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关键词： Average glandular dose   Diagnostic reference level   Digital photography   Radiation dose   Radiation dose optimization  

摘要： Objective To investigate the radiation dose levels of digital radiography (DR) in adult patients and explore the diagnostic reference level (DRL) of radiation dose in Beijing. Methods Radiation dose data were collected from 39 medical institutions in Beijing on 18 930 DR examinations of chest anterior and lateral view, abdomen anterior and posterior view, abdomen standing view, cervical spine anterior and lateral view, lumbar spine anterior and lateral view, knee joint anterior and lateral view as well as 5 266 digital mammography (CC view and MLO view). For ordinary DR examinations, the incident air kinetic energy (K_{a, i}), incident air specific kinetic energy area product (P_KA) and effective dose (E) to the examined individuals were used for the investigation and estimation of radiation dose. For digital mammography, the average glandular dose (AGD) was calculated. DRLs should be set at the 75^th percentile of median values obtained in each medical institution. Results The K_{a, i}, P_KA and E of DRL for Chest (PA), Chest (lateral), abdominal(PA), abdominal (AP), Pelvic(AP), Cervical (AP), Cervical (lateral), Lumbar (AP), Lumbar (lateral), Knee joint (AP) and Knee joint (lateral) of conventional DR were 0.14, 0.31, 1.25, 2.18, 1.86, 0.51, 0.14, 2.97, 8.39, 0.37, 0.37 mGy, 159, 259, 1 917, 2 336, 2 867, 312, 301, 3 500, 3 359, 269, 255 mGy·cm², 0.03, 0.05, 0.20, 0.43, 0.23, 0.03, 0.02, 0.47, 0.35, <0.001, <0.001 mSv. The DRLs for digital mammography were calculated to be 1.87 mGy (CC view), 1.94 mGy (MLO view) and 3.99 mGy (accumulated for one examination). Conclusions The radiation dose from DR examinations is relatively low. In clinical practice, the selection of imaging parameters should be further standardized on the basis of the local DRL. © 2025 Chinese Medical Journals Publishing House ***. All rights reserved.

关键词： 分子动力学模拟   铜铁合金   扩散系数   扩散激活能   结合能  

摘要： 利用分子动力学模拟的方法从原子层面揭示了材料演化过程的细节,架起了沟通微观与宏观世界的桥梁,可以指导高性能材料的开发研究。采用分子动力学方法研究了Cu-Fe合金的时效过程。采用嵌入原子势(EAM)模拟了不同Fe原子百分比含量Cu-Fe合金在不同温度下的时效扩散行为,结合扩散系数、扩散激活能、结合能等探讨温度及Fe原子含量对时效过程的影响。结果表明:Cu-Fe合金时效温度的升高会促进合金中Fe原子的扩散,而Cu-Fe合金中Fe原子含量的增加反而会抑制Fe原子的扩散行为。同时,Cu-Fe合金时效过程中Fe原子会慢慢聚集形成小团簇,部分小团簇最终会合并形成大团簇。

关键词： 高中物理实验   信息技术   双缝干涉   光的波长   实验教学  

摘要： 信息技术在教育领域被广泛应用。以高中物理实验教学“用双缝干涉测光的波长”为例,教师要积极探索信息技术与物理实验教学的深度融合,明确实验的目的和要求,改进实验设备,让学生了解实验装置和操作步骤,在实验过程中进一步理解知识,深入研究问题,提升物理学习兴趣和学科核心素养。

关键词： C-H-O同位素   Fe同位素   裂变径迹   成矿机制   淋湘金矿床   镇旬盆地  

摘要： 淋湘金矿床是南秦岭镇安-旬阳盆地南缘一处典型的微细浸染型金矿床。关于其成矿物质和成矿流体的来源,学界存在不同观点,且对成矿机制的认识尚不充分。本研究选取Ⅱ-Ⅲ主成矿阶段的石英和黄铁矿,分别进行了C-H-O同位素和Fe同位素分析,并采集了仁河口-双河镇断裂两侧志留系样品进行裂变径迹分析。研究结果表明,淋湘金矿床主成矿期δ^(13)CV-PDB值为-10.59‰~-9.22‰,δ^(18)O_(V-SMOW)值为14.06‰~15.57‰,δD水-SMOW值为-82.10‰~-68.30‰,δ^(18)O水值为4.52‰~8.97‰,表明成矿流体在运移中沿构造萃取地层成矿物质,并在成矿后期有深部岩浆的加入。δ^(56)Fe值为-0.87~0.23,δ^(57)Fe值为-0.43~0.18,指示成矿早期阶段成矿物质以壳源物质为主,随后幔源物质加入成矿作用。裂变径迹结果显示磊石沟地区120~0 Ma以来经历3个阶段,南沙沟地区120~0 Ma以来经历4个阶段,与镇旬盆地金成矿关系密切的太平洋板块向欧亚板块俯冲作用持续至90 Ma左右,45 Ma左右印度板块与欧亚板块碰撞的远场响应到达仁河口-双河镇断裂。镇旬盆地总体剥蚀厚度为(4.98±0.33)km,矿体被剥蚀程度较弱,深部具备良好的金成矿条件和巨大的找矿潜力。结合前人对南秦岭构造演化的认识,笔者认为在三叠纪时期陆内造山演化阶段形成大量含Au变质流体,在陆内造山运动晚期,盆地基底演化为伸展环境或碰撞后挤压-伸展过渡环境,幔源物质和流体随岩浆在减压条件下沿深大断裂上涌到地壳浅部,为金矿体的形成提供了热源、挥发分和少量成矿物质。

关键词： China-US competition   cost sharing   responsibility sharing   US-Europe alliance  

摘要： Burden sharing has been a perennial issue in the transatlantic alliance,primarily entailing cost sharing and responsibility *** the first Trump administration,the dispute over cost sharing had been prominent,while the Biden administration placed more emphasis on responsibility sharing to facilitate its strategic goal of“outcompeting”*** Ukraine crisis had prompted a US-Europe consensus on cost sharing,but the urgency of responsibility sharing subsequently *** shift from jointly providing the economic resources to extensively sharing the security responsibilities ref lects the recalibration of the US strategic focus and its higher expectations for the role of European ***,Europe's response to the US call for responsibility sharing has been relatively *** responsibility sharing within the US-Europe alliance and their future relationship will be subject to the strategic coordination between the two sides and multiple complex factors.