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  • quasicrystalssuperspace crystallographystructure analysisphasonsX-ray diffuse scattering  (2)
  • 05. General::05.07. Space and Planetary sciences::05.07.02. Space weather  (1)
  • Bayesian particle polishingbeam-induced motion correctioncryo-EMsingle-particle analysiselectron cryo-microscopy  (1)
  • International Union of Crystallography (IUCr)  (3)
  • American Institute of Physics  (1)
Collection
Keywords
Publisher
Years
  • 1
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    From COST 238 To COST 296: Four European COST Actions On Ionospheric Physics And Radio Propagation (2008)
    American Institute of Physics
    Details
    Publication Date: 2017-04-04
    Description: COST (Co-operation in the field of Scientific and Technical Research) is an important instrument supporting co-operation among scientists and researchers across Europe now joining 35 member countries. Scientific projects in the COST framework are called COST Actions and have the objectives embodied in their respective Memorandum of Understanding (MoU). The main objectives of the COST Actions within the European ionospheric and radio propagation community have been: to study the influence of upper atmospheric conditions on terrestrial and Earthspace communications, to develop methods and techniques to improve existing and generate new ionospheric and propagation models over Europe for telecommunication and navigation applications and to transfer the results to the appropriate national and international organizations, institutions and industry dealing with the modern communication systems. This paper summarises in brief the background and historical context of four ionospheric COST Actions and outlines their main objectives and results. In addition, the paper discusses the dissemination of the results and the collaboration among the participating institutions and researchers.
    Description: DRS Codem Systems Ball Aerospace Corporation University of Massachusetts Lowell
    Description: Published
    Description: Lowell, Massachusetts, U.S.A., April 29, 2007
    Description: 3.9. Fisica della magnetosfera, ionosfera e meteorologia spaziale
    Description: open
    Keywords: Physics of the Ionosphere ; 01. Atmosphere::01.02. Ionosphere::01.02.99. General or miscellaneous ; 05. General::05.07. Space and Planetary sciences::05.07.02. Space weather
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: Conference paper
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  • 2
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    Mysteries of icosahedral quasicrystals: how are the atoms arranged? (2016)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2016-06-28
    Keywords: quasicrystalssuperspace crystallographystructure analysisphasonsX-ray diffuse scattering
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 3
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    Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal (2016)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2016-06-15
    Description: The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K2/K1 = −0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of `high-Qperp' reflections.
    Keywords: quasicrystalssuperspace crystallographystructure analysisphasonsX-ray diffuse scattering
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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  • 4
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    A Bayesian approach to beam-induced motion correction in cryo-EM single-particle analysis (2018)
    International Union of Crystallography (IUCr)
    In: IUCrJ
    Details
    Publication Date: 2018-11-09
    Description: A new method to estimate the trajectories of particle motion and the amount of cumulative beam damage in electron cryo-microscopy (cryo-EM) single-particle analysis is presented. The motion within the sample is modelled through the use of Gaussian process regression. This allows a prior likelihood that favours spatially and temporally smooth motion to be associated with each hypothetical set of particle trajectories without imposing hard constraints. This formulation enables the a posteriori likelihood of a set of particle trajectories to be expressed as a product of that prior likelihood and an observation likelihood given by the data, and this a posteriori likelihood to then be maximized. Since the smoothness prior requires three parameters that describe the statistics of the observed motion, an efficient stochastic method to estimate these parameters is also proposed. Finally, a practical algorithm is proposed that estimates the average amount of cumulative radiation damage as a function of radiation dose and spatial frequency, and then fits relative B factors to that damage in a robust way. The method is evaluated on three publicly available data sets, and its usefulness is illustrated by comparison with state-of-the-art methods and previously published results. The new method has been implemented as Bayesian polishing in RELION-3, where it replaces the existing particle-polishing method, as it outperforms the latter in all tests conducted.
    Keywords: Bayesian particle polishingbeam-induced motion correctioncryo-EMsingle-particle analysiselectron cryo-microscopy
    Electronic ISSN: 2052-2525
    Topics: Geosciences , Physics
    Published by International Union of Crystallography (IUCr)
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