Representations in Density Dependent Hadronic Field Theory and compatibility with QCD sum-rules

Different representations of an effective, covariant theory of the hadronic interaction are examined. For this purpose we have introduced nucleon-meson vertices parametrized in terms of scalar combinations of hadronic fields, extending the conceptual frame of the Density Dependent Hadronic Field Theory. Nuclear matter properties at zero temperature are examined in the Mean Field Approximation, including the equation of state, the Landau parameters, and collective modes. The treatment of isospin channels in terms of QCD sum rules inputs is outlined.Comment: 23 pages, 6 PostScript figures, Revtex4 clas

Two Tunnels to Inflation

We investigate the formation via tunneling of inflating (false-vacuum) bubbles in a true-vacuum background, and the reverse process. Using effective potentials from the junction condition formalism, all true- and false-vacuum bubble solutions with positive interior and exterior cosmological constant, and arbitrary mass are catalogued. We find that tunneling through the same effective potential appears to describe two distinct processes: one in which the initial and final states are separated by a wormhole (the Farhi-Guth-Guven mechanism), and one in which they are either in the same hubble volume or separated by a cosmological horizon. In the zero-mass limit, the first process corresponds to the creation of an inhomogenous universe from nothing, while the second mechanism is equivalent to the nucleation of true- or false-vacuum Coleman-De Luccia bubbles. We compute the probabilities of both mechanisms in the WKB approximation using semi-classical Hamiltonian methods, and find that -- assuming both process are allowed -- neither mechanism dominates in all regimes.Comment: 16 PRD-style pages, 13 figures. PRD, in press. Revised to match published versio

Modelamiento y simulación de algoritmos adaptivos de alocación de bits para sistemas multiuser

Este proyecto se enfoca en el análisis y desarrollo de un algoritmo que nos permitirá entender con mayor facilidad lo que es la alocación adaptiva de bit en un sistema multiuser OFDM.La solución que hemos planteado para el desarrollo de este proyecto es de tipo “Multi-userdiscrete bit-loading”, la cual podremos ver desarrollada más adelante {3.3}, pero que con una sencilla explicación podemos decir que esta solución trata de encontrar la forma más optima de transmitir una cierta cantidad de bits, con el único propósito de minimizar la potencia total de transmisión.la solución planteada será desarrollada en un escenario específico con valores determinados con la finalidad de que cumpla con las condiciones necesarias para trabajar en un medio VDSL2. Gracias a análisis realizado se pudo verificar la eficiencia del algoritmo y la gran utilidad al momento de realizar la alocación ya que permite minimizar al máximo la potencia total de transmición. El algoritmo planteado en este proyecto fue desarrollado en el software MATLAB, ya que consideramos que es un software nos permite recopilar datos de una manera más real, con el propósito de brindar la explicación más clara a lector

Pulsation Period Changes as a Tool to Identify Pre-Zero Age Horizontal Branch Stars

One of the most dramatic events in the life of a low-mass star is the He flash, which takes place at the tip of the red giant branch (RGB) and is followed by a series of secondary flashes before the star settles into the zero-age horizontal branch (ZAHB). Yet, no stars have been positively identified in this key evolutionary phase, mainly for two reasons: first, this pre-ZAHB phase is very short compared to other major evolutionary phases in the life of a star; and second, these pre-ZAHB stars are expected to overlap the loci occupied by asymptotic giant branch (AGB), HB and RGB stars observed in the color-magnitude diagram (CMD). We investigate the possibility of detecting these stars through stellar pulsations, since some of them are expected to rapidly cross the Cepheid/RR Lyrae instability strip in their route from the RGB tip to the ZAHB, thus becoming pulsating stars along the way. As a consequence of their very high evolutionary speed, some of these stars may present anomalously large period change rates. We constructed an extensive grid of stellar models and produced pre-ZAHB Monte Carlo simulations appropriate for the case of the Galactic globular cluster M3 (NGC 5272), where a number of RR Lyrae stars with high period change rates are found. Our results suggest that some -- but certainly not all -- of the RR Lyrae stars in M3 with large period change rates are in fact pre-ZAHB pulsators.Comment: Conference Proceedings HELAS Workshop on 'Synergies between solar and stellar modelling', Rome, June 2009, Astrophys. Space Sci., in the pres

Spatial Structure of Ion Beams in an Expanding Plasma

We report spatially resolved perpendicular and parallel, to the magnetic field, ion velocity distribution function (IVDF) measurements in an expanding argon helicon plasma. The parallel IVDFs, obtained through laser induced fluorescence (LIF), show an ion beam with v ≈ 8000 m/s flowing downstream and confined to the center of the discharge. The ion beam is measurable for tens of centimeters along the expansion axis before the LIF signal fades, likely a result of metastable quenching of the beam ions. The parallel ion beam velocity slows in agreement with expectations for the measured parallel electric field. The perpendicular IVDFs show an ion population with a radially outward flow that increases with distance from the plasma axis. Structures aligned to the expanding magnetic field appear in the DC electric field, the electron temperature, and the plasma density in the plasma plume. These measurements demonstrate that at least two-dimensional and perhaps fully three-dimensional models are needed to accurately describe the spontaneous acceleration of ion beams in expanding plasmas

Modelos mentales de comunicación y consumo. Una comparación intercultural de publicidad televisiva

Este estudio prospectivo plantea la interrogante si la publicidad televisiva difiere entre distintas culturas y si es así, cómo y en qué medida. En contraste a la mayoría de los estudios respectivos, nos hemos concentrado en un protocolo detallado basado en un análisis formal que está estadísticamente orientado. En una perspectiva más amplia, la relación entre la comunicación cara-a-cara y la comunicación mediatizada por la tecnología está escrutada. Asumiendo que hay varias diferencias, una hipótesis sería que éstas se originan en hábitos de comunicación antiguos a aquellos encontrados en la comunicación por medios tecnológicos. En parte, eso supondría una transferencia entre diferentes medios, relacionando la organización del habla con la de las imágenes. Como solamente por medio de estudios comparativos se puede responder dichas interrogantes, se compararon dos muestras de publicidad alemana y ecuatoriana. Para evitar una sobreestimación de las diferencias culturales es inevitable el investigar también el nivel intercultural para evaluar las fluctuaciones relacionadas con los contenidos

Synchronization of interconnected networks: the role of connector nodes

In this Letter we identify the general rules that determine the synchronization properties of interconnected networks. We study analytically, numerically and experimentally how the degree of the nodes through which two networks are connected influences the ability of the whole system to synchronize. We show that connecting the high-degree (low-degree) nodes of each network turns out to be the most (least) effective strategy to achieve synchronization. We find the functional relation between synchronizability and size for a given network-of-networks, and report the existence of the optimal connector link weights for the different interconnection strategies. Finally, we perform an electronic experiment with two coupled star networks and conclude that the analytical results are indeed valid in the presence of noise and parameter mismatches.Comment: Accepted for publication in Physical Review Letters. Main text: 5 pages, 4 figures. Supplemental material: 8 pages, 3 figure

The missing metals problem. III How many metals are expelled from galaxies?

[Abridged] We revisit the metal budget at z~2. In the first two papers of this series, we already showed that ~30% (to <60% if extrapolating the LF) of the metals are observed in all z~2.5 galaxies detected in current surveys. Here, we extend our analysis to the metals outside galaxies, i.e. in intergalactic medium (IGM), using observational data and analytical calculations. Our results for the two are strikingly similar: (1) Observationally, we find that, besides the small (5%) contribution of DLAs, the forest and sub-DLAs contribute subtantially to make <30--45% of the metal budget, but neither of these appear to be sufficient to close the metal budget. The forest accounts for 15--30% depending on the UV background, and sub-DLAs for >2% to <17% depending on the ionization fraction. Together, the `missing metals' problem is substantially eased. (2) We perform analytical calculations based on the effective yield--mass relation. At z=2, we find that the method predicts that 2$--50% of the metals have been ejected from galaxies into the IGM, consistent with the observations. The metal ejection is predominantly by L<1/3L_B^*(z=2) galaxies, which are responsible for 90% the metal enrichment, while the 50 percentile is at L~1/10L^*_B(z=2). As a consequence, if indeed 50% of the metals have been ejected from galaxies, 3--5 bursts of star formation are required per galaxy prior to z=2. The ratio between the mass of metals outside galaxies to those in stars has changed from z=2 to z=0: it was 2:1 or 1:1 and is now 1:8 or 1:9. This evolution implies that a significant fraction of the IGM metals will cool and fall back into galaxies.Comment: 18pages, MNRAS, in press; small changes to match proofs; extended version with summary tabl

Landau parameters for isospin asymmetric nuclear matter based on a relativistic model of composite and finite extension nucleons

We study the properties of cold asymmetric nuclear matter at high density, applying the quark meson coupling model with excluded volume corrections in the framework of the Landau theory of relativistic Fermi liquids. We discuss the role of the finite spatial extension of composite baryons on dynamical and statistical properties such as the Landau parameters, the compressibility, and the symmetry energy. We have also calculated the low lying collective eigenfrequencies arising from the collisionless quasiparticle transport equation, considering both unstable and stable modes. An overall analysis of the excluded volume correlations on the collective properties is performed.Comment: 24 pages, 6 figure