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Sökning: L773:0028 0836 OR L773:1476 4687 > (2010-2019) > (2018)

  • Resultat 21-30 av 77
  • Föregående 12[3]4567...8Nästa
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21.
  • Leo, N., et al. (författare)
  • Magnetoelectric inversion of domain patterns
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 560:7719, s. 466-
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>The inversion of inhomogeneous physical states has great technological importance; for example, active noise reduction relies on the emission of an inverted sound wave that interferes destructively with the noise of the emitter(1), and inverting the evolution of a spin system by using a magnetic-field pulse enables magnetic resonance tomography(2). In contrast to these examples, inversion of a distribution of ferromagnetic or ferroelectric domains within a material is surprisingly difficult: field poling creates a single-domain state, and piece-by-piece inversion using a scanning tip is impractical. Here we report inversion of entire ferromagnetic and ferroelectric domain patterns in the magnetoelectric material Co3TeO6 and the multiferroic material Mn2GeO4, respectively. In these materials, an applied magnetic field reverses the magnetization or polarization, respectively, of each domain, but leaves the domain pattern intact. Landau theory indicates that this type of magnetoelectric inversion is universal across materials that exhibit complex ordering, with one order parameter holding the memory of the domain structure and another setting its overall sign. Domain-pattern inversion is only one example of a previously unnoticed effect in systems such as multiferroics, in which several order parameters are available for combination. Exploring these effects could therefore advance multiferroics towards new levels of functionality.</p>
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22.
  • Lindgren, Amelie, et al. (författare)
  • Extensive loss of past permafrost carbon but a net accumulation into present-day soils
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 560:7717, s. 219-
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Atmospheric concentrations of carbon dioxide increased between the Last Glacial Maximum (LGM, around 21,000 years ago) and the preindustrial era(1). It is thought that the evolution of this atmospheric carbon dioxide (and that of atmospheric methane) during the glacial-to-interglacial transition was influenced by organic carbon that was stored in permafrost during the LGM and then underwent decomposition and release following thaw(2,3). It has also been suggested that the rather erratic atmospheric delta C-13 and Delta C-14 signals seen during deglaciation(1.4) could partly be explained by the presence of a large terrestrial inert LGM carbon stock, despite the biosphere being less productive (and therefore storing less carbon)(5,6). Here we present an empirically derived estimate of the carbon stored in permafrost during the LGM by reconstructing the extent and carbon content of LGM biomes, peatland regions and deep sedimentary deposits. We find that the total estimated soil carbon stock for the LGM northern permafrost region is smaller than the estimated present-day storage (in both permafrost and non-permafrost soils) for the same region. A substantial decrease in the permafrost area from the LGM to the present day has been accompanied by a roughly 400-petagram increase in the total soil carbon stock. This increase in soil carbon suggests that permafrost carbon has made no net contribution to the atmospheric carbon pool since the LGM. However, our results also indicate potential postglacial reductions in the portion of the carbon stock that is trapped in permafrost, of around 1,000 petagrams, supporting earlier studies(7). We further find that carbon has shifted from being primarily stored in permafrost mineral soils and loess deposits during the LGM, to being roughly equally divided between peatlands, mineral soils and permafrost loess deposits today.</p>
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23.
  • Lindgren, Johan, et al. (författare)
  • Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur
  • 2018
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 564:7736, s. 359-365
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life.</p>
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24.
  • Margulis, Walter (författare)
  • Glowing fabrics communicate
  • 2018
  • Ingår i: Nature. - NATURE PUBLISHING GROUP. - 0028-0836 .- 1476-4687. ; 560:7717, s. 170-171
  • Tidskriftsartikel (övrigt vetenskapligt)
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25.
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26.
  • Mathieson, Iain, et al. (författare)
  • The Genomic History of Southeastern Europe
  • 2018
  • Ingår i: Nature. - Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 555:695, s. 197-203
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Farming was first introduced to Europe in the mid-seventh millennium bc, and was associated with migrants from Anatolia who settled in the southeast before spreading throughout Europe. Here, to understand the dynamics of this process, we analysed genome-wide ancient DNA data from 225 individuals who lived in southeastern Europe and surrounding regions between 12000 and 500 bc. We document a west–east cline of ancestry in indigenous huntergatherers and, in eastern Europe, the early stages in the formation of Bronze Age steppe ancestry. We show that the first farmers of northern and western Europe dispersed through southeastern Europe with limited hunter-gatherer admixture, but that some early groups in the southeast mixed extensively with hunter-gatherers without the sex-biased admixture that prevailed later in the north and west. We also show that southeastern Europe continued to be a nexus between east and west after the arrival of farmers, with intermittent genetic contact with steppe populations occurring up to 2,000 years earlier than the migrations from the steppe that ultimately replaced much of the population of northern Europe.</p>
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27.
  • Mirman, Zachary, et al. (författare)
  • 53BP1-RIF1-shieldin counteracts DSB resection through CST- and Polα-dependent fill-in.
  • 2018
  • Ingår i: Nature. - Springer. - 0028-0836 .- 1476-4687. ; 560:7716, s. 112-116
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>In DNA repair, the resection of double-strand breaks dictates the choice between homology-directed repair-which requires a 3' overhang-and classical non-homologous end joining, which can join unresected ends1,2. BRCA1-mutant cancers show minimal resection of double-strand breaks, which renders them deficient in homology-directed repair and sensitive to inhibitors of poly(ADP-ribose) polymerase 1 (PARP1)3-8. When BRCA1 is absent, the resection of double-strand breaks is thought to be prevented by 53BP1, RIF1 and the REV7-SHLD1-SHLD2-SHLD3 (shieldin) complex, and loss of these factors diminishes sensitivity to PARP1 inhibitors4,6-9. Here we address the mechanism by which 53BP1-RIF1-shieldin regulates the generation of recombinogenic 3' overhangs. We report that CTC1-STN1-TEN1 (CST)10, a complex similar to replication protein A that functions as an accessory factor of polymerase-α (Polα)-primase11, is a downstream effector in the 53BP1 pathway. CST interacts with shieldin and localizes with Polα to sites of DNA damage in a 53BP1- and shieldin-dependent manner. As with loss of 53BP1, RIF1 or shieldin, the depletion of CST leads to increased resection. In BRCA1-deficient cells, CST blocks RAD51 loading and promotes the efficacy of PARP1 inhibitors. In addition, Polα inhibition diminishes the effect of PARP1 inhibitors. These data suggest that CST-Polα-mediated fill-in helps to control the repair of double-strand breaks by 53BP1, RIF1 and shieldin.</p>
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28.
  • Mooley, K., et al. (författare)
  • A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 554:7691, s. 207-210
  • Tidskriftsartikel (refereegranskat)abstract
    • GW170817 was the first gravitational-wave detection of a binary neutron-star merger. It was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance of 40 megaparsecs. It has been proposed that the observed γ-ray, X-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis). The presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-γ-ray bursts. Here we report that the radio light curve of GW170817 has no direct signature of the afterglow of an off-axis jet. Although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed γ-ray emission could not have originated from such a jet. Instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. Because the cocoon model explains the radio light curve of GW170817, as well as the γ-ray and X-ray emission (and possibly also the ultraviolet and optical emission), it is the model that is most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, X-ray and γ-ray transients in the local Universe.
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29.
  • Mooley, K. P., et al. (författare)
  • A mildly relativistic wide-angle outflow in the neutron-star merger event GW170817
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 554:7691, s. 207-
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>GW170817 was the first gravitational-wave detection of a binary neutron-star merger(1). It was accompanied by radiation across the electromagnetic spectrum and localized(2) to the galaxy NGC 4993 at a distance of 40 megaparsecs. It has been proposed that the observed gamma-ray, X-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis)(3-6). The presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-gamma-ray bursts(7,8). Here we report that the radio light curve of GW170817 has no direct signature of the afterglow of an off-axis jet. Although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed gamma-ray emission could not have originated from such a jet. Instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. Because the cocoon model explains the radio light curve of GW170817, as well as the gamma-ray and X-ray emission (and possibly also the ultraviolet and optical emission)(9-15), it is the model that is most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, X-ray and gamma-ray transients in the local Universe.</p>
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30.
  • Mooley, K., et al. (författare)
  • Superluminal motion of a relativistic jet in the neutron-star merger GW170817
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 561:7723, s. 355-359
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • The binary neutron-star merger GW1708171was accompanied by radiation across the electromagnetic spectrum2and localized2to the galaxy NGC 4993 at a distance3of about 41 megaparsecs from Earth. The radio and X-ray afterglows of GW170817 exhibited delayed onset4–7, a gradual increase8in the emission with time (proportional to t0.8) to a peak about 150 days after the merger event9, followed by a relatively rapid decline9,10. So far, various models have been proposed to explain the afterglow emission, including a choked-jet cocoon4,8,11–13and a successful-jet cocoon4,8,11–18(also called a structured jet). However, the observational data have remained inconclusive10,15,19,20as to whether GW170817 launched a successful relativistic jet. Here we report radio observations using very long-baseline interferometry. We find that the compact radio source associated with GW170817 exhibits superluminal apparent motion between 75 days and 230 days after the merger event. This measurement breaks the degeneracy between the choked- and successful-jet cocoon models and indicates that, although the early-time radio emission was powered by a wide-angle outflow8(a cocoon), the late-time emission was most probably dominated by an energetic and narrowly collimated jet (with an opening angle of less than five degrees) and observed from a viewing angle of about 20 degrees. The imaging of a collimated relativistic outflow emerging from GW170817 adds substantial weight to the evidence linking binary neutron-star mergers and short γ-ray bursts.
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  • Resultat 21-30 av 77
  • Föregående 12[3]4567...8Nästa
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