The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo abla...The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo ablation issues,which can cause catastrophic accidents.Due to the excellent high-temperature stability and ablation resistance,HfC exhibits outstanding thermal expansion coefficient matching that of C/SiC composites.2.5D needle-punched C/SiC composites coated with HfC are prepared using a plasma spraying process,and a high-enthalpy arc-heated wind tunnel is employed to simulate the re-entry environment of aircraft at 8 Mach and an altitude of 32 km.The plasma-sprayed HfC-coated 2.5D needle-punched C/SiC composites are subjected to long-term dynamic testing,and their properties are investigated.Specifically,after the thermal assessment ablation experiment,the composite retains its overall structure and profile;the total mass ablation rate is 0.07445 g/s,the average linear ablation rate in the thickness direction is-0.0675μm/s,and the average linear ablation rate in the length direction is 13.907μm/s.Results verify that plasma-sprayed HfC coating exhibits excellent anti-oxidation and ablation resistance properties.Besides,the microstructure and ablation mechanism of the C/SiC composites are studied.It is believed that this work will offer guideline for the development of thermal protection materials and the assessment of structural thermal performance.展开更多
目的分析2022年疾病诊断相关分组(diagnosis related group,DRG)改革效果及其对不同科室的影响,为DRG实施创造有利的政策环境。方法本研究数据来源于北京市二级、三级医院住院病案首页数据库,共纳入北京市城镇职工医疗保险住院患者的住...目的分析2022年疾病诊断相关分组(diagnosis related group,DRG)改革效果及其对不同科室的影响,为DRG实施创造有利的政策环境。方法本研究数据来源于北京市二级、三级医院住院病案首页数据库,共纳入北京市城镇职工医疗保险住院患者的住院病案记录1603989条。构建双重差分模型,采用事件研究法进行平行趋势检验,应用医院月度汇总数据分析2022年DRG改革对城镇职工医疗保险住院患者次均住院费用、平均住院日、30 d再入院患者比例、60 d再入院患者比例和经门诊入院患者比例的影响;在此基础上,选取内科、外科、妇产科和肿瘤科的月度汇总数据进一步分析DRG改革对不同科室住院服务利用的影响。结果相较于非DRG医院,DRG改革使住院患者的次均住院费用下降约9.79%,平均住院日下降约5.35%,而对再入院风险和经门诊入院患者比例无显著影响;DRG改革降低了内科、外科和妇产科的次均住院费用,降低了内科和外科的平均住院日,对所选4个科室的再入院风险和经门诊入院患者比例均无显著影响。结论北京市DRG改革降低了住院患者的次均住院费用,但应注意对医疗行为的持续监督,同时发挥其他支付方式在弥补DRG缺陷方面的作用;DRG改革对不同科室的影响存在差异,需制订适当的支持性政策以维持其良性发展。展开更多
基金financially supported by the National Key R&D Program of China(No.2022YFB3-401900)the National Natural Science Foundation of China(No.U21A20134)the Shandong Provincial Natural Science Foundation(Excellent Young Fund,No.ZR2022YQ48).
文摘The working environment of aerospace engines is extremely harsh with temperature exceeding 1700℃and accompanied by thermal coupling effects.In this condition,the materials employed in hypersonic aircraft undergo ablation issues,which can cause catastrophic accidents.Due to the excellent high-temperature stability and ablation resistance,HfC exhibits outstanding thermal expansion coefficient matching that of C/SiC composites.2.5D needle-punched C/SiC composites coated with HfC are prepared using a plasma spraying process,and a high-enthalpy arc-heated wind tunnel is employed to simulate the re-entry environment of aircraft at 8 Mach and an altitude of 32 km.The plasma-sprayed HfC-coated 2.5D needle-punched C/SiC composites are subjected to long-term dynamic testing,and their properties are investigated.Specifically,after the thermal assessment ablation experiment,the composite retains its overall structure and profile;the total mass ablation rate is 0.07445 g/s,the average linear ablation rate in the thickness direction is-0.0675μm/s,and the average linear ablation rate in the length direction is 13.907μm/s.Results verify that plasma-sprayed HfC coating exhibits excellent anti-oxidation and ablation resistance properties.Besides,the microstructure and ablation mechanism of the C/SiC composites are studied.It is believed that this work will offer guideline for the development of thermal protection materials and the assessment of structural thermal performance.
文摘目的分析2022年疾病诊断相关分组(diagnosis related group,DRG)改革效果及其对不同科室的影响,为DRG实施创造有利的政策环境。方法本研究数据来源于北京市二级、三级医院住院病案首页数据库,共纳入北京市城镇职工医疗保险住院患者的住院病案记录1603989条。构建双重差分模型,采用事件研究法进行平行趋势检验,应用医院月度汇总数据分析2022年DRG改革对城镇职工医疗保险住院患者次均住院费用、平均住院日、30 d再入院患者比例、60 d再入院患者比例和经门诊入院患者比例的影响;在此基础上,选取内科、外科、妇产科和肿瘤科的月度汇总数据进一步分析DRG改革对不同科室住院服务利用的影响。结果相较于非DRG医院,DRG改革使住院患者的次均住院费用下降约9.79%,平均住院日下降约5.35%,而对再入院风险和经门诊入院患者比例无显著影响;DRG改革降低了内科、外科和妇产科的次均住院费用,降低了内科和外科的平均住院日,对所选4个科室的再入院风险和经门诊入院患者比例均无显著影响。结论北京市DRG改革降低了住院患者的次均住院费用,但应注意对医疗行为的持续监督,同时发挥其他支付方式在弥补DRG缺陷方面的作用;DRG改革对不同科室的影响存在差异,需制订适当的支持性政策以维持其良性发展。
