Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6

Magnetic dc susceptibility ($\chi$) and electron spin resonance (ESR) measurements in the paramagnetic regime, are presented. We found a Curie-Weiss (CW) behavior for $\chi$(T) with a ferromagnetic $\Theta = 446(5)$ K and $\mu_{eff} = 4.72(9) \mu_{B}/f.u.$, this being lower than that expected for either $Fe^{3+}(5.9\mu_{B})$ or $Fe^{2+}(4.9\mu_{B})$ ions. The ESR g-factor $g = 2.01(2)$, is associated with $Fe^{3+}$. We obtained an excellent description of the experiments in terms of two interacting sublattices: the localized $Fe^{3+}$ ($3d^{5}$) cores and the delocalized electrons. The coupled equations were solved in a mean-field approximation, assuming for the itinerant electrons a bare susceptibility independent on $T$. We obtained $\chi_{e}^{0} = 3.7$ $10^{-4}$ emu/mol. We show that the reduction of $\mu_{eff}$ for $Fe^{3+}$ arises from the strong antiferromagnetic (AFM) interaction between the two sublattices. At variance with classical ferrimagnets, we found that $\Theta$ is ferromagnetic. Within the same model, we show that the ESR spectrum can be described by Bloch-Hasegawa type equations. Bottleneck is evidenced by the absence of a $g$-shift. Surprisingly, as observed in CMR manganites, no narrowing effects of the ESR linewidth is detected in spite of the presence of the strong magnetic coupling. These results provide evidence that the magnetic order in $Sr_{2}FeMoO_{6}$ does not originates in superexchange interactions, but from a novel mechanism recently proposed for double perovskites

Use of nanomaterials to conserve the stone of the Roman Theatre of Cartagena

[EN] The Roman Theatre of Cartagena is an important example of the monumental architecture of Hispania. Various types of local stone were used in its construction, including a type of sandstone known as Tabaire. This paper describes the physical characteristics of Tabaire. We also identify its deterioration patterns and study its consolidation using lime nanoparticles and silicon dioxide (ethyl silicate). Initial analyses using the imaging techniques Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and X-Ray Tomography (CT) show that it is an extremely porous, soft stone. The effectiveness of the consolidating treatments was verified using non-destructive methods based on identifying dispersion and penetrability in the substrate (OM and SEM) and detecting colour variation (CIE-L*a*b*) or minimally destructive methods, such as the peeling test and Shore-D hardness, to determine their effect on the characteristics of the material.[ES] El Teatro de Cartagena es un importante exponente de la arquitectura monumental de la Hispania romana. Para su construcción fueron utilizados diversos pétreos locales, entre ellos una arenisca conocida como Tabaire. Este artículo tiene como objetivo la caracterización física del Tabaire, así como la identificación de sus formas de deterioro y el estudio de su consolidación mediante nanopartículas de cal y de dióxido de silicio (silicato de etilo). Los análisis iniciales mediante técnicas de imagen como la Microscopía Óptica (OM), Microscopía Electrónica de Barrido (SEM) y Tomografía de Rayos X (CT) muestran que es una roca de elevada porosidad y escasa dureza. La eficacia de los tratamientos consolidantes se comprobó mediante métodos no destructivos, basados en la identificación de la dispersión y penetrabilidad en el sustrato (OM y SEM) y en la detección de la variación del color (CIE-L*a*b*), o mínimamente destructivos, como el peeling test y la dureza Shore-D, para conocer su incidencia en las características del material.Navarro-Moreno, D.; Martínez-Arredondo, A.; García-Vera, VE.; Lanzón, M. (2023). Uso de nanomateriales para la conservación de la piedra del Teatro Romano de Cartagena. Loggia, Arquitectura & Restauración. (36):106-119. https://doi.org/10.4995/loggia.2023.193601061193

Financial Soundness Prediction Using a Multi-classification Model: Evidence from Current Financial Crisis in OECD Banks

The paper aims to develop an early warning model that separates previously rated banks (337 Fitch-rated banks from OECD) into three classes, based on their financial health and using a one-year window. The early warning system is based on a classification model which estimates the Fitch ratings using Bankscope bankspecific data, regulatory and macroeconomic data as input variables. The authors propose a “hybridization technique” that combines the Extreme learning machine and the Synthetic Minority Over-sampling Technique. Due to the imbalanced nature of the problem, the authors apply an oversampling technique on the data aiming to improve the classification results on the minority groups. The methodology proposed outperforms other existing classification techniques used to predict bank solvency. It proved essential in improving average accuracy and especially the performance of the minority groups

Model selection for spectro-polarimetric inversions

Inferring magnetic and thermodynamic information from spectropolarimetric observations relies on the assumption of a parameterized model atmosphere whose parameters are tuned by comparison with observations. Often, the choice of the underlying atmospheric model is based on subjective reasons. In other cases, complex models are chosen based on objective reasons (for instance, the necessity to explain asymmetries in the Stokes profiles) but it is not clear what degree of complexity is needed. The lack of an objective way of comparing models has, sometimes, led to opposing views of the solar magnetism because the inferred physical scenarios are essentially different. We present the first quantitative model comparison based on the computation of the Bayesian evidence ratios for spectropolarimetric observations. Our results show that there is not a single model appropriate for all profiles simultaneously. Data with moderate signal-to-noise ratios favor models without gradients along the line-of-sight. If the observations shows clear circular and linear polarization signals above the noise level, models with gradients along the line are preferred. As a general rule, observations with large signal-to-noise ratios favor more complex models. We demonstrate that the evidence ratios correlate well with simple proxies. Therefore, we propose to calculate these proxies when carrying out standard least-squares inversions to allow for model comparison in the future.Comment: 16 pages, 2 figures, 8 tables, accepted for publication in Ap

Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects

Under the terms of the Creative Commons Attribution (CC BY) license to their work.We report on the modification of the optical and mechanical properties of a silicon 1D optomechanical crystal cavity due to thermo-optic effects in a high phonon/photon population regime. The cavity heats up due to light absorption in a way that shifts the optical modes towards longer wavelengths and the mechanical modes to lower frequencies. By combining the experimental optical results with finite-difference time-domain simulations, we establish a direct relation between the observed wavelength drift and the actual effective temperature increase of the cavity. By assuming that the Young's modulus decreases accordingly to the temperature increase, we find a good agreement between the mechanical mode drift predicted using a finite element method and the experimental one.This work was supported by the EU through the project TAILPHOX (ICT-FP7-233883) and the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish projects TAPHOR (MAT2012-31392).Peer Reviewe

Microwave Background Anisotropies and Nonlinear Structures I. Improved Theoretical Models

A new method is proposed for modelling spherically symmetric inhomogeneities in the Universe. The inhomogeneities have finite size and are compensated, so they do not exert any measurable gravitational force beyond their boundary. The region exterior to the perturbation is represented by a Friedmann-Robertson-Walker (FRW) Universe, which we use to study the anisotropy in the cosmic microwave background (CMB) induced by the cluster. All calculations are performed in a single, global coordinate system, with nonlinear gravitational effects fully incorporated. An advantage of the gauge choices employed here is that the resultant equations are essentially Newtonian in form. Examination of the problem of specifying initial data shows that the new model presented here has many advantages over `Swiss cheese' and other models. Numerical implementation of the equations derived here is described in a subsequent paper.Comment: 10 pages, 4 figures; Monthly Notices of the Royal Astronomical Society (MNRAS), in pres

Solar abundance corrections derived through 3D magnetoconvection simulations

We explore the effect of the magnetic field when using realistic three-dimensional convection experiments to determine solar element abundances. By carrying out magnetoconvection simulations with a radiation-hydro code (the Copenhagen stagger code) and through a-posteriori spectral synthesis of three Fe I lines, we obtain evidence that moderate amounts of mean magnetic flux cause a noticeable change in the derived equivalent widths compared with those for a non-magnetic case. The corresponding Fe abundance correction for a mean flux density of 200 G reaches up to ~0.1 dex in magnitude. These results are based on space- and time-averaged line profiles over a time span of 2.5 solar hours in the statistically stationary regime of the convection. The main factors causing the change in equivalent widths, namely the Zeeman broadening and the modification of the temperature stratification, act in different amounts and, for the iron lines considered here, in opposite directions; yet, the resulting $|\Delta\log\epsilon_{\odot}(Fe)|$ coincides within a factor two in all of them, even though the sign of the total abundance correction is different for the visible and infrared lines. We conclude that magnetic effects should be taken into account when discussing precise values of the solar and stellar abundances and that an extended study is warranted.Comment: ApJ accepte

Integrable models and degenerate horizons in two-dimensional gravity

We analyse an integrable model of two-dimensional gravity which can be reduced to a pair of Liouville fields in conformal gauge. Its general solution represents a pair of ``mirror'' black holes with the same temperature. The ground state is a degenerate constant dilaton configuration similar to the Nariai solution of the Schwarzschild-de Sitter case. The existence of $\phi=const.$ solutions and their relation with the solution given by the 2D Birkhoff's theorem is then investigated in a more general context. We also point out some interesting features of the semiclassical theory of our model and the similarity with the behaviour of AdS$_2$ black holes.Comment: Latex, 16 pages, 1 figur

Efectos del mindfulness y EMDR en la regulación emocional en trastornos de ansiedad, depresión y TEPT

El presente trabajo tiene como objetivo analizar los efectos y la efectividad del Mindfulness en la regulación emocional en pacientes con trastornos de ansiedad y depresión. Así como los efectos de EMDR (Eye Movement Desensitization and Reprocessing) en el Trastorno de Estrés Post-traumático (TEPT). Para ello se ha revisado literatura científica en estas áreas, describiendo los conceptos clave e investigando los efectos en pacientes con estos trastornos. Los resultados sugieren una mejoría significativa en los síntomas emocionales en los pacientes que han sido tratados con ambas terapias en sus respectivos trastornos, lo que sugiere que el mindfulness debe estar integrado en el tratamiento de los trastornos de ansiedad y depresión, y que el EMDR es una terapia muy efectiva para el TEPT.The aim of this study is to analyze the effects and effectiveness of mindfulness on emotional regulation in patients with anxiety and depression disorders, as well as the effects of EMDR (Eye Movement Desensitization and Reprocessing) in Post-Traumatic Stress Disorder. To this end, scientific literature in these areas has been reviewed, describing the key concepts and investigating the effects on patients with these disorders. The results suggest a significant improvement in emotional symptoms in patients who have been treated with both therapies in their respective disorders, suggesting that mindfulness should be integrated into the treatment of anxiety and depression disorders, and that EMDR is a highly effective therapy for PTSD