Global phase portraits of the quadratic systems having a singular and irreducible invariant curve of degree 3

Any singular irreducible cubic curve (or simply, cubic) after an affine transformation can be written as either y2=x3 , or y2=x2(x+1) , or y2=x2(x-1) . We classify the phase portraits of all quadratic polynomial differential systems having the invariant cubic y2=x2(x+1) . We prove that there are 63 different topological phase portraits for such quadratic polynomial differential systems. We control all the bifurcations among these distinct topological phase portraits. These systems have no limit cycles. Only three phase portraits have a center, 19 of these phase portraits have one polycycle, three of these phase portraits have two polycycles. The maximum number of separartices that have these phase portraits is 26 and the minimum number is nine, the maximum number of canonical regions of these phase portraits is seven and the minimum is three.C. Pantazi is also partially supported by the grant PID-2021-122954NB-100 funded by MCIN/AEI/10.13039/501100011033 and by “ERDF A way of making Europe”.Peer ReviewedPostprint (published version

Phase portraits of separable Hamiltonian systems

We study some generalizations of potential Hamiltonian systems (H(x, y) = y 2 + F(x)) with one degree of freedom. In particular, we are interested in Hamiltonian systems with Hamiltonian functions of type H(x, y) = F(x) + G(y) arising in applied mechanical problems. We present an algorithm to plot the phase portrait (include the behavior at infinity) of any Hamiltonian system of type H(x, y) = F(x) +G(y), where F and G are arbitrary polynomials. We are able to give the full description in the Poincaré disk according to the graphs of F and G, extending the well-known method for the “finite”phase portrait of potential systems

Counterexample to a conjecture on the algebraic limit cycles of polynomial vector fields

In Geometriae Dedicata 79 (2000), 101{108, Rudolf Winkel conjectured: For a given algebraic curve f = 0 of degree m > 4 there is in general no polynomial vector ¯eld of degree less than 2m ¡ 1 leaving invariant f = 0 and having exactly the ovals of f = 0 as limit cycles. Here we show that this conjecture is not true

Polynomial differential systems having a given Darbouxian first integral

The Darbouxian theory of integrability allows to determine when a polynomial differential system in C2 has a first integral of the kind f λ1 1 ···f λp p exp(g/h) where fi , g and h are polynomials in C[x, y], and λi ∈ C for i = 1, . . . ,p. The functions of this form are called Darbouxian functions. Here, we solve the inverse problem, i.e. we characterize the polynomial vector fields in C2 having a given Darbouxian function as a first integral. On the other hand, using information about the degree of the invariant algebraic curves of a polynomial vector field, we improve the conditions for the existence of an integrating factor in the Darbouxian theory of integrability.Peer Reviewe

Darboux integrals for Schrödinger planar vector fields via Darboux transformations

In this paper we study the Darboux transformations of planar vector fields of Schrödinger type. Using the isogaloisian property of Darboux transformation we prove the “invariance” of the elements of the “Darboux Theory of Integrability”. In particular, we also show how the shape invariance property of the potential is important in order to preserve the structure of the transformed vector field. Free particle, square well, harmonic oscillator, three dimensional harmonic oscillator and Coulomb potential, are presented as natural examples coming from supersymmetric quantum mechanics.Preprin

Experimental investigation of the processes of dehumidification of coniferous biomass

This work includes the results of experimental studies of the moisture removal processes in the temperature range from 333 K to 413 K from coniferous woods which are typical for many regions. There are obtained the dependences of the mass rate of moisture removal on time and temperature. The effect of the evaporation of bound moisture was identified for the wood species studied. There are calculated the accommodation coefficient and the partial pressure at the evaporation surface for each type of biomass

Darboux integrability and dynamics of the Basener-Ross population model

We deal with the Basener and Ross model for the evolution of human population in Easter island. We study the Darboux integrability of this model and characterize all its global dynamics in the Poincaré disc, obtaining 15 different topological phase portraits

Three-dimensional Lotka-Volterra systems with 3:−1:2-Resonance

We study the local integrability at the origin of a nine-parameter family of three-dimensional Lotka-Volterra differential systems with (3:− 1:2)-resonance. We give necessary and sufficient conditions on the parameters of the family that guarantee the existence of two independent local first integrals at the origin of coordinates. Additionally, we classify those cases where the origin is linearizable