The lifetime problem of evaporating black holes: mutiny or resignation

It is logically possible that regularly evaporating black holes exist in nature. In fact, the prevalent theoretical view is that these are indeed the real objects behind the curtain in astrophysical scenarios. There are several proposals for regularizing the classical singularity of black holes so that their formation and evaporation do not lead to information-loss problems. One characteristic is shared by most of these proposals: these regularly evaporating black holes present long-lived trapping horizons, with absolutely enormous evaporation lifetimes in whatever measure. Guided by the discomfort with these enormous and thus inaccessible lifetimes, we elaborate here on an alternative regularization of the classical singularity, previously proposed by the authors in an emergent gravity framework, which leads to a completely different scenario. In our scheme the collapse of a stellar object would result in a genuine time-symmetric bounce, which in geometrical terms amounts to the connection of a black-hole geometry with a white-hole geometry in a regular manner. The two most differential characteristics of this proposal are: i) the complete bouncing geometry is a solution of standard classical general relativity everywhere except in a transient region that necessarily extends beyond the gravitational radius associated with the total mass of the collapsing object; and ii) the duration of the bounce as seen by external observers is very brief (fractions of milliseconds for neutron-star-like collapses). This scenario motivates the search for new forms of stellar equilibrium different from black holes. In a brief epilogue we compare our proposal with a similar geometrical setting recently proposed by Haggard and Rovelli.Comment: 20 pages, 2 figures; v2: published version, references adde

Electromagnetism as an emergent phenomenon: a step-by-step guide

We give a detailed description of electrodynamics as an emergent theory from condensed-matter-like structures, not only {\it per se} but also as a warm-up for the study of the much more complex case of gravity. We will concentrate on two scenarios that, although qualitatively different, share some important features, with the idea of extracting the basic generic ingredients that give rise to emergent electrodynamics and, more generally, to gauge theories. We start with Maxwell's mechanical model for electrodynamics, where Maxwell's equations appear as dynamical consistency conditions. We next take a superfluid $^3$He-like system as representative of a broad class of fermionic quantum systems whose low-energy physics reproduces classical electrodynamics (Dirac and Maxwell equations as dynamical low-energy laws). An important lesson that can be derived from both analyses is that the vector potential has a microscopic physical reality and that it is only in the low-energy regime that this physical reality is blurred in favour of gauge invariance, which in addition turns out to be secondary to effective Lorentz invariance.Comment: 41 pages, 4 figures; v2: references added, version accepted for publicatio

Calibración de sensores de humedad capacitivos usando redes neuronales

X Jornadas de Investigación de la Zona no Saturada del Suelo, Salamanca (España), 2011El estudio de la variabilidad espacial de la humedad del suelo a escala de parcela o cuenca agrícola requiere el uso de redes de sensores de humedad de bajo coste, que suelen mostrar una fiabilidad limitada y requieren de calibraciones específicas, especialmente en suelos con elevados contenidos en arcilla. El presente trabajo pretende plantear una calibración más fiable de sondas de humedad mediante un análisis mixto campo-laboratorio. Para la calibración de campo se dispone de datos gravimétricos; para la calibración en laboratorio se han usado columnas de suelo inalterado que tras ser saturadas fueron desecadas en un entorno controlado mientras se monitorizaba la evolución de su peso y la de su humedad volumétrica, medida con diferentes sondas capacitivas Decagon. Tras obtener curvas de secado y la relación entre la humedad gravimétrica y la volumétrica es posible realizar una calibración mejorada específica para cada tipo de suelo. Las redes neuronales son particularmente útiles para el modelado de procesos físicos y el ajuste de modelos. En este trabajo se propone el empleo de dichas herramientas para obtener calibraciones para las sondas analizadas en el tipo de suelo objeto de estudio. Los resultados muestran que dichas calibraciones permiten mejorar la precisión de las mediciones de humedad realizadas.The study of the spatial variability of soil water content at agricultural plot or catchment scales requires the use of low-cost soil water content sensor networks, which usually show a limited reliability and require specific calibrations, specially for soils with a high clay content. This work proposes a more reliable calibration of soil water content probes with a laboratory analysis. Minimally disturbed soil columns were saturated with water and dried in a controlled environment while monitorizing the evolution of their volumetric soil water content (with different capacitive Decagon Probes) and weights. After obtaining the drying curves and the relation between the volumetric and the measured gravimetric soil water contents it is possible to achieve an improved calibration specific for different kinds of soil. Neural networks are especially interesting for the modeling of physical processes and model adjustment. In this work, these tools were used in order to obtain improved calibrations for the analyzed probes in the studied soil type. Results show that this calibration improves the accuracy and pMinisterio de Ciencia e Innovación AGL2009 C03-03Junta de Andalucía AGR-478

Attenuation lengths of high energy photoelectrons in compact and mesoporous SiO2 films

El pdf del artículo es la versión post-print.We have experimentally evaluated attenuation lengths (AL) of photoelectrons traveling in compact and micro and mesoporous (∼ 45% voids) SiO 2 thin films with high (8.2-13.2 keV) kinetic energies. The films were grown on polished Si(100) wafers. ALs were deduced from the intensity ratio of the Si 1s signal from the SiO 2 film and Si substrate using the two-peaks overlayer method. We obtain ALs of 15-22 nm and 23-32 nm for the compact and porous SiO 2 films for the range of kinetic energies considered. The observed AL values follow a power law dependence on the kinetic energy of the electrons where the exponent takes the values 0.81 ± 0.13 and 0.72 ± 0.12 for compact and porous materials, respectively. © 2012 Elsevier B.V. All rights reserved.We thank the Spanish MICINN (projects MAT2010-18447 and Consolider CSD2008-00023 and CPAN CSD2007-42) for financial support.Peer Reviewe

Impact of successive spring frosts on leaf phenology and radial growth in three deciduous tree species with contrasting climate requirements in central Spain

Rear-edge tree populations forming the equatorward limit of distribution of temperate species are assumed to be more adapted to climate variability than central (core) populations. However, climate is expected to become more variable and the frequency of climate extremes is forecasted to increase. Climatic extreme events such as heat waves, dry spells and spring frosts could become more frequent, and negatively impact and jeopardize rear-edge stands. To evaluate these ideas, we analyzed the growth response of trees to successive spring frosts in a mixed forest, where two temperate deciduous species, Fagus sylvatica L. (European beech) and Quercus petraea (Matt.) Liebl. (sessile oak), both at their southernmost edge, coexist with the Mediterranean Quercus pyrenaica Willd. (Pyrenean oak). Growth reductions in spring-frost years ranked across species as F. sylvatica > Q. petraea > Q. pyrenaica. Leaf flushing occurred earlier in F. sylvatica and later in Q. pyrenaica, suggesting that leaf phenology was a strong determinant of spring frost damage and stem growth reduction. The frost impact depended on prior climate conditions, since warmer days prior to frost occurrence predisposed to frost damage. Autumn Normalized Difference Vegetation Index data showed delayed leaf senescence in spring-frost years and subsequent years as compared with pre-frost years. In the studied forest, the negative impact of spring frosts on Q. petraea and especially on F. sylvatica growth, was considerably higher than the impacts due to drought. The succession of four spring frosts in the last two decades determined a trend of decreasing resistance of radial growth to frosts in F. sylvatica. The increased frequency of spring frosts might prevent the expansion and persistence of F. sylvatica in this rear-edge Mediterranean population

Implementation of Signal Processing Methods in a Structural Health Monitoring (SHM) System based on Ultrasonic Guided Waves for Defect Detection in Different Materials and Structures

The local defect inspection in longitudinal structures such as plates or pipelines implies high economical costs and it is time consuming mainly in underground infrastructures, energy or water, and aerospace sectors. Moreover, if these structures are non-accessible, their local inspection is not possible. Ultrasonic (US) inspection technique based on guided waves is one of the potential alternatives to address this issue. The US inspection based on these type of waves could be applied in many scenarios to monitor the damage state of structures; i.e., in water underground pipelines to identify the wall thickness losses or impact damage detection on Carbon Fiber Reinforced Composites (CFRC). A SHM system based on guided waves requires a special signal processing in order to identify possible damage in the structure. The signal emitted and received is a combination of different propagation modes which are difficult to identify and analyse. However, if the signals are compared to each other (signal related to non-damaged components compared to damaged signal) it is possible to measure their difference as a distance that can be used to estimate the damage level. In this work, signals corresponding to non-damaged samples have been captured and then different types of damage have been applied for different cases. After the data acquisition phase, the comparison between signals has been carried out by applying different mathematical methods and distance metrics (SDC, DTW, Euclidean, Manhattan and Chebyshev), with the aim of detecting defects in different structures and materials. For this purpose, two cases have been analysed: 1) In CFRC plates subjected to impact damage and deformations and 2) In a pipe coated by cement-mortar in order to quantify the wall thickness losses. In both cases ultrasonic PZT sensors, an ultrasonic multichannel pulser/receiver and a software developed ad-hoc have been used. Although the SHM system components were similar, it must be noted that the type of ultrasonic guided waves used were different; in the case of CFRC plates, Lamb waves were excited whereas in the case of the pipeline, Love waves have been used. A comparison between the above mentioned methods is provided. The results show the validity of the approach for damage characterization.Authors would like to acknowledge the Basque Government funding within the ELKARTEK Programme (AIRHEM)

The kinematics of the quadrupolar nebula M1-75 and the identification of its central star

The link between the shaping of bipolar planetary nebulae and their central stars is still poorly understood. The kinematics and shaping of the multipolar nebula M 1-75 are hereby investigated, and the location and nature of its central star are briefly discussed. Fabry-Perot data from GHaFAS on the WHT sampling the Doppler shift of the [N II] 658.3 nm line are used to study the dynamics of the nebula, by means of a detailed 3-D spatio-kinematical model. Multi-wavelength images and spectra from the WFC and IDS on the INT, and from ACAM on the WHT, allowed us to constrain the parameters of the central star. The two pairs of lobes, angularly separated by ~22 degrees, were ejected simultaneously approx. ~3500-5000 years ago, at the adopted distance range from 3.5 to 5.0 kpc. The larger lobes show evidence of a slight degree of point symmetry. The shaping of the nebula could be explained by wind interaction in a system consisting of a post-AGB star surrounded by a disc warped by radiative instabilities. This requires the system to be a close binary or a single star which engulfed a planet as it died. On the other hand, we present broad- and narrow-band images and a low S/N optical spectrum of the highly-reddened, previously unnoticed star which is likely the nebular progenitor. Its estimated V-I colour allows us to derive a rough estimate of the parameters and nature of the central star.Comment: 8 pages, 6 figures, accepted for publication in Astronomy & Astrophysic

Terapia de Aceptación y Compromiso en un niño con celos y rumia disfuncionales

Acceptance and Commitment Therapy (ACT) is becoming a promising intervention in childhood psychological problems. This study addresses the intervention from ACT in a case of a 9-year-old child (J) who shows multiple disruptive behaviors in the family context, especially in situations involving his younger brother, and who also has a very extended rumination pattern. An A-B single case design with follow-up measures was used. The results show a significant improvement in the intervention objectives. The main exercises and metaphors that were used to increase the psychological flexibility of J are presented, as well as the intervention carried out with the parents: both in the management of their own psychological barriers as well as the guidelines that were provided to them to promote a more flexible behavior in their child.La Terapia de Aceptación y Compromiso (ACT) se está convirtiendo en una vía de intervención prometedora en los problemas psicológicos en la infancia. En el presente estudio se aborda la intervención desde ACT en un caso de un niño de 9 años (J) que muestra numerosas conductas disruptivas en el contexto familiar, especialmente en situaciones que involucran a su hermano menor, y un patrón de rumia muy extendido. Se utilizó un diseño de caso único A-B con medidas de seguimiento. Los resultados muestran una reducción clínicamente significativa de las conductas disruptivas e incremento de flexibilidad psicológica tanto en el niño como en los padres. Se presentan los principales ejercicios y metáforas que se utilizaron para incrementar la flexibilidad psicológica de J, así como la intervención realizada con los padres, tanto de cara a la gestión de sus propias barreras psicológicas como las pautas para potenciar un comportamiento más flexible en su hijo

Estilos de aprendizaje y evaluación formativa: Estudio con universitarios de Educación Física chilenos

Assessment contributes to students learning. Formative assessment is a useful strategy of the initial teacher training. Perceptions about the assessment of Chilean university Physical Education students (n = 95), depending on their learning style, gender and academic course were analyzed. The Learning Styles Questionnaire and the Spanish version of the Assessment Experience Questionnaire were used. The results showed negative perceptions about the assessment process. Significant differences were observed in the perceptions about the use of feedback depending on the learning style of the students (F = 1.062, p =. 004). Significant differences were observed in the perception about the amount of effort (F = 5.888, p =. 000), the suitability of the evaluation (F = 3.282, p =. 015) and the shallow approach to the learning (F = 5.472, p =. 001), depending on the academic course. Gender was not a determinant of perceptions. The findings suggest the use of traditional procedures of assessment (summative assessment) with the students. On the other hand, findings show the influence of learning stylesand the academic course on student perceptionsand learning styles and feedback. This information contributes to a deeper understanding of the learning mode of the students according to their characteristics and context.La evaluación contribuye a la formación del aprendizaje, facilitando el avance del estudiante. La evaluación formativa se presenta como una estrategia eficaz dentro de la formación inicial docente. Se analizaron las percepciones sobre la evaluación de universitarios de Educación Física chilenos (n = 95), en función de su estilo de aprendizaje, género y curso académico. Se utilizaron el Cuestionario de Estilos de Aprendizaje y la versión en castellano del Assessment Experience Questionnaire. Los resultados mostraron percepciones negativas sobre el proceso evaluativo. Se observaron diferencias significativas en las percepciones sobre el uso del feedback en función del estilo de aprendizaje (F= 1.062, p = .004). Se observaron diferencias significativas en la percepción de la cantidad de esfuerzo (F= 5.888, p = .000), la adecuación de la evaluación (F= 3.282, p = .015)y la aproximación superficial al aprendizaje (F= 5.472, p = .001), en función del curso académico. El género no fue determinante de las percepciones. Los hallazgos sugieren la utilización de procedimientos de evaluación tradicional con los encuestados. Se encontraron relaciones entre el estilo de enseñanza y el feedback, y entre el curso académico y las percepciones de evaluación. Esta información contribuye a un entendimiento más profundo del modo de aprender de los estudiantes en función de sus características y contexto

ZnO-mesoporous glass scaffolds loaded with osteostatin and mesenchymal cells improve bone healing in a rabbit bone defect.

The use of 3D scaffolds based on mesoporous bioactive glasses (MBG) enhanced with therapeutic ions, biomolecules and cells is emerging as a strategy to improve bone healing. In this paper, the osteogenic capability of ZnO-enriched MBG scaffolds loaded or not with osteostatin (OST) and human mesenchymal stem cells (MSC) was evaluated after implantation in New Zealand rabbits. Cylindrical meso-macroporous scaffolds with composition (mol %) 82.2SiO2–10.3CaO–3.3P2O5–4.2ZnO (4ZN) were obtained by rapid prototyping and then, coated with gelatin for easy handling and potentiating the release of inorganic ions and OST. Bone defects (7.5 mm diameter, 12 mm depth) were drilled in the distal femoral epiphysis and filled with 4ZN, 4ZN+MSC, 4ZN+OST or 4ZN+MSC+OST materials to evaluate and compare their osteogenic features. Rabbits were sacrificed at 3 months extracting the distal third of bone specimens for necropsy, histological and microtomography (µCT) evaluations. Systems investigated exhibited bone regeneration capability. Thus, trabecular bone volume density (BV/TV) values obtained from µCT showed that the good bone healing capability of 4ZN was significantly improved by the scaffolds coated with OST and MSC. Our findings in vivo suggest the interest of these MBG complete systems to improve bone repair in the clinical practice