Now showing items 249-268 of 345

• #### On the Dynamics of Higgins–Selkov, Selkov and Brusellator Oscillators ﻿

(MDPI, 2022)
A complete algebraic characterization of the first integrals of the Higgins–Selkov, Selkov and Brusellator oscillators is given here. The existence of symmetries sometimes forces the existence of such first integrals. ...
• #### On the extensions of the Darboux theory of integrability ﻿

(IOP Publishing, 2013)
Recently some extensions of the classical Darboux integrability theory to autonomous and non-autonomous polynomial vector fields were completed. The classical Darboux integrability theory and its recent extensions are based ...
• #### On the Formal Integrability Problem for Planar Differential Systems ﻿

(Hindawi Publishing Corporation, 2013)
We study the analytic integrability problem through the formal integrability problem and we show its connection, in some cases, with the existence of invariant analytic (sometimes algebraic) curves. From the results ...
• #### On the Integrability of Liénard systems with a strong saddle ﻿

(Elsevier, 2017)
We study the local analytic integrability for real Li\'{e}nard systems, $\dot x=y-F(x),$ $\dot y= x$, with $F(0)=0$ but $F'(0)\ne0,$ which implies that it has a strong saddle at the origin. First we prove that this problem ...
• #### On the Laplacian spectra of token graphs ﻿

(Elsevier, 2021)
We study the Laplacian spectrum of token graphs, also called symmetric powers of graphs. The k-token graph Fk(G) of a graph G is the graph whose vertices are the k-subsets of vertices from G, two of which being adjacent ...
• #### On the multiple zeros of a real analytic function with applications to the averaging theory of differential equations ﻿

(IOP Publishing, 2018-11-21)
In this work we consider real analytic functions $d(z,\la,\e)$, where $d : \Omega \times \mathbb{R}^p \times I \to \Omega$, $\Omega$ is a bounded open subset of $\R$, $I \subset \mathbb{R}$ is an interval containing the ...
• #### On the origin of the deflection of light ﻿

(Elsevier, 2008)
Action at distance in Newtonian physics is replaced by finite propagation speeds in classical post–Newtonian physics. As a result, the differential equations of motion in Newtonian physics are replaced by functional ...
• #### On the origin of the inertia: the modified Newtonian dynamics theory ﻿

(Elsevier, 2009)
The sameness between the inertial mass and the gravitational mass is an assumption and not a consequence of the equivalent principle is shown. In the context of the Sciama’s inertia theory, the sameness between the inertial ...
• #### On the periodic orbit bifurcating from a Hopf bifurcation in systems with two slow and one fast variables ﻿

(Elsevier, 2014)
The Hopf bifurcation in slow-fast systems with two slow variables and one fast variable has been studied recently, mainly from a numerical point of view. Our goal is to provide an analytic proof of the existence of the ...
• #### On the planar integrable differential systems ﻿

(Springer Verlag, 2011)
Under very general assumptions we prove that the planar differential systems having a first integral are essentially the linear differential systems u˙ = u, ˙v = v. Additionally such systems always have a Lie symmetry. We ...
• #### On the Randić index of graphs ﻿

(Elsevier, 2018-09-11)
For a given graph G = (V, E), the degree mean rate of an edge uv ∈ E is a half of the quotient between the geometric and arithmetic means of its end-vertex degrees d(u) and d(v). In this note, we derive tight bounds for ...
• #### On the spectra and eigenspaces of the universal adjacency matrices of arbitrary lifts of graphs ﻿

(Taylor & Francis, 2022-02-19)
The universal adjacency matrix U of a graph Γ, with adjacency matrix A, is a linear combination of A, the diagonal matrix D of vertex degrees, the identity matrix I, and the all-1 matrix J with real coefficients, that is, ...
• #### On Vosperian and Superconnected Vertex-Transitive Digraphs ﻿

(Springer, 2013)
We investigate the structure of a digraph having a transitive automorphism group where every cutset of minimal cardinality consists of all successors or all predecessors of some vertex. We give a complete characterization ...
• #### Open problems involving super edge-magic labelings and related topics ﻿

(Institute of Combinatorics and its Applications, 2012)
Graph labelings has experimented a fast development during the last four decades. Two books dedicated to this topic, a very complete survey on the subject and over 1000 papers in the literature constitute a good proof of ...
• #### Optimizing the enzymatic elimination of clogging of a microfiltration membrane by Parellada grape cake ﻿

(Wiley, 2016)
Clogging of the filtration membranes is one of the main problems in the process of obtaining grape must for white wine; therefore, clogging must be reduced to the maximum. The aim of this work was to find the optimal values ...
• #### Orbital Reversibility of Planar Vector Fields ﻿

(MDPI, 2021)
In this work we use the normal form theory to establish an algorithm to determine if a planar vector field is orbitally reversible. In previous works only algorithms to determine the reversibility and conjugate reversibility ...
• #### Perfect (super) Edge-Magic Crowns ﻿

(Springer, 2017)
A graph G is called edge-magic if there is a bijective function f from the set of vertices and edges to the set {1,2, ,|V(G)|+|E(G)|} such that the sum f(x)+f(xy)+f(y) for any xy in E(G) is constant. Such a function is ...
• #### Period annulus of the harmonic oscillator with zero cyclicity under perturbations with a homogeneous polynomial field ﻿

(Bolyai Institute. University of Szeged; Hungarian Academy of Sciences, 2019-01-14)
In this work we prove, using averaging theory at any order in the small perturbation parameter, that the period annulus of the harmonic oscillator has cyclicity zero (no limit cycles bifurcate) when it is perturbed by any ...
• #### Periodic orbits in Hyperchaotic Chen systems ﻿

(Texas State University, 2015)
In this work, we show a zero-Hopf bifurcation in a Hyperchaotic Chen system. Using averaging theory, we prove the existence of two periodic orbits bifurcating from the zero-Hopf equilibria located at the origin of ...
• #### Periodic solutions for nonlinear differential systems: the second order bifurcation function ﻿

(Nicolaus Copernicus University in Torun, Juliusz Schauder Centre for Nonlinear Studies, 2014)
We are concerned here with the classical problem of Poincaré of persistence of periodic solutions under small perturbations. The main contribution of this work is to give the expression of the second order bifurcation ...