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Träfflista för sökning "WFRF:(Pierson Jean Francois) srt2:(2010-2014)"

Search: WFRF:(Pierson Jean Francois) > (2010-2014)

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1.
  • El Albani, Abderrazak, et al. (author)
  • Large colonial organisms with coordinated growth in oxygenated environments 2.1 Gyr ago
  • 2010
  • In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 466:7302, s. 100-104
  • Journal article (peer-reviewed)abstract
    • The evidence for macroscopic life during the Palaeoproterozoic era (2.5-1.6 Gyr ago) is controversial(1-5). Except for the nearly 2-Gyr-old coil-shaped fossil Grypania spiralis(6,7), which may have been eukaryotic, evidence for morphological and taxonomic bio-diversification of macroorganisms only occurs towards the beginning of the Mesoproterozoic era (1.6-1.0 Gyr)(8). Here we report the discovery of centimetre-sized structures from the 2.1-Gyr-old black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, which we interpret as highly organized and spatially discrete populations of colonial organisms. The structures are up to 12 cm in size and have characteristic shapes, with a simple but distinct ground pattern of flexible sheets and, usually, a permeating radial fabric. Geochemical analyses suggest that the sediments were deposited under an oxygenated water column. Carbon and sulphur isotopic data indicate that the structures were distinct biogenic objects, fossilized by pyritization early in the formation of the rock. The growth patterns deduced from the fossil morphologies suggest that the organisms showed cell-to-cell signalling and coordinated responses, as is commonly associated with multicellular organization(9). The Gabon fossils, occurring after the 2.45-2.32-Gyr increase in atmospheric oxygen concentration(10), may be seen as ancient representatives of multicellular life, which expanded so rapidly 1.5 Gyr later, in the Cambrian explosion.
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2.
  • Horwat, David, et al. (author)
  • On the deactivation of the dopant and electronic structure in reactively sputtered transparent Al-doped ZnO thin films
  • 2010
  • In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 43:13, s. 132003-
  • Journal article (peer-reviewed)abstract
    • We report on the possible origin of electrical heterogeneities in 4 at% Al-doped ZnO (AZO) reactively sputtered films. It is found through the Zn L-3 and Al K edge x-ray absorption near-edge structure that a fraction of the Al dopant is deactivated by its positioning in octahedral conformation with oxygen. This fraction as well as the conductivity, optical bandgap and c-axis parameter of ZnO wurtzite are all found to depend on the sample position during deposition. The present results suggest the formation of a metastable Al2O3 (ZnO) m homologous phase that degrades the electrical conductivity.
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3.
  • Norrby, Niklas, 1984- (author)
  • Microstructural evolution of TiAlN hard coatings at elevated pressures and temperatures
  • 2014
  • Doctoral thesis (other academic/artistic)abstract
    • A typical hard coating on metal cutting inserts used in for example turning, milling or drilling operations is TiAlN. At elevated temperatures, TiAlN exhibits a well characterized spinodal decomposition into coherent cubic TiN and AlN rich domains, which is followed by a transformation from cubic to hexagonal AlN. Using in-situ synchrotron x-ray radiation, the kinetics of the second transformation was investigated in this thesis and the strong temperature dependence on the transformation rate indicated a diffusion based nucleation and growth mechanism. The results gave additional information regarding activation energy of the transformation and the critical wavelength of the cubic domains at the onset of hexagonal AlN. After nucleation and growth, the hexagonal domains showed a striking resemblance with the preexisting cubic AlN microstructure.During metal cutting, the tool protecting coating is subjected to temperatures of ~900 ºC and pressure levels in the GPa range. The results in this thesis have shown a twofold effect of the pressure on the decomposition steps. Firstly, the spinodal decomposition was promoted by the applied pressure during metal cutting which was shown by comparisons with annealed samples at similar temperatures. Secondly, the detrimental transformation from cubic to hexagonal AlN was shown to be suppressed at elevated hydrostatic pressures. A theoretical pressure/temperature phase diagram, validated with experimental results, also showed suppression of hexagonal AlN by an increased temperature at elevated pressures.The spinodal decomposition during annealing and metal cutting was in this work also shown to be strongly affected by the elastic anisotropy of TiAlN, where the phase separation was aligned along the elastically softer <100> directions in the crystal. The presence of the anisotropic microstructure enhanced the mechanical properties compared to the isotropic case, mainly due to a shorter distance between the c-AlN and c-TiN domains in the anisotropic case. Further improvement of the metal cutting behavior was realized by depositing individual layers with an alternating bias. The individual bias layers exhibited microstructural differences with different residual stress states. The results of the metal cutting tests showed an enhanced wear resistance in terms of both crater and flank wear compared to coatings deposited with a fixed bias.
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  • Result 1-3 of 3

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