Investigations of moiréartifacts induced by flux fluctuations in x-ray dark-field imaging

X-ray dark-field imaging using a grating interferometer has shown potential benefits for a variety of applications in recent years.X-ray dark-field image is commonly retrieved by using discrete Fourier transform from the acquired phasestepping data.The retrieval process assumes a constant phase step size and a constant flux for each stepped grating position.However,stepping errors and flux fluctuations inevitably occur due to external vibrations and/or thermal drift during data acquisition.Previous studies have shown that those influences introduce errors in the acquired phase-stepping data,which cause obvious moiréartifacts in the retrieved refraction image.This work investigates moiréartifacts in x-ray dark-field imaging as a result of flux fluctuations.For the retrieved mean intensity,amplitude,visibility and dark-field images,the dependence of moiréartifacts on flux fluctuation factors is theoretically derived respectively by using a first-order Taylor series expansion.Results of synchrotron radiation experiments verify the validity of the derived analytical formulas.The spatial frequency characteristics of moiréartifacts are analyzed and compared to those induced by phase-stepping errors.It illustrates that moiréartifacts can be estimated by a weighted mean of flux fluctuation factors,with the weighting factors dependent on the moiréphase and different greatly for each retrieved image.Furthermore,moiréartifacts can even be affected by object’s features not displayed in the particular contrast.These results can be used to interpret images correctly,identify sources of moiréartifacts,and develop dedicated algorithms to remove moiréartifacts in the retrieved multi-contrast images.

Development of X-ray dark-field imaging towards clinical application

Review of X-ray dark-field imaging under development is presented. Its goal is its application to clinical diagnosis of organs that have been invisible by the ordinary techniques. In order to clinically visualize tissues in detail one needs high contrast and high spatial resolution say ～50 μm. This X-ray optics comprises a Bragg asymmetric monochro-collimator and a Bragg case or a Laue case filter with capability of analyzing angle in a parallel position. Their diffraction index is 4,4,0 and the X-ray energy 35 keV (λ= 0.0354 nm). The filter has 0.6 mm thickness in the Bragg case or 1.075 mm or 2.15 mm thickness in the Laue case. Under this condition only the refracted X-rays from object can transmit through the filter while the beam that may receive absorption and/or phase change will not. Soft tissues at human joints thus taken show high contrast images so that the DFI is promising for clinical diagnosis. Preliminary X-ray absorption images of another clinical candidates of ear bones are also shown.

Dark-field line confocal imaging with point confocality and extended line field for bulk defects detection

Fabrication of high-quality optics puts a strong demand on high-throughput detection of macroscopic bulk defects in optical components.A dark-field line confocal imaging method is proposed with two distinct advantages:(ⅰ)a point-to-line confocal scheme formed by a columnar elliptical mirror and an optical fiber bundle breaks through the constraint on light collection angle and field of view in the traditional line confocal microscopy using an objective,allowing for an extended confocal line field of more than 100 mm while maintaining a light collection angle of 27°;(ⅱ)the bulk defects are independently illuminated as a function of time to eliminate the cross talk in the direction of the confocal slit,thus preserving point confocality and showing the optical section thicknesses to be 162μm in the axial direction,and 19 and 22μm in the orthogonal transverse directions.The experimental results verify that the method has a minimum detectable bulk defect of less than 5μm and an imaging efficiency of 400 mm2/s.The method shows great potential in high-throughput and highsensitivity bulk defects detection.

单纳米粒子表面的甲醇电催化氧化过程

由于全球资源短缺和环境污染等问题日益加剧,开发利用洁净高效的新能源已成为当今社会研究热点.其中,直接甲醇燃料电池(DMFC)具有低温启动、无需重整制氢、洁净环保和体积小巧等特性,展现出较好的应用前景.DMFC的阳极反应为甲醇氧化反应,甲醇的完全氧化涉及到复杂的六步电子转移反应过程.揭示甲醇氧化的反应路径与机理,阐明催化剂的真实活性中心以及毒化效应,对于高效催化剂的设计和制备至关重要.随着纳米技术的发展,在单颗粒水平对纳米催化剂进行表征受到了越来越多的关注.因此,亟需发展具有高灵敏度的原位界面表征方法,实现纳米尺度的精准测量,排除催化剂平均效应,获取纳米表界面真实的催化反应信息.本文结合纳米等离子共振散射光谱与电化学技术,获得了单个纳米催化剂的同步光电响应信号,实现单颗粒水平纳米粒子表面化学、电化学反应过程(如电荷转移、分子吸附等)的高灵敏监测,揭示纳米尺度表界面催化反应机制.利用这一技术,动态监测了单个金/铂包金纳米颗粒表面的甲醇氧化过程.结果表明,在金纳米颗粒表面,甲醇氧化主要通过HCOOH路径,生成产物为HCOOH或CO_(2).其中,反应中间体与羟基离子的竞争性吸附起到重要作用,反应决速步为Au-OH和Au-CHO的共吸附.而铂催化甲醇氧化主要经过CO路径,决速步为Pt-OH和Pt-CO氧化生成Pt-COOH过程.此外,观测到金和铂氢氧化物为催化反应的活性物种,进一步证实了金属氧化物对于催化活性的钝化作用.结合密度泛函理论模拟,明确了甲醇氧化反应中间体吸附与金属氢氧化物演变之间的内在联系.综上,本文利用纳米等离子共振散射光谱,原位监测了单个纳米粒子表面的甲醇电催化氧化过程,实现了催化剂真实活性物种演变与失活过程的直接观测,揭示了不同催化剂表面的决速步骤,为提高催化反应效率提供了更加准确的反应信息.本文将有益于纳米等离子共振散射光谱在电催化反应高灵敏监测方面的广泛应用,并为高效甲醇催化剂的制备提供参考.

Visually monitoring the etching process of gold nanoparticles by KI/12 at single-nanoparticle level using scattered-light dark-field microscopic imaging

Real-time monitoring of reaction processes is helpful for understanding the reaction mechanisms. In this study we investigated the etching mechanism of gold nanopartides （AuNPs） by iodine on a single-nanopartide level because AuNPs have become important nanoprobes with applications in sensing and bioimaging fields owing to their specific localized surface plasmon resonance （LSPR） properties. By using a scattered-light dark-field microscopic imaging （iDFM） technique, the in situ KI/I2-treated etching processes of various shapes of AuNPs, including nanospheres （AuNSs）, nanorods （AuNRs）, and nanotrigonal prisms （AuNTs）, were monitored in real time. It was found that the scattered light of the different shapes of AuNPs exhibited noticeable color changes upon exposure to the etching solution. The scattering spectra during the etching process showed obvious blue-shifts with decreasing scattered intensity owing to the oxidation of Au atoms into [AuI2]-. Both finite-difference time-domain （FDTD） simulations and monitoring of morphological variations proved that the etching was a thermodynamic-dependent process through a chamfering mechanism coupled with layer-by-layer peeling, resulting in isotropic spheres with decreased particle sizes.

Dark-field detection method of shallow scratches on the super-smooth optical surface based on the technology of adaptive smoothing and morphological differencing

In recent years, modern optical processing technologies, such as single point diamond turning, ion beam etching, and magneto-theological finishing, arc getting break- throughs. Machining precisions of super-smooth optics have also been significantly improved. However, with increasing demands for the optical surface quality,

高速大像素CMOS图像传感器中钳位光电二极管形状设计的研究进展

采用钳位光电二极管(PPD)的CMOS图像传感器,由于其优异的性能,已成为图像传感领域中占主导地位的技术。然而,更大尺寸PPD的应用在电荷传输速度和效率方面存在挑战,特别是在微光、高速探测的场景中,传统的像素设计难以满足必要的性能标准。一种有效的方法是通过PPD的形状设计来提升大像素性能。首先全面概述了产生PPD横向电场的两种机制:边缘电场设计和钳位电压调制,并探讨了基于这两种设计策略的各种设计改进。然后总结了传输栅-浮空扩散(TG-FD)节点收集结构及像素整体布局优化的相关研究进展。此外,还研究了PPD的形状设计对暗电流的影响。通过全面分析PPD形状设计中采用的方法,为提升大像素设计提供了参考。

Dark-field Imaging of Supercoiled DNA

With the discovery and further understanding of topoisomerases, it becomes clear that the supercoiling of double stranded DNA plays an important role in DNA replication, RNA transcription and even in the control of gene expression. Although the small circular DNA can be separated by means of density gradient centrifugation or gel electrophoresis and

Rapid ultrasensitive monitoring the single-particle surface-enhanced Raman scattering (SERS) using a dark-field microspectroscopy assisted system

The observation of single-particle surface-enhanced Raman scattering(SERS) has generated considerable interest both in the nanomaterials filed and in the single-particle spectroscopy community.It is a challenge to realize rapid,facile,and high throughput SERS at single nanoparticle level.Here,without the complex experimental device and difficult experimental operations,a general single-particle SERS technique has been achieved by using dark-field-assisted surface-enhanced Raman spectroscopy(DFSERS).This advanced method provides in-situ characterization of the chemical reaction performance at single gold nanorod.

Dark Matter Particles May Never Be Directly Detected by Instruments—A Dark Matter Mechanism That Does Not Exceed the Standard Model Framework

A dark matter mechanism within the framework of the standard model (SM) of particle physics is proposed in this article that the essence of dark matter may be the excited virtual particle field by the gravitational field of ordinary matter, which contains virtual photons, virtual positive and negative electron pairs, virtual gluons, virtual positive and negative quark pairs, virtual neutrinos etc. In this mechanism, there are two basic assumptions: 1) the stronger the gravitational field of ordinary matter, the greater the excited energy (mass) density of virtual particle field;2) The excited virtual particle field is generally very weak in self-interaction. The virtual particle field excited by gravity can exhibit the properties of dark matter and may become a dark matter candidate. Based on this new dark matter mechanism, the hydrodynamic equations and cosmic perturbation equations describing cosmic matter are improved, and this may be meaningful for solving the challenges faced by the standard cosmological model (Lambda-CDM or LCDM) and developing and perfecting LCDM model.

Prolonged hypervolemic hemodilution decreases functional capillary density of ileal mucosa in pigs revealed by sidestream dark-field imaging

Objective:Hemodilution changes the physical properties of blood by reducing its hematocrit and blood viscosity.We tested whether prolonged hypervolemic hemodilution (HHD) impairs functional capillary density (FCD) of ileal mucosa in healthy mechanically-ventilated pigs and if there is any correlation between changes in FCD of ileal and sublingual mucosas during HHD.Methods:Sixteen domestic female pigs were anesthetized,mechanically-ventilated,and randomly assigned to the HHD (20 ml/(kg·h) Hartmann's solution for 3 h) or fluid restrictive (5 ml/(kg·h) Hartmann's solution for 3 h) group.Microcirculations of sublingual and ileal mucosas via ileostomy were visualized using sidestream dark-field (SDF) imaging at baseline conditions (t=0 h) and at selected time intervals of fluid therapy (t=1,2,and 3 h).Results:A significant decrease of ileal FCD (285 (278-292) cm/cm 2) in the HHD group was observed after the third hour of HHD when compared to the baseline (360 (350-370) cm/cm 2) (P<0.01).This trend was not observed in the restrictive group,where the ileal mucosa FCD was significantly higher after the third hour of fluid therapy as compared to the HHD group (P<0.01).No correlation between microhemodynamic parameters obtained from sublingual and ileal mucosas was found throughout the study.Conclusions:Prolonged HHD established by crystalloid solution significantly decreased ileal villus FCD when compared to restrictive fluid regimen.An inappropriate degree of HHD can be harmful during uncomplicated abdominal surgery.

基于光栅干涉仪的暗场成像的Cramér-Rao下界

在光栅相衬成像中,通常使用相位步进法进行数据采集和信息提取。然而,对于相位步进法在提取暗场信号的算法效率还没有得到充分的评估。本研究引入Cramér-Rao下界对提取暗场信号的算法效率进行评估。基于理论分析和数值计算发现目前完全有效的算法仅适用于三步相位步进法,其他更多步数的相位步进法都是次优的。本研究以Cramér-Rao下界作为依据,定量地分析了相位步进数和可见度对算法效率的影响。结果表明在低可见度的情况下,相位步进法可以接近理论的最佳效率;在高可见度的情况下,当相位步进数大于5时,算法效率仅为77.4%,这可为基于X射线和中子光栅干涉仪的暗场成像的信噪比优化提高、剂量优化提供指导。

Lithium mapping in a Mg-9Li-4Al-1Zn alloy using electron energy-loss spectroscopy

Magnesium-lithium alloys with high lithium content have been attracting significant attention because of their low density,high formability and corrosion resistance.These properties are dependent on the distribution of lithium,which is difficult to map in the presence of magnesium.In this work,a ratio spectrum-imaging method with electron energy-loss spectroscopy(EELS)is demonstrated,which enables the mapping of lithium.In application to LAZ941(Mg-9Li-4Al-1Zn in wt.%),this technique revealed that a key precipitate in the microstructure,previously thought by some to be Mg_(17)Al_(12),is in fact rich in lithium.This result was corroborated with a structural investigation by high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM),showing this phase to be Al_(1-x)Zn_(x)Li,with x<<1.This work indicates the potential offered by this technique for mapping lithium in materials.

一种5倍暗场金相物镜的设计

为解决现有5倍暗场金相物镜照明亮度低且不均匀的问题,采用一体化设计新方法。首先通过选择光学结构,在光学设计软件ZEMAX中合理设置操作数,利用光学软件设计优化出光学系统;然后依据暗场照明约束条件设置反射光线,利用CAD软件设计出反射曲面。通过光学传递函数、暗场照明光束利用率、光斑尺寸和光斑均匀度等参数对物镜性能进行评价。结果表明新5倍暗场金相物镜像质优良、视场明亮均匀,新的设计方法可行。

基于机器视觉的ITO导电玻璃缺陷检测系统设计

针对传统人工检测ITO导电玻璃缺陷时存在错检、漏检、效率低等问题,提出一种基于机器视觉的ITO导电玻璃缺陷检测方法。首先,提出了一种基于线扫描相机和多光源同时曝光合成图像的成像方案,使表面缺陷检测项与易误干扰项形成不同特征;其次,采用Blob分析方法对明暗场图像分类处理实现对划痕、气泡、划伤等表面缺陷的检测;最后,利用C#Winform实现具备友好的人机操作界面的检测软件系统。实验结果表明,系统综合漏检率为0.25%、误判率为4.07%,对单片玻璃的检测时间为2.3s,同传统人工目检方式相比,系统检测具有较高的效率和正确率,具备较高的实用价值。

基于暗场线扫技术的球体表面缺陷检测技术

钢球的球体几何特性令表面上的缺陷难以连贯成像引起漏检或缺陷畸变被误判,且钢球的镜面反射效应可能造成缺陷信号被周围环境的像和高反亮斑淹没,导致缺陷漏检。为此,提出了一种基于光学暗场线扫描技术的钢球表面缺陷检测方法,设计搭建了一套适用于高反射率钢球的暗场线扫表面缺陷检测系统,开发了图像预处理、畸变校正、缺陷提取、点云重建、分割和过滤等算法,建立球面图像点间的空间几何关系,成功将钢球表面缺陷在三维球面上重构,实现了轴承钢球表面缺陷的三维连贯检测。实验结果表明,对表面完好的无损球测量重复性为0.14%,对表面带有缺陷的磨损球测量重复性为0.11%。

扫描电镜中扫描透射成像装置的研制及应用

使用扫描电镜自带的背散射电子探头(BSED)作透射散射电子探测器,设计了一套适合FEI Quanta 650FEG扫描电镜使用的扫描透射(STEM)成像装置,并制定了该STEM成像装置的操作说明。以埃洛石复合ZrO_(2)纳米颗粒为观察对象,对自制STEM成像装置的实用性进行了验证。结果表明:STEM像衬度与背散射电子探头到样品之间的距离相关,通过调整背散射电子探头与样品之间的距离,可以实现高角环形暗场像的采集,使ZrO_(2)纳米颗粒的亮度明显高于埃洛石;STEM像衬度与透射电镜采集的HAADF-STEM像一致,元素分布状态也与埃洛石和ZrO_(2)纳米颗粒对应,表明所研制的STEM成像装置具有较好的实用性。

暗场显微镜下的彩色“纳米星”

具有独特局域表面等离子共振散射特性的贵金属纳米粒子,在可见光区域表现出明显的吸收和散射光谱特性。在过去的几十年中,基于纳米金和纳米银溶液的可视化颜色传感器,被广泛应用在金属离子、生物分子、农药等灵敏检测。自2000年,暗场显微镜的出现,实现了纳米尺度下等离子共振散射光谱的精准获取,将传感尺度从传统的实验试管发展到单纳米颗粒界面。单颗粒检测消除了本体溶液中大量纳米粒子产生的平均效应,可提供更加准确的反应信息。纳米粒子的散射光谱主要取决于颗粒的尺寸、形貌、成分以及颗粒间耦合作用等,因此,具有特定散射颜色的单个纳米粒子,可以作为优异的纳米探针。这篇综述聚焦于单颗粒纳米传感,首先介绍了纳米粒子局域表面等离子共振的原理和发展历史。随后,主要讨论了单个贵金属纳米粒子作为颜色编码传感器,在生物分子、环境污染物以及能源等领域的应用,尤其是基于单颗粒的原位纳米光谱电化学传感及其在电催化反应中的应用。例如,利用纳米粒子的溶出和生长过程,精巧地设计了针对不同待测物的纳米探针。另一方面,对单纳米粒子结构演变过程的原位监测,也有助于对纳米材料制备机理的理解。最后,着重探讨了纳米颜色传感器信号提取放大的检测手段,包括将肉眼识别的颜色转换为可读的三原色信息以及偏振光检测技术等,进一步扩展单颗粒颜色传感的应用范围。

基于暗态扫频法的Rb-Xe自旋交换体系弛豫时间测量方法

在87Rb-129Xe自旋交换体系中,87Rb和129Xe弛豫时间的准确测量对于磁共振陀螺及磁力仪相关应用非常重要。针对该需求,分析了泵浦光与激励磁场对87Rb弛豫时间的影响以及暗态下的87Rb和129Xe自旋交换过程,并在理论分析基础上提出了暗态扫频测量方法。实现了对87Rb以及129Xe的纵向弛豫时间的测量。使用本方法测得了87Rb的横向弛豫时间和纵向弛豫时间分别为1.36和5.18 ms,129Xe的纵向弛豫时间为519 s,其拟合R2=0.9999,具有极高的拟合优度。相较于以往的测量方法,暗态扫频法可以彻底消除泵浦光造成的磁场梯度的影响,具有高准确度的优点且操作简便。研究对磁共振陀螺及磁力仪的性能分析与标定具有较高的参考价值。

全内反射照明光学元件损伤检测信噪比分析

适合的光学元件照明对终端光学元件损伤检测成像至关重要。基于平板光学元件的全内反射原理,将阵列LED边缘照明光耦合进大口径光学元件,光学元件上疵点处的全内反射条件被破坏,光线从疵点出射,用相机对元件成像,散射光就会在相机CCD上形成疵点的图像,它是暗背景中的亮点,因此图像信噪比很高,解决了损伤检测过程中疵点到底归属于光学系统中哪块光学元件的难题。建立了被检测元件损伤点的信噪比模型,分析了临近损伤元件损伤对检测结果的影响。离线验证结果表明:对于310 mm×310 mm口径的平面光学元件,全口径检测分辨率优于120μm×120μm。