Articles de revista
http://hdl.handle.net/2117/3918
Wed, 04 May 2016 02:18:38 GMT
20160504T02:18:38Z

Secular instability in the threebody problem
http://hdl.handle.net/2117/86530
Secular instability in the threebody problem
Fejoz, J.; Guàrdia Munarriz, Marcel
© 2016 European Union Consider the threebody problem, in the regime where one body revolves far away around the other two, in space, the masses of the bodies being arbitrary but fixed; in this regime, there are no resonances in mean motions. The socalled secular dynamics governs the slow evolution of the Keplerian ellipses. We show that it contains a horseshoe and all the chaotic dynamics which goes along with it, corresponding to motions along which the eccentricity of the inner ellipse undergoes large, random excursions. The proof goes through the surprisingly explicit computation of the homoclinic solution of the first order secular system, its complex singularities and the Melnikov potential.
Tue, 03 May 2016 11:49:55 GMT
http://hdl.handle.net/2117/86530
20160503T11:49:55Z
Fejoz, J.
Guàrdia Munarriz, Marcel
© 2016 European Union Consider the threebody problem, in the regime where one body revolves far away around the other two, in space, the masses of the bodies being arbitrary but fixed; in this regime, there are no resonances in mean motions. The socalled secular dynamics governs the slow evolution of the Keplerian ellipses. We show that it contains a horseshoe and all the chaotic dynamics which goes along with it, corresponding to motions along which the eccentricity of the inner ellipse undergoes large, random excursions. The proof goes through the surprisingly explicit computation of the homoclinic solution of the first order secular system, its complex singularities and the Melnikov potential.

Oscillatory motions for the restricted planar circular three body problem
http://hdl.handle.net/2117/86502
Oscillatory motions for the restricted planar circular three body problem
Guàrdia Munarriz, Marcel; Martín, Pau; MartínezSeara Alonso, M. Teresa
© 2015, SpringerVerlag Berlin Heidelberg. The restricted three body problem models the motion of a massless body under the influence of the Newtonian gravitational force caused by two other bodies called the primaries. When they move along circular Keplerian orbits and the third body moves in the same plane, one has the restricted planar circular three body problem (RPC3BP). In suitable coordinates, it is a Hamiltonian system of two degrees of freedom. The conserved energy is usually called the Jacobi constant. Llibre and Simó [Math Ann 248(2):153–184, 1980] proved the existence of oscillatory motions for this system. That is, orbits which leave every bounded region but which return infinitely often to some fixed bounded region. To prove their existence they had to assume the ratio between the masses of the primaries to be small enough. In this paper we prove the existence of such motions for any value of the mass ratio(Formula presented.) closing the problem of existence of oscillatory motions in the RPC3BP. To obtain such motions, we restrict ourselves to the level sets of the Jacobi constant. We show that, for any value of the mass ratio and for large values of the Jacobi constant, there exist transversal intersections between the stable and unstable manifolds of infinity in these level sets. These transversal intersections guarantee the existence of a symbolic dynamics that creates the oscillatory orbits. The main achievement is to prove the existence of these orbits without assuming the mass ratio (Formula presented.) small. When (Formula presented.) is not small, this transversality can not be checked by means of classical perturbation theory. Since our method is valid for all values of v, we are able to detect a curve in the parameter space, formed by (Formula presented.) and the Jacobi constant, where cubic homoclinic tangencies between the invariant manifolds of infinity appear.
Mon, 02 May 2016 17:44:48 GMT
http://hdl.handle.net/2117/86502
20160502T17:44:48Z
Guàrdia Munarriz, Marcel
Martín, Pau
MartínezSeara Alonso, M. Teresa
© 2015, SpringerVerlag Berlin Heidelberg. The restricted three body problem models the motion of a massless body under the influence of the Newtonian gravitational force caused by two other bodies called the primaries. When they move along circular Keplerian orbits and the third body moves in the same plane, one has the restricted planar circular three body problem (RPC3BP). In suitable coordinates, it is a Hamiltonian system of two degrees of freedom. The conserved energy is usually called the Jacobi constant. Llibre and Simó [Math Ann 248(2):153–184, 1980] proved the existence of oscillatory motions for this system. That is, orbits which leave every bounded region but which return infinitely often to some fixed bounded region. To prove their existence they had to assume the ratio between the masses of the primaries to be small enough. In this paper we prove the existence of such motions for any value of the mass ratio(Formula presented.) closing the problem of existence of oscillatory motions in the RPC3BP. To obtain such motions, we restrict ourselves to the level sets of the Jacobi constant. We show that, for any value of the mass ratio and for large values of the Jacobi constant, there exist transversal intersections between the stable and unstable manifolds of infinity in these level sets. These transversal intersections guarantee the existence of a symbolic dynamics that creates the oscillatory orbits. The main achievement is to prove the existence of these orbits without assuming the mass ratio (Formula presented.) small. When (Formula presented.) is not small, this transversality can not be checked by means of classical perturbation theory. Since our method is valid for all values of v, we are able to detect a curve in the parameter space, formed by (Formula presented.) and the Jacobi constant, where cubic homoclinic tangencies between the invariant manifolds of infinity appear.

El impacto de las políticas de evaluación del profesorado en la posición en los ránquines universitarios: el caso de la Universidad Politécnica de Cataluña
http://hdl.handle.net/2117/86427
El impacto de las políticas de evaluación del profesorado en la posición en los ránquines universitarios: el caso de la Universidad Politécnica de Cataluña
GarcíaBerro Montilla, Enrique; Roca Martín, Santiago; Navallas Ramos, Francisco Javier; Soriano Ibáñez, Miguel; Ras Sabido, Antoni
La universidad española ha afrontado con éxito el tránsito entre una universidad clásica, eminentemente docente, y una universidad moderna, en la que la investigación juega un papel esencial. Gran parte de este éxito reside en la instauración de sistemas de evaluación. No obstante, a pesar de los indiscutibles logros, aún queda un camino importante por recorrer para situarla en los lugares que le corresponden en las clasificaciones internacionales por el lugar que ocupamos dentro de los países de nuestro entorno. La Universidad Politécnica de Cataluña dispone de un modelo de evaluación docente, así como de información sobre la actividad investigadora del profesorado. Ello ha permitido implementar un modelo de evaluación global, que presentamos en este artículo. Asimismo, usando una muestra de 4.996 evaluaciones individuales de unos 1.700 profesores, analizamos la evolución temporal de las evaluaciones de los años 2011, 2012 y 2013, estudiamos si existen diferencias entre los ámbitos de conocimiento y examinamos si existe una relación entre la productividad académica así evaluada y la posición de la universidad en los ránquines universitarios. Los datos de este estudio corroboran que el modelo ha tenido éxito, al haber permitido que la universidad progresara en el ranquin Quacquarelli Symonds del puesto 350 al 337.
Spanish universities have moved from a classical model, a teaching university, to a modern one, in which research is essential. Part of this success is due to the implementation of quality assessment policies. Nonetheless, and in spite of this, there is still a long way to place it at the level of similar countries in university rankings. The Universidad Politécnica de Cataluña has an evaluation model of the teaching performance of its staff, and also abundant information of their research. This has allowed implementing a global evaluation model. Here we present the evaluation model. Also, using 4,996 individual evaluations corresponding to about 1,700 academic staff members we analyze the evolution of the results of the evaluations of years 2011, 2012 and 2013, we study if there are differences among the various academic fields, and we examine if there exists a correlation between the evolution of the academic productivity measured using this model and the position of the university in the university rankings. We show that this model has allowed the university to improve its classification in the Quacquarelli Symonds Top University Ranking, from position 350 to 337.
Fri, 29 Apr 2016 12:32:32 GMT
http://hdl.handle.net/2117/86427
20160429T12:32:32Z
GarcíaBerro Montilla, Enrique
Roca Martín, Santiago
Navallas Ramos, Francisco Javier
Soriano Ibáñez, Miguel
Ras Sabido, Antoni
La universidad española ha afrontado con éxito el tránsito entre una universidad clásica, eminentemente docente, y una universidad moderna, en la que la investigación juega un papel esencial. Gran parte de este éxito reside en la instauración de sistemas de evaluación. No obstante, a pesar de los indiscutibles logros, aún queda un camino importante por recorrer para situarla en los lugares que le corresponden en las clasificaciones internacionales por el lugar que ocupamos dentro de los países de nuestro entorno. La Universidad Politécnica de Cataluña dispone de un modelo de evaluación docente, así como de información sobre la actividad investigadora del profesorado. Ello ha permitido implementar un modelo de evaluación global, que presentamos en este artículo. Asimismo, usando una muestra de 4.996 evaluaciones individuales de unos 1.700 profesores, analizamos la evolución temporal de las evaluaciones de los años 2011, 2012 y 2013, estudiamos si existen diferencias entre los ámbitos de conocimiento y examinamos si existe una relación entre la productividad académica así evaluada y la posición de la universidad en los ránquines universitarios. Los datos de este estudio corroboran que el modelo ha tenido éxito, al haber permitido que la universidad progresara en el ranquin Quacquarelli Symonds del puesto 350 al 337.
Spanish universities have moved from a classical model, a teaching university, to a modern one, in which research is essential. Part of this success is due to the implementation of quality assessment policies. Nonetheless, and in spite of this, there is still a long way to place it at the level of similar countries in university rankings. The Universidad Politécnica de Cataluña has an evaluation model of the teaching performance of its staff, and also abundant information of their research. This has allowed implementing a global evaluation model. Here we present the evaluation model. Also, using 4,996 individual evaluations corresponding to about 1,700 academic staff members we analyze the evolution of the results of the evaluations of years 2011, 2012 and 2013, we study if there are differences among the various academic fields, and we examine if there exists a correlation between the evolution of the academic productivity measured using this model and the position of the university in the university rankings. We show that this model has allowed the university to improve its classification in the Quacquarelli Symonds Top University Ranking, from position 350 to 337.

Polygons as sections of higherdimensional polytopes
http://hdl.handle.net/2117/86389
Polygons as sections of higherdimensional polytopes
Padrol Sureda, Arnau; Pfeifle, Julián
We show that every heptagon is a section of a 3polytope with 6 vertices. This implies that every ngon with n >= 7 can be obtained as a section of a (2 + [n/7])dimensional polytope with at most [6n/7] vertices; and provides a geometric proof of the fact that every nonnegative n x rn matrix of rank 3 has nonnegative rank not larger than [6min(n,m)/7]. This result has been independently proved, algebraically, by Shitov (J. Combin. Theory Ser. A 122, 2014).
Thu, 28 Apr 2016 14:55:10 GMT
http://hdl.handle.net/2117/86389
20160428T14:55:10Z
Padrol Sureda, Arnau
Pfeifle, Julián
We show that every heptagon is a section of a 3polytope with 6 vertices. This implies that every ngon with n >= 7 can be obtained as a section of a (2 + [n/7])dimensional polytope with at most [6n/7] vertices; and provides a geometric proof of the fact that every nonnegative n x rn matrix of rank 3 has nonnegative rank not larger than [6min(n,m)/7]. This result has been independently proved, algebraically, by Shitov (J. Combin. Theory Ser. A 122, 2014).

Automorphisms and reduction of Heegner points on Shimura curves at CerednikDrinfeld primes
http://hdl.handle.net/2117/86360
Automorphisms and reduction of Heegner points on Shimura curves at CerednikDrinfeld primes
Molina Blanco, Santiago; Rotger Cerdà, Víctor
The aim of this short note is to show how the interplay of the action of the automorphism
group of a Shimura curve on the special fiber of its CerednikDrinfeld’s integral model at a prime of bad reduction
and its sets of Heegner points, can be exploited to prove some instances of a conjecture that predicts that any
automorphism must be an AtkinLehner involution.
Thu, 28 Apr 2016 11:11:59 GMT
http://hdl.handle.net/2117/86360
20160428T11:11:59Z
Molina Blanco, Santiago
Rotger Cerdà, Víctor
The aim of this short note is to show how the interplay of the action of the automorphism
group of a Shimura curve on the special fiber of its CerednikDrinfeld’s integral model at a prime of bad reduction
and its sets of Heegner points, can be exploited to prove some instances of a conjecture that predicts that any
automorphism must be an AtkinLehner involution.

The kernel of Ribet’s isogeny for genus three Shimura curves
http://hdl.handle.net/2117/86355
The kernel of Ribet’s isogeny for genus three Shimura curves
Molina Blanco, Santiago; González Rovira, Josep
There are exactly nine reduced discriminants D of indefinite quaternion algebras over Q for which the Shimura curve XD attached to D has genus 3. We present equations for these nine curves. Moreover, for each D we determine a subgroup c(D) of cuspidal divisors of degree zero of the new part of the Jacobian of the modular curve of level D such that the abelian variety quotient by c(D) is the jacobian of the curve XD.
Thu, 28 Apr 2016 10:52:55 GMT
http://hdl.handle.net/2117/86355
20160428T10:52:55Z
Molina Blanco, Santiago
González Rovira, Josep
There are exactly nine reduced discriminants D of indefinite quaternion algebras over Q for which the Shimura curve XD attached to D has genus 3. We present equations for these nine curves. Moreover, for each D we determine a subgroup c(D) of cuspidal divisors of degree zero of the new part of the Jacobian of the modular curve of level D such that the abelian variety quotient by c(D) is the jacobian of the curve XD.

Cellcentred model for the simulation of curved cellular monolayers
http://hdl.handle.net/2117/86189
Cellcentred model for the simulation of curved cellular monolayers
Mosafa, Payman; Asadipour, Nina; Millán, Raúl Daniel; Rodríguez Ferran, Antonio; Muñoz Romero, José
This paper presents a cellcentred model for the simulation of planar and curved multicellular soft tissues. We propose a computational model that includes stress relaxation due to cell reorganisation (intercellular connectivity changes) and cytoskeleton remodelling (intracellular changes). Cells are represented by their cell centres, and their mechanical interaction is modelled through active nonlinear elastic laws with a dynamically changing resting length. Special attention is paid to the handling of connectivity changes between cells, and the relaxation that the tissues exhibit under these topological changes. Cellcell connectivity is computed by resorting to a Delaunay triangulation, which is combined with a mapping technique in order to obtain triangulations on curved manifolds. Our numerical results show that even a linear elastic cellcell interaction model may induce a global nonlinear response due to the reorganisation of the cell connectivity. This plasticlike behaviour is combined with a nonlinear rheological law where the resting length depends on the elastic strain, mimicking the global viscoelastic response of tissues. The model is applied to simulate the elongation of planar and curved monolayers.
Tue, 26 Apr 2016 10:28:30 GMT
http://hdl.handle.net/2117/86189
20160426T10:28:30Z
Mosafa, Payman
Asadipour, Nina
Millán, Raúl Daniel
Rodríguez Ferran, Antonio
Muñoz Romero, José
This paper presents a cellcentred model for the simulation of planar and curved multicellular soft tissues. We propose a computational model that includes stress relaxation due to cell reorganisation (intercellular connectivity changes) and cytoskeleton remodelling (intracellular changes). Cells are represented by their cell centres, and their mechanical interaction is modelled through active nonlinear elastic laws with a dynamically changing resting length. Special attention is paid to the handling of connectivity changes between cells, and the relaxation that the tissues exhibit under these topological changes. Cellcell connectivity is computed by resorting to a Delaunay triangulation, which is combined with a mapping technique in order to obtain triangulations on curved manifolds. Our numerical results show that even a linear elastic cellcell interaction model may induce a global nonlinear response due to the reorganisation of the cell connectivity. This plasticlike behaviour is combined with a nonlinear rheological law where the resting length depends on the elastic strain, mimicking the global viscoelastic response of tissues. The model is applied to simulate the elongation of planar and curved monolayers.

Instability of stationary solutions of reactiondiffusionequations on graphs
http://hdl.handle.net/2117/86116
Instability of stationary solutions of reactiondiffusionequations on graphs
Von Below, Joachim; Lubary Martínez, José Antonio
The nonexistence of stable stationary nonconstant solutions of reactiondiffusionequations partial derivative(t)u(j) = partial derivative(j)(a(j)(x(j))partial derivative(j)u(j)) + f(j)(u(j)) on the edges of a finite (topological) graph is investigated under continuity and consistent Kirchhoff flow conditions at all vertices of the graph. In particular, it is shown that in the balanced autonomous case f(u) = u  u(3), no such stable stationary solution can exist on any finite graph. Finally, the balanced autonomous case is discussed on the twosided unbounded path with equal edge lengths.
Fri, 22 Apr 2016 17:54:59 GMT
http://hdl.handle.net/2117/86116
20160422T17:54:59Z
Von Below, Joachim
Lubary Martínez, José Antonio
The nonexistence of stable stationary nonconstant solutions of reactiondiffusionequations partial derivative(t)u(j) = partial derivative(j)(a(j)(x(j))partial derivative(j)u(j)) + f(j)(u(j)) on the edges of a finite (topological) graph is investigated under continuity and consistent Kirchhoff flow conditions at all vertices of the graph. In particular, it is shown that in the balanced autonomous case f(u) = u  u(3), no such stable stationary solution can exist on any finite graph. Finally, the balanced autonomous case is discussed on the twosided unbounded path with equal edge lengths.

On the complexity of exchanging
http://hdl.handle.net/2117/86068
On the complexity of exchanging
Molinero Albareda, Xavier; Olsen, Martin; Serna Iglesias, María José
We analyze the computational complexity of the problem of deciding whether, for a given simple game, there exists the possibility of rearranging the participants in a set of j given losing coalitions into a set of j winning coalitions. We also look at the problem of turning winning coalitions into losing coalitions. We analyze the problem when the simple game is represented by a list of wining, losing, minimal winning or maximal loosing coalitions.
Thu, 21 Apr 2016 13:57:53 GMT
http://hdl.handle.net/2117/86068
20160421T13:57:53Z
Molinero Albareda, Xavier
Olsen, Martin
Serna Iglesias, María José
We analyze the computational complexity of the problem of deciding whether, for a given simple game, there exists the possibility of rearranging the participants in a set of j given losing coalitions into a set of j winning coalitions. We also look at the problem of turning winning coalitions into losing coalitions. We analyze the problem when the simple game is represented by a list of wining, losing, minimal winning or maximal loosing coalitions.

Opening the black box of energy throughputs in farm systems: a decomposition analysis between the energy returns to external inputs, internal biomass reuses and total inputs consumed (the Vallès County, Catalonia, c.1860 and 1999)
http://hdl.handle.net/2117/86061
Opening the black box of energy throughputs in farm systems: a decomposition analysis between the energy returns to external inputs, internal biomass reuses and total inputs consumed (the Vallès County, Catalonia, c.1860 and 1999)
Tello, E.; Galán, E.; Sacristán Adinolfi, Vera; Cunfer, G.; Guzmán, G. I.; González de Molina, M.; Krausmann, F.; Gringrich, S.; Padró, R.; Marco, I.; MorenoDelgado, D.
We present an energy analysis of past and present farm systems aimed to contribute to their sustainability assessment. Looking at agroecosystems as a set of energy loops between nature and society, and adopting a farmoperator standpoint at landscape level to set the system boundaries, enthalpy values of energy carriers are accounted for net Final Produce going outside as well as for Biomass Reused cycling inside, and External Inputs are accounted using embodied values. Human Labour is accounted for the fraction of the energy intake of labouring people devoted to perform farm work, considering the local or external origin of their food basket. In this approach the proportion of internal Biomass Reused becomes a hallmark of organic farm systems that tend to save External Inputs, whereas industrial farming and livestock breeding in feedlots tend to get rid of reuses replacing them with inputs coming from outside. Hence, decomposing the internal or external energy throughputs may bring to light their contrasting sociometabolic profiles. A Catalan case study in 1860 and 1990 is used as a test bench to show how revealing this decomposing analysis may be to plot the energy profiles of farm systems and their possible improvement pathways.
Thu, 21 Apr 2016 12:18:30 GMT
http://hdl.handle.net/2117/86061
20160421T12:18:30Z
Tello, E.
Galán, E.
Sacristán Adinolfi, Vera
Cunfer, G.
Guzmán, G. I.
González de Molina, M.
Krausmann, F.
Gringrich, S.
Padró, R.
Marco, I.
MorenoDelgado, D.
We present an energy analysis of past and present farm systems aimed to contribute to their sustainability assessment. Looking at agroecosystems as a set of energy loops between nature and society, and adopting a farmoperator standpoint at landscape level to set the system boundaries, enthalpy values of energy carriers are accounted for net Final Produce going outside as well as for Biomass Reused cycling inside, and External Inputs are accounted using embodied values. Human Labour is accounted for the fraction of the energy intake of labouring people devoted to perform farm work, considering the local or external origin of their food basket. In this approach the proportion of internal Biomass Reused becomes a hallmark of organic farm systems that tend to save External Inputs, whereas industrial farming and livestock breeding in feedlots tend to get rid of reuses replacing them with inputs coming from outside. Hence, decomposing the internal or external energy throughputs may bring to light their contrasting sociometabolic profiles. A Catalan case study in 1860 and 1990 is used as a test bench to show how revealing this decomposing analysis may be to plot the energy profiles of farm systems and their possible improvement pathways.