于两体纠缠态的远程态制备

本文研究了量子噪声对分别以Einstein-Podolsky-Rosen （EPR）态和两体部分纠缠态作为量子信道来远程制备单比特态的量子过程的影响. 通过求解Lindblad形式的主方程,得到量子信道随时间的演化,采用迹距离来度量不同噪声情况下输出态与初态的接近程度. 研究表明,作用在z方向的噪声对远程态制备的影响最弱,而同时作用在x,y,z方向的噪声对远程态制备的影响最强. 关键词： 远程态制备 迹距离 纠缠态 噪声信道     

多点边值问题的插值矩阵法及误差分析

插值矩阵法是求解多点边值问题的数值法。本文给出的该法的误差分析,论证了插值矩阵法解得的y(x),y'(x),…,y^(m)(x)有相同的精度,并对二阶方程,给出该法的稳定性证明和收敛阶。     

MgB2各向异性光学性质的第一性原理研究

使用密度泛函第一性原理研究了超导体MgB₂单晶各向异性的光学性质.在描述光学性质的基本理论和计算方法的基础上,计算了MgB₂的光电导谱、反射谱以及电子能量损失谱,并通过MgB₂的各个原子分解态密度图对所得到的反射谱和损失谱的各个谱峰做了详尽地分析.从光电导谱上来看,x方向与z方向有着很大差别,而在反射谱与电子能量损失谱中,x方向与z方向的特征峰位置都是相互符合的.从光导谱来看,沿 关键词： 超导体 电子结构 光学性质     

强耦合混沌系统中的近似同步

以单向驱动耦合Lorenz振子一维链为研究对象，研究振子间的混沌同步行为. 数值计算结果表明，对于变量y驱动x的耦合方式，在合适的耦合强度下，会出现第一个振子和第二个振子不同步，而与次近邻非直接连接的振子(如第三个振子)近似同步. 进一步研究表明，出现这一现象的原因是在大耦合强度下，对于这种驱动方式，第一个振子和第二个振子间出现驱动单变量近似同步；虽然它们之间未出现所有变量的完全同步，但是驱动信号事实上已经传递下去了. 关键词： Lorenz振子 混沌同步 近似同步     

基于光反馈的单向耦合注入垂直腔表面发射激光器的矢量混沌同步特性研究

基于自旋反向模型(SFM)，数值研究了基于光反馈的单向耦合注入垂直腔表面发射激光器的矢量混沌同步特性，研究结果表明：当外部光反馈时间等于光从发射系统到接收系统传输时间时， x偏振模和y偏振模都能接收最好的完全混沌同步质量.若外部光反馈时间不等于传输时间且注入电流接近阈值电流时，占主导的y偏振模能暂时实现较好的完全混沌同步质量.相比较而言，占主导地位的x偏振模至始至终获得很差的同步质量，另外，当系统输出为混合偏振模时，混合偏振模中的每一个线性偏振模获得很差完全同步质量.然而，当注入电流远大于阈值电流时，系统输出仅为y偏振模，这时y偏振模能稳定地实现最好的完全混沌同步质量.最后，当接收激光器受到线性偏振模的强注入时，每一个注入线性偏振模能与接收激光器输出的对应的线性偏振模实现很好的注入锁定同步.然而，每一个占主导的线性偏振模比另一被抑制的线性偏振模获得更差注入锁定同步质量、如果有相等的能量的两个线性偏振模同时存在，这两个线性偏振模获得差不多一致的注入锁定混同步质量， 换句话说，能量较少的线性偏振能获得较高的注入锁定同步质量. 关键词： 线性偏振态 垂直腔表面发射激光器 完全矢量混沌同步 强注入锁定矢量混沌同步     

部分相干径向偏振光束传输中相干性研究

根据广义惠更斯理论及相干偏振统一理论, 研究部分相干径向偏振光束在自由空间中传输时, 不同参考点处复相干度随传输距离的变化规律. 研究表明, 部分相干径向偏振光束在自由空间中传输, 不同参考点处, 复相干度模值随距离的变化规律有所差别. 当参考点位于原点时, 随着传输距离增大, μ_xx模值及μ_xy模值分布形式不变, 分布范围增大; 当参考点位于x轴上时, μ_xx模值由单峰值向三峰两谷对称形式演化, μ_xy模值由单侧两峰向四峰四谷对称形式演化, 完成演化所需传输距离与参考点距离x轴中心的远近有关, 参考点距离x轴中心越近, 完成演化所需的传输距离越短; 当参考点位于y轴时, 随着距离增大, μ_xx模值分布形式不变, 分布范围增大, μ_xy模值由上侧两峰向四峰四谷对称形式演化, 演化所需传输距离与参考点距y轴中心远近有关, 参考点距y轴中心越近, 完成演化所需的传输距离越短; 当参考点位于其他位置时(非特殊位置), μ_xx模值及μ_xy 模值分布规律, 遵从各自参考点在x轴, y轴上的分布规律的结合即参考点位于其他位置时, μ_xx模值及μ_xy模值分别随距离变化逐渐演化成三峰结构、四峰结构.     

中红外高双折射高非线性宽带正常色散As2 S3光子晶体光纤

设计了一种中红外As₂S₃光子晶体光纤,利用多极法研究了这种光纤的双折射、色散和非线性特性.数值研究发现,该光纤在中红外波段λ = 3.625 μm处双折射B高达0.098;其x偏振方向的非线性系数γ_x达到了1.69 m^-1 ·W^-1, y偏振方向的非线性系数γ_y达到了0.78 m^{- 关键词： 光子晶体光纤 中红外波段 双折射 非线性}     

Mg-Al-N三元团簇的密度泛函理论研究

运用杂化密度泛函方法B3LYP在6-311+G^*计算水平上研究Mg_xAl_yN(x,y=1-5)团簇的结构.对Mg_xAl_yN团簇最低能量结构的稳定性和电子特性进行研究.结果表明,Mg_xAl_yN(x+y≤4)团簇的构型主要是平面结构.Mg_xAl_yN团簇的最低能量结构主要是由Al_nN或Mg_x-1Al_y+1N的构型演变而来.Mg_xAl_yN团簇离解成原子或者较小团簇是相对稳定的.和相邻团簇相比,MgAl₃N和Mg₃Al₃N拥有较高的稳定性.随着团簇尺寸的增加,Mg_xAl_yN团簇同时表现出共价键,离子键和金属键的特点.另外,随着团簇尺寸的增加,团簇的垂直电离势和电子亲合能呈现小的震荡,但并没发现整体的变化规律.     

利用非稳定子态容错实现密集旋转操作

Non-Clifford操作不能在量子纠错码上自然横向实现, 但可通过辅助量子态和在量子纠错码上能横向实现的Clifford操作来容错实现, 从而取得容错量子计算的通用性. 非平庸的单量子比特操作是Non-Clifford操作, 可以分解为绕z轴和绕x轴非平庸旋转操作的组合. 本文首先介绍了利用非稳定子态容错实现绕z轴和绕x轴旋转的操作, 进而设计线路利用魔幻态容错制备非稳定子态集, 最后讨论了运用制备的非稳定子态集模拟任意非平庸单量子比特操作的问题. 与之前工作相比, 制备非稳定子态的线路得到简化, 成功概率提高, 且在高精度模拟任意单量子比特操作时所消耗的非稳定子态数目减少了50%. 关键词： 容错量子计算 非稳定子态 魔幻态 Clifford操作     

A continuum model of a solid with a free surface: I. Normal mode analysis of the model

A complete analysis is made of the normal modes of an isotropic continuum model of a solid which occupies the region (0, 0, 0) < (x, y, z) < (X, Y, Z), the limit (X, Y, Z) → (∞,∞,∞) being taken. The surface z = 0 is a free surface and that z = Z is fixed; cyclic boundary conditions are used in the x and y directions. The modal displacements (vectors), modal frequencies (as a function of the wave-vectors), and wave-vector-densities are obtained for all types of normal modes; the work is a modification and extension of that of earlier workers.     

Influence of Nd substitution on the superconducting properties of ceramics in the 2212 system Bi2−wPbwSr2−xCa1−yNdx+yCu2O8+z

In the system Bi_2−wPb_wSr_2−xCa_1−yNd_x+yCu₂O_8+z different fractions of Nd are substituted on either Sr of Ca sites in order to introduce intrinsic insulating pinning centres. It is shown that a Nd concentration around x or y = 0.2 is likewise favourable with an average Nd---Nd distance in the range of the coherence length in the a, b-plane. However, clear evidence of flux pinning is only present for charge compensation with Pb²⁺. A simultaneous substitution of the Bi-based 2212 superconductor with moderate amounts of Nd³⁺ and Pb²⁺ improves the superconducting properties by strengthening the flux pinning forces.     

二维平板间驻波声流的MRT-LBM数值研究

采用多松弛时间格子玻尔兹曼方法（Multiple Relaxation Time Lattice Boltzmann Method,MRT-LBM）对二维平板间的驻波声流进行数值模拟,模拟结果与Rayleigh流近似解析解相符,研究黏度和板间宽度对驻波声流的影响,得到不同黏度下x=L/4截面无量纲水平速度分布和x=L/2截面无量纲竖直速度分布,板间宽度对边界层内声流区域厚度的影响及驻波声流的形成过程,结果表明MRT-LBM模型能有效模拟驻波声流效应.     

特低渗透油藏面积井网见水时间计算

特低渗透油藏在水驱开发过程中常表现出渗透率各向异性和流体非达西渗流特征,运用非达西渗流公式及流线积分法,得到特低渗透油藏五点井网、反九点井网和菱形反九点井网在油水两相非活塞式驱替条件下的油井见水时间.计算长庆鄂尔多斯盆地某特低渗透油藏井网见水时间,结果与实际动态符合较好.分析油水黏度比、渗透率各向异性及启动压力梯度对油井见水时间的影响,结果表明：油水黏度比越大,油井的见水时间越早;当菱形反九点井网长轴方向井距与短轴方向井距之比与渗透率各向异性强度大致相等时,长轴方向与短轴方向上的角井能实现均衡驱替;启动压力梯度延缓了油井的见水时间,且生产井距越大,启动压力梯度的影响越显著.     

Localized canting of spins structure in the spinel oxide system: ZnzTizFe2−x−zCrx−zCoO4

The spinel oxide system Zn_zTi_zFe_2−x−zCr_x−zCoO₄; z=x²; x=0.60, 0.65, 0.70 and 0.80, was studied using neutron diffraction technique, low field DC magnetization measurements (ZFC–FC measurements), magnetic hysterisis, Mössbauer spectroscopy and low field AC susceptibility measurements. All the compositions show significantly less B-site magnetic moments at 10 K temperature derived from neutron diffraction data than the free ions site moments deduced assuming collinear arrangement of spins. This combined with some other features seen in the low temperature neutron diffraction patterns suggest localized canting of spins (LCS) type of magnetic ordering in the present system where a long range order of longitudinal component of moments co-exists along with totally disordered transverse component of moments. The conclusion is also supported by the features seen in the other measurements. The magnetic moments derived from 10 K neutron diffraction data are explained using the LCS approach for different exchange integrals ratios.     

Scaling limit of deeply virtual compton scattering

I outline a perturbative QCD approach to the analysis of the deeply virtual Compton scattering process γ^*p → γp′ in the limit of vanishing momentum transfer t = (p′ − p)². The DVCS amplitude in this limit exhibits a scaling behavior described by two-argument distributions F(x,y) which specify the fractions of the initial momentum p and the momentum transfer r ≡ p′ − p carried by the constituents of the nucleon. The kernel R(x,y;ξ,η) governing the evolution of the non-forward distributions F(x,y) has a remarkable property: it produces the GLAPD evolution kernel P(x/ξ) when integrated over y and reduces to the Brodsky-Lepage evolution kernel V(y,η) after the x-integration. This property is used to construct the solution of the one-loop evolution equation for the flavor non-singlet part of the non-forward quark distribution.     

Effect of cobalt substitution on cationic distribution in LiNi1 − y CoyO2 electrode materials

A crystal chemistry study of LiNi_{1 − y}Co_yO₂ phases, used as positive electrode in lithium batteries, is presented. These materials crystallize in the rhombohedral system (space group: R m) with a layered structure. Rietveld profile refinement of the X-ray data shows that for low substitution amounts ( ≤ 0.20) extra-nickel ions are always present leading to the Li_{1 − z}Ni_{1 + z − t}CotO₂ (t = y(1 + z)) formula (z * > 0), while for y ≥ 0.30, a pure 2D structure is obtained (z = 0). The stabilization of the 2D character of the structure by cobalt substitution in lithium nickelate leads to the improvement of the electrochemical properties.     

Holographic imaging of side-scattering particles

An off-axis holographic system in the side-scattering mode has been studied, and the requirements of fringe resolution and film sensitivity associated with holographic imaging of side-scattering particles analysed. By assuming the Mie scattering model, the fringe distribution about the y-axis (perpendicular to the plane of incidence of the reference light) was found to be asymmetrical, with unevenly distributed spacing, that is narrower in one x direction but greater in the side that is close to the origin. It was demonstrated that commercially available holographic film was sufficient to resolve the fringe frequency over the entire area of the holographic plate, at 60 ° for z = 120 mm, and that images of particles as small as 20 μm could be recorded. Astigmatism was found to occur and be responsible for the distortions of the particle images.     

Response of line focus acoustic microscope to specimen containing a subsurface crack

A numerical model is presented to calculate V(z) and V(x, z) curves for a line focus acoustic microscope and a specimen containing a subsurface crack. In this model, a Gaussian beam which is tracked through the lens into the coupling fluid and into the specimen, interacts with the crack. The numerical approach is based on the solution of singular integral equations by the boundary element method. The system of singular integral equations follows from the conditions at the interface of the coupling fluid and the specimen and on the faces of the crack. An electromechanical reciprocity relation is used to express the voltage at the terminals of the microscope's transducer in terms of the calculated incident and back-scattered fields. V(z) and V(x, z) curves are presented for various locations and orientations of the crack. The characteristic features of the V(z) and particularly the V(x, z) curves, as they relate to crack configuration, are discussed in some detail.     

Effects of magnetic field on the evolution of the wave function of a charged particle with an angular momentum

We have calculated the effect of a magnetic field on the evolution of angular momentum eigenfunctions of a charged particle. An additional harmonic potential is supplemented to trap the wave packet. We find the probability density of the wave function is oscillating in the radial direction with a time period determined by the strength of the effective harmonic potential. When the magnetic field is along the z direction, if the initial wave function is an eigenfunction of ${\hat{L}}_{z}$, the probability density of the particle remains axis-symmetric. While for the case of an eigenfunction of ${\hat{L}}_{x}$, it is anisotropic in the x−y plane and rotates with a time period inverse proportional to the strength of the external magnetic field. We also extend the results in a phenomenological way to the case with an external magnetic field that varies harmonically in time.