盘荷波导栏片圆弧对频率和尾场的影响

利用变分法详尽地研究了X-波段盘荷波导中栏片圆弧对纵向模和横向模的影响,比较了不同栏片形状下加速模和横向模的频率与尾场。研究表明栏片形状对频率的影响较小,但对尾场的影响较大。在圆弧栏片和直边栏片两种情况下,最危险的EH16模的尾场相差超过15%,因此栏片圆弧的作用是不能忽略的。     

下一代直线对撞机失谐结构尾场的精确计算—盘荷波导电磁场的研究

利用变分法研究了周期性盘荷波导中零极模、二极模及更高极模式的电磁场特性.该方法考虑了栏片的圆弧,对真实结构没有做任何近似,是一种高精度方法,计算表明该方法的结果与实验测量值基本符合,与其它程序相比有很高的计算精度.这为下一步精确研究下一代直线对撞机失谐结构的尾场提供了一个很好的方法与工具.     

基于微波工作室的盘荷波导耦合器设计方法

提出了一种新的盘荷波导耦合器数值设计方法; 通过分析Kyhl提出的耦合器调节原理, 将输入阻抗之间的相差关系转换为耦合器输入波导的边界条件关系, 由此 利用Microwave Studio的EigenMode Solver求解本征值问题来实现对耦合器 调谐、调匹配过程的模拟; 并给出一个实例来说明数值计算方法的可行性和可靠性.     

下一代直线对撞机失谐结构尾场的精确计算：—盘荷波导电磁 …

利用变分法研究了周期性盘荷波导中零极模、二极模及更高极模式的电磁场特性。该方法考虑了栏片的圆弧，对真实结构没有做任何近似，是一种高精度方法，计算表明该方法的结果与实验测量值基本符合，与其它程序相比有很高的计算精度，这为下一步精确研究下一代直线对机失谐结构的尾场提供了一个很好的方法与工具。     

介质壁加速器尾场阻抗的模拟计算

为了研究尾场效应引起的束流不稳定性,建立了由非对称Blumlein脉冲形成线、导体层和微堆层构成的介质壁加速器单元模块模型,用有限积分法对强流电子束在此结构中产生的尾场进行了计算,分别计算单组元和2组单元加速模块中的尾场势和尾场阻抗。从模拟的结果来看,x,y方向的尾场势和尾场阻抗都很小,束流尾场对横向的影响比较小。z方向的尾场势和尾场阻抗影响较大,尾场阻抗达到100Ω量级。证明了由于介质壁加速器结构在加速腔长度和束流通过路径的连续性方面都具有很大的优势,横向阻抗小,束流尾场效应在束流不稳定性方面的影响相对较小,束流传输时的要求也会降低。     

介质壁加速器尾场阻抗的模拟计算

为了研究尾场效应引起的束流不稳定性,建立了由非对称Blumlein脉冲形成线、导体层和微堆层构成的介质壁加速器单元模块模型,用有限积分法对强流电子束在此结构中产生的尾场进行了计算,分别计算单组元和2组单元加速模块中的尾场势和尾场阻抗。从模拟的结果来看,x, y方向的尾场势和尾场阻抗都很小,束流尾场对横向的影响比较小。z方向的尾场势和尾场阻抗影响较大,尾场阻抗达到100 Ω量级。证明了由于介质壁加速器结构在加速腔长度和束流通过路径的连续性方面都具有很大的优势,横向阻抗小,束流尾场效应在束流不稳定性方面的影响相对较小,束流传输时的要求也会降低。     

等离子体尾场加速器中静电波特性

本文在线性近似下求得了等离子体尾场加速器中静电波的频率特征与增长率,对尾场形成机制作了物理解释。     

非线性光波导中基波和二次谐波的模场分布研究

非线性波导是一种重要的光量子器件。采用马卡梯里近似,可以近似描述波导的模场分布特征。针对ee-e准相位匹配的周期极化铌酸锂波导,分析波长为1 064 nm的基波和532 nm的二次谐波的基模模场分布。结果表明:如果波导为嵌入型正方形波导,基波和二次谐波的光斑基本为圆形,基波场分布范围较大;在截面正方形边长为5 μm并且芯区比包层折射率略高0.02时,波导就能将两种光波场基本约束在芯区中,但是这种波导边长为0.5 μm时约束能力就变得很差;如果采用芯区与包层折射率差别较大的波导,芯区边长为0.5 μm就可以将两种场分布基本约束在芯区中。结果对分析其他类型的非线性波导的模场分布具有指导意义。     

γ辐射对光纤波导电磁场分布的影响

开展了光纤波导中的电磁场传输理论分析,得到了光纤折射率变化对波导中电磁场分布的影响规律,建立了块状融石英材料及光纤光栅在60Co 辐射作用下折射率变化的测量系统,开展了折射率随辐射剂量变化及光纤模场测量实验。结果表明:光纤的折射率随辐射剂量的增加而增大,折射率的变化会引起波导中传输模式的场强分布变化,从而导致光纤的辐射感生波导损耗;在一定的辐射剂量范围（0～2000 Gy）内,光纤仍满足弱导边界条件,能够维持对传输模式的约束能力。     

尾波场与相对论效应对激光脉冲自相位调制及频移影响的比较研究

对共振和非共振情形下尾波场效应与相对论效应对强激光脉冲在稀薄等离子体中传输的影响 作了详细比较.尾波场效应导致脉冲自相位调制的不对称性，其大小与初始脉冲形状和脉宽 大小有关.在长脉冲极限下，尾波场效应远小于相对论效应，从而可以忽略；在短脉冲极限 下，尾波场效应可以抵消相对论效应.在共振情况下，尾波场效应导致脉冲内大部分光子减 速. 关键词： 脉冲传输 等离子体 相对论效应 尾波场效应 自相位调制     

弯曲振动薄圆盘的共振频率和等效电路参数研究

机电等效电路是分析复合换能器常用的一种解析方法, 但对薄圆盘而言, 由于弯曲振动的复杂性, 其等效集中参数很难获得, 该方法很少被应用. 本文从分布参数系统与集中参数系统等效角度, 根据动能相等原则和势能相等原则, 给出了弯曲振动薄圆盘的集中参数: 等效质量和等效弹性系数, 得到了共振频率方程, 并用ATILA软件模拟了其振动分布情况, 可以看出解析结果与数值结果趋于一致. 最后给出了分析复合振动系统时薄圆盘集中参数模型的等效电路. 本文的结果对弯曲振动复合换能器的设计提供了理论参考.     

同轴膜片加载圆波导相对论行波管注-波互作用线性理论研究

从改善圆盘加载波导作为相对论行波管慢波结构的特性入手,加入同轴内导体,着重研究其小信号理论。利用场匹配法导出了“热”色散方程并计算求解,具体分析了系统的电子注参量及慢波结构几何尺寸对小信号增益及慢波相速的影响,为同轴圆盘加载相对论行波管的设计提供了理论基础。     

Wall and gravitational effects on the fine structure of interface layers at two-phase coexistence: Some rigorous results

A rigorous inequality is derived relating density gradient, interface thickness, transverse correlation length, and distance of the interface from the wall in the presence of an explicit gravitational (resp. wall potential). The results are relevant to various possible scenarios, e.g. (critical) wetting, drying, roughening, free interfaces (i.e., far away from a wall). Attention is concentrated on the structure of the liquid-gas interface in a gravitational field. Results seem to indicate that the usual intuition concerning the fine structure of the liquid-gas interface (e.g., the capillary wave picture) cannot be entirely correct. The predictions are particularly puzzling in space dimension two. The results are physically interpreted, giving a more refined picture of the interface layer.     

基于边缘几何特征和频域相关技术的图像匹配方法

提出了一种基于图像特征提取和变换域相关的图像匹配方法。借助提取图像的大边缘信息，以其几何特征构造边缘方向角曲线作为图像匹配的依据。通过对差分的计算，并比较两幅图像边缘方向曲线的相对链码，得到2幅图像之间可能的旋转角度。对旋转矫正后的图像进行2维傅里叶变换，计算频域内2图的相位相关矩阵，并从中找到相关系数最大的位置，这个位置就代表了2图的坐标位移量，通过平移达到图像间的精确匹配。实验表明：该方法匹配准确，速度快，减少了人为因素的干扰，对于图像间存在较小灰度差和噪声情况均有很好的匹配效果。     

Influence of crystal structure,ligand environment and morphology on Co L‐edge XAS spectral characteristics in cobalt compounds

The electronic structure of a material plays an important role in its functionality for different applications which can be probed using synchrotron‐based spectroscopy techniques. Here, various cobalt‐based compounds, differing in crystal structure, ligands surrounding the central metal ion and morphology, have been studied by soft X‐ray absorption spectroscopy (XAS) at the Co L‐edge in order to measure the effect of these parameters on the electronic structure. A careful qualitative analysis of the spectral branching ratio and relative intensities of the L₃ and L₂ peaks provide useful insight into the electronic properties of compounds such as CoO/Co(OH)₂, CoCl₂.6H₂O/CoF₂.4H₂O, CoCl₂/CoF₂, Co₃O₄ (bulk/nano/micro). For further detailed analysis of the XAS spectra, quantitative analysis has been performed by fitting the spectral profile with simulated spectra for a number of cobalt compounds using crystal field atomic multiplet calculations.     

Determination of the best carrier frequency based on the system and environmental parameters in underwater acoustic systems

One of the most challenging features of underwater acoustic (UWA) channel in comparison with its terrestrial radio frequency counterpart is highly frequency-dependent path loss. Thus, utilizing efficient carrier frequencies in UWA systems can considerably reduce the path loss. In this context, this paper presents an approximate formula for determining the best carrier frequency based on both the system and environmental parameters. To achieve this goal, this research first addresses a simple algorithm including general steps for tuning the parameters of Francois and Garrison (FG) formula in the frequency range of 10 to 100 kHz based on the appropriate experimental data which can be acquired from any interest region. Second, for a more accurate modeling of path loss, this paper considers the loss due to the reflections of sound from both the rough surface and bottom of the sea by employing the ray theory. Third, this study presents a general algorithm for modification of the power spectral density (PSD) of ambient noise based on Wenz formula in the frequency range of 10 to 100 kHz and the required experimental measurements which can be simply collected from any interest channel. Moreover, it is mathematically demonstrated that the ambient noise in the frequency range of 10 to 100 kHz, can be generally approximated with a strict sense stationary (SSS) colored normal stochastic process which is ergodic not only in mean and covariance but also in distribution. Finally, an approximate formula for the best carrier frequency is derived by maximizing the sound to noise intensity ratio (SNR). To verify the validity of simplifications and approximations utilized in this study and to assess the performance of our proposed algorithms and formulas, experimental results obtained in the Strait of Hormuz (SoH) are compared with the original, simplified, and modified models under different scenarios.     

石墨烯和六方氮化硼纳米片的几何结构、电子结构、磁性及边缘特性研究

采用基于密度泛函理论(DFT)的第一性原理计算方法,计算了多种尺寸的石墨烯和六方氮化硼纳米片的性质,系统研究了其中的量子尺寸效应.研究的最大尺寸纳米片的直径约为5.5 nm,包含816个原子.对纳米片及其边缘的几何结构、电子结构、磁性性质以及电子分布进行了深入探讨,发现石墨烯和六方氮化硼纳米片最外层原子有由锯齿形向圆形变化的趋势,使得纳米片最外层更加平滑.随着纳米片尺寸的增加,能级由分立逐渐变得连续,纳米片由孤立分子态逐渐变得接近无限的晶体;禁带宽度总体有下降的趋势,符合量子尺寸效应.纳米片存在明显的磁性,磁矩主要集中在最外层原子上,且在相对平滑的地方容易出现磁性,相对弯曲的地方不易出现磁性.当增加体系的电子数时,增加的电子主要分布在最外层,使得纳米片整体磁性呈递减的趋势;当减少体系的电子数时,减少的电子的分布逐渐由最外层向内收缩,体系的总磁矩略有增加.研究结果对石墨烯和六方氮化硼纳米片的应用有参考价值.     

Study of the structure factor anisotropy and long range correlations of ferrofluids in the dilute low-coupling regime

Dipolar soft-sphere (DSS) fluids in the dilute low-coupling regime are studied via Molecular Dynamic simulations and the extension of a theoretical formalism previously used for dipolar hard spheres in which new terms for the virial expansion of the radial distribution function corresponding to the three-particle contribution are presented and tested for the zero and non-zero magnetic field case. A thorough comparison with simulations shows that the extended formalism is able to account for the structure factors of DSS with and without externally applied magnetic fields in the dilute low-coupling regime: quantitative agreement between theory and simulations is found for dipolar coupling parameters λ?2, and volume fraction φ?0.25. When λ>1 the new added term to the virial expansion is observed to play a crucial role in order to match quantitatively theory and simulations at zero field. In the presence of an external magnetic field our tests show that further improvements are needed and only new terms with Langevin function dependences can significatively contribute to improve the predictions for the dilute low-coupling regime. Numerical simulations show that despite that the ferrofluids considered here are in the dilute low-coupling regime, when an external field is applied, important correlations along the parallel direction to the field and depletion phenomena along the perpendicular direction are observed in the averaged density surrounding a particle.     

The effects of temperature and frequency on the magnetization switching mode in circular MI sensors

This paper presents results computed using a meshless method in a point collocation formulation to investigate the effects of temperature and frequency on the magnetization switching mode in the circular amorphous magneto-impedance sensor (element). Specifically, the solutions characterizing the MI effect are solved from a set of coupled nonlinear equations consisting of the Maxwell’s equations, the Landau-Lifshitz-Gilbert equation, and the thermal diffusion equation. This coupled nonlinear space-time model predicts the formation and propagation of dynamic domain walls in switching and it is shown how they contribute to experimentally observed temperature and frequency effects. Computed results (that agree well with reported experimental data) suggest radial domain walls may play a larger role in the MI effect than originally believed even for the realistic conditions considered here at 1 MHz or more.