小入射角条件下气动光学成像偏移

针对超声速飞行器在大气中飞行时由于气动光学效应产生的成像偏移,推导了光线偏折角和流场折射率梯度之间的关系,给出了小入射角情况下,离散折射率场光线偏折角的一种计算方法;利用不同流场的计算流体力学数据计算出对应的折射率场;使用光线追迹法得到光线通过不同流场后的偏折角和传播路径上的折射率梯度分布。仿真结果表明,新的偏折角计算方法所得结果在入射角小于30°时与Runge-Kutta和Snell光线追迹法具有很好的一致性;同一高度下小入射角时,光线的偏折角并不随着飞行速度的增加而增加,而是基本保持稳定;光线通过流场的偏折是正负折射率梯度区域共同作用的结果,负的折射率梯度区域可以减少光线偏折,起到部分"校正"作用。     

一种基于恒星光线偏折的大气折射率估计方法

基于标准大气环境的大气折射率理论模型不能反映实际大气折射率的波动性,针对该问题,提出了一种基于恒星光线偏折的大气折射率估计方法。基于光学卫星的恒星观测数据,分析恒星光线经大气折射发生偏折的现象,建立恒星光线经大气折射后进入光学卫星传感器的光路模型,在分层球形大气的假设下证明该光路模型的对称性。研究一种利用恒星实测光线和恒星理论光线迭代前向反馈的方法,用以估计分层大气折射率。最后,利用光学卫星的恒星观测数据进行有效性验证,计算出的大气折射率与理论大气折射率相符,且能够反映短期波动性。对测试用的恒星实测数据进行处理,结果表明:88%以上的恒星理论视线与实测视线的估计值相差不超过1%,其余部分观测数据估计偏差基本不超过20%。     

基于坐标变换的引力透镜模拟

光线在引力场中会发生偏折是广义相对论理论所预言的现象之一.而引力透镜效应则是指,当观测者与背景光源之间存在较大质量的前景天体时,大质量天体的引力场使背景光源发出光线的传播方向发生改变而导致的一系列观测效应,在天体物理、宇宙学等方向的研究中具有重要意义.本文主要介绍了基于坐标变换的引力透镜模拟,对于前景天体考虑了两种透镜模型,并推导了相应的透镜方程及光线偏折角表达式.然后对于同一类透镜模型下背景光源三种不同的表面亮度分布进行研究,通过计算机生成了相应的引力透镜成像结果.     

基于光线偏折的复杂流动密度重建方法

由穿过扰动流场的光线偏折角测值重建流场密度,对深入认识复杂流动现象具有重要的意义。在由风洞视频测量方法得到穿过扰动流场光线偏折角的基础上,开展了复杂流动密度重建方法的研究。根据密度与折射率、光线偏折角的关系,运用变分法推导了带有先验信息的密度偏微分方程;通过人工神经网络对测量数据进行建模,有效抑制了由局部峰值丢失带来的误差放大问题。数值仿真和风洞实验结果表明,本文方法所得的密度重建结果明显优于直接求偏导数方法,尤其是在峰值处,本法方法在量值上具有更高的精准度,为复杂流动结构的定量分析提供了新途径。     

广义相对论和Brans-Dicke引力理论下的行星进动与星光偏折

作为两种重要的候选引力理论,广义相对论以及Brans-Dicke引力理论对于理解天体及宇宙的形成与演化具有重要的意义.本文在广义相对论和Brans-Dicke引力理论下,考察恒星附近的行星进动以及星光偏折效应.首先推导出恒星周围的静态球对称背景时空下粒子轨道方程的普适形式;然后分别针对两种引力理论,进一步利用相应的真空场方程的静态球对称精确解推导出描述行星及星光轨道方程,其为非线性的二阶常微分方程;利用微扰法求解轨道方程,得到了含高阶修正的近似解,进而给出了对应的行星进动角和星光偏折角.本文对利用更高精度的实验观测来检验、甄别引力理论具有重要的意义.     

关于广义相对论的第四个验证

广义相对论的三大验证(引力、红移、光线偏折和水星近日点进动)是爱因斯坦在建立广义相对论时提出来的.1964年Shapiro提出了第四个检验,即“雷达回波时间延迟”实验[1].后来,实验结果以越来越高的精度证明了广义相对论的这个预言.本文的目的是介绍时间延迟效应的理论计算和实验     

溶液扩散系数的测量

水和盐溶液在界面上扩散时将形成一具有浓度梯度溶液。溶液扩散系数的测量方法已有一些介绍,但无论在操作还是计算上都有诸多不便,本文将我们的作法向大家作一介绍。一、原理光线穿过具有浓度梯度的溶液后,将出现偏折,而其中偏折最大点是最具有特征的,我们实验原理就是以此为基础的。 1.光线的偏向角与折射率梯度的关系α_1光线在溶液中的偏向角α_2光线射出溶液后在空气中的偏向角 e水槽厚度 n光线入射点液体的折射率α水槽至屏的距离由惠更斯波动原理,经计算有     

计算光在引力场中偏折的新方法

利用光的量子论,能量守恒及弱等效原理得出电磁波传播在几何近似下,光线在引力场中的偏转角和波矢的关系. 利用引力场中电磁波方程,在弱场近似下给出了一般的计算光线偏转角度的方法. 具体计算了Schwarzchild引力场中光线的偏折及Kerr-Newman引力场中光线的偏折. 关键词： 引力场 电磁波方程 能量守恒 弱场近似     

基于棱镜模型多次折射法的海水盐度检测系统

为了提高光学折射法海水盐度检测精度,综合分析现有检测方法,认为其海水盐度检测精度低的主要原因是其检测光路为平行平板模型.由此,提出了棱镜模型多次折射法检测方案.利用棱镜模型而不是平行平板模型,提高了光线的偏折角;通过设置多个棱镜模块,进一步扩大偏折角,从而大大提高系统的分辨力.设计了光路并进行仿真分析,研制了样机并进行...     

近红外白天恒星探测对比度分析

 红外波段可以探测到足够多的星体用以导航。恒星-背景对比度是白天恒星探测时的一个重要指标,分析近红外波段,6星等恒星对比度随太阳天顶角、探测器高度和探测方位角的变化情况。结果显示,恒星-背景对比度随太阳天顶角近似于指数增长,40°太阳天顶角时对比度是20°时的2.69倍左右;一定高度时,对比度随探测器高度的增加近似指数增加,低于15 km时对比度仍小于3, 80 km时对比度达到60左右;随着探测方位角的增大,恒星-背景对比度基本上线性增大,30°探测方位角时的对比度是0°探测方位角时对比度的2.38倍。     

Rigorous solution of a problem for a cylindrical cavity containing a ferrite and a dielectric

A rigorous solution is given for modes of TM_nmo type. The complex resonant frequency _n is expressed via a transcendental characteristic equation. Some particular cases are discussed.Read at the Third All-Union Conference on Ferrites, Leningrad, 23 October 1963.     

Solving a relativistic quasipotential equation for a superposition of a nonlocal separable and a local quasipotential

Within the relativistic quasipotential approach to quantum field theory, a method is developed for solving a finite-difference quasipotential equation for the case where a total quasipotential describing the interaction of two relativistic spinless particles of unequal masses is a superposition of a nonlocal separable and a local quasipotential. The cases are investigated where the local component of the total interaction—it is assumed to be known—either admits or does not admit the existence of bound states. This makes it possible to obtain an exact expression for the increment of the phase shift, to determine the conditions of the existence of bound states, and to give a generalization of the Levinson theorem.     

Tunnelling process between a semiconductor or a metal and a polymer

The tunnelling lifetime of an electron lying in a p-type orbital localised at a given distance from a semiconductor or a metal is calculated by using Bardeen's method. It is then shown that even in the absence of broad bands, the hole injection process from semiconductors and metals into polymers should follow a Fowler-Nordheim dependence, provided that the current is not bulk-limited. In the semiconductor case, the current can be expressed by a fully analytical formula, and by an approximate one in the case of a metal. It is demonstrated that the effective Fowler-Nordheim barrier is not the mere difference between the metal work function or the semiconductor electron affinity and the HOMO level of the polymer, but a simple function of both levels. Received 6 April 2001 and Received in final form 29 May 2001     

Towards a predictive scenario of a burning accident in a mining passage

To reveal the inner mechanisms of a combustion accident in a coalmine, the key stages and characteristics of premixed flame front evolution such as the flame shapes, propagation speeds, acceleration rates, run-up distances and flame-generated velocity profiles are scrutinised. The theories of globally spherical, expanding flames and of finger-flame acceleration are combined into a general analytical formulation. Two-dimensional and cylindrical mining passages are studied, with noticeably stronger acceleration found in the cylindrical geometry. The entire acceleration scenario may promote the total burning rate by up to two orders of magnitude, to a near-sonic value. Starting with gaseous combustion, the analysis is subsequently extended to gaseous-dusty environments. Specifically, combustible dust (e.g. coal), inert dust (e.g. sand), and their combination are considered, and the influence of the size and concentration of the dust particles is quantified. In particular, small particles influence flame propagation more than large ones, and flame acceleration increases with the concentration of a combustible dust, until the concentration attains a certain limit.     

Growth of a nonuniform ripple on a Gaussian beam in a plasma

In the present paper we have investigated the growth of a radially symmetrical ripple, superimposed on a Gaussian beam propagating in a plasma. The effect of the position and the width of the ripple on its growth has been studied in some detail. The present analysis considers two mechanisms for the redistribution of carriers in the plasma and the effect of redistribution on the growth of the ripple; the two mechanisms are nonuniform collision dominated heating of the carriers and the ponderomotive force arising on account of nonuniform intensity distribution. Work supported by NSF (USA) and CSIR (India).     

Formation of a bistructure of a solid in a computer experiment

Molecular-dynamics was used to investigate the structural changes occurring in a three-dimensional solid when the solid is transferred from an amorphous into a crystalline state. Crystal cells of a new type — pentadecahedrons with five square lateral faces and ten regular triangular faces at the vertices of a cell — were found for the first time in a computer experiment. It is shown that a bistructure consisting of crystal cells of different types, including cells with five-fold symmetry axes, are stable in the solid. Fiz. Tverd. Tela (St. Petersburg) 40, 1919–1924 (October 1998)