在近平衡态QGP中费米子的分布函数

从QGP动力论出发,得到QGP在色场涨落扰动下偏离平衡态而处于近平衡时的分布函数, 进而分析了决定偏离因子的物理因素.并分别讨论了在高温低密和低温高密区偏离因子特征.     

瑞利-泰勒不稳定性线性增长的密度梯度致稳

 研究了密度梯度对瑞利-泰勒不稳定性的致稳作用,采用有限元算法求解钱得拉塞卡方程本征值问题,得到不同密度分布下理想不可压流体力学量的扰动线性增长率及扰动速度分布。扰动增长率结果与修正的Lindl公式的计算结果比较发现：扰动分布的峰值位于密度梯度标长的取值位置处,波长与密度标长可比拟时,扰动增长率显著偏离Lindl公式,而长波和短波极限情况下,数值解和Lindl公式符合较好。     

用相衬成象系统探测等离子体密度湍动谱的新方法

研究表明，将相板的相移沟槽偏离中心，激光相衬成象系统具有空间带通传递特性。应用此系统，单点探测好可对等离子体密度扰动进行具有波数分辨的测量。本文给产用的单点探测宽频型密度扰动功率谱的方法。     

二维不可压流体瑞利-泰勒不稳定性的非线性阈值公式

分析了二维情况下平面几何、柱几何和球几何中瑞利-泰勒不稳定性发生非线性偏离的阈值问题，给出了三种几何中密度扰动振幅的定义，以及与界面扰动振幅的关系.由此得到了三种几何中密度扰动的非线性阈值公式，用高精度流体程序对三种几何中的不稳定性进行了数值模拟，验证了得到的非线性阈值公式. 关键词： 瑞利-泰勒不稳定性 非线性阈值 密度振幅     

偏光棱镜调制器调制光强扰动的理论分析

以格兰-泰勒棱镜为例，根据实验现象对透射光强随旋转角扰动的原因进行了理论分析。实验中发现，透射光强曲线随着入射角的微小变化而偏离马吕斯定律，出现了周期性扰动。通过格兰-泰勒棱镜的单色偏振光束产生的干涉，再加上晶体-空气隙界面处反射比的因素，使得出射光强依赖于入射角。引入了扰动因子的概念，并系统讨论了扰动因子所造成的影响，从而得出了减小扰动的方法。理论研究结果与实验符合较好。为偏光棱镜的优化设计、生产及使用提供了理论基础。     

分子间相互作用对联合散射谱带强度的影响

测量了苯在八种溶液中不同浓度下联合散射谱带992厘米^-1的积分强度及溶液折射率。研究了谱带强度、浓度、折射率与苯在这些溶液中吸收频率之间的相互关系。结果表明,谱带强度随浓度的偏离系与溶液折射率与苯折射率之差成正比。在不同溶液中的谱带强度与其折射率成直线关系,即强度与溶液的性质无关,只与折射率有关。谱带强度与苯在这些溶液中的吸收频率共振因子成正比关系,从介质对电子吸收谱带的扰动观点以共振联合散射效应讨论了实验结果。     

光纤中扰动的小信号增益

从非线性薛定谔方程出发,在小信号近似下,推导并求解了光纤中扰动相位和幅度的演化方程,利用得到的扰动相位及功率增益的表达式,研究了初相位和频率对传输过程中扰动增益的影响。研究表明：扰动的初相位对扰动增益的初值和初始阶段的演化规律有重要影响;取决于扰动初相位,任何一个频率的扰动增益都有可能达到一个共同的最大值;在被认为无调制不稳定的正色散区和扰动频率大于截止频率的负色散区,扰动增益随距离是振荡的;在被认为有调制不稳定的扰动频率小于截止频率的负色散区,频率相同而初相位不同的扰动增益将经历不同形式的演化后趋于同一正值。     

非相干自适应光学系统

<正> 人类使用光学仪器已经有七百多年的历史了。尽管光学仪器品种繁多,用途各异,但基本作用是相同的,即都是对光的波前进行变换,通过调节光程长度,产生希望的波前。光路上的扰动或光学系统的缺陷,都会使波前偏离理想波前的位置。这种偏离叫波前畸变,在光学成像系统中,波前畸变会影响成像的质量,使影像模糊,因此光学系统中允许的畸变量是很小的。传统的光学技术是利用玻璃之类     

神光Ⅱ装置上辐射驱动瑞利-泰勒不稳定性实验北大核心CSCD

在神光Ⅱ装置上开展了辐射驱动RT不稳定性的一系列实验,获得了不同初始扰动幅度、不同扰动波长、不同材料样品等条件下辐射烧蚀RT不稳定性增长的高时空分辨背光图像,特别是在大初始扰动幅度样品实验中获得了扰动增长的清晰图像,观察到了扰动增长从线性区到非线性区的过渡过程,二次和三次谐波的产生和发展清楚可见。充实了数值模拟程序考核的实验数据库,对间接驱动ICF点火靶设计和研究具有重要作用。     

神光Ⅱ装置上辐射驱动瑞利-泰勒不稳定性实验

在神光Ⅱ装置上开展了辐射驱动RT不稳定性的一系列实验,获得了不同初始扰动幅度、不同扰动波长、不同材料样品等条件下辐射烧蚀RT不稳定性增长的高时空分辨背光图像,特别是在大初始扰动幅度样品实验中获得了扰动增长的清晰图像,观察到了扰动增长从线性区到非线性区的过渡过程,二次和三次谐波的产生和发展清楚可见。充实了数值模拟程序考核的实验数据库,对间接驱动ICF点火靶设计和研究具有重要作用。     

具有周期非均匀扰动的色散管理系统中的孤子传输

在准理想的色散管理系统中建立了非均匀扰动模型,研究了它们对孤子传输和相互作用的影响.这些扰动导致孤子崩塌,加剧了孤子间相互作用.它们影响的大小与周期长度和扰动强度有关,并且存在最坏周期长度和扰动共振现像.最后,引入非线性增益和滤波器来有效控制这些扰动的影响.     

Soliton dynamics of symmetry-endowed two-soliton solutions of the nonlinear Schrodinger equation

A comprehensive analysis is presented of the propagation of symmetry-endowed two-soliton solutions under the influence of various perturbations important in nonlinear optics. Thus, we begin by introducing the analytical expressions of these two-soliton solutions. Then, by considering perturbations which preserve the initial symmetry of the two-soliton solutions, the dependence of the soliton parameters on the propagation distance is determined by using an adiabatic perturbation method. As perturbations of this kind, important for soliton-based communication systems, we consider the bandwidth-limited amplification, nonlinear amplification, and amplitude and phase modulation. Moreover, the results obtained by the adiabatic perturbation method are compared with those obtained by direct numerical simulations of the corresponding governing differential equations. (c) 2000 American Institute of Physics.     

Evolutions of perturbations with special frequencies in lossless optical fibers

Expressing the perturbation optical field in terms of module and phase, using the linearized nonlinear Schrodinger equation governing the evolution of perturbations, we have deduced the analytical expressions of the modules, phases, and gain coefficients of the perturbations with zero or cut-off frequency, and studied the evolutions of the two perturbations travelling along lossless optical fibers in the negative dispersion regime. The results indicate that the phase of the perturbation with zero (or cut-off) frequency increases (or decreases) with the propagation distance monotonously and tends to its asymptotic value nπ + π/2 (or nπ) eventually. The evolution rates of the phases are closely related to the initial phase values. Although the asymptotic values of the field gain coefficients of the above mentioned two perturbations are equal to zero, and the increasing fashion of the modules is different from the familiar exponential type, it still suggests that the perturbations have a divergent nature when the propagation distance goes to infinity,indicating that the two kinds of perturbations can both lead to instability.     

Propagation of Perturbations in a Boundary Layer under Strong Hypersonic Interaction

Doklady Physics - Nonstationary processes in a hypersonic boundary layer are studied. A phase shift by propagation of perturbations upstream was found caused by a finite upstream propagation...     

飞秒光孤立波解传输的稳定性分析

针对高阶非线性薛定谔方程任意参量下的飞秒光孤立波解，用数值演化方法考察了该光脉冲在受到各种初始扰动时的稳定性。结果表明：当飞秒光脉冲受到振幅及波形扰动时可以稳定传输，对于随机噪声及啁啾的扰动，在一定范围内也可传输，这有可能为进一步实现飞秒光脉冲在光纤中的无畸变传输提供一定的理论依据。     

Normal modes for electromagnetically induced transparency in the presence of off-resonance transitions

Electromagnetically induced transparency in ideal Λ atoms involves lossless propagation for paired fields with locked phase difference. Coupled equations for atomic and field vectors are solved to demonstrate that such a normal-mode propagation is stable against perturbations produced by off-resonance transitions, which can be present in real atoms.     

Current discontinuities on superconducting cosmic strings

The propagation of current perturbations on superconducting cosmic strings is considered. The conditions for the existence of discontinuities similar to shock waves have been found. The formulas relating the string parameters and the discontinuity propagation speed are derived. The current growth law in a shock wave is deduced. The propagation speeds of shock waves with arbitrary amplitudes are calculated. The reason why there are no shock waves in the case of time-like currents (in the “electric” regime) is explained; this is attributable to the shock wave instability with respect to perturbations of the string world sheet.     

Stability borders and classification of density perturbation propagations in deDonder-gauge on a cosmological background

We investigate the propagation and the stability borders of density and metric perturbations on a cosmological background in linear perturbation theory in deDonder-gauge. We obtain the algebraic equations for the generally time-dependent stability borders by setting the typical time for perturbation contrasts infinite in the set of differential equations, while all other typical times stay finite. In dD-gauge there are in general three stability borders whereas in synchronous gauge there is only one. In the limiting cases of radiation perturbations and dustlike perturbations we obtain in deDonder-gauge no stability border resp. only one stability border (the ordinary Jeans limit). The first case is in contrast to the synchronous gauge and means that radiation perturbations cannot become unstable. During the recombination there could be three stability borders. We classify the propagation solutions and the systems of differential equations governing them by comparing the characteristic times in the original general system of differential equations, in deDonder-gauge and synchronous gauge. The greatest differences for the propagation of density contrasts arise from the presence of a gravitational wave time scale in deDonder-gauge. This becomes significant if the density perturbations are relativistic with respect to the velocity of sound. Gravitational retardation effects are the origin of the 6-dimensionality of the solution space for density contrasts. This reflects the necessity and physical meaning of gauge solutions.     

Explizite Darstellungsformeln GREENscher Funktionen von kovarianten Wellengleichungen im schwachen Gravitationsfeld. II. Linearisierte EINSTEINsche Gravitationsgleichungen

The propagation equations for small perturbations of a background gravitational field satisfying the EINSTEIN equations are considered. For the perturbation potential the covariantly generalized EINSTEIN -HILBERT gauge is chosen. With the aid of the method used in [10], bitensor GREEN 's functions for the propagation equations in a weak vacuum field are given explicitly. The tail term is obtained to be an integral of the first-order RIEMANN curvature tensor. As an application of the formulae, GREEN 's functions for perturbations of the SCHWARZSCHILD metric are calculated to first order in the mass parameter.