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  • Springer  (88,702)
  • International Union of Crystallography (IUCr)  (2,924)
  • 1995-1999
  • 1980-1984
  • 1975-1979  (91,626)
  • 1925-1929
  • 1978  (46,314)
  • 1977  (45,312)
Collection
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  • 1995-1999
  • 1980-1984
  • 1975-1979  (91,626)
  • 1925-1929
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  • 1
    Electronic Resource
    Electronic Resource
    A general, weighted least-squares method for the evaluation of small-angle X-ray data without desmearing (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 73-79 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: In order to avoid some of the disadvantages associated with the desmearing methods, a procedure has been developed where the smeared, primary, intensity data can be evaluated directly without desmearing. The procedure consists of the following: first, a model depending on a vector of unknowns, x = (x1, ...., xn), is constructed; then, an iterative search is made for the vector x, and a scale factor s, which corresponds to a local minimum in the error square sum based on the primary, slit-smeared, intensity data. The main advantages with the present method are that the comparison between theory and experiment is made directly with the experimental quantity; thus the experimental errors can be considered in this comparison. Furthermore, some of the disadvantages associated with the desmearing methods are avoided; the method is numerically stable and no extrapolations outside the measured angular range are necessary. Several data sets measured at different concentrations and with different, completely arbitrary, primary-beam weighting functions can be considered in the same refinement. The interparticle scattering effect may also be included in the least-squares refinement. The method is general, so that different models can be tested simply by changing only one subroutine of the computer program. It may also be used to evaluate data impaired by other types of resolution errors; for example, effects due to polychromatic radiation or resolution errors in neutron scattering. Two constructed examples of the application of the method are given: (1) the calculation of the dimensions and the molecular weight of particles with a shape which can be approximated with an ellipsoid of revolution; (2) the calculation of the dimensions and electron-density distribution for spherical particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012807
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  • 2
    Electronic Resource
    Electronic Resource
    The analysis of single-crystal Bragg reflections from profile measurements (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 114-120 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is described for finding the peak limits of a Bragg reflection from an analysis of its profile. A `window' of ± 0.67σ[φ)(x)] is set up on each ordinate φ(x) in the tails of the profile and the pattern of the following ordinates is observed through the window. As the ordinate moves from the peak to the background the pattern changes and the limits of the peak may be recognized. Bragg reflections from three crystals have been analysed by this method and the limits found were generally wider than those determined by the method of Lehmann & Larsen [Acta Cryst. (1974), A30, 580–584] applied to the same data. The value of σ(I)/I was near the minimum and similar to the value from the corrected Lehmann–Larsen limits. The behaviour of the methods is also compared by representing the reflections by equivalent Gaussian profiles, and it is found that 〉99% of the Gaussian peak is within the limits found by the present method.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012856
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  • 3
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    Scherrer after sixty years: A survey and some new results in the determination of crystallite size (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 102-113 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Existing knowledge about Scherrer constants is reviewed and a summary is given of the interpretation of the broadening arising from small crystallites. Early work involving the half-width as a measure of breadth has been completed and Scherrer constants of simple regular shapes have been determined for all low-angle reflections (h2 + k2 + l2 ≤ 100) for four measures of breadth. The systematic variation of Scherrer constant with hkl is discussed and a convenient representation in the form of contour maps is applied to simple shapes. The relation between the `apparent' crystallite size, as determined by X-ray methods, and the `true' size is considered for crystallites having the same shape. If they are of the same size, then the normal Scherrer constant applies, but if there is a distribution of sizes, a modified Scherrer constant must be used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012844
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  • 4
    Electronic Resource
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    Optimum resolution in X-ray energy-dispersive diffractometry (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 137-140 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The resolution problem in X-ray energy-dispersive diffractometry is discussed. It is shown that for a given characteristic of the solid-state detector system and a given range of interplanar spacings, an optimum scattering angle can be easily found for any divergence of the incident and scattered beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188987801290X
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  • 5
    Electronic Resource
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    Spherical monocrystals for X-ray work obtained by plasma remelting of alloy powder (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 148-150 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Spherical crystals of alloy phases too hard and brittle for grinding can be obtained by partial remelting and solidification of a powder sample. The alloy powder is blown through an argon-plasma jet melting the surface material of individual fragments, which solidify again as nearly perfect spheres. The yield is a mixture of different materials in which it is possible, however, after heat treatment to find good single crystals of the original composition. Spherical single crystals of Cu9Al4 have been produced by this method and used for a high-precision X-ray investigation described elsewhere.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012923
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  • 6
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    Crystal data and crystal growth of PbGe3O7 (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 157-158 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Completely transparent and colourless single crystals of PbGe3O7 were grown from a melt of composition PbO.2GeO2 at 1040 K by spontaneous crystallization. The compound melts incongruently at 1070 K. The unit cell is orthorhombic with lattice constants a = 5.270 (2), b = 14.088 (4), c = 16.054 (4) Å; D293 = 5.94 (4), Dx = 5.985 g cm−3 for Z = 8. The probable space group is Pcab (D152h). A reported phase of composition PbGe205 is shown to be a mixture of PbGe3O7 and α-PbGeO3. X-ray powder data are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878012972
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  • 7
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    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 
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    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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  • 8
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    X-ray misorientation contrast for a (lineage) subgrain boundary (1977)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 10 (1977), S. 57-59 
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    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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  • 9
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    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.
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    URL: http://dx.doi.org/10.1107/S0021889877012825
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  • 10
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    The absorption factor for a cylindrical specimen perpendicular to a cylindrical beam of the same radius. Application to the X-ray study of CsDNA with the use of synchrotron radiation (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 238-242 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An X-ray diffraction study of CsDNA has been carried out with the use of synchrotron radiation of wavelength λ = 1.2 Å. The geometry corresponds to a cylindrical specimen brought into a cylindrical beam of the same diameter and the absorption factor and the primary-beam attenuation factor have been calculated as functions of specimen μR for this geometry. The optimum size of a specimen is here about 1.5 times greater than that in the case of a plane-parallel beam used in International Tables for X-ray Crystallography [Vol. II, (1967), 2nd ed., p. 295. Birmingham: Kynoch Press]. Experimental and calculated primary-beam attenuation factors have been compared and the experimental value of the linear absorption coefficient μ of CsDNA has been estimated for various humidities. The agreement between μc = 78.1 and μo = 78.2 ± 3.6 cm−1 (relative humidity 66–75%) indicates that the geometrical model used is suitable to describe polymer fibres in a cylindrical beam of nearly the same size. It is seen from the observed μ values that there is one caesium ion per nucleotide (monomer unit of DNA molecule) in the specimens used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878013230
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  • 11
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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 
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    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.
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    URL: http://dx.doi.org/10.1107/S0021889877013223
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  • 12
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    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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  • 13
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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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  • 14
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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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  • 15
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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 
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    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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  • 16
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    Crystal technology by W. L. Bond (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 293-294 
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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/S0021889878013424
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  • 17
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    Notes and News (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 293-293 
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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/S0021889878013412
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  • 18
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    Electron and photn interactions with atoms edited by H. Kleinpoppen and M. R. C. McDowell (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 294-294 
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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/S0021889878013436
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  • 19
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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.
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    URL: http://dx.doi.org/10.1107/S0021889877013181
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  • 20
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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.
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    URL: http://dx.doi.org/10.1107/S002188987701320X
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  • 21
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    Recent developments in polymer applications of small-angle neutron, X-ray and light scattering (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 346-375 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Recent advances in the small-angle scattering of X-rays, neutrons and light by polymers are reviewed. The three techniques are compared, from both experimental and theoretical points of view. Applications are discussed for the study of homophase and heterophase polymers, both in solution and in the solid state, as well as for unoriented and oriented crystalline polymers.
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  • 22
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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
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    URL: http://dx.doi.org/10.1107/S0021889877013326
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  • 23
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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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  • 24
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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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  • 25
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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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  • 26
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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.
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    URL: http://dx.doi.org/10.1107/S0021889877013879
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  • 27
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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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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    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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    On the conformation of antibodies in the presence and absence of antigen (small-angle X-ray studies) (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 477-477 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The conformations of different IgG antibodies were studied before and after interaction with antigen (hapten). In every case a strong change of the conformation was observed. Binding of hapten caused a decrease of the radius of gyration by 2 to 8% and a decrease of the volume by 3 to 10%, depending on the degree of saturation with hapten. Two IgG antibodies (anti-poly-d-alanyl) were split by enzymes into fragments which contain one binding site (Fab′) and two binding sites (Fab′)2, respectively, for hapten. No changes of conformation were observed with these fragments upon the interaction with hapten. These findings lead to the conclusion that the conformation change does not take place within the area of the combining site but relatively far away, at the area of the hinge region and/or the Fc-fragment.
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    Design study of a time-of-flight small-angle diffractometer for a pulsed neutron source (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 464-465 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A design study was made of a neutron small-angle scattering (SAS) instrument for use at Argonne National Laboratory's proposed Intense Pulsed Neutron Source, IPNS-II (Carpenter & Werner, 1976; Werner, 1977; Carpenter, 1977). The instrument design incorporates several features: a converging-slit collimator, wavelength band-limiting choppers, capacity for large samples, and a two-dimensional detector. Machine design-dependent parameters are considered in a Monte-Carlo code that produces estimates of the instrumental resolution function and available flux at the sample. It was found that the calculated flux on sample exceeds that at steady-state reactor instruments of comparable resolution.
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    Large-angle X-ray diffuse scattering, a new method for investigating changes in the conformation of globular proteins in solutions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 473-477 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A comparative analysis of the sperm-whale myoglobin structure in the crystal and in solution has been carried out with the technique previously formulated by the authors which uses the large-angle X-ray diffuse scattering for investigating the protein structure in solution. A `modified cube method', correctly taking into account the cavities within the protein molecule accessible to the solvent, is proposed for an accurate estimate of the solvent influence and for calculation of the scattering intensities. A comparison of the theoretical myoglobin scattering curves with the experimental scattering curve of this protein obtained by Stuhrmann shows rather noticeable quantitative divergences, which can be eliminated by a small increase in the distance between the `hairpin' GH and the other part of the protein molecule. It is also shown that several other physically reasonable shifts of helices (or groups of helices) do not lead to an agreement between the experimental and theoretical scattering indicatrices.
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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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    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
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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
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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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Density-contrast studies of macromolecules in solution. Cross verification of X-ray scattering and pycnometry experiments (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 466-472 
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    Notes: The density-contrast method, commonly used in X-ray (and neutron) small-angle scattering studies of macromolecules in solution, can yield a wealth of information if; (a) the solute is monodisperse and the solution is ideal: (b) each macromolecule in solution has a volume associated with it inside of which the density distribution is independent of the density of the solvent. More specifically it has been pointed out that in this case an expression of the molecular weight can be obtained which does not involve the partial specific volume, provided that the X-ray experiments are performed on an absolute scale. On the other hand, it is well known that X-ray scattering experiments on an ideal solution of identical macromolecules can yield the molecular weight for any composition of the solvent, provided solute, solvent and partial specific volumes are defined and measured at constant chemical potential. Therefore a combination of X-ray scattering and densimetry experiments allows one to verify to what extent condition (b) holds true. Such a set of experiments has been performed on Rhesus monkey low-density serum lipoproteins, the solvent being water containing variable amounts of NaBr. It is concluded that in this case condition (b) is fulfilled. Moreover several important aspects of the analysis of the X-ray scattering curves can be verified.
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    The measurement of the locations and radii of gyration of proteins in the 30S ribosomal subunit of E. coli by neutron scattering (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 479-482 
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    Notes: The theory of the technique currently in use for measuring distances between subunits in macromolecular aggregates by neutron small-angle scattering is outlined. It is shown that estimates for the radii of gyration of subunits within aggregates can be extracted from neutron distance data, in addition to the distances themselves. The current status of efforts to apply these methods to determine the structure of the E. coli ribosome is discussed.
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    Neutron-scattering studies of chromatin subunits under a variety of contrast conditions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 483-484 
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    Notes: Neutron-scattering studies of chromatin core particles in solutions containing various mixtures of D2O/H2O and small molecules (glycerol) show that the water closely associated (or bound) with the particles is largely in the outer DNA-rich regions. This confirms the fact that the particles contain a core composed of the hydrophobic regions of histone proteins.
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    Small-angle X-ray scattering studies on polymer chain conformations in concentrated solutions and in bulk (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 514-519 
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    Notes: The use of the polymers tagged with heavy atoms in random positions along the chains (randomly tagged polymers) in small-angle X-ray scattering is proposed as a new method for measuring the chain conformations in concentrated solutions and in bulk polymers. The experimentally determined excess scattering from the tagged chains dispersed in the system is shown to be proportional to the scattering function of the hypothetical chains that have no tags but have the conformation of the tagged chains when the heavy atoms have sufficiently large scattering power. It has been experimentally verified that the effect of the tags on the chain conformation can be eliminated by the extrapolation of the apparent values, measured for a series of tagged polymers with various tag content, to zero tag content. The radii of gyration of the polystyrene chains (M = 1.1 × 105) in the bulk and in concentrated solutions in a good solvent and a θ-solvent have been determined. The chain dimension in a good solvent (toluene at 25°C) decreases rapidly first and then gradually approaches the unperturbed dimension with increasing polymer concentration. The dimension in a θ-solvent (trans-decalin at 21.2°C) is independent of the polymer concentration. The conformation of the polystyrene chains in the bulk was found to be a Gaussian coil.
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    Small-angle X-ray scattering of polyethylene single-crystal suspensions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 525-530 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Small-angle X-ray scattering from oriented mats and random suspensions of polyethylene single crystals has been studied. A modification of the Guinier equation for platelets was derived to accommodate the two-phase nature of polymer lamellae. This modification also permitted the modelling of various degrees of interaction between lamellae and suspending media. Dried crystal mats show an increase in fold period on contact with potential solvents. Crystals which have never been dried show no evidence of penetration of the fold surface by the same liquids. Apparently the drying process causes a reorganization of the surface of the lamellae. Since the fold surfaces of crystals in suspension are unaffected by the liquids used, it is reasonable to assume a `tight' fold surface model. Crystallinities calculated with this model are in excellent agreement with recent differential scanning calorimetric data on crystals kept in suspension.
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    Organization in semi-dilute polyelectrolyte solutions observed by small-angle neutron scattering (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 519-523 
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    Notes: The study of semi-dilute polyelectrolyte solutions by small-angle neutron scattering shows that the correlation function S(q) of all the chains presents a peak for a value q = qh of the scattering vector q. This is taken as evidence for some organization among the elongated polyions. This phenomenon has been observed for a fraction of polymethacrylic acid of very low molecular weight. The experiments show essentially: (1) the progressive vanishing of the peak with the addition of a neutral salt at constant polyelectrolyte concentration; (2) the variation of qh with the polyelectrolyte concentration c, qh ∝ c1/2; (3) the decrease of the peak intensity as the charge density of the chain increases. These results, which indicate the important role of the electrostatic interactions on this organization phenomenon, are discussed in terms of a lattice model and a recently proposed isotropic model.
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    Determination of the interface distribution function of lamellar two-phase systems (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 535-539 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The concept of interface distribution functions [Ruland (1977). Colloid Polym. Sci. 255, 417–427] has been applied to the evaluation of the small-angle scattering of a series of polyethylene samples. The results indicate that the statistics of the lamellar stacking is not necessarily determined by next-neighbor interactions and that non-negligible volume fractions of amorphous domains outside the lamellar systems are observed in a number of samples.
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    A dynamic study of the crystallization of polyethylene from the melt (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 551-557 
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    Notes: Crystallization of a linear polyethylene from the melt was followed in situ with the ORNL 10-meter SAXS camera [Hendricks (1978). J. Appl. Cryst. 11, 15–30]. Specimens were rapidly cooled in the X-ray beam in tandem birdcage furnaces from 1̃80°C to temperatures between 115 and 126°C, and scattering patterns were recorded for 30 s in 50 s intervals. Because of this relatively high-speed data acquisition rate, it was possible to obtain data in time periods which were short compared to the rate of change of the scattering patterns. The SAXS curves showed shapes which changed continuously during crystallization. The scattering curves are the superposition of a zero-angle peak and a Bragg maximum. Guinier plots of the zero-angle peak manifest scattering by lamellae of constant thickness. The thickness value is nearly that expected for crystallites at these crystallization temperatures. A model in which skeletal spherulites form and then later fill in is consistent with these results. Decreasing SAXS intensity and changing Bragg peak intensities indicate crystal thickening during cooling to room temperature.
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    Small-angle X-ray scattering from block copolymers as an ideal model system for a pseudo two-phase solid texture (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 558-563 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The microdomain structure of polystyrene-polyisoprene A-B type block copolymers was analysed by small-angle X-ray scattering (SAXS) as an ideal model system for a pseudo two-phase solid structure. The structure was analysed in terms of spatial distribution, size, and the interracial structure of the dispersed domains of one component (A segments) in the matrix of the other (B segments). The SAXS analyses were performed with two collimating systems, a Rigaku Denki camera (essentially a four-slit system with the addition of Soller slits) and a Kratky camera, which had widely different slit-length and slit-width weighting functions and was used to investigate instrumental effects, especially the role of the Soller slits in the obtaining of reliable desmeared intensity data in the tail of the SAXS curve. Comparison of the results indicated that the Soller slits facilitate the accurate evaluation of the interfacial thickness from the desmeared intensity data in the tail. The accuracy of the infinite slit-height approximation and the effect of truncating the higher-order terms in Ih (the intensity associated with the interphase) on the estimated interfacial thickness are discussed. The infinite slit-height approximation leads to values 25–35% smaller than the exact value (23 Å), and the truncation also leads to a value of the interfacial thickness smaller (19 Å) than the value (23 Å) based on the full analysis. The value obtained is in good agreement with the values predicted from the statistical-mechanical theories of block copolymers in bulk.
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    Neutron small-angle scattering study of phase decomposition in Au–Pt (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 572-577 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Isothermal decomposition of a Au-60 at.% Pt alloy, quenched from the solid as well as the liquid state, has been studied with the D11 neutron small-angle scattering spectrometer at ILL, Grenoble. An incident neutron wavelength of 6.7 Å was used and measurements were carried out in the range of scattering vector [β = 4πsin θ/λ] from 2.8 × 10−2 to 21 × 10−2 Å−1. The preliminary results indicate that decomposition of this alloy at 550°C takes place by a spinodal mode, although deviations were observed from linear spinodal theory, even at very early times. Slower aging kinetics were observed in liquid-quenched alloy as compared with solid-quenched. Liquid quenching is more efficient in suppressing quench clustering than is solid quenching. However, liquid quenching yields an extremely fine-grained material, which thereby enhances discontinuous precipitation at grain boundaries, competing with decomposition in the bulk. A Rundman–Hilliard analysis was used for the early stages of the spinodal reaction to obtain an interdiffusion coefficient of the order of 10−16 cm2 s−1 at 550°C for the solid-quenched alloy.
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    Small-angle electron scattering in the transmission electron microscope (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 564-568 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Two methods for performing small-angle electron scattering (SAES) experiments in transmission electron microscopes are described: the long-camera-length method and the selected-area-diffraction method. It is shown experimentally that angular resolutions of a few microradians and a few tenths of milliradians, respectively, are easily obtained by these two methods. A number of examples of the application of SAES to problems in materials science are presented. The use of new high-brightness electron sources is expected to produce significant increases in angular resolution, and the use of electron-energy analyzers will permit the separation of most of the inelastic contribution to the SAES intensity distribution.
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    A small-angle neutron scattering study of the temperature and stress dependence of the microstructure of nimonic alloys (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 583-588 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The creep properties in high-temperature alloys are dependent on the presence of second and higher phase components. In particular in the nimonic group of alloys the size distribution and concentration of the γ′ phase are crucial factors in the resistance to creep. A possible mechanism for degradation of creep resistance is the Ostwald ripening of the γ′ phase. A sample of Nimonic 105 (Trademark of Henry Wiggin and Co. Ltd) was subjected simultaneously to a stress of 500 MPa and a temperature of 800°C in situ in the beam using a specially developed cell on the small-angle scattering facility (D 11A) at the Institut Laue Langevin. Scattering patterns were taken continuously and spectra were recorded every ̃20 min; the macroscopic creep was also recorded. Measurements were taken up to the point of fracture. A peak in the intensity was observed at a scattering vector κ (= 4π sin θ/λ) of 0.005 Å−1 which is believed to be the lowest value at which such an effect has been observed in alloys. The observed variation in the scattering after treatment for multiple scattering and absorption corrections is discussed in terms of particle size and size distribution.
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    A modified mirror monochromator for rotation photography of large-unit-cell crystals (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 658-661 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A double-mirror monochromator in which one of the mirrors is considerably longer than conventionally employed has been used to collect diffraction data from crystalline tobacco mosaic virus (TMV) protein (unit cell: 224 × 228 × 174 Å). Considerable improvements in speed of data collection are observed over both customary focusing optics and pinhole collimation. Quantitative comparisons are made of the quality of data collected from TMV protein by this method and by the use of nickel-filtered radiation.
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    Anisotropy in the flux-line lattice symmetry of a low-κ Type II superconductor (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 654-657 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Correlation between the symmetry of the two-dimensional flux-line lattice (FLL) and the real crystal lattice (CL) has been studied in a superconducting niobium sphere by means of small-angle neutron diffraction. A double-perfect-silicon-crystal diffractometer enabled precise determination of the three interfluxoid distances corresponding to the FLL basic cell. A systematic study of the anisotropic behavior was made as a function of temperature and magnetic field amplitude for fields parallel to a few high-symmetry CL axes in the (1{\bar 1}0) plane. In addition, at T = 4.30 K progressive deformation of the FLL was studied as the sample was rotated in the (1{\bar 1}0) and (100) planes. The FLL was found to be hexagonal only for fields parallel to the threefold CL axis. Twofold symmetry prevailed for other CL directions in these planes except near the fourfold axis, where either of two distorted triangular lattices existed, preserving the reflection symmetry in composite, but not individually. When compared to current models for fluxoid-CL interactions, the present results show that no theory predicts the observed behavior quantitatively under general conditions, but some models agree well for certain high-symmetry CL axes.
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    An error in several published tables of the multiplicities of powder reflexions (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 669-669 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Some multiplicities for the Laue class \bar 31m are not correct in several standard texts.
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    Determination of low-field critical parameters of superconducting niobium by small-angle neutron diffraction (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 650-653 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The double-perfect-crystal small-angle diffraction technique enables measurement of scattering angles to within an accuracy of 0.3′′ of arc. At a wavelength of 2.55 Å, this provides a resolution of 3 × 10−6 Å−1 in the scattering vector. This technique has been used to study the anisotropic behavior of the critical parameters B0 and Hc1, characteristic of the first-order magnetic phase transition which occurs in low-κ type II superconductors. Magnetic fields were applied parallel to several crystal axes in the (1{\bar 1}0) and (100) planes of a large single-crystal sphere of pure niobium, resulting in well defined flux-line lattices (FLL). Measurement of the FLL cell area in the intermediate, mixed-state-field region gives the equilibrium flux density B0, which results from an attractive interaction between fluxoids. In addition, field variation of the scattered neutron intensity allows measurement of the transition field between the mixed state and intermediate mixed state. This transition field is related to the lower critical field Hc1 and enables its determination to a precision of 0.2%. Data at T = 4.3 K display a small anisotropic effect of about 2% in B0 and 1% in Hc1. Although orientation effects of this magnitude are difficult to resolve by bulk measurements, the neutron data are in accord with magnetization data. The temperature dependence of these parameters is found to be in qualitative but not quantitative agreement with current theoretical models.
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    A computer program for determining multiplicities of powder reflections: a correction (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 669-669 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An amendment to a computer program for determining multiplicities of powder reflections [Rouse & Cooper (1977). J. Appl. Cryst. 10, 134–135] has been made to correct an error in the multiplicity values given for some reflections for space groups with {\bar 3}1m Laue symmetry, which exists in some of the standard texts.
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    Precision lattice parameter measurement by the X-ray divergent-beam technique (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 662-668 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is described for precision measurement of lattice parameters in cubic crystals, interplanar spacings and angles between crystallographic directions for single crystals of any system. The minimum measurable values of angle between crystallographic directions, Δd/d and Δa/a have been found to be ̃105 rad, ̃3 × 10−5, and ̃5 × 10−5, respectively.
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    Crystal data for diphenylsilanediol, (C6H3)2Si(OH)2 (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 670-671 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The cell constants of recrystallized diphenylsilanediol were refined from precision powder data taken with Cr Kα1 (2.28962 Å): a = 14.493 (5); b = 15.012 (6); c = 9.897 (6) Å; α = 100.84 (9); β = 100.01 (5); γ = 120.77 (5); U = 1721.6 Å3; Z = 6; Dm (25°C) = 1.255 (3); Dx = 1.252 g cm−3.
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    Lattice parameter measurements in epitaxic layers (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 671-671 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Crystal growth and materials edited by E. Kaldis and H. J. Scheel (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 673-674 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Simulation of photographs on a storage display. Application to X-ray topography and TEM (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 675-680 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The simulation of the photography remains the worst part in the calculation of transmission electron micrographs and X-ray topographs. Storage displays have been used to enhance this part of the process and the different possibilities of these screens studied. The quality of all simulations has been substantially increased by using these displays, which are now in common use.
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    High-resolution energy-dispersive diffraction using synchrotron radiation (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 684-687 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A high-resolution energy-dispersive diffractometer is described, which uses a synchrotron source and a scanning channel-cut silicon crystal. The technique is demonstrated with a powdered sample of BaTiO3 and analysis of the profiles demonstrates the anomalous particle-size effect reported by Anliker, Brugger & Känzig [Helv. Phys. Acta (1954), 27, 99–124].
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    Diffraction from materials edited by L. H. Schwartz and J. B. Cohen (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 719-720 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Crystal growth 1977 edited by R. L. Parker, A. A. Chernov, G. W. Cullen and J. B. Mullin (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 720-720 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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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
    Topics: Geosciences , Physics
    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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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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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
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    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
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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    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
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    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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    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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    ISSN: 1600-5724
    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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    ISSN: 1600-5724
    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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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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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 
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    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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    The valence-charge density of graphite (1977)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 33 (1977), S. 823-828 
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    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A full sphere of data extending to (sin θ/λ) = 1.2 Å-1 and containing 1595 reflections was measured with small, natural, single crystals of graphite and Mo Kα radiation. With the structure assumed to be in space group P63/mmc, the valence-charge density of the two independent C atoms was represented by a finite multipole expansion containing products of single-exponential radial functions and tesseral harmonics. A full-matrix, least-squares refinement of the model charge was computed where populations of the multipole deformations, thermal parameters, scale, and extinction parameters were refined. The experimental data fit a model charge density containing highly directional build-ups of charge to 2 e Å-3 between nearest neighbors in the basal plane. No structure was evident in the charge density between the basal planes. The refinable parameter, α, in the exponential radial function was 3.16 ± 0.05 bohr-1. The charge density and associated parameters are consistent with strong covalent bonding of sp2 character in the basal plane of graphite and minimal interactions between the layers.
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