Directionality in van der Waals Interactions: the Case of 4-Acetylbiphenyl Adsorbed on Au(111)

We report on a theoretical study of adsorption of 4-Acetylbiphenyl molecule and its diffusion properties in the main directions of the Au(111) surface. Structural changes of the molecule, which are induced by adsorption lead to stronger conjugation of the $\pi$-system. The molecule is adsorbed in a flat configuration on the surface with roughly the same binding energy along the [110] and [112] directions, in good agreement with experiments. Furthermore, the diffusion barriers imply an important directionality of the molecule-surface interactions. This is somewhat surprising because our calculations show that the prevailing interaction is the long-range molecule-surface van der Waals interaction. Despite of its weakness, the van der Waals interaction discriminates the preferential adsorption sites as well as imposes a molecular geometry that needs to be considered when rationalizing the diffusion barriers

Baja presión en aspersores de impacto en coberturas de riego: análisis técnico y agronómico

La eficiencia energética en riego presurizado se ha abordado desde la gestión hidráulica de las infraestructuras de red y la eficiencia en los bombeos, sin embargo, es necesario analizar los ahorros que pueden realizarse a escala de parcela. Resultados preliminares indican que la reducción de la presión de funcionamiento de un aspersor de impacto de 300 kPa a 200 kPa ligeramente reduce la uniformidad del riego. En este trabajo se evalúa en campo la calidad del riego y los resultados agronómicos de tres configuraciones aspersor+presión: 1) un aspersor de impacto convencional trabajando a 300 kPa (AC 300), 2) un aspersor convencional trabajando a 200 kPa (AC 200) y 3) un aspersor modificado con una pequeña placa deflectora sobre el brazo de impacto trabajando a 200 kPa (APD 200). En una parcela experimental de cobertura total formada por 12 subparcelas, se realizó un ensayo en bloques al azar sobre un cultivo de maíz durante la campaña 2015. Se caracterizaron las condiciones meteorológicas (velocidad y dirección del viento) de los riegos aplicados al maíz. Para cada tratamiento se realizaron ensayos de uniformidad, evaluaciones agronómicas, cosecha manual de biomasa aérea y cosecha de grano. Los resultados indican que la uniformidad media evaluada no fue significativamente diferente entre tratamientos. La biomasa y producción de grano del tratamiento de 300 kPa resultaron menores que las de los tratamientos a 200 kPa (AC 200 y APD 200), no resultando significativas las diferencias entre ambos tratamientos de 200 kPa. Se detectó un problema en el crecimiento de cultivo que afectó principalmente a las subparcelas de 300 kPa, por lo que los resultados deben de considerarse con cuidado y realizar el ensayo en una o dos temporadas más.Ministerio de Economía y Competitivida

Magnetism in assembled and supported silicon endohedral cages: First-principles electronic structure calculations

First principles electronic structure calculations on a free CrSi12cluster, a (CrSi12)2 dimer, and CrSi12 clusters supported on Si(111) surfaces have been carried out within a gradient corrected density functional formalism using a supercell approach. The ground state of CrSi12 is a Cr centered hexagonal biprism of Si atoms in which the Cr spin moment is completely quenched. As two CrSi12 motifs are brought together, they form different composite units depending on initial direction of approach and, in most cases, the composite cluster is found to have a net spin moment. Cluster assemblies obtained by depositing CrSi12 motifs on a Si(111) surface exhibit similar finite spin moments for several initial directions of approach. An analysis of the electronic states shows that the origin of the magnetic moment lies in those Cr d-states that do not mix with silicon sp states. The studies suggest the possibility of forming silicon-based magnetic semiconductors through such assemblies

Covariant N=2 heterotic string in four dimensions

We construct a covariant formulation of the heterotic superstring on K3 times T^2 with manifest N=2 supersymmetry. We show how projective superspace appears naturally in the hybrid formulation giving a (partially) geometric interpretation of the harmonic parameter. The low-energy effective action for this theory is given by a non-standard form of N=2 supergravity which is intimately related to the N=1 old-minimal formulation. This formalism can be used to derive new descriptions of interacting projective superspace field theories using Berkovits' open string field theory and the the heterotic Berkovits-Okawa-Zwiebach construction.Comment: 11+3 page

Stable T2Sin (T=Fe,Co,Ni,1≤n≤8) cluster motifs

First principles studies on the geometry, electronic structure, and magnetic properties of neutral and anionic Fe2Sin, Co2Sin, and Ni2Sin (1≤n≤8) clusters have been carried out within a gradient corrected density functional framework. It is shown that these clusters display a variety of magnetic species with varying magnetic moment and different magnetic coupling between the two transition metal atoms. While Fe2Sin clusters are mostly ferromagnetic with large moments, Ni2Sin clusters are mostly nonmagnetic. Our studies of the variation of the binding energy upon addition of successive Si atoms and the gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital indicate that many of the motifs are quite stable and could be suitable as building blocks for generating magnetic cluster assembled materials. The studies also reveal motifs that could be used in molecular electronic devices to generate spin polarized currents or large magnetoresistance

Discriminación económica de género en los egresados de administración y finanzas de Los Mochis, Sinaloa (Gender economic discrimination in administration and finance graduates from Los Mochis, Sinaloa)

Abstract. In this documents is described the gender discrimination of the administration gradutes, 1999-2003 generation from Universidad de Occidente (U de O) in Los Mochis. In general terms the average of incomes has no difference on the gender, mainly due to the high standard deviation of individual incomes. The income differences can not be explained neither by the family dimension such as marital status, nor the number of children, nor the working condition, nor the educational degree for the parents or spouse; nor by the educational dimension, but by the occupational dimension. Gender discrimination is due to the labour market’s segmentation that is, there are jobs destined to a single gender. The exclusive jobs for female administrator are in the category of under employment; whereas those for males have higher average of income. Resumen. En este trabajo se describe la discriminación económica de género de los egresados de la generación 1999 – 2003 de la Licenciatura en Administración y Finanzas de la Universidad de Occidente (U de O). Se muestra que el promedio de ingresos no es diferente entre ambos géneros debido principalmente a la alta desviación estándar de los ingresos individuales de hombres y mujeres. Las diferencias en los ingresos salariales no pudieron ser explicadas ni por la dimensión familiar, ni por la dimensión educativa, pero sí por la dimensión ocupacional. Se encontró que existe discriminación de género debido a la segmentación del mercado laboral, es decir, existen puestos destinados a un solo género. Los puestos exclusivos para las licenciadas en administración y finanzas se encuentran en la categoría del subempleo; mientras que los de los hombres sí tienen un promedio de ingresos superior

Oxidation of Pdn (n=1–7,10) clusters supported on alumina/NiAl(110)

First-principles theoretical investigations on the oxidation of Pdn (n=1–7, 10) clusters deposited on alumina/NiAl(110) have been carried out using a gradient-corrected density-functional approach. Our studies indicate that the free Pdn clusters are compact and maintain their compact structures when deposited on the surface, undergoing only small relaxations of the Pd-Pd distance. The clusters bind to the surface via a pair of Pd atoms and with a binding energy of around 1.0 eV. Studies of oxidation through an O2molecule show that O2 occupies sites closer to the surface for Pd1, Pd4, Pd5, and Pd6 while, in other cases, the binding is highest to Pd atoms farther from the surface. An analysis of the charge gained by the O2 molecule upon absorption shows that, while O2 always gains charge, the amount of charge contributed by the Pdn cluster or the surface can vary significantly. In particular, in the case of Pd4, only a small charge is donated by the cluster, thus accounting for the recently observed lack of shift in the x-ray photoelectron spectroscopy levels

Energetics and stability of dangling-bond silicon wires on H passivated Si(100)

We evaluate the electronic, geometric and energetic properties of quasi 1-D wires formed by dangling bonds on Si(100)-H (2 x 1). The calculations are performed with density functional theory (DFT). Infinite wires are found to be insulating and Peierls distorted, however finite wires develop localized electronic states that can be of great use for molecular-based devices. The ground state solution of finite wires does not correspond to a geometrical distortion but rather to an antiferromagnetic ordering. For the stability of wires, the presence of abundant H atoms in nearby Si atoms can be a problem. We have evaluated the energy barriers for intradimer and intrarow diffusion finding all of them about 1 eV or larger, even in the case where a H impurity is already sitting on the wire. These results are encouraging for using dangling-bond wires in future devices.Comment: 8 pages, 6 figure

Engaging without over-powering: A case study of a FLOSS project

This is the post-print version of the published chapter. The original publication is available at the link below. Copyright @ 2010 IFIP International Federation for Information Processing.The role of Open Source Software (OSS) in the e-learning business has become more and more fundamental in the last 10 years, as long as corporate and government organizations have developed their educational and training programs based on OSS out-of-the-box tools. This paper qualitatively documents the decision of the largest UK e-learning provider, the Open University, to adopt the Moodle e-learning system, and how it has been successfully deployed in its site after a multi-million investment. A further quantitative study also provides evidence of how a commercial stakeholder has been engaged with, and produced outputs for, the Moodle community. Lessons learned from this experience by the stakeholders include the crucial factors of contributing to the OSS community, and adapting to an evolving technology. It also becomes evident how commercial partners helped this OSS system to achieve the transition from an “average” OSS system to a successful multi-site, collaborative and community-based OSS project