UAB Digital Repository of Documents 238 records found  1 - 10nextend  jump to record: Search took 0.01 seconds. 
1.
20 p, 971.1 KB Planar central configurations of some restricted (4 + 1)-body problems / Corbera Subirana, Montserrat (Universitat de Vic - Universitat Central de Catalunya. Departament d'Enginyeries) ; Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
We start with the 13 central configurations of the restricted (4 + 1) body problem having four primaries with equal masses at the vertices of a square. Then, we describe the evolution of these central configurations when some of the masses of the four primaries tend to zero and the remainder ones keep constant. [...]
2022 - 10.1063/5.0091642
Journal of Mathematical Physics, Vol. 63, Issue 12 (December 2022) , art. 122901  
2.
22 p, 1.3 MB Existence of a cylinder foliated by periodic orbits in the generalized Chazy differential equation / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Novaes, Douglas D. (Universidade Estadual de Campinas. Instituto de Matemática, Estatística e Computação Científica. Departamento de Matemática) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemática)
The generalized Chazy differential equation corresponds to the following two-parameter family of differential equations x ⃛ + | x | q x ¨ + k | x | q x x ˙ 2 = 0, which has its regularity varying with q, a positive integer. [...]
2023 - 10.1063/5.0138309
Chaos, Vol. 33, Issue 7 (July 2023) , art. 73104  
3.
19 p, 300.3 KB An extension of the 16th Hilbert problem for continuous piecewise linear-quadratic centers separated by a non-regular line / Esteban, Marina (Universidad de Córdoba. Departamento de Informática y Análisis Numérico) ; Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento Matemática)
In the last few decades, there has been much interest in studying piecewise differential systems. This is mainly due to the fact that these differential systems allow us to modelize many natural phenomena. [...]
2023 - 10.1063/5.0167089
Chaos, Vol. 33, Issue 12 (December 2023) , art. 123120  
4.
17 p, 3.2 MB Phase portraits on the unit sphere of the stretch-twist-fold flow / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
The so-called stretch-twist-fold flow consists in a Stokes flow depending on two parameters defined in a unit closed ball B¯ that is associated with the motion of a fluid particle coming from the dynamo theory, and it models a mechanism for studying the magnetic field of the Earth and the Sun. [...]
2023 - 10.15388/namc.2023.28.33088
Nonlinear Analysis: Modelling and Control, Vol. 28, Issue 5 (September 2023) , p. 1020-1036  
5.
Polynomial differential systems with hyperbolic limit cycles / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
One of the main problems of the qualitative theory of the planar differential equations is the study their limit cycles. In this paper given an algebraic curve of degree n we characterize the planar polynomial differential systems of degree greater or equal than n which admit the ovals of the algebraic curve as hyperbolic limit cycles.
2023 - 10.1016/j.geomphys.2023.104983
Journal of geometry and physics, Vol. 194 (December 2023) , art. 104983  
6.
Limit cycles of a continuous piecewise differential system formed by a quadratic center and two linear centers / Anacleto, Maria Elisa (Universidad del Bío-Bío. Departamento de Matemática) ; Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica) ; Vidal, Claudio (Universidad del Bío-Bío. Departamento de Matemática)
The study of limit cycles of planar differential systems is one of the main and difficult problems for understanding their dynamics. Thus the objective of this paper is to study the limit cycles of continuous piecewise differential systems in the plane separated by a non-regular line Σ. [...]
2023 - 10.1007/s40590-023-00501-7
Boletin de la Sociedad Matematica Mexicana, Vol. 29, Issue 2 (July 2023) , art. 29  
7.
Invariants of polynomial vector fields / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
We characterize the existence of first integrals and invariants (first integrals depending on the time) for the polynomial vector fields which are invariant under an involution.
2023 - 10.1016/j.jde.2023.05.024
Journal of differential equations, Vol. 365 (August 2023) , p. 895-904  
8.
On the "traveling pulses" of the limit of the FitzHugh-Nagumo equation when ɛ→0 / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
A solution (u(s), v(s)) of the differential system u = v, v = −cv−u(u−a)(1−u) + w, w = −(ɛ/c)(u−γw) with a, c, ɛ ∈ R such that (u(s), v(s)) → (0,0) when s → ± ∞ is a traveling pulse of the FitzHugh-Nagumo equation. [...]
2023 - 10.1016/j.nonrwa.2023.103891
Nonlinear Analysis: Real World Applications, Vol. 73 (October 2023) , art. 103891  
9.
10 p, 584.9 KB Menstrual health and management during the COVID-19 syndemic in the Barcelona area (Spain) : A qualitative study / Holst, Anna Sofie (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; Jacques-Aviñó, Constanza (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; Berenguera, Anna (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; Martínez-Bueno, Cristina (Universitat de Barcelona) ; Munrós-Feliu, Jordina (Institut Català de la Salut) ; Pinzón-Sanabria, Diana (SomiArte Taller) ; Valls-Llobet, Carme (Centre d'Anàlisis Programes Sanitaris (Barcelona, Catalunya)) ; López-Jiménez, Tomàs (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; García-Egea, Andrea (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; Vicente-Hernández, María Mercedes (Grup de Recerca en Salut Sexual i Reproductiva) ; Medina-Perucha, Laura (Institut Universitari d'Investigació en Atenció Primària Jordi Gol) ; Universitat Autònoma de Barcelona
Available evidence suggests that menstrual health and management have been impaired during the COVID-19 syndemic. However, research in this area is scarce, and it is failing to voice the experiences of women and people who menstruate regarding their menstrual experiences. [...]
2023 - 10.1177/17455057231166644
Women's Health, Vol. 19 (april 2023)  
10.
42 p, 672.9 KB The improved Euler-Jacobi formula and the planar cubic polynomial vector fields in ℝ2 / Llibre, Jaume (Universitat Autònoma de Barcelona. Departament de Matemàtiques) ; Valls, Clàudia 1973- (Universidade de Lisboa. Instituto Superior Técnico. Departamento de Matemàtica)
The new Euler-Jacobi formula for points with multiplicity two provides an algebraic relation between the singular points of a polynomial vector field and their topological indices. Using this formula we obtain the configuration of the singular points together with their topological indices for the planar cubic polynomial differential systems when these systems have eight finite singular points, being one of them with multiplicity two. [...]
2022 - 10.1080/14689367.2022.2066508
Dynamical Systems, Vol. 37, Issue 3 (2022) , p. 403-443  

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