With the completion of Chinese BeiDou Navigation Satellite System(BDS),the world has begun to enjoy the Positioning,Navigation,and Timing(PNT)services of four Global Navigation Satellite Systems(GNSS).In order to impr...With the completion of Chinese BeiDou Navigation Satellite System(BDS),the world has begun to enjoy the Positioning,Navigation,and Timing(PNT)services of four Global Navigation Satellite Systems(GNSS).In order to improve the GNSS performance and expand its applications,Low Earth Orbit(LEO)Enhanced Global Navigation Satellite System(LeGNSS)is being vigorously advocated.Combined with high-,medium-,and low-earth orbit satellites,it can improve GNSS performance in terms of orbit determination,Precise Point Positioning(PPP)convergence time,etc.This paper comprehensively reviews the current status of LeGNSS,focusing on analyzing its advantages and challenges for precise orbit and clock determination,PPP convergence,earth rotation parameter estimation,and global ionosphere modeling.Thanks to the fast geometric change brought by LEO satellites,LeGNSS is expected to fundamentally solve the problem of the long convergence time of PPP without any augmentation.The convergence time can be shortened within 1 minute if appropriate LEO constellations are deployed.However,there are still some issues to overcome,such as the optimization of LEO constellation as well as the real time LEO precise orbit and clock determination.展开更多
The recently emerged Omicron variant of severe acute respiratory syndrome coronavirus 2(SARS‐CoV‐2)has quickly spread around the world.Although many consensus mutations of the Omicron variant have been recognized,li...The recently emerged Omicron variant of severe acute respiratory syndrome coronavirus 2(SARS‐CoV‐2)has quickly spread around the world.Although many consensus mutations of the Omicron variant have been recognized,little is known about its genetic variation during its transmission in the population.Here,we comprehensively analyzed the genetic differentiation and diversity of the Omicron variant during its early outbreak.We found that Omicron achieved more structural variations,especially deletions,on the SARS‐CoV‐2 genome than the other four variants of concern(Alpha,Beta,Gamma,and Delta)in the same timescale.In addition,the Omicron variant acquired,except for 50 consensus mutations,seven great new non‐synonymous nucleotide substitutions during its spread.Three of them are on the S protein,including S_A701V,S_L1081V,and S_R346K,which belong to the receptor‐binding domain(RBD).The Omicron BA.1 branch could be divided into five divergent groups spreading across different countries and regions based on these seven novel mutations.Furthermore,we found that the Omicron variant possesses more mutations related to a faster transmission rate than the other SARS‐CoV‐2 variants by assessing the relationship between the genetic diversity and transmission rate.The findings indicated that more attention should be paid to the significant genetic differentiation and diversity of the Omicron variant for better disease prevention and control.展开更多
基金the National Natural Science Funds of China[grant numbers 41874030,42074026]Natural Science Funds of Shanghai[grant number 21ZR1465600]+3 种基金the Program of Shanghai Academic Research Leader[grant number 20XD1423800]the Innovation Program of Shanghai Municipal Education Commission[grant number 2021-01-07-00-07-E00095]the“Shuguang Program”supported by Shanghai Education Development Foundation and Shanghai Municipal Education Commission[grant number 20SG18]the Scientific and Technological Innovation Plan from Shanghai Science and Technology Committee[grant numbers 20511103302,20511103402 and 20511103702].
文摘With the completion of Chinese BeiDou Navigation Satellite System(BDS),the world has begun to enjoy the Positioning,Navigation,and Timing(PNT)services of four Global Navigation Satellite Systems(GNSS).In order to improve the GNSS performance and expand its applications,Low Earth Orbit(LEO)Enhanced Global Navigation Satellite System(LeGNSS)is being vigorously advocated.Combined with high-,medium-,and low-earth orbit satellites,it can improve GNSS performance in terms of orbit determination,Precise Point Positioning(PPP)convergence time,etc.This paper comprehensively reviews the current status of LeGNSS,focusing on analyzing its advantages and challenges for precise orbit and clock determination,PPP convergence,earth rotation parameter estimation,and global ionosphere modeling.Thanks to the fast geometric change brought by LEO satellites,LeGNSS is expected to fundamentally solve the problem of the long convergence time of PPP without any augmentation.The convergence time can be shortened within 1 minute if appropriate LEO constellations are deployed.However,there are still some issues to overcome,such as the optimization of LEO constellation as well as the real time LEO precise orbit and clock determination.
基金supported by the National key research and development program(2021YFC2301300)the CAMS Innovation Fund for Medical Sciences(2021-I2M-1-061)+2 种基金the National Natural Science Foundation of China(92169106,31900472)the special research fund for central universities,Peking Union Medical College(2021-PT180-001)Suzhou science and technology development plan(szs2020311).
文摘The recently emerged Omicron variant of severe acute respiratory syndrome coronavirus 2(SARS‐CoV‐2)has quickly spread around the world.Although many consensus mutations of the Omicron variant have been recognized,little is known about its genetic variation during its transmission in the population.Here,we comprehensively analyzed the genetic differentiation and diversity of the Omicron variant during its early outbreak.We found that Omicron achieved more structural variations,especially deletions,on the SARS‐CoV‐2 genome than the other four variants of concern(Alpha,Beta,Gamma,and Delta)in the same timescale.In addition,the Omicron variant acquired,except for 50 consensus mutations,seven great new non‐synonymous nucleotide substitutions during its spread.Three of them are on the S protein,including S_A701V,S_L1081V,and S_R346K,which belong to the receptor‐binding domain(RBD).The Omicron BA.1 branch could be divided into five divergent groups spreading across different countries and regions based on these seven novel mutations.Furthermore,we found that the Omicron variant possesses more mutations related to a faster transmission rate than the other SARS‐CoV‐2 variants by assessing the relationship between the genetic diversity and transmission rate.The findings indicated that more attention should be paid to the significant genetic differentiation and diversity of the Omicron variant for better disease prevention and control.
