分类： 核科学技术 >> 裂变堆工程技术 提交时间： 2023-06-18 合作期刊: 《Nuclear Science and Techniques》
摘要： The radiation shielding calculations of large nuclear facilities are complicated due to their bulk shields and complex geometries. A program system based on three-dimensional discrete ordinates (SN)-Monte Carlo (MC) coupled method has been developed to solve this kind of shielding problems. SN method is used to treat the deep penetration problem in the bulk shield, and MC simulation is performed with complex geometry. The coupled method is implemented in the interface program to calculate the probability of particle variables from the SN angular flux distribution. A special source routine is written and linked to MC code to processed these probability arrays and sample the particle variables to generate source for the use of MC code. The H. B. Robinson Unit 2 pressure vessel benchmark was used to validate the SN-MC coupled program system. The specific activities for the six dosimeters in the surveillance capsule were calculated. Satisfactory agreements were obtained from the comparisons of SN-MC results with those obtained from measurement and other computer codes. The result demonstrates that the SN-MC coupling scheme with the program system is suitable to treat three dimensional shielding problems with satisfactory accuracy.
分类： 生物学 >> 生物物理学 提交时间： 2016-05-15
Zhang, Shaodan
Zhang, Chun
Zhang, Shaodan
Wang, Bo
Zhu, SenHua
Xie, Yuan
Qing, Guoping
Wang, Ningli
Thomas, Ravi
Thomas, Ravi
摘要： PURPOSE. To assess the cortical structure and cerebral blood flow changes in the brain of patients with primary open-angle glaucoma (POAG). METHODS. High-resolution anatomical magnetic resonance imaging (MRI) and arterial spin labeling (ASL)-MRI were performed in 23 POAG patients and 29 controls. Patients were further divided into early-moderate and advanced groups based on mean deviation (MD) cutoff of 12 dB. A baseline scan was obtained and repeated during visual stimulation to the central preserved visual field in the more affected eye of POAG patients and a randomly selected eye of controls. Gray matter volume (GMV) and cerebral blood flow (CBF) throughout the whole brain were compared between patients and controls. RESULTS. Compared to controls, a region with significant reduction of GMV was detected in the anterior calcarine fissure of advanced POAG patients (P < 0.001, voxels = 503, 1698 mm3). Patients with early-moderate POAG had resting CBF similar to that of controls. However, a region with marked CBF decrease was detected in the anterior calcarine fissure of advanced POAG patients (P < 0.001, voxels = 1687, 13,496 mm(3)). The region with CBF reduction in advanced POAG showed good colocalization with the region with GMV decrease in this group. Following visual stimulation, patients with advanced POAG showed significantly lower increase in CBF in the occipital lobes (P < 0.001, voxels = 112, 896 mm(3)) as compared to controls (P < 0.001, voxels = 1880, 15,040 mm(3)) and early-moderate POAG (P < 0.001, voxels = 2233, 17,864 mm(3)). CONCLUSIONS. Primary open-angle glaucoma patients demonstrate a disease severity-dependent retinotopic pattern of cortical atrophy and CBF abnormalities in the visual cortex. Cerebral blood flow may be a potential biomarker for the brain involvement in glaucoma.
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