Mejora en Imágenes Acústicas Utilizando Rango Dinámico Alto (RDA)

Las imágenes acústicas se obtienen mediante algoritmos de pos proceso. Estos utilizan los datos adquiridos a través de una distribución de sensores de presión o arreglo de micrófonos. Este arreglo, limita el rango dinámico de la imagen acústica. Por lo tanto, si existen fuentes de ruido con diferencia de nivel de presión sonora mayor al rango dinámico del arreglo no se podrán distinguir ya que los lóbulos laterales de la fuente principal cubrirán las fuentes sonoras menores. Esto puede solucionarse aumentando el número de micrófonos y así aumentar el rango dinámico pero se incrementaría el costo del hardware. Otra forma de solucionar este problema es mediante el pos proceso adecuado de los datos. Por lo tanto, debido al aumento en la capacidad de cálculo computacional es conveniente utilizar algoritmos que logren este cometido como lo es el Rango Dinámico Alto (RDA). La idea básica del método es extraer del mapa de ruido la máxima fuente sonora incluyendo sus lóbulos laterales y colocarlo en un mapa “limpio”, luego con las señales sin la fuente principal se vuelve a reconstruir el mapa de ruido y nuevamente se extrae la segunda fuente dominante con sus lóbulos laterales. De esta manera se puede aplicar sucesivamente el método hasta extraer la cantidad de fuentes seleccionadas. Esto permite obtener un mapa de ruido con baja influencia de fuentes fantasmas y aumentar el rango dinámico de la imagen acústica. En este trabajo se presenta un sistema de formación de imágenes acústicas optimizado. En primer lugar se optimizó una distribución de micrófonos para mejorar el rango dinámico de la imagen acústica. Y en segundo lugar, se presenta el algoritmo RDA que permite aumentar más aún la escala de medición de la imagen acústica basado en las técnicas de retardo y suma convencional en el dominio del tiempo.Fil: O'brien, Ronald Julián. Universidad Nacional de Río Cuarto; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Molisani Yolitti, Leonardo. Universidad Nacional de Río Cuarto; ArgentinaFil: Burdisso, Ricardo. Virginia Tech University; Estados Unido

A new look into credit procyclicality: International panel evidence

The goal of this paper is to provide up-to-date worldwide evidence on the short-term relationship between credit changes and output changes. Standard correlation methods, stateof-the-art panel Granger causality tests, and panel regressions were applied on a maximum sample of 144 countries over the period 1990-2007. Our results openly clash with two popular economic statements, namely, that credit is procyclical and that changes in credit have strong effects on private expenditure. According to the evidence produced, credit procyclicality -in the sense that the simple correlation coefficient is positive and significant at 10% or less- prevails in just 45% of the countries when annual data are used (23% with quarterly data). As for time precedence, our work suggests that, for the full sample, Granger causality runs from GDP to credit, while the often claimed causality from credit to GDP is a feature observable much less frequently - this behavior is observed only in financially developed countries. Results are robust to random resampling. Furthermore, after considering the potential presence of endogeneity, we contend that our results uncover not just mere Granger causality but economic causality. All in all, these findings have vast academic and policy implications

Analysis and Synthesis of Tonal Aircraft Noise Sources

Fixed and rotary wing aircraft operations can have a significant impact on communities in proximity to airports. Simulation of predicted aircraft flyover noise, paired with listening tests, is useful to noise reduction efforts since it allows direct annoyance evaluation of aircraft or operations currently in the design phase. This paper describes efforts to improve the realism of synthesized source noise by including short term fluctuations, specifically for inlet-radiated tones resulting from the fan stage of turbomachinery. It details analysis performed on an existing set of recorded turbofan data to isolate inlet-radiated tonal fan noise, then extract and model short term tonal fluctuations using the analytic signal. Methodologies for synthesizing time-variant tonal and broadband turbofan noise sources using measured fluctuations are also described. Finally, subjective listening test results are discussed which indicate that time-variant synthesized source noise is perceived to be very similar to recordings

Acoustic Measurements of a Large Civil Transport Main Landing Gear Model

Microphone phased array acoustic measurements of a 26 percent-scale, Boeing 777-200 main landing gear model with and without noise reduction fairings installed were obtained in the anechoic configuration of the Virginia Tech Stability Tunnel. Data were acquired at Mach numbers of 0.12, 0.15, and 0.17 with the latter speed used as the nominal test condition. The fully and partially dressed gear with the truck angle set at 13 degrees toe-up landing configuration were the two most extensively tested configurations, serving as the baselines for comparison purposes. Acoustic measurements were also acquired for the same two baseline configurations with the truck angle set at 0 degrees. In addition, a previously tested noise reducing, toboggan-shaped fairing was re-evaluated extensively to address some of the lingering questions regarding the extent of acoustic benefit achievable with this device. The integrated spectra generated from the acoustic source maps reconfirm, in general terms, the previously reported noise reduction performance of the toboggan fairing as installed on an isolated gear. With the recent improvements to the Virginia Tech tunnel acoustic quality and microphone array capabilities, the present measurements provide an additional, higher quality database to the acoustic information available for this gear model

Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz

Active control of aircraft engine inlet noise using compact sound sources and distributed error sensors

An active noise control system using a compact sound source is effective to reduce aircraft engine duct noise. The fan noise from a turbofan engine is controlled using an adaptive filtered-x LMS algorithm. Single multi channel control systems are used to control the fan blade passage frequency (BPF) tone and the BPF tone and the first harmonic of the BPF tone for a plane wave excitation. A multi channel control system is used to control any spinning mode. The multi channel control system to control both fan tones and a high pressure compressor BPF tone simultaneously. In order to make active control of turbofan inlet noise a viable technology, a compact sound source is employed to generate the control field. This control field sound source consists of an array of identical thin, cylindrically curved panels with an inner radius of curvature corresponding to that of the engine inlet. These panels are flush mounted inside the inlet duct and sealed on all edges to prevent leakage around the panel and to minimize the aerodynamic losses created by the addition of the panels. Each panel is driven by one or more piezoelectric force transducers mounted on the surface of the panel. The response of the panel to excitation is maximized when it is driven at its resonance; therefore, the panel is designed such that its fundamental frequency is near the tone to be canceled, typically 2000-4000 Hz

Credit vs. payment services: financial development and economic activity revisited

The purpose of this paper is to assess whether the banking system, over and beyond its credit function, has a significant impact on per capita GDP by providing means of payment. An annual database of 85 countries spanning the 1980-2008 period is exploited to this end. On the descriptive front, we find that richer economies exhibit higher and increasing levels of demand deposits and lower levels of currency than poor countries. While this was to be expected, more surprising is the fact that the currency to GDP ratio did not decrease much over time, regardless of income level differences. In turn, our regressions confidently support the hypothesis that banks contribute to economic development not only as credit suppliers but also by facilitating transactions. Specifically, along with the ratio of private credit to GDP, the ratio of demand deposits to currency seems to exert a positive influence on per capita GDP. The results are robust for different model specifications. These findings have valuable implications for a better understanding of the channels through which the banking system affects the economy.Departamento de Economí

Credit vs. payment services: financial development and economic activity revisited

The purpose of this paper is to assess whether the banking system, over and beyond its credit function, has a significant impact on per capita GDP by providing means of payment. An annual database of 85 countries spanning the 1980-2008 period is exploited to this end. On the descriptive front, we find that richer economies exhibit higher and increasing levels of demand deposits and lower levels of currency than poor countries. While this was to be expected, more surprising is the fact that the currency to GDP ratio did not decrease much over time, regardless of income level differences. In turn, our regressions confidently support the hypothesis that banks contribute to economic development not only as credit suppliers but also by facilitating transactions. Specifically, along with the ratio of private credit to GDP, the ratio of demand deposits to currency seems to exert a positive influence on per capita GDP. The results are robust for different model specifications. These findings have valuable implications for a better understanding of the channels through which the banking system affects the economy.Departamento de Economí

Técnicas avanzadas para la detección de fuentes sonoras

En la actualidad existen diferentes tipos de técnicas para cuantificar y detectar la posición de una fuente sonora. Las técnicas modernas más utilizadas son las imágenes acústicas, éstas se obtienen mediante el proceso de datos adquiridos por un arreglo de micrófonos localizado a una distancia relativa del aparato emisor de ruido. En cuanto a los tipos de post procesos, “Beamforming” (BF) es uno de los más utilizados pero desafortunadamente presenta poca capacidad de distinguir la localización de dos fuentes de ruido emitiendo a baja frecuencia. Para superar esta desventaja, en este esfuerzo se investigaron diferentes técnicas. En primera instancia, se implementó “Robust Adaptive Beamforming” (RABF), en el cual se utiliza la información recolectada mediante los micrófonos para eliminar ruido blanco en la imagen acústica y evitar fuentes espurias en el mapa de ruido. Luego, se utiliza un método de alta resolución como es el caso de “MUltiple SIgnal Clasification” (MUSIC). En este método como desventaja, se puede señalar, que falla con señales altamente correlacionadas y cuando la relación señal - ruido es baja. Estas técnicas se utilizan en el dominio de la frecuencia. Por último, se utilizó “Delay and Sum” (DS), el cual en comparación con los métodos anteriores, se realiza en el dominio del tiempo, lo que permite tener mayor resolución temporal de los mapas de ruido. Se presenta como desventaja, que para señales con bajo contenido señal-ruido (SNR) la reconstrucción del mapa de ruido no permite ubicar con exactitud las fuentes de ruido. Para superar este inconveniente, el método se utiliza en el dominio de la frecuencia. En este trabajo se proponer utilizar la transformada Cepstrum para mejorar la formación del mapa de ruido. Esta nueva técnica de “Delay and Sum – Cepstrum” permitirá eliminar ecos de la señal y detectar periodicidad en el espectro para mejorar la relación SNR y así optimizar los mapas de ruidos para ser utilizados en aplicaciones tecnológicas.Fil: O'brien, Ronald Julián. Universidad Nacional de Rio Cuarto. Facultad de Ingeniería. Departamento de Mecanica. Grupo de Acustica y Vibraciones; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Molisani Yolitti, Leonardo. Universidad Nacional de Rio Cuarto. Facultad de Ingeniería. Departamento de Mecanica. Grupo de Acustica y Vibraciones; ArgentinaFil: Burdisso, Ricardo. Virginia Tech University; Estados Unido

Credit vs. payment services: financial development and economic activity revisited

The purpose of this paper is to assess whether the banking system, over and beyond its credit function, has a significant impact on per capita GDP by providing means of payment. An annual database of 85 countries spanning the 1980-2008 period is exploited to this end. On the descriptive front, we find that richer economies exhibit higher and increasing levels of demand deposits and lower levels of currency than poor countries. While this was to be expected, more surprising is the fact that the currency to GDP ratio did not decrease much over time, regardless of income level differences. In turn, our regressions confidently support the hypothesis that banks contribute to economic development not only as credit suppliers but also by facilitating transactions. Specifically, along with the ratio of private credit to GDP, the ratio of demand deposits to currency seems to exert a positive influence on per capita GDP. The results are robust for different model specifications. These findings have valuable implications for a better understanding of the channels through which the banking system affects the economy.Departamento de Economí