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1.
  • Abbasi, R., et al. (författare)
  • An absence of neutrinos associated with cosmic-ray acceleration in gamma-ray bursts
  • 2012
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 484:7394, s. 351-354
  • Tidskriftsartikel (refereegranskat)abstract
    • Very energetic astrophysical events are required to accelerate cosmic rays to above 10(18) electronvolts. GRBs (c-ray bursts) have been proposed as possible candidate sources(1-3). In the GRB 'fireball' model, cosmic-ray acceleration should be accompanied by neutrinos produced in the decay of charged pions created in interactions between the high-energy cosmic-ray protons and gamma-rays(4). Previous searches for such neutrinos found none, but the constraints were weak because the sensitivity was at best approximately equal to the predicted flux(5-7). Here we report an upper limit on the flux of energetic neutrinos associated with GRBs that is at least a factor of 3.7 below the predictions(4,8-10). This implies either that GRBs are not the only sources of cosmic rays with energies exceeding 10(18) electronvolts or that the efficiency of neutrino production is much lower than has been predicted.
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2.
  • Abdi-Jalebi, Mojtaba, et al. (författare)
  • Maximizing and stabilizing luminescence from halide perovskites with potassium passivation
  • 2018
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 555, s. 497-501
  • Tidskriftsartikel (refereegranskat)abstract
    • Metal halide perovskites are of great interest for various high-performance optoelectronic applications. The ability to tune the perovskite bandgap continuously by modifying the chemical composition opens up applications for perovskites as coloured emitters, in building-integrated photovoltaics, and as components of tandem photovoltaics to increase the power conversion efficiency. Nevertheless, performance is limited by non-radiative losses, with luminescence yields in state-of-the-art perovskite solar cells still far from 100 per cent under standard solar illumination conditions. Furthermore, in mixed halide perovskite systems designed for continuous bandgap tunability2 (bandgaps of approximately 1.7 to 1.9 electronvolts), photoinduced ion segregation leads to bandgap instabilities. Here we demonstrate substantial mitigation of both non-radiative losses and photoinduced ion migration in perovskite films and interfaces by decorating the surfaces and grain boundaries with passivating potassium halide layers. We demonstrate external photoluminescence quantum yields of 66 per cent, which translate to internal yields that exceed 95 per cent. The high luminescence yields are achieved while maintaining high mobilities of more than 40 square centimetres per volt per second, providing the elusive combination of both high luminescence and excellent charge transport. When interfaced with electrodes in a solar cell device stack, the external luminescence yield—a quantity that must be maximized to obtain high efficiency—remains as high as 15 per cent, indicating very clean interfaces. We also demonstrate the inhibition of transient photoinduced ion-migration processes across a wide range of mixed halide perovskite bandgaps in materials that exhibit bandgap instabilities when unpassivated. We validate these results in fully operating solar cells. Our work represents an important advance in the construction of tunable metal halide perovskite films and interfaces that can approach the efficiency limits in tandem solar cells, coloured-light-emitting diodes and other optoelectronic applications.
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3.
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4.
  • Ahlberg, Per E. (författare)
  • Birth of the jawed vertebrates
  • 2009
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 457, s. 1094-1095
  • Tidskriftsartikel (övrigt vetenskapligt)abstract
    • The discovery of embryos in certain fossil fishes not only shows that internal fertilization and live birth evolved early in vertebrate history, but also raises questions about the origin of jawed vertebrates.
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5.
  • Ahlberg, Per E. (författare)
  • Coelacanth fins and evolution
  • 1992
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 358, s. 459
  • Tidskriftsartikel (refereegranskat)
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6.
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7.
  • Ahlberg, Per E. (författare)
  • Fossil fishes from Gogo
  • 1989
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 337, s. 511-512
  • Tidskriftsartikel (övrigt vetenskapligt)
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8.
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9.
  • Ahlberg, Per Erik (författare)
  • Glimpsing the hidden majority
  • 1990
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 344, s. 23
  • Tidskriftsartikel (övrigt vetenskapligt)
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10.
  • Ahlberg, Per E. (författare)
  • How to keep a head in order
  • 1997
  • Ingår i: Nature. - 0028-0836 .- 1476-4687. ; 385, s. 489-490
  • Tidskriftsartikel (övrigt vetenskapligt)
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