Cumplimiento de las recomendaciones de práctica de actividad física y percepción de barreras en estudiantes de bachillerato

El objetivo de este estudio fue conocer los niveles de actividad física (AF) así como la percepción de barreras para la realización de AF en estudiantes de Bachillerato, analizando dichas variables en función del género, curso académico, práctica deportiva extraescolar y tipo de jornada. Se realizó un estudio descriptivo transversal en el que participaron 248 adolescentes, 120 chicos y 128 chicas ( M = 15.32; DT = 1.81), 144 de 1º de Bachillerato y 104 de 2º de Bachillerato. Se utilizó el Cuestionario Internacional de AF en su versión corta (IPAQ-SF) y la Escala de Barreras para la práctica de AF . Los resultados señalaron que menos del 30% de los estudiantes de Bachillerato alcanza las recomendaciones de práctica de AF, siendo el grado de cumplimiento más elevado en los chicos (38.3%), en el alumnado de 1º de Bachillerato (30.6%), en el alumnado que realiza práctica deportiva extraescolar (36.7%) y entre semana (31%). Por otro lado, las barreras referentes al tiempo fueron superiores en el alumnado de 2º de Bachillerato, mientras que las barreras relativas al disfrute fueron superiores en las chicas y en el alumnado que no realizaba práctica deportiva extraescolar. Los resultados destacan la importancia de promover la práctica regular de AF en Bachillerato, especialmente en las chicas y en los adolescentes de 2º curso, a través de programas de intervención que ayuden a mejorar la gestión del tiempo de ocio y estimulen el desarrollo de los procesos motivacionales. The aim of this study was to analyze physical activity (PA) levels and perceived barriers to PA in High School students. Similarly, differences in gender, academic year, out-of-school sport and type of day were analyzed among these variables. In this cross-sectional study, 248 adolescents, 120 boys and 128 girls (M = 15.32; SD = 1.81), were involved. The sample was made up of 144 12th grade students (58.1%) and 104 13th grade students. The International PA Questionnaire-Short Form (IPAQ-SF) and the Scale of Barriers to PA were used. The results showed that less than 30% of High School students comply with the PA guidelines, being higher in boys (38.3%), in the 12th High School students (30.6%), in the students who practiced extracurricular sports (36.7%) and weekdays (31%). On the other hand, barriers relating to time adolescents were higher in students of 13th High School, while barriers relate to enjoyment were higher in girls and students who did not practice extracurricular sports. The results highlight the importance of promoting PA in High School students, especially in girls and 12th High School, through intervention programs that help improve the management of their leisure time and development of motivational processes

Magnetic structure and critical behavior of GdRhIn5_{5}: resonant x-ray diffraction and renormalization group analysis

The magnetic structure and fluctuations of tetragonal GdRhIn5 were studied by resonant x-ray diffraction at the Gd LII and LIII edges, followed by a renormalization group analysis for this and other related Gd-based compounds, namely Gd2IrIn8 and GdIn3. These compounds are spin-only analogs of the isostructural Ce-based heavy-fermion superconductors. The ground state of GdRhIn5 shows a commensurate antiferromagnetic spin structure with propagation vector tau = (0,1/2, 1/2), corresponding to a parallel spin alignment along the a-direction and antiparallel alignment along b and c. A comparison between this magnetic structure and those of other members of the Rm(Co,Rh,Ir)n In3m+2n family (R =rare earth, n = 0, 1; m = 1, 2) indicates that, in general, tau is determined by a competition between first-(J1) and second-neighbor(J2) antiferromagnetic (AFM) interactions. While a large J1 /J2 ratio favors an antiparallel alignment along the three directions (the so-called G-AFM structure), a smaller ratio favors the magnetic structure of GdRhIn5 (C-AFM). In particular, it is inferred that the heavy-fermion superconductor CeRhIn5 is in a frontier between these two ground states, which may explain its non-collinear spiral magnetic structure. The critical behavior of GdRhIn5 close to the paramagnetic transition at TN = 39 K was also studied in detail. A typical second-order transition with the ordered magnetization critical parameter beta = 0.35 was experimentally found, and theoretically investigated by means of a renormalization group analysis.Comment: 22 pages, 4 figure

Spin structure and first-order transition of GdIn(3): Near-surface magnetism, buried amplitude-modulated phase, and interface delocalization

A resonant x-ray magnetic diffraction study was performed for pure and (Cd,Ga)-doped GdIn(3) single crystals with cubic structure. All studied samples show an equal-magnitude antiferromagnetic spin structure with propagation vector (tau) over right arrow=[1/2, 1/2,0] at low temperatures, corresponding to a parallel spin propagation along the (c) over right arrow direction (normal to the studied surfaces) and antiparallel propagation along (a) over right arrow and (b) over right arrow. A complex magnetic behavior in the submicrometric near-surface region (NSR) was found close to T(N)(bulk) similar to 44 K. For both pure and substituted samples, a fairly strong signal from the equal-magnitude magnetic phase was found to survive above T(N)(bulk) and abruptly disappears at T(N)(NSR) similar to T(N)(bulk)+ 0.7 K, indicating that the NSR may show a larger T(N) than the bulk for all studied samples. For the pure compound only, satellite peaks consistent with an amplitude-modulated magnetic phase with a wavelength of 380 angstrom were found between T(N)(bulk) and T(N)(NSR). A successful fit of the scattering profile around several magnetic Bragg positions and photon energies, using a simple phase coexistence model, confirmed that the amplitude-modulated phase develops underneath the most superficial region showing the equal magnitude structure. The evolution of the magnetic scattering profile on cooling indicates that the interface between equal-magnitude and amplitude-modulated phases diverges towards the bulk as T -> T(N)(bulk) from above. A detailed analysis of the magnetic scattering, as well as the existence of a single bulk transition within the experimental sensitivity of our specific heat and magnetic susceptibility measurements, in contrast to the rich behavior shown by the near-surface region, indicates that the amplitude-modulated phase is not bulk representative, being actually sandwiched between the bulk paramagnetic and the equal-magnitude phases. Depth-temperature phase diagrams for pure and (Ga,Cd)-doped GdIn(3) are drawn on the basis of our results, which are discussed in terms of a three-phase coexistence scenario theoretically proposed for first-order transitions in the NSR.77

Magnetic dimers and trimers in the disordered S=3/2 spin system BaTi1/2Mn1/2O3

FAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOWe report a structural-magnetic investigation by x-ray absorption spectroscopy (XAS), neutron diffraction, dc susceptibility (X-dc), and electron spin resonance (ESR) of the 12R-type perovskite BaTi1/2Mn1/2O3. Our structural analysis by neutron diffraction supports the existence of structural trimers with chemically disordered occupancy of Mn4+ and Ti4+ ions, with the valence of the Mn ions confirmed by the XAS measurements. The magnetic properties are explored by combining dc-susceptibility and X-band (9.4 GHz) electron spin resonance, both in the temperature interval of 2 <= T <= 1000 K. A scenario is presented under which the magnetism is explained by considering magnetic dimers and trimers, with exchange constants J(a)/k(B) = 200 (2) K and J(b)/k(B) = 130 (10) K, and orphan spins. Thus, BaTi1/2Mn1/2O3 is proposed as a rare case of an intrinsically disordered S = 3/2 spin gap system with a frustrated ground state.We report a structural-magnetic investigation by x-ray absorption spectroscopy (XAS), neutron diffraction, dc susceptibility (X-dc), and electron spin resonance (ESR) of the 12R-type perovskite BaTi1/2Mn1/2O3. Our structural analysis by neutron diffraction supports the existence of structural trimers with chemically disordered occupancy of Mn4+ and Ti4+ ions, with the valence of the Mn ions confirmed by the XAS measurements. The magnetic properties are explored by combining dc-susceptibility and X-band (9.4 GHz) electron spin resonance, both in the temperature interval of 2 <= T <= 1000 K. A scenario is presented under which the magnetism is explained by considering magnetic dimers and trimers, with exchange constants J(a)/k(B) = 200 (2) K and J(b)/k(B) = 130 (10) K, and orphan spins. Thus, BaTi1/2Mn1/2O3 is proposed as a rare case of an intrinsically disordered S = 3/2 spin gap system with a frustrated ground state.912218FAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOFAPEMIG - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE MINAS GERAISCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPq [308355/2009-1, 482549/2010-6]APQ-01577-09APQ-02253-122010-EXA0232012-EXA011308355/2009-1482549/2010-62011/22261-5The work is being financed by FAPEMIG (MG-Brazil) Grants No. APQ-01577-09, APQ-02253-12, 2010-EXA023, and 2012-EXA011, CNPq (Brazil) Grants 308355/2009-1, 482549/2010-6, and PICT 1043. F. A. Garcia would like to acknowledge FAPESP Grant No. 2011/22261-5 for the financial support during the work and Eric Andrade for fruitful discussions on the basics of frustrated systems

Differential branching fraction and angular analysis of the decay B0→K∗0μ+μ−

The angular distribution and differential branching fraction of the decay B 0→ K ∗0 μ + μ − are studied using a data sample, collected by the LHCb experiment in pp collisions at s√=7 TeV, corresponding to an integrated luminosity of 1.0 fb−1. Several angular observables are measured in bins of the dimuon invariant mass squared, q 2. A first measurement of the zero-crossing point of the forward-backward asymmetry of the dimuon system is also presented. The zero-crossing point is measured to be q20=4.9±0.9GeV2/c4 , where the uncertainty is the sum of statistical and systematic uncertainties. The results are consistent with the Standard Model predictions

Observation of two new Ξb−\Xi_b^- baryon resonances

Two structures are observed close to the kinematic threshold in the $\Xi_b^0 \pi^-$ mass spectrum in a sample of proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$ recorded by the LHCb experiment. In the quark model, two baryonic resonances with quark content $bds$ are expected in this mass region: the spin-parity $J^P = \frac{1}{2}^+$ and $J^P=\frac{3}{2}^+$ states, denoted $\Xi_b^{\prime -}$ and $\Xi_b^{*-}$. Interpreting the structures as these resonances, we measure the mass differences and the width of the heavier state to be $m(\Xi_b^{\prime -}) - m(\Xi_b^0) - m(\pi^{-}) = 3.653 \pm 0.018 \pm 0.006$ MeV$/c^2$, $m(\Xi_b^{*-}) - m(\Xi_b^0) - m(\pi^{-}) = 23.96 \pm 0.12 \pm 0.06$ MeV$/c^2$, $\Gamma(\Xi_b^{*-}) = 1.65 \pm 0.31 \pm 0.10$ MeV, where the first and second uncertainties are statistical and systematic, respectively. The width of the lighter state is consistent with zero, and we place an upper limit of $\Gamma(\Xi_b^{\prime -}) < 0.08$ MeV at 95% confidence level. Relative production rates of these states are also reported.Comment: 17 pages, 2 figure

Opposite-side flavour tagging of B mesons at the LHCb experiment

The calibration and performance of the oppositeside flavour tagging algorithms used for the measurements of time-dependent asymmetries at the LHCb experiment are described. The algorithms have been developed using simulated events and optimized and calibrated with B + →J/ψK +, B0 →J/ψK ∗0 and B0 →D ∗− μ + νμ decay modes with 0.37 fb−1 of data collected in pp collisions at √ s = 7 TeV during the 2011 physics run. The oppositeside tagging power is determined in the B + → J/ψK + channel to be (2.10 ± 0.08 ± 0.24) %, where the first uncertainty is statistical and the second is systematic

Measurement of the mass and lifetime of the Ωb−\Omega_b^- baryon

A proton-proton collision data sample, corresponding to an integrated luminosity of 3 fb$^{-1}$ collected by LHCb at $\sqrt{s}=7$ and 8 TeV, is used to reconstruct $63\pm9$ $\Omega_b^-\to\Omega_c^0\pi^-$, $\Omega_c^0\to pK^-K^-\pi^+$ decays. Using the $\Xi_b^-\to\Xi_c^0\pi^-$, $\Xi_c^0\to pK^-K^-\pi^+$ decay mode for calibration, the lifetime ratio and absolute lifetime of the $\Omega_b^-$ baryon are measured to be \begin{align*} \frac{\tau_{\Omega_b^-}}{\tau_{\Xi_b^-}} &= 1.11\pm0.16\pm0.03, \\ \tau_{\Omega_b^-} &= 1.78\pm0.26\pm0.05\pm0.06~{\rm ps}, \end{align*} where the uncertainties are statistical, systematic and from the calibration mode (for $\tau_{\Omega_b^-}$ only). A measurement is also made of the mass difference, $m_{\Omega_b^-}-m_{\Xi_b^-}$, and the corresponding $\Omega_b^-$ mass, which yields \begin{align*} m_{\Omega_b^-}-m_{\Xi_b^-} &= 247.4\pm3.2\pm0.5~{\rm MeV}/c^2, \\ m_{\Omega_b^-} &= 6045.1\pm3.2\pm 0.5\pm0.6~{\rm MeV}/c^2. \end{align*} These results are consistent with previous measurements.Comment: 11 pages, 5 figures, All figures and tables, along with any supplementary material and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/LHCbProjectPublic/LHCb-PAPER-2016-008.htm