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951.
  •  
952.
  • Veres, P., et al. (författare)
  • Observation of inverse Compton emission from a long gamma-ray burst
  • 2019
  • Ingår i: Nature. - NATURE PUBLISHING GROUP. - 0028-0836. ; 575:7783, s. 459-
  • Tidskriftsartikel (refereegranskat)abstract
    • Long-duration gamma-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectron volt-to-mega electronvoltband, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission(1,2). Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands(1-6). The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock(7-9). Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C(10,11). Here we report multifrequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 x 10(-6) to 10(12) electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs.
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953.
  •  
954.
955.
  •  
956.
  • Virtanen, Annele, et al. (författare)
  • An amorphous solid state of biogenic secondary organic aerosol particles
  • 2010
  • Ingår i: Nature. - 0028-0836. ; 467:7317, s. 824-827
  • Tidskriftsartikel (refereegranskat)abstract
    • Secondary organic aerosol (SOA) particles are formed in the atmosphere from condensable oxidation products of anthropogenic and biogenic volatile organic compounds (VOCs)(1-7). On a global scale, biogenic VOCs account for about 90% of VOC emissions(1,8) and of SOA formation (90 billion kilograms of carbon per year)(1-4). SOA particles can scatter radiation and act as cloud condensation or ice nuclei, and thereby influence the Earth's radiation balance and climate(1,2,5,9,10). They consist of a myriad of different compounds with varying physicochemical properties, and little information is available on the phase state of SOA particles. Gas-particle partitioning models usually assume that SOA particles are liquid(1,5,11), but here we present experimental evidence that they can be solid under ambient conditions. We investigated biogenic SOA particles formed from oxidation products of VOCs in plant chamber experiments and in boreal forests within a few hours after atmospheric nucleation events. On the basis of observed particle bouncing in an aerosol impactor and of electron microscopy we conclude that biogenic SOA particles can adopt an amorphous solid-most probably glassy-state. This amorphous solid state should provoke a rethinking of SOA processes because it may influence the partitioning of semi-volatile compounds, reduce the rate of heterogeneous chemical reactions, affect the particles' ability to accommodate water and act as cloud condensation or ice nuclei, and change the atmospheric lifetime of the particles(12-15). Thus, the results of this study challenge traditional views of the kinetics and thermodynamics of SOA formation and transformation in the atmosphere and their implications for air quality and climate.
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957.
  • von Schantz, Torbjörn, et al. (författare)
  • Female choice - Reply
  • 1989
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836. ; 339:6224, s. 432-433
  • Tidskriftsartikel (refereegranskat)
958.
  • Vonk, J. E., et al. (författare)
  • Activation of old carbon by erosion of coastal and subsea permafrost in Arctic Siberia
  • 2012
  • Ingår i: Nature. - 0028-0836. ; 489:7414, s. 137-140
  • Tidskriftsartikel (refereegranskat)abstract
    • The future trajectory of greenhouse gas concentrations depends on interactions between climate and the biogeosphere(1,2). Thawing of Arctic permafrost could release significant amounts of carbon into the atmosphere in this century(3). Ancient Ice Complex deposits outcropping along the similar to 7,000-kilometre-long coastline of the East Siberian Arctic Shelf (ESAS)(4,5), and associated shallow subsea permafrost(6,7), are two large pools of permafrost carbon(8), yet their vulnerabilities towards thawing and decomposition are largely unknown(9-11). Recent Arctic warming is stronger than has been predicted by several degrees, and is particularly pronounced over the coastal ESAS region(12,13). There is thus a pressing need to improve our understanding of the links between permafrost carbon and climate in this relatively inaccessible region. Here we show that extensive release of carbon from these Ice Complex deposits dominates (57 +/- 2 per cent) the sedimentary carbon budget of the ESAS, the world's largest continental shelf, overwhelming the marine and topsoil terrestrial components. Inverse modelling of the dual-carbon isotope composition of organic carbon accumulating in ESAS surface sediments, using Monte Carlo simulations to account for uncertainties, suggests that 44 +/- 10 teragrams of old carbon is activated annually from Ice Complex permafrost, an order of magnitude more than has been suggested by previous studies(14). We estimate that about two-thirds (66 +/- 16 per cent) of this old carbon escapes to the atmosphere as carbon dioxide, with the remainder being re-buried in shelf sediments. Thermal collapse and erosion of these carbon-rich Pleistocene coastline and seafloor deposits may accelerate with Arctic amplification of climate warming(2,13).
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959.
  • Wagner, W, et al. (författare)
  • Europe ambivalent on biotechnology
  • 1997
  • Ingår i: Nature. - 0028-0836. ; 387, s. 845-847
  • Tidskriftsartikel (refereegranskat)abstract
    • The Eurobarometer on Biotechnology (46.1) was conducted during October and November 1996. The survey conducted in each EU (European Union) country used a multi-stage random sampling procedure and provided a statistically representative sample of national residents aged 15 and over. The total sample within the EU was 16,246 respondents (about 1,000 per EU country). The survey questionnaire was designed by the authors as part of a larger study involving the comparative analysis of public perceptions, media coverage and public policy in relation to biotechnology from 1973 to the present.
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960.
  •  
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