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  • Springer Nature  (3,956)
  • International Union of Crystallography (IUCr)  (1,369)
  • American Meteorological Society
  • 1975-1979  (6,098)
  • 1979  (6,098)
Collection
Publisher
Years
  • 1975-1979  (6,098)
Year
  • 1
    Electronic Resource
    Electronic Resource
    A review of my papers on crystal optics 1912 to 1968 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1-9 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The theory of the diffraction of X-rays by crystals was developed by Ewald as part of a unified study of the interaction of light of all wavelengths with crystals, beginning with the work for his 1912 thesis and extending to his papers in 1968. The formulation of the problem in terms of the interaction of electromagnetic radiation with a periodic array of dipoles is placed in its historical perspective and is compared with Laue's version based on the assumption of a continuous electron density distribution. The Borrmann effect, hinted at in 1917, is derived readily from consideration of the dispersion surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000024
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  • 2
    Electronic Resource
    Electronic Resource
    Conditional phase probability distributions of structure factors in a Karle–Hauptman matrix (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 105-107 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: From the joint probability distribution of all structure factors in a Karle-Hauptman matrix new phase probability distributions are obtained. These calculations lead to a reformulation of the maximum-determinant rule for phase determination. In addition a new function is derived whose maximum corresponds to the most probable values for the phases of an arbitrary subset of the structure factors in a Karle-Hauptman matrix. This function accounts for the interaction among phases in a Karle-Hauptman matrix through triple products and quartets simultaneously.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000188
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  • 3
    Electronic Resource
    Electronic Resource
    Ewald dynamical diffraction symposium (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1-1 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000012
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  • 4
    Electronic Resource
    Electronic Resource
    Permissible angles for coincidence-site-lattice rotations (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 255-259 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In addition to symmetry rotations (Σ = 1), lattices may admit coincidence-site-lattice (c.s.l.) rotations of various degrees of coincidence, Σ. The conditions for the occurrence of c.s.l, rotations are formulated in general terms by introducing the metric matrix of a lattice. When all lattices are considered, it is found that there are 4Σ possible values for the angle of rotation which give rise to a degree of coincidence Σ. These angles have cosines which are integral multiples of 1/2Σ. A particular lattice admits only some of these c.s.l, rotations. Cubic lattices are discussed in detail and it is shown that the number of permissible rotation angles for each odd value of Σ is approximately 3.414 × √Σ. Conversely, a particular rotation angle originates a c.s.l, of degree of coincidence Σ in those lattices which satisfy particular metric conditions. Finally, the effect of a uniform strain due to temperature or pressure changes is analysed, and it is shown that while symmetry rotations are invariant to this form of strain, only very few c.s.l, rotations are unaffected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000553
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  • 5
    Electronic Resource
    Electronic Resource
    Some consequences of the presence of antisymmetric atomic features in noncentrosymmetric structures (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 260-265 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Noncentrosymmetric structures are considered in terms of a generalized substructure formulation. Inclusion of dispersion, bonding and anharmonicity leads to generalized expressions for Bijvoet ratios. Methods of numerically estimating the effects due to bonding and anharmonicity upon the Bijvoet ratios are suggested. Allowance for bonding and anharmonicity is shown to have wide implications for the breakdown of Friedel's law. Subsets of reflections that obey Friedel's law in the conventional approximation are now shown to violate it. These violations are of considerable importance for measuring antisymmetric contributions due to bonding and anharmonic thermal vibrations. The possibility that bonding effects will result in the appearance of Bijvoet differences in noncentrosymmetric structures of elements is explored.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000565
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  • 6
    Electronic Resource
    Electronic Resource
    A priori estimates of errors in intensities for imperfectly spherical crystals (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 78-82 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A priori estimates of errors in intensities for spheres arising from non-sphericity in crystal shape may now be readily determined from a recently published table of (1/A*)(∂A*/∂μR) values [Flack & Vincent (1978). Acta Cryst. A34, 489-491] using an expression given by Jeffery & Rose [Acta Cryst. (1964), 17, 343-350]. However, a new relationship between σ(R) and σ(r) is determined. The effects of crystal radius, non-sphericity and wavelength on intensity errors are discussed. The importance to the selection of crystals for electron density measurements is stressed. Universal curves of σ(r)/r, the error due to non-sphericity, against μr calculated for a range of intensity errors at θ = 0 and 45 ° are given.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000140
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  • 7
    Electronic Resource
    Electronic Resource
    A simplified calculation and tabulation of tensorial covariants for magnetic point groups belonging to the same Laue class (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 95-101 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Four types of static tensors can be distinguished according to their parity with respect to space inversion and to time reversal. However, all magnetic point groups belonging to the same (oriented) Laue class consist, apart from inversions, of the same proper rotations. Tensors differing only by parities transform identically under the same proper rotations; their transformation properties under different groups of the same Laue class may therefore differ only by an additional change of sign, which depends on the tensor parity and on the way in which inversions are combined with proper rotations in a given group. It is shown that, for a certain natural choice of typical representations of magnetic point groups of the same Laue class, it is sufficient to calculate tensorial covariants (symmetry-adapted tensorial bases) of even parity with respect to both space inversion and time reversal for the group of proper rotations. Tensorial covariants of other parities and for other magnetic point groups of the same Laue class can then be obtained by the use of a simple conversion table and of parity arguments. The scheme is illustrated by an example from the Laue class D4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000164
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  • 8
    Electronic Resource
    Electronic Resource
    X-ray high-order refinements of hydrogen atoms: a theoretical approach (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 137-139 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Recent work in X-ray crystallography has demonstrated that reasonable nuclear H positional parameters can be obtained by refinements using high-order data only. A theoretical model for high-order refinements of H atoms has been developed which simulates the experimental results. For a suitable choice of the lower sin θ/λ cut-off, the H atoms are shown to refine to their actual nuclear positions. The calculations imply that the proper cut-off is indeed dependent on the type of atom to which the H is bonded, in agreement with experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000231
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  • 9
    Electronic Resource
    Electronic Resource
    On the treatment of protein data measured on the oscillation camera (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 146-157 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The method used in Oxford for the collection and reduction of protein data from the Arndt-Wonacott oscillation camera [Arndt, Champness, Phizackerley & Wonacott (1973). J. Appl. Cryst. 6, 457-463] is described. The photographs are digitized with an Optronics Photoscan P-1000 drum scanner operated in an off-line mode, and the magnetic tapes are subsequently processed on an ICL 1906A computer. Results are presented for the protein phosphorylase b. The estimation of standard deviations for both fully and partially recorded observations is discussed, and the intensities for these two categories of term are compared.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000267
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  • 10
    Electronic Resource
    Electronic Resource
    Extinction in sodium fluoride (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 176-180 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray intensity measurements for a single crystal of sodium fluoride obtained at four wavelengths by Howard & Jones [Acta Cryst. (1977). A33, 776-783] have been reanalysed using both the Cooper-Rouse and Becker-Coppens extinction formalisms in order to study the wavelength dependence of the extinction in this crystal, since the original analysis was unable to account for the wavelength dependence of the intensities of the strong reflections. The results indicate that the crystal is intermediate between type I and type II in nature and are consistent with the wavelength dependence predicted by the theories, although the extinction is not large enough at the shorter wavelengths to provide a useful test of the validity of the theoretical wavelength dependence. The analysis also demonstrates some of the possible consequences of the use of unbalanced weighting schemes and of inappropriate models for the scattering factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479000309
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