The Poincaré–Birkhoff Theorem for a Class of Degenerate Planar Hamiltonian Systems

In this paper, we investigate the problem of the existence and multiplicity of periodic solutions to the planar Hamiltonian system x ′ = - λ ⁢ α ⁢ ( t ) ⁢ f ⁢ ( y ) x^{\prime}=-\lambda\alpha(t)f(y) , y ′ = λ ⁢ β ⁢ ( t ) ⁢ g ⁢ ( x ) y^{\prime}=\lambda\beta(t)g(x) , where α , β \alpha,\beta are non-negative 𝑇-periodic coefficients and λ > 0 \lambda>0 . We focus our study to the so-called “degenerate” situation, namely when the set Z := supp ⁡ α ∩ supp ⁡ β Z:=\operatorname{supp}\alpha\cap\operatorname{supp}\beta has Lebesgue measure zero. It is known that, in this case, for some choices of 𝛼 and 𝛽, no nontrivial 𝑇-periodic solution exists. On the opposite, we show that, depending of some geometric configurations of 𝛼 and 𝛽, the existence of a large number of 𝑇-periodic solutions (as well as subharmonic solutions) is guaranteed (for λ > 0 \lambda>0 and large). Our proof is based on the Poincaré–Birkhoff twist theorem. Applications are given to Volterra’s predator-prey model with seasonal effects.

Subharmonic solutions of bounded coupled Hamiltonian systems with sublinear growth

<p style='text-indent:20px;'>We prove the existence and multiplicity of subharmonic solutions for bounded coupled Hamiltonian systems. The nonlinearities are assumed to satisfy Landesman-Lazer conditions at the zero eigenvalue, and to have some kind of sublinear behavior at infinity. The proof is based on phase plane analysis and a higher dimensional version of the Poincaré-Birkhoff twist theorem by Fonda and Ureña. The results obtained generalize the previous works for scalar second-order differential equations or relativistic equations to higher dimensional systems.</p>

Harmonic and subharmonic solutions of quadratic Liénard type systems with sublinearity

<abstract><p>In this paper, we prove the existence of harmonic solutions and infinitely many subharmonic solutions of dissipative second order sublinear differential equations named quadratic Liénard type systems. The method of the proof is based on the Poincaré-Birkhoff twist theorem.</p></abstract>

The Existence of Invariant Tori and Quasiperiodic Solutions of the Nosé–Hoover Oscillator

In this paper, we consider an equivalent form of the Nosé–Hoover oscillator, x ′ = y , y ′ = − x − y z , and z ′ = y 2 − a , where a is a positive real parameter. Under a series of transformations, it is transformed into a 2-dimensional reversible system about action-angle variables. By applying a version of twist theorem established by Liu and Song in 2004 for reversible mappings, we find infinitely many invariant tori whenever a is sufficiently small, which eventually turns out that the solutions starting on the invariant tori are quasiperiodic. The discussion about quasiperiodic solutions of such 3-dimensional system is relatively new.