Two-dimensional(2 D) materials provide a platform to exploit the novel physical properties of functional nanodevices.Here, we report on the formation of a new 2 D layered material, a well-ordered monolayer TiTe_2, on ...Two-dimensional(2 D) materials provide a platform to exploit the novel physical properties of functional nanodevices.Here, we report on the formation of a new 2 D layered material, a well-ordered monolayer TiTe_2, on a Au(111) surface by molecular beam epitaxy(MBE). Low-energy electron diffraction(LEED) measurements of the samples indicate that the TiTe_2 film forms(√3 ×√7) superlattice with respect to the Au(111) substrate, which has three different orientations. Scanning tunneling microscopy(STM) measurements clearly show three ordered domains consistent with the LEED patterns.Density functional theory(DFT) calculations further confirm the formation of 2 H-TiTe_2 monolayer on the Au(111) surface with Te as buffer layer. The fabrication of this 2 D layered heterostructure expands 2 D material database, which may bring new physical properties for future applications.展开更多
As the torso is critical to the coordinated movement and flexibility of vertebrates,a 6-(Degree of Freedom)DOF bionic parallel torso with noteworthy motion space was designed in our previous work.To improve the compli...As the torso is critical to the coordinated movement and flexibility of vertebrates,a 6-(Degree of Freedom)DOF bionic parallel torso with noteworthy motion space was designed in our previous work.To improve the compliance of the parallel mechanism,a pair of virtual muscle models is constructed on both sides of the rotating joints of each link of the mechanism,and a bionic muscle control algorithm is introduced.By analyzing the control parameters of the muscle model,dynamic characteristics similar to those of biological muscle are obtained.An adaptive stiffness control is proposed to adaptively adjust the stiffness coefficient with the change in the external load of the parallel mechanism.The attitude closed-loop control can effectively keep the attitude angle unchanged when the position of the moving platform changes.The simulations and experiments are undertaken to validate compliant movements and the flexibility and adaptability of the parallel mechanism.展开更多
Fresh water resource scarcity and soil salt accumulation in the root-zone are two key limiting factors for sustainable agricultural development in the oasis region of arid inland basin, northwest China. The aim of thi...Fresh water resource scarcity and soil salt accumulation in the root-zone are two key limiting factors for sustainable agricultural development in the oasis region of arid inland basin, northwest China. The aim of this study was to explore an appropriate irrigation scheme to maintain sustainable crop cultivation in this region. The effects of four irrigation levels (full irrigation, mild deficit, moderate deficit, and severe deficit) and three irrigation methods (border, surface drip and subsurface drip) on soil water and salt dynamics, highland barley (Hordeum vulgare L.) yield, and crop water use efficiency were studied by field plot experiments. The results showed that soil salt in 0-100 cm profile was accumulated under all experimental treatments after one season of highland barley planting, but the accumulated salt mass decreased with the decrease of the lower limit of irrigation. Salt mass in 0-100 cm soil profile under subsurface drip irrigation was 16.8%-57.8% and 2.9%-58.4% less than that under border and surface drip irrigation, respectively. The grain yield of highland barley decreased first and then increased with the decrease of the lower limit of irrigation under surface drip and subsurface drip irrigation, but it was on the contrary under border irrigation. Mean grain yield for all irrigation levels under subsurface drip irrigation was 5.7% and 18.8% higher than that under border and surface drip irrigation, respectively. Water use efficiency increased with the decrease of the lower limit of irrigation, and the averaged water use efficiency of all irrigation levels under subsurface drip irrigation was 11.9% and 14.2% higher than that under border and surface drip irrigation, respectively. Considering economic benefit and irrigation water requirement, subsurface drip irrigation with the lower limit of irrigation of 50%-55% field capacity is suggested for highland barley planting in the arid oasis region.展开更多
With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be alw...With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be always deployed to the expected pose.For some precision optical mechanisms,even a minor deviation can result in significant error,so it needs to be measured and corrected.In this paper,the deployment process was modeled and simplified as rotation under single-rotation-axis constraint and translation under single-direction constraint.To solve the problem,a method based on cross-ratio invariability was proposed.The proposed method does not rely on camera calibration techniques,as well as artificial marking points,both of which are necessary in PnP.Instead,only three calibration images before launch and a measurement image on orbit were required.Simulations and experiments demonstrated that the proposed method is more accurate than PnP.In addition,experiments also proved that the feasibility of the proposed method under dark conditions with the aid of a light source and some reflective marking points.展开更多
Motion tracking via Inertial Measurement Units(IMUs)on mobile and wearable devices has attracted significant interest in recent years.High-accuracy IMU-tracking can be applied in various applications,such as indoor na...Motion tracking via Inertial Measurement Units(IMUs)on mobile and wearable devices has attracted significant interest in recent years.High-accuracy IMU-tracking can be applied in various applications,such as indoor navigation,gesture recognition,text input,etc.Many efforts have been devoted to improving IMU-based motion tracking in the last two decades,from early calibration techniques on ships or airplanes,to recent arm motion models used on wearable smart devices.In this paper,we present a comprehensive survey on IMU-tracking techniques on mobile and wearable devices.We also reveal the key challenges in IMU-based motion tracking on mobile and wearable devices and possible directions to address these challenges.展开更多
Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,...Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,is one of the ultimate goals in the catalytic field.Here,we report the formation of monolayer titanium selenide(TiSe2)with line defects.The low-temperature scanning tunneling microscopy/spectroscopy(STM/S)measurements revealed the structure and electronic states of the line defect.Density functional theory(DFT)calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results.Further,DFT calculations show that monolayer TiSe_(2) with line defects have good catalytic activity for hydrogen evolution reaction(HER).If the defects are decorated with single Pt atom,the HER catalytic activity will be enhanced dramatically(|△GH|=0.006 eV),which is much better than Pt metal(|△GH|=0.09 eV).Line defects in monolayer TiSe_(2)/Au(111)provide a wonderful platform for the design of high-performance catalysts.展开更多
基金Project supported by the National Key Research&Development Program of China(Grant Nos.2016YFA0202300 and 2018YFA0305800)the National Natural Science Foundation of China(Grant Nos.61504149,61725107,51572290,and 61622116)+2 种基金the Strategic Priority Research Program of Chinese Academy of Sciences(Grant Nos.XDB30000000 and XDB28000000)the University of Chinese Academy of Sciencesthe CAS Key Laboratory of Vacuum Physics
文摘Two-dimensional(2 D) materials provide a platform to exploit the novel physical properties of functional nanodevices.Here, we report on the formation of a new 2 D layered material, a well-ordered monolayer TiTe_2, on a Au(111) surface by molecular beam epitaxy(MBE). Low-energy electron diffraction(LEED) measurements of the samples indicate that the TiTe_2 film forms(√3 ×√7) superlattice with respect to the Au(111) substrate, which has three different orientations. Scanning tunneling microscopy(STM) measurements clearly show three ordered domains consistent with the LEED patterns.Density functional theory(DFT) calculations further confirm the formation of 2 H-TiTe_2 monolayer on the Au(111) surface with Te as buffer layer. The fabrication of this 2 D layered heterostructure expands 2 D material database, which may bring new physical properties for future applications.
基金supported by the National Natural Science Foundation of China(52173094 and 52003062)Guangxi Natural Science Foundation of China(2019GXNSFFA245010)the Scientific and Technological Plan of Guilin City(20220110-1).
基金the National Natural Science Foundation of China(Grant No.51605039)the Open Foundation of Shanghai Collaborative Innovation Center of Intelligent Manufacturing Robot Technology for Large Components,in part by the China Postdoctoral Science Foundation(Grant No.2018T111005)the Fundamental Research Funds for the Central Universities(Grant Nos.300102259308,300102259401,and 300102252503).
文摘As the torso is critical to the coordinated movement and flexibility of vertebrates,a 6-(Degree of Freedom)DOF bionic parallel torso with noteworthy motion space was designed in our previous work.To improve the compliance of the parallel mechanism,a pair of virtual muscle models is constructed on both sides of the rotating joints of each link of the mechanism,and a bionic muscle control algorithm is introduced.By analyzing the control parameters of the muscle model,dynamic characteristics similar to those of biological muscle are obtained.An adaptive stiffness control is proposed to adaptively adjust the stiffness coefficient with the change in the external load of the parallel mechanism.The attitude closed-loop control can effectively keep the attitude angle unchanged when the position of the moving platform changes.The simulations and experiments are undertaken to validate compliant movements and the flexibility and adaptability of the parallel mechanism.
基金supported by the National Key Research and Development Program of China (Grant No.2018YFC0406604).
文摘Fresh water resource scarcity and soil salt accumulation in the root-zone are two key limiting factors for sustainable agricultural development in the oasis region of arid inland basin, northwest China. The aim of this study was to explore an appropriate irrigation scheme to maintain sustainable crop cultivation in this region. The effects of four irrigation levels (full irrigation, mild deficit, moderate deficit, and severe deficit) and three irrigation methods (border, surface drip and subsurface drip) on soil water and salt dynamics, highland barley (Hordeum vulgare L.) yield, and crop water use efficiency were studied by field plot experiments. The results showed that soil salt in 0-100 cm profile was accumulated under all experimental treatments after one season of highland barley planting, but the accumulated salt mass decreased with the decrease of the lower limit of irrigation. Salt mass in 0-100 cm soil profile under subsurface drip irrigation was 16.8%-57.8% and 2.9%-58.4% less than that under border and surface drip irrigation, respectively. The grain yield of highland barley decreased first and then increased with the decrease of the lower limit of irrigation under surface drip and subsurface drip irrigation, but it was on the contrary under border irrigation. Mean grain yield for all irrigation levels under subsurface drip irrigation was 5.7% and 18.8% higher than that under border and surface drip irrigation, respectively. Water use efficiency increased with the decrease of the lower limit of irrigation, and the averaged water use efficiency of all irrigation levels under subsurface drip irrigation was 11.9% and 14.2% higher than that under border and surface drip irrigation, respectively. Considering economic benefit and irrigation water requirement, subsurface drip irrigation with the lower limit of irrigation of 50%-55% field capacity is suggested for highland barley planting in the arid oasis region.
基金Supported in part by the National Natural Science Foundation of China(No.62271148).
文摘With the rapid development of space science projects,large deployable mechanisms have been widely used.However,due to the effects of mechanical friction and gravitational acceleration,on-orbit mechanisms cannot be always deployed to the expected pose.For some precision optical mechanisms,even a minor deviation can result in significant error,so it needs to be measured and corrected.In this paper,the deployment process was modeled and simplified as rotation under single-rotation-axis constraint and translation under single-direction constraint.To solve the problem,a method based on cross-ratio invariability was proposed.The proposed method does not rely on camera calibration techniques,as well as artificial marking points,both of which are necessary in PnP.Instead,only three calibration images before launch and a measurement image on orbit were required.Simulations and experiments demonstrated that the proposed method is more accurate than PnP.In addition,experiments also proved that the feasibility of the proposed method under dark conditions with the aid of a light source and some reflective marking points.
基金part supported by the National Key R&D Program of China(No.2018YFB1004800)the National Natural Science Foundation of China(No.61932013)。
文摘Motion tracking via Inertial Measurement Units(IMUs)on mobile and wearable devices has attracted significant interest in recent years.High-accuracy IMU-tracking can be applied in various applications,such as indoor navigation,gesture recognition,text input,etc.Many efforts have been devoted to improving IMU-based motion tracking in the last two decades,from early calibration techniques on ships or airplanes,to recent arm motion models used on wearable smart devices.In this paper,we present a comprehensive survey on IMU-tracking techniques on mobile and wearable devices.We also reveal the key challenges in IMU-based motion tracking on mobile and wearable devices and possible directions to address these challenges.
基金We thank Guangchao Chen for his help.This work was supported by the National Key R&D Program of China(Nos.2019YFA0308500 and 2018YFA0305800)the National Natural Science Foundation of China(Nos.61925111 and 61888102)+1 种基金Strategic Priority Research Program of Chinese Academy of Sciences(Nos.XDB28000000 and XDB30000000)the Fundamental Research Funds for the Central Universities,and CAS Key Laboratory of Vacuum Physics.
文摘Two-dimensional(2D)materials with defects are desired for catalysis after the adsorption of monodispersed noble metal atoms.High-performance catalysts with the absolute value of Gibbs free energy(|△GH|)close to zero,is one of the ultimate goals in the catalytic field.Here,we report the formation of monolayer titanium selenide(TiSe2)with line defects.The low-temperature scanning tunneling microscopy/spectroscopy(STM/S)measurements revealed the structure and electronic states of the line defect.Density functional theory(DFT)calculation results confirmed that the line defects were induced by selenium vacancies and the STM simulation was in good agreement with the experimental results.Further,DFT calculations show that monolayer TiSe_(2) with line defects have good catalytic activity for hydrogen evolution reaction(HER).If the defects are decorated with single Pt atom,the HER catalytic activity will be enhanced dramatically(|△GH|=0.006 eV),which is much better than Pt metal(|△GH|=0.09 eV).Line defects in monolayer TiSe_(2)/Au(111)provide a wonderful platform for the design of high-performance catalysts.
