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Publicacions matemàtiques 16 records found  Search took 0.00 seconds. 
1.
33 p, 348.6 KB Quadratic vector fields with a weak focus of third order / Artés Ferragud, Joan Carles (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques)
We study phase portraits of quadratic vector fields with a weak focus of third order at the origin. We show numerically the existence of at least 20 different global phase portraits for such vector fields coming from exactly 16 different local phase portraits available for these vector fields. [...]
1997 - 10.5565/PUBLMAT_41197_02
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 7-39  
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2.
16 p, 131.0 KB The null divergence factor / Chavarriga Soriano, Javier (Universitat de Lleida. Departament de Matemàtica) ; Giacomini, Hector (Université de Tours. Laboratoire de Mathématiques et Physique Théorique) ; Giné, Jaume (Universitat de Lleida. Departament de Matemàtica)
Let (P,Q) be a C1 vectorfield defined in a open subset U ⊂ R2. We call a null divergence factor a C1 solution V (x, y) of the equation P ∂V ∂x + Q∂V ∂y = ∂P ∂x + ∂Q ∂y V . In previous works it has been shown that this function plays a fundamental role in the problem of the center and in the determination of the limit cycles. [...]
1997 - 10.5565/PUBLMAT_41197_03
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 41-56  
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3.
27 p, 181.7 KB Invariant tori for periodically perturbed oscillators / Chicone, C.
The response of an oscillator to a small amplitude periodic excitation is discussed. In particular, sufficient conditions are formulated for the perturbed oscillator to have an invariant torus in the phase cylinder. [...]
1997 - 10.5565/PUBLMAT_41197_04
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 57-83  
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4.
16 p, 156.9 KB A polynomial class of Markus-Yamabe counterexamples / Cimà, Anna (Universitat Politècnica de Catalunya. Departament de Matemàtica Aplicada II) ; Gasull, Armengol (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Mañosas Capellades, Francesc (Universitat Autònoma de Barcelona. Departament de Matemàtiques)
In the paper [CEGHM] a polynomial counterexample to the Markus-Yamabe Conjecture and to the discrete Markus-Yamabe Question in dimension n ≥ 3 are given. In the present paper we explain a way for obtaining a family of polynomial counterexamples containing the above ones. [...]
1997 - 10.5565/PUBLMAT_41197_05
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 85-100  
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5.
25 p, 214.6 KB Psi-series of quadratic vector fields on the plane / Delshams, Amadeu ; Mir, A.
Psi-series (i. e. , logarithmic series) for the solutions of quadratic vector fields on the plane are considered. Its existence and convergence is studied, and an algorithm for the location of logarithmic singularities is developed. [...]
1997 - 10.5565/PUBLMAT_41197_06
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 101-125  
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6.
8 p, 96.3 KB The first derivative of the period function of a plane vector field / Françoise, J.-P.
The algorithm of the successive derivatives introduced in \cite{5} was implemented in \cite{7}, \cite{8}. This algorithm is based on the existence of a decomposition of 1-forms associated to the relative cohomology of the Hamiltonian function which is perturbed. [...]
1997 - 10.5565/PUBLMAT_41197_07
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 127-134  
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7.
14 p, 171.0 KB Hopf-like bifurcations in planar piecewise linear systems / Freire, E. ; Ponce, Enrique ; Torres, F.
Continuous planar piecewise linear systems with two linear zones are considered. Due to their low differentiability specific techniques of analysis must be developed. Several bifurcations giving rise to limit cycles are pointed out.
1997 - 10.5565/PUBLMAT_41197_08
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 135-148  
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8.
19 p, 180.0 KB Limit cycles in the Holling-Tanner model / Gasull, Armengol (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Torregrosa, Joan (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Kooij, Robert E. (University of Technology Delft. Fac. of Tech. Mathematics & Informatics)
This paper deals with the following question: does the asymptotic stability of the positive equilibrium of the Holling-Tanner model imply it is also globally stable? We will show that the answer to this question is negative. [...]
1997 - 10.5565/PUBLMAT_41197_09
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 149-167  
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9.
11 p, 128.9 KB Planar vector field versions of Carathéodory's and Loewner's conjectures / Gutierrez, Carlos (Instituto de Matemática Pura e Aplicada (Rio de Janeiro, Brasil)) ; Sánchez-Bringas, Federico (Universidad Nacional Autónoma de México. Departamento de Matemáticas)
Let r = 3, 4, . . . ,∞, ω. The Cr-Carathéodory's Conjecture states that every Cr convex embedding of a 2-sphere into R3 must have at least two umbilics. The Cr-Loewner's conjecture (stronger thanthe one of Carathéodory) states that there are no umbilics of index bigger than one. [...]
1997 - 10.5565/PUBLMAT_41197_10
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 169-179  
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10.
18 p, 152.2 KB Hopf bifurcation from infinity for planar control systems / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Ponce, Enrique (Universidad de Sevilla. Escuela Técnica Superior de Ingeniería)
Symmetric piecewise linear bi-dimensional systems are very common in control engineering. They constitute a class of non-differentiable vector fields for which classical Hopf bifurcation theorems are not applicable. [...]
1997 - 10.5565/PUBLMAT_41197_11
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 181-198  
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11.
10 p, 106.3 KB Five limit cycles for a simple cubic system / Lloyd, N. G. ; Pearson, J. M.
We resolve the centre-focus problem for a specific class of cubic systems and determine the number of limit cycles which can bifurcate from a fine focus. We also describe the methods which we have developed to investigate these questions in general. [...]
1997 - 10.5565/PUBLMAT_41197_12
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 199-208  
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12.
14 p, 160.6 KB The well-behaved Catalan and Brownian averages and their applications to real resummation / Menous, F.
The aim of this expository paper is to introduce the well-behaved uniformizing averages, which are useful in resummation theory. These averages associate three essential, but often antithetic, properties: respecting convolution; preserving realness; reproducing lateral growth. [...]
1997 - 10.5565/PUBLMAT_41197_13
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 209-222  
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13.
20 p, 170.2 KB Meandering of trajectories of polynomial vector fields in the affine n-space / Novikov, D. (Weizmann Institute of Science (Israel). Department of Science Teaching) ; Yakovenko, S. (Weizmann Institute of Science (Israel). Department of Science Teaching)
We give an explicit upper bound for the number of isolated intersections between an integral curve of a polynomial vector field in Rn and an affine hyperplane. The problem turns out to be closely related to finding an explicit upper bound for the length of ascending chains of polynomial ideals spanned by consecutive derivatives. [...]
1997 - 10.5565/PUBLMAT_41197_14
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 223-242  
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14.
26 p, 206.5 KB Smoothness property for bifurcation diagrams / Roussarie, Robert
Strata of bifurcation sets related to the nature of the singular points or to connections between hyperbolic saddles in smooth families of planar vector fields, are smoothly equivalent to sub-analytic sets. [...]
1997 - 10.5565/PUBLMAT_41197_15
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 243-268  
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15.
27 p, 211.0 KB Basic algebro-geometric concepts in the study of planar polynomial vector fields / Schlomiuk, Dana
In this work we show that basic algebro-geometric concepts such as the concept of intersection multiplicity of projective curves at a point in the complex projective plane, are needed in the study of planar polynomial vector fields and in particular in summing up the information supplied by bifurcation diagrams of global families of polynomial systems. [...]
1997 - 10.5565/PUBLMAT_41197_16
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 269-295  
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16.
20 p, 165.3 KB Generic bifurcation of reversible vector fields on a 2-dimensional manifold / Teixeira, Marco Antonio
In this paper we deal with reversible vector fields on a 2-dimensional manifold having a codimension one submanifold as its symmetry axis. We classify generically the one parameter families of such vector fields. [...]
1997 - 10.5565/PUBLMAT_41197_17
Publicacions matemàtiques, V. 41 n. 1 (1997) p. 297-316  
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