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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 163 records · Page 9
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NASA NTRS1986

KPD 2146+4117 - The coolest DBA white dwarf

When Wickramasinghe and Whelan (1977) discovered the first DBA white dwarf LDS 785A, the possibility was considered that this object represented an exotic oddity. The fact that Shipman et al. (1985) have discovered five additional objects of this type suggests that the DBA stars are in fact a real class of degenerate object. This paper is concerned with the DBA white dwarf KPD 2146+4117, which was observed spectroscopically in October 1982 on a 1.5-m telescope with an image-tube scanner. The spectrum, obtained with 13 A resolution, covered the 3900-6800 A range. It reveals prominent absorption lines of both hydrogen and He I. Methods of analysis are discussed.

Downes, R. A.↗
NASA NTRS1985

Studying antiprotons from balloons and Space Station

Experimental measurements are proposed to determine the existence of cosmic antiprotons and to differentiate between various hypothetical origins for them. The balloon-borne experiment proposed by Balasubrahmanyan et al. (1983) for detecting 50-220-MeV antiprotons and measuring their energy distribution is described; the astrophysical significance of antiproton measurements is considered; the antiproton/proton ratios predicted by various cosmic-ray and exotic models are presented graphically; and the performance required of a Space Station superconducting-magnet detector for the 10-1000-GeV range is discussed. It is concluded that an instrument with 0.3-sq m sr geometry could distinguish (at a 5-sigma level) between hypotheses with spectral-exponent separation of 0.1 in observing time about 1 month, assuming a spectral exponent as steep as E to the -3rd.

Ormes, J. F.↗
NASA NTRS1986

Magnetic configurations of planetary obstacles

The interaction between planetary magnetospheres and solar wind flow is discussed. A proper planetary magnetosphere results from the interaction of a flowing plasma with a planet having an intrinsic, global, magnetic field of sufficient strength to stand off the impinging plasma. Upstream of such an obstacle a bow shock usually exists. The known magnetospheres have severely asymmetric shapes, being elongated approximately along the solar wind flow direction. Conditions which fundamentally determine the structure of a proper planetary magnetosphere are the state of the externally flowing plasma, the planet's magnetic moment, its vector spin, and the presence and nature of internal plasma sources and any plasma sinks. Planets known to have proper magnetospheres are Earth, Mercury, Jupiter, and Saturn. Uranus and Neptune may also have magnetospheres, with that of Uranus promising to have an exotic field configuration, because the planet's magnetic moment is expected to be nearly aligned with the solar wind flow direction. Venus and Mars are also discussed. Magnetopause surface waves are mentioned.

Lepping, R. P.↗
NASA NTRS1986

Heating of the stellar corona

The present state of development of the theory of coronal heating is summarized. Coronal heating is the general cause of stellar X-ray emission, and it is also the cause of stellar mass loss in most stars. Hence a quantitive theory of coronal heating is an essential part of X-ray astronomy, and the development of a correct theory of coronal heating should be a primary concern of X-ray astronomers. The magnetohydrodynamical effects involved in coronal heating are not without interest in their own right, representing phenomena largely unknown in the terrestrial laboratory. Until these effects can be evaluated and assembled into a comprehensive theory of coronal heating for at least one star, the interpretation of the X-ray emissions of all stars is a phenomenological study at best, based on arbitrary organization and display of X-ray luminosity against bolometric luminosity, rotation rate, etc. The sun provides the one opportunity to pursue the exotic physical effects that combine to heat a stellar corona.

Parker, E. N.↗
NASA NTRS1987

Trimming an aircraft model for flight simulation

Real-time piloted aircraft simulations with digital computers have been performed at Ames Research Center (ARC) for over two decades. For the simulation of conventional aircraft models, the establishment of initial vehicle and control orientations at various operational flight regimes has been adequately handled by either analog techniques or simple inversion processes. However, exotic helicopter configurations have been introduced recently that require more sophisticated techniques because of their expanded degrees of freedom and environmental vibration levels. At ARC, these techniques are used for the backward solutions to real-time simulation models as required for the generation of trim points. These techniques are presented in this paper with examples from a blade-element helicopter simulation model.

Mcfarland, Richard E.↗
NASA NTRS1986

Petrology, chemistry, and origin of Apollo 15 regolith breccias

Variations in modal petrology, mineral compositions, and bulk compositions were determined for ten Apollo 15 regolith breccias for comparison with local soils and assessment of the intrasite petrologic variability of the Apollo 15 regolith. Based on the above criteria the breccias are of local origin and mimic the soils from the corresponding sampling stations, with the exception of station 2 breccia 15205. This sample formed from an anomalous regolith, and although not considered exotic to the site is not representative of the soil at the site. KREEP basalt and green glass components vary from trace amounts to dominant in the breccias, evidence that these materials entered the regolith prior to formation of the breccias. Breccias from the edge of Hadley Rille are modally richer in highland fragments than the soils, whereas at the base of Hadley Delta the reverse is true. This is explained by the loss of material into the Rille to be replaced by basalt-derived material, making the soils more basalt-rich. At the base of Hadley Delta highland material is accumulating and the soils are becoming more highland-rich. Over billions of years these processes have developed differences between the present day, evolving soils, and 'fossil' nonevolving soils represented by the regolith breccias. This shows that there has been little change in the geology and the morphology of the Apollo 15 site, probably since the eruption of mare basalts at the site (about 3.3 b.y.).

Simon, S. B.↗
NASA NTRS1987

Quasi-static winds from neutron stars

A series of numerical models is constructed for radiatively driven, quasi-static winds from the surfaces of hot neutron stars. A mathematical technique is devised that in many cases facilitates the integration of the fluid equations in the vicinity of the sonic point, and an improved treatment of radiative transfer is developed that is appropriate to the exotic physical conditions encountered in the models. Boundary conditions which are more realistic than previous ones are used in these models. In agreement with earlier studies, it is found that radiatively driven winds are likely to be directly relevant to the existence of precursors in fast X-ray transients and to apparent radius variations during the course of some type I bursts, and that the presence of such a wind should prevent the bolometric luminosity of a neutron star from exceeding the Eddington limit by more than a small fractional amount. Formulas describing the wind models are presented which are usable as boundary conditions for calculations of the evolution of the deeper, hydrostatic layers of a neutron-star envelope.

Joss, Paul C.↗
NASA NTRS1987

Chemical composition and origin of Apollo 15 impact melts

Fourteen Apollo 15 impact melt rocks were analyzed for major (fused bead microprobe) and trace element (INAA) abundances, and the compositions of these Apennine Front rocks were compared with samples from other landing sites. The rocks show a wide range in trace element abundances, although all but one have a typical KREEP incompatible element pattern and have low-K Fra Mauro basaltic or medium-K Fra Mauro basaltic compositions. The melt chemistries appear to form five groups (labeled A to E in order of decreasing incompatible elements), with the compositions unlike nearly all other impact melts and regoliths from highland sites. All groups except Group A may represent single impact events (either Imbrian or post-Imbrian). One unique sample has a non-KREEP incompatible element pattern, with low abundances and a positive Eu anomaly. Its target is believed to be either a pre-Imbrian melt or exotic.

Ryder, Graham↗
NASA NTRS1987

On the presolar origin of the 'normal planetary' noble gas component in meteorites

Several components of planetary noble gases, including CCFXe (Xe-X), s-process Kr and Xe, and Ne-E, are now thought to have had a presolar origin. It is proposed that the 'normal planetary' noble gas component, which contains most of the planetary Ar, Kr, and Xe, is also presolar. This component was trapped in carbonaceous mantles as the mantles formed on grain surfaces in the molecular cloud. The presolar dust grains and their carbonaceous mantles were then incorporated into primitive meteorites. This model naturally explains: (1) the affinity of 'normal planetary' noble gases for carbonaceous material in primitive chondrites; (2) the near absence of He and Ne in the 'normal planetary' component; (3) the elemental fractionation patterns of the 'exotic' and 'normal planetary' components; (4) the similarity of the isotopic compositions of 'normal planetary' and trapped solar Ar, Kr, and Xe; (5) the high noble gas content of the 'normal planetary' gas carrier; (6) several aspects of the chemistry of the 'normal planetary' gas carrier; (7) the correlation of planetary noble gases with the fine-grained material in primitive chondrites; and (8) the widespread occurrence of the planetary fractionation pattern throughout the solar system.

Huss, Gary R.↗
NASA NTRS1987

The planetary and interstellar components of meteorites - A review

Recent analyses show that, although most meteorites are collisional debris of asteroids, three meteorites collected on the Antarctic ice sheet were projected to earth from the highlands of the moon, and eight meteorites have chemical and isotopic compositions suggestive of derivation from Mars. Although meteorites are primarily of interest to planetary scientists for the abundance of clues they hold to the materials and processes that formed the solar system, they have begun to engage the attention of astrochemists because of isotopic and mineralogical indications that they contain interstellar components. Although each individual observation to this effect is inconclusive, the body of evidence is becoming ever more persuasive. This paper reviews the main classes of meteorites and their probable sources, with special emphasis on components that appear to be exotic to the solar system.

Marvin, Ursula B.↗
NASA NTRS1987

Surrogate measures: A proposed alternative in human factors assessment of operational measures of performance

Surrogate measures are proposed as an alternative to direct assessment of operational performance for purposes of screening agents who may have to work under unusual stresses or in exotic environments. Such measures are particularly proposed when the surrogate can be empirically validated against the operational criterion. The focus is on cognitive (or throughput) performances in humans as opposed to sensory (input) or motor (output) measures, but the methods should be applicable for development of batteries which will tap input/output functions. A menu of performance tasks is under development for implementation on a battery-operated portable microcomputer, with 21 tests currently available. The tasks are reliable and become stable in minimum amounts of time; appear sensitive to some agents; comprise constructs related to actual job tasks; and are easily administered in most environments. Implications for human factors engineering studies in environmental stress are discussed.

Kennedy, Robert S.↗
NASA NTRS1988

History of wildland fires on Vandenberg Air Force Base, California

The fire history of the past 50 years for Vandenberg AFB, California was determined using aerial photography, field investigation, and historical and current written records. This constitutes a record of the vegetation age classes for the entire base. The location, cause, and fuel type for sixty fires from this time period were determined. The fires were mapped and entered into a geographic infomation system (GIS) for Vandenberg. Fire history maps derived from this GIS were printed at 1:9600 scale and are on deposit at the Vandenberg Environmental Task Force Office. Although some ecologically significant plant communities on Vandenberg are adapted to fire, no natural fire frequency could be determined, since only one fire possibly caused by lightning occurred in the area now within the base since 1937. Observations made during this study suggest that burning may encourage the invasion of exotic species into chaparral, in particular Burton Mesa or sandhill chaparral, an unusual and geographically limited form of chaparral found on the base.

Hickson, Diana E.↗
NASA NTRS1987

Biological invasion by Myrica faya alters ecosystem development in Hawaii

The exotic nitrogen-fixing tree Myrica faya invades young volcanic sites where the growth of native plants is limited by a lack of nitrogen. Myrica quadruples the amount of nitrogen entering certain sites and increases the overall biological availability of nitrogen, thereby altering the nature of ecosystem development after volcanic eruptions.

Vitousek, Peter M.↗
NASA NTRS1987

O-16 excesses in Murchison and Murray hibonites - A case against a late supernova injection origin of isotopic anomalies in O, Mg, Ca, and Ti

Ion probe measurements of the oxygen isotopic composition of seven hibonite samples from the CM chondrites Murchison and Murray are reported. All samples show large O-16 excesses relative to terrestrial oxygen. The data for all samples plot along the carbonaceous chondrite O-16-rich mixing line and show no evidence for isotopic mass fractionation effects characteristic of FUN inclusions. These hibonites have the largest Ca-48 and Ti-50 isotopic anomalies found to date; thus there is no intrinsic relationship between anomalies of a nucleosynthetic origin and isotopic mass fractionation effects. The large O-16 excess seen in the sample with the largest measured Ca-48 and Ti-50 depletions argues against a late injection of exotic material from a nearby supernova as a source for the isotopic anomalies.

Fahey, A. J.↗
NASA NTRS1988

Compact radio sources in the galactic plane

The preliminary results of a search for infrared counterparts to compact continuum radio sources found within 0.5 deg of the Galactic plane are presented. Out of 75 positions searched, nine very red sources, each with a probability of less than 0.01 of being a random field star, were found. Most of the nine sources are characterized by deep silicate absorption features at 10 microns and a red energy distribution that continues to rise beyond 25 microns. Six of the sources are best explained as late O or early B stars exciting a compact H II region. The radio emission is close to that expected for the rate of emission of ionizing photons for a normal main-sequence star. Although these H II regions are compact, they are not sufficiently dusty in the immediate environment of the star to significantly reduce the ionizing flux. Three of the sources show considerably more emission than expected for a main-sequence star, indicating they are either hotter than a main-sequence star with the same luminosity or the radio emision is nonthermal and coming from a more exotic object.

Jones, Terry Jay↗
NASA NTRS1988

A forecast of new test capabilities using Magnetic Suspension and Balance Systems

This paper outlines the potential of Magnetic Suspension and Balance System (MSBS) technology to solve existing problems related to support interference in wind tunnels. Improvement of existing test techniques and exciting new techniques are envisioned as a result of applying MSBS. These include improved data accuracy, dynamic stability testing, two-body/stores release testing, and pilot/designer-in-the-loop tests. It also discusses the use of MSBS for testing exotic configurations such as hybrid hypersonic vehicles. A new facility concept that combines features of ballistic tubes, magnetic suspension, and cryogenic tunnels is described.

Lawing, Pierce L.↗
NASA NTRS1987

Volatile inventory of Mars-2: Primordial sources and fractionating processes

The total volatile inventory of Mars has been modeled using meteoritic and presumed primordial abundances in the early solar system. Evidence is presented which indicates that the elemental abundances of the noble gases on Earth and Mars are similar, and their ratios are comparable to those in average carbonaceous chondrites with the exception of xenon and krypton. In order to account for presently observed variations in gas abundances, two primordial sources were used. One was the solar composition similar to the solar wind, and the other of carbonaceous grains that were the source for trace exotic components. For Mars, a model in which the early, high solar EUV flux with continued hydrogen production by differentiation results in mass fractionation of the primordial atmosphere, early depletion of xenon, and later depletion of gases lighter than krypton. The result is that the primordial Mars water inventory may have been on the order of 20 to 30 km if spread over the planet.

Pepin, R. O.↗
NASA NTRS1988

Deccan volcanism at the Cretaceous-Tertiary boundary

The accuracy with which one can claim that Deccan trap volcanism occurred at the Cretaceous-Tertiary boundary (KTB) over a very short time interval is of key importance in deciding whether a volcanic origin of the KTB events should be taken seriously. In the two years since paleomagnetic, paleontological and geodynamic evidence was published, further data have become available and the case now appears to be well constrained. The Ar-40/Ar-39 results from six labs have yielded some 24 reliable plateau ages that narrow the age range to 65 to 69 Ma. Moreover, it appears that a significant part of this range results from inter-lab spread and possible minor alteration. Paleontology demonstrates that volcanism started in the Maestrichtian, more precisely in the A. mayaroensis zone. Paleomagnetism shows that volcanism spanned only 3 chrons and only one correlation remains possible, that of the main central reversed chron with 29R. Therefore, whereas Ar-40/Ar-39 is able only to restrict the duration of volcanism to some 4 Ma, paleomagnetism restricts it to 0.5 Ma. Using some geochemical indicators such as C-13 as proxy, it is suggested that volcanism actually consists of a few shorter events of unequal magnitude. Extrusion rates may be as high as 100 cu km/yr and fissure lengths as long as several 100 km. Such a scenario appears to be at least as successful as others in accounting for most anomalies observed at the KTB. Particularly important are Iridium and other platinum group elements (PGE) profiles, Sr-87/Sr-86, C-13, 0-18, other exotic geochemical signatures, spherules, soot, shocked minerals, selective and stepwise extinctions. The environmental impact of CO2 possibly released during explosive phases of volcanism, and SO2 released during effusive phases, and the ability of volcanism to ensure worldwide distribution of KTB products are now all addressed. In conclusion, the case for a causal link between internal hotspot activity, birth of the Reunion hotspot itself as the Deccan and KTB events appears to rest on an increasingly stronger basis.

Courtillot, V.↗