目的系统评价体外序贯双除颤(DSED)对顽固性室颤患者自主循环恢复(ROSC)的影响。方法检索中英文数据库Web of science、EMBASE、Medline及万方数据库、中国学术期刊全文数据库、中国生物医学文献数据库等,筛选发表至2022年3月的顽固性...目的系统评价体外序贯双除颤(DSED)对顽固性室颤患者自主循环恢复(ROSC)的影响。方法检索中英文数据库Web of science、EMBASE、Medline及万方数据库、中国学术期刊全文数据库、中国生物医学文献数据库等,筛选发表至2022年3月的顽固性室颤使用DSED的观察性研究和随机对照研究。结果共纳入5篇文献,其中1篇为随机对照研究,4篇为观察性研究。纳入1152例院外心脏骤停(out-of hospital cardiac arrest,OHCA)顽固性室颤患者,其中272例接受DSED,880例接受标准除颤。DSED组和标准除颤组患者ROSC分别为33.1%和39.0%,OR=0.75(95%CI 0.55~1.01,P=0.06),室颤终止分别为51.5%和53.6%,OR=0.74(95%CI 0.55~1.00,P=0.05)。两组患者入院时存活率和出院时存活率差异无统计学意义。结论DSED未增加顽固性室颤患者ROSC成功率。展开更多
A series of tensile and ratcheting experiments for compacted polytetrafluoroethylene (PTFE) and bronze filled PTFE (PTFE/bronze) were conducted on dynamic mechanical analyzer (DMA-Q800). The effects of mean stre...A series of tensile and ratcheting experiments for compacted polytetrafluoroethylene (PTFE) and bronze filled PTFE (PTFE/bronze) were conducted on dynamic mechanical analyzer (DMA-Q800). The effects of mean stress, stress amplitude and temperature on the ratcheting behaviors of PTFE and PTFE/bronze were investigated. It is found that the stress-strain response of PTFE/bronze is nonlinear and its elastic modulus is higher than that of pure PTFE. For uniaxial ratcheting test, the dissipation strain energy density (DSED) decreases rapidly in the first l0 cycles and approaches a constant after 20 cycles. The ratcheting strain and the DSED corresponding to 100 cycles increase with increasing mean stress, stress amplitude and temperature. Additionally, the DSED and ratcheting strain of PTFE/bronze are much lower than those of pure PTFE under the same experimental conditions. It is also found that both pure PTFE and PTFE/bronze present cyclic hardening characteristics. Above all, the addition of bronze can improve both the uniaxial tensile property and the cyclic property of PTFE.展开更多
目前,面向牵引的电力电子变换器应用广泛,但是这类大功率装置对可靠性的要求较高,并且需要避免器件应力导致的过压问题,因而对直流母线电压的稳定性提出了很高的要求。由于牵引变流器的工况随着机车运行情况的变化而变化,因此其单向整...目前,面向牵引的电力电子变换器应用广泛,但是这类大功率装置对可靠性的要求较高,并且需要避免器件应力导致的过压问题,因而对直流母线电压的稳定性提出了很高的要求。由于牵引变流器的工况随着机车运行情况的变化而变化,因此其单向整流器的控制策略应具有可靠的高性能,以保证直流母线电压的抗扰性和随动性。该文提出针对牵引变流器的单相整流器能量平衡控制策略,该策略能够提高单相整流器动态性能。在研究控制策略的过程中,需要进行多组参数的对比测试以及多种工况的仿真,因此需要一种高效、高精度、收敛性好的仿真工具。该文利用离散状态事件驱动(discrete state event driven,DSED)仿真方法,针对牵引变流器搭建了数值仿真平台,在同平台实现了多时间尺度(系统级动态过程和器件级瞬态过程)的高效、准确仿真评估。基于DSED牵引变流器仿真平台,将单相能量平衡控制与经典PI控制方法进行了对比。实验结果表明:能量平衡控制在各类动态过程中均表现出响应速度快,有效抑制直流母线波动的特点。同时,结合能量平衡控制与模组电容连接母排结构,能够明显减小关断电应力和器件使用所需留出的余量。展开更多
基金The authors gratefully acknowledge financial support for this work from Tianjin Natural Science Foundation (No. 09JCYBJC03100) and China Postdoctoral Science Foundation (No. 2012T50226).
文摘A series of tensile and ratcheting experiments for compacted polytetrafluoroethylene (PTFE) and bronze filled PTFE (PTFE/bronze) were conducted on dynamic mechanical analyzer (DMA-Q800). The effects of mean stress, stress amplitude and temperature on the ratcheting behaviors of PTFE and PTFE/bronze were investigated. It is found that the stress-strain response of PTFE/bronze is nonlinear and its elastic modulus is higher than that of pure PTFE. For uniaxial ratcheting test, the dissipation strain energy density (DSED) decreases rapidly in the first l0 cycles and approaches a constant after 20 cycles. The ratcheting strain and the DSED corresponding to 100 cycles increase with increasing mean stress, stress amplitude and temperature. Additionally, the DSED and ratcheting strain of PTFE/bronze are much lower than those of pure PTFE under the same experimental conditions. It is also found that both pure PTFE and PTFE/bronze present cyclic hardening characteristics. Above all, the addition of bronze can improve both the uniaxial tensile property and the cyclic property of PTFE.
文摘目前,面向牵引的电力电子变换器应用广泛,但是这类大功率装置对可靠性的要求较高,并且需要避免器件应力导致的过压问题,因而对直流母线电压的稳定性提出了很高的要求。由于牵引变流器的工况随着机车运行情况的变化而变化,因此其单向整流器的控制策略应具有可靠的高性能,以保证直流母线电压的抗扰性和随动性。该文提出针对牵引变流器的单相整流器能量平衡控制策略,该策略能够提高单相整流器动态性能。在研究控制策略的过程中,需要进行多组参数的对比测试以及多种工况的仿真,因此需要一种高效、高精度、收敛性好的仿真工具。该文利用离散状态事件驱动(discrete state event driven,DSED)仿真方法,针对牵引变流器搭建了数值仿真平台,在同平台实现了多时间尺度(系统级动态过程和器件级瞬态过程)的高效、准确仿真评估。基于DSED牵引变流器仿真平台,将单相能量平衡控制与经典PI控制方法进行了对比。实验结果表明:能量平衡控制在各类动态过程中均表现出响应速度快,有效抑制直流母线波动的特点。同时,结合能量平衡控制与模组电容连接母排结构,能够明显减小关断电应力和器件使用所需留出的余量。