5,668 research outputs found
The evolution with temperature of magnetic polaron state in an antiferromagnetic chain with impurities
The thermal behavior of a one-dimensional antiferromagnetic chain doped by
donor impurities was analyzed. The ground state of such a chain corresponds to
the formation of a set of ferromagnetically correlated regions localized near
impurities (bound magnetic polarons). At finite temperatures, the magnetic
structure of the chain was calculated simultaneously with the wave function of
a conduction electron bound by an impurity. The calculations were performed
using an approximate variational method and a Monte Carlo simulation. Both
these methods give similar results. The analysis of the temperature dependence
of correlation functions for neighboring local spins demonstrated that the
ferromagnetic correlations inside a magnetic polaron remain significant even
above the N\'eel temperature implying rather high stability of the
magnetic polaron state. In the case when the electron-impurity coupling energy
is not too high (for lower that the electron hopping integral ), the
magnetic polaron could be depinned from impurity retaining its magnetic
structure. Such a depinning occurs at temperatures of the order of . At
even higher temperatures () magnetic polarons disappear and the chain
becomes completely disordered.Comment: 17 pages, 5 figures, RevTe
Sarcophagidae (Diptera) atraídos a cadáveres de cochinillo, con nuevas citas para la fauna portuguesa
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Magnetic polarons in doped 1D antiferromagnetic chain
The structure of magnetic polarons (ferrons) is studied for an 1D
antiferromagnetic chain doped by non-magnetic donor impurities. The conduction
electrons are assumed to be bound by the impurities. Such a chain can be
described as a set of ferrons at the antiferromagnetic background. We found
that two types of ferrons can exist in the system. The ground state of the
chain corresponds to the ferrons with the sizes of the order of the
localization length of the electron near the impurity. The ferrons of the
second type produce a more extended distortion of spins in the chain. They are
stable within a finite domain of the system parameters and can be treated as
excitations above the ground state. The ferrons in the excited states can
appear in pairs only. The energy of the excited states decreases with the
growth in density of impurities. This can be interpreted as a manifestation of
an attractive interaction between ferrons.Comment: 6 pages, 5 figures, RevTex4, submitted to PR
Variability and evolution of the optical polarization of a sample of gamma-ray blazars
We present a polarization variability analysis of a sample of 26 -ray
blazars monitored by the Steward Observatory between 2008 and 2018 in the
optical band. We investigate the properties and long-term variability of their
optical polarization, searching for differences between blazar types. We
observe that BL Lac objects are typically less polarized and less variable than
flat spectrum radio quasars (FSRQs). Moreover, BL Lacs display a distribution
of their polarization angle typically oriented in a preferential direction,
contrary to the rather random distribution of FSRQs. For the latter blazar
type, as well as those sources showing a bright stellar emission, we take into
account the depolarizing effect introduced by the broad line region and the
host galaxy on the measured polarization degree. In this sample we also observe
that BL Lacs present an uncorrelated evolution of the flux and the
polarization. Contrary, FSRQs show a correlation before the depolarization
correction, that is lost however after considering this effect. In addition, we
study the behaviour of the polarization angle, searching for angle rotations in
its long-term evolution. We derive that the FSRQs studied here show rotations
more frequently than BL Lac objects by a factor 1.5. During these periods
we also observe a systematic decrease of the polarization fraction, as well as
a marginal flux increase, not significant however to connect rotations with
optical flares. We interpret these results within the extended shock-in-jet
scenario, able to explain the overall features observed here for the
polarization of the blazar sample.Comment: Accepted for publication in MNRA
WSO/UV: World Space Observatory/Ultraviolet
We summarize the capabilities of the World Space Observatory (UV) Project
(WSO/UV). An example of the importance of this project (with a planned launch
date of 2007/8) for the study of Classical Novae is given.Comment: 4 pages, To appear in the proceeedings of the "Classical Nova
Explosions" conference, eds. M. Hernanz and J. Jose, AI
Association of Motivational Climate With Addictive Behaviors Depending on Type of Sport in University Students: Structural Equation Analysis
This research study aims at contrasting a structural model of the associations between the alcohol consumption, tobacco
dependence, and the problematic use of video games with motivational climate toward sport depending on the category of
sports practiced in a sample of Physical Education university students. The sample consisted of 775 university students from
the Autonomous Community of Andalusia (Spain), aged between 21 and 35 (22.22 ± 3.76) years. The instruments used
were the Perceived Motivational Climate in Sport Questionnaire (PMCSQ-2), the Alcohol Use Disorders Identification Test
(AUDIT), the Fagerström Test for Nicotine Dependence (FTND), and the Questionnaire of Experiences Related to Video
Games (QERV) questionnaires. A path model that fitted properly in the multigroup analysis for both categories of sports was
used, χ2 = 19.843; gl = 8; p = .011; comparative fit index (CFI) = 0.911; normed fit index (NFI) = 0.903; incremental fit
index (IFI) = 0.912; root mean square error approximation (RMSEA) = 0.085. An inverse association was shown between
task climate and tobacco consumption in individual sports, being weaker in collective sports. This association is not significant
for collective sports, but it is for individual sports for ego climate. However, a positive association was found between ego
climate and the use of video games in individual sports, not being significant in the case of collective sports. The importance
of promoting motivational climates oriented toward tasks that are based on the practice of collective sports is established,
because they could act as protective factors against the development of addictive behavior in university students.This
research study has been supported by the Education Innovation
Project PID 16-45, named “Implementation of digital resources in
the classroom for the development of psychosocial and motivational
factors in students of the degree in Primary Education with
the speciality in Physical Education,” funded by the University of
Granada. Education Innovation Project PIBD Advanced 470,
named “Program of teaching intervention in students of the degree
in primary education and early childhood education through the use
of new technologies for the improvement of the psychosocial factors
of the students,” funded by the University of Granada. Project
I+D+I “DISPERSA,” with code number TIN2015-67149-C3-R,
named “Design of Pervasive Games Based on Learning Experiences
Sensitive to Context” funded by the Ministry of Economy and
Competitiveness. Precompetitive Research Projects for Young
Researchers (PPJI_B-05); Self-plan Research of the University of
Granada
Vasoactive intestinal peptide axis is dysfunctional in patients with Graves’ disease
Vasoactive intestinal peptide (VIP) is a neuropeptide with potent immunoregulatory properties. Reduced serum VIP levels and alterations in VIP receptors/signaling on immune cells have been associated with different inflammatory/autoimmune diseases. However, its role in autoimmune thyroid diseases (AITD) remains unknown. This study examined the interrelationship between VIP system, autoimmune background and thyroid hormones in peripheral immune cells in patients with AITD. Only Graves’ disease (GD) patients showed significantly lower serum VIP levels when compared to healthy subjects and to Hashimoto’s thyroiditis patients. Serum VIP levels were lower at the onset of GD, showing a significant negative correlation with thyroid hormone levels. The expression of VIP receptors, VPAC1 and VPAC2, was significantly upregulated in peripheral blood mononuclear cells (PBMC) from GD patients. There was an impairment of VIP signalling in these patients, probably attributable to a dysfunction of VPAC1 with preservation of VPAC2. The correlation between VPAC1 and thyroid hormone receptor expression in PBMC from healthy subjects was lost in GD patients. In summary, the VIP system is altered in peripheral immune cells of GD patients and this finding is associated with different thyroid hormone receptor patterns, showing a dynamic inter-regulation and a prominent role of VIP in this setting.This work has been supported by Instituto de Salud Carlos III, Spain, cofinanced by FEDER, European Union: RETICS program, Red de Investigación en Inflamación y Enfermedades Reumáticas (RD16/0012/0008, PI17/00027, PI16-02091, PIE13-0004) and from Consejería de Educación, Juventud y Deporte, Comunidad de Madrid: B2017/BMD372
Fomento de hábitos saludables a través de la coordinación del profesorado de educación física
The aim of this research is to analyze the degree of pedagogical coordination existing among physical education teachers, based on the promotion of a healthy lifestyle among the students. Specifically, an attempt was made to determine whether or not there was a tendency to work collaboratively in order to achieve specific objectives in the area of Physical Education. To do this, a questionnaire was prepared for this research, which was composed of 25 items, aimed at teachers with the specialty of physical education in practice. From a simple random sampling, 300 responses were obtained from teachers in the province of Granada. Among the results, it emphasizes the importance of motivation in the conjugation of the professional teaching performance of the specialist in the area of physical education. In this way, a strong correlation exists between motivation and social inclusion and healthy life, as well as between motivation and curricular innovation.La presente investigación tiene por objetivo analizar el grado de coordinación pedagógica existente entre el profesorado de educación física, a partir de la promoción de un estilo de vida saludable entre el alumnado. En concreto, se trató de determinar si existía o no una tendencia a trabajar colaborativamente en aras a conseguir unos objetivos específicos en el área de Educación Física. Para ello, se realizó un cuestionario elaborado para esta investigación, que estaba compuesto por 25 ítems, dirigido a maestros con la especialidad de educación física en ejercicio. A partir de un muestreo aleatorio simple, se consiguieron 300 respuestas de maestros de la provincia de Granada. Entre los resultados, destaca la importancia de la motivación en la conjugación del desempeño profesional docente del especialista del área de educación física. De este modo, se aprecia una fuerte correlación existente entre motivación e inclusión social y vida saludable, así como entre motivacióne innovación curricular
Light elements in stars with exoplanets
It is well known that stars orbited by giant planets have higher abundances
of heavy elements when compared with average field dwarfs. A number of studies
have also addressed the possibility that light element abundances are different
in these stars. In this paper we will review the present status of these
studies. The most significant trends will be discussed.Comment: 10 pages, 6 figures. Submitted to the proceedings of IAU symposium
268: Light elements in the universe
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