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  • Articles  (166,114)
  • American Institute of Physics  (120,588)
  • Cell Press  (39,072)
  • International Union of Crystallography (IUCr)
  • 2005-2009  (108,959)
  • 1985-1989  (53,369)
  • 1945-1949  (3,786)
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  • 101
    Electronic Resource
    Electronic Resource
    SHAMGAR's OXGOAD: A new approach to the problem of resolution corrections for triple-axis neutron inelastic scattering data using parallel processors (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 493-498 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: One problem in the analysis of triple-axis neutron inelastic scattering data is the large numerical computations involved in applying full resolution corrections, which in one extreme involves an often-repeated four-dimensional numerical integral. A program called SHAMGAR has been written for an ICL Distributed Array Processor that will both calculate the full convolution of a model scattering function with the resolution function and allow refinement of the model simultaneously to many sets of experimental data by a non-linear least-squares fit. Sample results and performance figures are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010767
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  • 102
    Electronic Resource
    Electronic Resource
    Molecular surface Triangulation (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 499-505 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method is presented for triangulating the surface of a molecule. A triangulated surface is a polyhedron, all of whose faces are triangles. The triangles are created by subdividing the curved faces of an analytical molecular surface that has been precalculated by an earlier algorithm. The triangulated surface has many applications. Molecular areas and volumes may be calculated from it. Packing defects in proteins may be identified. It may be used to determine whether a particular water molecule lies in the interior of the protein or on the surface. The triangulated surface may be drawn on pen plotters, vector graphics systems and raster graphics terminals. Mathematical functions defined on the surface may be contoured. Local maxima and minima of functions may be located. While the triangulated surface is less accurate than the analytical molecular surface it is derived from, it has the advantage of being much simpler and easier to deal with. It combines the simplicity of a dot surface with the continuity of an analytical surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010779
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  • 103
    Electronic Resource
    Electronic Resource
    Use of kinematical diffraction in X-ray topography (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 509-512 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A new X-ray topographic method is proposed that makes use of the kinematical diffraction component, which is significantly more sensitive to the crystal-surface imperfections than dynamical Laue–Bragg diffraction. The sensitivity of the method has been studied using a triple crystal diffractometer to separate kinematical and dynamical components of the diffraction intensity curve when the Bragg condition is nearly satisfied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010792
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  • 104
    Electronic Resource
    Electronic Resource
    Statistical treatment of measured orientation relationships in orientation space (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 311-316 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Measured orientation relationships between neighbouring grains in single-phase α- and β- and dual-phase α + β-brasses are analysed by means of the χ2-test. The orientation relationships are characterized by the three Euler angles and hence can be represented as points in orientation space. A description of the symmetry relations of equivalent points in this space is given and then the distribution function for random orientation relationships is derived. This distribution is compared with the distribution of the measured orientation relationships using only a single χ2-test for each boundary type. The results of the tests are the same as obtained from the analysis of axis-angle pairs, in which case twoχ2-tests are necessary. None of the measured distributions is random.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888002316
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  • 105
    Electronic Resource
    Electronic Resource
    Determination of single-crystal elastic constants from a cubic polycrystalline aggregate (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 513-518 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for determining cubic stiffness constants from polcrystalline Young's modulus and X-ray elastic constants is described. The relations used among these elastic constants are those based on Kröner's quasiisotropic model. The X-ray elastic constants required [S1(hkl)] are obtained by measuring various (hkl) d spacings of a stressed specimen under symmetric θ–2θ scan mode. An application to an Fe–31Ni alloy has given the results: C11 = 1.47, C12 = 1.05 and C44 = 1.24 × 1011 Pa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010809
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  • 106
    Electronic Resource
    Electronic Resource
    Observations of growth defects in berlinite by high-temperature X-ray topography (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 533-534 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Growth defects in a synthetic berlinite sample were studied at high temperature (300–500 K) by X-ray topography. Preliminary observations of contrast changes with temperature are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010834
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  • 107
    Electronic Resource
    Electronic Resource
    Structural information on proteins obtainable from small-angle X-ray scattering with heavy-atom labeling. Application to solubilized bacteriorhodopsin (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 355-362 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The heavy-atom labeling method is applied to small-angle X-ray scattering (SAXS) based on contrast variation in order to derive information on the inner structure of proteins. The formulation of the contrast variation is extended to express explicitly the contribution of the bound heavy atoms to SAXS. The present method reveals two important features concerning bound heavy atoms, namely their number and their distribution. The application of this method to solubilized bacteriorhodopsin (bR) with iodination revealed the following characteristics of structure. The number of bound iodine atoms is 20, indicating that the solubilized bR is composed of a trimer of bR molecules. The mean square distance between the iodine position and the center of the trimer is about 1660 Å2, indicating that the most active tyrosine residues are located near the outer rim of a bR trimer. The distribution of iodine atoms is symmetric about the center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988800319X
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  • 108
    Electronic Resource
    Electronic Resource
    Feasibility of running the dynamical HREM multislice program on a 16-bit minicomputer (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 369-371 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The program of multislice calculations written by Ishizuka [User's Manual of Multislice and Image-Simulation Programs (1982). Center for Solid-State Science, Arizona State University, USA] for large central computers has been successfully transferred to the 16-bit PDP-11/24 minicomputer, without disturbing its features and capacities. The structural modifications of the transferred program lead to a great reduction of the calculation time for running on the PDP-11/24. The function of halftone output of calculated diffraction patterns has been developed and added to the package. This package proves to be especially effective in image simulations for complex structures (medium or large unit cells) on a minicomputer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888002304
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  • 109
    Electronic Resource
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    Crystallographers (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 380-381 
    Details
    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/S0021889888005655
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  • 110
    Electronic Resource
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    Computer program for calculation of interface structures (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 381-382 
    Details
    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/S0021889888003656
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  • 111
    Electronic Resource
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    New Commercial Products (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 382-382 
    Details
    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/S0021889888099728
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  • 112
    Electronic Resource
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    Quartz by M. O'Donohue (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 384-384 
    Details
    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/S0021889888001244
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  • 113
    Electronic Resource
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    Synchrotron Laue topography studies of pseudo-hexagonal twinning (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 406-415 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Pseudo-hexagonally twinned orthorhombic crystals generally exhibit three domain variants related by mirror planes or (approximately) by 120° rotations. The reciprocal lattices of the three domains coincide partially. Those reciprocal-lattice points hkl with h + k = 2N coincide or are split depending upon the deviation of the a:b ratio from orthohexagonality (i.e. a:b = tan 60°). With (white-beam) synchrotron radiation these domains are simultaneously imaged by Laue X-ray topography for these reflections. Lattice points hkl with h + k = 2N + 1 are `single' and only one of the three domain variants is imaged in such reflections. Two examples of these twins are presented, LiNH4SO4 and (NH4)2SO4. In the former case the lattice is closer to the ideal ratio a:b = tan 60° than the latter. These two cases are contrasted. Both materials are subject to some extent to radiation damage in the synchrotron beam.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188988800408X
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  • 114
    Electronic Resource
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    Bimodal distributions of profile-broadening effects in Rietveld refinement (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 416-425 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is demonstrated with computer simulations that a bimodal distribution (narrow and broad) of reflection profile broadening effects, such as crystallite size and microstrain, can lead to several spurious results when the profiles are modeled by single pseudo-Voigt functions in Rietveld refinement (RR), e.g. mixing parameter η 〉 1 (`super-Lorentzian'), a few observed data points lying consistently above the calculated peak maxima for some reflections, misrepresentation of the background level and shape, and in special cases well defined small observed peaks not seen in the calculated pattern as though they belonged to an additional minor phase. With a bimodal model (two pseudo-Voigt functions) the RR's accurately returned the profile, mixing, and background parameters used in the data synthesis both without and with counting statistical fluctuations simulated in the data. The RR method thus demonstrates remarkable ability to sort out complex specimen characteristics when accurate modeling functions are used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004091
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  • 115
    Electronic Resource
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    Synchrotron X-ray and neutron powder diffraction studies of the structure of α-CrPO4 (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 452-457 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The crystal structure of α-CrPO4, previously solved from high-resolution synchrotron powder X-ray data, has been refined by the Rietveld method. The peak shape variation is well fitted by a convolution of Gaussian and Lorentzian terms, which incorporate both instrumental and sample-broadening contributions. The structure has also been refined using medium-resolution neutron diffraction data, and the results of the two experiments are compared with a reported single-crystal study. The three sets of coordinates are found to be in good agreement, demonstrating the potential of structure determination and refinement using powder data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004625
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  • 116
    Electronic Resource
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    Crystallographers (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 544-544 
    Details
    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/S0021889885010913
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  • 117
    Electronic Resource
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    Crystal data for 1.3-dibromo-5-methylbenzene at 293 K (1985)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 18 (1985), S. 542-542 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The title compound C7H6Br2 (also called 3,5-dibromotoluene) is orthorhombic, space group P212121 with a = 14.426(2), b = 13.636(2), c = 4.076(1) Å, V = 801.8(3) Å3, Z = 4, Dx = 2.071 Mg m−3. The space group and preliminary cell parameters have been determined by single-crystal diffraction methods (Bragg, Weissenberg and precession patterns). The cell dimensions have been refined by least squares from accurate powder diffractometer data recorded at T = 293(1) K (quartz as internal standard, Cu Kα1−Kα2 correction so that λ = 1.54056 Å). The indexed powder data are given. No phase transition is detected between 123 K and the melting point 311.1(2) K (differential scanning calorimetry and Guinier–Lenné analysis). The results show that 1,3-dibromo-5-methylbenzene is isomorphous with 1,3,5-trichlorobenzene and 1,3,5-tribromobenzene. The JCPDS Diffraction File No. For C7H6Br2 is 36-1991.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889885010895
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  • 118
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    Effect of divergence and receiving slit dimensions on peak profile parameters in Rietveld analysis of X-ray diffractometer data (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 398-405 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A range of `normal' divergence (0.25, 1.0°) and receiving (0.1, 0.2, 0.4 mm) slit dimensions has been used to determine their effect on the peak profile parameters obtained by Rietveld analysis of X-ray powder diffraction data from a conventional X-ray source. The instrument is a standard Bragg–Brentano diffractometer equipped with a diffracted-beam monochromator and Soller slits. The instrumental profile characteristics are provided by a sample of coarsely crystalline Si, and the effects of small particle size and isotropic strain by fluorite, CaF2. Results are discussed for refinements of the full diffraction patterns (24 to 140°), and of the individual peaks at 28, 47 and 88° in each pattern. The use of a wide receiving slit aperture (i.e. 0.4 vs 0.1 mm) provides (i) increased peak intensities, (ii) much improved values of the Rietveld agreement indices (especially at low angles), (iii) slightly more Gaussian peak shapes, and (iv) slightly wider peaks. A wider divergence slit (i.e. 1.0 vs 0.25°) has only a small effect on the refinement results. The Voigt and pseudo-Voigt peak shape models are seriously deficient for low-angle peaks when axial divergence is larger than about 2°, but are otherwise satisfactory. The CaF2 peaks are wider and more Lorentzian in character (at high angles) than those obtained for Si, owing to the presence of very small (350 Å) and strained crystals; in this case, the peak shape/width characteristics can be adequately modelled at all diffraction angles, regardless of axial divergence. Quantitative information about crystal size and strain can be extracted from the CaF2 pattern by direct incorporation of the instrumental profile into the parameters of the Voigt function during Rietveld refinement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888003474
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  • 119
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    Instrumental resolution effects in small-angle neutron scattering (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 438-451 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Experimentally measured scattering data differ from theoretical curves because of departures from point geometry in a real instrument. In a small-angle neutron scattering (SANS) instrument, there are essentially three contributions to the smearing of an ideal curve: (1) the finite divergence of the beam, (2) the finite resolution of the detector, and (3) the poly chromatic nature of the beam. Where the scattering is azimuthally symmetric about the incident beam, indirect Fourier transform (IFT) methods may be used not only to smear an ideal scattering curve, but also to desmear an observed pattern. For experiments where the assumption of azimuthal symmetry cannot be made, alternative procedures based on Monte Carlo (MC) techniques have been developed which simulate the smearing of a given theoretical scattering function. This procedure permits the evaluation of smearing effects in anisotropic systems. Both IFT and MC procedures are illustrated with a range of applications from data taken on the 30 m SANS facility at Oak Ridge National Laboratory. It is shown that for experiments with scattering dimensions 〈 200 Å smearing effects are small (〈 5%) and that dimensions up to ̃1200 Å may be accurately resolved after proper evaluation of resolution effects. The procedures described may also be extended to include small-angle X-ray scattering, and an example of one such application is given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888004273
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  • 120
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    Integration of single-crystal reflections using area multidetectors (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 471-478 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The development of multidetectors for use in X-ray and neutron scattering experiments has created an interest in methods for integrating Bragg peaks in three-dimensional data arrays representing intensity scattered from single crystals. A method of using a priori information, extracted from the strongest peaks, to obtain statistically optimum results has been developed at the Institut Laue–Langevin (ILL), Grenoble. The method is outlined in this paper and results of its application to neutron diffraction are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005400
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  • 121
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    Principles of differential energy-dispersive X-ray spectroscopy (DEDXS) (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 496-503 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Conventional methods and problems of differential X-ray spectroscopy using characteristic radiation are briefly described. The principles of energy-dispersive methods of differential spectroscopy are then described, covering both high- and low-resolution systems. By using digital electronics to control the modulation, errors associated with timing are reduced to well below those associated with the random nature of X-ray emission. By delaying demodulation until the final counting stage, thus using only one chain of electronic processors, errors associated with two chains of different characteristics are eliminated. Stability of the source is no longer an important criterion and the method is ideally suited for use with synchrotron radiation sources where beam intensity decays with a half-life of a few hours. It is also possible to derive the modulation cycles from the oscillator that controls the electron bunches in the storage ring, thereby making possible time-resolved and phase-sensitive studies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005643
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  • 122
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    Use of a shared-memory parallel processor in the restrained least-squares procedure of Hendrickson and Konnert (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 512-515 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The restrained least-squares refinement procedure PROLSQ of Hendrickson & Konnert [Hendrickson (1985). Methods in Enzymology, Vol. 115, edited by H.W. Wyckoff, C. H.W. Hirs & S.N. Timasheff, pp. 252–270. Orlando: Academic Press] has been implemented on a 30-processor Sequent Balance 21000 shared-memory parallel processor. The adaptation of PROLSQ to a general-purpose parallel computer offers the potential of performance increase as the physical limits are approached in traditional sequential and vector processing hardware.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888005813
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  • 123
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    Interface roughness and period variations in MQW structures determined by X-ray diffraction (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 524-529 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for estimating the interface widths in multiple quantum well (MQW) structures is described. Generally it has been assumed that the average interface shapes on each side of a quantum well are the same, yet there is no reason to assume that this is correct. The method presented here can predict the interface profile on both sides of a quantum well and therefore detect the presence of any asymmetry. The results are compared with the more familiar predictive Fourier transform approach and qualitative agreement is observed, although the latter cannot predict any asymmetry. Deducing the interface width from the predictive Fourier transform method can be difficult because of series termination effects and could possibly be misleading if insufficient satellites are measured. The limitations are essentially by-passed with the described approach. A simple method for deriving period variations is also given and in the example presented this amounts to about two monolayers. The interface widths in this example are 6.5 and 5.4 monolayers and these best-fit values give an R-factor just above that which could be expected from the data. Also the fit for two similarly graded interfaces results in a significant worsening in the agreement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889888006569
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  • 124
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    Scattering exponents for polydisperse surface and mass fractals (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 25-27 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Scattering exponents are discussed for systems of power-law polydisperse surface and mass fractals. It is found that the scattering exponent for power-law polydisperse mass fractals lies on the interval [0, d] and always depends on the mass fractal dimension. The scattering exponent for power-law polydisperse surface fractals lies on [0, d + 1] and is independent of the surface fractal dimension for a large range of the polydispersity exponent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889886090052
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  • 125
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    A real-time interactive graphics program to determine crystal orientation for the analysis of oscillation diffraction photographs (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 28-33 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper describes a powerful preliminary to various least-squares programs for finding the exact crystal orientation for the oscillation method. It is well suited to cases of large initial misorientation. It uses the real-time rotation and clipping capabilities of the high-performance graphics system PS300 from Evans & Sutherland. A program has been written that performs a geometrical inversion of reciprocal space through its origin and manipulates this transformed image in place of the direct one. The Ewald sphere is thus transformed into a plane that can be superimposed on the film. The crossing of any reciprocal-lattice point through the Ewald sphere is then replaced by the crossing of its transform through the film plane. Clipping allows elimination of all the points too far away from this plane, i.e. those that are not in a diffraction condition. Determination of the correct orientation is achieved by superimposing the inverted reciprocal-lattice image on the corresponding transformed image of the observed film.
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    Systematic errors in precision lattice-parameter determination of single crystals caused by asymmetric line profiles (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 34-38 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The convolution of the various contributions to X-ray intensity distribution curves measured in lattice-parameter determination leads to peak shifts and, hence, to systematic errors in the case that at least one of the contributing curves is asymmetric. For perfect crystals, depending on the collimator divergence, this effect may reach the order of magnitude of the refraction correction. It is caused by the asymmetry of the spectral distribution curve, which includes intrinsic asymmetry, dispersion and angle dependence of intensity (ADI). For imperfect crystals characterized by orientation and interplanar-spacing distributions, the distribution curves should be measured in order to correct accurately the peak shift. Examples of simulation calculations are given for Si, Cu Kα1, Bond method for various reflections of perfect crystals and for crystals having orientation distributions, 444 reflection.
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    Accuracy and resolution in small-angle crystallographic analyses. A comparison with solution scattering studies (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 51-60 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: This paper is an extension of the preceding one and deals with the problem of assessing the potential accuracy of low-resolution crystallographic analyses restricted to the same angular range as solution scattering studies. The mathematical treatment is very similar in the two papers; similarly, the final result takes the form of a curve relating the normalized variances of the positional and chromatic structure parameters. In the absence of `small-angle' data – these are utterly disregarded in routine protein crystallographic analyses – an ideal experiment performed on a low-density serum lipoprotein, under conditions similar to those that prevailed in the experimental study of methionyl t-RNA synthetase, is used as an illustration. The potential accuracy estimated for this putative crystallographic analysis is found to be quite close to that assessed for the solution scattering experiment. In the case of protein crystallographic analyses, the projection information associated with the `small-angle' reflections is estimated and it is shown that it amounts to a substantial fraction of the whole of the experimental information. More precisely, the average information per reflection is almost 40 times larger for the `small-angle' than for the other reflections. The conclusion is reached that 'small-angle' reflections should be involved in protein crystallographic analyses and it is suggested that in the early stage of the phasing process `small-angle' crystallographic data and solution scattering experiments be combined together to locate and orient the molecule(s) in the cell and to draw the molecular envelope.
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    URL: http://dx.doi.org/10.1107/S0021889886090015
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    Information content and retrieval in solution scattering studies. II. Evaluation of accuracy and resolution (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 39-50 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The aim of this paper is to assess the potential accuracy of structure analyses based upon solution X-ray scattering experiments, before the structure problem is solved. In other words, an algorithm is sought expressing accuracy in terms of the experimental observations and associated errors, independently of the value of the structure parameters. The mathematical treatment involves five steps: (a) Data reduction, namely the definition in experimental space of the degrees of freedom of the problem and the determination of their probability law. (b) Choice of representation of the structure consistent with the coarse resolution of solution scattering experiments; a set of sharp pseudo-atoms is adopted, so that the degrees of freedom in real space are the position and electron density of each pseudo-atom. (c) Introduction to a `virtual experiment' defined by a noise distorting the structure parameters, and determination of the corresponding probability law in the experimental space. (d) Comparison of the real and the virtual experiments, or more precisely of the probability laws of the degrees of freedom in experimental space, yielding a relation between the variances of the position and electron density uncertainties, the number of the pseudo-atoms and the value of the structure parameters. (e) Attenuation of the structure dependence via the introduction of a hypothesis of quasi-spherical symmetry, whose effect is to reduce the expression of the variances to a function of the experimental observations, independent of the knowledge of the structure of the particle. This analysis is applied to solution X-ray scattering experiments at variable contrast, interpreted within the framework of the invariant volume hypothesis. The final result takes the form of a curve relating the variances of the position and electron density uncertainties, divided by the number of pseudo-atoms. The example of a low-density serum lipoprotein is used to illustrate these results.
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    Powder diffraction peak shapes. Parameterization of the pseudo-Voigt as a Voigt function (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 63-64 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The Voigt function is now recognized to be one of the best mathematical descriptions of the symmetrical component of the peak shape in constant-wavelength X-ray and neutron powder diffraction. The simpler pseudo-Voigt function has been used previously to provide an empirical fit to observed peak shapes. In this paper, a parameterization of this function is obtained to make it, to a very good approximation, equivalent to a Voigt function, and, additionally, it is described by the half-width parameters of the Gaussian and Lorentzian components of that Voigt function. This new construction allows for greater flexibility in peak-shape description and, in particular, allows for a more straightforward convolution of additional functional contributions into the `Voigt' component of a peak shape description.
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    Strategies for collecting screen-less oscillation data (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 61-62 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Screen-less oscillation photography is the method of choice for recording three-dimensional X-ray diffraction data for crystals of biological macromolecules. The geometry of an oscillation camera is extremely simple. However, the manner in which the reciprocal lattice is recorded in any experiment is fairly complex. This depends on the Laue symmetry of the reciprocal lattice, the lattice type, the orientation of the crystal on the camera and to a lesser extent on the unit-cell dimensions. Exploring the relative efficiency of collecting X-ray diffraction data for different crystal orientations prior to data collection might reduce the number of films required to record most of the unique data and the consequent amount of time required for processing these films. Here algorithms are presented suitable for this purpose and results are reported for the 11 Laue groups, different lattice types and crystal orientations often employed in data collection.
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    SANS studies of the microstructure of a three-componnent microemulsion (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 835-839 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle neutron scattering measurements have been performed on a three-component microemulsion system consisting of water, hexane and didodecyl-dimethylammonium bromide. For a water-to-surfactant weight ratio of 0.95 and less than 5 wt% surfactant, these measurements are best fit by a model with a Gaussian size distribution of spherical water droplets in hexane. The average water core radius is determined to be about 2.9 nm. On addition of water while the same water-to-surfactant ratio is maintained, there is some evidence that the basic unit of the microstructure remains a sphere with the same radius. The interaction between the spheres is found to be attractive, and the spheres may be connected for volume fractions of water larger than 5%.
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    SANS study of sintering of rough surfaces (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 864-869 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle scattering has been used to follow the heat-induced smoothing of rough fumed silica particles by viscous sintering. When analyzed by a fractal surface model, the surfaces evolved from a fractal dimension of 2.5–2.7 to 2.0. The specific surface area σ(r) for a given resolution r could be described by the simple law σ(r) = σ0(r/r*)2−D, where σ0 is the specific surface area for smooth particles and r* is a characteristic length that is the same for all the fumed silicas studied and is comparable to the primary particle size. This is the first indication of a universal relation between fractal surfaces, albeit within a closely related class of materials.
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    Cell dynamical system study of phase separation dynamics (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 883-885 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A cell dynamical system (CDS) is defined by a map which takes a configuration on a lattice at a time t to a configuration at time t + 1. Phase-ordering dynamics, block copolymers etc. have been modeled in terms of CDS. With the phase-ordering dynamics model, the scaling exponent (and the universal function) for the form factor in the scaling regime and the effect of noise on these have been studied. It is clearly observed that, for the ordering process in the (critically quenched) conserved order parameter case, the scaling exponent crosses over from ̃0.28 to ̃0.33. This crossover is delayed with the introduction of noise, with larger amplitudes of noise causing a greater delay.
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    High-resolution synchrotron X-ray powder diffraction with a linear position-sensitive detector (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 905-910 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: X-ray synchrotron powder data were collected from a capillary sample of a small-molecule organic peptide compound, glycylglycine (NH2CH2CONHCH2COOH) by step-scanning at 1° intervals with a linear position-sensitive detector covering an angular range of 2.7° in order to test the feasibility of recording a high-resolution pattern and using the data for Rietveld analysis. Appropriate corrections for detector linearity and position were implemented, and comparison with a diagram recorded with a single scintillation detector and a crystal analyser system showed similar quality for the two sets of data. A detailed comparison of the refined atomic coordinates and those of an earlier X-ray single-crystal study showed the estimated standard deviations to be significantly underestimated in both refinements. A linear detector should be particularly useful for small samples and capillary specimens of moderately absorbing materials.
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    On the calculation of diffracted intensities from SiC crystals undergoing 2H to 6H transformation by the layer displacement mechanism (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 935-942 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Computer simulation of 2H to 6H transformation by non-random insertion of layer displacement faults in a random space and time sequence has been performed. The model employed by Pandey, Lele & Krishna [Proc. R. Soc. London Ser. A, (1980), 369, 435–477], which is based on the sequential insertion of layer displacement faults, allows faulting of one-third of the total number of layers on completion of the transformation. The results of the simulation show that the transformation gets arrested because of the formation of interfaces by the impingement of independently formed 6H regions and that the fraction of faulted layers which can be inserted is just 0.276. It is shown that these interfaces are such that they do not lead to any broadening of the 6H reflections common with 2H. While this is in agreement with the theoretical predictions of Pandey et al., the diffuse intensity distribution calculated for the arrested state shows significant departures.
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    Einfluss der Valenzelektronenkonzentration auf die Bildung der Phasen vom Ni2In-Strukturtyp am Beispiel der ternären Verbindungen Mn2Ga0.5As0.5(m),Fe3GaAs und Co2Ga0.5As0.5 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 80-85 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The structures of the metastable phase Mn2Ga0.5As0.5 (m) and the stable phases Fe3GaAs and Co2Ga0.5As0.5 are isotypic with Ni2In. X-ray powder diffraction data are reported. Lattice constants and macroscopic densities were measured in the entire range of homogeneity. Crystal chemical parameters of these ternary phases and of the quasi-homologous isovalent phases are compared and discussed from the point of view of the valence-electron concentration and of the number of atoms in the unit cell. It is concluded that the valence-electron concentration is a very important but not a sufficient energetic factor for the stability of phases with the Ni2In structure.
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    Lattice thermal expansion behaviour of spinel HgCr2Se4 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 86-89 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An accurate value of the lattice parameter of the spinel ferromagnetic semiconductor HgCr2Se4 has been determined at different temperatures, ranging from 298 to 770 K, by X-ray powder diffraction. The data have been used to evaluate the coefficient of thermal expansion, α, at various temperatures. The temperature dependence of the coefficient of expansion can be represented by the equation α = 10.059 × 10−6 − 1.862 × 10−8 T + 3.017 × 10−11 T2, where T is the temperature in K. The diffraction pattern of HgCr2Se4, obtained at 785(5) K, was completely different from that at room temperature. The high-temperature phase persisted up to 900 K, and above this the compound decomposed. Furthermore, the new phase was retained when the sample was cooled from 900 K to room temperature. These results suggest an irreversible structural phase transformation in HgCr2Se4 at 785 K. An attempt is made to explain this interesting high-temperature thermal behaviour of HgCr2Se4 in relation to its structure and other physical properties.
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    CAMAL – a new component of the Cambridge Structural Database software system (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 90-91 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The efficient use of crystallographic databases necessitates the use of statistical techniques. CAMAL is a library of Fortran subroutines for performing simple and multivariate statistical calculations. The library is intended for use with the Cambridge Structural Database and is distributed by the Cambridge Crystallographic Data Centre.
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    Interactive graphics for rapid indexing of oscillation films from large unit cells (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 101-104 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An interactive graphics program for the Evans & Sutherland PS330 has been written to display and index screenless X-ray oscillation films from macromolecular crystals with unit-cell edges of at least 500 Å. ALIGN, a Fortran program which works in conjunction with M. G. Rossmann's program OSCMGR, accurately displays densitometered reflection intensities, provides the required transformation between predicted and observed reflection coordinates, and is useful in determining crystal mosaicity and detecting unit-cell changes.
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    Stroboscopic X-ray topography of quartz resonators (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 967-971 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Stroboscopic X-ray topography has been performed to observe the different states of acoustic vibrations in quartz resonators with a time resolution of 1 ns. These experiments have been made at LURE (Orsay, France) using the pulsed light delivered by the DCI storage ring. The studied resonators have shown that the vibration is affected by the nature, the density and the distribution of the defects.
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    Accurate determination of lattice parameters from XRD oscillation photographs (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 991-991 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    QUIDCRYST-87, a software package for X-ray data collection using a two-circle computer-controlled diffractometer (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 993-993 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    MISSYM1.1 – a flexible new release (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 983-984 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Version 1.1 of MISSYM is now available and the following new features have been added: a HELP facility to guide and caution the user; the input of a distance tolerance for axes and planes, and a separate tolerance for inversion centers and translations; the possibility of flagging atomic positions as `possibly disordered'; the possibility of allowing for errors in assigning chemical types; the possibility to extract the symmetry for a single atom type; the option to run from sensible default values. This version is more flexible than, but not quite as fast as, the original. Only one-third of structures require the full application of MISSYM because simple conditions, simultaneously satisfied by about two-thirds of the structures published recently, rule out the possibility of extra symmetry in the model. The existence of an efficient computer program for flagging the cases of overlooked symmetry should not give a false sense of security or be used to justify short cuts in the preliminary study of crystal symmetry.
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    High-reflectivity multilayer monochromators for neutrons (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 123-130 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Ni–Ti multilayers were fabricated in an r.f. sputtering system. Reflectivities of the multilayers were measured with a neutron beam having a beam divergence of 0.29 mrad and a beam width of 0.32 mm. Reflectivities of the multilayers and their diffraction properties were compared with results obtained from the dynamical theory for perfect multilayers. Attempts were then made to minimize the imperfections in multilayers and obtain good-reflectivity multilayers with small d spacings. Multilayers with d spacings from 60 Å up could be fabricated with reflectivities between 0.95 and 1.00.
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    The determination of molecular orientation: an efficient reciprocal-space algorithm for the small computer (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 131-133 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A rotation function is formulated in terms of a Fourier–Bessel-series expansion of the Patterson coefficients of the search model. The function provides an efficient algorithm for performing rotational analyses of small molecules on computers with limited memory and storage requirements.
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    Post-refinement of oscillation diffraction data collected at a synchrotron radiation source (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 134-139 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: `Post-refinement' is a technique used to compare the intensity of partially recorded reflections on oscillation photographs with their full intensity observed elsewhere on the same or a different film. A reflection's partiality depends on crystal orientation, crystal cell dimension and crystal mosaicity, and post-refinement is a very sensitive tool for the refinement of these parameters. A previous paper [Rossmann, Leslie, Abdel-Meguid & Tsukihara (1979). J. Appl. Cryst. 12, 570–581] describes how post-refinement can be applied to data derived from a set of oscillation films. In this paper the technique has been extended to the refinement of anisotropic beam divergence and wavelength dispersion as is normally found on synchrotron sources. In an example it is shown that post-refinement is sufficiently sensitive to detect small wavelength variations due to changes in temperature of the monochromating crystal.
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    Identification of Burgers vectors along 〈111〉 in In-doped GaAs, by X-ray transmission topography and image simulation (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 140-141 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Long dislocations with Burgers vectors along 〈111〉 are unusual in f.c.c. lattices. X-ray topographs have been obtained of as-grown GaAs crystals doped with 1020 atoms cm−3 of In, where the usual extinction criterion g.b = 0 leads to this type of defect. However, for several g satisfying the condition g.b = 0 with b = a [111], the images of these dislocations were still clearly visible. Comparison between experimental and computer-simulated X-ray topographic sections of these defects confirms the existence of Burgers vectors along 〈111〉.
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    Crystal data for 1-4-epoxy-4-[(4-nitrophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (C22H15NO6) and 1,4-epoxy-4-[(4-bromophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (C22H15BrO4) (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 142-142 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The indexed X-ray diffraction powder data of 1,4-epoxy-4-[(4-nitrophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (OZONO, C22H15NO6) and 1,4-epoxy-4-[(4-bromophenyl)methyl]-1-phenyl-1H-2,3-benzodioxepin-5(4H)-one (OZOBR, C22H15BrO4) are reported. OZONO and OZOBR crystallize in the monoclinic space groups P21/c and P21/a, respectively. The cell constants are a = 8.200 (4), b = 14.574 (6), c = 15.908 (7) Å, β = 100.30 (3)°, V = 1870.5 Å3, Dm = 1.36 (1), Dx = 1.38 Mg m−3 for OZONO and a = 12.217 (5), b = 8.945 (2), c = 17.062 (5) Å, β = 96.85 (2)°, V = 1851.2 Å3, Dm = 1.49 (1), Dx = 1.52 Mg m−3 for OZOBR. The quantitative figures of merit (FN) are F20 = 62(0.007, 48) and F26 = 28(0.016, 58) deg−1, respectively. The JCPDS Diffraction File No. for OZONO is 36-1988 and for OZOBR 36-1989.
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    A comparison of the source emissivity distributions for two standard X-ray tubes (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 143-143 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Phase separation in glass edited by O. V. Mazurin and E. A. Porai-Koshits (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 144-144 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Easy and economic ways of handling air-sensitive crystals for X-ray diffraction studies (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 182-183 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Easy and convenient techniques have been developed to handle air-sensitive compounds in terms of measuring their single-crystal X-ray diffraction intensities. These methods have also been fruitfully applied in collecting X-ray data of several highly air-sensitive inorganic and organometallic compounds without using a cold stream of nitrogen.
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    Nominations for the Ewald Prize (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 187-187 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    A high-resolution diffuse X-ray scattering study of defects in dislocation-free silicon crystals grown by the float-zone method and comparison with Czochralski-grown crystals (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 209-215 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Point-defect aggregates in (111) dislocation-free silicon single crystals grown by the float-zone (FZ) method have been studied by diffuse X-ray scattering (DXS) and compared with those in the Czochralski-grown (CZ) crystals. A two-axis X-ray diffractometer was used. It employs three monochromators in (+, −, −) setting to obtain a highly collimated and monochromatic Mo Kα1 beam. DXS measurements were made around the 111 reciprocal-lattice point (r.l.p.) with K* along ±[111] and ±[01{\bar 1}]; K is the vector which joins the elemental volume of the reciprocal space under investigation to the nearest r.l.p. For FZ crystals for a given K* the DXS intensity was higher for θ 〈 θB in comparison with that for θ 〉 θB showing that the anisotropy (DXS Iθ 〉 θB − DXS Iθ 〈 θB) is negative, as expected for vacancy clusters. For CZ crystals the anisotropy was positive, owing to the presence of interstitial clusters. The magnitude of anisotropy in the FZ crystals was smaller than that observed in the CZ crystals. The DXS intensity varies approximately as K−2 near Bragg peaks (Huang scattering) and as K*−4 (Stokes–Wilson scattering) away from it. From the K* values where the changeover from Huang to Stokes–Wilson scattering takes place the size of the clusters assumed to be the origin of the observed DXS is estimated as ̃2 × 10−4 and 2.6 × 10−3 mm for FZ and ̃5.5 × 10−4 and 3 × 10−3 mm for CZ crystals. The experimental data were compared with theoretically calculated DXS distributions assuming the defects to be dislocation loops. The number of point defects in a loop has been estimated.
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    The influence of texture on the radial distribution function of solid carbons (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 205-208 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The effect of texture on the interpretation of the classical radial distribution function (RDF) is studied. A model of axial texture is presented which enables the calculation of the effect for individual interatomic distances and an analysis of the effect on the global RDF. The example shows that the shift of the RDF closest-neighbour peak position can be as large as 0.06 Å.
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    On the selection of measurement directions in second-rank tensor (e.g. elastic strain) determination of single crystals (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 216-221 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The components of a symmetric second-rank tensor (e.g. the strain tensor) can be calculated from measurements of that tensor property in at least six directions. A system of simultaneous equations (t(m) = Σ6i = 1 amiti) must be solved. The coefficient matrix ami is determined by the measurement directions, and therefore it is of great importance to choose these directions properly. Part 1 deals with the necessary condition: rank (ami)〈〉 0. Rules are given by which it is easy to decide whether rank (ami) = 0 or rank (ami) ≷0 without calculating the rank. In part 2 methods are developed to find optimized sets of measurement directions. An optimized set is one for which the inevitable measurement errors will give errors of the calculated tensor components as small as possible. Special attention is given to the case of X-ray strain measurement of single crystals.
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  • 156
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    Average Rayleigh-wave velocity of a computer-simulated crystallographic plane (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 181-187 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A model is proposed for calculating the Rayleigh-wave velocity as obtained by an acoustic lens, taking into account the anisotropy of the material under study and the profile of the miniature acoustic probe. The results obtained by this model on different `cuts' of single-crystal silicon agree with both those published in the literature and our own experimental results. In addition, the model has been applied to the non-destructive thickness measurement of opaque thin films deposited on different anisotropic substrates. More significantly, using the model and experimental acoustic material signature (AMS) curves obtained with this acoustic measurement system, the thickness of tungsten thin films deposited on silicon (100) have been measured. The results are in good agreement with measurements made using a Rutherford back-scattering technique.
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    Report on a round-robin study of diffuse X-ray scattering (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 188-194 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffuse scattering in a volume in reciprocal space from NbC0.72 was measured on an absolute scale at two synchrotron sources (in the US and in Japan) and with a high-intensity rotating-anode source (in Japan). The shape and actual absolute intensities agreed to a few percent. Special problems associated with such measurements at a synchrotron are noted, especially with an insertion device. The high resolution possible at such sources reduces the need for an evacuated sample chamber. Detailed measurements can be completed in 1–2 d, making such studies much more accessible than is possible with sealed-tube X-ray generation.
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  • 158
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    Diffraction from quasi-crystals and disordered twinned aggregates (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 308-314 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Following the discovery of systems with diffraction patterns exhibiting icosahedral symmetry by Shechtman, Blecht, Gratias & Cahn [Phys. Rev. Lett. (1984), 53, 1951–1953], which is forbidden in classical crystallography, interest has centred on Penrose tiling and its generalizations as a model for the explanation of these patterns, although Pauling [Nature (London) (1985), 317, 512–514; Phys. Rev. Lett. (1987), 58, 365–368] has proposed an alternative explanation in terms of crystal twinning. In an attempt to reconcile these two points of view a computer algorithm has been developed, following the methods outlined by Wolny, Pytlik & Lebech [J. Phys. C (1988), 21, 2267–2277], to grow a number of different structures which all tile the two-dimensional (2D) plane without defects. With the same two types of basic unit, it is shown that it is possible, on the one hand, to produce structures similar to the Penrose tiling pattern and, on the other, different types of twinned and disordered structures, with a continuous sequence of intermediates. Optical diffraction patterns of these structures have been obtained for comparison with real quasi-crystals.
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    High-pressure single-crystal X-ray diffraction studies of MoO3. I. Lattice parameters up to 7.4 GPa. Erratum (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 380-380 
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    Notes: Owing to a printer's error, the fourth equation given in the Abstract of the paper by Åsbrink, Kihlborg & Malinowski [J. Appl. Cryst. (1988). 21, 960–962] is incorrect. The correct equation is {\bar \beta}_c(0–7.41 GPa) = −3.35 × 10−4 (GPa)−1.
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    NRCVAX – an interactive program system for structure analysis (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 384-387 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: NRCVAX is a complete system of programs, covering all aspects of crystal structure analysis from data reduction to the presentation of results. The system, which is written in a `neutral' Fortran 77, presently exists in two forms. The first runs on a VAX computer under VMS, on an 80386 PC under UNIX and under IBM VM/CMS and MVS/TSO. The second is an adaptation which runs on PC-XT, AT, PS/2 and comparable microcomputers under MS-DOS. The two versions differ somewhat in structure, but very little in code, operation or functionality except for the graphics. The many options of the programs can be selected in a highly interactive manner and because of this the system is very flexible. Most options are assigned default values, however, and it is usually safe to run the routines with a minimum of user input using the defaults. The system will accept data from a wide variety of sources and has interface routines for several other systems. Graphics in the VAX/UNIX version are based on the widely available Tektronix 4000 series protocol, while the microcomputer version supports most common display adapters. It is also possible to prepare files for a variety of plotters, dot-matrix printers and laser printers. Source code is distributed and it should not be difficult to adapt the system to any computer with virtual memory and a Fortran 77 compiler.
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    A procedure for the selection and transferring of crystals at low temperatures to diffractometers (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 394-395 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    DREADD – data reduction and error analysis for single-crystal diffractometer data (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 396-397 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    New Commercial Products (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 398-400 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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    Crystal data for p-bromochlorobenzene/p-dibromobenzene mixed crystals at 293 K (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 202-202 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The powder data for p-bromochlorobenzene/p-dibromobenzene mixed crystals [pBCB]x[pDBB]1 − x at 293 K are reported; their thermal stability at 293 K is given. Vertical diffractometer, graphite monochromator, Cu Kα, λ = 1.54056 Å. They are all isomorphous, monoclinic, P21/a with Z = 2. a = 15.176(6), b = 5.847(3), c = 4.078(2) Å, β = 112.57(3)°, V = 334.2 Å3, Dx = 1.947 Mg m−3 for [pBCB]0.90[pDBB]0.10; JCPDS No. 36-1975. a = 15.222 (7), b = 5.847 (3), c = 4.083(2) Å, β = 112.60(3)°, V = 335.5 Å3, Dx = 1.984 Mg m−3 for [pBCB]0.80[pDBB]0.20; JCPDS No. 36-1974. a = 15.260(5), b = 5.839(2), c = 4.084(2) Å, β = 112.57(1)°, V = 336.1 Å3, Dx = 2.024 Mg m−3 for [pBCB]0.70[pDBB]0.30; JCPDS No. 36-1973. a = 15.298(4), b = 5.845(3), c = 4.091(2) Å, β = 112.60(2), V = 337.7 Å3, Dx = 2.058 Mg m−3 for [pBCB]0.60[pDBB]0.40; JCPDS No. 36-1972. a = 15.340(4), b = 5.844(2), c = 4.092(2) Å, β = 112.60(2)°, V = 338.7 Å3, Dx = 2.096 Mg m−3 for [pBCB]0.50[pDBB]0.50; JCPDS No. 36-1971. a = 15.370(5), b = 5.843(2), c = 4.097(2) Å, β = 112.62(2)°, V = 339.6 Å3, Dx = 2.134 Mg m−3 for [pBCB]0.40[pDBB]0.60; JCPDS No. 36-1970. a = 15.404(6), b = 5.840(2), c = 4.100(2) Å, β = 112.67(2)°, V = 340.4 Å3, Dx = 2.172 Mg m−3 for [pBCB]0.30[pDBB]0.70; JCPDS No. 36-1969. a = 15.437(5), b = 5.842(2), c = 4.103(2) Å, β = 112.66(2)°, V = 341.4 Å3, Dx = 2.209 Mg m−3 for [pBCB]0.20[pDBB]0.80; JCPDS No. 36-1968. a = 15.468(4), b = 5.838(2), c = 4.104(2) Å, β = 112.70(2)°, V = 341.9 Å3, Dx = 2.249 Mg m−3 for [pBCB]0.10[pDBB]0.90; JCPDS No. 36-1967.
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    The energy dependence of the neutron coherent scattering length of europium (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 476-482 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: General considerations are given for the importance of providing an energy/wavelength-dependent database of neutron coherent scattering lengths, and of the possibility of constructing such a base from the range of neutron cross-section data that are generally available for a wide range of nuclides. The case of europium is considered in detail, partly because it is a good example of an element with strong resonance effects in the wavelength region of importance in crystallographic and condensed-matter studies, and partly because it is an exceptional case from the nuclear point of view, having multi-level interference effects. From the available cross-section data the complex coherent scattering length is constructed as a function of neutron energy up to 0.7 eV, for the isotopes and for the natural element. Some single-level approximations for the scattering-length function of 151Eu are given.
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    Correction for detector misalignment in a four-circle diffractometer (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 222-223 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: The treatment of the angular errors arising in a four-circle diffractometer from the displacement of the detector slit and collimator from the equatorial plane is described. The method affords an accurate means of assessing and correcting the displacement from measured setting angles.
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    Collection and processing of X-ray diffraction data from protein crystals at high pressure (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 208-213 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Apparatus for collecting X-ray diffraction data from protein crystals at pressures up to 0.2 GPa is described. The modified techniques required for crystal mounting, determination of crystal orientation in the beryllium pressure cell, and centering in the X-ray beam are described. Special attention is required for intensity absorption corrections due to the marked attenuation (90%) of the beam. Data have been collected from tetragonal hen egg white lysozyme crystals at 1000 atm to 2.0 Å nominal resolution using Cu Kα radiation (1 atm = 1.01325 × 105 Pa). The crystals, crystallized in 0.86 M NaCl, require 1.4 M NaCl in the stabilizing solution to prevent cracking at several hundred atmospheres and higher. The crystals show no measurable hysteresis when cycled through several 1 to 1000 atm transitions. Altered intensities relaxed to their new value within 1 min on pressurization, but required about 90 rain to recover their starting values on pressure release. The unit-cell volume decreases 1.1% at 1000 atm.
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    A Monte Carlo error simulation applied to calibration-free X-ray diffraction phase analysis (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 217-221 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Quantitative phase analysis of a system of n phases can be effected without the need for calibration standards provided at least n different mixtures of these phases are available. A series of linear equations relating diffracted X-ray intensities, weight fractions and quantitation factors coupled with mass balance relationships can be solved for the unknown weight fractions and factors. Uncertainties associated with the measured X-ray intensities, owing to counting of random X-ray quanta, are used to estimate the errors in the calculated parameters utilizing a Monte Carlo simulation. The Monte Carlo approach can be generalized and applied to any quantitative X-ray diffraction phase analysis method. Two examples utilizing mixtures of CaCO3, Fe2O3 and CaF2 with an α-SiO2 (quartz) internal standard illustrate the quantitative method and corresponding error analysis. One example is well conditioned; the other is poorly conditioned and, therefore, very sensitive to errors in the measured intensities.
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    Quantitative texture measurement on thin wires (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 533-538 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: A method is proposed for measuring textures on the surfaces of thin wires. The method is based on a numerical absorption correction analysis of the sample. Analytical formulas are given for thicker or more strongly absorbing specimens. Experimental work is presented to illustrate the use of the method.
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    Grazing-incidence small-angle X-ray scattering: new tool for studying thin film growth (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 528-532 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Grazing-incidence small-angle X-ray scattering (GISAXS) is introduced as a method of studying discontinuous thin films. In this method, the incident beam is totally externally reflected from the substrate followed by small-angle scattering of the refracted beam by the thin film. The experiment described establishes the ability of GISAXS to provide size information for islands formed in the initial stages of thin film growth. The data presented are for gold films of 7 and 15 Å average thicknesses on Corning 7059 glass substrates. The advantages of this technique are that it is non-destructive, can be done in situ, provides excellent sampling statistics, does not necessarily require a synchrotron source, and is not limited to thin or conducting substrates.
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    Calculation of the crystal orientation distribution function from synchrotron radiation experimental data (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 559-561 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Notes: Series-expansion coefficients for an orientation distribution function (ODF) of cold-rolled aluminium sheet were calculated from the intensity of Debye–Scherrer rings obtained in an experiment using synchrotron radiation. Calculated and observed pole figures demonstrate that a sufficiently good approximation to the ODF is obtained from coefficients calculated to l = 8.
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    X-ray study of CuGaxIn1−xSe2 solid solutions (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 578-583 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The semiconducting compound CuGaxIn1 − xSe2 crystallizes in the chalcopyrite structure (space group I{\bar 4}2d, Z = 4). The X-ray powder data for x = 1, 0.75, 0.6, 0.5, 0.4, 0.25 and 0.0 have been collected and it is found that the lattice parameters a and c and their ratio c/a vary linearly with x. Thus the composition of any chalcopyrite in the pseudo-binary system CuGaSe2 and CuInSe2 can be obtained from the accurate lattice parameters. The crystallite size determined from the (112) plane is minimum for x = 0.50 ( ̃1000 Å) and away from x = 0.50 it increases. A value of u = 0.240 (5) has been established for fixing the Se-atom positions in the CuGa0.5In0.5Se2 solid solution. The JCPDS Diffraction File No. for CuInSe2 is 40-1487 and for CuGa0.5In0.5Se2 is 40-1488.
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    Crystallographers (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 641-641 
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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/S0021889889011192
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    J. D. Hanawalt Powder Diffraction Award (1989)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 22 (1989), S. 642-642 
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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/S0021889889011209
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    Improvement of the accuracy of HAUP, high-accuracy universal polarimeter: application to ferroelectric [N(CH3)4]ZnCl4 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 377-381 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that in fixing the crossed Nicols positions a systematic error must invariably be introduced caused by the parasitic ellipticities of the polarizer and analyzer and the refraction of the light beam by the specimen. A method has been derived by which this systematic error can be removed from the original HAUP method. The improved method has been successfully applied to the measurement of the temperature dependence of the gyration-tensor component g23 of [N(CH3)4]2ZnCl4, although it is as small as 10−7. The study of optical activity shows directly that the order parameter of the incommensurate phase of the (NH4)2SO4 family is complex and that a phason exists in this phase. It can be shown that the optical activity of the incommensurate phases can be classified into three types, [N(CH3)4]2ZnCl4 corresponding to the case where the nearly commensurate domains are optically active. The extensive usefulness of optical activity to the study of phase transitions is suggested.
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    Multi-site correlations and the atomic size effect (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 382-389 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Optical diffraction patterns are presented which illustrate the effect of multi-site correlations on the diffraction pattern of a model disordered alloy consisting of different sized atoms placed on a simple square lattice. Monte Carlo methods were used to apply size-effect distortions to a number of example lattices containing various multi-site correlations. The presence of a four-site correlation between the four sites of the unit square resulted in correlations between the atomic displacements transverse to the correlation direction, and this resulted in clearly discernible extra diffuse peaks. Even though the magnitude of the four-site correlation was close to the physical limit for such a term the effect on the diffraction pattern was relatively small, the major component still being the sinusoidal modulations of the simple `size effect' which depend purely on the two-site correlations. The introduction of a three-site correlation between three of the four sites of the unit square, on the other hand, resulted in a substantial contribution to the scattering in the form of additional sinusoidal modulations along a diagonal direction.
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    Mounting a 10 K cooling device without rotating seals on a four-circle diffractometer (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 390-394 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Instrumentation has been developed for collection of three-dimensional X-ray and neutron diffraction data at temperatures below the boiling point of liquid nitrogen. A closed-cycle two-stage refrigerator has been mounted on the φ shaft of a four-circle goniometer. The sample crystal is attached to the nominal 10 K station. The refrigerator mount functions as a goniometer head without arcs. The x−y−z centering device has a range of ± 5 mm for the z direction along the φ axis and ± 2 mm along x and y. Dovetails and eccentrics with narrow tolerances allow a precise firmly lockable centering of the crystal. The whole refrigerator unit undergoes all the normal φ, χ and ω movements during data collection without any rotating vacuum seals. These are usually integral vulnerable parts of existing liquid-helium-temperature cryocoolers. When refrigeration is not required, the cryo-unit can be dismounted in a few minutes and replaced by a device for mounting an ordinary goniometer head for room-temperature data collection. Thus, the system is simple, robust and easy to operate, both at room temperature and at cryogenic temperatures. Furthermore, the use of a closed-cycle refrigerator makes the system more economical than comparable cryocooler systems based on flow cryostats.
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    An X-ray determination of the thermal expansion of α-phase Ag–Al alloys at high temperatures (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 484-485 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The lattice expansion of four Ag–Al alloys of different composition has been determined by X-ray measurements. The alloys, which contain 5.8, 9.2, 15.8 and 18.2 at.% Al, have been investigated in the temperature range 303–928 K. αav for the four compositions are 20.41, 19.69, 19.93 and 20.37 × 106 K−1.
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    A new method for determination of the crystal setting matrix for interpreting oscillation photographs (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 482-484 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The standard procedure for indexing oscillation photographs makes use of the partial reflections from two Laue photographs of a crystal taken with the incident beam parallel to any two principal axes of the crystal. A procedure is described using a graphics terminal of a microcomputer to display the calculated and observed diffraction patterns for an oscillation photograph and to examine visually all necessary rotations to get the best orientation matrix for the crystal. This method is particularly useful when the crystal is sensitive to X-rays and not easily amenable to setting photographs or Laue photographs.
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    Crystal data for uranium phosphorus pentoxide, UPO5, and uranium arsenic pentoxide, UAsO5 (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 486-486 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Guinier powder patterns [λ(Cu Kα1) = 1.5406 Å] of UPO5 and UAsO5 have been indexed. UPO5 is triclinic. The cell dimensions are: a = 5.472(2), b = 5.646(2), c = 7.027(1) Å, α = 87.39(2), β = 93.39(2), γ = 106.51(1)°, V = 207.7 Å3, Z = 2, Dx = 5.58 g cm−3. The new compound UAsO5 appears monoclinic. The unit cell has dimensions: a = 8.833(2), b = 6.858(1), c = 7.151(1) Å, β = 96.88(1)°, V = 430.1 Å3, Z = 4, Dx = 6.07 g cm−3. The space group is P21/c. The data show the presence of a strong triclinic C subcell: a = 5.591(1), b = 5.591(1), c = 7.151(1) Å, α = 84.57(1), β = 95.43(1), γ = 104.35(1)°, which suggests that both compounds are structurally related. The JCPDS Diffraction File No. for UPO5 is 37-1462 and for UAsO5 37-1461.
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    Use of a new array processor in the restrained least-squares procedure of Hendrickson and Konnert (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 486-488 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The restrained least-squares refinement procedure of Hendrickson & Konnert [Hendrickson (1985). Methods in Enzymology, Vol. 115, edited by H. W. Wyckoff, C. H. W. Hirs & S. N. Timasheff, pp. 252–270. Orlando: Academic Press] has been implemented on a Digital Equipment Corporation VAX 11/780 equipped with a 30 MFLOP (million floating point operations per second) Numerix MARS-432 array processor. The modified program executes in only one twentieth of the time required for the unmodified version on the same VAX and an estimated half of the time required for execution on an IBM 3081.
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    Errors in a recent critique of the Borie–Sparks method in diffuse scattering (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 491-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    XFPS, a program for automatic Fourier, Patterson and superposition methods (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 488-491 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A program is presented that solves crystal structures completely using Patterson function, symmetry minimum function, atomic minimum superposition and advanced Fourier methods. The program works most efficiently for structures with one or several heavier atoms in the asymmetric unit.
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    Prices of Acta Crystallographica and Journal of Applied Crystallography (1986)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 19 (1986), S. 491-492 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
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    Gunnar Hägg, 1903-1986 (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 1-2 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 186
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    X-ray diffraction study of anharmonic thermal vibrations in β-AgI (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 3-7 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Intensity data were collected at room temperature from an extended-face crystal of AgI using Mo Kα radiation. Least-squares refinement indicates that the thermal motion of the Ag+ ions is large with a considerable anharmonic component. The wurtzite positional parameter, u, was found to be 0.3748(2). The proportion of point defects was determined to be no greater than 0.9%. The proportion of random staking faults was determined by two experimental techniques to be no greater than 2%.
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    The effect of crystallographic orientation on the optical anisotropy of graphite layers on diamond surfaces (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 11-15 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The optical anisotropy of polycrystalline graphite layers formed after catalytic graphitization of single-crystal diamond surfaces has been studied as a function of crystallographic substrate orientation. It was found that the shapes and orientations of the two-dimensional indicatrices of the graphite coatings were in complete agreement with the two-dimensional point-group symmetry of the underlying diamond surfaces. This means the graphite crystallites have one or more preferential orientations imposed by the substrate.
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    Lattice-parameter-difference measurement of heteroepitaxial structures by means of extremely asymmetrical Bragg diffraction (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 8-10 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The sensitivity of measurements of the lattice-parameter difference in monocrystalline heterostructures can be enhanced by use of an extremely asymmetrical diffraction geometry. If the angle of incidence is somewhat higher than the critical angle for total external reflection, the Bragg peak is shifted from the position calculated by kinematic theory. The amount of shift depends on the angle of incidence as well as on the mass density of the material used. For heteroepitaxic structures both the layer and the substrate peaks are shifted but by different amounts. Therefore it becomes possible to characterize layers of totally lattice-matched structures also.
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    A small-angle X-ray camera using a two-dimensional multiwire proportional chamber (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 16-22 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The construction and performance of a small-angle X-ray camera equipped with a two-dimensional multiwire proportional chamber (two-dimensional MWPC) are described. The system has been used for studies of the structure of biological samples with a conventional rotating-anode X-ray source. The small-angle camera is of Franks type with two orthogonal platinum-coated bent optical flats placed in a helium-tight box. The specimen-to-detector distance is variable between 60 and 260 cm. The sensitive area of the two-dimensional MWPC is 256 × 256 mm with 256 × 256 resolution elements. The camera covers high angles up to about 5 Å, although diffraction line widths in this region are highly broadened owing to parallax. The electronic system comprises NIM modules, a hand-made module and a commercially available compact two-dimensional multichannel analyser (two-dimensional MCA). The two-dimensional MCA has a memory size of 256 × 256 channels (24 bits/channel). The estimated dead time of this system is approximately 5 μs, which permits a maximum count rate of 20 kHz at 10% loss. Diffraction patterns of a Langmuir–Blodgett film of arachidic acid and stacked purple membranes and a solution scattering of horse spleen apoferritin are demonstrated as examples.
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    The N-crystal spectrometer (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 23-27 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It is shown that a recurrence relation exists such that the resolution function and luminosity of an optical system consisting of any number of alternate collimators and reflecting crystals can be calculated analytically. Certain cases of practical interest in neutron and X-ray diffraction are evaluated explicitly using a Gaussian approximation for the transmission functions of the collimators, and for the mosaic spread distributions or reflection profiles of the crystals. It is shown that true absorption has a negligible effect on luminosity when the Darwin width of a reflection is of the order of the opening angle of the X-ray beam from a synchrotron source.
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    Absolute calibration of small-angle neutron scattering data (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 28-40 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Absolute calibration forms a valuable diagnostic tool in small-angle neutron scattering (SANS) experiments, and allows the parameters of a given model to be restricted to the set which reproduces the observed intensity. Discrepancies between the observed and calculated intensities may arise from potential artifacts or even new physical processes and absolute calibration methods are useful in delineating these circumstances. General methods which are available for absolute scaling are discussed along with estimates of the degree of internal consistency which may be achieved between the various standards. In order to minimize the time devoted to calibration in a given experimental program, emphasis is placed on developing a set of precalibrated strongly scattering standards which may be run in the chosen experimental geometry. Comparison of such a set developed at the National Center for Small-Angle Scattering Research (Oak Ridge) with independent determinations by SANS users indicates consistency to within ± 5%.
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    Easy-to-use indirect Fourier transformation routines for evaluation of slit-length-smeared SAXS curves of polystyrene in solution (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 41-47 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two easy-to-use indirect Fourier-transformation routines for the evaluation of slit-length-smeared SAXS curves of polystyrene in solution are demonstrated. For approximation of the SAXS curve, analytically transformable Gaussian and Lorentzian functions are chosen. The nonlinear least-squares fit is transformed to a linear one by specifying fixed non-linear coefficients. The fit is constrained by allowing only positive linear coefficients. The range over which nonlinear coefficients have to be specified can be easily obtained from the SAXS curve. An exact specification of this range is unnecessary for the fit. The method allows direct and clear control of the indirect Fourier transformation.
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    A model-fitting procedure incorporating the double-null technique for use in protein structure refinements (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 48-53 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The double-null technique in conjunction with the conjugate-gradient algorithm gives an efficient method of regularizing protein structures. The double-null technique constrains planar groups by introducing two artificial atoms which are geometrically the apices of tetrahedra from three selected atoms in the planar group. The model-fitting procedure is simply concerned with reconciling information on (x, y, z) atomic coordinates with information on bond length, bond angle and planarity constraints. This can be done without treatment of hydrogen-bond, van der Waals or electrostatic interactions and consequently the minimization function is nearly quadratic. The equations which have to be solved have many unknowns but few coefficients and an effective iterative method can be used.
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    Crystal data for p-chloroiodobenzene and p-bromochlorobenzene/p-chloroiodobenzene mixed crystals at 293 K (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 48-48 
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    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The powder data for p-chloroiodobenzene and p-bromochlorobenzene/p-chloroiodobenzene mixed crystals [pBCB]x[pCIB]1 − x at 293 K are reported; their stability at 293 K is given. The cell dimensions have been refined by least squares from accurate powder diffractometer data recorded at T = 293 (1) K (quartz as internal standard). Vertical diffractometer, graphite monochromator, Cu Kα1−Cu Kα2 correction so that λ = 1.54056 Å. They are all isomorphous, monoclinic, P21/a with Z = 2. a = 15.818(4), b = 5.912(2), c = 4.214(2) Å, β = 113.61(1)°, V = 361.1 Å3, Dx = 2.193 Mg m−3 for pCIB; JCPDS No. 37–2000. a = 15.210(5), b = 5.860(3), c = 4.091(2) Å, β = 112.64(2)°, V = 336.5 Å3, Dx = 1.936 Mg m−3 for [pBCB]0.90[pCIB]0.10; JCPDS No. 37–1989. a = 15.287(6), b = 5.870(3), c = 4.111(2) Å, β = 112.78(2)°, V = 340.1 Å3, Dx = 1.961 Mg m−3 for [pBCB]0.80[pCIB]0.20; JCPDS No. 37–1990. a = 15.360(5), b = 5.880(2), c = 4.126(1) Å, β = 112.87(2)°, V = 343.3 Å3, Dx = 1.988 Mg m−3 for [pBCB]0.70[pCIB]0.30; JCPDS No. 37–1991. a = 15.424(5), b = 5.889(3), c = 4.137(2) Å, β = 112.99(2)°, V = 346.0 Å3, Dx = 2.018 Mg m−3 for [pBCB]0.60[pCIB]0.40; JCPDS No. 37–1992. a = 15.493(4), b = 5.896(2), c = 4.155(2) Å, β = 113.09(2)°, V= 349.1 Å3, Dx = 2.045 Mg m−3 for [pBCB]0.50[pCIB]0.50; JCPDS No. 37–1993. a = 15.566(5), b = 5.901(3), c = 4.168(2) Å, β = 113.20(2)°, V = 351.9 Å3, Dx = 2.073 Mg m−3 for [pBCB]0.40[pCIB]0.60; JCPDS No. 37–1994. a = 15.623(5), b = 5.904(3), c = 4.178(3) Å, β = 113.26(2), V = 354.0 Å3, Dx = 2.105 Mg m−3 for [pBCB]0.30[pCIB]0.70; JCPDS No. 37–1995. a = 15.691(4), b = 5.913(3), c = 4.195(2)Å, β = 113.43(2)°, V = 357.1 Å3, Dx = 2.130 Mg m−3 for [pBCB]0.20[pCIB]0.80; JCPDS No. 37–1996. a = 15.759(4), b = 5.906(2), c = 4.204(2) Å, β = 113.55(2)°, V = 358.7 Å3, Dx = 2.164 Mg m−3 for [pBCB]0.10[pCIB]0.90; JCPDS No. 37–1999.
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    Incorporation of fast Fourier transforms to speed restrained least-squares refinement of protein structures (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 53-55 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Modifications to the restrained least-squares refinement program of Hendrickson & Konnert [Biomolecular Structure, Function, Conformation, and Evolution, edited by R. Srinivasan, pp. 43–57 (1980). Oxford: Pergamon Press] are described that result in dramatic acceleration of the refinement of protein structures. Proven fast-Fourier-transform-based algorithms for computing structure factors and least-squares matrix elements are incorporated that reduce up to a hundredfold the computation time required for a single cycle. The modified program is shown to give results comparable to refinement by conventional methods and has been successfully applied to the refinement of several protein crystal structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087144
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  • 196
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    Addition of symmetry-related contact restraints to PROTIN and PROLSQ (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 55-57 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Symmetry-related van der Waals contacts and hydrogen bonds are stereochemical restraints which are often ignored in macromolecular structure refinement programs. PROTIN and PROLSQ have been modified to account for symmetry-related contacts. The derivatives calculated for an atom in its symmetry-transformed position need only be multiplied by the appropriate rotation matrix to be applied to the atom in its untransformed position. Therefore the code already present in PROLSQ for van der Waals contacts is readily adapted to account for symmetry-related contacts. The `cubing' algorithm, shown to be much faster than residue-by-residue center and radius methods for generating potential contacts, has been incorporated in PROTIN.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087132
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  • 197
    Electronic Resource
    Electronic Resource
    An efficient algorithm for incommensurate structure refinement (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 57-59 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A least-squares algorithm to refine incommensurate structures in the framework of (3 + 1)-dimensional crystallographic symmetry is described in some detail. It is applicable to the cases of occupational and/or harmonic displacive modulation. Compact analytical expressions for the structure factor and its partial derivatives well suited for structure refinement by the least-squares method have been obtained. The efficiency of the algorithm is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087120
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  • 198
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    Electronic Resource
    Crystallographers (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 60-60 
    Details
    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/S0021889887087119
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  • 199
    Electronic Resource
    Electronic Resource
    New Commercial Products (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 60-60 
    Details
    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/S0021889887085996
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  • 200
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    Crystal chemistry and thermoelectric properties of Gd2Te3 (1987)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 20 (1987), S. 102-104 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Gd2Te3, Mr = 697.30, orthorhombic, Pnma, a = 12.009(9), b = 4.3012(6), c = 11.818(2) Å, V = 610.4(6) Å3, Z = 4, Dm = 7.384, Dx = 7.59 g cm−3, Mo Kα, λ = 0.71069 Å, μ = 357 cm−1, F(000) = 1136, room temperature, R = 0.033, 822 observed reflections. The redetermination confirms that Gd2Te3 is isostructural with Sb2S3 (stibnite). The reported solid-solution series Gd2Te3–Gd3Te4 does not exist. Gd–Te bond lengths vary from 3.104(1) to 3.240(3) Å and Gd is in sevenfold coordination. Gd2Te3 has a power factor S2/ρ = 0.6 × 10−6 V2 K−2 Ω−1 cm−1 at 1273 K. It is not suitable as a high-temperature thermoelectric material because it decomposes to GdTe which is metallic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889887087065
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