分类： 核科学技术 >> 核科学与技术 提交时间： 2024-01-10
Chuxiang Zhao
Sangang Li
Rongrong Su
Yang Li
Mingzhe Liu
Qingyue Xue
Shan Liao
Zhi Zhou
Qingshan Tan
Xianguo Tuo
Yi Cheng
摘要： To measure the weak currents generated by the neutron ionization chamber, a dedicated weak current measurement system was designed. This system incorporates a second-order low-pass filter circuit and the Kalman filtering algorithm to effectively filter out noise and minimize interference on the measurement results. Testing conducted under normal temperature conditions has demonstrated the system's high precision performance. However, it was observed that temperature variations can affect the measurement performance. To address this issue, data was collected across temperatures ranging from -20 to 70C, and a temperature correction model was established through linear regression fitting. The feasibility of the temperature correction model was confirmed at temperatures of -5 and 40C, where relative errors remained below 0.1% after applying the temperature correction. The research indicate that the designed measurement system exhibits excellent temperature adaptability and high precision, making it particularly suitable for measuring weak currents.
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.
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.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： We present three-dimensional magnetic power spectra in wavevector space to investigate anisotropy and scalings of sub-Alfv\'enic solar wind turbulence at magnetohydrodynamic (MHD) scale using the Magnetospheric Multiscale spacecraft. The magnetic power distributions are organized in a new coordinate determined by wavevectors (k) and background magnetic field ($b_0$) in Fourier space. This study utilizes two approaches to determine wavevectors: singular value decomposition method and timing analysis. The combination of the two methods allows an examination of magnetic field properties in terms of mode compositions without any spatiotemporal hypothesis. Observations show that fluctuations ($\delta B_{\perp1}$) in the direction perpendicular to k and $b_0$ prominently cascade perpendicular to $b_0$, and such anisotropy increases with wavenumber. The reduced power spectra of $\delta B_{\perp1}$ follow Goldreich-Sridhar scalings: $P(k_\perp)\sim k_\perp^{-5/3}$ and $P(k_{||}) \sim k_{||}^{-2}$. In contrast, fluctuations within $kb_0$ plane show isotropic behaviors: perpendicular power distributions are approximately the same as parallel distributions. The reduced power spectra of fluctuations within $kb_0$ plane follow the scalings: $P(k_\perp)\sim k_\perp^{-3/2}$ and $P(k_{||})\sim k_{||}^{-3/2}$. Comparing frequency-wavevector spectra with theoretical dispersion relations of MHD modes, we find that $\delta B_{\perp1}$ are probably associated with Alfven modes. Moreover, for the Alfv\'enic component, the ratio of cascading time to the wave period is found to be a factor of a few, consistent with critical balance in the strong turbulence regime. The magnetic field fluctuations within $kb_0$ plane more likely originate from fast modes based on isotropic behaviors.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jia Huang
J. C. Kasper
L. A. Fisk
Davin E. Larson
Michael D. McManus
C. H. K. Chen
Mihailo M. Martinović
K. G. Klein
Luke Thomas
Mingzhe Liu
Bennett A. Maruca
Lingling Zhao
Yu Chen
Qiang Hu
Lan K. Jian
J. L. Verniero
Marco Velli
Roberto Livi
P. Whittlesey
Ali Rahmati
摘要： Switchbacks are rapid magnetic field reversals that last from seconds to hours. Current Parker Solar Probe (PSP) observations pose many open questions in regards to the nature of switchbacks. For example, are they stable as they propagate through the inner heliosphere, and how are they formed? In this work, we aim to investigate the structure and origin of switchbacks. In order to study the stability of switchbacks, we suppose the small scale current sheets therein may work to braid and stabilize the switchbacks. Thus, we use the partial variance of increments method to identify the small scale current sheets, and then compare their distributions in switchbacks. With more than one thousand switchbacks identified with PSP observations in seven encounters, we find many more current sheets inside than outside switchbacks, indicating that these micro-structures should work to stabilize the S-shape structures of switchbacks. Additionally, with the helium measurements, we study the variations of helium abundance ratios and alpha-proton differential speeds to trace switchbacks to their origins. We find both helium-rich and helium-poor populations in switchbacks, implying the switchbacks could originate from both closed and open magnetic field regions in the Sun. Moreover, we observe that the alpha-proton differential speeds also show complex variations as compared to the local Alfv\'en speed. The joint distributions of both parameters show that low helium abundance together with low differential speed is the dominant state in switchbacks. The presence of small scale current sheets in switchbacks along with the helium features are in line with the hypothesis that switchbacks could originate from the Sun via interchange reconnection process. However, other formation mechanisms are not excluded.
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