近场水下爆炸作用下箱形梁整体损伤特性研究

当水下近距爆炸载荷对舰船产生耦合激励作用时,舰船的总体损伤特点是一个值得深入研究的问题。以水面箱形梁模型为研究对象,建立了梁模型在水下近距爆炸载荷作用下动态响应的有限元仿真方法,最后利用数值仿真和具体试验相结合的方法,对自由梁在水下特定爆炸工况下的整体损伤特性进行了研究。结果发现：数值计算结果和试验结果具有较好的一致性;在爆炸气泡脉动频率与梁模型一阶湿频率相近的条件下,随着爆径比的增大,梁的整体响应状态由整体中垂塑性弯曲转变为鞭状运动。     

Parallel spiral search algorithm applied to integer motion estimation

Thanks to its flexible coding structure, high-efficiency video coding (HEVC) can save more coding bit rates than the previous standard, H.264. However, it also increases the complexity of integer-pixel motion estimation (IME). To speed up the encoding process, we propose a parallel spiral search (PSS) algorithm, which features the following characteristics and advantages. First, the proposed algorithm is hardware-friendly. PSS has both a fix search order that cuts the correlation between search points and a high data reuse level that facilitates the pipeline application in hardware implementation. Second, the PSS algorithm processes all prediction units (PU) blocks in parallel, which speeds up the RD calculation. Finally, the early termination strategy is proposed to end the search for unnecessary search points and further reduce search time. Experimental results show that the proposed algorithm outperforms other popular hardware-oriented IME algorithms in terms of coding speed, with the same loss of RD performance. Compared with the default full search algorithm (FSA) in the HEVC test model HM-16.7, the proposed algorithm achieves average time saving ratio of up to 92.55%, with BD-PSNR loss of 0.056 dB and an increase by 1.38% in terms of BD-BR.     

High-sensitivity crack-based flexible strain sensor with dual hydrogen bond-assisted structure for monitoring tiny human motions and writing behavior

Owing to their ultrahigh sensitivity, crack-based flexible strain sensors have garnered considerable attention in recent years. In this study, a practical, and reliable chemical bonding-based dip-coating method is proposed to fabricate high sensitivity and high stability crack-based flexible strain sensor with dual hydrogen bond-assisted structure. The strain sensor has a sandwich structure, which is composed of graphene nanoplatelets (GNPs)/poly (sodium-p-styrenesulfonate) (PSS) conductive layer, ultra-violet (UV) adhesive substrate layer, and UV adhesive covering layer. The fabrication process, principle of dual hydrogen bond-assisted structure, strain sensing mechanism, and various properties of the proposed sensor are examined. It is demonstrated that the cracks and the dual hydrogen bond-assisted structure facilitate a practical strain sensor with high sensitivity (gauge factor of 19.65 in the strain range of 0–30%), long-term stability (over 10,000 cycles), good linearity, negligible drift, fast response time (~50 ms), and low detection limit (0.10%). Meanwhile, the proposed crack-based flexible strain sensor can be used as a wearable device, which can be directly mounted on human skin to monitor tiny human motions and writing behavior. Consequently, it exhibits immense potential for wearable applications including artificial skin, human-machine interfaces, and medical healthcare.     

Mobile Ferroelastic Domain Walls in Nanocrystalline PZT Films: the Direct Piezoelectric Effect

Ferroelastic (90°) domain wall motion occurs readily in bulk samples of displacive ferroelectrics such as Pb(Zr,Ti)O₃ (PZT), dictating critical piezoelectric, dielectric, and polarization switching properties. Many prior studies have used converse piezoelectric measurements to probe the dynamics of ferroelastic domains in thin films; however, such experiments are strongly influenced by the mechanical clamping effect of the substrate, which inhibits electric field‐induced 90° domain wall motion. Nevertheless, these observations raise a tantalizing question: Does the application of mechanical stress, rather than electric field, result in an entirely different response in thin films? Here we report biaxial stress‐driven crystallographic reorientation of (100)/(001) textured, 70 nm thick Pb(Zr_0.25Ti_0.75)O₃ films via 90° domain wall motion, measured in situ by both x‐ray diffraction and piezoforce microscopy. Visual evidence of nanoscale mechanisms that underlie the direct piezoelectric effect is shown. Mobile 90° domain walls effect complete orientation switching in the grains in which they operate, without apparent wall pinning, indicating that bulk‐like ferroelastic behavior can extend to nanocrystalline films in the absence of substrate clamping.     

基于运动自适应的非均匀比率图像扩展算法

讨论了传统的4：3格式的标准清晰度电视信号转换为16：9格式的高清晰度电视信号的运动自适应的非均匀比率扩展变换算法，算法结合视频图像的运动检测，采用K－均值聚类法，根据图像的运动重心（motion center of gravity-MCOG)选择合适的扩展比率，并针对不同的图像区域进行扩展变换，算法符合人的视觉系统对图像的运动区域具有较强感知度的视觉特性，有效的减小了视频格式转换的图像变形，实验表明了本文提出算法的有效性。     

基于PMAC的稳定平台伺服系统设计

研制了一套基于PMAC运动控制卡的陀螺稳定平台系统。该系统以PMAC为核心控制模块,光纤陀螺为速度环反馈传感器,光电编码器为位置环反馈传感器,实现了稳定平台的位置跟踪和伺服稳定两个功能。介绍了系统的工作原理和控制结构,分析了系统的软硬件设计,以及伺服控制算法描述。实验结果表明,该系统完全达到稳定平台性能要求,系统稳定性好且控制精度高。     

液压自由活塞发动机的活塞运动不对称特征研究

结合液压自由活塞发动机基本原理,建立了系统分析模型,通过仿真和样机试验结果分析了活塞运动不对称性及其影响因素。研究结果表明：液压自由活塞发动机活塞上止点运动呈现不对称性特征,能量传递特征和活塞受力特征决定了该不对称性是固有的。在上止点附近,气体压力对活塞运动状态起决定性作用,活塞压缩过程越快,对应的膨胀过程也越快。配流阀响应对活塞上止点运动状态影响不明显,不同负载压力形成位置主要影响膨胀过程后期。     

基于TMS320DM642的MPEG-4编码器设计和优化

给出在TMS320DM642 DSP平台上实现MPEG-4视频编码器所用到的优化方法.这些方法包括算法的改进及存储器的合理分配,以提高程序代码的并行性,减少计算量,重点是运动估计模块及其相关问题的设计优化.该编码器可以在CIF大小图像格式下以25f/s左右的速度进行编码,满足实时视频编码的要求.     

数字化电视设备浅析

由于各电视台现有设备及经济状况各不相同,向数字化过渡的途径又有多种,针对部分数字化电视设备,对数字接口、数据压缩标准、节目的采集和编辑等几个方面作一些探讨。     

智能视频监控中目标跟踪的研究与实现

目标跟踪是智能监控领域的关键技术,本文主要是研究实现这一关键技术。提出一种融合运动目标的面积和矩特征进行匹配的算法,并结合运动估计算法对下一时刻目标最可能存在的方位进行预测,实现了对运动目标的跟踪。实验表明该算法能够准确跟踪运动目标,在一定程度上满足了实时性的要求。