非负矩阵与有向图的谱半径

本文给出非负矩阵的谱半径的上界、下界,由此给出有向图的谱半径的界.     

Random oscillations in the Van der Pol system under the action of a broadband random process

We construct the second approximation for random oscillations described by the Van der Pol equation which are under the action of a broadband random process. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 50, No. 11, pp. 1517–1521, November, 1998.     

压缩迭加态及其特性

压缩迭加态是由迭加态通过压缩系统后产生的一种辐射经典态。这种具备了Ｗｉｇｎｅｒ相空间压缩和相干迭加压缩两种机制。详细讨论了这种压缩迭加态的量子统计性质及压缩特性。     

激光调Q CAI

从激光调Q速率方程出发,分析推导了激光调Q过程中,腔内光子数与工作物质内反转粒子数间的关系.再根据激光调Q的过程中,对腔Q值控制方式不同,将激光调Q技术分为:转镜调Q、声光调Q、电光调Q、饱和吸收调Q和脉冲透射式调Q.用C语言进行了激光调Q CAI软件的开发研制,获得了将文学、图形、动画和计算融为一体的,直观而生动地将调Q的理论和过程再现于屏幕的CAI课件.介绍了课件的内容、结构及其特点.     

叶栅全三维粘性反问题的数值解

本文发展了一种解叶栅全三维粘性反问题的新的数值方法.基于非正交曲线坐标与相应的非正交速度分量下完全守恒型的Navier－Stokes方程,全三维反问题规定叶片表面的无量纲压力分布反求叶型。计算中叶片表面的边界条件采用一种特殊的方式来处理，即一方面强加给定的压力分布条件,另方面叶面的几何位置在迭代过程中又是可移动的，其移动速度将与Navier—Stokes方程在当地的解联系起来，从而形成一种解定常问题的新的不定常过程.试算证明了本文方法的可行性。     

基于光子数目比较的激光测距法

提出了一种新颖的激光测距方法。该方法避开了传统激光测距法中使用复杂辅助电子设备对脉冲计时或比较相位差的过程,而主要通过光学手段分析和提取待测距离信息,最终通过比较大量光子数目的方法求得待测距离。并利用单轴晶体的双折射和全内双反射性质,用特殊结构的单块LiNbO3晶体设计了实施该方法的主体装置。结果表明,该激光测距法同目前普遍使用的激光测距法相比,不但简化了结构,而且有很高的测距精度,从而为激光测距开拓了一种新的思路。     

Stability control of the electrooptic effect with new maleimide copolymers containing photoreactive tricyanopyrrolidene‐based chromophores

New photocrosslinkable maleimide copolymers have been synthesized by the attachment of a tricyanopyrrolidene‐based chromophore. The 2‐(3‐cyano‐4‐(2‐{4‐[hexyl‐(6‐hydroxy‐hexyl)‐amino]‐phenyl}‐vinyl)‐5‐oxo‐1‐{4‐[4‐(3‐oxo‐3‐phenyl‐propenyl)‐ phenoxy]‐butyl}‐1,5‐dihydro‐pyrrol‐2‐ylidene)‐malononitrile chromophore exhibits nonlinear optical activity and contains a chalcone moiety that is sensitive to UV light (λ = 330–360 nm) for crosslink formation. The maleimide monomers have also been functionalized with chalcone moieties. The resultant copolymers exhibit great processability, and one of them shows a maximum electrooptic coefficient of 90 pm/V at 1300 nm. We could control the thermal stability of the electrooptic coefficient with the newly synthesized photoreactive copolymers successfully. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 531–542, 2007     

Actively mode-locked dual-wavelength fiber laser with close wavelength spacing using a fiber Bragg grating

A simple actively mode-locked fiber ring laser is proposed and successfully demonstrated to generate dual-wavelength picosecond pulses with close wavelength spacing using one Bragg grating in standard single-mode fiber. The proposed laser can be made to operate in stable dual-wavelength at room temperature, due to the birefringence characteristic of the FBG induced by transverse strain. Transverse strain loading on the FBG allows the wavelength spacing to be controlled. Generation of stable dual-wavelength pulses with a pulsewidth of 212–234 ps and a tunable wavelength separation from 0.2 to 0.44 nm at a pulse rate of 1.05 GHz was demonstrated.     

基于平稳小波变换及奇异值分解的湖底回波分类

提出一种水下目标回波的特征提取方法。该方法根据平稳小波变换的冗余性和奇异值的稳健性,将湖底回波信号的平稳小波变换系数矩阵的奇异值作为特征向量。它本质上是利用平稳小波变换将信号分解到多个子空间,再采用K-L变换实现对子信号的特征压缩。实测数据分析表明,本文方法与子带能量特征法相比: (1)在相同的样本集和类内距条件下,得到的类间距大于后者, (2)不论所选测试样本和训练样本是否属于同次湖试所得,分类正确识别率均高于后者, (3)随样本集的变动,其正确识别率抖动程度远小于后者。因此,该方法能得到更加稳健、有效的特征以及更好的分类效果。     

Lotka-Volterra型N-种群竞争系统的持久性和稳定性

本文研究一类具有无穷时滞的概周期Lotka-Volterra型N-种群竞争系统的持久性和全局渐近稳定性.一些新的充分条件被得到.