X射线在影象增强器中背向散射特性的研究

本文用蒙特卡罗方法模拟了轫致辐射Ｘ射线在影象增强器中的背向散射特性。针对Ｘ线源管电压为３０－１２０ｋＶ的轨致辐射入射，给出了背向散射光子的角分布及能谱分布；同时，还给出了背向散射光子的平均能量和平均出射角与管电压的关系以及吸收光子数和直透光子数与管电压的关系。     

Analysis of Scattering Properties from an Infinite Plasma Cylinder

In this paper, the scattering characteristics of an infinite plasma cylinder are studied theoretically by using the method of eigenfunction expansion. The backscattering cross sections of plasma cylinder in the transverse magnetic (TM) polarization case are calculated in detail. Effects of different parameters on the backscattering cross section are illustrated. Some errors in determining the complex wave number in plasma, as appeared in literatures published previously, are also rectified.     

激光气象雷达多次后向散射信号特性分析

利用小角近似方法，分别给出了单次和多次后向散射激光雷达方程.通过引入的多次散射评价参量，分析了接收视场角和光学厚度等因素对多次后向散射信号的影响.理论研究表明:多次后向散射主要与接收视场角和光学厚度密切相关，当接收视场角比发射视场角大10倍，光学厚度超过3时, 多次后向散射信号逐渐增大并占主要优势，当接收视场角比发射视场角大100倍时，光学厚度超过1时，多次后向散射信号开始明显增强.     

Coherent backscattering effects for discrete random media: Numerical and theoretical results

Manifestation of the backscattering enhancement phenomenon in the reflection matrix elements of the coherent component of scattered radiation is considered. The dependence of the coherent backscattering effects on the microphysical properties of the medium scatterers are investigated. It is shown that random media of fractal-like clusters exhibit brightness and polarization opposition effects, which are like those observed for some atmosphereless Solar system bodies. Conditions for a bimodal angle dependence in the degree of linear polarization are discussed and the manifestation of the enhanced backscattering phenomenon in the intensity of scattered radiation is studied.     

Raman激光雷达探测气溶胶光学特性

介绍了武汉大学自行研制的Raman多通道激光雷达系统,给出了整个系统的设计原理及主要技术参量.详细描述了利用Raman激光雷达原理反演大气气溶胶消光系数、后向散射系数和激光雷达比等光学特性的方法,并对求解消光系数过程中的关键部分做了讨论分析.同时对武汉上空对流层低空大气气溶胶、云以及边界层等光学特性进行了实时探测反演.实验结果表明:该Raman多通道激光雷达系统在夜晚对低空气溶胶的垂直分布特性具有较好的探测能力,工作性能可靠.     

用于亚微米颗粒测量的后向散射光谱法

针对后向散射光谱粒径测量法对亚微米颗粒测量准确度较差的问题,提出了一种采用紫外光作为光源的测量方法.通过快速傅里叶变换计算了粒径为0.25~1 μm的聚苯乙烯亚微米颗粒的后向散射频谱,将频谱峰值对应的频率值与相应的颗粒粒径进行线性回归,各粒径值相对于回归直线的平均误差为±0.02 μm. 结果表明,本文提出的300~400 nm的紫外光适用于测量0.25~1 μm的亚微米颗粒,相比目前国外最新的采用可见光谱或红外光谱的方法准确度提高了一个数量级,同时该方法也适用于测量双峰分布亚微米颗粒系.     

基于激光云高仪的雾霾过程探测

利用激光云高仪数据资料,得出气溶胶后向散射系数时序图、消光系数廓线图以及能见度,结合探空资料、自动气象站数据以及能见度仪数据,综合分析了雾霾天气过程.结果表明:雾霾天气的出现受气象要素的影响较大,静、小风有利于霾的出现,较高的相对湿度有利于雾霾共存,并且对能见度产生较大影响;雾后向散射强度较大,后向散射系数在垂直方向变化率大,出现高度较低;霾后向散射强度较小,霾空间分布均匀,后向散射系数垂直变化小,出现高度较高.利用激光云高仪数据反演水平能见度和垂直能见度,所得水平能见度与能见度仪所测能见度基本一致.垂直能见度与相对湿度日变化趋势大致相反,与风速日变化趋势基本一致;分析雾和霾天气下后向散射系数随时间变化特征发现,雾霾天气下傅里叶变换的功率谱分布,与雾和霾的边界特征相对应.     

A new network model for the integer quantum Hall effect

A Landauer–Büttiker-type formulation of backscattering between pairs of opposite directed channels is used to describe the coupling at the nodes of a network. Physically, these nodes correspond to saddle points of a slowly varying lateral potential modulation in a 2D electron system in the high magnetic field regime. We show that the network can be solved without needing a transfer matrix as used by Chalker and Coddington. We use an exponential dependence of the coupling on the filling factor of the associated Landau level. We demonstrate that our network representation allows a quantitative modeling of almost every realistic sample geometry in the quantum Hall regime, including the effect of gate electrodes across a Hall bar.