国家预印本平台

Online continuous refueling is one of the main features of a pebble-bed high-temperature gas-cooled reactor (PB-HTR). During the normal operation of a PB-HTR, positive reactivity is mainly introduced through refueling, whereas negative reactivity is introduced through depletion. Therefore, evaluating the refueling reactivity coefficient is crucial for the safe and stable operation of PB-HTRs. In this study, the perturbation theory is used to calculate the refueling reactivity coefficient, and the effect of key parameters on the refueling reactivity coefficient is examined based on the HTR-PM equilibrium core. The refueling reactivity introduced into the reactor core is driven by the gradient of the nuclide atomic density, particularly U-235. The neutron flux modulates the spatial distribution of the refueling reactivity. The loading fraction of the fresh fuel directly and positively influences the refueling reactivity coefficient. This study provides comprehensive insights into the effect of these parameters on the refueling of PB-HTRs, paving the way for efficient fuel management.

针对传统股票预测模型精度不足、落地性弱的痛点，本文以港股腾讯控股（00700.HK）为研究对象，采用LightGBM算法构建股票收益率预测模型，设计配套的趋势跟踪+止损量化投资策略。研究以2018—2023年日线数据为训练样本，2024—2025年为样本外回测区间。实证结果表明，模型涨跌方向判断准确率达60%，策略实现36.65%的年化收益率，最大回撤仅12.21%，显著优于买入持有基准，可为个人投资者提供低门槛的港股量化投资方案。

We positively answer `Open Question 1' in the paper of Feng and Wang [Adv. Math. 222 (2009)].

背景　我国全科医生细分领域拓展职责发展仍处于起步阶段，面临培养规范化不足、缺乏统一考核及认证机制等挑战。在全科医生亚专长能力培养的必要性、路径与模式等方面，业内从管理、教学、临床实践等不同层面尚未形成共识。目的　以国际全科医学细分领域的拓展职责为参考，结合国内全专结合的工作模式，采用德尔菲专家咨询法及问卷调研法探讨培养全科医生亚专长能力的必要性、主要路径和培养方式。方法　研究团队结合文献分析和前期开展的上海市社区卫生服务中心全专结合医疗能力发展的调研结果，初步提出全科医生培养亚专长能力培养条目池；于2024年3—7月，采取德尔菲专家咨询法，邀请60名专家作为咨询论证对象，进行两轮咨询，确定全科医生亚专长能力的作用及必要性条目；同时调研专家对于培养路径与模式的倾向性意见，设计调查问卷维度，内容包括：全科医生亚专长能力的培养方式、培养时间阶段、知识技能范畴、专业方向选择偏好以及考核认定机构等。结果　两轮专家咨询问卷有效回收率均为100.0%，专家权威系数分别为0.92和0.94，专家协调系数分别为0.146和0.165（P<0.001）。经两轮专家咨询最终形成由3个一级条目、15个二级条目组成的全科医生培养亚专长能力的作用及必要性条目。全科医生培养亚专长能力的作用及必要性方面：3个一级条目（全科医生发展亚专长能力在基层医疗中的作用；全科医疗基础工作与专病/专科亚专长工作的协同与互补；全科医生培养亚专长能力的必要性）的重要性赋值均数为4.90~4.93分，满分率为88.3%~91.7%，变异系数为0.05~0.06；15个二级条目的重要性赋值均数为4.42~4.98分，满分率为45.0%~98.3%，变异系数为0.03~0.13。在全科医生亚专长能力培养路径与模式方面：96.7%（58/60）专家选择全科医师到具有培养资质的三级医疗机构专科进修、93.3%（56/60）专家选择师带徒方式培养（由具有培养资质的三级医疗机构专家带教）；78.3%（47/60）专家选择主治医师职称阶段，11.7%（7/60）专家选择规范化培训结束后住院医师工作阶段。结论　全科医生细分领域拓展职责的培养是基层医疗发展必须推进的实践逻辑。应确立以“主治医师阶段”为细分领域发展的筹划起点，以“三级医院进修结合导师制”为现行策略，优先发展皮肤、康复亚专长，着力激发和培育非医院专科的细分领域。

Stationary computed tomography (CT) is an innovative CT technology that significantly boosts scanning speed and reduces motion artifacts by utilizing sequentially activated distributed X-ray sources instead of the conventional helical scanning with a single source. This paper presents an S-band multi-beam accelerating structure designed to serve as a distributed megavolt-peak (MVp)-level X-ray source for industrial stationary CT applications. This structure comprises seven parallel-distributed accelerating cavities and six coupling cavities operating in the π/2 standing-wave mode with a center frequency of 2998 MHz. Each cavity can generate electron beams with an average energy of 0.76 MeV and peak current of 105 mA, with a total power input of 2.1 MW according to beam dynamics simulation. This novel structure can fill a critical gap in industrial stationary CT by offering an urgently required distributed MVp-level X-ray source that is compact and cost-effective.