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Resultats de la cerca223 resultats

  • Visual Representation Of Enhanced Sand Pile Models

    Pla Castells, M.; García Fernández, I.; Martínez Durá, R. J.

    (2003). Article

    Proceedings of the Industrial Simulation Conference 2003, 141-146 This paper overviews some models based on the Chip Firing Game and propose a modification of the Abelian Sand Pile Model in a lattice in order to implement a realistic simulation of a pile of sand falling and finding an stable configuration. We have modified the update rule in the way that now is based on the comparision among neighbour nodes. We found that the simulations can be suitable for doing them in real time and propose as a future work a better solution to reduce the computational cost of the algorithms.

  • New Models for Fast Contact Force Computation

    García Fernández, I.; Pla Castells, M.; martínez Durá, R. J.

    (2003). Article

    Proceedings of the Industrial Simulation Conference 2003, 401-407 This work focuses on the subject of impact response modeling in Real Time rigid body simulation, and more precisely in those applications where a very high accuracy in the solution is not required. The problem of impact response has several aspects to overcome, such as the instantaneous nature of the forces that appear during the contact, the absence of a unique solution in the case of contacts with friction, of the stiffness of the resultant models. This makes the impact management to be one of the most problematic parts to resolve during the implementation of computational models for rigid body systems. We present a model...

    Proceedings of the Industrial Simulation Conference 2003, 401-407 This work focuses on the subject of impact response modeling in Real Time rigid body simulation, and more precisely in those applications where a very high accuracy in the solution is not required. The problem of impact response has several aspects to overcome, such as the instantaneous nature of the forces that appear during the contact, the absence of a unique solution in the case of contacts with friction, of the stiffness of the resultant models. This makes the impact management to be one of the most problematic parts to resolve during the implementation of computational models for rigid body systems. We present a model for contacts that is much simpler than the usual methods and that achieves an accuracy of the same order than the integration step size respect to the usual method. The model is valid both for frictional and non-frictional contacts.

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  • Nested trellis codes and shaping for the transmitter side information problem

    Beferull-Lozano, B.; Diggavi, S.

    (2003). Article

    In this paper, we specifically focus on the problem of power shaping and we examine nested constructions based on trellis codes, which build on simple low dimensional lattices. We propose the idea of performing shaping through a coarse lattice (source code) and we also show how this method can actually be combined with shaping through a fine lattice (channel code) so that a joint shaping can be performed by the fine and coarse lattices in the communication channel with transmitter side-information simultaneously.

  • Efficient Quantization for Overcomplete Expansions in R^n

    Beferull-Lozano, B.; Ortega, A.

    (2003). Article

    We study construction of structured regular quantizers for overcomplete expansions in RN. Our goal is to design structured quantizers which allow simple reconstruction algorithms with low complexity and which have good performance in terms of accuracy. Most related work to date in quantized redundant expansions has assumed that the same uniform scalar quantizer was used on all the expansion coefficients. Several approaches have been proposed to improve the reconstruction accuracy, with some of these methods having significant complexity. Instead, we consider the joint design of the overcomplete expansion and the scalar quantizers (allowing different step sizes) in such a way as to produce...

    We study construction of structured regular quantizers for overcomplete expansions in RN. Our goal is to design structured quantizers which allow simple reconstruction algorithms with low complexity and which have good performance in terms of accuracy. Most related work to date in quantized redundant expansions has assumed that the same uniform scalar quantizer was used on all the expansion coefficients. Several approaches have been proposed to improve the reconstruction accuracy, with some of these methods having significant complexity. Instead, we consider the joint design of the overcomplete expansion and the scalar quantizers (allowing different step sizes) in such a way as to produce an equivalent vector quantizer (EVQ) with periodic structure. The construction of a periodic quantizer is based on lattices in RN and the concept of geometrically scaled- similar sublattices. The periodicity makes it possible to achieve good accuracy using simple reconstruction algorithms (e.g., linear reconstruction or a small lookup table).

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  • Quantizing using lattice intersections, Discrete and Computational Geometry

    Sloane, N. J. A.; Beferull-Lozano, B.

    (2003). Article

    The usual quantizer based on an n-dimensional lattice # maps a point x # R n to a closest lattice point. Suppose # is the intersection of lattices # 1 , . . . , # r . Then one may instead combine the information obtained by simultaneously quantizing x with respect to each of the # i . This corresponds to decomposing R n into a honeycomb of cells which are the intersections of the Voronoi cells for the # i , and identifying the cell to which x belongs. This paper shows how to write several standard lattices (the face-centered and body-centered cubic lattices, the root lattices D 4 , E # 6 , E 8 , the Coxeter-Todd, Barnes-Wall and Leech lattices, etc.) in a canonical way as intersections of a...

    The usual quantizer based on an n-dimensional lattice # maps a point x # R n to a closest lattice point. Suppose # is the intersection of lattices # 1 , . . . , # r . Then one may instead combine the information obtained by simultaneously quantizing x with respect to each of the # i . This corresponds to decomposing R n into a honeycomb of cells which are the intersections of the Voronoi cells for the # i , and identifying the cell to which x belongs. This paper shows how to write several standard lattices (the face-centered and body-centered cubic lattices, the root lattices D 4 , E # 6 , E 8 , the Coxeter-Todd, Barnes-Wall and Leech lattices, etc.) in a canonical way as intersections of a small number of simpler, decomposable, lattices. The cells of the honeycombs are given explicitly and the mean squared quantizing error calculated in the cases when the intersection lattice is the face-centered or body-centered cubic lattice or the lattice D 4 . 1.

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  • Diseño Interactivo de Escenarios para Simulación de Conducción

    Coma, Inmaculada;Rueda, Silvia; Sánchez, Mar; Fernández, Marcos

    (2002). Article

    Revista de Enseñanza y Tecnología.

    El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows. El diseño de escenarios para simulación de conducción es una tarea compleja ya que...

    El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows. El diseño de escenarios para simulación de conducción es una tarea compleja ya que requiere, por una parte el diseño del escenario tridimensional, y por otra el diseño de las situaciones dinámicas de conducción. Habitualmente estos escenarios se diseñan utilizando herramientas de modelado de propósito general, y mediante un lenguaje de programación o un lenguaje script para el diseño de las situaciones dinámicas. En el presente trabajo se presenta una herramienta que permite tanto el diseño de la escena como las situaciones dinámicas mediante un interfaz. Esta herramienta funciona sobre plataforma Windows.

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  • Robust phoneme discrimination using acoustic waveforms

    Cvetkovic, Z.; Beferull-Lozano, B.; Buja, A.

    (2002). Article

    We present a study of separability of acoustic waveforms of speech at phoneme level. The analyzed data consist of 64 ms segments of acoustic waveforms of individual phonemes from TIMIT data base, sampled at 16 kHz. For each phoneme, by means of principal component analysis, we identify subspaces which contain a given proportion of the total energy of the available waveforms in the time-domain, and also in the spectral-magnitude domain. In order to assess the separation between phonemes in the two domains, we perform pairwise classification of phonemes on clean data and on data immersed in white additive Gaussian noise up to 0 dB signal to noise ratio. While the classification based on...

    We present a study of separability of acoustic waveforms of speech at phoneme level. The analyzed data consist of 64 ms segments of acoustic waveforms of individual phonemes from TIMIT data base, sampled at 16 kHz. For each phoneme, by means of principal component analysis, we identify subspaces which contain a given proportion of the total energy of the available waveforms in the time-domain, and also in the spectral-magnitude domain. In order to assess the separation between phonemes in the two domains, we perform pairwise classification of phonemes on clean data and on data immersed in white additive Gaussian noise up to 0 dB signal to noise ratio. While the classification based on spectral magnitudes exhibits high sensitivity to additive noise, the time-domain classification proves to be very robust.

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  • DSC'2001:An integrated system for the whole design process of driving simulation experiments.

    Coma, Inmaculada; Fernández, Marcos; Pollock, Donna; Pareja, Ignacio; Rueda, Silvia

    (2001). Article

    Estructuras de datos para el diseño de ejercicios en simulación de conducción. The use of driving simulators in research provides researchers with a tool that combines the advantages of control in the presentation of driving scenarios, experimental situations, and critical events as well as precision in the measurement of driving performance. In addition, many risk factors that would be dangerous to reproduce in a real driving context, can be safely studied in a simulator.

  • A Discrete Model for the Dynamics of Sandpile Surfaces

    garcía Fernández, I.; Pla Castells, M.; Martínez Durá, R. J.

    (2001). Article

    Proceedings of the Industrial Simulation Conference 2007, 64-68 A new Cellular Automata model for the dynamics of sandpile surfaces is presented in this work. Following the BCRE model (Bouchaud et al., 1994) main ideas, we propose the use of two variables, instead of only the one that has been used in Cellular Automata models so far. The model predicts sandpile properties observed in other models, and in real systems, such as slope roughness decay or uphill propagation of avalanches. In addition, the introduction of the second variable allows the prediction of characteristics, such as the appearance of a second critical angle, that have been predicted by continuous models. The main...

    Proceedings of the Industrial Simulation Conference 2007, 64-68 A new Cellular Automata model for the dynamics of sandpile surfaces is presented in this work. Following the BCRE model (Bouchaud et al., 1994) main ideas, we propose the use of two variables, instead of only the one that has been used in Cellular Automata models so far. The model predicts sandpile properties observed in other models, and in real systems, such as slope roughness decay or uphill propagation of avalanches. In addition, the introduction of the second variable allows the prediction of characteristics, such as the appearance of a second critical angle, that have been predicted by continuous models. The main advantage of the proposed model is that its formulation is simpler and easier to interpret than that of the continuous models. Also, the resulting numerical scheme is simpler and more efficient, allowing for a wider range of applications, including interactive simulation.

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  • Efficient Quantization for Overcomplete Expansions in

    Beferull-Lozano, B.; ortega, A.

    (2001). Article

    The use of quantized redundant expansions is useful in applications where the cost of having oversampling in the representation is much lower than the use of a high-resolution quantization (e.g., oversampled A/D). Most work to date has assumed that simple uniform quantization was used on the redundant expansion and then has dealt with methods to improve the reconstruction. Instead, we consider the design of quantizers for overcomplete expansions. Our goal is to design quantizers such that simple reconstruction algorithms (e.g., linear) provide as good reconstructions as with more complex algorithms. We achieve this goal by designing quantizers with different step sizes for each coefficient...

    The use of quantized redundant expansions is useful in applications where the cost of having oversampling in the representation is much lower than the use of a high-resolution quantization (e.g., oversampled A/D). Most work to date has assumed that simple uniform quantization was used on the redundant expansion and then has dealt with methods to improve the reconstruction. Instead, we consider the design of quantizers for overcomplete expansions. Our goal is to design quantizers such that simple reconstruction algorithms (e.g., linear) provide as good reconstructions as with more complex algorithms. We achieve this goal by designing quantizers with different step sizes for each coefficient of the expansion in such a way as to produce a quantizer with periodic structure.

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