光载超宽带脉冲雷达信号传输性能研究

采用双并行马赫曾德尔调制器产生高斯脉冲一阶微分和二阶微分型超宽带脉冲雷达信号和光载无线电传输技术,通过仿真研究了两种超宽带脉冲雷达信号在标准单模光纤中的传输特性.结果表明,高斯脉冲一阶微分型脉冲随着传输距离的增大而不断展宽,而高斯脉冲二阶微分型脉冲则先压缩后展宽.经100km标准单模光纤传输之后,在传输终端采用色散补偿光纤对传输信号进行不同程度的色散补偿,可获得满足美国联邦通信委员会规范要求的不同宽度高斯脉冲一阶微分和二阶微分型脉冲信号.     

光载超宽带脉冲雷达信号传输性能研究

采用双并行马赫曾德尔调制器产生高斯脉冲一阶微分和二阶微分型超宽带脉冲雷达信号和光载无线电传输技术,通过仿真研究了两种超宽带脉冲雷达信号在标准单模光纤中的传输特性.结果表明,高斯脉冲一阶微分型脉冲随着传输距离的增大而不断展宽,而高斯脉冲二阶微分型脉冲则先压缩后展宽.经100km标准单模光纤传输之后,在传输终端采用色散补偿光纤对传输信号进行不同程度的色散补偿,可获得满足美国联邦通信委员会规范要求的不同宽度高斯脉冲一阶微分和二阶微分型脉冲信号.     

基于双二次微分的联合变换相关识别

提出一种提高联合相关识别的有效方法，该方法通过对识别图像和联合变换功率谱分别进行二次微分，抽取识别图像的特征信息，增强联合变换功率谱中调制条纹的对比度和调制条纹的结构，有效地提高了联合变换相关器的相关输出；在此基础上，构造了基于双二次微分的１ｆ实时光电联合相关识别系统，实验结果表明：该方法较二元联合变换相关，提高了图像相关识别能力     

实时彩色编码微分干涉

在光栅谱衍射干涉法的基础上,本文提出用色散效应产生的相位体微分干涉条纹,进行实时假彩色编码的原理.编码色与相位梯度间具有直接对应的周期性变化关系.分析了编码色为单谱线纯色,高纯度混色和艳色的条件,讨论了光栅参数的选择.首先实现了微分干涉条纹的真正彩色化.     

基于对数坐标二阶微分峰值法的感应热成像内部缺陷识别研究

针对感应热成像检测中金属工件内部缺陷检测较为困难的问题,对常用的铁磁材料45#钢和非铁磁材料铝试件进行了研究。提取45#钢和铝试件上宽深比不同缺陷的降温曲线,对其进行归一化对数温度-对数时间拟合并求取二阶微分,利用二阶微分极小峰值时间作为特征量对缺陷深度进行定量。结果表明,对45#钢试件,缺陷宽深比大于等于2时,二阶微分极小峰值所对应的时间与缺陷深度平方呈线性关系,可以用来对缺陷深度进行定量;铝试件处理后降温曲线的二阶微分极小峰值时间不受缺陷深度变化影响,不能作为特征量定量缺陷深度。最后通过实验验证了仿真结果。     

He2+离子与H原子的重粒子碰撞电离过程

利用初态程函近似的连续扭曲波方法研究了He²⁺离子与Ｈ原子的碰撞电离过程. 计 算得到了入射离子能量从30keV/u到2000keV/u的碰撞电离总截面、随电离电子能量和角度变 化的一阶和二阶微分散射截面，及随入射离子能量变化的电离电子平均能量.计算的总电离 截面与其他理论和实验结果进行了比较，在入射离子能量大于100keV／u的能区，计算结果 与实验符合得很好；在较低的能区，各种理论结果之间有较大差别，计算结果比实验约小50 ％.利用计算的二阶微分散射截面讨论了软碰撞、电子俘获到入射离子连续态、两体相遇碰 撞等碰撞电离机理. 关键词： 重粒子碰撞电离 初态程函近似 总截面 一阶和二阶微分散射截面     

剪切散斑干涉术的统计分析

本文用统计光学方法分析了剪切散斑图的成象过程;散斑图的频谱分布以及全场滤波干涉条纹的形成.发现剪切散斑干涉条纹不仅与三维位移微分有关,而且与面内位移量有关.在此基础上又讨论了影响干涉条纹质量的有关因素,并作了实验验证.     

基于对数二阶微分极小峰值时间的测厚方法研究

本文提出了一种反射式脉冲红外热波技术中采用对数温度-对数时间二 阶微分极小峰值时间作为特征时间进行缺陷深度定量测量的方法. 首先, 介绍了反射式脉冲红外热波技术的基本原理, 在半无限厚平板解的基础上得到了对数温度-对数时间二阶微分极小峰值时间与缺陷深度平方的关系式. 其次, 利用不锈钢和铝材料制作平底洞试件并得到红外热图序列, 提取对数二阶微分极小峰值时间. 该特征时间与缺陷深度平方实验结果显示其具有很好线性关系, 该线性关系可用于实际缺陷深度定量测量, 并讨论了与应用广泛的对数二阶微分极大峰值法相比的优缺点. 关键词： 红外热波 定量测量 缺陷深度 极小峰值     

散斑剪切干涉条纹特性的实验研究

本文通过位移位相存在的真实性实验、小孔滤波的必要性实验、位移梯度的解相关性实验,证实了散斑剪切于涉术的条纹是由物体变形所引起的“位移位相”和“位移微分位相”以及由位移和位移微分共同决定的“附加位相”之和的余弦条纹。实验证实这种余弦条纹的分布,随着滤波孔的位置而变化,它的衬比随着位移和位移梯度的增大而下降。特别是,当在象面上一点相遇的两个物点的象面散斑位移之差的模值大于散斑的直径时,两者相遇的象点上的条纹消失。     

二阶可降阶微分约束系统的形式不变性

研究具有二阶可降阶微分约束的力学系统的形式不变性．采用两种方法：一是用不可降阶微分约束系统的方法；另一是用降阶后系统的方法．研究两种方法之间的关系．结果表明，用后一种方法可能会失掉一些对称性． 关键词： 约束力学系统 微分约束 降阶 形式不变性 守恒量     

复杂高阶对象的预测PID控制

针对复杂高阶对象提出了一种基于数值最优模型降阶方法,并基于这种降阶模型设计了预测PID控制器,将此控制器应用于原始模型能够得到很好地控制效果。数值最优模型降阶算法使高阶对象能近似为一阶加时滞对象或二阶加时滞对象,通过模型阶跃响应和Bode图对比,降阶模型曲线很好地逼近原始模型曲线。预测PID对大时滞对象有着很好地控制效果,模型降阶使得预测PID很好地控制复杂高阶对象,且其结构简单,可调参数少的特点。     

Determination of the ten second order intensity moments

The general astigmatic beam can be characterized by its ten second order moments in first order approach. Most intensity moments, except the beam twist, can be determined by measuring the intensity in a reasonable number of positions around the waist of the beam. The beam twist is determined by applying a rotated cylindrical lens. The ten intensity moments of two kinds of astigmatic beam were determined: a simple astigmatic TEM_8,0 Hermite–Gaussian beam and a twisted beam generated from the TEM_8,0 mode. The experimental results were compared with the theoretical calculations and demonstrate that the ten second order moments of a beam can be determined in a rather simple way.     

电磁场法向边值关系的严密数学理论

阐述了矢量场穿过2阶无穷小平面的通量虽然也是2阶无穷小量,但特殊情况下要求计算精度必须达到3阶无穷小量,为此目的需要把2阶无穷小平面分成无穷多个4阶无穷小面元来计算通量,并且给出如此计算所得结果遵循的规律——3阶无穷小精度下矢量场穿过2阶无穷小平面的通量定理.最后介绍了这个定理在散度理论和电磁场法向边值关系理论中的应用.     

Hamilton Formulation for Continuous Systems with Second Order Derivatives

In this paper the Hamilton formulation for continuous systems with second order derivatives has been developed. We generalized the Hamilton formulation for continuous systems with second order derivatives and apply this new formulation to Podolsky generalized electrodynamics, comparing with the results obtained through Dirac’s method.     

Analysis of the pressure derivatives of the shear modulii in ionic solids

Suitably modified theory based on Lundqvist potential of ionic cohesion, to explain the pressure derivatives of the solids, has been applied to evaluate the pressure derivatives of second order elastic (SOE) constants and the values of third order elastic (TOE) constants of ionic solids. The calculated values of the pressure derivatives of SOE constants are in good agreement with the experimental values.     

含有高次微商的量子理论

这篇短文比较了两种含有高次微商的量子理论。一个是在某些情形下可用的,它将变数q表为许多适合二阶方程的Q的线性组合,而在量子化时,各个Q分别地被量子化。另一个是先将q的运动方程正则化,再引入量子条件。我们证明了两个理论,无论就各种量的对易关系而言,或就总哈密顿而言,是等效的。     

三阶色散影响下二阶孤子间互作用及抑制

在色散位移光纤中，研究了三阶色散影响下同相和反相二阶孤子之间的互作用，分析了同相和反相二阶孤子对衰变后时域波形和频域频移的变化，发现三阶色散使二阶孤子分裂出一大一小两个不同振幅的基阶孤子，并彼此分离，但孤子对中心频率频移量却减小。通过采用非线性增益控制的方法可以有效抑制二阶孤子间的互作用，使孤子保型传输而不发生衰变。同时通过周期性改变三阶色散系数，可以减小三阶色散的不利影响，抑制孤子中心频率的频移，使孤子对不偏离原来时间槽，稳定孤子传输。     

Investigation of the particular features of the structure factor of liquid Al-based alloys

We study the structure of liquid binary and ternary alloys of aluminum with transition metals (Al-TM) obtained by Reverse Monte Carlo (RMC) and Molecular Dynamics (MD) simulation methods. Two distinctive features of their structure factor are discussed: the shoulder on the second peak and the prepeak on the left side of the main peak. The quadruples of mutually neighboring atoms (Delaunay simplexes) with a shape close to a regular tetrahedron's (quasi-regular tetrahedra) have been selected in the models and examined. They combine into clusters of different morphology (polytetrahedra) forming a polytetrahedral order (PTO), and there are no compact clusters of these tetrahedra similar to icosahedron in our alloys. It is discussed that the second peak feature of the structure factor is associated with PTO, and does not require for its explanation the presence of icosahedral short-range order (ISRO) in the liquid alloys. The prepeak is caused by the chemical short-range order (CSRO). In our models it is observed mainly on the subsystem of atoms which is complementary to the subsystem of the polytetrahedra. Simulation of the CSRO was performed on a model of monatomic liquid. A new length scale responsible for the prepeak has been obtained in this simulation.     

Quantum theory of conductivity of spatially inhomogeneous systems

A quantum theory of conductivity is constructed for semiconductor objects such as quantum wells, wires, and dots. The mean values of current and charge densities induced by a weak electromagnetic field are calculated. It is shown that the mean values of current and charge densities consist of two parts, the first of which is expressed in terms of the electric field and the second is expressed in terms of derivatives of the electric field with respect to spatial coordinates. Appropriate expressions are derived for the conductivity tensor that depends on coordinates; these expressions can be applied to any spatially inhomogeneous systems. The results obtained can be used in the theory of secondary radiation from objects of reduced dimension in the cases of monochromatic or pulsed irradiation.     

Third order elastic constants of V3Si and V3Ge

General expressions have been derived for the second order elastic constants and third order elastic constants of the A-15 structure compounds with the nearest neighbour central interaction. The second order elastic constants, the third order elastic constants and the pressure derivatives of the second order elastic constants of V₃Si and V₃Ge are reported and compared with the available experimental measurements.