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Search Results: 1 - 10 of 195221 matches for " Dario G. Perez "
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The fractional Brownian motion property of the turbulent refractive index and the Fermat's Extremal Principle
Dario G Perez
Physics , 2002,
Abstract: We introduce fractional Brownian motion processes (fBm) as an alternative model for the turbulent index of refraction. These processes allow to reconstruct most of the index properties, but they are not differentiable. We overcome the apparent impossibility of their use in the variational equation coming from the Fermat's Principle with the introduction of a Stochastic Calculus. Afterwards, we successfully provide a solution for the stochastic ray equation; moreover, its implications in the statistical analysis of experimental data is discussed.
Light Propagation in Turbulent Media
Dario G. Perez
Physics , 2003,
Abstract: First, we make a revision of the up-to-date Passive Scalar Fields properties: also, the refractive index is among them. Afterwards, we formulated the properties that make the family of `isotropic' fractional Brownian motion (with parameter H) a good candidate to simulate the turbulent refractive index. Moreover, we obtained its fractal dimension which matches the estimated by Constantin for passive scalar, and thus the parameter H determines the state of the turbulence. Next, using a path integral velocity representation, with the Markovian model, to calculate the effects of the turbulence over a system of grids. Finally, with the tools of Stochastic Calculus for fractional Brownian motions we studied the ray-equation coming from the Geometric Optics in the turbulent case. Our analysis covers those cases where average temperature gradients are relevant.
The fractional Brownian motion property of the turbulent refractive within Geometric Optics
Dario G. Perez
Physics , 2003,
Abstract: We introduce fractional Brownian motion processes (fBm) as an alternative model for the turbulent index of refraction. These processes allow to reconstruct most of the refractive index properties, but they are not differentiable. We overcome the apparent impossibility of their use within the Ray Optics approximation introducing a Stochastic Calculus. Afterwards, we successfully provide a solution for the stochastic ray-equation; moreover, its implications in the statistical analysis of experimental data is discussed. In particular, we analyze the dependence of the averaged solution against the characteristic variables of a simple propagation problem.
Modeling turbulent wave-front phase as a fractional Brownian motion: a new approach
Dario G. Perez,Luciano Zunino,Mario Garavaglia
Physics , 2004, DOI: 10.1364/JOSAA.21.001962
Abstract: This paper introduces a general and new formalism to model the turbulent wave-front phase using fractional Brownian motion processes. Moreover, it extends results to non-Kolmogorov turbulence. In particular, generalized expressions for the Strehl ratio and the angle-of-arrival variance are obtained. These are dependent on the dynamic state of the turbulence.
A fractional Brownian motion model for the turbulent refractive index in lightwave propagation
Dario G. Perez,Luciano Zunino,Mario Garavaglia
Physics , 2003, DOI: 10.1016/j.optcom.2004.08.007
Abstract: It is discussed the limitations of the widely used markovian approximation applied to model the turbulent refractive index in lightwave propagation. It is well-known the index is a passive scalar field. Thus, the actual knowledge about these quantities is used to propose an alternative stochastic process to the markovian approximation: the fractional Brownian motion. This generalizes the former introducing memory; that is, there is correlation along the propagation path.
Characterization of Laser Propagation Through Turbulent Media by Quantifiers Based on the Wavelet Transform
Luciano Zunino,Dario G. Perez,Osvaldo A. Rosso,Mario Garavaglia
Physics , 2003, DOI: 10.1142/S0218348X04002471
Abstract: The propagation of a laser beam through turbulent media is modeled as a fractional Brownian motion (fBm). Time series corresponding to the center position of the laser spot (coordinates x and y) after traveling across air in turbulent motion, with different strength, are analyzed by the wavelet theory. Two quantifiers are calculated, the Hurst exponent and the mean Normalized Total Wavelet Entropy. It is verified that both quantifiers gives complementary information about the turbulence state.
Characterization of laser propagation through turbulent media by quantifiers based on the wavelet transform: dynamic study
Luciano Zunino,Dario G. Perez,Mario Garavaglia,Osvaldo A. Rosso
Physics , 2005, DOI: 10.1016/j.physa.2005.09.054
Abstract: We analyze, within the wavelet theory framework, the wandering over a screen of the centroid of a laser beam after it has propagated through a time-changing laboratory-generated turbulence. Following a previous work (Fractals 12 (2004) 223) two quantifiers are used, the Hurst parameter, $H$, and the Normalized Total Wavelet Entropy, $\text{NTWS}$. The temporal evolution of both quantifiers, obtained from the laser spot data stream is studied and compared. This allows us to extract information of the stochastic process associated to the turbulence dynamics.
Wavelet entropy and fractional Brownian motion time series
Dario G. Perez,Luciano Zunino,Mario Garavaglia,Osvaldo A. Rosso
Physics , 2005, DOI: 10.1016/j.physa.2005.09.060
Abstract: We study the functional link between the Hurst parameter and the Normalized Total Wavelet Entropy when analyzing fractional Brownian motion (fBm) time series--these series are synthetically generated. Both quantifiers are mainly used to identify fractional Brownian motion processes (Fractals 12 (2004) 223). The aim of this work is understand the differences in the information obtained from them, if any.
Multifractal characteristics of optical turbulence measured through a single beam holographic process
Dario G. Perez,Regis Barille,Yohann Morille,Sonia Zielinska,Ewelina Ortyl
Physics , 2014, DOI: 10.1364/OE.22.019538
Abstract: We have previously shown that azopolymer thin films exposed to coherent light that has travelled through a turbulent medium produces a surface relief grating containing information about the intensity of the turbulence; for instance, a relation between the refractive index structure constant C2 as a function of the surface parameters was obtained. In this work, we show that these films capture much more information about the turbulence dynamics. Multifractal detrended fluctuation and fractal dimension analysis from images of the surface roughness produced by the light on the azopolymer reveals scaling properties related to those of the optical turbulence.
MODELIZACIóN MATEMáTICA DE LA VALORACIóN BURSáTIL - CASO DE EMPRESAS COLOMBIANAS
ARANGO,MARTíN DARIO; PEREZ,GIOVANNY; ALVAREZ,KARLA CRISTINA;
DYNA , 2009,
Abstract: in this article shows obtaining equations explanatory market capitalization of a set of colombian companies, which have been selected because of their relative importance in generating rates in the bag that are traded, and in particular col20 (index of profitability or liquidity that reflects variations in prices of the 20 most liquid shares of colombia stock exchange) and igbc (general index of colombia stock exchange), from the financial resources provided by the colombia of values superintendence. through a combination of principal components analysis and multiple regression equations have been estimated valuation of key enterprises, synthesizing information available on the market and avoiding the frequent problem of multicolinealidad. thus, in addition to conventional methods, there is other additional criterion for evaluating companies, being useful in ipos, in the process of concentration or for the financial management of these companies.
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