Objective:This study elaborated the natural history parameters of Delta variant,explored the differences in detection cycle thresholds(Ct)among cases.Methods:Natural history parameters were calculated based on the dif...Objective:This study elaborated the natural history parameters of Delta variant,explored the differences in detection cycle thresholds(Ct)among cases.Methods:Natural history parameters were calculated based on the different onset time and exposure time of the cases.Intergenerational relationships between generations of cases were calculated.Differences in Ct values of cases by gender,age,and mode of detection were analyzed statistically to assess the detoxification capacity of cases.Results:The median incubation period was 4 days;the detection time for cases decreased from 25 to 7 h as the outbreak continued.The average generation time(GT),time interval between transmission generations(TG)and serial interval(SI)were 3.6±2.6 days,1.67±2.11 days and 1.7±3.0 days.Among the Ct values,we found little differences in testing across companies,but there were some differences in the gender of detected genes.The Ct values continuous to decreased with age,but increased when the age was greater than 60.Conclusion:This epidemic was started from aggregation of factories.It is more reasonable to use SI to calculate the effective reproduction number and the time-varying reproduction number.And the analysis of Ct values can improve the positive detection rate and improve prevention and control measures.展开更多
Thin-wall structures of Ti-6A1-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward...Thin-wall structures of Ti-6A1-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward the top of melt pool tail. This resulted in a microstructure mainly composed of long and thin prior epitaxial β columnar grains (average width ^200μm). A periodic pattern in epitaxial growth of grains was observed, which was shown to depend upon laser traverse direction. Utilizing this, a novel means was proposed to determine accurately the fusion boundary of each deposited layer by inspection of the periodic wave patterns. As a result it was applied to investigate the influence of thermal cycling on microstructure evolution. Results showed that acicular martensite,α' phase, and a small amount of Widmanstatten, a laths, gradually converted to elongated acicular a and a large fraction of Widmanstatten a laths under layer-wise thermal cycling. Tensile tests showed that the yield strength, ultimate tensile strength and elongation of Ti-6Al-4V thin wall in the build direction were 9.1 %, 17.3% and 42% higher respectively than those typically observed in forged solids of the same alloy. It also showed the yield strength and ultimate tensile strength of the transverse tensile samples both were 13.3% higher than those from the build direction due to the strengthening effect of a large number of vertical β grain boundaries, but the elongation was 69.7% lower than that of the build direction due to the uneven grain deformation of β grains.展开更多
基金This work was partly supported by the Bill&Melinda Gates Foundation(INV-005834)the National Key Research and Development Program of China(2021YFC2301604)the Fujian Provincial Department of Science and Technology pilot project(2020D019).
文摘Objective:This study elaborated the natural history parameters of Delta variant,explored the differences in detection cycle thresholds(Ct)among cases.Methods:Natural history parameters were calculated based on the different onset time and exposure time of the cases.Intergenerational relationships between generations of cases were calculated.Differences in Ct values of cases by gender,age,and mode of detection were analyzed statistically to assess the detoxification capacity of cases.Results:The median incubation period was 4 days;the detection time for cases decreased from 25 to 7 h as the outbreak continued.The average generation time(GT),time interval between transmission generations(TG)and serial interval(SI)were 3.6±2.6 days,1.67±2.11 days and 1.7±3.0 days.Among the Ct values,we found little differences in testing across companies,but there were some differences in the gender of detected genes.The Ct values continuous to decreased with age,but increased when the age was greater than 60.Conclusion:This epidemic was started from aggregation of factories.It is more reasonable to use SI to calculate the effective reproduction number and the time-varying reproduction number.And the analysis of Ct values can improve the positive detection rate and improve prevention and control measures.
基金supported by the National Key Research and Development Program of China (No. 2018YFB1106302)the National Natural Science Foundation of China (Grant No. 51475380)the Aeronautical Science Foundation of China (Grant No. 2016ZE53)
文摘Thin-wall structures of Ti-6A1-4V were fabricated by low-power pulsed laser directed energy deposition. During deposition, consistent with prior reports, columnar grains were observed which grew from the bottom toward the top of melt pool tail. This resulted in a microstructure mainly composed of long and thin prior epitaxial β columnar grains (average width ^200μm). A periodic pattern in epitaxial growth of grains was observed, which was shown to depend upon laser traverse direction. Utilizing this, a novel means was proposed to determine accurately the fusion boundary of each deposited layer by inspection of the periodic wave patterns. As a result it was applied to investigate the influence of thermal cycling on microstructure evolution. Results showed that acicular martensite,α' phase, and a small amount of Widmanstatten, a laths, gradually converted to elongated acicular a and a large fraction of Widmanstatten a laths under layer-wise thermal cycling. Tensile tests showed that the yield strength, ultimate tensile strength and elongation of Ti-6Al-4V thin wall in the build direction were 9.1 %, 17.3% and 42% higher respectively than those typically observed in forged solids of the same alloy. It also showed the yield strength and ultimate tensile strength of the transverse tensile samples both were 13.3% higher than those from the build direction due to the strengthening effect of a large number of vertical β grain boundaries, but the elongation was 69.7% lower than that of the build direction due to the uneven grain deformation of β grains.
