Time filter

Source Type

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.

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.

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.

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.

Discover hidden collaborations