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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The Borealis Basin of Mars

Why the lowlands of Mars are concentrated in the Northern Hemisphere and the highlands in the Southern Hemisphere is probably the most fundamental unsolved problem in martian geology. No explanation that accounts both for this asymmetric distribution and for the isostatic equilibrium across the scarp or sloping transition zone dividing the two provinces has been generally accepted; thinning of the lithosphere in the northern hemisphere by internal processes has been suggested. Because other lowland-highland distributions on Mars, Moon, and Mercury are controlled by impact basins, it is proposed that a giant basin formed early in Mars' history has caused the martian hemispheric dichotomy as well.

Wilhelms, D. E.↗
NASA NTRS1984

The boundary layer on compressor cascade blades

The characteristics of the flow field about highly loaded turbocompressor blades in a cascade wind tunnel were investigated. Experimental tests were conducted at chord Reynolds number (R sub c) near 500,000. A laser Doppler anemometer was employed in flow velocity measurement. Suction surface mean velocity and turbulence intensity profiles at a single incidence angle are presented. These data contribute to further understanding of two-dimensional boundary layer profiles, points of separation, and transition zones for turbomachine blades, and concomitantly, to compressor cascade predictive models.

Deutsch, S.↗
NASA NTRS1983

The effect of heavy element opacity on the structure of H II regions

In the modeling of H II regions, there generally has been universal dismissal of opacity due to elements other than H and He. It is found that in certain cases, the trace elements do contribute substantially to the opacity, modifying the ionization equilibrium directly and having feedback on the thermal structure. When important, this effect will reduce the volume where some lines from high ionization states are produced and will decouple transition zones that have traditionally been assumed to be coextensive. The possible reconciliation of some recent problems where observations and theory appeared to be inconsistent with one another are discussed.

Rubin, R. H.↗
NASA NTRS1983

Seismicity, fault plane solutions, depth of faulting, and active tectonics of the Andes of Peru, Ecuador, and southern Colombia

The long-period P waveforms observed for 17 earthquakes in the Peruvian Andes during 1963-1976 are compared with synthetic waveforms to obtain fault-plane solutions and focal depths. The morphological units of the Peruvian Andes are characterized: coastal plains, Cordillera Occidental, altiplano and central high plateau, Cordillera Oriental, and sub-Andes. The data base and analysis methodology are discussed, and the results are presented in tables, diagrams, graphs, maps, and photographs illustrating typical formations. Most of the earthquakes are shown to occur in the transition zone from the sub-Andes to the Cordillera Oriental under formations of about 1 km elevation at focal depths of 10-38 km. It is suggested that the sub-Andean earthquakes reflect hinterland deformation of a detached fold and thrust belt, perhaps like that which occurred in parts of the Canadian Rockies. From the total crustal shortening evident in Andean morphology and the shortening rate of the recent earthquakes it is estimated that the topography and crustal root of the Andes have been formed during the last 90-135 Myr.

Suarez, G.↗
NASA NTRS1984

The martian hemispheric dichotomy may be due to a giant impact

Of the two approximately hemispherical, fundamentally different geological provinces into which Mars is divided, the more southerly province is heavily cratered, while the northern is lightly cratered and contains younger geological units. Lowlands occupy about one-third of Mars, and these are separated from the highlands by a distinct scarp or by a sloping transitional zone which is characterized by a variety of landforms that are unknown on other planets. It is presently proposed that the largest expanse of lowlands is substantially due to the formation of a large impact basin early in the planet's history, which has markedly influenced the character of the Martian surface.

Wilhelms, D. E.↗
NASA NTRS1984

Waveform inversion of mantle Love waves - The Born seismogram approach

Normal mode theory, extended to the slightly laterally heterogeneous earth by the first-order Born approximation, is applied to the waveform inversion of mantle Love waves (200-500 sec) for the earth's lateral heterogeneity at l = 2 and a spherically symmetric anelasticity (Q sub mu) structure. The data are from the Global Digital Seismograph Network (GDSN). The l = 2 pattern is very similar to the results of other studies that used either different methods, such as phase velocity measurements and multiplet location measurements, or a different data set, such as mantle Rayleigh waves from different instruments. The results are carefully analyzed for variance reduction and are most naturally explained by heterogeneity in the upper 420 km. Because of the poor resolution of the data set for the deep interior, however, a fairly large heterogeneity in the transition zones, of the order of up to 3.5 percent in shear wave velocity, is allowed. It is noteworthy that Love waves of this period range can not constrain the structure below 420 km and thus any model presented by similar studies below this depth are likely to be constrained by Rayleigh waves (spheroidal modes) only.

Tanimoto, T.↗
NASA NTRS1984

A unified N-body and statistical treatment of stellar dynamics. I - The hybrid code. II - Applications to globular cluster cores

A unified N-body and statistical treatment of stellar dynamics is developed and applied to the late stages of core collapse and early stages of post collapse evolution in globular clusters. A 'hybrid' computer code is joined to a direct N-body code which is used to calculate exactly the behavior of particles in the inner spatial region, and the combination is used to follow particles statistically in the outer spatial region. A transition zone allows the exchange of particles and energy between the two regions. The main application results include: formation of a hard central binary system, reversal of core collapse and expansion due to the heat input from this binary, ejection of the binary from the core, and recollapse of the core; density profiles that form a one-parameter sequence during the core oscillations; and indications that these oscillations will eventually cease.

Mcmillan, S. L. W.↗
NASA NTRS1984

A review and analysis of boundary layer transition data for turbine application

A symposium on transition in turbines was held at the NASA Lewis Research Center. One recommendation of the working groups was the collection of existing transition data to provide standard cases against which models could be tested. A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information from the heat transfer data. The data sets reviewed cover a wide range of flow conditions, from low speed, flat plate tests to full scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Gaugler, R. E.↗
NASA NTRS1985

Temporal and spectral characteristics of solar flare hard X-ray emission

Solar Maximum Mission observations of three flares that impose stringent constraints on physical models of the hard X-ray production during the impulsive phase are presented. Hard X-ray imaging observations of the flares on 1980 November 5 at 22:33 UT show two patches in the 16 to 30 keV images that are separated by 70,000 km and that brighten simultaneously to within 5 s. Observations to O V from one of the footprints show simultaneity of the brightening in this transition zone line and in the total hard X-ray flux to within a second or two. These results suggest but do not require the existence of electron beams in this flare. The rapid fluctuations of the hard X-ray flux within some flares on the time scales of 1 s also provide evidence for electron beams and limits on the time scale of the energy release mechanism. Observations of a flare on 1980 June 6 at 22:34 UT show variations in the 28 keV X-ray counting rate from one 20 ms interval to the next over a period of 10 s. The hard X-ray spectral variations measured with 128 ms time resolution for one 0.5 s spike during this flare are consistent with the predictions of thick-target non-thermal beam model.

Dennis, B. R.↗
NASA NTRS1984

The boundary layer on compressor cascade blades

The flow field about an airfoil in a cascade at chord Reynolds number (R sub C) near 50,000. The program is experimental and combines laser Doppler anemometry (LDA) with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation and the transition zone) on a cascade of highly-loaded compressor blades. The information provided is to serve as benchmark data for the evaluation of current and future compressor cascade predictive models, in this way aiding in the compressor design process. The completed pressure surface mean velocity profiles, as well as two detailed near wake velocity profiles, all at a single incidence angle are provided.

Deutsch, S.↗
NASA NTRS1985

The Geology of Mt. Hope, a Silicic Volcanic Center in West Central Arizona

The purpose was to establish a detailed history of the sequence of geologic events which occurred at Mt. Hope and an area 6.8 miles in diameter surrounding it. The final result will be comprised of information collected during field mapping, with data from petrographic studies and wet chemical analyses. From this it should be possible to suggest relationships to other volcanic regions, particularly bimodal suites in the transition zone, and gain a clearer picture of the petrologic nature of this area. Field work conducted this past summer confirmed the bimodal nature of volcanism at Mt. Hope. The symmetrical, radial cone is comprised of several rhyolites with numerous intrusions of intermediate-composition dikes and two breccia pipes near the summit.

Simmons, A. M.↗
NASA NTRS1985

Permafrost and Subsurface Ice in the Solar System

The properties and behavior of planetary permafrost are discussed with reference to the ability of such surfaces to sustain loads characteristics of spacecraft landing and planetary bases. In most occurrences, water ice is in close proximity to, or in contact with, finely divided silicate mineral matter. When ice contacts silicate mineral surfaces, a liquid-like, transition zone is created. Its thickness ranges from several hundred Angstron units at temperatures near 0 degrees C to about three Angstrom units at -150 degrees C. When soluble substances are present, the resulting brine enlarges the interfacial zone. When clays are involved, although the interfacial zone may be small, its extent is large. The unfrozen, interfacial water may amount to 100% or more weight at a temperature of -5 degrees C. The presence of this interfacial unfrozen water acts to confer plasticity to permafrost, enabling it to exhibit creep at all imposed levels of stress. Nucleation processes and load-bearing capacity are examined.

Anderson, D. M.↗
NASA NTRS1985

Cometary atmospheres: Modeling the spatial distribution of observed neutral radicals

Progress on modeling the spatial distributions of cometary radicals is described. The Monte Carlo particle-trajectory model was generalized to include the full time dependencies of initial comet expansion velocities, nucleus vaporization rates, photochemical lifetimes and photon emission rates which enter the problem through the comet's changing heliocentric distance and velocity. The effect of multiple collisions in the transition zone from collisional coupling to true free flow were also included. Currently available observations of the spatial distributions of the neutral radicals, as well as the latest available photochemical data were re-evaluated. Preliminary exploratory model results testing the effects of various processes on observable spatial distributions are also discussed.

Combi, M. R.↗
NASA NTRS1985

A review and analysis of boundary layer transition data for turbine application

A number of data sets from the open literature that include heat transfer data in apparently transitional boundary layers, with particular application to the turbine environment, were reviewed and analyzed to extract transition information. The data were analyzed by using a version of the STAN5 two-dimensional boundary layer code. The transition starting and ending points were determined by adjusting parameters in STAN5 until the calculations matched the data. The results are presented as a table of the deduced transition location and length as functions of the test parameters. The data sets reviewed cover a wide range of flow conditions, from low-speed, flat-plate tests to full-scale turbine airfoils operating at simulated turbine engine conditions. The results indicate that free-stream turbulence and pressure gradient have strong, and opposite, effects on the location of the start of transition and on the length of the transition zone.

Gaugler, R. E.↗
NASA NTRS1985

High Resolution Telescope and Spectrograph (HRTS)

The major objectives of the high resolution telescope and spectrograph (HRTS) are: (1) the investigation of the energy balance and mass balance of the temperature minimum, chromosphere, transition zone, and corona in quiet regions on the Sun as well as in plages, flares, and sunspots; (2) the investigation of the velocity field of the lower corona to study the origin of the solar wind; (3) the investigation of preflare and flare phenomena. The HRTS instruments consists of a telescope, an ultraviolet spectrograph, and ultraviolet spectroheliograph, and an H alpha slit display system, all housed in a thermal control canister mounted on an instrument pointing system.

Moore, R. L.↗
NASA NTRS1984

Investigations of Thematic Mapper data dimensionality and features using field spectrometer data

Landsat-4 TM and MSS data, simulated from field reflectance spectra, are used to determine the dimensionality and structure of TM data (excluding the thermal band), demonstrate the relationships between the two sensors, and derive a Tasseled Cap Transformation for TM data. The simulated TM data are found to primarily occupy three dimensions, and to be concentrated into two adjoining and orthogonal planes and a transition zone between the two. The 'Plane of Vegetation' is shown to be comparable to the MSS Tasseled Cap plane, while the 'Plane of Soils' represents new information. The potential for improved spectral estimation of the relative mix of vegegation and soil in the field of view, and for improved monitoring of soil moisture status, is demonstrated.

Crist, E. P.↗
NASA NTRS1984

The many faces of Capella - A search for rotational modulations and a study of systematic velocities of emission lines in the ultraviolet

The UV spectra of Capella were monitored for fluctuations using IUE instrumentation, and radial velocities of the emission lines were determined. The possible fluctuations were studied from March through April 1981, and radial velocity data were taken over six days in 1982. The Capella surface activity emissions proved to be steady, while redshifts from high excitation were found in the photospheric plasma. Downflows of 100,000 K plasma in the stellar transition zone could produce the redshifts. The FWHMs of the emission lines exceeded the redshift by an order of magnitude, suggesting that the observed excitations could be only averaged values of the dynamics of the outer atmosphere of Capella.

Ayres, T. R.↗
NASA NTRS1984

The impulsive phase of a solar limb flare

The limb flare of 1980 November 18 at 14:51 UT is studied with the X-ray instruments on board the Solar Maximum Mission (SMM). Evidence is found for release of a significant fraction, 10 percent or more, of the flare energy before the impulsive hard X-ray burst. In the impulsive phase the hard X-rays emitted during the rapidly varying part of the burst are observed on the limb, at a level consistent with the chromosphere. During the final stages of the hard X-ray burst, when the fast time structure has disappeared, the hard X-rays clearly come from the corona, at which time the spectrum is softer. Throughout the decay phase of the flare the X-rays also originate in the corona. It is concluded that initially the flare energy is deposited below the transition zone, from which point the chromospheric plasma is ablated. When this plasma has expanded into the corona to the energy release site, particle acceleration associated with such energy release is quenched. The altitude of this site is estimated at 6000 + or - 1500 km above the photosphere. The sequence of observations is consistent with the bulk of the energy being contained in suprathermal protons, in the energy region 100-1000 keV, during the impulsive phase.

Simnett, G. M.↗