Suppression of stimulated Raman scattering(SRS)by means of chirped and tilted fiber Bragg gratings(CTFBGs)has become a key topic.However,research on high-power systems is still lacking due to two problems.Firstly,afte...Suppression of stimulated Raman scattering(SRS)by means of chirped and tilted fiber Bragg gratings(CTFBGs)has become a key topic.However,research on high-power systems is still lacking due to two problems.Firstly,after the inscription,there are a large number of hydroxyl compounds and hydrogen molecules in CTFBGs that cause significant heating due to their strong infrared absorption.Secondly,CTFBGs can couple Stokes light from the core to the cladding and the coating,which causes serious heating in the coating of the CTFBG.Aimed at overcoming these bottlenecks,a process that combines constant-low-temperature and variable-high-temperature annealing is used to reduce the thermal slope of the CTFBG.Also,a segmented-corrosion cladding power stripping technology is used on the CTFBG to remove the Stokes light which is coupled to the cladding,which solves the problem of overheating in the coating of the CTFBG.Thereby,a CTFBG with both a kilowatt-level power-carrying load and the ability to suppress SRS in a fiber laser has been developed.Further,we establish a kW-level CW oscillator to test the CTFBG.Experimental results demonstrate that the power-carrying load of the CTFBG is close to 1 kW,the thermal slope is lower than 0.015 ℃/W,and the SRS suppression ratio is nearly 23 dB.展开更多
The COVID-19 outbreak has already become a global pandemic and containing this rapid worldwide transmission is of great challenge.The impacts of temperature and humidity on the COVID-19 transmission rate are still und...The COVID-19 outbreak has already become a global pandemic and containing this rapid worldwide transmission is of great challenge.The impacts of temperature and humidity on the COVID-19 transmission rate are still under discussion.Here,we elucidated these relationships by utilizing two unique scenarios,repeated measurement and natural experiment,using the COVID-19 cases reported from January 23–February 21,2020,in China.The modeling results revealed that higher temperature was most strongly associated with decreased COVID-19 transmission at a lag time of 8 days.Relative humidity(RH)appeared to have only a slight effect.These findings were verified by assessing SARSCoV-2 infectivity under the relevant conditions of temperature(4C–37C)and RH(>40%).We concluded that temperature increase made an important,but not determined,contribution to restrain the COVID19 outbreak in China.It suggests that the emphasis of other effective controlling polices should be strictly implemented to restrain COVID19 transmission in cold seasons.展开更多
A new series of medical antibacterial high-entropy alloys(HEAs)with composition Ti 50 Zr 25 Nb 20 Cu 5-x Ag x(x=0 at.%,1 at.%,and 2.5 at.%)were developed by arc-melting the mixture of pure elements under a high-purity...A new series of medical antibacterial high-entropy alloys(HEAs)with composition Ti 50 Zr 25 Nb 20 Cu 5-x Ag x(x=0 at.%,1 at.%,and 2.5 at.%)were developed by arc-melting the mixture of pure elements under a high-purity argon atmosphere.The cytotoxicity,osteo-conductivity,and antibacterial properties of these HEAs were systematically investigated in vitro,along with their in vivo biocompatibility and antibacte-rial properties.These HEAs,especially Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5),showed better antibacterial ability against Staphylococcus aureus than Ti-6Al-4V,which has a nearly 99%antibacterial rate in vitro.Moreover,ion release and cytotoxicity tests showed that these HEAs had excellent biosafety,similar to or better than that of Ti-6Al-4V.Osteoblasts were used to evaluate the osteogenic activity of these HEAs,and good osteo-conductivity was observed in vitro.In a Sprague-Dawley rat infection model,Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5)showed remarkable antibacterial properties compared to Ti-6Al-4V.The in vivo biocompatibility results showed that Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5)did not increase biotoxicity compared to Ti-6Al-4V.The excellent bio-compatibility and antibacterial properties of the Ti-Zr-Nb-Cu-Ag HEAs are expected to enable the pre-vention of periprosthetic/peri-implant infections in the future.展开更多
为了压缩总长度,红外热像仪普遍采用双反射镜折布局(U型)及箱式壳体,而现有传函仪仅能测量非折转布局(一字型)的光学系统的调制传递函数(Modulation Transfer Function,MTF),导致传函仪无法接到U型光学系统的像面,因此无法测量其MTF。...为了压缩总长度,红外热像仪普遍采用双反射镜折布局(U型)及箱式壳体,而现有传函仪仅能测量非折转布局(一字型)的光学系统的调制传递函数(Modulation Transfer Function,MTF),导致传函仪无法接到U型光学系统的像面,因此无法测量其MTF。为了解决该难题,本文采用光瞳衔接的方式,设计和加工一个中继镜组把U型光学系统的像面引出,通过测量组合系统的MTF,再计算出U型光学系统的MTF,从而解决其MTF测量的难题。然后使用6个同一个型号的红外热像仪对测量方法进行验证,在排除影响测量的干扰因素以后,通过测量组合系统MTF,再计算出U型光学系统的MTF。同时,在测量过程中发现5#、6#红外热像仪的U型光学系统的MTF下降较多,通过红外中心偏差测量仪的测量,发现第三、四镜片的中心偏差较大,故重新装调和控制,从而使U型光学系统的MTF有大幅提升。该方法为U型光学系统的MTF测量和性能提升提供了新的思路。展开更多
基金supported by the National Key Research and Development Program of China(No.2017YFB1104400)
文摘Suppression of stimulated Raman scattering(SRS)by means of chirped and tilted fiber Bragg gratings(CTFBGs)has become a key topic.However,research on high-power systems is still lacking due to two problems.Firstly,after the inscription,there are a large number of hydroxyl compounds and hydrogen molecules in CTFBGs that cause significant heating due to their strong infrared absorption.Secondly,CTFBGs can couple Stokes light from the core to the cladding and the coating,which causes serious heating in the coating of the CTFBG.Aimed at overcoming these bottlenecks,a process that combines constant-low-temperature and variable-high-temperature annealing is used to reduce the thermal slope of the CTFBG.Also,a segmented-corrosion cladding power stripping technology is used on the CTFBG to remove the Stokes light which is coupled to the cladding,which solves the problem of overheating in the coating of the CTFBG.Thereby,a CTFBG with both a kilowatt-level power-carrying load and the ability to suppress SRS in a fiber laser has been developed.Further,we establish a kW-level CW oscillator to test the CTFBG.Experimental results demonstrate that the power-carrying load of the CTFBG is close to 1 kW,the thermal slope is lower than 0.015 ℃/W,and the SRS suppression ratio is nearly 23 dB.
基金We would like to express our gratitude for discussions with the researchers from the environmental exposure and human health working group of the China Cohort Consortium(http://chinacohort.bjmu.edu.cn/),as well as special thanks to Dr.Ping Zhong and Dr.Wentao Wang for their instructive guidance.This work was supported by the National Key Research and Development Program,P.R.China(Grant No.2020YFC0846300 and 2020YFC0846200)the National Natural Science Foundation of China(Grant No.41771527,41922057).
文摘The COVID-19 outbreak has already become a global pandemic and containing this rapid worldwide transmission is of great challenge.The impacts of temperature and humidity on the COVID-19 transmission rate are still under discussion.Here,we elucidated these relationships by utilizing two unique scenarios,repeated measurement and natural experiment,using the COVID-19 cases reported from January 23–February 21,2020,in China.The modeling results revealed that higher temperature was most strongly associated with decreased COVID-19 transmission at a lag time of 8 days.Relative humidity(RH)appeared to have only a slight effect.These findings were verified by assessing SARSCoV-2 infectivity under the relevant conditions of temperature(4C–37C)and RH(>40%).We concluded that temperature increase made an important,but not determined,contribution to restrain the COVID19 outbreak in China.It suggests that the emphasis of other effective controlling polices should be strictly implemented to restrain COVID19 transmission in cold seasons.
基金supported by the Beijing Xicheng Sci-ence,Technology and Informatization bureau(No.XCSTS-SD2018-693)and by Beijing Municipal Science and Technology Commission(No.Z181100001918028).
文摘A new series of medical antibacterial high-entropy alloys(HEAs)with composition Ti 50 Zr 25 Nb 20 Cu 5-x Ag x(x=0 at.%,1 at.%,and 2.5 at.%)were developed by arc-melting the mixture of pure elements under a high-purity argon atmosphere.The cytotoxicity,osteo-conductivity,and antibacterial properties of these HEAs were systematically investigated in vitro,along with their in vivo biocompatibility and antibacte-rial properties.These HEAs,especially Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5),showed better antibacterial ability against Staphylococcus aureus than Ti-6Al-4V,which has a nearly 99%antibacterial rate in vitro.Moreover,ion release and cytotoxicity tests showed that these HEAs had excellent biosafety,similar to or better than that of Ti-6Al-4V.Osteoblasts were used to evaluate the osteogenic activity of these HEAs,and good osteo-conductivity was observed in vitro.In a Sprague-Dawley rat infection model,Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5)showed remarkable antibacterial properties compared to Ti-6Al-4V.The in vivo biocompatibility results showed that Ti_(50)Zr_(25)Nb_(20)Cu_(2.5)Ag_(2.5)did not increase biotoxicity compared to Ti-6Al-4V.The excellent bio-compatibility and antibacterial properties of the Ti-Zr-Nb-Cu-Ag HEAs are expected to enable the pre-vention of periprosthetic/peri-implant infections in the future.
文摘为了压缩总长度,红外热像仪普遍采用双反射镜折布局(U型)及箱式壳体,而现有传函仪仅能测量非折转布局(一字型)的光学系统的调制传递函数(Modulation Transfer Function,MTF),导致传函仪无法接到U型光学系统的像面,因此无法测量其MTF。为了解决该难题,本文采用光瞳衔接的方式,设计和加工一个中继镜组把U型光学系统的像面引出,通过测量组合系统的MTF,再计算出U型光学系统的MTF,从而解决其MTF测量的难题。然后使用6个同一个型号的红外热像仪对测量方法进行验证,在排除影响测量的干扰因素以后,通过测量组合系统MTF,再计算出U型光学系统的MTF。同时,在测量过程中发现5#、6#红外热像仪的U型光学系统的MTF下降较多,通过红外中心偏差测量仪的测量,发现第三、四镜片的中心偏差较大,故重新装调和控制,从而使U型光学系统的MTF有大幅提升。该方法为U型光学系统的MTF测量和性能提升提供了新的思路。
