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  • 1
    Electronic Resource
    Electronic Resource
    Méthode directe de correction des profils de raies de diffraction des rayons X. I. Méthode numérique de déconvolution (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 335-338 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A new method of correction of X-ray powder diffraction line profiles by deconvolution is being developed. The convolution equation, representing the phenomenon of deformation of a true diffraction line profile, is approached with the help of a quadrature formula by a system of linear equations. The bad conditioning of this system has led to the use of a stabilization method enabling one to obtain a result converging to the true solution which satisfies the physical phenomenon. The quadrature formulae which are used are described. This method has been programmed in Fortran II for the IBM 1620.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739469000544
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  • 2
    Electronic Resource
    Electronic Resource
    Crystallography, geometry and physics in higher dimensions. II. Point symmetry of holohedries of the two hypercubic crystal systems in four-dimensional space (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 331-337 
    Details
    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
    URL: http://dx.doi.org/10.1107/S0108767384000714
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  • 3
    Electronic Resource
    Electronic Resource
    Crystallography, geometry and physics in higher dimensions. III. Geometrical symbols for the 227 crystallographic point groups in four-dimensional space (1987)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 43 (1987), S. 294-304 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: A geometrical 'WPV' notation for crystallographic point symmetry groups (PSG) in four-dimensional space is proposed. This simple notation generalizes the Hermann-Mauguin notation and makes it possible to retrieve the PSG elements easily. Tables classifying all elements of each PSG for systems 1 to 28 are presented. For higher systems, from 29 up to 33 inclusive, the results of the work are not reported owing to the space required, but they are at the disposal of the reader upon request.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387099367
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  • 4
    Electronic Resource
    Electronic Resource
    Structure du nitrate de nickel tétrahydraté (1967)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 22 (1967), S. 699-705 
    Details
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0365110X67001392
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  • 5
    Electronic Resource
    Electronic Resource
    Méthode directe de correction des profils de raies de diffraction des rayons X. II. Influence de la fente réceptrice sur l'enregistrement d'un profil de raie de diffraction X (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 338-350 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The numerical method of deconvolution described in part I is applied to a study of a broadening factor of the diffractometer: the receiving slit. By considering this factor the validity of this direct method of deconvolution, which can also be applied to analytical profiles and to experimental profiles, is verified. These results are compared with those obtained with the Stokes method for the Fourier analysis of line profiles and with those obtained with the Ergun method. An experimental study shows the importance of the divergence of parallelism between the receiving slit and the beam of X-rays.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739469000556
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  • 6
    Electronic Resource
    Electronic Resource
    Définition algébrique des groupes de symetrie (d'isométries) des cristaux et autres objets parfaits de l'espace à n dimensions (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 432-441 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Using isomorphism properties of translation groups, an intrinsic definition of the classes of perfect objects belonging to n dimensional space, such as crystals, semicrystals, non-crystals and perfect gas, is given. Through the partition of space group G with respect to its (invariant) translation sub-group T, its point group is defined, an isomorph of the group of classes G/T. Examples are given, with symmorphic or non-symmorphic objects in spaces E2, E3, E4 and En. Moreover, the unsuitable expression 'Bravais lattice' should be changed into 'Bravais type of cell'.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478000868
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  • 7
    Electronic Resource
    Electronic Resource
    Sesquioxyde de plomb, Pb2O3. I. Determination de la structure (1970)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 26 (1970), S. 501-510 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The structure proposed for lead sesquioxide by Byström (1947) is incorrect. The space group found in the present work is P21/a with four Pb2O3 in the unit cell; the unit-cell dimensions are: a = 7.814, b = 5.625, c = 8.466 Å (all ± 0.003 Å); β = 124°48′ ± 5′. The structure has been determined by means of X-ray and neutron-diffraction powder data, and refined by a full-matrix least-squares method. The Pb4+ ions are surrounded by six oxygen atoms forming deformed octahedra, with an average Pb–O distance of 2.18 Å. These octahedra share edges and corners to form a two-dimensional framework parallel to (001). These layers are interconnected by pb2+ ions having sixfold coordination, with Pb–O separations ranging from 2.30 to 3.00 Å. The three shortest distances Pb2+–O2− give rise to a Pb2+ coordination reminiscent of the threefold coordination of Pb2+ in Pb3O4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739470001316
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  • 8
    Electronic Resource
    Electronic Resource
    Sesquioxyde de plomb, Pb2O3. II. Etude de la dilatation thermique d'un monocristal (1970)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 26 (1970), S. 510-514 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The thermal expansion of Pb2O3 has been determined by X-ray diffraction in the temperature range 22–160°C. The linear coefficients of the thermal expansion tensor, calculated by least-squares analysis of experimental data, are: α1 = 8.6 ± 0.5, α2 = 21.9 ± 0.3, α3 = 18.0 ± 0.5 (all 10−6°C−1); ψ = (a, a1) = −28° 20′ ± 2°. The anisotropy of thermal expansion is explained, in agreement with the structure found for Pb2O3, by interionic repulsions between Pb4+ and Pb2+ ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739470001328
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  • 9
    Electronic Resource
    Electronic Resource
    Modèles analytiques d'évolution structurale: calcul des paramètres de la maille orthorhombique de Pb3O4 en fonction de la température (1982)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 195-200 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: From elementary equations it is possible to express the a, b, c cell parameters of the Pb3O4 orthorhombic phase as analytical functions of temperature. Analytical laws of the variation of thermal expansion coefficients are postulated. Models may be refined from experimental data. Analytical functions a(T) or b(T) explain the experimental laws of variation. The negative value of the ae coefficient of the orthorhombic phase is also justified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739482000448
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  • 10
    Electronic Resource
    Electronic Resource
    Les cristaux deux-colorés deux-dimensionnels considérés comme projections cotées de semi-cristaux (2+1)-dimensionnels (1984)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 40 (1984), S. 631-635 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Two-colour two-dimensional crystals may be considered as heightened projections of (2 +1)- dimensional semi-crystals. In these semi-crystals, the structure spreads on both sides of a plane; the positions are repeated by a translation lattice parallel to the plane; there is no crystal-lattice repetition in the third dimension. It is possible to classify the two-colour two-dimensional crystals as follows: (1) One-colour crystals, which are the projections of the semi-crystals whose equivalent positions are all situated on the same side of the plane for a given set. (2) Two-colour crystals based on ordinary lattices, which are the projections of the semi-crystals possessing equivalent positions situated on both sides of the plane; but this plane is neither a reflection nor a glide plane of the semi-crystals. (3) Two-colour crystals based on coloured lattices, which are also the projections of the semi-crystals possessing equivalent positions on both sides of the plane; this plane is a glide plane of the semi-crystals. (4) Grey crystals, which are the projections of the semi-crystals with equivalent positions on both sides of the plane; this plane is a reflection plane of the semi-crystals. The sets of equivalent positions of the coloured groups are easily obtained from the sets of equivalent positions of the symmetry groups of the semi-crystal by a method due to Wood [Bell Syst. Tech. J. (1964), 43, 541-559; Bell Teleph. Syst. Tech. Publ. (1964), Monogr. No. 4680].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767384001306
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