Phase retrieval with unidirectional differential phase-contrast image requires integration with noisy data, which is an illposed inverse problem. Conventional direct integration method would result in severe streak artifacts. Total variation (TV) regularization-based method would reduce the streak artifacts, but the edges parallel with phase-contrast sensitivity direction are likely to be over smoothed. We propose an improved weighted TV regularization phase retrieval method by introducing a weighting factor to the conventional TV term. When applied to simulation and experimental data, this method shows an advantage of preserving the sharpness of the edges while preserving the ability of reducing streak artifacts compared with conventional TV-regularization method.
Carbon fiber composites have been wildly used in aerospace industry due to the excellent performance. However, the research on defect evolution law and the performance analysis have been limited by the lack of effective tools. Two kinds of computed tomography (CT) slice images of carbon fiber composites, x-ray attenuation contrast and phase contrast, were obtained with the diffraction enhancement imaging (DEI) device at Beijing Synchrotron Radiation Facility (BSRF). The structure details and the defects in the sample could be clearly distinguished from the image. Moreover, phase contrast CT provides higher contrast and can identify the defects difficult to be recognized in attenuation contrast CT. DEI provides a method for in-situ observation of the carbon fiber composites and would be a valuable tool for the development of carbon fiber composite material.
With the progresses of material sciences and technologies, carbon fiber composite shell-plate structures have been widely used in aerospace industry. Suffering from the drastic change of penetration thickness during the 360°scanning, conventional computed tomography (CT) is difficult to be applied to this kind of structures with a big length-width-thickness ratio, and not easy to implement the defect detection and the performance analysis. Based on the existing diffraction enhanced imaging (DEI) device at Beijing Synchrotron Radiation Facility beam-line 4W1A, a new computed laminography (CL) scanning system was designed and developed. It was integrated with the DEI device to form a synchrotron radiation DEI-CL system for plate-shell structures. Within this system, the components such as light source, detector and turntable and the working principle were discussed in detail. The experiment results of a decimeter-scale carbon fiber composite laminate sample validate the developed scanning system.
The High Energy cosmic-Radiation Detection (HERD) facility is one of several space astronomy payloads of the cosmic lighthouse program onboard China's Space Station, which is planned for operation starting around 2020 for about 10 years. The main scientific objectives of HERD are indirect dark matter search, precise cosmic ray spectrum and composition measurements up to the knee energy, and high energy gamma-ray monitoring and survey. HERD is composed of a 3-D cubic calorimeter (CALO) surrounded by microstrip silicon trackers (STKs) from five sides except the bottom. CALO is made of about 104 cubes of LYSO crystals, corresponding to about 55 radiation lengths and 3 nuclear interaction lengths, respectively. The top STK microstrips of seven X-Y layers are sandwiched with tungsten converters to make precise directional measurements of incoming electrons and gamma-rays. In the baseline design, each of the four side SKTs is made of only three layers microstrips. All STKs will also be used for measuring the charge and incoming directions of cosmic rays, as well as identifying back scattered tracks. With this design, HERD can achieve the following performance: energy resolution of 1% for electrons and gamma-rays beyond 100 GeV, 20% for protons from 100 GeV to 1 PeV; electron/proton separation power better than 10-5; effective geometrical factors of >3 m2sr for electron and diffuse gamma-rays, >2 m2sr for cosmic ray nuclei. R and D is under way for reading out the LYSO signals with optical fiber coupled to image intensified CCD and the prototype of one layer of CALO.