Fourier Analysis

The Fourier phase spectrum plays a central role regarding where in an image contours occur, thereby defining the spatial relationship between those structures in the overall scene. Only a handful of studies have demonstrated
psychophysically the relevance of the Fourier phase spectrum with respect to human visual processing, and none have demonstrated the relative amount of local cross-scale spatial phase alignment needed to perceptually
extract meaningful structure from an image. We investigated the relative amount of spatial phase alignment needed for humans to perceptually match natural scene image structures at three different spatial frequencies [3, 6, and 12 cycles per degree (cpd)] as a function of the number of structures within the image (i.e., “structural sparseness”). The results showed that (1) the amount of spatial phase alignment needed to match structures depends on structural sparseness, with a bias for matching structures at 6 cpd and (2) the ability to match partially phase-randomized images at a given spatial frequency is independent of structural sparseness at other spatial frequencies. The findings of the current study are discussed in terms of a network of feature integrators in the human visual system.

Time-frequency distribution methods are being widely used for the analysis of a variety of biomedical signals. Recently, they have been applied also to study otoacoustic emissions (OAE's), the active acoustic response of the hearing end organ. Click-evoked otoacoustic emissions (CEOAE's) are time-varying signals with a clear frequency dispersion along with the time axis. Analysis of CEOAE's is of considerable interest due to their close relation with cochlear mechanisms. In this paper, several basic time-frequency distribution methods are considered and compared on the basis of both simulated signals and real CEOAE's. The particular structure of CEOAE's requires a method with both a satisfactory time and frequency resolution. Results from simulations and real CEOAE's revealed that the wavelet approach is highly suitable for the analysis of such signals. Some examples of the application of the wavelet transform to CEOAE's are provided here. Applications range from the extraction of normative data from adult and neonatal OAE's to the extraction of quantitative parameters for clinical purposes.

Este artículo esboza algunas claves para pensar los procesos que configuran el ordenamiento corporal en las ciudades capitalistas. Indaga la relación entre cuerpos, estructura urbana y estructura social en dos configuraciones socio-espaciales particulares: la Venecia Shakesperiana y el Falansterio de Charles Fourier.  Primero, se retoman fragmentos de El Mercader de Venecia, enfatizando los modos en que el extrañamiento y la distancia social repercuten en (y son subsidiarios de) la configuración de los espacios reservados a esos cuerpos extraños recluidos dentro de los muros del ghetto judío. Seguidamente, se discute el proyecto del Falansterio, orientado a la reconfiguración del vínculo social sobre la base del placer y los deseos reprimidos por el imperio de la razón industrial de comienzos del siglo XIX.

Simulation results on dynamic yaw stability derivatives of a gull bird by means of computational fluid dynamics are presented. Two different kinds of motions are used for determining the dynamic yaw stability derivatives CNr and CNbeta . Concerning the first one, simple lateral translation and yaw rotary motions in yaw are considered. The second one consists of combined motions. To determine dynamic yaw stability derivatives of the bird, the simulation of an unsteady flow with a bird model showing a harmonic motion is performed. The unsteady flow solution for each time step is obtained by solving unsteady Euler equations based on a finite volume approach for a smaller reduced frequency. Then, an evaluation of unsteady forces and moments for one cycle is conducted using harmonic Fourier analysis. The results on the dynamic yaw stability derivatives for both simulations of the model motion show a good agreement.

Abstract. In this article we will give a characterization of so-lutions for the equation ∂2 ∂t2 u + ∆xu − 2x · ∇xu = 0 which are Poisson-Hermite integral of Lp(γn)-functions, 1 ≤ p ≤ ∞, follow-ing the classical case of characterization of harmonic functions as Poisson ...

Water energy which is very good to be used as a source of electrical energy in underdeveloped areas has not been reached by electricity. The purpose of this research is to utilize water energy for the generation of electrical energy is to choose a four nozzle cross flow water turbine. The method used is to test a Cross Flow turbine with four nozzles as a micro-scale hydroelectric power generator. The results showed that a cross flow turbine with four nozzles is very good as a permanent magnet Direct Current generator that can work at a flow that is not too high. At a water discharge of 4.2x 10-3 m 3 /s and an outer diameter of 200 mm cross flow turbine with 24 blades, it can produce Cross Flow Turbine power with four nozzles is 3.251 Watt and generator power is 1.528 Watt.

Fourier analyses allow extracting parameters from the outline of tooth crowns, which can be used in multivariate analyses. However, the great complexity of some dental shapes forces to check for the intrinsic error produced in this procedure. The main goal of this paper is to apply and validate the Fourier analysis in the study of second lower molar (M2) crown shape of four Hominoidea species to explore the interspecific morphometric variability, as well as determine the intra- and interobserver error rates. The occlusal surfaces outlines were digitized, derived Fourier functions were calculated, and Discriminant Analyses and Mantel Tests (Pearson correlations) were performed in order to determine the error rates between measurements and interspecific tooth shape variability. Results show that Fourier analyses are able to discriminate variability of molar shapes within Hominoidea primate species. In addition, the high correlation found, both intra- (r>0.9) and inter-observers (r>0.7) suggest that tooth morphometric description by Fourier methods from different observers can be pooled for joint analyses.

Keywords: Hominoidea, tooth, shape, elliptic Fourier analysis.

Resumen
Los análisis de Fourier permiten caracterizar el contorno del diente y obtener una serie de parámetros para un posterior análisis multivariante. Sin embargo, la gran complejidad que presentan algunas formas obliga a determinar el error de medición intrínseco que se produce. El objetivo de este trabajo es aplicar y validar los análisis de Fourier en el estudio de la forma dental del segundo molar inferior (M2) de cuatro especies de primates Hominoidea para explorar la variabilidad morfométrica interespecífica, así como determinar el error de medición a un nivel intra- e interobservador. El contorno de la superficie oclusal del diente fue definido digitalmente y con las funciones derivadas del análisis de Fourier se realizaron Análisis Discriminantes y Test de Mantel (correlaciones de Pearson) para determinar las diferencias de forma a partir de las mediciones tomadas. Los resultados indican que el análisis de Fourier muestra la variabilidad de forma en dientes molares en especies de primates Hominoidea. Adicionalmente, los altos niveles de correlación a nivel intra- (r>0,9) como inter-observador (r>0,7) sugieren que la descripción morfométrica del diente a partir de métodos de Fourier realizados por diferentes observadores puede ser agrupada para posteriores análisis.

Palabras clave: Hominoidea, diente, forma, análisis elíptico de Fourier.