Articles de revista
http://hdl.handle.net/2117/3918
Thu, 23 Feb 2017 02:57:17 GMT2017-02-23T02:57:17ZArnold's mechanism of diffusion in the spatial circular restricted three-body problem: A semi-analytical argument
http://hdl.handle.net/2117/101125
Arnold's mechanism of diffusion in the spatial circular restricted three-body problem: A semi-analytical argument
Delshams Valdés, Amadeu; Gidea, Marian; Roldán, Pablo
We consider the spatial circular restricted three-body problem, on the motion of an infinitesimal body under the gravity of Sun and Earth. This can be described by a 3-degree of freedom Hamiltonian system. We fix an energy level close to that of the collinear libration point L1, located between Sun and Earth. Near L1 there exists a normally hyperbolic invariant manifold, diffeomorphic to a 3-sphere. For an orbit confined to this 3-sphere, the amplitude of the motion relative to the ecliptic (the plane of the orbits of Sun and Earth) can vary only slightly.
We show that we can obtain new orbits whose amplitude of motion relative to the ecliptic changes significantly, by following orbits of the flow restricted to the 3-sphere alternatively with homoclinic orbits that turn around the Earth. We provide an abstract theorem for the existence of such ‘diffusing’ orbits, and numerical evidence that the premises of the theorem are satisfied in the three-body problem considered here. We provide an explicit construction of diffusing orbits.
The geometric mechanism underlying this construction is reminiscent of the Arnold diffusion problem for Hamiltonian systems. Our argument, however, does not involve transition chains of tori as in the classical example of Arnold. We exploit mostly the ‘outer dynamics’ along homoclinic orbits, and use very little information on the ‘inner dynamics’ restricted to the 3-sphere.
As a possible application to astrodynamics, diffusing orbits as above can be used to design low cost maneuvers to change the inclination of an orbit of a satellite near L1 from a nearly-planar orbit to a tilted orbit with respect to the ecliptic. We explore different energy levels, and estimate the largest orbital inclination that can be achieved through our construction.
Thu, 16 Feb 2017 09:57:15 GMThttp://hdl.handle.net/2117/1011252017-02-16T09:57:15ZDelshams Valdés, AmadeuGidea, MarianRoldán, PabloWe consider the spatial circular restricted three-body problem, on the motion of an infinitesimal body under the gravity of Sun and Earth. This can be described by a 3-degree of freedom Hamiltonian system. We fix an energy level close to that of the collinear libration point L1, located between Sun and Earth. Near L1 there exists a normally hyperbolic invariant manifold, diffeomorphic to a 3-sphere. For an orbit confined to this 3-sphere, the amplitude of the motion relative to the ecliptic (the plane of the orbits of Sun and Earth) can vary only slightly.
We show that we can obtain new orbits whose amplitude of motion relative to the ecliptic changes significantly, by following orbits of the flow restricted to the 3-sphere alternatively with homoclinic orbits that turn around the Earth. We provide an abstract theorem for the existence of such ‘diffusing’ orbits, and numerical evidence that the premises of the theorem are satisfied in the three-body problem considered here. We provide an explicit construction of diffusing orbits.
The geometric mechanism underlying this construction is reminiscent of the Arnold diffusion problem for Hamiltonian systems. Our argument, however, does not involve transition chains of tori as in the classical example of Arnold. We exploit mostly the ‘outer dynamics’ along homoclinic orbits, and use very little information on the ‘inner dynamics’ restricted to the 3-sphere.
As a possible application to astrodynamics, diffusing orbits as above can be used to design low cost maneuvers to change the inclination of an orbit of a satellite near L1 from a nearly-planar orbit to a tilted orbit with respect to the ecliptic. We explore different energy levels, and estimate the largest orbital inclination that can be achieved through our construction.Diseño y construcción de un prototipo de plataforma Stewart
http://hdl.handle.net/2117/101116
Diseño y construcción de un prototipo de plataforma Stewart
Rossell Garriga, Josep Maria; Blanes Priego, Manel; Vicente Rodrigo, Jesús; Rubió Massegú, Josep; Palacios Quiñonero, Francisco
Wed, 15 Feb 2017 16:31:47 GMThttp://hdl.handle.net/2117/1011162017-02-15T16:31:47ZRossell Garriga, Josep MariaBlanes Priego, ManelVicente Rodrigo, JesúsRubió Massegú, JosepPalacios Quiñonero, Francisco30 anys del Seminari de Teoria de Nombres de Barcelona, STNB 2016
http://hdl.handle.net/2117/101086
30 anys del Seminari de Teoria de Nombres de Barcelona, STNB 2016
Alsina Aubach, Montserrat
Wed, 15 Feb 2017 14:07:17 GMThttp://hdl.handle.net/2117/1010862017-02-15T14:07:17ZAlsina Aubach, MontserratEn record de Jacqueline (Jackie) Anne Stedall (1950-2014)
http://hdl.handle.net/2117/101066
En record de Jacqueline (Jackie) Anne Stedall (1950-2014)
Massa Esteve, Maria Rosa
Wed, 15 Feb 2017 10:55:05 GMThttp://hdl.handle.net/2117/1010662017-02-15T10:55:05ZMassa Esteve, Maria RosaPredictive control of irrigation canals - robust design and real-time implementation
http://hdl.handle.net/2117/101064
Predictive control of irrigation canals - robust design and real-time implementation
Aguilar, Jose V.; Langarita, Pedro; Rodellar Benedé, José; Linares, Lorenzo; Horvath, Klaudia
Predictive control is one of the most commonly used control methods in a variety of application areas, including hydraulic processes such as water distribution canals for irrigation. This article presents the design and application of predictive control for the water discharge entering into an irrigation canal located in Spain. First, a discrete time linear model of the process is described and its parameters are experimentally identified. The model is well validated within the usual canal operating range and is used to formulate a predictive control law with an incremental formulation. Finally, experimental and simulation results are presented in which predictive control has shown better performance than a well-tuned proportional, integral and derivative controller to automatically manage demanded water discharges.
Wed, 15 Feb 2017 10:32:46 GMThttp://hdl.handle.net/2117/1010642017-02-15T10:32:46ZAguilar, Jose V.Langarita, PedroRodellar Benedé, JoséLinares, LorenzoHorvath, KlaudiaPredictive control is one of the most commonly used control methods in a variety of application areas, including hydraulic processes such as water distribution canals for irrigation. This article presents the design and application of predictive control for the water discharge entering into an irrigation canal located in Spain. First, a discrete time linear model of the process is described and its parameters are experimentally identified. The model is well validated within the usual canal operating range and is used to formulate a predictive control law with an incremental formulation. Finally, experimental and simulation results are presented in which predictive control has shown better performance than a well-tuned proportional, integral and derivative controller to automatically manage demanded water discharges.Warp evidence in precessing galactic bar models
http://hdl.handle.net/2117/101062
Warp evidence in precessing galactic bar models
Sanchez Martin, P; Romero Gómez, Mercè; Masdemont Soler, Josep
Most galaxies have a warped shape when they are seen edge-on. The reason for this curious form is not completely known so far, so in this work we apply dynamical system tools to contribute to its explanation. Starting from a simple, but realistic model formed by a bar and a disc, we study the effect of a small misalignment between the angular momentum of the system and its angular velocity. To this end, a precession model was developed and considered, assuming that the bar behaves like a rigid body. After checking that the periodic orbits inside the bar continue to be the skeleton of the inner system even after inflicting a precession to the potential, we computed the invariant manifolds of the unstable periodic orbits departing from the equilibrium points at the ends of the bar to find evidence of their warped shapes. As is well known, the invariant manifolds associated with these periodic orbits drive the arms and rings of barred galaxies and constitute the skeleton of these building blocks. Looking at them from a side-on viewpoint, we find that these manifolds present warped shapes like those recognised in observations. Lastly, test particle simulations have been performed to determine how the stars are affected by the applied precession, this way confirming the theoretical results.
Wed, 15 Feb 2017 10:12:26 GMThttp://hdl.handle.net/2117/1010622017-02-15T10:12:26ZSanchez Martin, PRomero Gómez, MercèMasdemont Soler, JosepMost galaxies have a warped shape when they are seen edge-on. The reason for this curious form is not completely known so far, so in this work we apply dynamical system tools to contribute to its explanation. Starting from a simple, but realistic model formed by a bar and a disc, we study the effect of a small misalignment between the angular momentum of the system and its angular velocity. To this end, a precession model was developed and considered, assuming that the bar behaves like a rigid body. After checking that the periodic orbits inside the bar continue to be the skeleton of the inner system even after inflicting a precession to the potential, we computed the invariant manifolds of the unstable periodic orbits departing from the equilibrium points at the ends of the bar to find evidence of their warped shapes. As is well known, the invariant manifolds associated with these periodic orbits drive the arms and rings of barred galaxies and constitute the skeleton of these building blocks. Looking at them from a side-on viewpoint, we find that these manifolds present warped shapes like those recognised in observations. Lastly, test particle simulations have been performed to determine how the stars are affected by the applied precession, this way confirming the theoretical results.Segmentation-based skinning
http://hdl.handle.net/2117/101060
Segmentation-based skinning
Susín Sánchez, Antonio; Ramírez Flores, Jorge Eduardo
Skeleton-driven animation is popular by its simplicity and intuitive control of the limbs of a character. Linear blend skinning (LBS) is up to date the most efficient and simple deformation method; however, painting influence skinning weights is not intuitive, and it suffers the candy-wrapper artifact. In this paper, we propose an approach based on mesh segmentation for skinning and skeleton-driven computer animation. We propose a novel and fast method, based in watershed segmentation to deal with characters in T-Pose and arbitrary poses, a simple weight assign algorithm based in the rigid skinning obtained with the segmentation algorithm for the LBS deformation method, and finally, a modified version of the LBS that avoids the loss of volume in twist rotations using the segmentation stage output values.
Wed, 15 Feb 2017 09:51:43 GMThttp://hdl.handle.net/2117/1010602017-02-15T09:51:43ZSusín Sánchez, AntonioRamírez Flores, Jorge EduardoSkeleton-driven animation is popular by its simplicity and intuitive control of the limbs of a character. Linear blend skinning (LBS) is up to date the most efficient and simple deformation method; however, painting influence skinning weights is not intuitive, and it suffers the candy-wrapper artifact. In this paper, we propose an approach based on mesh segmentation for skinning and skeleton-driven computer animation. We propose a novel and fast method, based in watershed segmentation to deal with characters in T-Pose and arbitrary poses, a simple weight assign algorithm based in the rigid skinning obtained with the segmentation algorithm for the LBS deformation method, and finally, a modified version of the LBS that avoids the loss of volume in twist rotations using the segmentation stage output values.Quasi-periodically driven quantum systems
http://hdl.handle.net/2117/101055
Quasi-periodically driven quantum systems
Verdeny, Albert; Puig Sadurní, Joaquim; Mintert, Florian
Floquet theory provides rigorous foundations for the theory of periodically driven quantum systems. In the case of non-periodic driving, however, the situation is not so well understood. Here, we provide a critical review of the theoretical framework developed for quasi-periodically driven quantum systems. Although the theoretical footing is still under development, we argue that quasi-periodically driven quantum systems can be treated with generalisations of Floquet theory in suitable parameter regimes. Moreover, we provide a generalisation of the Floquet-Magnus expansion and argue that quasi-periodic driving offers a promising route for quantum simulations.
Wed, 15 Feb 2017 09:18:28 GMThttp://hdl.handle.net/2117/1010552017-02-15T09:18:28ZVerdeny, AlbertPuig Sadurní, JoaquimMintert, FlorianFloquet theory provides rigorous foundations for the theory of periodically driven quantum systems. In the case of non-periodic driving, however, the situation is not so well understood. Here, we provide a critical review of the theoretical framework developed for quasi-periodically driven quantum systems. Although the theoretical footing is still under development, we argue that quasi-periodically driven quantum systems can be treated with generalisations of Floquet theory in suitable parameter regimes. Moreover, we provide a generalisation of the Floquet-Magnus expansion and argue that quasi-periodic driving offers a promising route for quantum simulations.Determining plane curve singularities from its polars
http://hdl.handle.net/2117/101047
Determining plane curve singularities from its polars
González Alonso, Víctor; Alberich Carramiñana, Maria
This paper addresses a very classical topic that goes back at least to Plücker: how to understand a plane curve singularity using its polar curves. Here, we explicitly construct the singular points of a plane curve singularity directly from the weighted cluster of base points of its polars. In particular, we determine the equisingularity class (or topological equivalence class) of a germ of plane curve from the equisingularity class of generic polars and combinatorial data about the non-singular points shared by them.
Wed, 15 Feb 2017 07:52:09 GMThttp://hdl.handle.net/2117/1010472017-02-15T07:52:09ZGonzález Alonso, VíctorAlberich Carramiñana, MariaThis paper addresses a very classical topic that goes back at least to Plücker: how to understand a plane curve singularity using its polar curves. Here, we explicitly construct the singular points of a plane curve singularity directly from the weighted cluster of base points of its polars. In particular, we determine the equisingularity class (or topological equivalence class) of a germ of plane curve from the equisingularity class of generic polars and combinatorial data about the non-singular points shared by them.Real-time lattice boltzmann shallow waters method for breaking wave simulations
http://hdl.handle.net/2117/101044
Real-time lattice boltzmann shallow waters method for breaking wave simulations
Ojeda Contreras, Jesús; Susín Sánchez, Antonio
We present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.
Wed, 15 Feb 2017 07:09:56 GMThttp://hdl.handle.net/2117/1010442017-02-15T07:09:56ZOjeda Contreras, JesúsSusín Sánchez, AntonioWe present a new approach for the simulation of surfacebased fluids based in a hybrid formulation of Lattice Boltzmann Method for Shallow Waters and particle systems. The modified LBM can handle arbitrary underlying terrain conditions and arbitrary fluid depth. It also introduces a novel method for tracking dry-wet regions and moving boundaries. Dynamic rigid bodies are also included in our simulations using a two-way coupling. Certain features of the simulation that the LBM can not handle because of its heightfield nature, as breaking waves, are detected and automatically turned into splash particles. Here we use a ballistic particle system, but our hybrid method can handle more complex systems as SPH. Both the LBM and particle systems are implemented in CUDA, although dynamic rigid bodies are simulated in CPU. We show the effectiveness of our method with various examples which achieve real-time on consumer-level hardware.