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  • critical current density  (3)
  • Key words 210Pb dating  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Environmental geology 28 (1996), S. 78-87 
    ISSN: 1432-0495
    Keywords: Key words 210Pb dating ; Chronology ; Sedimentation rate ; Accumulation rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract  Much discussion has centered around which 210Pb dating method should be used, the constant initial concentration (CIC) model or the constant rate of supply (CRS) model. In this study, the activity data from 22 lacustrine sediment cores from the Canadian prairies were used to compare the determination of sediment accumulation using the two models. Other relative and absolute dating techniques have been used to calibrate the methodology. For half of the core sites examined, the mass sedimentation rate was constant, and thus both the CIC and CRS models were found to be valid. For the other half, variability was observed in the CRS mass accumulation rate trend. The validity of the CIC model for these cores was dependent on the degree of variability of the mass sedimentation rate. Where the variability is moderate to high, the CRS model may be more satisfactory. Caution should be exercised when using chronological data determined with the CRS model, however, as the accuracy of chronology in the lower reaches of a profile is questionable.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 6 (1993), S. 37-41 
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The variation of critical current density at 77 K as a function of film thickness was studied for YBa2Cu3O7 films on (100) LaAlO3 substrates. Film thicknesses were in the range 0.2–1.6μm. The films were deposited by co-evaporation and post-annealed under conditions which have previously resulted in high-quality films (750°C and an oxygen partial pressure of 29 Pa). The critical current density at 77 K exceeds 1 MA cm−2 for the thinner films, and decreases with increasing film thickness in excess of about 0.4μm. The decrease is in rough agreement with a switch fromc-axis toa-axis growth at about this critical thickness. A good anticorrelation was found between room temperature resistivity and critical current density at 77 K. The results are compared to those obtained before by post-annealing at 850°C in 1 atm of oxygen.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 5 (1992), S. 143-147 
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; critical current density ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Post-annealing of thin films of YBa2Cu3O7 (YBCO) has been performed at 29 Pa and 750°C. For films 0.6 μm thick, a critical current density 〉1 MA cm−2 is obtained at 77 K, with a sharp eddy current response at 25 MHz. Microstructural investigation of these films by crosssectional and planar transmission electron microscopy reveals that the YBCO film has thec-axis normal to the plane of the substrate in a continuous sheet of varying thickness, frequently covering the entire thickness of the film. Mutually perpendicular rods with thec-axis in the plane of the LaAlO3 substrate are also seen. The microstructure and critical current density of these films are compared with those of previously reported films post-annealed in atmosphericpressure oxygen.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of superconductivity 8 (1995), S. 95-98 
    ISSN: 1572-9605
    Keywords: Superconducting films ; YBa2Cu3O7 ; degradation of superconducting properties ; critical current density
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The degradation of epitaxial thin films of YBa2Cu3O7 has been studied as a function of annealing temperature in air and in vacuum; some samples had an evaporated overlayer of CaF2. Degradation was monitored by the measurement of electrical properties after consecutive 30-min annealing treatments. The room-temperature resistance registered significant increases for all samples after annealing at temperatures above about 200°C; the critical current density at 77 K was degraded for annealing temperatures ≥400°C in air, and ≥200–250°C in vacuum. By annealing in oxygen at 550°C, electrical properties were restored in degraded bare YBCO samples annealed in vacuum, but not for those annealed in air.
    Type of Medium: Electronic Resource
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