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  • Wiley-Blackwell  (15,624)
  • International Union of Crystallography (IUCr)  (2,439)
  • American Association for the Advancement of Science (AAAS)  (2,336)
  • Cell Press
  • 1995-1999
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  • 1980-1984  (12,875)
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  • 1940-1944
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  • 1977  (9,249)
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  • 1995-1999
  • 1985-1989
  • 1980-1984  (12,875)
  • 1975-1979  (9,249)
  • 1940-1944
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  • 1
    Electronic Resource
    Electronic Resource
    Further studies on the dielectric behaviour of cadmium iodide polytypes (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 32-36 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The dielectric constants (εr) of several cadmium iodide polytypes have been measured and found to be higher than that of the parent 4H structure. The dielectric constants for several long-period polytypes have been found to lie between 60 and 190 whereas the 4H parent structure has a value in the range of about 15 to 30. In particular, both increasing polytype periodicity and increasing disorder increase the dielectric constant, e.g. from 16 for an ordered 4H structure to 114 for a 32H structure and 67 for a highly disordered 4H structure. In the absence of disorder a particular polytype has its own characteristic dielectric constant value, e.g. the two 14H polytypes which have a common εr value of 63.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987701276X
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  • 2
    Electronic Resource
    Electronic Resource
    X-ray misorientation contrast for a (lineage) subgrain boundary (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 57-59 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The separation or overlapping of adjacent subgrain images in Berg–Barrett X-ray (reflection) micrographs is described for a reasonably general misorientation between the crystal subgrains. The five crystallographic parameters which describe the diffraction experiment also specify, effectively, the direction of the rotation axis for the misorientation, the amount of the angular misorientation, and the relative orientation of the subgrain boundary interface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877012801
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  • 3
    Electronic Resource
    Electronic Resource
    Recording of electron-diffraction patterns of radiation-sensitive materials in the high-voltage electron microscope with luminescent radiographic screens (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 62-63 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An effective method for greatly reducing the electron exposure of radiation-sensitive organic or biological specimens while recording their diffraction patterns in a high-voltage (MeV range) electron microscope is described. It involves recording on double-coated screen-type medical X-ray film and backing it with a luminescent radiographic screen which intercepts the transmitted electrons and emits visible light that exposes the bottom emulsion of the film. Values of sensitivity, resolution, and enhancement ratio are tabulated: the latter values range up to 41. Typical patterns taken with l-valine are shown.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877012825
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  • 4
    Electronic Resource
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    X-ray line-profile analysis. II. Determination of the crystallite-diameter distribution function (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 191-196 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new procedure for solving the integral equation which connects the crystallite-diameter distribution function pν(D) to the pure diffraction profile is presented here. The representation of pν(D) is based on a polynomial expansion modulated by a generalized Cauchy function. The influence of the truncation of the diffraction profile and of the number of coefficients of the polynomial expansion is studied. This procedure has been applied with success to some catalysts, the granulometry of which is known by other experimental approaches.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013223
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  • 5
    Electronic Resource
    Electronic Resource
    Crystal data for methylammonium manganese(II) trichloride dihydrate, CH3NH3MnCl3.2H2O (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 201-202 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Methylammonium manganese(II) trichloride dihydrate crystallizes with a monoclinic unit cell, a = 7.795 (2), b = 9.154 (2), c = 11.462 (4) Å, β = 91.28 (3)°, space group P21/c. Its structure is related to that of α-RbMnCl3.2H2O.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013259
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  • 6
    Electronic Resource
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    Crystal data for the low-temperature phase of Pb3(VO4)2 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 132-132 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Pb3(VO4)2 is monoclinic at low temperatures with space group P21. The lattice constants are a = 15.042, b = 6.106, c = 18.586 Å, β = 111.88°. The indexed powder diagram is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013077
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  • 7
    Electronic Resource
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    Paracrystalline nature of myelin (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 141-146 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of thickness variances from an electron-microscope cross-section of myelin sheath shows that the standard deviation varies proportionally to the square root of the number of intervening lamellae. This result implies that the lamellar irregularities are additive and that a paracrystalline stacking model is an appropriate representation for the myelin structure. The X-ray diffraction data from myelin exhibit the characteristics of a paracrystalline material. Both electron microscope and X-ray diffraction evidence suggest that myelin is paracrystalline rather than crystalline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013132
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  • 8
    Electronic Resource
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    A further solution for a two-dimensional model of crystal-growth disorder (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 344-348 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The paper refers to a previously described two-dimensional model of crystal-growth disorder in which the type of molecule or atom at a given lattice site is dependent on the previous neighbour in the two crystal directions. It is shown that a special case of the model for which some mathematical and simulation results have been published corresponds to the situation when the statistical properties of the lattice are symmetric to reflection in a plane. This symmetry may be achieved by applying a constraint to the growth probability parameters and, moreover, enables a solution to be found for the statistical properties of the lattices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013582
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  • 9
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    The small-angle scattering of neutrons by surface imperfections (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 172-176 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that the neutron small-angle scattering of pure polycrystalline metals is strongly connected with surface imperfections in the samples (surface irregularities and oxide layers) rather then with the grain boundaries. It is also shown that the asymptotic form of the scattering cross section of the surface imperfections is q−4 like the Porod law.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013181
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  • 10
    Electronic Resource
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    Temperature dependence of the orthorhombic asymmetry of gallium metal (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 180-183 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Precision strain-gauge measurements of the basal-plane lattice asymmetry (a−b)/[(a + b)/2] in gallium metal have been made in the temperature range 190 K 〈 T〈 300 K. When analyzed in conjunction with previously published data these results indicate that the asymmetry is positive from the melting point, TM = 303 K, down to at least 2 K. The asymmetry reaches a limiting value of 5750 × 10−6 at low temperatures and is decreasing rapidly toward zero near TM. The extrapolated `tetragonality' temperature is T* ̃354 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987701320X
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  • 11
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    Crystallographers (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 210-210 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013326
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  • 12
    Electronic Resource
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    International Tables for X-ray Crystallography (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 211-211 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S002188987701334X
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  • 13
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    Developments in electron microscopy and analysis edited by J. A. Venables (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 212-212 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877013387
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  • 14
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    Profile analysis of X-ray powder diffractometer data: structural refinement of La0.75Sr0.25CrO3 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 405-411 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Data have been collected from a standard silicon sample with Cu Kβ radiation selected by means of a pyrolytic graphite monochromator mounted in the scattered beam. The peak shapes can be described reasonably well by Lorentz-type functions, but not by a Gaussian function. These results have been applied to the profile refinement of data for rhombohedral La0.75Sr0.25CrO3, a perovskite-type compound which is slightly distorted from the ideal cubic structure. The analysis, which employs a slightly modified version of a neutron profile program [Rietveld (1969), J. Appl. Cryst. 2, 65–71] indicates that the best compromise for the peak shape is a modified Lorentz function of the form A[1 + C(Δ2&thgr;)2]−1.5 fitted over a range of two halfwidths on each side of the Bragg peak position. The results are compared with a similar refinement of neutron data collected from the same sample.
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    URL: http://dx.doi.org/10.1107/S0021889877013855
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  • 15
    Electronic Resource
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    A new method for the evaluation of small-angle scattering data (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 415-421 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new numerical method is presented for simultaneous smoothing, desmearing and Fourier transformation of X-ray and neutron small-angle scattering data. The method can only be applied to scattering curves from dilute particle systems, i.e. for scattering media whose distance distributions are zero beyond a certain value. The distance distribution of the scattering medium is approximated by a linear combination of about 20 to 30 cubic B-splines. These spline functions have a restricted extension in real space. Their coefficients are adjusted by a weighted least-squares operation so that the series, after being Fourier transformed and smeared according to the geometry and wavelength distribution, represents an optimum smoothed approximation of the experimental data. Tendencies towards oscillations in the least-squares operation are suppressed by a new stabilization routine. The method offers a new possibility for the estimation of the radius of gyration, which is generally superior to the Guinier approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877013879
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  • 16
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    A comparison of the porosities of the β-phases of (4-methylpyridine)4Ni(NCS)2 and (4-vinylpyridine)4Co(NCS)2 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 315-320 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The channel systems of (4-methylpyridine)4Ni(NCS)2 and (4-vinylpyridine)4Co(NCS)2 are described and compared. Much similarity is found and the minimum diameters of free passage are estimated in each case. It is concluded that both complexes are clathrates with notable zeolitic properties.
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    URL: http://dx.doi.org/10.1107/S0021889877013533
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  • 17
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    Laser-induced twinning in ferroelastic Gd2(MoO4)3 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 349-350 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Gadolinium molybdate was twinned by irradiating the crystals for a few seconds with a 10.6 μm CO2 laser. Slit-shaped regions were irradiated to produce localized heating, thereby setting up suitably oriented thermal stresses of sufficient size to induce mechanical twinning. Ferroelastic twin patterns are difficult to control by this method because the required slit orientations are not parallel to domain-wall directions.
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    URL: http://dx.doi.org/10.1107/S0021889877013594
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  • 18
    Electronic Resource
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    Crystal data for Ba2ZnS3 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 356-356 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877013636
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  • 19
    Electronic Resource
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    Crystal orientation where the calculated adjustment exceeds the allowed movement on one arc (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 502-503 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877014125
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  • 20
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    Two modifications of commercial units available for the automation of X-ray diffractometers (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 503-503 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877014150
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  • 21
    Electronic Resource
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    Turning cylindrical crystals in a common lathe (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 504-504 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877014162
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  • 22
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    Prices of Acta Crystallographica and Journal of Applied Crystallography (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 507-508 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889877014204
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  • 23
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    Industrial crystallisation by J. W. Mullin (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 508-509 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877014228
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  • 24
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    Electron microscopy in the study of materials by P. J. Grundy and G. A. Jones (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 509-510 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    URL: http://dx.doi.org/10.1107/S0021889877014241
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  • 25
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    Design criteria for a laboratory EXAFS facility (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 3-7 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: There has recently been an increased amount of interest in laboratory equipment for extended X-ray absorption fine-structure (EXAFS) measurements. In an earlier paper a facility for performing such measurements easily in a few hours was described in some detail. In this paper, further development of the techniques is reported. The use of high-power rotating-anode X-ray generator, the design of an X-ray curved-crystal spectrometer, the factors governing the proper choice of monochromator crystals and the design of fast-counting detectors and electronics are discussed. In addition, it is shown how errors caused by characteristic lines in the spectrum can be eliminated by use of a flux stabilization circuit.
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    URL: http://dx.doi.org/10.1107/S0021889881008571
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  • 26
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    Neutron photographic measurements of protein single-crystal reflections (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 24-27 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Photographic neutron intensity measurements on a 2 mm3 single-crystal of triclinic lysozyme are compared with conventional neutron diffractometer data. The reflections were recorded with the oscillation technique. The structure factors were derived from the optical densities scanned by an automatic microdensitometer and processed by computer programs. A statistical analysis shows that the photographic data are of about the same accuracy as recently collected diffractometer data. For the same flux and crystal volume the data collection time is reduced by up to two orders of magnitude.
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    URL: http://dx.doi.org/10.1107/S0021889881008601
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  • 27
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    A device for accurate single-crystal X-ray diffraction investigations at non-ambient temperatures: 83–1120 K (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 43-50 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A device is described which uses liquid nitrogen to generate a cold or hot gas stream which is blown directly onto the crystal mounted on an X-ray diffractometer. With a specially constructed high-vacuum (〈 1.3 × 10–5 Pa) jacketed silica Dewar tube, it can operate between 83 and 1120 K with a stability over long time periods of ± ¼ K below and ± 1 K above ambient temperature. In the latter case the short-time stability is ± ¼ K for hours. It gives an inert atmosphere at elevated temperatures and allows extensive data collection for the accurate determination of crystal structures. The evaporator, the automatic refilling system and the silica Dewar tube are described.
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    URL: http://dx.doi.org/10.1107/S0021889881008649
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  • 28
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    A fitting method for X-ray diffraction profiles (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 60-61 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A fitting method is proposed for X-ray diffraction profiles which requires only a small number of parameters.
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    URL: http://dx.doi.org/10.1107/S0021889881008686
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  • 29
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    Crystal data for two series of solid solutions: (RbxK1−x)MgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 61-62 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Complete solid solution is observed amongst the compounds of the type M1MgCr2(VO4)3 (where M1 = K, Rb or Tl). The solid-solution series obtained show linear changes in peak positions and peak intensities in their X-ray diffraction patterns. The crystallographic behaviour with respect to the value of x for (RbxK1−xMgCr2(VO4)3 and (TlxK1−x)MgCr2(VO4)3 solid solutions is discussed.
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    URL: http://dx.doi.org/10.1107/S0021889881008698
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  • 30
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    Crystal data for ferric molybdate: Fe2(MoO4)3 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 64-65 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Indexed powder patterns of the monoclinic phase, stable at room temperature, and of the orthorhombic phase, stable for T 〉 786 K, are given. The cell dimensions are: a = 15.737 (8), b = 9.231 (5), c = 18.224 (9) Å, β = 125.46 (2)° at 295 K; a = 9.330 (3), b = 12.868 (5), c = 9.242 (3) Å at 818.6 K. Linear equations describing the thermal expansion of the two phases of ferric molybdate are reported. To verify if ferric molybdate can incorporate excess MoO3, measurements on non-stoichiometric samples were also made: no evidence of the presence of excess MoO3 was found.
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    URL: http://dx.doi.org/10.1107/S0021889881008716
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    Crystal data for high-temperature As2O5 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 68-68 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: High-temperature As2O5 at 768 ± 5 K is tetragonal with a = 8.577 (1), c = 4.637 (1) Å, V = 341.2 Å3, Z = 4, Dc = 4.475 Mg m−3. Indexed powder data are given.
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    Characteristics of a flat multiwire area detector for protein crystallography (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 85-93 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A flat, relatively thin (9 mm) xenon-filled multiwire proportional counter with two-dimensional, 2 μs delay line readout of a 270 × 300 mm active area has been developed for use as a position-sensitive area X-ray detector in the 8 keV energy region (Cu Kα) used in crystallographic structure work with large biological molecules. Its quantum detection efficiency for 8 keV X-ray photons is about 0.5, a value which is spatially uniform to within ± 2%. Its dead-time loss fraction at a typical data collection rate of 30000 photons s−1 is 12%. The detector has spatial resolution for X-rays of 0.6 mm FWHM in the horizontal direction and 2 mm, the anode wire spacing, in the vertical direction. The effects of parallax are found to be limited and do not seriously increase the apparent size of the diffracted beams. The position sensitivity of this detector is geometrically linear to within 0.5 mm across its active surface. Routine maintenance of the detector requires the attention of a skilled technician but is not time consuming. For four years, this detector has been used to measure millions of reflection intensities from crystals of many different proteins. The down time due to the detector has averaged less than four days per year, considerably less than the down time of other components of the data collection system. Four new protein structures have now been solved using data from this detector. Also, a considerable amount of data have been collected at higher resolution or at different temperatures with crystals of other proteins.
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    An assessment of instrumental parameters which control the accuracy of stress measurement using the X-ray diffractometer method (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 124-130 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The sources of systematic error in the X-ray diffractometer method of stress measurement are discussed. The errors in stress measurement and correction procedures for their elimination are described and quantitatively assessed.
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    The use of cell and symmetry information for single-crystal orientation on diffractometers (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 117-123 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffraction aspect and rough cell parameters of a crystal to be studied are usually known before mounting the crystal on a diffractometer. Such data are used for orientation purposes in the method described. An ordered list of indexed 2θ values is calculated from which an optimum 2θ for a peak search is derived. The peaks found are centered, their possible unique indices are derived by comparison of the observed 2θ values with the calculated values. Two intense reflections with few indexing ambiguities are selected to define the crystal orientation. Their possible pairs of indices are found by considering combinations of indices related to the unique indices by the Laue-group symmetry and for which the calculated angle between the reciprocal vectors is comparable with the observed angle. Only the non-equivalent orientations defined by these initial pairs will be accepted. An initial pair will be rejected if the indices of both reflections can be transformed into those of a previously accepted pair by a single Laue-group symmetry operator of the first kind. The correct setting is usually obvious from a very short list of possible orientations and is retained. This simple approach has been programmed and treats all symmetries without branching of the logic. Rhombohedral crystals can be referred to hR or rP cells. The possible non-equivalent settings due to metric ambiguities, to pseudo-symmetry or to symmetry are exhaustively listed, but no symmetry-related setting is indicated. This scheme has automatically oriented more than 40 crystals from the seven crystal systems in 20–50 min each. The wavelength, the cell parameters and the short symbol of a valid space group in the correct diffraction aspect are the only input.
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    Neutron powder diffraction of forsterite, Mg2SiO4: a comparison with single-crystal investigations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 137-139 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Neutron time-of-flight powder data have been collected for forsterite [Mg2SiO4; Pbnm (D162h, No. 62); Z = 4, a = 4.7534 (1), b = 10.1989 (2), c = 5.9813 (1) Å] with the ZING-P′ high-resolution diffractometer at Argonne National Laboratory. Forty-seven variables, including anisotropic temperature-factor coefficients, were refined with a profile-fitting procedure to R(profile) = 2.10% and R(Rietveld) = 3.53%. Positional and thermal parameters are in good agreement with those determined from recent X-ray and neutron single-crystal diffraction experiments. Results suggest that powder data can be used to obtain accurate positional parameters and reasonable temperature factors for moderately complex structures.
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    Adaptation of a Kratky camera to use with a one-dimensional position-sensitive detector (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 139-141 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A Kratky small-angle X-ray camera was modified so as to allow the use of a one-dimensional (one-dimensional) position-sensitive detector (PSD) with it. The modification was designed in such a way that most of the calibrations, necessary for subsequent correction of the collected intensity data, can be performed with little alteration in the collimation geometry or the electronics settings. In particular, the calibration of the uniformity of detector efficiency can be performed by repeated vertical travel of the detector at a constant speed across a beam scattered from a sample.
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    XPKFIT: peak separation with arbitrary relations among the component peaks (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 145-148 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program for the separation of a composite peak into the components and the background has been written in Fortran. Each component is approximated by a function of the form y(x) = c [1 + ({{x - d}\over{e}})^{2}]^{-f}, where c, d, e and f are the parameters to be determined by a least-squares method. Arbitrary, known or assumed relations among the parameters of different components may be read in to reduce the number of independent parameters and save computation time or, in other cases, to offer a better chance of separating a complex composite peak by varying a subset of the parameters.
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    BLOKJE, a computer program to calculate the domain of an atom in a structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 151-153 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A computer program has been written with the aim of calculating the domain of an atom in a structure. The domain may be limited by planes situated half-way between the atoms, or at a distance that takes into account the relative radii of the atoms. Data concerning this domain and the corresponding coordination polyhedron are computed and printed. Punched cards, to be used in a special plotting program, can also be produced. Three types of weighted coordination number are calculated.
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    The use of continuous diffraction data as a phase constraint. I. One-dimensional theory (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 160-168 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Intensity can often be measured as a continuous function of scattering angle in diffraction from non-crystalline specimens. An analysis of the amount of information contained in one-dimensional continuous diffraction data is presented here. This analysis, based on the sampling theorem and the theory of entire functions, indicates that there is a limited but often rather large number of possible phase solutions to any given continuous intensity distribution. A refinement technique has been developed which allows phase solutions to be found that are consistent with the diffraction data and with other physical and chemical data. In favourable cases, when diffraction data is used in coordination with other kinds of data, there can be enough information in a diffraction pattern to identify a unique structural solution.
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    The small-angle neutron scattering spectrometer at the University of Missouri research reactor (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 370-382 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A small-angle neutron scattering (SANS) spectrometer has been constructed at the University of Missouri Research Reactor Facility (MURR). The design of the MURR–SANS is unusual in that the size of the reactor containment building constrains the flight path to be vertical. This is achieved by Bragg scattering upward through 90° from a set of slightly misaligned pyrolytic graphite crystals to provide a neutron beam at 4.75 Å with a wavelength spread of approximately 4.1%. The beam incident on the sample is defined by two matched variable apertures located either 3.0 or 4.5 m apart. The evacuated scattered flight path is designed with removable extensions to match the primary flight path in length. The instrument has an automatic sample handling capability provided by its own dedicated PDP 11/03 computer. The detector is a large assembly of commercially available linear 3He detectors as an economic alternative to a crossed-wire two-dimensional multi-detector. An array of 43 position-sensitive proportional counters, 24 in (609.6 mm) long and 0.5 in (12.7 mm) in diameter, using charge division gives a spatial resolution of 5 x 12.7 mm. The area-averaged detector efficiency is about 84% at a wavelength of 4.75 Å. The range of scattering vectors that can be measured is 0.005 〈 Q〈 0.15 Å−1. The instrument is well suited to a wide variety of experiments on specimens having characteristic dimensions between 20 and 500 Å. MURR–SANS is designed as a user-oriented facility which provides both reasonable resolution and intensity on sample at a modest cost, and forms part of a neutron scattering center.
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    A study of the ordered structures of the Au–Mn system by high-voltage–high-resolution electron microscopy. II. Two-dimensional antiphase structures based on the DO22 structure (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 392-400 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two-dimensional antiphase domain structures existing in the composition range 20–23 at.% Mn were investigated by a high-resolution structure-imaging technique with a 1 MV electron microscope. The structures are based on the DO22 structure and consist of parallelogram-shaped domains containing 4 × 3 columns of Mn atoms and lozenge-shaped domains with 4 × 4 and 3 × 3 columns, and the domains are separated by two-dimensional antiphase boundaries parallel to the ({\bar 2}40) and (240) planes of the fundamental face-centred structure. The configuration of the domains changes delicately with a slight change of composition or annealing temperature, and the symmetry of the structure is lowered below about 670 K. The ideal structure models have compositions of about 22.7 at.% Mn. The images of about half of the specimen area of the 22.6 at.% Mn alloy annealed at 570 K do not correspond to these new structures, but bear a resemblance to the image expected from the two-dimensional antiphase structure proposed by Watanabe [J. Phys. Soc. Jpn (1960), 15, 1030–1040] for Au3Mn, which is based on the L12 structure and has boundaries parallel to the (100) and (010) planes.
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    Comparison of two numerical methods for the integration of the Takagi–Taupin equations (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 432-436 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two methods for the numerical resolution of the Takagi-Taupin equations are compared. It is shown that for a small integration step Taupin's [Acta Cryst. (1967), 23, 25–35] extension to two dimensions of the one-dimensional Runge–Kutta third-order method is more accurate than the algorithm of Authier, Malgrange & Tournarie [Acta Cryst. (1968), A24, 126–136] but, for a given precision, Authier, Malgrange & Tournarie's method is faster than Taupin's so the former will usually be preferred for numerical calculation.
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    Dependence of cooling rate of SAXS spectra from a B2O3–PbO–Al2O3 glass (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 444-446 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The phase separation of an 80% B2O3–15% PbO–5% Al2O3 (weight %) glass after splat-cooling was studied by small-angle X-ray scattering. The wavenumber which receives maximal amplification and the scattering intensity corresponding to this wavenumber were determined as a function of the cooling rate of the glass. The experimental results qualitatively agree with the main features of previous calculations based on the linear theory of spinodal decomposition, but no quantitative agreement is obtained.
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    Phase assignment to diffraction patterns based on the analytic properties of scattered fields applied to the structure of nerve myelin (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 455-461 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An analysis of published X-ray diffraction data from nerve myelin is given based on the properties of analytic functions. Functions defined by a finite Fourier transform may be described by their distribution of zeros. This description allows a phase function to be determined from real data, which is unique in principle. A solution to the phase assignment is given and compared with corresponding published solutions derived by other methods. The strong measure of agreement for the phases of the first nine diffraction orders, and the stability of this agreement against the efforts of experimental error, leads to the conclusion that these phases are probably correct.
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    Crystal data for [2.1.2.1]paracyclophan C30H28 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 465-465 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The powder data for [2.1.2.1]paracyclophan is reported. This compound is monoclinic with a = 21.44 (4), b = 17.22 (6), c = 9.70 (4) Å, γ = 141.30 (3)°, Z = 4.
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    Report of Executive Committee for 1980 (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 491-491 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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  • 47
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    X-ray line-profile analysis. I. A method for unfolding diffraction profiles (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 184-190 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A new method for unfolding X-ray diffraction profiles is reported. The procedure is based on the minimization of an economical function defined as the sum of the squared relative differences between the experimental function and a calculated profile. The latter is numerically computed from the convolution equation by fitting the pure diffraction profile with a damped polynomial. The influence of the truncation and the width of the instrumental function is studied; some results are given concerning the evaluation of a constant background for both the experimental and instrumental functions and its influence on the precision of the results. Finally, the perturbation produced by the simulation of statistical noise is discussed.
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    Données cristallo-chimiques sur le tétrapolyphosphate mixte de germanium et ammonium: (NH4)2GeP4O13 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 200-200 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The tetrapolyphosphate (NH4)2GeP4O13 is triclinic (P{\bar 1}), with a unit cell: a = 15.08 (1), b = 7.763 (5), c = 4.914 (5) Å, β = 98.18 (1), β = 96.53 (1), γ = 84.04 (1)° and Z = 2. This salt is isotypic with the corresponding salt of silicon: (NH4)2SiP4O13, previously described by the author.
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    Crystal data for two series of solid solutions: (RbxK1−x) Ag4I5 and (RBxK1−x)2AgI3 (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 203-205 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Cell data for cubic solid electrolytes RbAg4I5 (i) and KAg4I5 (ii) are accurately given: (i) a = 11.235±0.006 Å, (ii) a = 11.143±0.006 Å. Precise crystal data are also shown for orthorhombic Rb2AgI3 (a = 19.957 + 0.006, b = 10.227±0.003, c = 4.896±0.003 Å) and K2AgI3 (a = 19.522±0.009, b = 10.011± 0.003, c = 4.775±0.003 Å). Crystallographic behaviour with respect to the value of x for (RbxK1−x)Ag4I5 and (RbxK1−x)2AgI3 solid solutions is described.
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    The proper description of low-temperature X-ray diffraction apparatus (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 209-210 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes and News (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 211-211 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Perfection et stabilité thermique des structures lamellaires de l'eutectique Pb–Sn (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 213-219 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: In directionally solidified Pb–Sn eutectic, prepared by the Bridgman technique, it has been found that it is possible to obtain grains of nearly perfect lamellar structure and stable at elevated temperatures. The interlamellar spacing λ is 1 μm and the mean distance \bar D between fault lines 20 λ whereas they are respectively 1.5 μm and 7 λ in neighbouring grains. The orientation relation is: growth direction || [2\bar 11]Pb and ⊥ (12\bar 1)Sn, lamellar interfaces || (47\bar 1)Pb and (523)Sn. The spacing between planes perpendicular to the growth direction is the same in both phases. By studing the orientation relation with Bollmann's theory, zero planes and interfaces are found to be parallel. The coherent interphase boundary can explain the particularities of these grains. Their origin is discussed and related to the nucleation conditions.
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    Structural model for the \def\lambdabar{\ifvmode\noindent\fi{\hbox{$\lambda$}\kern-0.35em\raise0.7ex\hbox{-}\kern0.2em}}\lambdabar"-phase transformation (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 220-227 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The intensity distribution observed in neutron diffraction experiments in Zr–20% Nb alloys is analyzed in terms of the essential anharmonicity in the free energy, believed to be important in the Group IVb transition metals. It is found that a second-order approximation in the atomic displacements for calculating the diffuse intensity readily accounts for the main features of the intensity distribution. In particular, the observed ratio of intensities between certain superlattice reflections is shown to be related in a straightforward manner to the ratio of harmonic to anharmonic free-energy coefficients. Furthermore. in order to describe the observed curvature in the diffuse streaking in some Ti and Hf alloys, the displacement field of a localized ω-like particle is obtained by adding longitudinal displacement plane waves with wave vectors distributed on one octant of a spherical surface centered at the 〈111〉 octahedral site of the reciprocal lattice, and passing through point km ∼ 0.71 [ 111 ]. Computer-generated patterns of dots simulating such displacement fields were Fourier-transformed optically, yielding diffuse intensity' in excellent agreement with the circular streaking found experimentally in electron diffraction patterns of certain Ti and Hf alloys.
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    X-ray diffraction studies of aqueous solutions of urea (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 256-261 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An X-ray diffraction method has been used to study the influence of solute concentration on molecular associations in aqueous solutions of urea. Calculations, from experimental intensities, of unsharpened electronic radial distribution functions (RDF) are presented for the range of urea concentration from 0.83 to 16.8 mol Kg−1 (5 to 100% solutions). The changes in RDF with increasing urea concentration are complex. Unequivocal interpretation of the distribution functions is not possible, but the major effect of the relatively bulky urea molecules on the water structure appears to be caused by distortion of the water matrix. At urea concentrations of 50% and 100%, features of the RDF not visible in the RDF's at lower concentrations indicate the presence of long-range (over a distance of about 8 Å) structural relationships possibly due to urea–urea interactions: such an interpretation would make urea–urea hydrogen-bonded associations unlikely at lower urea concentrations.
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    Powder neutron diffraction–refinement of the total pattern (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 277-280 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A technique for including all neutrons scattered by the specimen in the refinement procedure is described. This eliminates the sensitivity of atomic parameters to the choice of background level which occurs when only the profile is used in the refinement.
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    Dislocation contrast in X-ray synchrotron topographs (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 281-286 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The contrast of dislocations in X-ray topographs taken in the Guinier–Tennevin mode with synchrotron radiation has been studied. In reflections where high orders were insignificant, dislocation images appeared very similar to those in Lang topographs taken with characteristic radiation. At large specimen-to-plate distances orientation contrast is important in the direct image. The sense of the Burgers vector of dislocations showing double contrast can be deduced.
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    Interprétation de la déformation et de la recristallisation monocristaux d'aluminium tractionnés suivant un axe 〈011〉 à l'aide de modèle de transformation de Rowland (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 308-314 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Aluminium single crystals have been elongated at 78 K along an axis close to 〈110)〉. During the recrystallisation process new crystals appear in the vicinity of the deformation bands (deformation heterogeneities) and have only two orientations. The mechanism of the single and double Rowland transformations of the matrix may be responsible of these orientations. It is also found that the double Rowland transformation may account for the change between the initial and final orientations of the matrix (after an 80° elongation). The correspondence between the slip deformation of the matrix and a deformation, due to the double Rowland transformation which may be localized in the deformation bands, is established.
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    A simple procedure for fitting a backgound to a certain class of measured spectra (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 226-229 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A numerical procedure using orthogonal polynomials is used for extracting the background in measured spectra. An X-ray spectrum obtained with the energy-dispersive method is considered as an example.
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    Low-angle X-ray scattering with C Kα radiation (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 412-414 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Polystyrene latex spheres of 1.011 and 0.234 μm diameter were used to observe low-angle X-ray scattering. For particles of about 1 μm in diameter the central scattering has not been observed accurately with characteristic X-rays such as Cu Kα and Mo Kα radiations, because it is strongly affected by the primary beam and the parasitic scattering of the slits. The present results show that the central scattering of particles of this size can be measured within 22′ without such influences by the use of C Kα radiation (wavelength 44.7 Å).
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    The use of integrals of the Airy diffraction intensity profile in X-ray topography of `spike' diffuse reflexions (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 422-425 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The average radius of platelet-like defects in crystals may be estimated by the non-destructive technique of X-ray topography of `spike' diffuse reflections, applicable to platelet radii several orders of magnitude smaller than the resolution limit of conventional X-ray topographic techniques. With the most favourable diffraction geometry, the diffuse topograph image may be regarded simply as the convolution of the platelet number density projected along the diffracted beam direction with the Airy diffraction intensity pattern appropriate to the radius of individual platelets. Different integrals of the Airy diffraction intensity profile are involved in photometric traverses of `spike' section topographs and of `spike' projection topographs. The required integrals are evaluated and discussed.
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    X-ray energy-dispersive diffractometry using synchrotron radiation (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 431-438 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The special features of X-ray energy-dispersive powder and single-crystal diffraction using synchrotron radiation are discussed on the basis of experiments performed at the Deutsches Elektronen-Synchrotron, DESY. The method is shown to be of particular value for fast structure identifications, experiments for which large scattering vectors are important, studies of phase transformations and chemical reactions at elevated temperatures and high-pressure studies. Studies of time-dependent phenomena using pulsed external fields are discussed.
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    Méthode vectorielle d'analyse de la texture des matériaux polycristallins de réseau cubique (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 458-464 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new method of texture analysis is presented that possesses the main advantages of both the Bunge–Roe and Williams methods. The general relations between pole densities and orientation distribution are given as well as an example of the result that can be obtained when only a single incomplete pole figure is available.
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    A new automatic triple-crystal X-ray diffractometer for the precision measurement of intensity distribution of Bragg diffraction and Huang scattering (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 450-457 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A computer-controlled diffractometer has been built which permits intensity measurements to be made in any direction in reciprocal space in the diffraction plane with step sizes down to 0.01′′ of arc. Three examples illustrate the performance and application of the instrument: (a) perfect silicon, (b) gadolinium gallium garnet with growth striations and (c) niobium with low-angle grain boundaries.
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    Refraction corrections to the diffractometer angles of centered reflections from extended-face single crystals (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 247-252 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The effect of refraction on the observed diffractometer angles θr, ωr and χr of a centered reflection is discussed for general asymmetric reflection from a finitely absorbing extended-face crystal. Formulae are presented for θr, ωr and χr for symmetric reflection and for θr and ωr for the two extreme positions of asymmetric reflection in terms of the angles calculated assuming that refraction can be neglected.
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    Complete determination of subgrain misorientation by an X-ray topographic method (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 265-269 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A modification of the Berg-Barrett X-ray topographic method was developed which enables measurement of all three misorientation parameters of a general subgrain boundary. The described method is based on the evaluation of three topographs of a single, arbitrarily oriented crystal surface taken by symmetric zero-layer reflections. In practical tests performed on an as-grown Fe–3 Wt% Si single crystal, relative accuracy of 10% and angular sensitivity better than 1′ were achieved.
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    An interactive graphics system for comparing the model building of macromolecules (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 274-279 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An interactive graphics program is described for use with the Evans & Sutherland Picture System 2 which is suitable for the comparison and refinement of protein structures. Several protein molecules and electron density maps can be viewed simultaneously, while great flexibility exists in creating, modifying and manipulating the picture on the screen. As the program is file oriented, it can be run on a small computer system with only 32 K memory.
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    Anomalous thermal expansion of silver gallium telluride (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 281-284 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A precise X-ray determination of the lattice parameters of silver gallium telluride, AgGaTe2, has been made in the temperature range 301 to 667 K with a Unicam 190 mm high-temperature powder camera. The data have been used to evaluate the coefficients of thermal expansion, α⊥ and α\parallel, at various temperatures. It has been observed that the `c' parameter decreases while the `a' parameter increases with increasing temperature as in the case of AgGaSe2 and AgGaS2, which also have a chalcopyrite-type structure. The magnitudes of both α⊥ and α\parallel increase non-linearly with increasing temperature.
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    X-ray extinction contrast in deformed single crystals (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 285-290 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Berg–Barrett topography gives information on large-scale dislocation distribution in deformed single crystals. The Burgers vectors are determined by disappearance of the dark `extinction contrast'. This contrast cannot be extinguished by any single diffracting condition when different types of non-coplanar Burgers vectors are present simultaneously; complementary information by electron transmission microscopy agrees well with this inference. These general remarks are illustrated by some examples on deformed single crystals of α-Al2O3, (Al2O3)1.8MgO, NaCl and Cu2O.
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    Diffraction by layer structures containing different kinds of layers and stacking faults (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 300-304 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A description is given of a mathematical formalism which allows the study of diffraction by stacks which contain, simultaneously or not, (i) layers of different kinds, (ii) different translations or rotations between layers and (iii) different thicknesses. The formalism allows the calculation of intensities for all the hkl reflections or (h,k) reciprocal rods, and not just the 00l reflections. It accounts for an Sth-neighbour interaction (S≥1).
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    A pilot study of the use and unfocused monochromatic radiation from a storage ring in powder diffraction (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 315-320 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The results of a trial powder diffraction experiment on the ADONE storage ring at the Frascati National Laboratories (Italy) are described. A (220) channel-cut Si crystal was used to provide a monochromatic beam and it was demonstrated that Debye–Scherrer photographs could be obtained in several hours. It was also shown that very high resolution can be obtained simply by increasing the camera dimensions. Finally, it is shown that with the higher fluxes of the SRS at the Daresbury Laboratory (England) very fast exposures will be possible without the need for focusing.
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    Modulated structure of iron–carbon martensite studied by electron microscopy and diffraction (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 329-336 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Satellite spots appear around every fundamental spot in electron diffraction patterns of iron-carbon martensite (α′) tempered in a temperature range from 273 to 363 K. High-resolution electron microscopic observations show that they are due to the formation of a modulated structure, in which interstitial carbon atom clusters smaller than 10 Å are distributed randomly in a plane nearly parallel to (102)α′, with inter-cluster distance of 10–20 Å and such carbon-rich planar regions are spaced periodically with intervals of 10–20 Å, depending on the carbon content of the martensite. A structure analysis was made by measuring the satellite spot intensity of the electron diffraction patterns, and the displacements of atoms from their average positions in martensite were determined. The result supports the above cluster model for the modulated structure.
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    Crystal data for the double oxides MSbO4 (M=Cr, Fe) (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 348-349 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: MSbO4, (M = Cr, Fe) are tetragonal, rutile-type compounds, P42/mnm (No. 136); Z = 1. M and Sb are randomly distributed in 2(a) positions and O in 4(f). For CrSbO4, Dm = 5.31, Dx = 5.35 Mg m−1, a = 4.5899 (2), c = 3.0525 (2) Å, U = 64.307 (8) Å3, x = 0.318, R = 4.6; Cr and Sb are coordinated with two O atoms at 2.064 and four O atoms at 1.930 Å.
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    The fabrication of a dual-element X-ray divergent-beam target (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 352-353 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    World Directory of Crystallographers, Sixth Edition (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 354-354 
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    Laser crystals edited by A. A. Kaminskii (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 355-356 
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    Crystal data for the oxidation product of bis(2,2'-bipyridyl)copper(I) perchlorate in nitroalkanes (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 475-477 
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    Notes: Single crystals of [Cu(bpy)2NO2]ClO4, [Cu(C10H8N2)2NO2]ClO4, C20H16CuN5O2.ClO4, with space group P21/c, were grown from the reacting mixture of bis(2,2′-bipyridyl)copper(I) perchlorate with molecular oxygen in nitroalkanes. The unit-cell parameters are a = 10.83 (2), b = 12.51 (1), c = 17.04 (1) Å, β = 112.0 (2)°, Z = 4, Dm = 1.62 (1) Mg m−3.
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    Crystal data for the decavanadates of 2,4-, 3,4-, and 3,5- dimethylpyridine and 2,4,6-trimethylpyridine (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 472-473 
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    Notes: Indexed powder patterns of four monoclinic compounds of general formula (BH)3H3V10O28 .xH2O, where x = 1-2.5 and B = 2,4-dimethylpyridine (J8), (C7H10N)3H3V10O28.1.0H2O, 3,4-dimethylpyridine (J10), (C7H10N)3H3V10O28.1.0H2O, 3,5-dimethylpyridine (J11), (C7H10N)3H3V10O28.2.5H2O, and 2,4,6-trimethylpyridine (J12), (C8H12N)3H3V10O28.1.0H2O are given. The cell dimensions of the unit cells with two molecules are: J8 a = 18.360 (2), b = 10.438 (2), c = 13.503 (2) Å, β = 95.99 (1)°; J10 a = 12.538 (3), b = 13.634 (5), c = 16.662 (5) Å, β = 111.82 (2)°; J11 a = 19.483 (5), b = 10.711 (2), c = 13.020 (4) Å, β = 101.52 (2)°; J12 a = 12.776 (3), b = 22.470 (4), c = 11.790 (3) Å, β = 91.54 (1)°.
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    The XIIth Congress of the IUCr, Ottawa, August 1981. An informal report (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 487-489 
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    Crystallographers (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 490-490 
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    Notes and News (1981)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 14 (1981), S. 491-492 
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    Establishment of a President's Fund (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 685-685 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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    Report of the International Mineralogical Association (IMA)–International Union of Crystallography (IUCr) Joint Committee on Nomenclature (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 681-684 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: This report lists nomenclature recommendations resulting from a six-year study of problems common to the disciplines of mineralogy and crystallography. The recommendations include definitions of polytypism, topotaxy, syntaxy, and epitaxy, certain criteria for mineral names, preferred format for chemical formulae, and preferred symbols for crystallographic axes and repeat distances. Two recommended systems of structural symbols to be used to differentiate polytypes are presented.
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    Optical properties of ions in solids (Proceedings of NATO Advanced Study Institute, Erice, Italy, june 1974) by B. Di Bartolo (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 685-686 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Analysis of a faulted 4H structure of CdI2 (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 687-689 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A faulted 4H structure of CdI2 gives a diffraction pattern composed of sharp spots and diffuse streaks. The structure was solved by assuming that the sharp spots come from the 'average structure' and the diffuse streaks from one-dimensional disorder.
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    Sextets in P1: The probabilistic theory of the six-phase structure invariant φ = φh + φk + φl + φm + φn + φp (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 697-701 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It is assumed that a crystal structure P1 is fixed and that the 31 non-negative numbers R1, R2, . . ., R6; R12, R13, . . ., R56; R123, R124, . . ., R156 are also specified. The random variables (vectors) h, k, 1, m, n, p are assumed to be uniformly and independently distributed in the regions of reciprocal space defined by and |Eh| = R1, |Ek| = R2, . . . , |Ep| = R6; (1) |Eh + k| = R12, |Eh + l| = R13, . . . , |En + p| = R56; (2) |Eh + k + l| = R123, |Eh + k + m| = R124, . . . , |Eh + n + p| = R156; (3) and h + k + l + m + n + p = 0. (4) Then the structure invariant φ = φh + φk + φl + φm + φn + φp, as a function of the primitive random variables h, k, l, m, n, p, is itself a random variable, and its conditional probability distribution, given (1), (2) and (3), is derived from the main result of the previous paper [equation (3.1); Fortier & Hauptman (1977). Acta Cryst. A33, 694-696.] and compared with the distribution when only (1) is given. The distribution leads to estimates for cos φ in terms of the 31 magnitudes (1), (2) and (3).
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    Verification of crystal elastic anisotropy theory by ultrasonic diffraction experiments (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 704-705 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: This paper points out an indirect but convincing experimental verification of certain theories concerning elastic-wave propagation in anisotropic media. Relations between the Poynting vector and the propagation vector for longitudinal wave propagation near, but not exactly parallel to, certain pure-mode axes permit the calculation of the ultrasonic diffraction from large single apertures (transducers) oriented for propagation exactly along the pure-mode axes. Then the diffraction loss versus distance, measured in oriented single crystals, permits the verification of the theories concerning these relations and concerning ultrasonic diffraction. It is shown that five items of theory have been verified by the ultrasonic diffraction measurements.
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    Transformation orientée de l'hydrate 2H2O β en hydrate 2H2O α du nitrate de calcium. Interprétation structurale des formes cristallines des deux hydrates (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 717-722 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The observed habits of crystals of the compounds α-Ca(NO3)2.2H2O and β-Ca(NO3)2.2H2O can be explained in terms of the crystal structure with the Hartman theory. A structural interpretation is given of the growth of α-phase crystals from a β-phase crystal with the [110] directions of the two phases parallel.
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    Continuous distribution of dislocations in intercrystalline boundaries (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 730-739 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure of a dislocation network in a crystal boundary depends, among other parameters, on the two crystal structures and their relation, i.e. the linear transformation leading from one crystal lattice to the other. For the same transformation, the structure of the network is related to the crystal structure. The link between the transformation and the many possible dislocation networks is described by a theorem which states that the displacement field of the linear transformation in the boundary can be described in an infinite number of ways by continuous dislocation distributions. The discrete dislocations are then obtained by grouping the continuous dislocations. The O-lattice theory is discussed in relation to these new aspects, particularly with respect to the features which tend to be conserved in the boundary. A special discussion is given of the case where a common crystallographic axis, without the relaxation pattern being periodic, represents the preferred state.
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    On the application of phase relationships to complex structures. XI. A theory of magic integers (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 750-757 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Magic integers enable several unknown phases to be expressed in terms of a single variable at the expense of introducing some error in the phases represented. The economy of variables is particularly useful in a multisolution direct-methods program like MULTAN where a successful solution may depend upon the ability to use a large number of phases at the beginning of phase determination and the computing time is proportional to the number of variables. Formulae are presented which give the phase errors in the magic-integer representation. A recipe is given for the generation of efficient magic-integer sequences in which the r.m.s. error is spread evenly over all the phases represented. These sequences minimize the overall phase error for a given maximum integer in the sequence. It is found that the errors are minimized when the differences between adjacent members of the magic-integer sequence form the terms of a geometric progression and the smallest integer is greater than half the largest.
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    Problems in the numerical calculation of the contrast of defects in X-ray traverse topographs (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 758-767 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The simulation of section topographs of distorted crystals may be performed with good accuracy; it is now possible to use it as a tool to determine the quantitative parameters of various defects. The simulation of traverse topographs is a more complicated problem: it needs a tremendous amount of computation time, but the main difficulty arises from the numerical method itself. Reasons and a demonstration, with simulations of the contrast of a dislocation, are given why the only way to compute the traverse topograph is by the addition of the intensities due to an incident spherical wave. Nevertheless, the accuracy of the result remains poor.
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    The transverse magnetoresistance of chromium in the temperature range 15–80°C (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 767-770 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Electrical measurements have been carried out on a 4N5 Cr single crystal in multi-Q and single-Q domains. It was found that the Néel temperature depends neither on the direction of current, nor on the existence of a magnetic field. In the multi-Q domains, the transverse magnetoresistance G changes according to G = AHn. The magnetoresistance decreases with increasing temperature showing an anomaly at 40°C. For the single-Q domain specimen, measurements with H ⊥ Q showed in the antiferromagnetic state the existence of saturation in the curve G = G(H). In the paramagnetic state, the transverse magnetoresistance is an increasing function of the magnetic field. Measurements with H || Q showed that G increases according to G = AHn, and this is ascribed to the existence of open orbits along the direction of polarization.
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    Coulombic nonbonded interatomic potential functions derived from crystal-lattice vibrational frequencies in hydrocarbons (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 771-776 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method of calculation of crystal-lattice normal-mode frequencies of hydrocarbons was sharpened to include bond foreshortening of C-H bonds, dynamic derivatives, and atomic point charges. A test of the method was made with 118 observed structural parameters from 18 aromatic and saturated hydrocarbon crystal structures, and 58 observed crystal frequencies from five aromatic hydrocarbon crystal structures. The use of dynamic derivatives significantly improved the fit to the observed frequencies. The use of atomic point charges also significantly improved the fit to the observed frequencies; the optimum values found for the point charges were essentially identical to the optimum values obtained from structural data alone. The direct parameter-fit method, although giving reasonable results for the structural parameters, was found not to transfer well to the calculation of lattice frequencies. The force-fit method gave significantly better results for the lattice frequencies. The final optimum (exp-6-1) nonbonded interatomic potential functions derived from the combined structural and vibrational data were very similar to the functions derived from the structural data alone.
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    An X-ray diffraction study of NaF (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 776-783 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: NaF gives rise to very weak odd-index reflexions in X-ray diffraction. These reflexions have been studied to determine the best models for electron distribution in the NaF crystal. Data were obtained from a single crystal at room temperature for Ag Kα, Mo Kα, Cu Kα and Co Kα radiations. Least-squares analyses were made on the Ag Kα and Mo Kα data. Scattering factors for Hartree-Fock singly charged free ions allowed a good fit to the data, and there was a marginal improvement of the fit with similar scattering factors modified for effects of crystalline environment. The mean thermal parameter for the ions was {\bar B} = 0.905 ± 0.025 Å2. An attempt to account for the wavelength dependence of intensities of the strong reflexions, with current theories of extinction, was unsuccessful.
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    Electron diffraction study of short-range-order diffuse scattering from disordered binary alloys (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 784-788 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A qualitative study was made by electron diffraction of the short-range-order diffuse scattering from disordered Au-Pd, α phase Au-Zn, and α phase Ag-Mg alloys. Twofold and fourfold splittings of diffuse maxima are observed at 100, 110 and equivalent positions on the diffraction patterns with the incident beam parallel to [001], in the composition ranges from about 28 to 62 at.% Pd for Au-Pd, from about 7 to 24 at.% Zn for Au-Zn and from about 11 to 28 at.% Mg for Ag-Mg systems. The separation of the split diffuse maxima increases monotonically with Pd, Zn or Mg content. The results can be interpreted with the Fermi-surface-imaging concept proposed by Krivoglaz. The variation with composition of the Fermi wave vector parallel to the [110] directions is discussed with the nearly-free-electron and the rigid-band models. The latter model is also applied to the experimental results for disordered Cu-Pd and Cu-Pt alloys reported by the present authors [Ohshima & Watanabe (1973). Acta Cryst. A29, 520-526].
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    Extinction in deformed copper single crystals. A combined study by γ-ray diffractometry and neutron structure refinement (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 789-800 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Neutron diffraction and γ-ray rocking-curve measurements were performed on plastically deformed single crystals of Cu in order to compare the mosaic distribution parameters obtained from least-squares structural refinement with those seen by the γ-diffractometer. Neutron data were collected at two wavelengths (λ = 0.538 and 0.741 Å) for one crystal with very homogeneous mosaic distribution, and for another crystal with less good but more typical mosaic structure data were collected for λ = 0.538 Å. Maximum sin θ/λ was 1.52 Å-1 and maximum extinction correction was less than 30%. For the latter crystal no comparison could be made between the two sets of observed distribution parameters because of the uneven mosaic distribution. The former crystal was found from the γ-ray measurements to be bent, but when this was taken into consideration in the Coppens-Hamilton [Acta Cryst. (1970), A26, 71-83] formalism for anisotropic extinction correction good agreement was found between mosaic parameters obtained by γ-ray and neutron measurements for directions not affected by the crystal curvature, whereas the structure refinement did not, as expected, reflect the complete crystal curvature when this effect was dominant.
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    Correction factors for neutron diffraction from lamellar structures (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 813-818 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In a spectrometer with finite beam divergence the vertical size of the reflections will increase with the order of reflection. This effect will be more pronounced if the mosaic width of the sample is large, which is often the case with biological samples. When the size of the reflection is greater than the detector size, a correction factor has to be introduced to account for this loss of intensity. A method of calculating this correction factor for a given beam divergence and mosaic width has been developed.
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    A structure-factor least-squares refinement procedure for macromolecular structures using constrained and restrained parameters (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 800-804 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method of structure-factor least-squares refinement of constrained groups linked by distance restraints has been developed for the refinement of macromolecular structures. Each constrained group can have any number of variable dihedral rotation parameters within the group in addition to the rigid-body translational, rotational and thermal parameters. The matrix of normal equations may be either full or sparse and provision is made for solution by matrix inversion or the conjugate-gradient iterative method. This procedure has been successfully used for 3 Å data and should be applicable even for lower-resolution data and especially for cases with a poorer data-per-atom ratio. The structure of yeast phenylalanine tRNA has been refined with this procedure from a starting crystallographic R value of 42% to a final R value of 25% with isotropic 'group" thermal parameters and 22% with isotropic atomic thermal parameters for 8207 independent reflections at 2.7 Å resolution. The proper stereochemistry of bond distances, angles and van der Waals contacts for the restrained atoms was maintained within reasonable limits throughout the refinement. Although originally developed for nucleic acids, this procedure is directly applicable to the refinement of protein structures. In addition, a combination of applying distance restraints between groups and least-squares fitting of these groups to target coordinates has been used purely as an idealization process for imposing proper stereochemistry on an approximate model.
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    Expansion of the Madelung parameters of non-cubic structures as a function of the ratio of two lattice parameters (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 819-822 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new method is described to express the Madelung parameter of a structure with a non-cubic Bravais lattice as a function of a lattice parameter by means of a power series expansion. The method is derived for the case of a cubic lattice which is tetragonally distorted. The generalization to other crystal structures is shown. For illustration the method is applied to the rutile and cadmium iodide structures.
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    Structural properties of vanadium oxides (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 834-837 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It is shown that two vanadium oxides of unknown composition, i.e. VOx [Tilley & Hyde, J. Phys. Chem. Solids, (1970), 31, 1613-1619] and phase Q [Colpaert, PhD Thesis, Rijksuniv. Gent (1972)] are identical with V4O9 [Théobald, Cabala & Bernard, C. R. Acad. Sci. Paris, SOr. C, (1969), 269, 1209-1212]. The unit cell of V4O9 is orthorhombic, with a = 8.235, b = 10.32, c = 16.47 Å. A model for the structure of V4O9 is proposed. It is based on an ordered superlattice of O vacancies in V2O5, and is in agreement with X-ray oscillation photographs. The model accounts for the low density of this material, its low temperature of formation, the typical appearance of twins and the topotaxic growth of V4O9 on V2O5.
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    Quantitative statistical critera for use in the cumulative, semi-cumulative and distribution function tests for centrosymmetry (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 838-844 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Several criteria suitable for taking a decision regarding the centrosymmetry of crystals by the study of the goodness-of-fit of the observed and expected cumulative, semi-cumulative and distribution functions of normalized structure amplitudes are suggested. Practical aspects of the various tests are discussed. From a study of the performance of these tests on four crystals a safe method of conducting these tests is suggested.
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