11,309 research outputs found

    Regional significance of volcanic geochemistry in the Far Triple Junction, Ethiopia

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    Regional significance of volcanic geochemistry in far Triple Junction, Ethiopi

    Notes on the Afar triple junction

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    Geological anomalies of Afar and bordering plateau

    Ethiopian rift and plateaus - Some volcanic petrochemical differences

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    Volcanic petrochemical differences in Ethiopian rift and plateau

    Optical Turbulence Measurements and Models for Mount John University Observatory

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    Site measurements were collected at Mount John University Observatory in 2005 and 2007 using a purpose-built scintillation detection and ranging system. Cn2(h)C_n^2(h) profiling indicates a weak layer located at 12 - 14 km above sea level and strong low altitude turbulence extending up to 5 km. During calm weather conditions, an additional layer was detected at 6 - 8 km above sea level. V(h)V(h) profiling suggests that tropopause layer velocities are nominally 12 - 30 m/s, and near-ground velocities range between 2 -- 20 m/s, dependent on weather. Little seasonal variation was detected in either Cn2(h)C_n^2(h) and V(h)V(h) profiles. The average coherence length, r0r_0, was found to be 7±17 \pm 1 cm for the full profile at a wavelength of 589 nm. The average isoplanatic angle, θ0\theta_0, was 1.0±0.11.0 \pm 0.1 arcsec. The mean turbulence altitude, h0ˉ\bar{h_0}, was found to be 2.0±0.72.0\pm0.7 km above sea level. No average in the Greenwood frequency, fGf_G, could be established due to the gaps present in the \vw\s profiles obtained. A modified Hufnagel-Valley model was developed to describe the Cn2(h)C_n^2(h) profiles at Mount John, which estimates r0r_0 at 6 cm and θ0\theta_0 at 0.9 arcsec. A series of V(h)V(h) models were developed, based on the Greenwood wind model with an additional peak located at low altitudes. Using the Cn2(h)C_n^2(h) model and the suggested V(h)V(h) model for moderate ground wind speeds, fGf_G is estimated at 79 Hz.Comment: 14 pages; accepted for publication in PAS

    QED self-energy contribution to highly-excited atomic states

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    We present numerical values for the self-energy shifts predicted by QED (Quantum Electrodynamics) for hydrogenlike ions (nuclear charge 60Z11060 \le Z \le 110) with an electron in an n=3n=3, 4 or 5 level with high angular momentum (5/2j9/25/2\le j \le 9/2). Applications include predictions of precision transition energies and studies of the outer-shell structure of atoms and ions.Comment: 20 pages, 5 figure

    Modification of nuclear transitions in stellar plasma by electronic processes: K-isomers in 176Lu and 180Ta under s-process conditions

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    The influence of the stellar plasma on the production and destruction of K-isomers is studied for the examples 176Lu and 180Ta. Individual electromagnetic transitions are enhanced predominantly by nuclear excitation by electron capture, whereas the other mechanisms of electron scattering and nuclear excitation by electron transition give only minor contributions. It is found that individual transitions can be enhanced significantly for low transition energies below 100 keV. Transitions with higher energies above 200 keV are practically not affected. Although one low-energy transition in 180Ta is enhanced by up to a factor of 10, the stellar transition rates from low-K to high-K states via so-called intermediate states in 176Lu and 180Ta do not change significantly under s-process conditions. The s-process nucleosynthesis of 176Lu and 180Ta remains essentially unchanged.Comment: 10 pages, 10 figures, Phys. Rev. C, accepte