[Objective] The aim was to explore the special methods for amplification of large-family genes by using primers with high degeneracy.[Method] By using the primers with high degeneracy,conventional PCR,conventional tou...[Objective] The aim was to explore the special methods for amplification of large-family genes by using primers with high degeneracy.[Method] By using the primers with high degeneracy,conventional PCR,conventional touchdown PCR and the optimized abnormal touchdown PCR were respectively carried out to amplify the genomic DNA of Cyprinus carpio.[Result] Only one evident electrophoretic band and a few Sox genes were obtained by using normal PCR;no obvious electrophoretic band but dispersive product was obtained by normal touchdown PCR;ideal result was obtained by the abnormal touchdown PCR that three evident electrophoretic bands and much more Sox genes were amplified.[Conclusion] The research provided theoretical basis for the optimization and selection of PCR amplification conditions of the large-family genes.展开更多
When China Southern Airlines touches down at the Jomo Kenyatta International Airport in Nairobi on August 5,it will be the first time a Chinese airline has made a direct journey to the African continent,heralding a ne...When China Southern Airlines touches down at the Jomo Kenyatta International Airport in Nairobi on August 5,it will be the first time a Chinese airline has made a direct journey to the African continent,heralding a new era in aviation.The flight is expected to operate three times a week from China’s southerncity of Guangzhou to the Kenyan capital and offer an alternative service for Kenyan travelers.展开更多
This study proposed a novel experimental platform to conduct dynamic loading tests of a truncated model steel catenary riser(SCR)within the touchdown zone(TDZ).The facilities of the platform,including a soil tank,a lo...This study proposed a novel experimental platform to conduct dynamic loading tests of a truncated model steel catenary riser(SCR)within the touchdown zone(TDZ).The facilities of the platform,including a soil tank,a loading system,and a soil stirring system,are introduced in detail.A steel pipe with the same diameter as the in situ SCR has been used in the laboratory tests to investigate the vertical motion of the pipe and the effect of the trench on the lateral motion.As the amplitude of the vertical motion increases,the depth of the trench deepens,the bending moment range increases,and the excess pore water pressure at the bottom of the pipeline first accumulates and then dissipates during loading.The development trend of the trench depth and the influence of the soil strength on the SCR bending moment are also studied.During the test,a seabed trench develops,and its shape is similar to that of the in situ trench.展开更多
In an asteroid sample-return mission,accurate position estimation of the spacecraft relative to the asteroid is essential for landing at the target point.During the missions of Hayabusa and Hayabusa2,the main part of ...In an asteroid sample-return mission,accurate position estimation of the spacecraft relative to the asteroid is essential for landing at the target point.During the missions of Hayabusa and Hayabusa2,the main part of the visual position estimation procedure was performed by human operators on the Earth based on a sequence of asteroid images acquired and sent by the spacecraft.Although this approach is still adopted in critical space missions,there is an increasing demand for automated visual position estimation,so that the time and cost of human intervention may be reduced.In this paper,we propose a method for estimating the relative position of the spacecraft and asteroid during the descent phase for touchdown from an image sequence using state-of-the-art techniques of image processing,feature extraction,and structure from motion.We apply this method to real Ryugu images that were taken by Hayabusa2 from altitudes of 20 km-500 m.It is demonstrated that the method has practical relevance for altitudes within the range of 5-1 km.This result indicates that our method could improve the efficiency of the ground operation in the global mapping and navigation during the touchdown sequence,whereas full automation and autonomous on-board estimation are beyond the scope of this study.Furthermore,we discuss the challenges of developing a completely automatic position estimation framework.展开更多
Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu.The Hayabusa2 spacecraft was launched on 3 December 2014 and arrived at Ryugu on 27 June 2018.It stayed there until December 2019 for in situ obser...Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu.The Hayabusa2 spacecraft was launched on 3 December 2014 and arrived at Ryugu on 27 June 2018.It stayed there until December 2019 for in situ observation and soil sample collection,and will return to the Earth in November or December 2020.During the stay,the spacecraft performed the first touchdown operation on 22 February 2019 and the second touchdown on 11 July 2019,which were both completed sucssfully.Because the surface of Ryugu is rough and covered with boulders,it was not easy to find target areas for touchdown.There were several technical challenges to overcome,including demanding guidance,navigation,and control accuracy,to realize the touchdown operation.In this paper,strategies and technical details of the guidance,navigation,and control systems are presented.The flight results prove that the performance of the systems was satisfactory and largely contributed to the success of the operation.展开更多
文摘[Objective] The aim was to explore the special methods for amplification of large-family genes by using primers with high degeneracy.[Method] By using the primers with high degeneracy,conventional PCR,conventional touchdown PCR and the optimized abnormal touchdown PCR were respectively carried out to amplify the genomic DNA of Cyprinus carpio.[Result] Only one evident electrophoretic band and a few Sox genes were obtained by using normal PCR;no obvious electrophoretic band but dispersive product was obtained by normal touchdown PCR;ideal result was obtained by the abnormal touchdown PCR that three evident electrophoretic bands and much more Sox genes were amplified.[Conclusion] The research provided theoretical basis for the optimization and selection of PCR amplification conditions of the large-family genes.
文摘When China Southern Airlines touches down at the Jomo Kenyatta International Airport in Nairobi on August 5,it will be the first time a Chinese airline has made a direct journey to the African continent,heralding a new era in aviation.The flight is expected to operate three times a week from China’s southerncity of Guangzhou to the Kenyan capital and offer an alternative service for Kenyan travelers.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51879189 and 52071234).
文摘This study proposed a novel experimental platform to conduct dynamic loading tests of a truncated model steel catenary riser(SCR)within the touchdown zone(TDZ).The facilities of the platform,including a soil tank,a loading system,and a soil stirring system,are introduced in detail.A steel pipe with the same diameter as the in situ SCR has been used in the laboratory tests to investigate the vertical motion of the pipe and the effect of the trench on the lateral motion.As the amplitude of the vertical motion increases,the depth of the trench deepens,the bending moment range increases,and the excess pore water pressure at the bottom of the pipeline first accumulates and then dissipates during loading.The development trend of the trench depth and the influence of the soil strength on the SCR bending moment are also studied.During the test,a seabed trench develops,and its shape is similar to that of the in situ trench.
基金This work was partially supported by JSPS KAKENHI Grant No.18H01628.
文摘In an asteroid sample-return mission,accurate position estimation of the spacecraft relative to the asteroid is essential for landing at the target point.During the missions of Hayabusa and Hayabusa2,the main part of the visual position estimation procedure was performed by human operators on the Earth based on a sequence of asteroid images acquired and sent by the spacecraft.Although this approach is still adopted in critical space missions,there is an increasing demand for automated visual position estimation,so that the time and cost of human intervention may be reduced.In this paper,we propose a method for estimating the relative position of the spacecraft and asteroid during the descent phase for touchdown from an image sequence using state-of-the-art techniques of image processing,feature extraction,and structure from motion.We apply this method to real Ryugu images that were taken by Hayabusa2 from altitudes of 20 km-500 m.It is demonstrated that the method has practical relevance for altitudes within the range of 5-1 km.This result indicates that our method could improve the efficiency of the ground operation in the global mapping and navigation during the touchdown sequence,whereas full automation and autonomous on-board estimation are beyond the scope of this study.Furthermore,we discuss the challenges of developing a completely automatic position estimation framework.
文摘Hayabusa2 is a Japanese sample return mission from the asteroid Ryugu.The Hayabusa2 spacecraft was launched on 3 December 2014 and arrived at Ryugu on 27 June 2018.It stayed there until December 2019 for in situ observation and soil sample collection,and will return to the Earth in November or December 2020.During the stay,the spacecraft performed the first touchdown operation on 22 February 2019 and the second touchdown on 11 July 2019,which were both completed sucssfully.Because the surface of Ryugu is rough and covered with boulders,it was not easy to find target areas for touchdown.There were several technical challenges to overcome,including demanding guidance,navigation,and control accuracy,to realize the touchdown operation.In this paper,strategies and technical details of the guidance,navigation,and control systems are presented.The flight results prove that the performance of the systems was satisfactory and largely contributed to the success of the operation.
