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  • 1
    Electronic Resource
    Electronic Resource
    Structure of manganese(II) iodide tetrahydrate, MnI2.4H2O (1985)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 1284-1286 
    Details
    ISSN: 1600-5759
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108270185007466
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  • 2
    Electronic Resource
    Electronic Resource
    Exact random-walk models in crystallographic statistics. II. The bicentric distribution for the space group P\overline{1} (1985)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 41 (1985), S. 55-59 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An exact probability density function for the magnitude of the normalized structure factor |E| has been derived for the space group P\bar 1, taking account of the presence of one non-crystallographic center of symmetry. The function is based on the exact solution of the corresponding random-walk model and its expansion into a Fourier series. The above result is compared with simulated semi-cumulative distributions based on hypothetical structures and very good agreement is obtained for the equal-atom case, as well as for a heterogeneous asymmetric subunit containing fourteen carbon atoms and one uranium atom. The new exact bicentric probability density functions of |E|, for the space group P\bar 1, reduce to the well known asymptotic expressions that are valid for equal-atom structures and a large number of atoms in the asymmetric unit of the space group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767385000095
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  • 3
    Electronic Resource
    Electronic Resource
    Electron diffraction patterns of chrysotile: effect of specimen orientation (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 70-76 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Electron diffraction patterns of chrysotile asbestos fibrils should have the 2mm symmetry of a rotation photograph because the layers in the structure are curled as cylinders. The way in which the fibril orientation affects the diffraction patterns is considered theoretically. The departures from ideal symmetry attributable to specimen orientation are noted: they affect mainly the h00 reflections close to the fibre axis. Actual diffraction patterns show a consistent difference in the separation of the h0l-h0\bar l pairs on the upper levels, and \bar h0l-\bar h0\bar l pairs on the lower. The experimental conclusion [Yada (1979). Can. Mineral. 17, 679-691] that this difference is not an effect of specimen orientation is confirmed theoretically but its cause remains obscure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387009267
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  • 4
    Electronic Resource
    Electronic Resource
    The structure determination of a common cold virus, human rhinovirus 14 (1987)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 43 (1987), S. 346-361 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The methods used to solve the structure of human rhinovirus 14 at 3.0 Å resolution are described in detail. The crystals are cubic, space group P213, a = 445.1 Å with 20-fold non-crystallographic redundancy and with approximately 55% solvent and RNA content. The data used to solve the structure were collected at the Cornell High Energy Synchrotron Source (CHESS) using oscillation photography. Most of the computations were performed on Purdue University's Cyber 205 supercomputer. Two heavy-atom derivative data sets from crystals soaked in 1 and 5 mM KAu(CN)2 were used to provide isomorphous phasing to 4 Å resolution, although it was subsequently shown that phases beyond 5 Å resolution were random. The phases were refined at 5 Å resolution by five cycles of real-space molecular replacement. Phase extension from 5 to 3 Å was then performed using 60 cycles of real-space molecular replacement while extending the resolution in steps of three reciprocal-lattice points at a time once every three cycles. The 3.5 Å skew-averaged map was easily interpreted and showed 811 of the 855 amino acids in the four distinct viral polypeptide chains. A complete atomic model has been built using FRODO on an Evans & Sutherland PS300 graphics system with respect to the 3.08 Å resolution electron density map. The roles of the non-crystallographic symmetry, solvent content, errors in amplitudes, orientation and translation in the molecular replacement process are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387099306
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  • 5
    Electronic Resource
    Electronic Resource
    The mosaic spread of very small crystals deduced from Laue diffraction patterns (1987)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 43 (1987), S. 70-73 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Laue diffraction patterns have been recorded with synchrotron radiation for some very small crystals; in most of them the reflections are elongated radially. The Laue geometry is particularly sensitive to mosaic spread, and a relationship between mosaic spread and Laue spot extension is deduced. It appears that many very small crystals have a large mosaic spread (0.5-1° or more) which is probably the reason why they did not grow bigger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387099872
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  • 6
    Electronic Resource
    Electronic Resource
    Extinction in time-of-flight neutron powder diffractometry (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 374-379 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Time-of-flight data have been collected from polycrystalline specimens of magnesium oxide in which the grain size distribution is known. These data were obtained at scattering angles of 150, 90 and 60°. A primary extinction factor given in an analytical form by Sabine [Acta Cryst. (1988), A44, 368-373] is included in a Rietveld program. The experimental data from the two high-angle histograms are refined to give an effective mosaic block size and overall temperature factors. The effective mosaic block size is used in the calculation of an extinction factor for each reflection. This factor is then compared with the ratio of measured integrated intensities. The theoretical form of the extinction factor is verified to a level of 0.30. The temperature factors measured from each specimen are identical and in agreement with the best literature value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767388000625
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  • 7
    Electronic Resource
    Electronic Resource
    Scattering exponents for polydisperse surface and mass fractals (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 25-27 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Scattering exponents are discussed for systems of power-law polydisperse surface and mass fractals. It is found that the scattering exponent for power-law polydisperse mass fractals lies on the interval [0, d] and always depends on the mass fractal dimension. The scattering exponent for power-law polydisperse surface fractals lies on [0, d + 1] and is independent of the surface fractal dimension for a large range of the polydispersity exponent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889886090052
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  • 8
    Electronic Resource
    Electronic Resource
    High-pressure single-crystal neutron diffraction (to 20 kbar) using a pulsed source: preliminary investigation of Tl3PSe4 (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 145-149 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new technique is described for performing high-pressure single-crystal neutron diffraction [up to 20 kbar (2 GPa) at room temperature], using a BeCu pressure cell, an area detector and the Los Alamos National Laboratory pulsed neutron source. Success of this method depends on the increase in information available with a multi-wavelength pulse neutron source, a novel orientation of a cylindrically symmetric pressure cell with its axis coincident with the neutron beam and a specific crystal orientation within the pressure cell. Bragg scattering from the pressure cell is avoided and background for a given 2θ is constant. For a crystal of orthorhombic or higher symmetry oriented with the incident beam passing midway between the major lattice vectors, it will be possible to refine a complete three-dimensional structure with data collected from only one pressure loading. Preliminary investigations of Tl3PSe4 lattice parameters (space group Pcmn) at 15(1)kbar yielded linear compressibilities (× 1000 in kbar−1) of Ka = 1.05(8), Kb = 1.50(10), Kc = 1.20(8). The anisotropic compressibility is explained by examination of the ambient-pressure room-temperature structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010007
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  • 9
    Electronic Resource
    Electronic Resource
    Phase separation in an Ni–12·5 at.% Al alloy at 575 K (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 873-877 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The phase separation in a supersaturated Ni–12.5 at.% Al alloy has been investigated by high-angle diffuse scattering, small-angle scattering, transmission electron microscopy and electrical resistivity methods. High-angle X-ray diffuse scattering measured at room temperature on a bulk single-crystal homogenized and quenched from 1323 K showed well developed short-range atomic ordering. An electrical resistivity isochrone shows a marked peak at about 675 K. Small-angle scattering measurements on samples annealed at 823 K clearly indicate that, at this temperature, phase separation occurs by a nucleation and growth process. It has been argued that a cluster coagulation model well represents the processes occurring at 823 K. It is, however, not required that the same process be operational at lower temperatures, particularly below the break in the resistivity isochrone. Measurements for annealing times up to 840 h at 575 K reveal weak small-angle scattering which has some of the characteristics of a continuous transformation. However, much longer transformation times at the lower temperature will need to be investigated before the possibility that this is only a kinetic effect associated with slow nucleation of the second phase can be ruled out.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005333
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  • 10
    Electronic Resource
    Electronic Resource
    Scattering from fractals (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 61-78 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The concepts of dilation symmetry and the fractal dimension are introduced, and from these basic concepts scattering functions are computed for surface and mass fractals. It is then shown how the fractal structure of various random media has been elucidated from scattering measurements, and how these observations relate to specific models of fractal geometry. Examples include colloidal aggregates, gels, soot and the fractal porosity of rocks of various sorts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087107
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