Reactive Materials(RMs),a new material with structural and energy release characteristics under shockinduced chemical reactions,are promising in extensive applications in national defense and military fields.They can ...Reactive Materials(RMs),a new material with structural and energy release characteristics under shockinduced chemical reactions,are promising in extensive applications in national defense and military fields.They can increase the lethality of warheads due to their dual functionality.This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading.Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs,temperature distribution,peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material(RM)warhead casings by using high-speed camera,infrared thermal imager temperature and peak overpressure testing and scanning electron microscope.Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings.The RM casings can improve the peak overpressure of the air shock wave under explosion loading,though the results are different with different charge ratios.According to the energy release characteristics of the RM,increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave,while reducing the thickness will increase the peak overpressure of the far-field air shock wave.展开更多
The appearance of high-entropy alloys (HEAs) makes it possible for a material to possess both high strength and high ductility. It is with great potential to apply HEAs under extreme conditions such as in the penetrat...The appearance of high-entropy alloys (HEAs) makes it possible for a material to possess both high strength and high ductility. It is with great potential to apply HEAs under extreme conditions such as in the penetration process. In this paper, experiments of WFeNiMo HEA and tungsten heavy alloy (WHA) projectiles penetrating medium-carbon steel were conducted by using the ballistic gun and two-stage light-gas gun that can accelerate projectiles to impact velocities ranging from 1162 m/s to 2130 m/s. Depth of penetration (DOP) at elevated impact velocities of HEA and WHA projectiles were obtained firstly. Combined with the macroscopic and microscopic analysis of the residual projectiles, the transition of the penetration mode of the WFeNiMo HEA projectile was identified systemically. The experimental results indicated that the penetration mode of the HEA projectile changes from self-sharpening to mushrooming with the increase of impact velocity, while for the WHA projectile, the penetration mode is always mushrooming. The microstructure of the residual HEA projectiles showed that the phases tangle with each other and the morphology of the microstructure of the phases differs in the two penetration modes. Besides, the evolution of shear bands and fractures varies in the two modes. The evolution of the microstructure of HEAs causes the sharp-pointed nose to disappear and the HEA projectile ultimately becomes blunt as the impact velocity increases.展开更多
BACKGROUND New and more severe clinical manifestations associated with the coronavirus disease 2019(COVID-19) are emerging constantly in the pediatric age group.Patients in this age group are also primary carriers of ...BACKGROUND New and more severe clinical manifestations associated with the coronavirus disease 2019(COVID-19) are emerging constantly in the pediatric age group.Patients in this age group are also primary carriers of the influenza virus and are at a higher risk of developing severe infection.However,studies comparing influenza and COVID-19 to show which condition causes a more severe form of disease amongst the pediatric age group are scarce.AIM To compare the laboratory results,clinical symptoms and clinical outcomes in pediatric patients with COVID-19 and influenza.METHODS A systematic and comprehensive search was carried out in databases and search engines,including EMBASE,Cochrane,MEDLINE,ScienceDirect and Google Scholar from 1964 until January 2022.A meta-analysis was carried out using a random-effects model and pooled odds ratio(OR) or standardized mean difference(SMD) and 95%CI.RESULTS A total of 16 studies satisfied the inclusion criteria.Pediatric COVID-19 patients had a significantly reduced risk of cough(pooled OR = 0.16;95%CI:0.09 to 0.27),fever(pooled OR = 0.23;95%CI:0.12 to 0.43),and dyspnea(pooled OR = 0.54;95%CI:0.33 to 0.88) compared to influenza patients.Furthermore,total hemoglobin levels(pooled SMD = 1.22;95%CI:0.29 to 2.14) in COVID-19 patients were significantly higher as compared to pediatric influenza patients.There was no significant difference in symptoms such as sore throat,white blood cell count,platelets,neutrophil and lymphocytes levels,and outcomes like mortality,intensive care unit admission,mechanical ventilation or length of hospital stay.CONCLUSION COVID-19 is associated with a significantly lower rate of clinical symptoms and abnormal laboratory indexes compared to influenza in the pediatric age group.However,further longitudinal studies of the outcomes between influenza and COVID-19 pediatric patients are needed.展开更多
基金the Fundamental Research Funds for the Central Universities(No.30920021108)Open Foundation of Hypervelocity Impact Research Center of CARDC(20200106).
文摘Reactive Materials(RMs),a new material with structural and energy release characteristics under shockinduced chemical reactions,are promising in extensive applications in national defense and military fields.They can increase the lethality of warheads due to their dual functionality.This paper focuses on the energy release characteristics of RM casings prepared by alloy melting and casting process under explosive loading.Explosion experiments of RM and conventional 2A12 aluminum alloy casings were conducted in free field to capture the explosive fireballs,temperature distribution,peak overpressure of the air shock wave and the fracture morphology of fragments of reactive material(RM)warhead casings by using high-speed camera,infrared thermal imager temperature and peak overpressure testing and scanning electron microscope.Results showed that an increase of both the fireball temperature and air shock wave were observed in all RM casings compared to conventional 2A12 aluminum ally casings.The RM casings can improve the peak overpressure of the air shock wave under explosion loading,though the results are different with different charge ratios.According to the energy release characteristics of the RM,increasing the thickness of RM casings will increase the peak overpressure of the near-field air shock wave,while reducing the thickness will increase the peak overpressure of the far-field air shock wave.
基金This work is funded by the National Natural Science Foundation of China(No.11790292)the NSAF Joint Fund(No.U1730101).
文摘The appearance of high-entropy alloys (HEAs) makes it possible for a material to possess both high strength and high ductility. It is with great potential to apply HEAs under extreme conditions such as in the penetration process. In this paper, experiments of WFeNiMo HEA and tungsten heavy alloy (WHA) projectiles penetrating medium-carbon steel were conducted by using the ballistic gun and two-stage light-gas gun that can accelerate projectiles to impact velocities ranging from 1162 m/s to 2130 m/s. Depth of penetration (DOP) at elevated impact velocities of HEA and WHA projectiles were obtained firstly. Combined with the macroscopic and microscopic analysis of the residual projectiles, the transition of the penetration mode of the WFeNiMo HEA projectile was identified systemically. The experimental results indicated that the penetration mode of the HEA projectile changes from self-sharpening to mushrooming with the increase of impact velocity, while for the WHA projectile, the penetration mode is always mushrooming. The microstructure of the residual HEA projectiles showed that the phases tangle with each other and the morphology of the microstructure of the phases differs in the two penetration modes. Besides, the evolution of shear bands and fractures varies in the two modes. The evolution of the microstructure of HEAs causes the sharp-pointed nose to disappear and the HEA projectile ultimately becomes blunt as the impact velocity increases.
文摘BACKGROUND New and more severe clinical manifestations associated with the coronavirus disease 2019(COVID-19) are emerging constantly in the pediatric age group.Patients in this age group are also primary carriers of the influenza virus and are at a higher risk of developing severe infection.However,studies comparing influenza and COVID-19 to show which condition causes a more severe form of disease amongst the pediatric age group are scarce.AIM To compare the laboratory results,clinical symptoms and clinical outcomes in pediatric patients with COVID-19 and influenza.METHODS A systematic and comprehensive search was carried out in databases and search engines,including EMBASE,Cochrane,MEDLINE,ScienceDirect and Google Scholar from 1964 until January 2022.A meta-analysis was carried out using a random-effects model and pooled odds ratio(OR) or standardized mean difference(SMD) and 95%CI.RESULTS A total of 16 studies satisfied the inclusion criteria.Pediatric COVID-19 patients had a significantly reduced risk of cough(pooled OR = 0.16;95%CI:0.09 to 0.27),fever(pooled OR = 0.23;95%CI:0.12 to 0.43),and dyspnea(pooled OR = 0.54;95%CI:0.33 to 0.88) compared to influenza patients.Furthermore,total hemoglobin levels(pooled SMD = 1.22;95%CI:0.29 to 2.14) in COVID-19 patients were significantly higher as compared to pediatric influenza patients.There was no significant difference in symptoms such as sore throat,white blood cell count,platelets,neutrophil and lymphocytes levels,and outcomes like mortality,intensive care unit admission,mechanical ventilation or length of hospital stay.CONCLUSION COVID-19 is associated with a significantly lower rate of clinical symptoms and abnormal laboratory indexes compared to influenza in the pediatric age group.However,further longitudinal studies of the outcomes between influenza and COVID-19 pediatric patients are needed.
