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Start date: 1987End date: 1987Subject: search.filters.subject.530Institute: search.filters.UBSInstitut.Institut für Theoretische und Angewandte Physik (aufgelöst)Publication Type: search.filters.UBSTyp.Zeitschriftenartikel

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Now showing 1 - 4 of 4
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    Metallic glasses and chiral nematic liquid crystals
    (1987) Trebin, Hans-Rainer; Longa, Lech; Salzgeber, Benno
    Geometrical frustration exists in both metallic glasses and chiral nematic liquid crystals. Applying results from the Landau-Ginzburg theory of liquid crystals and from polytope models for the amorphous state, a frustrated free-energy density for metallic glasses is derived. It is expressed in terms of an order parameter that characterizes the bond orientation of neighbouring atoms.
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    Disclinations in quasicrystals [Erratum]
    (1987) Bohsung, Jörg; Trebin, Hans-Rainer
    The most significant feature in the transition from the quasicrystalline to the amorphous state is the loss of long-range bond-orientational order. Disclinations are candidates for elementary excitations which destroy angular correlations. Generalizing the topological defect classification, we investigate point singularities in two-dimensional pentagonal quasicrystals and construct disclinations, dislocations, and disclination dipoles.
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    An extension of the Landau-Ginzburg-de Gennes theory for liquid crystals
    (1987) Longa, Lech; Monselesan, Didier; Trebin, Hans-Rainer
    Using angular momentum representation a method is proposed that allows the systematic construction of a generalized Landau-de Gennes elastic free energy of liquid crystals, in powers of a symmetric and traceless tensor order parameter, polarization field, of external fields and all respective derivatives. By this method all linearly independent elastic invariants and surface terms are constructed for nematics and cholesterics up to fourth order terms. In particular it is shown that up to fourth order in the tensor order parameter there are nineteen bulk elastic constants and four surface terms in the free energy of a general, biaxial nematic. In addition, the stability of this expansion is studied in detail. Some special cases of the elastic free energy of liquid crystals, already discussed in the literature, are reexamined and discrepancies with our results are emphasized. Finally, a thermo-dynamically correct way of establishing contact between the generalized de Gennes elastic free energy and other theories, like those of Oseen-Frank or Meyer, is proposed by applying fluctuation theory. Thus, the degeneracy of splay and bend elastic constants is removed even when these are calculated from the standard de Gennes free energy. Restrictions on higher order elastic constants are also obtained by comparing mean field relations and stability conditions with available experimental data.
  • Thumbnail Image
    ItemOpen Access
    Disclinations in quasicrystals
    (1987) Bohsung, Jörg; Trebin, Hans-Rainer
    The most significant feature in the transition from the quasicrystalline to the amorphous state is the loss of long-range bond-orientational order. Disclinations are candidates for elementary excitations which destroy angular correlations. Generalizing the topological defect classification, we investigate point singularities in two-dimensional pentagonal quasicrystals and construct disclinations, dislocations, and disclination dipoles.