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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Is the galactic corona produced by galactic flares

The effect of the differential rotation of the disk of the galaxy on magnetic field which penetrates the disk is considered. The magnetic field will be progressively distorted from a potential (current-free) form and will at some stage become unstable. We expect, from knowledge of solar flares, that an MHD instability, a resistive instability, or a combination of the two, will result in the release of the excess magnetic energy, and that part of the released energy will be converted into heat. By estimating the energy release and the rate at which this process will occur and by assuming that this energy input is balanced by radiation, we obtain estimates of the parameters of the resulting plasma. It appears that this process alone can heat a galactic corona to temperatures of order one-million K.

Sturrock, P. A.↗
NASA NTRS1980

Shock-induced effects in calcite from Cactus Crater

The paper discusses shock metamorphism of calcite from coralline limestone samples retrieved from a borehole drilled into rocks beneath Cactus Crater, a nuclear explosion crater at Eniwetok Atoll. The metamorphism was detected and quantified using electron spin resonance (ESR); the ESR spectra of Mn(+) present as a trace constituent in the coral samples, show a consistent decrease in hyperfine peak splitting with decreasing depth of sample. It is suggested that the decrease in hyperfine peak splitting reflects a decrease in crystal field splitting, and therefore, small increases on cation-anion distances produced by mechanical energy input during the shock process. Two alternative crater models suggested by the ESR results are a depiction of a steady decay of the shock wave, and a delineation of a breccia lens with a breccia-bedrock interface at 20 plus or minus 5 m.

Vizgirda, J.↗
NASA NTRS1980

Studies of auroral X-ray imaging from high altitude spacecraft

Results of a study of techniques for imaging the aurora from a high altitude satellite at X-ray wavelengths are summarized. The X-ray observations allow the straightforward derivation of the primary auroral X-ray spectrum and can be made at all local times, day and night. Five candidate imaging systems are identified: X-ray telescope, multiple pinhole camera, coded aperture, rastered collimator, and imaging collimator. Examples of each are specified, subject to common weight and size limits which allow them to be intercompared. The imaging ability of each system is tested using a wide variety of sample spectra which are based on previous satellite observations. The study shows that the pinhole camera and coded aperture are both good auroral imaging systems. The two collimated detectors are significantly less sensitive. The X-ray telescope provides better image quality than the other systems in almost all cases, but a limitation to energies below about 4 keV prevents this system from providing the spectra data essential to deriving electron spectra, energy input to the atmosphere, and atmospheric densities and conductivities. The orbit selection requires a tradeoff between spatial resolution and duty cycle.

Mckenzie, D. L.↗
NASA NTRS1980

Experimental compliance calibration of the compact fracture toughness specimen

Compliances and stress intensity coefficients were determined over crack length to width ratios from 0.1 to 0.8. Displacements were measured at the load points, load line, and crack mouth. Special fixturing was devised to permit accurate measurement of load point displacement. The results are in agreement with the currently used results of boundary collocation analyses. The errors which occur in stress intensity coefficients or specimen energy input determinations made from load line displacement measurements rather than from load point measurements are emphasized.

Fisher, D. M.↗
NASA NTRS1981

Need for measurements in the lower atmosphere

Areas of investigation that are discussed include: the relative importance of the turbopause versus winds in determining the composition of the thermosphere; the mechanism of the coupling between the mesosphere and the thermosphere and how important wave dissipation is in this coupling; and the morphology and variation of magnetospheric energy inputs at high latitudes. The need to investigate the propagation characteristics of atmospheric gravity waves in the altitude region between 100 and 200 km is emphasized.

Reber, C. A.↗
NASA NTRS1981

The thermal emission spectrum of Io and a determination of the heat flux from its hot spots

Observations of thermal emission from Io in the near infrared made during an eclipse were combined with unpublished 8- to 13-micron intermediate band photometry and a 16- to 22-micron spectrum to specify Io's emission spectrum from 2.2 to 22 microns. Models were calculated having 'hot spots' at several different temperatures superposed on a surface, the major part of which is assumed to be at the solar equilibrium temperature. It was possible to fit the entire composite spectrum with this model. It is argued that the total emission from the hot spots can be equated to the nonsolar energy input into Io. The disk-averaged heat radiated by the hot spots is found to be 180 + or 60 microwatts/sq cm = 43 + or - 14 microcalories/sq cm-sec. A possible bimodal temperature distribution of the hot spots is discussed.

Sinton, W. M.↗
NASA NTRS1981

The LAMAR: A high throughput X-ray astronomy facility for a moderate cost mission

The performance of a large area modular array of reflectors (LAMAR) is considered in several hypothetical observations relevant to: (1) cosmology, the X-ray background, and large scale structure of the universe; (2) clusters of galaxies and their evolution; (3) quasars and other active galactic nuclei; (4) compact objects in our galaxy; (5) stellar coronae; and (6) energy input to the interstellar medium.

Gorenstein, P.↗
NASA NTRS1982

Chromospheric, transition layer and coronal emission of metal deficient stars

It is shown that while MgII k line emission decreases for metal deficient stars, the Ly alpha emission increases. The sum of chromospheric hydrogen and metallic emission appears to be independent of metal abundances. The total chromospheric energy loss is estimated to be 0.0004 F sub bol. The chromospheric energy input does not seem to decrease for increasing age. The transition layer emission is reduced for metal deficient stars, but it is not known whether the reduction is larger than can be explained by curve of growth effects only. Coronal X-ray emission was measured for 4 metal deficient stars. Within a 12 limit it could still be consistent with the emission of solar abundance stars.

Boehm-Vitense, E.↗
NASA NTRS1981

Ultraviolet spectroscopy of comets

Results of observations of comets in the ultraviolet are reviewed in relation to their significance for the chemistry and physics of the cometary coma and the composition of the cometary ice. Ultraviolet cometary observations began in 1970, when a hydrogen envelope was discovered extending millions of kilometers from the nucleus of comet Bennett, and continued with the discovery of oxygen and carbon in comet Kohoutek and the acquisition of comprehensive UV spectra from comets West (1976 VI), Seargent (1978 XV) and Bradfield (1979 X). The available cometary spectra are remarkably similar, indicative of a common composition and origin for comets and the insignificance of chemical reactions in the inner coma to species abundances. Ultraviolet spectroscopy has also allowed the determination of gas production rates from either the surface brightness or the total luminosity in a given spectral line. IUE observations of comet Bradfield reveal the water production rate to vary as the -3.7 power of heliocentric distance from 0.71 to 1.55 AU, incompatible with solar energy input as the controlling influence on water vaporization.

Feldman, P. D.↗
NASA NTRS1982

Relationships between the Birkeland currents, ionospheric currents, and electric fields

Currents and electric fields in the ionosphere are calculated using a global model of the electron density including conjugate coupling along field lines. Incoherent scatter and rocket measurements of high-latitude electron densities are used to derive realistic variations of the polar conductivities as a function of magnetic activity. The Birkeland currents are specified in terms of three indices, and the relationship between these parameters and the auroral electrojets indices is examined along with the polar cap potential and the electric field at lower latitudes. A mathematical model of the currents, electric fields, and energy inputs produced by field aligned currents is developed, which is consistent with and specifiable in terms of measured geophysical indices.

Bleuler, E.↗
NASA NTRS1982

Gamma radiation and photospheric white-light flare continuum

It is noted that recent gamma-ray observations of solar flares have provided a better means for estimating the heating of the solar atmosphere by energetic protons. This type of heating has been suggested as the explanation of the continuum emission of the white-light flare. The effects on the photosphere of high-energy particles capable of producing the intense gamma-ray emission observed in the flare of July 11, 1978, are analyzed. A simple energy-balance argument is used, and hydrogen ionization is taken into account. It is found that energy deposition increases with height for the inferred proton spectra and is not strongly dependent upon the assumed angle of incidence. At the top of the photosphere, the computed energy inputs fall in the range 10-100 ergs/cu cm-s.

Hudson, H. S.↗
NASA NTRS1982

A global model of the neutral thermosphere in magnetic coordinates based on OGO 6 data

Data from the OGO 6 satellite have been analyzed in magnetic latitude and magnetic local time coordinates for various seasons and magnetic activity levels. These measurements show considerable detail, particularly in the auroral regions where the energy inputs are well organized in this coordinate system. This detail is not readily observed in models based on geographic coordinates. Atomic oxygen and helium densities and a parameter related to the molecular nitrogen density were analyzed. The long-term averages of these quantities are presented in graphical form and as analytic functions to provide models of these thermospheric parameters. The atomic oxygen and helium densities show minima at high latitudes in the postmidnight sector for nearly all seasons and magnetic activity levels. The exospheric temperature inferred from the N2 density increases toward high latitudes for all seasons and all magnetic activity levels. This inferred temperature is about 300 deg K higher at the summer magnetic pole than at the winter magnetic pole.

Stehle, C. G.↗
NASA NTRS1982

Observational constraints for a theoretical model describing the soft X-ray flare

High-resolution solar flare X-ray spectra have recently been obtained from X-ray spectrometer experiments flown on an Air Force spacecraft (P78-1) launched on 1979 February 24. Interpretation of the spectra has produced new results concerning the physical conditions and time behavior of the thermal soft X-ray emitting plasma at temperatures near 20,000,000 K. It is argued that soft and hard X-ray events are not causally related to each other, but are simply two different manifestations of flare energy release. They probably occur in different plasma volumes. The source of the preflare plasma appears to be in the cooler parts of the solar atmosphere, perhaps transition region loops with initial temperatures of 100,000 K and densities of 10 to the 11th per cu cm. Continuous energy input, rather than sequential activation of loops, is required to explain the observations. Compression coupled with chromospheric ablation may produce the high densities in coronal flare loops.

Feldman, U.↗
NASA NTRS1981

Energy balance in solar and stellar chromospheres

Net radiative cooling rates for quiet and active regions of the solar chromosphere and for two stellar chromospheres are calculated from corresponding atmospheric models. Models of chromospheric temperature and microvelocity distributions are derived from observed spectra of a dark point within a cell, the average sun and a very bright network element on the quiet sun, a solar plage and flare, and the stars Alpha Boo and Lambda And. Net radiative cooling rates due to the transitions of various atoms and ions are then calculated from the models as a function of depth. Large values of the net radiative cooling rate are found at the base of the chromosphere-corona transition region which are due primarily to Lyman alpha emission, and a temperature plateau is obtained in the transition region itself. In the chromospheric regions, the calculated cooling rate is equal to the mechanical energy input as a function of height and thus provides a direct constraint on theories of chromospheric heating.

Avrett, E. H.↗
NASA NTRS1982

Multiple-spacecraft and correlated riometer study of magnetospheric substorm phenomena

Double-spacecraft observations presented suggest that growth phase phenomena are widespread in the outer magnetosphere and can occur simultaneously at nightside locations 4-5 hours apart in local time. Evidence is also adduced from multiple-spacecraft data and comprehensive magnetometer and riometer data against the concept that growth phase features are not generally due to substorm activity at other locations in the auroral or polar regions. A close relationship is noted between putative energy input to the magnetosphere and the sensitive response of the magnetic field and energetic particles at pre- and near-midnight geostationary orbit locations. This relationship is shown explicitly for the cases of three event periods. Data are also presented which suggest that growth phase features at synchronous orbit can be strictly controlled by IMF orientations.

Baker, D. N.↗
NASA NTRS1982

Effects of the Kelvin-Helmholtz surface instability on supersonic jets

An exact numerical calculation is provided for of linear growth and phase velocity of Kelvin-Helmholtz unstable wave modes on a supersonic jet of cylindrical cross section. An expression for the maximally unstable wavenumber of each wave mode is found. Provided a sharp velocity discontinuity exists all wave modes are unstable. A combination of rapid jet expansion and velocity shear across a jet can effectively stabilize all wave modes. The more likely case of slow jet expansion and of velocity shear at the jet surface allows wave modes with maximally unstable wavelength longer than or on the order of the jet radius to grow. The relative energy in different wave modes and effect on the jet is investigated. Energy input into a jet resulting from surface instability is discussed.

Hardee, P. E.↗
NASA NTRS1983

Io escape and ionization of atmospheric gases

Exploratory model calculations for the Io atomic oxygen cloud have provided two-dimensional sky-plane intensities for the 6300 A, 1304 A and 880 A lines, where volume excitation and ionization rates are determined by impact collisions with Io plasma torus electrons. Comparison of model results with observations at 6300 A suggests an isotropic oxygen flux from Io of about 1.5x109 atoms 1 sq cm/sec. The effects of including a neutral sulfur cloud and also of including charge exchange reactions between plasma torus ions and neutral OI and SI were evaluated to be significant and were roughly estimated to increase the required oxygen flux to 1.2 x 10 to the 10th atoms/sq cm/sec. In addition, increases in the estimates for the ion loading, cloud mass loss, plasma mass loading and ion energy input rates were also made. Model calculations for an Io sulfur cloud, excluding charge exchange reactions but assuming an SI flux of 7.5 x 10 to the 8th atoms/sq cm/sec (i.e., half of the oxygen flux), were also performed and provided sky plane intensities for a number of visible and IR emission lines.

Smyth, W. H.↗
NASA NTRS1983

Radioactive models of type 1 supernovae

In recent years, considerable progress has been made toward understanding Type I supernovae within the context of radioactive energy input. Much effort has gone into determining the peak magnitude of the supernovae, particularly in the B-band, and its relation to the Hubble constant. If the distances inferred for Type I events are at all accurate, and/or the Hubble constant has a value near 50 km per s per Mpc, it is clear that models must reach a peak magnitude approximately -20 in order to be consistent. The present investigation is concerned with models which achieve peak magnitudes near this value and contain 0.8 solar mass of Ni-56. The B-band light curve declines much more rapidly after peak than the bolometric light curve. The mass and velocity of Ni-56 (at least for the A models) are within the region defined by Axelrod (1980) for configurations which produce acceptable spectra at late times. The models are consistent with the absence of a neutron star after the explosion. There remain, however, many difficult problems.

Schurmann, S. R.↗