基于改进MobileFaceNet的人脸识别方法北大核心

针对目前大多数人脸识别算法参数多、计算量大,难以部署到移动端和嵌入式设备中的问题,提出了一种基于改进MobileFaceNet的人脸识别方法。通过对MobileFaceNet模型结构的调整,将bottleneck模块优化为sandglass模块,改良深度卷积和逐点卷积的相对位置,适当增大sandglass模块的输出通道数,从而减少特征压缩时的信息丢失,增强人脸空间特征的提取。实验结果表明:改进后的方法在LFW测试数据集上准确率达99.15%,模型大小和计算量分别仅为原算法的61%和45%,验证了所提方法的有效性。     

基于事件触发的互联电网负荷频率模型预测输出反馈控制

开放式通信环境不可避免地会导致通信延迟现象的产生,针对多区域负荷频率控制系统提出了基于事件触发的模型预测输出反馈控制方案。模型预测控制器通过延迟通信网络交换预测输入序列,构造Luenberger型观测器以提供传输到本地控制器的状态估计。此外,通过比较实际状态观测值与模型输出反馈控制器中使用的估计值之间的偏差来设计事件触发条件,扩展最大允许的时间间隔,从而减少通信资源的利用。最后,对四区域负荷频率控制系统进行仿真研究,结果表明在具有时变延迟和随机分组丢失的非理想通信网络中,所提出的方法能够提高系统的控制性能,并减少网络信息传输量。     

Impact of stray inductances of the power loop on false trigger‐on in the zero‐voltage‐switching full‐bridge converter

Here, we propose an exhaustive theoretical investigation and experimental verification of the false trigger‐on phenomenon, which would lead to the interaction between the upper and lower devices during the switching transient, in the zero‐voltage‐switching (ZVS) full‐bridge converter. An equivalent model of the converter, which takes not only the parasitic capacitors of the metal–oxide–semiconductor field‐effect transistors into account but also the stray inductances of the main circuit, is presented. Based on the model, a comprehensive study of the false trigger‐on phenomenon is carried out. According to the analysis results, the stray inductances of the metal–oxide–semiconductor field‐effect transistors have negligible influence on the false trigger‐on phenomena since the soft‐switching is realized. The false trigger‐on phenomenon is induced by the stray inductances of the main circuit. Moreover, the arrangement of the switching sequence would cause significant discriminations in the false trigger‐on phenomena because of the specific working mode of the ZVS full‐bridge converter. According to the investigation results, optimization methods are presented to suppress the induced voltage. At last, the theoretical investigations are verified by tests of a ZVS full‐bridge converter. Copyright © 2016 John Wiley & Sons, Ltd.     

多传感轨道扣件检测的数据同步采集系统设计

针对轨道扣件检测的多传感数据同步采集,首先,在分析线阵CCD相机成像原理的基础上,根据系统的要求对相机的关键参数进行了选择并设计了采集方案。然后,设计了传感器的信号调理电路,包括电平调整电路以及抗混叠滤波器的设计,提高了传感器的抗干扰能力。并通过STM32获取光电编码器的等间隔脉冲信息,对各个传感器进行触发控制,设计了线阵相机与惯性传感器的同步触发方案。最后,编写了上位机软件实现了数据的同步采集。实验结果表明,该系统能够精确采集各传感器的数据,具有较强的抗干扰能力和稳定性。     

Study on the plasma generation characteristics of an induction-triggered coaxial pulsed plasma thruster

At present,spark plugs are used to trigger discharge in pulsed plasma thrusters (PPT),which are known to be life-limiting components due to plasma corrosion and carbon deposition.A strong electric field could be formed in a cathode triple junction (CTJ) to achieve a trigger function under vacuum conditions.We propose an induction-triggered electrode structure on the basis of the CTJ trigger principle.The induction-triggered electrode structure could increase the electric field strength of the CTJ without changing the voltage between electrodes,contributing to a reduction in the electrode breakdown voltage.Additionally,it can maintain the plasma generation effect when the breakdown voltage is reduced in the discharge experiments.The induction-triggered electrode structure could ensure an effective trigger when the ablation distance of Teflon increases,and the magnetic field produced by the discharge current could further improve the plasma density and propagation velocity.The induction-triggered coaxial PPT we propose has a simplified trigger structure,and it is an effective attempt to optimize the micro-satellite thruster.     

dsPIC30F6014的晶闸管触发电路装置设计

介绍了一种基于dsPIC30F6014单片机控制的三相晶闸管触发实验装置,详细阐述了其软硬件结构。测试实验证明,该装置电路简单,产生的触发脉冲稳定性好、触发精度高、易于调试、操作方便、具有实用价值,能够进一步开发用于实验教学。     

An improved technology for eliminating nondeterministic latency in the L1 trigger system

Gamma Ray Array Detector(GRAD) is one of external target facility subsystems in the Cooling Storage Ring on the Heavy Ion Research Facility at Lanzhou(HIRFL-CSR).The trigger subsystem of GRAD is required to make a fast L1 trigger decision with a fixed latency for the data acquisition.Because the hit signals from the detector are asynchronous with the local clock of the trigger system,a nondeterministic latency(the value changes between zero and one clock period) is generated when the synchronous receivers of the conventional trigger system process the hit signals.In this paper,an improved trigger logic based on a field-programmable gate array is developed,and comprised of zero-delay broadening circuits as receivers and an improved adding circuit designed for the new receivers.Software simulation and experimental measurement have been conducted.Comparison with the conventional trigger logic,the improved trigger logic has the advantage of eliminating the nondeterministic latency and reducing the total processing latency.     

On multiobjective combinatorial optimization and dynamic interim hedging of efficient portfolios

A dynamic portfolio policy is one that periodically rebalances an optimally diversified portfolio to account for time‐varying correlations. In order to sustain target‐level Sharpe performance ratios between rebalancing points, the efficient portfolio must be hedged with an optimal number of contingent claim contracts. This research presents a mixed‐integer nonlinear goal program (MINLGP) that is directed to solve the hierarchical multiple goal portfolio optimization model when the decision maker is faced with a binary hedging decision between portfolio rebalance periods. The MINLGP applied to this problem is formed by extending the separable programming foundation of a lexicographic nonlinear goal program (NLGP) to include branch‐and‐bound constraints. We establish the economic efficiency of applying this normative approach to dynamic portfolio rebalancing by comparing the risk‐adjusted performance measures of a hedged optimal portfolio to those of a naively diversified portfolio. We find that a hedged equally weighted small portfolio and a hedged efficiently diversified small portfolio perform similarly when comparing risk‐adjusted return metrics. However, when percentile risk measures are used to measure performance, the hedged optimally diversified portfolio clearly produces less expected catastrophic loss than does its nonhedged and naively diversified counterpart.     

气体开关触发间隙与过压间隙击穿特性研究

为研究快脉冲直线变压器驱动源（FLTD）多间隙气体开关的触发击穿特性，针对一种环形电极两间隙等效实验开关，开展不同触发电压、工作系数和电极材料下的击穿特性实验，对比两个间隙的击穿延时和抖动，分析间隙击穿特性的主要影响因素和作用机制。实验结果表明：触发间隙击穿延时主要受触发电压影响，而工作系数是过压间隙击穿延时的主要影响因素；开关抖动主要来自于触发间隙，触发间隙抖动随触发电压的增大明显减小，过压间隙抖动基本不随触发电压和工作系数变化且维持在较低值；石墨电极开关的击穿延时和抖动明显小于不锈钢、黄铜和钨铜电极开关，具有良好的触发击穿性能。通过分析指出，是否有预电离可能是两个间隙击穿特性差异的主要原因。     

蓄电池机车新型直流斩波控制触发板的设计

介绍蓄电池机车新型控制触发板的设计方法。