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近年来，大规模风电汇集系统实际运行中频繁出现电压反复波动现象，具有波动幅度大、波动峰谷值切换速率达秒级的特点，与风能随机性、无功补偿装置动作引起的电压波动现象具有显著区别，运行中多次造成风电机组因连续穿越失败而脱网，严重威胁了电网安全稳定运行。上述现象涉及风电机组故障穿越策略与弱电网功率-电压特性的耦合作用，难以通过传统电力系统电压稳定分析方法直接解释。提出了考虑风电机组低电压穿越特性的系统有功-电压曲线（PV曲线）分析方法，准确刻画波动过程中系统运行点轨迹变化规律，并通过仿真进行了验证。在此基础上，提出了抑制电压反复波动的风电机组低电压穿越优化控制策略，基于实际算例的仿真分析表明，提高风电机组退出低电压穿越阈值及采用穿越期间维持有功的策略可以有效抑制电压反复波动现象。

罕见低温天气可能导致大规模风电机组非计划停运，威胁电力系统的可靠安全运行。研究低温天气对风力发电停运容量影响的时空规律，对于未来高比例甚至100%可再生能源电力系统的发展，具有重要意义。以风力发电机组的设计运行温度下限为阈值，关注低于阈值的低温天气。结合全国2481个地面气象站点历史48年（1970—2017年）的日气温观测数据及国家电网有限公司经营区的实际风电场分布数据，从发生频率、持续时间、反复穿越阈值次数、影响国土面积、风电停运容量等指标，对中国区域低温天气及其对风力发电的影响进行了统计分析，并总结了低温天气对风力发电的影响规律，可为未来高比例可再生能源电力系统的规划和运行提供基础。

风电场经柔性直流并网存在几赫兹至几百赫兹频率范围的振荡风险。首先，为复现宽频域振荡特征，基于频率扫描的测量方法，建立双馈风电场孤岛接入柔性直流的振荡分析模型。然后，采用网络阻尼稳定性判据并结合时域仿真，剖析互联系统在次/超同步频率范围和中高频范围的振荡机理。之后，考虑风机、柔性直流控制参数以及风速和并网风机台数的变化，分别针对次/超同步频段、中频段、高频段的振荡情况分析系统阻抗特性，利用阻抗聚合法量化评估各个影响因素与系统潜在振荡风险的关系，给出不同影响因素的变化对系统振荡频率的影响。最后，总结了双馈风电场经柔性直流并网系统在不同频段范围发生振荡的关键影响因素，为宽频域振荡控制提供指导思路。

风电场经柔性直流孤岛送出时，其交流故障特性与采用交流电网送出时不同，传统的低电压穿越策略不适用于孤岛接入柔性直流的场景。因此，需结合风电场和柔性直流系统的控制目标、运行约束和故障特性，研究提出新的故障穿越策略。首先，将风电场交流对称接地故障分为4个发展阶段，分析故障时风电场和换流站对交流电压的耦合影响；随后，分析风电场不同电流输出策略对交流故障穿越特性的影响；提出了在故障稳态阶段送端换流站采用定电流控制、风电机组采用有功电流注入，以及在故障恢复阶段交流电压斜坡建立的故障联合穿越策略。通过PSCAD搭建了双馈风电场和双端柔性直流系统模型进行仿真，结果表明，上述策略可充分利用风电场和柔性直流的功率输出能力，实现交流故障的联合穿越，验证了所提策略的有效性。

柔性直流输电技术是实现弱电网条件下大规模新能源送出的有效技术手段。对于以柔性直流输电系统作为唯一输电通道的大规模新能源集群，必须通过有功控制系统保障送端换流站运行在其可行PQ范围内。在分析其越限风险和控制需求的基础上，提出了激进型和保守型两种有功控制策略，并引入超短期预测作为分群指标以提高动态发电指标再分配的准确性。在此基础上提出了基于时序生产模拟的大规模新能源集群有功控制裕度确定方法，并以张北柔直电网及其汇集新能源为例进行了仿真分析。结果表明，激进型有功控制策略需要预留更大的控制裕度，但是对于发电空间的利用更加充分，新能源场站利用小时数更高。研究结果对于指导张北柔直电网送端新能源集群有功控制及安全裕度设置有参考意义。

由于柔直电网“隔离”了频率信号，互联多区域协同调频问题亟待研究。现有研究大多利用换流站的下垂控制以及直流电压偏差实现频率信号的传递，但忽略了风电集群接入后由风电功率正常波动引起的直流电压偏差干扰，可能导致风电集群在无需调频时频繁地调整出力。对此，提出了基于直流电压偏差及其特征量的多区域协同调频策略，分别针对电网频率偏移和风电功率波动两种场景提取直流电压偏差特征量，包含电压变化量、电压变化率和滤波后的电压分量幅值3个特征，并基于二者的差异设置换流站启动下垂控制的判据。仿真结果验证了所提方法的有效性。

目前新能源集群电压分层控制研究主要针对接入交流电网的情况，由于孤岛系统的电压控制与交流大电网解耦，其优化控制的目标、对象和方式均与传统电网存在较大差异，故需要结合其特性，制定新的电压控制策略。本文对孤岛方式下新能源集群无功电压控制原理进行论述，设计了送出孤岛系统区域两级电压控制框架，提出了考虑换流站PQ运行区间约束的电压优化策略，在优化目标中综合考虑网损及换流站无功裕度。基于张北柔直示范工程未来规划拓扑的仿真算例表明，该策略可以在保持换流站母线电压在安全运行范围内的前提下，实现电网运行的安全性和经济性的协调。

柔性直流输电技术在大规模风电送出中应用越来越广泛，但存在因风电和柔直各自电力电子设备控制相互作用而引发系统振荡风险。首先，为从物理意义上解释振荡机理，以阻抗分析法为基础，推导基于等效电路阻尼的互联系统稳定性判据。然后，基于此判据和时域仿真结果，分析风机网侧变流器、锁相环和柔性直流换流器的控制带宽与振荡风险的关系，指出系统振荡频率随控制参数改变的变化规律。最后，分析风速和并网风机台数对风电经柔性直流送出系统的等效电路阻尼特性影响，提出振荡稳定性约束的控制参数设计要求。

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Few studies examined Chinese American teachers' diasporic lives in U.S. K–12 schools and society, even as research on teachers of Color increases. In responding to such scarcity, the author connects tenets of empire and AsianCrit to illustrate how the legacies of imperialism and geopolitics of race have influenced three Chinese American teachers' diasporic trajectories and teaching practices. Implications include how scholars can use these theoretical orientations to historicize research on Chinese American teachers, apply Asian Diaspora as a framework in researching Asian American teachers, and prepare Asian American teachers to unsettle racism and imperialism in schools. [ABSTRACT FROM AUTHOR]

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2 )is still spreading widely around the world, and it is estimated that there are more than 760 million confirmed cases of SARS-CoV-2 infection (COVID-19) . Although most of the infected patients can be cured, there are still many patients who experience persistent clinical symptoms such as dizziness, fatigue, weakness, coughing and chest pain, etc. at two to three months or even longer after being infected with SARS-CoV-2. Internationally, this type of discomforts is referred to as long COVID. The emergence of long COVID has brought a new crisis to people’s health, which not only affects the quality of life and work of patients, but also brings great pressure on the health care of the society. Continuously exploring the impact of long COVID and its underlying mechanism, developing health management strategies for long COVID, and better prevention and treatment of long COVID are still the focus of research worldwide. The article introduces the definition of long COVID and reviews recent research progress in its underlying mechanism, common systemic clinical manifestations, risk factors, and health management of long COVID, aiming to provide more ideas for deepening clinicians’ understanding of long COVID. [ABSTRACT FROM AUTHOR]

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目的 探讨以执业能力培养为导向的多元化教学模式在《健康评估》课程教学中的应用效果。 方法 选取广西卫生职业技术学院2021级和2022级高职助产专业2022年2月至2023年6月共160例学生 作为研究对象,其中将2022级高职助产专业学生81人作为多元化教学组,将2021级高职助产专业学生79人 作为常规教学组,多元化教学组学生实施以执业能力培养为导向的多元化教学模式,常规教学组学生实施常规 教学模式。比较两组学生的理论和实践成绩、综合能力评分和教学满意度。结果 课程结束后,多元化教学组 学生理论和实践成绩均高于常规教学组,差异均有统计学意义(P <0.05);课程结束后,多元化教学组学生表现 能力、沟通能力、评估思维、护理决策评分均高于常规教学组,差异均有统计学意义(P <0.05);课程结束后,多 元化教学组学生课程内容满意度、教学方法满意度、教学效果、教师评价和课程评价评分均高于常规教学组,差 异均有统计学意义(P <0.05)。结论 以执业能力培养为导向的多元化教学模式能够提高学生理论和实践成 绩,提高学生综合能力,提高教学模式有效率。 [ABSTRACT FROM AUTHOR]

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The qualification for medical practice is the legal prevention of the crime of illegal medical practice; the identification of the qualification status is the key to the application of the crime of illegal practice medical practice. The “single certificate theory” and “double certificate theory” which only consider the formal value, risk improperly expanding the application of illegal medical practice crime. The focus should be carried out around the legal interests and only the individual who infringes upon the legal interests of public health security can constitute the crime of illegal medical practices. When unqualified individuals and qualified medical practitioners jointly engage in medical activities, the behavior does not constitute the crime of illegal medical practice, and only if a qualified doctor who fails to guide and supervise the medical behavior may commit the crime of illegal medical practice. [ABSTRACT FROM AUTHOR]

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Aim To predict the anti-atherosclerotic targets and signal pathways of Morinda officinalis by using traditional Chinese medicine system pharmacology, small molecule drug target prediction and disease genome database, and combined with the molecular docking technology. Methods The technology platform of Chinese medicine system pharmacology (TCMSP) and the online platform for small molecule drug target prediction ( Swiss Target Prediction) were used to explore the active components of Morinda officinalis and the targets of its response. GeneCards, OMIM, Disgenet and UniProt were used to collect and screen the disease targets related to atherosclerosis. The intersection genes were obtained and imported into the String 11. 5 database to construct the disease-drug protein-protein interaction (String-PPI) network map. Cytoscape 3. 9. 1 software was used to visualize key target networks. Then, GO and KEGG enrichment were performed using Metascape online platform to explore the molecular targets of anti-atherosclerosis, the pathway map was drawn through KEGG database. Finally, Autodock vina 1. 1. 2 software was used to verify the molecular docking of core compounds and target genes of Morinda officinalis. Results A total of 17 effective drug compounds including β-sitosterol and anthraquinone, 73 core targets and 1 450 key disease genes were collected from the above databases, then 35 core genes of Morinda officinalis acted on atherosclerosis were obtained after the intersection. 32 genes including SRC, PGTS2, TGFβ1, REN, ESR1 and CASP3, were identified by String-PPI. KEGG enriched 75 signaling pathways, involving lipid-atherosclerosis, advanced glycosylation end products and receptors and PI3K-Akt signaling pathway, among which lipid-atherosclerosis pathway mainly involves six target genes such as SRC, BCL2, BAX, CASP3, GSK3B and RXRA. Molecular docking showed that the main chemical components of Morinda officinalis had strong binding activity with core genes. Conclusion Morinda officinalis can regulate the expression of 32 major genes including SRC, PGTS2, TGFβ1, REN, RXRA,ESR1, CASP3 through β-sitosterol, anthraquinone and other major chemical components, controls vascular endothelial inflammation and inhibits cell proliferation, migration and apoptosis, therefore plays the certain role of anti-atherosclerosis. [ABSTRACT FROM AUTHOR]

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