The Chang’e-4 mission obtained spectral data of multiple rock targets on the lunar surface.The Modified Gaussian Model(MGM)is usually applied to the spectral interpretation of powder samples,its applicability and acc...The Chang’e-4 mission obtained spectral data of multiple rock targets on the lunar surface.The Modified Gaussian Model(MGM)is usually applied to the spectral interpretation of powder samples,its applicability and accuracy on the rock targets remain to be further evaluated.The rock slice of lunar meteorite NWA 4734 is used to conduct comprehensive analysis of the petrography,mineralogy and laboratory spectroscopy,which will provide important ground truth for the MGM interpretation of lunar in situ spectra of rock samples.First,a scanning electron microscope(SEM),Energy Dispersive Spectrometer(EDS),and Electron Probe Micro-Analyzer(EPMA)analysis results indicate that:(1)almost all plagioclase in NWA 4734 have been converted to maskelynites,which indicate that the meteorite has undergone severe impact metamorphism;(2)the chemical composition of pyroxene and olivine is significantly heterogeneous,showing a distribution characteristic of magnesium-rich core and iron-rich rim,further indicating that NWA 4734 has undergone multiple crystallization and differentiation.Second,this article focuses on the rock slice of NWA 4734ʼs greyscale image of the Back Scattering Electron(BSE),and obtains the proportion of High-Calcium Pyroxene(HCP)in the total pyroxenes of this sample by calculating the area percentage using the pixel counting method.The result shows that the proportion of HCP is 72%±5.4%,which can be used as a ground truth to evaluate the interpretation applicability and accuracy of MGM.A field spectrometer(ASD)is used to measure the visible and near-infrared reflectance spectra(450-2500 nm)of the rock slice from NWA 4734 in the same area as the BSE image obtained by SEM,and MGM is used to deconvolve the ASD spectra,and the average proportion of HCP is estimated to be 71%±10.1%.The results between the MGM and the pixel counting are comparable within the error range,which demonstrates the applicability of MGM on interpretation of the rock samples on the lunar surface.展开更多
POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard th...POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard the Chinese space laboratory Tiangong-2(TG-2) on 2016 September 15.After being switched on a few days later,tens of gigabytes of raw detection data were produced in-orbit by POLAR and transferred to the ground every day.Before the launch date,a full pipeline and related software were designed and developed for the purpose of quickly pre-processing all the raw data from POLAR,which include both science data and engineering data,then to generate the high level scientific data products that are suitable for later science analysis.This pipeline has been successfully applied for use by the POLAR Science Data Center in the Institute of High Energy Physics(IHEP) after POLAR was launched and switched on.A detailed introduction to the pipeline and some of the core relevant algorithms are presented in this paper.展开更多
Ground-based radio observations below 30 MHz are susceptible to the ionosphere of the Earth and the radio frequency interference.Compared with other space mission concepts,making low frequency observations using an in...Ground-based radio observations below 30 MHz are susceptible to the ionosphere of the Earth and the radio frequency interference.Compared with other space mission concepts,making low frequency observations using an interferometer array on lunar orbit is one of the most feasible ones due to a number of technical and economic advantages.Different from traditional interferometer arrays,the interferometer array on lunar orbit faces some complications such as the three-dimensional distribution of baselines and the changing sky blockage by the Moon.Although the brute-force method based on the linear mapping relationship between the visibilities and the sky temperature can produce satisfactory results in general,there are still large residual errors on account of the loss of the edge information.To obtain the full-sky maps with higher accuracy,in this paper we propose a novel imaging method based on reweighted total variation(RTV)for a lunar orbit interferometer array.Meanwhile,a split Bregman iteration method is introduced to optimize the proposed RTV model so as to decrease the computation time.The simulation results show that,compared with the traditional brute-force method,the RTV regularization method can effectively reduce the reconstruction errors and obtain more accurate sky maps,which proves the effectiveness of the proposed method.展开更多
The double revolving fiber positioning technology is one of the key technologies for the success of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST).The accuracy of fiber positioning will directly...The double revolving fiber positioning technology is one of the key technologies for the success of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST).The accuracy of fiber positioning will directly affect the observation efficiency of LAMOST.To achieve higher fiber positioning accuracy,the original open-loop controlled fiber positioning system urgently needs to be upgraded into a closed-loop control system.The fiber detection is the most important part of the closed-loop controlled fiber positioning system.The back-illuminated detection method is usually used to detect the fiber position by directly detecting the light spot generated at the fiber end in the multi-fiber spectral surveys.In this paper,we introduce a new method to measure the fiber position based on the image of the front-illuminated LAMOST focal plane.The front-illuminated image does not require lighting devices inside the spectrograph,and it could reduce the instability and light pollution in the spectrograph end.Our method measures the fiber position by fitting the profile of the fiber pinhole with a 2D Gaussian function.A series of tests show that the relative position measurement precision of the front-illuminated method is about 012,and the method could have the same accuracy as the back-illuminated method once the system bias is calibrated by a simple radial correction function.The required fiber positioning accuracy of LAMOST is 04,and the new method satisfies the requirement of LAMOST fiber detection accuracy and could be used in the closed-loop fiber control system.展开更多
In this paper,an effective active vibration control method was investigated to further improve the positioning accuracy of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)feed cabin.The actual operation...In this paper,an effective active vibration control method was investigated to further improve the positioning accuracy of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)feed cabin.The actual operation data of FAST was collected to analyze the vibration characteristics of the feed cabin in multiple directions.A simplified model of the cabin-cable system was established to evaluate the effects of a mass damper on different vibration frequencies and modes.On this basis,an active mass damper system and control system were designed for the cabin with multiple degrees of freedom and modal variation characteristics.Theoretical calculation and simulation proved that it has a significant effect on improving the damping of the cabin-cable system and suppressing the vibration of the FAST feed cabin.展开更多
文摘The Chang’e-4 mission obtained spectral data of multiple rock targets on the lunar surface.The Modified Gaussian Model(MGM)is usually applied to the spectral interpretation of powder samples,its applicability and accuracy on the rock targets remain to be further evaluated.The rock slice of lunar meteorite NWA 4734 is used to conduct comprehensive analysis of the petrography,mineralogy and laboratory spectroscopy,which will provide important ground truth for the MGM interpretation of lunar in situ spectra of rock samples.First,a scanning electron microscope(SEM),Energy Dispersive Spectrometer(EDS),and Electron Probe Micro-Analyzer(EPMA)analysis results indicate that:(1)almost all plagioclase in NWA 4734 have been converted to maskelynites,which indicate that the meteorite has undergone severe impact metamorphism;(2)the chemical composition of pyroxene and olivine is significantly heterogeneous,showing a distribution characteristic of magnesium-rich core and iron-rich rim,further indicating that NWA 4734 has undergone multiple crystallization and differentiation.Second,this article focuses on the rock slice of NWA 4734ʼs greyscale image of the Back Scattering Electron(BSE),and obtains the proportion of High-Calcium Pyroxene(HCP)in the total pyroxenes of this sample by calculating the area percentage using the pixel counting method.The result shows that the proportion of HCP is 72%±5.4%,which can be used as a ground truth to evaluate the interpretation applicability and accuracy of MGM.A field spectrometer(ASD)is used to measure the visible and near-infrared reflectance spectra(450-2500 nm)of the rock slice from NWA 4734 in the same area as the BSE image obtained by SEM,and MGM is used to deconvolve the ASD spectra,and the average proportion of HCP is estimated to be 71%±10.1%.The results between the MGM and the pixel counting are comparable within the error range,which demonstrates the applicability of MGM on interpretation of the rock samples on the lunar surface.
基金financial support from the Joint Research Fund in Astronomy under a cooperative agreement between the National Natural Science Foundation of China and the Chinese Academy of Sciences (Grant No. U1631242)the National Natural Science Foundation of China (Grant Nos. 11503028 and 11403028)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences (XDB23040400)the National Basic Research Program (973 Program) of China (2014CB845800)
文摘POLAR is a compact space-borne detector initially designed to measure the polarization of hard X-rays emitted from Gamma-Ray Bursts in the energy range 50–500 ke V.This instrument was launched successfully onboard the Chinese space laboratory Tiangong-2(TG-2) on 2016 September 15.After being switched on a few days later,tens of gigabytes of raw detection data were produced in-orbit by POLAR and transferred to the ground every day.Before the launch date,a full pipeline and related software were designed and developed for the purpose of quickly pre-processing all the raw data from POLAR,which include both science data and engineering data,then to generate the high level scientific data products that are suitable for later science analysis.This pipeline has been successfully applied for use by the POLAR Science Data Center in the Institute of High Energy Physics(IHEP) after POLAR was launched and switched on.A detailed introduction to the pipeline and some of the core relevant algorithms are presented in this paper.
基金supported by the Specialized Research Fund for State Key Laboratories under Grant 202217the Key Laboratory of Solar Activity and Space Weather(NSSC)under Grant E26600021S。
文摘Ground-based radio observations below 30 MHz are susceptible to the ionosphere of the Earth and the radio frequency interference.Compared with other space mission concepts,making low frequency observations using an interferometer array on lunar orbit is one of the most feasible ones due to a number of technical and economic advantages.Different from traditional interferometer arrays,the interferometer array on lunar orbit faces some complications such as the three-dimensional distribution of baselines and the changing sky blockage by the Moon.Although the brute-force method based on the linear mapping relationship between the visibilities and the sky temperature can produce satisfactory results in general,there are still large residual errors on account of the loss of the edge information.To obtain the full-sky maps with higher accuracy,in this paper we propose a novel imaging method based on reweighted total variation(RTV)for a lunar orbit interferometer array.Meanwhile,a split Bregman iteration method is introduced to optimize the proposed RTV model so as to decrease the computation time.The simulation results show that,compared with the traditional brute-force method,the RTV regularization method can effectively reduce the reconstruction errors and obtain more accurate sky maps,which proves the effectiveness of the proposed method.
基金supported by the Maintenance and renovation project of Major Science and Technology foundational facility of the Chinese Academy of Sciences,DSS-WXGZ-2020-0009 and DSS-WXGZ-2021-0004the support of the National Key R&D Program of China(2019YFA0405000)+3 种基金NFSC 12090041,U1931207,U2031207 and U1931126the support of the National Natural Science for Youth Foundation of China(No.11603043)Guo Shou Jing Telescope(the Large sky Area Multi-Object fiber Spectroscopic Telescope,LAMOST)is a National Major Scientific Project built by the Chinese Academy of Sciences.Funding for the project has been provided by the National Development and Reform CommissionLAMOST is operated and managed by the National Astronomical Observatories,Chinese Academy of Sciences。
文摘The double revolving fiber positioning technology is one of the key technologies for the success of the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST).The accuracy of fiber positioning will directly affect the observation efficiency of LAMOST.To achieve higher fiber positioning accuracy,the original open-loop controlled fiber positioning system urgently needs to be upgraded into a closed-loop control system.The fiber detection is the most important part of the closed-loop controlled fiber positioning system.The back-illuminated detection method is usually used to detect the fiber position by directly detecting the light spot generated at the fiber end in the multi-fiber spectral surveys.In this paper,we introduce a new method to measure the fiber position based on the image of the front-illuminated LAMOST focal plane.The front-illuminated image does not require lighting devices inside the spectrograph,and it could reduce the instability and light pollution in the spectrograph end.Our method measures the fiber position by fitting the profile of the fiber pinhole with a 2D Gaussian function.A series of tests show that the relative position measurement precision of the front-illuminated method is about 012,and the method could have the same accuracy as the back-illuminated method once the system bias is calibrated by a simple radial correction function.The required fiber positioning accuracy of LAMOST is 04,and the new method satisfies the requirement of LAMOST fiber detection accuracy and could be used in the closed-loop fiber control system.
文摘In this paper,an effective active vibration control method was investigated to further improve the positioning accuracy of the Five-hundred-meter Aperture Spherical radio Telescope(FAST)feed cabin.The actual operation data of FAST was collected to analyze the vibration characteristics of the feed cabin in multiple directions.A simplified model of the cabin-cable system was established to evaluate the effects of a mass damper on different vibration frequencies and modes.On this basis,an active mass damper system and control system were designed for the cabin with multiple degrees of freedom and modal variation characteristics.Theoretical calculation and simulation proved that it has a significant effect on improving the damping of the cabin-cable system and suppressing the vibration of the FAST feed cabin.
