Diffusion of Hydrogen in Pd Assisted by Inelastic Ballistic Hot Electrons

Sykes {\it et al.} [Proc. Natl. Acad. Sci. {\bf 102}, 17907 (2005)] have reported how electrons injected from a scanning tunneling microscope modify the diffusion rates of H buried beneath Pd(111). A key point in that experiment is the symmetry between positive and negative voltages for H extraction, which is difficult to explain in view of the large asymmetry in Pd between the electron and hole densities of states. Combining concepts from the theory of ballistic electron microscopy and electron-phonon scattering we show that H diffusion is driven by the $s$-band electrons only, which explains the observed symmetry.Comment: 5 pages and 4 figure

Conversation with Lisa Garforth / Conversatorio con Lisa Garforth

\ua9 2023, Universidad Compultense Madrid. All rights reserved. Julia Ram\uedrez-Blanco interviews Lisa Garforth, author of the book Green Utopias and specialist in environmental utopias. With her, we talk about the possible ways of defining ecotopias, and how they manifest themselves both in literature and in different forms of social practice

Measures for a Transdimensional Multiverse

The multiverse/landscape paradigm that has emerged from eternal inflation and string theory, describes a large-scale multiverse populated by "pocket universes" which come in a huge variety of different types, including different dimensionalities. In order to make predictions in the multiverse, we need a probability measure. In $(3+1)d$ landscapes, the scale factor cutoff measure has been previously shown to have a number of attractive properties. Here we consider possible generalizations of this measure to a transdimensional multiverse. We find that a straightforward extension of scale factor cutoff to the transdimensional case gives a measure that strongly disfavors large amounts of slow-roll inflation and predicts low values for the density parameter $\Omega$, in conflict with observations. A suitable generalization, which retains all the good properties of the original measure, is the "volume factor" cutoff, which regularizes the infinite spacetime volume using cutoff surfaces of constant volume expansion factor.Comment: 30 pages, 1 figure Minor revisions, reference adde

CFD modeling of a road tunnel with multiple sources of Co. case of study: boqueron-I tunnel

This work aims to the modeling of CO transport in one section considered critical of the Boqueron I tunnel, located on the outskirts of Caracas, the capital city of Venezuela, with a scenario where vehicles are stopped by an interruption of traffic. This scenario considers a relationship between the number of large-sized vehicles (buses or trucks) and small-sized vehicles (passenger cars) reported by transit statistics and also, it considers the semi-transverse ventilation system in the tunnel. It is explored the influence of the ventilation on the flow patterns and its relationship to the regions with the highest CO concentration. The finite-volume based finite element method is used for the discretization of the computational domain and the integration of the governing equations. The transient 3D-incompressible Navier-Stokes, energy, mass and species conservation equations, along with the k-e turbulence equations, were discretized, using higher-order numerical schemes in space. The numerical simulation is performed using a fully implicit coupled treatment of the set of resulting discrete transport equation

VISIR-VLT high resolution study of the extended emission of four obscured post-AGB candidates

The onset of the asymmetry of planetary nebulae (PNe) is expected to occur during the late Asymptotic Giant Branch (AGB) and early post-AGB phases of low- and intermediate-mass stars. Among all post-AGB objects, the most heavily obscured ones might have escaped the selection criteria of previous studies detecting extreme axysimmetric structures in young PNe. Since the most heavily obscured post-AGB sources can be expected to descend from the most massive PN progenitors, these should exhibit clear asymmetric morphologies. We have obtained VISIR-VLT mid-IR images of four heavily obscured post-AGB objects barely resolved in previous Spitzer IRAC observations to analyze their morphology and physical conditions across the mid-IR. The VISIR-VLT images have been deconvolved, flux calibrated, and used to construct RGB composite pictures as well as color and optical depth maps that allow us to study the morphology and physical properties of the extended emission of these sources. We have detected extended emission from the four objects in our sample and resolved it into several structural components that are greatly enhanced in the temperature and optical depth maps. They reveal the presence of asymmetry in three young PNe (IRAS 15534-5422, IRAS 17009-4154, and IRAS 18454+0001), where the asymmetries can be associated with dusty torii and slightly bipolar outflows. The fourth source (IRAS 18229-1127), a possible post-AGB star, is better described as a rhomboidal detached shell. The heavily obscured sources in our sample do not show extreme axisymmetric morphologies. This is at odds with the expectation of highly asymmetrical morphologies in post-AGB sources descending from massive PN progenitors. The sources presented in this paper may be sampling critical early phases in the evolution of massive PN progenitors, before extreme asymmetries develop.Comment: 9 pages, 4 figure

Rotation of Hot Horizontal Branch Stars in the Globular Clusters NGC 1904, NGC 2808, NGC 6093 and NGC 7078

We present high resolution UVES+VLT spectroscopic observations of 56 stars in the extended horizontal branch (EHB) of the Galactic globular clusters NGC 1904, NGC 2808, NGC 6093, and NGC 7078. Our data reveal for the first time the presence in NGC 1904 of a sizable population of fast (vsini > 20 km/s) horizontal branch (HB) rotators, confined to the cool end of the EHB, similar to that found in M13. We also confirm the fast rotators already observed in NGC 7078. The cooler stars (Teff < 11,500 K) in these three clusters show a range of rotation rates, with a group of stars rotating at ~ 15 km/s or less, and a fast rotating group at ~ 30 km/s. Apparently, the fast rotators are relatively more abundant in NGC 1904 and M13, than in NGC 7078. No fast rotators have been identified in NGC 2808 and NGC 6093. All the stars hotter than Teff ~ 11,500 K have projected rotational velocities vsini < 12 km/s, but less than 20% have vsini < 2 km/s. The connection between photometric gaps in the HB and the change in the projected rotational velocities is not confirmed by the new data. However, our data are consistent with a relation between this discontinuity and the HB jump. We discuss a number of possibilities for the origin of the stellar rotation distribution along the HB. We conclude that none of them can yet provide a satisfactory explanation of the observations.Comment: 12 pages, 3 figures, ApJ Letter, accepte

Estudio de la entalpía de inmersión y de la adsorción de fenoles hidroxilados desde solución acuosa sobre carbón activado

Se determinan las entalpías de inmersión de un carbón activado granular comercial CarbochemTM –PS230, CAG, en función de la cantidad adsorbida de derivados fenólicos hidroxilados, fenol, catecol, resorcinol, hidroquinona y pirogalol en soluciones acuosas, con el fin de caracterizar la interacción sólido-solución acuosa y evaluar la influencia de la posición, del número de hidroxilos en el anillo aromático y la solubilidad de los fenoles en la adsorción sobre el carbón activado. Los resultados muestran una variación en la entalpía de inmersión, que se relaciona conla capacidad de adsorción y que favorece la interacción del resorcinol sobre el carbón activado, con un valor de entalpía de inmersión de 41,00 J·g-1, que permite observar que la intensidad de la interacción cambia en función de la solubilidad y de la contribución del número de sustituyentes hidroxilo en el anillo aromático.