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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 15 (1997), S. 1548-1556 
    ISSN: 0992-7689
    Keywords: Auroral ionosphere ; Magnetosphere-ionosphere interactions ; MHD waves and instabilities HF Dopplre ; ULF Waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geographic: 69.6°N 19.2°E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated with pulsations in ground magnetometer data, exhibit periods in the range 100–400 s and have azimuthal wave numbers in the range 3–8. They are interpreted here as local field line resonances. Phase information provided by O- and X-mode Doppler data support the view that these are associated with field line resonances having large azimuthal scale sizes. The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generation of Doppler signatures from incident ULF waves. The outcome suggests that the dominant mechanism involved in producing the Doppler signature is the vertical component of an E × B bulk motion of the local plasma caused by the electric field perturbation of the ULF wave.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Annales geophysicae 16 (1998), S. 1190-1199 
    ISSN: 0992-7689
    Keywords: Magnetosphere-ionosphere interactions ; MHD waves and instabilities ; Radio science ; Ionospheric physics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract Since the middle of 1995, an HF Doppler sounder has been running almost continuously in northern Norway, with the receiver at Ramfjordmoen and the transmitter at Seljelvnes. Concurrent operation of the EISCAT UHF radar in common programme (CP-1) mode has made it possible to study the ionospheric signature of a magnetospheric ULF wave. These are the first results of such wave signatures observed simultaneously in both instruments. It has been demonstrated that the observed Doppler signature was mainly due to the vertical bulk motion of the ionosphere caused by the electric field perturbation of the ULF wave and the first direct observational confirmation of a numerical simulation has been achieved. The wave, which was Alfvénic in nature, was detected by the instruments 8° equatorward of the broad resonance region. The implications for the deduced wave modes in the ionosphere and the mechanism producing the HF Doppler variations are discussed.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.25.Ha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Specific-heat measurements with improved precision on two new samples of YBa2Cu3O7−δ with relatively low concentrations of paramagnetic centers are reported. For one sample the measurements were made for different values of δ. The data are analyzed, and the data reported earlier for another sample reanalyzed, with an improved fitting expression. In each case, the data give a well defined H1/2T term in the mixed state. No persuasive evidence for a T2 term in the superconducting state is found.
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  • 4
    ISSN: 1573-7357
    Keywords: 74.25.Bt ; 74.25.Ha
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Specific heat data on two samples of YBa2Cu3O7−δ with relatively low concentrations of paramagnetic centers show the presence of both spin-2 and spin-1/2 moments. Measurements on one sample following incremental increases in δ show that for δ≤0.2 approximately one spin-1/2 moment is produced for each 100 O vacancies, with no substantial increase in the linear term of the specific heat. For several reasons it is concluded that these O-vacancy related moments are different from those that have figured in previously reported correlations with parameters characteristic of the superconductivity.
    Type of Medium: Electronic Resource
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