Now showing items 231-250 of 259

    • The Hopf cyclicity of the centers of a class of quintic polynomial vector fields 

      García, I. A. (Isaac A.); Llibre, Jaume; Maza Sabido, Susanna (Elsevier, 2015-01-20)
      We consider families of planar polynomial vector fields having a singularity with purely imaginary eigenvalues for which a basis of its Bautin ideal B is known. We provide an algorithm for computing an upper bound of the ...
    • The inverse integrating factor and the Poincaré map 

      García, I. A. (Isaac A.); Giacomini, Héctor; Grau Montaña, Maite (American Mathematical Society, 2010)
      This work is concerned with planar real analytic differential systems with an analytic inverse integrating factor defined in a neighborhood of a regular orbit. We show that the inverse integrating factor defines an ...
    • The jumping knight and other (super) edge-magic constructions 

      López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Springer, 2014)
      Let G be a graph of order p and size q with loops allowed. A bijective function f:V(G)∪E(G)→{i}p+qi=1 is an edge-magic labeling of G if the sum f(u)+f(uv)+f(v)=k is independent of the choice of the edge uv. The constant k ...
    • The Manhattan Product of Digraphs 

      Comellas, Francesc; Dalfó, Cristina; Fiol, Miguel Angel (Indonesian Combinatorial Society (InaCombS); Graph Theory and Applications (GTA) Research Centre; University of Newcastle, Australia; Institut Teknologi Bandung (ITB), Indonesia, 2013)
      We study the main properties of a new product of bipartite digraphs which we call Manhattan product. This product allows us to understand the subjacent product in the Manhattan street networks and can be used to built other ...
    • The null divergence factor 

      Chavarriga Soriano, Javier; Giacomini, Héctor; Giné, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques, 1997)
      Let (P, Q) be a C 1 vector field defined in a open subset U ⊂ R2 . We call a null divergence factor a C 1 solution V (x, y) of the equation P ∂V + Q ∂V = ∂P + ∂Q V . In previous works ∂x ∂y ∂x ∂y it has been ...
    • The power of digraph products applied to labelings 

      Ichishima, R.; López Masip, Susana-Clara; Muntaner Batle, F. A.; Rius Font, Miquel (Elsevier, 2012)
      The ⊗h-product was introduced in 2008 by Figueroa-Centeno et al. as a way to construct new families of (super) edge-magic graphs and to prove that some of those families admit an exponential number of (super) edge-magic ...
    • The problem of distinguishing between a center and a focus for nilpotent and degenerate analytic systems 

      Giacomini, Héctor; Giné, Jaume; Llibre, Jaume (Elsevier, 2006)
      In this work we study the centers of planar analytic vector fields which are limit of linear type centers. It is proved that all the nilpotent centers are limit of linear type centers and consequently the Poincaré–Liapunov ...
    • The role of algebraic solutions in planar polynomial differential systems 

      Giacomini, Héctor; Giné, Jaume; Grau Montaña, Maite (Cambridge University Press, 2007)
      We study a planar polynomial differential system, given by . We consider a function , where gi(x) are algebraic functions of with ak(x) and algebraic functions, A0(x,y) and A1(x,y) do not share any common factor, h2(x) is ...
    • The spectra of lifted digraphs 

      Dalfó, Cristina; Fiol, Miguel Angel; Sirán, Jozef (Springer, 2019-01-02)
      We present a method to derive the complete spectrum of the lift Γα of a base digraph Γ , with voltage assignment α on a (finite) group G. The method is based on assigning to Γ a quotient-like matrix whose entries are ...
    • The spectra of subKautz and cyclic Kautz digraphs 

      Dalfó, Cristina (Elsevier, 2017)
      Kautz digraphs K(d, `) are a well-known family of dense digraphs, widely studied as a good model for interconnection networks. Closely related with these, the cyclic Kautz CK(d, `) and the subKautz sK(d, 2) digraphs were ...
    • The spectral excess theorem for graphs with few eigenvalues whose distance- 2 or distance-1-or-2 graph is strongly regular 

      Dalfó, Cristina; Fiol, Miguel Angel; Koolen, Jack (Taylor & Francis, 2018-07-13)
      We study regular graphs whose distance-2 graph or distance-1-or-2 graph is strongly regular. We provide a characterization of such graphs Γ (among regular graphs with few distinct eigenvalues) in terms of the spectrum and ...
    • The three-dimensional center problem for the zero-Hopf singularity 

      García, I. A. (Isaac A.); Valls, Claudia (American Institute of Mathematical Sciences, 2016-03-01)
      In this work we extend well-known techniques for solving the Poincar\'e-Lyapunov nondegenerate analytic center problem in the plane to the 3-dimensional center problem at the zero-Hopf singularity. Thus we characterize the ...
    • The unique mixed almost moore graph with parameters k = 2, r = 2 and z = 1 

      Buset, Dominique; López Lorenzo, Ignacio; Miret, Josep M. (Josep Maria) (World Scientific Publishing, 2017-11-02)
      A natural upper bound for the maximum number of vertices in a mixed graph with maximum undirected degree r, maximum directed out-degree z and diameter k is given by the mixed Moore bound. Graphs with order attaining the ...
    • Towards a quantum universe 

      Giné, Jaume (Springer Verlag, 2012)
      In this short review we study the state of the art of the great problems in cosmology and their interrelationships. The reconciliation of these problems passes undoubtedly through the idea of a quantum universe.
    • Transversal conics and the existence of limit cycles 

      Giacomini, Héctor; Grau Montaña, Maite (Elsevier, 2015)
      This paper deals with the problem of location and existence of limit cycles for real planar polynomial differential systems. We provide a method to construct Poincaré-Bendixson regions by using transversal conics. We present ...
    • Triangle randomization for social network data anonymization 

      Brankovic, Ljiljana; López Lorenzo, Ignacio; Miller, Mirka; Sebé Feixas, Francesc (Society of Mathematicians, Physicists and Astronomers of SloveniaInstitute of Mathematics, Physics, and MechanicsUniversity of Primorska (Slovenia), 2014-06-27)
      In order to protect privacy of social network participants, network graph data should be anonymised prior to its release. Most proposals in the literature aim to achieve $k$-anonymity under specific assumptions about the ...
    • Trisection for supersingular genur 2 curves in characteristic 2 

      Miret, Josep M. (Josep Maria); Pujolàs Boix, Jordi; Thériault, Nicolas (American Institute of Mathematical Sciences (AIMS), 2014)
      By reversing reduction in divisor class arithmetic we provide efficient trisection algorithms for Jacobians of supersingular genus 2 curves over finite fields of characteristic 2. With our technique we obtain new results ...
    • Two different epidemiological scenarios of border disease in the populations of Pyrenean chamois (Rupicapra p. pyrenaica) after the first disease outbreaks 

      Fernández Sirera, Laura; Cabezón Ponsoda, Óscar; Allepuz Palau, Alberto; Rosell Bellsola, Rosa; Riquelme Guerrero, Cristina; Serrano Ferrón, Emmanuel; Lavín González, Santiago; Marco Sánchez, Ignasi (Public Library of Science, 2012)
      Since 2001 several outbreaks of a new disease associated with Border disease virus (BDV) infection have caused important declines in Pyrenean chamois (Rupicapra pyrenaica) populations in the Pyrenees. The goal of this ...
    • Universal centers and composition conditions 

      Giné, Jaume; Grau Montaña, Maite; Llibre, Jaume (London Mathematical Society, 2013)
      In this paper, we characterize the universal centres of the ordinary differential equations , where ai(θ) are trigonometric polynomials, in terms of the composition conditions. These centres are closely related with the ...
    • Universal centers in the cubic trigonometric Abel equation 

      Giné, Jaume; Grau Montaña, Maite; Santallusia Esvert, Xavier (Bolyai Institute. University of SzegedHungarian Academy of Sciences, 2014)
      We study the center problem for the trigonometric Abel equation dρ/dθ=a1(θ)ρ2+a2(θ)ρ3,dρ/dθ=a1(θ)ρ2+a2(θ)ρ3, where a1(θ)a1(θ) and a2(θ)a2(θ) are cubic trigonometric polynomials in θθ. This problem is closely connected with ...