Realidad Virtual Acústica: El Abordaje de las Redes Neuronales Artificiales

This work presents a new approach to obtain the Binaural Impulse Responses (BIRs) for an auralization system by using a committee of artificial neuronal networks (ANNs). The proposed method is capable to reconstruct the desired modified Head Related Impulse Responses (HRIRs) by means of spectral modification and spatial interpolation. In order to cover the entire auditory reception space, without increasing the network’s architecture complexity, a structure with multiple RNAs (committee) was adopted, where each network operates in la specific reception region (bud). The modeling error, in the frequency domain, is investigated considering the logarithmic nature of the human hearing. It was observed that the proposed methodology obtained a computational gain of approximately 62%, in terms of processing time reduction, compared to the classical signal processing method used to obtain auralizations.The applicability of the new method in auralization systems is validated by comparative analysis of the results, which includes the BIR’s generation and calculation of one binaural acoustic parameter (IACF), showing very low magnitude errors. En este trabajo se presenta un nuevo abordaje para obtener las respuestas impulsivas biauriculares (BIRs) para un sistema de aurilización utilizando un conjunto de redes neuronales artificiales (RNAs). El método propuesto es capaz de reconstruir las respuestas impulsivas asociadas a la cabeza humana (HRIRs) por medio de modificación espectral y de interpolación espacial. Para poder cubrir todo el espacio auditivo de recepción, sin aumentar la complejidad de la arquitectura de la red, una estructura con varias RNAs (conjunto) fue adoptada, donde cada red opera en una región específica del espacio (gomo). El error de modelaje en el dominio de la frecuencia es investigado considerando la naturaleza logarítmica de la audición humana. A través de la metodología propuesta se obtuvo un ahorro del tiempo de procesamiento computacional de aproximadamente 62% en relación al método tradicional de procesamiento de señales utilizado para aurilización. La aplicabilidad del nuevo método en sistemas de aurilización es reforzada mediante un análisis comparativo de los resultados, que incluyen la generación de las BIRs y el cálculo de un parámetro acústico biauricular (IACF), los cuales muestran errores con magnitudes reducidas

Comportamento termoelástico transiente em meios seccionalmente homegêneos

The temperature transiente after the coupling of a pre-heated hollow cylinder with a solid one of different material is determined. The principal stresses field is then obtained suposing a quasi-static process anda linear thermoelastic behaviar of the materials. One case of pre-heating leading to a non-uniform initial temperature field was compared with the uniform one with respect to shrinkage efficiency and the possibility of yelding of the material during the cooling process.Determina-se o transiente de temperatura desenvolvido após o acoplamento de um cilindro circular oco, previamente aquecido, com outro maciço, de material diferente. Obtém-se em seguida o campo de tensões principais supondo um processo quase estático e um comportamento termoelástico linear dos materiais. Um caso de pré-aquecimento levando a uma condição inicial de temperatura não uniforme foi comparado com o caso uniforme quanto à possibilidade de ocorrência de plastificação durante o resfriamento e quanto a tensão residual de fretagem

3D Sound applied to the design of Assisted Navigation Devices for the Visually Impaired

This work presents an approach to generate 3D sound by using a set of artificial neural networks (ANNs). The proposed method is capable to reconstruct the Head Related Impulse Responses (HRIRs) by means of spatial interpolation. In order to cover the whole reception auditory space, without increasing the network complexity, a structure of multiple networks (set), each one modeling a specific area was adopted. The three main factors that influence the model accuracy --- the network's architecture, the reception area's aperture angles and the HRIR's time shifts --- are investigated and an optimal setup is presented. The computational effort to process the ANN is shown to be slightly smaller than traditional interpolation methods and all error calculation reached very low levels, validating the method to be used in the design of a 3D sound emitter capable of provide navigation aid for the visually impaired. Two approaches are presented in order to detect obstacles, one which makes use of computational vision techniques and other with laser proximity sensors. Este trabajo presenta un abordaje para generar sonido 3D utilizando un conjunto de redes neuronales artificiales (RNAs). El método propuesto es capaz de reconstruir la Respuestas Impulsivas Asociadas a Cabeza Humana (HRIRs) mediante interpolación espacial. Con el fin de cubrir todo el espacio de recepción auditivo, sin aumentar la complejidad de la red, fue adoptada una estructura de múltiples redes (conjunto), cada una modelando un área específica. Los tres factores principales que influyen en la exactitud del modelo --- la arquitectura de la red, ángulos de apertura de la zona de recepción y los cambios de tiempo del HRIR --- son investigados y es presentada una configuración óptima. El esfuerzo computacional necesario para procesar la RNA muestra ser menor que métodos tradicionales de interpolación y todos los cálculos de error alcanzan niveles muy bajos, validando el método para ser utilizado en el diseño de un emisor de sonido 3D capaz de proporcionar asistencia en la navegación de discapacitados visuales. Dos enfoques se presentan con el fin de detectar obstáculos, uno que hace uso de técnicas de visión computacional y otro con sensores de proximidad de láser.&nbsp

Dimensionality reduction by minimizing nearest-neighbor classification error

There is a great interest in dimensionality reduction techniques for tackling the problem of high-dimensional pattern classification. This paper addresses the topic of supervised learning of a linear dimension reduction mapping suitable for classification problems. The proposed optimization procedure is based on minimizing an estimation of the nearest neighbor classifier error probability, and it learns a linear projection and a small set of prototypes that support the class boundaries. The learned classifier has the property of being very computationally efficient, making the classification much faster than state-of-the-art classifiers, such as SVMs, while having competitive recognition accuracy. The approach has been assessed through a series of experiments, showing a uniformly good behavior, and competitive compared with some recently proposed supervised dimensionality reduction techniques. © 2010 Elsevier B.V. All rights reserved.Work partially supported by the Spanish projects TIN2008-04571 and Consolider Ingenio 2010: MIPRCV (CSD2007-00018).Villegas, M.; Paredes Palacios, R. (2011). Dimensionality reduction by minimizing nearest-neighbor classification error. Pattern Recognition Letters. 32(4):633-639. https://doi.org/10.1016/j.patrec.2010.12.002S63363932

Masses, radii, and orbits of small Kepler planets : The transition from gaseous to rocky planets

We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O).Peer reviewedFinal Accepted Versio

Masses, radii, and orbits of small Kepler planets: the transition from gaseous to rocky planets

We report on the masses, sizes, and orbits of the planets orbiting 22 Kepler stars. There are 49 planet candidates around these stars, including 42 detected through transits and 7 revealed by precise Doppler measurements of the host stars. Based on an analysis of the Kepler brightness measurements, along with high-resolution imaging and spectroscopy, Doppler spectroscopy, and (for 11 stars) asteroseismology, we establish low false-positive probabilities (FPPs) for all of the transiting planets (41 of 42 have an FPP under 1%), and we constrain their sizes and masses. Most of the transiting planets are smaller than three times the size of Earth. For 16 planets, the Doppler signal was securely detected, providing a direct measurement of the planet's mass. For the other 26 planets we provide either marginal mass measurements or upper limits to their masses and densities; in many cases we can rule out a rocky composition. We identify six planets with densities above 5 g cm-3, suggesting a mostly rocky interior for them. Indeed, the only planets that are compatible with a purely rocky composition are smaller than 2 R ⊕. Larger planets evidently contain a larger fraction of low-density material (H, He, and H2O)

Carta de 1984-02-28 a José Ferrater Mora des de San Juan (Puerto Rico) (Puerto Rico)

Agraeix la carta de Ferrater en que li manifestava com estava complagut pel bon tracte rebu

Carta de 1983-10-28 a José Ferrater Mora des de San Juan (Puerto Rico) (Puerto Rico)

Detalls del desplaçament per al simpos

A new technique to identify arbitrarily shaped noise sources

Abstract. Acoustic intensity is one of the available tools for evaluating sound radiation from vibrating bodies. Active intensity may, in some situations, not give a faithful insight about how much energy is in fact carried into the far field. It was then proposed a new parameter, the supersonic acoustic intensity, which takes into account only the intensity generated by components having a smaller wavenumber than the acoustic one. However, the method is only efective for simple sources, such as plane plates, cylinders and spheres. This work presents a new technique, based on the Boundary Elements Method and the Singular Value Decomposition, to compute the supersonic acoustic intensity for arbitrarily shaped sources. The technique is based in the Kirchoff-Helmholtz equation in a discretized approach, leading to a radiation operator that relates the normal velocity on the source's surface mesh with the pressure at grid points located in the field. Then, the singular value decomposition technique is set to the radiation operator and a cutoff criterion is applied to remove non propagating components. Some numerical examples are presented