13,463 research outputs found

    Thermoelectric Figure of Merit of Strongly Correlated Superlattice Semiconductors

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    We solved the Anderson Lattice Hamiltonian to get the energy bands of a strongly correlated semiconductor by using slave boson mean field theory. The transport properties were calculated in the relaxation-time approximation,and the thermoelectric figure of merit was obtained for the strongly correlated semiconductor and its superlattice structures. We found that at room temperature ZTZT can reach nearly 2 for the quantum wire lattice structure.We believe that it is possible to find high values of thermoelectric figure of merit from strongly correlated semiconductor superlattice systems.Comment: 4 pages, 3 figure

    Warps and correlations with intrinsic parameters of galaxies in the visible and radio

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    From a comparison of the different parameters of warped galaxies in the radio, and especially in the visible, we find that: a) No large galaxy (large mass or radius) has been found to have high amplitude in the warp, and there is no correlation of size/mass with the degree of asymmetry of the warp. b) The disc density and the ratio of dark to luminous mass show an opposing trend: smaller values give more asymmetric warps in the inner radii (optical warps) but show no correlation with the amplitude of the warp; however, in the external radii neither is there any correlation with the asymmetry. c) A third anticorrelation arises from a comparison of the amplitude and degree of asymmetry in the warped galaxies. Hence, it seems that very massive dark matter haloes have nothing to do with the formation of warps but only with the degree of symmetry in the inner radii, and are unrelated to the warp shape for the outermost radii. Denser discs show up the same dependence.Comment: 13 pages, 2 figures, accepted to be published in A&

    Changes in and the mediating role of physical activity in relation to active school transport, fitness and adiposity among Spanish youth: the UP&DOWN longitudinal study

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    Background Longitudinal changes in child and adolescent active school transport (AST), and the mediating role of different intensities of daily physical activity (PA) levels in relation to AST and physical fitness and adiposity indicators is unclear. This study aimed to: 1) describe longitudinal changes in AST, light PA (LPA), moderate- to vigorous-intensity PA (MVPA), physical fitness and adiposity indicators over three time-points; and 2) investigate the mediating role of LPA and MVPA levels on associations between AST and physical fitness and adiposity indicators over three time-points among children and adolescents. Methods This longitudinal study comprised 1646 Spanish children and adolescents (48.8% girls, mean age 12.5 years +/- 2.5) at baseline, recruited from schools in Cadiz and Madrid. Mode of commuting to school was self-reported at baseline (T0, 2011-12), 1-year (T1) and 2-year follow-up (T2). PA was assessed using accelerometers. Handgrip strength, standing long jump and cardiorespiratory fitness (CRF) assessed physical fitness. Height, weight, body mass index, waist circumference, and triceps and subscapular skinfold thickness were measured. Multilevel linear regression analyses assessed changes in AST, PA levels, physical fitness and adiposity indicators over three time-points (T0-T1-T2). Additionally, longitudinal path analysis (n = 453; mean age [years] 12.6 +/- 2.4) was used to test the mediating effects of LPA and MVPA levels on the association between AST and physical fitness and adiposity indicators. Results Multilevel analyses observed decreases in LPA between T0-T1 (beta = - 11.27; p < 0.001) and T0-T2 (beta = - 16.27; p < 0.001) and decreases in MVPA between T0-T2 (beta = - 4.51; p = 0.011). Moreover, changes over time showed increases in handgrip between T0-T1 (beta = 0.78; p = 0.028) and T0-T2 (beta = 0.81; p = 0.046). Path analyses showed that AST was directly positively associated with MVPA at T1 (all, beta approximate to 0.33; p < 0.001). MVPA at T1 mediated associations between AST and CRF at T2 (beta = 0.20; p = 0.040), but not the other outcomes. LPA did not mediate any associations. Conclusions Results from longitudinal path analysis suggest that participation in more AST may help attenuate declines in MVPA that typically occur with age and improve CRF. Therefore, we encourage health authorities to promote AST, as a way to increase MVPA levels and CRF among youth

    Herschel/HIFI observations of molecular emission in protoplanetary nebulae and young planetary nebulae

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    We performed Herschel/HIFI observations of intermediate-excitation molecular lines in the far-infrared/submillimeter range in a sample of ten protoplanetary nebulae and young planetary nebulae. The high spectral resolution provided by HIFI yields accurate measurements of the line profiles. The observation of these high-energy transitions allows an accurate study of the excitation conditions, particularly in the warm gas, which cannot be properly studied from the low-energy lines. We have detected FIR/sub-mm lines of several molecules, in particular of 12CO, 13CO, and H2O. Emission from other species, like NH3, OH, H2^{18}O, HCN, SiO, etc, has been also detected. Wide profiles showing sometimes spectacular line wings have been found. We have mainly studied the excitation properties of the high-velocity emission, which is known to come from fast bipolar outflows. From comparison with general theoretical predictions, we find that CRL 618 shows a particularly warm fast wind, with characteristic kinetic temperature Tk >~ 200 K. In contrast, the fast winds in OH 231.8+4.2 and NGC 6302 are cold, Tk ~ 30 K. Other nebulae, like CRL 2688, show intermediate temperatures, with characteristic values around 100 K. We also discuss how the complex structure of the nebulae can affect our estimates, considering two-component models. We argue that the differences in temperature in the different nebulae can be due to cooling after the gas acceleration (that is probably due to shocks); for instance, CRL 618 is a case of very recent acceleration, less than ~ 100 yr ago, while the fast gas in OH 231.8+4.2 was accelerated ~ 1000 yr ago. We also find indications that the densest gas tends to be cooler, which may be explained by the expected increase of the radiative cooling efficiency with the density.Comment: 24 pages, 31 figure

    Fossil group origins V. The dependence of the luminosity function on the magnitude gap

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    In nature we observe galaxy aggregations that span a wide range of magnitude gaps between the two first-ranked galaxies of a system (Δm12\Delta m_{12}). There are systems with gaps close to zero (e.g., the Coma cluster), and at the other extreme of the distribution, the largest gaps are found among the so-called fossil systems. Fossil and non-fossil systems could have different galaxy populations that should be reflected in their luminosity functions. In this work we study, for the first time, the dependence of the luminosity function parameters on Δm12\Delta m_{12} using data obtained by the fossil group origins (FOGO) project. We constructed a hybrid luminosity function for 102 groups and clusters at z≀0.25z \le 0.25. We stacked all the individual luminosity functions, dividing them into bins of Δm12\Delta m_{12}, and studied their best-fit Schechter parameters. We additionally computed a relative luminosity function, expressed as a function of the central galaxy luminosity, which boosts our capacity to detect differences, especially at the bright end. We find trends as a function of Δm12\Delta m_{12} at both the bright and faint ends of the luminosity function. In particular, at the bright end, the larger the magnitude gap, the fainter the characteristic magnitude M∗M^\ast. We also find differences at the faint end. In this region, the larger the gap, the flatter the faint-end slope α\alpha. The differences found at the bright end support a dissipationless, dynamical friction-driven merging model for the growth of the central galaxy in group- and cluster-sized halos. The differences in the faint end cannot be explained by this mechanism. Other processes, such as enhanced tidal disruption due to early infall and/or prevalence of eccentric orbits, may play a role. However, a larger sample of systems with Δm12>1.5\Delta m_{12} > 1.5 is needed to establish the differences at the faint end.Comment: 11 pages, 10 figures, accepted for publication in A&

    Mechanical canopy and trunk shaking for the harvesting mechanization of table olive orchards

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    Table olive harvesting is highly dependent on manual labour and may jeopardize the crop benefit. The introduction of a mechanical harvest system requires a global evaluation of the whole process. A trunk shaker along with shaker combs and a continuous canopy shaker harvester have been tested in two orchards with different tree training and layout to determine their feasibility to mechanical harvesting in table olives. For that purpose, several parameters have been evaluated. Canopy shaker required adapted orchard layout and hedge of canopies for reaching an acceptable harvesting efficiency about 80% and trunk shaker performed a higher efficiency of more than 95% but depended highly on labour. Both systems had a high field capacity about 0.15 ha h-1 but low for the trunk shaker considering the people (0.01 ha h-1 person-1). The vibration pattern that applied on branches was totally different although the quantitative tree damages were no significative different. There were no significant differences in fruit bruising between both systems, but there were between the different sampling points, mainly in the detachment. The fruit bruising index of the remaining fruit on canopy suggests that it is possible to perform a second harvest. Both mechanical systems are suitable for table olive harvesting whilst improving the efficiency of manual systems with bearable damages, but each one has pros and cons that must be considered bearing in mind that require an adaptation of the orchard where there are applied. Highlights Table olives mechanization is possible by integrating with the fruit liquid store. Trunk shaker performed high efficiency in adapted orchards but depended on labour. Canopy shakers require the adaption of orchard and machine for commercial purposes. There were no differences in detached fruit bruising between both mechanical systems. The bruising index of the remaining fruit on trees suggest second harvesting pass.Table olive harvesting is highly dependent on manual labour and may jeopardize the crop benefit. The introduction of a mechanical harvest system requires a global evaluation of the whole process. A trunk shaker along with shaker combs and a continuous canopy shaker harvester have been tested in two orchards with different tree training and layout to determine their feasibility to mechanical harvesting in table olives. For that purpose, several parameters have been evaluated. Canopy shaker required adapted orchard layout and hedge of canopies for reaching an acceptable harvesting efficiency about 80% and trunk shaker performed a higher efficiency of more than 95% but depended highly on labour. Both systems had a high field capacity about 0.15 ha h-1 but low for the trunk shaker considering the people (0.01 ha h-1 person-1). The vibration pattern that applied on branches was totally different although the quantitative tree damages were no significative different. There were no significant differences in fruit bruising between both systems, but there were between the different sampling points, mainly in the detachment. The fruit bruising index of the remaining fruit on canopy suggests that it is possible to perform a second harvest. Both mechanical systems are suitable for table olive harvesting whilst improving the efficiency of manual systems with bearable damages, but each one has pros and cons that must be considered bearing in mind that require an adaptation of the orchard where there are applied. Highlights Table olives mechanization is possible by integrating with the fruit liquid store. Trunk shaker performed high efficiency in adapted orchards but depended on labour. Canopy shakers require the adaption of orchard and machine for commercial purposes. There were no differences in detached fruit bruising between both mechanical systems. The bruising index of the remaining fruit on trees suggest second harvesting pass

    Fossil Groups Origins III. The relation between optical and X-ray luminosities

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    This study is part of the FOssil Groups Origin (FOGO) project which aims at carrying out a systematic and multiwavelength study of a large sample of fossil systems. Here we focus on the relation between the optical luminosity (Lopt) and X-ray luminosity (Lx). Out of a sample of 28 candidate fossil systems, we consider a sample of 12 systems whose fossil classification has been confirmed by a companion study. They are compared with the complementary sample of 16 systems whose fossil nature is not confirmed and with a subsample of 102 galaxy systems from the RASS-SDSS galaxy cluster survey. Fossil and normal systems span the same redshift range 0<z<0.5 and have the same Lx distribution. For each fossil system, the Lx in the 0.1-2.4 keV band is computed using data from the ROSAT All Sky Survey. For each fossil and normal system we homogeneously compute Lopt in the r-band within the characteristic cluster radius, using data from the SDSS DR7. We sample the Lx-Lopt relation over two orders of magnitude in Lx. Our analysis shows that fossil systems are not statistically distinguishable from the normal systems both through the 2D KS test and the fit of the Lx-Lopt relation. The optical luminosity of the galaxy system does strongly correlate with the X-ray luminosity of the hot gas component, independently of whether the system is fossil or not. We conclude that our results are consistent with the classical "merging scenario" of the brightest galaxy formed via merger/cannibalism of other group galaxies, with conservation of the optical light. We find no evidence for a peculiar state of the hot intracluster medium.Comment: A&A, 12 pages, 4 figures, 3 tables, typos corr. and paper re-numbe
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