Germanene: a novel two-dimensional Germanium allotrope akin to Graphene and Silicene

Using a gold (111) surface as a substrate we have grown in situ by molecular beam epitaxy an atom-thin, ordered, two-dimensional multi-phase film. Its growth bears strong similarity with the formation of silicene layers on silver (111) templates. One of the phases, forming large domains, as observed in Scanning Tunneling Microscopy, shows a clear, nearly flat, honeycomb structure. Thanks to thorough synchrotron radiation core-level spectroscopy measurements and advanced Density Functional Theory calculations we can identify it to a $\sqrt{3}$x$\sqrt{3}$R(30{\deg}) germanene layer in coincidence with a $\sqrt{7}$x$\sqrt{7}$R(19.1{\deg}) Au(111) supercell, thence, presenting the first compelling evidence of the birth of a novel synthetic germanium-based cousin of graphene.Comment: 16 pages, 4 figures, 1 tabl

Análisis de los factores que determinan la inestabilidad del sistema tori-uke en la técnica del uchi-mata en judo

El objetivo de la presente investigación fue estudiar la inestabilidad del sistema tori-uke (atacante- defensor), al ejecutar Uchi Mata en condiciones de competición. Se emplearon dos cámaras de vídeo Panasonic S-VHS, 50 Hz, un sistema de referencia previamente calibrado y se siguieron los pasos y procedimientos del método fotogramétrico tridimensional. Se seleccionaron 12 parejas de judokas (seis del Campeonato Senior de Andalucía, Córdoba, 1999; seis del Campeonato Mundial Universitario de Judo, Málaga, 2000) que ejecutaron uchi mata y obtuvieron IPPON como resultado de su proyección. Los resultados muestran que todos los sujetos analizados incrementaron de manera progresiva el ángulo de inestabilidad, de modo que durante la fase de barrido y antes de que el defensor (uke) perdiese el contacto con el suelo, el ángulo fue mayor de 90º, haciendo que el sistema tori-uke fuese inestable. Se comprueba que existe una interrelación entre la flexión del tronco tanto de tori como de uke, las fuerzas de tracción de tori, producidas a través de los agarres, la disminución del tamaño de la base de sustentación y el ángulo de inestabilidad del sistema.Peer Reviewe

Large tectonic earthquakes induce sharp temporary decreases in seismic velocity in Volcán de Colima, Mexico

International audienceWe used the ambient noise cross-correlation and stretching methods to calculate variations in seismic velocities in the region of Volcán de Colima, Mexico. More than 15 years of continuous records were processed, producing long time series of velocity variations related to volcanic activity, meteorological effects, and earthquakes. Velocity variations associated with eruptive activity are tenuous, which probably reflects the open state of the volcano during the study period. Fifteen events among 26 regional tectonic earthquakes produced sharp, temporary decreases in seismic velocities, which then recovered progressively following a linear trend as a function of the logarithm of time. For the 15 events, the amplitude of the perturbation increased almost linearly with the logarithm of the amplitude of the seismic waves that shook the edifice. The most dramatic apparent velocity variation was a drop of up to 2.6% during the nearby M7.4 Tecomán earthquake in 2003. In order to locate the perturbation in the horizontal plane we applied an inverse method based on the radiative transfer approximation. We also used an original approach based on the frequency dependence of velocity variations to estimate the depth of the perturbation. Our results show that the velocity variation was well localized in the shallow layers (< 800 m) of the volcano, with almost no variations occurring outside the edifice. We discuss several possible interpretations and conclude that the most plausible explanation for the velocity decreases is the nonlinear elastic behavior of the granular volcanic material and its mechanical softening induced by transient strains

Multiplicity of 2-nodal solutions the Yamabe equation

Given any closed Riemannian manifold $(M, g)$, we use the gradient flow method and Sign-Changing Critical Point Theory to prove multiplicity results for 2-nodal solutions of a subcritical Yamabe type equation on $(M, g)$. If $(N, h)$ is a closed Riemannian manifold of constant positive scalar curvature our result gives multiplicity results for the type Yamabe equation on the Riemannian product $(M x N, g + \epsilon h)$, for $\epsilon > 0$ small

A retarded coupling approach to intermolecular interactions

A wide range of physical phenomena such as optical binding and resonance energy transfer involve electronic coupling between adjacent molecules. A quantum electrodynamical description of these intermolecular interactions reveals the presence of retardation effects. The clarity of the procedure associated with the construction of the quantum amplitudes and the precision of the ensuing results for observable energies and rates are widely acknowledged. However, the length and complexity of the derivations involved in such quantum electrodynamical descriptions increase rapidly with the order of the process under study. Whether through the use of time-ordering approaches, or the more expedient state-sequence method, time-consuming calculations cannot usually be bypassed. A simple and succinct method is now presented, which provides for a direct and still entirely rigorous determination of the quantum electrodynamical amplitudes for processes of arbitrarily high order. Using the approach, new results for optical binding in two- and three-particle systems are secured and discussed

Bending behavior analysis of geogrid reinforced adobe walls

La tierra cruda constituye el material de construcción más importante en muchas regiones del planeta. Dado el riesgo sísmico existente en la mayor parte de estas regiones, es necesario el desarrollo de técnicas de refuerzo eficaces y adecuadas desde un punto de vista tecnológico y socioeconómico. Este artículo analiza desde un punto experimental y analítico el comportamiento a flexión de muros de adobe reforzados con geomallas. Las leyes momento-curvatura de los muros ensayados son aproximadas mediante una serie de modelos analíticos que permiten analizar el comportamiento del material compuesto adobe-geomalla. Los resultados obtenidos muestran como la geomalla mejora el comportamiento de la mampostería de adobe en términos de resistencia y ductilidad, mejorando así su comportamiento en caso de movimiento sísmico.Rammed earth is a widely used building material in many regions of the world. Due to the high seismic risk in those areas, earthen constructions require suitable and efficient reinforcement techniques from a technological and socioeconomic point of view. This paper analyzes the bending behavior of geogrid reinforced adobe walls from an experimental and analytical point of view. The experimental bending moment-curvature relationships are analytically approached. The results show how geogrid reinforcement improves the performance of adobe masonry in terms of strength and ductility. Thus, a better seismic performance is achieve

Effective action for Einstein-Maxwell theory at order RF**4

We use a recently derived integral representation of the one-loop effective action in Einstein-Maxwell theory for an explicit calculation of the part of the effective action containing the information on the low energy limit of the five-point amplitudes involving one graviton, four photons and either a scalar or spinor loop. All available identities are used to get the result into a relatively compact form.Comment: 13 pages, no figure

Bending behavior analysis of geogrid reinforced adobe walls

La tierra cruda constituye el material de construcción más importante en muchas regiones del planeta. Dado el riesgo sísmico existente en la mayor parte de estas regiones, es necesario el desarrollo de técnicas de refuerzo eficaces y adecuadas desde un punto de vista tecnológico y socioeconómico. Este artículo analiza desde un punto experimental y analítico el comportamiento a flexión de muros de adobe reforzados con geomallas. Las leyes momento-curvatura de los muros ensayados son aproximadas mediante una serie de modelos analíticos que permiten analizar el comportamiento del material compuesto adobe-geomalla. Los resultados obtenidos muestran como la geomalla mejora el comportamiento de la mampostería de adobe en términos de resistencia y ductilidad, mejorando así su comportamiento en caso de movimiento sísmico.Rammed earth is a widely used building material in many regions of the world. Due to the high seismic risk in those areas, earthen constructions require suitable and efficient reinforcement techniques from a technological and socioeconomic point of view. This paper analyzes the bending behavior of geogrid reinforced adobe walls from an experimental and analytical point of view. The experimental bending moment-curvature relationships are analytically approached. The results show how geogrid reinforcement improves the performance of adobe masonry in terms of strength and ductility. Thus, a better seismic performance is achieve

Evaluación biomédica de implantes dentales sometidos a cargas oblicuas: combinación de varias características geométricas

Objective: an efficient and simple methodology, based on virtual simulation and computer modelling, for the assessment and evaluation of dental implants design is proposed in this work. Materials and methods: the finite element method, a very common tool in engineering applications, is used for the evaluation the biomechanical performance of the biomedical devices. Von Mises stress is used as the main parameter to assess the suitability of the implant, when it is subjected to functional and biological loading. Also, this work reports the effects on the implant caused by geometrical variations such as length, diameter, thread, cortical bone thickness and abutment inclination. The useful-life of the implant was estimated by performing, in a virtual way, the fatigue tests required by the ISO:14801 standard. Results: for all the analyzed cases, maximum stress was obtained at the connecting screw under oblique loading. The estimated useful-life of the implant was around 5.000.000 cycles, which satisfies both ISO standard and functional requirements. Also, maximum stress was found in the compact-bone tissue surrounding the implant, which is in very good agreement with previous reports. Conclusion: a dental implant with optimal characteristics is proposed and validated using the discussed methodology.Peer ReviewedPostprint (published version