On asymptotic equivalence of linear and quasilinear difference equations

The asymptotic equivalence of systems of difference equations of linear and quasilinear type is investigated. The first result on the asymptotic equivalence of linear systems is a discrete analog of an improved version of the Levinson's well-known theorem on asymptotic equivalence of linear differential equations, while the second one providing conditions for asymptotic equivalence of linear and quasilinear systems is related to that of Yakubovich in differential equations case.     

Asymptotic forms of positive solutions of quasilinear ordinary differential equations with singular nonlinearities

In this paper we consider positive solutions of second order quasilinear ordinary differential equations with singular nonlinearities. We obtain asymptotic equivalence theorems for asymptotically superlinear solutions and decaying solutions. By using these theorems, exact asymptotic forms of such solutions are determined. Furthermore, we can establish the uniqueness of decaying solutions as an application of our results.     

The differential equations on time scales through impulsive differential equations

In this paper we investigate differential equations on certain time scales with transition conditions (DETC) on the basis of reduction to the impulsive differential equations (IDE). DETC are in some sense more general than dynamic equations on time scales [M. Bohner, A. Peterson, Dynamic equations on time scales, in: An Introduction With Applications, Birkhäuser Boston, Inc., Boston, MA, 2001, p. x+358; V. Laksmikantham, S. Sivasundaram, B. Kaymakcalan, Dynamical Systems on Measure Chains, in: Math. and its Appl., vol. 370, Kluwer Academic, Dordrecht, 1996]. The basic properties of linear systems, the existence and stability of periodic solutions, and almost periodic solutions are considered. Appropriate examples are given to illustrate the theory.     

Linearly implicit Liénard systems

The presence of nonlinearities in the capacitance and the inductance in van der Pol type electrical circuits defines a linearly implicit (or quasilinear) counterpart of the classical Liénard systems. When the reactances remain positive, the existence of a unique attracting periodic solution follows, with minor modifications, as in the classical setting. Novel results are obtained when the values of reactances may vanish at certain points of the state space; these points yield singularities of the model, and the existence of an attracting periodic solution can be characterized in terms of the behavior of certain smooth solutions crossing the singular manifold through so-called I-singularities.     

Formation and decay of electromagnetic shock waves

Résumé Ce traité se rapporte principalement à la dérivation de la loi de détérioration asymptotique pour les ondes de choc électromagnetiques faibles se propageant dans un milieu de type ferromagnétique. On dérive la loi de détérioration pour les paramètres de choc en utilisant une, technique de corrélation entre une des solutions d'une onde simple et les équations d'un choc faible.     

Some remarks on bounds to eigenvalues of Sturm-Liouville problems with discontinuous coefficients

Upper and lower bounds on the eigenvalues of Sturm-Liouville problems with discontinuous coefficients are discussed. Rayleigh-Ritz approximations based both on Rayleigh's quotient and the dual Rayleigh quotient are used for obtaining upper bounds for the eigenvalues. Though previous studies have indicated that such approximations yield poor results when large discontinuities in the coefficients occur, it is shown in this paper by means of numerical examples that thesame rate of convergence can be achieved as for systems with continuous coefficients, provided the trial functions are allowed to have arbitrary jump discontinuities in their derivatives across the points where the coefficients suffer discontinuities. New explicit lower bounds in terms of the coefficients are also established. The accuracy of the new estimates is illustrated by numerical examples.

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Résumé On discute les bornes supérieures et inférieures des valeurs caractéristiques des problèmes de Sturm-Liouville avec des coefficients discontinus. Les approximations de Rayleigh-Ritz, basées sur le quotient de Rayleigh et le quotient jumelé de Rayleigh, sont utilisées pour obtenir les bornes supérieures des valeurs caractéristiques. Bien que les études antérieures aient indiqué que ces approximations donnent des résultats médiocres quand les coefficients ont de grandes discontinuités, on démontre dans cet article par des exemples numériques qu'on peut réaliser le même degré de convergence que pour les systèmes á coefficients continuous, pourvu que les fonctions d'essai admises aient des sauts arbitraires dans leurs dérivées á travers les points où les coefficients subissent des discontinuités. De nouvelles bornes inférieures sont déterminées sous une forme explicite en fonction des coefficients. On montre l'exactitude des nouveaux résultats par des exemples numériques.

     

Slow divergence integral and its application to classical Liénard equations of degree 5

The slow divergence integral is a crucial tool to study the cyclicity of a slow–fast cycle for singularly perturbed planar vector fields. In this paper, we deduce a useful form for this integral in order to apply it to various problems. As an example, we use it to prove that the slow divergence integral along any non-degenerate slow–fast cycle for singular perturbations of classical Liénard equations of degree 5 has at most one zero, and the zero is simple if it exists; hence the cyclicity of any non-degenerate slow–fast cycle in this class of equations is at most 2. Up to now there were many interesting results about Liénard equations of degree 3, 4 and ≥6, but almost nothing is known about degree 5. The result in this paper can be seen as a first stage to study the uniform property for classical Liénard equations of degree 5.     

A generalized thin-film equation in multidimensional space

This paper deals with the existence and nonnegativity of the weak periodic-domain solution for a degenerate fourth-order parabolic equation modeling the evolution of thin films. This study in the multidimensional domain follows the recent results related to the resolution in one-dimensional space [J.E. Rakotoson, J.M. Rakotoson, C. Verbeke, Generalized lubrification models blow-up and global existence, RACSAM 99 (2) (2005) 235–241; C. Verbeke, Quelques modèles d’équations d’évolution de surfaces: Explosion en temps fini et diverses propriétés qualitatives, Thèse de doctorat de l’Université de Poitiers (15 Décembre 2005); J.E. Rakotoson, J.M. Rakotoson, C. Verbeke, Higher-order equations related to thin film: Blow up and global existence, the influence of the initial data, (submitted for publication)].     

Existence and uniqueness results for impulsive functional differential equations with scalar multiple delay and infinite delay

In this paper, we discuss local and global existence and uniqueness results for first order impulsive functional differential equations with multiple delay. We shall rely on a nonlinear alternative of Leray–Schauder. For the global existence and uniqueness we apply a recent nonlinear alternative of Leray–Schauder type in Fréchet spaces, due to M. Frigon and A. Granas [Résultats de type Leray–Schauder pour des contractions sur des espaces de Fréchet, Ann. Sci. Math. Québec 22 (2) (1998) 161–168]. The goal of this paper is to extend the problems considered by A. Ouahab [Local and global existence and uniqueness results for impulsive differential equations with multiple delay, J. Math. Anal. Appl. 323 (2006) 456–472].     

The asymptotic periodicity in a Schoener’s competitive model

This paper deals with a two species model with Schoener’s competitive interaction. The existence and the asymptotic behavior of T-periodic solutions for the periodic system of quasilinear parabolic equations under nonlinear boundary conditions are given by using upper and lower solutions and corresponding iteration. The numerical simulations are also presented to illustrate our result. It is shown that periodic solutions may exist if the inter-specific competition rates are weak.     

Approximate solutions of certain integral equations for the diffraction by two strips

Integral equations associated with the diffraction of obliquely incident plane waves of various kinds by two coplanar and parallel infinite strips and slits are solved approximately for low frequencies. The solutions are presented as expansions in terms of a suitable perturbation parameter.

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Résumé Certaines équations intégrales en relation avec la diffraction d'ondes planes, de types divers, incidentes par rapport à deux bandes et deux fentes coplanaires infinies, sont résolues approximativement pour les basses fréquences. Les solutions sont présentées sous forme de développements dependant d'un paramètre de perturbation approprié.

     

Resonance bifurcation from homoclinic cycles

Differential equations that are equivariant under the action of a finite group can possess robust homoclinic cycles that can moreover be asymptotically stable. For differential equations in R⁴ there exists a classification of different robust homoclinic cycles for which moreover eigenvalue conditions for asymptotic stability are known. We study resonance bifurcations that destroy the asymptotic stability of robust ‘simple homoclinic cycles’ in four-dimensional differential equations. We establish that typically a periodic trajectory near the cycle is created, asymptotically stable in the supercritical case.     

Free-convection boundary layer on an isothermal horizontal cylinder

The free convection on a horizontal circular cylinder whose temperature is suddenly increased is studied at large Grashof number. An accurate numerical method is described for determining the solution of the time-dependent boundary-layer equations. The development of the various physical properties of the flow are calculated and compared with their values at small and large times as obtained from the previously obtained analytical solutions.

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Résumé Cette étude considère la convection libre à nombre de Grashof élevé au dessus d'un cylindre horizontal de section circulaire lorsqu'on augmente brusquement sa température. On présente une méthode numérique qui permet de déterminer avec précision la solution des équations instationnaires de la couche limite. Le développement des caractéristiques physiques de l'écoulement est calculé et les résultats sont comparés avec ceux qui ont été déjà obtenus analytiquement pour les petites et grandes valeurs de la variable du temps.

     

Jumps of the fundamental solution matrix in discontinuous systems and applications

This paper deals with differential equations with discontinuous right-hand side. The concept of a solution for a discontinuous system is defined on the basis of differential inclusions using Filippov’s method. We study in particular the behaviour of solutions crossing a discontinuity surface transversally. A formula characterizing jumps of the fundamental solution matrix is derived. As an application of it, the concept of Poincaré mapping is defined for such systems.     

Étude de l'établissement d'un jet liquide laminaire émergeant d'une conduite cylindrique verticale semi-infinie et soumis à l'influence de la gravité

Résumé On étudie l'écoulement libre d'un jet liquide laminaire axisymétrique émergeant d'une conduite cylindrique verticale semi-infinie, à grands nombres de Reynolds et grands nombres de Froude. Dans de telles conditions, si l'on exclut le cas des tubes capillaires, le nombre de Weber de l'écoulement est suffisamment grand pour que les effets de tension superficielle s'avèrent négligeables, ainsi que le confirme cette étude. Les équations sont simplifiées par une analyse de type couche limite. L'utilisation de la méthode des développements asymptotiques raccordés conduit à des solutions approchées semianalytiques faisant apparaitre les paramètres de similitude de l'écoulement. Ces solutions prévoient la distribution des vitesses et la forme du jet sous l'influence des forces de pesanteur et de viscosité. Des résultats expérimentaux obtenus par photographie du jet et visualisation holographique du champ des vitesses confirment les prévisions théoriques.

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This paper is concerned with the laminar flow of a free liquid jet emerging from a semi infinite vertical cylindrical pipe at high Reynolds and Froude numbers. In that case, excepting the capillary tubes, the Weber number is sufficiently high so that surface tension effects may be neglected. The general equations are simplified by a boundary layer analysis and solved by using the matched asymptotic expansion's method. Approximate semi analytical solutions are presented showing parameters of similarity. These solutions predict the velocity distribution and the jet shape under the influence of body and viscous forces. Experimental results obtained by jet photography and holographic visualization of the velocity field confirm the accuracy of the calculations.

     

The flow of an electrically conducting fluid at a rear stagnation point

Summary We consider the impulsively generated magnetohydrodynamic flow at a rear stagnation point. The work of Leibovich is carried further by formulating the inner viscous problem and providing analytical solutions and complete numerical solutions for the entire range of the interaction parameter. It is shown that the present results are consistent with previously obtained numerical solutions to the steady equations of both similarity and non-similarity form.

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Résumé Nous considérons l'écoulement magneto-hydrodynamique impulsivement engendré à un point de stagnation arrière. On porte plus loin l'étude de Leibovich par la formulation du problème visqueux intérieur et en fournissant des solutions analytiques et numériques complètes correspondantes au champ entier du paramètre d'interaction. On montre que les résultats actuels sont en accord avec les solutions numériques, et de similitude et de non-similitude, déjà connues des équations stationnaires.

     

Inequalities for solutions of singular initial problems for Carathéodory systems via Ważewski’s principle

In this paper we give sufficient conditions for solvability of a singular initial problem formulated for Carathéodory systems of ordinary differential equations. The existence of solutions is proved by the supposition that corresponding auxiliary lower and upper singular problems have solutions. The proof technique uses a notion of a regular polyfacial subset which is developed for Carathéodory systems of ordinary differential equations and a modification of the topological method for such systems given by Palamides, Sficas and Staikos. An application concerning the existence of positive solutions for a special class of singular problems is given as well.     

Positive almost periodic solution for a class of Nicholson’s blowflies model with multiple time-varying delays

In this paper, we study the existence and exponential convergence of positive almost periodic solutions for the generalized Nicholson’s blowflies model with multiple time-varying delays. Under proper conditions, we establish some criteria to ensure that the solutions of this model converge locally exponentially to a positive almost periodic solution. Moreover, we give some examples to illustrate our main results.     

Buckling and vibration of cross-ply laminated circular cylindrical panels

Summary The free vibration problem of a thin cross-ply composite laminated circular cylindrical panel subjected to arbitrary combinations of axial and circumferential initial compressions is studied. The equations of motion are derived, in the framework of the Donnell-type theory, in terms of the panel middle surface displacements components. Closed form solutions are obtained, for simply-supported panels, and numerical results for both antisymmetric and unsymmetric laminated cross-ply panels are presented.

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Résumé On étudie le problème de libre vibration d'une coque cylindrique ouverte, composée de fines lamelles croisées, soumise aux combinaisons arbitraires des compressions initiales de la circonférence et de l'axe. Les équations de vibrations dérivent, en accord avec la théorie de Donnell, des composantes de déplacement de la surface moyenne de la coque ouverte. On obtient des solutions exactes pour les coques cylindriques ouvertes posées librement et on présente des résultats numériques pour les coques cylindriques ouvertes composées de fines lamelles croisées antisymétriques et non symétriques.

     

Periodic fluid transients in rectangular ducts with transverse magnetic fields,II

Summary This paper treats periodic fluid transients in liquid metals contained in constant-area rectangular ducts with uniform, transverse, applied magnetic fields and with insulating walls parallel to the magnetic field and perfectly conducting walls perpendicular to it. The magnetic Reynolds and Mach numbers are assumed to be small, and the Reynolds number is assumed to be large. First, asymptotic solutions are obtained for small values of the interaction parameter and then approximate solutions are obtained for arbitrary values of the interaction parameter using a Galerkin method with modified Fourier series.

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Résumé Cet article traite des ondes de compression périodiques dans un métal liquide contenu dans une conduite rectangulaire à section rectangulaire constante, à laquelle un champ magnétique transverse et uniforme est appliqué et dont deux parois sont isolantes et parallèles au champ magnétique, les deux autres étant parfaitement conductrices. On admet que le nombre magnétique de Reynolds et le nombre de Mach sont petits et que le nombre de Reynolds est grand. Quand le nombre d'intéraction est petit, les solutions seront asymptotiques et quand le nombre d'intéraction est arbitrarire, on trouvera les solutions approximatives par la méthode de Galerkin avec les series modifiées de Fourier.