Anticorrelation between Ion Acceleration and Nonlinear Coherent Structures from Laser-Underdense Plasma Interaction

In laser-plasma experiments, we observed that ion acceleration from the Coulomb explosion of the plasma channel bored by the laser, is prevented when multiple plasma instabilities such as filamentation and hosing, and nonlinear coherent structures (vortices/post-solitons) appear in the wake of an ultrashort laser pulse. The tailoring of the longitudinal plasma density ramp allows us to control the onset of these insabilities. We deduced that the laser pulse is depleted into these structures in our conditions, when a plasma at about 10% of the critical density exhibits a gradient on the order of 250 {\mu}m (gaussian fit), thus hindering the acceleration. A promising experimental setup with a long pulse is demonstrated enabling the excitation of an isolated coherent structure for polarimetric measurements and, in further perspectives, parametric studies of ion plasma acceleration efficiency.Comment: 4 pages, 5 figure

Steel profiles for repairing deteriorated timber beam ends

Se describe un procedimiento para la consolidación de viguetas de forjado de madera con deterioro en las cabezas mediante perfiles de acero conectados a la madera desde la cara superior del forjado. La pieza de refuerzo es un perfil en U de acero S275 conformado en frío con pletinas soldadas insertadas en la madera y conectada mediante tirafondos. Se ensayaron 30 piezas a flexión obteniendo la rigidez y la capacidad de carga. Las probetas se dividieron en tres grupos. El primero compuesto por 10 piezas de madera laminada encolada de abeto con una sección de 180 x 200 mm y una longitud de 4.000 mm; el segundo consistía en 10 piezas de madera aserrada de pino silvestre con la misma sección y longitud y, el tercero, estaba formado por otras 10 piezas de madera del género Pinus con una sección de 130 x 150 mm y 3.000 mm de longitud, procedentes de un edificio de Madrid con 120 años de antigüedad. Cada grupo de 10 piezas se dividió a su vez en dos grupos de 5 piezas. El primer subgrupo estaba formado por las piezas completas de madera y constituía el grupo de referencia. Las piezas del segundo subgrupo tenían una longitud inferior que se salvaba con una extensión del refuerzo metálico. Los resultados indican que el sistema de refuerzo metálico permite resolver los problemas de falta de apoyo de la vigueta por deterioro de la madera que afecte en una longitud limitada (aproximadamente entre el 10 y el 20% de la longitud)

Comparación de la clasificación visual de la madera en condiciones húmedas y secas de acuerdo con la norma española UNE 56544 y la alemana DIN 4074-1

Visual strength grading is widely used to estimate mechanical properties of structural timber. National visual grades are allocated to strength classes according to European standard EN1912. The recent discussion about the proper function of visual strength grading standards and the assignment of strength classes shows the need for further research in this field. Spanish-sourced radiata, Scots, Salzmann and maritime pine timber samples were visually graded in wet and dry condition according to the Spanish UNE56544 (2011) and German DIN4074-1 (2012) standards. Rejection was far higher dry due to distortion (warping) parameters. However, this rejection could be significantly mitigated by adopting a higher twist limit (2 mm / 25 mm width). UNE 56544 is more suitable for visually grading these species because it was specifically designed for them and a Spanish source. However, both standards underestimated the Scots pine rejection pieces which mechanical properties fulfill the MEG and S10 grades.La clasificación visual es ampliamente utilizada para estimar las propiedades mecánicas de la madera. Las calidades visuales son asignadas a clases resistentes de acuerdo a la norma europea EN1912. La reciente discusión sobre el apropiado funcionamiento de las normas de clasificación visual y de la asignación de clases resistentes hace necesario seguir investigando sobre el tema. Madera de pino radiata, silvestre, laricio y pinaster fue clasificada visualmente en condiciones húmedas y secas de acuerdo a la norma española UNE56544 y la alemana DIN4074-1. Muchas más piezas fueron rechazadas en seco debido a las deformaciones. Sin embargo, este rechazo se ve significativamente reducido adoptando un nuevo límite de alabeo (2 mm / 25 mm). UNE56544 es más adecuada para la clasificación visual de estas especies pues fue diseñada para ellas y procedencia española. Sin embargo, ambas normas infravaloran el lote rechazado de pino silvestre, cuyas propiedades mecánicas cumplen MEG y S10

Making robot’s attitudes predictable: a stereotype content model for human-robot interaction in groups

Stereotypes play a key role both in human and in robot perception. As such, these may play an important role in predicting behavior towards the targets of said stereotypes. In this paper, we argue for the usefulness of exploring how stable dimensions of stereotype content, more specific?ally warmth and competence, apply to HRI. We propose to do so by examining the impact of these characteristics, displayed by robots, on the emotions, behaviors and future intention of participants to interact and work with robots. We chose these two stereotypical dimensions given that research has demonstrated their underlying and ubiquitous influence on people perception and responses. Moreover, we decided to explore this issue in the context of small group interactions due to the ever-common nature of this type of social arrangements in people’s everyday life.info:eu-repo/semantics/acceptedVersio

AI trust: Can explainable AI enhance warranted trust?

Explainable artificial intelligence (XAI), known to produce explanations so that predictions from AI models can be understood, is commonly used to mitigate possible AI mistrust. The underlying premise is that the explanations of the XAI models enhance AI trust. However, such an increase may depend on many factors. This article examined how trust in an AI recommendation system is affected by the presence of explanations, the performance of the system, and the level of risk. Our experimental study, conducted with 215 participants, has shown that the presence of explanations increases AI trust, but only in certain conditions. AI trust was higher when explanations with feature importance were provided than with counterfactual explanations. Moreover, when the system performance is not guaranteed, the use of explanations seems to lead to an overreliance on the system. Lastly, system performance had a stronger impact on trust, compared to the effects of other factors (explanation and risk).info:eu-repo/semantics/publishedVersio

Are the effects of unreal violent videogames pronounced when playing with a virtual reality system?

This study was conducted to analyze the short-term effects of violent electronic games, played with or without a virtual reality (VR) device, on the instigation of aggressive behavior. Physiological arousal (heart rate (HR)), priming of aggressive thoughts, and state hostility were also measured to test their possible mediation on the relationship between playing the violent game (VG) and aggression. The participants—148 undergraduate students—were randomly assigned to four treatment conditions: two groups played a violent computer game (Unreal Tournament), and the other two a non-violent game (Motocross Madness), half with a VR device and the remaining participants on the computer screen. In order to assess the game effects the following instruments were used: a BIOPAC System MP100 to measure HR, an Emotional Stroop task to analyze the priming of aggressive and fear thoughts, a self-report State Hostility Scale to measure hostility, and a competitive reaction-time task to assess aggressive behavior. The main results indicated that the violent computer game had effects on state hostility and aggression. Although no significant mediation effect could be detected, regression analyses showed an indirect effect of state hostility between playing a VG and aggressio

Coeficientes de rozamiento estático y dinámico en la madera de pino silvestre (Pinus sylvestris L.), según las direcciones paralela y perpendicular a la fibra

In this study the static (µe) and kinetic (µd) coefficients of friction were obtained for Pinus sylvestis L. sawn timber of Spanish origin. Friction between transverse surfaces sliding perpendicular to the grain (tangential direction) and radial surfaces sliding parallel to the grain was analyzed. A specifically designed device was used for tests, which makes it possible to apply contact pressure and measure displacements and applied loads simultaneously. Coefficients of friction between transverse surfaces (µe = 0,24; µd = 0,17) were about twice of the coefficients of friction between radial surfaces (µe = 0,12; µd = 0,08). Furthermore, these values are located within normal values of those commonly reported for softwood. The results are considered preliminary due to the small number of specimens.En este estudio se determinaron los coeficientes de rozamiento, estático (µe) y dinámico (µd), en madera aserrada de Pinus sylvestris L. de procedencia española, diferenciando si se produce el contacto entre secciones de corte transversal con deslizamiento en dirección perpendicular a la fibra (en dirección tangencial), o entre secciones de corte radial con deslizamiento paralelo a la fibra. Para la realización de los ensayos se ha utilizado un dispositivo, diseñado específicamente, que posibilita la aplicación de una presión de contacto y la medición del desplazamiento y de la fuerza aplicada de manera simultánea, permitiendo la obtención de los coeficientes de rozamiento estático y dinámico. Los coeficientes de rozamiento obtenidos entre secciones transversales (µe = 0.24; µd = 0.17) fueron del orden del doble de los coeficientes de rozamiento entre secciones radiales (µe = 0.12; µd = 0.08). Además, estos valores se encuentran dentro de los valores que aparecen habitualmente en la bibliografía para madera de coníferas. Debido al escaso tamaño de la muestra los resultados se consideran preliminares

100 anos depois: onde está o Watson?

info:eu-repo/semantics/publishedVersio