Lithium-sulfur batteries(LSBs)are considered as the promising solution to replace conventional lithium-ion batteries due to satisfactory energy density.In recent times,the LSBs field has been found to face some diffic...Lithium-sulfur batteries(LSBs)are considered as the promising solution to replace conventional lithium-ion batteries due to satisfactory energy density.In recent times,the LSBs field has been found to face some difficulties in exploring practical applications in which cycling stability and cycle life are awful owing to the shuttling effect of lithium polysulfides(LiPSs)and low sulfur utilization.In this work,by synthesizing Co_(3)Se_(4) nanoparticles onto N-doped carbon(NC)polyhedra interconnected with carbon nanotubes(CNTs),NC@Co_(3)Se_(4)/CNTs is proposed as a multifunctional sulfur carrier.The Co_(3)Se_(4) nanoparticles fleetly catalyze the conversion of LiPSs and availably immobilize LiPSs.Meanwhile,the NC polyhedral skeleton enhances the electronic conductivity of active sulfur,while the CNTs facilitate Li+diffusion and supply a mass of conductive channels.Density-functional theory(DFT)calculations demonstrate the relevant mechanisms.That is to say,the NC@Co_(3)Se_(4)/CNTs benefit from the synergistic effect of Co_(3)Se_(4) nanoparticles(highly catalytic ability and strong adsorbability for LiPSs)and the special carbonaceous structure,rapidly converting LiPSs and inhibiting the shuttle of LiPSs.Therefore,lithium-sulfur battery assembled with S/NC@Co_(3)Se_(4)/CNTs cathode as well as nitrogen and sulfur co-doped carbon-coated polypropylene(N,S-C/PP)separator possesses a high initial discharge capacity of 1413 mAh·g-1 at 0.12C and persistently circulates for 1000 cycles at 1C with a capacity attenuation rate per cycle of 0.034%.This work provides a realistic idea for the use of transition metal selenide in the field of high-performance LSBs.展开更多
Reusable and flexible capturing of space debris is highly required in future aerospace technologies.A tendon-actuated flexible robotic arm is therefore proposed for capturing floating targets in this paper.Firstly,an ...Reusable and flexible capturing of space debris is highly required in future aerospace technologies.A tendon-actuated flexible robotic arm is therefore proposed for capturing floating targets in this paper.Firstly,an accurate dynamic model of the flexible robotic arm is established by using the absolute nodal coordinate formulation(ANCF)in the framework of the arbitrary Lagrangian-Eulerian(ALE)description and the natural coordinate formulation(NCF).The contact and self-contact dynamics of the flexible robotic arm when bending and grasping an object are considered via a fast contact detection approach.Then,the dynamic simulations of the flexible robotic arm for capturing floating targets are carried out to study the influence of the position,size,and mass of the target object on the grasping performance.Finally,a principle prototype of the tendon-actuated flexible robotic arm is manufactured to validate the dynamic model.The corresponding grasping experiments for objects of various shapes are also conducted to illustrate the excellent performance of the flexible robotic arm.展开更多
When the space robot captures a floating target, contact impact occurs inevitably and frequently between the manipulator hand and the target, which seriously impacts the position and attitude of the robot and grasping...When the space robot captures a floating target, contact impact occurs inevitably and frequently between the manipulator hand and the target, which seriously impacts the position and attitude of the robot and grasping security. ＂Dynamic grasping area＂ is introduced to describe the collision process of manipulator grasping target, and grasping area control equation is established. By analyzing the impact of grasping control parameters, base and target mass on the grasping process and combining the life experience, it is found that if the product of speed control parameter and dB adjustment parameter is close to but smaller than the minimum grasping speed, collision impact in the grasping process could be reduced greatly, and then an ideal grasping strategy is proposed. Simulation results indicate that during the same period, the strategy grasping is superior to the accelerating grasping, in that the amplitude of impact force is reduced to 20%, and the attitude control torque is reduced to 15%, and the impact on the robot is eliminated significantly. The results would have important academic value and engineering significance.展开更多
Biomechanics is the study of physiological properties of data and the measurement of human behavior.In normal conditions,behavioural properties in stable form are created using various inputs of subconscious/conscious...Biomechanics is the study of physiological properties of data and the measurement of human behavior.In normal conditions,behavioural properties in stable form are created using various inputs of subconscious/conscious human activities such as speech style,body movements in walking patterns,writing style and voice tunes.One cannot perform any change in these inputs that make results reliable and increase the accuracy.The aim of our study is to perform a comparative analysis between the marker-based motion capturing system(MBMCS)and the marker-less motion capturing system(MLMCS)using the lower body joint angles of human gait patterns.In both the MLMCS and MBMCS,we collected trajectories of all the participants and performed joint angle computation to identify a person and recognize an activity(walk and running).Using five state of the art machine learning algorithms,we obtained 44.6%and 64.3%accuracy in person identification using MBMCS and MLMCS respectively with an ensemble algorithm(two angles as features).In the second set of experiments,we used six machine learning algorithms to obtain 65.9%accuracy with the k-nearest neighbor(KNN)algorithm(two angles as features)and 74.6%accuracy with an ensemble algorithm.Also,by increasing features(6 angles),we obtained higher accuracy of 99.3%in MBMCS for person recognition and 98.1%accuracy in MBMCS for activity recognition using the KNN algorithm.MBMCS is computationally expensive and if we redesign the model of OpenPose with more body joint points and employ more features,MLMCS(low-cost system)can be an effective approach for video data analysis in a person identification and activity recognition process.展开更多
The growing amount of space debris poses a threat to operational spacecraft and the long-term sustainability of activities in outer space. According to the orbital mechanics, an uncontrolled space object will be tumbl...The growing amount of space debris poses a threat to operational spacecraft and the long-term sustainability of activities in outer space. According to the orbital mechanics, an uncontrolled space object will be tumbling, bringing great challenge to capture and remove it. In this paper, a dual-arm coordinated ‘‘Area-Oriented Capture'(AOC) method is proposed to capture a non-cooperative tumbling target. Firstly, the motion equation of the tumbling target is established, based on which, the dynamic properties are analyzed. Then, the ‘‘Area-Oriented Capture'concept is presented to deal with the problem of large pose(position and attitude) deviation and tumbling motion. An area rather than fixed points/devices is taken as the object to be tracked and captured. As long as the manipulators’ end-effectors move to a specified range of the objective areas(not fixed points on the target, but areas), the target satellite will be hugged by the two arms.At last, the proposed method and the traditional method(i.e. fixed-point oriented capture method)are compared and analyzed through simulation. The results show that the proposed method has larger pose tolerance and takes shorter time for capturing a tumbling target.展开更多
The rotational motion of a tumbling target brings great challenges to space robot on successfully capturing the tumbling target.Therefore,it is necessary to reduce the target's rotation to a rate at which capture ...The rotational motion of a tumbling target brings great challenges to space robot on successfully capturing the tumbling target.Therefore,it is necessary to reduce the target's rotation to a rate at which capture can be accomplished by the space robot.In this paper,a detumbling strategy based on friction control of dual-arm space robot for capturing tumbling target is proposed.This strategy can reduce the target's rotational velocity while maintaining base attitude stability through the establishment of the rotation attenuation controller and base attitude adjustment controller.The rotation attenuation controller adopts the multi-space hybrid impedance control method to control the friction precisely.The base attitude adjustment controller applies the dual-arm extended Jacobian matrix to stabilize the base attitude.The main contributions of this paper are as follows:(1)The compliant control method is adopted to achieve a precise friction control,which can reduce the target angular velocity steadily;(2)The dual-arm extended Jacobian matrix is applied to stabilize the base attitude without affecting the target capture task;(3)The detumbling strategy of dualarm space robot is designed considering base attitude stabilization,realizing coordinated planning of the base attitude and the arms.The strategy is verified by a dual-arm space robot with two 7-DOF(degrees of freedom)arms.Simulation results show that,target with a rotation velocity of 20(°)/s can be effectively controlled to stop within 30 s,and the final deflection of the base attitude is less than 0.15°without affecting the target capture task,verifying the correctness and effectiveness of the strategy.Except to the tumbling target capture task,the control strategy can also be applied to other typical on-orbit operation tasks such as space debris removal and spacecraft maintenance.展开更多
The impact dynamics, impact effect, and post-impact unstable motion sup- pression of free-floating space manipulator capturing a satellite on orbit are analyzed. Firstly, the dynamics equation of free-floating space m...The impact dynamics, impact effect, and post-impact unstable motion sup- pression of free-floating space manipulator capturing a satellite on orbit are analyzed. Firstly, the dynamics equation of free-floating space manipulator is derived using the sec- ond Lagrangian equation. Combining the momentum conservation principle, the impact dynamics and effect between the space manipulator end-effector and satellite of the cap- ture process are analyzed with the momentum impulse method. Focusing on the unstable motion of space manipulator due to the above impact effect, a robust adaptive compound control algorithm is designed to suppress the above unstable motion. There is no need to control the free-floating base position to save the jet fuel. Finally, the simulation is proposed to show the impact effect and verify the validity of the control algorithm.展开更多
To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakw...To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakwater(SDBB), is proposed in the paper. The floating breakwater is composed of HDPE cylindrical double buoys and horizontal axis Savonius rotors, and has the functions of wave-absorbing and energy-capturing. Based on the linear wave theory and energy conservation law, the Fourier Transform was applied to separate the two-dimensional wave frequency domain, and the energy captured by the rotors and absorbed by the floating breakwater were calculated.Experiments were conducted in a two-dimensional wave-making flume, and the transmitted waves at different wave heights and periods, the tension of mooring lines, and the rotational torque exerted on the Savonius rotor were measured. A series of performance comparison tests were also performed on the new floating breakwater and the traditional double-floating breakwater. Results show that the new floating breakwater is better than the traditional one in terms of reducing wave transmittance, and the combination of the floating breakwater with Savonius rotors can provide for marine aquaculture equipments with green power supply to a certain degree of self-sufficiency.展开更多
Lithium-sulfur(Li-S) batteries as extremely promising high-density energy storage devices have attracted extensive concern. However, practical applications of Li-S batteries are severely restricted by not only intrins...Lithium-sulfur(Li-S) batteries as extremely promising high-density energy storage devices have attracted extensive concern. However, practical applications of Li-S batteries are severely restricted by not only intrinsic polysulfides shuttle resulting from their concentration gradient diffusion and sluggish conversion kinetics but also serious safety issue caused by thermolabile and combustible polymer separators.Herein, it is presented for the first time that a robust and multifunctional separator with urchin-like Co-doped Fe OOH microspheres and multiwalled carbon nanotubes(MWCNTs) as an interlayer simultaneously achieves to suppress polysulfides shuttle as well as improves thermotolerance and nonflammability of commercial PP separator. Accordingly, Li-S batteries with modified separator exhibit remarkable performance in a wide range temperatures of-25–100 ℃. Typically, under 25 ℃, ultrahigh initial capacities of 1441 and 827.29 m A h g-1 at 1 C and 2 C are delivered, and remained capacities of 936 and 663.18 mA h g-1 can be obtained after 500 cycles, respectively. At 0.1 C, the S utilization can reach up to 97%. Significantly, at 1 C, the batteries also deliver an excellent performance with remained capacities of high to862.3, 608.4 and 420.6 m A h g-1 after 100, 300 and 450 cycles under 75, 0 and-25 ℃, respectively. This work provides a new insight for developing stable and safe high-performance Li-S batteries.展开更多
In this paper,a new strategy for a sub-element-based shock capturing for discontinuous Galerkin(DG)approximations is presented.The idea is to interpret a DG element as a col-lection of data and construct a hierarchy o...In this paper,a new strategy for a sub-element-based shock capturing for discontinuous Galerkin(DG)approximations is presented.The idea is to interpret a DG element as a col-lection of data and construct a hierarchy of low-to-high-order discretizations on this set of data,including a first-order finite volume scheme up to the full-order DG scheme.The dif-ferent DG discretizations are then blended according to sub-element troubled cell indicators,resulting in a final discretization that adaptively blends from low to high order within a single DG element.The goal is to retain as much high-order accuracy as possible,even in simula-tions with very strong shocks,as,e.g.,presented in the Sedov test.The framework retains the locality of the standard DG scheme and is hence well suited for a combination with adaptive mesh refinement and parallel computing.The numerical tests demonstrate the sub-element adaptive behavior of the new shock capturing approach and its high accuracy.展开更多
Ultrafine NdFeB waste is a relatively clean waste produced during NdFeB magnet processing.Fluorinecontaining wastewater is a common type of industrial wastewater,such as stainless steel pickling wastewater.In this wor...Ultrafine NdFeB waste is a relatively clean waste produced during NdFeB magnet processing.Fluorinecontaining wastewater is a common type of industrial wastewater,such as stainless steel pickling wastewater.In this work,rare earth element neodynium was recycled from ultrafine NdFeB waste by capturing fluorine ions in the fluorine-containing wastewater and prepared into neodynium oxyfluoride.The reaction process was investigated through UV-Vis-NIR,thermogravimetry/differential thermogravimetry(TG/DTG),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The neodymium hydroxide in the ultrafine NdFeB waste reacted with fluorine ions to form Nd(OH)_(2) F,and Nd(OH)_(2) F was then transformed into neodymium oxyfluoride after decomposition.The formed neodymium oxyfluoride is found to be particles with rhombohedral structure and a particle size of around 50 nm.The reaction kinetics of forming Nd(OH)_(2) F was investigated.The reaction kinetic equation was established and the reaction activation energy was calculated.The effect of fluorine ion concentration on the reaction rate and products was evaluated.The results show that the reaction rate increases with the increase of fluorine ion concentration in the range of 0.01-1.5 mol/L,but it has little effect.In addition,the fluorine ion concentration affects the crystallinity of formed neodymium oxyfluoride.The recycling process not only realizes the sustainable utilization of rare earths,but also reduces the concentration of fluorine ions in the fluorine-containing wastewater,achieving two goals with one stone.展开更多
In this paper,the dynamic evolution for a dualarm space robot capturing a spacecraft is studied,the impact effect and the coordinated stabilization control problem for postimpact closed chain system are discussed.At f...In this paper,the dynamic evolution for a dualarm space robot capturing a spacecraft is studied,the impact effect and the coordinated stabilization control problem for postimpact closed chain system are discussed.At first,the pre-impact dynamic equations of open chain dual-arm space robot are established by Lagrangian approach,and the dynamic equations of a spacecraft are obtained by Newton-Euler method.Based on the results,with the process of integral and simplify,the response of the dual-arm space robot impacted by the spacecraft is analyzed by momentum conservation law and force transfer law.The closed chain system is formed in the post-impact phase.Closed chain constraint equations are obtained by the constraints of closed-loop geometry and kinematics.With the closed chain constraint equations,the composite system dynamic equations are derived.Secondly,the recurrent fuzzy neural network control scheme is designed for calm motion of unstable closed chain system with uncertain system parameter.In order to overcome the effects of uncertain system inertial parameters,the recurrent fuzzy neural network is used to approximate the unknown part,the control method with H∞tracking characteristic.According to the Lyapunov theory,the global stability is demonstrated.Meanwhile,the weighted minimum-norm theory is introduced to distribute torques guarantee that cooperative operation between manipulators.At last,numerical examples simulate the response of the collision,and the efficiency of the control scheme is verified by the simulation results.展开更多
This paper carries out systematical investigations on the performance of several typical shock-capturing schemes for the discontinuous Galerkin （DG） method, including the total variation bounded （TVB） limiter and ...This paper carries out systematical investigations on the performance of several typical shock-capturing schemes for the discontinuous Galerkin （DG） method, including the total variation bounded （TVB） limiter and three artificial diffusivity schemes （the basis function-based （BF） scheme, the face residual-based （FR） scheme, and the element residual-based （ER） scheme）. Shock-dominated flows （the Sod problem, the Shu- Osher problem, the double Mach reflection problem, and the transonic NACA0012 flow） are considered, addressing the issues of accuracy, non-oscillatory property, dependence on user-specified constants, resolution of discontinuities, and capability for steady solutions. Numerical results indicate that the TVB limiter is more efficient and robust, while the artificial diffusivity schemes are able to preserve small-scale flow structures better. In high order cases, the artificial diffusivity schemes have demonstrated superior performance over the TVB limiter.展开更多
Motivated by inconveniences of present hybrid methods,a gradient-augmented hybrid interface capturing method（GAHM） is presented for incompressible two-phase flow.A front tracking method（FTM） is used as the skeleto...Motivated by inconveniences of present hybrid methods,a gradient-augmented hybrid interface capturing method（GAHM） is presented for incompressible two-phase flow.A front tracking method（FTM） is used as the skeleton of the GAHM for low mass loss and resources.Smooth eulerian level set values are calculated from the FTM interface,and are used for a local interface reconstruction.The reconstruction avoids marker particle redistribution and enables an automatic treatment of interfacial topology change.The cubic Hermit interpolation is employed in all steps of the GAHM to capture subgrid structures within a single spacial cell.The performance of the GAHM is carefully evaluated in a benchmark test.Results show significant improvements of mass loss,clear subgrid structures,highly accurate derivatives（normals and curvatures） and low cost.The GAHM is further coupled with an incompressible multiphase flow solver,Super CE/SE,for more complex and practical applications.The updated solver is evaluated through comparison with an early droplet research.展开更多
With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture...With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture process,such as excessive collision and fast tumbling of targets,manipulator with redundant Degrees of Freedom(DOFs)can be used to improve the compliance and therefore solve these problems.The Rope-Driven Snake Manipulator(RDSM)is a combina-tion of hyper-redundant DOFs and better compliance,and therefore it is suitable for capturing mis-sion.In this paper,a snake manipulator mechanism is designed,and the complete kinematic model and system dynamic model considering RDSM,target and contact is established.Then,to obtain the configuration of joint with hyper-redundant DOFs,an improved motion dexterity index is pro-posed as the joint motion optimization target.Besides,the force-position collaborative optimization index is designed to adjust active stiffness,and the impedance control method based on the modified index is used to capture the space target.Finally,the proposed force-position collaborative opti-mization method is verified by virtual prototype co-simulation.The results demonstrate that based on the proposed method,the collision force is reduced by about 25%compared to normal impe-dance control,showing higher safety.展开更多
This paper proposes a human body motion capturing system using the depth images. It consists of three processes to estimate the human pose parameters. First, we develop a pixel-based body part classifier to segment th...This paper proposes a human body motion capturing system using the depth images. It consists of three processes to estimate the human pose parameters. First, we develop a pixel-based body part classifier to segment the human silhouette into different body part sub-regions and extract the primary joints. Second, we convert the distribution of the joints to the feature vector and apply the regression forest to estimate human pose parameters. Third, we apply the temporal constraints mechanism to find the best human pose parameter with the minimum estimation error. In experiments, we show that our system can operate in real-time with sufficient accuracy.展开更多
Microplastics are emerging micropollutants in water threatening aquatic and land organisms.The microplastic–water system is complicated due to the multiple constituents in the water system and the minuscule size of t...Microplastics are emerging micropollutants in water threatening aquatic and land organisms.The microplastic–water system is complicated due to the multiple constituents in the water system and the minuscule size of the plastic waste.Although typical plastic-based materials are inert,the behavior of fragmented plastics is arbitrary and indefinite.When exposed to erratic water environments with the presence of organic and synthetic impurities,pH,temperature,and salt,microplastic surfaces may be potentially active and generate charges in water.These phenomena determine microplastics in water as a colloidal system.The classical Derjaguin Landau Verwey and Overbeek(DLVO)theory can be used to identify the microplastic surface behavior in water.The modification of microplastic surfaces eventually determines the overall interactions between microplastics and other constituents in water.Moreover,the geometry of microplastics and additives present in microcontaminants play a crucial role in their net interactions.Hence,multiple microplastic removal techniques,such as coagulation,filtration,and air flotation,can be developed to address the issue.In many cases,a combination of these methods may be needed to achieve the overall procedure in water treatment plants or generic water systems.Selection of an appropriate microplastic removal technique is crucial and should be based on the water environment and intended water use to ensure its safety.展开更多
Mount Aragats is an intersection of divinity,science,and living off the land.In Armenia,Mount Aragats looms overhead as a permanent fixture in the sky,a fourpeaked volcano massif that rises from rivers and plains arou...Mount Aragats is an intersection of divinity,science,and living off the land.In Armenia,Mount Aragats looms overhead as a permanent fixture in the sky,a fourpeaked volcano massif that rises from rivers and plains around its base.The mountain is more than just a physical presence:It’s also a divine symbol.Gregory the Illuminator,the patron saint of Armenia who converted展开更多
A two-stage vacuum pressure swing adsorption(VPSA)process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue ...A two-stage vacuum pressure swing adsorption(VPSA)process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas(85%N_(2)/15%CO_(2)).In the first enriching stage,carbon molecular sieve(CMS),which shows kinetic selectivity for CO_(2)/N_(2),is adopted as the adsorbent to remove most N_(2)in feed gas,thereby upgrading CO_(2)and significantly reducing the amount for further refinement.The second stage loads zeolite 13X as adsorbent to purify the CO_(2)-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory.Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis.The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here.The optimal results achieved 95.1%purity and 92.9%recovery with a high CO_(2)productivity(1.89 mol CO_(2)·h^(-1)·kg^(-1))and an appropriate energy consumption of 1.07 MJ·(kg CO_(2))^(-1).Further analysis has been carried out by simulation for explicating the temperature,pressure,and concentration distribution at cyclic steady state.展开更多
The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current.However,the average velocity in most territorial waters of China is smaller than 1 m/s,and the lift type of airfoil bl...The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current.However,the average velocity in most territorial waters of China is smaller than 1 m/s,and the lift type of airfoil blades has limited application in most of these conditions.Therefore,it is of great significance to study the tidal current energy capture of blades in sub-low speed sea areas.The effect of flow impact resistance on the blade at sub-low current speed is considered and a new type of thin-walled blade based on the lift type of blade is proposed,and then the lift-impact combined hydrodynamic model of horizontal axis blade is established.Based on this model,and considering the characteristics of tidal current and velocity in the sea area of Yushan Islands,simulation and optimization of blade design are carried out.Additionally,the horizontal axis thin-walled blade and the NACA airfoil contrast blade under the same conditions are developed.By using a synthetical experimental test system,the power,torque,rotational speed and load characteristics of these two blades are tested.The performance of the thin-walled blade and the design theory are verified.It shows that this type of blade has much better energy capture efficiency in the sub-low speed sea area.This research will promote the study and development of turbines that can be used in low-speed current sea areas in the future.展开更多
基金supported by the National Natural Science Foundation of China(Nos.52130101 and 52271217)the Project of Science and Technology Development Plan of Jilin Province in China(Nos.20210402058GH,20220201114GX).
文摘Lithium-sulfur batteries(LSBs)are considered as the promising solution to replace conventional lithium-ion batteries due to satisfactory energy density.In recent times,the LSBs field has been found to face some difficulties in exploring practical applications in which cycling stability and cycle life are awful owing to the shuttling effect of lithium polysulfides(LiPSs)and low sulfur utilization.In this work,by synthesizing Co_(3)Se_(4) nanoparticles onto N-doped carbon(NC)polyhedra interconnected with carbon nanotubes(CNTs),NC@Co_(3)Se_(4)/CNTs is proposed as a multifunctional sulfur carrier.The Co_(3)Se_(4) nanoparticles fleetly catalyze the conversion of LiPSs and availably immobilize LiPSs.Meanwhile,the NC polyhedral skeleton enhances the electronic conductivity of active sulfur,while the CNTs facilitate Li+diffusion and supply a mass of conductive channels.Density-functional theory(DFT)calculations demonstrate the relevant mechanisms.That is to say,the NC@Co_(3)Se_(4)/CNTs benefit from the synergistic effect of Co_(3)Se_(4) nanoparticles(highly catalytic ability and strong adsorbability for LiPSs)and the special carbonaceous structure,rapidly converting LiPSs and inhibiting the shuttle of LiPSs.Therefore,lithium-sulfur battery assembled with S/NC@Co_(3)Se_(4)/CNTs cathode as well as nitrogen and sulfur co-doped carbon-coated polypropylene(N,S-C/PP)separator possesses a high initial discharge capacity of 1413 mAh·g-1 at 0.12C and persistently circulates for 1000 cycles at 1C with a capacity attenuation rate per cycle of 0.034%.This work provides a realistic idea for the use of transition metal selenide in the field of high-performance LSBs.
基金funded by the"14th Five-Year Plan"Civil Aerospace Pre-research Project of China(Grant No.D010301).
文摘Reusable and flexible capturing of space debris is highly required in future aerospace technologies.A tendon-actuated flexible robotic arm is therefore proposed for capturing floating targets in this paper.Firstly,an accurate dynamic model of the flexible robotic arm is established by using the absolute nodal coordinate formulation(ANCF)in the framework of the arbitrary Lagrangian-Eulerian(ALE)description and the natural coordinate formulation(NCF).The contact and self-contact dynamics of the flexible robotic arm when bending and grasping an object are considered via a fast contact detection approach.Then,the dynamic simulations of the flexible robotic arm for capturing floating targets are carried out to study the influence of the position,size,and mass of the target object on the grasping performance.Finally,a principle prototype of the tendon-actuated flexible robotic arm is manufactured to validate the dynamic model.The corresponding grasping experiments for objects of various shapes are also conducted to illustrate the excellent performance of the flexible robotic arm.
基金Program for Innovative Research Team in University(IRT520)CAST of China (20090703)
文摘When the space robot captures a floating target, contact impact occurs inevitably and frequently between the manipulator hand and the target, which seriously impacts the position and attitude of the robot and grasping security. ＂Dynamic grasping area＂ is introduced to describe the collision process of manipulator grasping target, and grasping area control equation is established. By analyzing the impact of grasping control parameters, base and target mass on the grasping process and combining the life experience, it is found that if the product of speed control parameter and dB adjustment parameter is close to but smaller than the minimum grasping speed, collision impact in the grasping process could be reduced greatly, and then an ideal grasping strategy is proposed. Simulation results indicate that during the same period, the strategy grasping is superior to the accelerating grasping, in that the amplitude of impact force is reduced to 20%, and the attitude control torque is reduced to 15%, and the impact on the robot is eliminated significantly. The results would have important academic value and engineering significance.
基金Data and Artificial Intelligence Scientific Chair at Umm Al-Qura University.
文摘Biomechanics is the study of physiological properties of data and the measurement of human behavior.In normal conditions,behavioural properties in stable form are created using various inputs of subconscious/conscious human activities such as speech style,body movements in walking patterns,writing style and voice tunes.One cannot perform any change in these inputs that make results reliable and increase the accuracy.The aim of our study is to perform a comparative analysis between the marker-based motion capturing system(MBMCS)and the marker-less motion capturing system(MLMCS)using the lower body joint angles of human gait patterns.In both the MLMCS and MBMCS,we collected trajectories of all the participants and performed joint angle computation to identify a person and recognize an activity(walk and running).Using five state of the art machine learning algorithms,we obtained 44.6%and 64.3%accuracy in person identification using MBMCS and MLMCS respectively with an ensemble algorithm(two angles as features).In the second set of experiments,we used six machine learning algorithms to obtain 65.9%accuracy with the k-nearest neighbor(KNN)algorithm(two angles as features)and 74.6%accuracy with an ensemble algorithm.Also,by increasing features(6 angles),we obtained higher accuracy of 99.3%in MBMCS for person recognition and 98.1%accuracy in MBMCS for activity recognition using the KNN algorithm.MBMCS is computationally expensive and if we redesign the model of OpenPose with more body joint points and employ more features,MLMCS(low-cost system)can be an effective approach for video data analysis in a person identification and activity recognition process.
基金supported by the National Natural Science Foundation of China (No. U1613227)Guangdong Special Support Program (No. 2017TX04X0071)+1 种基金Self-Planned Task of State Key Labora-tory of Robotics and System (HIT) (No. SKLRS201817B)Shenzhen Key Lab Fund of Mechanisms and Control in Aerospace (No. ZDSYS201703031002066)
文摘The growing amount of space debris poses a threat to operational spacecraft and the long-term sustainability of activities in outer space. According to the orbital mechanics, an uncontrolled space object will be tumbling, bringing great challenge to capture and remove it. In this paper, a dual-arm coordinated ‘‘Area-Oriented Capture'(AOC) method is proposed to capture a non-cooperative tumbling target. Firstly, the motion equation of the tumbling target is established, based on which, the dynamic properties are analyzed. Then, the ‘‘Area-Oriented Capture'concept is presented to deal with the problem of large pose(position and attitude) deviation and tumbling motion. An area rather than fixed points/devices is taken as the object to be tracked and captured. As long as the manipulators’ end-effectors move to a specified range of the objective areas(not fixed points on the target, but areas), the target satellite will be hugged by the two arms.At last, the proposed method and the traditional method(i.e. fixed-point oriented capture method)are compared and analyzed through simulation. The results show that the proposed method has larger pose tolerance and takes shorter time for capturing a tumbling target.
基金co-supported by the National Natural Science Foundation of China(Nos.61403038 and 61573066)the Open Research Fund of Key Laboratory of Space Utilization,Chinese Academy of Sciences(Nos.LSU-2016-05-2 and LSUKJTS-2017-02)。
文摘The rotational motion of a tumbling target brings great challenges to space robot on successfully capturing the tumbling target.Therefore,it is necessary to reduce the target's rotation to a rate at which capture can be accomplished by the space robot.In this paper,a detumbling strategy based on friction control of dual-arm space robot for capturing tumbling target is proposed.This strategy can reduce the target's rotational velocity while maintaining base attitude stability through the establishment of the rotation attenuation controller and base attitude adjustment controller.The rotation attenuation controller adopts the multi-space hybrid impedance control method to control the friction precisely.The base attitude adjustment controller applies the dual-arm extended Jacobian matrix to stabilize the base attitude.The main contributions of this paper are as follows:(1)The compliant control method is adopted to achieve a precise friction control,which can reduce the target angular velocity steadily;(2)The dual-arm extended Jacobian matrix is applied to stabilize the base attitude without affecting the target capture task;(3)The detumbling strategy of dualarm space robot is designed considering base attitude stabilization,realizing coordinated planning of the base attitude and the arms.The strategy is verified by a dual-arm space robot with two 7-DOF(degrees of freedom)arms.Simulation results show that,target with a rotation velocity of 20(°)/s can be effectively controlled to stop within 30 s,and the final deflection of the base attitude is less than 0.15°without affecting the target capture task,verifying the correctness and effectiveness of the strategy.Except to the tumbling target capture task,the control strategy can also be applied to other typical on-orbit operation tasks such as space debris removal and spacecraft maintenance.
基金supported by the National Natural Science Foundation of China(Nos.11072061 and 11372073)the Natural Science Foundation of Fujian Province(No.2010J01003)
文摘The impact dynamics, impact effect, and post-impact unstable motion sup- pression of free-floating space manipulator capturing a satellite on orbit are analyzed. Firstly, the dynamics equation of free-floating space manipulator is derived using the sec- ond Lagrangian equation. Combining the momentum conservation principle, the impact dynamics and effect between the space manipulator end-effector and satellite of the cap- ture process are analyzed with the momentum impulse method. Focusing on the unstable motion of space manipulator due to the above impact effect, a robust adaptive compound control algorithm is designed to suppress the above unstable motion. There is no need to control the free-floating base position to save the jet fuel. Finally, the simulation is proposed to show the impact effect and verify the validity of the control algorithm.
基金financially supported by the National Natural Science Foundation of China (Grant no. 51605431)Major Science and Technology Projects of Ningbo (Grant no. 2015C110015 and 2017C110005)。
文摘To avoid the damage caused by big wind and wave in cage culture, and to solve the problem of energy supply faced by automatic breeding equipment, a new type of floating breakwater, named as Savonius double buoy breakwater(SDBB), is proposed in the paper. The floating breakwater is composed of HDPE cylindrical double buoys and horizontal axis Savonius rotors, and has the functions of wave-absorbing and energy-capturing. Based on the linear wave theory and energy conservation law, the Fourier Transform was applied to separate the two-dimensional wave frequency domain, and the energy captured by the rotors and absorbed by the floating breakwater were calculated.Experiments were conducted in a two-dimensional wave-making flume, and the transmitted waves at different wave heights and periods, the tension of mooring lines, and the rotational torque exerted on the Savonius rotor were measured. A series of performance comparison tests were also performed on the new floating breakwater and the traditional double-floating breakwater. Results show that the new floating breakwater is better than the traditional one in terms of reducing wave transmittance, and the combination of the floating breakwater with Savonius rotors can provide for marine aquaculture equipments with green power supply to a certain degree of self-sufficiency.
基金the National Natural Science Foundation of China(51773134)the Program for the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(51721091)+2 种基金the Sichuan Province Science and Technology Project(2019YFH0112)the Sichuan Province Youth Science and Technology Innovation Team(2017TD0006)the Fundamental Research Funds for the Central Universities(2017SCU04A14 and YJ201821)。
文摘Lithium-sulfur(Li-S) batteries as extremely promising high-density energy storage devices have attracted extensive concern. However, practical applications of Li-S batteries are severely restricted by not only intrinsic polysulfides shuttle resulting from their concentration gradient diffusion and sluggish conversion kinetics but also serious safety issue caused by thermolabile and combustible polymer separators.Herein, it is presented for the first time that a robust and multifunctional separator with urchin-like Co-doped Fe OOH microspheres and multiwalled carbon nanotubes(MWCNTs) as an interlayer simultaneously achieves to suppress polysulfides shuttle as well as improves thermotolerance and nonflammability of commercial PP separator. Accordingly, Li-S batteries with modified separator exhibit remarkable performance in a wide range temperatures of-25–100 ℃. Typically, under 25 ℃, ultrahigh initial capacities of 1441 and 827.29 m A h g-1 at 1 C and 2 C are delivered, and remained capacities of 936 and 663.18 mA h g-1 can be obtained after 500 cycles, respectively. At 0.1 C, the S utilization can reach up to 97%. Significantly, at 1 C, the batteries also deliver an excellent performance with remained capacities of high to862.3, 608.4 and 420.6 m A h g-1 after 100, 300 and 450 cycles under 75, 0 and-25 ℃, respectively. This work provides a new insight for developing stable and safe high-performance Li-S batteries.
文摘In this paper,a new strategy for a sub-element-based shock capturing for discontinuous Galerkin(DG)approximations is presented.The idea is to interpret a DG element as a col-lection of data and construct a hierarchy of low-to-high-order discretizations on this set of data,including a first-order finite volume scheme up to the full-order DG scheme.The dif-ferent DG discretizations are then blended according to sub-element troubled cell indicators,resulting in a final discretization that adaptively blends from low to high order within a single DG element.The goal is to retain as much high-order accuracy as possible,even in simula-tions with very strong shocks,as,e.g.,presented in the Sedov test.The framework retains the locality of the standard DG scheme and is hence well suited for a combination with adaptive mesh refinement and parallel computing.The numerical tests demonstrate the sub-element adaptive behavior of the new shock capturing approach and its high accuracy.
基金Project supported by the Natural Science Foundation of Inner Mongolia(2020BS05033,2020MS05012)Inner Mongolia Major Basic Research Open Project(0406091701)。
文摘Ultrafine NdFeB waste is a relatively clean waste produced during NdFeB magnet processing.Fluorinecontaining wastewater is a common type of industrial wastewater,such as stainless steel pickling wastewater.In this work,rare earth element neodynium was recycled from ultrafine NdFeB waste by capturing fluorine ions in the fluorine-containing wastewater and prepared into neodynium oxyfluoride.The reaction process was investigated through UV-Vis-NIR,thermogravimetry/differential thermogravimetry(TG/DTG),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The neodymium hydroxide in the ultrafine NdFeB waste reacted with fluorine ions to form Nd(OH)_(2) F,and Nd(OH)_(2) F was then transformed into neodymium oxyfluoride after decomposition.The formed neodymium oxyfluoride is found to be particles with rhombohedral structure and a particle size of around 50 nm.The reaction kinetics of forming Nd(OH)_(2) F was investigated.The reaction kinetic equation was established and the reaction activation energy was calculated.The effect of fluorine ion concentration on the reaction rate and products was evaluated.The results show that the reaction rate increases with the increase of fluorine ion concentration in the range of 0.01-1.5 mol/L,but it has little effect.In addition,the fluorine ion concentration affects the crystallinity of formed neodymium oxyfluoride.The recycling process not only realizes the sustainable utilization of rare earths,but also reduces the concentration of fluorine ions in the fluorine-containing wastewater,achieving two goals with one stone.
基金supported by the National Natural Science Foundation of China(11372073,11072061)。
文摘In this paper,the dynamic evolution for a dualarm space robot capturing a spacecraft is studied,the impact effect and the coordinated stabilization control problem for postimpact closed chain system are discussed.At first,the pre-impact dynamic equations of open chain dual-arm space robot are established by Lagrangian approach,and the dynamic equations of a spacecraft are obtained by Newton-Euler method.Based on the results,with the process of integral and simplify,the response of the dual-arm space robot impacted by the spacecraft is analyzed by momentum conservation law and force transfer law.The closed chain system is formed in the post-impact phase.Closed chain constraint equations are obtained by the constraints of closed-loop geometry and kinematics.With the closed chain constraint equations,the composite system dynamic equations are derived.Secondly,the recurrent fuzzy neural network control scheme is designed for calm motion of unstable closed chain system with uncertain system parameter.In order to overcome the effects of uncertain system inertial parameters,the recurrent fuzzy neural network is used to approximate the unknown part,the control method with H∞tracking characteristic.According to the Lyapunov theory,the global stability is demonstrated.Meanwhile,the weighted minimum-norm theory is introduced to distribute torques guarantee that cooperative operation between manipulators.At last,numerical examples simulate the response of the collision,and the efficiency of the control scheme is verified by the simulation results.
基金Research supported by the National Basic Research Program of China(No.2009CB724104)
文摘This paper carries out systematical investigations on the performance of several typical shock-capturing schemes for the discontinuous Galerkin （DG） method, including the total variation bounded （TVB） limiter and three artificial diffusivity schemes （the basis function-based （BF） scheme, the face residual-based （FR） scheme, and the element residual-based （ER） scheme）. Shock-dominated flows （the Sod problem, the Shu- Osher problem, the double Mach reflection problem, and the transonic NACA0012 flow） are considered, addressing the issues of accuracy, non-oscillatory property, dependence on user-specified constants, resolution of discontinuities, and capability for steady solutions. Numerical results indicate that the TVB limiter is more efficient and robust, while the artificial diffusivity schemes are able to preserve small-scale flow structures better. In high order cases, the artificial diffusivity schemes have demonstrated superior performance over the TVB limiter.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.10972010,11028206,11371069,11372052,11402029,and 11472060)the Science and Technology Development Foundation of China Academy of Engineering Physics(CAEP),China(Grant No.2014B0201030)the Defense Industrial Technology Development Program of China(Grant No.B1520132012)
文摘Motivated by inconveniences of present hybrid methods,a gradient-augmented hybrid interface capturing method（GAHM） is presented for incompressible two-phase flow.A front tracking method（FTM） is used as the skeleton of the GAHM for low mass loss and resources.Smooth eulerian level set values are calculated from the FTM interface,and are used for a local interface reconstruction.The reconstruction avoids marker particle redistribution and enables an automatic treatment of interfacial topology change.The cubic Hermit interpolation is employed in all steps of the GAHM to capture subgrid structures within a single spacial cell.The performance of the GAHM is carefully evaluated in a benchmark test.Results show significant improvements of mass loss,clear subgrid structures,highly accurate derivatives（normals and curvatures） and low cost.The GAHM is further coupled with an incompressible multiphase flow solver,Super CE/SE,for more complex and practical applications.The updated solver is evaluated through comparison with an early droplet research.
文摘With the rapid development of space activities,non-cooperative space targets increase swiftly,such as failed satellites and upper stages,threating normal spacecrafts seriously.As there are some problems in the capture process,such as excessive collision and fast tumbling of targets,manipulator with redundant Degrees of Freedom(DOFs)can be used to improve the compliance and therefore solve these problems.The Rope-Driven Snake Manipulator(RDSM)is a combina-tion of hyper-redundant DOFs and better compliance,and therefore it is suitable for capturing mis-sion.In this paper,a snake manipulator mechanism is designed,and the complete kinematic model and system dynamic model considering RDSM,target and contact is established.Then,to obtain the configuration of joint with hyper-redundant DOFs,an improved motion dexterity index is pro-posed as the joint motion optimization target.Besides,the force-position collaborative optimization index is designed to adjust active stiffness,and the impedance control method based on the modified index is used to capture the space target.Finally,the proposed force-position collaborative opti-mization method is verified by virtual prototype co-simulation.The results demonstrate that based on the proposed method,the collision force is reduced by about 25%compared to normal impe-dance control,showing higher safety.
基金supported by“MOST”under Grant No.103-2221-E-468-006-MY2
文摘This paper proposes a human body motion capturing system using the depth images. It consists of three processes to estimate the human pose parameters. First, we develop a pixel-based body part classifier to segment the human silhouette into different body part sub-regions and extract the primary joints. Second, we convert the distribution of the joints to the feature vector and apply the regression forest to estimate human pose parameters. Third, we apply the temporal constraints mechanism to find the best human pose parameter with the minimum estimation error. In experiments, we show that our system can operate in real-time with sufficient accuracy.
基金supported by the Universiti Sains Malaysia Apex Era Research Grant(Grant No.1001.PBAHAN.881008).
文摘Microplastics are emerging micropollutants in water threatening aquatic and land organisms.The microplastic–water system is complicated due to the multiple constituents in the water system and the minuscule size of the plastic waste.Although typical plastic-based materials are inert,the behavior of fragmented plastics is arbitrary and indefinite.When exposed to erratic water environments with the presence of organic and synthetic impurities,pH,temperature,and salt,microplastic surfaces may be potentially active and generate charges in water.These phenomena determine microplastics in water as a colloidal system.The classical Derjaguin Landau Verwey and Overbeek(DLVO)theory can be used to identify the microplastic surface behavior in water.The modification of microplastic surfaces eventually determines the overall interactions between microplastics and other constituents in water.Moreover,the geometry of microplastics and additives present in microcontaminants play a crucial role in their net interactions.Hence,multiple microplastic removal techniques,such as coagulation,filtration,and air flotation,can be developed to address the issue.In many cases,a combination of these methods may be needed to achieve the overall procedure in water treatment plants or generic water systems.Selection of an appropriate microplastic removal technique is crucial and should be based on the water environment and intended water use to ensure its safety.
文摘Mount Aragats is an intersection of divinity,science,and living off the land.In Armenia,Mount Aragats looms overhead as a permanent fixture in the sky,a fourpeaked volcano massif that rises from rivers and plains around its base.The mountain is more than just a physical presence:It’s also a divine symbol.Gregory the Illuminator,the patron saint of Armenia who converted
基金financially supported by the Renewable Energy and Hydrogen Projects National Key Research&Development Program of China(2019YFB1505000)。
文摘A two-stage vacuum pressure swing adsorption(VPSA)process that coupled kinetically controlled and equilibrium controlled separation process with reflux has been investigated for capturing carbon dioxide from dry flue gas(85%N_(2)/15%CO_(2)).In the first enriching stage,carbon molecular sieve(CMS),which shows kinetic selectivity for CO_(2)/N_(2),is adopted as the adsorbent to remove most N_(2)in feed gas,thereby upgrading CO_(2)and significantly reducing the amount for further refinement.The second stage loads zeolite 13X as adsorbent to purify the CO_(2)-rich flow from the first stage for meeting the requirements of National Energy Technology Laboratory.Series of experiments have been conducted for adsorption isotherms measuring and lab-scale experimental validation as well as analysis.The effect of feed composition on the separation performance of the PSA system was studied experimentally and theoretically here.The optimal results achieved 95.1%purity and 92.9%recovery with a high CO_(2)productivity(1.89 mol CO_(2)·h^(-1)·kg^(-1))and an appropriate energy consumption of 1.07 MJ·(kg CO_(2))^(-1).Further analysis has been carried out by simulation for explicating the temperature,pressure,and concentration distribution at cyclic steady state.
基金This work was financially supported by the Special Funds of the State Oceanic Administration(Grant No.NBME2011CL02)Ningbo Major Science and Technology Public Relations Project(Grant No.2015C110015)Ningbo Natural Science Foundation Project(Grant No.2014A610091).
文摘The research on the hydrodynamics of blades is mainly focused on sea areas with high-speed current.However,the average velocity in most territorial waters of China is smaller than 1 m/s,and the lift type of airfoil blades has limited application in most of these conditions.Therefore,it is of great significance to study the tidal current energy capture of blades in sub-low speed sea areas.The effect of flow impact resistance on the blade at sub-low current speed is considered and a new type of thin-walled blade based on the lift type of blade is proposed,and then the lift-impact combined hydrodynamic model of horizontal axis blade is established.Based on this model,and considering the characteristics of tidal current and velocity in the sea area of Yushan Islands,simulation and optimization of blade design are carried out.Additionally,the horizontal axis thin-walled blade and the NACA airfoil contrast blade under the same conditions are developed.By using a synthetical experimental test system,the power,torque,rotational speed and load characteristics of these two blades are tested.The performance of the thin-walled blade and the design theory are verified.It shows that this type of blade has much better energy capture efficiency in the sub-low speed sea area.This research will promote the study and development of turbines that can be used in low-speed current sea areas in the future.
