This research is the first application of Unmanned Aerial Vehicles(UAVs)equipped with Multi-access Edge Computing(MEC)servers to offshore wind farms,providing a new task offloading solution to address the challenge of...This research is the first application of Unmanned Aerial Vehicles(UAVs)equipped with Multi-access Edge Computing(MEC)servers to offshore wind farms,providing a new task offloading solution to address the challenge of scarce edge servers in offshore wind farms.The proposed strategy is to offload the computational tasks in this scenario to other MEC servers and compute them proportionally,which effectively reduces the computational pressure on local MEC servers when wind turbine data are abnormal.Finally,the task offloading problem is modeled as a multi-intelligent deep reinforcement learning problem,and a task offloading model based on MultiAgent Deep Reinforcement Learning(MADRL)is established.The Adaptive Genetic Algorithm(AGA)is used to explore the action space of the Deep Deterministic Policy Gradient(DDPG),which effectively solves the problem of slow convergence of the DDPG algorithm in the high-dimensional action space.The simulation results show that the proposed algorithm,AGA-DDPG,saves approximately 61.8%,55%,21%,and 33%of the overall overhead compared to local MEC,random offloading,TD3,and DDPG,respectively.The proposed strategy is potentially important for improving real-time monitoring,big data analysis,and predictive maintenance of offshore wind farm operation and maintenance systems.展开更多
The International GNSS Service(IGS) final products(ephemeris and clocks-correction) have made the GNSS an indispensable low-cost tool for scientific research, for example sub-daily atmospheric water vapor monitoring. ...The International GNSS Service(IGS) final products(ephemeris and clocks-correction) have made the GNSS an indispensable low-cost tool for scientific research, for example sub-daily atmospheric water vapor monitoring. In this study, we investigate if there is a systematic difference coming from the choice between the Vienna Mapping Function 1(VMF1) and the Global Mapping Function(GMF) for the modeling of Zenith Total Delay(ZTD) estimates, as well as the Integrated Precipitable Water Vapor(IPWV) estimates that are deduced from them. As ZTD estimates cannot be fully separated from coordinate estimates, we also investigated the coordinate repeatability between subsequent measurements.For this purpose, we monitored twelve GNSS stations on a global scale, for each of the three climatic zones(polar, mid-latitudes and tropical), with four stations on each zone. We used an automated processing based on the Bernese GNSS Software Version 5.2 by applying the Precise Point Positioning(PPP)approach, L3 Ionosphere-free linear combination, 7 cutoff elevation angle and 2 h sampling. We noticed an excellent agreement with the ZTD estimates and coordinate repeatability for all the stations w.r.t to CODE(the Center for Orbit Determination in Europe) and USNO(US Naval Observatory) products, except for the Antarctic station(Davis) which shows systematic biases for the GMF related results. As a final step, we investigated the effect of using two mapping functions(VMF1 and GMF) to estimate the IPWV,w.r.t the IPWV estimates provided by the Integrated Global Radiosonde Archive(IGRA). The GPS-derived IPWV estimates are very close to the radiosonde-derived IPWV estimates, except for one station in the tropics(Tahiti).展开更多
Tianwen-1 is China's first independent interplanetary exploration mission,targeting Mars,and includes orbiting,landing,and rover phases.Similar to previous Mars missions,the Tianwen-1 orbiter was designed for pola...Tianwen-1 is China's first independent interplanetary exploration mission,targeting Mars,and includes orbiting,landing,and rover phases.Similar to previous Mars missions,the Tianwen-1 orbiter was designed for polar orbits during the scientific mission period but has an exceptional eccentricity of approximately 0.59.We provide the first independent eight-degree Martian gravity field model in this paper,which was developed exclusively by a team working in China with our independent software as well,based on about two months of radiometric Doppler and range data from only the Tianwen-1 mission.This model is independent from the models created by the groups at NASA Jet Propulsion Laboratory and Goddard Space Flight Center in the United States,as well as the Centre National d'Etudes Spatiales in France.Furthermore,in order to optimize the engineering and scientific benefits,we proposed a number of potential orbits for the extended Tianwen-1 mission.In order to solve a higher-degree independent Mars gravity field model,the viability of modifying the perigee height was investigated,with the priority considerations of fuel savings and implementation hazards being controlled.展开更多
It is significant for identifying mass movement patterns to invert horizontal tectonic stresses at different depths underneath Tibet.In recent years,a large number of achievements focusing on two-dimensional tectonic ...It is significant for identifying mass movement patterns to invert horizontal tectonic stresses at different depths underneath Tibet.In recent years,a large number of achievements focusing on two-dimensional tectonic stresses have been obtained from gravity data.However,three-dimensional tectonic stresses in Tibet are still unknown or debatable.Therefore,in the present study an improved method to multilayer horizontal tectonic stresses using gravity observations is developed.The inverted multilayer horizontal tectonic stresses are in agreement with those from previous studies.In addition,rich tectonic structure and development can be revealed from the inverted multilayer horizontal tectonic stresses:(1)the distribution of horizontal tectonic stresses at various depths shows strong correlation with that of the tectonic elements,where major faults and earthquake epicenters are corresponding with stress highs and the stable basins are consistent with stress lows.(2)the mass movement patterns of whole Tibet present clockwise,and the material movement directions in the west and east are approximately southnorth and east-west,respectively.(3)in eastern Tibet,the eastward materials caused by the south-north extrusion between Indian and Eurasian plates are divided into two parts by the stable Sichuan Block,one flowing nearly southeast and the other moving almost northeast.The inverted multilayer horizontal tectonic stresses may provide direct evidences for mass movement patterns in Tibet.展开更多
It is significant for establishing gravity datum to construct precise gravity solid tidal model,A simple method with relatively low performance is to interpolate tidal parameters from the global gravity solid tide mod...It is significant for establishing gravity datum to construct precise gravity solid tidal model,A simple method with relatively low performance is to interpolate tidal parameters from the global gravity solid tide models.A competitive approach is to determine local gravity solid tidal model by harmonic analysis using long-time serial gravity observations.In this paper a new high-precision gravity solid tidal model for Precision Gravity Measurement Facility is estimated from two co-site gravimeters in the cave laboratory using modern international standard data processing techniques,whose accuracy is evaluated further by comparing with previous publications.The results show that:(1)the determined gravity solid tidal models from two co-site gravimeters are in good agreement with each other,of which the maximum differences for amplitude factors and phase delays don’t exceed 0.01700%and 2.50990°,respectively.(2)the performance of the obtained gravity solid tidal model is 0.00411 for amplitude factors and 0.24120°for phase delays,which is a little better than that of previous publications using superconducting gravity data from Wuhan station.(3)our results and methods are corrective and effective.(4)our model is tiny different from that provided by Wuhan station,which implies that it is necessary to construct a gravity solid tidal model for Precision Gravity Measurement Facility,rather than just adopting existing models at Wuhan station.Our results are helpful in realizing the goal of Precision Gravity Measurement Facility.展开更多
The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radi...The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radio science research topics such as the Mars gravity field model, ephemeris, and radio occultation experiments. At this stage, the need for imaging takes the highest priority, leading to frequent attitude adjustments for the spacecraft, which presents challenges for Precise Orbit Determination (POD). To improve the accuracy of the spacecraft’s orbit, this study analyzes the effects of arc length, the empirical acceleration, and the solar radiation pressure parameters on POD, considering the limited number of radio tracking observations. For one-day arcs, the POD is not able to adequately account for wheel off-loading and a few unknown forces with limited observations, but reasonable fitting is performed for the wheel off-loading occurring during tracking periods or the gap between two tracking periods. When extending the POD arc to three days, the estimated empirical acceleration can be well-fitted and reflects the aggregation feature, but the solar radiation pressure parameter has little impact on POD results. The root mean square of two-way range-rate residuals after POD is about 0.18-0.35 mm/s;the orbital position accuracy of 60% of the arcs is better than 100 m.展开更多
Background and Aims:There is a lack of data supporting the notion that antiviral treatments can beneft children with chronic hepatitis B(CHB)having high viremia and normal or mildly elevated serum alanine aminotransfe...Background and Aims:There is a lack of data supporting the notion that antiviral treatments can beneft children with chronic hepatitis B(CHB)having high viremia and normal or mildly elevated serum alanine aminotransferase(ALT)levels.We aimed t analyze the efficacy of antiviral treatments in children with CHB and explore the factors associated with functional cure.Methods:Forty-eight children with CHB having high viremia and normal or mildly elevated serum ALT levels were screened in this real-world study.Thirty-two children received either interferon-alpha(IFN-α)monother-apy,IFN-a therapy with a nucleoside analog(NA)add-on,or IFN-α and NA combination therapy.The 16 children in the control group did not receive antiviral treatment.All 48 chil-dren were available for follow-up assessments for the entire 36-month study period.We identified a functional cure with respect to hepatitis B virus(HBV)DNA loss,loss/seroconver-sion of circulating hepatitis B e antigen(HBeAg),and loss of hepatitis B surface antigen(HBsAg)with or without serocon-version.Cox regression analysis was employed to evaluate the factors that may have influenced the functional cure.Re-sults:After 36 months,the cumulative functional cure rate was 56.25%(18/32)in the treated group and 0%(0/16)in the control group(p<0.001).In the treated group,the serum HBV DNA levels declined rapidly at the end of a 6-month visit and the cured children achieved a loss rate of 100%(18/18)within 16 months of beginning treatment,compared with 64.29%(9/14)of the uncured children(p<0.001).The rates of HBeAg seroconversion were significantly higher among the cured children than among the uncured children(p<0.001).All 16 children in the control group maintained high levels of serum HBV DNA and were positive for both serum HBeAg and HBsAg during the entire 36 months of the study period.Func tional cure was associated with younger ages(1-6 vs.7-14 years,p=0.013),CD8^(+)T lymphocyte counts(p=0.013),and B lymphocyte counts(p=0.003).No serious adverse events were observed.Conclusions:Antiviral treatment achieved a functional cure of CHB in a high proportion of children having high-level viremia and normal or mildly elevated ALT levels.Younger age and high peripheral lymphocyte counts were as sociated with this functional cure.展开更多
Mapping and monitoring the distribution of croplands and crop types support policymakers and international organizations by reducing the risks to food security,notably from climate change and,for that purpose,remote s...Mapping and monitoring the distribution of croplands and crop types support policymakers and international organizations by reducing the risks to food security,notably from climate change and,for that purpose,remote sensing is routinely used.However,identifying specific crop types,cropland,and cropping patterns using space-based observations is challenging because different crop types and cropping patterns have similarity spectral signatures.This study applied a methodology to identify cropland and specific crop types,including tobacco,wheat,barley,and gram,as well as the following cropping patterns:wheat-tobacco,wheat-gram,wheat-barley,and wheat-maize,which are common in Gujranwala District,Pakistan,the study region.The methodology consists of combining optical remote sensing images from Sentinel-2 and Landsat-8 with Machine Learning(ML)methods,namely a Decision Tree Classifier(DTC)and a Random Forest(RF)algorithm.The best time-periods for differentiating cropland from other land cover types were identified,and then Sentinel-2 and Landsat 8 NDVI-based time-series were linked to phenological parameters to determine the different crop types and cropping patterns over the study region using their temporal indices and ML algorithms.The methodology was subsequently evaluated using Landsat images,crop statistical data for 2020 and 2021,and field data on cropping patterns.The results highlight the high level of accuracy of the methodological approach presented using Sentinel-2 and Landsat-8 images,together with ML techniques,for mapping not only the distribution of cropland,but also crop types and cropping patterns when validated at the county level.These results reveal that this methodology has benefits for monitoring and evaluating food security in Pakistan,adding to the evidence base of other studies on the use of remote sensing to identify crop types and cropping patterns in other countries.展开更多
This study focuses on the illumination and temperature at China’s next lunar candidate landing site Shackleton crater.We used the NASA’s SPICE system to evaluate the terrain obscuration effect on real-time illuminat...This study focuses on the illumination and temperature at China’s next lunar candidate landing site Shackleton crater.We used the NASA’s SPICE system to evaluate the terrain obscuration effect on real-time illumination;the resulting illumination map resembles previous studies,validating the methodologies used in our study.In addition,we estimated an accumulated illumination map for the period of likely rover movement.The map indicates the illuminated inner wall of the Shackleton crater is close to 27%of the whole,meaning that the rover will likely receive solar radiation during its movement.Using the real-time illumination and the distributed 1-D thermal diffusion model,we continuously evaluated the regolith temperature for more than 20 years to stabilize the temperature,and selected the temperature of the end time as the initial value used in a thermal study set for July 20,2023 and May 8,2027.Our results indicate the temperature in the permanent shadow region remains nearly constant,thus validating the stability of our estimated initial temperature.Our results also indicate that the surface temperature is more sensitive to transient illumination,but the subsurface temperature is more likely to be associated with the accumulated illumination.This difference indirectly implies that the conductivity of the lunar regolith is inefficient.The locations receiving more solar radiation show a temperature larger than the threshold(~112 K)of ice stability.The permanently shadowed regions can be as cold as 25 K,and such extreme coldness is a hazard to the rover.There are suitable temperature locations which have a warm surface but cold subsurface to preserve water ice.To further ensure normal rover movement,we provided a map of suitable temperature sites and found that these locations exist not only in the Shackleton crater’s inner wall,but also outside the crater.We suggested four trade-off sampling sites with suitable temperatures and gradual slopes.展开更多
Explorations for the interior structure of the Moon mainly involve three technologies: the early gravitational observations via circumlunar satellites, the moonquake observations during the Apollo period, and the rece...Explorations for the interior structure of the Moon mainly involve three technologies: the early gravitational observations via circumlunar satellites, the moonquake observations during the Apollo period, and the recent high-resolution remote sensing observations. Based on these technologies, we divided the development of the moon's interior structure into three stages. The first stage is the discovery of high-density anomalous masses(mascons) on the lunar surface with the low-order gravitational field models, which were obtained by observing perturbations of the early lunar orbital satellites. The second stage is the preliminary understanding of the layer structure with the help of moonquake observations during the Apollo period. The third stage is the deep understanding of the structure of the lunar crust, mantle, and core, with the use of high-resolution remote sensing data and the reassessment of moonquake data from the Apollo's mission. This paper gave detailed introduction and comments on different observation technologies, gathered data, and data processing techniques used at the three stages. In addition, this paper analyzed the current issues in the researches on the Moon's internal structure and discussed the prospects for future explorations.展开更多
This paper investigates the homing control problem of a flexible aerial delivery system with external wind,at-mospheric turbulence,and aerodynamic uncertainties.An accurate homing control strategy is presented,consist...This paper investigates the homing control problem of a flexible aerial delivery system with external wind,at-mospheric turbulence,and aerodynamic uncertainties.An accurate homing control strategy is presented,consisting of a trajectory generation algorithm and a lateral tracking controller.A high-altitude trajectory generation is de-veloped with system characteristics explicitly considered to generate the desired trajectory for the aerial delivery control system design.It significantly compensates for the altitude deviation of the existing multiphase theory based trajectory generation methodologies.A novel adaptive vector field control law is then designed to accomplish the lateral tracking maneuvers.The key feature of the proposed method is that the complete lateral closed-loop control,including position and heading angle loops,is achieved in the presence of disturbances and dynamic uncertainties.The homing control with high landing accuracy is therefore achieved.Simulation and hardware-in-loop testing results are finally presented to validate the proposed method’s effectiveness compared to a conventional homing control scheme.展开更多
Volcanism is the most important endogenic geological process of the Moon,which is closely related to its internal structure and thermal history.Lunar volcanism is one of the most important topics for lunar science and...Volcanism is the most important endogenic geological process of the Moon,which is closely related to its internal structure and thermal history.Lunar volcanism is one of the most important topics for lunar science and explorations.Recent lunar orbital observations,in situ explorations,and sample return missions have returned a new generation of high-resolution datasets,which greatly enriched our knowledge of lunar volcanism.Here,we summarize recent advances in the duration and spatial distribution of lunar mare volcanism,as well as origin of volcanic landforms such as lava flows,sinuous rilles,lava tubes,domes,and cones.We proposed several outstanding problems in the study of temporal and spatial span of lunar volcanism,the formation mechanism of the varied volcanic landforms,and their relation with deep structures.To solve these problems,more in situ explorations and sample return missions from various volcanic units are needed.展开更多
基金supported in part by the National Natural Science Foundation of China under grant 61861007the Guizhou Province Science and Technology Planning Project ZK[2021]303+2 种基金the Guizhou Province Science Technology Support Plan under grant[2022]264,[2023]096,[2023]409 and[2023]412the Science Technology Project of POWERCHINA Guizhou Engineering Co.,Ltd.(DJ-ZDXM-2022-44)the Project of POWERCHINA Guiyang Engineering Corporation Limited(YJ2022-12).
文摘This research is the first application of Unmanned Aerial Vehicles(UAVs)equipped with Multi-access Edge Computing(MEC)servers to offshore wind farms,providing a new task offloading solution to address the challenge of scarce edge servers in offshore wind farms.The proposed strategy is to offload the computational tasks in this scenario to other MEC servers and compute them proportionally,which effectively reduces the computational pressure on local MEC servers when wind turbine data are abnormal.Finally,the task offloading problem is modeled as a multi-intelligent deep reinforcement learning problem,and a task offloading model based on MultiAgent Deep Reinforcement Learning(MADRL)is established.The Adaptive Genetic Algorithm(AGA)is used to explore the action space of the Deep Deterministic Policy Gradient(DDPG),which effectively solves the problem of slow convergence of the DDPG algorithm in the high-dimensional action space.The simulation results show that the proposed algorithm,AGA-DDPG,saves approximately 61.8%,55%,21%,and 33%of the overall overhead compared to local MEC,random offloading,TD3,and DDPG,respectively.The proposed strategy is potentially important for improving real-time monitoring,big data analysis,and predictive maintenance of offshore wind farm operation and maintenance systems.
基金the innovation carrier project by Zhejiang provincial science and Technology Department (2017F10008)the French Space Agency (CNES) for their funding, through a DAR grant to the Geodesy Observatory of Tahiti
文摘The International GNSS Service(IGS) final products(ephemeris and clocks-correction) have made the GNSS an indispensable low-cost tool for scientific research, for example sub-daily atmospheric water vapor monitoring. In this study, we investigate if there is a systematic difference coming from the choice between the Vienna Mapping Function 1(VMF1) and the Global Mapping Function(GMF) for the modeling of Zenith Total Delay(ZTD) estimates, as well as the Integrated Precipitable Water Vapor(IPWV) estimates that are deduced from them. As ZTD estimates cannot be fully separated from coordinate estimates, we also investigated the coordinate repeatability between subsequent measurements.For this purpose, we monitored twelve GNSS stations on a global scale, for each of the three climatic zones(polar, mid-latitudes and tropical), with four stations on each zone. We used an automated processing based on the Bernese GNSS Software Version 5.2 by applying the Precise Point Positioning(PPP)approach, L3 Ionosphere-free linear combination, 7 cutoff elevation angle and 2 h sampling. We noticed an excellent agreement with the ZTD estimates and coordinate repeatability for all the stations w.r.t to CODE(the Center for Orbit Determination in Europe) and USNO(US Naval Observatory) products, except for the Antarctic station(Davis) which shows systematic biases for the GMF related results. As a final step, we investigated the effect of using two mapping functions(VMF1 and GMF) to estimate the IPWV,w.r.t the IPWV estimates provided by the Integrated Global Radiosonde Archive(IGRA). The GPS-derived IPWV estimates are very close to the radiosonde-derived IPWV estimates, except for one station in the tropics(Tahiti).
基金supported by the National Natural Science Foundation of China(NSFC)under Nos.12203002 and 42241116Key Laboratory of Geospace Environment and Geodesy,Ministry of Education,Wuhan University under No.21-01-01funded by a DAR grant in planetology from the French Space Agency(CNES)。
文摘Tianwen-1 is China's first independent interplanetary exploration mission,targeting Mars,and includes orbiting,landing,and rover phases.Similar to previous Mars missions,the Tianwen-1 orbiter was designed for polar orbits during the scientific mission period but has an exceptional eccentricity of approximately 0.59.We provide the first independent eight-degree Martian gravity field model in this paper,which was developed exclusively by a team working in China with our independent software as well,based on about two months of radiometric Doppler and range data from only the Tianwen-1 mission.This model is independent from the models created by the groups at NASA Jet Propulsion Laboratory and Goddard Space Flight Center in the United States,as well as the Centre National d'Etudes Spatiales in France.Furthermore,in order to optimize the engineering and scientific benefits,we proposed a number of potential orbits for the extended Tianwen-1 mission.In order to solve a higher-degree independent Mars gravity field model,the viability of modifying the perigee height was investigated,with the priority considerations of fuel savings and implementation hazards being controlled.
基金supported by the National Natural Science Foundation of China(Grant No.41974014)the Open Fund of State Laboratory of Information Engineering in Surveying,Mapping and Remote Sensing,Wuhan University(Grant No.19P01)+1 种基金the Foundation of Young Creative Talents in Higher Education of Guangdong Province(Grant No.2019KQNCX009)the Open Fund of Guangxi Key Laboratory of Spatial Information and Geomatics(Grant No.19-050-11-03)
文摘It is significant for identifying mass movement patterns to invert horizontal tectonic stresses at different depths underneath Tibet.In recent years,a large number of achievements focusing on two-dimensional tectonic stresses have been obtained from gravity data.However,three-dimensional tectonic stresses in Tibet are still unknown or debatable.Therefore,in the present study an improved method to multilayer horizontal tectonic stresses using gravity observations is developed.The inverted multilayer horizontal tectonic stresses are in agreement with those from previous studies.In addition,rich tectonic structure and development can be revealed from the inverted multilayer horizontal tectonic stresses:(1)the distribution of horizontal tectonic stresses at various depths shows strong correlation with that of the tectonic elements,where major faults and earthquake epicenters are corresponding with stress highs and the stable basins are consistent with stress lows.(2)the mass movement patterns of whole Tibet present clockwise,and the material movement directions in the west and east are approximately southnorth and east-west,respectively.(3)in eastern Tibet,the eastward materials caused by the south-north extrusion between Indian and Eurasian plates are divided into two parts by the stable Sichuan Block,one flowing nearly southeast and the other moving almost northeast.The inverted multilayer horizontal tectonic stresses may provide direct evidences for mass movement patterns in Tibet.
基金supported by the National Natural Science Foundation of China(Grant No.41974014)the Open Fund of State Laboratory of Information Engineering in Surveying,Mapping and Remote Sensing,Wuhan University(Grant No.19P01)
文摘It is significant for establishing gravity datum to construct precise gravity solid tidal model,A simple method with relatively low performance is to interpolate tidal parameters from the global gravity solid tide models.A competitive approach is to determine local gravity solid tidal model by harmonic analysis using long-time serial gravity observations.In this paper a new high-precision gravity solid tidal model for Precision Gravity Measurement Facility is estimated from two co-site gravimeters in the cave laboratory using modern international standard data processing techniques,whose accuracy is evaluated further by comparing with previous publications.The results show that:(1)the determined gravity solid tidal models from two co-site gravimeters are in good agreement with each other,of which the maximum differences for amplitude factors and phase delays don’t exceed 0.01700%and 2.50990°,respectively.(2)the performance of the obtained gravity solid tidal model is 0.00411 for amplitude factors and 0.24120°for phase delays,which is a little better than that of previous publications using superconducting gravity data from Wuhan station.(3)our results and methods are corrective and effective.(4)our model is tiny different from that provided by Wuhan station,which implies that it is necessary to construct a gravity solid tidal model for Precision Gravity Measurement Facility,rather than just adopting existing models at Wuhan station.Our results are helpful in realizing the goal of Precision Gravity Measurement Facility.
基金supported by the National Natural Science Foundation of China(Grant Nos.12203002 and 42241116)National Key R&D Program of China(No.2022YFF0503202).
文摘The mapping phase is a key stage of the Tianwen-1 orbiter. It has the longest exploration time and gathers abundant radio tracking data via the Chinese deep space network. Thus, it also provides opportunities for radio science research topics such as the Mars gravity field model, ephemeris, and radio occultation experiments. At this stage, the need for imaging takes the highest priority, leading to frequent attitude adjustments for the spacecraft, which presents challenges for Precise Orbit Determination (POD). To improve the accuracy of the spacecraft’s orbit, this study analyzes the effects of arc length, the empirical acceleration, and the solar radiation pressure parameters on POD, considering the limited number of radio tracking observations. For one-day arcs, the POD is not able to adequately account for wheel off-loading and a few unknown forces with limited observations, but reasonable fitting is performed for the wheel off-loading occurring during tracking periods or the gap between two tracking periods. When extending the POD arc to three days, the estimated empirical acceleration can be well-fitted and reflects the aggregation feature, but the solar radiation pressure parameter has little impact on POD results. The root mean square of two-way range-rate residuals after POD is about 0.18-0.35 mm/s;the orbital position accuracy of 60% of the arcs is better than 100 m.
基金supported by Innovation Groups of the National Natural Science Foundation of China(81721002)the China National Natural Science Foundation(82130019)the National Key R&D Program of China(2019YFC0840704).
文摘Background and Aims:There is a lack of data supporting the notion that antiviral treatments can beneft children with chronic hepatitis B(CHB)having high viremia and normal or mildly elevated serum alanine aminotransferase(ALT)levels.We aimed t analyze the efficacy of antiviral treatments in children with CHB and explore the factors associated with functional cure.Methods:Forty-eight children with CHB having high viremia and normal or mildly elevated serum ALT levels were screened in this real-world study.Thirty-two children received either interferon-alpha(IFN-α)monother-apy,IFN-a therapy with a nucleoside analog(NA)add-on,or IFN-α and NA combination therapy.The 16 children in the control group did not receive antiviral treatment.All 48 chil-dren were available for follow-up assessments for the entire 36-month study period.We identified a functional cure with respect to hepatitis B virus(HBV)DNA loss,loss/seroconver-sion of circulating hepatitis B e antigen(HBeAg),and loss of hepatitis B surface antigen(HBsAg)with or without serocon-version.Cox regression analysis was employed to evaluate the factors that may have influenced the functional cure.Re-sults:After 36 months,the cumulative functional cure rate was 56.25%(18/32)in the treated group and 0%(0/16)in the control group(p<0.001).In the treated group,the serum HBV DNA levels declined rapidly at the end of a 6-month visit and the cured children achieved a loss rate of 100%(18/18)within 16 months of beginning treatment,compared with 64.29%(9/14)of the uncured children(p<0.001).The rates of HBeAg seroconversion were significantly higher among the cured children than among the uncured children(p<0.001).All 16 children in the control group maintained high levels of serum HBV DNA and were positive for both serum HBeAg and HBsAg during the entire 36 months of the study period.Func tional cure was associated with younger ages(1-6 vs.7-14 years,p=0.013),CD8^(+)T lymphocyte counts(p=0.013),and B lymphocyte counts(p=0.003).No serious adverse events were observed.Conclusions:Antiviral treatment achieved a functional cure of CHB in a high proportion of children having high-level viremia and normal or mildly elevated ALT levels.Younger age and high peripheral lymphocyte counts were as sociated with this functional cure.
文摘Mapping and monitoring the distribution of croplands and crop types support policymakers and international organizations by reducing the risks to food security,notably from climate change and,for that purpose,remote sensing is routinely used.However,identifying specific crop types,cropland,and cropping patterns using space-based observations is challenging because different crop types and cropping patterns have similarity spectral signatures.This study applied a methodology to identify cropland and specific crop types,including tobacco,wheat,barley,and gram,as well as the following cropping patterns:wheat-tobacco,wheat-gram,wheat-barley,and wheat-maize,which are common in Gujranwala District,Pakistan,the study region.The methodology consists of combining optical remote sensing images from Sentinel-2 and Landsat-8 with Machine Learning(ML)methods,namely a Decision Tree Classifier(DTC)and a Random Forest(RF)algorithm.The best time-periods for differentiating cropland from other land cover types were identified,and then Sentinel-2 and Landsat 8 NDVI-based time-series were linked to phenological parameters to determine the different crop types and cropping patterns over the study region using their temporal indices and ML algorithms.The methodology was subsequently evaluated using Landsat images,crop statistical data for 2020 and 2021,and field data on cropping patterns.The results highlight the high level of accuracy of the methodological approach presented using Sentinel-2 and Landsat-8 images,together with ML techniques,for mapping not only the distribution of cropland,but also crop types and cropping patterns when validated at the county level.These results reveal that this methodology has benefits for monitoring and evaluating food security in Pakistan,adding to the evidence base of other studies on the use of remote sensing to identify crop types and cropping patterns in other countries.
基金funded by the National Natural Science Foundation of China(Grant Nos.41864001 and 42030110)funded by a DAR Grant in Planetology from the France Space Agency(CNES)。
文摘This study focuses on the illumination and temperature at China’s next lunar candidate landing site Shackleton crater.We used the NASA’s SPICE system to evaluate the terrain obscuration effect on real-time illumination;the resulting illumination map resembles previous studies,validating the methodologies used in our study.In addition,we estimated an accumulated illumination map for the period of likely rover movement.The map indicates the illuminated inner wall of the Shackleton crater is close to 27%of the whole,meaning that the rover will likely receive solar radiation during its movement.Using the real-time illumination and the distributed 1-D thermal diffusion model,we continuously evaluated the regolith temperature for more than 20 years to stabilize the temperature,and selected the temperature of the end time as the initial value used in a thermal study set for July 20,2023 and May 8,2027.Our results indicate the temperature in the permanent shadow region remains nearly constant,thus validating the stability of our estimated initial temperature.Our results also indicate that the surface temperature is more sensitive to transient illumination,but the subsurface temperature is more likely to be associated with the accumulated illumination.This difference indirectly implies that the conductivity of the lunar regolith is inefficient.The locations receiving more solar radiation show a temperature larger than the threshold(~112 K)of ice stability.The permanently shadowed regions can be as cold as 25 K,and such extreme coldness is a hazard to the rover.There are suitable temperature locations which have a warm surface but cold subsurface to preserve water ice.To further ensure normal rover movement,we provided a map of suitable temperature sites and found that these locations exist not only in the Shackleton crater’s inner wall,but also outside the crater.We suggested four trade-off sampling sites with suitable temperatures and gradual slopes.
基金supported in part by the National Natural Science Foundation of China (Grant Nos. 41604004, 41374024)the Hubei Province Natural Science Foundation Innovation Group Project (Grant No. 2015CFA011)
文摘Explorations for the interior structure of the Moon mainly involve three technologies: the early gravitational observations via circumlunar satellites, the moonquake observations during the Apollo period, and the recent high-resolution remote sensing observations. Based on these technologies, we divided the development of the moon's interior structure into three stages. The first stage is the discovery of high-density anomalous masses(mascons) on the lunar surface with the low-order gravitational field models, which were obtained by observing perturbations of the early lunar orbital satellites. The second stage is the preliminary understanding of the layer structure with the help of moonquake observations during the Apollo period. The third stage is the deep understanding of the structure of the lunar crust, mantle, and core, with the use of high-resolution remote sensing data and the reassessment of moonquake data from the Apollo's mission. This paper gave detailed introduction and comments on different observation technologies, gathered data, and data processing techniques used at the three stages. In addition, this paper analyzed the current issues in the researches on the Moon's internal structure and discussed the prospects for future explorations.
基金supported by the National Natural Science Foundation of China(No.61873207)the IndustryUniversity-Research Innovation Fund in Ministry of Education of China(No.2021ZYA03006)the Key R&D Plan of Shaanxi Province of China(No.2020SF-376)。
文摘This paper investigates the homing control problem of a flexible aerial delivery system with external wind,at-mospheric turbulence,and aerodynamic uncertainties.An accurate homing control strategy is presented,consisting of a trajectory generation algorithm and a lateral tracking controller.A high-altitude trajectory generation is de-veloped with system characteristics explicitly considered to generate the desired trajectory for the aerial delivery control system design.It significantly compensates for the altitude deviation of the existing multiphase theory based trajectory generation methodologies.A novel adaptive vector field control law is then designed to accomplish the lateral tracking maneuvers.The key feature of the proposed method is that the complete lateral closed-loop control,including position and heading angle loops,is achieved in the presence of disturbances and dynamic uncertainties.The homing control with high landing accuracy is therefore achieved.Simulation and hardware-in-loop testing results are finally presented to validate the proposed method’s effectiveness compared to a conventional homing control scheme.
基金supported by the National Natural Science Foundation of China(42241111,42030108,42241107,12273044,and 41904119)the China Postdoctoral Science Foundation(2021M702999)+7 种基金the Fundamental Research Funds for the Central Universities(CUG2106122 and CUG2106109)the National Key Research and Development Program of China(2022YFF0503100 and 2021YFA0715100)the Pre-research Project on Civil Aerospace Technologies of CNSA(D020101 and D020204)the Key Research Program of the Chinese Academy of Sciences(KGFZD-145-2023-15)the Science and Technology Development Fund,Macao SAR(0049/2020/A1)the Opening Fund of Key Laboratory of Geological Survey and Evaluation of Ministry of Education(GLAB2022ZR09)Young Scholars Program of Shandong University,Weihai(No.202207)the National Natural Science Foundation of China-Academic Divisions of Chinese Academy of Sciences Frontier Inter-disciplinary Research Strategic Research Joint Funding Project(L2224032 and XK2022DXC004).
文摘Volcanism is the most important endogenic geological process of the Moon,which is closely related to its internal structure and thermal history.Lunar volcanism is one of the most important topics for lunar science and explorations.Recent lunar orbital observations,in situ explorations,and sample return missions have returned a new generation of high-resolution datasets,which greatly enriched our knowledge of lunar volcanism.Here,we summarize recent advances in the duration and spatial distribution of lunar mare volcanism,as well as origin of volcanic landforms such as lava flows,sinuous rilles,lava tubes,domes,and cones.We proposed several outstanding problems in the study of temporal and spatial span of lunar volcanism,the formation mechanism of the varied volcanic landforms,and their relation with deep structures.To solve these problems,more in situ explorations and sample return missions from various volcanic units are needed.
