跳/扩频测控信号自适应波束形成方法

为解决跳/扩频测控中阵列天线设计所面临的信号频带宽、空域范围广、干扰强度大等问题,将线性约束法与二阶锥规划方法相结合,得到能够同时满足频率不变、方向不变的波束形成算法.利用二阶锥规划将波束形成器的设计转化为给定频率响应的FIR滤波器设计,针对用于宽带波束形成的FIR滤波器的非线性相位特点,采用最小均方误差准则,使所设计FIR滤波器的频率响应逼近于期望滤波器.通过增加约束条件,使不同空间指向的主瓣宽度基本保持不变,并在干扰方向形成宽零陷来有效抑制宽带干扰.仿真计算表明,在跳/扩频信号的工作频带内,波束方向图能够保持很好的频率不变特性,且在±60°范围内波束方向图的主瓣束宽、增益、零陷与参考波束基本保持一致,能够更好地满足航天测控任务对阵列天线的需求.     

基于最差性能最优的稳健宽带恒定束宽波束形成

针对存在指向误差时传统宽带波束形成器性能下降的问题,提出一种基于最差性能最优的稳健宽带恒定束宽自适应波束形成算法.该算法首先利用空间响应变化约束,实现宽带恒定束宽;然后在约束边界上推导最差性能最优方法的等式约束表达式,并利用拉格朗日乘子法求解最优权矢量;最后给出了拉格朗日乘子的取值范围.仿真实验和理论分析表明:该算法在实现恒定束宽的同时具有较高的阵列输出性能和较好的稳健性;另外,该算法的参数选取方法较为简单,避免了传统最差性能最优方法中的广义特征值分解、牛顿迭代及二阶锥规划求解等,计算量较低.     

基于压缩感知的频率不变波束旁瓣水平优化方法

频率不变波束形成技术属于恒定束宽波束形成,能解决宽带信号中不同频率分量对应的波束响应不一致的问题.针对现有的一类将恒定主瓣宽度作为约束条件的频率不变波束形成方法,当阵元个数确定以后,形成的波束旁瓣水平往往达不到实际需求的问题,借助压缩感知理论,提出了一种改善波束旁瓣水平的新方法.提出的方法引入压缩感知理论(compressed sensing,CS)进行信号的预处理,并利用二阶锥规划(second order cone programming,SOCP)进行频率不变波束形成.由于压缩感知的恢复算法可以对压缩采样矩阵采集的信号进行精确重构,从而达到以更少的阵元获得相同的波束形成器性能.换言之,在相同的阵元个数条件下,通过阵列虚拟扩展增大了阵列的孔径,提出的方法比基于SOCP的频率不变波束形成方法有更低的旁瓣水平,仿真结果也表明了该方法的有效性,在相关的工程实践中具有一定的参考价值.     

嵌套复合阵恒定束宽波束形成的多率实现方法

提出一种嵌套复合阵恒定束宽自适应波束形成的多率子带实现方法.复合阵以处理一倍频程的多个均匀间距的线性子阵嵌套组成,多率子带的实现以通用参数滤波器组为基础.每个子阵根据所处理的子带信号带宽不同而选择不同的加权数目.这种结构的阵列处理器不仅实现了将宽带信号分解成多个较窄的子带信号来并行处理,还使每个子阵工作在较低的采样速率下,降低了处理器算法的运算量,提高了波束形成器的权值更新速度.仿真结果表明,此结构的处理器能实现恒定束宽波束形成.     

甚宽频信号波束形成方法

介绍了基于直线阵列的常规相移一时延波束形成理论,分析了直线阵列的指向性以及影响其指向性的因素,并对其空间增益进行了定性分析。在此基础之上,提出了一种根据频率的变化改变基阵各阵元的加权,基于最小均方误差条件下的宽带自适应恒定束宽波束形成方法,在整个工作频带内波束宽度基本保持大致相等,可有效抑制因波束形成带来的频率畸变。文中给出了相应的波束形成仿真结果。     

一种宽带恒定束宽数字波束形成器的设计

该文提出了一种应用DFT正交预处理在数字波束形成（DBF）天线上实现宽带恒定束宽方向的方案。DFT正交预处理将宽带输入信号分解为频带内不同频率点的正交输出信号。采用遗传算法对参考频率上的复数权向量进行设计使陈列响应满足给定的方向图要求。其它频率点上满足宽带恒定束宽要求的复权向量可以根据参考频率上的复数权值通过折算求得。计算机方针结果表明该方案是有效的。     

带指向约束的多目标调零天线

在卫星导航接收机中,传统调零天线无法形成对卫星信号的主瓣指向.为了能同时形成多个天线方向图主瓣,并分别对准不同卫星信号,从而提高阵列增益,文中引入导向约束条件,采用直接矩阵求逆方法求解每个卫星信号的最优权矢量解,并完成波束合成;分析了文中算法的运算量,给出了阵列增益的解析表达式.研究表明,文中算法不仅抑制了外部干扰,而且克服了卫星信号间的相互干扰,形成了对每个卫星信号的主瓣指向,提高了输出信噪比.方向图和期望信号输出信干噪比的仿真结果验证了该算法的有效性.     

基于多参数二次规划的零陷展宽和旁瓣控制方法

自适应波束形成算法能将零陷自动对准干扰方向,但在干扰源角度抖动等情况下,会使自适应权和数据失配.此外,在快拍数较少的情况下,传统的自适应波束形成方法可能会出现很高的旁瓣.针对上述问题,提出了一种有效的基于多参数二次规划的零陷展宽和旁瓣控制方法.首先,利用锥化矩阵修正采样协方差矩阵展宽干扰源的零陷;然后,用主瓣区域外的多个二次不等式控制旁瓣;最后用多参数二次规划方法求解优化问题.该方法不仅能获得更高的阵列输出增益,而且可以通过实值计算得到最优权向量.仿真结果验证了算法的有效性.     

一种基于Bayesian方法的鲁棒自适应波束形成算法

由于在实际环境中,期望信号的阵列响应与实际阵列响应之间存在偏差,使得现存的一些自适应波束形成算法的性能下降.针对上述问题,基于Bayesian方法提出了鲁棒自适应波束形成算法,并且给出其递推形式.该算法利用接收到的采样信号对实际信号方向向量进行估计,降低了信号到来方向的不确定性,对信号方向向量的偏差具有较强的鲁棒性,从而可以保证输出阵列的信干噪比接近最优值.采用递推方法来计算逆矩阵,大大地降低了计算的复杂度,能够满足实时处理的要求.仿真实验表明,与传统自适应波束形成算法相比,所提鲁棒自适应波束形成算法具有更好的性能.     

基于改进粒子群算法的自适应波束形成

基于最小均方误差准则,将自适应波束形成的权值求解问题表示为多目标优化模型,利用提出的改进粒子群优化算法,获得了阵列最优权值向量.改进粒子群优化算法中引入动态邻域拓扑结构,自适应调整粒子的领域搜索范围,避免粒子陷入局部最优.仿真结果表明:所提算法的收敛速度优于传统算法.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with