雷诺数效应对翼型抖振特性的影响

飞行器抖振是一种非线性气动弹性问题,当飞行器进入抖振阶段时,将会对飞行器的性能产生严重影响。而在跨声速条件下,激波附面层相互作用会诱导机翼抖振。本文开展了跨声速条件下翼型抖振特性雷诺数效应的实验研究,揭示了翼型跨声速抖振起始迎角、激波运动前缘边界、频谱特性、抖振频率与雷诺数变化的基本规律。结论如下:雷诺数变化会导致抖振起始边界的改变,对抖振起始迎角下的功率谱密度峰值有明显影响;随着雷诺数的增大,激波运动的前缘后移。雷诺数变化对抖振频率有明显影响,随着马赫数增大,雷诺数效应增强。     

小波模极大值法与数学形态学边缘检测细化结果

图像边缘检测的关键是尽可能多的检测到边缘并且抑制噪声的同时,尽可能的满足单线的边缘定位精度;为此选取了一种融合小波模极大值和数学形态学的边缘检测方法来获取图像边缘;首先在对图像进行小波分解,分别利用模极大值法和多尺度多结构数学形态学方法来处理小波分解的高频分量和低频分量,利用差影法对二者的结果进行融合;然后利用大律法得到二值化图像,并用形态学边缘细化算法细化图像边缘得到最后结果;实验结果显示,融合的方法可以得到比较完善的边缘,经过二值化和边缘细化后,获得的单线宽边缘更加清晰,定位精度更高。     

基于迭代拟合的集装箱角件边缘检测算法

噪声通常是影响集装箱角件图像中低层次语义信息提取精度的重要因素,传统的边缘检测算法通常通过改进滤波器和阈值来消除图像中的物理噪声和环境噪声,但是却无法去除边缘检测后的噪声,为解决这一问题,提出了一种基于迭代拟合的边缘检测算法。首先,对角件图像进行一系列预处理操作获取边缘点集,其次,使用拟合算法处理点集并且得到函数表达式,然后定义偏差值度量并计算,用于衡量目标点集到拟合或者检测结果的偏差,最后,去除定义下距离拟合结果最远的指定数量的点,如此迭代拟合直至评价函数收敛。实验结果与分析表明,该算法可以有效地去除边缘点集中的非真实边缘点,相比于传统的边缘检测算法更能去除特殊噪声,算法具有收敛速度快、准确率较高、灵活性好等特点。     

基于ARM的视觉导航AGV图像处理方法研究

为了实现更加简单高效的标识线图像的检测与处理,提出了一种优化的基于ARM的视觉导航AGV标识线图像处理方法。首先对采集到的图像进行灰度化处理并使用Otsu算法对图像进行阈值分割;然后采用优化的中值滤波算法进行图像滤波并使用高效的边缘提取策略获取路径边缘特征;最后采用角度判断的方法剔除错误点并使用最小二乘法拟合成路径的中心线。实验结果表明,该方法有较高的准确率和较好的实时性,可以满足工业生产中的实际需求,适用于基于嵌入式系统开发的视觉导航AGV。     

一种基于块模糊增强的玉米田遥感图像边缘检测方法

针对高分一号卫星(GF-1)玉米田遥感图像中玉米田光谱复杂和地块边缘模糊导致的面积统计误差大的问题,本文提出一种块模糊增强和最小值边缘提取相结合的边缘检测方法进行玉米田地块分割处理,以减小面积统计误差。首先将彩色遥感图像从RGB变换到I¹I²I³彩色空间,提取出含丰富特征的单色图I¹;然后利用模糊理论对I¹进行基于块的增强处理;再对增强后的图像进行最小值边缘提取;最后利用Full Lambda-Schedule算法对区域边缘进行优化。通过与Canny和Sobel等边缘提取方法比较,证明本文的边缘检测结果能有效地分割出玉米田地块目标,减少了玉米田光谱复杂和边缘模糊带来的影响,检测出的边缘更符合玉米田实际分布,玉米田面积统计结果更符合实际。     

基于Facet模型的闪光图像边缘检测

针对闪光图像的特点,对经典边缘检测算子进行了分析,发现存在检测出的边缘粗和对噪声的干扰比较敏感的缺点,提出了一种基于Facet模型的爆轰实验图像边缘检测算法。该方法吸取了其它同类方法的优点,引进了正交基简化了运算,用离散正交多项式对图像每个像素的邻域作最佳曲面拟合,在此基础上使用整体梯度算子寻求二阶方向导数的零交叉点,最终提取边缘点。结果表明:该方法检测出的边缘细,并且光滑连续,对图像噪声干扰有较强的抑制能力,对于孤立的边缘能够给出较精确的定位。     

序列图像中运动目标的自动提取方法

针对目标检测与跟踪领域中的运动目标自动提取问题,提出了一种新的运动目标自动提取方法.利用已有的图像帧滤波后初始化背景,并在运动目标检测过程中,利用检测结果,不断地自动更新背景.使用背景差法检测运动区域,并对差分图像进行动态阈值分割,以及边缘链接,使其边缘处于基本连续状态.在得到的二值图上,提取轮廓,并根据目标大小选择面积阈值,剔除由于噪音或者背景提取不干净造成的虚假轮廓,将得到的轮廓掩模图像与原图像做逻辑与运算,提取出目标.实验结果表明,该方法可以有效地提取出刚体或非刚体运动目标.     

Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

Glassy carbon electrode (GCE) coated with anisotropic gold nanoplates (aAuNPs) was used for the study of oxygen reduction reaction (ORR) in 0.5 M sulfuric acid instead of bulk gold electrodes. The electrode cleaning/activation procedure lead to the removal of any charged and uncharged residues on the gold nanoplates, leaving the nanostructured surface highly active towards oxygen reduction. The advantages: much lower overpotential and larger current densities of oxygen reduction are ascribed to the unique nanostructures present on the carbon electrode surface‐the gold nanoplates. They are rich in edges providing a large population of Au (100) sites with unsaturated coordination exposed to the solution, and catalytically active. Measurements performed using a rotating disc electrode, modified with the gold nanoplates, confirmed that ORR proceeds via two separate steps: oxygen is reduced to hydrogen peroxide, and the peroxide is further reduced in a two‐electron reduction to water.     

Oxygen Evolution Reaction at Carbon Edge Sites: Investigation of Activity Evolution and Structure–Function Relationships with Polycyclic Aromatic Hydrocarbons

The abundance of available surface chemical information and edge structures of carbon materials have attracted tremendous interest in catalysis. For the oxygen evolution reaction (OER), the edge effects of carbon materials have rarely been studied in detail because of the complexity of various coexisting edge configurations and the controversy between carbon corrosion and carbon catalysis. Herein, the exact roles of common carbon active edge sites in the OER were interrogated using polycyclic aromatic hydrocarbons (PAHs) with designated configurations (zigzag and armchair) as model probe molecules, with a focus on structure–function relationships. Zigzag configurations of PAHs showed high activity for the OER while also showing a good stability at a reasonable potential. They show a TOF value of 0.276 s^?1 in 0.1 m KOH. The catalytic activity of carbon edge sites was further effectively regulated by extending the π conjugation structure at a molecular level.     

Phosphorene-Based van der Waals Heterojunction for Solar Water Splitting

As a clean and renewable future energy source, hydrogen fuel can be produced via solar water splitting. Two-dimensional (2D) black phosphorene (black-P) can harvest visible light due to the desirable band gap, which promises it as a metal-free photocatalyst. However, black-P can be only used to produce hydrogen since the oxidation potential of water locates lower than the position of the valence band maximum. To improve the photocatalytic performance of black-P, here, using black-P and blue phosphorene (blue-P) monolayers, we propose a 2D van der Waals (vdW) heterojunction. Theoretical results, including the band structures, density of states, Bader charge population, charge density di erence, and optical absorption spectra, clearly reveal that the visible light absorption ability is obviously improved, and the band edge alignment of the proposed vdW heterojunction displays a typical type-II feature to effectively separate the photogenerated carriers. At the same time, the built-in interfacialelectric field prevents the electron-hole recombination. These predictions suggest that the examined phosphorene-based vdW heterojunction is an efficient photocatalyst for solar water splitting.