4,388 research outputs found

    Determining the luminosity function of Swift long gamma-ray bursts with pseudo-redshifts

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    The determination of luminosity function (LF) of gamma-ray bursts (GRBs) is of an important role for the cosmological applications of the GRBs, which is however hindered seriously by some selection effects due to redshift measurements. In order to avoid these selection effects, we suggest to calculate pseudo-redshifts for Swift GRBs according to the empirical L-E_p relationship. Here, such a LEpL-E_p relationship is determined by reconciling the distributions of pseudo- and real redshifts of redshift-known GRBs. The values of E_p taken from Butler's GRB catalog are estimated with Bayesian statistics rather than observed. Using the GRB sample with pseudo-redshifts of a relatively large number, we fit the redshift-resolved luminosity distributions of the GRBs with a broken-power-law LF. The fitting results suggest that the LF could evolve with redshift by a redshift-dependent break luminosity, e.g., L_b=1.2\times10^{51}(1+z)^2\rm erg s^{-1}. The low- and high-luminosity indices are constrained to 0.8 and 2.0, respectively. It is found that the proportional coefficient between GRB event rate and star formation rate should correspondingly decrease with increasing redshifts.Comment: 5 pages, 5 figures, accepted for publication in ApJ

    Multi-Decadal Change of Atmospheric Aerosols and their Effect on Surface Radiation

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    We present an investigation on multi-decadal changes of atmospheric aerosols and their effects on surface radiation using a global chemistry transport model, GOCART, along with the near-term to long-term data records. We focus on a 28-year time period of satellite era from 1980 to 2007 during which a suite of aerosol data from satellite observations, ground-based measurements, and intensive field experiments have become available. Particularly: (1) We compare the model calculated clear sky downward radiation at the surface with surface network data from BSRN and CMA (2) We compare the model and surface data with satellite derived downward radiation products from ISCCP and SRS (3) We analyze the long-term global and regional aerosol trends in major anthropogenic source regions (North America, Europe, Asia) that have been experiencing considerable changes of emissions during the three decades, dust and biomass burning regions that have large interannual variability, downwind regions that are directly affected by the changes in the source area, and remote regions that are considered to representing "background" conditions. The comparisons and methods from this study can be applied to multiple model analysis in the AeroCom framework

    Multi-Decadal Change of Atmospheric Aerosols and Their Effect on Surface Radiation

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    We present an investigation on multi-decadal changes of atmospheric aerosols and their effects on surface radiation using a global chemistry transport model along with the near-term to long-term data records. We focus on a 28-year time period of satellite era from 1980 to 2007, during which a suite of aerosol data from satellite observations and ground-based remote sensing and in-situ measurements have become available. We analyze the long-term global and regional aerosol optical depth and concentration trends and their relationship to the changes of emissions" and assess the role aerosols play in the multi-decadal change of solar radiation reaching the surface (known as "dimming" or "brightening") at different regions of the world, including the major anthropogenic source regions (North America, Europe, Asia) that have been experiencing considerable changes of emissions, dust and biomass burning regions that have large interannual variabilities, downwind regions that are directly affected by the changes in the source area, and remote regions that are considered to representing "background" conditions

    Implications of the cosmic infrared background excess for the cosmic star formation

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    By phenomenologically describing the high-redshift star formation history, i.e., ρ˙(z)[(1+z)/4.5]α\dot{\rho}_{*}(z)\propto[(1+z)/4.5]^{-\alpha}, and semi-analytically calculating the fractions of high-redshift Pop I/II and Pop III stars, we investigate the contributions from both high-redshfit Pop I/II and Pop III stars to the observed near-infrared (3μm<λ<5μm3 \mu\rm m<\lambda<5 \mu m) excess in the cosmic infrared background emission. In order to account for the observational level of the near-infrared excess, the power-law index α\alpha of the assumed star formation history is constrained to within the range of 0α10\lesssim\alpha\lesssim1. Such a constraint is obtained under the condition that the virial temperature of dark matter halos belongs to the range of 500KTvir104500 {\rm K}\leq T_{\rm vir}\leq10^4 K.Comment: 6 pages, 5 figures, published in SCIENCE CHINA Physics, Mechanics and Astronom

    Cosmic histories of star formation and reionization: An analysis with a power-law approximation

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    With a simple power-law approximation of high-redshift (3.5\gtrsim3.5) star formation history, i.e., ρ˙(z)[(1+z)/4.5]α\dot{\rho}_*(z)\propto [(1+z)/4.5]^{-\alpha}, we investigate the reionization of intergalactic medium (IGM) and the consequent Thomson scattering optical depth for cosmic microwave background (CMB) photons. A constraint on the evolution index α\alpha is derived from the CMB optical depth measured by the {\it Wilkinson Microwave Anisotropy Probe} (WMAP) experiment, which reads α2.18lgNγ3.89\alpha\approx2.18\lg{\mathscr{N}_{\gamma}}-3.89, where the free parameter Nγ\mathscr{N}_\gamma is the number of the escaped ionizing ultraviolet photons per baryon. Moreover, the redshift for full reionization, zfz_f, can also be expressed as a function of α\alpha as well as Nγ\mathscr{N}_{\gamma}. By further taking into account the implication of the Gunn-Peterson trough observations to quasars for the full reionization redshift, i.e., 6zf76\lesssim z_f \lesssim7, we obtain 0.3α1.30.3\lesssim\alpha\lesssim1.3 and 80Nγ23080\lesssim\mathscr{N}_{\gamma}\lesssim230. For a typical number of 4000\sim4000 of ionizing photons released per baryon of normal stars, the fraction of these photons escaping from the stars, fescf_{\rm esc}, can be constrained to within the range of (2.05.8)(2.0-5.8)%.Comment: 10 pages, 4 figures, accepted for publication in JCA

    Joint constraint on the jet structure from the short GRB population and GRB 170817A

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    The nearest GRB 170817A provided an opportunity to probe the angular structure of the jet of this short gamma-ray burst (SGRB), by using its off-axis observed afterglow emission. It is investigated that whether the afterglow-constrained jet structures can be consistent with the luminosity of the prompt emission of GRB 170817A. Furthermore, by assuming that all SGRBs including GRB 170817A have the same explosive mechanism and jet structure, we apply the different jet structures into the calculation of the flux and redshfit distributions of the SGRB population, in comparison with the observational distributions of the Swift and Fermi sources. As a result, it is found that the single-Gaussian structure can be basically ruled out, whereas the power-law and two-Gaussian models can in principle survive.Comment: 9 pages,6 figure

    Photocatalytic fabrics based on reduced graphene oxide and TiO2 coatings

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    Supplementary data associated with this article can be found, in the online version, at: http://dx.doi.org/10.1016/j.mseb.2015.04.013The purpose of this work is to obtain photocatalytic fabrics based on reduced graphene oxide (RGO) and TiO2 coatings on polyester fabrics. The influence of the applied number of RGO coatings on properties such as light absorption, conductivity, electroactivity and photocatalytic properties of the fabrics was established. An improvement of these properties with the number of RGO coatings applied was obtained. FESEM, EDX, XPS and FTIR-ATR showed the incorporation of the TiO2 nanoparticles on the fabrics. FTIR-ATR showed the formation of a bidentate carboxylic ligand with titanium atoms. The photocatalytic properties of the fabrics were tested with Rhodamine B dye solutions. Photocatalytic efficiency increased with the number of RGO coatings, due to the increased light absorption, and better electrical properties. The charge transfer resistance (Rct) and its time constant (τ) decreased, indicating a better electron transfer which helps to increase the lifetime of the pair electron/hole.Authors wish to thank to the Spanish Ministerio de Ciencia e Innovación (contract CTM2011-23583) for the financial sup port. J. Molina is grateful to the Conselleria d’Educació, Formació i Ocupació (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship. Electron Microscopy Service of the UPV (Universitat Politècnica de València) is gratefully acknowledged for help with FESEM and EDX characterization. Timothy Vickers is gratefully acknowledged for help with English revision.info:eu-repo/semantics/publishedVersio

    Look, the World is Watching How We Treat Migrants! The Making of the Anti-Trafficking Legislation during the Ma Administration

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    Employing the spiral model, this research analyses how anti-human trafficking legislation was promulgated during the Ma Ying-jeou (Ma Yingjiu) presidency. This research found that the gov- ernment of Taiwan was just as accountable for the violation of mi- grants’ human rights as the exploitive placement agencies and abusive employers. This research argues that, given its reliance on the United States for political and security support, Taiwan has made great ef- forts to improve its human rights records and meet US standards for protecting human rights. The reform was a result of multilevel inputs, including US pressure and collaboration between transnational and domestic advocacy groups. A major contribution of this research is to challenge the belief that human rights protection is intrinsic to dem- ocracy. In the same light, this research also cautions against Taiwan’s subscription to US norms since the reform was achieved at the cost of stereotyping trafficking victimhood, legitimising state surveillance, and further marginalising sex workers
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