Knowing the optimal operating parameters of Stirling engines is important for efficient combustion through adaptability to changed pressures and oxygen atmospheres. In this study, the optimum operating conditions for ...Knowing the optimal operating parameters of Stirling engines is important for efficient combustion through adaptability to changed pressures and oxygen atmospheres. In this study, the optimum operating conditions for efficient combustion in a singular Stirling engine combustor at different oxygen atmospheres were investigated and determined. Numerical simulations were performed to investigate the effects of ejection ratio and pressure on combustion performance. In an oxygen/carbon dioxide atmosphere, the results show that increasing the ejection ratio substantially alters the flame distribution in the Stirling engine combustor, increasing heat transfer and external combustion efficiency. In contrast, increasing the ejection ratio reduces the average and maximum temperatures of the Stirling engine combustor. Increased pressure affects the flame distribution in the Stirling engine combustor and impedes the flow and convective heat transfer in the combustor, reducing the overall external combustion efficiency at pressures above 6.5 MPa. In an air/carbon dioxide atmosphere, an increased ejection ratio reduces the average and maximum temperatures in the Stirling engine combustor. However, the overall flame distribution does not change substantially. The external combustion efficiency tends to increase and then decrease because of two opposing factors: the increase in the convective heat transfer coefficient and the decrease in the temperature difference. Increasing pressure inhibits forced convection heat transfer in the Stirling engine combustor, reducing external combustion efficiency, which drops from 78% to 65% when pressure increases from 0.2 MPa to 0.5 MPa.展开更多
Background Elderly patients(age≥60 years)with ST-segment elevation myocardial infarction(STEMI)are at an elevated risk of mortality.This study aimed to investigate the association of the creatinine to ejection fracti...Background Elderly patients(age≥60 years)with ST-segment elevation myocardial infarction(STEMI)are at an elevated risk of mortality.This study aimed to investigate the association of the creatinine to ejection fraction ratio(CER)with in-hospital and 1-year death in elderly patients with STEMI.Methods A total of 753 consecutive elderly patients(age≥60 years)with STEMI undergoing percutaneous coronary intervention(PCI)were enrolled and divided into three groups according to the tertiles of CER at admission:<1.5(n=250),1.5-2.2(n=249)and>2.2(n=254).Multivariate analyses were performed to evaluate the prognostic value of CRE for short-term death in this population.Results The in-hospital and 1-year mortality reached 6.0%and 13.3%,respectively.Patients with higher CER exhibited a higher in-hospital mortality(0.8%vs.2.8%vs.14.2%,P<0.001).An optimal cut-off value of 2.5 for CER was identified for predicting in-hospital death by receiver operating characteristic curve analysis,yielding a sensitivity of 77.8%and a specificity of 76.1%[area under curve(AUC):0.791,95%confidence interval(CI):0.734-0.847,P<0.001].Multivariate regression analyses revealed that CER>2.5 was an independent risk factor for both in-hospital[adjusted odds ratio(OR):9.006,95%CI:2.707-29.967,P<0.001]and 1-year mortality[adjusted hazard ratio(HR):5.082,95%CI:2.462-10.490,P<0.001].Conclusions Elevated CER is associated with adverse short-term mortality in elderly STEMI patients undergone PCI,offering valuable insights for the early identification and management of high-risk individuals in clinical practice.展开更多
Accurate prediction of rockburst proneness is one of challenges for assessing the rockburst risk and selecting effective control measures.This study aims to assess rockburst proneness by considering the energy charact...Accurate prediction of rockburst proneness is one of challenges for assessing the rockburst risk and selecting effective control measures.This study aims to assess rockburst proneness by considering the energy characteristics and qualitative information during rock failure.Several representative rock types in cylindrical and cuboidal sample shapes were tested under uniaxial compression conditions and the failure progress was detected by a high-speed camera.The far-field ejection mass ratio(FEMR)was determined considering the qualitative failure information of the rock samples.The peak-strength energy impact index and the residual elastic energy index were used to quantitatively evaluate the rockburst proneness of both cylindrical and cuboidal samples.Further,the performance of these two indices was analyzed by comparing their estimates with the FEMR.The results show that the accuracy of the residual elastic energy index is significantly higher than that of the peak-strength energy impact index.The residual elastic energy index and the FEMR are in good agreement for both cylindrical and cuboidal rock materials.This is because these two indices can essentially reflect the common energy release mechanism characterized by the mass,ejection velocity,and ejection distance of rock fragments.It suggests that both the FEMR and the residual elastic energy index can be used to accurately measure the rockburst proneness of cylindrical and cuboidal samples based on uniaxial compression test.展开更多
基金Supported by the Shanghai Rising Star Program (Grant No. 21QB1403900)the Shanghai Municipal Commission of Science and Technology (Grant No. 22170712600)。
文摘Knowing the optimal operating parameters of Stirling engines is important for efficient combustion through adaptability to changed pressures and oxygen atmospheres. In this study, the optimum operating conditions for efficient combustion in a singular Stirling engine combustor at different oxygen atmospheres were investigated and determined. Numerical simulations were performed to investigate the effects of ejection ratio and pressure on combustion performance. In an oxygen/carbon dioxide atmosphere, the results show that increasing the ejection ratio substantially alters the flame distribution in the Stirling engine combustor, increasing heat transfer and external combustion efficiency. In contrast, increasing the ejection ratio reduces the average and maximum temperatures of the Stirling engine combustor. Increased pressure affects the flame distribution in the Stirling engine combustor and impedes the flow and convective heat transfer in the combustor, reducing the overall external combustion efficiency at pressures above 6.5 MPa. In an air/carbon dioxide atmosphere, an increased ejection ratio reduces the average and maximum temperatures in the Stirling engine combustor. However, the overall flame distribution does not change substantially. The external combustion efficiency tends to increase and then decrease because of two opposing factors: the increase in the convective heat transfer coefficient and the decrease in the temperature difference. Increasing pressure inhibits forced convection heat transfer in the Stirling engine combustor, reducing external combustion efficiency, which drops from 78% to 65% when pressure increases from 0.2 MPa to 0.5 MPa.
文摘Background Elderly patients(age≥60 years)with ST-segment elevation myocardial infarction(STEMI)are at an elevated risk of mortality.This study aimed to investigate the association of the creatinine to ejection fraction ratio(CER)with in-hospital and 1-year death in elderly patients with STEMI.Methods A total of 753 consecutive elderly patients(age≥60 years)with STEMI undergoing percutaneous coronary intervention(PCI)were enrolled and divided into three groups according to the tertiles of CER at admission:<1.5(n=250),1.5-2.2(n=249)and>2.2(n=254).Multivariate analyses were performed to evaluate the prognostic value of CRE for short-term death in this population.Results The in-hospital and 1-year mortality reached 6.0%and 13.3%,respectively.Patients with higher CER exhibited a higher in-hospital mortality(0.8%vs.2.8%vs.14.2%,P<0.001).An optimal cut-off value of 2.5 for CER was identified for predicting in-hospital death by receiver operating characteristic curve analysis,yielding a sensitivity of 77.8%and a specificity of 76.1%[area under curve(AUC):0.791,95%confidence interval(CI):0.734-0.847,P<0.001].Multivariate regression analyses revealed that CER>2.5 was an independent risk factor for both in-hospital[adjusted odds ratio(OR):9.006,95%CI:2.707-29.967,P<0.001]and 1-year mortality[adjusted hazard ratio(HR):5.082,95%CI:2.462-10.490,P<0.001].Conclusions Elevated CER is associated with adverse short-term mortality in elderly STEMI patients undergone PCI,offering valuable insights for the early identification and management of high-risk individuals in clinical practice.
基金supported by the National Natural Science Foundation of China(Grant Nos.41877272 and 42077244)the National Key Research and Development Program of China e 2023 Key Special Project(Grant No.2023YFC2907400).
文摘Accurate prediction of rockburst proneness is one of challenges for assessing the rockburst risk and selecting effective control measures.This study aims to assess rockburst proneness by considering the energy characteristics and qualitative information during rock failure.Several representative rock types in cylindrical and cuboidal sample shapes were tested under uniaxial compression conditions and the failure progress was detected by a high-speed camera.The far-field ejection mass ratio(FEMR)was determined considering the qualitative failure information of the rock samples.The peak-strength energy impact index and the residual elastic energy index were used to quantitatively evaluate the rockburst proneness of both cylindrical and cuboidal samples.Further,the performance of these two indices was analyzed by comparing their estimates with the FEMR.The results show that the accuracy of the residual elastic energy index is significantly higher than that of the peak-strength energy impact index.The residual elastic energy index and the FEMR are in good agreement for both cylindrical and cuboidal rock materials.This is because these two indices can essentially reflect the common energy release mechanism characterized by the mass,ejection velocity,and ejection distance of rock fragments.It suggests that both the FEMR and the residual elastic energy index can be used to accurately measure the rockburst proneness of cylindrical and cuboidal samples based on uniaxial compression test.
