Vibrational anharmonicity of small gold and silver clusters using the VSCF method

We study the vibrational spectra of small neutral gold (Au2–Au10) and silver (Ag2–Au5) clusters using the vibrational self-consistent field method (VSCF) in order to account for anharmonicity. We report harmonic, VSCF, and correlation-corrected VSCF calculations obtained using a vibrational configuration interaction approach (VSCF/VCI). Our implementation of the method is based on an efficient calculation of the potential energy surfaces (PES), using periodic density functional theory (DFT) with a plane-wave pseudopotential basis. In some cases, we use an efficient technique (fast-VSCF) assisted by the Voter–Chen potential in order to get an efficient reduction of the number of pair-couplings between modes. This allows us to efficiently reduce the computing time of 2D-PES without degrading the accuracy. We found that anharmonicity of the gold clusters is very small with maximum rms deviations of about 1 cm−1, although for some particular modes anharmonicity reaches values slightly larger than 2 cm−1. Silver clusters show slightly larger anharmonicity. In both cases, large differences between calculated and experimental vibrational frequencies (when available) stem more likely from the quality of the electronic structure method used than from vibrational anharmonicity. We show that noble gas embedding often affects the vibrational properties of these clusters more than anharmonicity, and discuss our results in the context of experimental studies

The nature and role of the gold-krypton interactions in small neutral gold clusters

© 2015 American Chemical Society. We investigate the nature and role of krypton embedding in small neutral gold clusters. For some of these clusters, we observe a particular site-dependent character of the Kr binding that does not completely follow the criterion of binding at low-coordinated sites, widely accepted for interaction of a noble gas with closed-shell metal systems such as metal surfaces. We aim at understanding the effect of low dimensionality and open-shell electronic structure of the odd-numbered clusters on the noble gas-metal cluster interaction. First, we investigate the role of attractive and repulsive forces, and the frontier molecular orbitals. Second, we investigate the Au-Kr interaction in terms of reactivity and bonding character. We use a reactivity index derived from Fukui formalism, and criteria provided by the electron localization function (ELF), in order to classify the type of bonding. We carry out this study on the minimum energy structures of neutral gold clusters, as obtained using pseudo potential plane-wave density functional theory (DFT). A model is proposed that includes the effect of attractive electrostatic, van der Waals and repulsive forces, together with effects originating from orbital overlap. This satisfactorily explains minimum configurations of the noble gas-gold cluster systems, the site preference of the noble gas atoms, and changes in electronic properties

La usurpación de la identidad con fines paródicos en la red social Twitter: ¿manifestaciones de descortesía verbal?

En este trabajo exploratorio nos ocupamos de los perfiles o cuentas paródicos creados en Twitter, cuyo propósito parece ser el de vulnerar la imagen de numerosos personajes públicos. Con base en los planteamientos de la pragmática sociocultural, investigamos las principales actividades de imagen llevadas a cabo por los administradores de estas cuentas y comprobamos en qué medida sus mensajes tienen efectos negativos, esto es, constituyen manifestaciones de descortesía para el personaje suplantado, para el autor de los mensajes o para los destinatarios. Por medio del análisis cualitativo de un corpus de 5030 tuits, observamos que la parodia en este contexto tiene un efecto negativo sobre la imagen del personaje público, pero permite reforzar los lazos sociales con los propios seguidores.In this exploratory study we focus on fake profiles created on Twitter, whose purpose seems to be threatening the face of public figures and celebrities. Following a sociocultural pragmatic approach, we investigate the main face work strategies adopted by the administrators of these profiles and verify whether the messages they publish have negative effects on the mocked public figure, the administrator or the listeners’ faces, being an expression of impoliteness. The qualitative analysis of a corpus of 5030 tweets leads to the conclusion that parody in this context has a negative effect on the public figure’s face, but, at the same time, it strengthens the social ties with followers

An alternative methodology to assess the quality of empirical potentials for small gold clusters

We present a methodology based on local comparisons of potential energy surfaces (PES) in order to assess the quality of empirical potentials. We compare five typical empirical potentials using a criterion that shows which of these potentials resembles better a PES obtained with a high-level electronic structure method. The methodology relies on a many-body expansion in terms of normal coordinates of both the empirical and high-level theory PES. Then we investigate in a systematical way, how the features of the reference high-level theory PES are reproduced by each empirical potential in the vicinity of a given minimum energy structure. We use plane-wave density functional theory (DFT) as a reference, in particular the Perdew–Burke–Ernzerhof (PBE) exchange–correlation functional and an ultrasoft Vanderbilt pseudo potential. This study is carried out on neutral gold clusters with up to five atoms

Los marcadores del discurso en la construcción de habla de contacto en un contexto de servicio en el español peninsular

Basándonos en grabaciones de interacciones espontáneas, analizamos en este trabajo una serie de marcadores del discurso empleados en la construcción de habla de contacto, (small talk) –un tipo de habla relacional– (cfr. compilaciones de Coupland 2000a; Placencia/García 2008a) en interacciones de servicio en bares de Sevilla, durante el momento del desayuno. Mostramos la riqueza de formas en uso en la (re)creación de relaciones familiares entre camareros y clientes, que sin embargo, como ilustramos en este trabajo, parece estar supeditada a factores situacionales, entre otros. Así pues, por un lado intentamos con este análisis hacer una aportación a los estudios de habla de contacto en contextos transaccionales, en los cuales los marcadores del discurso han recibido escasa atención; mientras que por otro lado pretendemos también contribuir al análisis de los marcadores del discurso en general. Estos, si bien es cierto que ya han sido extensamente estudiados en múltiples trabajos sobre la lengua española, no han recibido suficiente atención en contextos de servicio. El propósito de la presente investigación es también aportar nuevos datos sobre el modo del que los sevillanos conducen sus relaciones interpersonales en interacciones de servicio en bares pertenecientes a dos contextos diferentes: uno en el que camareros y clientes se conocen, ya que realizan el intercambio comercial de manera habitual, y otro en el que mantienen una relación esporádica

A reassortant H9N2 influenza virus containing 2009 pandemic H1N1 internal-protein genes acquired enhanced pig-to-pig transmission after serial passages in swine

Avian H9N2 and 2009 pandemic H1N1 (pH1N1) influenza viruses can infect pigs and humans, raising the concern that H9N2: pH1N1 reassortant viruses could emerge. Such reassortants demonstrated increased replication and transmissibility in pig, but were still inefficient when compared to pH1N1. Here, we evaluated if a reassortant virus containing the hemagglutinin and neuraminidase of A/quail/ Hong Kong/G1/1997 (H9N2) in the A/California/04/2009 (pH1N1) backbone could become better adapted to pigs by serial passaging. The tropism of the original H9N2: pH1N1 (P0) virus was restricted to the nasal mucosa, with no virus detected in the trachea or lungs. Nevertheless, after seven passages the H9N2: pH1N1 (P7) virus replicated in the entire respiratory tract. We also compared the transmissibility of H9N2: pH1N1 (P0), H9N2: pH1N1 (P7) and pH1N1. While only 2/6 direct-contact pigs showed nasal virus excretion of H9N2: pH1N1 (P0) >= five days, 4/6 direct-contact animals shed the H9N2: pH1N1 (P7). Interestingly, those four animals shed virus with titers similar to those of the pH1N1, which readily transmitted to all six contact animals. The broader tissue tropism and the increased post-transmission replication after seven passages were associated with the HA-D225G substitution. Our data demonstrate that the pH1N1 internal-protein genes together with the serial passages favour H9N2 virus adaptation to pigs

Does Training on Broad Band Tactile Stimulation Promote the Generalization of Perceptual Learning?

Given the clear role of sensory feedback in successful motor control, there is a growing interest in integrating substitutionary tactile feedback into robotic limb devices. To enhance the utility of such feedback, here we investigate how to best improve the limited generalization of tactile learning across body parts and stimulus properties. Specifically, we sought to understand how perceptual learning with different types of tactile stimuli may give rise to different patterns of learning generalization. To address this, we utilized vibro-tactile effectors to present patterns of stimulation in a match-to-sample paradigm. One group of participants trained on narrow-band stimulation consisting of simple sinusoidal vibrations, and the other on broad-band stimulation generated from music. We hypothesized that training on broad-band tactile stimulation would promote greater generalization of learning outcomes. We found training with broad-band stimuli generalized to underlying stimulus features of frequency discrimination but showed weaker generalization to un-trained digits. This study provides a first step towards devising perceptual learning paradigms that will generalize broadly to the untrained perceptual contexts