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  • 72.20  (1)
  • 74.50. +r  (1)
  • Key words Regeneration  (1)
  • Springer  (3)
  • 1995-1999  (3)
  • 1975-1979
  • 1
    ISSN: 1432-0630
    Schlagwort(e): 72.20 ; 72.80 ; 78.65
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Fine-grained (d≈0.1 μm), polycrytalline SiC films were prepared on top of insulating and optically transparent sapphire substrates by means of a thermal crystallization technique. Optical absorption measurements indicate that the individual SiC grains consist of relatively defect-free β-SiC surrounded by high-defect density grain-boundary material. Nominally undoped material exhibits a low de conductivity (δ≈10−8 Ω−1 cm−1) in the dark and an efficient photoconductivity apon illumination with short-wavelength UV light. The temperature dependence of the de transport exhibits a quasi-Arrhenius-type behaviour with average activation energies of the order to 0.6 eV. A characteristic feature of this kind of transport is a continuous increase in activation energy with increasing film temperature. Upon doping with N, P and Al ions, the average activation energy is decreased and room temperature conductivities of the order of 0.1 Ω−1 cm−1 are reached. Doping with B ions, on the other hand, only leads to high-resistivity material. It is shown that the electronic transport in doped SiC-On-Sapphire (SiCOS) films can be successfully modelled in terms of a grain-boundary-dominated conduction process. In this process thermal activation across potential barriers at the grain-boundary surfaces competes with funneling through these same barriers.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Development genes and evolution 206 (1996), S. 344-348 
    ISSN: 1432-041X
    Schlagwort(e): Key words Regeneration ; Pattern formation ; Vitamin A ; Homeosis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract  Homeosis, the ectopic formation of a body part, is one of the key phenomena that prompted the identification of the essential selector genes controlling body organization. Shared elements of such homeotic genes exist in all studied animal classes, but homeotic transformations of the same order of magnitude as in insects, such as the duplication of the thorax in Drosophila mutants, have not been described in vertebrates. Here we investigate the capacity of retinoic acid to modify tail regeneration in amphibians. We show that retinoic acid causes the formation of an additional body segment in regenerating tails of Rana temporaria tadpoles. A second pelvic section, including vertebral elements, pelvic girdle elements and limb buds, forms at the mid-tail level. This is the first report of a homeotic duplication of a whole body segment in vertebrate axial regeneration.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    ISSN: 1573-7357
    Schlagwort(e): 74.50. +r ; 74.70. Vy ; 73.40. Gk
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A periodic structure has been observed in the tunneling characteristics of HTSC break junctions. This structure is explained in terms of the electron-hole interference effect in the surface layer, which causes the formation of bound states in the normal regions N of the SNINS-type junctions. Good qualitative agreement has been found between experimental data and the predictions of the Arnolds proximity model. Several parameters of the SNINS-type structures have been derived from studies of Fiske resonances in HTSC Josephson break junctions in weak magnetic fields.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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