4,548 research outputs found
Caracterización de suelos forestales de la provincia de Huelva
Se pretende estudiar los suelos de la provincia de Huelva, en cuanto a sus aptitudes para los distintos usos forestales. Para elo, se hace un análisis previo de la variedad del medio provincial y se escogen, como zonas de trabajo, dos hojas de mapa 1:25.000 que contienen una proporción importante de la diversidad ecológica onubense. Se revisa la importancia del suelo sobre la calidad del medio, con especial atención a la capacidad hídrica y el espesor, considerados fundamentales en el medio forestal mediterráneo. Se obtuvieron las principales relaciones causa-efecto entre el medio y el suelo, resultando ser el tipo de roca el factor más influyente, seguido por los aspectos del relieve relacionados con la llegada lateral de agua a cada punto de muestreo (área de drenaje específico). Los resultados del trabajo se trasladaron a una cartografía general de suelos, así como de sus propiedades hídricas y su profundidad. Toda esta información fue generada a partir del levantamiento de más de cien calicatas y sondeos diversos, con sus correspondientes analíticas, para luego insertar la información en una base de datos diseñada al efecto. El método cartográfico utilizado se basó sobre la formación de unidades geomorfolitológicas, realizándose una revisión completa de este método frente a otras sendas
Turbo EP-based Equalization: a Filter-Type Implementation
This manuscript has been submitted to Transactions on Communications on
September 7, 2017; revised on January 10, 2018 and March 27, 2018; and accepted
on April 25, 2018
We propose a novel filter-type equalizer to improve the solution of the
linear minimum-mean squared-error (LMMSE) turbo equalizer, with computational
complexity constrained to be quadratic in the filter length. When high-order
modulations and/or large memory channels are used the optimal BCJR equalizer is
unavailable, due to its computational complexity. In this scenario, the
filter-type LMMSE turbo equalization exhibits a good performance compared to
other approximations. In this paper, we show that this solution can be
significantly improved by using expectation propagation (EP) in the estimation
of the a posteriori probabilities. First, it yields a more accurate estimation
of the extrinsic distribution to be sent to the channel decoder. Second,
compared to other solutions based on EP the computational complexity of the
proposed solution is constrained to be quadratic in the length of the finite
impulse response (FIR). In addition, we review previous EP-based turbo
equalization implementations. Instead of considering default uniform priors we
exploit the outputs of the decoder. Some simulation results are included to
show that this new EP-based filter remarkably outperforms the turbo approach of
previous versions of the EP algorithm and also improves the LMMSE solution,
with and without turbo equalization
Evaluation of the stiffness tensor of a fractured medium with harmonic experiments
A fractured medium behaves as an anisotropic medium when the wavelength is much larger than the distance between fractures. These are modeled as boundary discontinuities in the displacement and particle velocity. When the set of fractures is plane, the theory predicts that the equivalent medium is transversely isotropic and viscoelastic (TIV). We present a novel procedure to determine the complex and frequency-dependent stiffness components. The methodology amounts to perform numerical compressibility and shear harmonic tests on a representative sample of the medium. These tests are described by a collection of elliptic boundary-value problems formulated in the space-frequency domain, which are solved with a Galerkin finite-element procedure. The examples illustrate the implementation of the tests to determine the set of stiffnesses and the associated phase velocities and quality factors.Fil: Santos, Juan Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto del Gas y del Petróleo; Argentina. Universidad Nacional de La Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Benedettini, Stefano. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Carcione, José M.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Itali
Rasmussen, Chenery and Watanabe, and labour-based multiplier analysis and sensitivity analysis of input coefficients for Spain in 2009
In this paper we identify the key sectors of the Spanish economy with the last input-output available data following the approaches by Rasmussen and by Chenery and Watanabe. We also calculate labour-based multipliers and sensitivity of input coefficients and we compare the results in order to present useful advice for sector policiesEn este trabajo analizamos cuáles son los sectores claves en España con los últimos datos publicados del marco input-output. Seguimos las metodologías de Rasmussen y de Chenery y Watanabe. También hacemos uso de los multiplicadores de remuneraciones, trabajadores y asalariados así como de la técnica de sensibilidad de coeficientes. En las conclusiones se presentan los principales hallazgos que permiten diseñar una política sectorial eficaz para Españ
Numerical experiments of fracture-induced velocity and attenuation anisotropy
Fractures are common in the Earth's crust due to different factors, for instance, tectonic stresses and natural or artificial hydraulic fracturing caused by a pressurized fluid. A dense set of fractures behaves as an effective long-wavelength anisotropic medium, leading to azimuthally varying velocity and attenuation of seismic waves. Effective in this case means that the predominant wavelength is much longer than the fracture spacing. Here, fractures are represented by surface discontinuities in the displacement u and particle velocity v as [κ · u + η · v], where the brackets denote the discontinuity across the surface, κ is a fracture stiffness and η is a fracture viscosity. We consider an isotropic background medium, where a set of fractures are embedded. There exists an analytical solution-with five stiffness components-for equispaced plane fractures and an homogeneous background medium. The theory predicts that the equivalent medium is transversely isotropic and viscoelastic. We then perform harmonic numerical experiments to compute the stiffness components as a function of frequency, by using a Galerkin finite-element procedure, and obtain the complex velocities of the medium as a function of frequency and propagation direction, which provide the phase velocities, energy velocities (wavefronts) and quality factors. The algorithm is tested with the analytical solution and then used to obtain the stiffness components for general heterogeneous cases, where fractal variations of the fracture compliances and background stiffnesses are considered.Este documento tiene una corrección (ver documento relacionado).Facultad de Ciencias Astronómicas y Geofísica
Anisotropic poroelasticity and wave-induced fluid flow: Harmonic finite-element simulations
A dominant P-wave attenuation mechanism in reservoir rocks at seismic frequencies is due to wave-induced fluid flow (mesoscopic loss). The P-wave induces a fluid-pressure difference at mesoscopic-scale inhomogeneities (larger than the pore size but smaller than the wavelength), generating fluid flow and slow (diffusion) Biot waves. The theory has been developed in the 1970s for the symmetry axis of the equivalent transversely isotropic (TI) medium corresponding to a finely layered medium, and has recently been generalized to all propagation angles. The new theory states that the fluid-flow direction is perpendicular to the layering plane and it is independent of the loading direction. As a consequence, the relaxation behaviour can be described by a single relaxation function, since the medium consists of plane homogeneous layers. Besides P-wave losses, the coupling between the qP and qSV waves generates shear-wave anisotropic velocity dispersion and attenuation. In this work, we introduce a set of quasi-static numerical experiments to determine the equivalent viscoelastic TI medium to a finely layered poroelastic medium, which is validated using a recently developed analytical solution. The modelling technique is the finite-element (FE) method, where the equations of motion are solved in the space-frequency domain. Numerical rock physics may, in many circumstances, offer an alternative to laboratory measurements. Numerical experiments are inexpensive and informative since the physical process of wave propagation can be inspected during the experiment. Moreover, they are repeatable, essentially free from experimental errors, and may easily be run using alternative models of the rock and fluid properties. We apply the methodology to the Utsira aquifer of the North Sea, where carbon dioxide (CO2) has been injected during the last 15 years. The tests consider alternating layers of the same rock saturated with gas and brine and a sequence of gas-saturated sandstone and mudstone layers, which represent possible models of the reservoir and cap rock of the aquifer system. The numerical examples confirm the new theory and illustrate the implementation of the harmonic tests to determine the complex and frequency-dependent effective stiffnesses and the associated wave velocities and quality factors.Facultad de Ciencias Astronómicas y Geofísica
Fast Integrated Spectra Analyzer: A New Computational Tool For Age and Reddening Determination of Small Angular Diameter Open Clusters
We present a new algorithm called 'Fast Integrated Spectra Analyzer" (FISA)
that permits fast and reasonably accurate age and reddening determinations for
small angular diameter open clusters by using their integrated spectra in the
(3600-7400) \AA \ range and currently available template spectrum libraries.
This algorithm and its implementation help to achieve astrophysical results in
shorter times than from other methods. A brief review is given of the
integrated spectroscopic technique applied to the study of open clusters as
well as the basic assumptions that justify its use. We describe the numerical
algorithm employed in detail, show examples of its application, and provide a
link to the code. Our method has successfully been applied to integrated
spectroscopy of open clusters, both in the Galaxy and in the Magellanic Clouds,
to determine ages and reddenings.Comment: 27 Pages, 7 Figures, 1 table. Accepted to PAS
Numerical experiments of fracture-induced velocity and attenuation anisotropy
Fractures are common in the Earth's crust due to different factors, for instance, tectonic stresses and natural or artificial hydraulic fracturing caused by a pressurized fluid. A dense set of fractures behaves as an effective long-wavelength anisotropic medium, leading to azimuthally varying velocity and attenuation of seismic waves. Effective in this case means that the predominant wavelength is much longer than the fracture spacing. Here, fractures are represented by surface discontinuities in the displacement u and particle velocity v as [κ · u + η · v], where the brackets denote the discontinuity across the surface, κ is a fracture stiffness and η is a fracture viscosity. We consider an isotropic background medium, where a set of fractures are embedded. There exists an analytical solution-with five stiffness components-for equispaced plane fractures and an homogeneous background medium. The theory predicts that the equivalent medium is transversely isotropic and viscoelastic. We then perform harmonic numerical experiments to compute the stiffness components as a function of frequency, by using a Galerkin finite-element procedure, and obtain the complex velocities of the medium as a function of frequency and propagation direction, which provide the phase velocities, energy velocities (wavefronts) and quality factors. The algorithm is tested with the analytical solution and then used to obtain the stiffness components for general heterogeneous cases, where fractal variations of the fracture compliances and background stiffnesses are considered.Este documento tiene una corrección (ver documento relacionado).Facultad de Ciencias Astronómicas y Geofísica
Fracture-induced anisotropic attenuation
The triaxial nature of the tectonic stress in the earth's crust favors the appearance of vertical fractures. The resulting rheology is usually effective anisotropy with orthorhombic and monoclinic symmetries. In addition, the presence of fluids leads to azimuthally varying attenuation of seismic waves. A dense set of fractures embedded in a background medium enhances anisotropy and rock compliance. Fractures are modeled as boundary discontinuities in the displacement u and particle velocity v as [ κ · u + ν · v] where the brackets denote discontinuities across the fracture surface, j is a fracture stiffness, and g is a viscosity related to the energy loss. We consider a transversely isotropic background medium (e.g., thin horizontal plane layers), with sets of long vertical fractures. Schoenberg and Muir's theory combines the background medium and sets of vertical fractures to provide the 13 complex stiffnesses of the long-wavelength equivalent monoclinic and viscoelastic medium. Long-wavelength equivalent means that the dominant wavelength of the signal is much longer than the fracture spacing. The symmetry plane is the horizontal plane. The equations for orthorhombic and transversely isotropic media follow as particular cases. We compute the complex velocities of the medium as a function of frequency and propagation direction, which provide the phase velocities, energy velocities (wavefronts), and quality factors. The effective medium ranges from monoclinic symmetry to hexagonal (transversely isotropic) symmetry from the low-to the high-frequency limits in the case of a particle-velocity discontinuity (lossy case) and the attenuation shows typical Zener relaxation peaks as a function of frequency. The attenuation of the coupled waves may show important differences when computed versus the ray or phase angles, with triplication appearing in the Q factor of the qS wave. We have performed a full-wave simulation to compute the field corresponding to the coupled qP-qS waves in the symmetry plane of an effective monoclinic medium. The simulations agree with the predictions of the plane-wave analysis.Fil: Carcione, Jose M.. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; ItaliaFil: Santos, Juan Enrique. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto del Gas y del Petróleo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Picotti, Stefano. Istituto Nazionale di Oceanografia e di Geofisica Sperimentale; Itali
- …