By providing a means of separating the airborne emissions of patients from the air breathed by healthcare workers(HCWs),vented individual patient(VIP)hoods,a form of local exhaust ventilation(LEV),offer a new approach...By providing a means of separating the airborne emissions of patients from the air breathed by healthcare workers(HCWs),vented individual patient(VIP)hoods,a form of local exhaust ventilation(LEV),offer a new approach to reduce hospital-acquired infection(HAI).Results from recent studies have demonstrated that,for typical patient-emitted aerosols,VIP hoods provide protection at least equivalent to that of an N95 mask.Unlike a mask,hood performance can be easily monitored and HCWs can be alerted to failure by alarms.The appropriate use of these relatively simple devices could both reduce the reliance on personal protective equipment(PPE)for infection control and provide a low-cost and energy-efficient form of protection for hospitals and clinics.Although the development and deployment of VIP hoods has been accelerated by the coronavirus disease 2019(COVID-19)pandemic,these devices are currently an immature technology.In this review,we describe the state of the art of VIP hoods and identify aspects in need of further development,both in terms of device design and the protocols associated with their use.The broader concept of individual patient hoods has the potential to be expanded beyond ventilation to the provision of clean conditions for individual patients and personalized control over other environmental factors such as temperature and humidity.展开更多
High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase...High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase and retained nanocrystalline;second is the alternating bands of amorphous phase and high defect density crystalline.As a result,post deformation annealing(PDA)at 500-700℃leads to the non-uniform distribution of martensite and parent phase grains.The grains of martensite are twice larger compared to that of parent phase.The nanocrystalline and ultrafine grains form after annealing at 500-600℃and 700℃,respectively.The twinning mechanism does not change with the reduction of martensitic grains up to^35 nm.The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80±0.39 GPa nm^1/2.展开更多
Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H...Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.展开更多
文摘By providing a means of separating the airborne emissions of patients from the air breathed by healthcare workers(HCWs),vented individual patient(VIP)hoods,a form of local exhaust ventilation(LEV),offer a new approach to reduce hospital-acquired infection(HAI).Results from recent studies have demonstrated that,for typical patient-emitted aerosols,VIP hoods provide protection at least equivalent to that of an N95 mask.Unlike a mask,hood performance can be easily monitored and HCWs can be alerted to failure by alarms.The appropriate use of these relatively simple devices could both reduce the reliance on personal protective equipment(PPE)for infection control and provide a low-cost and energy-efficient form of protection for hospitals and clinics.Although the development and deployment of VIP hoods has been accelerated by the coronavirus disease 2019(COVID-19)pandemic,these devices are currently an immature technology.In this review,we describe the state of the art of VIP hoods and identify aspects in need of further development,both in terms of device design and the protocols associated with their use.The broader concept of individual patient hoods has the potential to be expanded beyond ventilation to the provision of clean conditions for individual patients and personalized control over other environmental factors such as temperature and humidity.
基金supported by National Key R&D Program of China[grant number 2017YFE0123500]National Natural Science Foundation of China[grant number 51971072,51671064]+2 种基金the Fundamental Research Funds for the Central University[grant number HEUCFG201836]the support from the RFBR-CNPq-DST research project№19-58-80018the support in part from the Russian Foundation for Basic Research(project No.20-03-00614)。
文摘High-pressure torsion(HPT)processing under a pressure of 6.0 GPa was applied to Ti29.7Ni50.3Hf20(at.%)alloy.Two types of structure were observed after HPT with 3 revolutions:first one is the mixture of amorphous phase and retained nanocrystalline;second is the alternating bands of amorphous phase and high defect density crystalline.As a result,post deformation annealing(PDA)at 500-700℃leads to the non-uniform distribution of martensite and parent phase grains.The grains of martensite are twice larger compared to that of parent phase.The nanocrystalline and ultrafine grains form after annealing at 500-600℃and 700℃,respectively.The twinning mechanism does not change with the reduction of martensitic grains up to^35 nm.The relationship between strength and grain size in Ti29.7Ni50.3Hf20 alloy obeys the classical Hall-Petch relationship with a coefficient of 10.80±0.39 GPa nm^1/2.
基金supported by the National Natural Sci-ence Foundation of China(Nos.52050410340 and 51971072)the Fundamental Research Funds for the Central University(No.3072021CFJ1002).
文摘Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys.This paper discusses the precipitation,coarsening and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy during isothermal aging at temperatures between 450℃and 650℃for time to 75 h.The H-phase mean size and volume fraction were determined using transmission electron microscopy.Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law.From these analyses,a Time-Temperature-Transformation diagram was constructed.The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures.The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for nondilute solutions.Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data.Moreover,time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni_(50)Ti_(30)Hf_(20)alloy.
