Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-in...Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress,especially that of the intermediate principal stress.The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation,and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load.Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress,intermediate principal stress,and detonation pressure,whereas negatively correlated with Poisson ratio and decoupling coefficient.The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior.The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress.As the in-situ stress increased from 0 to 70 MPa,the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.展开更多
This paper proposed an improved temperature prediction model for oil-immersed transformer.The influences of the environmental temperature and heat-sinking capability changing with temperature were considered.When calc...This paper proposed an improved temperature prediction model for oil-immersed transformer.The influences of the environmental temperature and heat-sinking capability changing with temperature were considered.When calculating the heat dissipation from the transformer tank to surroundings,the average oil temperature was selected as the node value in the thermal circuit.The new thermal models will be validated with the delivery experimental data of three transformers: a 220 kV-300 MV.A unit,a 110 kV40 MV.A unit and a 220 kV-75 MV.A unit.Meanwhile,the results from the proposed model were also compared with two methods recommended in the IEC loading guide.展开更多
The mechanical properties, corrosion resistance and microstructures of high performance steel （HPS） was investigated by tensile testing machine, Charpy V-Notch （CVN） testing machine, cyclic immersion corrosion tes...The mechanical properties, corrosion resistance and microstructures of high performance steel （HPS） was investigated by tensile testing machine, Charpy V-Notch （CVN） testing machine, cyclic immersion corrosion tester, XRD, optical microscopy （OM）, scanning electron microscopy （SEM）, and electron probe micro-analyzer （EPMA）. The results showed that significant differences existed in the tensile strength, yield strength and impact toughness between HPS and PCS. After 72 h cyclic immersion accelerated corrosion test, the inner rust layer on HPS was com- posed of a-FeOOH phase and denser than that on PCS that was a mixture of a-FeOOH and Fe3 04. The rust formed on HPS provides better protection and HPS has lower corrosion rates than PCS. Copper and chromium in HPS en- rich in the rust layer and enhance the compactness of the rust layer. Based on the results of the accelerated corrosion tests and rust layer analysis, the roles of Cu and Cr against corrosion are discussed, providing HPS with chemical specification which has been industrially successful to produce weathering steel for bridge structure.展开更多
Background Low diastolic blood pressure(DBP)was reported to be associated with reduced coronary blood flow,subclinical myocardial damage,and cardiovascular events. The aim of this study was to explore the impact of lo...Background Low diastolic blood pressure(DBP)was reported to be associated with reduced coronary blood flow,subclinical myocardial damage,and cardiovascular events. The aim of this study was to explore the impact of low DBP on clinical outcomes in patients with ST-elevation myocardial infarction(STEMI)undergoing percutaneous coronary intervention(PCI). Methods A total of 1232 patients with STEMI were retrospectively enrolled and divided into two groups according to admission DBP level:≥70 mm Hg(n=817)and < 70 mm Hg(n=415). The relationship between DBP and in-hospital and 1-year adverse events was evaluated.Results In-hospital death occurred in 2.4% of patients. The in-hospital mortality(5.3% vs. 1.0%,P<0.001)and major adverse clinical events(11.1% vs. 7.5%,P=0.033)were significantly higher in patients with a low DBP.DBP <70 mm Hg was associated with in-hospital death(adjusted odds rate=3.31,95%CI:1.36-8.07,P=0.009).Additional significant indicators included eGFR < 60 mL/min/1.73 m^2 and intra aorta balloon pump(IABP)treatment. Seventy-seven(6.3%)patients died in the one-year follow-up. DBP < 70 mm Hg was associated with increased risk of 1-year death(8.9% vs. 4.8%,Log-rank=9.9,P=0.002). Conclusion Low DBP was associated with increased risk of in-hospital and 1-year adverse prognosis in patients with STEMI undergoing PCI,which could be a tool for risk assessment.展开更多
基金Project(2021JJ10063)supported by the Natural Science Foundation of Hunan Province,ChinaProject(202115)supported by the Science and Technology Progress and Innovation Project of Hunan Provincial Department of Transportation,ChinaProject(2021K094-Z)supported by the Science and Technology Research and Development Program of China Railway Guangzhou Group Co.,Ltd。
文摘Blasting-induced cracks in the rock surrounding deeply buried tunnels can result in water gushing and rock mass collapse,posing significant safety risks.However,previous theoretical studies on the range of blasting-induced cracks often ignore the impact of the in-situ stress,especially that of the intermediate principal stress.The particle displacement−crack radius relationship was established in this paper by utilizing the blasthole cavity expansion equation,and theoretical analytical formulas of the stress−displacement relationship and the crack radius were derived with unified strength theory to accurately assess the range of cracks in deep surrounding rock under a blasting load.Parameter analysis showed that the crushing zone size was positively correlated with in-situ stress,intermediate principal stress,and detonation pressure,whereas negatively correlated with Poisson ratio and decoupling coefficient.The dilatancy angle-crushing zone size relationship exhibited nonmonotonic behavior.The relationships in the crushing zone and the fracture zone exhibited opposite trends under the influence of only in-situ stress or intermediate principal stress.As the in-situ stress increased from 0 to 70 MPa,the rate of change in the crack range and the attenuation rate of the peak vibration velocity gradually slowed.
文摘This paper proposed an improved temperature prediction model for oil-immersed transformer.The influences of the environmental temperature and heat-sinking capability changing with temperature were considered.When calculating the heat dissipation from the transformer tank to surroundings,the average oil temperature was selected as the node value in the thermal circuit.The new thermal models will be validated with the delivery experimental data of three transformers: a 220 kV-300 MV.A unit,a 110 kV40 MV.A unit and a 220 kV-75 MV.A unit.Meanwhile,the results from the proposed model were also compared with two methods recommended in the IEC loading guide.
文摘The mechanical properties, corrosion resistance and microstructures of high performance steel （HPS） was investigated by tensile testing machine, Charpy V-Notch （CVN） testing machine, cyclic immersion corrosion tester, XRD, optical microscopy （OM）, scanning electron microscopy （SEM）, and electron probe micro-analyzer （EPMA）. The results showed that significant differences existed in the tensile strength, yield strength and impact toughness between HPS and PCS. After 72 h cyclic immersion accelerated corrosion test, the inner rust layer on HPS was com- posed of a-FeOOH phase and denser than that on PCS that was a mixture of a-FeOOH and Fe3 04. The rust formed on HPS provides better protection and HPS has lower corrosion rates than PCS. Copper and chromium in HPS en- rich in the rust layer and enhance the compactness of the rust layer. Based on the results of the accelerated corrosion tests and rust layer analysis, the roles of Cu and Cr against corrosion are discussed, providing HPS with chemical specification which has been industrially successful to produce weathering steel for bridge structure.
基金supported by Shenzhen Science and Technology Innovation Commission(No.JCYJ20180302150203732).
文摘Background Low diastolic blood pressure(DBP)was reported to be associated with reduced coronary blood flow,subclinical myocardial damage,and cardiovascular events. The aim of this study was to explore the impact of low DBP on clinical outcomes in patients with ST-elevation myocardial infarction(STEMI)undergoing percutaneous coronary intervention(PCI). Methods A total of 1232 patients with STEMI were retrospectively enrolled and divided into two groups according to admission DBP level:≥70 mm Hg(n=817)and < 70 mm Hg(n=415). The relationship between DBP and in-hospital and 1-year adverse events was evaluated.Results In-hospital death occurred in 2.4% of patients. The in-hospital mortality(5.3% vs. 1.0%,P<0.001)and major adverse clinical events(11.1% vs. 7.5%,P=0.033)were significantly higher in patients with a low DBP.DBP <70 mm Hg was associated with in-hospital death(adjusted odds rate=3.31,95%CI:1.36-8.07,P=0.009).Additional significant indicators included eGFR < 60 mL/min/1.73 m^2 and intra aorta balloon pump(IABP)treatment. Seventy-seven(6.3%)patients died in the one-year follow-up. DBP < 70 mm Hg was associated with increased risk of 1-year death(8.9% vs. 4.8%,Log-rank=9.9,P=0.002). Conclusion Low DBP was associated with increased risk of in-hospital and 1-year adverse prognosis in patients with STEMI undergoing PCI,which could be a tool for risk assessment.
