The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the hi...The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy （FESEM）. It was found that the size of inclusion has significant effect on the fatigue behavior. For AtSI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curve displays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 pro. In the case of internal inclusion-induced fractures at cycles beyond about 1×10^6 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet （GBF） was observed in the vicinity around the inclusion. The GBF sizes increase with increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×10^6. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.展开更多
Lung infections are usually caused by pathogenic microorganisms and are a disease with high morbidity and mortality. In clinical practice, the use of broad-spectrum antibiotics has become increasingly common, but this...Lung infections are usually caused by pathogenic microorganisms and are a disease with high morbidity and mortality. In clinical practice, the use of broad-spectrum antibiotics has become increasingly common, but this has also led to the problem of antibiotic abuse and irrational use, which in turn has spawned the emergence of multidrug-resistant bacteria, making the treatment of lung infections more complex and difficult. In the human immune system, γδ T cells play a crucial role in defense against foreign pathogens and regulation of autoimmune responses. These cells act as a bridge between innate and adaptive immunity and can be rapidly activated in the early stages of infection to produce inflammatory factors and chemokines that attract other immune cells to the site of infection. Recent advances have shown that γδ T cells not only play a direct role in the innate immunity of pathogen infection, but are also involved in regulating the subsequent adaptive immune response. The aim of this review is to explore the mechanism of γδ T cells in lung infections and to summarize the current progress of clinical research, with the aim of providing new scientific basis and therapeutic strategies for the treatment of lung infections.展开更多
基金the National Key Basic Research and Development Program of China under grant No.2004CB619104.
文摘The fatigue fracture behavior of four ultrahigh strength steels with different melting processes and therefore different inclusion sizes were studied by using a rotating bar two-point bending fatigue machine in the high-cycle regime up to 107 cycles of loading. The fracture surfaces were observed by field emission scanning electron microscopy （FESEM）. It was found that the size of inclusion has significant effect on the fatigue behavior. For AtSI 4340 steel in which the inclusion size is smaller than 5.5 μm, all the fatigue cracks except one did not initiated from inclusion but from specimen surface and conventional S-N curve exists. For 65Si2MnWE and Aermet 100 steels in which the average inclusion sizes are 12.2 and 14.9 μm, respectively, fatigue cracks initiated from inclusions at lower stress amplitudes and stepwise S-N curves were observed. The S-N curve displays a continuous decline and fatigue failures originated from large oxide inclusion for 60Si2CrVA steel in which the average inclusion size is 44.4 pro. In the case of internal inclusion-induced fractures at cycles beyond about 1×10^6 for 65Si2MnWE and 60Si2CrVA steels, inclusion was always found inside the fish-eye and a granular bright facet （GBF） was observed in the vicinity around the inclusion. The GBF sizes increase with increasing the number of cycles to failure Nf in the long-life regime. The values of stress intensity factor range at crack initiation site for the GBF are almost constant with Nf, and are almost equal to that for the surface inclusion and the internal inclusion at cycles lower than about 1×10^6. Neither fish-eye nor GBF was observed for Aermet 100 steel in the present study.
文摘Lung infections are usually caused by pathogenic microorganisms and are a disease with high morbidity and mortality. In clinical practice, the use of broad-spectrum antibiotics has become increasingly common, but this has also led to the problem of antibiotic abuse and irrational use, which in turn has spawned the emergence of multidrug-resistant bacteria, making the treatment of lung infections more complex and difficult. In the human immune system, γδ T cells play a crucial role in defense against foreign pathogens and regulation of autoimmune responses. These cells act as a bridge between innate and adaptive immunity and can be rapidly activated in the early stages of infection to produce inflammatory factors and chemokines that attract other immune cells to the site of infection. Recent advances have shown that γδ T cells not only play a direct role in the innate immunity of pathogen infection, but are also involved in regulating the subsequent adaptive immune response. The aim of this review is to explore the mechanism of γδ T cells in lung infections and to summarize the current progress of clinical research, with the aim of providing new scientific basis and therapeutic strategies for the treatment of lung infections.
