On the void explanation of the Cold Spot

The integrated Sachs-Wolfe (ISW) contribution induced on the cosmic microwave background by the presence of a supervoid as the one detected by Szapudi et al. (2015) is reviewed in this letter in order to check whether it could explain the Cold Spot (CS) anomaly. Two different models, previously used for the same purpose, are considered to describe the matter density profile of the void: a top hat function and a compensated profile produced by a Gaussian potential. The analysis shows that, even enabling ellipticity changes or different values for the dark-energy equation of state parameter $\omega$, the ISW contribution due to the presence of the void does not reproduce the properties of the CS. Finally, the probability of alignment between the void and the CS is also questioned as an argument in favor of a physical connection between these two phenomena

Exploring two-spin internal linear combinations for the recovery of the CMB polarization

We present a methodology to recover cosmic microwave background (CMB) polarization in which the quantity $P = Q+ iU$ is linearly combined at different frequencies using complex coefficients. This is the most general linear combination of the $Q$ and $U$ Stokes parameters which preserves the physical coherence of the residual contribution on the CMB estimation. The approach is applied to the internal linear combination (ILC) and the internal template fitting (ITF) methodologies. The variance of $P$ of the resulting map is minimized to compute the coefficients of the linear combination. One of the key aspects of this procedure is that it serves to account for a global frequency-dependent shift of the polarization phase. Although in the standard case, in which no global E-B transference depending on frequency is expected in the foreground components, minimizing $\left\langle |P|^2\right\rangle$ is similar to minimizing $\left\langle Q^2\right\rangle$ and $\left\langle U^2\right\rangle$ separately (as previous methodologies proceed), multiplying $Q$ and $U$ by different coefficients induces arbitrary changes in the polarization angle and it does not preserve the coherence between the spinorial components. The approach is tested on simulations, obtaining a similar residual level with respect to the one obtained with other implementations of the ILC, and perceiving the polarization rotation of a toy model with the frequency dependence of the Faraday rotation.Comment: 14 pages, 8 figures, 2 tables. Accepted for publication in MNRA

Searching for a dipole modulation in the large-scale structure of the Universe

Several statistical anomalies in the CMB temperature anisotropies seem to defy the assumption of a homogeneous and isotropic universe. In particular, a dipole modulation has been detected both in WMAP and Planck data. We adapt the methodology proposed by Eriksen et al. (2007) on CMB data to galaxy surveys, tracing the large-scale structure. We analyse the NRAO VLA Sky Survey (NVSS) data at a resolution of ~2 degrees for three different flux thresholds: 2.5, 5.0 and 10.0 mJy respectively. No evidence of a dipole modulation is found. This result suggests that the origin of the dipole asymmetry found in the CMB cannot be assigned to secondary anisotropies produced at redshifts around z = 1. However, it could still have been generated at redshifts higher or lower, such as the integrated Sachs-Wolfe effect produced by the local structures. Other all-sky surveys, like the infrared WISE catalogue, could help to explore with a high sensitivity a redshift interval closer than the one probed with NVSS.Comment: 6 pages, 2 figures. Some minor changes have been done from the original manuscript. This paper is accepted by MNRA

Compressed k2-Triples for Full-In-Memory RDF Engines

Current "data deluge" has flooded the Web of Data with very large RDF datasets. They are hosted and queried through SPARQL endpoints which act as nodes of a semantic net built on the principles of the Linked Data project. Although this is a realistic philosophy for global data publishing, its query performance is diminished when the RDF engines (behind the endpoints) manage these huge datasets. Their indexes cannot be fully loaded in main memory, hence these systems need to perform slow disk accesses to solve SPARQL queries. This paper addresses this problem by a compact indexed RDF structure (called k2-triples) applying compact k2-tree structures to the well-known vertical-partitioning technique. It obtains an ultra-compressed representation of large RDF graphs and allows SPARQL queries to be full-in-memory performed without decompression. We show that k2-triples clearly outperforms state-of-the-art compressibility and traditional vertical-partitioning query resolution, remaining very competitive with multi-index solutions.Comment: In Proc. of AMCIS'201

The Spontaneous Video and its Impact on the Digital Press

Most of us now have instant access mobile phones with integrated cameras so we are able to record an unplanned video at any time and place within a matter of seconds. Modern technology has provided us with the ability to create spontaneous videos. Spontaneous videos are a new way of portraying our society and communicating events and, by means of the internet and web 2.0 applications, they have the potential to reach every corner of the globe, form an integral part of mass media news reports, and influence public opinion. This study establishes the basis for identifying and understanding the spontaneous video, analysing its application in video activism and citizen journalism, and investigating its impact on the digital press. To this end, we have analysed spontaneous videos created and shared online by IES Lluís Vives students in Valencia on the 15th of February, 2012. Students held a protest on this date against education cuts carried out by the Valencian Community government in Spain. The resulting spontaneous videos had a great impact on the media and were reported by Spanish digital newspapers including El País, El Mundo, La Razón, ABC and Público.El hecho de transportar continuamente un teléfono móvil con cámara de vídeo integrada ofrece la posibilidad de grabar en vídeo de forma espontánea, en pocos segundos, sin planificación previa, en todo momento y lugar, cualquier acontecimiento. El vídeo espontáneo se muestra como una nueva forma de retratar nuestra sociedad y comunicar un suceso que, a través de Internet y la Web 2.0, se puede distribuir por cualquier rincón del planeta, puede llegar a formar parte de una noticia de medios de comunicación convencionales e influir en la opinión pública. Este trabajo establece las bases para identificar y comprender el vídeo espontáneo, trata su aplicación en el videoactivismo y el periodismo ciudadano, y estudia su impacto en la prensa digital. Para ello, se analizaron los vídeos espontáneos creados y difundidos en Internet por estudiantes del IES Lluís Vives de Valencia, el 15 de febrero de 2012, que se manifestaron en contra de los recortes en educación realizados por el gobierno de la Comunidad Valenciana (España). Los vídeos espontáneos resultantes generaron un importante impacto mediático y algunos de ellos formaron parte de noticias digitales de periódicos españoles como El País, El Mundo, La Razón, ABC y Público

Variational description of Gibbs-non-Gibbs dynamical transitions for spin flip systems with a Kac-type interaction

We continue our study of Gibbs-non-Gibbs dynamical transitions. In the present paper we consider a system of Ising spins on a large discrete torus with a Kac-type interaction subject to an independent spin-¿ip dynamics (in¿nite-temperature Glauber dynamics). We show that, in accordance with the program outlined in [11], in the thermodynamic limit Gibbs-non-Gibbs dynamical transitions are equivalent to bifurcations in the set of global minima of the large-deviation rate function for the trajectories of the empirical density conditional on their endpoint. More precisely, the time-evolved measure is non-Gibbs if and only if this set is not a singleton for some value of the endpoint. A partial description of the possible scenarios of bifurcation is given, leading to a characterization of passages from Gibbs to non-Gibbs and vice versa, with sharp transition times. Our analysis provides a conceptual step-up from our earlier work on Gibbs-non-Gibbs dynamical transitions for the Curie-Weiss model, where the mean-¿eld interaction allowed us to focus on trajectories of the empirical magnetization rather than the empirical density

Analysis of the influence of microstructural traps on hydrogen assisted fatigue

We investigate the influence of microstructural traps on hydrogen diffusion and embrittlement in the presence of cyclic loads. A mechanistic, multi-trap model for hydrogen transport is developed, implemented into a finite element framework, and used to capture the variation of crack tip lattice and trapped hydrogen concentrations as a function of the loading frequency, the trap binding energies and the trap densities. We show that the maximum value attained by the lattice hydrogen concentration during the cyclic analysis exhibits a notable sensitivity to the ratio between the loading frequency and the effective diffusion coefficient. This is observed for both hydrogen pre-charged samples (closed-systems) and samples exposed to a permanent source of hydrogen (open-systems). Experiments are used to determine the critical concentration for embrittlement, by mapping the range of frequencies where the output is the same as testing in inert environments. We then quantitatively investigate and discuss the implications of developing materials with higher trap densities in mitigating embrittlement in the presence of cyclic loads. It is shown that, unlike the static case, increasing the density of "beneficial traps" is a viable strategy in designing alloys resistant to hydrogen assisted fatigue for both closed- and open-systems