192,328 research outputs found

    On the Radial Stellar Content of Early-Type Galaxies as a Function of Mass and Environment

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    Using optical-optical and optical-NIR colors, we analyze the radial dependence of age and metallicity inside massive (M* > 10^10.5 MSun), low-redshift (z<0.1), early-type galaxies (ETGs), residing in both high-density group regions and the field. On average, internal color gradients of ETGs are mainly driven by metallicity, consistent with previous studies. However, we find that group galaxies feature positive age gradients, Nabla_t, i.e. a younger stellar population in the galaxy center, and steeper metallicity gradients, compared to the field sample, whose Nabla_t ranges from negative in lower mass galaxies, to positive gradients at higher mass. These dependencies yield new constraints to models of galaxy formation and evolution. We speculate that age and metallicity gradients of group ETGs result from (either gas-rich or minor-dry) mergers and/or cold-gas accretion, while field ETGs exhibit the characteristic flatter gradients expected from younger, more metal-rich, stars formed inside--out by later gas-cooling.Comment: 2 figures, accepted for publication on ApJ

    Network recovery after massive failures

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    This paper addresses the problem of efficiently restoring sufficient resources in a communications network to support the demand of mission critical services after a large scale disruption. We give a formulation of the problem as an MILP and show that it is NP-hard. We propose a polynomial time heuristic, called Iterative Split and Prune (ISP) that decomposes the original problem recursively into smaller problems, until it determines the set of network components to be restored. We performed extensive simulations by varying the topologies, the demand intensity, the number of critical services, and the disruption model. Compared to several greedy approaches ISP performs better in terms of number of repaired components, and does not result in any demand loss. It performs very close to the optimal when the demand is low with respect to the supply network capacities, thanks to the ability of the algorithm to maximize sharing of repaired resources

    4-F : la veu femenina

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    The Different Environmental Dependencies of Star-formation for Giant and Dwarf Galaxies

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    We examine the origins of the bimodality observed in the global properties of galaxies around a stellar mass of 3x10^10 M_sun by comparing the environmental dependencies of star-formation for the giant and dwarf galaxy populations. The Sloan Digital Sky Survey DR4 spectroscopic dataset is used to produce a sample of galaxies in the vicinity of the supercluster centered on the cluster A2199 at z=0.03 that is ~90% complete to a magnitude limit of M*+3.3. From these we measure global trends with environment for both giant (M_r<-20 mag) and dwarf (-19<M_r<-17.8 mag) subsamples using the luminosity-weighted mean stellar age and H_alpha emission as independent measures of star-formation history. The fraction of giant galaxies classed as old (t>7 Gyr) or passive (EW[H_alpha]<4 A) falls gradually from ~80% in the cluster cores to ~40% in field regions beyond 3-4 R_virial, as found in previous studies. In contrast, we find that the dwarf galaxy population shows a sharp transition at ~1 R_virial, from being predominantly old/passive within the cluster, to outside where virtually all galaxies are forming stars and old/passive galaxies are only found as satellites to more massive galaxies. These results imply fundamental differences in the evolution of giant and dwarf galaxies: whereas the star-formation histories of giant galaxies are determined primarily by their merger history, star-formation in dwarf galaxies is much more resilient to the effects of major mergers. Instead dwarf galaxies become passive only once they become satellites within a more massive halo, by losing their halo gas reservoir to the host halo, or through other environment-related processes such as galaxy harassment and/or ram-pressure stripping.Comment: 4 pages, 4 figures, accepted for publication in ApJ

    The impact of stapling technique and surgeon specialism on anastomotic failure after right-sided colorectal resection. An international multi-centre, prospective audit

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    There is little evidence to support choice of technique and configuration for stapled anastomoses after right hemicolectomy and ileocaecal resection. This study aimed to determine the relationship between stapling technique and anastomotic failure

    The role of fluorine in F-La/TiO2 photocatalysts on photocatalytic decomposition of methanol-water solution

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    F-La/TiO2 photocatalysts were studied in photocatalytic decomposition water-methanol solution. The structural, textural, optical, and electronic properties of F-La/TiO2 photocatalysts were studied by combination of X-ray powder diffraction (XRD), nitrogen physisorption, Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), Electrochemical impedance spectroscopy (EIS), and X-ray fluorescence (XPS). The production of hydrogen in the presence of 2.8F-La/TiO2 was nearly up to 3 times higher than in the presence of pure TiO2. The photocatalytic performance of F-La/TiO2 increased with increasing photocurrent response and conductivity originating from the higher amount of fluorine presented in the lattice of TiO2.Web of Science1218art. no. 286

    Evidence for complex order parameter in La_{1.83}Sr_{0.17}CuO_4

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    The in-plane magnetic field penetration depth (\lambda_{ab}) in single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the muon-spin rotation (\muSR) technique. The temperature dependence of \lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and \Delta_2^s(0)=1.57(8)meV.Comment: 5 pages, 3 figure

    Muon-spin-rotation measurements of the penetration depth in Li_2Pd_3B

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    Measurements of the magnetic field penetration depth λ\lambda in the ternary boride superconductor Li2_2Pd3_3B (Tc7.3T_c\simeq7.3 K) have been carried out by means of muon-spin rotation (μ\muSR). The absolute values of λ\lambda, the Ginzburg-Landau parameter κ\kappa, and the first Hc1H_{c1} and the second Hc2H_{c2} critical fields at T=0 obtained from μ\muSR were found to be λ(0)=252(2)\lambda(0)=252(2) nm, κ(0)=27(1)\kappa(0)=27(1), μ0Hc1(0)=9.5(1)\mu_0H_{c1}(0)=9.5(1) mT, and μ0Hc2(0)=3.66(8)\mu_0H_{c2}(0)=3.66(8) T, respectively. The zero-temperature value of the superconducting gap Δ0=\Delta_0=1.31(3) meV was found, corresponding to the ratio 2Δ0/kBTc=4.0(1)2\Delta_0/k_BT_c=4.0(1). At low temperatures λ(T)\lambda(T) saturates and becomes constant below T0.2TcT\simeq 0.2T_c, in agreement with what is expected for s-wave BCS superconductors. Our results suggest that Li2_2Pd3_3B is a s-wave BCS superconductor with the only one isotropic energy gap.Comment: 6 pages, 7 figure
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