Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-lay...Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-layer heterogeneity.To mitigate such anisotropy,it is of great significance to understand the effects of processing parameters on the property evolution and thus metallurgy of fabrication process.This research proposes one-factor-at-a-time experiment to investigate the influences of laser power and scanning speed on the surface qual-ity,microstructures and mechanical properties of selective laser melted Ti-6Al-4V parts.Surface quality is assessed by roughness around the printings while mechanical properties are evaluated through microhardness and tensile strengths.Phases in microstructure are quantified by XRD to correlate with mechanical properties.Fracture morphology is analyzed to understand the effect of defects and microstructure on mechanical performance.The optimized parameter corresponding to best surface quality and mechanical properties has been found respect-ively in laser power of 190 W and scanning speed of 800 mm/s.After optimization,surface roughness has decreased by 44.47%for upper surface.Yielding strength,tensile strength and elongation rate have improved by 13.17%,43.34%and 64.51%,respectively,with similar hardness and Young’s modulus.In addition,heterogeneity of mechanical properties has great improvement by a range of 31.63%-92.68%.展开更多
Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured v...Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding（VARTM） and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan（CS）-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle（WCA） will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.展开更多
目的通过Meta分析探讨不同孕前体质量指数与早产(preterm birth,PTB)的剂量-反应关系。方法搜索Pubmed、EMBASE、Cochrane Central Register of Controlled Trials、CNKI和中国生物医学文献服务系统数据库,限定时间为2012年1月到2022年1...目的通过Meta分析探讨不同孕前体质量指数与早产(preterm birth,PTB)的剂量-反应关系。方法搜索Pubmed、EMBASE、Cochrane Central Register of Controlled Trials、CNKI和中国生物医学文献服务系统数据库,限定时间为2012年1月到2022年12月,同时手动筛选部分灰色文献和其他出版物的评论文章。由两名作者独立地使用纽卡斯尔-渥太华量表(NOS)对纳入文献进行质量评估。本文分析采用Review manager 5.4软件进行。剂量-反应分析将采用RStudio软件,分析BMI和PTB结果之间潜在的非线性剂量-反应关系,使用限制性立方样条函数和广义最小二乘估计法构建剂量-反应的非线性模型,通过Wald检验进行非线性检验,若P<0.05则认为两者存在非线性剂量。结果最终纳入文献17篇,样本量共计1976740例。Meta分析结果显示:孕前BMI越低,孕妇发生早产的风险越高(OR=1.09,95%CI=1.04-1.15)。超重孕妇发生早产的风险比正常体重孕妇高(OR=1.16,95%CI=1.10-1.24)。肥胖组孕妇发生早产的风险高于正常体重组孕妇(OR=1.40,95%CI=1.34-1.46)。不同孕前BMI与早产之间的关系近似于“V”型,早产率最低点的BMI大均为22.5 kg/m2。结论孕前低BMI、超重、肥胖均增加了早产的风险。不同的BMI与早产之间存在着近似“V”型的剂量-反应关系。展开更多
基金Project was supported by the Natural Science Foundation of Fujian Province(Grant No.2020J01873)Science and Technology Major Project of Fujian Province(Grant No.2020HZ03018)+1 种基金Fujian Provincial Foreign Cooperation Project of Science and Technology(Grant No.2020I1003)Fujian Provincial Special Project for Marine Economy Development(Grant No.2021-517).
文摘Due to the layer-by-layer manufacturing characteristics,metallurgical process of selective laser melting(SLM)is inherently dif-ferent in the building direction because of varying conditions,thereby resulting inter-layer heterogeneity.To mitigate such anisotropy,it is of great significance to understand the effects of processing parameters on the property evolution and thus metallurgy of fabrication process.This research proposes one-factor-at-a-time experiment to investigate the influences of laser power and scanning speed on the surface qual-ity,microstructures and mechanical properties of selective laser melted Ti-6Al-4V parts.Surface quality is assessed by roughness around the printings while mechanical properties are evaluated through microhardness and tensile strengths.Phases in microstructure are quantified by XRD to correlate with mechanical properties.Fracture morphology is analyzed to understand the effect of defects and microstructure on mechanical performance.The optimized parameter corresponding to best surface quality and mechanical properties has been found respect-ively in laser power of 190 W and scanning speed of 800 mm/s.After optimization,surface roughness has decreased by 44.47%for upper surface.Yielding strength,tensile strength and elongation rate have improved by 13.17%,43.34%and 64.51%,respectively,with similar hardness and Young’s modulus.In addition,heterogeneity of mechanical properties has great improvement by a range of 31.63%-92.68%.
基金Supported by the Research Fund of Fujian University of Technology(Nos.GY-Z15091,GY-Z160121)the External Cooperative Projects of Fujian Province(No.2018I0001)+2 种基金the Young Teachers Education Research Project(No.JAT170377)the Outstanding Young Scientific Research Personnel Training Plan in Colleges and Universities of Fujian Province(No.GY-Z160146)Fujian Province Undergraduate Training Program for Innovation and Entrepreneurship(No.201710388055)
文摘Graded porous scaffold can be applied to study the interactions between cells and scaffold with different pore sizes. Polydimethylsiloxane（PDMS） scaffold with an axial pore size grade was successfully manufactured via vacuum-assisted resin transfer moulding（VARTM） and particle leaching technologies. The properties of graded PDMS scaffolds, including porosity, water absorption, interconnectivity, compression modulus, as well as compression strength were investigated. The results showed that the smaller the size of the NaCl particles is, the higher the porosity and water absorption of graded PDMS scaffolds would be. The graded PDMS scaffold fabricated had a compressive modulus and a compressive strength of 19.69±1.42 kPa and 4.76±0.22 kPa, respectively. Moreover, the graded chitosan（CS）-coated PDMS scaffolds were prepared by using dip-coating technique under low vacuum and their hydrophilicity was examined. It is found that the water contact angle（WCA） will decrease with an increase in the CS solution concentration and the coating time, which indicates that CS-coated PDMS scaffolds exhibit noticeable hydrophilicity compared with graded PDMS scaffold.
文摘早产(preterm birth,PTB)是指妊娠>28周且<37周的分娩,在此期间出生的新生儿称为早产儿,体重约为1000~2499 g。根据原因,可分为自发性(sPTB)、未足月胎膜早破早产(preterm preturely rutured membranes,PPROM)和治疗性早产(preterm birth for medical and obsterical indications,mPTB)。
文摘目的通过Meta分析探讨不同孕前体质量指数与早产(preterm birth,PTB)的剂量-反应关系。方法搜索Pubmed、EMBASE、Cochrane Central Register of Controlled Trials、CNKI和中国生物医学文献服务系统数据库,限定时间为2012年1月到2022年12月,同时手动筛选部分灰色文献和其他出版物的评论文章。由两名作者独立地使用纽卡斯尔-渥太华量表(NOS)对纳入文献进行质量评估。本文分析采用Review manager 5.4软件进行。剂量-反应分析将采用RStudio软件,分析BMI和PTB结果之间潜在的非线性剂量-反应关系,使用限制性立方样条函数和广义最小二乘估计法构建剂量-反应的非线性模型,通过Wald检验进行非线性检验,若P<0.05则认为两者存在非线性剂量。结果最终纳入文献17篇,样本量共计1976740例。Meta分析结果显示:孕前BMI越低,孕妇发生早产的风险越高(OR=1.09,95%CI=1.04-1.15)。超重孕妇发生早产的风险比正常体重孕妇高(OR=1.16,95%CI=1.10-1.24)。肥胖组孕妇发生早产的风险高于正常体重组孕妇(OR=1.40,95%CI=1.34-1.46)。不同孕前BMI与早产之间的关系近似于“V”型,早产率最低点的BMI大均为22.5 kg/m2。结论孕前低BMI、超重、肥胖均增加了早产的风险。不同的BMI与早产之间存在着近似“V”型的剂量-反应关系。
