Regular and Chaotic Dynamics最新文献

We study the spike activity of two mutually coupled FitzHugh – Nagumo neurons, which is influenced by two-frequency signals. The ratio of frequencies in the external signal corresponds to musical intervals (consonances). It has been discovered that this system can exhibit selective properties for identifying musical intervals. The mechanism of selectivity is shown, which is associated with the influence on the spiking frequency of neurons by intensity of the external signal and nature of the interaction of neurons.

The positively curved three-body problem is a natural extension of the planar Newtonian three-body problem to the sphere(mathbb{S}^{2}). In this paper we study the extensions of the Euler and Lagrange relativeequilibria ((RE) for short) on the plane to the sphere.

The (RE) on (mathbb{S}^{2}) are not isolated in general.They usually have one-dimensional continuation in the three-dimensional shape space.We show that there are two types of bifurcations. One is the bifurcations betweenLagrange (RE) and Euler (RE). Another one is between the different types of the shapes of Lagrange (RE). We prove thatbifurcations between equilateral and isosceles Lagrange (RE) existfor the case of equal masses, and that bifurcations between isosceles and scaleneLagrange (RE) exist for the partial equal masses case.

We consider the infinite-dimensional vector of frequencies (omega(mathtt{m})=(sqrt{j^{2}+mathtt{m}})_{jinmathbb{Z}}), (mathtt{m}in[1,2])arising from a linear Klein – Gordon equation on the one-dimensional torus and prove that there exists a positive measure set of masses (mathtt{m}^{prime})s for which (omega(mathtt{m})) satisfies a Diophantine condition similar to the one introduced by Bourgain in [14],in the context of the Schrödinger equation with convolution potential.The main difficulties we have to deal with arethe asymptotically linear nature of the (infinitely many) (omega_{j}^{prime})s and the degeneracy coming from having only one parameter at disposal for their modulation.As an application we provide estimates on the inverse of the adjoint action of the associated quadratic Hamiltonian on homogenenous polynomials of any degree in Gevrey category.

In this paper we consider the persistence of elliptic lower-dimensional invariant tori with prescribed frequencies in Hamiltonian systems with small parameters. Under the Brjuno nondegeneracy condition,if the prescribed frequencies satisfy a Diophantine condition, by the KAM technique we prove that for most of small parameters in the sense of Lebesgue measure, the Hamiltonian systems admit a lower-dimensionalinvariant torus whose frequency vector is a dilation of the prescribed frequencies.

We study the KAM-stability of several single star two-planetnonresonant extrasolar systems. It is likely that the observedexoplanets are the most massive of the system considered. Therefore,their robust stability is a crucial and necessary condition for thelong-term survival of the system when considering potentialadditional exoplanets yet to be seen. Our study is based on theconstruction of a combination of lower-dimensional elliptic and KAMtori, so as to better approximate the dynamics in the framework ofaccurate secular models. For each extrasolar system, we explore theparameter space of both inclinations: the one with respect to theline of sight and the mutual inclination between the planets. Ourapproach shows that remarkable inclinations, resulting inthree-dimensional architectures that are far from being coplanar,can be compatible with the KAM stability of the system. We findthat the highest values of the mutual inclinations are comparable tothose of the few systems for which the said inclinations are determinedby the observations.

This paper considers a class of nearly integrable reversible systemswhose unperturbed part has a degenerate frequency mapping and a degenerate equilibrium point.Based on some KAM techniquesand the topological degree theory, we prove the persistence of multiscale degenerate hyperbolic lower-dimensional invariant tori with prescribed frequencies.

In this note, we discuss the topology of Diophantine numbers, giving simple explicitexamples of Diophantine isolated numbers (among those with the same Diophantine constants),showing that Diophantine sets are not always Cantor sets.

General properties of isolated Diophantine numbers are also briefly discussed.

We review Kolmogorov’s 1954 fundamental paper On the persistence of conditionally periodic motions under a small change in the Hamilton function (Dokl. akad. nauk SSSR, 1954, vol. 98, pp. 527–530), both from the historical and the mathematical point of view.In particular, we discuss Theorem 2 (which deals with the measure in phase space of persistent tori), the proof of which is not discussed at all by Kolmogorov, notwithstanding its centrality in his program in classical mechanics.

In Appendix, an interview (May 28, 2021) to Ya. Sinai on Kolmogorov’s legacy in classical mechanics is reported.

In the last years substantial mathematical progress has been made in KAM theoryfor quasi-linear/fully nonlinearHamiltonian partial differential equations, notably forwater waves and Euler equations.In this survey we focus on recent advances in quasi-periodic vortex patchsolutions of the (2d)-Euler equation in (mathbb{R}^{2})close to uniformly rotating Kirchhoff elliptical vortices,with aspect ratios belonging to a set of asymptotically full Lebesgue measure.The problem is reformulated into a quasi-linear Hamiltonian equation for a radial displacement from the ellipse. A major difficulty of the KAM proof is the presence of a zero normal mode frequency, which is due to the conservation of the angular momentum. The key novelty to overcome this degeneracy is to perform a perturbative symplectic reduction of the angular momentum, introducing it as a symplectic variable in the spirit of the Darboux – Carathéodory theorem of symplectic rectification, valid in finite dimension.This approach is particularly delicate in an infinite-dimensional phase space: our symplecticchange of variables is a nonlinear modification of the transport flow generated by the angularmomentum itself.