Analysis of railway subgrade frost heave deformation based on GPS

In order to analyze the connection between the railway subgrade frost heave deformation and temperature variation, five GPS stations＇ data were used to monitor the deformation on a certain section of railway subgrade in northeast China. GAMIT software is used to process the data, providing daily solution, daytime solution and nighttime solution. Vertical trends of these five stations were analyzed to investigate frost heave effect on railway subgrade deformation. The results show that the temperature difference between daytime and night induces stations, significant vertical displacement, and the temperature difference between seasons causes settlement of station which appears linear trend.

青年近视人群视网膜劈裂的OCT特征

目的:通过频域光学相干断层扫描(SD-OCT)观察青年近视人群视网膜劈裂的类型、患病率、组成比例、分布规律及临床特征,探讨青年近视人群视网膜劈裂的SD-OCT影像学特点。方法:横断面研究。收集2020年7—12月于河北医科大学第二医院眼科近视激光手术门诊就诊的近视患者523例(1046眼),其中低度近视(-3.00~0 D)227眼(21.7%),中度近视(>-6.00~<-3.00 D)405眼(38.7%),高度近视(≤-6.00 D)414眼(39.6%)。受检者接受完整的眼科检查,包括最佳矫正视力、眼轴长度、屈光度、彩色眼底照相和SD-OCT等检查。SD-OCT扫描范围为视网膜颞侧及鼻侧上、下血管弓和黄斑中央凹处。观察视网膜劈裂在视网膜4个象限的分布情况,统计视网膜劈裂的类型、患病率、组成比例及临床特征。血管旁内层、外层视网膜劈裂的分布情况的统计分析采用Pearson卡方检验。中层视网膜劈裂的分布情况的分析采用Fisher精确检验。年龄、屈光度在血管旁视网膜劈裂的亚组间的比较分析采用Kruskal-Wallis秩和检验,眼轴长度在血管旁视网膜劈裂的亚组间比较采用ANOVA。结果:SD-OCT检测出血管旁视网膜劈裂30眼(2.9%),未检测出近视黄斑视网膜劈裂。内层视网膜劈裂、中层视网膜劈裂和外层视网膜劈裂这3种血管旁视网膜劈裂在青年近视人群中总的患病率分别为2.9%、0.8%、1.5%。在发生血管旁视网膜劈裂的30眼中,内层、中层、外层的视网膜劈裂分别有30、8、16眼。3种血管旁视网膜劈裂(内层:χ^(2)=13.468,P<0.001;中层:P=0.002;外层:χ^(2)=13.576,P<0.001)沿颞侧血管弓分布频率较高。结论:青年近视患者血管旁视网膜劈裂最常沿颞侧血管弓分布。内层视网膜劈裂可能是青年人血管旁视网膜劈裂最常见的亚型。青年人近视眼中内层视网膜劈裂主要与玻璃体后皮质的切线牵拉及视网膜血管的前后牵拉有关。