工业钼靶X射线光机能谱的蒙特卡罗模拟

利用蒙特卡罗模拟程序EGSnrc,构建出工业钼靶X射线光机模型,进行了28 keV的电子束经过钼靶产生的光子在光机各组件中的传输模拟,得到距源焦点50 cm处, 射野半径为5 cm平面上的粒子相空间文件,通过对相空间文件分析得到粒子注量、能谱分布、角分布、平均能量等信息,模拟计算了过滤材料和管电压对钼靶X射线谱分布的影响。钼过滤下钼靶X射线的平均能量小于铑过滤,但对较高能量部分的影响要大于铑过滤;随着管电压的升高,钼靶光机的光子产生效率呈上升趋势,平均能量增加。25,28,30,35 kV 4组辐射质条件下,钼靶X射线能谱的平均能量分别为16.0,16.6,17.0,17.8 keV,与实验测量值接近,相对误差在1%以内。     

Applications of autocorrelation function method for spatial characteristics analysis of dielectric barrier discharge

In this paper, spatial characteristics of dielectric barrier discharge (DBD) are analyzed using autocorrelation function (ACF) method. The filamentary, homogeneous and periodic discharge produced in a plate and mesh electrode, respectively, are quantitatively identified by analysis of the spatial structure of the discharge images in DBD with the ACF method. The influences of the size of the mesh electrode on spatial characteristics of discharge in DBD are also investigated by using the ACF, current waveform and Lissajous figures measurements. Moreover, the spatial structure and evolution of patterns in DBD are studied using this method. The results show that an exponential decay and random oscillation are exhibited in the radial and angular distribution of the ACF in a filamentary discharge, respectively. Both the radial and angular distribution of the ACF display a periodic oscillation in a periodic discharge. while the radial and angular distribution of the ACF are both approximately to 1 in a homogeneous discharge. With the decrease of mesh size, it can be seen from the corresponding radial distribution of the ACF that the discharge transits from a periodic discharge with its discharge period gradually decreasing to a filamentary discharge in air at atmospheric pressure when the voltage is kept fixed. It means that there is a optimal mesh size for the formation of the homogeneous spatial structure. Furthermore, the radial distribution of the ACF transits from a exponential decay, an periodic oscillation and into approximately to 1 with the increase of the applied voltage in air/argon mixture. It indicates that the discharge transit from the filamentary mode, the periodic patterned mode into the homogeneous mode. Moreover, two different periodic patterned discharge, the hexagon pattern and the square pattern are recognized quantitatively from the angular distribution of the ACF, which are coincident with the known experimental results. These results demonstrate that the ACF is a simple and effective method to analyze the spatial characteristics of DBD.     

Anamorphic Multiple Matched Filter for Character Recognition,Performance with Signals of Equal Size

Abstract

The construction and performance of an anamorphic multiple matched filter for character recognition is presented, in the usual situation of characters of equal input size and having the same size in the target. So a simple anamorphic correlator can be employed to obtain the recognition of a given character. In order to avoid false alarms the characters in the target are rotated by different angles depending on the angular tolerance of the correlator, which is rotationally variant and smaller than in symmetrical systems within a certain angular region. Thus the number of signals to which the filter can be matched can be greater than with spherical optics correlators.     

Wiener-like correlation filters

We introduce a new, to our knowledge, design for a Wiener-like correlation filter, which consists of cascading a phase-only filter (POF) with a photorefractive Wiener-like filter. Its performance is compared with that of the POF and the Wiener correlation filter (WCF). Correlation results show that for intermediate and higher levels of noise this correlation filter has a peak-to-noise ratio that is larger than that of either the POF or the WCF while still preserving a correlation peak that is almost as high as that of the POF.     

CAVITY MODELS FOR SOLID AND HOLLOW PROJECTILES

Two analytical models for the crater size generated by long-rod and thick-walled tube projectiles are presented. The first is based on energy; in a steady-state penetration, the kinetic energy loss of a projectile is related to the total energy deposited in the target. This simple approach provides an upper bound for the crater size. The second approach is based on the observation that two mechanisms are involved in cavity growth due to long projectiles: flow of projectile erosion products, which exerts radial stress on the target and opens a cavity, and radial momentum of the target as it flows around the projectile nose (cavitation). This analysis includes the centrifugal force exerted by the projectile, radial momentum of the target, and the strength of the target. Thus, it can estimate the extent of cavity growth due to projectile mushrooming, which cannot be predicted by other analyses. This model is shown to be in good agreement with experimental data.     

Non-diffracting beams with controlled spatial coherence

We investigate the propagation properties of partially coherent non-diffracting beams. They are obtained as a superposition of plane waves possessing a single radial frequency and interfering with controlled angular correlation. The theoretical model is adapted to the experiments based on the use of the Fourier spatial filter illuminated by the Gaussian shell-model source. As an example, the influence of the partial coherence on the intensity distribution and phase properties of optical vortices is examined.     

基于多通道能量极值点的两层粒子滤波跟踪

传统多通道跟踪常采用少数离散通道并认为通道间互不相关,忽略了多通道特征渐变的“多峰”型可信度分布.本文提出一种基于多通道能量极值点集的两层粒子滤波目标跟踪方法.首先将目标分解为多个频率、多个角度的通道,提取极值点集合作为目标特征.其后提出两层粒子滤波框架,以一级粒子作为目标运动状态整体性约束;二级粒子表征其下属的多通道...     

Improving binary phase correlation filters using iterative techniques

An iterative technique has been used to improve the design and performance of the binary phase version of a tandem-component correlation filter. The results are compared to a regular matched filter, a phase-only filter (POF), and a binary phase POF, in terms of optical efficiency, SNR, and peak correlation intensity.     

多坐标系下目标跟踪的联合滤波

针对雷达目标观测和处理在不同的坐标系下完成，本文提出了联合滤波算法来跟踪机动目标。该算法以卡尔曼滤波器为基础，直角坐标系下和极坐标系下的算法相联合，不仅克服了两种坐标系下滤波算法的不足，而且对机动目标有很好的跟踪效果。仿真实验结果表明了该算法的有效性。     

纯角度跟踪的球面坐标降维算法

从解决目标跟踪中的非线性问题入手,分析了不同的解决方法,并结合地面红外搜索跟踪（IRST）系统单独使用时的实际特点,提出了球面坐标降维模型,给出了相应的目标纯角度跟踪算法。目标状态方程和量测方程得到了简化。最后进行了目标跟踪的仿真试验,结果表明这种纯角度跟踪算法具有很好的性能。     

Static deformations of functionally graded polar-orthotropic cylinders with elliptical inner and circular outer surfaces

Functionally graded materials (FGMs) enable one to tailor the spatial variation of material properties so as to fully use the material everywhere. For example, in a hollow circular cylinder one can vary, in the radial direction, the material moduli to make the hoop stress constant. Whereas the problem for a hollow cylinder with the inner and the outer surfaces circular has been studied, that of a cylinder with a circular outer surface and a non-circular inner surface or vice versa has not been investigated. We study here such a plane-strain problem when the cylinder material is polar-orthotropic, material properties vary exponentially in the radial direction, and deformations are independent of the axial coordinate. The problem is challenging since the cylinder thickness varies with the angular position of a point, and the cylinder material is inhomogeneous. Equilibrium equations are solved by expanding the radial and the circumferential displacements in Fourier series in the angular coordinate. The method of Frobenius series is used to solve ordinary differential equations for coefficients of the Fourier series, and boundary conditions are satisfied in the sense of Fourier series. A parametric study has been conducted that delineates effects on stresses of the eccentricity of the ellipse, the material property gradation index and loads applied on boundaries of the cylinder. The analytical solutions presented here will serve as benchmarks for comparing solutions derived by numerical methods.     

Porphyrin Organic Framework Hollow Spheres and Their Applications in Lithium–Sulfur Batteries

Organic frameworks represent an emerging family of advanced materials that can be precisely controlled at the atomic level. However, morphology control of organic frameworks remains perplexing and difficult, strongly limiting the advantages of organic frameworks in multiple practical applications. Herein, porphyrin organic framework hollow spheres (POF‐HSs) are fabricated by a template method as a proof of concept of organic frameworks with precisely controlled morphology. POF‐HS exhibits explicit chemical structures of 2D POF and an expected hollow structure. The morphology of POF‐HS is further regulated in terms of void size and shell thickness. Benefited from the polar chemical structures and the hollow spherical morphology, POF‐HS sufficiently mitigates the shuttle of polysulfides by taking the dual effects of chemical adsorption and physical confinement and functions as a desirable host material for sulfur cathode to endow lithium–sulfur batteries with high capacity, long cycling life, and excellent rate performance. The accurate synthesis of POF‐HSs demonstrates the highly controllable and versatile morphology of organic framework materials beyond precise integration of organic building blocks and represents infinite possibility of offering exotic organic frameworks for chemistry, sustainable energy, and material science.     

非轴对称移动载荷下有限长圆柱厚壳的动力响应

本文在介绍圆柱厚壳应力与位移理论分析发展的前提下,建立了有限长圆柱厚壳在非轴对称移动载荷作用下的三维力学模型,假设沿厚度方向径向剪切应变二次分布、径向正应变线性分布,且建立了为满足边界条件待定的位移表达式,采用Heaviside函数和Dirac函数表达移动和作用变化着的移动载荷的基础上,用最小势能原理建立了该圆柱厚壳的动力学微分方程组,应用Galerkin法和修正的Runge–Kutta–Fehlberg法,求得了非轴对称移动载荷作用下的圆柱厚壳的动力响应。通过具体算例,对有限长圆柱厚壳的位移响应和应力状态进行了分析,并将动态响应的理论解与ANSYS数值解进行了对比,从而相互印证了解的可靠性。     

Optimum filter for detection of a target in nonoverlapping scene noise

A filter function is derived for input signals containing a target that is spatially disjoint (that is, nonoverlapping) with the input scene noise. The optimization metric is the ratio of the square of the expected value of the correlation peak to the expected value of the output signal energy. In this model the effects of the nonwhiteness of the scene noise, the nonstationarity of the scene noise that is due to the limited size of the input scene, the nonoverlapping of the target and the scene noise, and the unknown variations of the target illumination are considered. We show that, for the nonoverlapping target and the scene noise, the target window and the scene-noise window strongly influence the optimum filter function.     

光电探测中空间目标和恒星目标运动特性分析

地基大视场天文光电观测系统获取的序列图像中,空间目标和数目众多的恒星目标成像特性相似,两者的区别主要是其运动特性差异.以圆轨道空间目标为例,并忽略地球自转的影响,分析了低轨道空间目标在不同仰角处的运动特性;在建立地平坐标系和时角坐标系这两种天球坐标系的基础上,分析了恒星目标·在不同方位不同仰角处的运动特性;比较了空间目标和恒星目标在视场中运动特性的差异,结果表明恒星目标的运动体现为慢速运动,而空间目标表现为明显的运动特性,且在短时间内可以认为是匀速直线运动.     

The Effect of the Angular and Radial Distributions of Trajectories on the Structure of Axisymmetric Electron and Ion Beams with Compensated Charge in a Longitudinal Magnetic Field

The structure of beams with compensated charge is described using a multiflow collisionless model in which the current is split into N interacting tubes of current. The effect of the boundary angular distribution of the tubes of current, as well as of the boundary radial distribution of current, on the configuration of electron and ion beams is studied. It is demonstrated that a crisis of flow arises in the absence of an external magnetic field at a certain value of current. An external longitudinal magnetic field expands the region of noncritical flow and promotes the laminarity of flow. The boundaries of the critical mode are determined for different angular and radial distributions, and the trajectories of the tubes of current in the subcritical and supercritical regions are calculated.     

Transverse or axial superresolution with radial birefringent filter

The superresolution technique is well known for its ability to compress the central diffraction spot to a size that is smaller than the Airy diffraction spot. The radial birefringent filter, which consists of two parallel polarizers and a rotationally symmetric birefringent element, is introduced into the superresolution technology, and the pupil function of it is deduced. It is shown that such a filter can be adapted either for transverse superresolution or for axial superresolution simply by changing the angle between either of the two polarizers and the radial birefringent element. At the same time the superresolution parameters are discussed. The filter is relatively simple in construction as it requires no phase changes, and low-cost replication is possible.     

空时级联滤波红外点目标检测

时域递归最大值滤波是一种较易实现的红外小目标检测方法,但是在递归过程中存在目标膨胀的缺陷,影响了该方法的应用。通过研究分析,提出了条件最小值滤波替换最小值滤波抑制目标膨胀,较好解决了目标膨胀问题。结合空域最大中值滤波预测背景,将点目标和强噪声保留在预测残差中,再通过递归最大值滤波对预测残差进行时域递归处理,以完成能量累积提高信噪比,设计完成的算法实现了对尺度为 1 个像素,运动速度小于 1 像素每帧的点目标的可靠检测。     

Features of the transition radiation generated by weakly-relativistic electrons in the regime of grazing escape from a flat target

Features of the transition radiation (TR) generated in the vacuum ultraviolet range by weakly-relativistic electrons escaping from a target at small (grazing) angles have been theoretically studied. A significant (more than tenfold) increase in the angular density of TR with decreasing escape angle is predicted. It is established that the spectral and angular distribution of the TR intensity significantly depends on the target permittivity and the electron energy and escape angle.     

An Investigation of Spatial Distribution of Characteristics of a Plasma Stream Formed by a Hall Discharge in a Channel with Metal Walls

The effect of the system of delivery of the working medium on the characteristics of a plasma stream in a Hall accelerator with closed azimuthal current is experimentally investigated. The gas delivery system utilizes a porous diaphragm from a carbon–carbon composite material whose pore size is comparable with the Debye radius of the electrons of plasma formed in a discharge channel. The calorimetric method is used to determine the degree of azimuthal and radial nonuniformity of distribution of the energy of plasma stream developed by the accelerator, namely, the distribution of temperature of a titanium target mounted perpendicularly to the incident stream is taken with the aid of an infrared imager. The probe method is used to measure the spatial distribution of temperature and the concentration of charge-exchange plasma at the accelerator channel exit. It is shown that the ratio of the kinetic energy of the flow of heavy particles to the expended electric energy (energy efficiency) exceeds 0.5.