重塑黄土一维应变实验粒子速度测试波形的拉格朗日分析

利用57 mm口径一级轻气炮,飞片选用有机玻璃,对密度1.8 g/cm³、饱和度22%的重塑黄土,进行了一系列一维应变实验。通过在重塑黄土试样内布设多根Π形电磁粒子速度计,直接测得了多个粒子速度波形。该文详细介绍了一维应变条件下Lagrange分析方法的理论推导及求解过程,并对实测粒子速度波形进行了Lagrange分析,得到了加、卸载全过程的应力、应变波形。给出了3发不同压力条件下重塑黄土的应力-应变关系曲线,揭示了重塑黄土介质的本构滞回效应。并使用该应力-应变关系对试样内应力波传播过程进行了反分析,最后对Lagrange分析过程中遇到的问题进行了讨论。     

重塑黄土内球面应力波粒子速度测量波形的拉格朗日分析

选用密度为1.8 g/cm³、饱和度为22%的重塑黄土作为应力波传播介质,在其中心处安装0.125 g TNT当量微型炸药球,建立起了尺度为Ф1370 mm×1200 mm的球面波发生装置。在重塑黄土样品中心圆形环面上布设多根圆环形电磁粒子速度计,测量了一系列粒子速度波形。为研究重塑黄土样品粘弹性区域的本构关系,为有限元数值模拟提供可靠的数据支持,以实测粒子速度波形为基础,使用Lagrange分析方法对该区域的应力-应变关系展开了研究。该文详细介绍了一维球对称条件下Lagrange分析方法的理论推导及求解过程,对实测粒子速度波形运用Lagrange分析方法计算了对应的应变、应力及应变率波形,得到了各量计安装位置处,重塑黄土完整的压缩、拉伸全过程应力-应变滞回曲线。并对Lagrange分析方法使用中遇到的问题提出了几点认识。     

Metformin Attenuates Slow-to-Fast Fiber Shift and Proteolysis Markers Increase in Rat Soleus after 7 Days of Rat Hindlimb Unloading

Muscle unloading leads to signaling alterations that cause muscle atrophy and weakness. The cellular energy sensor AMPK can regulate myofiber-type shift, calcium-dependent signaling and ubiquitin-proteasome system markers. We hypothesized that the prevention of p-AMPK downregulation during the first week of muscle unloading would impede atrophy development and the slow-to-fast shift of soleus muscle fibers, and the aim of the study was to test this hypothesis. Thirty-two male Wistar rats were randomly assigned to four groups: placebo control (C), control rats treated with metformin (C + M), 7 days of hindlimb suspension (HS) + placebo (7HS), and 7 days of HS + metformin administration (7HS + M). In the soleus of the 7HS rats, we detected a slow-to-fast fiber-type shift as well as a significant downregulation of MEF-2D and p300 in the nuclei. In the 7HS group, we also found decreases in p-ACC (AMPK target) protein level and in the expression of E3 ubiquitin ligases and p-CaMK II protein level vs. the C group. The 7-day metformin treatment for soleus muscle unloading (1) prevented slow-to-fast fiber-type shift; (2) counteracted changes in the p-ACC protein level; (3) hindered changes in the nuclear protein level of the slow myosin expression activators MEF-2D and p300, but did not affect NFATc1 signaling; and (4) attenuated the unloading-induced upregulation of MuRF-1, atrogin-1, ubiquitin and myostatin mRNA expression, but did not prevent soleus muscle atrophy. Thus, metformin treatment during muscle disuse could be useful to prevent the decrease in the percentage of slow-type fatigue-resistant muscle fibers.     

快速卸车系统在太原选煤厂的应用

通过对太原选煤厂原煤卸车系统的改造,实现了原煤卸车系统的全自动运行,降低了职工的劳动强度,提高了原煤的小时处理能力.     

某框架加固方案的研讨

本文以石狮市某框架底层柱配筋不足、水平地震力作用下层间位移角偏大为例,综合考虑各种加固方法的经济性、适用性及结合本工程实际特点,研究探讨了采用增加柱间交叉斜撑的方法进行加固的可行性,以资借鉴.     

国家体育馆屋盖滑移支撑转换变形分析

国家体育馆在滑移施工过程中一个非常关键的步骤是七点支撑转变为三点支撑,文章给出两种转换方案,分析此过程中结构的位移、支撑架反力、杆件应力的变化情况。     

高温水冷后循环加卸载条件下花岗岩的渗透性

针对水下隧道火灾喷水灭火降温过程中围岩的渗透性问题,对高温水冷后循环加卸载条件下花岗岩的渗透性开展了试验研究.以高温(25、400和900 ℃)水冷后的花岗岩试样为研究对象,通过轴向压应力循环加卸载过程中气体渗透性试验,研究花岗岩渗透率变化规律.结果表明:轴向压应力循环加卸载试验过程中,花岗岩试样的卸载模量随着高温水冷处理温度升高而减小,随着轴向压应力增大,卸载模量总体呈上升趋势,气体渗透率随温度升高而增大;花岗岩BET比表面积与BJH孔体积在900 ℃高温水冷后明显减小.     

Numerical Simulation of Rock Burst in Circular Tunnels Under Unloading Conditions

Rock burst in a circular tunnel under high in-situ stress conditions was investigated with a numerical method coupled the rock failure process theory (RFPA) and discontinuous deformation theory (DDA).Some numerical tests were carraied out to investigate the failuer patterns of circular tunnel under unloading conditions.Compared the results under loading conditions, the shapes of failure zones are more regular under the unloading conditions.The failure patterns in the same type of rock mass are clearly different because of non-homogeneity of the rock material.The extension of cracks shows some predictability with an increasing of in-situ stress.When the homogeneity index of rocks (m) is either relatively high or low and lateral pressure coefficients (λ) is high, the number of regular shear slide cracks decreases and the probability of a rock burst also becomes lower.Our numerical simulation results show that the stability of surface rock and the natural bedding stratification of rock material greatly affect rock bursts.Installing bolts with due diligence and suitably can effectively prevent rock bursts.However, it is not effective to control rock bursts by releasing the strain energy with normal pre-boreholes.