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
  • International Union of Crystallography (IUCr)
  • 1980-1984  (1,211)
  • 1984  (1,211)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 88-88 
    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 ...
  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 167-167 
    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 40 (1984), S. 297-305 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A realistic molecular dynamics calculation for naphthalene is presented and a comparison is made between the simulation and the crystallographic data. The molecular dynamics sample consists of 4096 molecules arranged in a volume with cyclic boundary conditions, each molecule being associated with one processing element of the ICL DAP computer. The potential functions used are the same as those used for lattice dynamics, and are developed from atom- atom 6-exp functions. A comparison with a lattice dynamical result establishes the correctness of the program. Temperature is introduced in the usual molecular dynamics way, resulting in a true modelling of anharmonic behaviour. The calculation proceeds at zero pressure throughout, yielding the temperature variation of the crystalline unit cell, the mean molecular orientation and the rigid-body thermal vibration tensors T and L. These are compared with the recently reported results measured by neutron scattering from powder samples and analysed through constrained refinements. The variation of unit-cell volume with temperature is particularly close to the experimental result, though discrepancies begin to be significant in measurements involving the orientational behaviour of the molecules.
    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 40 (1984), S. 309-310 
    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 ...
  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 309-309 
    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 ...
  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 308-309 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The incorrect assignment of atom type leads not only to incorrect thermal parameters but in unfavourable circumstances, such as having a limited data set or through overweighting low-order reflections, to incorrect bond distances.
    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 40 (1984), S. 310-310 
    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 40 (1984), S. 312-312 
    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 40 (1984), S. 340-346 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An a posteriori method of the determination of a correct set of structure-factor phases based on a comparison between the trial and theoretical distribution functions of semivariants, using the χ2 test, makes possible the full utilization of a priori structure information contained in the phase relationships. It is expected that the application of this method should raise the efficiency of existing direct methods.
    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 40 (1984), S. 42-50 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Three-periodic nets are connected graphs which permit embeddings having a threefold periodicity. To many crystal structures such nets can be meaningfully assigned and used to express the topology of the structures. It is shown that such a net can be fully characterized by a finite graph in which the edges are labelled in a suitable way. The reversal of the process of assigning a labelled finite graph to a given net can be used to generate nets of real and hypothetical crystal structures in a systematic fashion.
    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 40 (1984), S. 116-120 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The internal strain parameter (or the bond-bending parameter) of zinc-blende-structure materials can be obtained from the stress dependence of the intensity of weak reflections in uniaxially stressed crystals. The theory, including dispersion and temperature effects, is presented and applied to the reanalysis of earlier work on gallium arsenide. The results are inconsistent, leaving the bond-bending parameter of this material unknown.
    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 40 (1984), S. 502-507 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In this paper is described the realization of an idea due to J. W. M. Dumond who, almost 50 years ago, suggested that Bragg diffraction peaks might be made narrower by multiple reflection [Dumond (1937). Phys. Rev. 52, 872-883]. The optical elements which result belong to a family of harmonic free monochromators, X-ray and neutron polarizers whose properties make feasible many new Bragg diffraction optical systems.
    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 40 (1984), S. 264-269 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The hydrous lanthanide oxides comprise a complicated series of both crystalline and amorphous compounds. The amorphous short-range-order (SRO) phase of hydrous erbium oxide is the subject of this work. A thorough discussion of the instrumental arrangement and electronic counting chain for the X-radiation diffraction data collection is included. The scattering profiles for hydrous erbium oxide are shown and details of the ensuing data correction procedures are given. A radial distribution analysis of the calculated interference function, Si(S), was performed. SRO interatomic distances and the first-shell coordination number are reported. The mean Er-O bond distance is found to be 2.36 Å and the erbium metal is nine coordinated. Comparison of the experimental radial distribution curve to ones calculated from crystalline systems lend credibility to the experimentally determined distances.
    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 40 (1984), S. 269-277 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A procedure is suggested for the refinement of a set of protein phases and for its extension to a higher resolution, which is a development of the approach of Agarwal & Isaacs [Proc. Natl Acad. Sci. USA, (1977), 74, 2835-2839]. A new set of phases is obtained by combining the starting phases with those calculated from a stereochemically non-conditioned coarse 'atomic' model which is automatically constructed and subjected to a least-squares refinement in reciprocal space. The method has been tested with actinidin data generated from atomic coordinates. Starting from the phases calculated to 3 Å resolution and the amplitudes calculated to 2 Å resolution a new set of phases was obtained with a mean error of 31° for 12 713 non-centrosymmetric reflections in the range to 2 Å. The refinement of the phases to 3 Å, resolution for γ-crystallin IIIb from calf lens and its extension to 2.7 Å resolution resulted in a noticeable improvement in the electron density map.
    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 40 (1984), S. 283-291 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The problem of calculating the two-wave X-ray field on the basis of the Takagi-Taupin equations is discussed for the general case of curved lattice planes. A two-dimensional integral equation which incorporates the nature of the incoming radiation, the form of the crystal/vacuum boundary, and the curvature of the structure, is deduced. Analytical solutions for the symmetrical Laue case with incoming plane waves are obtained directly for perfect crystals by means of iteration. The same method permits a simple derivation of the narrow-wave Laue and Bragg cases. Modulated wave fronts are discussed, and it is shown that a cut-off in the width of an incoming plane wave leads to lateral oscillations which are superimposed on the Pendellösung fringes. Bragg and Laue shadow fields are obtained. The influence of a non-zero kernel is discussed and a numerical procedure for calculating wave amplitudes in curved crystals is presented.
    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 40 (1984), S. 313-313 
    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 ...
  • 17
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 338-340 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The aim of the phase determination is formulated as a minimization of a function of estimated errors in the phases. It is concluded that a good phase-determining procedure in direct methods has to fulfil the following requirements. 1. The probability distributions of seminvariants used should contain the maximal amount of a priori structure information. 2. The whole information contained in probability distributions should be employed. 3. The choice of the starting set and the set of phase relations used should minimize Σ|FH|2 var φH. The procedures that are able to fulfil these requirements are described in the following papers [Hašek (1984). Acta Cryst. A40, 340-346, 346-350, 350-352].
    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 40 (1984), S. 331-337 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The interpretation of physical properties of incommensurate modulated crystals leads to the use of their point groups and their total character tables in their superspaces. Examples are chosen of point groups of holohedries of the two hypercubic crystal systems - primitive and body-centred- in four-dimensional space. A geometrical presentation is given of the point group - including its character table - of the primitive hypercubic crystal system, as it is useful for the prediction and simplification of tensorial physical properties of the corresponding crystals. Through geometrical considerations, the exceptional splitting of the hypercubic family of \bb E4 into two crystal systems is easily proved. Finally, the two different relations - according to the parity of n - existing between the point group of the primitive hypercube of \bb En and its subgroup of rotations are explained.
    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 40 (1984), S. 350-352 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The proposed method of determination of a correct set of phases is based on a comparison between the trial and theoretical distributions of seminvariants using the Kolmogorov test. If the Kolmogorov test is restricted to a single region of magnitudes where only a small variance around the mean seminvariant value is expected, then the test is reduced to a simple rule. The smaller the number of seminvariants differing significantly from the expected mean value, the more probable the set of phases. In this simple form the Kolmogorov test has been used since the very beginnings of direct methods. In spite of the fact that the method seems to be less efficient than the distribution fitting using the x2 test [Hašek (1984). Acta Cryst. A40, its simplicity and low claim on computing time enables one to survey a large number of trial sets and so to increase the power of the method based on a combination of the Kolmogorov test with the x2 test, or with the low-order distribution moment test.
    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 40 (1984), S. 364-366 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A comparison of the two methods available for the calculation of exact values of pseudorotation parameters P, τm, i.e. the Fourier-series (FS) method [Rao, Westhof & Sundaralingam (1981). Acta Cryst. A37, 421-425] and the least-squares (LS) method [Jaskólski (1983). J. Chem. Educ. 60, 980-981] reveals that they yield identical values for τm and P. The variances σ2(τm) and σ2(P) calculated by these methods are, however, different since they have different interpretations.
    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 40 (1984), S. 355-363 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: By its two-dimensional nature, the Δω, Δ2θ intensity distribution of a Bragg X-ray reflexion has greater angular resolution and greater information content than the corresponding one-dimensional Δω reflexion profile. It allows for the measurement of integrated intensity, exactly and equally truncated, over the full range of θ. Also, it is potentially correctable point by point for extinction and simultaneous diffraction. Consequently, it has inherent capabilities for the estimation of structure-factor values with improved accuracy. To realize this potential, it is necessary to identify and appreciate the various factors which, convoluted together, determine the 2D distribution. Among these factors, important ones are the crystal mosaic/fragment distribution, μ, the X-ray source emission distribution and the wavelength distribution. By first treating the situation for a hypothetical point source, the relation of the reflectivity (or 'level of interaction') with the μ distribution is highlighted. Extension to a real source indicates the probable need for deconvolution in practical cases to extract meaningful estimates of the μ distribution and hence the reflectivity distribution, the most significant measured quantity for accurate structure-factor evaluation. The 2D distribution is discussed in relation to single (H) scattering, multiple (H.{\bar H}) scattering (extinction) and simultaneous (H. K) scattering.
    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 40 (1984), S. 374-379 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: On the basis of a common characteristic observed in previously derived formulas for the evaluation of triplet phase invariants from either isomorphous replacement data or anomalous dispersion data, it has been found possible to combine mathematical expressions, certain differences of magnitudes, arising in the analysis of the two techniques to form a myriad of new mixed formulas. The common characteristic is that the various types of differences of magnitudes that are involved in the formulas are all definable in terms of the heavy-atom structure. The formulas involve the mixing of terms arising from several isomorphous derivatives or from a combination of such terms with various types of terms arising in anomalous dispersion or the mixing of various terms arising in anomalous dispersion alone. The evaluation of the triplet phase invariants is facilitated by the use of a simple rule, called the General Rule, that is generally applicable to the case of one predominant type of anomalous scatterer. In the case of more than one predominant type of anomalous scatterer, a slightly more complicated calculation is required and is described. Test calculations show that a very large number of invariants may be evaluated by these means with reliabilities that are potentially high, but depend, of course, on the reliability of the experimental data. A benefit from having the large variety of formulas is that triplet phase invariants can be evaluated at many points throughout the range -π to π and their reliability is enhanced because much information is obtained from only the largest differences of magnitudes.
    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 40 (1984), S. 394-398 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Using a double crystal diffractometer with an additional crystal between the two crystals used as X-ray-optical polarizer and analyzer the phase relation between mutually perpendicularly polarized wave fields is examined in the Bragg case. The additional crystal is a (110)-surface oriented silicon crystal adjusted for the symmetric 220 Cu Kα1 Bragg case. In the case of coherent excitation of both σ- and π-polarized wave fields in the silicon crystal it is experimentally shown that a unique phase relation exists. In a further experiment it is demonstrated that in the case of incoherent excitation the rocking curve is the sum of the σ- and π-polarized intensities without any phase relation. Owing to the different half width of these two curves, step-shaped flanks of the rocking curve are found at excitation with unpolarized radiation.
    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 40 (1984), S. 445-450 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Multiple Laue rocking curves of perfect crystals show a narrow central peak with a width of some 10-3s arc and an additional oscillatory structure. The finite structure of these curves is analyzed for two- and three-crystal Laue arrangements. These profiles can be used for precise determinations of structure factors and for an extension of small-angle scattering experiments to the extreme small-angle regime where large objects and long-range particle correlations become visible. An extremely high angular resolution can be achieved without significant reduction of the intensity, owing to a decoupling of the angular resolution from angular width of the beam. The analytically calculated rocking curves are compared to numerical results and to experimental results and show good agreement with both.
    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 40 (1984), S. 459-465 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Diffraction experiments with resonant γ-radiation were performed on a single crystal of silicon at room temperature. The high energy resolution of the Mössbauer effect was used to separate elastically and inelastically scattered radiation. A special experimental setup is described, which in addition allows the determination of the total thermal diffuse scattered intensity. Inelastically scattered radiation was observed in the whole investigated angular range. In the vicinity of Bragg reflections the ratio of the integrated intensities of inelastically to elastically scattered radiation was in very good agreement with the results of calculations using different computer programs based on first-order thermal diffuse scattering theory for a wide range of chosen scan lengths. The measured ratios of the elastically scattered radiation of different Bragg reflections were used to determine the temperature factor B.
    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 40 (1984), S. 482-484 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The anomalous dispersion factor, f', of sulfur for Cu Kα radiation has been determined to be 0.60 (3) using measurements of Bijvoet differences of 175 selected reflections for a 6-(4-nitrobenzyl)thioinosine crystal.
    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 40 (1984), S. 487-488 
    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 ...
  • 28
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 489-495 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A direct-methods procedure has been proposed for separating the phase doublet resulting from the use of either isomorphous replacement or anomalous scattering techniques. The phase doublet is expressed as φH = φ′H ± |ΔφH|. Formulae combining the structure-factor relationships with the phase-doublet information are given. Problems concerning the practical applications are also discussed. A test calculation with the error-free data for the protein insulin showed a satisfactory result.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 29
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 498-502 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The application of hydrostatic pressure to crystals in which some atoms occupy sites with polar point-group symmetry causes the position coordinates of these atoms to change. This phenomenon is here related to inner compressibility tensors. These arise naturally in the theory of inner elasticity, where they are linear combinations of the macroscopic linear compressibilities weighted by components of the internal strain tensors, and they indicate the ease with which the separation between pairs of sublattices may change under pressure. The form of the inner compressibility tensors is presented for eleven simple crystal structures involving up to four atoms in the basis. Finally, the inner compressibilities and con- straining equations for components of the internal strain are obtained from the pressure dependence of the structure of the elements As, Sb, Bi, Se, Te and I.
    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 40 (1984), S. 723-723 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A printers error is corrected in Table 2 on page 407 of Whittaker [Acta Cryst. (1984), A40, 404-407]. The correct lines are: Family XVII; wx/yzw[0111]*w[0110]/z[0\bar 110]: wx[0110].
    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 40 (1984), S. 726-727 
    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 ...
  • 32
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 728-728 
    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 40 (1984), S. 624-631 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: From a given standard setting (O, A, B) (conventional unit-cell origin and vectors) of a two-dimensional space group G(p4), it is possible, for each isomorphic subgroup g(p4), to select exactly one standard setting (o, a, b) subject to the following conditions. (1) Vector conditions: a = p1A + p2B, b = -p2A + p1B, P1 〉 0, P2 ≥ 0 (P1, P2 ∈ \bb Z). (2) Origin conditions: (a) if (P1 + P2) is odd, then the coordinates X, Y of o, with respect to (O, A, B), obey the next conditions: X, Y integers, 0 ≤ X 〈 GCD(P1, P2), 0 ≤ Y 〈 (P21 + P22)/ GCD(P1, P2), GCD = greatest common divisor; (b) if (P1 + P2)/GCD(P1,P2) is even, then 2X and 2Y are both even or odd, 0 ≤ X 〈 GCD(P1, P2), 0 ≤ Y 〈 (P21 + P22)/2GCD(P1, P2); (c) if P1, P2 are even and (P1 + P2)/GCD(P1, P2) is odd then 2X and 2Y are both even or odd, 0 ≤ X 〈 GCD (P1, P2)/2 and 0 ≤ Y 〈 (P21 + P22) /GCD(P1, P2). In any case there are exactly (P21 + P22) subgroups relevant to the same vector conditions. Tables of isomorphic subgroups p(4) are given for indices up to 25.
    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 40 (1984), S. 642-645 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Orientation relationships between two crystal lattices are frequently specified in terms of parallel directions and planes in each lattice. The corresponding matrix, relating the vector bases of the lattices, can be obtained by a general method involving the metric matrices of the two lattices and the crystallographic indices of parallel planes and directions. Equivalent matrices can be defined by changing the lattice bases: different selections of the invariants of such matrices are indicated. Finally, criteria for choosing the 'best' matrix relating the two lattices are discussed in the context of phase transformations and of interfacial structure.
    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 40 (1984), S. 727-728 
    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 ...
  • 36
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 58-66 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The nature of the four-dimensional crystallographic symmetry operations is clarified by representation of their effects in hyperstereograms presented in the form of stereo-pairs. Appropriate graphical symbols have been devised to indicate the orientations of the corresponding symmetry elements. Typographical symbols have been devised for the operations themselves, and for their symmetry elements, which are adaptable for use in a system of symbolic nomenclature of the four-dimensional classes 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 ...
  • 37
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 88-88 
    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 40 (1984), S. 99-102 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Anomalous scattering lengths of natural Sm for thermal neutrons with wavelengths between 0.827 and 1.300 Å have been determined by single-crystal diffraction from a Sm complex of known structure. 140 selected reflections were measured at a temperature of 37 K at each wavelength and b0 + b' and b" refined in each case. The values obtained are in good agreement with values obtained from a Breit-Wigner calculation using tabulated absorption resonance parameters for 149Sm. A value of b0 = 4.3 ± 0.2 fm is deduced from the diffraction experiments.
    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 40 (1984), S. 143-151 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Many-beam lattice images obtained at 200 kV from V2O3 crystals are discussed in comparison with those calculated in the Bloch-wave approach. The technique of optical diffractogram and equal-thickness fringes is utilized, if possible, to determine the defocus value and the crystal thickness which are the essential parameters for objective interpretation at atomic resolution. Whereas images observed in a thin region (∼ 50 Å) of crystal have been reproduced fairly well by simulation, there are others from thicker regions which are not always explained for lack of knowledge of the parameters. As for the effect of the partial coherence, the validity of the envelope-function approximation is examined with the aid of the first principle involving image-intensity summation, and under the experimental conditions used it proved to be satisfactory for qualitatively reproducing the observed image even for relatively thick (∼ 450 Å) regions.
    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 40 (1984), S. 12-16 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A tabulation of some 40 measured values of the polarization ratio K (a measure of the fractional polarization introduced into an X-ray beam by a crystal monochromator) is presented. The values may be represented through the parameter n given by K = cosn2θM. The measured values of n cluster around unity and the theoretical rationale for this result is discussed. Possible explanations of outlying values are considered. A recommendation is made that the polarization ratio of an apparatus be measured using a direct method whenever possible, but methods for estimating a value of K are also given.
    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 40 (1984), S. 4-11 
    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 anomalous dispersion experiments, it has been possible to derive simple rules, Rano, 1, Rano, 2 and Rano, 3, that permit the selection of triplet phase invariants, in a single-wavelength experiment, that have values close to π/2, -π/2, 0 and other values in the range from -π to π. The rules, Rano, 1, Rano, 2 and Rano, 3, apply to the case of a single type of predominant anomalous scatterer. The simple generalization to more than one type of predominant anomalous scatterer is also described. Test examples show that large numbers of invariants may be evaluated by these means with reliabilities that are potentially high, but depend, of course, on the reliability of the experimental data. The only information required besides the measurements of the diffraction intensities is the chemical composition of the anomalously scattering atoms. In some cases, even this information is not required if two alternative sets of estimates of the values of the triplet phase invariants are considered.
    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 40 (1984), S. 137-142 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An iterative procedure for the determination of the signs of scattering amplitudes is considered. It is assumed that the scattering density is a one-dimensional antisymmetric function with a limited range of definition. The convergence of the method to a rigorous solution is proved. The stability of the procedure with respect to various experimental errors is shown in model examples. The proof can be generalized for a one-dimensional phase determination of a continuous intensity distribution.
    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 40 (1984), S. 162-162 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In the paper by Stevenson & Harada [Acta Cryst. (1983), A39, 202-207] the calculated values of Δ' (and consequently δ{\bar B}) in Table 1 are in error. For KCl and BaF2 the conventional (rather than primitive) unit-cell volumes were mistakenly used when calculating qzB. For CdS and CdSe the factor used to get q'zB from qzB was incorrect. The new (corrected) Table 1 is given below. The agreement between δ{\bar B} and δ{\bar B}obs is, with the new δ{\bar B} values, generally better; with δ{\bar B} for KCl closer to the δ{\bar B}obs value given by Cooper & Rouse [Acta Cryst. (1968), A24, 405-410], namely 0.16 Å2. The calculated value of the "overall" temperature parameter for CdS becomes 1.29 Å2. It should also be noted that there is a factor of 2 missing from the denominator of equation (15).
    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 40 (1984), S. 66-67 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: That positivity of all the Karle-Hauptman determinants and the positivity of the electron density in the unit cell are equivalent conditions is well known. A simple way of deriving this result is presented providing at the same time a relation between these determinants and the logarithm of the electron density. The relationship of this logarithm of the electron density to the entropy is also discussed.
    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 40 (1984), S. 86-87 
    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 ...
  • 46
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 88-88 
    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 ...
  • 47
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 95-99 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method for choosing OD layers in a structure is given. For any structure one of four cases is possible: I. the structure cannot be interpreted as an OD structure consisting of layers; 2. the OD layers are uniquely determined; 3. the limits between OD layers may be changed with keeping the OD groupoid family; and 4. the limits may be changed with changing the OD groupoid family.
    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 40 (1984), S. 108-112 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The derivation of the generating function given by Bleris & Delavignette [Acta Cryst. (1981), A37, 779- 786] is simplified and made rigorous. It is shown that their main result can also be deduced directly from Grimmer [Acta Cryst. (1974), A30, 685-688]. The following applications of the generating function are described: determining all rotations that generate coincidence site lattices (CSLs) by giving their axis and angle or their matrix, determining the equivalence classes of rotations with respect to cubic symmetry and the 180° and minimum-angle rotations that they contain, determining the number of rotations in each equivalence class and the total number of rotations that generate a CSL with given unit-cell volume Σ. We also discuss how a basis for the CSL can be computed and how a bicrystal with a plane grain boundary can be characterized.
    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 40 (1984), S. 127-133 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The temperature dependence of the atomic thermal motion in lead has been studied by analysis of diffraction measurements with 0.535 and 0.844 Å neutrons. Full single-crystal data sets were collected at ten temperatures ranging from 100 K to the vicinity of the melting point at 600 K. The data were interpreted in the anharmonic one-particle-potential formalism. Significant values for both isotropic and anisotropic quartic-anharmonic potential parameters were obtained, but a single temperature-independent one- particle potential was found sufficient to describe the temperature dependence of the atomic temperature factor only above 4̃θM, where θM is the Debye temperature.
    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 40 (1984), S. 133-137 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An extension of the tables for the site-symmetry restrictions on the thermal-motion-tensor coefficients to include tensors up to rank 6 (up to rank 8 for cubic, hexagonal, tetragonal and trigonal site symmetries) is presented. The dependence relationships of these symmetric polar tensors are calculated in their natural crystallographic lattice frames using a direct method.
    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 40 (1984), S. 161-162 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: By Taylor expansion, peak position and peak heights in the γ' synthesis are derived. The first approximation gives a fairly good evaluation for heights of P and Q peaks in the range of convergence.
    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 40 (1984), S. 152-160 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Cooper-Nathans formulation of the resolution function of a triple-axis crystal spectrometer for neutron-scattering experiments gives a singular resolution matrix when the scattering angle is small. The origin of this singularity is discussed and an alternative derivation, of the resolution matrix given which avoids this difficulty. The results are illustrated by numerical calculations for several typical experiments showing that resolution corrections may be large and very significant for experiments at small scattering angles.
    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 40 (1984), S. 165-166 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: For comparing two molecules, since the most general positional relationship is the combination of a translation and a rotation, where the translational component can be removed by referring both molecules to their centres of gravity, a rotation taking one to the other must be found. Rather than using a 3 × 3 rotation matrix, it is better to represent the rotation by a unit quaternion, since the equations to be solved to find, by least squares, the best quaternion, are linear.
    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 40 (1984), S. 167-167 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Table 1 of Schapink, Forghany & Buxton [Acta Cryst. (1983). A39, 805-813] contains several printing errors. The correct table is given.
    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 40 (1984), S. 168-168 
    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 40 (1984), S. 228-240 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The local atomic arrangement in the stainless-steel alloy Fe0.56Cr0.21Ni0.23 has been investigated by thermal neutron diffuse scattering from single crystals. The variation of contrast has been obtained by isotopic substitution: three single crystals of different isotopic compositions have been used. The Warren-Cowley parameters of the three heterogeneous pairs have been determined. It is shown that ordering occurs between Ni and Cr atoms. The correlation lengths are small and are of about one cell length. The static displacements are shown to be small. Analysis procedures of diffuse scattering from ternary alloys are developed from neutron scattering and in the Appendix for X-ray scattering.
    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 40 (1984), S. 241-251 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: After a comparison of Kato's theory of extinction with the conventional energy-transfer coupling model, it is shown that both models can be solved exactly for crystals with planar boundaries. Integrated reflecting power can be obtained analytically for a parallelepipedic crystal, which allows for a comparison with approximate treatments (such as the Becker-Coppens Laue formula or the infinite slab expression). For general geometric conditions, numerical integration may be needed. Respective usefulness of various models is discussed.
    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 40 (1984), S. 484-484 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Parentheses have been incorrectly placed in the first equation of page 62 of Whittaker [Acta Cryst. (1984). A40, 58-66]. The right-hand side of the equation should consist of two 4 × 4 matrices. The correct equation is given.
    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 40 (1984), S. 484-484 
    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 ...
  • 60
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 255-261 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A group-theoretical method is presented to determine the tensorial classification of ferroic crystals with respect to an arbitrary macroscopic tensorial property. This method is used to derive tables of the tensorial classification in the special case where the components of the tensorial property transform as a single irreducible representation of the prototypic point group. It is also shown how these tables facilitate implementation of this method in the general case. Examples are given of the application of this method and the use of these tables in determining the tensorial classification of ferroeleetric and gyrotropie ferroic crystals.
    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 40 (1984), S. 352-355 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It has been shown that by measuring the angular dependence of X-ray diffraction scattering far from the Bragg peak, information on the structure perfection of thin subsurface layers can be directly obtained. This is associated with the fact that the waves generated in the crystal bulk compensate one another, and the intensity of rocking-curve tails is due mainly to scattering in the subsurface layer. The typical thickness of a scattering layer is related to the deviation angle by a simple relationship: Δz∼ Lexω0/α, where α is the deviation angle of the specimen from the exact Bragg position, ω0 the diffraction maximum width, and Lex the extinction length. The method of three-crystal diffractometry permitted the observation for the first time with a conventional X-ray source of a distorted layer with a thickness of 1̃0 nm.
    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 40 (1984), S. 389-394 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The asymptotic distribution of αh is calculated via the distribution of the resultant of complex random vectors whose phase values are distributed according to Von Mises distributions. The statistical results suggest that the phase of the resultant, say θh, is distributed around the phase φh, approximately according to a Von Mises distribution.
    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 40 (1984), S. 573-580 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Various means of enumerating the three-dimensional three-colored space groups are discussed: a direct algebraic method equivalent to the Zachariasen method, an induction method, and a technique using the third-order cyclic representations of the ordinary space groups.
    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 40 (1984), S. 580-587 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A periodic lattice in \bb En is associated with an n-grid and its dual, and with a point symmetry group G. Given a subgroup H of G, a subspace \bb Em, m 〈 n, of \bb En, invariant under H, is chosen and a projection of the n-grid from \bb En to \bb Em is defined. The translational and point symmetries of the projected n-grid are analyzed. A projection of the cubic n-grid from \bb En to \bb En-1 based on H = S(n) yields a periodic n-grid. A projection of the cubic 12-grid from \bb E12 to \bb E3 based on H = A(5) yields a non-periodic 12-grid. This 12- grid is characterized by three real numbers and from its projection has a well defined orientation. The dual to this 12-grid yields a generalization of the non-periodic Penrose patterns from two to three dimensions.
    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 40 (1984), S. 616-616 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: There is a printing error in Table 8 of Parthé & Gelato [Acta Cryst. (1984), A40, 169-183]. For PuBr3 the published space group was Ccmm, while that for the standardized data is Cmcm.
    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 40 (1984), S. 451-459 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A method is described to apply molecular symmetry constraints to the crystallographic refinement of a macromolecule at low resolution using the constrained-restrained parameter structure-factor least-squares refinement program CORELS [Sussman, Holbrook, Church & Kim (1977). Acta Cryst. A33, 800-804]. The parameter shifts calculated by CORELS are adjusted to ensure that the refined structure possesses exactly the desired molecular symmetry. This procedure has been used to refine the structure of apo-D-glyceraldehyde 3-phosphate dehyodrogenase from Bacillus stearothermophilus at 4 Å resolution, imposing 222 molecular symmetry. The starting model was the partially refined structure of the holoenzyme at 2.7 A resolution. The possible advantages of using CORELS refinement when dealing with more general problems involving two distinct molecular conformations which are related by simple rigid-body domain movements are also considered.
    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 40 (1984), S. 465-468 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Mössbauer diffraction experiments have been performed on a LiNbO3 single crystal at room temperature for scattering angles between 14.5 and 40.5°. A large contribution of inelastically scattered intensity was detectable for all scattering angles. Radiation damage caused by the high-energy components of the radiation emitted by the 57Co Mössbauer source was observed. An attempt was made to estimate the temperature factor B from the measured inelastically scattered radiation assuming that first- order thermal diffuse scattering (TDS) is dominant. Both the TDS contribution to the integrated intensity within the Bragg peak and the ratio of the integrated first-order TDS included in the Bragg peak to that included in the background were calculated with various programs from the elastic constants and compared with the experimental values.
    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 40 (1984), S. 473-482 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Group theory is used to establish three results likely to be useful in solving the crystal structures of complicated incommensurate phases. In the first of these it is demonstrated that an incommensurate structure with paired scattering vectors ± q must contain two different component structures, one modulated with cos q.r and the other with sin q.r. The second theorem states that the two components have different but related symmetries if the average structure has at least one element in its space group which turns q into -q. In that case, each aspect of the modulation is assigned uniquely by symmetry to either the cosine or sine factor. The third result concerns the Patterson function that may be constructed from the intensity scattered by the incommensurate modulation. This is also necessarily two-dimensional, the plus difference Patterson function being the sum of the Patterson functions obtained separately for the two component structures, while the minus difference Patterson function contains cross terms between the two components. Other symmetry arguments are mentioned, including symmetry signatures in Patterson functions, and systematic equalities in satellite intensities which arise from systematic extinctions in the scattering from one component or the other.
    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 40 (1984), S. 526-531 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In a previous investigation, a system of exact algebraic equations was derived for any number and type of anomalous scatterers. Solution of the equations provides information concerning intensities of scattering and certain phase differences. In this paper, it is shown that when appropriate combinations of the phase differences and their values are made, the result is the evaluation of the differences of pairs of triplet phase invariants, one associated with the macromolecular structure and the second associated with the structure of the anomalous scatterers. It is usually easy to satisfy the condition that the values of triplet phase invariants associated with the structures of the anomalous scatterers be close to zero.
    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 40 (1984), S. 587-593 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Scattering factors for outer shells of the first- and second-row series of atoms have been obtained by expansions with Jacobi functions. Both canonical and density-localized shell form factors have been studied. For κ refinements, both first and second derivatives are computed by analytical methods. Density-localized shell distributions differ from canonical shell distributions within a small sphere (〈 0.5 Å) about the nucleus. Shell population and κ refinements on uracil at the monopole level give virtually identical results with canonical and density-localized form factors.
    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 40 (1984), S. 728-728 
    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 ...
  • 72
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 728-728 
    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 ...
  • 73
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 572-573 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Double groups G+ and non-symmorphic space groups Ge have similar algebraic structures. Consequently, their subgroups can be classified along the same criteria and enumerated using the same methods.
    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 40 (1984), S. 559-567 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A well-defined and efficient algorithm, which enables the derivation of any crystallographic space group and full characterization of its symmetry operations and elements, is described and illustrated. The algorithm is based on a representation of crystallographic point groups in terms of cyclic groups, and on isomorphism relations between the point groups and the corresponding factor-group representations of the space groups. The characterization of the symmetry operations and the corresponding symmetry elements is also presented in an algorithmic manner, with particular emphasis on the orientation of the axes of rotation and their location vectors. The above algorithms have been implemented in a computer program, an application of which to the space group Pa\bar 3 is shown and some relevant programming considerations are given. The input to this general program can be fully adapted to the space-group tables in Vol. A of International Tables for Crystallography [(1983). Dordrecht: Reidel].
    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 40 (1984), S. 593-600 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A hierarchy of classifications for subgroups of space groups by means of Euclidean and affine normalizers is introduced. The different levels of this classification scheme are illustrated in detail with examples and its usefulness for various problems is demonstrated. The Euclidean (or affine) normalizers of a space group G and of one of its subgroups U may either coincide [N(G)=N(U)], or form a group-subgroup pair [N(G) ⊃ N(U) or N(G) ⊂ N(U)], or share only a common subgroup [N(G) ⫆N(U) and N(G) ¢ N(U)]. The different implications of these cases on the equivalence classes of subgroups (or supergroups) are discussed. A procedure is given to calculate the normalizers. The same concept may be applied to number of equivalent subgroups or supergroups, other crystallographic groups without problems.
    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 40 (1984), S. 600-610 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new rapid method of comparing three-dimensional protein structures using the sequence of dihedral angles is described. Systematic screening of protein structures by this method followed by detailed analysis reveals in particular that the calcium-binding protein carp parvalbumin is similar to cytochrome C2 from Rhodospirillum rubrum, cytochrome C is similar to hen lysozyme, carboxypeptidase A is similar to phage lysozyme. These results are completely unexpected and show interesting correlation with the recently determined intron-exon pattern in the genes coding for some of them.
    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 40 (1984), S. 616-616 
    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 ...
  • 78
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 696-701 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A computer program has been developed to study the lattice dynamics of molecular crystals in the harmonic approximation with the external Born-von Kármán formalism and an atom-atom potential function. Dispersion curves are obtained for monoclinic phenothiazine together with frequency distribution functions and external mode contribution to thermodynamic functions. Lattice dynamical T, L and S rigid-body tensors are obtained and individual thermal tensors are compared with experiment. The disagreement with respect to experimental results is of the same order as the disagreement with a Schomaker-Trueblood fit of experimental data.
    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 40 (1984), S. 701-703 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Strengthened translation functions have been defined [Doesburg & Beurskens (1983). Acta Cryst. A39, 368- 376] as convolutions of two electron density functions: i.e. the electron density representing the known fragment and the electron density obtained by the application of the DIRDIF procedures [Beurskens et al. (1982). In Conformation in Biology, edited by R. Srinivasan & R. H. Sarma. New York: Adenine Press]. Similar translation functions are defined as convolutions of the DIRDIF Fourier map with itself. The new functions are less powerful. The combination of the two types of functions, however, results in a more reliable method for the positioning of a fragment, if the fragment constitutes at least 10% of the total scattering power of the primitive unit cell. Examples of applications to known structures are given.
    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 40 (1984), S. 723-724 
    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 ...
  • 81
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 725-726 
    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 ...
  • 82
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 728-728 
    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 ...
  • 83
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 716-721 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Quantum-mechanical calculations of the modification of the X-ray scattering factor of an atom/ion in an electric field are compared with predictions of the semi-classical shell model. If the shell parameters are fitted to the dipole polarizability of the ion, the shell model is a very good representation of the scattering factor of the deformed ion, giving support to its use in estimating the effect of ionic deformation on X-ray diffuse scattering and X-ray Debye-Waller factors.
    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 40 (1984), S. 722-723 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It is demonstrated that a recent publication by Tindle [Acta Cryst. (1984), A40, 103-107] on the normalization of resolution functions for a three-axis spectrometer is in error. The complete normalization factor derived by this author is the same as that obtained in previous works. However, Tindle's interpretation of data for the peak reflectivity of mosaic crystals is incorrect. This error leads him to contradict erroneously previously published results.
    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 40 (1984), S. 726-726 
    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 ...
  • 86
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 728-728 
    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 ...
  • 87
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 728-728 
    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 ...
  • 88
    Electronic Resource
    Electronic Resource
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 32-34 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Many proteins contain a number of atoms of the same kind which are potential anomalous scatterers. It is shown that from two data sets, one normal and one with anomalous scattering, it is possible to extract the contribution of the anomalous scatterers and to solve for them by normal direct methods. From the phases of the structure factors of the anomalous scatterers alone the phases of the normal protein structure factors may, in principle, be found exactly.
    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 40 (1984), S. 168-168 
    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 40 (1984), S. 34-42 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The symmetry of an incommensurately modulated structure may be described in terms of the basic structure (B) and the modulation pattern (M). This description contrasts with the superspace-group approach, in which the structure is defined in a space of dimension 3 + d, where d is the number of rationally independent modulation vectors. Space groups GB and GM are defined, consisting of symmetry operations of B and M which are simply interrelated. These groups together characterize the total symmetry; they lead to a classification which for d = 1 is equivalent to the superspace groups. With this dualistic approach, all symmetry operations can be based on symmetry elements in the space of the crystal, and the lattice types can be composed simply from those of GB and GM. .
    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 40 (1984), S. 195-200 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new multi-dimensional search approach, incorporating packing criteria with R-factor calculations for low-resolution X-ray data, proved to be extremely efficient for the solution of large molecular structures. A computer program, ULTIMA, based on this approach solved ab initio the structure of a double-helical DNA octamer and also reproduced the correct solutions of a double-helical DNA dodecamer and of a tRNA molecule (322, 486 and 1652 non-hydrogen atoms, respectively). The efficiency of the procedure is enhanced by using group scatterers in lieu of individual atoms. The method allows, for more complex structures, the separation of parameters in the multi-dimensional space, either by using one-dimensional reflection data or by approximating the entire molecule to a 'super-atom' scatterer.
    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 40 (1984), S. 261-263 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: If a rocking curve is measured in symmetric Laue geometry for two different X-ray polarizations, and the incident beam meets the geometrical conditions for diffraction, i.e. the incident beam is much less divergent than the sample mosaic, then the intensity ratio Robs, for the intensities measured with each polarization, will depend upon the reflectivity at each point on the rocking curve. From the variation of Robs vs the observed intensity, Iobs, the absolute reflectivities and secondary extinction can be determined. If absorption is properly treated, then all data taken in this geometry should lie on a single curve of Robs vs Iobs. Failure to fit this curve is evidence that the sample has other processes occurring such as multiple scattering or primary extinction.
    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 40 (1984), S. 278-283 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A probabilistic approach is described which is able to estimate triplet cosine invariants via their second representation. The experimental tests on structures of different complexity show that triplets with positive cosine are estimated with an accuracy better than via Cochran's distribution. Furthermore, in favourable cases, a large percentage of negative triplets can be found.
    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 40 (1984), S. 291-296 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: In close-packed ordered alloys of composition ABn the lattice constant a and all interatomic distances are determined to a good approximation by the quantity (RA + nRB). This observation, the Pauling-Simon law [Pauling (1957). Acta Cryst. 10, 374-375; Simon (1983). Angew. Chem. 22, 95-113], is analogous to Vegard's law [Pearson (1972). The Chemistry and Physics of Metals and Alloys. New York: Wiley] for random alloys. No exact proof is possible but here a theoretical discussion is given using the spirit of Froyen & Herring's 'proof' of Vegard's law [Froyen & Herring (1981). J. Appl. Phys. 52, 7165-7167]. The effect of a change in radius ratio can be discussed precisely with the virial Σi FiDi either in terms of the exact crystal structure surrounding each type of atom or by approximating it as a close-packed medium treated as a uniform isotropic continuum. The essential point is that the A and B sites have to be elastically equivalent in the sense that a radius change δR on either site has to produce the same overall volume change. From this it is found that the interatomic force constant is proportional to D-m, where D is the spacing between atoms and m lies between 3 and 4, more or less consistent with Badger's law [Badger (1934). J. Chem. Phys. 2, 128-131].
    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 40 (1984), S. 1-4 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A formula is presented for the calculation of the values of the |Fnh|, the structure-factor magnitudes in the absence of anomalous dispersion, from the observed structure-factor magnitudes, |Fλh| and |Fλh|, that are affected by anomalous dispersion and hence vary with wavelength. Since the values of the |Fnh| are independent of wavelength, the calculation can provide the basis for relatively scaling data that are collected at different wavelengths. Test calculations of the formula with use of accurate data indicate that the formula has the potential to scale relatively experimental data in multiple-wavelength anomalous-dispersion experiments involving heavy-atom-substituted macromolecules to accuracies of 1 or 2% or better.
    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 40 (1984), S. 346-350 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The proposed method of determination of the correct set of phases of structure factors enables in principle full benefit to be taken of a priori structure information contained in the probability distributions of seminvariants. Unlike the direct comparison of the probability distributions discussed in the preceding paper, the method discussed here, by neglecting the moments of higher orders, allows concentration on the main characteristics of the distributions taken for the test. The basic principle of the method for determination of the correct set of phases using the fit between moments of the theoretical and trial distributions has been widely used in different modifications. However, most of these figures of merit compare only first distribution moments. In many cases this results in insufficient discriminating ability. The comparison of the second moments raises the effectiveness of these methods and may be useful in the last stage of the phase-problem solution. The utilization of moments of higher orders may be dangerous, especially using the global coefficient of moments fitting and in the case of a small number of seminvariants (unreliable determination of higher moments). The method of successive comparison of moments of different orders seems to be more reliable and economical. It permits the survey of a large number of potential solutions, thus increasing the likelihood that a correct solution is included. From the economic point of view, it is convenient to include only those regions of magnitudes and those distribution types which have not been used in the preceding step of the search of the trial solutions. It explains the excellent results obtained using figures of merit based on the special seminvariant types, e.g. NQEST, NQC [De Titta, Edmonds, Langs & Hauptman (1975). Acta Cryst. A31, 472-479; Schenk (1974). Acta Cryst. A30, 477- 481].
    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 40 (1984), S. 366-373 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Several simple rules, Rano,4, Rano,5, Rano,6 and Rano,7, have been derived on the basis of the mathematical and physical characteristics of anomalous dispersion experiments that permit the estimation of values for triplet phase invariants. They apply to two-wavelength experiments and concern a variety of values defined in terms of the real and imaginary corrections to atomic scattering factors. The rules apply to the case of a single type of predominant anomalous scatterer. The generalization to more than one type of predominant anomalous scatterer is also described. Test examples show that large numbers of invariants may be evaluated by these means with reliabilities that, in certain circumstances, are at a potentially useful level, but the ultimate applicability depends, of course, on the reliability of the experimental data. The only information required besides the measurements of the diffraction intensities is the chemical composition of the anomalously scattering atoms. If there is more than one type of predominant anomalous scatterer, information concerning the relative proportion of the different types is also required.
    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 40 (1984), S. 379-389 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The dynamical three-beam problem in Renninger geometry is cast in a pseudo-two-beam formulation for the primary OH reflection, with the inverse of the excitation error ξL with respect to the third reciprocal-lattice point L acting as a perturbation parameter for modifying the true two-beam solutions. This approach introduces a quasi-universal angular scale x for measuring the onset of all three-beam effects, and it leads to a first-order solution that preserves all features of a two-beam case, but around a shifted Lorentz point, and with modified structure factors. The modified structure factors, odd in x, cause pronounced asymmetries in the diffracted intensities on both sides of the three-beam point, for |x| \rsim 1. In this range of x, the first-order solution provides a simple analytic expression for the integrated diffracted intensity vs angle, for a sequence of neighboring three-beam or higher-order points. This is exemplified for the Ge 222 primary reflection. The physics of the onset of the three-beam interaction, and the limitations of the first-order solution are also discussed.
    Type of Medium: Electronic Resource
    Location Call Number Expected Availability
    BibTip Others were also interested in ...
  • 99
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An earlier report [Acta Cryst. (1977), A33, 681-684] by a joint IUCr-IMA committee on the nomenclature of polytypism has been revised and extended. Two kinds of symbolism are recommended for use with either simple or complicated polytypic structures. The first consists of 'indicative symbols' in a modified Gard notation, the second of 'descriptive symbols' based on earlier proposals by Dornberger-Schiff, Durovic and Zvyagin. The polytypism of ZnS and SrGeO3 provides examples for the use of descriptive symbolism.
    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 40 (1984), S. 468-473 
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: First and second moments of the probability density of the function R = ΣH Eo2Ec2 are evaluated for n-atom models consisting of i correctly and n - i incorrectly placed atoms of an N-atom structure. Formulas are valid for space groups P1 and P{\bar 1}, and describe the influence of the size of the model as well as data truncation. Introduction of the concept of an averaged structure leads to structure-independent conclusions about the behaviour of the resolving power of the product function R in rotation searches. The signal (model with i = n) stands out more clearly against the random noise (models with i = 0) when intensities below a certain threshold are removed from the data set. Results are verified against simulated experiments as well as a real structure.
    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...