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Fiasconaro A.,University of Zaragoza | Fiasconaro A.,Centro Universitario Of La Defensa Of Zaragoza | Mazo J.J.,University of Zaragoza
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The mean first passage time of a Brownian particle from an initial unstable state in a metastable system with damping is investigated. The system is analyzed in the low to high damping regime, and the role played by the damping parameter is studied. We observe the noise enhanced stability effect for all the initial unstable states under study and for all values of the damping parameter γ investigated. The curves show a behavior of the mean first passage time vs γ very close to that observed for an overdamped particle in the presence of colored noise as a function of the correlation time. © 2010 The American Physical Society.

De Leon-Perez F.,Centro Universitario Of La Defensa Of Zaragoza | De Leon-Perez F.,University of Zaragoza | Garcia-Vidal F.J.,Autonomous University of Madrid | Martin-Moreno L.,University of Zaragoza
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The optical emittance of a hole pair perforated in an opaque metal film is studied from first principles using the coupled-mode method. The geometrical simplicity of this system helps us to understand the fundamental role played by surface plasmon polaritons (SPPs) in its optical response. A SPP interference model without fitting parameters is developed from the rigorous solution of Maxwell's equations. The calculations show that the interference pattern of the hole pair is determined by two scattering mechanisms: (i) the electric field excited by the external illumination at the hole openings before the hole-hole interaction is established and (ii) the re-illumination of the holes by the in-plane SPP radiation. The conditions for constructive and destructive interference only depend on the phase difference provided by each of the two scattering mechanisms. © 2011 American Physical Society.

Villate-Guio F.,University of Zaragoza | Lopez-Tejeira F.,CSIC - Institute for the Structure of Matter | Garcia-Vidal F.J.,Autonomous University of Madrid | Martin-Moreno L.,University of Zaragoza | And 2 more authors.
Optics Express | Year: 2012

One-dimensional light harvesting structures with a realistic geometry nano-patterned on an opaque metallic film are optimized to render high transmission efficiencies at optical and infrared frequencies. Simple design rules are developed for the particular case of a slit-groove array with a given number of grooves that are symmetrically distributed with respect to a central slit. These rules take advantage of the hybridization of Fabry-Perot modes in the slit and surface modes of the corrugated metal surface. Same design rules apply for optical and infrared frequencies. The parameter space of the groove array is also examined with a conjugate gradient optimization algorithm that used as a seed the geometries optimized following physical intuition. Both uniform and nonuniform groove arrays are considered. The largest transmission enhancement, with respect to a uniform array, is obtained for a chirped groove profile. Such relative enhancement is a function of the wavelength. It decreases from 39 % in the optical part of the spectrum to 15 % at the long wavelength infrared. © 2012 Optical Society of America.

Yi J.-M.,University of Strasbourg | Cuche A.,University of Strasbourg | De Leon-Perez F.,Centro Universitario Of La Defensa Of Zaragoza | De Leon-Perez F.,University of Zaragoza | And 7 more authors.
Physical Review Letters | Year: 2012

We investigate both experimentally and theoretically the far-field diffraction patterns of single circular apertures as a function of their diameters d and at a given illumination wavelength λ. We observe the transition between the well-known pseudoscalar regime of large holes (dλ) and the less-known vectorial regime of subwavelength ones (dλ). Four different diffraction regimes are identified for different d/λ regions, each one with its polarization dependence. A thorough comparison with a theoretical model, which takes into account both finite hole size and the dielectric properties of the metal, allows us to explain and understand the physical processes leading to this behavior. Our results reveal the subtle interplay between two competing factors, one related to polarization symmetries associated with surface-plasmon excitations and the other originating in the coupling of the field to the waveguide mode of the aperture. © 2012 American Physical Society.

Alonso-Carne J.,University of Zaragoza | Garcia-Martin A.,Centro Universitario Of La Defensa Of Zaragoza | Garcia-Martin A.,University of Zaragoza | Estrada-Pena A.,University of Zaragoza
Experimental and Applied Acarology | Year: 2015

Ticks are sensitive to changes in relative humidity and saturation deficit at the microclimate scale. Trends and changes in rainfall are commonly used as descriptors of field observations of tick populations, to capture the climate niche of ticks or to predict the climate suitability for ticks under future climate scenarios. We evaluated daily and monthly relationships between rainfall, relative humidity and saturation deficit over different ecosystems in Europe using daily climate values from 177 stations over a period of 10 years. We demonstrate that rainfall is poorly correlated with both relative humidity and saturation deficit in any of the ecological domains studied. We conclude that the amount of rainfall recorded in 1 day does not correlate with the values of humidity or saturation deficit recorded 24 h later: rainfall is not an adequate surrogate for evaluating the physiological processes of ticks at regional scales. We compared the Normalized Difference Vegetation Index (NDVI), a descriptor of photosynthetic activity, at a spatial resolution of 0.05°, with monthly averages of relative humidity and saturation deficit and also determined a lack of significant correlation. With the limitations of spatial scale and habitat coverage of this study, we suggest that the rainfall or NDVI cannot replace relative humidity or saturation deficit as descriptors of tick processes. © 2014, Springer International Publishing Switzerland.

Fonts I.,Centro Universitario Of La Defensa Of Zaragoza | Fonts I.,Aragon Institute of Engineering Research | Gea G.,Aragon Institute of Engineering Research | Azuara M.,Aragon Institute of Engineering Research | And 2 more authors.
Renewable and Sustainable Energy Reviews | Year: 2012

The high output of sewage sludge, which is increasing during recent years, and the limitations of the existing means of disposing sewage sludge highlight the need to find alternative routes to manage this waste. Biomass and residues like sewage sludge are the only renewable energy sources that can provide C and H, thus it is interesting to process them by means of treatments that enable to obtain chemically valuable products like fuels and not only heat and power; pyrolysis can be one of these treatments. The main objective of this review is to provide an account of the state of the art of sewage sludge pyrolysis for liquid production, which is under study during recent years. This process yields around 50 wt% (daf) of liquid. Typically, this liquid is heterogeneous and it usually separates into two or three phases. Some of these organic phases have very high gross heating values, even similar to those of petroleum-based fuels. The only industrial sewage sludge pyrolysis plant operated to date is currently closed due to some technical challenges and problems of economic viability. © 2012 Elsevier Ltd. All rights reserved.

Montealegre A.L.,University of Zaragoza | Lamelas M.T.,University of Zaragoza | Lamelas M.T.,Centro Universitario Of La Defensa Of Zaragoza | Tanase M.A.,University of Melbourne | De la Riva J.,University of Zaragoza
Remote Sensing | Year: 2014

Mediterranean pine forests in Spain experience wildland fire events with different frequencies, intensities, and severities which result in diverse socio-ecological consequences. In order to predict fire severity, spectral indices derived from remotely sensed images have been used extensively. Such spectral indices are usually used in combination with ground sampling to relate detected radiometric changes to actual fire effects. However, the potential of the tridimensional information captured by Airborne Laser Scanners (ALS) to severity mapping has been less explored. With the objective of addressing this question, in this paper, explanatory variables extracted from ALS point clouds are related to field estimations of the Composite Burn Index collected in four fires located in Aragón (Spain). Logistic regression models were developed and statistically tested and validated to map fire severity with up to 85.5% accuracy. The canopy relief ratio and the percentage of all returns above one meter height were the most significant variables and were therefore used to create a continuous map of severity levels. © 2014 by the authors.

Fiasconaro A.,Centro Universitario Of La Defensa Of Zaragoza | Fiasconaro A.,University of Zaragoza | Spagnolo B.,University of Palermo
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2011

This work analyzes numerically the role played by the asymmetry of a piecewise linear potential, in the presence of both a Gaussian white noise and a dichotomous noise, on the resonant activation phenomenon. The features of the asymmetry of the potential barrier arise by investigating the stochastic transitions far behind the potential maximum, from the initial well to the bottom of the adjacent potential well. Because of the asymmetry of the potential profile together with the random external force uniform in space, we find, for the different asymmetries: (1) an inversion of the curves of the mean first passage time in the resonant region of the correlation time τ of the dichotomous noise, for low thermal noise intensities; (2) a maximum of the mean velocity of the Brownian particle as a function of τ; and (3) an inversion of the curves of the mean velocity and a very weak current reversal in the miniratchet system obtained with the asymmetrical potential profiles investigated. An inversion of the mean first passage time curves is also observed by varying the amplitude of the dichotomous noise, behavior confirmed by recent experiments. © 2011 American Physical Society.

Valero C.,Aragon Institute of Engineering Research | Javierre E.,Centro Universitario Of La Defensa Of Zaragoza | Garcia-Aznar J.M.,Aragon Institute of Engineering Research | Gomez-Benito M.J.,Aragon Institute of Engineering Research
PLoS ONE | Year: 2014

Wound healing is a process driven by cells. The ability of cells to sense mechanical stimuli from the extracellular matrix that surrounds them is used to regulate the forces that cells exert on the tissue. Stresses exerted by cells play a central role in wound contraction and have been broadly modelled. Traditionally, these stresses are assumed to be dependent on variables such as the extracellular matrix and cell or collagen densities. However, we postulate that cells are able to regulate the healing process through a mechanosensing mechanism regulated by the contraction that they exert. We propose that cells adjust the contraction level to determine the tissue functions regulating all main activities, such as proliferation, differentiation and matrix production. Hence, a closed-regulatory feedback loop is proposed between contraction and tissue formation. The model consists of a system of partial differential equations that simulates the evolution of fibroblasts, myofibroblasts, collagen and a generic growth factor, as well as the deformation of the extracellular matrix. This model is able to predict the wound healing outcome without requiring the addition of phenomenological laws to describe the time-dependent contraction evolution. We have reproduced two in vivo experiments to evaluate the predictive capacity of the model, and we conclude that there is feedback between the level of cell contraction and the tissue regenerated in the wound. © 2014 Valero et al.

Gonzalez Chapela J.,Centro Universitario Of La Defensa Of Zaragoza
Information Economics and Policy | Year: 2015

The large negative impact of income on time spent online observed among internet adopters has been interpreted as an own-price effect created by the variation in the opportunity cost of time across income strata. However, the regression coefficient on income could also be capturing an income effect. This paper estimates a standard demand function for time online in Spain that includes a measure of the opportunity cost of time in addition to a measure of income. The effect of income barely changed when the opportunity cost of time was included. Results rather suggest that time spent online is an inferior leisure activity. © 2015 Elsevier B.V.

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