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  • LUNAR AND PLANETARY EXPLORATION  (35)
  • FLUID MECHANICS AND HEAT TRANSFER  (25)
  • 2005-2009
  • 1990-1994  (60)
  • 1
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    Influence of cross-flow on nonlinear Tollmien-Schlichting/vortex interaction (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The transition of an incompressible three-dimensional boundary layer with strong cross-flow is considered theoretically and computationally in the context of vortex/wave interactions. Specifically the work centers on two lower-branch Tollmien-Schlichting waves which mutually interact nonlinearly to induce a longitudinal vortex flow. The vortex motion in turn gives rise to significant wave modulation via wall-shear forcing. The characteristic Reynolds number is large and, as a consequence, the waves' and the vortex motion are governed primarily by triple deck theory. The nonlinear interaction is captured by a viscous partial-differential system for the vortex coupled with a pair of amplitude equations for each wave pressure. Following analysis and computation over a wide range of parameters, three distinct responses are found to emerge in the nonlinear behavior of the flow solution downstream: an algebraic finite-distance singularity, far-downstream saturation or far-downstream wave decay leaving pure vortex flow. These depend on the input conditions, the wave angles and the size of the cross flow.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Royal Society (London) Proceedings, Series A - Mathematical and Physical Sciences (ISSN 0962-8444); 446; 1927; p. 319-340
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  • 2
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    The linear stability of plane stagnation-point flow against general disturbances (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The linear-stability theory of plane stagnation-point flow against an infinite flat plate is re-examined. Disturbances are generalized from those of Goertler type to include other types of variations along the plate. It is shown that Hiemenz flow is linearly stable and that the Goertler-type modes are those that decay slowest. This work then rationalizes the use of such self-similar disturbances on Hiemenz flow and shows how questions of disturbance structure can be approached on other self-similar flows.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Quarterly Journal of Mechanics and Applied Mathematics (ISSN 0033-5614); 44; 135-146
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  • 3
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    A model of Saturn's magnetic field based on all available data (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model of Saturn's magnetic field, called Saturn Pioneer Voyager (SPV), is developed on the basis of an analysis of three sets of data: those from the Pioneer 11, the Voyager 1, and the Voyager 2 magnetometers. It is shown that the SPV model fits the data observed between 1.3 and 8.0 Saturn radii from the planet's center with a 1.13 percent weighted rms average of the percent differences between the observed and modeled fields, which is substantially better than the fits yielded by any of the previous models.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 15257-15
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  • 4
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    Discontinuities in the shallow Martian crust at Lunae, Syria, and Sinai Plana (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Detailed photoclinometric data are presented for a variety of surface features (pits, troughs, wall valleys, and grabens) within three study areas in the western equatorial regions of Mars (Lunae, Syria, and Sinai Plana) that provide evidence for mechanical discontinuities within the shallow Martian crust in these regions. The data's relation to some of the previously proposed mechanical discontinuities within the Martian crust is discussed, and the geologic significance of these features is speculated upon.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Journal of Geophysical Research (ISSN 0148-0227); 95; 14231-14
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  • 5
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    Phosphates in pallasite meteorites as probes of mantle processes in small planetary bodies (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Trace element analyses of the phosphates minerals in stony-iron pallasite meteorites are used here to investigate the magmatic history of the silicate portions of pallasites. In Eagle Station and seven other pallasites, the phosphates have relatively low concentrations of REEs and are strongly enriched in heavy relative to light REE. These patterns are consistent with formation of phosphate by subsolidus reactions between metal and silicate, in which phosphate inherits the REE pattern of olivine. In Springwater and Santa Rosalia, calcium-rich phosphates have higher concentrations of REE, are enriched in light relative to heavy REE, and have negative europium anomalies. These patterns are consistent with crystallization of phosphate from a europium-depleted chondritic liquid. This is unlikely to have happened near the base of the differentiating parent-body mantle; it suggests that some pallasites may come from regions of their parent bodies much nearer the surface than the core-mantle boundary.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 353; 637-640
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  • 6
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    Isotope mass fractionation during evaporation of Mg2SiO4 (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Synthetic forsterite (Mg2SiO4) was partially evaporated in vacuum for various durations and at different temperatures. The residual charges obtained when molten Mg2SiO4 was evaporated to 12 percent of its initial mass were enriched in heavy isotopes by about 20, 30, and 15 per mil/amu for O, Mg, and Si, respectively, whereas solid forsterite evaporated to a similar residual mass fraction showed negligible fractionations. These results imply that calcium and aluminum-rich refractory inclusions in carbonaceous chondrites must have been at least partially molten in the primordial solar nebula if the observed large mass fractionation effects were caused by evaporation processes in the nebula.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 347; 655-658
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  • 7
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    Long-wave morphological instabilities in the directional solidification of a dilute binary mixture (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Long-wave instabilities in a directionally-solidified binary mixture may occur in several limits. Sivashinsky (1983) identified a small-segregation-coefficient limit and obtained a weakly nonlinear evolution equation governing subcritical two-dimensional bifurcation. Brattkus and Davis (1988) identified a near-absolute-stability limit and obtained a strongly nonlinear evolution equation governing supercritical two-dimensional bifurcation. The present investigation identifies a third strongly nonlinear evolution equation, arising in the small-segregation-coefficient, large-surface-energy limit. This equation links both of the former and describes the change from the sub- to super-critical bifurcations. This study sets the previous long-wave analyses into a logical framework.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: SIAM Journal on Applied Mathematics (ISSN 0036-1399); 50; 420-436
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  • 8
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    Duration of liquid water habitats on early Mars (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The duration of ice-covered lakes after the initial freezing of the early Mars is presently estimated via a climate model whose critical parameter is the existence of peak seasonal temperatures above freezing, and in which the variability of insolation is included. Under conditions in which meltwater was supplied by an ice source, it is found that water habitats could have been maintained under relatively thin ice sheets for as many as 700 million years after the onset of below-freezing global temperatures. The duration of such habitats on the early Mars therefore exceeds the upper limit of the time envisioned for the emergence of aquatic life on earth.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 90; 214-221
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  • 9
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    Prediction of solar flares for the Space Exploration Initiative (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The 21st century is likely to see the start of the manned exploration and settlement of the inner solar system. NASA's plans for this endeavor are focused upon the Space Exploration Initiative which calls for a return to the Moon, to stay, followed by manned missions to Mars. To execute these missions safely provides solar physics with both a challenge and an opportunity. As the past solar maximum has clearly demonstrated, the Sun, through the solar flare process, is capable of generating and accelerating to high energies large fluxes of protons whose cumulative dose to unprotected astronauts can be fatal. It will be the responsibility of solar physicists to develop an accurate physical description of the mechanisms of flare energy storage and release, and of particle acceleration and propagation through interplanetary space upon which to base a sound method of flare and energetic particle prediction.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 14; 6; p. (6)33-(6)42
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  • 10
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    Hydrodynamic interactions in directional solidification (1990)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A binary liquid undergoes unidirectional solidification. The one-dimensional steady state is susceptible to morphological instability that causes the solid/liquid interface to change from a planar state to a cellular pattern. This paper examines the effects on this transition of volume-change convection, buoyancy-driven convection or forced flows. It emphasizes how flows alter stability limits, create scale and pattern changes in morphology, and create, through coupling, new instabilities. Emphasis is placed on the physical mechanisms of the interactions.
    Keywords: FLUID MECHANICS AND HEAT TRANSFER
    Type: Journal of Fluid Mechanics (ISSN 0022-1120); 212; 241-262
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