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At least 433 records · Page 24

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NASA NTRS1976

Behavior of the sodium and hydroxyl nighttime emissions during a stratospheric warming

The behavior of the sodium and hydroxyl nighttime emissions during a stratospheric warming has been studied principally by use of data from the airglow photometers on the OGO 4 satellite. During the late stages of a major warming, both emissions increased appreciably, with the sodium emission returning to normal values prior to the decrease in the hydroxyl emission. The emission behaviors are attributed to temperature and density variations from 70 to 94 km, and a one-dimensional hydrostatic model for that altitude range is used to calculate the effects on the emissions and on the mesospheric ozone densities. These results support the existence of a warming in the upper part of the mesosphere that is correlated with a major stratospheric warming.

Walker, J. D.↗

NASA NTRS1976

A statistical method for treating molecular line opacities

A method for treating atomic and molecular line opacities in cool stellar atmospheres by a statistical opacity sampling is investigated. Under the usual assumptions of plane-parallel geometry, radiative equilibrium, hydrostatic equilibrium, and LTE, each radiative quantity is computed monochromatically at each chosen frequency and depth without any averaging of the opacity. The number of frequencies needed to allow an accurate integration of the energy flux over a given spectral interval is investigated as a function of depth, including opacity for both CN and C2. This method is extended to the calculation of a model atmosphere of a star, and the effect of the number and placement of frequency points is studied. The method is applied to treating molecular lines of CO, C2, and CN in a cool carbon star. Significant advantages of the opacity sampling method are its flexibility, which permits computation of models having arbitrary variations of chemical composition and of opacity with wavelength and depth, and generalizability to include departures from LTE.

Sneden, C.↗

NASA NTRS1976

Lunar global figure from mare surface elevations

Laser altimetry data from the Apollo 15, 16, and 17 missions show that the ringed maria surfaces lie on one particular reference surface and that the center of gravity is definitely displaced from the optical center. If these extensive surfaces are assumed to be near-hydrostatic surfaces, then there must have existed a time in lunar history when lunar tides, internal processes, or both were much different than they are today.

Sjogren, W. L.↗

NASA NTRS1976

Symmetric stiffness matrix for incompressible hyperelastic materials

Symmetric structure matrices are derived for solving plane strain and axisymmetric problems involving incompressible hyperelastic materials. An infinite hollow cylinder subjected to internal pressure is considered as an example. Displacement and hydrostatic pressure profiles are calculated using the Newton-Raphson iteration technique. The results are in good agreement with the exact curves.

Takamatsu, T.↗

NASA NTRS1975

On the equilibrium distribution of gas in clusters of galaxies

The hydrostatic-equilibrium solution for a polytropic gas in a cluster of galaxies has been calculated. The gas has a wider distribution than the galaxies. If the central gas density is 0.0008 particles/cu cm for gamma = 5/3 or 0.002 per cu cm for gamma = 1.35, the total X-ray emission from a model Coma cluster is equal to the observed emission. The spatial extent and spectrum for the source are also well-represented by the model if gamma = 1.35.

Lea, S. M.↗

NASA NTRS1976

Gas dynamics of semidetached binaries. II - The vertical structure of the stream

The letter considers the three-dimensional dynamics of the stream in semidetached binaries undergoing Roche-lobe overflow. Results of an earlier communication are generalized to include the dynamic effects in the direction perpendicular to the orbital plane. It is found that the scale height of the stream characteristically exceeds its corresponding hydrostatic value by a significant factor because the inertia of the gas prevents it from responding instantaneously to the changing gravitational field. This effect is important for the interpretation of observations relating to stream-disk impacts in cataclysmic variables and in binary X-ray sources of low total mass.

Lubow, S. H.↗

NASA NTRS1976

A numerical circulation model with topography for the Martian southern hemisphere

A two-level numerical model taking account of the observed planetary topography is applied to the general circulation of the Martian atmosphere in the southern hemisphere. The physics of this model is based on the assumption of a hydrostatic quasi-geostrophic ideal-gas atmosphere composed entirely of carbon dioxide; radiative transfer among the atmosphere, space, and the ground is included along with surface friction. The calculations indicate the development of near-equilibrium weather systems after about five model days, weather systems and velocity fields whose positions appear to be connected with topography, and a midlatitude jet stream strikingly similar to the terrestrial case. The results also suggest that the vertical and horizontal wind components in western Hellas and eastern Argyre produce copious amounts of suspendible dust each year, that both major and minor dust storms should be a common occurrence on Mars, and that the entire south circumpolar zone appears to be a dust sink in winter.

Mass, C.↗

NASA NTRS1976

Large deflections of shallow conical membrane

Large deflections of a shallow elastic conical membrane fixed at the outer edge and loaded by either uniform or hydrostatic pressure are investigated. The overning equations were solved by the method of matched asymptotic expansions and by a finite difference method. Agreement between the two methods was excellent for the small values of the perturbation parameter.

Chang, W. H.↗

NASA NTRS1976

Optimum step design for centering of pistons moving in an incompressible fluid

Hydrodynamic effects are analyzed for a stepped piston moving within a tight clearance tube filled with an incompressible fluid. Hydrostatic effects are analyzed and a complete solution is obtained and an optimum step design for centering of the piston is suggested. The axial speed resulting from an axial driving force is calculated, and some experimental results for pistons falling in a water-filled tube are presented.

Etsion, I.↗

NASA NTRS1976

A three-dimensional, time-dependent model of Mobile Bay

A three-dimensional, time-variant mathematical model for momentum and mass transport in estuaries was developed and its solution implemented on a digital computer. The mathematical model is based on state and conservation equations applied to turbulent flow of a two-component, incompressible fluid having a free surface. Thus, bouyancy effects caused by density differences between the fresh and salt water, inertia from thare river and tidal currents, and differences in hydrostatic head are taken into account. The conservation equations, which are partial differential equations, are solved numerically by an explicit, one-step finite difference scheme and the solutions displayed numerically and graphically. To test the validity of the model, a specific estuary for which scaled model and experimental field data are available, Mobile Bay, was simulated. Comparisons of velocity, salinity and water level data show that the model is valid and a viable means of simulating the hydrodynamics and mass transport in non-idealized estuaries.

Pitts, F. H.↗

NASA NTRS1977

Automated electroencephalography system and electroencephalographic correlates of space motion sickness, part 3

Computer quantification methods were used to analyze the Skylab electroencephalographic data obtained during the course of the M133 series of experiments. This undertaking was prompted by initial observations made during visual analysis of the tape-recorded sleep records where there appeared to be an increase of the alpha-rhythm frequency during some inflight recording sessions, as compared to preflight baseline observations. A number of potential etiological factors are identified and their various possible influences discussed. The presence of the zero-g state is thought to be an important factor, possibly influencing EEG through alteration of vestibular function and/or by producing fluid shifts secondary to loss of hydrostatic pressure.

Frost, J. D., Jr.↗

NASA NTRS1976

The global reference atmospheric model, mod 2 (with two scale perturbation model)

The Global Reference Atmospheric Model was improved to produce more realistic simulations of vertical profiles of atmospheric parameters. A revised two scale random perturbation model using perturbation magnitudes which are adjusted to conform to constraints imposed by the perfect gas law and the hydrostatic condition is described. The two scale perturbation model produces appropriately correlated (horizontally and vertically) small scale and large scale perturbations. These stochastically simulated perturbations are representative of the magnitudes and wavelengths of perturbations produced by tides and planetary scale waves (large scale) and turbulence and gravity waves (small scale). Other new features of the model are: (1) a second order geostrophic wind relation for use at low latitudes which does not "blow up" at low latitudes as the ordinary geostrophic relation does; and (2) revised quasi-biennial amplitudes and phases and revised stationary perturbations, based on data through 1972.

Justus, C. G.↗

NASA NTRS1977

Room-temperature-operation visible-emission semiconductor diode lasers

There were two main approaches taken to develop shorter wavelength lasers. (1) Based on (AlGa)As and liquid-phase epitaxy, significant new results were obtained: Properties of these laser diodes (power output, spectra, and beam patterns), materials considerations, laser theory, and growth problems are discussed. The design of (AlGa)As layers is discussed from the vertical point of view, and various design curves are given. Horizontal structural requirements are also discussed. Experimental results from measurements done as a function of hydrostatic pressure are correlated with other results. (2) The first heterojunction laser structures using GaAs sub l-x P sub x and In sub y Ga sub l-y P at compositions, where the lattice constants are matched, were grown using vapor-phase growth technology and are described in detail, including experimental device results. Threshold current densities from 3,000 to 5,000 A per sq cm. and emission wavelengths from 6,520 A to 6,640 A were obtained at 77 K. The limiting factor in these devices is nonradiative recombination at the heterojunctions. Life tests on facet-coated (AlGa)As CW diodes are reported.

Ladany, I.↗

NASA NTRS1977

Design considerations in mechanical face seals for improved performance. 2: Lubrication

The importance of sealing technology in our industrial, chemical-oriented society in regard to maintenance and environmental contamination is pointed out. It is stated that seal performance (leakage, life) is directly related to seal lubrication. Current thinking in regard to seal lubrication is reviewed; the effect of energy dissipation in the thin lubricating film separating the sealing faces is pointed out, and the results of vaporization due to heating are illustrated. Also, hydrodynamic lubrication is reviewed, and an inherent tendency for the seal to operate with angular misalignment is shown. Recent work on hydrostatic effects is summarized and the conditions for seal instability are discussed. Four different modes of seal lubrication are postulated with the mode type being a strong function of speed and pressure.

Ludwig, L. P.↗

NASA NTRS1976

On the origin of the solar system and of Jupiter and its satellites

The evolution of the middle part of the primitive solar nebula is traced through seven stages: (1) a gravitational instability which clumps condensed material into bodies of appreciable size; (2) the formation of a larger body as a result of mutual collisions; (3) gravitational condensation of the gas in the nebula; (4) subsequent hydrodynamic collapse of the gas onto a heavy-element planetary core; (5) the attainment of a highly distended hydrostatic configuration and its subsequent slow gravitational contraction; (6) the formation of a gaseous disk around proto-Jupiter; and (7) the formation of the Galilean satellites (and Amalthea) within this disk. Different theories on the origin of the primitive solar nebula are reviewed, models of Jupiter are evaluated, and the origin and evolution of the planet are traced through the indicated stages. It is proposed that Jupiter's current excess luminosity is due mostly to a loss of internal energy generated during the initially more rapid contraction period and, to a lesser degree, to the planet's current release of gravitational energy. The question of when the icy constituent was added to the outer two Galilean satellites is considered.

Cameron, A. G. W.↗

NASA NTRS1977

The equilibrium figures of Phobos and other small bodies

Computations of figures of hydrostatic equilibrium for isolated rotating bodies are discussed. It is shown that the theoretical figure of equilibrium for Phobos is a triaxial ellipsoid whose a and b axes differ by about 25% and that this difference is less than 2% for Deimos. A density of less than 3.9 g/cu cm is estimated for Phobos. Equilibrium figures are also examined for the inner satellites of Jupiter and Saturn as well as for small asteroids.

Soter, S.↗

NASA NTRS1977

Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise

It is difficult to separate the effects of reduction in hydrostatic pressure from that of reduced energy expenditure when investigating the confinement deconditioning problem. Experiments were conducted on seven healthy young men aged 19-21 yr with the purpose of separating these two factors by using isotonic physical exercise during bed rest to provide a daily energy expenditure greater than normal ambulatory levels. Fluid and electrolyte shifts were measured during three two-week bed rest periods, each of which being separated by a three-week ambulatory recovery period. During two of the three bed rest periods they performed isometric and isotonic exercises to compare their effects on fluid and electrolyte shifts during bed rest. It is shown that during bed rest, preservation of the extracellular volume takes precedence over maintenance of the plasma volume and that this mechanism is independent of the effects of isometric or isotonic exercise.

Greenleaf, J. E.↗

NASA NTRS1976

Intense magnetic fields and umbral dots

Intense magnetic fields (of one or two kilogauss) situated in a background of weak field and umbral dots (regions of weak field) situated in a background of intense field (the sunspot) have both received considerable, though largely unrelated, discussion in the recent literature. It is suggested that the two phenomena may in fact be less disparate than hitherto presumed. Applying a simple (hydrostatic) model calculation to both phenomena and assuming temperature differences to be constant with height, the depth of each of these structures can be estimated.

Roberts, B.↗