http://hdl.handle.net/2117/3965 2013-05-24T05:43:07Z http://hdl.handle.net/2117/14928 Title: Modelling shoreline sand waves: application to the coast of Namibia Authors: Falqués Serra, Albert; Van den Berg, Niels; Ribas Prats, Francesca; Caballeria Suriñach, Miquel Abstract: The SW coast of Africa (Namibia and part of Angola) features very long sandy beaches and a wave climate dominated by energetic swells from the SSW, therefore approaching the coast with a very high obliquity. Satellite images reveal that along that coast there are many shoreline sand waves with wavelengths ranging from 2 to 8 km. A more detailed study, including a Fourier analysis of the shoreline position, confirms a high spectral density concentration at these lengths scales. Also, it becomes apparent that at least some of the sand waves are dynamically active rather than being controlled by the geological setting. A morphodynamic model is used to test the hypothesis that these sand waves could emerge as free morphodynamic instabilities of the coastline due to the obliquity in wave incidence. It is found that the wave period, Tp, is crucial to establish the tendency to stability or instability, instability increasing for decreasing period, whilst there is some discrepancy in the observed periods. Model results for Tp = 7 s clearly show the tendency for the coast to develop free sand waves at 2 km wavelength within a few years, which migrate to the north at rates of 0.6-0.7 km/yr. For Tp = 8 s, instability is weaker and rather sensitive to other factors as the underlying bathymetry. In this case, the coast seems to be nearly at neutral stability so that sand waves originated from other mechanisms can propagate downdrift with little decay. http://hdl.handle.net/2117/16259 Title: Rehabilitación energética de edificios escolares en clima mediterráneo: caso de estudio, Barcelona Authors: Bosch González, Montserrat; Rodríguez Cantalapiedra, Inma; Álvarez del Castillo, Javier Abstract: necesidad de reducir el consumo energético se hace cada día más evidente, especialmente en Europa debido a su situación de dependencia energética de países externos a la Unión y también por razones relacionadas con el impacto ambiental y las emisiones asociadas. En este contexto, la rehabilitación energética de edificios es una línea de trabajo prioritaria que actúa sobre el parque edificado, y los edificios públicos deben ser un modelo o ejemplo para impulsar este tipo de actuaciones. Los centros docentes, con un potencial de ahorro muy importante y con unos consumos energéticos asociados básicamente a dos grandes conceptos, la iluminación y la climatización, pueden considerarse como un laboratorio de investigación en cuanto a eficiencia energética. A partir de las experiencias adquiridas durante más de 10 años se ha desarrollado una metodología de análisis para la intervención en edificios docentes en Barcelona con los siguientes objetivos: definir los indicadores estratégicos para identificar las oportunidades de ahorro, evaluar las posibles medidas de reducción de consumos a partir de la limitación de la demanda, analizar y dar contenido al papel de cada uno de los actores que intervienen en las estrategias de uso y gestión de los edificios escolares y establecer los criterios que deben considerarse para realizar las futuras intervenciones de rehabilitación energética. El método, como manera de pensar ordenadamente, ha de permitir optimizar los recursos y descubrir les rutas de trabajo que nos conduzcan al objetivo final: reducir el consumo energético del parque edificado http://hdl.handle.net/2117/19318 Title: Percolation experiments in complex fractal media Authors: Redondo Apraiz, José Manuel; Tarquis, Ana Maria; Cherubini, Claudia; Lopez Gonzalez-Nieto, Pilar; Vila, Teresa 2013-05-16T16:20:33Z http://hdl.handle.net/2117/19317 Title: SAR measurements of coastal features in the NW Mediterranean Authors: Redondo Apraiz, José Manuel; Martínez Benjamín, Juan José; Díez Rilova, Margarita; Lopez Gonzalez-Nieto, Pilar 2013-05-16T16:15:04Z http://hdl.handle.net/2117/19289 Title: White dwarf mergers and the origin of R coronae borealis stars Authors: Lorén Aguilar, Pablo; Longland, Richard Leigh; José Pont, Jordi; García-Berro Montilla, Enrique; Althaus, Leandro G.; Isern-Fontanet, J. Abstract: We present a nucleosynthesis study of the merger of a 0.4 M⊙ helium white dwarf with a 0.8 M⊙ carbon-oxygen white dwarf, coupling the thermodynamic history of Smoothed Particle Hydrodynamics particles with a post-processing code. The resulting chemical abundance pattern, particularly for oxygen and fluorine, is in qualitative agreement with the observed abundances in R Coronae Borealis stars. 2013-05-16T11:56:45Z http://hdl.handle.net/2117/19233 Title: Bounds on the possible evolution of the gravitational constant from cosmological type-Ia supernovae Authors: Gaztañaga, E; García-Berro Montilla, Enrique; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Domínguez, I Abstract: Recent high-redshift type-Ia supernovae results can be used to set new bounds on a possible variation of the gravitational constant G. If the local value of G at the space-time location of distant supernovae is different, it would change both the kinetic energy release and the amount of 56Ni synthesized in the supernova outburst. Both effects are related to a change in the Chandrasekhar mass MCh∝G-3/2. In addition, the integrated variation of G with time would also affect the cosmic evolution and therefore the luminosity distance relation. We show that the later effect in the magnitudes of type-Ia supernovae is typically several times smaller than the change produced by the corresponding variation of the Chandrasekhar mass. We investigate in a consistent way how a varying G could modify the Hubble diagram of type-Ia supernovae and how these results can be used to set upper bounds to a hypothetical variation of G. We find G/G0≲1.1 and Ġ/G≲10-11yr-1 at redshifts z≃0.5. These new bounds extend the currently available constraints on the evolution of G all the way from solar and stellar distances to typical scales of Gpc/Gyr, i.e., by more than 15 orders of magnitude in time and distance. 2013-05-15T10:00:45Z http://hdl.handle.net/2117/19232 Title: A practical tool for sizing optimal shading devices Authors: Jorge Sánchez, Juan; Puigdomènech Franquesa, Joan; Cusidó Fàbregas, Joan Antoni Abstract: A nomogram is presented for use in regions with a Mediterranean climate. Architects can use this tool as an easy way to optimize the design of shading devices. The nomogram allows the performance of a proposed external fixed shading device to be evaluated. The input variables required are (i) the location of the building, (ii) the orientation of the facade and (iii) two adimensional characteristics corresponding to the opening-shading device system. The accuracy reaches its minimum value during intermediate seasons but the margin of error is less than 10%. 2013-05-15T09:04:50Z http://hdl.handle.net/2117/19231 Title: A daylight criterion on solar controls for comparing sky radiance models Authors: Jorge Sánchez, Juan; Puigdomènech Franquesa, Joan Abstract: The obstruction of solar radiation by solar controls must be balanced with the required daylight contribution. Solar controls are characterized by the percentage of non-obstructed external radiance. The estimation of this radiance, particularly its diffuse component, depends on the sky radiance distribution used. In this work, we have compared three models (isotropic, CIE clear sky and Perez) before deciding which one is the most suitable for calculating natural light without forgetting the aspect of energy. The incident energy on an aperture where solar control is installed and its daily factor (DF) are the two parameters that have been adopted to analyze the three models. The energy allows us to compare the models and the DF allows us to discuss the weight of each part of the sky dome for each model. It is deduced that the isotropic model is not suitable for calculating the natural light available in the presence of solar control. The small differences observed between the results obtained with the other two models justify the advantage of using Perez's model in calculations of natural illumination due to its simple formulation. 2013-05-15T08:56:22Z http://hdl.handle.net/2117/19174 Title: SIXE: An X-ray experiment for the MINISAT platform Authors: Bravo Guil, Eduardo; García-Berro Montilla, Enrique; Gutierrez Cabello, Jorge Luis; José Pont, Jordi; García Senz, Domingo; Cabestany Moncusí, Joan; Madrenas Boadas, Jordi 2013-05-13T09:46:38Z http://hdl.handle.net/2117/19147 Title: Scaling laws and the modern city Authors: Isalgue Buxeda, Antonio; Coch Roura, Helena; Serra Florensa, Rafael Abstract: A detrended fluctuation analysis (DFA) is applied to the statistics of Korean treasury bond (KTB) futures from which the logarithmic increments, volatilities, and traded volumes are estimated over a specific time lag. In this study, the logarithmic increment of futures prices has no long-memory property, while the volatility and the traded volume exhibit the existence of the long-memory property. To analyze and calculate whether the volatility clustering is due to a inherent higher-order correlation not detected by with the direct application of the DFA to logarithmic increments of KTB futures, it is of importance to shuffle the original tick data of future prices and to generate a geometric Brownian random walk with the same mean and standard deviation. It was found from a comparison of the three tick data that the higher-order correlation inherent in logarithmic increments leads to volatility clustering. Particularly, the result of the DFA on volatilities and traded volumes can be supported by the hypothesis of price changes. 2013-05-09T10:56:38Z http://hdl.handle.net/2117/19055 Title: Stochastic Phase-Field simulations of symmetric alloy solidification Authors: Benítez Iglesias, Raúl; Ramírez de la Piscina Millán, Laureano Abstract: We study initial transient stages in directional solidification by means of a non-variational phase field model with fluctuations. This model applies for the symmetric solidification of dilute binary solutions and does not invoke fluctuation-dissipation theorem to account for the fluctuation statistics. We devote our attention to the transient regime during which concentration gradients are building up and fluctuations act to destabilize the interface. To this end, we calculate both the temporally dependent growth rate of each mode and the power spectrum of the interface evolving under the effect of fluctuations. Quantitative agreement is found when comparing the phase-field simulations with theoretical predictions. 2013-04-30T11:08:59Z http://hdl.handle.net/2117/19053 Title: Phase-field models in interfacial pattern formation out of equilibrium Authors: González Cinca, Ricardo; Folch, R.; Benítez Iglesias, Raúl; Ramírez de la Piscina Millán, Laureano; Casademunt, Jaume; Hernández-Machado, A. 2013-04-30T10:58:31Z http://hdl.handle.net/2117/19024 Title: On the internal composition of white dwarfs Authors: Isern Vilaboy, Jordi; Bravo Guil, Eduardo; García-Berro Montilla, Enrique; Domínguez, I; Salaris, M 2013-04-26T16:56:35Z http://hdl.handle.net/2117/18967 Title: The evolution and C, N and O yields of intermediate-mass Z = 10-5 stars in isolation and in close binary systems Authors: Gil Pons, Pilar; Doherty, Carolyn L.; Suda, T.; Campbell, Simon; Lau, H.; Mansouri Guilani, Shervin; Lattanzio, John Abstract: We have computed the evolution of Z = 10−5 stars of masses between 4 and 9 M , from their main sequence till the late TP-(S)AGB phase.We use a recent version of the Mount Stromlo Stellar Evolution code, in which molecular opacities include the effects of variable C/O abundances ratio, [1]. By computing hundreds (or thousands) of thermal pulses, we have been able either to remove the bulk of the stellar envelopes or to obtain stellar cores very close to MCh. Using [2] prescription for the mass loss rates the computed stars lose their envelopes before their cores reach MCh. This would forbid the occurrence of SN 1.5 for Z = 10−5 stars. Nevertheless the results by [3] suggest that the former prescription might overestimate the mass-loss rates. Therefore we have decreased the rates by [2]. For all the cases we present, even a decrease of one order of magnitude let the stellar cores reach MCh before the envelope is lost. Therefore the occurrence of SN1.5 at Z = 10 −5 and their potential contribution to the chemical evolution of the Universe should not be discarded. We consider the combined effects of the deep/corrosive 2 nd dredge-up and Roche Lobe Overflow (RLOF) during the E-AGB to help to constrain the contribution of massive Z = 10 −5 AGB stars to the CEMPs problem. Our results have implications for the chemical evolution of the Universe and might provide another piece for the puzzle of the CEMPs problem. 2013-04-23T14:39:01Z http://hdl.handle.net/2117/18961 Title: Dependency of calcium alternans on Ryanodine Receptor Refractoriness Authors: Álvarez Lacalle, Enrique; Rodríguez Cantalapiedra, Inma; Peñaranda Ayllón, Angelina; Cinca, J.; Hove-Madsen, Leif; Echebarría Domínguez, Blas Abstract: Background Rapid pacing rates induce alternations in the cytosolic calcium concentration caused by fluctuations in calcium rele However, the relationship between calcium alternans and refractoriness of the SR calcium release channel (RyR2) Methodology/Principal Findings To investigate how ryanodine receptor (RyR2) refractoriness modulates calcium handling on a beat-to-beat basis u used a mathematical rabbit cardiomyocyte model to study the beat-to-beat calcium response as a function of RyR were constructed depicting the beat-to-beat response. When alternans was observed, a novel numerical clamping was caused by oscillations in SR calcium loading or by RyR2 refractoriness. Using this protocol, we identified regio loading or RyR2 refractoriness underlie the induction of calcium alternans, and we found that at the onset of altern inactivation rates of the RyR2, calcium alternans was caused by alternation in SR calcium loading, while at low act level of available RyR2s. Conclusions/Significance We have mapped cardiomyocyte beat-to-beat responses as a function of RyR2 activation and inactivation, identify refractoriness underlie the induction of calcium alternans. A corollary of this work is that RyR2 refractoriness due t of calcium alternans even when alternation in SR calcium load is present. 2013-04-23T13:08:23Z