Multi-level meta-analysis of physical activity interventions during childhood: effects of physical activity on cognition and academic achievement

There is evidence that physical activity positively influences cognition and academic outcomes in childhood. This systematic review used a three-level meta-analytic approach, which handles nested effect sizes, to assess the impact of physical activity interventions. Ninety-two randomised control trials in typically developing children (5-12 years old, N = 25,334) were identified. Control group type and intervention characteristics including duration, frequency and teacher qualification were explored as potential moderators. Results showed physical activity interventions improved on-task behaviour with a large effect size (g = 1.04, p = 0.03 (95% CI: 0.08 – 2.00), very low-certainty evidence) and led to moderate improvements in creativity (g = 0.70, p < 0.01 (0.20 – 1.20), low-certainty evidence). Small beneficial effects were found for fluid intelligence (g = 0.16, p = 0.03 (0.02, 0.30), moderate-certainty evidence) and working memory (g = 0.18, p = 0.01 (0.07 – 0.29) very low-certainty evidence) but no overall benefit was observed for attention, inhibitory control, planning, cognitive flexibility or academic outcomes. Heterogeneity was high and moderator analyses indicated beneficial effects of PA with academic instruction of 6 – 10-week duration with moderate or moderate to vigorous intensity on mathematics outcomes and enriched PA programmes on language outcomes. In contrast, aerobic PA with moderate to vigorous intensity benefitted executive function outcomes. These results therefore suggest differential mechanisms of impact of different types of PA on different aspects of cognition

The population of X-ray supernova remnants in the Large Magellanic Cloud

We present a comprehensive X-ray study of the population of supernova remnants (SNRs) in the LMC. Using primarily XMM-Newton, we conduct a systematic spectral analysis of LMC SNRs to gain new insights on their evolution and the interplay with their host galaxy. We combined all the archival XMM observations of the LMC with those of our Very Large Programme survey. We produced X-ray images and spectra of 51 SNRs, out of a list of 59. Using a careful modelling of the background, we consistently analysed all the X-ray spectra and measure temperatures, luminosities, and chemical compositions. We investigated the spatial distribution of SNRs in the LMC and the connection with their environment, characterised by various SFHs. We tentatively typed all LMC SNRs to constrain the ratio of core-collapse to type Ia SN rates in the LMC. We compared the X-ray-derived column densities to HI maps to probe the three-dimensional structure of the LMC. This work provides the first homogeneous catalogue of X-ray spectral properties of LMC SNRs. It offers a complete census of LMC SNRs exhibiting Fe K lines (13% of the sample), or revealing contribution from hot SN ejecta (39%). Abundances in the LMC ISM are found to be 0.2-0.5 solar, with a lower [$\alpha$/Fe] than in the Milky Way. The ratio of CC/type Ia SN in the LMC is $N_{\mathrm{CC}}/N_{\mathrm{Ia}} = 1.35(_{-0.24}^{+0.11})$, lower than in local SN surveys and galaxy clusters. Comparison of X-ray luminosity functions of SNRs in Local Group galaxies reveals an intriguing excess of bright objects in the LMC. We confirm that 30 Doradus and the LMC Bar are offset from the main disc of the LMC, to the far and near sides, respectively. (abridged)Comment: Accepted for publication in Astronomy and Astrophysics. 54 pages, 18 figures, 12 tables. The resolution of the figures has been reduced compared to the journal version; v2: New title, minor text edits; v3: Correct version

Electron transport in Coulomb- and tunnel-coupled one-dimensional systems

We develop a linear theory of electron transport for a system of two identical quantum wires in a wide range of the wire length L, unifying both the ballistic and diffusive transport regimes. The microscopic model, involving the interaction of electrons with each other and with bulk acoustical phonons allows a reduction of the quantum kinetic equation to a set of coupled equations for the local chemical potentials for forward- and backward-moving electrons in the wires. As an application of the general solution of these equations, we consider different kinds of electrical contacts to the double-wire system and calculate the direct resistance, the transresistance, in the presence of tunneling and Coulomb drag, and the tunneling resistance. If L is smaller than the backscattering length l_P, both the tunneling and the drag lead to a negative transresistance, while in the diffusive regime (L >>l_P) the tunneling opposes the drag and leads to a positive transresistance. If L is smaller than the phase-breaking length, the tunneling leads to interference oscillations of the resistances that are damped exponentially with L.Comment: Text 14 pages in Latex/Revtex format, 4 Postscript figure

Spin-dependent (magneto)transport through a ring due to spin-orbit interaction

Electron transport through a one-dimensional ring connected with two external leads, in the presence of spin-orbit interaction (SOI) of strength \alpha and a perpendicular magnetic field is studied. Applying Griffith's boundary conditions we derive analytic expressions for the reflection and transmission coefficients of the corresponding one-electron scattering problem. We generalize earlier conductance results by Nitta et al. [Appl. Phys. Lett. 75, 695 (1999)] and investigate the influence of \alpha, temperature, and a weak magnetic field on the conductance. Varying \alpha and temperature changes the position of the minima and maxima of the magnetic-field dependent conductance, and it may even convert a maximum into a minimum and vice versa.Comment: 19 pages, 9 figure

Correlations, inhomogeneous screening, and suppression of spin-splitting in quantum wires at strong magnetic fields

A self-consistent treatment of exchange and correlation interactions in a quantum wire (QW) subject to a strong perpendicular magnetic field is presented using a modified local-density approximation (MLDA). The influence of many-body interactions on the spin-splitting between the two lowest Landau levels (LLs) is calculated within the screened Hartree-Fock approximation (SHFA), for filling factor \nu=1, and the strong spatial dependence of the screening properties of electrons is taken into account. In comparison with the Hartree-Fock result, the spatial behavior of the occupied LL in a QW is strongly modified when correlations are included. Correlations caused by screening at the edges strongly suppress the exchange splitting and smoothen the energy dispersion at the edges. The theory accounts well for the experimentally observed strong suppression of the spin-splitting pertinent to the \nu=1 quantum Hall effect (QHE) state as well as the destruction of this state in long, quasi-ballistic GaAlAs/GaAs QWs.Comment: Text 23 pages in Latex/Revtex/preprint format, 6 Postscript figures, submitted to Physical Review