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The genesis and elimination of early afterdepolarizations (EADs) have been investigated in guinea pig cardiac ventricular fibers after a short period of cooling (5h, 2—4℃). After rewarming them to 37℃, EADs could be induced by K~+-free superfusion at an appropriate driving stimulation (0.2 Hz) in all preparations. A high level plateau, which linearly increases its duration with time, appears ahead of EADs. The critical point of the plateau occurred steadily at the level of -47±4 mV. Two types of triggered activity, all of which are the rhythmic activities in low level of membrane potential (-50 to -60 mV), appear on the platcau. There is no significant change after overdriving. Agonists of the Na-K pump (K~+ and Tl~+) could stop the rhythmic activity immediately and turn the low level of membrane potential to high one. The results showed that high level plateau is the basis of genesis of EADs, and the activation of Na-K pump plays an important part in stopping triggered rhythms arising from EADs. 相似文献
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本文在短期低温处理后(5h,2—4℃)的豚鼠心室肌标本上,探讨了早发后去极化(EAD)的发生。在适当地驱动刺激(0.2Hz)下,复温后的心室肌标本经无钾溶液灌流后均可诱发EAD产生。EAD出现之前,动作电位于复极3期首先形成一新的“低位平台”。此平台可随时间呈线性增长,其拐点恒定在动作电位复极至—47±4mV的膜电位水平。由EAD触发形成的非驱动反应呈两种电位形式,但均属低膜电位水平(—50——60 mV)的节律性活动。超速驱动无明显影响,钠泵激动剂(K~+及Tl~+)可有效而迅速地终止触发性节律活动,并使低膜电位转变为高膜电位。结果表明:“低位平台”是EAD形成的基础;钠泵的激动在消除EAD触发的节律活动中起重要作用。 相似文献
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工程实际中直升机的旋翼和风力机的叶片等可简化为旋转柔性悬臂梁的动力学问题。针对旋转FGM圆环形截面柔性悬臂梁的横向振动问题,基于Euler-Bernoulli梁理论和Hamilton原理,建立了自由振动时的运动微分方程。对运动微分方程和边界条件进行量纲归一化处理,采用微分求积法对其进行离散化,得到了系统的广义特征方程。分析了旋转FGM圆环形截面柔性梁的前三阶量纲为一的固有频率随梯度指标和不同梯度指标、径长比下量纲为一的固有频率随轮毂量纲为一的角速度的变化关系。数值计算结果表明,在给定某些参数情况下,旋转FGM环形截面悬臂梁的前三阶量纲为一的固有频率随轮毂量纲为一的角速度的增大而增大,第二阶、第三阶量纲为一的固有频率随梯度指标的增大而增大的趋势较为明显。 相似文献
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研究了切向均布随从力作用下热弹耦合轴向运动梁的稳定性问题。建立了热弹耦合轴向运动梁
在随从力作用下的运动微分方程,采用归一化幂级数法,推导出了2种边界条件下热弹耦合轴向运动梁在随
从力作用下的特征方程。计算了系统的前3阶量纲一复频率,分析了量纲一运动速度、量纲一热弹耦合系数
和量纲一随从力等参数对梁的稳定性的影响。 相似文献
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The non-linear governing differential equations of immovably simply supported functionally graded material (FGM) rod subjected to thermal loads were derived. The thermal post-buckling behaviors of FGM rod made of ZrO2 and Ti-6Al-4Vwere analyzed by shooting method. Firstly, the thermal post-buckling equilibrium paths of the FGM rod with different gradient index in the uniform temperature field were plotted, and compared with the behaviors of the homogeneous rods made of ZrO2 and Ti-6A1-4V materials, respectively. For given value of end rotation angles, the influence of gradient index on the thermal post-buckling behaviors of FGM rod was discussed. Secondly, the thermal post-buckling characteristics of the FGM rod were analyzed when the temperature difference parameter is changed while the bottom temperature parameter remains constant, and when the bottom temperature parameter is changed while the temperature difference parameter remains constant, and compared with the characteristics of the two homogeneous material rods. 相似文献
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机械系统中摩擦模型的研究进展 总被引:14,自引:1,他引:13
摩擦现象在机械系统中的作用日益突出,
合理地解决机械系统中摩擦环节尤其是非线性摩擦环节的制约问题
已成为当前研究的重点. 由于摩擦的复杂性,
很难从机理上获得其准确唯一的数学模型, 迄今已提出的摩擦模
型有数十种. 鉴于目前机械系统中摩擦建模的发展状况,
首先描述了几种重要的摩擦现象, 如库仑摩擦、黏性
摩擦、Stribeck效应、预滑动摩擦、可变的静态摩擦力和摩擦记忆效应等.
其次, 系统地介绍了几种较为重要的、 常用的摩擦模型,
包括6种静态摩擦模型和7种动态摩擦模型, 并对每一种模型的构成,
特点和适用范围等 进行了较为详细地论述. 比较而言,
静态摩擦模型结构简单, 参数辨识容易, 但是无法描述摩擦的动态特性,
动态摩擦模型能够比较全面的描述摩擦现象, 但结构复杂,
参数辨识难度较大. 再次, 简要概述了摩擦建模
对机械系统动力学行为的影响, 以及在高精度定位系统的控制中的作用.
最后, 针对当前机械系统中摩擦建 模方面存在的一些不足提出了几点展望.
为今后摩擦模型的选用和新摩擦模型的建立提供了参考. 相似文献
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