This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological ...This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological factors and building obstructions.The results reveal a progressive degradation in seeing as the monitoring setup passively changed:the median values were 0."76(the original location),0."83 during the Terrace,and 0."99 at the new Dome(temporarily considered the permanent monitoring location).Once the instruments are fully deployed,wind speed and wind direction critically affect seeing quality,with optimal conditions occurring when the wind speed is 2–6 m s^(−1) and the wind direction is between 180°and 270°.However,in 2023 and 2024,the wind speeds decreased,and the prevailing wind direction shifted from southwest to northwest,correlating with poorer seeing.Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field,increasing turbulence around the Dome,especially when the winds blow from 225°to 255°.In contrast,Platform A,located in a higher and more open area,consistently maintained better seeing,particularly after midnight,likely due to fewer obstructions and lower nocturnal heat release.展开更多
Alzheimer's disease(AD)is a common cause of dementia,characterised by cerebral amyloid-βdeposition,pathological tau and neurodegeneration.The prodromal stage of AD(pAD)refers to patients with mild cognitive impai...Alzheimer's disease(AD)is a common cause of dementia,characterised by cerebral amyloid-βdeposition,pathological tau and neurodegeneration.The prodromal stage of AD(pAD)refers to patients with mild cognitive impairment(MCl)and evidence of AD's pathology.At this stage,disease-modifying interventions should be used to prevent the progression to dementia.Given the inherent heterogeneity of MCl,more specific biomarkers are needed to elucidate the underlying AD's pathology.Although the uses of cerebrospinal fluid and positron emission tomography are widely accepted methods for detecting AD's pathology,their clinical applications are limited by their high costs and invasiveness,particularly in low-income areas in China.Therefore,to improve the early detection of Alzheimer's disease(AD)pathology through cost-effective screening methods,a panel of 45neurologists,psychiatrists andgerontologistswas invited to establish a formal consensus on the screening of pAD in China.The supportive evidence and grades of recommendations are based on a systematic literature review andfocus group discussion.National meetings were held to allow participants to review,vote and provide their expert opinions to reach a consensus.A majority(two-thirds)decision was used for questions for which consensus could not be reached.Recommended screening methods are presented in this publication,including neuropsychological assessment,peripheral biomarkers and brain imaging.In addition,a general workflow for Screening pAD in China is established,which will help clinicians identify individuals at high risk and determine therapeutic targets.展开更多
Raindrop size distribution(DSD)plays a crucial role in enhancing the accuracy of radar quantitative precipitation estimates in the Tibetan Plateau(TP).However,there is a notable scarcity of long-term,high-resolution o...Raindrop size distribution(DSD)plays a crucial role in enhancing the accuracy of radar quantitative precipitation estimates in the Tibetan Plateau(TP).However,there is a notable scarcity of long-term,high-resolution observations in this region.To address this issue,long-term observations from a two-dimensional video disdrometer(2DVD)were leveraged to refine the radar and satellite-based algorithms for quantifying precipitation in the hinterland of the TP.It was observed that weak precipitation(R<1,mm h-1)accounts for 86%of the total precipitation time,while small raindrops(D<2 mm)comprise 99%of the total raindrop count.Furthermore,the average spectral width of the DSD increases with increasing rain rate.The DSD characteristics of convective and stratiform precipitation were discussed across five different rain rates,revealing that convective precipitation in Yangbajain(YBJ)exhibits characteristics similar to maritime-like precipitation.The constrained relationships between the slopeΛand shapeμ,D_(m)and N_(w)of gamma DSDs were derived.Additionally,we established a correlation between the equivalent diameter and drop axis ratio and found that raindrops on the TP attain a nearly spherical shape.Consequently,the application of the rainfall retrieval algorithms of the dual-frequency precipitation radar in the TP is improved based on the statistical results of the DSD.展开更多
Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s positio...Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.展开更多
Long period variable(LPV)stars are very promising distance indicators in the infrared bands.We selected asymptotic giant branch(AGB)stars in the Large and Small Magellanic Cloud(LMC and SMC)from the Gaia Data Release ...Long period variable(LPV)stars are very promising distance indicators in the infrared bands.We selected asymptotic giant branch(AGB)stars in the Large and Small Magellanic Cloud(LMC and SMC)from the Gaia Data Release 3 LPV catalog,and classified them into oxygen-rich(O-rich)and carbon-rich(C-rich)AGB stars.Using the Wide-field Infrared Survey Explorer database,we determined the W1-and W2-band period-luminosity relations(PLRs)for each pulsation-mode sequence of AGB stars.The dispersion of the PLRs of O-rich AGB stars in sequences C'and C is relatively small,around 0.14 mag.The PLRs of LMC and SMC are consistent in each sequence.In the W2 band,the PLR of large-amplitude C-rich AGB stars is steeper than that of small-amplitude C-rich AGB stars,due to their more circumstellar dust.By two methods,we find that some PLR sequences of O-rich AGB stars in the LMC are dependent on metallicity.The coefficients of the metallicity effect areβ=-0.533±0.213 mag dex~1andβ=-0.767±0.158 mag dex~1for sequence C in W1 and W2 bands,respectively.The significance of the metallicity effect in W1 band for the four sequences is 2.2-3.5σ.Both of these imply that distance measurements using O-rich Mira may need to take the metallicity effect into account.展开更多
Detecting primordial fluctuations from the cosmic dark ages requires extremely large low-frequency radio telescope arrays deployed on the far side of the Moon.The antenna of such an array must be lightweight,easily st...Detecting primordial fluctuations from the cosmic dark ages requires extremely large low-frequency radio telescope arrays deployed on the far side of the Moon.The antenna of such an array must be lightweight,easily storable and transportable,deployable on a large scale,durable,and capable of good electrical performance.A membrane antenna is an excellent candidate to meet these criteria.We study the design of a low-frequency membrane antenna for a lunar-based low-frequency(<30 MHz)radio telescope constructed from polyimide film widely used in aerospace applications,owing to its excellent dielectric properties and high stability as a substrate material.We first design and optimize an antenna in free space through dipole deformation and coupling principles,then simulate an antenna on the lunar surface with a simple lunar soil model,yielding an efficiency greater than 90%in the range of 12-19 MHz and greater than 10%in the range of 5-35 MHz.The antenna inherits the omni-directional radiation pattern of a simple dipole antenna in the 5-30 MHz frequency band,giving a large field of view and allowing detection of the 21 cm global signal when used alone.A demonstration prototype is constructed,and its measured electrical property is found to be consistent with simulated results using|S11|measurements.This membrane antenna can potentially fulfill the requirements of a lunar low-frequency array,establishing a solid technical foundation for future large-scale arrays for exploring the cosmic dark ages.展开更多
Correction to:Radiation Detection Technology and Methods(2024)8:1-1105.https://doi.org/10.1007/s41605-024-00463-y.In this article all authors name was missing in the springer link.It has been corrected.The original ar...Correction to:Radiation Detection Technology and Methods(2024)8:1-1105.https://doi.org/10.1007/s41605-024-00463-y.In this article all authors name was missing in the springer link.It has been corrected.The original article has been corrected.展开更多
The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 3...The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.展开更多
The High Altitude Detection of Astronomical Radiation(HADAR)experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique.It focuses the Cherenkov light emitted by extensi...The High Altitude Detection of Astronomical Radiation(HADAR)experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique.It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energyγ-rays and cosmic rays.With the advantages of a large field-of-view(FOV)and low energy threshold,the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources.This study presents the prospects of using the HADAR experiment for the sky survey of TeVγ-ray sources from TeVCat and provids a one-year survey of statistical significance.Results from the simulation show that a total of 23 galactic point sources,including five supernova remnant sources and superbubbles,four pulsar wind nebula sources,and 14 unidentified sources,were detected in the HADAR FOV with a significance greater than 5 standard deviations(σ).The statistical significance for the Crab Nebula during one year of operation reached 346.0σand the one-year integral sensitivity of HADAR above 1 TeV was~1.3%–2.4%of the flux from the Crab Nebula.展开更多
Purpose Theγ-ray astronomy at 100 TeV is important to unravel the puzzles related to the origin and acceleration of the Galactic cosmic rays up to PeV energy.The YangBaJing Hybrid Array(YBJ-HA),about 2%the scale of L...Purpose Theγ-ray astronomy at 100 TeV is important to unravel the puzzles related to the origin and acceleration of the Galactic cosmic rays up to PeV energy.The YangBaJing Hybrid Array(YBJ-HA),about 2%the scale of LHAASO-KM2A,is such a kind of detection instrument capable of detecting 100 TeVγ-rays.And the muon detection efficiency stability of the MD array in YBJ-HA is crucial for high qualityγ-ray observation.To measure and monitor the muon detection efficiency,we develop a method in this work.Methods We develop a muon bundle method to measure and monitor the efficiency of each muon detector.In this method,muon detection efficiency of the target MD unit is calculated based on the surrounding MD units and the MC simulation.Results The average actual muon detection efficiency of the 16 MD units is up to 83.4%during 4 years’observation.Conclusions The muon detection efficiency of each MD unit is found to be stable during 4 years’operation.In the future,a similar method may be applicable to the muon detection efficiency study for LHAASO.展开更多
基金supported by the grant 2023FY101100 of the Ministry of Science and Technology of China(MOST)the key project of the National Natural Science Foundation of China(NSFC,grant No.12233009)the support from the National Natural Science Foundation of China(NSFC,grant Nos.12273064,42222408,12322306,and 12373093).
文摘This paper statistically analyzes the seeing data at the Lenghu site Platform C from 2018 to 2024,during which extensive construction modified the original landscape.The study focuses on the impacts of meteorological factors and building obstructions.The results reveal a progressive degradation in seeing as the monitoring setup passively changed:the median values were 0."76(the original location),0."83 during the Terrace,and 0."99 at the new Dome(temporarily considered the permanent monitoring location).Once the instruments are fully deployed,wind speed and wind direction critically affect seeing quality,with optimal conditions occurring when the wind speed is 2–6 m s^(−1) and the wind direction is between 180°and 270°.However,in 2023 and 2024,the wind speeds decreased,and the prevailing wind direction shifted from southwest to northwest,correlating with poorer seeing.Computational Fluid Dynamics simulations reveal that the construction of the Wide Field Survey Telescope altered the local wind field,increasing turbulence around the Dome,especially when the winds blow from 225°to 255°.In contrast,Platform A,located in a higher and more open area,consistently maintained better seeing,particularly after midnight,likely due to fewer obstructions and lower nocturnal heat release.
基金the National Natural Science Foundation of China(82171198,U20A20354)the Sci-Tech Innovation 2030 Agenda of China(2022ZD0211603).
文摘Alzheimer's disease(AD)is a common cause of dementia,characterised by cerebral amyloid-βdeposition,pathological tau and neurodegeneration.The prodromal stage of AD(pAD)refers to patients with mild cognitive impairment(MCl)and evidence of AD's pathology.At this stage,disease-modifying interventions should be used to prevent the progression to dementia.Given the inherent heterogeneity of MCl,more specific biomarkers are needed to elucidate the underlying AD's pathology.Although the uses of cerebrospinal fluid and positron emission tomography are widely accepted methods for detecting AD's pathology,their clinical applications are limited by their high costs and invasiveness,particularly in low-income areas in China.Therefore,to improve the early detection of Alzheimer's disease(AD)pathology through cost-effective screening methods,a panel of 45neurologists,psychiatrists andgerontologistswas invited to establish a formal consensus on the screening of pAD in China.The supportive evidence and grades of recommendations are based on a systematic literature review andfocus group discussion.National meetings were held to allow participants to review,vote and provide their expert opinions to reach a consensus.A majority(two-thirds)decision was used for questions for which consensus could not be reached.Recommended screening methods are presented in this publication,including neuropsychological assessment,peripheral biomarkers and brain imaging.In addition,a general workflow for Screening pAD in China is established,which will help clinicians identify individuals at high risk and determine therapeutic targets.
基金funded by the second Tibetan Plateau Scientific Expe-dition and Research Program(2019QZKK0604).
文摘Raindrop size distribution(DSD)plays a crucial role in enhancing the accuracy of radar quantitative precipitation estimates in the Tibetan Plateau(TP).However,there is a notable scarcity of long-term,high-resolution observations in this region.To address this issue,long-term observations from a two-dimensional video disdrometer(2DVD)were leveraged to refine the radar and satellite-based algorithms for quantifying precipitation in the hinterland of the TP.It was observed that weak precipitation(R<1,mm h-1)accounts for 86%of the total precipitation time,while small raindrops(D<2 mm)comprise 99%of the total raindrop count.Furthermore,the average spectral width of the DSD increases with increasing rain rate.The DSD characteristics of convective and stratiform precipitation were discussed across five different rain rates,revealing that convective precipitation in Yangbajain(YBJ)exhibits characteristics similar to maritime-like precipitation.The constrained relationships between the slopeΛand shapeμ,D_(m)and N_(w)of gamma DSDs were derived.Additionally,we established a correlation between the equivalent diameter and drop axis ratio and found that raindrops on the TP attain a nearly spherical shape.Consequently,the application of the rainfall retrieval algorithms of the dual-frequency precipitation radar in the TP is improved based on the statistical results of the DSD.
基金supported by the National Natural Science Foundation of China(12041303)the National SKA Program of China(2020SKA0120200)+2 种基金the CAS Project for Young Scientists in Basic Research YSBR-063the National Natural Science Foundation of China(NSFC grant Nos.12203070 and Nos.12203072)the CAS-MPG LEGACY project。
文摘Timing newly discovered pulsars requires gradually building up a timing model that connects observations taken days to months apart.This sometimes can be challenging when our initial knowledge of the pulsar’s position is arcminutes off from its true position.Such a position error leads to significant arrival time shifts as a result of the Earth’s orbital motion.Traditional down-hill fitting timing algorithms become ineffective when our model predicts the wrong pulse rotations for our next observation.For some pulsars whose model prediction is not too far off,the correct rotation number could be found by trial-and-error methods.For the remaining challenging pulsars,a more generalized method is called for.This paper proposes a GPU-based algorithm that could exhaustively search a large area of trail positions for probable timing solutions.This could help find phase-connected timing solutions for new pulsars using brute force.
基金supported by the National Natural Science Foundation of China(NSFC,Grant Nos.12173047,12322306,12003046,12233009,and 12133002)support from the Youth Innovation Promotion Association of the Chinese Academy of Sciences(no.2022055 and 2023065)support from the National Key Research and Development Program of China,grants 2022YFF0503404 and 2019YFA0405504。
文摘Long period variable(LPV)stars are very promising distance indicators in the infrared bands.We selected asymptotic giant branch(AGB)stars in the Large and Small Magellanic Cloud(LMC and SMC)from the Gaia Data Release 3 LPV catalog,and classified them into oxygen-rich(O-rich)and carbon-rich(C-rich)AGB stars.Using the Wide-field Infrared Survey Explorer database,we determined the W1-and W2-band period-luminosity relations(PLRs)for each pulsation-mode sequence of AGB stars.The dispersion of the PLRs of O-rich AGB stars in sequences C'and C is relatively small,around 0.14 mag.The PLRs of LMC and SMC are consistent in each sequence.In the W2 band,the PLR of large-amplitude C-rich AGB stars is steeper than that of small-amplitude C-rich AGB stars,due to their more circumstellar dust.By two methods,we find that some PLR sequences of O-rich AGB stars in the LMC are dependent on metallicity.The coefficients of the metallicity effect areβ=-0.533±0.213 mag dex~1andβ=-0.767±0.158 mag dex~1for sequence C in W1 and W2 bands,respectively.The significance of the metallicity effect in W1 band for the four sequences is 2.2-3.5σ.Both of these imply that distance measurements using O-rich Mira may need to take the metallicity effect into account.
基金We acknowledge the support of the National SKA program of China(2022SKA0110100,2022SKA0110101)the Natural Science Foundation of China(12273070,12203061,1236114814,12303004).
文摘Detecting primordial fluctuations from the cosmic dark ages requires extremely large low-frequency radio telescope arrays deployed on the far side of the Moon.The antenna of such an array must be lightweight,easily storable and transportable,deployable on a large scale,durable,and capable of good electrical performance.A membrane antenna is an excellent candidate to meet these criteria.We study the design of a low-frequency membrane antenna for a lunar-based low-frequency(<30 MHz)radio telescope constructed from polyimide film widely used in aerospace applications,owing to its excellent dielectric properties and high stability as a substrate material.We first design and optimize an antenna in free space through dipole deformation and coupling principles,then simulate an antenna on the lunar surface with a simple lunar soil model,yielding an efficiency greater than 90%in the range of 12-19 MHz and greater than 10%in the range of 5-35 MHz.The antenna inherits the omni-directional radiation pattern of a simple dipole antenna in the 5-30 MHz frequency band,giving a large field of view and allowing detection of the 21 cm global signal when used alone.A demonstration prototype is constructed,and its measured electrical property is found to be consistent with simulated results using|S11|measurements.This membrane antenna can potentially fulfill the requirements of a lunar low-frequency array,establishing a solid technical foundation for future large-scale arrays for exploring the cosmic dark ages.
文摘Correction to:Radiation Detection Technology and Methods(2024)8:1-1105.https://doi.org/10.1007/s41605-024-00463-y.In this article all authors name was missing in the springer link.It has been corrected.The original article has been corrected.
基金support from diverse funding sources,including the National Key Program for S&T Research and Development of the Ministry of Science and Technology(MOST),Yifang Wang's Science Studio of the Ten Thousand Talents Project,the CAS Key Foreign Cooperation Grant,the National Natural Science Foundation of China(NSFC)Beijing Municipal Science&Technology Commission,the CAS Focused Science Grant,the IHEP Innovation Grant,the CAS Lead Special Training Programthe CAS Center for Excellence in Particle Physics,the CAS International Partnership Program,and the CAS/SAFEA International Partnership Program for Creative Research Teams.
文摘The Circular Electron Positron Collider(CEPC)is a large scientific project initiated and hosted by China,fostered through extensive collaboration with international partners.The complex comprises four accelerators:a 30 GeV Linac,a 1.1 GeV Damping Ring,a Booster capable of achieving energies up to 180 GeV,and a Collider operating at varying energy modes(Z,W,H,and tt).The Linac and Damping Ring are situated on the surface,while the subterranean Booster and Collider are housed in a 100 km circumference underground tunnel,strategically accommodating future expansion with provisions for a potential Super Proton Proton Collider(SPPC).The CEPC primarily serves as a Higgs factory.In its baseline design with synchrotron radiation(SR)power of 30 MW per beam,it can achieve a luminosity of 5×10^(34)cm^(-2)s^(-1)per interaction point(IP),resulting in an integrated luminosity of 13 ab^(-1)for two IPs over a decade,producing 2.6 million Higgs bosons.Increasing the SR power to 50 MW per beam expands the CEPC's capability to generate 4.3 million Higgs bosons,facilitating precise measurements of Higgs coupling at sub-percent levels,exceeding the precision expected from the HL-LHC by an order of magnitude.This Technical Design Report(TDR)follows the Preliminary Conceptual Design Report(Pre-CDR,2015)and the Conceptual Design Report(CDR,2018),comprehensively detailing the machine's layout,performance metrics,physical design and analysis,technical systems design,R&D and prototyping efforts,and associated civil engineering aspects.Additionally,it includes a cost estimate and a preliminary construction timeline,establishing a framework for forthcoming engineering design phase and site selection procedures.Construction is anticipated to begin around 2027-2028,pending government approval,with an estimated duration of 8 years.The commencement of experiments and data collection could potentially be initiated in the mid-2030s.
基金support from the National Natural Science Foundation of China(Nos.11873005,11705103,12005120,12147218,U1831208,U1632104,11875264,and U2031110).
文摘The High Altitude Detection of Astronomical Radiation(HADAR)experiment is a refracting terrestrial telescope array based on the atmospheric Cherenkov imaging technique.It focuses the Cherenkov light emitted by extensive air showers through a large aperture water-lens system for observing very-high-energyγ-rays and cosmic rays.With the advantages of a large field-of-view(FOV)and low energy threshold,the HADAR experiment operates in a large-scale sky scanning mode to observe galactic sources.This study presents the prospects of using the HADAR experiment for the sky survey of TeVγ-ray sources from TeVCat and provids a one-year survey of statistical significance.Results from the simulation show that a total of 23 galactic point sources,including five supernova remnant sources and superbubbles,four pulsar wind nebula sources,and 14 unidentified sources,were detected in the HADAR FOV with a significance greater than 5 standard deviations(σ).The statistical significance for the Crab Nebula during one year of operation reached 346.0σand the one-year integral sensitivity of HADAR above 1 TeV was~1.3%–2.4%of the flux from the Crab Nebula.
基金National Natural Science Foundation of China under Grant:11635011,11761141001,11873005,11775233National Key R&D Program of China:2018YFA0404202.
文摘Purpose Theγ-ray astronomy at 100 TeV is important to unravel the puzzles related to the origin and acceleration of the Galactic cosmic rays up to PeV energy.The YangBaJing Hybrid Array(YBJ-HA),about 2%the scale of LHAASO-KM2A,is such a kind of detection instrument capable of detecting 100 TeVγ-rays.And the muon detection efficiency stability of the MD array in YBJ-HA is crucial for high qualityγ-ray observation.To measure and monitor the muon detection efficiency,we develop a method in this work.Methods We develop a muon bundle method to measure and monitor the efficiency of each muon detector.In this method,muon detection efficiency of the target MD unit is calculated based on the surrounding MD units and the MC simulation.Results The average actual muon detection efficiency of the 16 MD units is up to 83.4%during 4 years’observation.Conclusions The muon detection efficiency of each MD unit is found to be stable during 4 years’operation.In the future,a similar method may be applicable to the muon detection efficiency study for LHAASO.
