GaAs的光学常数的计算

为深入认识GaAs的光学性质,采用从头算法计算其电子结构,并依据线性响应理论计算出它的复介电常数,进而得到复折射率,反射系数,吸收系数等光学常数。     

DBV-RCS中一种提高时延性能的时隙分配方法(英文)

在DVB-RCS卫星通信中,为某个业务分配的时隙在MF-TDMA帧中的位置分布将影响该业务的时延特性。本文分别针对固定速率和实时可变速率业务,对MF-TDMA的帧长度、终端分配的时隙数量及位置分布与业务时延性能之间的关系进行了建模分析。理论分析表明时隙位置是影响业务时延的一个重要因素,位置分布越均匀,越能提高业务的时延性能;时隙均匀分配相比传统的时隙连续分配可以有效降低业务平均时延,且时延不随帧长的变化而变化;在时隙均匀分配方式下,提高实时可变速率业务的带宽分配可以更有效的提高时延性能。在DVB-RCS标准基础上,提出了一种与标准完全兼容的时隙均匀分配方法(TUAM),通过计算机仿真验证了算法的有效性以及建模分析的正确性,该算法可有效地保证业务具有极低的平均时延和时延抖动,使得VoIP等实时业务不会由于端到端时延过大而丢包,提高了DVB-RCS系统对于实时业务QoS的保障能力。     

Predictive Modeling and Parameter Optimization of Cutting Forces During Orbital Drilling

To optimize cutting control parameters and provide scientific evidence for controlling cutting forces,cutting force modeling and cutting control parameter optimization are researched with one tool adopted to orbital drill holes in aluminum alloy 6061.Firstly,four cutting control parameters(tool rotation speed,tool revolution speed,axial feeding pitch and tool revolution radius)and affecting cutting forces are identified after orbital drilling kinematics analysis.Secondly,hybrid level orthogonal experiment method is utilized in modeling experiment.By nonlinear regression analysis,two quadratic prediction models for axial and radial forces are established,where the above four control parameters are used as input variables.Then,model accuracy and cutting control parameters are analyzed.Upon axial and radial forces models,two optimal combinations of cutting control parameters are obtained for processing a13mm hole,corresponding to the minimum axial force and the radial force respectively.Finally,each optimal combination is applied in verification experiment.The verification experiment results of cutting force are in good agreement with prediction model,which confirms accracy of the research method in practical production.     

适应拓扑变化的拥塞最小化网络更新策略

软件定义网络的出现推动了航空集群机载网络的发展，同时也为机载网络的一致性更新带来了挑战。针对拓扑变化导致的网络更新期间可用路径失效问题，提出适应拓扑变化的拥塞最小化网络更新策略。首先，为减少可用路径失效带来的数据包丢失，在更新之前采用重路由机制进行处理；然后，针对重路由机制可能引起的网络拥塞，设计了贪婪流迁移算法缓解拥塞；最后，通过瞬时拥塞最小化更新算法完成整个网络更新。仿真结果表明：与传统的拥塞一致性更新算法相比，所提更新策略用规则开销、瞬时网络拥塞方面的少量提高换取了网络更新期间数据包丢失的显著降低。     

石英陶瓷与碳纤维增强复合材料间胶接增强的优化工艺

为提高硅橡胶胶黏剂胶接石英陶瓷和碳纤维增强复合材料的强度和耐温性能,研究了胶接面湿热状态、打磨程度、胶层厚度、操作等待时间等工艺参数对胶接强度的影响。在试片正常烘干、打磨的情况下,当胶层厚度为0.4 mm、操作等待时间小于0.5 h时,胶接效果最优,其压缩剪切强度达到了3.06 MPa。探索了底涂剂处理对胶接强度和耐温性能的影响。在温度不高于100℃时,底涂剂A的效果较好。经底涂剂A处理后,胶接试片常温下的强度提高了13.7%,达到3.48 MPa;100℃时的强度提升率达到37.7%。在更高温度下,底涂剂B的效果更为显著。经底涂剂B处理后,胶接试片常温下的强度提升了10.1%,达到3.37 MPa;300℃时的强度提升了44.0%,达到1.57 MPa;200℃时的强度提升率最高,为49.0%。测试结果为高温条件下石英陶瓷胶接结构的胶接工艺优化及其应用提供了参考。     

Exponent及Gauss型遥测数据建模初始化算法

在对某大型航天电子设备的遥测数据建模时,经常遇到含有指数类变化规律的数据,对其进行建模可以为研究设备性能的变化规律、实际与设计的差异等提供手段。针对有指数变化趋势的遥测数据,采用Exponent模型、Gauss模型对遥测数据建模,给出了这种数据模型的表达式,研究了2种模型的参数初始化算法。通过数值实验说明模型参数初始化算法的有效性,为后续利用最优化理论求解模型精确参数提供了良好的初试点。     

系留气球囊体外形优化研究

利用基于约束的Kanikdale修正算法,以及一套用于确定尾翼尺寸和系留缆绳外形的方法,并借助基于GA的GADO优化器,对系留气球囊体形状进行了优化研究。结果表明,通过多材料组合方式生成的囊体,其有效载重能力能够提升6.5%左右。     

A novel signal processing approach for LEO space debris based on a fence-type space surveillance radar system

The increase in space debris can seriously threaten regular activities in the Low Earth Orbit (LEO) environment. Therefore, it is necessary to develop robust, efficient and reliable techniques to understand the potential motions of the LEO debris. In this paper, we propose a novel signal processing approach to detect and estimate the motions of LEO space debris that is based on a fence-type space surveillance radar system. Because of the sparse distribution of the orbiting debris through the fence in our observations, we formulate the signal detection and the motion parameter estimation as a sparse signal reconstruction problem with respect to an over-complete dictionary. Moreover, we propose a new scheme to reduce the size of the original over-complete dictionary without the loss of the important information. This new scheme is based on a careful analysis of the relations between the acceleration and the directions of arrival for the corresponding LEO space debris. Our simulation results show that the proposed approach can achieve extremely good performance in terms of the accuracy for detection and estimation. Furthermore, our simulation results demonstrate the robustness of the approach in scenarios with a low Signal-to-Noise Ratio (SNR) and the super-resolution properties. We hope our signal processing approach can stimulate further work on monitoring LEO space debris.     

Fast coating analysis and modeling for RCS reduction of aircraft

In order to fast analyze the aircraft Radar Cross Section(RCS) and accurately reduce it with Radar Absorbing Materials(RAM), a comprehensive analysis method based on Higher-Order Method of Moments(HOMOM), termed Locally Coating Method(LCM), is proposed in this paper. There are two steps to fast analyze coatings for RCS reduction in this method: analyze the RCS of various parts before coating the aircraft; model a coating over the aircraft and analyze the wave absorbing effect of it. The aircraft RCS is calculated as a whole but analyzed in various parts by LCM, and thus the RCS contribution of different parts can be compared without disturbing the current continuity. A model expansion algorithm is also presented in LCM to model absorption coatings on specified aircraft parts for later stage RCS calculation of the coated aircraft.