Now showing items 159-178 of 244

    • New problems related to the valences of (super) edge-magic labelings 

      López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (2013)
      A graph G of order p and size q is edge-magic if there is a bijective function f : V (G) ∪ E(G) −→ {i} p+q i=1 such that f(x) + f(xy) + f(y) = k , for all xy ∈ E(G) . The function f is an edge-magic labeling of G and the ...
    • Nilpotent centres via inverse integrating factors 

      Algaba, Antonio; García, Cristóbal; Giné, Jaume (Cambridge University Press, 2016-10)
      In this paper we are interested in the nilpotent center problem of planar analytic monodromic vector fields. It is known that the formal integrability is not enough to characterize such centers. More general objects are ...
    • Non existence of almost Moore digraphs of diameter three 

      Conde Colom, Josep; Gimbert i Quintilla, Joan; Miret, Josep M. (Josep Maria); Moreno Chiral, Ramiro; Gonzàlez, J. (Electronic Journal of Combinatorics, 2008)
      Almost Moore digraphs appear in the context of the degree/diameter problem as a class of extremal directed graphs, in the sense that their order is one less than the unattainable Moore bound M(d; k) = 1 + d + + dk, where ...
    • Non-existence of limit cycles for planar vector fields 

      Giné, Jaume (Texas State University. Department of Mathematics, 2014)
      This article presents sufficient conditions for the non-existence of limit cycles for planar vector fields. Classical methods for the nonexistence of limit cycles are connected with the theory developed here.
    • Non-smooth quadratic centers defined in two arbitrary sectors 

      García, I. A. (Isaac A.) (Elsevier, 2016-11-25)
      In this paper we analyze the center-focus problem of some families of piecewise planar quadratic vector fields on two zones of R2. The zones we consider are two unbounded sectors defined by an arbitrary angle α and a fixed ...
    • Nondegenerate centers for Abel polynomial differential equations of second kind 

      Giné, Jaume; Valls, Claudia (Elsevier, 2017)
      In this paper we study the center problem for Abel polynomial differential equations of second kind. Computing the focal values and using modular arithmetics and Gröbner bases we find the center conditions for such systems ...
    • On bipartite-mixed graphs 

      Dalfó, Cristina; Fiol, Miguel Angel; López Lorenzo, Ignacio (Wiley, 2018-04-04)
      Mixed graphs can be seen as digraphs that have both arcs and edges (or digons, that is, two opposite arcs). In this arti- cle, we consider the case where such graphs are bipartite. As main results, we show that in this ...
    • On Middle Cube Graphs 

      Dalfó, Cristina; Fiol, Miguel Angel; Mitjana, Margarida (Indonesian Combinatorial Society (InaCombS); Graph Theory and Applications (GTA) Research Centre; University of Newcastle, Australia; Institut Teknologi Bandung (ITB), Indonesia, 2015)
      We study a family of graphs related to the $n$-cube. The middle cube graph of parameter k is the subgraph of $Q_{2k-1}$ induced by the set of vertices whose binary representation has either $k-1$ or $k$ number of ones. The ...
    • On mixed almost Moore graphs of diameter two 

      López Lorenzo, Ignacio; Miret, Josep M. (Josep Maria) (Electronic Journal of Combinatorics, 2016-04-01)
      Mixed almost Moore graphs appear in the context of the Degree/Diameter problem as a class of extremal mixed graphs, in the sense that their order is one less than the Moore bound for mixed graphs. The problem of their ...
    • On super edge-magic decomposable graphs 

      López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Springer, 2012)
      Let G be any graph and let {Hi}i∈I be a family of graphs such that E(Hi) ∩ E(Hj ) = ∅ when i 6= j, ∪i∈IE(Hi) = E(G) and E(Hi) 6= ∅ for all i ∈ I. In this paper we introduce the concept of {Hi}i∈I -super edge-magic decomposable ...
    • On the ℓ-adic valuation of the cardinality of elliptic curves over finite extensions of Fq 

      Miret, Josep M. (Josep Maria); Pujolàs Boix, Jordi; Valera Martín, Javier (Springer Verlag, 2015)
      Let E be an elliptic curve defined over a finite field Fq of odd characteristic. Let l≠2 be a prime number different from the characteristic and dividing #E(Fq). We describe how the l-adic valuation of the number of points ...
    • On the beta-number of forests with isomorphic components 

      Ichishima, R.; López Masip, Susana-Clara; Muntaner Batle, F. A.; Oshima, A. (De Gruyter Open, 2018)
      The beta-number, β (G), of a graph G is defined to be either the smallest positive integer n for which there exists an injective function f : V (G) → {0, 1, . . . , n} such that each uv ∈ E (G) is labeled |f (u) − f (v)| ...
    • On the center conditions for analytic monodromic degenerate singularities 

      Giné, Jaume; Llibre, Jaume (World Scientific Publishing, 2012)
      In this paper we present two methods for detecting centers of monodromic degenerate singularities of planar analytic vector fields. These methods use auxiliary symmetric vector fields can be applied independently that the ...
    • On the extensions of the Darboux theory of integrability 

      Giné, Jaume; Grau Montaña, Maite; Llibre, Jaume (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 

      Giné, Jaume; Algaba, Antonio; García, Cristóbal (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 

      Giné, Jaume; Llibre, Jaume (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 multiple zeros of a real analytic function with applications to the averaging theory of differential equations 

      García, I. A. (Isaac A.); Llibre, Jaume; Maza Sabido, Susana (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 

      Giné, Jaume (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 

      Giné, Jaume (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 

      García, I. A. (Isaac A.); Llibre, Jaume; Maza Sabido, Susana (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 ...