A Poisson multi-Bernoulli mixture filter with spawning based on Kullback–Leibler divergence minimization

In the classical form, the Poisson Multi-Bernoulli Mixture (PMBM) filter uses a PMBM density to describe target birth, surviving, and death, which does not model the appearance of spawned targets. Although such a model can handle target birth, surviving, and death well, its performance may degrade when target spawning arises. The reason for this is that the original PMBM filter treats the spawned targets as birth targets, ignoring the surviving targets’ information. In this paper, we propose a Kullback–Leibler Divergence (KLD) minimization based derivation for the PMBM prediction step, including target spawning, in which the spawned targets are modeled using a Poisson Point Process (PPP). Furthermore, to improve the computational efficiency, three approximations are used to implement the proposed algorithm, such as the Variational Multi-Bernoulli (VMB) filter, the Measurement-Oriented marginal MeMBer/Poisson (MOMB/P) filter, and the Track-Oriented marginal MeMBer/Poisson (TOMB/P) filter. Finally, simulation results demonstrate the validity of the proposed filter by using the spawning model in these three approximations.     

复杂目标GRECO方法的分屏显示计算

图形电磁计算(GRECO)是一种计算复杂目标雷达散射截面(RCS)的有效方法,但必须先有一个易于提取外形参数的数据文件.基于GRECO法,针对用各种通用商业软件造型生成的模型文件,利用商业软件Rhino进行转化,生成适于RCS计算的数据文件,这种处理数据的方法具有广泛的适用性,且不会丢失任何局部细节.通过分屏显示计算方法,提高了对电大尺寸目标的计算精度;采用OpenGL的显示列表技术使得程序运行花费较少的时间.结合GRECO的特点,提出了一种分析目标散射源的简便的方法,便于分析目标的雷达散射截面特性.结果表明,本方法与面劈法的计算结果吻合较好,具有较好的工程应用价值.     

电子束熔化成形Ti-6Al-4V钛合金研究进展和应用现状

电子束熔化成形技术(EBM)具有成形速度快、能量利用率高和真空环境无污染等优点,适合于Ti-6Al-4V钛合金的制备,在航空航天、生物医疗等领域得到广泛应用。然而,EBM成形Ti-6Al-4V钛合金构件仍然存在的内部孔隙、粗糙的表面和残余拉应力等缺陷,严重影响了成形件的疲劳性能。通过工艺参数的优化及后处理工艺,如热等静压和表面处理等,可以显著改善EBM成形件的疲劳性能。综述了EBM成形Ti-6Al-4V钛合金的成形工艺、微观组织、力学性能和典型的应用现状。重点讨论了影响疲劳性能的因素,并总结了一些提高疲劳性能的后处理方法。最后对EBM技术未来的发展前景进行了展望。     

用画法几何方法解决机务工作中一些空间机构的度量问题

本文以构架式飞机起落架和副翼操纵机构为例说明用画法几何方法求解空间构件受力和运动位移、速度等问题。所建议的方法只需三视图和简单的绘图工具,适于在外场机务工作条件下使用。     

Low-energy Earth–Moon transfers involving manifolds through isomorphic mapping

Analysis and design of low-energy transfers to the Moon has been a subject of great interest for decades. Exterior and interior transfers, based on the transit through the regions where the collinear libration points are located, have been studied for a long time and some space missions have already taken advantage of the results of these studies. This paper is concerned with a geometrical approach for low-energy Earth-to-Moon mission analysis, based on isomorphic mapping. The isomorphic mapping of trajectories allows a visual, intuitive representation of periodic orbits and of the related invariant manifolds, which correspond to tubes that emanate from the curve associated with the periodic orbit. Two types of Earth-to-Moon missions are considered. The first mission is composed of the following arcs: (i) transfer trajectory from a circular low Earth orbit to the stable invariant manifold associated with the Lyapunov orbit at L₁ (corresponding to a specified energy level) and (ii) transfer trajectory along the unstable manifold associated with the Lyapunov orbit at L₁, with final injection in a periodic orbit around the Moon. The second mission is composed of the following arcs: (i) transfer trajectory from a circular low Earth orbit to the stable invariant manifold associated with the Lyapunov orbit at L₁ (corresponding to a specified energy level) and (ii) transfer trajectory along the unstable manifold associated with the Lyapunov orbit at L₁, with final injection in a capture (non-periodic) orbit around the Moon. In both cases three velocity impulses are needed to perform the transfer: the first at an unknown initial point along the low Earth orbit, the second at injection on the stable manifold, the third at injection in the final (periodic or capture) orbit. The final goal is in finding the optimization parameters, which are represented by the locations, directions, and magnitudes of the velocity impulses such that the overall delta-v of the transfer is minimized. This work proves how isomorphic mapping (in two distinct forms) can be profitably employed to optimize such transfers, by determining in a geometrical fashion the desired optimization parameters that minimize the delta-v budget required to perform the transfer.     

A study on the quintic nonlinear beam vibrations using asymptotic approximate approaches

This paper intends to promote the application of modern analytical approaches to the governing equation of transversely vibrating quintic nonlinear beams. Four new studied methods are Stiffness analytical approximation method, Homotopy Perturbation Method with an Auxiliary Term, Max–Min Approach (MMA) and Iteration Perturbation Method (IPM). The powerful analytical approaches are used to obtain the nonlinear frequency–amplitude relationship for dynamic behavior of vibrating beams with quintic nonlinearity. It is demonstrated that the first terms in series expansions of all methods are sufficient to obtain a highly accurate solution. Finally, a numerical example is conducted to verify the integrity of the asymptotic methods.     

VGA文本状态下显示汉字的方法

本文涉及的是微机的实用技术,即如何在西文系统下,使用西文软件直接编制汉字的应用软件的方法。这对于充分利用进口的软件资源,开发和善及微机在民航中的应用软件起到促进作用。在本文中具体给出了如何使用 TURBOC 编制汉字应用软件的方法。     

电子飞行仪表的显示系统

电子飞行仪表系统的显示系统，要求快速快，图形质量高，并有特殊性，本文分别从硬件和软件两方面，介绍选用ＡＭＬＣＤ和图形处理器ＴＭＳ３４０１０构成并采和了一些特殊算法的座舱图形显示系统，这种系统具有图形处理简单，图形更新快，分辨率高，开放性强的特点。     

基于GPU的高光谱遥感图像PPI并行优化

传统高光谱遥感信息处理算法的执行效率较低,无法满足海量遥感数据的实时处理需求。文章对基于图形处理器（graphic processing unit,GPU）的高光谱遥感信息处理并行优化方法进行了研究,针对高光谱遥感图像混合像元分解中广泛使用的纯净像元指数算法,提出了一种基于矩阵乘法的GPU并行优化算法,并给出了实验比较和性能测试数据。实验表明,该优化方法在保证结果准确性的同时,运行效率显著提升,算法加速比最高达到634倍,验证了基于GPU的高光谱数据处理并行优化算法的有效性,能够较好地满足高光谱遥感信息实时处理的应用需求。     

激光选区熔化制备钛合金点阵材料无损表征

通过激光选区熔化制备BCC和DOD结构的钛合金金属点阵,使用Micro–CT对两种结构的钛合金点阵材料进行扫描和三维重建。Micro–CT图像清晰地显示金属点阵内部结构,BCC和DOD单胞整齐地以周期性进行排列,且内部存在少量圆形、椭圆形缺陷。通过将实际样品三维数据与CATIA数模进行比对,发现钛合金点阵在制备过程中出现一定程度翘曲。此外使用共聚焦显微镜并基于Micro–CT图像对BCC和DOD两种金属点阵进行表面粗糙度测定。结果表明,Micro–CT在钛合金点阵材料内部结构、缺陷、制备误差、粗糙度测试等表征方面具有显著的应用价值。