光电编码器在调速系统中的应用

本文阐述了用光电编码器代替传统的测速电机和旋转变压器作调速系统反馈元件的技术。结果表明,光电编码器可有效地简化转换电路,更精确地测定出速度和位移两个参数。     

Combined variance reduction techniques in fully sequential selection procedures

In the past several decades, many ranking‐and‐selection (R&S) procedures have been developed to select the best simulated system with the largest (or smallest) mean performance measure from a finite number of alternatives. A major issue to address in these R&S problems is to balance the trade‐off between the effectiveness (ie, making a correct selection with a high probability) and the efficiency (ie, using a small total number of observations). In this paper, we take a frequentist's point of view by setting a predetermined probability of correct selection while trying to reduce the total sample size, that is, to improve the efficiency but also maintain the effectiveness. In particular, in order to achieve this goal, we investigate combining various variance reduction techniques into the fully sequential framework, resulting in different R&S procedures with either finite‐time or asymptotic statistical validity. Extensive numerical experiments show great improvement in the efficiency of our proposed procedures as compared with several existing procedures.     

Augmented nested sampling for stochastic programs with recourse and endogenous uncertainty

We propose a novel simulation‐based approach for solving two‐stage stochastic programs with recourse and endogenous (decision dependent) uncertainty. The proposed augmented nested sampling approach recasts the stochastic optimization problem as a simulation problem by treating the decision variables as random. The optimal decision is obtained via the mode of the augmented probability model. We illustrate our methodology on a newsvendor problem with stock‐dependent uncertain demand both in single and multi‐item (news‐stand) cases. We provide performance comparisons with Markov chain Monte Carlo and traditional Monte Carlo simulation‐based optimization schemes. Finally, we conclude with directions for future research.     

Terrorism,Radicalisation and Moral Panics: Media and Academic Analysis and Reporting of 2016 and 2017 ‘Terrorism’

Radicalism or radicalisation has become a serious political and academic theme in recent years and any incident involving Muslims now almost automatically acquires the cachet, as events in 2016 and 2017 have shown. However, despite vast sums and resources expended on the subject no one can define what they mean by ‘it’. This should make us pause and question what precisely it is that causes so much alarm and is it worth the resources, time and effort employed to respond to it?     

GNSS接收机离散化处理对解扩性能的影响

建立扩频信号防混叠滤波、采样、量化与解扩输出关系的数学解析模型,推导得到解扩输出信噪比的解析表达式。分析与仿真表明,当量化位数大于等于4 bit,解扩得到总的信噪比损失可以分解为由量化引起的损失和滤波加采样引起损失的乘积,且量化器最优限幅系数只与量化位数相关;当量化位数小于4 bit时,信噪比损失在一定条件下可近似为量化损失和滤波加采样损失的乘积。当量化位数大于4 bit、滤波器带宽大于5倍码率、采样频率大于4倍码率时,再增大上述参数引起的信噪比损失波动小于0.05 dB,对解扩性能提升不明显。该结论可为实用型全球导航卫星系统接收机前端离散化处理优化设计提供理论指导。     

战场QPSK通信系统干扰注入仿真研究

无线射频干扰注入可对无线通信网络系统进行干扰,甚至实现非授权接入实施网电攻击。若捕获敌方的通信协议,掌握其采用的通信模式,如何进行干扰甚至将虚假的信息注入无线网络,是实施网电攻击的技术难点。针对指挥通信系统中的无线开放环节,基于软件无线电技术,分析了战场通信目标信号系统的技术指标,对编码方式、信号带宽、载波频率、调制方式和调制滚降系数等主要参数进行分析,在MATLAB/Simulink环境下建立QPSK数字频带传输系统和射频干扰注入系统模型,并且对关键节点进行仿真。仿真结果表明,在不同干扰方式下,通信系统会受到较明显的干扰,或者解调出与注入一致的干扰信息,达到了验证设计的目的。     

地/海杂波背景下机载火控雷达效能评估

战斗机在对地/海攻击时,地/海杂波对机载火控雷达的工作效能会产生较大影响。分别针对无干扰和压制干扰条件下两类典型体制的机载火控雷达,给出地/海杂波功率的确定方法,建立了地/海杂波背景下机载火控雷达效能评估模型。通过仿真,分析了无干扰与压制干扰条件下地/海杂波对机载火控雷达工作效能的影响,为机载火控雷达技术的研究提供了一定参考。     

宽带噪声环境中FH-FDM/TDMA信号性能分析

新一代高跳速、大带宽通信系统将跳频通信与频分复用、时分多址技术相结合,不仅增加了通信系统容量,形成了灵活的多址方案,同时FH-FDM/TDMA信号具有抗干扰、低截获的能力。为此,在分析FH-FDM/TDMA信号机理的基础上,就同步环路机制进行了深入研究,重点对宽带噪声下的同步捕获环路的相关峰值、跟踪环路的跟踪误差、解调环路的误码率进行了推导;进一步对宽带噪声干扰下的跳频接收环路进行了仿真。结果表明,FH-FDM/TDMA信号具有更强的抗干扰性。     

射频隐身反隐身E&V系统的设计与实现

针对战机射频隐身性能很难评估的现实问题,提出一种射频隐身反隐身实验与验证半实物仿真系统的设计与实现方法。该系统不仅能对战机的射频隐身性能进行验证,同时还可以对飞机的隐身波形、辐射策略等设计提供理论依据和实验支撑。在分析辐射信号模型以及截获模型的基础上,详细介绍了该系统的各功能组成和结构框图。该系统可以开展对于射频隐身的作战需求、管控模型、使用准则等方面的定量研究,对于提高战机的生存能力、突防能力和作战能力具有重要的意义。     

Kinetic responses to global terrorism: Lessons from Africa

This essay recalls the immediate and longer-term responses of the US and its allies to the events of 9/11. It contends that the die for contemporary developments in transnational terrorism was cast in the immediate aftermath of 9/11 – in particular the launching of sustained ‘anti-terrorist’ military combat operations in Afghanistan and Iraq, and more covert ‘kinetic’ operations elsewhere in the Middle East and Africa. The essay seeks specifically to expose the counter-productivity of using military operations as the primary antidote to transnational terrorism. Focusing on the African ‘laboratory’ and the spread of transnational terrorism and Islamic militancy, particularly in West and East Africa, the essay concludes that radical Islamists have mastered the ‘battle of the narrative’ and that the Western penchant for dispensing a kinetic brand of medication is feeding rather than fighting the virus of global terrorism.