音圈式快速伺服刀架的分析与设计

自由曲面光学零件面形复杂,快刀伺服车削加工是其高效加工手段.针对压电陶瓷型伺服刀架行程小,加工能力有限的问题,提出一种基于音圈式直线电机驱动的快刀伺服方案.音圈式快速伺服刀架行程大,可大大拓宽快刀伺服加工范围.以典型光学零件加工为例,对快速伺服刀架所应具备的关键性能指标进行分析,给出了音圈电机的结构,对音圈式伺服刀架进行了理论建模、控制器设计以及实际性能测试.测试结果表明,所设计的音圈式伺服刀架行程大、频响高,在刀架行程为±100μm时可达到300Hz的频响能力,同样行程下的频响指标优于国外同类产品.     

几种典型加密体制分析

简要分析了几种典型加密体制的基本原理,通过比较得出各种加密技术的优、缺点,及其应用领域和前景展望。结合我军指挥自动化发展过程中对安全保密技术的实际要求,选择了一种或几种合适的加密体制,对我军将要建设的指挥自动化系统(C~3I)所应用的加密算法提出了建议。     

基于超外差变频结构接收机前端系统设计

近年来无线通信技术获得了惊人的发展,而短波接收技术作为其中发展最为迅速的一个分支,已经广泛应用到人们生活中的各个领域,具有很高的研究与开发价值。接收机射频前端作为接收机重要组成部分,是接收机动态性能的关键部件,它工作于射频前置滤波器的后面。以接收机射频前端作为研究重点,采用超外差变频体系结构,结合数字频率合成技术,完成了GMSK接收机射频模拟前端系统的设计与实现。设计过程中所涉及到的技术,具有一定的创新和独到之处。     

基于球坐标系下BLUE滤波的IMM算法

针对机动目标跟踪中常见的量测转换问题,提出了一种基于球坐标系下最优线性无偏估计滤波的交互多模型算法。该算法的核心思想是将最优线性无偏估计滤波作为交互多模型中的基本滤波,完成对机动目标的跟踪。在仿真试验中,将该算法与基于扩展卡尔曼滤波的交互多模型算法进行比较,结果表明该算法有效地抑制了扩展卡尔曼滤波中常见的滤波发散问题,并且提高了跟踪的精度,具有较好的实用性。     

调制气流声源振动系统参数分析

通过实验数据与理论计算结果的对比,分析了气流对振动系统的阻尼作用;并以实验声源为基础,以等效电路方法分析了调制气流声源振动系统的弹性系数、磁感应强度、音圈质量、电阻、电感以及绕线方式等参数对音圈振幅的影响;根据调制气流声源的用途差异,提出了用于语音广播和产生大功率低频声波时振动系统各参数的选择方法.     

Traffic channeling under uncertain conversion rates on e-commerce platforms

Traffic is the lifeblood of every e-commerce platform. The question of how to channel traffic to merchants operating on a platform lies at the heart of platform management. We consider a platform on which two independent merchants sell their products. Merchants compete on inventory in the sense that some of the unmet demand at one merchant will spill over to the other. The platform channels traffic based on products' conversion rates to maximize the total sale on the platform. We show that traffic channeling plays three roles. First, it allows more efficient allocation of traffic; that is, the merchant with a high conversion rate is given a higher priority in receiving traffic. Second, it allows the platform to control demand spillover between the merchants to maximize total sales. The platform either facilitates or prevents demand spillover, depending on product substitutability. Third, traffic channeling intensifies competition between the merchants and hence increases the total inventory. More efficient allocation of traffic and the increase in inventory increase sales inequality between the merchants. In contrast, demand spillover decreases sales inequality. While the platform always benefits from traffic channeling, the merchants do not benefit when their products are moderately substitutable. Interestingly, when the two products are owned and sold by the same merchant, the opposite happens–traffic channeling always benefits the merchant but may hurt the platform. Our study provides a basis for informed discussions on how platforms should channel traffic in response to conversion rates, and how traffic channeling affects the welfare of merchants and platforms.     

基于电磁能的生命探测技术研究(英文)

根据人体在电磁场中的感应特性以及电磁波的能量转换规律,提出了基于电磁能的生命探测器设计方案.首先探讨该探测器的理论原理,它是利用电磁波发送和接收的能量转换规律及人体在磁场中的感应特性,研究了人体对电磁场中能量转化的影响;接着利用该原理研制开发了生命探测器,并进行实验验证.实验结果表明,当人体进入该探测器产生的静电场时,探测器能够正确检测到人的存在.     

PWM调制方式对六相无刷直流电动机转矩脉动的影响分析

建立了六相无刷直流电动机(BLDC)的相绕组数学模型,在此基础上分析了该电机在 PWM 调制方式下的非换相期间关断相电流的产生过程.分析结果表明,在采用PWM_ON_PWM调制方式时,可以消除多相 BLDC 的非换相期间关断相电流,因此可以降低转矩脉动.此外,还分析了该电机在换相期间的转矩脉动情况,得到了由换相引起的转矩脉动解析表达式,并给出了消除转矩脉动应该满足的 PWM 占空比控制条件.     

Investigation on the spatial distribution characteristics of behind-armor debris formed by the perforation of EFP through steel target

The behind-armor debris (BAD) formed by the perforation of an EFP is the main damage factor for the secondary destruction to the behind-armor components. Aiming at investigating the BAD caused by EFP, flash X-ray radiography combined with an experimental witness plate test method was used, and the FEM-SPH adaptive conversion algorithm in LS-DYNA software was employed to model the perforation process. The simulation results of the debris cloud shape and number of debris were in good agreement with the flash X-ray radiographs and perforated holes on the witness plate, respectively. Three-dimensional numerical simulations of EFP's penetration under various impact conditions were conducted. The results show that, an ellipsoidal debris cloud, with the major-to-minor axis radio (a/b) smaller than that caused by shaped charge jets, was formed behind the target. With the increase of target thickness (h) and decrease of impact velocity (v₀) and obliquity (θ), the value of a/b decreases. The number of debris ejected from target is significantly higher than that from EFP. Based on the statistical analysis of the spatial distribution of the BAD, An engineering calculation model was established considering the influence of h, v₀ and θ. The model can with reasonable accuracy predict the quantity and velocity distribution characteristics of BAD formed by EFP.     

H2O2对镁合金稀土转化膜性能的影响

选择AZ91D镁合金为实验材料,利用扫描电镜和能谱分析、Tafel曲线和阻抗谱等分析手段,研究了H2O2的添加量对铈转化膜的微观形貌以及耐蚀性能的影响。结果表明：随H2O2添加量的增多,转化膜表面状态越不均匀,自腐蚀电位降低,转化膜电阻Rf变小,较为合适的H2O2添加量为5 mL/L。