In this paper,to study the mechanical responses of a solid propellant subjected to ultrahigh acceleration overload during the gun-launch process,specifically designed projectile flight tests with an onboard measuremen...In this paper,to study the mechanical responses of a solid propellant subjected to ultrahigh acceleration overload during the gun-launch process,specifically designed projectile flight tests with an onboard measurement system were performed.Two projectiles containing dummy HTPB propellant grains were successfully recovered after the flight tests with an ultrahigh acceleration overload value of 8100 g.The onboard-measured time-resolved axial displacement,contact stress and overload values were successfully obtained and analysed.Uniaxial compression tests of the dummy HTPB propellant used in the gunlaunched tests were carried out at low and intermediate strain rates to characterize the propellant's dynamic properties.A linear viscoelastic constitutive model was employed and applied in finite-element simulations of the projectile-launching process.During the launch process,the dummy propellant grain exhibited large deformation due to the high acceleration overload,possibly leading to friction between the motor case and propellant grain.The calculated contact stress showed good agreement with the experimental results,though discrepancies in the overall displacement of the dummy propellant grain were observed.The dynamic mechanical response process of the dummy propellant grain was analysed in detail.The results can be used to estimate the structural integrity of the analysed dummy propellant grain during the gun-launch process.展开更多
Segmentally assembled bridges are increasinglyfinding engineering applications in recent years due to their unique advantages,especially as urban viaducts.Vehicle loads are one of the most important variable loads acti...Segmentally assembled bridges are increasinglyfinding engineering applications in recent years due to their unique advantages,especially as urban viaducts.Vehicle loads are one of the most important variable loads acting on bridge structures.Accordingly,the influence of overloaded vehicles on existing assembled bridge structures is an urgent concern at present.This paper establishes thefinite element model of the segmentally assembled bridge based on ABAQUS software and analyzes the influence of vehicle overload on an assembled girder bridge struc-ture.First,afinite element model corresponding to the target bridge is established based on ABAQUS software,and the load is controlled to simulate vehicle movement in each area of the traveling zone at different times.Sec-ond,the key cross-sections of segmental girder bridges are monitored in real time based on the force character-istics of continuous girder bridges,and they are compared with the simulation results.Finally,a material damage ontology model is introduced,and the structural damage caused by different overloading rates is compared and analyzed.Results show that thefinite element modeling method is accurate by comparing with on-site measured data,and it is suitable for the numerical simulation of segmental girder bridges;Dynamic sensors installed at 1/4L,1/2L,and 3/4L of the segmental girder main beams could be used to identify the dynamic response of segmental girder bridges;The bottom plate of the segmental girder bridge is mostly damaged at the position where the length of the precast beam section changes and the midspan position.With the increase in load,damage in the direction of the bridge develops faster than that in the direction of the transverse bridge.Thefindings of this study can guide maintenance departments in the management and maintenance of bridges and vehicles.展开更多
Increasing evidence indicates that disruption of normal iron homeostasis may contribute to pathological development of Alzheimer＇s disease.Icariin,astragalus,and puerarin have been shown to suppress iron overload in ...Increasing evidence indicates that disruption of normal iron homeostasis may contribute to pathological development of Alzheimer＇s disease.Icariin,astragalus,and puerarin have been shown to suppress iron overload in the cerebral cortex and improve spatial learning and memory disorders in Alzheimer＇s disease mice,although the underlying mechanism remains unclear.In the present study,APPswe/PS1ΔE9 transgenic mice were administered icariin,astragalus,and puerarin（120,80,and 80 mg/kg,respectively,once a day,for 3 months）.Iron levels were detected by flame atomic absorption spectroscopy.Interleukin-1β,interleukin-6,and tumor necrosis factor-α levels were measured in the cerebral cortex by enzyme linked immunosorbent assay.Glutathione peroxidase and superoxide dismutase activity and malondialdehyde content were determined by colorimetry.Our results demonstrate that after treatment,iron levels and malondialdehyde content are decreased,while glutathione peroxidase and superoxide dismutase activities are increased.Further,interleukin-1β,interleukin-6,and tumor necrosis factor-α levels were reduced.These results confirm that compounds of icariin,astragalus,and puerarin may alleviate iron overload by reducing oxidative stress and the inflammatory response.展开更多
文摘In this paper,to study the mechanical responses of a solid propellant subjected to ultrahigh acceleration overload during the gun-launch process,specifically designed projectile flight tests with an onboard measurement system were performed.Two projectiles containing dummy HTPB propellant grains were successfully recovered after the flight tests with an ultrahigh acceleration overload value of 8100 g.The onboard-measured time-resolved axial displacement,contact stress and overload values were successfully obtained and analysed.Uniaxial compression tests of the dummy HTPB propellant used in the gunlaunched tests were carried out at low and intermediate strain rates to characterize the propellant's dynamic properties.A linear viscoelastic constitutive model was employed and applied in finite-element simulations of the projectile-launching process.During the launch process,the dummy propellant grain exhibited large deformation due to the high acceleration overload,possibly leading to friction between the motor case and propellant grain.The calculated contact stress showed good agreement with the experimental results,though discrepancies in the overall displacement of the dummy propellant grain were observed.The dynamic mechanical response process of the dummy propellant grain was analysed in detail.The results can be used to estimate the structural integrity of the analysed dummy propellant grain during the gun-launch process.
基金supported in part by the Key Research Projects of Higher Education Institutions in Henan Province(Grant No.24A560021)in part by the Henan Postdoctoral Foundation(Grant No.202102015).
文摘Segmentally assembled bridges are increasinglyfinding engineering applications in recent years due to their unique advantages,especially as urban viaducts.Vehicle loads are one of the most important variable loads acting on bridge structures.Accordingly,the influence of overloaded vehicles on existing assembled bridge structures is an urgent concern at present.This paper establishes thefinite element model of the segmentally assembled bridge based on ABAQUS software and analyzes the influence of vehicle overload on an assembled girder bridge struc-ture.First,afinite element model corresponding to the target bridge is established based on ABAQUS software,and the load is controlled to simulate vehicle movement in each area of the traveling zone at different times.Sec-ond,the key cross-sections of segmental girder bridges are monitored in real time based on the force character-istics of continuous girder bridges,and they are compared with the simulation results.Finally,a material damage ontology model is introduced,and the structural damage caused by different overloading rates is compared and analyzed.Results show that thefinite element modeling method is accurate by comparing with on-site measured data,and it is suitable for the numerical simulation of segmental girder bridges;Dynamic sensors installed at 1/4L,1/2L,and 3/4L of the segmental girder main beams could be used to identify the dynamic response of segmental girder bridges;The bottom plate of the segmental girder bridge is mostly damaged at the position where the length of the precast beam section changes and the midspan position.With the increase in load,damage in the direction of the bridge develops faster than that in the direction of the transverse bridge.Thefindings of this study can guide maintenance departments in the management and maintenance of bridges and vehicles.
基金supported by the National Natural Science Foundation of China,No.81273983
文摘Increasing evidence indicates that disruption of normal iron homeostasis may contribute to pathological development of Alzheimer＇s disease.Icariin,astragalus,and puerarin have been shown to suppress iron overload in the cerebral cortex and improve spatial learning and memory disorders in Alzheimer＇s disease mice,although the underlying mechanism remains unclear.In the present study,APPswe/PS1ΔE9 transgenic mice were administered icariin,astragalus,and puerarin（120,80,and 80 mg/kg,respectively,once a day,for 3 months）.Iron levels were detected by flame atomic absorption spectroscopy.Interleukin-1β,interleukin-6,and tumor necrosis factor-α levels were measured in the cerebral cortex by enzyme linked immunosorbent assay.Glutathione peroxidase and superoxide dismutase activity and malondialdehyde content were determined by colorimetry.Our results demonstrate that after treatment,iron levels and malondialdehyde content are decreased,while glutathione peroxidase and superoxide dismutase activities are increased.Further,interleukin-1β,interleukin-6,and tumor necrosis factor-α levels were reduced.These results confirm that compounds of icariin,astragalus,and puerarin may alleviate iron overload by reducing oxidative stress and the inflammatory response.
