稀疏约束的时空正则相关滤波无人机视觉跟踪

目的 基于相关滤波的跟踪算法在无人机(unmanned aerial vehicle,UAV)视觉跟踪领域表现出卓越的性能。现有的相关滤波类跟踪算法从样本区域的所有特征中学习滤波器,然而某些来自遮挡或形变的特征可能会污染滤波器,降低模型判别能力。针对此问题,提出一种稀疏约束的时空正则相关滤波跟踪算法。方法 在相关滤波目标函数上施加空间弹性网络约束以自适应地抑制跟踪过程中的干扰特征,同时集成空间—时间正则相关滤波算法(spatial-temporal regularized correlation filter,STRCF)中的时间正则项以增强滤波器抑制畸变的能力。采用交替方向乘子法(alternating direction method of multipliers,ADMM)将带有约束项的目标函数转化为两个具有闭式解的子问题迭代求局部最优解。此外,提出一种相关滤波框架通用的加速策略,根据当前帧的目标位移量,对检测定位阶段的特征矩阵进行等距离的循环移位,将其作为在线学习阶段的特征矩阵,每帧可节省一次训练样本的特征提取操作,提高跟踪速度。结果 在3个UAV数据集上与14种主流跟踪算法进...     

Least squares decoding in binomial frequency division multiplexing

This paper proposes a method that can reduce the complexity of a system matrix by analyzing the characteristics of a pseudoinverse matrix to receive a binomial frequency division multiplexing (BFDM) signal and decode it using the least squares (LS) method. The system matrix of BFDM can be expressed as a band matrix, and as this matrix contains many zeros, its amount of calculation when generating a transmission signal is quite small. The LS solution can be obtained by multiplying the received signal by the pseudoinverse matrix of the system matrix. The singular value decomposition of the system matrix indicates that the pseudoinverse matrix is a band matrix. The signal-to-interference ratio is obtained from their eigenvalues. Meanwhile, entries that do not contribute to signal generation are erased to enhance calculation efficiency. We decode the received signal using the pseudoinverse matrix and the removed pseudoinverse matrix to obtain the bit error rate performance and to analyze the difference.     

基于循环生成对抗网络的含遮挡人脸识别

人脸图像的遮挡会严重影响人脸识别准确率,当前处理带遮挡人脸识别的方法主要有丢弃法和修复法两种。丢弃法因忽略或丢弃大量遮挡区域的有效特征易造成识别准确率不高,而当前大多数修复法需要原图的相关信息,限制了其应用。针对现有含遮挡人脸识别方法存在的问题,提出一种基于循环生成对抗网络的人脸识别算法,通过利用2对生成器和判别器进行循环训练,实现遮挡人脸图像的盲修复,此过程不需要除遮挡区域外的原图信息。在此基础上,采用ResNet-50网络对修复后人脸进行识别,该网络通过跳跃连接消除深层卷积神经网络中的网络退化问题,能够降低网络训练的难度,且不会增加额外的参数和计算量。针对盲修复后人脸特征存在类内差异大和类间差异小的特性,引入一种能够量化类间距离的分类损失函数RegularFace作为识别网络损失函数。实验结果表明,与DCGAN+CNN算法相比,所提算法对不同遮挡类型和遮挡区域的人脸图像识别准确率均有所提高,当线性遮挡面积为40%时,所提算法的识别准确率提高了14.4个百分点。     

Influence of residual thermal stresses on fatigue crack growth life of discontinuous reinforcements in metal matrix composites

The fatigue life prediction model based on crack propagation from micro-structural features is derived and presented for planar and randomly oriented Discontinuous Reinforced Metal Matrix Composites (DRMMCs). The model contains the influence of micro-structural properties such as aspect ratio, volume fraction of particle/fibre and constraint between particle and the matrix. The effect of residual thermal stresses generated within the matrix during development of composite is considered. The particle/fibre plays a dominant role in the development of the cyclic plastic zone size ahead of the crack tip; moreover, it enhances the cyclic plastic deformation characteristics of DRMMC. The theoretical model-based evaluations for low cycle fatigue in DRMMCs are within the proximity of the experimental results.     

T700/5224复合材料在湿热环境和化学介质中的老化行为

研究T700/5224复合材料在湿热环境和15#液压油、4010#合成航空润滑油、RP-3航空煤油和AHC-1水基型清洗剂4种飞机上常用的化学介质中的老化行为、实验不同时间后的吸湿量及力学性能。采用红外光谱(IR)和动态力学(DMA)分析T700/5224复合材料在介质老化过程中的化学变化和玻璃化转变温度Tg。结果表明:在80℃-85%RH的湿热环境中实验1000h后吸湿量为1.05%,在80℃-100%RH的湿热环境中实验1000h后的吸湿量为1.35%;T700/5224复合材料湿热老化后,剪切性能随老化时间变化不大,弯曲性能下降较大,开孔拉伸性能变化较大,但总体上并没有降低,而开孔压缩性能一直缓慢下降。介质老化对T700/5224复合材料的力学性能影响不大,AHC-1水基型清洗剂对其影响大于其他3种介质,T700/5224复合材料在AHC-1水基型清洗剂中浸泡45天后其玻璃转变温度Tg下降10℃。     

石墨烯/银纳米颗粒复合材料的制备及其对双氧水的电化学检测

以氧化石墨烯(GO)和硝酸银为原材料,聚乙烯吡咯烷酮(PVP)为还原剂和稳定剂,通过水热法制备出还原氧化石墨烯/银纳米颗粒(rGO/AgNPs)复合材料。采用透射电子显微镜(TEM)、X射线衍射(XRD)及紫外-可见分光光度计(UV-Vis)对rGO/AgNPs复合材料的形貌、组成和结构进行表征。同时,将rGO/AgNPs复合材料修饰到玻碳电极表面制备出过氧化氢(H_2O_2)电化学传感器,通过循环伏安法(CV)和计时安培响应法(i-t)对传感器进行电化学性能测试。实验结果表明:制备的rGO/AgNPs传感器具有较好的电化学性能,其对H_2O_2检测的灵敏度为340.6μA·(mmol/L)~(-1)·cm~(-2),响应时间为3s,最低检测极限为7.5μmol/L(S/N=3),线性检测范围为20~4950μmol/L(线性相关系数为R=0.9973)。     

基于自组装技术的单晶硅表面镀铜工艺

本研究在单晶硅基底表面自组装制备了3-氨丙基三乙氧基硅烷(APTES)自组装薄膜,并在此基础上进行化学镀和电镀研究,最终得到了致密均匀的铜膜,镀层与单晶硅基底通过配位键连接,粘结力强。利用循环伏安(CV)法探索得到了最佳电镀工艺参数为:电流密度1.56A/dm2,电镀时间600s。借助接触角测试仪测定了不同试样表面的润湿性,通过X射线能谱仪(EDX)、扫描电子显微镜(SEM)对镀层的元素含量和表面形貌进行了表征。获得的铜镀层致密均匀并呈现金属光泽。     

预歧化处理的高性能锂离子电池SiO/C负极材料

以SiO和蔗糖为原料,SiO经高温歧化反应处理后,通过机械球磨、喷雾干燥、高温热解工艺制备出具有优异电化学性能的锂离子电池SiO/C负极材料。经XRD、FTIR、XPS、SEM、TEM结构分析表明,歧化反应处理的片状SiO包含非晶态SiO和纳米晶相Si、SiO_2,蔗糖热解形成的无定形碳包覆在细片状SiO的表面,组成球形SiO/C颗粒。电化学测试结果表明,预歧化处理的SiO/C复合材料的首次放电容量为1 314.6mAh/g,首次库伦效率达到71%;100周循环后的放电容量为851.2mAh/g,容量保持率达到78.5%,循环稳定性远高于未经歧化处理的SiO/C复合材料。电化学性能的提高归因于SiO预歧化反应及热解碳包覆。     

In Situ Chelating Synthesis of Hierarchical LiNi1/3Co1/3Mn1/3O2 Polyhedron Assemblies with Ultralong Cycle Life for Li‐Ion Batteries

Layered lithium transition‐metal oxides, with large capacity and high discharge platform, are promising cathode materials for Li‐ion batteries. However, their high‐rate cycling stability still remains a large challenge. Herein, hierarchical LiNi_1/3Co_1/3Mn_1/3O₂ polyhedron assemblies are obtained through in situ chelation of transition metal ions (Ni²⁺, Co²⁺, and Mn²⁺) with amide groups uniformly distributed along the backbone of modified polyacrylonitrile chains to achieve intimate mixing at the atomic level. The assemblies exhibit outstanding electrochemical performances: superior rate capability, high volumetric energy density, and especially ultralong high‐rate cyclability, due to the superiority of unique hierarchical structures. The polyhedrons with exposed active crystal facets provide more channels for Li⁺ diffusion, and meso/macropores serve as access shortcuts for fast migration of electrolytes, Li⁺ and electrons. The strategy proposed in this work can be extended to fabricate other mixed transition metal‐based materials for advanced batteries.     

Electrochemical Behavior of Single CuO Nanoparticles: Implications for the Assessment of their Environmental Fate

The electrochemical behavior of copper oxide nanoparticles is investigated at both the single particle and at the ensemble level in neutral aqueous solutions through the electrode‐particle collision method and cyclic voltammetry, respectively. The influence of Cl^? and NO₃^? anions on the electrochemical processes occurring at the nanoparticles is further evaluated. The electroactivity of CuO nanoparticles is found to differ between the two types of experiments. At the single‐particle scale, the reduction of the CuO nanoparticles proceeds to a higher extent in the presence of chloride ion than of nitrate ion containing solutions. However, at the multiparticle scale the CuO reduction proceeds to the same extent regardless of the type of anions present in solution. The implications for assessing realistically the environmental fate and therefore the toxicity of metal‐based nanoparticles in general, and copper‐based nanoparticles in particular, are discussed.