Direct resolution of unoccupied states in solids via two photon photoemission

Non-linear effects in photoemission are shown to open a new access to the band structure of unoccupied states in solids, totally different from hitherto used photoemission spectroscopy. Despite its second-order nature, strong resonant transitions occur, obeying exact selection rules of energy, crystal symmetry, and momentum. Ab-initio calculations are used to demonstrate that such structures are present in low-energy laser spectroscopy experimental measurements on Si previously published. Similar resonances are expected in ultraviolet angle-resolved photoemission spectra, as shown in a model calculation on Al.Comment: 12 pages, including 4 figure

Bounds of functional outputs for parabolic problems. Part II: Bounds of the exact solution

The paper introduces a methodology to compute upper and lower bounds for linear-functional outputs of the exact solutions of parabolic problems. In this second part, the bounds account for the error both in space and time. The assumption stating that the error introduced by the time marching scheme is negligible, used in the first part, is removed here. The bounds are computed starting from an approximation of the exact solution, associated with a spatial mesh and a time grid. Nevertheless, the bounds are guaranteed with respect to the exact solution, with no reference to any mesh or time discretization

Ecografía del tracto gastrointestinal en pequeños animales

En el presente artículo se realiza una descripción de la imagen ecográfica normal del tracto digestivo en el perro y en el gato y de las diferentes patologías que pueden observarse

News Session-Based Recommendations using Deep Neural Networks

News recommender systems are aimed to personalize users experiences and help them to discover relevant articles from a large and dynamic search space. Therefore, news domain is a challenging scenario for recommendations, due to its sparse user profiling, fast growing number of items, accelerated item's value decay, and users preferences dynamic shift. Some promising results have been recently achieved by the usage of Deep Learning techniques on Recommender Systems, specially for item's feature extraction and for session-based recommendations with Recurrent Neural Networks. In this paper, it is proposed an instantiation of the CHAMELEON -- a Deep Learning Meta-Architecture for News Recommender Systems. This architecture is composed of two modules, the first responsible to learn news articles representations, based on their text and metadata, and the second module aimed to provide session-based recommendations using Recurrent Neural Networks. The recommendation task addressed in this work is next-item prediction for users sessions: "what is the next most likely article a user might read in a session?" Users sessions context is leveraged by the architecture to provide additional information in such extreme cold-start scenario of news recommendation. Users' behavior and item features are both merged in an hybrid recommendation approach. A temporal offline evaluation method is also proposed as a complementary contribution, for a more realistic evaluation of such task, considering dynamic factors that affect global readership interests like popularity, recency, and seasonality. Experiments with an extensive number of session-based recommendation methods were performed and the proposed instantiation of CHAMELEON meta-architecture obtained a significant relative improvement in top-n accuracy and ranking metrics (10% on Hit Rate and 13% on MRR) over the best benchmark methods.Comment: Accepted for the Third Workshop on Deep Learning for Recommender Systems - DLRS 2018, October 02-07, 2018, Vancouver, Canada. https://recsys.acm.org/recsys18/dlrs

Coal mine ventilation air methane combustion in a catalytic reverse flow reactor: Influence of emission humidity

The role of the humidity content on the performance of catalytic reverse flow reactors (RFRs) for the abatement of methane emissions from coal mines is studied in this manuscript. It has been demonstrated that this technique is very useful for the abatement, and even upgrading, of these emissions. However, the effect of humidity on the reactor performance has not been addressed yet, in spite of being well known that water is an inhibitor in catalytic combustion. Experimental studies in a lab-scale isothermal fixed bed reactor demonstrated that water decreases the activity of a palladium on alumina catalyst for the combustion of methane, but this inhibition is entirely reversible, results fitting well to a Langmuir–Hinshelwood kinetic model. Then, the influence of water was studied in a bench-scale RFR operating at near adiabatic conditions at different switching times (100–600 s) and methane feed concentrations (2700–7200 ppm). Finally, a mathematical model for the reverse flow reactor, including the kinetic model with water inhibition, has been validated using the experimental results. This model is of key importance for designing this type of reactors for the treatment of mine ventilation emissions

Efectos de la disponibilidad de agua y nutrientes en el patrón de acumulación de carbohidratos en plántulas de tres especies de Quercus

6 páginas, 2 figuras y 2 tablasSe pretende estimar el efecto de un eventual cambio climático y edáfico sobre el patrón de almacenamiento de carbohidratos en plántulas de un año de tres especies leñosas mediterráneas del género Quercus. Para ello se han cultivado las plántulas bajo tres condiciones contrastadas de fertilidad y tres de riego, experimento no factorial, durante una estación de crecimiento. Se espera que en los medios menos fértiles se acumule carbono en forma de reservas debido a la limitación en el crecimiento por falta de nutrientes. Asimismo, en condiciones de riego bajo, aumente la concentración de glucosa para contribuir al ajuste osmótico de las hojas. Por último, esperamos que Q. faginea, la especie de crecimiento más rápido, invierta mayor cantidad de carbono en crecimiento y por tanto acumule menos almidón. Las concentración de almidón en raíz y tallo de Q. ilex y Q. coccifera fue inversamente proporcional al nivel de fertilización. La concentración de glucosa foliar mostró mayores concentraciones en las plántulas que experimentaron déficit hídrico. La especie que más carbohidratos almacenó fue Q. faginea. Nuestro estudio sugiere, que el efecto de un incremento de aridez sobre el almacenamiento de carbohidratos depende, no sólo de la especie, sino también de la fertilidad del suelo sobre el que se asiente.Universidad de Alcalá. Alcalá de Henares y Centro de Ciencias Medioambientales. CSICPeer reviewe

Non-equilibrium Anisotropic Phases, Nucleation and Critical Behavior in a Driven Lennard-Jones Fluid

We describe short-time kinetic and steady-state properties of the non--equilibrium phases, namely, solid, liquid and gas anisotropic phases in a driven Lennard-Jones fluid. This is a computationally-convenient two-dimensional model which exhibits a net current and striped structures at low temperature, thus resembling many situations in nature. We here focus on both critical behavior and details of the nucleation process. In spite of the anisotropy of the late--time spinodal decomposition process, earlier nucleation seems to proceed by Smoluchowski coagulation and Ostwald ripening, which are known to account for nucleation in equilibrium, isotropic lattice systems and actual fluids. On the other hand, a detailed analysis of the system critical behavior rises some intriguing questions on the role of symmetries; this concerns the computer and field-theoretical modeling of non-equilibrium fluids.Comment: 7 pages, 9 ps figures, to appear in PR

Editorial: Non-native tree species: Impacts and management

Non-native tree species are an important component of many forests around the world. These species were introduced for various reasons: the provision of wood and non-timber forest products, soil protection or rehabilitation, ornamental purposes, etc. In fact, they are important for sectoral economies, especially locally and in rural landscapes. However, there are multiple contexts in which some of these trees may have undesired negative effects, such as declines of biodiversity, increases of disturbance frequency, or disruptions of ecological balance of the native forests, greatly affecting the provision of ecosystem services. This Research Topic includes articles focusing on different aspects of relevance in the management of non-native tree species, ranging from identifying knowledge gaps and future implications, investigating the future use of non-native trees, providing governance approaches, assessment of impacts, and applying novel monitoring approaches

Electron scattering on disordered double-barrier GaAs-AlxGa1-xAs heterostructures

We present a novel model to calculate vertical transport properties such as conductance and current in unintentionally disordered double-barrier GaAs-AlxGa1-xAs heterostructures. The source of disorder comes from interface roughness at the heterojunctions (lateral disorder) as well as spatial inhomogeneities of the Al mole fraction in the barriers (compositional disorder). Both lateral and compositional disorder break translational symmetry along the lateral direction and therefore electrons can be scattered off the growth direction. The model correctly describes channel mixing due to these elastic scattering events. In particular, for realistic degree of disorder, we have found that the effects of compositional disorder on transport properties are negligible as compared to the effects due to lateral disorder