ALBERT

All Library Books, journals and Electronic Records Telegrafenberg

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • American Association for the Advancement of Science (AAAS)  (2,126)
  • International Union of Crystallography (IUCr)
  • Annual Reviews
  • 1980-1984  (4,128)
  • 1983  (4,128)
Collection
Publisher
Years
  • 1980-1984  (4,128)
Year
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 269-269 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: All exp (-i2πζ, exp(-iπζ/2), exp(-iπζ and exp(-i3πζ/2) in equations (21) in Onoda, Saeki & Kawada [Acta Cryst. (1980). A36, 952-957] are mis-expressed and to be replaced respectively by exp(i2πζ), exp (iπζ/2), exp (iπζ) and exp (i3πζ/2).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 2
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 282-286 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A partially analytic technique for the calculation of electron transmission functions used in multislice calculations is developed. This development utilizes the fact that atomic scattering amplitudes are generally available as fitting parameters to four Gaussians. The result is especially applicable to calculations with a large or infinite repeat distance in the incident-beam direction and initial test calculations give a time saving of a factor of four. Sample results are given for the calculation of images from an inclined stacking fault in gold.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 326-332 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A comparison is made of the treatments of absorption in the theories of secondary extinction by Werner [J. Appl. Phys. (1974), 45, 3246-3254] and by Becker & Coppens [Acta Cryst. (1974), A30, 129-147]. The Werner approach treats absorption and extinction together, whereas Becker & Coppens assume a prior correction for absorption, and make an approximate allowance for the effect of absorption on the extinction by modifying the parameter representing the effective crystal dimension. By consideration of the form of the corrections for a specially simple crystal shape, it is shown that the Becker & Coppens method predicts slightly greater extinction than does the unified treatment of Werner. However, the difference is small, and likely to be unimportant in practice The Werner solution of the Hamilton-Zachariasen transfer equations is exact, but not easy to use. The Becker & Coppens results are approximate, but they are presented in a form convenient for computation.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 377-387 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Generalized relations relating multipole population parameters to d-orbital occupancies of transition-metal atoms are presented. The relations are cast in the form of a 15 × 15 matrix which reduces to smaller size for site symmetries higher than {\bar 1}. The matrix takes into account differences in normalization of density functions and atomic orbitals. The expressions are applied to diffraction data on Cr(CO)6, Mn2(CO)10, Co2(CO)8, Co3(CO)9CH, Co(NH3)6Cr(CN)6 and Co(NH3)6- Co(CN)6. In all cases crystal-field destabilized orbitals are depopulated relative to stabilized orbitals. Results are in almost quantitative agreement with theoretical populations; small remaining discrepancies are to be analyzed further for their possible significance. Occupancy of e'g orbitals in the last two compounds indicates a degree of covalency of the metal-ligand interaction in these low-spin complexes which is larger for the cyano ligand than for the ammonia molecule in agreement with generally accepted conclusions based on spectroscopic data. Very little difference is observed between the relative orbital occupancies of the Cr(CN)3-6 and Cr(CO)6 species.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 422-422 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: As a result of a printer's error, Figs. 9(a) and 9(b) in Smith & O'Keefe [Acta Cryst. (1983), A39, 139-148] have been transposed, so that (a) is labelled (b) and (b) is labelled (a).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 481-499 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 503-503 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 9
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 512-515 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Statistical methodology originally introduced by French & Wilson [Acta Cryst. (1978). A34, 517-525] for the treatment of negative-intensity observations is shown to be useful for the estimation of anomalous-scattering differences. The general principles of this method are described, along with applications to data from a lead derivative of the enzyme carboxypeptidase A.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 10
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 533-538 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A discussion is given on simple grounds, not explicitly involving the dynamical deformation formalism, of the implications of having the outer part of the electron distribution vibrating significantly differently from the core. The use of a lattice dynamical shell model to represent this effect is examined in some detail, with particular reference to the framework within which such a model gives meaningful results. Predictions are given from the 14-parameter shell models and the 11-parameter valence-shell models for the difference between Debye-Waller B values of the shells and cores and also for the effective Debye-Waller factors for the deforming ions in 14 zinc-blende-structure compounds. It is concluded that the effective X-ray Debye-Waller B at very small sin θ/λ is typically several percent smaller than the core B value, owing to a very substantial reduction in the mean-square displacements of shells compared with cores. Results are also given for the 15-parameter deformation-dipole models for eight materials. These show effects broadly comparable in magnitude to the shell models but more varied in detail. Notably, some models show for the first time a larger rather than smaller Debye-Waller factor for the deforming ion.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 11
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 562-565 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: With the help of conditional probabilities formulas are derived for the first and second moment of R2 as a function of the size of the model. The formulas are valid in the space group P{\bar 1} for two extreme cases, viz completely correct and completely incorrect models. Incorporation of the observed intensities enables one to obtain accurate a priori estimates of (R2) and σ(R2). The theory agrees very well with simulated experiments.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 12
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 597-597 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 13
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 191-191 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 14
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 202-207 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The importance of carrying out TDS corrections is emphasized. Their relative effect on the derived temperature parameter values is discussed and shown to rely primarily on the experimental conditions and not on the softness of the crystal.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 15
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 245-251 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: 'Symmetrized' components are introduced in place of the standard ones to improve the method presented in paper I [Fumi & Ripamonti (1980). Acta Cryst. A36, 535-551]. These components, which are simply related to the standard ones, allow a further reduction of the computational task and also a further simplification of the results and of their use. This is illustrated by application to general two-dimensional tensors of ranks 6 and 8 and by particularization of the results to the cases of the third- and fourth-order elastic tensors.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 16
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 269-269 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Mis-expressed terms in equations (13) in Onoda & Kawada [Acta Cryst. (1980), A36, 134-139] should be corrected. All exp(--i2πζ, exp(-iπζ/2), exp(-iπζ and exp(-i3πζ/2) on page 137 are to be replaced respectively by exp(i2πζ), exp (iπζ/2), exp (iπζ) and exp (i3πζ/2).
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 17
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 270-271 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 18
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 272-272 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 19
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 693-697 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A correct calculation of the scale factor between the diffraction data of isomorphous crystals is shown on the basis of a statistics criterion. This scale factor requires no additional refinement, improves the signal-to-noise ratio of difference Patterson maps and Wilson's statistics and allows an estimation of the degree of non-isomorphism. The method has been tested for the 3 Å data sets of protein γ-crystallin crystals and a few of its heavy-atom isomorphous derivatives.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 20
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 740-746 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: High-angle X-ray diffuse scattering has been measured in a volume element in reciprocal space for a Ni-12.7 at.% Al alloy single crystal quenched from 1323 K. The Cowley-Warren order parameters were determined after separation of the first- and second-order size effects, using a procedure based on the Borie-Sparks quadratic approximation of atomic displacements. The experimental order coefficients were used to reconstruct the real-space locally ordered distribution of atoms, from which the spectrum of nearest-neighbor atomic configurations was determined. Some 61% of the Al atoms were found to be in a planar ordered configuration consisting of a nickel atom and four nearest-neighbor aluminum atoms, the basic structural unit of Ni3Al. These planar elementary ordered units were, of course, distributed on the three equivalent {100} planes. While most of the ordered 'domains' consisted of from one to three Ni3Al rings, a few domains were found to contain on the order of a hundred such elementary ordered units. The larger ordered domains may be thought of as embryos of the ordered Ni3Al phase which have formed during quenching of the bulk alloy single crystal. There is evidence that the spatial distribution of ordered domains is not random.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 21
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 767-772 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Experimental topographs may be simulated by addition of simulations where one point source is lit on the surface of the crystal. The accuracy of a varying-step integration of Takagi equations is good enough to allow such computations. It is shown that all parts of the contrast are sensitive to the width of the entrance slit and that accurate characterization of defects must take this parameter into account.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 22
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 548-552 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray intensity measurements from an extended-face single crystal of cubic zinc selenide obtained by Mcintyre, Moss & Barnea [Acta Cryst. (1980), A36, 482-490] have been reanalysed with a view to explaining the unresolved discrepancies between theory and experiment present in the original analysis of the most severely extinguished reflections. The results obtained are shown to complement the recent findings of a wavelength-dependent study using the same crystal specimen [Stevenson & Barnea (1983). Acta Cryst. A39, 538-547] and foreshadow the need to allow for the presence of the Borrmann effect.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 23
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 813-817 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A procedure is presented for three-dimensional refinement of heavy-atom parameters without the use of phase information in the methods of single and multiple isomorphous replacement. This procedure is based on the Patterson-function correlation method of Rossmann [Acta Cryst. (1960), 13, 221-226] except that the origins of the Patterson functions are now removed from this correlation and centric and acentric reflections are treated separately. The resulting procedure is shown theoretically and by application to three test cases to yield accurate and essentially unbiased estimates of the occupancies, thermal parameters, and positions of heavy-atom sites.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 24
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 824-824 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 25
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 597-598 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 26
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 598-598 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 27
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 647-650 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The recently published thermal parameters of Ba, Na, Mg, Ni, and NH4 thiosulphates have been analysed for the rigid-body motion of the S2O2-3 group using the TL and TLS treatments. In the cases of Ba, Na and NH4 the rigidity of the group has been established and justified by employing various rigidity tests. Librational corrections to bond lengths have been found to be appreciable. For the cases of Mg and Ni the rigidity has been observed, but due to high e.s.d.'s detailed analysis has not been made. Hamilton's test has shown that the TLS treatment is preferable to the TL in all cases.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 28
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 899-901 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: If electron density distributions of different provenance need to be compared, the evaluation of the charge contents of peaks in deformation densities is useful (besides the usual comparison of density sections). Since deformation peaks are often of approximately ellipsoidal shape, a procedure is proposed in which a rotation ellipsoid is placed in the peak position so that it encloses the peak and separates it from the neighbouring peaks. The charge contents of the peaks are calculated by numerical integration where positive; zero and negative values of the electron density are treated separately. This can be achieved by a minor alteration of a standard Fourier program. Numerical results are presented for p-dicyanobenzene. The C-C bond peaks contain 0.19-0.26 electrons, and the C-N bond peak about 0.26 electrons.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The average value of the residual R2 and its spread σ(R2) is described as a function of a threshold a, below which Eo2 values are omitted from the data set. Theoretical expressions, valid for finite data sets in the space groups P1 and P{\bar 1}, are derived for (R2) and σ(R2) as functions of a for models containing atoms correctly as well as incorrectly positioned. Use of a threshold causes a decrease in the resolving power of R2-based strategies used in automated structure evaluations. Random elimination of Eo values gives rise to a larger loss of resolving power than does the elimination of small Eo values.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 30
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 948-949 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 31
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 941-946 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In calculating the lattice-energy hypersurface by the systematic variation of the molecular rigid-body parameters and the lattice constants, the ranges to be scanned depend on the molecular symmetry and on the space group. A generalization of Hirshfeld's approach [Hirshfeld (1968). Acta Cryst. A24, 301-311] applicable to the case of variable lattice constants is suggested. The symmetry of the multidimensional parameter space is defined by the direct product of the molecular point group and a normalizer NA(F) of the space group F. The normalizer NA (F) is a group of affine transformations of the crystal axes that leave invariant the coordinates of equivalent positions. An asymmetric unit of the parameter space is obtained through keeping the lattice constants within such ranges that satisfy the Niggli reduced-cell conditions.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 32
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 187-187 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 33
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 189-190 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 34
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 287-297 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A refinement of earlier models used to compute intensity distributions for the diffuse to phase is described. The model includes both faulted to regions and untransformed b.c.c. regions. The diffuse intensity generated by this model is compared with experiment. A result of this calculation is that, unlike its predecessors, it causes the observed diffuse maxima under the sharp fundamental Bragg reflections. The model is shown to be compatible with measurements of the integrated intensities of the fundamental reflections. A correction to our single-variant intensity calculation to account for interference effects among the variants is displayed. Our result is compared with those of other structural models for the diffuse to phase, and the implications of its details are discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 35
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 322-325 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Mass attenuation coefficients for pyrolytic graphite have been determined by an X-ray energy-dispersive method with a relative experimental error of about 0.5%. Results are given for the Fe, Co, Cu and Mo Kα1 and Kβ1 lines.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 36
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 411-415 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The relationships associating the structure amplitudes, measured in a diffraction experiment, with the diamagnetic susceptibility and the static electron polarizability of ions for crystals with the NaCl-type structure are obtained. The calculations, carried out for a number of alkali halides and alkaline-earth oxides, have shown a good coincidence with the results of magnetic and optical measurements. The accuracy of the obtained results is analyzed; it is shown that when using accurate diffraction data the diamagnetic susceptibility and the electron polarizability may be determined with an accuracy of about 1%.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 37
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 425-480 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 38
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 576-584 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The small-angle approximation usually encountered in dynamical theories of fast electrons essentially leads to a transformation of the propagation-direction variable z into a time-like parameter [Berry (1971). J. Phys. C, 4, 697-722]. The three-dimensional stationary Schrödinger equation is then approximated by a two-dimensional 'time'-dependent equation which may be solved by using the standard time-perturbation techniques encountered in quantum mechanics. The basic idea of the present approach consists in studying the evolution operator U(z,z0) instead of the wave function. Depending on the choice of bases, the matrix elements of U(z,z0) represent either the transition probabilities of diffraction or the kernel function of the propagation issued from Feynman-path integral theory [Berry & Mount (1972). Rep. Prog. Phys. 35, 315-397; Van Dyck (1975). Phys. Status Solidi, 72, 321-336; Jap & Glaeser (1978). Acta Cryst. A34, 94-102]. Special attention is devoted to the so-called 'Bloch waves' and 'physical-optics' formulations which both correspond to the same perturbation expansion but with two different unperturbed 'Hamiltonians'.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 39
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 14-21 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In a previous paper [Moss & Feil (1981). Acta Cryst. A37, 414-421] a method was reported to calculate the electrostatic potential and the electrostatic interaction energy from single-crystal X-ray diffraction data. The method was applied to experimental pyrazine data; however, owing to the relatively low quality of the data, the results were inconclusive. In the present paper the results are presented of a model study in which the method has been applied to the analysis of ideal error-free diffraction data calculated from a theoretical wavefunction. The molecular quadrupole moments and the electrostatic interaction energies of two pyrazine molecules thus obtained are in very good agreement with the corresponding results derived directly from the wavefunction. Thus the proposed method may be used to determine the long-range electrostatic component of molecular interactions from highly accurate X-ray diffraction data.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 40
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 1-13 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Lattice dynamical calculations to the full accuracy of the models are presented for the Debye-Waller B values for 17 zinc-blende-structure materials over the temperature range 1 to 1000 K (where appropriate). The materials are GaP, GaSb, GaAs, InP, InSb, InAs, ZnO, ZnS, ZnSe, ZnTe, CdTe, HgSe, HgTe, CuCl, CuBr, CuI and SiC. The models considered were the best lattice dynamical models available that have been fitted to phonon frequencies measured by neutron scattering. These include the shell model, the valence-shell model, the deformation-dipole model, the deformation-ion model and the rigid-ion model. From one to five models were used for each material, depending on the availability of published parameters. For some materials different parametrizations of the same model were examined. Intermodel comparisons show that the substantial difference in B values predicted by different models is attributable principally to the different eigenvectors they produce. Comparisons with fairly recent experimental results highlight the paucity of reliable measured values as a function of temperature and the unreliability and frequent inadequacy of models. The 14-parameter shell model is generally found to be the best.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 41
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 26-28 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Application of limit theorems valid for large values of the sum of independent random variables shows that for an equiatomic structure with n atoms in the asymmetric unit in the space group P{\bar 1} the probability density distribution of the structure amplitude F for |F| large is p( x ) dx = [ n/2 π(1 - x2)]1/2 ( e /π)n/2 (1 - x )(n - 1)/2 dx where x = F/2nf is the unitary structure amplitude and f is the atomic scattering factor. The expression will be somewhat different for other space groups.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 42
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 74-76 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two questions which have been independently studied (the distribution of colors in colored lattices and lattice preservation in derivative lattices) are in fact closely related. It is possible, for instance, to determine the distribution of colors in rows and nets by the lattice-preservation indices cr and cp as functions of row indices [u0, v0, W0] and net indices (h0, k0, l0), respectively. A formula is also given for the number of classes of equivalent derivative lattices of a given index n.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 43
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 193-196 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract In recent years there have been a number of developments in direct methods involving refinement processes applied to initially random sets of phases. Procedures which have been used for refinement include least-squares and gradient methods applied to triple-phase relationships expressed as linear equations and also the tangent formula. In the present investigation seven functions are investigated for the refinement of random phases; because of the awkward form of these functions the refinement process used is based on a parameter-shift algorithm. Some of the functions appear to be more effective than others but the most effective one was discovered through making a mistake with one of the others and no rational explanation for its efficacy can be given. Trials have been made with known structures and with three unknown structures which were originally solved by the processes described in the paper.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 44
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 216-224 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: This paper describes a file structure that has been developed by a joint working party of the Data and Computing Commissions of the International Union of Crystallography. It is intended as a standard that can be used by those wishing to transfer any type of crystallographic data from one laboratory or program system to another.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 45
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 38-46 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The resolution function of a three-axis, X-ray spectrometer is considered for the case when the monochromator and analyser crystals are ideally perfect. It is shown that, for X-ray sources which produce either an ill-collimated monochromatic beam (conventional source) or a well-collimated white beam (synchrotron radiation), the resolution problem may be simplified. This simplification allows the profile of an arbitrary section of the resolution function to be expressed as a one-dimensional integral of the product of three functions; one to represent the source characteristics and the other two to describe the Darwin profiles of the monochromator and analyser crystals. The formalism is extended to describe the measurement of the resolution function by a perfect crystal mounted on the sample table of the spectrometer. Comparison of the a priori calculations with measurements made on a spectrometer at a conventional source yields very good agreement.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 46
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 90-94 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Programs have been written to calculate TDS corrections from Long Wave eigenvectors and modelled frequency Dispersion of the acoustic branches (LWD approximation). Calculations on naphthalene crystals with neutral and with charged atoms were carried out to check the convergence of the lattice dynamical calculations and of the numerical integration procedures used in the programs.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 47
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 98-101 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The relation Sp = SL SR between the signs of the triplet phase products Sp, the multiple diffraction line profiles SL and the crystal lattice rotations SR is applied to the structure determination of a centrosymmetric Cs10Ga6Se14 crystal [space group C2/m, a = 18.233 (7), b = 12.889 (5), c = 9.668 (3) Å, β = 108.2°, z = 2]. This structure could not be solved by the ordinary MULTAN program, including MUL TAN-80. From the profile analysis of the multiple diffraction pattern of 311 using a four-circle single-crystal diffractometer with Cu Kα radiation, 12 phase relations among closely linked reflections are determined. Four possible sets of 14 reflection phases are deduced. Using these four sets as the starting phases for MULTAN-74, 225 correct phases are developed. The final E map shows all the atomic positions of Cs, Ga and Se. The structure refinement gives R = 0.047, Rw = 0.053 [1907 reflections with I 〉 2σ(I)]. Details about the procedure are given.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 48
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 192-192 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 49
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 225-233 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The well-known acentric and centric distributions apply, asymptotically in the number of atoms in the unit cell, when there is no crystallographic symmetry or centrosymmetry only. Series expansions, involving Laguerre or Hermite polynomials, can be obtained, which take into account paucity of (heterogeneous) atoms and higher space-group symmetries. The asymptotic as well as the generalized distributions are further modified if (i) the crystal exhibits partial (non-space group) symmetry, and (ii) if some atoms exhibit appreciable dispersion. This article deals with the generalization of the asymptotic 'subcentric' distribution of the normalized intensity P(z) dz = (α2 - β2)1/2 exp(-αz) I0(βz) dz which accommodates both partial (non-crystallographic) centrosymmetry and effects of dispersion. A four-term Gram-Charlier expansion with appropriate orthogonal polynomials has been derived for the subcentric distribution and detailed expressions for the required moments of z have been obtained for the case of dispersion. This generalization, i.e. the orthogonal polynomials, the moments of z and the asymptotic subcentric distribution, incorporates the generalized acentric and dispersionless centric expansions as limiting cases. The above derivation has been brought to completion using computer-algebraic techniques, which permit the use of well-established but rarely used mathematical methods in an ab-initio generalization of a given asymptotic distribution of intensity.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 50
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 257-268 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Internal strain tensors describe the relative displacements of sublattices in stressed crystals in which some atoms occupy sites lacking inversion symmetry. The variation of |F(H)|2 in such crystals is shown to depend on inner compliance tensors which are essentially products of internal strain tensors with the macroscopic elastic compliance tensor. The forms of the inner compliance tensors and the uniaxial stress derivatives of |F(H)|2 are tabulated for 20 simple crystal structures in which the number of atoms per lattice point is 2, 3 or 4.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 51
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 148-158 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A general method for describing multimodal atomic densities is presented. It is based on series expansions of a harmonic Gaussian probability density function. The most suitable expansion is of the Gram-Charlier type; its Fourier transform can be easily inserted in a structure factor equation. This statistical method yields a satisfactory fit to the data and allows for a better interpretation of the fit parameters than sophisticated split-atom models. The method is especially useful for weakly resolved modes and allows a better distinction between disorder and anharmonic motion than in conventional Fourier syntheses. Calculations on CsPbCl3, ice Ih and RbAg4I5 are presented to show the strengths and the limitations of this method.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 52
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 139-148 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The conditions appropriate for direct structure imaging of silicon carbide polytypes in the high-resolution electron microscope have been investigated. Weak-phase-object calculations confirm that a resolution of better than 2.5 Å is necessary before polytypic stacking sequences can be identified directly. Furthermore, resolutions closely approaching 1 Å are required to resolve projected pairs of Si-C atoms, and considerably better than 1 Å is necessary to differentiate between the two species. Extensive multi-slice calculations, based on both current and projected electron-optical characteristics, show that polytype stacking should be recognizable at 500 kV up to thicknesses of 45-75 Å, but not at 100 kV, except possibly at the 'reversed' Scherzer defocus position with extremely coherent illumination. The occurrence of Fourier images complicates recognition of the correct objective-lens defocus particularly for thin crystals of the 3C polytype. In thicker-crystal regions (≥ 100 Å), where linear image contributions are small, mutual interference between diffracted beams results generally in polytype images of apparently improved resolution and, at specific thickness and defocus values, leads to images of 3C resembling the 'atom-pair' configuration. The latter are then explained by consideration of the image amplitude and intensity spectra. Finally, the problems of recovering specimen structure from crystals of intermediate thickness, as well as some of the factors affecting any quantitative experimental studies, are briefly discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 53
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 171-173 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The calculation of the diffraction from a one-dimensionally disordered crystal is shown to be easier using the matrix (M) method than with the probability tree (PT) method. If the order of the difference equation is high, an analytical solution cannot be obtained by the PT method unless the model is highly simplified. There is no such limitation in the M method.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 54
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 173-173 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Corrections are given for two of the coefficients for the analytical approximations to X-ray scattering factors in Table 2.2B of International Tables for X-ray Crystallography [(1974), Vol. IV. Birmingham: Kynoch press]. For Ru+4 (p. 100), the coefficient b3 should be 0.036495 rather than 0.36495; for Bi+5 (p. 101), the coefficient b2 should be 0.039042 rather than 0.39042.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 55
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 191-192 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 56
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 599-600 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 57
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 600-600 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 58
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 622-631 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A general method for phase extension and refinement is described. It consists of minimizing a conveniently defined functional {\tt M} by the steepest-descent or conjugate-gradient techniques. This functional consists of a term R = ½ Σ (|F| - |Fobs|)2 plus any given number of constraint equations selected according to the requirements of the particular problem considered. Several examples of the introduction of constraints are described in detail, both in direct and reciprocal space, and a few one-dimensional tests provide insight in the behavior of the different alternatives. Also, some general features that the calculated electron density function should fulfil, such as positivity and boundness, are directly introduced without the need of terms other than R in the functional {\tt M}. The connection between this approach and the ones which use the principle of maximum entropy is discussed. A critical analysis shows that those methods are just different ways of minimizing R with the constraints of positivity.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 59
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 651-658 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The nematic type I lyomesophase of K laurate/ KC1/water is studied by X-ray diffraction and optical microscopy. X-ray diffraction patterns of samples in very thin capillaries and chemically surface-treated capillaries indicate the existence of a hexagonal array of cylindrical micelles. In normal conditions, where only one oriented band is observed, it is possible to describe the lyomesophase structure as nematic. An analysis of the band width is made by comparing the experimental scattering curves with theoretical expressions obtained from different models. This analysis indicates that micellar positional correlations have to be introduced to explain the experimental results.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 60
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 407-410 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The conventional crystallographic least-squares procedure has been compared with a robust/resistant modification in which the weight of each reflection is multiplied by a function of the ratio of its residual to a resistant measure of the width of the residual distribution on the previous cycle. Three synthetic data sets were created by adding random errors, according to various probability distributions, to the calculated structure factors for a known crystal structure. A set with a Gaussian error distribution was refined with two sets of weights: one assigned correctly in proportion to the reciprocals of the variances of the data points, the other using unit weights throughout. The second error distribution was Gaussian contaminated by 10% drawn from another Gaussian distribution with its variance nine times greater. The third distribution was a long-tailed distribution derived by dividing a random variable with a Gaussian distribution by an independent random variable with a uniform distribution. Each of the first three cases was refined to convergence using both conventional and robust/resistant procedures, with the modified procedure leading to a result at least as close to the known structure as the conventional procedure. In the fourth case, the conventional procedure gave a poor fit, but the robust/ resistant procedure converged to a reasonable approximation to the correct structure.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 61
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 500-500 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 62
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 753-755 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The polarization ratio for a repeatedly reflected X-ray beam has been calculated, assuming the Darwin formulism, in the case where the diffracting planes of the crystals are parallel. It is shown that polarization ratios lie closer to unity than those obtained using the kinematic approximation. The integrated intensities and polarization ratios from a double-crystal spectrometer are discussed. The polarization ratio for a graphite monochromator has been measured experimentally and shown to be close to the value predicted by the Darwin theory and significantly different from the kinematic value.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 63
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 756-761 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Probability methods are used to investigate the effect of random errors on partially phased Fourier maps of non-centrosymmetric structures. Two sources of error are considered: (i) inaccuracies in the atomic coordinates of the phasing model; (ii) errors in the observed structure-factor magnitudes. Expressions for both the error level in the unit cell and the peak heights at the atomic positions are derived. The results are illustrated for neutron diffraction studies of proteins.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 64
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 800-805 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: On the basis of some mathematical and physical characteristics of isomorphous-replacement experiments, it has been possible to derive a simple rule called Riso that permits the selection of those triplet phase invariants that have values close to zero or π. Test examples show that large numbers of invariants may be evaluated by means of Riso with reliabilities that are potentially high, but depend, of course, on the reliability of the experimental data. In order to apply the rule, it is not necessary to know the chemical nature of the substituent atoms, their positions in the structure or their occupancy. The rule Riso affords new insights into the inter-relationships among isomorphous-replacement data and an alternative selection method to the use of the conditional joint probability distribution. A formula has also been derived for estimating the value of the cosine of triplet phase invariants for the native substance, cos (φhP + φkP + φ(h + k)P), in terms of measured structure factor magnitudes and structure factor magnitudes associated with the contribution from substituent atoms.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 65
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 819-820 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: For roughly isotropic and orthic cases the variance of Ueq is about one-sixth of the average of the variances of U11, U22, and U33, i.e. only about one-half of what would be estimated on ignoring the covariances of the diagonal elements of U.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 66
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 818-819 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The paper by Zhao, Lu & Lagally [Acta Cryst. (1982), A38, 800-802] is commented on and compared with a previous paper by Bertaut [Acta Cryst. (1950), 3, 14-18].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 67
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 823-823 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 68
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 825-837 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Tables of dynamic extinction lines which occur in convergent-beam electron diffraction patterns (GM lines) are given for all the space groups on the basis of the rules given by Gjønnes & Moodie [Acta Cryst. (1965), 19, 65-67]. It is found that 191 space groups can be identified by GM lines. A convenient experimental method which distinguishes a screw axis and a glide plane is demonstrated. Experimental results are shown in which the GM lines due to a screw axis and those due to a glide plane are separately observed. The GM lines appearing in a symmetrical four-beam pattern are demonstrated.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 69
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 615-621 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The eighth moment of the magnitude of the trigonometric structure factor has been computed for all the space groups and all the reflection subsets giving rise to different functional forms of this quantity. This extension of previously published computations of lower moments permits the construction of four-term generalized distributions of normalized intensity, which are necessary in treating problems arising from highly heterogeneous atomic compositions in various space-group symmetries. The related problem of odd-even mixed partial moments of the trigonometric structure factor has also been investigated, and these mixed moments were found to vanish for all the three-dimensional space groups, confirming the correctness of the hitherto published theoretical statistics. Similar computations for the plane groups showed that non-zero values of the mixed partial odd-even moments are obtained for p3, p31m, p3ml, p6 and p6m. This result calls for some modifications of the statistical formalism to be applied to two-dimensional sets of intensity data. The modifications required for the centrosymmetric case are indicated in some detail.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 70
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 671-678 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: For a number of incommensurate crystal phases with a one-dimensional modulation and for all those with a higher-dimensional modulation which are known to the authors, the Bravais class is determined. This is done partly to illustrate the use of the complete list of Bravais classes published in a previous paper [Janner, Janssen & de Wolff (1983). Acta Cryst. A39, 658-666] partly to give an overview of the crystals having higher-dimensional modulation.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 71
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 679-682 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The fundamental equations for dynamical magnetic neutron diffraction including an external magnetic field are given. The reflecting power is calculated for some special cases for asymmetrical Laue geometry. Some Pendellösung effects are discussed. Analytical and numerical results for the integrated reflecting power are presented
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 72
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 907-915 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Euclidean normalizers of space groups form the appropriate mathematical tool for several problems treated independently by crystallographers in the past, e.g. the comparison, the classification and the standardized description of crystal structures. Explicit tables are presented that enable the user to handle Euclidean normalizers in an easy way and, especially, to calculate all descriptions of a crystal structure compatible with a chosen space-group setting. The use of the tables is illustrated by different examples, and the role of Euclidean normalizers for crystal-structure determination is discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 73
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: First and second moments of P(R2) are evaluated for models denoted symbolically by {g, f; a}, containing a atoms known a priori to be correct, g (new) atoms correctly and f (new) atoms incorrectly placed. Formulas are derived, valid for the space groups P1 and P{\bar 1}, using explicitly the set of observed reflections as well as the a priori knowledge about the a atoms. It is demonstrated that the implementation of the latter information decreases σ(R2) and enhances considerably the resolving power of R2-based criteria to discriminate between a correct and an incorrect model.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 74
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 946-947 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The resolution attained with a JEOL 200CX electron microscope in top-entry configuration has allowed the direct elucidation of the structure of tetrahedrally bonded compounds. Computer simulation methods were used to calculate through-focus series of images at a range of thicknesses and the conditions for which structural features are interpretable on an atomic scale have been ascertained. In particular, various polytypes are differentiated and stacking faults are intuitively interpreted.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 75
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 868-875 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The concepts of semi-direct product, quasi semi-direct product and the method of constructing quasisymmetry (P-symmetry) groups [Krishnamurty, Prasad & Rama Mohana Rao (1978). J. Phys. A, 11, 805-811; (1980). J. Phys. A, 13, 1947-1956] have been explored and a general method of constructing quasisymmetry (P-symmetry) groups with the crystallographic space groups as generators is suggested. The study is restricted to only the cubic system for the chosen boundary condition Tx2 = Ty2 = Tz2 = E. The minor quasisymmetry cubic space groups so obtained are associated with the one-dimensional complex and two-dimensional real irreducible representations of the generator groups using the ideas of little groups and their one-dimensional allowable irreducible representations. The symmorphic cubic space groups F23, F432 and the non-symmorphic cubic space groups Fd3, Fd3m are exemplified. For the rest of the cubic space groups the results obtained are tabulated. Some suggestions have been made as to the possible studies in which the groups obtained here can be applied.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 76
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 642-646 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The formalism of the optical coherence has been applied to the description of the Bragg-case dynamical X-ray diffraction from crystals with randomly distributed amorphous spheres. Explicit formulas have been found for the reflection curves of such crystals in the first and second approximations of the iterative solution of the Takagi equations. It is shown that if the coherent plane wave falls on the crystal the diffracted wave consists of two parts - the plane coherent wave (which corresponds to the diffraction from a perfect crystal with a modified value of the Debye-Waller factor) and the partially coherent wave (diffusion scattering). The form of the partially coherent contribution to the reflection curve is discussed and its dependence on the defect diameter and the defect concentration. From the curves the integrated intensities are obtained. It is proved that the integrated intensity of the waves diffracted from such crystals depends linearly on the relative disturbed volume of the crystal and in the first approximation it does not depend on the defect diameter if this volume remains constant.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 77
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 658-666 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A full classification is given of the Bravais classes of lattices of symmetry groups of incommensurate crystal phases with an internal (additional) dimensionality d lower than four. These Bravais classes form the basis for the derivation of superspace groups needed for the symmetry classification of incommensurate crystal phases. By means of examples it is indicated how the information contained in the various tables can be extracted and used, for example, for the derivation of superspace groups.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 78
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 682-685 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The integrated reflecting powers of two nuclear and one magnetic reflexions of a DyFeO3 crystal have been measured. The results indicate that dynamical magnetic diffraction occurs. In addition, the integrated reflecting power of the magnetic reflexion was measured as a function of the magnetic field applied to the crystal, The results are discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 79
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 685-692 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The joint probability distribution method is applied in order to estimate phases when part of the crystal structure is correctly positioned. The mathematical approach is briefly described and the conclusive formulas are compared with those given by previous authors.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 80
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 711-718 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The application of dynamical diffraction theory to the 'phase problem' for centric crystals shows that the intensities diffracted in simultaneous three-beam interactions display characteristic maxima and minima. The sequence in Which these appear on chart recordings is a sensitive function of the phase of the triplet involved in the interaction. The sequence is the same for all triplet phases of the same sign; it is reversed for those of the opposite sign. In earlier work a number of triplet phases in perfect crystals were determined. In the present work, several hundred triplet phases in mosaic crystals have been determined. Details of one of these investigations are reported in the following paper [Gong & Post (1983). Acta Cryst. A39, 719-724].
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 81
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 706-711 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The influence of hydrogen/deuterium exchange on the intensity scattered by solutions of globular particles in neutron small-angle scattering experiments in 2H2O/1H2O buffers has been calculated. By separating the contribution of the change of the average scattering density of the solute from that of the inhomogeneities of the distribution of exchangeable hydrogens, equations similar to the classical equations of Stuhrman & Kirste [Z. Phys. Chem. (Frankfurt am Main) (1965), 46, 247-250] and Ibel & Stuhrman [J. MoI. Biol. (1975), 93, 255-265] are obtained. But the equations contain a contribution from the contrast-dependent fluctuations, and the geometrical parameters of the particle can no longer be simply extracted from a contrast variation study, if exchangeable hydrogens are not homogeneously distributed throughout the particle. Several examples are discussed and the potentialities of contrast variation in neutron and X-ray small-angle scattering" are compared.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 82
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 719-724 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The signs of large numbers of phases of reflections from centrosymmetric crystals of ZnWO4 have been determined by methods outlined by Post [Acta Cryst. (1979), A35, 17-21; (1983), A39, 711-718]. Fifty-three n-beam interactions were selected to illustrate the phase determination procedure. Methods of extracting three-beam phase information from such interactions are discussed and illustrated.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 83
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 94-97 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The least-squares refinement of macromolecular structures is characterized by a low ratio of observed data to refined parameters. Efforts have been made to compensate for this problem by incorporating subsidiary restraints into the observational equations. In this paper, a method is proposed and examples given for the introduction of additional observations into a least- squares refinement in the form of experimental phase information.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 84
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 123-130 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Hyperstereographic projections have been prepared (in the form of stereo-pairs) of the sixteen four-dimensional (geometric) crystal classes that contain only symmetry operations of order not greater than 2. These provide an initial demonstration of the usefulness of the hyperstereographic projection in visualizing the nature of four-dimensional symmetry elements and symmetry groups. The clarification thus introduced into the subject has suggested a rationalized system of symbolic nomenclature following the general principles of the Hermann-Mauguin notation.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 85
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 158-166 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Absorption effects usually present the most serious source of systematic error in the determination of structure factors from single-crystal X-ray diffraction measurements if the crystal is not ground to a sphere or cylinder. A novel method is proposed for the correction of these effects for data collected on a diffractometer. The method works from the premise that the manifestation of systematic errors due to absorption, unlike most other sources of systematic error, will not be evenly distributed through reciprocal space, but will be localized. A Fourier series in the polar angles of the incident and diffracted beam paths is used to model an absorption surface for the difference between the observed and calculated structure factors. Knowledge of crystal dimensions or linear absorption coefficient is not required, and the method does not necessitate the measurement of azimuthal scans or any extra data beyond the unique set. Moreover, application of the correction is not dependent upon the Laue symmetry of the crystal or the geometry of the diffractometer. The method is compared with other commonly used corrections and results are presented which demonstrate its potential.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 86
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 207-210 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The theory of X-ray diffraction by ideal crystals under the conditions when the incident and diffracted beams are directed at small angles to the entrance surface of a crystal has been developed. Besides the diffracted wave propagating inside the crystal (i.e. Laue-case diffraction) there are two specular reflected waves arising from incident and diffracted waves respectively. Such a diffraction scheme has been recently put into practice [Marra, Eisenberger & Cho (1979). J. Appl. Phys. 50, 6927-6933]. It is found that at small glancing angles of incidence there exist directions in which the intensity of the reflected diffracted wave is close to the incident wave intensity, while both the specular reflected wave and diffracted wave intensities are close to zero. The analytical expressions are obtained for the diffraction curve shape. It is shown that for diffraction curve measurements high collimation through the glancing angle of incidence of X-rays on the crystal, &PHgr;, is sufficient. There is no need to provide collimation through parameter a denoting deviation from exact Bragg conditions. Owing to the rigid relation between α, &PHgr; and the angle of emergence of the reflected diffracted wave from the entrance surface of the crystal, &PHgr;′, &PHgr;2 = α + &PHgr;′2, when measuring the intensity of the reflected diffracted wave as a function of &PHgr;, the intensity is obtained as a function of α. Measurement of &PHgr;′ with the accuracy of about 30′′ corresponds to accuracy through α of about 0.1′′. These facts sufficiently simplify the performance of experiment and open wide prospects for studies of crystal structure of thin subsurface layers with unique accuracy.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 87
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 252-256 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Electron density ideally is positive definite. The imperfect experimental data of an X-ray diffraction experiment do not lead to such a function when the density is obtained from structure factors by the linear relationship of Fourier transformation. At the price of certain but quite small bias, electron density may be represented by an otherwise completely general exponential model. The model is based on iterative correction of a logarithm which yields a density approximation of resolution substantially higher than that afforded by Fourier transformation of structure factors.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 88
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 269-270 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 89
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 271-271 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 90
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 278-279 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Three-dimensional diffractometer data collected from single crystals of large and anisotropic mosaic spread were shown to suffer from severe systematic errors. The application of anisotropic scaling of the structure factors in the refinement process proved to be very useful in correcting these errors, yielding more accurate parameters, comparable to those obtained from high- quality crystals.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 91
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 599-599 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 92
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 600-600 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 93
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 609-615 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Calculation of dynamical structure factors from a periodically curved crystal lattice have been carried out for the paraffin n-hexatriacontane, C36H74, and the linear polymer anhydrous nigeran, poly[(1 → 3)-α-D- maltose], (C12H20O10)n. These are compared to dynamical structure factors from a fiat crystal, and also to kinematic structure amplitudes from a bent lattice in order to determine the validity of considering each experimentally observed data perturbation separately. Individual treatment of these effects is found to be a good approximation so long as the crystal thickness and bend deformations are each small.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 94
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 47-60 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The problem of inverting crystallographic diffraction data to obtain structural information is examined within the maximum-entropy formulation of information theory. The principal features of the present method (termed statistical geometry) are: (i) all predictions of the method are consistent with the given information (constraints) and least biased with respect to missing information, (ii) the adoption of weak (typically non-linear) constraints for incorporating the major part of the structural information guarantees that a solution exists in practice and leads to filtering of the structure maps consistent with the accuracy of the data, (iii) general conditions are established which lead to unique solutions for the structure map, (iv) atomicity is not a prerequisite, (v) other methods of crystallographic inversion may be incorporated via the adoption of appropriate constraint relations, and (vi) the task of numerical solution is roughly linear in the number of reflexions and in the number of pixels in the structure, and involves only straightforward numerical techniques. These features suggest that the method is especially well suited to problems such as the structure determination of biological macromolecules, and the determination of high-resolution electron-density maps, although it manifestly provides a general framework for treating a wide class of image-processing problems.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 95
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 79-83 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Recognition of the intrinsic two-dimensional nature of the intensity distribution, I(ω, 2θ), of a Bragg X-ray reflexion allows identification of the spectral dispersion of the source and the fragment/mosaicity (f/m) distribution of the specimen small crystal. With this information as a basis for the measurement of integrated intensity, the spectral band (wavelength truncation) can be maintained constant from reflexion to reflexion and the real extent of the f/m distribution established by reference to a signal/noise index. With this procedure, the separation of peak from background is placed on an objective basis not feasible with the conventional analysis of the one-dimensional reflexion profile. The method is demonstrated using the ω, 2θ slice scan procedure [Mathieson (1982). Acta Cryst. A38, 378-387] but is also relevant to the use of linear position-sensitive detectors.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 96
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 170-171 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A reliable and automatic method of selecting three orientation parameters is presented. The refinement of these and of the symmetry-constrained unit-cell parameters from four-circle diffractometer data is described.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 97
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 174-185 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 98
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 187-187 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 187-188 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 100
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 39 (1983), S. 188-189 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...