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  • American Geophysical Union  (3,207)
  • International Union of Crystallography (IUCr)  (2,664)
  • 1975-1979  (5,871)
  • 1978  (3,126)
  • 1975  (2,745)
Collection
Years
  • 1975-1979  (5,871)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 29-36 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A stereographic projection method of analysis has been developed for analyzing the misorientation contrast of crystal subgrain boundaries which are observed in Berg–Barrett X-ray micrographs. The boundary appearance is described in terms of the geometry of the boundary with respect to the crystal surface, the angular misorientation of the adjacent subgrains, and the X-ray diffraction conditions. The rotation axis for the misorientation of adjacent subgrains, including the sense of the rotation, and the amount of misorientation is determined from the width and relative contrast of the boundary in various images. Experimental results are described for subgrain boundaries in zinc crystals solidified along different crystallographic growth directions. The Burgers vectors of the dislocations composing the subgrain boundary are indirectly determined by this method.
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  • 2
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 42-44 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A means of measuring strain and lattice parameter directly in epitaxic layers by `double-crystal' X-ray diffraction is presented. The method described has three major advantages; that it is achieved by a simple addition to a commercial goniometer; that the area of sample illuminated is defined solely by the collimator; and that single or double-crystal diffraction can be selected, simultaneously if needed, on exactly the same specimen area.
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  • 3
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 45-48 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A silicon powder Standard Reference Material, SRM-640, has been prepared for use as a standard in powder diffractometry. Powder diffraction measurements were performed with a tungsten internal standard and a high-angle goniometer. The measured a/λ is 3.525176. With λ(Cu Kα1 peak) taken as 1.5405981 Å, a = 5.430880 (35) Å, uncorrected for refraction. Comparison of a with values obtained with a single-crystal from one of the boules reveals a difference of 3 parts in 105. This difference suggests a subtle systematic error in powder diffractometry or a change in lattice spacing near crystal boundaries. Use of the SRM should permit individual measurements of lattice parameters to be made reproducible to near 1 part in 105 and an absolute accuracy of at least 3 parts in 105.
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  • 4
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 111-114 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The assumptions in the Borie & Sparks [Acta Cryst. (1971). A27, 198–201] procedure for the separation of order- and displacement-dependent components of diffuse X-ray scattering from a binary system AB are examined with the use of the concentration deviation (spin-like) notation. The more limiting assumption, that the structure-factor ratio η = (mAfA + mBfB)/(fA−fB) is constant in reciprocal space, is shown to produce an incomplete separation for normal variations in η. A matrix-inversion method for completing the separation is suggested for those cases in which the approximate equality of the Debye–Waller factors (DWF) of the individual atomic species indicates that some terms of the scattering equation may be neglected. The extension suggested by Ramesh & Ramaseshan [Acta Cryst. (1971). A27, 569–572] that anomalous dispersion induced changes in η could be used to separate the atomic static displacement properties of the various atomic pairs is shown to require a change in η greater than the variation of η across the reciprocal-space volume. Some difficulties of obtaining such a change are pointed out.
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  • 5
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 121-126 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The role of positional information in determining the thermodynamics of crystalline solid solutions is considered. It is noted that, with certain exceptions (e.g.b.c.c. Fe–B), such solutions can be classified as being exclusively either substitutional or interstitial with respect to each solute. Calculation of thermodynamic properties of intersitital solutions requires knowledge of the types of sites preferentially occupied by the solute. The problem of determining that occupancy is considered for several binary systems. A cumulant expansion technique, which meets with good success in describing dilute, high-temperature, interstitial solutions, is applied to the case of high-temperature binary substitutional systems of similar metals. The technique is shown to be of limited utility in this application.
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  • 6
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 127-127 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: It may be essential in certain cases (e.g. non-dilute alloys and dislocations) to take into account the (pair and higher-order) correlations in the defect distribution. To this end the kinematic expression for the total scattered intensity is rewritten.
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  • 7
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 132-132 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: If the occurrence of one or two-dimensional local order in alloys or in neutron-irradiated materials has been known for many years, the observation by X-ray and neutron scattering of quasi-one-dimensional order due to displacements or correlated motions of atoms along independent chains is more recent. Examples to be discussed are given.
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  • 8
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 75-75 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 9
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 76-76 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
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  • 10
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 128-128 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Structural studies showed that oxygen atoms in Ih ice are well ordered whereas hydrogen atoms are `statistically' distributed on two possible sites on each O–H–O bond.
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  • 11
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 185-185 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The integral Huang diffuse X-ray scattering from crystals containing small dislocation loops can be analyzed to obtain two types of information: (1) the size distribution of the loops and (2) the total number of point defects contained in the loops. This technique has been applied to copper crystals irradiated under a number of conditions of neutron irradiation flux, dose and temperature, for which loops are produced, and to selected annealing studies of these loops, with all X-ray measurements made at room temperature.
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  • 12
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 191-192 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Explanations for the broadening of X-ray line profiles of plastically deformed crystals in terms of the density and the distribution of the dislocations introduced during deformation are given.
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  • 13
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 140-140 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The ω phase transformation in Zr–Nb alloys has been studied by measuring the X-ray diffuse scattering in the (110) plane and the Mössbauer diffuse scattering along the 〈111〉 direction of separate single crystals with compositions ranging from 8 to 30% Nb.
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  • 14
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 141-141 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A simple crystallographic approach in obtaining the final martensitic structure [3R, 1R, 2H) from the initial displacive modes is presented.
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  • 15
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 142-142 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The theory of the diffuse scattering from crystals with small concentrations of point defects and small clusters is reviewed.
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  • 16
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 143-143 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analytic expressions for the dilation and the stress tensor in reciprocal space are discussed.
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  • 17
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 203-203 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The boundary between the −X and Z growth regions in synthetic quartz has been studied using X-ray topography and other techniques and it has been found that the crystal lattice remains coherent at the boundary.
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  • 18
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 204-204 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffraction of electrons is, in principle, a very sensitive probe of the relative atomic positions in ordered or disordered crystals. The full potential of electron diffraction and electron microscopy methods for the study of local atomic arrangements has not been realised because of the difficulties of conducting experiments under sufficiently well defined conditions and because of the complications introduced by the dynamical diffraction processes involved.
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  • 19
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 183-183 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The diffuse elastic neutron scattering due to distortion of the Pb host lattice around Bi substitutional atoms has been measured at the HFR in Grenoble and the results discussed.
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  • 20
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 175-183 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: For interstitials the scattering cross section between the Bragg reflections is very sensitive to the position of the defect atom and the displacements of the neighbouring lattice atoms. In contrast to this the scattering near the Bragg reflections (Huang scattering) is mainly governed by the displacement field at large distances from the defect and gives information about defect symmetry and strength [Trinkaus, H. (1972). Phys. Stat. Sol. (b) 51, 307–319]. For determining structures of point defects a measurement of scattering far from reciprocal-lattice points is therefore the best suited and most direct method. X-ray measurements of point-defect scattering in this region far from reciprocal-lattice points are difficult. With conventional X-ray set-ups it is not possible to separate the defect scattering from the thermal diffuse and Compton background scattering which is up to two orders of magnitude larger in the case of typical defect concentrations of some 10−4. Such measurements, however, become possible if large X-ray sources of high luminous density are used in connexion with multidetector arrangements. As an example an experimental arrangement [Haubold, H.-G. & Schilling, W. (1975). To be published; Haubold, H.-G. (1974). Rep. Kernforschungsanlage Jülich, JUL-1090-FF] is reviewed, in which the scattering cross-section of self-interstitials in aluminium was measured in samples containing an atomic density of interstitials up to 5 × 10−4.
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  • 21
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 184-184 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Second-order pseudopotential calculations are known to reproduce fairly well the structure and phonon spectra of many simple metals. The validity of the underlying assumption of linear screening for impurities with valences and core radii close to those of the host can be checked a posteriori and by comparing calculated properties with measurements on dilute alloys, and, especially, coherent elastic neutron scattering.
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  • 22
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 185-185 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Analytical methods to describe the scattering from crystals containing defect clusters with strong displacement fields are reviewed.
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  • 23
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 193-194 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Work which has been started at Pelindaba on small-angle scattering in neutron irradiated copper is described.
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  • 24
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    Applied crystallography online 8 (1975), S. 193-193 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Voids formed in neutron irradiated metals are faceted on various crystallographic planes. This faceting has been shown to cause significant anisotropy in the small-angle scattering pattern. It is shown that it is possible to obtain the specific void surface energies from small-angle diffuse scattering data.
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  • 25
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 224-224 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The weak-beam method of electron microscopy provides a means for studying lattice defects with greatly increased resolution compared with normal diffraction contrast techniques.
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  • 26
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 386-387 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The thermal expansion of cyclopentadienylthallium, TlC5H5, was determined in the range 78 to 295 K, using X-ray powder diffractometry. Expansion is very anisotropic: α1 = 125 ± 12, α2 = 97 ± 5, α3 = 0 ± 4 (all 10−6 K−1). Directions and ratio of the two greatest expansion coefficients: α1 and α2, are explained by considering the shortest distances Tl+–Tl|+ in this ionic structure.
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  • 27
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 392-395 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Several guanidinium salts have been studied since, because they contain six hydrogen atoms per unit charge, they are likely to contain multiple hydrogen bonding systems [see e.g. Adams & Small (1974). Acta Cryst. B30, 2191–2193], which are of interest in themselves and are also likely to cause stabilization of the structure. The crystal data of a range of salts were collected and are given. Space group and approximate cell dimensions were obtained from oscillation and Weissenberg photographs. Powder diffraction data [0° to 60° (2&thgr; using Cu Kα)] were indexed and the cell parameters refined using the programs PIRUM of Werner [Program No. 1, World List of Crystallographic Computer Programs (3rd. ed.): J. Appl. Cryst. (1973). 6, 309–346] and CELFIT of Bracher [UKAEA Research Report, AERE-R5412 (1967)].
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  • 28
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 397-397 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Unlike the position with negatively charged substituents, little has been done on benzaldehydes ortho-substituted with positively charged groups. This is more especially true in the field of crystallography where only the X-ray and neutron diffraction study of o-nitrobenzaldehyde has been reported [Coppens & Schmidt, Acta Cryst. (1964). 17, 222–228; Coppens, Acta Cryst. (1964). 17, 573–578]. Preliminary results of a structural investigation on Se- and Te-containing benzaldehydes are presented. The main purpose is to corroborate and to complete the conclusion of recent n.m.r. work on the conformation of these molecules [Baiwir, Llabres, Denoel & Piette, Mol. Phys. (1973). 25, 1–7]. The following compounds have been studied: C6H4.COH.TeCl, C6H4.COH.TeBr, C6H4.COH.TeI, C6H4 COH.SeCl, C6H4.COH.SeBr. The crystal structure of the second (TeBr) has been recently reported [Baiwir Llabres, Dideberg, Dupont & Piette, Acta Cryst. (1974). B30, 139–143] and the structure of the last (SeBr) is presently in the final stage of refinement.
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  • 29
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 402-402 
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  • 30
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 8 (1975), S. 403-403 
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  • 31
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    Applied crystallography online 8 (1975), S. 405-414 
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    Notes: Quantitative liquid-structure analysis using energy-scanning diffraction rather than the traditional angle-scanning diffraction is introduced. In the experimental method, white radiation and a solid-state detector are employed. This new method is inherently faster and less beset with problems of experimental instability than are angular-scanning methods. However, many differences in analysis are introduced. In particular, measurement of the primary beam spectrum, the nature of the absorption and dispersion corrections, details of the polarization correction, the ranges of the atomic scattering factor and of the incoherent scattering term, and the mating of different scattering regimes all require special consideration. Application of the new instrumental method and the reconstructed analytical procedure to liquid mercury at room temperature has produced a result in agreement with other recent studies.
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  • 32
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    Applied crystallography online 8 (1975), S. 421-429 
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    Topics: Geosciences , Physics
    Notes: A new small-angle X-ray scattering facility which utilizes a 6 kW rotating anode, pin-hole collimation, and a position-sensitive proportional counter has been developed. As presently constructed, the minimum scattering vector κ (= 4π sin &thgr;/2) which can be reached with Cu Kα radiation is 5 × 10−3 Å−1. Under these conditions the flux incident on the specimen has been found to be 6 × 105 photons s−1. The system has several advantages compared with traditional long-slit geometries; namely, (i) it can quantitatively measure anisotropic scattering distributions, (ii) it avoids large mathematical corrections of the data for slit-smearing effects, and (iii) it minimizes double Bragg scattering in crystalline materials and multiple diffuse scattering in amorphous or liquid materials. To illustrate the performance of this instrument, the scattering curves obtained from four widely different samples are shown. These are: polyethylene, a neutron-irradiated aluminium single-crystal containing voids, a dilute suspension of Ludox spheres, and duck tendon collagen. Quantitative comparisons of the performance with a Kratky camera and with the neutron small-angle scattering facility in Jülich are given.
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    Applied crystallography online 8 (1975), S. 457-458 
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    Notes: The lattice constants of a diamond platelet and of large single, undoped, crystals of silicon and germanium have been determined from measurements of multiple diffraction patterns by the method described in Part I [Post (1975). J. Appl. Cryst. 8, 452–456]. The mean values, based on measurements of eight to twelve reflections, and their standard deviations are: diamond a = 3.566986 Å, Aa/a = 2.6 × 10−6; silicon a = 5.430941 Å, Aa/a = 2 × 10−6; germanium a = 5.657820 Å, Δa/a = 1.6 × 10−6.
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    Applied crystallography online 8 (1975), S. 469-472 
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    Notes: The Mn3+ site distribution in a manganese-containing tsilaisite tourmaline sample has been determined as 46±3 wt. % in the larger Y octahedral sites and 54± 3 wt. % in the smaller Z octahedral sites. For this, a novel application of anomalous X-ray scattering techniques, in conjunction with the energy dispersive X-ray diffraction procedure, has been used. This method appears to be versatile and applicable to many different elements.
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    Applied crystallography online 8 (1975), S. 491-492 
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    Notes: An inexpensive calculation is outlined for determining those reflexions suffering large absorption errors, and for correcting those with smaller errors.
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  • 36
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    Applied crystallography online 8 (1975), S. 496-496 
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    Applied crystallography online 8 (1975), S. 496-497 
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    Applied crystallography online 8 (1975), S. 375-379 
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    Notes: The lattice parameters and the linear coefficient of the lattice thermal expansion of f.c.c. β-Cu2−xSe (1.86 ≥ 2−x ≥ 1.72) were determined by means of the Debye–Scherrer X-ray diffraction technique in the temperature range 25–336°C. The concentration and temperature dependence of the coefficient of thermal expansion are discussed. In addition the equilibrium phase diagram of the Cu–Se system in the region of a non-stoichiometric Cu2−xSe compound (2.00 ≥2−x ≥1.72) was redetermined, with special consideration of the homogeneity range of the f.c.c. β-Cu2−xSe, and compared with previously published results.
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    Applied crystallography online 8 (1975), S. 391-391 
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    Notes: Crystals of Tl2GeS3 were grown by solidification from melts. The compound is triclinic with lattice parameters a = 8.06, b = 12.70, c = 6.76 Å, α = 96°39′, β = 93°10′, γ = 99°31′. Powder data are given.
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  • 40
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    Applied crystallography online 8 (1975), S. 589-597 
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    Notes: A computer program has been written in Fortran for the numerical calculation, using generalized spherical harmonics, of the texture of a sample, even when it has no symmetry. Automatically plotted pole figures, corrected and normalized, make it possible to begin to control the results. Reconstituted pole figures are plotted as a function of Cmνl. The calculations, based on the theoretical developments of Bunge [Mathematische Methoden der Texturanalyse. (1969). Berlin: Akademie Verlag] were carried out with different numerical analyses so as to reduce the size of the calculation and the time taken.
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  • 41
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    Applied crystallography online 8 (1975), S. 578-581 
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    Notes: The white X-ray diffraction method with the use of a powder sample [Laine, Läihteenmäki & Kantola (1972). X-ray Spectrosc. 1, 93–98] was improved by paying special attention to the following four points: (i) the determination of the energy spectrum of incident white X-rays, (ii) the measurement of the energy dependence of the relative absorption coefficient, (iii) the correction for the contribution from thermal diffuse scattering, and (iv) the correction for the anomalous dispersion. The determination of the structure factors of GaP is shown as an example of its applications. The structure factors determined were compared with those obtained by the usual angle dispersive method with monochromated X-rays on the same sample. It is shown that these two sets of structure factors mostly agree within the limit of reproducibility.
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  • 42
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    Applied crystallography online 8 (1975), S. 612-614 
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    Notes: The errors in the Fourier coefficients of the α1 component obtained by α2 elimination are investigated analytically. The effects of counting statistics, of an incorrect intensity ratio of the α1 and α2 components and of an incorrect doublet separation are calculated. The mean-square error in the Fourier coefficient caused by counting statistics is a periodic function of the harmonic number, while errors in the intensity ratio and in the doublet separation primarily affect the first Fourier coefficients. The results are confirmed by computer simulations and by computations with experimental line profiles. The α2 elimination methods assume a perfect shape identity of the α1 and α2 components, but this assumption is not completely justified. Deviations might be interpreted as local errors in the doublet separation and the intensity ratio.
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  • 43
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    Applied crystallography online 8 (1975), S. 628-635 
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    Notes: The textures of undirectionally and reversed rolled aluminium sheets were measured using thermal neutrons and Cu and Mo Kα radiation. The samples for the X-ray measurements were prepared in three different ways so that the degree of correspondence between textures as measured with neutrons and X-rays could be investigated. It is shown that agreement can be achieved if the X-rays used penetrate sufficiently into the sample and if a composite type sample is used.
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  • 44
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    Applied crystallography online 11 (1978), S. 73-79 
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    Notes: In order to avoid some of the disadvantages associated with the desmearing methods, a procedure has been developed where the smeared, primary, intensity data can be evaluated directly without desmearing. The procedure consists of the following: first, a model depending on a vector of unknowns, x = (x1, ...., xn), is constructed; then, an iterative search is made for the vector x, and a scale factor s, which corresponds to a local minimum in the error square sum based on the primary, slit-smeared, intensity data. The main advantages with the present method are that the comparison between theory and experiment is made directly with the experimental quantity; thus the experimental errors can be considered in this comparison. Furthermore, some of the disadvantages associated with the desmearing methods are avoided; the method is numerically stable and no extrapolations outside the measured angular range are necessary. Several data sets measured at different concentrations and with different, completely arbitrary, primary-beam weighting functions can be considered in the same refinement. The interparticle scattering effect may also be included in the least-squares refinement. The method is general, so that different models can be tested simply by changing only one subroutine of the computer program. It may also be used to evaluate data impaired by other types of resolution errors; for example, effects due to polychromatic radiation or resolution errors in neutron scattering. Two constructed examples of the application of the method are given: (1) the calculation of the dimensions and the molecular weight of particles with a shape which can be approximated with an ellipsoid of revolution; (2) the calculation of the dimensions and electron-density distribution for spherical particles.
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    Applied crystallography online 11 (1978), S. 114-120 
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    Notes: A method is described for finding the peak limits of a Bragg reflection from an analysis of its profile. A `window' of ± 0.67σ[φ)(x)] is set up on each ordinate φ(x) in the tails of the profile and the pattern of the following ordinates is observed through the window. As the ordinate moves from the peak to the background the pattern changes and the limits of the peak may be recognized. Bragg reflections from three crystals have been analysed by this method and the limits found were generally wider than those determined by the method of Lehmann & Larsen [Acta Cryst. (1974), A30, 580–584] applied to the same data. The value of σ(I)/I was near the minimum and similar to the value from the corrected Lehmann–Larsen limits. The behaviour of the methods is also compared by representing the reflections by equivalent Gaussian profiles, and it is found that 〉99% of the Gaussian peak is within the limits found by the present method.
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    Applied crystallography online 11 (1978), S. 102-113 
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    Notes: Existing knowledge about Scherrer constants is reviewed and a summary is given of the interpretation of the broadening arising from small crystallites. Early work involving the half-width as a measure of breadth has been completed and Scherrer constants of simple regular shapes have been determined for all low-angle reflections (h2 + k2 + l2 ≤ 100) for four measures of breadth. The systematic variation of Scherrer constant with hkl is discussed and a convenient representation in the form of contour maps is applied to simple shapes. The relation between the `apparent' crystallite size, as determined by X-ray methods, and the `true' size is considered for crystallites having the same shape. If they are of the same size, then the normal Scherrer constant applies, but if there is a distribution of sizes, a modified Scherrer constant must be used.
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    Applied crystallography online 11 (1978), S. 137-140 
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    Notes: The resolution problem in X-ray energy-dispersive diffractometry is discussed. It is shown that for a given characteristic of the solid-state detector system and a given range of interplanar spacings, an optimum scattering angle can be easily found for any divergence of the incident and scattered beams.
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    Applied crystallography online 11 (1978), S. 148-150 
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    Notes: Spherical crystals of alloy phases too hard and brittle for grinding can be obtained by partial remelting and solidification of a powder sample. The alloy powder is blown through an argon-plasma jet melting the surface material of individual fragments, which solidify again as nearly perfect spheres. The yield is a mixture of different materials in which it is possible, however, after heat treatment to find good single crystals of the original composition. Spherical single crystals of Cu9Al4 have been produced by this method and used for a high-precision X-ray investigation described elsewhere.
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    Applied crystallography online 11 (1978), S. 157-158 
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    Notes: Completely transparent and colourless single crystals of PbGe3O7 were grown from a melt of composition PbO.2GeO2 at 1040 K by spontaneous crystallization. The compound melts incongruently at 1070 K. The unit cell is orthorhombic with lattice constants a = 5.270 (2), b = 14.088 (4), c = 16.054 (4) Å; D293 = 5.94 (4), Dx = 5.985 g cm−3 for Z = 8. The probable space group is Pcab (D152h). A reported phase of composition PbGe205 is shown to be a mixture of PbGe3O7 and α-PbGeO3. X-ray powder data are given.
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    Applied crystallography online 11 (1978), S. 238-242 
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    Notes: An X-ray diffraction study of CsDNA has been carried out with the use of synchrotron radiation of wavelength λ = 1.2 Å. The geometry corresponds to a cylindrical specimen brought into a cylindrical beam of the same diameter and the absorption factor and the primary-beam attenuation factor have been calculated as functions of specimen μR for this geometry. The optimum size of a specimen is here about 1.5 times greater than that in the case of a plane-parallel beam used in International Tables for X-ray Crystallography [Vol. II, (1967), 2nd ed., p. 295. Birmingham: Kynoch Press]. Experimental and calculated primary-beam attenuation factors have been compared and the experimental value of the linear absorption coefficient μ of CsDNA has been estimated for various humidities. The agreement between μc = 78.1 and μo = 78.2 ± 3.6 cm−1 (relative humidity 66–75%) indicates that the geometrical model used is suitable to describe polymer fibres in a cylindrical beam of nearly the same size. It is seen from the observed μ values that there is one caesium ion per nucleotide (monomer unit of DNA molecule) in the specimens used.
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    Applied crystallography online 11 (1978), S. 293-294 
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    Applied crystallography online 11 (1978), S. 293-293 
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    Applied crystallography online 11 (1978), S. 294-294 
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    Applied crystallography online 11 (1978), S. 346-375 
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    Notes: Recent advances in the small-angle scattering of X-rays, neutrons and light by polymers are reviewed. The three techniques are compared, from both experimental and theoretical points of view. Applications are discussed for the study of homophase and heterophase polymers, both in solution and in the solid state, as well as for unoriented and oriented crystalline polymers.
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    Applied crystallography online 11 (1978), S. 477-477 
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    Notes: The conformations of different IgG antibodies were studied before and after interaction with antigen (hapten). In every case a strong change of the conformation was observed. Binding of hapten caused a decrease of the radius of gyration by 2 to 8% and a decrease of the volume by 3 to 10%, depending on the degree of saturation with hapten. Two IgG antibodies (anti-poly-d-alanyl) were split by enzymes into fragments which contain one binding site (Fab′) and two binding sites (Fab′)2, respectively, for hapten. No changes of conformation were observed with these fragments upon the interaction with hapten. These findings lead to the conclusion that the conformation change does not take place within the area of the combining site but relatively far away, at the area of the hinge region and/or the Fc-fragment.
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    Applied crystallography online 11 (1978), S. 464-465 
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    Notes: A design study was made of a neutron small-angle scattering (SAS) instrument for use at Argonne National Laboratory's proposed Intense Pulsed Neutron Source, IPNS-II (Carpenter & Werner, 1976; Werner, 1977; Carpenter, 1977). The instrument design incorporates several features: a converging-slit collimator, wavelength band-limiting choppers, capacity for large samples, and a two-dimensional detector. Machine design-dependent parameters are considered in a Monte-Carlo code that produces estimates of the instrumental resolution function and available flux at the sample. It was found that the calculated flux on sample exceeds that at steady-state reactor instruments of comparable resolution.
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    Applied crystallography online 11 (1978), S. 473-477 
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    Notes: A comparative analysis of the sperm-whale myoglobin structure in the crystal and in solution has been carried out with the technique previously formulated by the authors which uses the large-angle X-ray diffuse scattering for investigating the protein structure in solution. A `modified cube method', correctly taking into account the cavities within the protein molecule accessible to the solvent, is proposed for an accurate estimate of the solvent influence and for calculation of the scattering intensities. A comparison of the theoretical myoglobin scattering curves with the experimental scattering curve of this protein obtained by Stuhrmann shows rather noticeable quantitative divergences, which can be eliminated by a small increase in the distance between the `hairpin' GH and the other part of the protein molecule. It is also shown that several other physically reasonable shifts of helices (or groups of helices) do not lead to an agreement between the experimental and theoretical scattering indicatrices.
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    Applied crystallography online 11 (1978), S. 466-472 
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    Notes: The density-contrast method, commonly used in X-ray (and neutron) small-angle scattering studies of macromolecules in solution, can yield a wealth of information if; (a) the solute is monodisperse and the solution is ideal: (b) each macromolecule in solution has a volume associated with it inside of which the density distribution is independent of the density of the solvent. More specifically it has been pointed out that in this case an expression of the molecular weight can be obtained which does not involve the partial specific volume, provided that the X-ray experiments are performed on an absolute scale. On the other hand, it is well known that X-ray scattering experiments on an ideal solution of identical macromolecules can yield the molecular weight for any composition of the solvent, provided solute, solvent and partial specific volumes are defined and measured at constant chemical potential. Therefore a combination of X-ray scattering and densimetry experiments allows one to verify to what extent condition (b) holds true. Such a set of experiments has been performed on Rhesus monkey low-density serum lipoproteins, the solvent being water containing variable amounts of NaBr. It is concluded that in this case condition (b) is fulfilled. Moreover several important aspects of the analysis of the X-ray scattering curves can be verified.
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    Applied crystallography online 11 (1978), S. 479-482 
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    Notes: The theory of the technique currently in use for measuring distances between subunits in macromolecular aggregates by neutron small-angle scattering is outlined. It is shown that estimates for the radii of gyration of subunits within aggregates can be extracted from neutron distance data, in addition to the distances themselves. The current status of efforts to apply these methods to determine the structure of the E. coli ribosome is discussed.
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    Applied crystallography online 8 (1975), S. 329-332 
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    Notes: Kyanite phases Al2SiO5 (I), Al2GeO5 (II) and Cr2GeO5 (III) were synthesized at 20 kb/1000°C (I, II) and at 1 atm/1150°C (III). Powder X-ray patterns for II and III are presented in comparison with that of I. Triclinic lattice constants are a0 = 7.127 (7.253, 7.422), b0 = 7.858 (8.011, 8.244), c0 = 5.570 (5.649, 5.815) Å, α = 89.99 (89.97, 90.58), β = 101.22 (101.23, 101.10), γ = 106.04 (106.05, 106.01)°, and V0 = 293.6 (308.9, 339.9) Å3 for the kyanite phases I (II, III, respectively). Infrared absorption spectra of I (II, III) were measured between 1400 and 200 cm−1. Band shifts produced by the isomorphous substitutions allow tentative band assignments of the Al2SiO5-kyanite spectrum: 1032, 1009, 940 cm−1 ν3 (SiO4); 898 cm−1 ν1 (SiO4); 720, 438 cm−1 ν4, ν2 (SiO4) ?; banes between 674 and 505 cm−1 and at 467 cm−1 are mainly due to octahedral Al–O vibrations.
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    Applied crystallography online 11 (1978), S. 483-484 
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    Notes: Neutron-scattering studies of chromatin core particles in solutions containing various mixtures of D2O/H2O and small molecules (glycerol) show that the water closely associated (or bound) with the particles is largely in the outer DNA-rich regions. This confirms the fact that the particles contain a core composed of the hydrophobic regions of histone proteins.
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    Applied crystallography online 8 (1975), S. 343-344 
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    Applied crystallography online 8 (1975), S. 343-343 
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    Applied crystallography online 8 (1975), S. 352-355 
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    Notes: An attractive use of a convergent-beam camera is described. Its advantages, with respect to classical methods, are pointed out. The short exposure time provided by this device is very useful in the selection and detailed study of polytypic crystals. Some X-ray photographs obtained from a titanium sulphide polytypic crystal are displayed.
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    Applied crystallography online 8 (1975), S. 365-371 
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    Notes: Solids characterized by lamellar structure are often made from ribbon or lath-shaped sheets. Such a morphology has been observed in phyllosilicates (hectorite or nontronite, for example) and in carbon fibres. This contribution aims to show that elongated planar sheets can be detected from the profile of the X-ray diffraction bands yielded by the powdered solid. The numerical technique originally developed by Brindley & Méring [Acta Cryst. (1951). 4, 441–447] for isometric layers, has been extended to ribbon or lath-shaped elementary layers. An example of application is given when the sheet is a carbon layer.
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    Applied crystallography online 8 (1975), S. 380-385 
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    Notes: About fifty X-ray powder diagrams were recorded in the range 15 to 295 K, by means of a prototype diffractometer and a high-efficiency cryostat, so that a very precise study of the anisotropic structural evolution of ferrocene could be made. The cell parameters and volume have been computed. These parameters present a discontinuity at 164 K; the cell is triclinic below and monoclinic above this temperature. The transition is first order. The principal thermal expansion coefficients have been computed and their evolution, in terms of temperature, has been related to the anisotropic change of the intermolecular contacts in the crystal. Assumptions about the mechanism of transition and about the ferrocene configuration in the ordered phase are expressed.
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    Applied crystallography online 8 (1975), S. 388-389 
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    Notes: A graphical construction on the Wulff net permits corrections on both arcs and the dial to be determined even if neither of the arcs is parallel to the film and/or the outer arc reading is large. The procedure requires that the orientation errors be multiplied by an arbitrary common factor smaller than ten, while the biggest multiplied error should be less than ten degrees: the corrections are obtained graphically and divided by the factor. Corrections thus obtained are within 10% of their true values.
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    Applied crystallography online 8 (1975), S. 398-400 
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    Notes: Tl2Mo7O22 is monoclinic with space groupe C2/c or Cc and with a = 20,512 (6); b = 5,526 (2); c = 19,460 (6) Å; β = 125,20 (3)°: Z = 4. Tl2Mo4O13 is orthorhombic with space group Pbca and with a = 7,583 (3); b = 15,409 (3); c = 18,798 (3) Å; Z = 8. Tl7Mo2O7 is monoclinic with a = 8,427 (2); b = 5,690 (2); c = 7,935 (2) Å; β = 108,90 (2)°; Z = 2. The indexed powder diagrams are given.
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    Applied crystallography online 8 (1975), S. 402-402 
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    Applied crystallography online 8 (1975), S. 403-403 
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    Applied crystallography online 11 (1978), S. 514-519 
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    Notes: The use of the polymers tagged with heavy atoms in random positions along the chains (randomly tagged polymers) in small-angle X-ray scattering is proposed as a new method for measuring the chain conformations in concentrated solutions and in bulk polymers. The experimentally determined excess scattering from the tagged chains dispersed in the system is shown to be proportional to the scattering function of the hypothetical chains that have no tags but have the conformation of the tagged chains when the heavy atoms have sufficiently large scattering power. It has been experimentally verified that the effect of the tags on the chain conformation can be eliminated by the extrapolation of the apparent values, measured for a series of tagged polymers with various tag content, to zero tag content. The radii of gyration of the polystyrene chains (M = 1.1 × 105) in the bulk and in concentrated solutions in a good solvent and a θ-solvent have been determined. The chain dimension in a good solvent (toluene at 25°C) decreases rapidly first and then gradually approaches the unperturbed dimension with increasing polymer concentration. The dimension in a θ-solvent (trans-decalin at 21.2°C) is independent of the polymer concentration. The conformation of the polystyrene chains in the bulk was found to be a Gaussian coil.
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  • 72
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    Applied crystallography online 11 (1978), S. 525-530 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Small-angle X-ray scattering from oriented mats and random suspensions of polyethylene single crystals has been studied. A modification of the Guinier equation for platelets was derived to accommodate the two-phase nature of polymer lamellae. This modification also permitted the modelling of various degrees of interaction between lamellae and suspending media. Dried crystal mats show an increase in fold period on contact with potential solvents. Crystals which have never been dried show no evidence of penetration of the fold surface by the same liquids. Apparently the drying process causes a reorganization of the surface of the lamellae. Since the fold surfaces of crystals in suspension are unaffected by the liquids used, it is reasonable to assume a `tight' fold surface model. Crystallinities calculated with this model are in excellent agreement with recent differential scanning calorimetric data on crystals kept in suspension.
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  • 73
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    Applied crystallography online 11 (1978), S. 519-523 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The study of semi-dilute polyelectrolyte solutions by small-angle neutron scattering shows that the correlation function S(q) of all the chains presents a peak for a value q = qh of the scattering vector q. This is taken as evidence for some organization among the elongated polyions. This phenomenon has been observed for a fraction of polymethacrylic acid of very low molecular weight. The experiments show essentially: (1) the progressive vanishing of the peak with the addition of a neutral salt at constant polyelectrolyte concentration; (2) the variation of qh with the polyelectrolyte concentration c, qh ∝ c1/2; (3) the decrease of the peak intensity as the charge density of the chain increases. These results, which indicate the important role of the electrostatic interactions on this organization phenomenon, are discussed in terms of a lattice model and a recently proposed isotropic model.
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  • 74
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    Applied crystallography online 11 (1978), S. 535-539 
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    Topics: Geosciences , Physics
    Notes: The concept of interface distribution functions [Ruland (1977). Colloid Polym. Sci. 255, 417–427] has been applied to the evaluation of the small-angle scattering of a series of polyethylene samples. The results indicate that the statistics of the lamellar stacking is not necessarily determined by next-neighbor interactions and that non-negligible volume fractions of amorphous domains outside the lamellar systems are observed in a number of samples.
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  • 75
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 551-557 
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    Topics: Geosciences , Physics
    Notes: Crystallization of a linear polyethylene from the melt was followed in situ with the ORNL 10-meter SAXS camera [Hendricks (1978). J. Appl. Cryst. 11, 15–30]. Specimens were rapidly cooled in the X-ray beam in tandem birdcage furnaces from 1̃80°C to temperatures between 115 and 126°C, and scattering patterns were recorded for 30 s in 50 s intervals. Because of this relatively high-speed data acquisition rate, it was possible to obtain data in time periods which were short compared to the rate of change of the scattering patterns. The SAXS curves showed shapes which changed continuously during crystallization. The scattering curves are the superposition of a zero-angle peak and a Bragg maximum. Guinier plots of the zero-angle peak manifest scattering by lamellae of constant thickness. The thickness value is nearly that expected for crystallites at these crystallization temperatures. A model in which skeletal spherulites form and then later fill in is consistent with these results. Decreasing SAXS intensity and changing Bragg peak intensities indicate crystal thickening during cooling to room temperature.
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  • 76
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    Applied crystallography online 11 (1978), S. 558-563 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The microdomain structure of polystyrene-polyisoprene A-B type block copolymers was analysed by small-angle X-ray scattering (SAXS) as an ideal model system for a pseudo two-phase solid structure. The structure was analysed in terms of spatial distribution, size, and the interracial structure of the dispersed domains of one component (A segments) in the matrix of the other (B segments). The SAXS analyses were performed with two collimating systems, a Rigaku Denki camera (essentially a four-slit system with the addition of Soller slits) and a Kratky camera, which had widely different slit-length and slit-width weighting functions and was used to investigate instrumental effects, especially the role of the Soller slits in the obtaining of reliable desmeared intensity data in the tail of the SAXS curve. Comparison of the results indicated that the Soller slits facilitate the accurate evaluation of the interfacial thickness from the desmeared intensity data in the tail. The accuracy of the infinite slit-height approximation and the effect of truncating the higher-order terms in Ih (the intensity associated with the interphase) on the estimated interfacial thickness are discussed. The infinite slit-height approximation leads to values 25–35% smaller than the exact value (23 Å), and the truncation also leads to a value of the interfacial thickness smaller (19 Å) than the value (23 Å) based on the full analysis. The value obtained is in good agreement with the values predicted from the statistical-mechanical theories of block copolymers in bulk.
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  • 77
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    Applied crystallography online 11 (1978), S. 572-577 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Isothermal decomposition of a Au-60 at.% Pt alloy, quenched from the solid as well as the liquid state, has been studied with the D11 neutron small-angle scattering spectrometer at ILL, Grenoble. An incident neutron wavelength of 6.7 Å was used and measurements were carried out in the range of scattering vector [β = 4πsin θ/λ] from 2.8 × 10−2 to 21 × 10−2 Å−1. The preliminary results indicate that decomposition of this alloy at 550°C takes place by a spinodal mode, although deviations were observed from linear spinodal theory, even at very early times. Slower aging kinetics were observed in liquid-quenched alloy as compared with solid-quenched. Liquid quenching is more efficient in suppressing quench clustering than is solid quenching. However, liquid quenching yields an extremely fine-grained material, which thereby enhances discontinuous precipitation at grain boundaries, competing with decomposition in the bulk. A Rundman–Hilliard analysis was used for the early stages of the spinodal reaction to obtain an interdiffusion coefficient of the order of 10−16 cm2 s−1 at 550°C for the solid-quenched alloy.
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  • 78
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    Applied crystallography online 11 (1978), S. 564-568 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Two methods for performing small-angle electron scattering (SAES) experiments in transmission electron microscopes are described: the long-camera-length method and the selected-area-diffraction method. It is shown experimentally that angular resolutions of a few microradians and a few tenths of milliradians, respectively, are easily obtained by these two methods. A number of examples of the application of SAES to problems in materials science are presented. The use of new high-brightness electron sources is expected to produce significant increases in angular resolution, and the use of electron-energy analyzers will permit the separation of most of the inelastic contribution to the SAES intensity distribution.
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  • 79
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    Applied crystallography online 11 (1978), S. 583-588 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The creep properties in high-temperature alloys are dependent on the presence of second and higher phase components. In particular in the nimonic group of alloys the size distribution and concentration of the γ′ phase are crucial factors in the resistance to creep. A possible mechanism for degradation of creep resistance is the Ostwald ripening of the γ′ phase. A sample of Nimonic 105 (Trademark of Henry Wiggin and Co. Ltd) was subjected simultaneously to a stress of 500 MPa and a temperature of 800°C in situ in the beam using a specially developed cell on the small-angle scattering facility (D 11A) at the Institut Laue Langevin. Scattering patterns were taken continuously and spectra were recorded every ̃20 min; the macroscopic creep was also recorded. Measurements were taken up to the point of fracture. A peak in the intensity was observed at a scattering vector κ (= 4π sin θ/λ) of 0.005 Å−1 which is believed to be the lowest value at which such an effect has been observed in alloys. The observed variation in the scattering after treatment for multiple scattering and absorption corrections is discussed in terms of particle size and size distribution.
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  • 80
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    Applied crystallography online 11 (1978), S. 658-661 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A double-mirror monochromator in which one of the mirrors is considerably longer than conventionally employed has been used to collect diffraction data from crystalline tobacco mosaic virus (TMV) protein (unit cell: 224 × 228 × 174 Å). Considerable improvements in speed of data collection are observed over both customary focusing optics and pinhole collimation. Quantitative comparisons are made of the quality of data collected from TMV protein by this method and by the use of nickel-filtered radiation.
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  • 81
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    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 654-657 
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    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Correlation between the symmetry of the two-dimensional flux-line lattice (FLL) and the real crystal lattice (CL) has been studied in a superconducting niobium sphere by means of small-angle neutron diffraction. A double-perfect-silicon-crystal diffractometer enabled precise determination of the three interfluxoid distances corresponding to the FLL basic cell. A systematic study of the anisotropic behavior was made as a function of temperature and magnetic field amplitude for fields parallel to a few high-symmetry CL axes in the (1{\bar 1}0) plane. In addition, at T = 4.30 K progressive deformation of the FLL was studied as the sample was rotated in the (1{\bar 1}0) and (100) planes. The FLL was found to be hexagonal only for fields parallel to the threefold CL axis. Twofold symmetry prevailed for other CL directions in these planes except near the fourfold axis, where either of two distorted triangular lattices existed, preserving the reflection symmetry in composite, but not individually. When compared to current models for fluxoid-CL interactions, the present results show that no theory predicts the observed behavior quantitatively under general conditions, but some models agree well for certain high-symmetry CL axes.
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  • 82
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    Applied crystallography online 11 (1978), S. 669-669 
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    Topics: Geosciences , Physics
    Notes: Some multiplicities for the Laue class \bar 31m are not correct in several standard texts.
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  • 83
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    Applied crystallography online 11 (1978), S. 650-653 
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    Topics: Geosciences , Physics
    Notes: The double-perfect-crystal small-angle diffraction technique enables measurement of scattering angles to within an accuracy of 0.3′′ of arc. At a wavelength of 2.55 Å, this provides a resolution of 3 × 10−6 Å−1 in the scattering vector. This technique has been used to study the anisotropic behavior of the critical parameters B0 and Hc1, characteristic of the first-order magnetic phase transition which occurs in low-κ type II superconductors. Magnetic fields were applied parallel to several crystal axes in the (1{\bar 1}0) and (100) planes of a large single-crystal sphere of pure niobium, resulting in well defined flux-line lattices (FLL). Measurement of the FLL cell area in the intermediate, mixed-state-field region gives the equilibrium flux density B0, which results from an attractive interaction between fluxoids. In addition, field variation of the scattered neutron intensity allows measurement of the transition field between the mixed state and intermediate mixed state. This transition field is related to the lower critical field Hc1 and enables its determination to a precision of 0.2%. Data at T = 4.3 K display a small anisotropic effect of about 2% in B0 and 1% in Hc1. Although orientation effects of this magnitude are difficult to resolve by bulk measurements, the neutron data are in accord with magnetization data. The temperature dependence of these parameters is found to be in qualitative but not quantitative agreement with current theoretical models.
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    Applied crystallography online 11 (1978), S. 669-669 
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    Topics: Geosciences , Physics
    Notes: An amendment to a computer program for determining multiplicities of powder reflections [Rouse & Cooper (1977). J. Appl. Cryst. 10, 134–135] has been made to correct an error in the multiplicity values given for some reflections for space groups with {\bar 3}1m Laue symmetry, which exists in some of the standard texts.
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    Applied crystallography online 11 (1978), S. 662-668 
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    Notes: A method is described for precision measurement of lattice parameters in cubic crystals, interplanar spacings and angles between crystallographic directions for single crystals of any system. The minimum measurable values of angle between crystallographic directions, Δd/d and Δa/a have been found to be ̃105 rad, ̃3 × 10−5, and ̃5 × 10−5, respectively.
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    Applied crystallography online 11 (1978), S. 670-671 
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    Topics: Geosciences , Physics
    Notes: The cell constants of recrystallized diphenylsilanediol were refined from precision powder data taken with Cr Kα1 (2.28962 Å): a = 14.493 (5); b = 15.012 (6); c = 9.897 (6) Å; α = 100.84 (9); β = 100.01 (5); γ = 120.77 (5); U = 1721.6 Å3; Z = 6; Dm (25°C) = 1.255 (3); Dx = 1.252 g cm−3.
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    Applied crystallography online 11 (1978), S. 671-671 
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    Applied crystallography online 11 (1978), S. 673-674 
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    Applied crystallography online 11 (1978), S. 675-680 
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    Notes: The simulation of the photography remains the worst part in the calculation of transmission electron micrographs and X-ray topographs. Storage displays have been used to enhance this part of the process and the different possibilities of these screens studied. The quality of all simulations has been substantially increased by using these displays, which are now in common use.
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    Applied crystallography online 11 (1978), S. 684-687 
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    Topics: Geosciences , Physics
    Notes: A high-resolution energy-dispersive diffractometer is described, which uses a synchrotron source and a scanning channel-cut silicon crystal. The technique is demonstrated with a powdered sample of BaTiO3 and analysis of the profiles demonstrates the anomalous particle-size effect reported by Anliker, Brugger & Känzig [Helv. Phys. Acta (1954), 27, 99–124].
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    Applied crystallography online 11 (1978), S. 719-720 
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    Applied crystallography online 11 (1978), S. 720-720 
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    Acta crystallographica 34 (1978), S. 1-2 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
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    Acta crystallographica 34 (1978), S. 27-30 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A probabilistic theory is described which is able to estimate in P{\bar 1} the values of two and three-phase structure seminvariants respectively.
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    Acta crystallographica 31 (1975), S. 1-7 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The resolution function is derived for a three-axis neutron spectrometer in which the monochromator scattering plane is at an angle to the specimen and analyser scattering planes. The analysis shows that the width of measured peaks is much more affected by the slope of the dispersion surface under investigation than by the angle between the planes. It is concluded that a spectrometer which is used on a hole inclined at 35° would have satisfactory resolution and intensity for most purposes.
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    Acta crystallographica 34 (1978), S. 31-38 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The use of magic integers in phase determination is examined in the light of the theory of Main [Acta Cryst. (I 977). A33, 750-757]. The integers may be used in the economical search of an n-dimensional function of the phases. An interpolation procedure in the n-dimensional phase space allows the use of integer sequences of quite high error, with a consequent reduction in the magnitudes of the integers used. The number of variables to be associated with the magic-integer sequences is also examined. It is found that this number has virtually no effect on either accuracy of phase representation or on computing time. The range of one of the variables can be restricted, where necessary, in order to define the enantiomorph, thus using several phases simultaneously to give a strong enantiomorph definition. A convergence procedure is described for choosing the phases to be represented by magic integers. Magic integers may also be used to choose sets of phase values for the reflexions used in MULTAN to start phase determination. This replaces the more usual quadrant permutation method and results in large savings in the number of starting sets to be explored. MULTA N is thus made more powerful for the same computing time as before.
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    Acta crystallographica 34 (1978), S. 43-47 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The real part, f' of the anomalous dispersion correction to atomic structure factors was measured by using Pendellösung fringes for Si 220 and {\bar 22}0 reflections in the wavelength range from Cu Kα1 to Rh Kα1. In order to avoid ambiguity in the Thomson-scattering term due to the nature of the bonding, the quantity (f'X - f'Ag) was compared with the available theoretical calculations. In this expression, f'X and f'Ag are the corrections for radiation X and Ag Kα1, which is used as the standard, respectively. The present experimental results fit best the values calculated by Cromer & Liberman [J. Chem. Phys. (1970), 53, 1891-1898].
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    Acta crystallographica 34 (1978), S. 48-51 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: By the use of convergent-beam and critical-voltage measurements it has become possible to measure the crystal potential to an accuracy of about 10-3. The possibility that the contribution from virtual inelastic scattering is greater than the errors in these experiments is examined and it is shown that only virtual scattering from single-electron excitations need be considered. Estimates are given for the Fourier coefficients of the virtual inelastic scattering potential for silicon, copper and germanium and these are compared with the errors in the critical-voltage experiments of Hewat & Humphreys [High Voltage Electron Microscopy (1974), edited by P. R. Swann, C. J. Humphreys & M. J. Goringe, pp. 52-56. London and New York: Academic Press]. It is concluded that the virtual inelastic scattering contribution is less than the experimental errors.
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    Acta crystallographica 34 (1978), S. 52-54 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Expressions are developed for the components of the linear Lagrangian, linear Eulerian, finite Lagrangian (Green's), and finite Eulerian (Almansi's) strain tensors in terms of a crystal's lattice parameters before and after a deformation. The development has been undertaken with the concepts and notations of linear algebra.
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    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 55-60 
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    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: An automatic method of obtaining periodic bond chains (p.b.c.) in AaBb compounds is presented. The program analyses every crystallographic short direction and for each it makes systematic trials of every atom succession that could be a p.b.c. The chain is built up with the atoms at the smallest distance from the line considered to be the p.b.c. This program is applied to crystals of rutile, anatase and barite, and it gives all their known p.b.c.'s, plus another two in the case of barite.
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