Nonautonomous Ordinary Differential Equations Research Articles

Flocking dynamics of agents moving with a constant speed and a randomly switching topology

Abstract In this paper, we present a sufficient framework to exhibit the sample path-wise asymptotic flocking dynamics of the Cucker–Smale model with unit-speed constraint and the randomly switching network topology. We employ a matrix formulation of the given equation, which allows us to evaluate the diameter of velocities with respect to the adjacency matrix of the network. Unlike the previous result on the randomly switching Cucker–Smale model, the unit-speed constraint disallows the system to be considered as a nonautonomous linear ordinary differential equation on velocity vector, which forces us to get a weaker form of the flocking estimate than the result for the original Cucker–Smale model.

Existence of solutions of a nonlinear eigenvalue problem and their properties

An eigenvalue problem is considered for a nonlinear nonautonomous ordinary differential equation of the second order on a closed interval with conditions of the first type and an additional (local) condition. The nonlinearity in the equation is due to a monotonically increasing nonnegative function with powerlike growth at infinity. The existence of infinite numbers of negative and positive eigenvalues is shown. Asymptotic formulae for the eigenvalues and the maxima of eigenfunctions are found, and comparison theorems are established. Bibliography: 20 titles.

A kinetic model with time‐dependent proliferative/destructive rates

This paper presents a new kinetic model with time‐dependent proliferative/destructive parameters, where the activity variable of the system attains its values in a discrete real subset. Therefore, a system of nonautonomous nonlinear ordinary differential equations is gained, with the related Cauchy problem. A first result of local existence and uniqueness of positive and bounded solution is proved. Then, the possibility of extend this result globally in time is discussed, with respect to the shape of nonconservative time‐dependent parameters. Numerical simulations are performed for some scenarios, corresponding to different shapes of time‐dependent parameters themselves. Furthermore, the pattern and long‐time behavior of solutions are numerically analyzed. Finally, these results show that equilibria and oscillations may occur.

Large time behavior of nonautonomous linear differential equations with Kirchhoff coefficients

Nonautonomous linear ordinary differential equations with Kirchhoff coefficients are considered. Under appropriate assumptions on the topology of the directed graphs of the coefficients, it is shown that if the Perron vectors of the coefficients are slowly varying at infinity, then every solution is asymptotic to a constant multiple of the Perron vectors at infinity. Our results improve and generalize some recent convergence theorems.

ASYMPTOTIC BEHAVIOR OF SOLUTIONS OF TWO-PART DIFFERENTIAL EQUATIONS WITH EXPONENTIAL NONLINEARITY

For a two-term nonautonomous ordinary differential equation of the fourth order with an exponential nonlinearity of the form y(4) = α0p0(t)[1 + r(t)]eσy where α0 ∈ {−1,1}, σ ≠ 0, the function p0(t) is continuous or continuously differentiable and nonzero in some left neighbourhood of ω (ω ≤ +∞), r(t) is a continuous function such that limt↑ωr(t) = 0, the asymptotic behaviour at t↑ω of one class of Pω(Y0, λ0)-solutions is studied. For this equation, in [1], the necessary and sufficient conditions for the existence of such solutions were obtained in the case when λ0 ∈ R∖ {0, 1/2, 2/3, 1}. The proof of sufficient conditions for existence was carried out under some additional conditions that are quite strict. The aim of this paper is to improve the results obtained in [1] for sufficient conditions of existence. An attempt is made to extend the results of this paper to conditions that are less stringent. In contrast to [1], the proof of the main result in this paper assumes that there is a finite or infinite limit limt↑ω πω(t)q’(t). The equation under study is reduced to a system of equations for which it is necessary to determine the existence of solutions vanishing at infinity. This fact is established using the known results of [2]. The question of the number of solutions of the equation with the found asymptotic images is also solved.

Selection pressure by specialist and generalist insect herbivores leads to optimal constitutive plant defense. A mathematical model.

Brassicaceae plants have the glucosinolate-myrosinase defense system, jointly active against herbivory. However, constitutive glucosinolate (GLS) defense is observed to occur at levels that do not deter all insects from feeding. That prompts the question of why Brassicaceae plants have not evolved a higher constitutive defense. The answer may lie in the contrasting relationship between plant defense and host plant preference of specialist and generalist herbivores. GLS content increases a plant's susceptibility to specialist insects. In contrast, generalists are deterred by the plant GLSs. Although GLSs can attract the natural enemies (predators and parasitoids) of these herbivores, enemies can reduce herbivore pressure to some extent only. So, plants can be overrun by specialists if GLS content is too high, whereas generalists can invade the plants if it is too low. Therefore, an optimal constitutive plant defense can minimize the overall herbivore pressure. To explain the optimal defense theoretically, we model the contrasting host selection behavior of insect herbivores and the emergence of their natural enemies by non-autonomous ordinary differential equations, where the independent variable is the plant GLS concentration. From the model, we quantify the optimal amount of GLSs, which minimizes total herbivore (specialists and generalists) pressure. That quite successfully explains the evolution of constitutive defense in plants from the perspective of optimality theory.

Constructive proofs for localised radial solutions of semilinear elliptic systems on

Ground state solutions of elliptic problems have been analysed extensively in the theory of partial differential equations, as they represent fundamental spatial patterns in many model equations. While the results for scalar equations, as well as certain specific classes of elliptic systems, are comprehensive, much less is known about these localised solutions in generic systems of nonlinear elliptic equations. In this paper we present a general method to prove constructively the existence of localised radially symmetric solutions of elliptic systems on . Such solutions are essentially described by systems of non-autonomous ordinary differential equations. We study these systems using dynamical systems theory and computer-assisted proof techniques, combining a suitably chosen Lyapunov–Perron operator with a Newton–Kantorovich type theorem. We demonstrate the power of this methodology by proving specific localised radial solutions of the cubic Klein–Gordon equation on , the Swift–Hohenberg equation on , and a three-component FitzHugh–Nagumo system on . These results illustrate that ground state solutions in a wide range of elliptic systems are tractable through constructive proofs.

OPTIMAL CONTROL OF A DYNAMIC SYSTEM WITH NON-SEPARADED POINT AND INTEGRAL CONDITIONS

. In the work, a numerical method is proposed to solve a system of linear nonautonomous ordinary differential equations with non-separated multipoint and integral conditions. The proposed approach is based on the introduced operation of convolution of integral conditions into local ones. The method allows to reduce the solution of the original problem to the solution of Cauchy problem with respect to a system of ordinary differential equations and of linear algebraic equations. The stability of the computational schemes is shown.

Generalized Pitchfork Bifurcations in D-Concave Nonautonomous Scalar Ordinary Differential Equations

AbstractThe global bifurcation diagrams for two different one-parametric perturbations ($$+\lambda x$$ + λ x and $$+\lambda x^2$$ + λ x 2 ) of a dissipative scalar nonautonomous ordinary differential equation $$x'=f(t,x)$$ x ′ = f ( t , x ) are described assuming that 0 is a constant solution, that f is recurrent in t, and that its first derivative with respect to x is a strictly concave function. The use of the skewproduct formalism allows us to identify bifurcations with changes in the number of minimal sets and in the shape of the global attractor. In the case of perturbation $$+\lambda x$$ + λ x , a so-called generalized pitchfork bifurcation may arise, with the particularity of lack of an analogue in autonomous dynamics. This new bifurcation pattern is extensively investigated in this work.

Modifying an existing SIMIODE project to create an in-depth project requiring a written report

This article considers starting with an existing SIMIODE modeling scenario [Winkel, B. (2015). 1-031-CoolIt-ModelingScenario. SIMIODE (Version 2.0). QUBES Educational Resources. https://doi.org/10.25334/3WG8-EC31] that develops Newton's law of cooling by considering data on the cooling of a beaker of water in a room, and expanding upon it to create a longer project modeling the temperature of a building with an internal heat pump that is also subject to a sinusoidal varying outside temperature. The proposed project was undertaken early on in the course, since little background was required, and a longer project format was utilised so that students could return to the project and see direct applications of new concepts, such as autonomous vs. nonautonomous ordinary differential equations, slope fields, and Euler's method as they were introduced. The project prompt is provided as well as a detailed discussion of the motivation behind the questions. Finally, the pros and cons of requiring the students to submit a written lab report for the project are reflected upon and a sample rubric is provided.

Nonlinear control of safety factor gradient in tokamaks using spatially variable electron cyclotron current drives

Active control of plasma properties may be necessary to achieve stable operation of next-generation tokamaks over large time scales. Such control algorithms can regulate the plasma properties to avoid the onset of magnetohydrodynamic (MHD) instabilities. For instance, the global and local properties of the safety factor profile are linked to the onset of neoclassical tearing modes (NTMs). This work proposes a model-based control approach for deterring/delaying NTMs through active modulation of one of the safety factor properties - the gradient of the safety factor profile at a particular rational safety factor surface. In particular, a novel control-oriented model for the local safety factor gradient is developed. The nonlinear control model is governed by a nonautonomous ordinary differential equation that accounts for a given rational safety factor surface’s spatial variation over time. To improve the controllability of the spatially evolving parameter, the control model treats ECH&CD positions, along with noninductive powers, as controllable variables. A nonlinear control algorithm based on feedback linearization with optimization is synthesized to achieve the objective of regulating the safety factor gradient around a given target. The proposed algorithm allocates optimal ECH&CD positions, in addition to auxiliary powers, at each time instant as the rational safety factor surface drifts to locations with a low control authority. Stability guarantees of the proposed control law are also discussed in this work. The proposed algorithm is tested for a DIII-D tokamak scenario in nonlinear simulations carried out using the Control Oriented Transport SIMulator (COTSIM). Both fixed and moving ECH&CD cases are studied, and their outcomes are compared. Simulation results demonstrate that enthusiastic regulation of the safety factor gradient can be achieved during the ramp-up and flat-top phases of tokamak operation in both fixed and moving ECH&CD cases. However, real-time updates of ECH&CD positions can prevent the saturation of auxiliary powers.

Bifurcation theory of attractors and minimal sets in d-concave nonautonomous scalar ordinary differential equations

Two one-parametric bifurcation problems for scalar nonautonomous ordinary differential equations are analyzed assuming the coercivity of the time-dependent function determining the equation and the concavity of its derivative with respect to the state variable. The skewproduct formalism leads to the analysis of the number and properties of the minimal sets and of the shape of the global attractor, whose abrupt variations determine the occurrence of local saddle-node, local transcritical and global pitchfork bifurcation points of minimal sets and of discontinuity points of the global attractor.

Conditional Lipschitz Shadowing for Ordinary Differential Equations

AbstractWe introduce the notion of conditional Lipschitz shadowing, which does not aim to shadow every pseudo-orbit, but only those which belong to a certain prescribed set. We establish two types of sufficient conditions under which certain nonautonomous ordinary differential equations have such a property. The first criterion applies to a semilinear differential equation provided that its linear part is hyperbolic and the nonlinearity is small in a neighborhood of the prescribed set. The second criterion requires that the logarithmic norm of the derivative of the right-hand side with respect to the state variable is uniformly negative in a neighborhood of the prescribed set. The results are applicable to important classes of model equations including the logistic equation, whose conditional shadowing has recently been studied. Several examples are constructed showing that the obtained conditions are optimal.

Energy computation and multistability in a class of second-order chaotic systems with simple nonlinearities: numerical, experimental and analytical results

The present work is aimed at the design, implementation and analysis of generic new second-order non-autonomous chaotic systems with simple nonlinear functions that have algebraically simple representations in mathematical form. These systems involve simple second-order non-autonomous ordinary differential equations with different simple nonlinearities like . The present study deals with numerical simulation, experimental analog circuit simulation results to demonstrate the ordered and chaotic phenomena being exhibited by these systems. Of most interest the striking phenomenon of multistability is uncovered for certain nonlinearities. Coexisting attractors are harnessed through the offset boosting approach. Also, the Hamilton energy is established through the Helmholtz theorem. It is found that both methods can be exploited as a non-bifurcation approach in characterizing multistability in the model. Further, analytical solutions developed for systems with certain nonlinearities are presented and the chaotic behavior of the systems studied using the solutions validating the numerical and experimental results are reported.

Asymptotic behaviour of solutions of one class of the fourth-order nonlinear differential equations

The asymptotic behaviour as t↑ω of one of the possible types of Pω(Y0, λ0)-solutions of a binomial non-autonomous fourth-order ordinary differential equation with exponential nonlinearity and a continuous and non-zero in some left neighbourhood ω(ω≤+∞) coefficient p(t) is investigated. First, using a priori asymptotic properties of the considered Pω(Y0, λ0)-solutions, necessary conditions for their existence are established, as well as asymptotic representations of these solutions and their derivatives up to the third order. The question of the actual existence of solutions with the obtained asymptotic representations is solved by reducing it to the question of the existence of solutions that vanish at a specific point of a system of quasilinear differential equations. This system is obtained as a result of some transformations of the original equation, taking into account the kind of established asymptotic representations. In addition, the question of the number of solutions with found asymptotic representations is also resolved.

A Lanczos-type procedure for tensors

The solution of linear non-autonomous ordinary differential equation systems (also known as the time-ordered exponential) is a computationally challenging problem arising in a variety of applications. In this work, we present and study a new framework for the computation of bilinear forms involving the time-ordered exponential. Such a framework is based on an extension of the non-Hermitian Lanczos algorithm to 4-mode tensors. Detailed results concerning its theoretical properties are presented. Moreover, computational results performed on real-world problems confirm the effectiveness of our approach.

A Lanczos-like method for non-autonomous linear ordinary differential equations

The time-ordered exponential is defined as the function that solves a system of coupled first-order linear differential equations with generally non-constant coefficients. In spite of being at the heart of much system dynamics, control theory, and model reduction problems, the time-ordered exponential function remains elusively difficult to evaluate. The *-Lanczos algorithm is a (symbolic) algorithm capable of evaluating it by producing a tridiagonalization of the original differential system. In this paper, we explain how the *-Lanczos algorithm is built from a generalization of Krylov subspaces, and we prove crucial properties, such as the matching moment property. A strategy for its numerical implementation is also outlined and will be subject of future investigation.

Quantifying periodic, multi-periodic, hidden and unstable regimes of a magnetic pendulum via semi-analytical, numerical and experimental methods

The dynamics of a magnetic pendulum mounted on a shaft with an elastic element is considered. The impulsive excitation of the pendulum is performed through the interaction of a strong neodymium magnet and an electric coil. The mathematical model of the pendulum is represented by the non-autonomous ordinary nonlinear differential equation. The model is verified in a wide range of motion regimes by the laboratory experiment. Periodic motions are considered in more detail by the semi-analytic approximate method utilizing the averaging ideas. The amplitude and phase shift of system solutions possess highly nonlinear features which we propose to approximate by the saw-tooth functions. This new approach allows one to improve the results of the application of the conventional averaging method and is promising for the application and analysis of nonlinear systems with a strong nonlinearity.

Lyapunov-Razumikhin techniques for state-dependent delay differential equations

We present Lyapunov stability and asymptotic stability theorems for steady state solutions of general state-dependent delay differential equations (DDEs) using Lyapunov-Razumikhin methods. Our results apply to DDEs with multiple discrete state-dependent delays, which may be nonautonomous for the Lyapunov stability result, but autonomous (or periodically forced) for the asymptotic stability result. Our main technique is to replace the DDE by a nonautonomous ordinary differential equation (ODE) where the delayed terms become source terms in the ODE. The asymptotic stability result is based on a contradiction argument together with the Arzelà-Ascoli theorem. This approach alleviates the need to construct auxiliary functions to ensure the asymptotic contraction, which is a feature of other Lyapunov-Razumikhin asymptotic stability results of which we are aware. We apply our results to a state-dependent model equation which includes Hayes equation as a special case, to directly establish asymptotic stability in parts of the stability domain together with lower bounds on the size of the basin of attraction.

Thermal Effects on the Nonlinear Forced Responses of Hinged-Clamped Beam with Multimodal interaction

Nonlinear analysis of a forced geometrically nonlinear Hinged-Clamped beam involving three modes interactions with internal resonance and submitted to thermal and mechanical loadings is investigated. Based on the extended Hamilton’s principle, the PDEs governing the thermoelastic vibration of planar motion is derived. Galerkin’s orthogonalization method is used to reduce the governing PDEs of motion into a set of nonlinear non-autonomous ordinary differential equations. The system is solved for the three modes involved by the use of the multiple scales method for amplitudes and phases. For steady states responses, the Newton-Raphson shooting technique is used to solve the three systems of six parametric nonlinear algebraic equations obtained. Results are presented in terms of influences of temperature variations on the response amplitudes of different substructures when each of the modes is excited. It is observed for all substructures and independent of the mode excited a shift within the frequency axis of the temperature influenced amplitude response curves on either side of the temperature free-response curve. Moreover, it is found that thermal loads diversely influence the interacting substructures. Depending on the directly excited mode, higher oscillation amplitudes are found in some substructures under negative temperature difference, while it is observed in others under positive temperature change and in some others for temperature free-response curves.