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  • 1
    Digitale Medien
    Digitale Medien
    X-ray topographic dislocation contrast visible in reflections orthogonal to the Burgers vectors of axial screw dislocations in hexagonal silicon carbide (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 20-26 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Contrast is associated with micropipes in X-ray topographs of SiC crystals obtained with prismatic reflections, representing an apparent violation of the g·b = 0 invisibility criterion. This is explained as a population of basal-plane dislocations with Burgers vectors of the set b = {\textstyle{1 \over 3}}〈11{\bar{2}}0〉 that occur in a high density within a few micrometers of the micropipes, below the resolution of X-ray topography. These basal-plane dislocations could be observed under an electron microscope. The presence of the surfaces of the micropipes influences the dislocation images in the topographs taken with prismatic reflections, often resulting in a band of light contrast along the axes of the micropipes.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889800017027
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  • 2
    Digitale Medien
    Digitale Medien
    Harmonic composition of synchrotron white-beam X-ray topographic back-reflection images of basal-cut silicon carbide single-crystal wafers (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 820-822 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Superscrew dislocations are visible in back-reflection synchrotron white-beam X-ray topographs of basal-cut SiC wafers in striking contrast as black rings surrounding white circles, even though such topographs suffer from extensive harmonic contamination. The contributions to the synchrotron white-beam topograph of each member of its series of harmonic reflections, {\bf g}=(0006n), where n=3 to 16, were calculated. Through intensity considerations and comparison with a {\bf g}=00018 topograph taken with Cu Kα1 radiation, the {\bf g}=00024 harmonic was determined to be the most important contributor. The contrast of features lying deep beneath the crystal's surface was attributed to higher harmonics with larger penetration depths.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889898004683
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  • 3
    Digitale Medien
    Digitale Medien
    Superscrew dislocation contrast on synchrotron white-beam topographs: an accurate description of the direct dislocation image (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 32 (1999), S. 516-524 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A kinematic (geometrical) diffraction simulation model has been developed to provide understanding of direct dislocation images on synchrotron white-beam X-ray topographs, and has been successfully applied to illustrate the contrast formation mechanisms involved in images of micropipe-related superscrew dislocations in silicon carbide crystals. The coincidence of the simulations with the contrast features of the superscrew dislocation images, recorded using a series of synchrotron topography techniques, shows that this model is capable of revealing the detailed diffraction behavior of the highly distorted region around the dislocation core and determining the quantitative characteristics of the dislocations. The simulation technique is thus demonstrated to be a simple but efficient method for interpretation of synchrotron topographs, and may be applied to explain the topographic contrast characters of general crystal defects.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889899002939
    Standort Signatur Einschränkungen Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Crystallization and preliminary X-ray analysis of human RCC1, the regulator of chromosome condensation (1999)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 272-275 
    Details
    ISSN: 1399-0047
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: RCC1, the regulator of chromosome condensation, is the guanine nucleotide-exchange factor (GEF) of the GTP-binding protein Ran. Its GEF activity on Ran makes it a key element in nucleo-cytoplasmic transport and cell-cycle regulation. Crystals of human RCC1 suitable for X-ray analysis have been obtained using the seeding technique in hanging drops with sodium citrate as a precipitant. The crystals diffract to 1.7 Å at 100 K and belong to the space group P1, with unit-cell parameters a = 49.5, b = 84.3, c = 84.9 Å, α = 113.0, β = 103.9,γ = 103.3°. The Matthews parameter (Vm) and the self-rotation function are consistent with three molecules in the unit cell, which is confirmed by the averaged single isomorphous replacement (SIR) electron-density map.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0907444998007768
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