We present the nearest neighbor distance (NND) analysis of SDSS DR5 galaxies. We give NND results for observed, mock and random sample, and discuss the differences. We find the observed sample gives us a significantly...We present the nearest neighbor distance (NND) analysis of SDSS DR5 galaxies. We give NND results for observed, mock and random sample, and discuss the differences. We find the observed sample gives us a significantly stronger aggregation characteristic than the random samples. Moreover, we investigate the direction of NND and find the direction has close relation with the size of the NND for the observed sample.展开更多
In a low energy moon return mission, due to the weak stability of the orbit, it is necessary to implement an accurate orbital maneuver to guarantee a successful return. During the process of getting the optimal thrust...In a low energy moon return mission, due to the weak stability of the orbit, it is necessary to implement an accurate orbital maneuver to guarantee a successful return. During the process of getting the optimal thrust control with these two kinds of methods, it is hard to guess the initial value of the co-states in the indirect method while a large amount of calculation is needed to insure the precision in the direct method. To solve the problem, in this paper a combined method is given which has the merit of both direct and indirect methods. In this method, the virtual satellite method(VSM) and the Gauss pseudo-spectral method(GPM)are applied, while the fuel optimal control strategy is computed with GPM to carry out a soft rendezvous between the spacecraft and a hypothetical virtual satellite running on the nominal low energy return orbit so that the spacecraft will enter the return orbit accurately. Compared with the direct and indirect methods, this combined method can avoid guessing the initial value of the co-states and the complexity of calculation is acceptable. According to the simulation results, the spacecraft is inserted to the target return orbit with a high accuracy and also the optimization is very effective.展开更多
Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the R...Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet.For China’s 2020 Mars exploration mission to achieve success,many key technologies must be realized.In this paper,China’s 2020 Mars mission and the spacecraft architecture are first introduced.Then,the preliminary launch opportunity,Earth–Mars transfer,Mars capture,and mission orbits are described.Finally,the main navigation schemes are summarized.展开更多
Human-robot collaboration is a promising means to promote orchard intelligence and reduce the over-reliance on manual work for complex agronomic practices such as fruit tree pruning,flower and fruit thinning,and harve...Human-robot collaboration is a promising means to promote orchard intelligence and reduce the over-reliance on manual work for complex agronomic practices such as fruit tree pruning,flower and fruit thinning,and harvesting.Accurate target detection and recognition of robots on humans are the basis and prerequisite for subsequent autonomous human-robot collaboration.In this study,detection and recognition of following robots for human torso were carried out in a standardized hilly orchard.A LiDAR-based human torso detection method was proposed based on the actual orchard environment.Breakpoint detection was used to cluster and segment the point clouds,and the segmentation thresholds were determined based on experimental results.The geometric attributes of the human torso were trained in the classification detection model,resulting in the extraction of six geometric attributes of the human torso.The classification model was then trained with various combinations to obtain the optimal feature combination[girth-depth-average curvature(G-D-k)]for human torso recognition in an orchard environment.Practical experiments were carried out to validate the feasibility and accuracy of the G-D-k feature combination.The experimental results demonstrate that the G-D-k feature combination can accurately recognize human bodies in orchards.The LiDAR-based detection method can achieve relatively accurate human detection and recognition in complex orchard environments,providing a reference for target detection in human-robot collaboration in orchards.展开更多
文摘We present the nearest neighbor distance (NND) analysis of SDSS DR5 galaxies. We give NND results for observed, mock and random sample, and discuss the differences. We find the observed sample gives us a significantly stronger aggregation characteristic than the random samples. Moreover, we investigate the direction of NND and find the direction has close relation with the size of the NND for the observed sample.
基金supported by National Natural Science Foundation of China(No.11172077)Autonomous Space System laboratory(ASSL) of Harbin Institute of Technology
文摘In a low energy moon return mission, due to the weak stability of the orbit, it is necessary to implement an accurate orbital maneuver to guarantee a successful return. During the process of getting the optimal thrust control with these two kinds of methods, it is hard to guess the initial value of the co-states in the indirect method while a large amount of calculation is needed to insure the precision in the direct method. To solve the problem, in this paper a combined method is given which has the merit of both direct and indirect methods. In this method, the virtual satellite method(VSM) and the Gauss pseudo-spectral method(GPM)are applied, while the fuel optimal control strategy is computed with GPM to carry out a soft rendezvous between the spacecraft and a hypothetical virtual satellite running on the nominal low energy return orbit so that the spacecraft will enter the return orbit accurately. Compared with the direct and indirect methods, this combined method can avoid guessing the initial value of the co-states and the complexity of calculation is acceptable. According to the simulation results, the spacecraft is inserted to the target return orbit with a high accuracy and also the optimization is very effective.
基金the National Natural Science Foundation of China(Grant No.11672126)Innovation Funded Project of Shanghai Aerospace Science and Technology(Grant No.SAST2015036)+4 种基金the Opening Grant from the Key Laboratory of Space Utilization,Chinese Academy of Sciences(LSU-2016-07-01)Funding of Jiangsu Innovation Program for Graduate Education(Grant No.KYZZ160170)the Fundamental Research Funds for the Central UniversitiesFunding for Outstanding Doctoral Dissertation in NUAA(Grant No.BCXJ16-10)The authors fully appreciate their financial supports.
文摘Scheduled for an Earth-to-Mars launch opportunity in 2020,the China’s Mars probe will arrive on Mars in 2021 with the primary objective of injecting an orbiter and placing a lander and a rover on the surface of the Red Planet.For China’s 2020 Mars exploration mission to achieve success,many key technologies must be realized.In this paper,China’s 2020 Mars mission and the spacecraft architecture are first introduced.Then,the preliminary launch opportunity,Earth–Mars transfer,Mars capture,and mission orbits are described.Finally,the main navigation schemes are summarized.
基金funded by the Agricultural Machinery Equipment Weak Core Technology Application Project of Hubei Province,China(Grant No.HBSNYT202219)Nature Science Foundation of Hubei Province,China(Grant No.2021CFB471)the National Key Research and Development Program of China(Grant No.2020YFD1000100).
文摘Human-robot collaboration is a promising means to promote orchard intelligence and reduce the over-reliance on manual work for complex agronomic practices such as fruit tree pruning,flower and fruit thinning,and harvesting.Accurate target detection and recognition of robots on humans are the basis and prerequisite for subsequent autonomous human-robot collaboration.In this study,detection and recognition of following robots for human torso were carried out in a standardized hilly orchard.A LiDAR-based human torso detection method was proposed based on the actual orchard environment.Breakpoint detection was used to cluster and segment the point clouds,and the segmentation thresholds were determined based on experimental results.The geometric attributes of the human torso were trained in the classification detection model,resulting in the extraction of six geometric attributes of the human torso.The classification model was then trained with various combinations to obtain the optimal feature combination[girth-depth-average curvature(G-D-k)]for human torso recognition in an orchard environment.Practical experiments were carried out to validate the feasibility and accuracy of the G-D-k feature combination.The experimental results demonstrate that the G-D-k feature combination can accurately recognize human bodies in orchards.The LiDAR-based detection method can achieve relatively accurate human detection and recognition in complex orchard environments,providing a reference for target detection in human-robot collaboration in orchards.
