Experimental studies were conducted on the tensile behaviors and fracture modes of TiAl（Ti-46.5Al-2Nb-2Cr） alloys with near gamma（NG） equiaxed and near lamellar（NL） microstructures over a temperature range from room temperature to 840 ℃ and a strain rate range of 0.001-1 350 s-1.The results indicate that the alloys are both temperature and strain rate dependent and they have a similar dependence.The dynamic strength is higher than the quasi-static strength but almost insensitive to high strain rate range of 320-1 350 s-1.The brittle-to-ductile transition temperature（BDTT） increases with increasing strain rates.NG TiAl yields obviously,while NL TiAl does not.Below BDTT,as the temperature increases,the fracture modes of the two alloys change from planar cleavage fracture to a mixture of transgranular and intergranular fractures,and finally to totally intergranular fracture.
目的系统评价中国不同地区孕妇B族链球菌(group B streptococcus,GBS)感染对妊娠结局的影响及相关性,旨在为临床医师筛查GBS提供理论依据。方法检索各个数据库从建库至2023年1月关于GBS感染与妊娠结局关系的相关文献,由两名研究员独立筛选文献、提取资料(第一作者、发表年份、地区、研究类型、入组孕周、样本量、GBS检测方法、主要结局指标),采用Stata 16.0进行Meta分析,用纽卡斯尔-渥太华质量评价量表(Newcastle-Ottawa Scale,NOS)对文献质量进行评估。采用漏斗图及Egger检验评估发表偏倚。结果共纳入18篇文献,包含我国17个地区,其中GBS阳性患者1722例,阴性患者8343例,文献质量整体在中等及以上。Meta分析结果显示,与GBS阴性患者相比,阳性患者更容易发生宫内感染、胎膜早破、胎儿窘迫、羊水污染、产后出血、早产和产褥感染。结论GBS感染是我国17个地区妊娠妇女不良妊娠结局的重要危险因素,应重视GBS感染的早期筛查与诊治。
