Interacting dark sector with variable vacuum energy

We examine a cosmological scenario where dark matter is coupled to a variable vacuum energy while baryons and photons are two decoupled components for a spatially flat Friedmann-Robertson-Walker spacetime. We apply the $\chi^{2}$ method to the updated observational Hubble data for constraining the cosmological parameters and analyze the amount of dark energy in the radiation era. We show that our model fulfills the severe bound of $\Omega_{x}(z\simeq 1100)<0.009$ at the $2\sigma$ level, so it is consistent with the recent analysis that includes cosmic microwave background anisotropy measurements from the Planck survey, the Atacama Cosmology Telescope, and the South Pole Telescope along with the future constraints achievable by the Euclid and CMBPol experiments, and fulfills the stringent bound $\Omega_{x}(z\simeq 10^{10})<0.04$ at the $2\sigma$ level in the big-bang nucleosynthesis epoch.Comment: 5 pages,3 figures, 2 tables. (http://prd.aps.org/abstract/PRD/v88/i8/e087301

Full two-photon downconversion of just a single photon

We demonstrate, both numerically and analytically, that it is possible to generate two photons from one and only one photon. We characterize the output two photon field and make our calculations close to reality by including losses. Our proposal relies on real or artificial three-level atoms with a cyclic transition strongly coupled to a one-dimensional waveguide. We show that close to perfect downconversion with efficiency over 99% is reachable using state-of-the-art Waveguide QED architectures such as photonic crystals or superconducting circuits. In particular, we sketch an implementation in circuit QED, where the three level atom is a transmon

Tracing high density gas in M 82 and NGC 4038

We present the first detection of CS in the Antennae galaxies towards the NGC 4038 nucleus, as well as the first detections of two high-J (5-4 and 7-6) CS lines in the center of M 82. The CS(7-6) line in M 82 shows a profile that is surprisingly different to those of other low-J CS transitions we observed. This implies the presence of a separate, denser and warmer molecular gas component. The derived physical properties and the likely location of the CS(7-6) emission suggests an association with the supershell in the centre of M 82.Comment: 10 pages, 3 figures, ApJ Letter - ACCEPTE

Hierarchy and Competition in CSCW applications: Model and case study

CSCW applications need to adapt themselves to the functional and organizational structures of people that use them. However they do not usually support division in groups with a certain hierarchical structure among them. In this paper, we propose and study a theoretical model of groupware appliations that reflects those hierarchical interactions. The proposed model is also intended to evaluate the effects in performance derived from competitive and collaborative relationships among the components of a hierarchy of groups. In order to demonstrate the above ideas, a groupware game, called Alymod, was designed and implemented using a modified version of a well-known CSCW Toolkit, namely Groupkit. Groupkit was modified in order to support group interactions in the same CSCW application. In Alymod, participants compete or collaborate within a hierarchical structure to achieve a common goal (completing gaps in a text, finishing numerical series, resolving University course examinations, etc.).Publicad

Técnicas SIG aplicadas al estudio del relieve de los Montes de León (NO de la Península Ibérica)

En este trabajo se presenta un método basado en el análisis de modelos digitales de elevación (MDE) a través de SIG, encaminado a realizar una cartografía preliminar de antiguas superficies de aplanamiento en los relieves que bordean la cuenca del Bierzo (oeste de la provincia de León, noroeste de la Península Ibérica). El área de estudio es un complejo sistema escalonado de niveles de aplanamiento elaborados sobre el basamento del Macizo Ibérico, constituyente de los relieves montañosos de la zona, deformado por la Orogenia Alpina durante el Cenozoico, en donde las superficies se encuentran elevadas, basculadas, fragmentadas y muy degradadas. Partiendo del MDE con paso de malla de 25 m del PNOA se realizó una caracterización general de la zona de estudio mediante la obtención de mapas derivados: pendientes, orientaciones de pendiente y sombreado, así como de la red de drenaje. Empleando la extensión EZ Profile para ArcGIS 9.3 se generaron 213 perfiles topográficos, sobre los principales cordales e interfluvios, con los que se localizaron y correlacionaron los elementos culminantes (indicios y restos de superficies de aplanamiento) presentes en toda la zona de estudio, lo que permitió reconstruir el relieve previo al desmantelamiento por parte de la red de drenaje. Una vez delimitadas las superficies de aplanamiento se procedió a su caracterización, agrupación y jerarquización, mediante el estudio de superficies de tendencia, el análisis de la red de drenaje y la relación con la actividad tectónica. Se realizó una reconstrucción teórica de cada uno de los aplanamientos a través de la interpolación de los puntos pertenecientes al antiguo relieve, generando así una superficie de tendencia de primer orden, de donde se obtuvo la orientación y pendiente de cada una de ellas. A su vez, se buscaron anomalías en los cauces de los ríos que atraviesan los aplanamientos, que pudieran indicar actividad tectónica reciente. Asimismo, se llevó a cabo un estudio de las cuencas de drenaje, sobre las que se realizaron cálculos de hipsometría y de asimetría (Factor de Asimetría). Por último, se calculó la incisión del drenaje sobre las superficies de aplanamiento cartografiadas. Como resultado se obtuvieron veinte superficies clasificadas en ocho niveles, desde los 1000m a los 2100m, en donde se observa cómo los distintos elementos de un mismo nivel se encuentran en extremos opuestos de la zona de estudio, ubicados en forma de orla perdiendo altura hacia la cuenca del Bierzo.Trabajo financiado por el proyecto de la Junta de Castilla y León LE311A12-2 y por el proyecto Consolider Ingenio 2006 CSD-2006, TopoIberia Geociencias en Iberia

Local Behavior of the First-Order Gradient Correction to the Thomas-Fermi Kinetic Energy Functional

The first order gradient correction to the Thomas-Fermi functional, proposed by Haq, Chattaraj and Deb (Chem. Phys. Lett. vol. 81, 8031, 1984) has been studied by evaluating both the total kinetic energy and the local kinetic energy density. For testing the kinetic energy density we evaluate its deviation from an exact result through a quality factor, a parameter that reflects the quality of the functionals in a better way than their relative errors. The study is performed on two different systems: light atoms (up to Z=18) and a noninteracting model of fermions confined in a Coulombic-type potential. It is found than this approximation gives very low relative errors and a better local behavior than any of the usual generalized gradient approximation semilocal kinetic density functionals.Comment: 7 pages, 2 tables, 4 figure

Petrov D vacuum spaces revisited: Identities and Invariant Classification

For Petrov D vacuum spaces, two simple identities are rederived and some new identities are obtained, in a manageable form, by a systematic and transparent analysis using the GHP formalism. This gives a complete involutive set of tables for the four GHP derivatives on each of the four GHP spin coefficients and the one Weyl tensor component. It follows directly from these results that the theoretical upper bound on the order of covariant differentiation of the Riemann tensor required for a Karlhede classification of these spaces is reduced to two.Comment: Proof about the Karlhede upper bound improved and discussion of case IIIA re-written. Acknowledgments section expanded. To appear in Classical and Quantum Gravit

A Mathematical Model to Study the Meningococcal Meningitis

AbstractThe main goal of this work is to introduce a novel mathematical model to study the spreading of meningococcal meningitis. Specifically, it is a discrete mathematical model based on cellular automata where the population is divided in five classes: sus- ceptible, asymptomatic infected, infected with symptoms, carriers, recovered and died. It catches the individual characteristics of people in order to give a prediction of both the individual behavior, and whole evolution of population

Molecular gas chemistry in AGN. II. High-resolution imaging of SiO emission in NGC1068: shocks or XDR?

This paper is part of a multi-species survey of line emission from the molecular gas in the circum-nuclear disk (CND) of the Seyfert 2 galaxy NGC1068. Single-dish observations have provided evidence that the abundance of silicon monoxide(SiO) in the CND of NGC1068 is enhanced by 3-4 orders of magnitude with respect to the values typically measured in quiescent molecular gas in the Galaxy. We aim at unveiling the mechanism(s) underlying the SiO enhancement. We have imaged with the IRAM Plateau de Bure interferometer the emission of the SiO(2-1) and CN(2--1) lines in NGC1068 at 150pc and 60pc spatial resolution, respectively. We have also obtained complementary IRAM 30m observations of HNCO and methanol (CH3OH) lines. SiO is detected in a disk of 400pc size around the AGN. SiO abundances in the CND of (1-5)xE-09 are about 1-2 orders of magnitude above those measured in the starburst ring. The overall abundance of CN in the CND is high: (0.2-1)xE-07. The abundances of SiO and CN are enhanced at the extreme velocities of gas associated with non-circular motions close to the AGN (r<70pc). Abundances measured for CN and SiO, and the correlation of CN/CO and SiO/CO ratios with hard X-ray irradiation, suggest that the CND of NGC1068 has become a giant X-ray dominated region (XDR). The extreme properties of molecular gas in the circum-nuclear molecular disk of NGC1068 result from the interplay between different processes directly linked to nuclear activity. Whereas XDR chemistry offers a simple explanation for CN and SiO in NGC1068, the relevance of shocks deserves further scrutiny. The inclusion of dust grain chemistry would help solve the controversy regarding the abundances of other molecular species, like HCN, which are under-predicted by XDR models.Comment: 18 pages, 13 figures, 2 tables; accepted for publication in A&