13,256 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

    Structural geology of the African rift system: Summary of new data from ERTS-1 imagery

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    ERTS imagery reveals for the first time the structural pattern of the African rift system as a whole. The strong influence of Precambrian structures on this pattern is clearly evident, especially along zones of cataclastic deformation, but the rift pattern is seen to be ultimately independent in origin and nature from Precambrian tectonism. Continuity of rift structures from one swell to another is noted. The widening of the Gregory rift as its northern end reflects an underlying Precambrian structural divergence, and is not a consequence of reaching the swell margin. Although the Western Rift is now proven to terminate at the Aswa Mylonite Zone, in southern Sudan, lineaments extend northeastwards from Lake Albert to the Eastern Rift at Lake Stefanie. The importance of en-echelon structures in the African rifts is seen to have been exaggerated

    Notes on the Afar triple junction

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    Geological anomalies of Afar and bordering plateau

    Mapping of the major structures of the African rift system

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    The author has identified the following significant results. The new fault map of the main Ethiopian rift, based on aerial photo compilations, generally agrees well with the maps produced from ERTS-1 imagery. Characteristically, the ERTS-1 imagery shows some of the major faults to be more extensive than realized from ground studies, though due to the angle of sun illumination some east-facing fault scarps are not easily discernible on the imagery. The Corbetti caldera, shows up surprisingly poor on the imagery, and is shown to be an adjunct to an older, larger caldera now occupied by Lakes Awassa and Shallo. The lithological boundaries mapped by De Paola in the rift are difficult to discern on the ERTS-1 imagery. On the Somalian plateau, east of the rift, a denuded caldera has been identified as the source of much of the lavas of the Batu Mountains. Further south, ERTS-1 imagery amplifies the structural and lithological mapping of the Precambrian rocks of the Shakisso-Arero area, and of the Kenya-Ethiopia border region. For the first time with some certainty, it is now possible to say that on the evidence of the ERTS-1 imagery, the Western Rift does not continue northeast beyond the Sudan-Uganda border, and is thus not to be sought in western Ethiopia

    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

    Coordinate-space approach to the bound-electron self-energy: Self-Energy screening calculation

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    The self-energy screening correction is evaluated in a model in which the effect of the screening electron is represented as a first-order perturbation of the self energy by an effective potential. The effective potential is the Coulomb potential of the spherically averaged charge density of the screening electron. We evaluate the energy shift due to a 1s1/21s_{1/2}, 2s1/22s_{1/2}, 2p1/22p_{1/2}, or 2p3/22p_{3/2} electron screening a 1s1/21s_{1/2}, 2s1/22s_{1/2}, 2p1/22p_{1/2}, or 2p3/22p_{3/2} electron, for nuclear charge Z in the range 5Z925 \le Z\le 92. A detailed comparison with other calculations is made.Comment: 54 pages, 10 figures, 4 table