4,213 research outputs found
Evidence of strong antiferromagnetic coupling between localized and itinerant electrons in ferromagnetic Sr2FeMoO6
Magnetic dc susceptibility () and electron spin resonance (ESR)
measurements in the paramagnetic regime, are presented. We found a Curie-Weiss
(CW) behavior for (T) with a ferromagnetic K and
, this being lower than that expected for
either or ions. The ESR g-factor , is associated with . We obtained an excellent description
of the experiments in terms of two interacting sublattices: the localized
() 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 . We obtained
emu/mol. We show that the reduction of for
arises from the strong antiferromagnetic (AFM) interaction between the two
sublattices. At variance with classical ferrimagnets, we found that 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 -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 does not originates in superexchange interactions,
but from a novel mechanism recently proposed for double perovskites
Remnants of Sagittarius Dwarf Spheroidal Galaxy around the young globular cluster Palomar 12
Photometry of a large field around the young globular cluster Palomar 12 has
revealed the main-sequence of a low surface-brightness stellar system. This
main-sequence is indicative of a stellar population that varies significantly
in metallicity and/or age, but in the mean is more metal poor than Pal 12.
Under different assumptions for the properties of this population, we find
distances from the Sun in the range 17-24 kpc, which encompasses the distance
to Pal 12, kpc. The stellar system is also detected in a field
2\arcdeg North of Pal 12, which indicates it has a minimum diameter of
kpc. The orbit of Pal 12 (Dinescu et al. 2000), the color-magnitude
diagram of the stellar system, their positions on the sky, and their distances
suggest that they are debris from the tidal disruption of the Sgr dSph galaxy.
We discuss briefly the implications for the evolution of Sgr and the Galactic
halo.Comment: 16 pages, 2 figures, accepted for ApJ Letters. Some importante
changes after revision, including a new figur
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
Environmental and social impact assessment of optimized post-tensioned concrete road bridges
[EN] Most of the definitions of sustainability include three basic pillars: economic, environmental, and social. The economic pillar has always been evaluated but not necessarily in the sense of economic sustainability. On the other hand, the environmental pillar is increasingly being considered, while the social pillar is weakly developed. Focusing on the environmental and social pillars, the use of methodologies to allow a wide assessment of these pillars and the integration of the assessment in a few understandable indicators is crucial. This article is structured into two parts. In the first part, a review of life cycle impact assessment methods, which allow a comprehensive assessment of the environmental and social pillars, is carried out. In the second part, a complete environmental and social sustainability assessment is made using the ecoinvent database and ReCiPe method, for the environmental pillar, and SOCA database and simple Social Impact Weighting method, for the social pillar. This methodology was used to compare three optimized bridges: two box-section post-tensioned concrete road bridges with a variety of initial and maintenance characteristics, and a pre-stressed concrete precast bridge. The results show that there is a high interrelation between the environmental and social impact for each life cycle stage.This research was funded by the Ministerio de Economia, Ciencia y Competitividad and FEDER funding grant number [BIA2017-85098-R]Penades-Pla, V.; Martínez-Muñoz, D.; García-Segura, T.; Navarro, IJ.; Yepes, V. (2020). Environmental and social impact assessment of optimized post-tensioned concrete road bridges. Sustainability. 12(10):4265-01-4265-18. https://doi.org/10.3390/su12104265S4265-014265-18121
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 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
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