This paper analyzes the fuzzy variable structure control algorithms for delay systems and describes the compensation mechanism of the integral factor to the effect of the delay. Based on the linearized model of the co...This paper analyzes the fuzzy variable structure control algorithms for delay systems and describes the compensation mechanism of the integral factor to the effect of the delay. Based on the linearized model of the congestion-avoidance flow-control mode of transmission control protocol (TCP), we present delay control algorithms for active queue management (AQM) and discuss the parameter tuning of the algorithms. The NS (network simulator) simulation results show that the proposed control scheme for the nonlinear TCP/AQM model has good performance and robustness with respect to the uncertainties of the round-trip time (RTT) and the number of active TCP sessions. Compared to other similar schemes, our algorithms perform better in terms of packet loss ratio, throughput and butter fluctuation.展开更多
In this paper, adaptive variable structure neural control is presented for a class of uncertain multi-input multi-output （MIMO） nonlinear systems with state time-varying delays and unknown nonlinear dead-zones. The ...In this paper, adaptive variable structure neural control is presented for a class of uncertain multi-input multi-output （MIMO） nonlinear systems with state time-varying delays and unknown nonlinear dead-zones. The unknown time-varying delay uncer- tainties are compensated for using appropriate Lyapunov-Krasovskii functionals in the design. The approach removes the assumption of linear function outside the deadband without necessarily constructing a dead-zone inverse as an added contribution. By utilizing the integral-type Lyapunov function and introducing an adaptive compensation term for the upper bound of the residual and optimal approximation error as well as the dead-zone disturbance, the closed-loop control system is proved to be semi-globally uniformly ultimately bounded. In addition, a modified adaptive control algorithm is given in order to avoid the high-frequency chattering phenomenon. Simulation results demonstrate the effectiveness of the approach.展开更多
We propose and demonstrate a simple method to accomplish arbitrary free spectral range(FSR)control of optical frequency combs(OFC).The approach is based on the combination of an optical tapped delay line(OTDL)structur...We propose and demonstrate a simple method to accomplish arbitrary free spectral range(FSR)control of optical frequency combs(OFC).The approach is based on the combination of an optical tapped delay line(OTDL)structure and a phase modulator(PM).The OTDL structure is utilized to multiply the FSR of input OFC,and the PM is used to divide the FSR of the consequent OFC.We illustrate that the proposed method allows one to divide or multiply the FSR of original OFC by any anticipated integer or fractional factor.Numerical simulation results match well with our theoretical analysis.展开更多
A discrete variable structure control(DVSC) method for the linear time invariant systems with time delay was presented. The continuous time delay systems are first transformed into the standard discrete form which con...A discrete variable structure control(DVSC) method for the linear time invariant systems with time delay was presented. The continuous time delay systems are first transformed into the standard discrete form which contains no time delay by augmenting the state variables. Then the switching surface is determined by using the ideal quasi sliding mode. As it is difficult for the state trajectory to reach the switching surface exactly, the reaching condition in the form of approach law is used to design the controller. The deduced switching surface and controller contain not only the current step of state feedback but also some former steps of controls. Stability analysis with and without time delay information is also investigated in this paper. Numerical simulation was carried out to demonstrate the effectiveness and feasibility of the presented control method.展开更多
A visual servoing tracking controller is proposed based on the sliding mode control theory in order to achieve strong robustness against parameter variations and external disturbances. A sliding plane with time delay ...A visual servoing tracking controller is proposed based on the sliding mode control theory in order to achieve strong robustness against parameter variations and external disturbances. A sliding plane with time delay compensation is presented by the pre-estimate of states. To reduce the chattering of the sliding mode controller, a modified exponential reaching law and hyperbolic tangent function are applied to the design of visual controller and robot joint controller. Simulation results show that the visual servoing control scheme is robust and has good tracking performance.展开更多
The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures ...The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures near the blade tip was discussed,and the unsteady behaviors and features in the tip flow field were analyzed.Additionally,the interaction between the tip leakage flow and the gap jet was revealed.The results show that,compared to the datum cascade,the blade tip load of the rear blade increases while that of the front blade decreases.Unsteady fluctuations of the tandem cascade are mainly caused by the interaction between the tip leakage flow and gap jet,and by the mixing of the vortex structures,but there is no essential change in the spectrum feature of the tip leakage flow.Finally,a detailed analysis of the development of vortices in the tip region is conducted by the topological structures of the flow field.Combined with the three-dimensional vortex structures,the schematic diagram of the vortex system of the datum single-row cascade and tandem cascade is summarized.展开更多
An optimal control method for seismic-excited building structures with multiple time delays is investigated in this paper. The system state equation with multiple time delays is discretized and transformed into a stan...An optimal control method for seismic-excited building structures with multiple time delays is investigated in this paper. The system state equation with multiple time delays is discretized and transformed into a standard discrete form without any explicit time delay by a particular augmenting for state variables. A time-delay controller is then designed based on this standard equation using the discrete optimal control method. Effectiveness of the proposed controller is demonstrated by numerical simulations. Simulation results indicate that a very small time delay may result in the instability of the control system if it is not compensated in the control design. Time delay may be compensated effectively by the proposed controller, in the mean time, an effective control may be obtained. The proposed controller is valid for both small and large time delays.展开更多
Deep neural networks(DNNs)are effective in solving both forward and inverse problems for nonlinear partial differential equations(PDEs).However,conventional DNNs are not effective in handling problems such as delay di...Deep neural networks(DNNs)are effective in solving both forward and inverse problems for nonlinear partial differential equations(PDEs).However,conventional DNNs are not effective in handling problems such as delay differential equations(DDEs)and delay integrodifferential equations(DIDEs)with constant delays,primarily due to their low regularity at delayinduced breaking points.In this paper,a DNN method that combines multi-task learning(MTL)which is proposed to solve both the forward and inverse problems of DIDEs.The core idea of this approach is to divide the original equation into multiple tasks based on the delay,using auxiliary outputs to represent the integral terms,followed by the use of MTL to seamlessly incorporate the properties at the breaking points into the loss function.Furthermore,given the increased training dificulty associated with multiple tasks and outputs,we employ a sequential training scheme to reduce training complexity and provide reference solutions for subsequent tasks.This approach significantly enhances the approximation accuracy of solving DIDEs with DNNs,as demonstrated by comparisons with traditional DNN methods.We validate the effectiveness of this method through several numerical experiments,test various parameter sharing structures in MTL and compare the testing results of these structures.Finally,this method is implemented to solve the inverse problem of nonlinear DIDE and the results show that the unknown parameters of DIDE can be discovered with sparse or noisy data.展开更多
Gansu Province in the northwest of China, so the research on the impact of delay retirement in Gansu province have a certain representation. This paper analyzes the current situation of human resources in Gansu provin...Gansu Province in the northwest of China, so the research on the impact of delay retirement in Gansu province have a certain representation. This paper analyzes the current situation of human resources in Gansu province the proportion of the labor force is relatively low, the age structure of aging, education, human resources quality is still not high, the use of theoretical analysis method of overlapping generations model and AHP method to verify the proposed implementation. The delay retirement policy to increase the effective adjustment of Gansu province to improve the structure of human resources, better solve the problem of human resources structure in Gansu Province, so as to enhance Gansu＇s core competitive advantage.展开更多
The anisotropy of magnetostatic surface wave(MSSW)propagating in finite width YIG/dielectric/metal layered structure is analyzed.This problem is solved by finding the rigorous solution of each layer from Maxwell equat...The anisotropy of magnetostatic surface wave(MSSW)propagating in finite width YIG/dielectric/metal layered structure is analyzed.This problem is solved by finding the rigorous solution of each layer from Maxwell equation and the appropriate transmission Green's function matrix G.From the relationship of Green's function matrixes of dielectric layer and ferrite layer,the dispersion equation is obtained.The MSSW filter is designed to verify the dispersion characteristics.The experiment results are in good agreement with the calculating data from the model.展开更多
In this paper,we consider the optimal boundary control problem of a two-species competitive system with time delay and size structure in a polluted environment.First,the well posedness of the system is studied by usin...In this paper,we consider the optimal boundary control problem of a two-species competitive system with time delay and size structure in a polluted environment.First,the well posedness of the system is studied by using the characteristic line method and the fixed point principle.Second,the necessary conditions for optimal boundary control are obtained by conjugate system and normal cone property.Finally,the existence and uniqueness of the optimal strategy are proved by Ekeland variational principle.展开更多
A periodic predator-prey model with stage structure for prey and time delays due to negative feed-back and gestation of predator is proposed.By using Gaines and Mawhin's continuation theorem of coincidencedegree t...A periodic predator-prey model with stage structure for prey and time delays due to negative feed-back and gestation of predator is proposed.By using Gaines and Mawhin's continuation theorem of coincidencedegree theory,sufficient conditions are derived for the existence of positive periodic solutions to the proposedmodel.Numerical simulations are presented to illustrate the feasibility of our main result.展开更多
Pathological basal ganglia oscillations are associated with the hypokinetic motor symptoms of Parkinson’s disease.In this paper,a memoryless feedback control strategy is proposed to suppress pathological oscillations...Pathological basal ganglia oscillations are associated with the hypokinetic motor symptoms of Parkinson’s disease.In this paper,a memoryless feedback control strategy is proposed to suppress pathological oscillations in the basal ganglia.In the most of closed-loop control strategies,the excitatory subthalamic nucleus populations are both monitored and stimulated targets,neglecting the important contribution of the external globus pallidus populations in suppressing pathological oscillations.To this end,we transform the original model into a time-delay system with a lower-triangular structure,and construct a memoryless state feedback controller utilizing the gain scaling method.It is proved by the Lyapunov–Krasovskii functional method that all the signals of the resulting closed-loop system are bounded,and the system states converge to an adjustable region of the origin.In addition,the input delay in stimulating the target is considered and a corresponding controller is designed to achieve convergence of the states in the resulting closed-loop system with both state delays and input delay.Moreover,simulation tests are conducted to explore the performance of the control strategy.This paper further explores the intrinsic dynamics in the neural system,and provides an effective strategy for closed-loop deep brain stimulation control.展开更多
A new active control method is presented to attenuate vibrations of a flexible beam with nonlinear hysteresis and time delay. The nonlinear and hysteretic behavior of the system is illustrated by the Bouc-Wen model. B...A new active control method is presented to attenuate vibrations of a flexible beam with nonlinear hysteresis and time delay. The nonlinear and hysteretic behavior of the system is illustrated by the Bouc-Wen model. By specific transformation and augmentation of state parameters, we can convert the motion equation of the system with explicit time delay to the standard state space representation without any explicit time delay. Then the instantaneous optimal control method and Runge-Kutta method in fourth-order are applied to the controller design with time delay. Finally, in order to verify the effectivity of the time-delay controller proposed, numerical simulations are implemented. It is indicated by the simulation results that the control performance will deteriorate if neglect the time delay in process of the controller design and proposed time delay controller works well with both small and large time delay problems.展开更多
A ratio-dependent predator-prey system with stage structure and time delays for both prey and predator is considered in this paper.Both the predator and prey have two stages,immature stage and mature stage,and the gro...A ratio-dependent predator-prey system with stage structure and time delays for both prey and predator is considered in this paper.Both the predator and prey have two stages,immature stage and mature stage,and the growth of them is of Lotka-Volterra nature.It is assumed that immature individuals and mature individuals of each species are divided by a fixed age,and that mature predators attack immature prey only.The global stability of three nonnegative equilibria and permanence are presented.展开更多
In this paper,a delayed two-species predator-prey system with stage structure and diffiusion is investigated.Based on the continuation theorem of coincidence degree theory,the suficient conditions for the existence of...In this paper,a delayed two-species predator-prey system with stage structure and diffiusion is investigated.Based on the continuation theorem of coincidence degree theory,the suficient conditions for the existence of positiveω-periodic solution to the system are derived.The numerical simulation of an example verifies our main result.展开更多
An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-...An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-carborane (7,8-dicarba-nido-undecaborane) cage,i.e.,at the ortho position to the cage,in the PhBMes2acceptor moiety of nido-carborane–triarylborane dyads (nido-1–4).The crystal structure of 8-H substituted nido-1 reveals the existence of steric congestion around the cage,resulting in a highly twisted connectivity between the cage plane and the Ph ring (θ=85.7°).All compounds with different 8-R groups (R=H,Me,iPr) exhibit strong TADF with long emission lifetimes (τ_(d)=4.8–9.7 μs in THF) in both THF and PMMA films,which is supported by a very small singlet–triplet energy splitting (ΔE_(ST)< 0.03 eV).Attaching an additional Me group to the ortho position of the BMes2group further enhances the intensity of delayed fluorescence (nido-4).Theoretical studies show that although nido-1–4 reach their local energy minima in a perpendicular arrangement between the cage plane and the Ph ring,there exist large energy barriers to cage rotation.In contrast,the reference compound lacking a 4-Me group,which exhibits very weak delayed fluorescence in solution,has low rotational energy barriers.展开更多
In this paper,we analyze two stochastic predator-prey models with distributed delay and stage structure for prey.For the nonautonomous periodic case of the model,by using Khasminskii’s theory of periodic solution,we ...In this paper,we analyze two stochastic predator-prey models with distributed delay and stage structure for prey.For the nonautonomous periodic case of the model,by using Khasminskii’s theory of periodic solution,we show that the system has at least one positive T-periodic solution.For the model which is disturbed by both white and telegraph noises,we obtain sufficient criteria for positive recurrence of the solutions to the model by constructing a suitable stochastic Lyapunov function with regime switching.The positive recurrence implies that both prey and predator populations will be persistent in the long term.展开更多
文摘This paper analyzes the fuzzy variable structure control algorithms for delay systems and describes the compensation mechanism of the integral factor to the effect of the delay. Based on the linearized model of the congestion-avoidance flow-control mode of transmission control protocol (TCP), we present delay control algorithms for active queue management (AQM) and discuss the parameter tuning of the algorithms. The NS (network simulator) simulation results show that the proposed control scheme for the nonlinear TCP/AQM model has good performance and robustness with respect to the uncertainties of the round-trip time (RTT) and the number of active TCP sessions. Compared to other similar schemes, our algorithms perform better in terms of packet loss ratio, throughput and butter fluctuation.
基金supported by National Natural Science Foundationof China (No. 60774017 and No. 60874045)
文摘In this paper, adaptive variable structure neural control is presented for a class of uncertain multi-input multi-output （MIMO） nonlinear systems with state time-varying delays and unknown nonlinear dead-zones. The unknown time-varying delay uncer- tainties are compensated for using appropriate Lyapunov-Krasovskii functionals in the design. The approach removes the assumption of linear function outside the deadband without necessarily constructing a dead-zone inverse as an added contribution. By utilizing the integral-type Lyapunov function and introducing an adaptive compensation term for the upper bound of the residual and optimal approximation error as well as the dead-zone disturbance, the closed-loop control system is proved to be semi-globally uniformly ultimately bounded. In addition, a modified adaptive control algorithm is given in order to avoid the high-frequency chattering phenomenon. Simulation results demonstrate the effectiveness of the approach.
基金supported by the Fundamental Research Funds for the Central Universities(No.2019JBM010)the National Natural Science Foundation of China(Nos.61775015 and 61827817)。
文摘We propose and demonstrate a simple method to accomplish arbitrary free spectral range(FSR)control of optical frequency combs(OFC).The approach is based on the combination of an optical tapped delay line(OTDL)structure and a phase modulator(PM).The OTDL structure is utilized to multiply the FSR of input OFC,and the PM is used to divide the FSR of the consequent OFC.We illustrate that the proposed method allows one to divide or multiply the FSR of original OFC by any anticipated integer or fractional factor.Numerical simulation results match well with our theoretical analysis.
文摘A discrete variable structure control(DVSC) method for the linear time invariant systems with time delay was presented. The continuous time delay systems are first transformed into the standard discrete form which contains no time delay by augmenting the state variables. Then the switching surface is determined by using the ideal quasi sliding mode. As it is difficult for the state trajectory to reach the switching surface exactly, the reaching condition in the form of approach law is used to design the controller. The deduced switching surface and controller contain not only the current step of state feedback but also some former steps of controls. Stability analysis with and without time delay information is also investigated in this paper. Numerical simulation was carried out to demonstrate the effectiveness and feasibility of the presented control method.
基金supported by China Postdoctoral Science Founda-tion (No. 20080441093)Key Laboratory Foundation of Liaoning Province (No. 2008S088).
文摘A visual servoing tracking controller is proposed based on the sliding mode control theory in order to achieve strong robustness against parameter variations and external disturbances. A sliding plane with time delay compensation is presented by the pre-estimate of states. To reduce the chattering of the sliding mode controller, a modified exponential reaching law and hyperbolic tangent function are applied to the design of visual controller and robot joint controller. Simulation results show that the visual servoing control scheme is robust and has good tracking performance.
基金co-supported by the National Science and Technology Major Project,China(No.2017-Ⅱ-0001-0013)the National Natural Science Foundation of China(Nos.52106057 and 51790512)+2 种基金the Fundamental Research Funds for the Central Universities,China(No.D5000210483)the Foundation of State Level Key Laboratory of Airfoil and Cascade Aerodynamics,China(Nos.D5150210006 and D5050210015)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(No.CX2022013).
文摘The complex flow characteristics in the tip region of a tandem cascade with tip clearance have been calculated and analyzed using Delayed Detached Eddy Simulation(DDES).The coherent mechanism of the vortex structures near the blade tip was discussed,and the unsteady behaviors and features in the tip flow field were analyzed.Additionally,the interaction between the tip leakage flow and the gap jet was revealed.The results show that,compared to the datum cascade,the blade tip load of the rear blade increases while that of the front blade decreases.Unsteady fluctuations of the tandem cascade are mainly caused by the interaction between the tip leakage flow and gap jet,and by the mixing of the vortex structures,but there is no essential change in the spectrum feature of the tip leakage flow.Finally,a detailed analysis of the development of vortices in the tip region is conducted by the topological structures of the flow field.Combined with the three-dimensional vortex structures,the schematic diagram of the vortex system of the datum single-row cascade and tandem cascade is summarized.
基金supported by the National Natural Science Foundation of China (Nos.10772112,10472065)the Key Project of Ministry of Education of China (No.107043)+2 种基金the Key Scientific Project of Shang-hai Municipal Education Commission (No.09ZZ17)the Specialized Research Fund for the DoctoralProgram of Higher Education of China (No.20070248032)the Research Project of State Key Laboratory of Ocean Engineering of China (No.GKZD010807)
文摘An optimal control method for seismic-excited building structures with multiple time delays is investigated in this paper. The system state equation with multiple time delays is discretized and transformed into a standard discrete form without any explicit time delay by a particular augmenting for state variables. A time-delay controller is then designed based on this standard equation using the discrete optimal control method. Effectiveness of the proposed controller is demonstrated by numerical simulations. Simulation results indicate that a very small time delay may result in the instability of the control system if it is not compensated in the control design. Time delay may be compensated effectively by the proposed controller, in the mean time, an effective control may be obtained. The proposed controller is valid for both small and large time delays.
文摘Deep neural networks(DNNs)are effective in solving both forward and inverse problems for nonlinear partial differential equations(PDEs).However,conventional DNNs are not effective in handling problems such as delay differential equations(DDEs)and delay integrodifferential equations(DIDEs)with constant delays,primarily due to their low regularity at delayinduced breaking points.In this paper,a DNN method that combines multi-task learning(MTL)which is proposed to solve both the forward and inverse problems of DIDEs.The core idea of this approach is to divide the original equation into multiple tasks based on the delay,using auxiliary outputs to represent the integral terms,followed by the use of MTL to seamlessly incorporate the properties at the breaking points into the loss function.Furthermore,given the increased training dificulty associated with multiple tasks and outputs,we employ a sequential training scheme to reduce training complexity and provide reference solutions for subsequent tasks.This approach significantly enhances the approximation accuracy of solving DIDEs with DNNs,as demonstrated by comparisons with traditional DNN methods.We validate the effectiveness of this method through several numerical experiments,test various parameter sharing structures in MTL and compare the testing results of these structures.Finally,this method is implemented to solve the inverse problem of nonlinear DIDE and the results show that the unknown parameters of DIDE can be discovered with sparse or noisy data.
文摘Gansu Province in the northwest of China, so the research on the impact of delay retirement in Gansu province have a certain representation. This paper analyzes the current situation of human resources in Gansu province the proportion of the labor force is relatively low, the age structure of aging, education, human resources quality is still not high, the use of theoretical analysis method of overlapping generations model and AHP method to verify the proposed implementation. The delay retirement policy to increase the effective adjustment of Gansu province to improve the structure of human resources, better solve the problem of human resources structure in Gansu Province, so as to enhance Gansu＇s core competitive advantage.
基金This work was supported by the National Basic Research Program of China(973)under Grant No.2007CB31407the International S&T Cooperation Program of China under Grant No.2006DFA53410.
文摘The anisotropy of magnetostatic surface wave(MSSW)propagating in finite width YIG/dielectric/metal layered structure is analyzed.This problem is solved by finding the rigorous solution of each layer from Maxwell equation and the appropriate transmission Green's function matrix G.From the relationship of Green's function matrixes of dielectric layer and ferrite layer,the dispersion equation is obtained.The MSSW filter is designed to verify the dispersion characteristics.The experiment results are in good agreement with the calculating data from the model.
基金project funded by the Natural Science Foundation of Ningxia Province(2023AAC03114)the First-class Discipline Construction Project of Ningxia Colleges and Universities(NXYLXK2021A03)the Graduate Innovation Project of Ningxia University(CXXM2023-10).
文摘In this paper,we consider the optimal boundary control problem of a two-species competitive system with time delay and size structure in a polluted environment.First,the well posedness of the system is studied by using the characteristic line method and the fixed point principle.Second,the necessary conditions for optimal boundary control are obtained by conjugate system and normal cone property.Finally,the existence and uniqueness of the optimal strategy are proved by Ekeland variational principle.
文摘A periodic predator-prey model with stage structure for prey and time delays due to negative feed-back and gestation of predator is proposed.By using Gaines and Mawhin's continuation theorem of coincidencedegree theory,sufficient conditions are derived for the existence of positive periodic solutions to the proposedmodel.Numerical simulations are presented to illustrate the feasibility of our main result.
基金supported by the Major Fundamental Research Program of the Natural Science Foundation of Shandong Province,China(No.ZR2020ZD25)the Autonomous Innovation Team Foundation for“20 Items of the New University”of Jinan City(No.202228087).
文摘Pathological basal ganglia oscillations are associated with the hypokinetic motor symptoms of Parkinson’s disease.In this paper,a memoryless feedback control strategy is proposed to suppress pathological oscillations in the basal ganglia.In the most of closed-loop control strategies,the excitatory subthalamic nucleus populations are both monitored and stimulated targets,neglecting the important contribution of the external globus pallidus populations in suppressing pathological oscillations.To this end,we transform the original model into a time-delay system with a lower-triangular structure,and construct a memoryless state feedback controller utilizing the gain scaling method.It is proved by the Lyapunov–Krasovskii functional method that all the signals of the resulting closed-loop system are bounded,and the system states converge to an adjustable region of the origin.In addition,the input delay in stimulating the target is considered and a corresponding controller is designed to achieve convergence of the states in the resulting closed-loop system with both state delays and input delay.Moreover,simulation tests are conducted to explore the performance of the control strategy.This paper further explores the intrinsic dynamics in the neural system,and provides an effective strategy for closed-loop deep brain stimulation control.
基金supported by the Key Project(11132001)the General Projects of Natural Science Foundation of China(11072146,11272202,and 11002087)the Specialized Research Fund for the Doctoral Program of Higher Education of China(20110073110008)
文摘A new active control method is presented to attenuate vibrations of a flexible beam with nonlinear hysteresis and time delay. The nonlinear and hysteretic behavior of the system is illustrated by the Bouc-Wen model. By specific transformation and augmentation of state parameters, we can convert the motion equation of the system with explicit time delay to the standard state space representation without any explicit time delay. Then the instantaneous optimal control method and Runge-Kutta method in fourth-order are applied to the controller design with time delay. Finally, in order to verify the effectivity of the time-delay controller proposed, numerical simulations are implemented. It is indicated by the simulation results that the control performance will deteriorate if neglect the time delay in process of the controller design and proposed time delay controller works well with both small and large time delay problems.
基金This work was supported by the National Natural Science Foundation of China(No.10572011).
文摘A ratio-dependent predator-prey system with stage structure and time delays for both prey and predator is considered in this paper.Both the predator and prey have two stages,immature stage and mature stage,and the growth of them is of Lotka-Volterra nature.It is assumed that immature individuals and mature individuals of each species are divided by a fixed age,and that mature predators attack immature prey only.The global stability of three nonnegative equilibria and permanence are presented.
基金Supported by the Basis and Frontier Science Research Foundation of Henan Province(072300410096)the Natural Science Foundation of Education Department of Henan Province(2009A110023)the Youth Foundation of Zhoukou Normal University
文摘In this paper,a delayed two-species predator-prey system with stage structure and diffiusion is investigated.Based on the continuation theorem of coincidence degree theory,the suficient conditions for the existence of positiveω-periodic solution to the system are derived.The numerical simulation of an example verifies our main result.
基金supported by the Basic Science Research Program funded by the Ministry of Science and ICT(NRF-2019R1A2C1084952 for M.H.Lee and NRF-2018R1A2B6006320 for S.U.Lee)through the National Research Foundation of Korea(NRF).
文摘An approach to enhance the thermally activated delayed fluorescence (TADF) of nido-carborane-appended triarylboranes is proposed.A methyl group is introduced into the 4-position of the phenylene ring bearing the nido-carborane (7,8-dicarba-nido-undecaborane) cage,i.e.,at the ortho position to the cage,in the PhBMes2acceptor moiety of nido-carborane–triarylborane dyads (nido-1–4).The crystal structure of 8-H substituted nido-1 reveals the existence of steric congestion around the cage,resulting in a highly twisted connectivity between the cage plane and the Ph ring (θ=85.7°).All compounds with different 8-R groups (R=H,Me,iPr) exhibit strong TADF with long emission lifetimes (τ_(d)=4.8–9.7 μs in THF) in both THF and PMMA films,which is supported by a very small singlet–triplet energy splitting (ΔE_(ST)< 0.03 eV).Attaching an additional Me group to the ortho position of the BMes2group further enhances the intensity of delayed fluorescence (nido-4).Theoretical studies show that although nido-1–4 reach their local energy minima in a perpendicular arrangement between the cage plane and the Ph ring,there exist large energy barriers to cage rotation.In contrast,the reference compound lacking a 4-Me group,which exhibits very weak delayed fluorescence in solution,has low rotational energy barriers.
基金This work is supported by the National Natural Science Foundation of China(Nos.12001090,11871473)Shandong Provincial Natural Science Foundation(No.ZR2019MA010)the Fundamental Research Funds for the Central Universities of China(No.2412020QD024).
文摘In this paper,we analyze two stochastic predator-prey models with distributed delay and stage structure for prey.For the nonautonomous periodic case of the model,by using Khasminskii’s theory of periodic solution,we show that the system has at least one positive T-periodic solution.For the model which is disturbed by both white and telegraph noises,we obtain sufficient criteria for positive recurrence of the solutions to the model by constructing a suitable stochastic Lyapunov function with regime switching.The positive recurrence implies that both prey and predator populations will be persistent in the long term.
