相干光注入半导体激光器锁定过程的稳定性和到达混沌态的各种不稳定现象

本文从半经典理论出发,导出半导体激光器相干光注入锁定过程的基本方程组,讨论了静态解的多支性及其稳定性,稳态调制特性及其稳定性,锁定区内外各种不稳定现象及其在光注入条件下参数平面上的分布,发现锁定区内不稳定区中部存在一混沌区,而在靠近稳定区下边界则存在一自脉动区,混沌区与自脉动区之间是其过渡区;发现到达混沌态可通过自脉动分岔(2^p型和非2^p型)、拍频自调制,以及其混合型等新的路径。 关键词：     

多叶应力区扭转光纤的耦合模理论

从线性极化模的耦合模理论出发,分析了双叶应力区扭转光纤,即扭转保偏光纤,和四叶应力区扭转光纤.推导应力引起的在光纤芯区各向异性的介质张量表达式;利用该表达式得到线性极化模在有转角时的多叶应力区光纤中传输的耦合模方程;从而推得多叶应力区扭转光纤中的超本地模,由超本地模的相位常数来确定该光纤的双折射.在双叶、四叶应力区理想对称的条件下,前者可以得到较高的椭圆双折射,而后者则无任何双折射.同样的结论可推广到8叶或16叶的扭转光纤,都无任何双折射.     

Region Graph Partition Function Expansion and Approximate Free Energy Landscapes: Theory and Some Numerical Results

Graphical models for finite-dimensional spin glasses and real-world combinatorial optimization and satisfaction problems usually have an abundant number of short loops. The cluster variation method and its extension, the region graph method, are theoretical approaches for treating the complicated short-loop-induced local correlations. For graphical models represented by non-redundant or redundant region graphs, approximate free energy landscapes are constructed in this paper through the mathematical framework of region graph partition function expansion. Several free energy functionals are obtained, each of which use a set of probability distribution functions or functionals as order parameters. These probability distribution function/functionals are required to satisfy the region graph belief-propagation equation or the region graph survey-propagation equation to ensure vanishing correction contributions of region subgraphs with dangling edges. As a simple application of the general theory, we perform region graph belief-propagation simulations on the square-lattice ferromagnetic Ising model and the Edwards-Anderson model. Considerable improvements over the conventional Bethe-Peierls approximation are achieved. Collective domains of different sizes in the disordered and frustrated square lattice are identified by the message-passing procedure. Such collective domains and the frustrations among them are responsible for the low-temperature glass-like dynamical behaviors of the system.     

基于模式转换及双峰谐振效应的薄包层镀膜长周期光纤光栅特性研究

基于耦合模理论,首先研究了镀膜长周期光纤光栅(LPFG)高阶包层模的模式转换,划分了高阶包层模的非模式转换区及模式转换区。分析了高阶包层模有效折射率随薄膜厚度增加的响应特性,包层模谐振波长在模式转换区的偏移量要大于非模式转换区。在此基础上,研究了不同包层半径下高阶包层模谐振波长随光栅周期的变化情况,结果表明,相同包层半径下模式转换区内双峰间距的偏移量大于非模式转换区;无论在模式转换区还是非模式转换区,包层半径的减小将增加双峰间距的偏移量。最后分析了不同包层半径下的高阶包层模双峰透射谱在模式转换区及非模式转换区内的折射率响应,进而提出了薄包层镀膜LPFG的优化设计方案,当选定敏感膜层厚度及折射率处于镀膜LPFG的模式转换区内,光栅周期靠近相位匹配转折点时,将得到灵敏度高于传统LPFG双峰传感器的镀膜LPFG折射率型双峰传感器;而减小包层半径,将进一步提高传感器的分辨本领。     

Effect of cold electron emission on diffusion plasma parameters and the sheath structure in a double plasma device

It is observed experimentally that by injecting cold electrons in the discharge region of a double plasma device, the plasma parameters and sheath structure can be controlled in the other region, which is devoid of any electrical discharge. The main discharge region is separated from the region under investigation by a grounded mesh grid. Both cold and hot ionizing electrons are emitted from separate sets of filaments in the discharge region. With an increase in the cold electron emission current, the plasma parameters in the discharge region get changed, which in turn alter the plasma parameters in the other region. Two important effects caused by cold electrons in the diffusion region are the increase in the plasma density and decrease in the plasma potential. The increase in the plasma density and decrease in the sheath potential drop therefore cause the contraction of the sheath.     

Analysis of dusty plasma in the positive column of glow discharges

The radial distributions of ions,electrons and dust particles in the positive colum of glow discharges are investigated in a tripled-pole diffusion model.The dust particles are mainly trapped in the region around the column axis where the electrostatic potential is the highest.The presence of the dust particles results in the ion density increasing and the electron density decreasiung in the dust-trapped region.The dust-trapped region is wider for a higher dust temperature or a smaller particulate redius.The ions and electrons in the dust-free region away from the column axis are in ambipolar diffusion.     

GaP:N液相外延材料发光区域的荧光测量

通过磨斜角,用光致发光法测量了ＧａＰ：Ｎ液相外延（ＬＰＥ）材料中ｎ区和ｐ区的发光强度。从被测 荧光谱中可以看出,ｎ区和ｐ区均为发光区域,但是在ｐ－ｎ结两侧氮（Ｎ）浓度大致相同的情况下,ｐ区的发光强度明显高于ｎ区的发光强度,约为ｎ区发光强度的３～５倍,此实验结果表明,在ｐ、ｎ结附近杂质浓度较低情况下,ＧａＰ：Ｎ绿色发光外延材料中的发光区域主要是在ｐ区。     

应用于多视点视频编码的基于深度特征的图像区域分割与区域视差估计

基于多视点视图深度特征,提出一种通过简单块匹配运算划分多视点视图区域并估计区域视差的算法.首先基于深度对象的概念确定图像中具有不同深度的区域数量以及这些区域对应的区域视差,再根据误差最小化准则初步确定每个图像块所属区域.当区域中图像块数量小于某个阈值时,采用区域合并算法将该区域中的每个图像块合并到与它的视差最为接近的其它图像区域,通过迭代形成最终的有效图像区域划分.实验表明,该算法能够以图像块为基本单元有效地划分各深度层区域,并准确估计对应的区域视差.     

基于高斯混合模型的多区域并行增长图像分割算法

为克服经典区域增长算法中生长规则以及特征选取的困难,提出了基于高斯混合模型的多区域并行区域增长图像分割算法。首先交互选择多个不同区域的种子点,并利用交互式选择的属于每个区域的子块得到混合模型的个数;然后利用最大期望估计混合模型参数作为区域增长的初始参数,并在增长过程中不停地调节模型参数。为了避免初始种子点位置选择对算法性能的影响,采用了多区域并行竞争增长策略。仿真实验获得了较好的分割效果,表明所提出的算法是合理可行的。     

基于区域进化的区域增长图像分割

为克服经典区域增长算法中门限选择困难、分割稳定性不高与串行处理速度慢的不足,提出了基于区域进化的快速区域增长图像分割算法。引入了新的区域能量表示模型,并给出了迭代进化形式。在区域增长过程中,逐渐增加区域增长的门限,通过对能量函数的动态优化来逼近最佳分割结果。仿真实验表明,该方法能有效地避免经典区域增长算法中门限选择的困难,采用区间连通处理技术代替单一像素串行迭代处理方式,可使分割速度提高十多倍。     

Spin waves in the isotropic heisenberg antiferromagnet above the Néel point

Spin waves in an isotropic antiferromagnet are described using a decoupling scheme for the Green's functions in the paramagnetic region. The results are interpreted with an ansatz for the scattering function suggested by Halperin and Hohenberg and show overdamping in a hydrodynamic region and damped propagating spin waves in a region of short wavelengths. Expressions for the dynamical susceptibilities and the Néel temperature are derived.     

液滴蒸发对周围气相场的影响域特性分析

液滴在气体中运动蒸发的过程中,两相间会发生相互作用。为了弄清液滴对气相场的影响,基于液滴在气体环境中蒸发过程的现象和机理解释,提出液滴蒸发的影响域的概念,定义了影响域半径,并通过数值计算分析了不同条件下的影响域特性。结果表明,影响域内,由于液滴的存在使得其周围气相场参数变化较为剧烈;其他条件相同时,无量纲影响域半径几乎是一个定值。提出的影响域概念,对于研究气液两相间的相互作用机制具有重要意义。     

The study and application of the improved region growing algorithm for liver segmentation

In order to improve the accuracy of the medical image segmentation and reduce the effect of selecting seed points using region growing algorithm, an improved region growing method is proposed in this paper. First, the source images are pre-processed using non-linear mapping method and the region of interest in the liver is selected by man–machine interaction; Quasi-Monte Carlo method is used for generating low-dispersion sequences points in the region of interest and the optical seed points are selected by computing these points; In addition, the region growing criteria is also improved. The improved region growing algorithm is used for segmenting three discontinuous abdomen CT images. Compared with the traditional region growing method, the improved method can get better liver segmentation effects. The proposed method can be effectively applied to liver segmentation and it can improve the accuracy of liver segmentation.     

高Rayleigh数条件下竖圆环夹层内自然对流换热的实验研究

对内壁维持恒热流和外壁向环境冷却的大高宽比竖圆环夹层内自然对流换热进行了实验研究。实验装置高宽比分别为２３５和６６６７，半径比分别为２．０３和３．９２。实验数据整理考虑了热辐射影响以获得对流规律。由于已有工作均未考虑高Ｒａ数区域，首次得到Ｒａ数高达１０￣９的区域内平均Ｎｕ数的换热准则式。在低Ｒａ数区域，亦取得了与前人工作一致的结论。本文结果改进了高Ｒａ数区域换热规律的预测能力。     

Etch pits in AgCl crystals

Single crystal sheets have been prepared by the capillarity method. The dislocations can be revealed with a sodium thiosulphate solution at surface orientations from two regions in the basic triangle. These are: region A around 001 pole up to ≈25°, and region B around 111 pole up to ≈pa 10°. In the remaining region C of the basic triangle the dislocations do not etch. In region A the etch pits have the shape of pyramids. In region B they are triangular pyramidal in shape. Evidence is given that the edge and screw components of annealed and fresh dislocations are revealed by etching. At surface orientations near either the {00l} or {111} planes the slip can be activated in such zones 〈110〉 that are nearly parallel to the surface of the sheets. The slip bands are then straight and predominantly of the edge type.     

Profile measurement system based on linnik-type interferometric microscope for visible-light region and infrared-light region

A profile measurement system consisting of linnik-type interferometric microscope, light source and cameras is developed based on white-light scanning interferometry extending from the visible-light region to the infrared-light region. Three-dimensional profiles of microstructures are obtained via a phase-stepping algorithm using a CMOS array camera for the visible-light region and an InGaAs CCD array camera for the infrared-light region. Errors of the measurement system along with extensive applications in MEMS device profile reconstruction of top surface, sidewall and internal structures are discussed in detail.     

Hybrid Particle–Continuum Simulations of Polymer Brushes in Shear Flow

A hybrid particle–continuum method is used to study the shear flow confined between two opposing walls, one of which is coated with polymer chains. Molecular dynamics (MD) is used in the particle region near the brush and Navier–Stokes (NS) equations are applied in the remaining region where the continuum assumption holds. The information exchange from the continuum region to the particle region is implemented using the constrained particle dynamics. Both Couette shear flow and oscillatory flow are considered in the present work. The effect of the shear flow on the conformational characteristics of polymer brushes is analyzed. In the overlap region, the velocities obtained from MD simulations are smoothly connected with those from NS equations. Our investigations demonstrate that the hybrid particle–continuum model is valid in exploring the shear behavior of polymer brushes.     

Solitons supported by defects of PT-invariant potentials with real part of dual-frequency lattices

The existence and stability of defect solitons in defective PT potentials with real part of dual-frequency lattices are reported. For positive defects, fundamental solitons are always stable in the semi-infinite gap and nonexistent in the first gap. While for negative defects, in the semi-infinite gap, fundamental solitons are stable in most of their existence region apart from low power region, but all the fundamental solitons are stable in the first gap. Dipole solitions are unstable in the whole semi-infinite gap regardless of defects, but in the first gap they can be stable in the low power region for positive defects.     

2×2熔锥型单模光纤耦合器的模型

选择适当的连续函数描述了熔锥型耦合器熔锥形状的渐变特性及其相互位置关系,然后分别应用局部模式理论和变分法分析了横截面沿纵向变化的锥形区域和横截面近似不变的耦合区域内的耦合行为,得出了耦合器中任一横截面处的耦合系数和耦合功率表达式计算表明,熔锥型耦合器的总功率耦合主要发生在耦合区域,在两锥形区域,对于纤芯归一化频率小于1.08的部分,也发生了相当程度的耦合为了使耦合器的理论模型更接近于实际物理情况,锥形区域的耦合作用也是不容忽略的,从而得到了一个更精细的熔锥型光纤耦合器的模型.     

Energieverluste von 50 keV-Elektronen an Ge und Si

Electron-Energy loss spectra of Ge and Si (amorphous, polycristalline and monocristalline) are measured in the low energy region of the band-band transitions and in the energy region of the plasma losses. These spectra are compared with the loss curve calculated from optical data: Discrepancies in the absolute values of the height and in the width of the plasma losses are found; the structures of the region of the bandband excitations show an agreement in the positions of the maxima, but not in their height. Additional electron energy loss maxima are observed.