基于X-ray CT图像的沥青混合料车辙过程空隙分布评估

X射线计算机断层扫描(X-ray computed tomography,X-ray CT)技术作为一种无损测试方法,已被广泛用于评估沥青混合料中的空隙结构和与空隙有关的病害。基于X-ray CT和图像处理技术,从细观结构层面探讨了车辙变形过程中沥青混合料的空隙结构特征。提出了体积等效球棍模型来表征空隙连通性的变化,用改进的环扇分割变异系数、位置偏心率和球度分别描述了空隙的分布和形状特征。结果表明,车辙对沥青混合料空隙结构的影响机制因混合料类型而异。与密级配沥青混凝土(AC-13)相比,沥青玛蹄脂碎石混合料(SMA-13)中的空隙更加不均匀和离散,尤其是那些体积小于0.01 mm^(3)的空隙。此外,SMA-13中的空隙连通性和分布更容易受到外部荷载的影响,其粗集料在变形过程中往往会产生定向移动进而改变初始位置。尽管车辙变形同时增加了2种混合料中空隙的水平不均匀性,但AC-13的竖向不均匀性减少,而SMA-13的竖向不均匀性增加。加载使AC-13混合料的空隙几何形状变得复杂和分散,而SMA-13则相反,预示着与AC混合料相比,SMA混合料在加载1 h后仍保持抵抗车辙破坏的潜力。总体而言,沥青混合料中空隙的拓扑特征及其在车辙变形过程中的动态响应主要取决于混合料的级配形式。

基于X-ray CT原位三轴剪切试验的砂土颗粒材料微观动力学

将X射线断层扫描技术(CT)与原位三轴剪切试验相结合,分析渥太华砂在剪切过程中的微观动力学演化规律.在试验过程中共完成15次X射线扫描,使用图像分割算法进行颗粒分割并使用球谐函数重构颗粒的表面形貌,根据颗粒的多尺度形态指标序列实现整个加载过程中颗粒的准确匹配与追踪,并分析颗粒位移、转动、局部非仿射运动和局部孔隙率等微观动力学和微观结构指标的演化规律.在剪切过程中颗粒体系的竖向位移分布呈现2个锥形区域,颗粒的转动分布出现明显的X型剪切带.用于度量局部塑性变形程度的局部非仿射运动和局部体积分数呈现出较为明显的相关关系,表明颗粒微观动力学与其微观结构之间存在因果关系,局部自由体积较大的地方更易发生塑性变形.

基于斜孔散射校正板的锥束X射线CT散射校正方法

锥束X射线CT和二维扇束、平行束CT系统相比具有扫描速度快、射线利用率高、重建图像轴向分辨率和水平分辨率一致等优点,是当前工业CT技术发展的重点。然而,由于散射线的存在,其成像质量受到影响。为了减小散射线对图像质量的影响,提出一种新的基于斜孔散射校正板的散射校正方法,对该方法的原理和实现进行了深入的研究,通过获取原始扫描数据以及斜孔散射校正板后的扫描数据,利用插值和平滑处理的方法获得散射场数据。然后,通过将原始数据减去散射场数据后进行重建,即可得到无散射的CT图像。通过与光栅式散射校正板校正方法进行对比,结果表明,该方法应用于涡轮叶片的锥束CT扫描结果校正,典型区域(叶片内冷却通道及叶片内壁)对比度噪声比分别提升了14.2%和56.8%,而光栅式散射校正板校正后,同一位置对比度噪声比分别仅提升了5.6%和27.6%,验证了基于斜孔散射校正板散射校正方法的优越性。

Microstructure Evolution of Sandstone Cemented by Microbe Cement Using X-ray Computed Tomography

The bio-sandstone, which was cemented by microbe cement, was firstly prepared, and then the microstructure evolution process was studied by X-ray computed tomography （X-CT） technique. The experimental results indicate that the microstructure of bio-sandstone becomes dense with the development of age. The evolution of inner structure at different positions is different due to the different contents of microbial induced precipitation calcite. Besides, the increase rate of microbial induced precipitation calcite gradually decreases because of the reduction of microbe absorption content with the decreasing pore size in bio-sandstone.

Use of high-resolution X-ray computed tomography and 3D image analysis to quantify mineral dissemination and pore space in oxide copper ore particles

Mineral dissemination and pore space distribution in ore particles are important features that influence heap leaching performance. To quantify the mineral dissemination and pore space distribution of an ore particle, a cylindrical copper oxide ore sample (I center dot 4.6 mm x 5.6 mm) was scanned using high-resolution X-ray computed tomography (HRXCT), a nondestructive imaging technology, at a spatial resolution of 4.85 mu m. Combined with three-dimensional (3D) image analysis techniques, the main mineral phases and pore space were segmented and the volume fraction of each phase was calculated. In addition, the mass fraction of each mineral phase was estimated and the result was validated with that obtained using traditional techniques. Furthermore, the pore phase features, including the pore size distribution, pore surface area, pore fractal dimension, pore centerline, and the pore connectivity, were investigated quantitatively. The pore space analysis results indicate that the pore size distribution closely fits a log-normal distribution and that the pore space morphology is complicated, with a large surface area and low connectivity. This study demonstrates that the combination of HRXCT and 3D image analysis is an effective tool for acquiring 3D mineralogical and pore structural data.

Three dimensional distribution of surfactant in microspheres revealed by synchrotron radiation X-ray microcomputed tomography

This study investigated the formulation mechanism of microspheres via internal surfactant distribution. Eudragit L100 based microspheres loaded with bovine serum albumin were prepared by solid in oil in oil emulsion solvent evaporation method using acetone and liquid paraffin system containing sucrose stearate as a surfactant. The fabricated microspheres were evaluated for encapsulation efficiency, particle size, production yield, and in vitro release characteristics. The internal structures of microspheres were characterized using synchrotron radiation X-ray microcomputed tomography(SR-μCT). The enhanced contrast made the sucrose stearate distinguished from Eudragit to have its three dimensional(3D) distribution. Results indicated that the content and concentration determined the state of sucrose stearate and had significant influences on the release kinetics of protein. The dispersity of sucrose stearate was the primary factor that controlled the structure of the microspheres and further affected the encapsulation efficiency, effective drug loading, as well as in vitro release behavior. In conclusion, the 3D internal distribution of surfactant in microspheres and its effects on protein release behaviors have been revealed for the first time. The highly resolved 3D architecture provides new evidence for the deep understanding of the microsphere formation mechanism.

Full-field mapping of internal strain distribution in red sandstone specimen under compression using digital volumetric speckle photography and X-ray computed tomography

It is always desirable to know the interior deformation pattern when a rock is subjected to mechanicalload. Few experimental techniques exist that can represent full-field three-dimensional （3D） straindistribution inside a rock specimen. And yet it is crucial that this information is available for fully understandingthe failure mechanism of rocks or other geomaterials. In this study, by using the newlydeveloped digital volumetric speckle photography （DVSP） technique in conjunction with X-ray computedtomography （CT） and taking advantage of natural 3D speckles formed inside the rock due to materialimpurities and voids, we can probe the interior of a rock to map its deformation pattern under load andshed light on its failure mechanism. We apply this technique to the analysis of a red sandstone specimenunder increasing uniaxial compressive load applied incrementally. The full-field 3D displacement fieldsare obtained in the specimen as a function of the load, from which both the volumetric and the deviatoricstrain fields are calculated. Strain localization zones which lead to the eventual failure of the rock areidentified. The results indicate that both shear and tension are contributing factors to the failuremechanism. 2015 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting byElsevier B.V. All rights reserved.

X-ray tomography study on the structure of the granular random loose packing

Random loose packing is the minimum-density granular packing which can maintain mechanical stability. In this study, x-ray tomography is used to investigate the internal structure of an isotropically prepared random loose packing through a special apparatus to minimize the effect of gravity. It is found that the minimum packing density is around 0.587. The microscopic structural analysis of the packing is also carried out.

Fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios

We present a fast synchrotron X-ray tomography study of the packing structures of rods with different aspect ratios. Utilizing the high flux of the X-rays generated from the third-generation synchrotron source, we can complete a high- resolution tomography scan within a short period of time, after which the three-dimensional （3D） packing structure can be obtained for the subsequent structural analysis. The image phase-retrieval procedure has been implemented to enhance the image contrast. We systematically investigated the effects of particle shape and aspect ratio on the structural properties including packing density and contact number. It turns out that large aspect ratio rod packings will have wider distributions of free volume fraction and larger mean contact numbers.

X-ray Computed Tomography Characterization of 3D Tufted Twill Textile Composite for Aerostructures

Damage assessments in three dimensional (3D) textile composites subjected to mechanical loading can be performed by non-destructive and destructive techniques.This paper applies the two techniques to investigate the fracture behavior of 3D tufted textile composites.X-ray computed tomography as a non-destructive evaluation method is appropriate to detect damage locations and identify their progression in 3D textile composites.Destructive methods such as sectioning toward observing damage provide valuable information about damage patterns.The results of this research could be utilized to evaluate the initial cause of rupture in 3D tufted composites used in aerospace structures and analyze fracture modes and damage progression.

Nondestructive analysis by combined X-ray tomography on a synchrotron radiation facility

A nondestructive X-ray analysis technique combining transmission tomography, fluorescence tomography and Compton tomography based on synchrotron radiation is described. This novel technique will be an optional experimental technique at SSRF's hard X-ray micro-focusing beamline under construction at present. An experimental result of combined X-ray tomography is obtained in NE-5A station of PF. The reconstructed images of test objects are given.

In situ compression and X-ray computed tomography of flow battery electrodes

Redox flow batteries offer a potential solution to an increase in renewable energy generation on the grid by offering long-term, large-scale storage and regulation of power. However, they are currently un- derutilised due to cost and performance issues, many of which are linked to the microstructure of the porous carbon electrodes used. Here, for the first time, we offer a detailed study of the in situ effects of compression on a commercially available carbon felt electrode. Visualisation of electrode structure us- ing X-ray computed tomography shows the non-linear way that these materials compress and various metrics are used to elucidate the changes in porosity, pore size distribution and tortuosity factor under compressions from 0%-90%.

Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal

It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate twodimensional （2D） images of sawtooth oscillation on the HT-7 tokamak using the Fourier-Bessel harmonic reconstruction method, and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasiinterchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows： the magnetic surface is made up of the crescent-shaped “hot core” and the circular “cold bubble”. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.

Quantification of 3D macropore networks in forest soils in Touzhai valley(Yunnan,China)using X-ray computed tomography and image analysis

The three dimensional(3D) geometry of soil macropores largely controls preferential flow, which is a significant infiltrating mechanism for rainfall in forest soils and affects slope stability. However, detailed studies on the 3D geometry of macropore networks in forest soils are rare. The intense rainfall-triggered potentially unstable slopes were threatening the villages at the downstream of Touzhai valley(Yunnan, China). We visualized and quantified the 3D macropore networks in undisturbed soil columns(Histosols) taken from a forest hillslope in Touzhai valley, and compared them with those in agricultural soils(corn and soybean in USA; barley, fodder beet and red fescue in Denmark) and grassland soils in USA. We took two large undisturbed soil columns(250 mm×250 mm×500 mm), and scanned the soil columns at in-situ soil water content conditions using X-ray computed tomography at a voxel resolution of 0.945 × 0.945 × 1.500 mm^3. After reconstruction and visualization, we quantified the characteristics of macropore networks. In the studiedforest soils, the main types of macropores were root channels, inter-aggregate voids, macropores without knowing origin, root-soil interface and stone-soil interface. While macropore networks tend to be more complex, larger, deeper and longer. The forest soils have high macroporosity, total macropore wall area density, node density, and large macropore volume, hydraulic radius, mean macropore length, angle, and low tortuosity. The findings suggest that macropore networks in the forest soils have high interconnectivity, vertical continuity, linearity and less vertically oriented.

X-Ray Computed Tomography for Root Quantification

Soil cores from a field growing barley and barley mutants without root hairs under conventional and minimum tillage were sampled. They were X-ray scanned to produce a 3D image and then the roots were washed out and weight and length were determined by conventional means. Root volume and surface area were then calculated from the 3D images using state of the art software and methodology, and the measured and calculated measures were correlated. The only strong and significant correlation was between measured weight and calculated volume for mutants without root hairs. It is concluded that the software cannot segment out very small roots, but segmentation accuracy also depends on root structure in some unknown way. Any study using X-ray computed tomography to quantify roots as they grow in situ should start with a calibration for the conditions in question.

Soft X-ray Tomography on HT-7

The soft X-ray imaging system on HT-7 is introduced. Fourier-Bessel expansion method is used to reconstruct the soft X-ray emission distribution. Simulation results show that the inversion accuracy is associated with the angular expansion limit and the hot core displacement. In addition, tomographic results of sawtooth oscillations in a typical low hybrid current drive （LHCD） plasma are presented. It is shown that the reconstructions are reliable to analyze the perturbative mode and the evolution.

Identification of m = 2 competent mode of complex magneto-hydro-dynamics activities during internal soft disruption based on singular value decomposition and tomography of soft-X-ray emission on the HT-7 tokamak

In this paper,the singular value decomposition（SVD） method as a filter is applied before the tomographic inversion of soft-X-ray emission.Series of ＇filtered＇ signals including specific chronos and topos are obtained.（Here,chronos and topos are the decomposed spatial vectors and the decomposed temporal vectors,respectively）.Given specific magnetic flux function with coupling m = 1 and m = 2 modes,the line-integrated soft-X-ray signals at all chords have been obtained.Then m = 1 and m = 2 modes have been identified by tomography of simulated ＇filtered＇ signals extracted by the SVD method.Finaly,using the experimental line-integrated soft-X-ray signals,m = 2 competent mode of complex magnetohydrodynamics（MHD） activities during internal soft disruption is observed.This result demonstrates that m = 2 mode plays an important role in internal disruption（Here,m is the poloidal mode number）.

Investigation of noise properties in grating-based x-ray phase tomography with reverse projection method

The relationship between noise variance and spatial resolution in grating-based x-ray phase computed tomography（PCT） imaging is investigated with reverse projection extraction method, and the noise variances of the reconstructed absorption coefficient and refractive index decrement are compared. For the differential phase contrast method, the noise variance in the differential projection images follows the same inverse-square law with spatial resolution as in conventional absorption-based x-ray imaging projections. However, both theoretical analysis and simulations demonstrate that in PCT the noise variance of the reconstructed refractive index decrement scales with spatial resolution follows an inverse linear relationship at fixed slice thickness, while the noise variance of the reconstructed absorption coefficient conforms with the inverse cubic law. The results indicate that, for the same noise variance level, PCT imaging may enable higher spatial resolution than conventional absorption computed tomography（ACT）, while ACT benefits more from degraded spatial resolution. This could be a useful guidance in imaging the inner structure of the sample in higher spatial resolution.

应用XCT断层扫描技术和GAN深度学习模型的多孔介质微观结构定量研究

物质在土壤中的迁移转化行为是研究地下水动力学的核心问题。定量化表征多孔介质拓扑结构并计算分析相关表面形态学参数,为研究复杂介质内物质运移微观机理提供了重要的数据基础和参数。应用微米级X射线计算机断层扫描(XCT)和图像处理技术,结合前沿的机器学习算法重建和定量分析多孔介质微观结构,可快速、批量创建高分辨率的复杂多孔介质研究样本。首先采用XCT技术,提取石英砂和散装土壤两类典型多孔介质的微观孔隙结构;而后基于生成对抗神经网络(GAN)模型重构复杂多孔介质的微观空间结构,与XCT扫描图像进行交叉验证;最后,计算获取Minkowski形态学参数,并基于多孔介质微观结构开展计算流体力学(CFD)数值模拟,计算石英砂和土壤多孔介质内的流动特征和渗透率。结果表明:1)GAN生成的合成数据与原始数据符合KS同分布,说明GAN能够成功合成与原始图像结构空间分布模式一致的图像;2)Minkowski宏观参数评价误差的较小,KS同分布结果表明,多孔介质样本的结构异质性会在一定程度上影响GAN模型的计算精度和效率;3)Open FOAM模拟计算得到的渗透率结果表明,GAN模型生成的多孔介质图像与原始图像具有一致的统计特征和物理性质。综上,综合运用前沿的XCT扫描、图像处理技术和机器学习算法,构建了土壤微观结构重建和定量分析模型,并结合多孔介质形态学和计算流体力学方法对模型进行了验证和分析。该研究为多孔介质微观结构研究提供了新技术和新方法,为进一步研究复杂多孔介质内溶质运移提供了科技支撑。

Usefulness of Chest Computed Tomography for Diagnosis of Idiopathic Pneumomediastinum with Negative Findings on Plain X-Ray

Idiopathic pneumomediastinum is rare in children. Few cases of patients with pneumomediastinum show negative findings on X-ray examination. Chest computed tomography (CT) was very useful for the diagnosis and evaluation of the extent of pneumomediastinum. We report here a case of idiopathic pneumomediastinum in a 15-year-old boy who exhibited no significant chest X-ray finding. The patient was referred to our institute for the further evaluation of pre-cordial pain and breathing difficulty. Precordial pain suddenly developed, when he was carrying a portable shrine on his shoulder (day of onset). He was admitted to another institute 3 days after onset because of worsening precordial pain. On admission, he presented with 98% saturation of hemoglobin in the peripheral blood under room air. Plain chest X-ray also revealed no abnormal findings. A half-dissolved gastrographin swallow showed no leakage of gastrographin from the pharynx and esophagus to the mediastinum, and no diverticulum within the esophagus. Plain chest CT revealed extensive emphysema around the trachea from the neck to the portion inferior to the carina of trachea. The patient was diagnosed with idiopathic pneumomediastinum because the cause was unclear. We decided to admit him to our institute under fasting conditions and rest. His symptoms improved 3 days after onset. The lesion had disap-peared 8 days after onset on chest CT. When young people experience precordial pain which increases on inspiration, we must consider pneumomediastinum in a differential diagnosis, and it is important to perform chest CT.