X-ray measurements on the influence of optical probes on gas–solid fluidized beds

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共轭梯度算法在画幅式层析成像光谱仪中的应用

介绍了画幅式层析成像光谱仪的基本原理及共轭梯度算法,解决了共轭梯度法在实际应用中的几个问题,如图像分割,先验算子的引入.通过对实际数据的计算,得到了95×95的像素,28个波段的数据立方体.实际证明本算法及程序在层析成像光谱仪上的应用是成功的.     

Application of the pair distribution function analysis for the study of cultural heritage materials

The study of cultural heritage objects represents a challenge for materials sciences, because of their intrinsic complexity as well as because of their rare and precious nature, which requires the use of non-destructive methods. One of the major difficulties encountered by the methods of structural analysis of these materials is the presence of mixtures of crystallized and amorphous phases, the conventional methods of crystallography being poorly adapted to the latter. Here we present the Pair Distribution Function analysis method, which based on diffraction data, allows access to the identification, microstructural characterization and quantification of phases constituting a complex mixture, independently of their amorphous or crystalline character. Two recent examples will be presented to illustrate the use of this method in studies of cultural heritage materials.     

混凝土单轴压缩下细观损伤特性的CT研究

混凝土是一种非均质的材料,在细观层次上将混凝土看作由骨料、砂浆和两者之间的界面组成的三相复合材料.本文利用CT技术对混凝土的细观损伤过程进行实时扫描观测,获得了混凝土试件实时静力压缩CT图像,提取出图像上各点的CT数并根据分区理论定义了一个基于CT数的统计损伤变量.通过对图像和CT数以及损伤变量的分析表明混凝土试件在静力压缩条件下经历了压密阶段、扩容阶段,损伤急剧增大到破坏的细观损伤演化全过程,以此反映了混凝土细观损伤演化的特性.进而通过细观损伤对混凝土材料裂纹的扩展、贯通以及最后失稳破坏的破坏实质进行了有益的探索.     

A General Methodology for Full-Field Plastic Strain Measurements Using X-ray Absorption Tomography and Internal Markers

Probing the strain locally and throughout the bulk of various materials has long been of interest in Materials Science. This article presents a general methodology for assessing the plastic strain in terms of the displacement gradient tensor throughout the bulk of opaque samples. The method relies on a homogenous distribution of marker particles throughout the bulk of a sample, markers which are detected through the application of synchrotron X-ray tomography. Making use of the morphology of individual markers, motion of individual markers is tracked during deformation allowing the local displacement field to be determined throughout the bulk. The local displacement gradient tensor is derived from the displacement field. Spatial resolution is directly related to marker particle density in the sample, here 30 μm. The accuracy of the displacement gradient tensor calculation is dependent on the accuracy with which each marker position is determined and is shown to be in the range from 0.005 to 0.012. The software implementation of the procedures and algorithms presented in this work has been collected to form the “3Dstrain” program package which is intended to be free for use by the scientific community. It is available at under GNU General Public License.     

Imaging through animal tissues with CW diode laser based broadband interferometry

We used a CW superluminescent laser diode, a CCD camera and broadband interferometry to image millimeter-size objects hidden in 15 mm chicken muscle, and demonstrate that the resolution and penetration depth is comparable to that obtained with femtosecond lasers. Coherent images are recovered from the diffused background by selectively homodyne amplifying the ‘least scattered light’ and by momentum-space filtering. A scattering rejection ratio as large as 1.1 × 10¹¹ (25 mean free paths) is achieved. We also investigated the limit of spatial resolution of our method in the diffusive region by random-phase path integration. A scaling relation among the resolution, the penetration depth and the coherence length of the light source is derived and verified by experiments.     

Reconstructing Boundary Points of Convex Sets from X-ray Pictures

A method for the reconstruction of boundary points of convex sets is provided starting from three X-ray pictures in two orthogonal directions and from a point.     

Study on cerebral microcirculation by Optical Doppler Tomography

Optical Doppler Tomography (ODT) provides a novel method to measure the blood flow velocity in vessels with the diameter at micrometer scale. Rats with cranial window are used as a model, and the changes in the blood flow velocity of cerebral arterioles in sensory cortex are measured in real time with an established ODT system, under electrical stimulation and drug administration. The results show significant differences in the blood flow velocity between experimental groups and control groups, demonstrating the feasibility of ODT in the cerebral microcirculation study. Compared with the conventional Doppler ultrasound, ODT provides much higher spatial resolution, and thus holds a promising future in the application of the cerebral microcirculation study, especially in the observation of the blood flow velocity in micrometer scale vessels. Supported by the National Hi-Tech Research and Development Program of China (863 Program)(Grant No. 2006AA02Z4E0), the National Natural Science Foundation of China (Grant Nos. 60378041, 60478040, 60878057 and 30770685), the Program for New Century Excellent Talents in University (Grant No. NCET-04-0528), and the Opening Project of MOE Key Laboratory of Laser Life Science, South China Normal University     

双源CT4D-CTA联合灌注成像在急性脑缺血性疾病中的应用价值

目的：探讨双源CT 4维血管造影（4D- CTA）及灌注成像（CTPI）在急性脑缺血性疾病中的应用价值。方法对30例临床拟诊为急性脑缺血性疾病的患者于发病2-24h内行头颅CT平扫和全脑CTPI检查,获得脑血流量、脑血容量、平均通过时间、达峰时间等参数图,同时获得4D- CTA图像;于发病的1-3d后行MRI检查,分析CT平扫、CTPI、4D- CTA、MRI表现。结果 CT平扫发现12例有16个缺血病灶,CTPI发现26例32个缺血病灶,MRI发现25例28个缺血病灶,4D- CTA显示有20例责任血管有不同程度的狭窄或闭塞。结论双源CT 4D- CTA联合灌注成像能为急性脑缺血患者提供全面、详细的影像学信息,对急性缺血性脑梗死的早期诊断和治疗有重要价值。     

Disrupted cortical connectivity theory as an explanatory model for autism spectrum disorders

Recent findings of neurological functioning in autism spectrum disorder (ASD) point to altered brain connectivity as a key feature of its pathophysiology. The cortical underconnectivity theory of ASD (Just et al., 2004) provides an integrated framework for addressing these new findings. This theory suggests that weaker functional connections among brain areas in those with ASD hamper their ability to accomplish complex cognitive and social tasks successfully. We will discuss this theory, but will modify the term underconnectivity to ‘disrupted cortical connectivity’ to capture patterns of both under- and over-connectivity in the brain. In this paper, we will review the existing literature on ASD to marshal supporting evidence for hypotheses formulated on the disrupted cortical connectivity theory. These hypotheses are: 1) underconnectivity in ASD is manifested mainly in long-distance cortical as well as subcortical connections rather than in short-distance cortical connections; 2) underconnectivity in ASD is manifested only in complex cognitive and social functions and not in low-level sensory and perceptual tasks; 3) functional underconnectivity in ASD may be the result of underlying anatomical abnormalities, such as problems in the integrity of white matter; 4) the ASD brain adapts to underconnectivity through compensatory strategies such as overconnectivity mainly in frontal and in posterior brain areas. This may be manifested as deficits in tasks that require frontal–parietal integration. While overconnectivity can be tested by examining the cortical minicolumn organization, long-distance underconnectivity can be tested by cognitively demanding tasks; and 5) functional underconnectivity in brain areas in ASD will be seen not only during complex tasks but also during task-free resting states. We will also discuss some empirical predictions that can be tested in future studies, such as: 1) how disrupted connectivity relates to cognitive impairments in skills such as Theory-of-Mind, cognitive flexibility, and information processing; and 2) how connection abnormalities relate to, and may determine, behavioral symptoms hallmarked by the triad of Impairments in ASD. Furthermore, we will relate the disrupted cortical connectivity model to existing cognitive and neural models of ASD.