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  • Grain boundary engineering for enhancing intergranular damage resistance of ferritic/martensitic steel P92

    分类: 核科学技术 >> 核科学技术其他学科 分类: 物理学 >> 核物理学 提交时间: 2024-02-28

    摘要: Ferritic/martensitic (F/M) steels have been widely used as structural material for thermal and nuclear power plants. However, it is susceptible to intergranular damage in service conditions, which is expected to be critical issues. In order to improve the intergranular damage resistance of F/M steel, thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in a kind of F/M steel P92 in this study. TMP, including cold rolling to 6%, 9%, and 12% thickness reduction, respectively, followed by austenization at 1323 K for 40 min plus tempering at 1053 K for 45 min, were applied on as-received (AR) P92 steel. Both prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and the connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared with AR specimen, the PAG size does not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3n boundaries along PAGBs decreases with increasing reduction ratio due to the recrystallization fraction increases with increasing reduction ratio. The PAGBs connectivity of the 6%-deformed specimen deteriorates compared with that of AR specimen slightly. Moreover, the potentiodynamic polarization studies revealed that the intergranular damage resistance of studied steel could be improved by enhancing the fraction of CSLBs along PAGBs, indicating that TMP, involving low deformation, could enhance the intergranular damage resistance.

  • 简化FMM算法在束流剖面测量中的应用

    分类: 核科学技术 >> 核科学技术其他学科 提交时间: 2023-11-09

    摘要: 加速器中利用荧光靶系统测量束流横向剖面,为进一步提高系统测量的准确度,本文提出了一种利用简化快速行进算法(Fast Matching Method,FMM)填充荧光靶标定线的方法,使填充后的荧光靶图像更真实地反映束流剖面信息。论文首先利用Matlab生成模拟荧光靶图像,对比分析了算法处理前后的模拟图像束流剖面参数,仿真结果表明经过处理后的模拟图像,其结构相似性(Structural Similarity Index measure,SSIM)更接近1、均方误差(Mean Square Error,MSE)更小。最后,利用医用重离子加速器HIMM(Heavy Ion Medical Machine)现场采集的荧光靶图像进行验证。结果表明,HIMM现场采集的图像经处理后,剖面测量结果接近评估值。本研究结果为后续束流横向剖面参数算法的FPGA算法加速提供了依据。

  • Optimization method of Hadamard coding plate in γ-ray computational ghost imaging

    分类: 核科学技术 >> 辐射物理与技术 分类: 物理学 >> 普通物理:统计和量子力学,量子信息等 分类: 光学 >> 计算中的光学 分类: 核科学技术 >> 核科学技术其他学科 提交时间: 2023-06-08

    摘要: Owing to the constraints on the fabrication of -ray coding plates with many pixels, few studies have been carried out on -ray computational ghost imaging. Thus, the development of coding plates with fewer pixels is essential to achieve -ray computational ghost imaging. Based on the regional similarity between Hadamard subcoding plates, this study presents an optimization method to reduce the number of pixels of Hadamard coding plates. First, a moving distance matrix was obtained to describe the regional similarity quantitatively. Second, based on the matrix, we used two ant colony optimization arrangement algorithms to maximize the reuse of pixels in the regional similarity area and obtain new compressed coding plates. With full sampling, these two algorithms improved the pixel utilization of the coding plate, and the compression ratio values were 54.2% and 58.9%, respectively. In addition, three undersampled sequences (the Harr, Russian dolls, and cake-cutting sequences) with different sampling rates were tested and discussed. With different sampling rates, our method reduced the number of pixels of all three sequences, especially for the Russian dolls and cake-cutting sequences. Therefore, our method can reduce the number of pixels, manufacturing cost, and difficulty of the coding plate, which is beneficial for the implementation and application of -ray computational ghost imaging.

  • Improved Cohen-Sutherland algorithm for TGS transmission imaging

    分类: 核科学技术 >> 核科学技术其他学科 提交时间: 2023-05-31

    摘要: Laminar -scanning (TGS), an advanced -ray nondestructive analysis technique, is capable of locating and analyzing the nuclides in radioactive nuclear waste, and the scanning of TGS falls into two parts (e.g., transmission measurement and emission measurement). To be specific, transmission measurement lays the basis for the accurate measurement of non-uniform radionuclide content in TGS scanning. The scan data were obtained using the Monte Carlo tool Geant4 simulation, and a total of 25 voxels were divided into 5 in length and 5 in width in a square barrel. In this study, the encoding cropping algorithm based on the draped foot vector judgment was adopted to rapidly calculate the voxel trace matrix within the square bucket of nuclear waste, and the transmission images were reconstructed using the Ordered Subsets Expectation-Maximization(OSEM). The results indicated that the cropping speed of the improved coding algorithm was significantly increased compared with the original algorithm, and the relative mean deviation (RMD) and root mean square error(RMSE) between the reconstructed attenuation coefficient and the reference standard value tended to decrease with the increase of the cropped line segments in the voxel, and the Pearson correlation coefficient(PCC) tended to converge to be 1.0. The image quality evaluation parameters of high media density materials were better than those of low media density materials in the above three indexes. The reconstruction effect was relatively poor under the more complex filling material. When there were more than 10 cropped line segments in the voxel, the reconstruction data generally tended to be stable. The graphical trimming algorithm is capable of rapidly calculating the trace matrix of the scanned voxels, it shows the advantages of speed and efficiency, and it can serve as a novel method to solve the trace matrix of TGS nuclear waste transmission scans.