Experimental investigation of heat transfer performance of corrugated tube with spring tape inserts

Turbulent forced convection in a corrugated tube with spring tape is investigated experimentally, for Reynolds numbers from 10,000 to 50,000. The working fluid is air. Experiments are performed for different pitch and spring ratios. Results show that Nusselt numbers can be increased considerably, depending on pitch and spring ratios. An overall assessment, considering the friction losses, is achieved using the thermo-hydraulic performance parameter. The latter is observed to take values larger than unity for all cases, where quite high values around 2.8 occur for cases with smallest pitch and spring ratios. Predictive Nusselt number and friction factor correlations are proposed.     

基于机器视觉的量子点STM形貌图像识别研究

为减轻量子点表面形貌分析过程中的人工工作,使量子点的STM图像分析更加自动化,基于机器视觉对衬底的斜切角及量子点的形貌特性展开研究.利用腐蚀和边缘检测提取台阶形状,并通过反三角变换计算斜切角.利用二值化和阈值下降对量子点的数量与空间坐标进行提取,在此基础上,通过邻域密度计算分析其均匀性,并在解决图像中的粘连问题后找出量子点的尺寸.实验结果显示,与人工统计相比,斜切角、量子点计数及尺寸的平均误差分别为5.02%, 0.7788%及1.12%;并实现量子点均匀性的自动化统计与分析.基于机器视觉算法的自动识别过程,对协助研究者分析量子点表面形貌有实际意义.     

Adaptive signal enhancement for overlapped peaks based on weighting factor selection

Peak-sharpening is an effective method for the peak position detection of overlapped spectra. However, the weighing factor parameter strongly affects the sharpening performance, and the derivative adopted in the peak-sharpening method is sensitive to noise. In this paper, an adaptive peak-sharpening method based on weighting factor selection is proposed. The relationship between the sharpening ratio and weighting factor is studied. In addition, the Savitzky–Golay filter is adopted due to its excellent noise reduction and peak shape retention abilities. First, the smoothed signal and second-order derivative signal are obtained by the Savitzky–Golay filter. Then, the parameters of the overlapped peaks are estimated for the weighting factor selection. Next, the peak position is detected by the peak-sharpening method. After that step, the estimated parameters are updated, and the above steps are iterated until the detection of the peak position converges. Finally, the converged results are considered to be the final detection results. The experimental results using a simulated dataset, a virtual mass spectra dataset and a polarography dataset show that the proposed method is effective for peak position detection.     

石墨二炔及其电子转移增强特性

石墨二炔是由sp和sp²杂化的碳原子构成的新的碳同素异形体。由于石墨二炔具有独特的拓扑结构和电子结构、较高的电荷迁移率及优异的电子传输性能,使其与其他材料相互作用,可表现出独特的电子转移增强特性。本文基于石墨二炔的电子转移增强特性,概述了石墨二炔及其电子转移增强特性的最新研究进展,包括金属氧化物/石墨二炔、金属纳米颗粒/石墨二炔、聚合物/石墨二炔以及染料分子/石墨二炔等多种石墨二炔基材料。本文从理论和实验研究两个方面详细阐述了石墨二炔的电子转移增强特性、石墨二炔与不同材料的相互作用以及相关的应用。希望该综述能对石墨炔化学的发展起到一定的积极作用。     

基于主成分分析和分层树集合划分的Huffman算法图像压缩研究

互联网的飞速发展,产生了大量的图像信息.为了减少图片占用的存储空间,提高图像质量,提出了一种将主成分分析（PCA）和分层树集合划分（SPIHT）压缩算法相结合的有损图像压缩算法.首先对图像进行主成分分解,选取主要特征值进行压缩,再利用SPIHT算法将图像分解成不同子带的小波系数进行压缩,对SPIHT压缩系数进行哈夫曼编码,实现图像二级压缩.将本文提出的算法与SPIHT、SPIHT的哈夫曼编码、JEPG2000、PCA压缩算法进行了比较,结果表明本算法较其他压缩算法具有更好的性能,在压缩比相同的情况下能获得更高的PNSR和SSIM.     

一种基于特征分解的图像融合方法

一幅图像可以分解成几何特征不同的纹理部分和卡通部分,基于这两大特征提出了一种图像融合方法.利用卡通和纹理特征的差异,通过学习分别得到卡通字典和纹理字典.在融合过程中,分别利用特定的卡通和纹理字典对源图像的卡通和纹理部分进行融合,融合后的卡通和纹理部分经简单相加得到融合图像.实验结果表明,所提方法是有效的.     

纳米球和核壳纳米球对有机太阳能电池光吸收增强效果的研究

研究了SiO2纳米球、Ag纳米球、SiO2@Ag核壳纳米球、Ag@SiO2核壳纳米球结构分别掺杂到有机太阳能电池的活性层中对器件活性层的光捕获能力增强作用.结果显示:相较于等效的平板结构,掺杂SiO2介质球使活性层光吸收提高了9.95;;Ag金属球则带来11.0;光吸收增强.表明在有机太阳能电池中的活性层中掺杂参数优化的金属球和介质球都能够带来活性层光吸收增强.另外,对活性层中掺杂核壳纳米球结构的研究表明:掺杂SiO2@Ag核壳纳米球的活性层光吸收随着包覆层厚度的增加而增加,当Ag壳厚度为16 nm时,增强效果与掺杂最优的介质球的效果接近,而且两者增强谱也基本相同;掺杂Ag@SiO2核壳纳米球结构中活性层光吸收随着介质包覆层厚度增加而减弱,当包覆层厚度为1 nm时,吸收效果与金属球相当,且吸收谱也是基本相同.通过在有机太阳能电池活性层中掺杂介质球、金属球以及核壳纳米球所带来的活性层光吸收增强效果的研究,为选择掺杂纳米球和核/壳纳米球来提高光捕获能力提供了指导.     

Characterization of a sCMOS‐based high‐resolution imaging system

The detection system is a key part of any imaging station. Here the performance of the novel sCMOS‐based detection system installed at the ID17 biomedical beamline of the European Synchrotron Radiation Facility and dedicated to high‐resolution computed‐tomography imaging is analysed. The system consists of an X‐ray–visible‐light converter, a visible‐light optics and a PCO.Edge5.5 sCMOS detector. Measurements of the optical characteristics, the linearity of the system, the detection lag, the modulation transfer function, the normalized power spectrum, the detective quantum efficiency and the photon transfer curve are presented and discussed. The study was carried out at two different X‐ray energies (35 and 50 keV) using both 2× and 1× optical magnification systems. The final pixel size resulted in 3.1 and 6.2 µm, respectively. The measured characteristic parameters of the PCO.Edge5.5 are in good agreement with the manufacturer specifications. Fast imaging can be achieved using this detection system, but at the price of unavoidable losses in terms of image quality. The way in which the X‐ray beam inhomogeneity limited some of the performances of the system is also discussed.     

Insight into 3D micro‐CT data: exploring segmentation algorithms through performance metrics

Three‐dimensional (3D) micro‐tomography (µ‐CT) has proven to be an important imaging modality in industry and scientific domains. Understanding the properties of material structure and behavior has produced many scientific advances. An important component of the 3D µ‐CT pipeline is image partitioning (or image segmentation), a step that is used to separate various phases or components in an image. Image partitioning schemes require specific rules for different scientific fields, but a common strategy consists of devising metrics to quantify performance and accuracy. The present article proposes a set of protocols to systematically analyze and compare the results of unsupervised classification methods used for segmentation of synchrotron‐based data. The proposed dataflow for Materials Segmentation and Metrics (MSM) provides 3D micro‐tomography image segmentation algorithms, such as statistical region merging (SRM), k‐means algorithm and parallel Markov random field (PMRF), while offering different metrics to evaluate segmentation quality, confidence and conformity with standards. Both experimental and synthetic data are assessed, illustrating quantitative results through the MSM dashboard, which can return sample information such as media porosity and permeability. The main contributions of this work are: (i) to deliver tools to improve material design and quality control; (ii) to provide datasets for benchmarking and reproducibility; (iii) to yield good practices in the absence of standards or ground‐truth for ceramic composite analysis.     

硬X射线焦斑环孔编码成像的理论与实验研究

针对几十~百keV能量的低强度X射线焦斑源测量,建立了高探测效率环孔编码成像技术。研究给出了环孔成像效率和信噪比与环孔结构参数的关系,采用微联结的环孔结构设计并模拟了联结区尺寸对成像质量的影响,解决了环孔结构同轴成像技术难题。所建立环孔成像系统应用于Unique-II X射线焦斑源成像实验。结果表明,X射线焦斑的空间分布近似为‘马鞍’形状,而且中间部分的强度低于两侧的强度,与针孔成像结果相似,但环孔的探测效率明显高于针孔的效率。最后,分析了维纳滤波与R-L两种复原图像方法的效果。