Response of a viscoelastic half-space to time dependent moving surface loads

Through the use of nonpolar viscoelasticity theory, the problem of traveling loads with time dependent magnitude variability is considered. Employing a moving Lagrangian observer, a quadratic form is developed to ascertain potential time dependent magnitude variability induced shifts, bifurcations and wavelength interdependencies in the critical speeds associated with Rayleigh, plane and transverse wave phenomena. In terms of the moving Lagrangian formulation, a solution is developed which enables the characterization of response behavior in the various sub, trans and supercritical speed ranges associated with each of the different wave types. Based on the solution, the results of several numerical experiments are presented. These demonstrate various aspects of the foregoing phenomena.     

移动荷载作用下桥梁动力响应的精细时程积分计算

桥梁与车辆的耦合振动方程为时变系数微分方程,用解析的方法求解这类问题有很大的局限性,解决这类问题的最为有效的工具之一是数值方法中的有限单元法.对移动衙载这种简化模型在时程积分时采用了精细积分法,为了保持精细时程积分法的高精度,对动力方程中的非齐次项进行离散计算时选用了积分精度较高的科茨积分格式,对于Euler-Bernouili梁单元采用二节点的Hermite插值函数,模拟了移动常量荷载、移动简谐荷载作用下的等截面和变截面简支梁桥模型的振动情况,并与解析的结果及一些其它的数值解法进行了对比,显示了采用精细时程积分时对动力响应过程的数值模拟的高精度.     

Iterative learning control-based tracking synchronization for linearly coupled reaction-diffusion neural networks with time delay and iteration-varying switching topology

In this paper, the D-type iterative learning control (ILC) protocol based on the local neighbor information is designed to achieve tracking synchronization for linearly coupled reaction-diffusion neural networks in presence of time delay and iteration-varying switching topology under a repetitive environment. Firstly, based on non-collocated sensors and actuators network, the proposed D-type ILC update law can realize tracking synchronization by utilizing output tracking errors. Then, by virtue of the contraction mapping principle, the sufficient convergence conditions of tracking synchronization errors are presented under the fixed commutation topology. Subsequently, the synchronization conclusions are extended to the iteration-varying commutation topology scenario. Finally, two numerical examples are provided to verify the efficacy of the obtained results.     

Green synthesis of bifunctional phthalocyanine-porphyrin COFs in water for efficient electrocatalytic CO2 reduction coupled with methanol oxidation

Electrocatalytic CO₂ reduction(ECR) coupled with organic oxidation is a promising strategy to produce high value-added chemicals and improve energy efficiency. However, achieving the efficient redox coupling reaction is still challenging due to the lack of suitable electrocatalysts. Herein, we designed two bifunctional polyimides-linked covalent organic frameworks(PI-COFs) through assembling phthalocyanine(Pc) and porphyrin(Por) by non-toxic hydrothermal methods in pure water to reali...     

Adaptive synchronization for a class of faulty and sampling coupled networks with its circuit implement

This paper is concerned with the asymptotic synchronization problem of a class of nonlinear complex networks with faulty and sampling couplings. A new version of the adaptive control strategy is proposed to adjust control parameters to compensate for the adverse impact of network attenuation faults, nonlinearities and sampling errors. Based on the adaptive adjustment laws, an approach that is application of knowledge of electricity is introduced to physically realize the adaptive controllers. Using Lyapunov stability theory for the synchronization error system, asymptotic synchronization of the overall networks can be established for the nonlinearly sampling and faulty couplings. Finally, the proposed adaptive control schemes are tested by simulation on Chua?s circuit network.     

模块化视角的产业演化动力机制初探——以GPS导航产业为例

以模块化为视角,在模块化相关理论模型的基础上分析出了三大影响产业规模扩张的动力因素;再以GPS导航产业为具体分析对象,结合社会网络分析法分析GPS导航不同发展阶段产业规模扩张的主要推动力,从而探索总结出不同产业阶段的主要演化动力,在产业发展前期主要为模块化,中期为模块再整合,后期为模块应用领域的扩展;研究对于如何引领产业的规模化,协助完成产业调整与升级有着重要的意义。     

Design of observers for a class of discrete-time uncertain nonlinear systems with time delay

This paper is concerned with the problem of observer design for a class of discrete-time Lipschitz nonlinear state delayed systems with, or without parameter uncertainty. The nonlinearities are assumed to appear in both the state and measured output equations. For both the cases with and without norm-bounded time-varying parameter uncertainties, a design method is proposed, which involves solving a linear matrix inequality (LMI). When a certain LMI is satisfied, the explicit expression of a desired nonlinear observer is also presented. An example is provided to demonstrate the applicability of the proposed approach.     

Estimating Eigenvalues for a class of Dynamic systems

In a previous work an approach was presented for extracting information about the eigenvalues of a linear, time-invariant dynamic system directly from a graphical model. In this paper a generalization is given of the results previously obtained. For some particular cases we can give the entire spectrum. For these cases the spectrum is shown as a function of the structure of an abstract form of the bond graph model. For more general cases, we give upper limits on the imaginery part, and upper and lower limits on the real parts, of the eigenvalues. In contrast to most existing methods, the information about the eigenvalues is generated prior to deriving the state equations. When suitably automated, the results obtained here can provide a considerable reduction in the computational effort required to get information about eigenvalues. This feature is particularly useful in an interactive design context.     

Scaled telerobotic control of a manipulator in real time with laser assistance for ADL tasks

In this paper we present a novel concept of shared autonomous and teleoperation control of a remote manipulator with a laser-based assistance in a hard real-time environment for people with disabilities to perform activities of daily living (ADL). The laser pointer enables the user to make high-level decisions, such as target object selection, and it enables the system to generate a trajectories and virtual constraints to be used for autonomous motion or scaled teleoperation. Autonomous, position-teleoperation and velocity-teleoperation control methods have been implemented in the control code. Scaling and virtual fixtures have been used in the teleoperation based control depending on the user preference.A real-time QNX operating system has been used to control a PUMA 560 robotic arm using a Phantom Omni master through a TCP/IP port. A SICK laser range finder was used to for the telerobotic control. The system was implemented with different control modes, and three healthy human subjects were trained to use the system for a pick-and-place task. Data were collected and presented for different control modes, and a comparison between these modes based on the time to complete the task was presented.     

Delay-dependent exponential stability for a class of neural networks with time delays and reaction-diffusion terms

In this paper, the exponential stability of a class of delayed neural networks described by nonlinear delay differential equations of the neutral type has been studied. By constructing appropriate Lyapunov functional and using the linear matrix inequality (LMI) optimization approach, a series of sufficient criteria is obtained ensuring the existence, uniqueness and global exponential stability of an equilibrium point of such a kind of delayed neural networks. These conditions are dependent on the size of the time delay and the measure of the space, which is usually less conservative than delay-independent and space-independent ones. And, these networks are generalized without assuming the boundedness and differentiability of the activate functions. The proposed LMI condition can be checked easily by recently developed algorithms. The results are new and improve the earlier work. Examples are provided to demonstrate the effectiveness and applicability of the proposed criteria.     

Global continuous output-feedback stabilization for a class of high-order nonlinear systems with multiple time delays

This paper addresses the global output-feedback stabilization for a class of high-order nonlinear systems with multiple time delays. A distinct property of the systems to be investigated is that powers on the upper bound restrictions of nonlinearities are allowed to take values on a continuous interval, another remarkable one rests with the existence of multiple time delays in growth conditions. By introducing a combined method of sign function, homogeneous domination and adding a power integrator, an output-feedback controller based on Lyapunov-Krasviskii theorem is designed recursively to guarantee the equilibrium of the closed-loop system globally uniformly asymptotically stable.     

Adaptive observer-based event-triggered finite time formation tracking for multi-agent systems with a non-cooperative leader

The event-triggered time-varying formation tracking for a class of second-order multi-agent systems (MASs) subject to a non-cooperative leader is investigated in this paper. First, in the presence of the unknown input of the leader and external disturbances, a distributed observer with adaptive parameters is put forward for followers to estimate the velocity tracking error. Then, based on the estimated tracking error and an auxiliary variable, a finite time formation controller is further constructed, which is updated depending on a pre-designed event-triggered mechanism. As a result, the desired time-varying formation configuration can be realized in finite time with less communication resource consumption. It’s noted that the constructed formation strategy doesn’t rely on any global information and thus is fully distributed. The stability of the controlled multi-agent system is proved rigorously and it’s verified that event-triggered intervals are with a positive lower bound. At last, simulations are carried out to illustrate the effectiveness of the presented algorithm.     

Stability analysis of a rotor-AMB system with time varying stiffness

A rotor-active magnetic bearing (AMB) system subjected to a periodically time-varying stiffness with quadratic and cubic nonlinear under tuned, and external excitation is studied. The method of multiple scales is applied to analyze the response of two modes of a rotor-AMB system near the simultaneous combined and sub-harmonic resonance. The stability of the steady-state solution for that resonance is determined and studied applying Rung–Kutta fourth order method. It is shown that the system exhibits many typical nonlinear behaviors, including multiple-valued solutions, jump phenomenon, hardening and softening nonlinear and chaos in the second mode of the system. The effects of the different parameters on the steady-state solutions are investigated and discussed.     

Spatial estimates for a system of coupled parabolic-hyperbolic equations under nonlinear boundary condition

The aim of this study is to present spatial estimates of Phragmen-Lindelof type for a dynamical system. We show that an appropriate measure of the solutions either tends to infinity by exponential rate or decays to zero by exponential rate.     

Cyclic gradient based iterative algorithm for a class of generalized coupled Sylvester-conjugate matrix equations

This paper focuses on the numerical solution of a class of generalized coupled Sylvester-conjugate matrix equations, which are general and contain many significance matrix equations as special cases, such as coupled discrete-time/continuous-time Markovian jump Lyapunov matrix equations, stochastic Lyapunov matrix equation, etc. By introducing the modular operator, a cyclic gradient based iterative (CGI) algorithm is provided. Different from some previous iterative algorithms, the most significant improvement of the proposed algorithm is that less information is used during each iteration update, which is conducive to saving memory and improving efficiency. The convergence of the proposed algorithm is discussed, and it is verified that the algorithm converges for any initial matrices under certain assumptions. Finally, the effectiveness and superiority of the proposed algorithm are verified with some numerical examples.     

The relaxed gradient-based iterative algorithms for a class of generalized coupled Sylvester-conjugate matrix equations

In this paper, two relaxed gradient-based iterative algorithms for solving a class of generalized coupled Sylvester-conjugate matrix equations are proposed. The proposed algorithm is different from the gradient-based iterative algorithm and the modified gradient-based iterative algorithm that are recently available in the literature. With the real representation of a complex matrix as a tool, the sufficient and necessary condition for the convergence factor is determined to guarantee that the iterative solution given by the proposed algorithms converge to the exact solution for any initial matrices. Moreover, some sufficient convergence conditions for the suggested algorithms are presented. Finally, numerical example is provided to illustrate the effectiveness of the proposed algorithms and testify the conclusions suggested in this paper.     

Fast fixed-time synchronization control analysis for a class of coupled delayed Cohen-Grossberg neural networks

In a fixed-time control system, the convergence rate and the fixed settling time are two important performance indexes. In this paper, a novel fixed-time control law is proposed and designed to control a class of coupled delayed Cohen-Grossberg neural networks to achieve synchronization with fast convergence rate within a fixed settling time. It should be emphasized that the derived settling time approach can provide a tighter settling time to more effectively reflect the performance for fast convergence rate of the considered controlled system. Moreover, to show the advantages of the proposed fixed-time control law and the derived fixed settling time approach, the existing related control laws and fixed settling time approaches are further discussed. In addition, the obtained fixed-time synchronization control theory is applied to a secure communication scenario, which further shows the feasibility and innovation of the addressed theoretical results.     

Stability analysis for systems with multiple/single time delays via a Cascade augmented L-K functional

This paper investigates stability of linear systems with multiple/single time-delays. Firstly, a three-level cascade augmented Lyapunov-Krasovskii (L-K) functional is introduced, in which interconnect information among delayed state vectors is fully taken into account. Based on a newly integral inequality and the cascade L-K functional, a novel stability criterion is derived for linear systems with multiple time-delays. Secondly, it is found that the proposed L-K functional is also suitable for linear systems with single time-delay if the delay-partitioning method is employed. This motivates us to obtain a less conservative stability condition for linear systems with single time-delay. Finally, Numerical examples are given to confirm the advantages of the proposed method.