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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Chemical differentiation and convective removal of internal heat make the Earth's lithosphere a thermal and a chemical boundary layer. Thin layers of chemically light material form near the Earth's surface and become embedded within the cold thermal boundary layer associated with interior heat removal. The likelihood of near-surface thermal and chemical boundary layer interactions influencing the Earth's thermotectonic evolution prompts the models presented herein. A simplified system, consisting of a chemically light layer within the upper thermal boundary layer of a denser thermally convecting layer, is explored through a suite of numerical experiments to see how its dynamic behaviour differs from similar, well-studied, thermal boundary layer systems. A major cause of differences between the two systems resides in the ability of the deformable near-surface chemical layer to alter the effective upper thermal boundary condition imposed on the convectively unstable layer below. In thermal equilibrium, regions of chemical boundary layer accumulation locally enforce an effectively near-constant heat-flux condition on the thermally convecting layer due to the finite thermal conductivity of chemical boundary layer material. For cases in which chemical accumulations translate laterally above the unstable layer, the thermal coupling condition between chemical boundary layer material and the unstable layer below is one of non-equilibrium type, i.e. the thermal condition at the top of the convectively unstable layer is time-, as well as space-, variable. A second major cause of differences is that, for the thermal/chemical system, chemically induced rheologic variations can offset, or compete with, those due to temperature. More specifically, the presence of chemically weak material can lubricate convective downwellings allowing for enhanced overturn of an, on average, strong upper thermal boundary layer. Both of these factors have low-order effects on internal flow structure and heat loss and lead to dynamic behaviour in which chemical boundary layer deformation is not only driven by flow in the thermally convecting interior layer but also feeds back and alters this flow. Some implications of this, in regard to elucidating how near-surface chemical boundary layer deformation, e.g. continental tectonics, might interact with, and influence, mantle convection, are discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 378 (1995), S. 709-711 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The behaviour shown in Fig. 1 has previously been interpreted as evidence of additional heat input into the base of old continental lithosphere due to a secondary scale of convection-that is, one of a smaller scale than that associated directly with the formation of tectonic plates at mid-ocean ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 245 (1973), S. 367-369 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] All those who hypothesise Capture acknowledge that it is an improbable event. So mostf~7 suggest that the Moon was made somewhere near the Eajrth, which seems contrary to the thermochemically inspired v^ish to make the Moon in a different part of the Solar System. All but one4-7, however, ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 303 (1983), S. 756-756 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE tracking of Earth satellites continues to produce new findings about Earth pro perties. The most recent finding, reported in this issue of Nature (p.757), uses 5.5 years' laser ranging to Lageos, a 60-centimetre ball of brass covered by retro-reflectors whose retrograde orbit lies at 6,000 km ...
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Earth, moon and planets 8 (1973), S. 469-483 
    ISSN: 1573-0794
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The analysis of lunar laser ranging data requires very accurate calculations of the lunar physical librations. Libration terms are given which arise from the additive and planetary terms in the lunar theory. The large size of the recently discovered terms due to third degree gravitational harmonics will allow some of these harmonics to be measured, in addition toβ andγ, by laser ranging to the Moon. Combining the laser ranging determinations ofβ = 630.6 ± 0.5 × 10−6 andγ = 226.4 ± 3.0 × 10−6 with lunar orbiter measurements ofC 20 andC 22 givesC/MR 2=0.395 -0.010 +0.006 . Numerical integration promises to be an effective method of calculating librations. Comparison of numerical integrations with analytic series indicates that the calculation of the series due to third and fourth degree harmonics is not yet as accurate as the more extensively developed second degree terms.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Celestial mechanics and dynamical astronomy 62 (1995), S. 23-41 
    ISSN: 1572-9478
    Keywords: Hamiltonian dynamics ; symplectic forms ; asteroid motion ; perturbation theory ; secular resonances
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract New techniques to study Hamiltonian systems with Hamiltonian forcing are proposed. They are based on singularly weighted symplectic forms and transformations which preserve these forms. Applications pertaining to asteroid motion are outlined. These involve the presence of both Jupiter and Saturn.
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  • 7
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Present ideas about the surface and interior of Venus are based on data obtained from (1) Earth-based radio and radar: temperature, rotation, shape, and topography; (2) fly-by and orbiting spacecraft: gravity and magnetic fields; and (3) landers: winds, local structure, gamma radiation. Surface features, including large basins, crater-like depressions, and a linear valley, have been recognized from recent ground-based radar images. Pictures of the surface acquired by the USSR's Venera 9 and 10 show abundant boulders and apparent wind erosion. On the Pioneer Venus 1978 Orbiter mission, the radar mapper experiment will determine surface heights, dielectric constant values and small-scale slope values along the sub-orbital track between 50°S and 75°N. This experiment will also estimate the global shape and provide coarse radar images (40–80 km identification resolution) of part of the surface. Gravity data will be obtained by radio tracking. Maps combining radar altimetry with spacecraft and ground-based images will be made. A fluxgate magnetometer will measure the magnetic fields around Venus. The radar and gravity data will provide clues to the level of crustal differentiation and tectonic activity. The magnetometer will determine the field variations accurately. Data from the combined experiments may constrain the dynamo mechanism; if so, a deeper understanding of both Venus and Earth will be gained.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Celestial mechanics and dynamical astronomy 72 (1998), S. 187-199 
    ISSN: 1572-9478
    Keywords: symplectic form ; symplectic mapping ; Hamiltonian formalism ; perturbation theory ; N-body problem
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mass-weighted symplectic forms provide a unified framework for the treatment of both finite and vanishingly small masses in the N-body problem. These forms are introduced, compared to previous approaches, and their properties are discussed. Applications to symplectic mappings, the definition of action-angle variables for the Kepler problem, and Hamiltonian perturbation theory are outlined
    Type of Medium: Electronic Resource
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  • 9
    Publication Date: 1967-10-01
    Print ISSN: 0031-9228
    Electronic ISSN: 1945-0699
    Topics: Physics
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  • 10
    Publication Date: 1973-10-01
    Print ISSN: 0027-0903
    Topics: Geosciences , Physics
    Published by Springer
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