1.Introduction Mobile communications have catalyzed a new era of informa-tion technology revolution,significantly broadening and deepen-ing human-to-human,human-to-machine,and machine-to-machine connections.With their...1.Introduction Mobile communications have catalyzed a new era of informa-tion technology revolution,significantly broadening and deepen-ing human-to-human,human-to-machine,and machine-to-machine connections.With their incredible speed of development and wide-reaching impact,mobile communications serve as the cornerstone of the Internet of Everything,profoundly reshaping human cognitive abilities and ways of thinking.Furthermore,mobile communications are altering the patterns of production and life,driving leaps in productivity quality,and strongly promot-ing innovation within human civilization.展开更多
A buckling-restrained steel plate shear wall(BRSPSW)structure with butterfly-shaped links on the lateral sides is introduced to improve the cooperative perfor-mance between the BRSPSW and the boundary frames.A one-spa...A buckling-restrained steel plate shear wall(BRSPSW)structure with butterfly-shaped links on the lateral sides is introduced to improve the cooperative perfor-mance between the BRSPSW and the boundary frames.A one-span two-story concrete-filled steel tube(CFT)column frame specimen equipped with lateral-side butterfly-shaped linked BRSPSWs(LBL-BRSPSWs)is evaluated under low-cycle reversed loading.A finite element(FE)model is developed and validated based on the test results.This FE model accurately simulates the failure modes and load-dis-placement curves.Parametric analyses are conducted on the butterfly-shaped links.The results show that the interactions between the CFT column frame and LBL-BRSPSWs are sig-nificantly influenced by the width ratio of the butterfly-shaped links,while the taper ratio and aspect ratio have relatively minor influences.Compared with traditional steel shear walls with four-sided connections,LBL-BRSPSWs reduce the additional axial forces and bending moments in the frame columns by 28%to 73%and 17%to 87%,respectively,with only a 9%to 30%decrease in the lateral resistance.The experimental and parametric analysis results indicate that setting butterfly-shaped links on the lateral sides of BRSPSWs can significantly enhance their cooperative performance with the boundary frame.The butterfly-shaped link width ratio has a linear relationship with the lateral-resistance performance of the specimens and the additional internal forces in the frame columns.To ensure that LBL-BRSPSW fails prior to the column frames,the link width ratio should be optimized.展开更多
The Tian Qin space-borne gravitational wave detector will orbit at an altitude of1.0×10^(5)km with an arm length of 1.7×10^(5)km,structured in an equilateral triangular satellite formation.The Tian Qin proje...The Tian Qin space-borne gravitational wave detector will orbit at an altitude of1.0×10^(5)km with an arm length of 1.7×10^(5)km,structured in an equilateral triangular satellite formation.The Tian Qin project delineates detailed requirements for orbit determination during both the launch phase and subsequent scientific experimentation.This paper pioneers the investigation of Precise Orbit Determination(POD)for Tian Qin utilizing the third generation of Bei Dou global navigation satellite system(BDS-3)Inter-Satellite Link(ISL)through simulation.By analyzing the visibility,the feasibility of using BDS-3 ISLs for Tian Qin POD is explored.Furthermore,a refined Solar Radiation Pressure(SRP)model is developed,and the POD accuracy of Tian Qin is assessed,considering factors such as arc length,ranging intervals,and error sources.The results indicate the following:(A)Visibility between Tian Qin and BDS-3 satellites is intermittent,with an average of 10.6 BDS-3 satellites visible to Tian Qin,and the average Root Mean Square(RMS)-value of Position Dilution of Precision(PDOP)for Tian Qin is 48.13.(B)POD accuracy improves with shorter ranging intervals.(C)The error in ephemeris is the dominant factor affecting the POD accuracy.(D)The establishment of three links between Tian Qin and the BDS-3 satellites satisfies the POD requirements of Tian Qin.With a ranging interval of 600 s and over a 7-day arc,the average three-Dimensional(3D)position accuracy of the three Tian Qin satellites is 1.35 m,while the 3D velocity accuracy is 0.08 mm/s.展开更多
Cooperative utilization of multidimensional resources including cache, power and spectrum in satellite-terrestrial integrated networks(STINs) can provide a feasible approach for massive streaming media content deliver...Cooperative utilization of multidimensional resources including cache, power and spectrum in satellite-terrestrial integrated networks(STINs) can provide a feasible approach for massive streaming media content delivery over the seamless global coverage area. However, the on-board supportable resources of a single satellite are extremely limited and lack of interaction with others. In this paper, we design a network model with two-layered cache deployment, i.e., satellite layer and ground base station layer, and two types of sharing links, i.e., terrestrial-satellite sharing(TSS) links and inter-satellite sharing(ISS) links, to enhance the capability of cooperative delivery over STINs. Thus, we use rateless codes for the content divided-packet transmission, and derive the total energy efficiency(EE) in the whole transmission procedure, which is defined as the ratio of traffic offloading and energy consumption. We formulate two optimization problems about maximizing EE in different sharing scenarios(only TSS and TSS-ISS),and propose two optimized algorithms to obtain the optimal content placement matrixes, respectively.Simulation results demonstrate that, enabling sharing links with optimized cache placement have more than 2 times improvement of EE performance than other traditional placement schemes. Particularly, TSS-ISS schemes have the higher EE performance than only TSS schemes under the conditions of enough number of satellites and smaller inter-satellite distances.展开更多
In this paper,for Multi-Spacecraft System(MSS)with a directed communication topology link and a static virtual leader,a controller is proposed to realize attitude consensus and attitude stabilization with stochastic l...In this paper,for Multi-Spacecraft System(MSS)with a directed communication topology link and a static virtual leader,a controller is proposed to realize attitude consensus and attitude stabilization with stochastic links failure and actuator saturation.First,an MSS attitude error model suitable for a directed topology link and with a static virtual leader based on SO(3)is derived,which considers that the attitude error on SO(3)cannot be defined based on algebraic subtraction.Then,we design a controller to realize the MSS on SO(3)with attitude consensus and attitude stabilization under stochastic links failure and actuator saturation.Finally,the simulation results of a multi-spacecraft system with stochastic links failure and a static virtual leader spacecraft are demonstrated to illustrate the efficiency of the attitude controller.展开更多
On June 30,2024,the much-anticipated Shenzhen-Zhongshan Link officially began trial operation.The world-class cross-sea cluster project integrating two bridges,two islands,and an underwater tunnel is expected to short...On June 30,2024,the much-anticipated Shenzhen-Zhongshan Link officially began trial operation.The world-class cross-sea cluster project integrating two bridges,two islands,and an underwater tunnel is expected to shorten the driving time from Shenzhen to Zhongshan from two hours to 30 minutes,helping create a 30-minute commute circle across the area.As the flow of innovation factors accelerates through the Shenzhen Zhongshan Link,Zhongshan City has been proactively exploring cooperation models such as“Shenzhen headquarters plus Zhongshan manufacturing,”“Shenzhen leading businesses plus Zhongshan support,”and“Shenzhen R&D plus Zhongshan commercialization”to form a one-hour science and technology industrial cooperation circle with Shenzhen and build a more open,coordinated,and efficient regional innovation system.展开更多
In order to suppress vibration in flexible manipulators, a new type of manipulator mechanism with controllable local degrees of freedom is proposed. This mechanism consists of a main chain and some branch links. The m...In order to suppress vibration in flexible manipulators, a new type of manipulator mechanism with controllable local degrees of freedom is proposed. This mechanism consists of a main chain and some branch links. The main chain is of a flexible open-chain configuration with an end-effector installed at its tip, and the rigid branch links are able to perform active movements. It is proved by kinematics and dynamic analysis that, the branch links bear no direct kinematic relation to the main chain, but their independent motions can strongly affect the dynamic behavior and performance of the flexible manipulator. Then comes a new idea of suppressing vibration, in which independent motions of the branch links are used to suppress the undesired vibration of the flexible main chain through dynamic coupling. On this basis, an optimal method for reducing vibration of flexible manipulators is proposed. Finally, the effectiveness of this method is verified by numerical simulations.展开更多
Under the conditions of joint torque output dead-zone and external disturbance,the trajectory tracking and vibration suppression for a free-floating space robot(FFSR)system with elastic base and flexible links were di...Under the conditions of joint torque output dead-zone and external disturbance,the trajectory tracking and vibration suppression for a free-floating space robot(FFSR)system with elastic base and flexible links were discussed.First,using the Lagrange equation of the second kind,the dynamic model of the system was derived.Second,utilizing singular perturbation theory,a slow subsystem describing the rigid motion and a fast subsystem corresponding to flexible vibration were obtained.For the slow subsystem,when the width of deadzone is uncertain,a dead-zone pre-compensator was designed to eliminate the impact of joint torque output dead-zone,and an integral sliding mode neural network control was proposed.The integral sliding mode term can reduce the steady state error.For the fast subsystem,an optimal linear quadratic regulator(LQR)controller was adopted to damp out the vibration of the flexible links and elastic base simultaneously.Finally,computer simulations show the effectiveness of the compound control method.展开更多
The chain/wire rope/chain combination is a common choice for mooring offshore floating platforms. However, data of the drag coefficients of chain links are rather limited, resulting in uncertainties with the calculati...The chain/wire rope/chain combination is a common choice for mooring offshore floating platforms. However, data of the drag coefficients of chain links are rather limited, resulting in uncertainties with the calculations of the drag force, and hence the damping of the mooring system. In this paper, the importance of the selection of the drag coefficient is first investigated. The computational fluid dynamics(CFD) method is then used to determine the drag coefficients of a studless chain under steady flows. Numerical model validation is first completed by simulating a smooth circular cylinder under steady flows. In particular, the performance of different turbulence models is assessed through the comparisons between the calculations and the experimental results. The large eddy simulation(LES) model is finally selected for the simulation of steady flows past a chain. The effects of the Reynolds number on the drag coefficient of a stud-less chain is also studied. The results show that the calculated drag coefficients of a stud-less chain are fairly consistent with the available experimental data.展开更多
Network information mining is the study of the network topology,which may answer a large number of applicationbased questions towards the structural evolution and the function of a real system.The question can be rela...Network information mining is the study of the network topology,which may answer a large number of applicationbased questions towards the structural evolution and the function of a real system.The question can be related to how the real system evolves or how individuals interact with each other in social networks.Although the evolution of the real system may seem to be found regularly,capturing patterns on the whole process of evolution is not trivial.Link prediction is one of the most important technologies in network information mining,which can help us understand the evolution mechanism of real-life network.Link prediction aims to uncover missing links or quantify the likelihood of the emergence of nonexistent links from known network structures.Currently,widely existing methods of link prediction almost focus on short-path networks that usually have a myriad of close triangular structures.However,these algorithms on highly sparse or longpath networks have poor performance.Here,we propose a new index that is associated with the principles of structural equivalence and shortest path length(SESPL)to estimate the likelihood of link existence in long-path networks.Through a test of 548 real networks,we find that SESPL is more effective and efficient than other similarity-based predictors in long-path networks.Meanwhile,we also exploit the performance of SESPL predictor and of embedding-based approaches via machine learning techniques.The results show that the performance of SESPL can achieve a gain of 44.09%over GraphWave and 7.93%over Node2vec.Finally,according to the matrix of maximal information coefficient(MIC)between all the similarity-based predictors,SESPL is a new independent feature in the space of traditional similarity features.展开更多
The paper deals with the dynamic response prediction of the composite structure,which consists of two linear components coupled by some nonlinear vibration isolators. Based on the measured impulse response functions o...The paper deals with the dynamic response prediction of the composite structure,which consists of two linear components coupled by some nonlinear vibration isolators. Based on the measured impulse response functions of the linear components, three kinds of dynamic equations of interfacial integration are proposed and a procedure to transform the dynamic equations of integral type into a set of ordinary differential equations is suggested. Computer simulations and a real test are given to verify the effectiveness of the theoretical results.展开更多
This paper reviews the progress of population geography in China since the 1980 s. The review results suggest that contrary to the common perception of its invisibility and marginalized status in the field, tremendous...This paper reviews the progress of population geography in China since the 1980 s. The review results suggest that contrary to the common perception of its invisibility and marginalized status in the field, tremendous progress has been made in population geography in China since the 1980 s. Population geographers have made significant contribution to the understanding of a wide range of population issues from geographical perspectives, including migration, urbanization, population distribution, the relationships between population, environment and resources, aging, marriage patterns, and migrants＇ crimes, although such contribution often did not appear in the geographical circle. Furthermore, population geographers have played an indispensable role in revitalizing population studies in China and forging its links to human geography, occupying an important position in this multi-disciplinary field. Population geographers＇ contribution to the areas of migration and urbanization research has been particularly significant, reflected in their leading roles in these areas＇ research. The paper demonstrates that as latecomers in the field after more than 20 years of isolation, population geographers in China have gone through a process of catching up and increasing engagement with developments in social sciences and increasing interaction with social scientists since the 1980 s, and have benefited greatly from it; however, there is a tendency for population geography to be increasingly alienated from the main stream human geography, a phenomenon similar to but not exactly the same as Anglo-American geography in the late 1990 s and early 2000 s. The paper argues that population geography is only half way in the course to forge the links between population studies and human geography, and it needs to return to geographical sciences to strike a healthy balance between the field of population studies and that of human geography, and promote its further development in a multi-disciplinary field.展开更多
This article generalizes our previous results for a quantum system of two nodes to a quantum system ofm(m ≥ 2) nodes. It shows that there is a one to one correspondence between 2m GHZ states for a quantum system ofm...This article generalizes our previous results for a quantum system of two nodes to a quantum system ofm(m ≥ 2) nodes. It shows that there is a one to one correspondence between 2m GHZ states for a quantum system ofm(m ≥ 2) nodes and 2m oriented links of the linkage N1 in knot theory, where N = 4 C2m = 2m(m - 1) is the numberof crossings of the link with m components, the subscript 1 denotes the order of the unoriented m components link withN crossings, i.e. the first type, actually the simplest type.展开更多
Like in other modalities of therapy,thecurative effects depend on both thetherapeutist and the patient.From clinicalexperience,the author summarized the fol-lowing important links for promoting thecurative effect of a...Like in other modalities of therapy,thecurative effects depend on both thetherapeutist and the patient.From clinicalexperience,the author summarized the fol-lowing important links for promoting thecurative effect of acupuncture.展开更多
The University s involvement in visits by ChinesePresident J iang Zemin and United States President BillClinton in September made it an unprecedentedmonth in the institution s history.On Wednesday 15 September Preside...The University s involvement in visits by ChinesePresident J iang Zemin and United States President BillClinton in September made it an unprecedentedmonth in the institution s history.On Wednesday 15 September President Jiang metstaff of the School of Forestry to discuss展开更多
The first long-term rainfall monitoring experiment using the commercial microwave links(CMLs)network in East China is introduced.The network,located in Jiangyin,Jiangsu Province,consists of 49 links with frequencies r...The first long-term rainfall monitoring experiment using the commercial microwave links(CMLs)network in East China is introduced.The network,located in Jiangyin,Jiangsu Province,consists of 49 links with frequencies ranging from 15 GHz to 26 GHz and lengths from 1.14 km to 4.78 km.An OTT PARSIVEL disdrometer is deployed to refine the local rain-induced attenuation relationship,and the CML observations are compared simultaneously with five rain gauges.The inversion parameters of the CML are optimized by minimizing the error of the accumulated rainfall of historical rainfall events.The inversion results show that the daily accumulated rainfall retrieved by the CMLs agrees well with the rain gauge measurements.As an opportunistic approach to monitor near-surface rainfall with high spatiotemporal representativeness and accuracy,the CML network can be used to monitor and forecast urban flood disasters,especially in regions where the widepread deployment of conventional meteorological instruments is impractical.展开更多
Magma is transported in brittle rock by diking.Diking plays a key role in tectonic phenomena such as continental rifting and plate divergence at mid-ocean ridges.In spite of the importance of understanding how magma is
We propose a model of edge-coupled interdependent networks with directed dependency links(EINDDLs)and develop the theoretical analysis framework of this model based on the self-consistent probabilities method.The phas...We propose a model of edge-coupled interdependent networks with directed dependency links(EINDDLs)and develop the theoretical analysis framework of this model based on the self-consistent probabilities method.The phase transition behaviors and parameter thresholds of this model under random attacks are analyzed theoretically on both random regular(RR)networks and Erd¨os-Renyi(ER)networks,and computer simulations are performed to verify the results.In this EINDDL model,a fractionβof connectivity links within network B depends on network A and a fraction(1-β)of connectivity links within network A depends on network B.It is found that randomly removing a fraction(1-p)of connectivity links in network A at the initial state,network A exhibits different types of phase transitions(first order,second order and hybrid).Network B is rarely affected by cascading failure whenβis small,and network B will gradually converge from the first-order to the second-order phase transition asβincreases.We present the critical values ofβfor the phase change process of networks A and B,and give the critical values of p andβfor network B at the critical point of collapse.Furthermore,a cascading prevention strategy is proposed.The findings are of great significance for understanding the robustness of EINDDLs.展开更多
基金supported by the National Key Research and Develop-ment Program of China(2019YFB1803400).
文摘1.Introduction Mobile communications have catalyzed a new era of informa-tion technology revolution,significantly broadening and deepen-ing human-to-human,human-to-machine,and machine-to-machine connections.With their incredible speed of development and wide-reaching impact,mobile communications serve as the cornerstone of the Internet of Everything,profoundly reshaping human cognitive abilities and ways of thinking.Furthermore,mobile communications are altering the patterns of production and life,driving leaps in productivity quality,and strongly promot-ing innovation within human civilization.
基金The National Key Research and Development Program of China(No.2023YFC3805005)Shanghai Municipal Science and Technology Commission Research Program(No.22DZ1201404).
文摘A buckling-restrained steel plate shear wall(BRSPSW)structure with butterfly-shaped links on the lateral sides is introduced to improve the cooperative perfor-mance between the BRSPSW and the boundary frames.A one-span two-story concrete-filled steel tube(CFT)column frame specimen equipped with lateral-side butterfly-shaped linked BRSPSWs(LBL-BRSPSWs)is evaluated under low-cycle reversed loading.A finite element(FE)model is developed and validated based on the test results.This FE model accurately simulates the failure modes and load-dis-placement curves.Parametric analyses are conducted on the butterfly-shaped links.The results show that the interactions between the CFT column frame and LBL-BRSPSWs are sig-nificantly influenced by the width ratio of the butterfly-shaped links,while the taper ratio and aspect ratio have relatively minor influences.Compared with traditional steel shear walls with four-sided connections,LBL-BRSPSWs reduce the additional axial forces and bending moments in the frame columns by 28%to 73%and 17%to 87%,respectively,with only a 9%to 30%decrease in the lateral resistance.The experimental and parametric analysis results indicate that setting butterfly-shaped links on the lateral sides of BRSPSWs can significantly enhance their cooperative performance with the boundary frame.The butterfly-shaped link width ratio has a linear relationship with the lateral-resistance performance of the specimens and the additional internal forces in the frame columns.To ensure that LBL-BRSPSW fails prior to the column frames,the link width ratio should be optimized.
基金co-supported by the Guangdong Major Project of Basic and Applied Basic Research,China(No.2019B030302001)the Guangdong Basic and Applied Basic Research Foundation,China(No.2022A1515110236)the Fundamental Research Funds for the Central Universities,Sun Yat-Sen University,China(No.23xkjc001)。
文摘The Tian Qin space-borne gravitational wave detector will orbit at an altitude of1.0×10^(5)km with an arm length of 1.7×10^(5)km,structured in an equilateral triangular satellite formation.The Tian Qin project delineates detailed requirements for orbit determination during both the launch phase and subsequent scientific experimentation.This paper pioneers the investigation of Precise Orbit Determination(POD)for Tian Qin utilizing the third generation of Bei Dou global navigation satellite system(BDS-3)Inter-Satellite Link(ISL)through simulation.By analyzing the visibility,the feasibility of using BDS-3 ISLs for Tian Qin POD is explored.Furthermore,a refined Solar Radiation Pressure(SRP)model is developed,and the POD accuracy of Tian Qin is assessed,considering factors such as arc length,ranging intervals,and error sources.The results indicate the following:(A)Visibility between Tian Qin and BDS-3 satellites is intermittent,with an average of 10.6 BDS-3 satellites visible to Tian Qin,and the average Root Mean Square(RMS)-value of Position Dilution of Precision(PDOP)for Tian Qin is 48.13.(B)POD accuracy improves with shorter ranging intervals.(C)The error in ephemeris is the dominant factor affecting the POD accuracy.(D)The establishment of three links between Tian Qin and the BDS-3 satellites satisfies the POD requirements of Tian Qin.With a ranging interval of 600 s and over a 7-day arc,the average three-Dimensional(3D)position accuracy of the three Tian Qin satellites is 1.35 m,while the 3D velocity accuracy is 0.08 mm/s.
基金supported by National Natural Sciences Foundation of China(No.62271165,62027802,61831008)the Guangdong Basic and Applied Basic Research Foundation(No.2023A1515030297,2021A1515011572)Shenzhen Science and Technology Program ZDSYS20210623091808025,Stable Support Plan Program GXWD20231129102638002.
文摘Cooperative utilization of multidimensional resources including cache, power and spectrum in satellite-terrestrial integrated networks(STINs) can provide a feasible approach for massive streaming media content delivery over the seamless global coverage area. However, the on-board supportable resources of a single satellite are extremely limited and lack of interaction with others. In this paper, we design a network model with two-layered cache deployment, i.e., satellite layer and ground base station layer, and two types of sharing links, i.e., terrestrial-satellite sharing(TSS) links and inter-satellite sharing(ISS) links, to enhance the capability of cooperative delivery over STINs. Thus, we use rateless codes for the content divided-packet transmission, and derive the total energy efficiency(EE) in the whole transmission procedure, which is defined as the ratio of traffic offloading and energy consumption. We formulate two optimization problems about maximizing EE in different sharing scenarios(only TSS and TSS-ISS),and propose two optimized algorithms to obtain the optimal content placement matrixes, respectively.Simulation results demonstrate that, enabling sharing links with optimized cache placement have more than 2 times improvement of EE performance than other traditional placement schemes. Particularly, TSS-ISS schemes have the higher EE performance than only TSS schemes under the conditions of enough number of satellites and smaller inter-satellite distances.
基金supported in part by the National Natural Science Foundation of China(Nos.U20B2054,U20B2056 and 62103275)the Natural Science Foundation of Shanghai,China(No.23ZR1432400)。
文摘In this paper,for Multi-Spacecraft System(MSS)with a directed communication topology link and a static virtual leader,a controller is proposed to realize attitude consensus and attitude stabilization with stochastic links failure and actuator saturation.First,an MSS attitude error model suitable for a directed topology link and with a static virtual leader based on SO(3)is derived,which considers that the attitude error on SO(3)cannot be defined based on algebraic subtraction.Then,we design a controller to realize the MSS on SO(3)with attitude consensus and attitude stabilization under stochastic links failure and actuator saturation.Finally,the simulation results of a multi-spacecraft system with stochastic links failure and a static virtual leader spacecraft are demonstrated to illustrate the efficiency of the attitude controller.
文摘On June 30,2024,the much-anticipated Shenzhen-Zhongshan Link officially began trial operation.The world-class cross-sea cluster project integrating two bridges,two islands,and an underwater tunnel is expected to shorten the driving time from Shenzhen to Zhongshan from two hours to 30 minutes,helping create a 30-minute commute circle across the area.As the flow of innovation factors accelerates through the Shenzhen Zhongshan Link,Zhongshan City has been proactively exploring cooperation models such as“Shenzhen headquarters plus Zhongshan manufacturing,”“Shenzhen leading businesses plus Zhongshan support,”and“Shenzhen R&D plus Zhongshan commercialization”to form a one-hour science and technology industrial cooperation circle with Shenzhen and build a more open,coordinated,and efficient regional innovation system.
基金Ministry of Education Important Research Project of Scienceand Technology of China(307005)National Hi-Tech Research and Development Program of China(SQ2007AA04Z231266)
文摘In order to suppress vibration in flexible manipulators, a new type of manipulator mechanism with controllable local degrees of freedom is proposed. This mechanism consists of a main chain and some branch links. The main chain is of a flexible open-chain configuration with an end-effector installed at its tip, and the rigid branch links are able to perform active movements. It is proved by kinematics and dynamic analysis that, the branch links bear no direct kinematic relation to the main chain, but their independent motions can strongly affect the dynamic behavior and performance of the flexible manipulator. Then comes a new idea of suppressing vibration, in which independent motions of the branch links are used to suppress the undesired vibration of the flexible main chain through dynamic coupling. On this basis, an optimal method for reducing vibration of flexible manipulators is proposed. Finally, the effectiveness of this method is verified by numerical simulations.
基金Supported by the National Natural Science Foundation of China(11372073,11072061)Industrial Robot Basic Component Technology Research and Development Platform,Fujian,China(2014H21010011)。
文摘Under the conditions of joint torque output dead-zone and external disturbance,the trajectory tracking and vibration suppression for a free-floating space robot(FFSR)system with elastic base and flexible links were discussed.First,using the Lagrange equation of the second kind,the dynamic model of the system was derived.Second,utilizing singular perturbation theory,a slow subsystem describing the rigid motion and a fast subsystem corresponding to flexible vibration were obtained.For the slow subsystem,when the width of deadzone is uncertain,a dead-zone pre-compensator was designed to eliminate the impact of joint torque output dead-zone,and an integral sliding mode neural network control was proposed.The integral sliding mode term can reduce the steady state error.For the fast subsystem,an optimal linear quadratic regulator(LQR)controller was adopted to damp out the vibration of the flexible links and elastic base simultaneously.Finally,computer simulations show the effectiveness of the compound control method.
基金financial support for the PhD study from GL-Nobel Denton based in London
文摘The chain/wire rope/chain combination is a common choice for mooring offshore floating platforms. However, data of the drag coefficients of chain links are rather limited, resulting in uncertainties with the calculations of the drag force, and hence the damping of the mooring system. In this paper, the importance of the selection of the drag coefficient is first investigated. The computational fluid dynamics(CFD) method is then used to determine the drag coefficients of a studless chain under steady flows. Numerical model validation is first completed by simulating a smooth circular cylinder under steady flows. In particular, the performance of different turbulence models is assessed through the comparisons between the calculations and the experimental results. The large eddy simulation(LES) model is finally selected for the simulation of steady flows past a chain. The effects of the Reynolds number on the drag coefficient of a stud-less chain is also studied. The results show that the calculated drag coefficients of a stud-less chain are fairly consistent with the available experimental data.
基金supported by the National Natural Science Foundation of China(Grant Nos.61773091 and 62173065)the Industry-University-Research Innovation Fund for Chinese Universities(Grant No.2021ALA03016)+2 种基金the Fund for University Innovation Research Group of Chongqing(Grant No.CXQT21005)the National Social Science Foundation of China(Grant No.20CTQ029)the Fundamental Research Funds for the Central Universities(Grant No.SWU119062).
文摘Network information mining is the study of the network topology,which may answer a large number of applicationbased questions towards the structural evolution and the function of a real system.The question can be related to how the real system evolves or how individuals interact with each other in social networks.Although the evolution of the real system may seem to be found regularly,capturing patterns on the whole process of evolution is not trivial.Link prediction is one of the most important technologies in network information mining,which can help us understand the evolution mechanism of real-life network.Link prediction aims to uncover missing links or quantify the likelihood of the emergence of nonexistent links from known network structures.Currently,widely existing methods of link prediction almost focus on short-path networks that usually have a myriad of close triangular structures.However,these algorithms on highly sparse or longpath networks have poor performance.Here,we propose a new index that is associated with the principles of structural equivalence and shortest path length(SESPL)to estimate the likelihood of link existence in long-path networks.Through a test of 548 real networks,we find that SESPL is more effective and efficient than other similarity-based predictors in long-path networks.Meanwhile,we also exploit the performance of SESPL predictor and of embedding-based approaches via machine learning techniques.The results show that the performance of SESPL can achieve a gain of 44.09%over GraphWave and 7.93%over Node2vec.Finally,according to the matrix of maximal information coefficient(MIC)between all the similarity-based predictors,SESPL is a new independent feature in the space of traditional similarity features.
文摘The paper deals with the dynamic response prediction of the composite structure,which consists of two linear components coupled by some nonlinear vibration isolators. Based on the measured impulse response functions of the linear components, three kinds of dynamic equations of interfacial integration are proposed and a procedure to transform the dynamic equations of integral type into a set of ordinary differential equations is suggested. Computer simulations and a real test are given to verify the effectiveness of the theoretical results.
基金National Natural Science Foundation of China,No.41471132,No.41501163
文摘This paper reviews the progress of population geography in China since the 1980 s. The review results suggest that contrary to the common perception of its invisibility and marginalized status in the field, tremendous progress has been made in population geography in China since the 1980 s. Population geographers have made significant contribution to the understanding of a wide range of population issues from geographical perspectives, including migration, urbanization, population distribution, the relationships between population, environment and resources, aging, marriage patterns, and migrants＇ crimes, although such contribution often did not appear in the geographical circle. Furthermore, population geographers have played an indispensable role in revitalizing population studies in China and forging its links to human geography, occupying an important position in this multi-disciplinary field. Population geographers＇ contribution to the areas of migration and urbanization research has been particularly significant, reflected in their leading roles in these areas＇ research. The paper demonstrates that as latecomers in the field after more than 20 years of isolation, population geographers in China have gone through a process of catching up and increasing engagement with developments in social sciences and increasing interaction with social scientists since the 1980 s, and have benefited greatly from it; however, there is a tendency for population geography to be increasingly alienated from the main stream human geography, a phenomenon similar to but not exactly the same as Anglo-American geography in the late 1990 s and early 2000 s. The paper argues that population geography is only half way in the course to forge the links between population studies and human geography, and it needs to return to geographical sciences to strike a healthy balance between the field of population studies and that of human geography, and promote its further development in a multi-disciplinary field.
文摘This article generalizes our previous results for a quantum system of two nodes to a quantum system ofm(m ≥ 2) nodes. It shows that there is a one to one correspondence between 2m GHZ states for a quantum system ofm(m ≥ 2) nodes and 2m oriented links of the linkage N1 in knot theory, where N = 4 C2m = 2m(m - 1) is the numberof crossings of the link with m components, the subscript 1 denotes the order of the unoriented m components link withN crossings, i.e. the first type, actually the simplest type.
文摘Like in other modalities of therapy,thecurative effects depend on both thetherapeutist and the patient.From clinicalexperience,the author summarized the fol-lowing important links for promoting thecurative effect of acupuncture.
文摘The University s involvement in visits by ChinesePresident J iang Zemin and United States President BillClinton in September made it an unprecedentedmonth in the institution s history.On Wednesday 15 September President Jiang metstaff of the School of Forestry to discuss
基金This research was funded by the China Postdoctoral Science Foundation(2021M701650)the Excellent Youth Scholars of the Natural Science Foundation of Hunan Province of China(2021JJ20046)+1 种基金the Open Grants of the State Key Laboratory of Severe Weather(Grant 2021LASW-A01)the National Natural Science Foundation of China(Grant No.42222505).
文摘The first long-term rainfall monitoring experiment using the commercial microwave links(CMLs)network in East China is introduced.The network,located in Jiangyin,Jiangsu Province,consists of 49 links with frequencies ranging from 15 GHz to 26 GHz and lengths from 1.14 km to 4.78 km.An OTT PARSIVEL disdrometer is deployed to refine the local rain-induced attenuation relationship,and the CML observations are compared simultaneously with five rain gauges.The inversion parameters of the CML are optimized by minimizing the error of the accumulated rainfall of historical rainfall events.The inversion results show that the daily accumulated rainfall retrieved by the CMLs agrees well with the rain gauge measurements.As an opportunistic approach to monitor near-surface rainfall with high spatiotemporal representativeness and accuracy,the CML network can be used to monitor and forecast urban flood disasters,especially in regions where the widepread deployment of conventional meteorological instruments is impractical.
文摘Magma is transported in brittle rock by diking.Diking plays a key role in tectonic phenomena such as continental rifting and plate divergence at mid-ocean ridges.In spite of the importance of understanding how magma is
基金the National Natural Science Foundation of China(Grant Nos.61973118,51741902,11761033,12075088,and 11835003)Project in JiangXi Province Department of Science and Technology(Grant Nos.20212BBE51010 and 20182BCB22009)the Natural Science Foundation of Zhejiang Province(Grant No.Y22F035316)。
文摘We propose a model of edge-coupled interdependent networks with directed dependency links(EINDDLs)and develop the theoretical analysis framework of this model based on the self-consistent probabilities method.The phase transition behaviors and parameter thresholds of this model under random attacks are analyzed theoretically on both random regular(RR)networks and Erd¨os-Renyi(ER)networks,and computer simulations are performed to verify the results.In this EINDDL model,a fractionβof connectivity links within network B depends on network A and a fraction(1-β)of connectivity links within network A depends on network B.It is found that randomly removing a fraction(1-p)of connectivity links in network A at the initial state,network A exhibits different types of phase transitions(first order,second order and hybrid).Network B is rarely affected by cascading failure whenβis small,and network B will gradually converge from the first-order to the second-order phase transition asβincreases.We present the critical values ofβfor the phase change process of networks A and B,and give the critical values of p andβfor network B at the critical point of collapse.Furthermore,a cascading prevention strategy is proposed.The findings are of great significance for understanding the robustness of EINDDLs.
