Reaction–Diffusion Equations with Nonlinear Boundary Delay

We consider dissipative scalar reaction–diffusion equations that include the ones of the form u _t–u=f(u(t)), subjected to boundary conditions that include small delays, that is, we consider boundary conditions of the form u/n _a=g(u(t), u(t–r)). We show the global existence and uniqueness of solutions in a convenient fractional power space, and furthermore, we show that, for r sufficiently small, all bounded solutions are asymptotic to the set of equilibria as t tends to infinity.     

Transition layers for singularly perturbed delay differential equations with monotone nonlinearities

Transition layers arising from square-wave-like periodic solutions of a singularly perturbed delay differential equation are studied. Such transition layers correspond to heteroclinic orbits connecting a pair of equilibria of an associated system of transition layer equations. Assuming a monotonicity condition in the nonlinearity, we prove these transition layer equations possess a unique heteroclinic orbit, and that this orbit is monotone. The proof involves a global continuation for heteroclinic orbits.     

Singularly perturbed reaction diffusion equations with time delay

Abstract A class of initial boundary value problems of differential-difference equations for reaction diffusion with a small time delay is considered. Under suitable conditions and by using the stretched variable method, a formal asymptotic solution is constructed. Then, by use of the theory of differential inequalities, the uniform validity of the solution is proved.     

STABILITY CRITERIA IN TERMS OF TWO MEASURES FOR DELAY DIFFERENTIAL EQUATIONS

ＩｎｔｒｏｄｕｃｔｉｏｎＡｓｗｅｋｎｏｗ ,ｉｎｔｈｅｉｎｖｅｓｔｉｇａｔｉｏｎｏｆｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｓｏｌｕｔｉｏｎｓｆｏｒｎｏｎｌｉｎｅａｒｄｉｆｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｓ,ｔｈｅｍｅｔｈｏｄｏｆｖａｒｉａｔｉｏｎｏｆｐａｒａｍｅｔｅｒｓｉｓａｎｅｆｆｅｃｔｉｖｅｔｏｏｌｉｎｔｈｅｃａｓｅｔｈａｔｔｈｅｃｏｒｒｅｓｐｏｎｄｉｎｇｕｎｐｅｒｔｕｒｂｅｄｔｅｒｍｓａｒｅｌｉｎｅａｒｏｒｏｆｃｅｒｔａｉｎｓｍｏｏｔｈｎｅｓｓｔｈｏｕｇｈｔｈｅｙａｒｅｎｏｎｌｉｎｅａｒ.Ｏｎｔｈｅ…     

Boundedness and persistence and global asymptotic stability for a class of delay difference equations with higher order

ＩｎｔｒｏｄｕｃｔｉｏｎＣｏｎｓｉｄｅｒｔｈｅｆｏｌｌｏｗｉｎｇｄｅｌａｙｄｉｆｆｅｒｅｎｃｅｅｑｕａｔｉｏｎｗｉｔｈｈｉｇｈｅｒｏｒｄｅｒｘｎ+1=Ａ0ｘｐ0ｎ+ Ａ1ｘｐ1 ｎ- 1+… + Ａｋｘｐｋｎ-ｋ　　 (ｎ=0 ,1 ,2 ,… ) ,( 1 )ｗｈｅｒｅＡｉ,ｐｉ ∈ [0 ,∞ )　　 (ｉ=0 ,1 ,2 ,…ｋ;ｋ∈ 1 ,2 ,… ) ( 2 )ａｎｄｔｈｅｉｎｉｔｉａｌｃｏｎｄｉｔｉｏｎｓｘ-ｋ,ｘ-ｋ+1,… ,ｘ- 1,ｘ0 ａｒｅａｒｂｉｔｒａｒｙｐｏｓｉｔｉｖｅｎｕｍｂｅｒｓ.Ｓｏｍｅｓｐｅｃｉａｌｃａｓｅｓｏｆｋ=1ｆｏｒＥｑ .( 1 )ｈａｖｅｂｅｅｎ…     

Noise and stability in differential delay equations

We study the stability of linear stochastic differential delay equations in the presence of additive or multiplicative white and colored noise. Using a stochastic analog of the second Liapunov method, sufficient conditions for mean square and stochastic stability are derived.     

Determination of source parameter in parabolic equations

The authors consider the problem of finding u=u(x, t) and p=p(t) which satisfy u = Lu + p(t) + F(x, t, u, _x, p(t)) in Q _T=Ω×(0, T], u(x, 0)=ø(x), x∈Ω, u(x, t)=g(x, t) on ?Ω×(0, T] and either ∫_G(t) Φ(x,t)u(x,t)dx = E(t), 0 ? t ? T or u(x₀, t)=E(t), 0≤t≤T, where Ω?R ⁿ is a bounded domain with smooth boundary ?Ω, x ₀∈Ω, L is a linear elliptic operator, G(t)?Ω, and F, ø, g, and E are known functions. For each of the two problems stated above, we demonstrate the existence, unicity and continuous dependence upon the data. Some considerations on the numerical solution for these two inverse problems are presented with examples.     

Numerical stability analysis of numerical methods for volterra integral equations with delay argument

The present paper deals with the stability properties of numerical methods for Volterra integral equations with delay argument. We assess the numerical stability of numerical methods with respect to the following test equations (0.1a) $$y\left( t \right) = \psi \left( 0 \right) + \int_0^t {\left( {py\left( s \right) + q\left( {s - \tau } \right)} \right)ds (0 \leqslant t \leqslant X)}$$ (0.1b) $$y\left( t \right) = \psi \left( t \right) \left( {t \in [ - \tau ,0)} \right)$$ where τ is a positive constant, and P and q are complex valued. We investigate the stability properties of reducible quadrature methods and θ-methods in the case of the above test equations     

ON STABILITY OF SOLUTIONS OF CERTAIN FOURTH-ORDER DELAY DIFFERENTIAL EQUATIONS

By the use of the Liapunov functional approach, a new result is obtained to ascertain the asymptotic stability of zero solution of a certain fourth-order non-linear differential equation with delay. The established result is less restrictive than those reported in the literature.     

On the perturbational global attractivity of nonautomous delay differential equations

Consider the perturbed nonautonomous linear delay differential equation x(t) = - a(t)x(t-τ) + F(t, x₁, t ⩾ 0 where x₁(s)=x(t+s) for −δ≤s≤0. Suppose that a(t) ∈ C([0,∞), (0,∞)), τ≥0,F:[0, ∞) x C[−δ,0] → R is a continuous functions and F(t,0) ≡ 0. Here C[−δ,0] is the space of continuous functions Φ: [−δ,0] → R with ∥Φ∥<H for the norm | Φ |, where |·| is any norm in R and 0<H≤+∞. Most of the known papers [1–5,7] have been concerned with the local or global asymptotic behavior of the zero solution of Eq. (*) when a(t) is independent of t i. e., a(t) is autonomous. The aim in this paper is to derive the sufficient conditions for the global attractivity of the zero solution of of Eq. (*) When a(t) is nonautomous. Our results, which extend and improve the known results, are even “sharp”. At the same time, the method used in this paper can be applicable to the perturbed nonlinear equation. Project supported by the Natural Science Foundation of Hunan     

Linearized oscillations for autonomous delay differential equations

ＩｎｔｒｏｄｕｃｔｉｏｎＣｏｎｓｉｄｅｒｔｈｅｎｏｎｌｉｎｅａｒａｕｔｏｎｏｍｏｕｓｄｅｌａｙｄｉｆｆｅｒｅｎｔｉａｌｅｑｕａｔｉｏｎｘ′(ｔ) ∑ｍｉ=1ｐｉｆｉ(ｘ(ｔ-τｉ) ) =0 (1 )ａｎｄｔｈｅｌｉｎｅａｒｅｑｕａｔｉｏｎｘ′(ｔ) ∑ｍｉ=1ｐｉｘ(ｔ-τｉ) =0 ,(2 )ｗｈｅｒｅ ,ｐｉ ∈ (0 ,∞ ) ,τｉ ∈ [0 ,∞ )ａｎｄｆｉ ∈Ｃ(Ｒ ,Ｒ)ｆｏｒｉ =1 ,… ,ｍ .ＩｎＲｅｆ.[1 ] ,ｔｈｅｌｉｎｅａｒｉｚｅｄｏｓｃｉｌｌａｔｉｏｎｓｏｆＥｑ .(1 )ｗａｓｓｔｕｄｉｅｄａｎｄｉｔｗａｓｐｒｏｖｅｄｔｈａｔｉｆｔ…     

A singular perturbation analysis with applications to delay differential equations

We prove an approximation result for the solutions of a singularly perturbed, nonautonomous ordinary differential equation which has interesting applications to problems in higher dimensions. Here our result is applied to a singularly perturbed, delay differential equation with state dependent time-lags (i.e., aninfinite dimensional problem). We find a new dynamical system (also in infinite dimensions), which describes, in a certain sense, the dynamics of our delay equations for very small values of the singular parameter.     

Nonlinear delay difference equations for housing dynamics assuming heterogeneous backward-looking expectations

China's first interest rate hike during the last decade, aiming to cool down the seemingly overheated real estate market, had aroused more caution on housing market. This paper aims to analyze the housing price dynamics after an unanticipated economic shock, which was believed to have similar properties with the back ward- looking expectation models. The analysis of the housing price dynamics is based on the cobweb model with a simple user cost affected demand and a stock-flow supply assumption. Several nth-order delay rational difference equations are set up to illustrate the properties of housing dynamics phenomena, such as the equilibrium or oscillations, overshoot or undershoot and convergent or divergent, for a kind of heterogeneous backward-looking expectation models. The results show that demand elasticity is less than supply elasticity is not a necessary condition for the occurrence of oscillation. The housing price dynamics will vary substantially with the heterogeneous backward-looking expectation assumption and some other endogenous factors.     

Boundary value problems for second order delay differential equations

In this paper,using a fixed point principle and existence principle given in[1],westudy the boundary value problems for second order differential equations.Some newexistence results are obtained.     

On stabilization of systems with delay

The optimization of the parameters of a controller of given structure for a controlled unstable scalar system with delay is studied. First, the original system with delay is approximated by a system without delay. To this end, the exponent is approximated by a fractional rational function. Since the structure of the controller is fixed, the quality of the approximation is assessed by comparing the stability domains of the original and approximating systems (in the space of controller coefficients). Next, the coefficients of the controller for the reduced system are optimized. The performance of the controller thus synthesized can be assessed by mathematically modeling the original system (with delay) whose feedback is determined by the controller coefficients found. The approach is exemplified by stabilizing an inverted mathematical pendulum with a PD controller. This example is used to examine the issue of synthesis of a robust controller __________ Translated from Prikladnaya Mekhanika, Vol. 44, No. 10, pp. 86–100, October 2008.     

LocalC α convergence of elliptic regularizations of parabolic equations

The solutions of elliptic regularizations of the heat equation converge to the solutions of the corresponding evolution equation in weak energy norms. The technique is of relevance in control theory as well as variational inequalities. We show that the convergence actually takes place in some Hölder space. The result holds for a class of parabolic equations in divergence form and sufficiently integrable forcing terms.

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Sommario Le soluzioni delle regolarizzanti ellittiche dell'equazione del calore, convergono alle soluzioni della corrispondente equazione di evoluzione in norme deboli dell'energia. Questa tecnica trova applicazione nelle teoric dei controlli e disuguaglianze variazionali. Si dimostra che la convergenza é forte ed ha luogo in norme Hölderiane. Il risultato si estende ad una classe di equazioni paraboliche in forma di divergenza con termini forzanti sufficientemente integrabili.

     

考虑主动时滞的汽车悬架系统控制特性研究

以汽车悬架系统为研究对象,采用理论和试验相结合的方法对考虑主动时滞的悬架系统控制特性进行分析。首先建立含时滞悬架系统动力学模型,分析系统的控制稳定性。理论和仿真结果均表明,采用传统二次型最优控制律不能保证含时滞系统的稳定性。系统时滞量存在稳定区间,时滞超出稳定区间时系统将失稳发散;为了保证控制系统的稳定性,采用状态变换法设计了含时滞系统的主动控制律,计算表明,该控制律可以保证系统稳定性。研究还发现,时滞量的变化会使系统振动幅值产生较大改变,为此在控制系统中引入主动时滞,研究主动时滞对系统振动特性的影响,计算表明,合理的主动时滞可以降低系统振动幅值;为验证结果的正确性,搭建了悬架时滞主动控制试验平台,通过对相同工况下仿真结果与试验结果进行对比,发现两者具有较好的一致性;而由于悬架受到的路面激励具有随机性,采用含时滞系统的主动控制律对路面随机激励下的悬架系统进行控制分析,发现当主动时滞为0.04 s时,车身加速度均方根值比无主动时滞降低了39.4%,说明主动时滞对悬架控制的有效性。本文研究对时滞主动控制的理论研究具有重要的促进作用。     

GLOBAL ATTRACTIVITY FOR A CLASS OF NONLINEARDELAY DIFFERENCE EQUATIONS

ＩｎｔｒｏｄｕｃｔｉｏｎＣｏｎｓｉｄｅｒｔｈｅｇｌｏｂａｌａｔｔｒａｃｔｉｖｉｔｙｏｆｔｈｅｎｏｎｌｉｎｅａｒｄｅｌａｙｄｉｆｆｅｒｅｎｃｅｅｑｕａｔｉｏｎΔｘｎ+ａｎｘｎ+ｆ(ｎ ,∑0ｓ=-ｋ ｑｓ,ｎｘｓ+ｎ) =0　 (ｎ=0 ,1 ,2 ,… ) . ( 1 )ＴｈｅｉｎｉｔｉａｌｖａｌｕｅｏｆＥｑ .( 1 )ｉｓｘｓ =φｓ　 (ｓ=-ｋ ,-ｋ+ 1 ,… ,-1 ,0 ) . ( 2 )Ｉｎｔｈｅｓｅｑｕｅｌ,ｗｅａｌｗａｙｓｓｕｐｐｏｓｅｔｈａｔＤ1) ａｎ ｉｓａｎｏｎｎｅｇａｔｉｖｅｒｅａｌｓｅｑｕｅｎｃｅ ,0 ≤ａｎ <1ａｎｄｋｉｓａｐｏｓｉｔｉｖｅ…     

Active control for a flexible beam with nonlinear hysteresis and time delay

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.