Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate ...Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.展开更多
A calculation scheme, which combines a horizontal upwind finite element method with vertical implicit differences, is used to establish a three-dimensional mathematical model of tidal motion and sediment transport in...A calculation scheme, which combines a horizontal upwind finite element method with vertical implicit differences, is used to establish a three-dimensional mathematical model of tidal motion and sediment transport in tidal current. Compared with those of the relative theoretical formula, the results are satisfactory. The model mentioned above has been applied to the water area of the Lianzhou Bay, Guangxi Province. On the basis of the analysis and comparison with the field data, it shows clearly that the model calculation results are reasonable.展开更多
目的了解医务人员佩戴医用防护口罩的行为现状,并分析未能规范佩戴医用防护口罩的影响因素,为改进口罩佩戴相关培训提供依据。方法2022年6月—2023年3月,选取某三级甲等医院的工作人员为研究对象,采用气溶胶凝结核计数法对市面上常见的...目的了解医务人员佩戴医用防护口罩的行为现状,并分析未能规范佩戴医用防护口罩的影响因素,为改进口罩佩戴相关培训提供依据。方法2022年6月—2023年3月,选取某三级甲等医院的工作人员为研究对象,采用气溶胶凝结核计数法对市面上常见的5款医用防护口罩进行实时定量适合性测试,通过测试仪器适合因数的变化、是否需要专业人员辅助调整综合判断医用防护口罩佩戴情况,应用自制的一般资料调查表对参与者进行问卷调查,借助三维(3D)激光扫描技术扫描参与者头面部,将扫描图像导入Geomagic Studio 2013软件测量头面部尺寸。结果共调查222名医务人员,完成991次实时测试,208次3D扫描。其中221次(22.30%)测试参与者未能规范佩戴医用防护口罩,5款医用防护口罩的不规范佩戴比率分别为30.56%、25.62%、25.87%、23.15%、7.35%。佩戴口罩不规范率:不同医用防护口罩形状,参与者职业、上一次医用防护口罩佩戴技能培训时间及是否有呼吸道传染病防治相关工作经验各组比较,差异均有统计学意义(均P<0.05);医用防护口罩品牌、尺寸,以及参与者性别、科室等各组比较,差异无统计学意义(均P>0.05)。折叠状医用防护口罩佩戴规范与不规范者身体质量指数(BMI)比较,差异均有统计学意义(均P<0.05)。结论医务人员佩戴医用防护口罩不规范受诸多因素影响,在正式的定量适合性测试之前推荐进行实时测试,能节省时间,提高测试效率。未来进行医用防护口罩佩戴培训时,对不同形状的口罩应进行针对性的培训,重点关注后勤人员、实习生、BMI高者,以及从未接受医用防护口罩佩戴培训者及未参加过呼吸道传染病防治相关工作者。展开更多
基金supported by the National Natural Science Foundation of China (10872096)the Open Fund of State Key Laboratory of Explosion Science and Technology, Beijing University of Science and Technology (KFJJ09-13)
文摘Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.
文摘A calculation scheme, which combines a horizontal upwind finite element method with vertical implicit differences, is used to establish a three-dimensional mathematical model of tidal motion and sediment transport in tidal current. Compared with those of the relative theoretical formula, the results are satisfactory. The model mentioned above has been applied to the water area of the Lianzhou Bay, Guangxi Province. On the basis of the analysis and comparison with the field data, it shows clearly that the model calculation results are reasonable.
文摘目的了解医务人员佩戴医用防护口罩的行为现状,并分析未能规范佩戴医用防护口罩的影响因素,为改进口罩佩戴相关培训提供依据。方法2022年6月—2023年3月,选取某三级甲等医院的工作人员为研究对象,采用气溶胶凝结核计数法对市面上常见的5款医用防护口罩进行实时定量适合性测试,通过测试仪器适合因数的变化、是否需要专业人员辅助调整综合判断医用防护口罩佩戴情况,应用自制的一般资料调查表对参与者进行问卷调查,借助三维(3D)激光扫描技术扫描参与者头面部,将扫描图像导入Geomagic Studio 2013软件测量头面部尺寸。结果共调查222名医务人员,完成991次实时测试,208次3D扫描。其中221次(22.30%)测试参与者未能规范佩戴医用防护口罩,5款医用防护口罩的不规范佩戴比率分别为30.56%、25.62%、25.87%、23.15%、7.35%。佩戴口罩不规范率:不同医用防护口罩形状,参与者职业、上一次医用防护口罩佩戴技能培训时间及是否有呼吸道传染病防治相关工作经验各组比较,差异均有统计学意义(均P<0.05);医用防护口罩品牌、尺寸,以及参与者性别、科室等各组比较,差异无统计学意义(均P>0.05)。折叠状医用防护口罩佩戴规范与不规范者身体质量指数(BMI)比较,差异均有统计学意义(均P<0.05)。结论医务人员佩戴医用防护口罩不规范受诸多因素影响,在正式的定量适合性测试之前推荐进行实时测试,能节省时间,提高测试效率。未来进行医用防护口罩佩戴培训时,对不同形状的口罩应进行针对性的培训,重点关注后勤人员、实习生、BMI高者,以及从未接受医用防护口罩佩戴培训者及未参加过呼吸道传染病防治相关工作者。
