An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic traje...An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.展开更多
NiO,an anodic electrochromic material,has applications in energy-saving windows,intelligent displays,and military camouflage.However,its electrochromic mechanism and reasons for its performance degradation in alkaline...NiO,an anodic electrochromic material,has applications in energy-saving windows,intelligent displays,and military camouflage.However,its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood,making it challenging to improve NiO thin films.We studied the phases and electrochemical characteristics of NiO films in different states(initial,colored,bleached and after 8000 cycles)and identified three main reasons for performance degradation.First,Ni(OH)_(2)is generated during electrochromic cycling and deposited on the NiO film surface,gradually yielding a NiO@Ni(OH)_(2)core-shell structure,isolating the internal NiO film from the electrolyte,and preventing ion transfer.Second,the core-shell structure causes the mode of electrical conduction to change from first-to second-order conduction,reducing the efficiency of ion transfer to the surface Ni(OH)_(2)layer.Third,Ni(OH)_(2)and NiOOH,which have similar crystal structures but different b-axis lattice parameters,are formed during electrochromic cycling,and large volume changes in the unit cell reduce the structural stability of the thin film.Finally,we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films,which will promote the development of electrochromic technology.展开更多
Synchronization of high-order discrete-time complex networks with undirected topologies is studied and the impacts of time delays are investigated. Firstly,by the state decomposition,synchronization problems are trans...Synchronization of high-order discrete-time complex networks with undirected topologies is studied and the impacts of time delays are investigated. Firstly,by the state decomposition,synchronization problems are transformed into asymptotic stability ones of multiple lower dimensional time-delayed subsystems. Then,linear matrix inequality( LMI) criteria for synchronization are given,which can guarantee the scalability of complex networks since they only include three LMI constraints independent of the number of agents. Moreover,an explicit expression of the synchronization function is presented,which can describe the synchronization behavior of all agents in complex networks. Finally,a numerical example is given to demonstrate the theoretical results,where it is shown that if the gain matrices of synchronization protocols satisfy LMI criteria for synchronization,synchronization can be achieved.展开更多
Despite widespread use for extending absorption bandwidth, the coexistence and coupling mechanism of multiple resonance is not well understood. We propose two models to describe the multi-resonant behavior of a broadb...Despite widespread use for extending absorption bandwidth, the coexistence and coupling mechanism of multiple resonance is not well understood. We propose two models to describe the multi-resonant behavior of a broadband metamaterial absorber with geometrical-array substrate （GAS）. The multi-resonance coupling of GAS is well described by logarithmic law. The interaction between metasurface and GAS can further broaden the absorption bandwidth by generating a new resonance which coexists with original resonances in substrate. The proposed models can thoroughly describe this multiple-resonance behavior, highlighting guidelines for designing broadband absorbers.展开更多
Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses...Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses demonstrated that Fe nanoparticles were deposited on the surface of the MWCNTs. The electromagnetic properties of the MWCNTs were significantly changed, and the absorbing capacity evidently improved after the Fe deposition on the MWCNT surface. A minimum reflection loss of -29.4 dB was observed at 8.39 GHz, and the less than -10 dB bandwidth was about 10.6 GHz, which covered the whole X band （8.2-12.4 GHz） and the whole Ku band （12.4-18 GHz）, indicating that the MWCNT-Fe composites could be used as an effective microwave absorption material.展开更多
First principles calculation is performed to study the co-adsorption behaviors of O_(2)and CO_(2)onδ-Pu(100)surface by using a slab model within the framework of density functional theory(DFT).The results demonstrate...First principles calculation is performed to study the co-adsorption behaviors of O_(2)and CO_(2)onδ-Pu(100)surface by using a slab model within the framework of density functional theory(DFT).The results demonstrate that the most favorable co-adsorption configurations are T_(v)-C_(4)O_(7)and T_(p1)-C_(2)O_(8),with adsorption energy of-17.296 e V and-23.131 e V for CO_(2)-based and O_(2)-based system,respectively.The C and O atoms mainly interact with the Pu surface atoms.Furthermore,the chemical bonding between C/O and Pu atom is mainly of ionic state,and the reaction mechanism is that C 2 s,C 2 p,O 2s,and O 2p orbitals overlap and hybridize with Pu 6 p,Pu 6 d,and Pu 5 f orbital,resulting in the occurrence of new band structure.The adsorption and dissociation of CO_(2)molecule are obviously promoted by preferentially occupying adsorbed O atoms,therefore,a potential CO_(2)protection mechanism for plutonium-based materials is that in CO_(2)molecule there occurs complete dissociation of CO_(2)→C+O+O,then the dissociated C atom combines with O atom from O_(2)dissociation and produces CO,which will inhibit the O_(2)from further oxidizing Pu surface,and slow down the corrosion rate of plutoniumbased materials.展开更多
The M?ller algorithm is a self-stabilizing minor component analysis algorithm.This research document involves the study of the convergence and dynamic characteristics of the M?ller algorithm using the deterministic di...The M?ller algorithm is a self-stabilizing minor component analysis algorithm.This research document involves the study of the convergence and dynamic characteristics of the M?ller algorithm using the deterministic discrete time(DDT)methodology.Unlike other analysis methodologies,the DDT methodology is capable of serving the distinct time characteristic and having no constraint conditions.Through analyzing the dynamic characteristics of the weight vector,several convergence conditions are drawn,which are beneficial for its application.The performing computer simulations and real applications demonstrate the correctness of the analysis’s conclusions.展开更多
The recently proposed method of our research group named as directional Lyapunov exponents（DLEs） is presented. Then, DLEs are used to analyze the eigenstructure of the output phase space around the equilibrium point...The recently proposed method of our research group named as directional Lyapunov exponents（DLEs） is presented. Then, DLEs are used to analyze the eigenstructure of the output phase space around the equilibrium points. Finally, the impacts of the superlattice parameter changes on the characteristics of the output chaotic signal are analyzed. The experimental results show that parameter changes of the superlattice will affect the eigenstructure around the equilibrium points in the output phase space, and DLEs are sensitive to these changes.展开更多
With limited number of labeled samples,hyperspectral image(HSI)classification is a difficult Problem in current research.The graph neural network(GNN)has emerged as an approach to semi-supervised classification,and th...With limited number of labeled samples,hyperspectral image(HSI)classification is a difficult Problem in current research.The graph neural network(GNN)has emerged as an approach to semi-supervised classification,and the application of GNN to hyperspectral images has attracted much attention.However,in the existing GNN-based methods a single graph neural network or graph filter is mainly used to extract HSI features,which does not take full advantage of various graph neural networks(graph filters).Moreover,the traditional GNNs have the problem of oversmoothing.To alleviate these shortcomings,we introduce a deep hybrid multi-graph neural network(DHMG),where two different graph filters,i.e.,the spectral filter and the autoregressive moving average(ARMA)filter,are utilized in two branches.The former can well extract the spectral features of the nodes,and the latter has a good suppression effect on graph noise.The network realizes information interaction between the two branches and takes good advantage of different graph filters.In addition,to address the problem of oversmoothing,a dense network is proposed,where the local graph features are preserved.The dense structure satisfies the needs of different classification targets presenting different features.Finally,we introduce a GraphSAGEbased network to refine the graph features produced by the deep hybrid network.Extensive experiments on three public HSI datasets strongly demonstrate that the DHMG dramatically outperforms the state-ofthe-art models.展开更多
Parallel groove surface textures with different area densities were fabricated on ASTM 1045 steel. Friction tests were con- ducted under dry sliding condition. Temperature rise, friction coefficient and wear of both t...Parallel groove surface textures with different area densities were fabricated on ASTM 1045 steel. Friction tests were con- ducted under dry sliding condition. Temperature rise, friction coefficient and wear of both the textured and untextured speci- mens were studied. An embedded K-type thermocouple beneath the friction surfaces was employed to measure frictional tem- perature rise. The results indicated that the temperature rise of the textured specimen was obviously reduced compared with that of the untextured specimen, although the difference between the friction coefficients was not significan.. The specimen with high texture density exhibited a small temperature rise. The difference in temperature rise between the specimens with different texture densities can be primarily attributed to differences in heat dissipation and energy allocation between the tri- bo-pairs caused by the textured structure. The energy consumed by wear and plastic deformation was small in ~：omparison with the total energy input by friction, thus, the influence of these factors on temperature rise can be considered to be~ negligible.展开更多
Principal/minor component analysis(PCA/MCA),generalized principal/minor component analysis(GPCA/GMCA),and singular value decomposition(SVD)algorithms are important techniques for feature extraction.In the convergence ...Principal/minor component analysis(PCA/MCA),generalized principal/minor component analysis(GPCA/GMCA),and singular value decomposition(SVD)algorithms are important techniques for feature extraction.In the convergence analysis of these algorithms,the deterministic discrete-time(DDT)method can reveal the dynamic behavior of PCA/MCA and GPCA/GMCA algorithms effectively.However,the dynamic behavior of SVD algorithms has not been studied quantitatively because of their special structure.In this paper,for the first time,we utilize the advantages of the DDT method in PCA algorithms analysis to study the dynamics of SVD algorithms.First,taking the cross-coupled Hebbian algorithm as an example,by concatenating the two cross-coupled variables into a single vector,we successfully get a PCA-like DDT system.Second,we analyze the discrete-time dynamic behavior and stability of the PCA-like DDT system in detail based on the DDT method,and obtain the boundedness of the weight vectors and learning rate.Moreover,further discussion shows the universality of the proposed method for analyzing other SVD algorithms.As a result,the proposed method provides a new way to study the dynamical convergence properties of SVD algorithms.展开更多
The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture wit...The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture with the self-interstitial atom(SIA), He interstitial atom and He-vacancy clusters. The simulation results indicate that Pu atoms around the fracture agglom-erate into an elliptic self-interstitial loop. Interstitial He atoms evolve into separate interstitial atoms, small He atom clustersand some substitutional He atoms. The He-vacancy cluster forms a spheric structure with a 1:1 He-to-vacancy ratio. Finally,the existence of self-interstitial atoms will lead to the local change of Pu lattice and an increasing disorder, and the wholesimulation cell shows a melting state at about 10.0 ps.展开更多
Birefringent optical elements that work in deep ultraviolet(DUV)region become increasingly important these years.However,most of the DUV optical elements have fixed birefringence which is hard to be tuned.Here,we inve...Birefringent optical elements that work in deep ultraviolet(DUV)region become increasingly important these years.However,most of the DUV optical elements have fixed birefringence which is hard to be tuned.Here,we invent a birefringence-tunable optical hydrogel with mechano-birefringence effect in the DUV region,based on two-dimensional(2D)low-cobalt-doped titanate.This 2D oxide material has an optical anisotropy factor of 1.5×10^(-11) C^(2)J^(-1) m-1,larger than maximum value obtained previously,leading to an extremely large specific magneto-optical Cotton-Mouton coefficient of 3.9×10^(6) T^(-2) m-1.The extremely large coefficient enables the fabrication of birefringent hydrogel in a small magnetic field with an ultra-low concentration of 2D oxide material.The hydrogel can stably and continuously modulate 303 nm DUV light with large phase tunability by varying the strain(compression or stretching)from 0 to 50%.Our work opens the door to design and fabricate new proof-of-concept DUV birefringence-tunable element,as demonstrated by optical hydrogels capable of DUV modulation by mechanical stimuli.展开更多
This paper considers the problem of delay-dependent robust stability for uncertain systems with interval time-varying delays. By using the direct Lyapunov method, a new Lyapunov-Krasovskii(L-K) functional is introduce...This paper considers the problem of delay-dependent robust stability for uncertain systems with interval time-varying delays. By using the direct Lyapunov method, a new Lyapunov-Krasovskii(L-K) functional is introduced based on decomposition approach, when dealing with the time derivative of L-K functional, a new tight integral inequality is adopted for bounding the cross terms. Then, a new less conservative delay-dependent stability criterion is formulated in terms of linear matrix inequalities(LMIs),which can be easily solved by optimization algorithms. Numerical examples are given to show the effectiveness and the benefits of the proposed method.展开更多
Summary of main observation and conclusion We present a new method for generating europium oxalate compounds by decomposing of N-methyl 2-pyrrolidone in HNO3 media.The reaction exhibits high selectivity towards Eu^3+ ...Summary of main observation and conclusion We present a new method for generating europium oxalate compounds by decomposing of N-methyl 2-pyrrolidone in HNO3 media.The reaction exhibits high selectivity towards Eu^3+ over UO2^2+,which suggests that these conditions could be applied to a selective crystallization based separation system for trivalent lanthanides and hexavalent actinides.展开更多
This paper considers the problem of delay-dependent non-fragile H∞control for a class of linear systems with interval time-varying delay. Based on the direct Lyapunov method, an appropriate Lyapunov-Krasovskii functi...This paper considers the problem of delay-dependent non-fragile H∞control for a class of linear systems with interval time-varying delay. Based on the direct Lyapunov method, an appropriate Lyapunov-Krasovskii functional(LKF) with triple-integral terms and augment terms is introduced. Then, by using the integral inequalities and convex combination technique, an improved H∞performance analysis criterion and non-fragile H∞controller are formulated in terms of linear matrix inequalities(LMIs), which can be easily solved by using standard numerical packages. At last, two numerical examples are provided to demonstrate the effectiveness of the obtained results.展开更多
Experiments were performed on 20 different types of materials to analyze the impact contact wear and to establish the wear mechanism map, The wear mechanism has been categorized into three prominent regions （delamina...Experiments were performed on 20 different types of materials to analyze the impact contact wear and to establish the wear mechanism map, The wear mechanism has been categorized into three prominent regions （delamination wear, quasi-nano wear and lamination-like wear） and is governed by two hardness thresholds （Hdq and Hql）. When the material hardness gcp〈Hdq, the delamination wear is the dominant wear mechanism; when Hcp〉Hql, the mechanism is lamination-like wear; however, whenHco is between Hdq and Hql, the mechanism is determined to be quasi-nano wear. Hdq is determined to be the threshold hardness between delamination wear and quasi-nano wear that reflects the cracks being produced in the subsurface layer, whereas, Hql is termed threshold hardness between quasi-nano wear and lamination-like wear with formation of nanostructure within the surface layer.展开更多
基金supported by the National Natural Science Foundation of China (Grant No.62103432)supported by Young Talent fund of University Association for Science and Technology in Shaanxi, China(Grant No.20210108)。
文摘An impact point prediction(IPP) guidance based on supervised learning is proposed to address the problem of precise guidance for the ballistic missile in high maneuver penetration condition.An accurate ballistic trajectory model is applied to generate training samples,and ablation experiments are conducted to determine the mapping relationship between the flight state and the impact point.At the same time,the impact point coordinates are decoupled to improve the prediction accuracy,and the sigmoid activation function is improved to ameliorate the prediction efficiency.Therefore,an IPP neural network model,which solves the contradiction between the accuracy and the speed of the IPP,is established.In view of the performance deviation of the divert control system,the mapping relationship between the guidance parameters and the impact deviation is analysed based on the variational principle.In addition,a fast iterative model of guidance parameters is designed for reference to the Newton iteration method,which solves the nonlinear strong coupling problem of the guidance parameter solution.Monte Carlo simulation results show that the prediction accuracy of the impact point is high,with a 3 σ prediction error of 4.5 m,and the guidance method is robust,with a 3 σ error of 7.5 m.On the STM32F407 singlechip microcomputer,a single IPP takes about 2.374 ms,and a single guidance solution takes about9.936 ms,which has a good real-time performance and a certain engineering application value.
基金supported by the Special Support Program for High-level Talents of Shaanxi Province(No.2020-44)Innnovative Talent Project of China and The Youth Innovation Team of Shaanxi Universities
文摘NiO,an anodic electrochromic material,has applications in energy-saving windows,intelligent displays,and military camouflage.However,its electrochromic mechanism and reasons for its performance degradation in alkaline aqueous electrolytes are complex and poorly understood,making it challenging to improve NiO thin films.We studied the phases and electrochemical characteristics of NiO films in different states(initial,colored,bleached and after 8000 cycles)and identified three main reasons for performance degradation.First,Ni(OH)_(2)is generated during electrochromic cycling and deposited on the NiO film surface,gradually yielding a NiO@Ni(OH)_(2)core-shell structure,isolating the internal NiO film from the electrolyte,and preventing ion transfer.Second,the core-shell structure causes the mode of electrical conduction to change from first-to second-order conduction,reducing the efficiency of ion transfer to the surface Ni(OH)_(2)layer.Third,Ni(OH)_(2)and NiOOH,which have similar crystal structures but different b-axis lattice parameters,are formed during electrochromic cycling,and large volume changes in the unit cell reduce the structural stability of the thin film.Finally,we clarified the mechanism of electrochromic performance degradation of NiO films in alkaline aqueous electrolytes and provide a route to activation of NiO films,which will promote the development of electrochromic technology.
基金Sponsored by the National Natural Science Foundation of China(Grant No.61374054,61174067,61263002)the Shaanxi Province Natural Science Foundation Research Projection(Grant No.2013JQ8038)
文摘Synchronization of high-order discrete-time complex networks with undirected topologies is studied and the impacts of time delays are investigated. Firstly,by the state decomposition,synchronization problems are transformed into asymptotic stability ones of multiple lower dimensional time-delayed subsystems. Then,linear matrix inequality( LMI) criteria for synchronization are given,which can guarantee the scalability of complex networks since they only include three LMI constraints independent of the number of agents. Moreover,an explicit expression of the synchronization function is presented,which can describe the synchronization behavior of all agents in complex networks. Finally,a numerical example is given to demonstrate the theoretical results,where it is shown that if the gain matrices of synchronization protocols satisfy LMI criteria for synchronization,synchronization can be achieved.
基金Project supported by the National Natural Science Foundation of China(Grant No.51302312)the Fund for Discipline Construction of Beijing University of Chemical Technology(Grant No.XK1702)the Fundamental Research Funds for the Central Universities,China(Grant No.Jd1601)
文摘Despite widespread use for extending absorption bandwidth, the coexistence and coupling mechanism of multiple resonance is not well understood. We propose two models to describe the multi-resonant behavior of a broadband metamaterial absorber with geometrical-array substrate （GAS）. The multi-resonance coupling of GAS is well described by logarithmic law. The interaction between metasurface and GAS can further broaden the absorption bandwidth by generating a new resonance which coexists with original resonances in substrate. The proposed models can thoroughly describe this multiple-resonance behavior, highlighting guidelines for designing broadband absorbers.
文摘Multi-walled carbon nanotube （MWCNT）-Fe composites were prepared via the metal organic chemical vapor deposi- tion by depositing iron pentacarbonyl on the surface of MWCNTs. The structural and morphological analyses demonstrated that Fe nanoparticles were deposited on the surface of the MWCNTs. The electromagnetic properties of the MWCNTs were significantly changed, and the absorbing capacity evidently improved after the Fe deposition on the MWCNT surface. A minimum reflection loss of -29.4 dB was observed at 8.39 GHz, and the less than -10 dB bandwidth was about 10.6 GHz, which covered the whole X band （8.2-12.4 GHz） and the whole Ku band （12.4-18 GHz）, indicating that the MWCNT-Fe composites could be used as an effective microwave absorption material.
文摘First principles calculation is performed to study the co-adsorption behaviors of O_(2)and CO_(2)onδ-Pu(100)surface by using a slab model within the framework of density functional theory(DFT).The results demonstrate that the most favorable co-adsorption configurations are T_(v)-C_(4)O_(7)and T_(p1)-C_(2)O_(8),with adsorption energy of-17.296 e V and-23.131 e V for CO_(2)-based and O_(2)-based system,respectively.The C and O atoms mainly interact with the Pu surface atoms.Furthermore,the chemical bonding between C/O and Pu atom is mainly of ionic state,and the reaction mechanism is that C 2 s,C 2 p,O 2s,and O 2p orbitals overlap and hybridize with Pu 6 p,Pu 6 d,and Pu 5 f orbital,resulting in the occurrence of new band structure.The adsorption and dissociation of CO_(2)molecule are obviously promoted by preferentially occupying adsorbed O atoms,therefore,a potential CO_(2)protection mechanism for plutonium-based materials is that in CO_(2)molecule there occurs complete dissociation of CO_(2)→C+O+O,then the dissociated C atom combines with O atom from O_(2)dissociation and produces CO,which will inhibit the O_(2)from further oxidizing Pu surface,and slow down the corrosion rate of plutoniumbased materials.
基金supported by the National Natural Science Foundation of China(61903375,61673387,61374120)Shaanxi Province Natural Science Foundation(2016JM6015)。
文摘The M?ller algorithm is a self-stabilizing minor component analysis algorithm.This research document involves the study of the convergence and dynamic characteristics of the M?ller algorithm using the deterministic discrete time(DDT)methodology.Unlike other analysis methodologies,the DDT methodology is capable of serving the distinct time characteristic and having no constraint conditions.Through analyzing the dynamic characteristics of the weight vector,several convergence conditions are drawn,which are beneficial for its application.The performing computer simulations and real applications demonstrate the correctness of the analysis’s conclusions.
文摘The recently proposed method of our research group named as directional Lyapunov exponents（DLEs） is presented. Then, DLEs are used to analyze the eigenstructure of the output phase space around the equilibrium points. Finally, the impacts of the superlattice parameter changes on the characteristics of the output chaotic signal are analyzed. The experimental results show that parameter changes of the superlattice will affect the eigenstructure around the equilibrium points in the output phase space, and DLEs are sensitive to these changes.
文摘With limited number of labeled samples,hyperspectral image(HSI)classification is a difficult Problem in current research.The graph neural network(GNN)has emerged as an approach to semi-supervised classification,and the application of GNN to hyperspectral images has attracted much attention.However,in the existing GNN-based methods a single graph neural network or graph filter is mainly used to extract HSI features,which does not take full advantage of various graph neural networks(graph filters).Moreover,the traditional GNNs have the problem of oversmoothing.To alleviate these shortcomings,we introduce a deep hybrid multi-graph neural network(DHMG),where two different graph filters,i.e.,the spectral filter and the autoregressive moving average(ARMA)filter,are utilized in two branches.The former can well extract the spectral features of the nodes,and the latter has a good suppression effect on graph noise.The network realizes information interaction between the two branches and takes good advantage of different graph filters.In addition,to address the problem of oversmoothing,a dense network is proposed,where the local graph features are preserved.The dense structure satisfies the needs of different classification targets presenting different features.Finally,we introduce a GraphSAGEbased network to refine the graph features produced by the deep hybrid network.Extensive experiments on three public HSI datasets strongly demonstrate that the DHMG dramatically outperforms the state-ofthe-art models.
基金supported by the National Basic Research Program of China(Grant No.2012CB934101)the National Natural Science Foundation of China(Grant No.51321092)
文摘Parallel groove surface textures with different area densities were fabricated on ASTM 1045 steel. Friction tests were con- ducted under dry sliding condition. Temperature rise, friction coefficient and wear of both the textured and untextured speci- mens were studied. An embedded K-type thermocouple beneath the friction surfaces was employed to measure frictional tem- perature rise. The results indicated that the temperature rise of the textured specimen was obviously reduced compared with that of the untextured specimen, although the difference between the friction coefficients was not significan.. The specimen with high texture density exhibited a small temperature rise. The difference in temperature rise between the specimens with different texture densities can be primarily attributed to differences in heat dissipation and energy allocation between the tri- bo-pairs caused by the textured structure. The energy consumed by wear and plastic deformation was small in ~：omparison with the total energy input by friction, thus, the influence of these factors on temperature rise can be considered to be~ negligible.
基金supported by the National Natural Science Foundation of China under Grant Nos.61903375,61673387 and 61773389the Natural Science Foundation of Shaanxi Province of China under Grant Nos.2020JM-356 and 2020JQ-298the Postdoctoral Science Foundation of China under Grant No.2019M663635.
文摘Principal/minor component analysis(PCA/MCA),generalized principal/minor component analysis(GPCA/GMCA),and singular value decomposition(SVD)algorithms are important techniques for feature extraction.In the convergence analysis of these algorithms,the deterministic discrete-time(DDT)method can reveal the dynamic behavior of PCA/MCA and GPCA/GMCA algorithms effectively.However,the dynamic behavior of SVD algorithms has not been studied quantitatively because of their special structure.In this paper,for the first time,we utilize the advantages of the DDT method in PCA algorithms analysis to study the dynamics of SVD algorithms.First,taking the cross-coupled Hebbian algorithm as an example,by concatenating the two cross-coupled variables into a single vector,we successfully get a PCA-like DDT system.Second,we analyze the discrete-time dynamic behavior and stability of the PCA-like DDT system in detail based on the DDT method,and obtain the boundedness of the weight vectors and learning rate.Moreover,further discussion shows the universality of the proposed method for analyzing other SVD algorithms.As a result,the proposed method provides a new way to study the dynamical convergence properties of SVD algorithms.
文摘The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture with the self-interstitial atom(SIA), He interstitial atom and He-vacancy clusters. The simulation results indicate that Pu atoms around the fracture agglom-erate into an elliptic self-interstitial loop. Interstitial He atoms evolve into separate interstitial atoms, small He atom clustersand some substitutional He atoms. The He-vacancy cluster forms a spheric structure with a 1:1 He-to-vacancy ratio. Finally,the existence of self-interstitial atoms will lead to the local change of Pu lattice and an increasing disorder, and the wholesimulation cell shows a melting state at about 10.0 ps.
基金support by the National Natural Science Foundation of China(Grants 51920105002,52273311 and 52125309)the Guangdong Innovative and Entrepreneurial Research Team Program(Grant 2017ZT07C341)+2 种基金the Shenzhen Basic Research Project(Grants JCYJ20190809180605522,and WDZC20200819095319002)the National Key R&D Program(Grant 2018YF A0307200)the National Program on Key Basic Research Project of China(Grant 2020JCJQ-ZD-06312).
文摘Birefringent optical elements that work in deep ultraviolet(DUV)region become increasingly important these years.However,most of the DUV optical elements have fixed birefringence which is hard to be tuned.Here,we invent a birefringence-tunable optical hydrogel with mechano-birefringence effect in the DUV region,based on two-dimensional(2D)low-cobalt-doped titanate.This 2D oxide material has an optical anisotropy factor of 1.5×10^(-11) C^(2)J^(-1) m-1,larger than maximum value obtained previously,leading to an extremely large specific magneto-optical Cotton-Mouton coefficient of 3.9×10^(6) T^(-2) m-1.The extremely large coefficient enables the fabrication of birefringent hydrogel in a small magnetic field with an ultra-low concentration of 2D oxide material.The hydrogel can stably and continuously modulate 303 nm DUV light with large phase tunability by varying the strain(compression or stretching)from 0 to 50%.Our work opens the door to design and fabricate new proof-of-concept DUV birefringence-tunable element,as demonstrated by optical hydrogels capable of DUV modulation by mechanical stimuli.
基金supported by National Natural Science Foundation of China(No.61074072)
文摘This paper considers the problem of delay-dependent robust stability for uncertain systems with interval time-varying delays. By using the direct Lyapunov method, a new Lyapunov-Krasovskii(L-K) functional is introduced based on decomposition approach, when dealing with the time derivative of L-K functional, a new tight integral inequality is adopted for bounding the cross terms. Then, a new less conservative delay-dependent stability criterion is formulated in terms of linear matrix inequalities(LMIs),which can be easily solved by optimization algorithms. Numerical examples are given to show the effectiveness and the benefits of the proposed method.
基金the National Natural Science Foundation of China (Nos.21790374,21790370,21761132019, 21806118)the Science Challenge Project (No.TZ2016004)+1 种基金a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD)the "Young Thousand Talented Program"in China.
文摘Summary of main observation and conclusion We present a new method for generating europium oxalate compounds by decomposing of N-methyl 2-pyrrolidone in HNO3 media.The reaction exhibits high selectivity towards Eu^3+ over UO2^2+,which suggests that these conditions could be applied to a selective crystallization based separation system for trivalent lanthanides and hexavalent actinides.
基金supported by National Natural Science Foundation of China(Nos.61074072 and 61374120)
文摘This paper considers the problem of delay-dependent non-fragile H∞control for a class of linear systems with interval time-varying delay. Based on the direct Lyapunov method, an appropriate Lyapunov-Krasovskii functional(LKF) with triple-integral terms and augment terms is introduced. Then, by using the integral inequalities and convex combination technique, an improved H∞performance analysis criterion and non-fragile H∞controller are formulated in terms of linear matrix inequalities(LMIs), which can be easily solved by using standard numerical packages. At last, two numerical examples are provided to demonstrate the effectiveness of the obtained results.
基金supported by the National Natural Science Foundation of China(Grant Nos.5860269,58971075,50071045,50471036)
文摘Experiments were performed on 20 different types of materials to analyze the impact contact wear and to establish the wear mechanism map, The wear mechanism has been categorized into three prominent regions （delamination wear, quasi-nano wear and lamination-like wear） and is governed by two hardness thresholds （Hdq and Hql）. When the material hardness gcp〈Hdq, the delamination wear is the dominant wear mechanism; when Hcp〉Hql, the mechanism is lamination-like wear; however, whenHco is between Hdq and Hql, the mechanism is determined to be quasi-nano wear. Hdq is determined to be the threshold hardness between delamination wear and quasi-nano wear that reflects the cracks being produced in the subsurface layer, whereas, Hql is termed threshold hardness between quasi-nano wear and lamination-like wear with formation of nanostructure within the surface layer.
