108,893 research outputs found

    Success stories in reversing land degradation and the role of UNCCD

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    Global impacts of land degradation

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    Study commissioned by the Scientific, Technical and Advisory Panel (STAP) of the Global Environment Facility (GEF) to support the development of the new GEF focal area of Land Degradatio

    Deviation of light curves of gamma-ray burst pulses from standard forms due to the curvature effect of spherical fireballs or uniform jets

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    As revealed previously, under the assumption that some pulses of gamma-ray bursts are produced by shocks in spherical fireballs or uniform jets of large opening angles, there exists a standard decay form of the profile of pulses arising from very narrow or suddenly dimming local (or intrinsic) pulses due to the relativistic curvature effect (the Doppler effect over the spherical shell surface). Profiles of pulses arising from other local pulses were previously found to possess a reverse S-feature deviation from the standard decay form. We show in this paper that, in addition to the standard decay form shown in Qin et al. (2004), there exists a marginal decay curve associated with a local δ\delta function pulse with a mono-color radiation. We employ the sample of Kocevski et al. (2003) to check this prediction and find that the phenomenon of the reverse S-feature is common, when compared with both the standard decay form and the marginal decay curve. We accordingly propose to take the marginal decay curve (whose function is simple) as a criteria to check if an observed pulse could be taken as a candidate suffered from the curvature effect. We introduce two quantities A1A_1 and A2A_2 to describe the mentioned deviations within and beyond the FWHMFWHM position of the decay phase, respectively. The values of A1A_1 and A2A_2 of pulses of the sample are calculated, and the result suggests that for most of these pulses their corresponding local pulses might contain a long decay time relative to the time scale of the curvature effect.Comment: 24 pages, 7 figures, 1 table accepted for publication in MNRA