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  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 650-655 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The rocking curve of protein crystals contains a lot of useful information concerning crystal quality, most of which is lost owing to the superimposition of spurious features appearing in these fragile materials after growth, during handling and mounting. To minimize such data spoiling, an experimental setup to perform in situ X-ray diffraction experiments during crystal growth has been designed. The setup, which includes video observation to allow the correlation of crystal shape, size and growth rate with X-ray data, has been used to assess the mosaicity of tetragonal lysozyme crystals during crystal growth. The full width at half maximum (FWHM) of diffraction peaks collected from these crystals changes during the growth process as a (directly proportional) response to the growth rates and the different development of different domain blocks. These changes in the domain distribution and FWHM with time involve a `zonation' of the crystals, which show very different rocking curves in different parts of their volume. The rocking curves recorded in situ from growing crystals are easier to understand than those from crystals that have suffered even minor handling.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 412-417 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Experimental evidence is presented for the first time for the development and time evolution of concentration-depletion zones around protein crystals growing in microgravity and gelled on-ground experiments. Crystal motion and buoyancy-driven fluid movements as a result of residual accelerations and g-jitters are demonstrated to have an adverse effect on the stability of these depletion zones, provoking the breakdown of their radial symmetry. These findings may explain some of the controversial results reported on the quality of single crystals grown under microgravity in previous space missions.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 57 (2001), S. 1119-1126 
    ISSN: 1399-0047
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Very high quality crystals of tetragonal hen egg-white lysozyme were grown in the Advanced Protein Crystallization Facility (APCF) on board the Space Shuttle using a modified free-interface diffusion (FID) reactor designed ad hoc to have a longer diffusion path. This design allows the performance of true counter-diffusion experiments. Crystals were obtained under the classical chemical conditions defined 50 y ago with NaCl as a crystallizing agent and acetate pH 4.5 as a buffer. Counter-diffusion crystallization allows a `physical' instead of chemical optimization of growth conditions: indeed, this method screens for the best supersaturation conditions in a single trial and yields crystals of very high quality. A complete diffraction data set was collected at atomic resolution from one of these crystals using synchrotron radiation at the DESY–EMBL beamlines. The overall Rmerge on intensities in the resolution range 31–0.94 Å was 5.2% and the data were 98.9% complete. Refinement was carried out with the programs CNS and SHELX97 to a final crystallographic R factor of 12.26% for 72 390 reflections. A mean standard uncertainty in the atomic positions of 0.024 Å was estimated from inversion of blocked least-squares matrices. 22 side chains show alternate conformations and the loop 59–75 adopts in the same crystal packing two conformations that were observed for either triclinic or tetragonal lysozyme in previous high-resolution studies. In addition to 255 water molecules, the crystallizing agent (one hexacoordinated sodium ion and five chloride anions) participates in the ordered lysozyme hydration shell.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 24 (1992), S. 61-71 
    ISSN: 1573-8868
    Keywords: fractal geometry ; quantitative geomorphology ; fluvial drainage systems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Fractal trees as a model for drainage systems are described in its generalized non-homogeneous form from the viewpoint of fractal geometry. Box covering techniques are used to show the numerical equivalence between the Hausdorff-Besicovitch dimension and the similarity dimension of the fractally-dominant dust formed by the sources. In this way, the similarity relationD=log (N)/log (1/r) is reinterpreted in terms of bifurcation and length ratio (r B andr L ) asD=log (r B )/log (r L ). We test this relation for non-homogeneous exact fractal trees and two natural drainage systems. The fact thatr B andr L are common parameters in quantitative geomorphology allows a trivial stimation of the fractal dimension of well-known drainage basins.
    Type of Medium: Electronic Resource
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