The Ce-substituted(Nd1-xCex)12.2 Fe81.6 B6.2(x=0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consis...The Ce-substituted(Nd1-xCex)12.2 Fe81.6 B6.2(x=0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consisting of a-Fe phase, Nd(Ce)-rich phases and RE2 Fe14 B(RE = Nd, Ce) phases. However, the coercivity of all annealed ribbons can reach a considerably high value without doping any heavy rare earth or other coercivity enhanced elements. A strong intergranular exchange coupling appears in these nanocrystalline ribbons. The Nd12.2 Fe81.6 B6.2 ribbons with multiphase have a coercivity of about 11.3 k Oe, and the coercivity decreases slightly with increasing Ce content. A coercivity of 7.5 kOe can be obtained when60 at% of Nd is replaced by Ce(x = 0.6) due to the grain refinement and the strong intergranular exchange coupling. This provides a practical approach of fabricating high coercivity Ce-substituted Nd-Fe-B materials.展开更多
We propose an approach for dependence tree structure learning via copula. A nonparametric algorithm for copula estimation is presented. Then a Chow-Liu like method based on dependence measure via copula is proposed to...We propose an approach for dependence tree structure learning via copula. A nonparametric algorithm for copula estimation is presented. Then a Chow-Liu like method based on dependence measure via copula is proposed to estimate maximum spanning bivariate copula associated with bivariate dependence relations. The main advantage of the approach is that learning with empirical copula focuses on dependence relations among random variables, without the need to know the properties of individual variables as well as without the requirement to specify parametric family of entire underlying distribution for individual variables. Experiments on two real-application data sets show the effectiveness of the proposed method.展开更多
CubeSats have become versatile platforms for various space missions(e.g.,on-orbit servicing and debris removal)owing to their low cost and flexibility.Many space tasks involve proximity operations that require precise...CubeSats have become versatile platforms for various space missions(e.g.,on-orbit servicing and debris removal)owing to their low cost and flexibility.Many space tasks involve proximity operations that require precise guidance,navigation,and control(GNC)algorithms.Vision-based navigation is attracting interest for such operations.However,extreme lighting conditions in space challenge optical techniques.The on-ground validation of such navigation systems for orbital GNC becomes crucial to ensure their reliability during space operations.These systems undergo rigorous testing within their anticipated operational parameters,including the exploration of potential edge cases.The ability of GNC algorithms to function effectively under extreme space conditions that exceed anticipated scenarios is crucial,particularly in space missions where the scope of errors is negligible.This paper presents the ground validation of a GNC algorithm designed for autonomous satellite rendezvous by leveraging hardware-in-the-loop experiments.This study focuses on two key areas.First,the rationale underlying the augmentation of the robot workspace(six-degree-of-freedom UR10e robot+linear rail)is investigated to emulate relatively longer trajectories with complete position and orientation states.Second,the control algorithm is assessed in response to uncertain pose observations from a vision-based navigation system.The results indicate increased control costs with uncertain navigation and exemplify the importance of on-ground testing for system validation before launch,particularly in extreme cases that are typically difficult to assess using software-based testing.展开更多
The lower-limb robotic prostheses can provide assistance for amputees’daily activities by restoring the biomechanical functions of missing limb(s).To set proper control strategies and develop the corresponding contro...The lower-limb robotic prostheses can provide assistance for amputees’daily activities by restoring the biomechanical functions of missing limb(s).To set proper control strategies and develop the corresponding controller for robotic prosthesis,a prosthesis user’s intent must be acquired in time,which is still a major challenge and has attracted intensive attentions.This work focuses on the robotic prosthesis user’s locomotion intent recognition based on the noninvasive sensing methods from the recognition task perspective(locomotion mode recognition,gait event detection,and continuous gait phase estimation)and reviews the state-ofthe-art intent recognition techniques in a lower-limb prosthesis scope.The current research status,including recognition approach,progress,challenges,and future prospects in the human’s intent recognition,has been reviewed.In particular for the recognition approach,the paper analyzes the recent studies and discusses the role of each element in locomotion intent recognition.This work summarizes the existing research results and problems and contributes a general framework for the intent recognition based on lower-limb prosthesis.展开更多
基金Project supported by the National Key Research and Development Program of China(2016YFB0700901)National Natural Science Foundation of China(51731001,11675006,51371009)
文摘The Ce-substituted(Nd1-xCex)12.2 Fe81.6 B6.2(x=0.0, 0.2, 0.4, 0.6) nanocrystalline ribbons were prepared by annealing amorphous ribbons from melt spinning. It is found that all ribbons are in a multiphase state consisting of a-Fe phase, Nd(Ce)-rich phases and RE2 Fe14 B(RE = Nd, Ce) phases. However, the coercivity of all annealed ribbons can reach a considerably high value without doping any heavy rare earth or other coercivity enhanced elements. A strong intergranular exchange coupling appears in these nanocrystalline ribbons. The Nd12.2 Fe81.6 B6.2 ribbons with multiphase have a coercivity of about 11.3 k Oe, and the coercivity decreases slightly with increasing Ce content. A coercivity of 7.5 kOe can be obtained when60 at% of Nd is replaced by Ce(x = 0.6) due to the grain refinement and the strong intergranular exchange coupling. This provides a practical approach of fabricating high coercivity Ce-substituted Nd-Fe-B materials.
文摘We propose an approach for dependence tree structure learning via copula. A nonparametric algorithm for copula estimation is presented. Then a Chow-Liu like method based on dependence measure via copula is proposed to estimate maximum spanning bivariate copula associated with bivariate dependence relations. The main advantage of the approach is that learning with empirical copula focuses on dependence relations among random variables, without the need to know the properties of individual variables as well as without the requirement to specify parametric family of entire underlying distribution for individual variables. Experiments on two real-application data sets show the effectiveness of the proposed method.
基金supported by the Luxembourg National Research Fund:INTER20/EUROSTARS/15254521/VBN/Olivares Mendez.The project,E115088-VBN,has received funding from the Eurostars-2 Joint Programme with cofunding from the European Union’s Horizon 2020 Research and Innovation Programme.
文摘CubeSats have become versatile platforms for various space missions(e.g.,on-orbit servicing and debris removal)owing to their low cost and flexibility.Many space tasks involve proximity operations that require precise guidance,navigation,and control(GNC)algorithms.Vision-based navigation is attracting interest for such operations.However,extreme lighting conditions in space challenge optical techniques.The on-ground validation of such navigation systems for orbital GNC becomes crucial to ensure their reliability during space operations.These systems undergo rigorous testing within their anticipated operational parameters,including the exploration of potential edge cases.The ability of GNC algorithms to function effectively under extreme space conditions that exceed anticipated scenarios is crucial,particularly in space missions where the scope of errors is negligible.This paper presents the ground validation of a GNC algorithm designed for autonomous satellite rendezvous by leveraging hardware-in-the-loop experiments.This study focuses on two key areas.First,the rationale underlying the augmentation of the robot workspace(six-degree-of-freedom UR10e robot+linear rail)is investigated to emulate relatively longer trajectories with complete position and orientation states.Second,the control algorithm is assessed in response to uncertain pose observations from a vision-based navigation system.The results indicate increased control costs with uncertain navigation and exemplify the importance of on-ground testing for system validation before launch,particularly in extreme cases that are typically difficult to assess using software-based testing.
基金supported by the National Key R&D Program of China(Nos.2018YFB1307302,2018YFF0300606),the National Natural Science Foundation of China(No.91648207)the Beijing Natural Science Foundation(No.L182001)the Beijing Municipal Science and Technology Project(No.Z181100009218007).
文摘The lower-limb robotic prostheses can provide assistance for amputees’daily activities by restoring the biomechanical functions of missing limb(s).To set proper control strategies and develop the corresponding controller for robotic prosthesis,a prosthesis user’s intent must be acquired in time,which is still a major challenge and has attracted intensive attentions.This work focuses on the robotic prosthesis user’s locomotion intent recognition based on the noninvasive sensing methods from the recognition task perspective(locomotion mode recognition,gait event detection,and continuous gait phase estimation)and reviews the state-ofthe-art intent recognition techniques in a lower-limb prosthesis scope.The current research status,including recognition approach,progress,challenges,and future prospects in the human’s intent recognition,has been reviewed.In particular for the recognition approach,the paper analyzes the recent studies and discusses the role of each element in locomotion intent recognition.This work summarizes the existing research results and problems and contributes a general framework for the intent recognition based on lower-limb prosthesis.
