http://hdl.handle.net/2117/3984 2013-05-25T21:54:55Z http://hdl.handle.net/2117/19286 Title: Interaction of Supernovae remnants: From the circumstellar medium to the terrestrial laboratory Authors: Velarde, P; García Senz, Domingo; Bravo Guil, Eduardo; Ogando, F; Relaño, A; Oliva, E Abstract: The evolution of supernova remnants (SNRs) represents a useful and natural laboratory for gasdynamics studies. In this paper the results of several hydrodynamical simulations of the propagation and early phases of interaction of two SNRs embedded in a homogeneous interstellar environment are shown. In particular, the hydrodynamic evolution and collision of twin SNRs during their self-similar stage has been simulated using a two-dimensional Lagrangian hydrocode. In addition, the results of a detailed simulation that attempts to set the adequate conditions to reproduce the same phenomenon through laser ablation of two plastic plugs at the laboratory scale are presented. These results indicate that both large-scale and small-scale simulations display several common features that can be used to design an experiment aimed to validate the hydrodynamical codes. Of particular interest are the structures found around the juncture of the two colliding shells produced by the interaction of the remnants. 2013-05-16T10:41:34Z http://hdl.handle.net/2117/19284 Title: Production of intermediate-mass and heavy nuclei Authors: Thielemann, F. K.; Frölich, Carla; Hirschi, R.; Liebendörfer, M.; Dillmann, I.; Mocelj, D.; Rauscher, t.; Martínez Pinedo, Gabriel; Langanke, K; Farouqi, K; Kratz, K.L.; Pfeiffer, B.; Panov, I.; Nadyozhin, D.K.; Blinnikov, S.; Bravo Guil, Eduardo; Hix, W.R.; Höflich, P.; Zinner, Ernst Abstract: Nucleosynthesis is the science related to all astrophysical processes which are responsible for the abundances of the elements and their isotopes in the universe. The astrophysical sites are the big bang and stellar objects. The working of nucleosynthesis processes is presented in a survey of events which act as abundance sources. For intermediate-mass and heavy elements, these are stellar evolution, type Ia and core collapse supernovae as well as hypernovae. We discuss successes and failures of existing processes and possible solutions via new (hitherto unknown) processes. Finally an analysis of their role is given in the puzzle to explain the evolution of the elemental and isotopic compositions found in galaxies, and especially the mixture found in the solar system. Different timescales due to the progenitor mass dependence of the endpoints of stellar evolution (type II supernova explosions — SNe II vs. planetary nebulae) or single vs. binary stellar systems (the latter being responsible for novae, type Ia supernovae — SNe Ia, or X-ray bursts) are the keys to understand galactic evolution. At very early times, the role of explosion energies of events, polluting pristine matter with a composition originating only from the big bang, might also play a role. We also speculate on the role of very massive stars not undergoing SN II explosions but rather causing “hypernovae” after the formation of a central black hole via core collapse. 2013-05-16T10:33:12Z http://hdl.handle.net/2117/19248 Title: Phase transitions with infinitely many absorbing states in complex networks Authors: Sander, Renan; Ferreira, Silvio C.; Pastor Satorras, Romualdo Abstract: We investigate the properties of the threshold contact process (TCP), a process showing an absorbing-state phase transition with infinitely many absorbing states, on random complex networks. The finite-size scaling exponents characterizing the transition are obtained in a heterogeneous mean-field (HMF) approximation and compared with extensive simulations, particularly in the case of heterogeneous scale-free networks. We observe that the TCP exhibits the same critical properties as the contact process, which undergoes an absorbing-state phase transition to a single absorbing state. The accordance among the critical exponents of different models and networks leads to conjecture that the critical behavior of the contact process in a HMF theory is a universal feature of absorbing-state phase transitions in complex networks, depending only on the locality of the interactions and independent of the number of absorbing states. The conditions for the applicability of the conjecture are discussed considering a parallel with the susceptible-infected-susceptible epidemic spreading model, which in fact belongs to a different universality class in complex networks. 2013-05-15T12:52:57Z http://hdl.handle.net/2117/19244 Title: Consequences of the Collision Between the Gas Ejected in the Collapse of a White Dwarf and a Low-Mass Star Authors: Serichol Augué, Núria; García Senz, Domingo; Bravo Guil, Eduardo 2013-05-15T11:07:44Z http://hdl.handle.net/2117/19243 Title: Recovery and treatment of spirulina platensis cells cultured in a continous photobioreactor to be used as food Authors: Morist, A; Montesinos, J L; Cusidó Fàbregas, Joan Antoni; Godia, F Abstract: The development of auto-regenerative biological life support systems for men in Space will be based on photosynthetic organisms, such as higher plants and algae, providing edible material. In this work, Spirulina platensis grown in a continuous photobioreactor was used to design a process for its recovery and further treatment to be used as food. Two different possibilities are studied (liquid or dry food). In each case, different steps are considered in the design of the process and further characterised: cell harvesting, washing, pasteurisation and spry-drying. Special emphasis is made on biomass quality, both in terms of potential microbial contamination and changes in its composition during the different steps of the process. Cell harvesting was conducted with a net recovery of solids and water higher than 95% with a solids concentration factor about 20–30. Biomass quality was shown as satisfactory in all the treatments tested. 2013-05-15T11:03:46Z http://hdl.handle.net/2117/19238 Title: Unified one-dimensional simulations of gamma-ray line emission from type Ia supernovae Authors: Milne, P A; Hungerford, A L; Fryer, C L; Evans, T M; Urbatsch, T J; Boggs, S E; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Hirschmann, A; Kumagai, S; Pinto, P A; The, L S Abstract: The light curves of Type Ia supernovae (SNe Ia) are powered by gamma rays emitted by the decay of radioactive elements such as 56Ni and its decay products. These gamma rays are downscattered, absorbed, and eventually reprocessed into the optical emission that makes up the bulk of all SN observations. Detection of the gamma rays that escape the expanding star provide the only direct means to study this power source for SN Ia light curves. Unfortunately, disagreements between calculations for the gamma-ray lines have made it difficult to interpret any gamma-ray observations. Here we present a detailed comparison of the major gamma-ray line transport codes for a series of one-dimensional SN Ia models. Discrepancies in past results were due to errors in the codes, and the corrected versions of the seven different codes yield very similar results. This convergence of the simulation results allows us to infer more reliable information from the current set of gamma-ray observations of SNe Ia. The observations of SN 1986G, SN 1991T, and SN 1998bu are consistent with explosion models based on their classification: subluminous, superluminous, and normally luminous, respectively. 2013-05-15T10:29:56Z 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/2117/19224 Title: SIXE: A Payload for MINISAT-02 Authors: Gómez, J; Isern Vilaboy, Jordi; Bravo Guil, Eduardo; Giovannelli, F; Padula, C L Abstract: A description of the X-ray instrument SIXE proposed for the MINISAT-02 mission is presented. The description includes the scientific goals and instrument performances. 2013-05-15T07:57:00Z http://hdl.handle.net/2117/19208 Title: El láser, fuente de fenómenos y dinámicas no lineales Authors: Vilaseca Alavedra, Ramon 2013-05-14T12:51:28Z http://hdl.handle.net/2117/19201 Title: A particle code for deflagrations in white dwarfs. I. Numerical techniques Authors: García Senz, Domingo; Bravo Guil, Eduardo; Serichol Augué, Núria Abstract: In this paper we report some specific features of the numerical technique used to study the dynamic evolution of massive white dwarfs following the explosive ignition of nuclear fuel under degenerate conditions. We focus on three important points: (1) how to construct a stable initial model for white dwarfs with a central density ρc > 109 g cm-3 in the context of smoothed particle hydrodynamics (SPH); (2) the procedure devised in the numerical handling of combustion fronts and thermal discontinuities; and (3) a proposed method based on techniques of analysis of dynamic sets of points to characterize the flame front structure. As we will show, the combination of these methods along with the standard SPH technique makes the study of deflagrations in massive white dwarfs feasible even in three dimensions. After explaining in detail the numerical scheme, we show the results of several calculations, in three dimensions, addressed to checking the ability of the hydrocode to handle deflagrations in massive white dwarfs in two density regimes. First, several tests were carried out under the physical conditions that characterize Chandrasekhar-mass models for Type Ia supernovae, and some of the results were compared with standard one-dimensional calculations. We also explored the consequences of deflagrations at very high densities, where electron captures play a fundamental role in the further evolution of the white dwarf, and where collapse to a neutron star instead of an explosion is expected. Our calculations support the idea that the SPH method and various fractal analysis techniques can successfully be used to model the gross features of deflagrations in white dwarfs provided that the nuclear energy injected at the first stages of the explosion is sufficient to dominate the numerical noise. An extensive number of calculations for both Type Ia supernovae explosions and accretion-induced collapse of a white dwarf to a neutron star are in progress and will be reported in future publications. 2013-05-14T11:38:27Z http://hdl.handle.net/2117/19200 Title: Constraining deflagration models of type Ia supernovae through intermediate-mass elements Authors: García Senz, Domingo; Bravo Guil, Eduardo; Cabezón Gómez, Rubén Martín; Woosley, S E Abstract: The physical structure of a nuclear flame is a basic ingredient of the theory of Type Ia supernovae (SNe Ia). Assuming an exponential density reduction with several characteristic times, we have followed the evolution of a planar nuclear flame in an expanding background from an initial density of 6.6 × 107 g cm-3 down to 2 × 106 g cm-3. The total amount of synthesized intermediate-mass elements (IMEs), from silicon to calcium, was monitored during the calculation. We have used the computed mass fractions, XIME, of these elements to estimate the total amount of IMEs synthesized during the deflagration of a massive white dwarf. Using XIME and adopting the usual hypothesis that the relevant flame speed is actually the turbulent speed on the integral length scale, we have built a simple geometrical approach to model the region where IMEs are thought to be produced. It turns out that a healthy production of IMEs involves the combination of not-too-short expansion times, τc ≥ 0.2 s, and high turbulent intensities. According to our results, it could be difficult to produce much more than 0.2 M☉ of intermediate-mass elements within the standard deflagrative paradigm. The calculations also suggest that the mass of the IMEs scales with the mass of the Fe-peak elements, making it difficult to reconcile energetic explosions with low ejected nickel masses, as in the well-observed supernova SN 1991bg or in SN 1998de. Thus, a large production of Si-peak elements, especially in combination with a low or moderate production of iron, could be better addressed either by the delayed detonation route in standard Chandrasekhar-mass models or, perhaps, by the off-center helium detonation in the sub-Chandrasekhar-mass scenario. 2013-05-14T11:16:11Z http://hdl.handle.net/2117/19199 Title: Neutrino-induced nucleosynthesis of a > 64 nuclei: The vp process Authors: Fröhlich, C; Martínez, G; Liebendörfer, M; Thielemann, F -K; Bravo Guil, Eduardo; Hix, W R; Langanke, K; Zinner, N T Abstract: We present a new nucleosynthesis process that we denote as the νp process, which occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino fluxes create proton-rich ejecta. In this process, antineutrino absorptions in the proton-rich environment produce neutrons that are immediately captured by neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with mass numbers A>64, making this process a possible candidate to explain the origin of the solar abundances of 92,94Mo and 96,98Ru. This process also offers a natural explanation for the large abundance of Sr seen in a hyper-metal-poor star. 2013-05-14T11:00:04Z http://hdl.handle.net/2117/19198 Title: Composition of the innermost core-collapse supernova ejecta Authors: Fröhlich, C; Hauser, P; Liebendörfer, M; Martínez, G; Thielemann, F -K; Bravo Guil, Eduardo; Zinner, N T; Hix, W R; Langanke, K; Mezzacappa, A; Nomoto, K Abstract: With currently known input physics and computer simulations in one dimension, a self-consistent treatment of core-collapse supernovae does not yet lead to successful explosions, while two-dimensional models show some promise. Thus, there are strong indications that the delayed neutrino mechanism works combined with a multidimensional convection treatment for unstable layers (possibly with the aid of rotation, magnetic fields and/or still existent uncertainties in neutrino opacities). On the other hand, there is a need to provide correct nucleosynthesis abundances for the progressing field of galactic evolution and observations of low-metallicity stars. The innermost ejecta is directly affected by the explosion mechanism, i.e., most strongly, the yields of Fe group nuclei for which an induced piston or thermal bomb treatment will not provide the correct yields because the effect of neutrino interactions is not included. We apply parameterized variations to the neutrino-scattering cross sections in order to mimic in one dimension the possible increase of neutrino luminosities caused by uncertainties in proto-neutron star convection. Alternatively, parameterized variations are applied to the neutrino absorption cross sections on nucleons in the "gain region" to mimic the increase in neutrino energy deposition enabled by convective turnover. We find that both measures lead to similar results, causing explosions and a Ye > 0.5 in the innermost ejected layers, due to the combined effect of a short weak-interaction timescale and a negligible electron degeneracy, unveiling the proton-neutron mass difference. We include all weak interactions (electron and positron capture, β-decay, neutrino and antineutrino capture on nuclei, and neutrino and antineutrino capture on nucleons) and present first nucleosynthesis results for these innermost ejected layers to discuss how they improve predictions for Fe group nuclei. The proton-rich environment results in enhanced abundances of 45Sc, 49Ti, and 64Zn as required by chemical evolution studies and observations of low-metallicity stars, as well as appreciable production of nuclei in the mass range up to A = 80. 2013-05-14T10:38:12Z