A study on improving shielding performance of shielded cable

With the developments in power electronics equipment, the electromagnetic environment has become severe for electronic equipment. In the smart facility field, the stable operation of electronic devices is indispensable, and noise countermeasures must be improved. To suppress intrusive noise from cables, shielded cables are used in many cases. However, electromagnetic induction cannot be suppressed when the shield is grounded at one end, and when grounding both ends of the shield, current flows through the shield creating intrusive noise in the cable. That is, even if a shielded cable is used, a sufficient effect cannot be obtained. Therefore, as a countermeasure, this study prototypes and evaluates cables that combine double shielded cables with magnetic cores. Evaluations conducted using the copper pipe method, triaxial method, and impulse test confirm that the shielded performance improved by 10–30 dB compared with the conventional shielded cable.     

Robust reversible image watermarking scheme based on spread spectrum

Robust reversible watermarking can provide robustness against various attacks besides the ability to recover the cover image. However, robustness and reversibility are somewhat separate in many schemes. The original cover image cannot be recovered even if the watermarked image suffers from a tiny distortion. This paper presents a new robust reversible watermarking scheme by exploring the reversibility of spread-spectrum codes. Watermark bits are embedded by a suggested adaptive spread-spectrum code. The embedding amplitude used in the algorithms is determined by quantizing the source interference of the cover. The proposed scheme is robust to various attacks. Furthermore, since the embedding amplitude is available at the receiver, the original image can be recovered losslessly when there is no attack. Even in the presence of attacks, the original cover images can still be partially recovered. Experimental results demonstrate that the proposed scheme performs well on robustness and watermarked image quality, and provide extra reversibility that resists image distortions.     

Measuring Mental Workload Using ERPs Based on FIR,ICA, and MARA

Mental workload is considered to be strongly linked to human performance, and the ability to measure it accurately is key for balancing human health and work. In this study, brain signals were elicited by mental arithmetic tasks of varying difficulty to stimulate different levels of mental workload. In addition, a finite impulse response (FIR) filter, independent component analysis (ICA), and multiple artifact rejection algorithms (MARAs) were used to filter event-related potentials (ERPs). Then, the data consisting of ERPs, subjective ratings of mental workload, and task performance, were analyzed through the use of variance and Spearman’s correlation during a simulated computer task. We found that participants responded faster and performed better in the easy task condition, followed by the medium and high-difficulty conditions, which verifies the validity of the ERP filtering. Moreover, larger P2 and P3 waveforms were evoked as the task difficulty increased, and a higher task difficulty elicited a more enhanced N300. Correlation analysis revealed a negative relationship between the amplitude of P3 and the subjective ratings, and a positive relationship between the P3 amplitude and accuracy. The results presented in this paper demonstrate that a combination of FIR, ICA, and MARA methods can filter ERPs in the non-invasive real-time measurement of workload. Additionally, frontocentral P2, N3, and parietal P3 components showed differences between genders. The proposed measurement of mental workload can be useful for real-time identification of mental states and can be applied to human–computer interaction in the future.     

Crack propagation of pipeline steel exposed to a near-neutral pH environment under variable pressure fluctuations

This investigation attempts to understand the corrosion fatigue crack propagation behavior of pipeline steels exposed to near-neutral pH environments. The fatigue loading was designed to simulate the underload-type variable amplitude pressure fluctuations found during pipeline operation. The effects of amplitudes (R ratios) of underload and minor cycles were investigated. It has been found from this investigation that the crack growth rate is enhanced significantly through load interaction of the variable amplitude fatigue. The acceleration factor is found to be up to 2.7 and 5.3 for tests in air and in the near-neutral pH solution, respectively. The crack growth rate decreases with R ratios of underload and minor cycles for tests both in air and in near-neutral pH environments. The latter could enhance crack propagation by a factor of up to 11, as compared with the crack growth rate in air. The critical R ratio of minor cycles at which the minor cycles do not contribute to crack propagation through load interaction was determined to be as high as 0.982, which is much lower than the threshold determined by constant amplitude fatigue. This critical R ratio could be utilized to demarcate stress corrosion cracking and corrosion fatigue, and should be incorporated as one of the design principles for components/structures subjected to variable amplitude cyclic loading.     

平面声场中四传声器阵列理论精度的对比分析

主要探讨了两种四传声器阵列的理论精度,针对相应的传声器布置形式进行数值计算,比较了正四面体和直角四面体传声器探头在不同工况下的幅值误差和方向误差。结果表明,在平面波作用下,1~4 k Hz范围内正四面体传声器的幅值误差小于直角四传声器,且两者均小于1 d B,外接球心位置的幅值精度在高频段优势明显;当频率小于5 k Hz时,方向误差均控制在2°以内,因此可以满足相关的建筑声学测试要求。     

Ti/Nb作中间层脉冲加压扩散连接TiC金属陶瓷与不锈钢

用Ti/Nb作中间层,在温度890℃、时间4~12min、脉冲压力2~10MPa、频率f=0.5Hz、恒压10MPa下,对TiC金属陶瓷和304不锈钢(304SS)进行脉冲加压与恒压扩散焊,获得了牢固的固相扩散焊接头。通过扫描电镜SEM、能谱EDS、X射线衍射XRD与剪切性能测试,对接头的显微组织、界面产物与强度进行分析。结果显示:两种接头的界面物相相似,主要有σ相,(β-Ti,Nb)与α+β-Ti固溶体。连接时间10min时,恒压下的TiC/304SS接头抗剪强度为55.6MPa,而脉冲加压下的接头抗剪强度达110MPa。恒压下接头断裂方式为TiC陶瓷断裂,而脉冲压力下接头断裂方式为TiC陶瓷与界面产物间交替进行的混合断裂。     

基于USB总线的机载多脉冲激光雷达产品测试系统研制

针对现有的机载激光雷达产品测试系统不能模拟特定信噪比,且系统使用复杂的问题,开发了基于USB总线的机载多脉冲激光雷达产品测试系统;测控软件可以设定信噪比、脉冲幅值、脉冲周期等参数,并根据静态测距和动态测距的实际需要,生成静态和动态模拟数据;另外,测试系统还能够采集外场数据,并在测控计算机上存储和分析;采集和生成的数据经过USB总线发送给基于FPGA+高速D/A转换器架构的数据转换器,再输出给激光雷达产品,保证了数据传输的高速性和灵活性;经过测试表明,信噪比在3~9的情况下,产生回波信号的距离误差控制在1%以内,信号幅值误差控制在0.5%以内;测试系统的各项指标都满足实际需要,为激光雷达产品调试提供了良好的模拟仿真平台。     

基于改进双曲正切函数的变步长最小平均p范数算法

在信号处理领域,传统的自适应滤波算法采用的固定步长会导致稳态误差和收敛速度无法同时兼顾。针对这个问题,对最小平均p范数(Least Mean p-norm,LMP)算法进行改进,提出了一种基于改进双曲正切(tanh)函数的变步长最小平均p范数算法。该算法利用改进的tanh函数来调节步长,采用移动加权平均法构造变步长函数;同时引入了一个调节函数以进一步提升算法的性能。通过在海洋脉冲噪声干扰下进行仿真,实验表明,与已有的固定步长和变步长算法相比,改进的变步长LMP算法较好地兼顾系统的收敛速度和稳态误差;引入调节函数后的新算法在保证原有算法收敛速度的同时进一步降低了算法的稳态误差,从而兼顾了算法的收敛性和稳定性,具有较好的可行性。     

一类控制量非负的新型脉冲随机控制模型

提出并研究了一类新型的脉冲随机控制模型,其状态结构由关于半鞅的线性随机微分方程所确定,其控制费用函数为关于控制前状态与控制量的二元函数且其控制量保持非负.首先建立了一类新型的变分方程并证明了其解的存在性.通过对变分方程的解函数进行一系列随机分析处理,证明了最佳控制的存在性且对其结构进行了深入分析.此外,由于本文模型与以往文献中的随机控制模型有着重大差异,因而在分析手法上与以往文献相比颇多差异之处.可以预期,本文不仅在随机控制的研究中将具有重要的理论意义,而且在金融控制及证券管理方面也将有着广泛的应用价值.