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  • Astrophysics  (2)
  • GEOPHYSICS  (2)
  • 1980-1984  (4)
  • 1955-1959
  • 1
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    On the Fragmentation of Rotating Interstellar Clouds (1981)
    In:  CASI
    Details
    Publication Date: 2005-11-09
    Description: Simple physical arguments are used to estimate the time scale for fragmentation of a collapsing, rotating, isothermal, interstellar cloud. This time scale is compared with a similarly estimated time scale for the collapse upon itself of a transitory ring structure. It is shown to be plausible for a cloud with a given ratio of rotational to gravitational energy (beta) that as the ratio of thermal to gravitational energy (alpha) is varied, there is an intermediate range of alpha where a ring forms and collapses on itself, prior to fragmentation. For higher or lower alpha however, the cloud fragments prior to ring self-collapse. The analysis is compared with the results of numerical multidimensional, gravitational, hydrodynamical collapse and shown to be in good agreement with them.
    Keywords: Astrophysics
    Type: Astrophysical Journal; Volume 244; 40-44
    Format: text
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  • 2
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    Time-dependent models of single- and double-layer mantle convection (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Time-dependent numerical models of two-dimensional convection which simulate mantle convection are presented. Starting from a fluid initially at rest with a purely conductive temperature profile, it is found that for a Rayleigh number of ten million, the model experiences a transient period of double-layer convection which lasts on the order of hundreds of millions of years when scaled to the earth's mantle. It is suggested that transient periods of double-layer convection in the earth's mantle may have existed in the past, whether or not such a period exists today.
    Keywords: GEOPHYSICS
    Type: Nature (ISSN 0028-0836); 308; 533-535
    Format: text
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  • 3
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    A Heuristic Criterion for Instability to Fragmentation in Rotating, Interstellar Clouds (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: A heuristic criterion, based on linear perturbation analysis, is applied to the initial growth of density perturbations in isothermal or adiabatic gas clouds, with initially uniform density and uniform rotation. The heuristic criterion is shown to be consistent with the available results from numerical calculations of cloud collapse. The criterion predicts that perturbations varying as cos (m(phi)) will be most likely to grow when )pi is small, unless the cloud is nearly pressureless.
    Keywords: Astrophysics
    Type: Astrophysical Journal (ISSN 0004-637X); Volume 259; 159-165
    Format: text
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  • 4
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    Finite-amplitude models of convection in the early mantle (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Models of finite-amplitude, time-dependent mantle convection at Reynolds number ten million are calculated. The models are based on the Boussinesq approximation for convection at infinite Prandtl number and treat convection in a two-dimensional, Cartesian coordinate box with an aspect ratio of 1.4. The initial conditions consist of a static fluid with a purely conductive temperature profile, while the boundary conditions are taken to be free slip, with impenetrable insulating side walls. The initial conditions are found to result in an initial burst of convection that reverses the horizontally averaged temperature gradient, making the middle layers stable with respect to convection. With bottom heating and cooling of the top, two distinct layers of convective cells occur; with top cooling only, the upper layer alone convects.
    Keywords: GEOPHYSICS
    Type: Physics of the Earth and Planetary Interiors (ISSN 0031-9201); 36; 328-336
    Format: text
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