Crack growth analysis for rock-like materials with ordered multiple pre-cracks under biaxial compression

The pre-burying iron sheets approach was used to prepare rock-like materials with ordered multiple pre-cracks. 60 specimens in total were prepared in these experiments. Through biaxial compression experiments, the influence of both the number of pre-cracks and pre-cracks angles to crack growth was analyzed. Meanwhile, species of rock bridge failure were summarized, namely, wing crack, secondary shear crack between horizontal pre-cracks and secondary shear crack between vertical pre-cracks. The wing crack plays a significant role in crack growth. Furthermore, fractal dimension was adopted to describe quantitatively the crack growth during the failure process. The results indicate that with the failure of specimens, corresponding fractal dimension for specimen monotonically increases, which indicates that the fractal dimension can be considered to the failure of the specimens quantitatively.

CD200和淋巴细胞亚群在儿童免疫性血小板减少症中的意义

目的探讨CD200和淋巴细胞亚群在儿童免疫性血小板减少症(immune thrombocytopenia,ITP)发病机制中的意义。方法收集2019年4月至2021年12月新乡医学院第一附属医院收治的初诊ITP患儿40例为ITP组,选择同期来院体检的健康儿童40例为对照组。采用流式细胞术检测ITP组和对照组外周血淋巴细胞亚群、淋巴细胞上CD200表达率和Treg百分率;使用XN-2000型全自动血细胞分析仪检测血小板(PLT)计数。结果ITP组Treg百分率、PLT计数、CD4^(+)T细胞百分比、CD4^(+)/CD8^(+)比值均显著低于对照组(P<0.05);ITP组CD8^(+)T细胞百分比显著高于对照组(P<0.05);ITP组CD19^(+)B细胞百分比与对照组比较差异无统计学意义(P>0.05)。CD200在ITP组CD3^(+)T细胞上的表达率显著低于对照组(P<0.05),但两组间CD19^(+)B细胞上的CD200表达率无统计学差异(P>0.05)。Pearson相关分析显示,ITP组Treg百分率与PLT计数无相关性(r=0.138,P>0.05),但CD3^(+)T细胞上CD200表达率与PLT计数、Treg百分率分别呈正相关(r分别=0.387、0.378,P均<0.05)。结论ITP患者外周血存在CD3^(+)T细胞上CD200表达减低以及Treg、CD4^(+)/CD8^(+)T淋巴细胞亚群失衡,提示ITP的发病机制与细胞免疫失衡以及CD200表达水平的异常有关。