Generalized Dicke model as an integrable dynamical system inverse to the nonlinear Schrödinger equation

We prove that a dynamical system obtained by the space-time inversion of the nonlinear Schrödinger equation is equivalent to a generalized Dicke model. We study the complete Liouville integrability of the obtained dynamical system.Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 47, No. 1, pp. 126–128, January, 1995.Thus, we have shown that the generalized Dicke model, inverse to the nonlinear Schrödinger equation, is a completely Liouville integrable Hamiltonian flow of hydrodynamic type.     

On the exponentially self-regulating population model

A new type of discrete dynamical systems model for populations, called an exponentially self-regulating (ESR) map, is introduced and analyzed in considerable detail for the case of two competing species. The ESR model exhibits many dynamical features consistent with the observed interactions of populations and subsumes some of the most successful discrete biological models that have been studied in the literature. For example, the well-known Tribolium model is an ESR map. It is shown that in addition to logistic dynamics – ranging from the very simple to manifestly chaotic one-dimensional regimes – the ESR model exhibits, for some parameter values, its own brands of bifurcation and chaos that are essentially two-dimensional in nature. In particular, it is proved that ESR systems have twisted horseshoe with bending tail dynamics associated to an essentially global strange attractor for certain parameter ranges. The existence of a global strange attractor makes the ESR map more plausible as a model for actual populations than several other extant models, including the Lotka–Volterra map.     

On noise modeling in a nerve fibre

We present a novel mathematical approach to model noise in dynamical systems. We do so by considering the dynamics of a chain of diffusively coupled Nagumo cells affected by noise. We show that the noise in a variable representing the transmembrane current can be effectively modeled as fluctuations in the model parameters corresponding to electric resistance and capacitance of the membrane. These fluctuations may account for the interactions between the membrane and the surrounding (physiological) solution as well as for the thermal effects. The proposed approach to model noise in a nerve fibre is an alternative to the standard technique based on the consideration of additive stochastic current perturbation (the Langevin type equations) and differs from it in important mathematical aspects, particularly, it points out to the non-Markov dynamics of transmembrane potential. Our scheme relates to a time scale which is shorter than the relaxation times of involved physiological processes.     

Singularities in dynamics: A catastrophic viewpoint

The article is about singularities of dynamical systems, a notion which is far from being as clear as for smooth maps. To give an idea of it, the beginning of “catastrophe theory” for dynamical systems (including very recent results) is developed, first in parallel with the well-known analogous theory for potentials, showing that dynamical versions of the Morse lemma with parameters already lead to difficult open problems. The second part of the paper makes it clear that the short-sighted view that singularities in dynamics are rest points and periodic orbits cannot resist serious investigation since many other specifically dynamical “singularities” are born from statics. A homage to René Thom, the whole article is written in the language of stratifications of function spaces-even though it deals with semi-local phenomena.     

Finite-time stabilization of nonlinear impulsive dynamical systems

Finite-time stability involves dynamical systems whose trajectories converge to a Lyapunov stable equilibrium state in finite time. For continuous-time dynamical systems finite-time convergence implies nonuniqueness of system solutions in reverse time, and hence, such systems possess non-Lipschitzian dynamics. For impulsive dynamical systems, however, it may be possible to reset the system states to an equilibrium state achieving finite-time convergence without requiring non-Lipschitzian system dynamics. In this paper, we develop sufficient conditions for finite-time stability of impulsive dynamical systems using both scalar and vector Lyapunov functions. Furthermore, we design hybrid finite-time stabilizing controllers for impulsive dynamical systems that are robust against full modelling uncertainty. Finally, we present a numerical example for finite-time stabilization of large-scale impulsive dynamical systems.     

Hybrid dynamical systems with controlled discrete transitions

This invited survey focuses on a new class of systems–hybrid dynamical systems with controlled discrete transitions. A type of system behavior referred to as the controlled infinitesimal dynamics is shown to arise in systems with widely divergent dynamic structures and application domains. This type of behavior is demonstrated to give rise to a new dynamic mode in hybrid system evolution–a controlled discrete transition. Conceptual and analytical frameworks for modeling of and controller synthesis for such transitions are detailed for two systems classes: one requiring bumpless switching among controllers with different properties, and the other–exhibiting single controlled impacts and controlled impact sequences under collision with constraints. The machinery developed for the latter systems is also shown to be capable of analysing the behavior of difficult to model systems characterized by accumulation points, or Zeno-type behavior, and unique system motion extensions beyond them in the form of sliding modes along the constraint boundary. The examples considered demonstrate that dynamical systems with controlled discrete transitions constitute a general class of hybrid systems.     

A model of an age-structured population in a multipatch environment

We propose a model of an age-structured population divided into N geographical patches. We distinguish two time scales, at the fast time scale we have the migration dynamics and at the slow time scale the demographic dynamics. The demographic process is described using the classical McKendrick-von Foerster model for each patch, and a simple matrix model including the transfer rates between patches depicts the migration process.Assuming that 0 is a simple strictly dominant eigenvalue for the migration matrix, we transform the model (an e.d.p. problem with N state variables) into a classical McKendrick-von Foerster model (scalar e.d.p. problem) for the global variable: total population density. We prove, under certain assumptions, that the semigroup associated to our problem has the property of positive asynchronous exponential growth and so we compare its asymptotic behaviour to that of the transformed scalar model. This type of study can be included in the so-called aggregation methods, where a large scale dynamical system is approximately described by a reduced system. Aggregation methods have been already developed for systems of ordinary differential equations and for discrete time models.An application of the results to the study of the dynamics of the Sole larvae is also provided.     

Transition Manifolds of Complex Metastable Systems

We consider complex dynamical systems showing metastable behavior, but no local separation of fast and slow time scales. The article raises the question of whether such systems exhibit a low-dimensional manifold supporting its effective dynamics. For answering this question, we aim at finding nonlinear coordinates, called reaction coordinates, such that the projection of the dynamics onto these coordinates preserves the dominant time scales of the dynamics. We show that, based on a specific reducibility property, the existence of good low-dimensional reaction coordinates preserving the dominant time scales is guaranteed. Based on this theoretical framework, we develop and test a novel numerical approach for computing good reaction coordinates. The proposed algorithmic approach is fully local and thus not prone to the curse of dimension with respect to the state space of the dynamics. Hence, it is a promising method for data-based model reduction of complex dynamical systems such as molecular dynamics.     

Dynamics of systems on infinite lattices

The dynamics of infinite-dimensional lattice systems is studied. A necessary and sufficient condition for asymptotic compactness of lattice dynamical systems is introduced. It is shown that a lattice system has a global attractor if and only if it has a bounded absorbing set and is asymptotically null. As an application, it is proved that the lattice reaction-diffusion equation has a global attractor in a weighted l² space, which is compact as well as contains traveling waves. The upper semicontinuity of global attractors is also obtained when the lattice reaction-diffusion equation is approached by finite-dimensional systems.     

不可压缩Navier-Stokes方程最优动力系统建模和分析

研究了同时满足任意速度边界条件和速度不可压条件的Navier-Stokes方程最优动力系统的建模方法.通过对方柱绕流问题的最优动力系统的建模与分析,发现该最优动力系统的动力学特性为极限环.同时,该最优动力系统仅使用了三个最优基函数就很好地描述了所有主要的流场特征和该问题的动力学特性,故满足任意速度边界条件和速度不可压条件Navier-Stokes方程最优动力系统的建模方法,能够用最少的基函数最大限度地描述复杂流体问题及其动力学特性.     

向量丛动力系统研究註记(Ⅱ)──部份1

过去,向量丛线性动力系统的整体线性性质研究已经显得相当广泛。现在,我们提议研究这种线性系统的扰动性质。我们要考虑的这种扰动系统将不再是线性的,但要研究的性质一般仍是整体性的。再者我们感兴趣的为非一致双曲性。在本文中我们给出了这种扰动的恰当的定义。它虽表现得有几分不太通常,然而它较深地植根于有关微分动力系统理论的典泛方程组中。这里一般的问题是要观察,当扰动发生后,原给系统的何种性质得以保持下来。本文的全部内容是要建立这种类型的一个定理。     

On the Analysis of a Simple Impact Drill Model using Set-Oriented Numerical Methods

Set-oriented numerical methods provide a relatively new way for obtaining global insight into a non-linear or even non-smooth dynamical system. The need for analysis of systems with dynamical behaviour of high complexity arose from investigations on a piezoelectric drilling device, in which vibrational energy is transmitted from an actuator to the drill stem via a free-flying, impacting mass. Detailed understanding of the dynamics inside of this device is missing to the present day. Here, the use of a set-oriented approach will be suggested and demonstrated on a basic model for the free-flying mass. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reversible dynamical systems: Dissipation-induced destabilization and follower forces

This paper uses results from the theory of reversible dynamical systems to examine the nonlinear stability of undamped follower force systems. The well-known dissipation-induced destabilization found in these systems is also examined and it is indicated how the postdestabilization dynamics can be determined using normal forms and an eigenvalue splitting criterion.     

On three types of dynamics and the notion of attractor

We propose a theoretical framework for explaining the numerically discovered phenomenon of the attractor–repeller merger. We identify regimes observed in dynamical systems with attractors as defined in a paper by Ruelle and show that these attractors can be of three different types. The first two types correspond to the well-known types of chaotic behavior, conservative and dissipative, while the attractors of the third type, reversible cores, provide a new type of chaos, the so-called mixed dynamics, characterized by the inseparability of dissipative and conservative regimes. We prove that every elliptic orbit of a generic non-conservative time-reversible system is a reversible core. We also prove that a generic reversible system with an elliptic orbit is universal; i.e., it displays dynamics of maximum possible richness and complexity.     

Evolving chaos: Identifying new attractors of the generalised Lorenz family

In a recent paper, we presented an intelligent evolutionary search technique through genetic programming (GP) for finding new analytical expressions of nonlinear dynamical systems, similar to the classical Lorenz attractor's which also exhibit chaotic behaviour in the phase space. In this paper, we extend our previous finding to explore yet another gallery of new chaotic attractors which are derived from the original Lorenz system of equations. Compared to the previous exploration with sinusoidal type transcendental nonlinearity, here we focus on only cross-product and higher-power type nonlinearities in the three state equations. We here report over 150 different structures of chaotic attractors along with their one set of parameter values, phase space dynamics and the Largest Lyapunov Exponents (LLE). The expressions of these new Lorenz-like nonlinear dynamical systems have been automatically evolved through multi-gene genetic programming (MGGP). In the past two decades, there have been many claims of designing new chaotic attractors as an incremental extension of the Lorenz family. We provide here a large family of chaotic systems whose structure closely resemble the original Lorenz system but with drastically different phase space dynamics. This advances the state of the art knowledge of discovering new chaotic systems which can find application in many real-world problems. This work may also find its archival value in future in the domain of new chaotic system discovery.     

On dominant poles and model reduction of second order time-delay systems

The method known as the dominant pole algorithm (DPA) has previously been successfully used in combination with model order reduction techniques to approximate standard linear time-invariant dynamical systems and second order dynamical systems. In this paper, we show how this approach can be adapted to a class of second order delay systems, which are large scale nonlinear problems whose transfer functions have an infinite number of simple poles. Deflation is a very important ingredient for this type of methods. Because of the nonlinearity, many deflation approaches for linear systems are not applicable. We therefore propose an alternative technique that essentially removes computed poles from the system?s input and output vectors. In general, this technique changes the residues, and hence, modifies the order of dominance of the poles, but we prove that, under certain conditions, the residues stay near the original residues. The new algorithm is illustrated by numerical examples.     

A Pseudo-rigid model for the inverse dynamics of an Euler beam

Inversion technique has been very successful in the tracking control of nonlinear dynamical systems. However, when applied to manipulators constructed with elastic links, inverse dynamics through direct integration in temporal space causes unbounded controller command. It has been suggested that seeking an inverse dynamics solution for a given tip trajectory with given initial conditions is an ill-posed problem. It has also been suggested that increasing model accuracy by including more terms in a truncated beam model worsens the controller’s ability to stabilize the system dynamics. In this paper, we seek to understand the nature of the inverse dynamics instability and to find an alternative solution. We appeal to the notion of a pseudo-rigid model which describes the beam deflection by a homogeneous displacement field. Particularly, we derive the mode shape in order to yield a bounded inverse dynamics solution. Different from most of the existing solutions where solution stability was achieved through modifying the output function, we modified the inverse dynamics model. A bounded inverse solution and model simplicity provide much needed ease in the design and implementation of an inversion controller. Numerical simulations and experiments have both been conducted to prove the validity of the proposed method.     

Switching systems and entropy

Switching systems are non-autonomous dynamical systems obtained by switching between two or more autonomous dynamical systems as time goes on. They can be mainly found in control theory, physics, economy, biomathematics, chaotic cryptography and of course in the theory of dynamical systems, in both discrete and continuous time. Much of the recent interest in these systems is related to the emergence of new properties by the mechanism of switching, a phenomenon known in the literature as Parrondo's paradox. In this paper we consider a discrete-time switching system composed of two affine transformations and show that the switched dynamics has the same topological entropy as the switching sequence. The complexity of the switching sequence, as measured by the topological entropy, is fully transferred, for example, to the switched dynamics in this particular case.     

The random environment of offshore systems

The analysis of the dynamical behavior of systems in ocean waves is an important part in offshore engineering. While a characterization of the response of a linearized model can be obtained in frequency domain, it has to be noted that offshore systems usually include components with nonlinear behavior. The systematic analysis of the nonlinear dynamics of floating structures is often facilitated by additional assumptions. One common example is the use of deterministic (harmonic) waves. Even though periodic waves may be a reasonable simplification for many applications, sea waves in general are usually better described by a spectral or probabilistic approach. This paper addresses different methods of describing random forces for the analysis of floating structures. Examples show the effects of different wave models on the analysis of a simple floating structure. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)