3,440 research outputs found

    Dynamical heating of the upper atmosphere

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    Dynamical heating rates of ionosphere - energy of upward propagating atmospheric gravity wave

    Two possible mechanisms for relating terrestrial atmospheric circulation to solar disturbances

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    During geomagnetic storms, which are initiated by solar disturbances, two cells of circulatory motion are established in the polar ionosphere. The torques that contribute to either cell might be as great as 10 to the 24 power dyne cm, and may persist for times of the order 100,000 sec. The angular momentum contributed to a cell may be as great as 10 to the 29th power g sq cm/sec. Angular momentum is discussed

    Atmospheric gravity waves- a new toy for the wave theorist

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    Atmospheric gravity waves - anistropy of propagation and anistropies and reflection processes arising in practice related to ionospheric and plasma propagatio

    Direct Evidence for the Source of Reported Magnetic Behavior in "CoTe"

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    In order to unambiguously identify the source of magnetism reported in recent studies of the Co-Te system, two sets of high-quality, epitaxial CoTex_x films (thickness ≃\simeq 300 nm) were prepared by pulse laser deposition (PLD). X-ray diffraction (XRD) shows that all of the films are epitaxial along the [001] direction and have the hexagonal NiAs structure. There is no indication of any second phase metallic Co peaks (either fccfcc or hcphcp) in the XRD patterns. The two sets of CoTex_x films were grown on various substrates with PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the measured lattice parameters c=5.396A˚c = 5.396 \AA for the former and c=5.402A˚c = 5.402\AA for the latter, the compositions CoTe1.71_{1.71} (63.1% Te) and CoTe1.76_{1.76} (63.8% Te), respectively, are assigned to the principal phase. Although XRD shows no trace of metallic Co second phase, the magnetic measurements do show a ferromagnetic contribution for both sets of films with the saturation magnetization values for the CoTe1.71_{1.71} films being approximately four times the values for the CoTe1.76_{1.76} films. 59^{59}Co spin-echo nuclear magnetic resonance (NMR) clearly shows the existence of metallic Co inclusions in the films. The source of weak ferromagnetism reported in several recent studies is due to the presence of metallic Co, since the stoichiometric composition "CoTe" does not exist.Comment: 19 pages, 7 figure

    Local Structure and It's Effect on The Ferromagnetic Properties of La0.5_{0.5}Sr0.5_{0.5}CoO3_3 thin films}

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    We have used high-resolution Extended X-ray Absorption Fine-Structure and diffraction techniques to measure the local structure of strained La0.5_{0.5}Sr0.5_{0.5}CoO3_3 films under compression and tension. The lattice mismatch strain in these compounds affects both the bond lengths and the bond angles, though the larger effect on the bandwidth is due to the bond length changes. The popular double exchange model for ferromagnetism in these compounds provides a correct qualitative description of the changes in Curie temperature TCT_C, but quantitatively underestimates the changes. A microscopic model for ferromagnetism that provides a much stronger dependence on the structural distortions is needed.Comment: 4 pages, 4 figure
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