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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 6810-6823 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Surface and ultrathin-film magnetocrystalline anisotropy in epitaxial fcc Fe thin films grown on room-temperature Cu(100) single crystals has been investigated, in situ, by the combined surface magneto-optical Kerr effects (SMOKE). In polar, longitudinal, and transverse Kerr effects, the direction of the applied magnetic field must be distinguished from the direction of magnetization during the switching process. For arbitrary orientations of the magnetization and field axis relative to the optical scattering plane, any of the three Kerr effects may contribute to the detected signal. A general expression for the normalized light intensity sensed by a photodiode detector, involving all three combined Kerr effects, is obtained both in the ultrathin-film limit and for bulk, at general oblique incidence angles and with different orientations of the polarizer, modulator, and analyzer. This expression is used to interpret the results of fcc Fe/Cu(100) SMOKE measurements. For films grown at room temperature, polar and longitudinal Kerr-effect magnetization loops show that the easy axis of magnetization rotates from the (canted) out-of-plane direction to the in-plane direction at a thickness of about 4.7 monolayers. Transverse Kerr-effect measurements indicate that the in-plane easy axes are biaxial.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 74 (1993), S. 7422-7430 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Correlation studies between thin film nanostructure and macroscopic magnetic properties in ultrathin fcc Fe films grown epitaxially on room temperature Cu(100) substrates were performed in situ using an ultrahigh vacuum scanning transmission electron microscope and the surface magneto-optic Kerr effect. Nanometer lateral spatial resolution secondary electron microscopy revealed no gross morphological changes in the 2–10 monolayer thickness range. The use of broad-beam Auger electron spectroscopy as an indicator of Cu surface cleanliness is shown to have insufficient sensitivity to detect surface contamination as evidenced by corresponding secondary electron micrographs. Cu(100) surfaces with both (nearly) perfect and imperfect surface structure, and identical Fe coverages, possess nearly identical polar and longitudinal Kerr hysteresis loops. Analysis of reflection high-energy electron diffraction patterns confirms that Fe films grown on room temperature Cu(100) remain fcc with the same in-plane lattice constant as the Cu template, for thicknesses up to 10 ML.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3761-3762 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Based on Davis' model for the lateral restoring force on a magnet levitated above a superconductor [J. Appl. Phys. 67, 2631 (1990)], we calculate the restoring force as a function of lateral displacement for a more realistic magnetic field profile.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7496-7499 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using quasistatic harmonic excitations, we have measured the lateral force between a permanent magnet and a Bi-based ceramic high-Tc superconductor (HTSC) for lateral displacement amplitudes down to 1 μm. We find clear evidence for a transition from elastic (nondissipative) to inelastic interaction, and attribute the effect to flux pinning. The crossover amplitude can easily reach several micrometers, with the consequence that the lateral disturbance of a levitated magnet will decay to this amplitude, whereas further damping will be extremely slow. For applications of HTSCs in magnetic bearing systems this can be a very relevant aspect of the interaction, and it can set the limit for precision positioning of levitated objects.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1471-0528
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Medizin
    Notizen: Objective To assess the capability of a computer software interpretation program, using intrapartum fetal heart rate and intrauterine pressure as recorded in a cardiotocogram to predict fetal acidosis at birth.Design and subjects A retrospective analysis of digitised fetal heart rate and uterine activity values obtained from 73 high risk women in labour.Setting Two university teaching hospitals.Methods A computer software program was constructed to analyse the digitised data and predict acidosis. The results of the analysis were compared with actual umbilical arterial blood pH and base excess at delivery.Results The software cardiotocogram interpreter was able to predict a pH of less than 7.15 with an accuracy of 77%, a sensitivity of 88% and specificity of 75% in this set of data. It was able to predict a base excess of less than –8 mmol/1 with an accuracy of 81%, a sensitivity of 76% and specificity of 82%.Conclusions A computerised method of analysing fetal heart rate and uterine activity using a simple algorithm has demonstrated a capability to predict fetal acidosis at the time of delivery. Further research in this area is warranted.
    Materialart: Digitale Medien
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  • 6
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The magnetic susceptibility, magnetization and the temperature and field dependence of the Hall coefficient have been measured for the magnetically ordered icosahedral quasicrystals Al70–xPd15Mn15Bx (x=0,2,4,6,8,10). The temperature dependence of the real and imaginary part of the complex ac susceptibility indicates re-entrant magnetic behavior and dc magnetization measurements are interpreted in the context of this behavior. The present Hall resistivity measurement shows the existence of both normal and anomalous Hall effects. The normal Hall coefficient is independent of temperature in all the alloys and changes from negative to positive with increasing boron concentration. This can be explained by the effects of s–d hybridization. The anomalous Hall coefficient is also found to be temperature independent and has a compositional dependence correlated to the spin–orbit scattering rate. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 3318-3322 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We consider a model system consisting of an infinitely long magnetic dipole line placed symmetrically above an infinitely long superconducting strip. Using the Meissner effect of superconductors, we derive analytical expressions of the levitation forces acting on the dipole line. At lowest-order approximation, we discuss the possible application of our model system to estimate the upper limit of the levitation forces in some magnetic bearing systems. In one example, the model correctly calculated the vertical vibration frequency of an experimental superconducting bearing.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 5278-5281 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The measurement of c-axis resistance in La2−xSrxCuO4 at different temperatures for fields at any orientation shows that the observed dissipation is not dominated by any Lorentz-force-dependent mechanism. To explain the experimental findings, a phenomenological model is developed for c-axis resistance as a function of temperature T, field B, and angle θ between B and ab plane. Excellent agreement between calculated and experimental curves in a wide transition region (5 decades) gives a strong support to the present approach. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 2097-2100 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Using an electromagnetically controlled mechanical pendulum, we measured the energy loss for different amplitudes in a magnetic levitation system that contained high temperature superconductors (HTSs). Two procedures were followed to measure losses at 77 K for frequencies of 93.8 mHz to 80 Hz. In the first procedure, the distance between the permanent magnet and the HTS levitator was the same as that during (field) cooling. In the second procedure, the magnet was lowered (after cooling) closer to the HTS levitator before the measurements were performed. The experimental data show that these two procedures give essentially the same results at the same distance despite different cooling (and magnetization) histories for melt-textured YBaCuO levitators, and the frequency-independent energy loss is a power-law function of amplitude. We attribute the energy loss to magnetic hysteresis in the superconductor. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 6833-6838 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Individual magnetic steel rotors were levitated by combining the attractive force between permanent magnets and the steel with the repulsive force between high-temperature superconductors and the steel. The free spindown of several rotors was observed, and the effective coefficient of friction for the bearing was calculated as a function of geometry. Low-speed coefficients of 〈10−8 were observed, and the velocity dependence of MnZn ferrite rotors suggest that coefficients of 〈10−6 are attainable at bearing rim velocities of 100 m/s.
    Materialart: Digitale Medien
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