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  • 1
    ISSN: 1432-0630
    Keywords: PACS: 71.20Tx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 82 using photoemission and electron energy-loss spectroscopy in transmission. In particular, the impact of the isomer symmetry of the C82 cage (Cs or C3v) on the electronic structure and on the optical properties is analysed in detail. For both isomers, combined XPS and XAS measurements of the Tm 4f and 4d states offer conclusive proof of a divalent encaged Tm ion. No significant change of the valence of the rare earth ion upon changes in the cage symmetry is observed. From the C 1s excitation spectra we find a more pronounced LUMO for the C3v(8) isomer, as is expected for the higher symmetry of the cage. Additional information about the optical properties was obtained from the low-energy loss function. With use of a Kramers–Kronig analysis, the dielectric function, ε, and the optical conductivity, σ, have been derived. ε(0) and the onset of the spectral weight are found to be 7.7 [12.8] and 0.6 eV [0.8 eV] for the Cs(6) {C3v(8)} isomer, respectively.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of geometry 21 (1983), S. 59-65 
    ISSN: 1420-8997
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract Affine planes which admit a point transitive collineation group and at least one affine elation are considered. Such a plane is shown to be (A,ℓ∞)-transitive for some point A on ℓt8 and to be a translation plane if at least two distinct elation centers exist. If the plane has at least (order)1/2+1 distinct elation centers and the group generated by the elations is nonsolvable then the plane is either Desarguesian or Lüneburg-Tits.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Bulletin of volcanology 57 (1995), S. 229-239 
    ISSN: 1432-0819
    Keywords: Lava dome ; Lava flowmechanisms ; Laboratory simulations ; Mt St Helens ; Soufrière of St Vincent ; Venus volcanism ; Pancake domes ; Planetary volcanism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract To better understand the factors controlling the shapes of lava domes, laboratory simulations, measurements from active and prehistoric flows and dimensional analysis were used to explore how effusion history and cooling rate affect the final geometry of a dome. Fifty experiments were conducted in which a fixed volume of polyethylene glycol wax was injected into a tank of cold sucrose solution, either as one continuous event or as a series of shorter pulses separated by repose periods. When the wax cooling rates exceeded a critical minimum value, the dome aspect ratios (height/diameter) increased steadily with erupted volume over the course of a single experiment and the rate at which height increased with volume depended linearly on the time-averaged effusion rate. Thus the average effusion rate could be estimated from observations of how the dome shape changed with time. Our experimental results and dimensional analyses were compared with several groups of natural lava flows: the recently emplaced Mount St Helens and Soufrière domes, which had been carefully monitored while active; three sets of prehistoric rhyolite domes that varied in eruptive style and shape; and two sets of Holocene domes with similar shapes, but different compositions. Geometric measurements suggest that dome morphology can be directly correlated with effusion rate for domes of similar composition from the same locality, and that shape alone can be related to a dimensionless number comparing effusion rate and cooling rate. Extrapolation to the venusian ‘pancake domes’ suggests that they formed from relatively viscous lavas extruded either episodically or at average effusion rates low enough to allow solidified surface crust to exert a dominating influence on the final morphology.
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  • 4
    ISSN: 1432-2048
    Keywords: Callose ; Cell culture (1,3-β-glucan synthase) ; Digitonin-1,3-β-Glucan synthase (purification, immunology) ; Glycine (1,3-β-glucan synthase)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The plasma-membrane-localized 1,3-β-glucan synthase (EC 2.4.1.34) from suspension cultures of Glycine max (L.) Merr. was greatly enriched by a three-step purification procedure. Starting with a microsomal preparation, a six- to eightfold enrichment of the enzyme was achieved by isolating plasma-membrane vesicles in a polyethyleneglycol/dextran two-phase system. The enzyme was solubilized with the nonionic detergent digitonin and further purified 12-fold by successive centrifugations on two linear sucrose density gradients. The most purified enzyme preparation showed enrichment in a 31-kilodalton (kDa) polypeptide and was used to raise polyspecific antibodies which precipitated 1,3-β-glucan synthase activity. These antibodies were purified by affinity chromatography against immobilized membrane protein fractions of lower molecular weight which were devoid of 1,3-β-glucan synthase activity. The purified antibodies specifically labelled a single polypeptide of 31 kDa in the 1,3-β-glucan-synthase-containing heavy fractions of the first sucrose gradient indicating that this polypeptide represents part of the active enzyme complex.
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  • 5
    ISSN: 1432-2048
    Keywords: Calcium (enzyme activation) ; 1,3-β-Glucan synthase ; Glycine (glucan synthase activation) ; Plasma membrane ; Polyamine ; Polycation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sucrose-density-gradient centrifugation and partitioning in a polyethylene glycol/dextran two-phase system were used to isolate plasmamembrane vesicles from microsomal preparations of soybean cell suspension cultures. Both methods resulted in the enrichment of the activity of a 1,3-β-glucan synthase which forms a polymer consisting of more than 99% of 1,3-linked glucose (callose). Digitonin increases the 1,3-β-glucan synthase activity in the various membrane fractions to a different degree, supporting the suggestion that this enzyme is vectorially arranged in the plasma membrane. The enzyme is greatly activated either by poly-l-ornithine or synergistically by Ca2+ and spermine, indicating that the same enzyme is affected and exhibits the regulatory properties necessary for callose synthesis.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 67 (1987), S. 9-14 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract X-ray induced photoelectron spectroscopy, bremsstrahlung-isochromat spectroscopy, and electron energy-loss spectroscopy were used to investigate the electronic structure of the high-temperature superconductor La2−x Sr x CuO4. In general, good agreement was obtained with band structure calculations of the tetragonal phase of La2CuO4. Near the Fermi energyE F the systems shows forx=0 a smeared out gap or a region of very low density of states ∼2eV wide. Upon replacement of La by Sr, the gap is filled with defect states, the intensity of which is proportional tox. The experimental data are not consistent with the closing of a Peierls gap alone.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 61 (1985), S. 463-468 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Several illustrating examples of recent electron energy-loss investigations of the electronic structure of solids are reviewed. In particular, studies on rare-gas bubbles in metals, on conducting polymers, and onL 2,3 edges of 3d transition metals are reported. Moreover, the electron energy-loss spectrometer, which was used for these investigations, is described briefly.
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  • 8
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electronic excitations with polarization parallel to the CuO2-planes in single-crystalline YBa2Cu3O7 and YBa2Cu3O6 have been investigated by optical reflectance and by highenergy electron energy-loss spectroscopy in transmission in the energy ranges from 50 meV to 6 eV and 0.2 eV to 150 eV, respectively. From a combination of these experimental data the dielectric function, the reflectivity and the optical conductivity have been obtained in a wide energy range. The observed spectra are interpreted in terms of optical phonons, free-carrier absorption, transitions across the charge-transfer gap, further interband transitions, low-lying core-level excitations, excitonic transitions and valence conservingd-d transitions within the Cu 3d shell combined with O 2p intraband transitions. The charge carrier plasmon and the 4 eV-excitation in YBa2Cu3O6 show quadratic dispersions in momentum transfer. From the dispersion constant of the plasmon a mean value of the Fermi velocity of the charge carriers parallel to the CuO2 planes has been derived.
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  • 9
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present results from electron energy-loss spectroscopy on Nd2−xCexCuO4. There is no clear evidence for Cu1+ but for holes at the oxygen sites. The valency of Ce is found to be close to 3.4. Thus our results do not corroboraten-type superconductivity in this compound.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 80 (1990), S. 181-185 
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Applying angle-resolved photoemission spectroscopy of high angular and energy resolution we have measured the electronic structure of single crystals of Bi2Sr2CaCu2O8 near the Fermi energy. Along the high symmetry direction ΓX a band is observed to disperse upwards and to cross the Fermi level, whose unoccupied part constitutes the hole-like carriers responsible for the superconductivity. From spectra along the Γ M direction we find evidence for an electron pocket around the M point. The measured band widths appear to be drastically reduced compared with band structure calculations indicating strong electronic correlation effects. From the observation of Fermi-Dirac-like cut-offs in the spectra due to band crossings through the Fermi level we can confirm the existence and, in particular, the shape of the Fermi surface as calculated by band structure calculations.
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