EGSA - Equacions Diferencials, Geometria, Sistemes Dinàmics i de Control, i Aplicacions
http://hdl.handle.net/2117/3227
Wed, 07 Oct 2015 06:59:55 GMT2015-10-07T06:59:55ZTraveling wave solutions in a half-space for boundary reactions
http://hdl.handle.net/2117/77011
Traveling wave solutions in a half-space for boundary reactions
Cabré Vilagut, Xavier; Consul Porras, M. Nieves; Mande Nieto, José Vicente
We prove the existence and uniqueness of a traveling front and of its speed for the homogeneous heat equation in the half-plane with a Neumann boundary reaction term of unbalanced bistable type or of combustion type. We also establish the monotonicity of the front and, in the bistable case, its behavior at infinity. In contrast with the classical bistable interior reaction model, its behavior at the side of the invading state is of power type, while at the side of the invaded state its decay is exponential. These decay results rely on the construction of a family of explicit bistable traveling fronts. Our existence results are obtained via a variational method, while the uniqueness of the speed and of the front rely on a comparison principle and the sliding method.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/2117/770112015-01-01T00:00:00ZQuasimatter domination parameters in bouncing cosmologies
http://hdl.handle.net/2117/76767
Quasimatter domination parameters in bouncing cosmologies
Elizalde, Emilio; Haro Cases, Jaume; Odintsov, Sergei D.
A fine set of parameters is introduced for bouncing cosmologies in order to describe the nearly matterdominated phase, and which play the same role that the usual slow-roll parameters play in inflationary cosmology. It is shown that, as in the inflation case, the spectral index and the running parameter for scalar perturbations in bouncing cosmologies can be best expressed in terms of these small parameters. Further, they explicitly exhibit the duality that exists between a nearly matter-dominated universe in its contracting phase and the quasi-de Sitter regime in the expanding one. The results obtained also confirm and extend the known evidence that the spectral index for an exactly matter-dominated universe (i.e., a pressureless universe) in the contracting phase is, in fact, the same as the spectral index for an exact de Sitter regime in the expanding phase. Finally, in both the inflationary and the matter bounce scenarios, the theoretical values of the spectral index and of the running parameter are compared with their experimental counterparts, obtained from the most recent Planck data, with the result that the bouncing models discussed here fit accurate astronomical observations well.
Thu, 19 Mar 2015 00:00:00 GMThttp://hdl.handle.net/2117/767672015-03-19T00:00:00ZA note on symplectic and Poisson linearization of semisimple Lie algebra actions
http://hdl.handle.net/2117/26960
A note on symplectic and Poisson linearization of semisimple Lie algebra actions
Miranda Galcerán, Eva
In this note we prove that an analytic symplectic action of a semisimple Lie algebra can be locally linearized in Darboux coordinates. This result yields simultaneous analytic linearization for Hamiltonian vector fields in a neighbourhood of a common zero. We also provide an example of smooth non-linearizable Hamiltonian action with semisimple linear part. The smooth analogue only holds if the semisimple Lie algebra is of compact type. An analytic equivariant b-Darboux theorem for b-Poisson manifolds and an analytic equivariant Weinstein splitting theorem for general Poisson manifolds are also obtained in the Poisson setting
Sun, 01 Mar 2015 00:00:00 GMThttp://hdl.handle.net/2117/269602015-03-01T00:00:00ZGeneric bifurcations of low codimension of planar Filippov Systems
http://hdl.handle.net/2117/26671
Generic bifurcations of low codimension of planar Filippov Systems
Martínez-Seara Alonso, M. Teresa; Guàrdia Munarriz, Marcel; Teixeira, Marco Antonio
In this article some qualitative and geometric aspects of non-smooth dynamical systems theory are discussed. The main aim of
this article is to develop a systematic method for studying local(and global) bifurcations in non-smooth dynamical systems. Our results deal with the classification and characterization of generic codimension-2 singularities of planar Filippov Systems as well as the presentation of the bifurcation diagrams and some dynamical consequences
Tue, 01 Feb 2011 00:00:00 GMThttp://hdl.handle.net/2117/266712011-02-01T00:00:00ZA distributed attitude control law for formation flying based on the Cucker-smale model
http://hdl.handle.net/2117/26670
A distributed attitude control law for formation flying based on the Cucker-smale model
Paita, Fabrizio; Gómez Muntané, Gerard; Masdemont Soler, Josep
In this paper we consider the attitude synchronization problem for a swarm of spacecrafts flying in formation.
Starting from previous works on consensus dynamics, we construct a distributed attitude control law and derive analytically
sufficient conditions for the formation to converge asymptotically towards a synchronized, non–accelerating state (possibly defined a priori). Moreover, motivated by the results obtained on a particular consensus model, first introduced by F. Cucker and S. Smale to modellize the translational dynamics of flocks, we numerically explore
the dependence of the convergence process on the dimension of the formation and the relative initial conditions of the spacecrafts. Finally, we generalize the class of weights defined by the previous authors in order to dampen the aforementioned effects, thus making our control law suitable for very large formations.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/2117/266702014-01-01T00:00:00ZMatrices positivas y aplicaciones
http://hdl.handle.net/2117/26622
Matrices positivas y aplicaciones
García Planas, María Isabel
Mon, 01 Sep 2008 00:00:00 GMThttp://hdl.handle.net/2117/266222008-09-01T00:00:00ZCredit risk contributions under the Vasicek one-factor model: a fast wavelet expansion approximation
http://hdl.handle.net/2117/26597
Credit risk contributions under the Vasicek one-factor model: a fast wavelet expansion approximation
Masdemont Soler, Josep; Ortiz-Gracia, Luis
To measure the contribution of individual transactions inside the total risk of a credit portfolio is a major issue in financial institutions. VaR Contributions (VaRC) and Expected Shortfall Contributions (ESC) have become two popular ways of quantifying the risks. However, the usual Monte Carlo (MC) approach is known to be a very time consum-
ing method for computing these risk contributions. In this paper we consider the Wavelet Approximation (WA) method for Value at Risk (VaR) computation presented in [Mas10] in order to calculate the Expected Shortfall (ES) and the risk contributions under the Vasicek
one-factor model framework. We decompose the VaR and the ES as a sum of sensitivities representing the marginal impact on the total portfolio risk. Moreover, we present technical improvements in the Wavelet Approximation (WA) that considerably reduce the computa-
tional effort in the approximation while, at the same time, the accuracy increases
Sun, 01 Jun 2014 00:00:00 GMThttp://hdl.handle.net/2117/265972014-06-01T00:00:00ZCom les Varietats Invariants formen Espirals i Anells en Galàxies barrades
http://hdl.handle.net/2117/26596
Com les Varietats Invariants formen Espirals i Anells en Galàxies barrades
Romero Gómez, Mercè; Sánchez-Martín, Patricia; Masdemont Soler, Josep
L'espectacularitat de les galàxies barrades consisteix no solament en la
presència de la barra, allargada en el centre de la galàxia, sinó també en els braços espirals o anells que es desenvolupen en les parts exteriors. No hi ha una teoria clara per a la formació d'anells i, fins fa poc, només n'hi havia una que explicava l'origen dels braços espirals en galàxies no barrades. En els darrers anys hem desenvolupat una teoria basada en els sistemes dinàmics que relaciona els braços espirals i els anells amb les varietats invariants hiperbòliques associades a òrbites periòdiques i quasiperiòdiques al voltant de punts d'equilibri colineals del sistema
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/2117/265962014-01-01T00:00:00ZAction-angle variables and a KAM theorem for b-Poisson manifolds
http://hdl.handle.net/2117/26390
Action-angle variables and a KAM theorem for b-Poisson manifolds
Kiesenhofer, Anna; Miranda Galcerán, Eva; Scott, Geoffrey
In this article we prove an action-angle theorem for b-integrable systems on b-Poisson manifolds improving the action-angle theorem contained in [LMV11] for general Poisson manifolds in this setting. As an application, we prove a KAM-type theorem for b-Poisson manifolds.
Sun, 01 Feb 2015 00:00:00 GMThttp://hdl.handle.net/2117/263902015-02-01T00:00:00ZStructural stability of planar bimodal linear systems
http://hdl.handle.net/2117/26226
Structural stability of planar bimodal linear systems
Ferrer Llop, Josep; Peña Carrera, Marta; Susín Sánchez, Antonio
Structural stability ensures that the qualitative behavior of a system is preserved under small perturbations. We study it for planar bimodal linear dynamical systems, that is, systems consisting of two linear dynamics acting on each side of a given hyperplane and assuming continuity along the separating hyperplane. We describe which one of these systems is structurally stable when (real) spiral does not appear and when it does we give necessary and sufficient conditions concerning finite periodic orbits and saddle connections. In particular, we study the finite periodic orbits and the homoclinic orbits in the saddle/spiral case.
Wed, 01 Jan 2014 00:00:00 GMThttp://hdl.handle.net/2117/262262014-01-01T00:00:00Z