The onset of hepatic decompensation in cirrhosis heralds an accelerated downhill course with poor outcome. The sole predictor of this decompensationin cirrhosis is increased hepatic vein to portal vein gradient hepati...The onset of hepatic decompensation in cirrhosis heralds an accelerated downhill course with poor outcome. The sole predictor of this decompensationin cirrhosis is increased hepatic vein to portal vein gradient hepatic venous pressure gradient(HVPG). Surrogate markers of liver function or hepatic reserve appear to be less relevant. The hepatic sinusoids become less elastic and more rigid as liver fibrosis and cirrhosis progress. We propose that the HagenPoiseuille's law,which applies to rigid,but not elastic vessels,determines the pressure-flow characteristics in the sinusoids. In the rigid cirrhotic liver,HVPG rises dramatically with any change in net surface area or radius,r4 of the vasculature that follows surgical resection. This review relates liver stiffness to the risk of decompensation in patients with cirrhosis. The liver has a unique dual blood supply comprising a low pressure portal vein and high pressure hepatic artery. We compare the complexity of autoregulation in the normal elastic liver with that in the rigid cirrhotic liver. Therapeutic modalities to reduce portal pressure may reduce the risk of hepatic decompensation and improve outcomes in cirrhosis.展开更多
文章对一个平面滑动型斜坡,考虑滑面介质有和上部岩体由不同力学性质的材料组成,上部岩体为弹性介质,滑带介质为应变软化介质。对应变软化介质,用W e ibu ll分布描述滑带介质的剪应力与应变关系,建立了斜坡系统的燕尾突变模型。通过分析...文章对一个平面滑动型斜坡,考虑滑面介质有和上部岩体由不同力学性质的材料组成,上部岩体为弹性介质,滑带介质为应变软化介质。对应变软化介质,用W e ibu ll分布描述滑带介质的剪应力与应变关系,建立了斜坡系统的燕尾突变模型。通过分析,发现斜坡失稳与刚度比具有极大关联性。随着刚度比的增大,斜坡开始滑动时的0ξ值降低不断降低,突跳时ξ*值也随着降低。此时的临界值x*增大,突跳量Δx变小。当刚度比增加到一定程度后,会出现无突跳式的滑动。展开更多
盾构管片所受土压力大小与盾构隧道施工过程中同步注浆、盾构机姿态、管片及地层刚度等因素紧密相关,上述问题的复杂性决定了已有理论公式和经验方法并未较好地反映盾构管片实际受力状态。文章通过收集35座盾构隧道的52个典型土压力监...盾构管片所受土压力大小与盾构隧道施工过程中同步注浆、盾构机姿态、管片及地层刚度等因素紧密相关,上述问题的复杂性决定了已有理论公式和经验方法并未较好地反映盾构管片实际受力状态。文章通过收集35座盾构隧道的52个典型土压力监测断面实测数据,基于实测数据统计分析了盾构隧道土压力分布规律和影响因素。结果表明:(1)盾构管片所受土压力在0~400 k Pa之间的占样本总量的90%以上,经验注浆压力取0.3~0.4 MPa较为合理;(2)管片所受土压力与埋深近似呈指数关系,最大土压力与稳定土压力差值随埋深增大而减小;(3)侧压力系数λ范围为(0.5,2.3),部分超出了规范推荐的Ⅵ级围岩(0.5,1.0)取值区间,直接沿用规范建议值有失稳妥;(4)管片所受土压力与管-土刚度比近似满足二次函数关系,管-土刚度比ψ=1.0时,管片受力最为合理;(5)粘土地层管片所受土压力时空分布具有典型的4个阶段,即拼装阶段—注浆影响阶段—固结收缩阶段—土压力回升阶段,环向土压力具有不对称分布特性;砂土地层土水压力监测曲线分别呈"弱衰减脉冲式波动"和"双驼峰"分布特征,稳定后环向土压力对称分布特性显著,水压力具有"下大上小"的灯泡型分布形态。其结论可为研究盾构隧道土压力作用机理及管片设计方法的完善提供参考和借鉴。展开更多
文摘The onset of hepatic decompensation in cirrhosis heralds an accelerated downhill course with poor outcome. The sole predictor of this decompensationin cirrhosis is increased hepatic vein to portal vein gradient hepatic venous pressure gradient(HVPG). Surrogate markers of liver function or hepatic reserve appear to be less relevant. The hepatic sinusoids become less elastic and more rigid as liver fibrosis and cirrhosis progress. We propose that the HagenPoiseuille's law,which applies to rigid,but not elastic vessels,determines the pressure-flow characteristics in the sinusoids. In the rigid cirrhotic liver,HVPG rises dramatically with any change in net surface area or radius,r4 of the vasculature that follows surgical resection. This review relates liver stiffness to the risk of decompensation in patients with cirrhosis. The liver has a unique dual blood supply comprising a low pressure portal vein and high pressure hepatic artery. We compare the complexity of autoregulation in the normal elastic liver with that in the rigid cirrhotic liver. Therapeutic modalities to reduce portal pressure may reduce the risk of hepatic decompensation and improve outcomes in cirrhosis.
文摘文章对一个平面滑动型斜坡,考虑滑面介质有和上部岩体由不同力学性质的材料组成,上部岩体为弹性介质,滑带介质为应变软化介质。对应变软化介质,用W e ibu ll分布描述滑带介质的剪应力与应变关系,建立了斜坡系统的燕尾突变模型。通过分析,发现斜坡失稳与刚度比具有极大关联性。随着刚度比的增大,斜坡开始滑动时的0ξ值降低不断降低,突跳时ξ*值也随着降低。此时的临界值x*增大,突跳量Δx变小。当刚度比增加到一定程度后,会出现无突跳式的滑动。
文摘盾构管片所受土压力大小与盾构隧道施工过程中同步注浆、盾构机姿态、管片及地层刚度等因素紧密相关,上述问题的复杂性决定了已有理论公式和经验方法并未较好地反映盾构管片实际受力状态。文章通过收集35座盾构隧道的52个典型土压力监测断面实测数据,基于实测数据统计分析了盾构隧道土压力分布规律和影响因素。结果表明:(1)盾构管片所受土压力在0~400 k Pa之间的占样本总量的90%以上,经验注浆压力取0.3~0.4 MPa较为合理;(2)管片所受土压力与埋深近似呈指数关系,最大土压力与稳定土压力差值随埋深增大而减小;(3)侧压力系数λ范围为(0.5,2.3),部分超出了规范推荐的Ⅵ级围岩(0.5,1.0)取值区间,直接沿用规范建议值有失稳妥;(4)管片所受土压力与管-土刚度比近似满足二次函数关系,管-土刚度比ψ=1.0时,管片受力最为合理;(5)粘土地层管片所受土压力时空分布具有典型的4个阶段,即拼装阶段—注浆影响阶段—固结收缩阶段—土压力回升阶段,环向土压力具有不对称分布特性;砂土地层土水压力监测曲线分别呈"弱衰减脉冲式波动"和"双驼峰"分布特征,稳定后环向土压力对称分布特性显著,水压力具有"下大上小"的灯泡型分布形态。其结论可为研究盾构隧道土压力作用机理及管片设计方法的完善提供参考和借鉴。
