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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
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

An X-ray survey of hot white dwarf stars - Evidence for a m(He)/n(H) versus Teff correlation

Observations of 13 white dwarf and subdwarf stars using the Einstein Observatory High Resolution Image are reported. Included are stars of classes DA, DB, DAV, sDO, and sDB, with optically determined effective temperatures in the range 10,000-60,000 K. X-ray emission was detected from two of the 13: the very hot (55,000 K) DA1 star WD 2309 + 105 (= EG 233), with a count rate one-fifth that of HZ 43, and the relatively cool (26,000 K) DA3 star WD 1052 - 273 (=GD 125). The effective temperatures determined from ultraviolet and optical observations were used to place limits on the He content of the white dwarf photospheres, presuming that trace photospheric He is the missing opacity source which quenches the thermal X-rays in these stars. When presently obtained results were combined with those available from the literature evidence was found for a correlation between Teff and n(He)/n(H), in which HZ 43 is a conspicuous exception to the general trend. Both this correlation and the exceptional behavior of HZ 43 are qualitatively accounted for by a radiative acceleration model, in which the rate of upward movement of the He is a function of temperature and surface gravity

Petre, R.↗
NASA NTRS1985

Ultraviolet spectra of N, R, and S stars

Ultraviolet IUE spectra of N, R, and S stars are displayed and discussed. Carbon stars of type N have IUE spectra similar to M stars except that the Mg II lines are much weaker and low-excitation lines from neutral metals are stronger. Spectra of early R stars (R0-R3) closely resemble those of late G or early K in both lines and continuum with no significant emission lines. Late R stars (R5-R8) show spectra like late K or early M stars except that lines from low levels of excitation are stronger. Ultraviolet spectra of S stars show a wide variation in the strength of Mg II lines.

Johnson, H. R.↗
NASA NTRS1986

Static current-sheet models of quiescent prominences

A particular class of theoretical models idealize the prominence to be a discrete flat electric-current sheet suspended vertically in a potential magnetic field. The weight of the prominence is supported by the Lorentz force in the current sheet. These models can be extended to have curved electric-current sheets and to vary three-dimensionally. The equation for force balance is 1 over 4 pi (del times B) times Bdel p- p9 z=zero. Using Cartesian coordinates we take, for simplicity, a uniform gravity with constant acceleration g in the direction -z. If we are interested not in the detailed internal structure of the prominence, but in the global magnetic configuration around the prominence, we may take prominence plasma to be cold. Consideration is given to how such equilibrium states can be constructed. To simplify the mathematical problem, suppose there is no electric current in the atmosphere except for the discrete currents in the cold prominence sheet. Let us take the plane z =0 to be the base of the atmosphere and restrict our attention to the domain z greater than 0. The task we have is to solve for a magnetic field which is everywhere potential except on some free surface S, subject to suit able to boundary conditions. The surface S is determined by requiring that it possesses a discrete electric current density such that the Lorentz force on it is everywhere vertically upward to balance the weight of the material m(S). Since the magnetic field is potential in the external atmosphere, the latter is decoupled from the magnetic field and its plane parallel hydrostatic pressure and density can be prescribed.

Wu, F.↗
NASA NTRS1987

Spectrophotometery of Brackett lines in very luminous IRAS galaxies

Observation of the Brackett-alpha and Brackett-gamma hydrogen recombination lines were made in a sample of galaxies chosen from the IRAS catalog to have high luminosities at infrared wavelengths. Most have strong Brackett line emission indicating large numbers of high mass stars; the formation of these stars may hence be the underlying source for the galaxies' luminosities. However, there are at least two exceptions that may not be explained in this manner: NGC 6240 and Arp 220. Additional evidence indicates that each of these exceptions may be more closely related to Seyfert-type galaxies or other active galactic nuclei.

Depoy, D. L.↗
NASA NTRS1987

Effect of variable inlet guide vanes on the operating characteristics of a tilt nacelle inlet/powered fan model

The effects of a variable inlet guide vane (VIGV) assembly on the operating characteristics of a V/STOL inlet and on the performance of a 20-in. (0.508-m) diameter fan engine were investigated. The data indicate that the VIGVs are effective thrust modulators over a wide range of free-stream velocities, nacelle angles of attack, and fan speeds. The thrust modulation ranges, including choking limits, fan stall limits, and inlet separation boundaries are presented. The presence of the VIGV assembly causes significant losses in inlet angle-of-attack capability and generally increases the blade stress levels at all limit conditions except at high angle of attack and high free-stream velocity. Reducing the fan nozzle exit area limited the positive VIGV actuation range and consequently decreased the range of thrust modulation at all limit conditions except at both high free-stream velocity and high angle of attack conditions.

Woollett, R. R.↗
NASA NTRS1986

Elemental, isotopic and molecular abundances in comets

The chemical composition of comet nuclei and the factors affecting it are discussed, summarizing the results of recent theoretical, experimental, and observational investigations. Consideration is given to the evidence supporting the view that the nucleus is radially differentiation (except for a thin outer layer), surface differentiation by heat processing and outgassing, and mantle buildup on an undifferentiated core. The nature of the refractory and volatile components is examined, and the elemental and isotopic compositions are given in tables and characterized. The uncertain (except for H2O) molecular composition of the volatile fraction is considered, and it is suggested that some oxides or aldehydes (such as CO, CO2, and H2CO), but no large amounts of fully hydrogenated compounds (such as CH4 and NH3) are included.

Delsemme, A. H.↗
NASA NTRS1986

Megaregolith insulation, internal temperatures, and bulk uranium content of the moon

Finite-difference models are used to study the effects of insulation by the megaregolith on lunar thermal evolution. Results indicate that the megaregolith has two important influences on heat flow: (1) Because the megaregolith is exceptionally thin in mare regions, heat passes more readily through them than through highland regions, and even flows laterally from the highland toward the mare. As a result, heat flow is exceptionally high along a boundary between highland and mare regions. (2) On a global scale, megaregolith insulation combined with lithosphere insulation causes slow cooling, which as a cumulative effect results in high present-day mantle temperatures and heat flow. Assuming that the global mean megaregolith thickness is 2 km, a heat flow of 12 mW/sq m is best matched by models with bulk moon U contents of 20-21 ng/g. Independent constraints on lunar internal temperatures derived from magnetic and tectonic data are best matched by models with about 14 ng/g U. Thus the bulk moon U content is roughly 17 ng/g. These results imply that the bulk moon contents of U, and related refractory lithophile elements such as Th, Al, Ca, etc., must be considerably lower than commonly assumed.

Warren, Paul H.↗
NASA NTRS1988

Lateral and longitudinal stability and control parameters for the space shuttle discovery as determined from flight test data

The Discovery vehicle was found to have longitudinal and lateral aerodynamic characteristics similar to those of the Columbia and Challenger vehicles. The values of the lateral and longitudinal parameters are compared with the preflight data book. The lateral parameters showed the same trends as the data book. With the exception of C sub l sub Beta for Mach numbers greater than 15, C sub n sub delta r for Mach numbers greater than 2 and for Mach numbers less than 1.5, where the variation boundaries were not well defined, ninety percent of the extracted values of the lateral parameters fell within the predicted variations. The longitudinal parameters showed more scatter, but scattered about the preflight predictions. With the exception of the Mach 1.5 to .5 region of the flight envelope, the preflight predictions seem a reasonable representation of the Shuttle aerodynamics. The models determined accounted for ninety percent of the actual flight time histories.

Suit, William T.↗
NASA NTRS1988

Immunofluorescence localization of dissociation supernatant and extracellular matrix components in Lytechinus pictus sectioned embryos

Indirect immunofluorescence was used to localize specific extracellular components in embryos of the sea urchin Lytechinus pictus. Hyalin and S2 (a group of components found in the disaggregation supernatant from Strongylocentrotus purpuratus blastulae) were uniformly present at all stages (unfertilized up to 32 hr) except hyalin could not be detected at the 12 hour early blastula stage. Laminin was found in 16 cell, 32 cell, 6 hour, 18 hour, 24 hour, and 32 hour stages, with especially bright fluorescence at 18 hours. Collagen I was present at all stages (freshly fertilized up to 32 hour) except little was detected at 12 hours. Fibronectin was uniformly present in blastocoelar fibers stained with anto-collagen I and anti-fibronectin. These results were compared with those for S. purpuratus to produce an overview of the localization of specific extracellular matrix components during development of two species of sea urchins. The results set the stage for future studies that will examine the function of these components at the various developmental stages.

Garciaflack, Ana Leticia↗
NASA NTRS1988

Eruptive viscosity and volcano morphology

Terrestrial central volcanoes formed predominantly from lava flows were classified as shields, stratovolcanoes, and domes. Shield volcanoes tend to be large in areal extent, have convex slopes, and are characterized by their resemblance to inverted hellenic war shields. Stratovolcanoes have concave slopes, whereas domes are smaller and have gentle convex slopes near the vent that increase near the perimeter. In addition to these differences in morphology, several other variations were observed. The most important is composition: shield volcanoes tend to be basaltic, stratovolcanoes tend to be andesitic, and domes tend to be dacitic. However, important exceptions include Fuji, Pico, Mayon, Izalco, and Fuego which have stratovolcano morphologies but are composed of basaltic lavas. Similarly, Ribkwo is a Kenyan shield volcano composed of trachyte and Suswa and Kilombe are shields composed of phonolite. These exceptions indicate that eruptive conditions, rather than composition, may be the primary factors that determine volcano morphology. The objective of this study is to determine the relationships, if any, between eruptive conditions (viscosity, erupted volume, and effusion rate) and effusive volcano morphology. Moreover, it is the goal of this study to incorporate these relationships into a model to predict the eruptive conditions of extraterrestrial (Martian) volcanoes based on their morphology.

Posin, Seth B.↗
NASA NTRS1987

Technology challenges for the National Aero-Space Plane

The National Aerospace Plane (NASP) will require an exceptionally high degree of integration between propulsion and aerodynamic configuration, in order to achieve the requisite specific impulse and low structural weight. This is to be achieved through the use of forebody shock compression and afterbody exhaust expansion. Attention is presently given to the materials and structural concepts required for the realization of these NASP airframe functions, in view of the exceptionally high aerothermodynamic loads that will be experienced at hypersonic speeds. Active cooling will have to be used in certain critical airframe and propulsion components. CFD characterizations of these processes must be carefully developed and fully validated.

Piland, William M.↗
NASA NTRS1987

Chemical and physical studies of type 3 chondrites. VIII - Thermoluminescence and metamorphism in the CO chondrites

A possible relationship between the thermoluminescence (TL) properties of CO chondrites and their metamorphic history was investigated by measuring the TL properties of seven normal CO chondrites and of the Colony and the Allan Hills A77307 (ALHA 77307) CO-related chondrites. With the exception of Colony and ALHA 77307, whose maximum induced TL emission is at approximately 350 C, the CO chondrites were found to exhibit two TL peaks: a 130 C and a 250 C peaks. Among the CO chondrites, the 130 C peak showed a 100-fold range in TL sensitivity and was found to correlate with various metamorphism-related phenomena, such as silicate heterogeneity, metal composition, and McSween's metamorphic subtypes. The peak at 250 did not show these correlations and, with exception of Colony, showed little variation.

Keck, Bradly D.↗
NASA NTRS1988

Interplanetary protons (Ep of about 1 MeV) 1973-1986 and out to 22.4 AU

This paper uses annual mean counting rate data from detectors on two long-lived spacecraft, Pioneer 11 and IMP 8, to study the temporal and heliocentric radial distance variations of the intensity of interplanetary protons (Ep of about 1 MeV) over solar activity cycle 21. The Pioneer 11 data cover the time period April 1973 through 1986 and the heliocentric radial distance range r of between 1.0 and 2.4 AU. IMP 8, in an approximately circular geocentric orbit of semimajor axis 35 earth radii, provides comparable data at 1 AU over the time period 1974-1986. The combination of the two bodies of data shows that the annual mean intensity of such protons varies as the inverse square of the distance from the sun, irrespective of solar activity as measured by the annual mean sunspot number S. Also it is found that the annual intensity at 1 AU is approximately proportional to S, except for anomalously low values in 1979 and 1980, and that the product of the annual mean intensity at Pioneer 11 by r-squared is also approximately proportional to S, except for anomalously low values in 1979, 1980 (in particular), and 1981. The common 1980 'anomaly' is attributed to gross changes in interplanetary conditions associated with the reversal of the polarity of the sun's polar magnetic field.

Van Allen, J. A.↗
NASA NTRS1988

Mesoscale spiral vortex embedded within a Lake Michigan snow squall band - High resolution satellite observations and numerical model simulations

It is known that Great Lakes snow squall convection occurs in a variety of different modes depending on various factors such as air-water temperature contrast, boundary-layer wind shear, and geostrophic wind direction. An exceptional and often neglected source of data for mesoscale cloud studies is the ultrahigh resolution multispectral data produced by Landsat satellites. On October 19, 1972, a clearly defined spiral vortex was noted in a Landsat-1 image near the southern end of Lake Michigan during an exceptionally early cold air outbreak over a still very warm lake. In a numerical simulation using a three-dimensional Eulerian hydrostatic primitive equation mesoscale model with an initially uniform wind field, a definite analog to the observed vortex was generated. This suggests that intense surface heating can be a principal cause in the development of a low-level mesoscale vortex.

Lyons, Walter A.↗
NASA NTRS1988

Physical studies of small asteroids and cometary cores

The main goal of the research is to carry on an extensive study of physical properties (colors and variability) of asteroids in the 1 to 10 km diameter range and of cometary cores, with the use of a charge coupled device (CCD) camera, PMT photometer, or both. Particular attention is paid to asteroids being observed by radar because the greatest gain is found from the combination of radar results with the data obtained by optical techniques. To satisfy the goal, 100 nights/year have been scheduled on the 2.3 m and 1.5 m telescopes. During the past 2 years small asteroids were observed. Out of 22 asteroids for which periods of rotation could be precisely measured, 17 have periods of rotation less than 5 hours. This indicates that small objects rotate faster. By now researchers know 14 asteroids with rotation periods in the 2 hour range. At the same time they confirmed the existence of a number of exceptionally slow rotators e.g., 1367 Nongoma with P = 5.65 days. Taxonomic observations lead to a conclusion that Apollo, Amor, and Aten asteroids represent a variety of classes and are not predominantly of class S. Apollo asteroid 3361 Orpheus was found to belong to the rare class V. In collaboration with Dr A. Harris of JPL the opposition effect was studied for 30 Urania and 64 Angelina. Seven comets: P/Helin, P/Brooks 2, P/Klemola, P/Borrelly, Wilson (1986 1) and Shoemaker (1987 o) were monitored for variability. The results were negative with the exception of P/Brooks 2 for which 0.35 mag amplitude was detected.

Wisniewski, Wieslaw Z.↗
NASA NTRS1989

Asymptotic methods for internal transonic flows

For many internal transonic flows of practical interest, some of the relevant nondimensional parameters typically are small enough that a perturbation scheme can be expected to give a useful level of numerical accuracy. A variety of steady and unsteady transonic channel and cascade flows is studied with the help of systematic perturbation methods which take advantage of this fact. Asymptotic representations are constructed for small changes in channel cross-section area, small flow deflection angles, small differences between the flow velocity and the sound speed, small amplitudes of imposed oscillations, and small reduced frequencies. Inside a channel the flow is nearly one-dimensional except in thin regions immediately downstream of a shock wave, at the channel entrance and exit, and near the channel throat. A study of two-dimensional cascade flow is extended to include a description of three-dimensional compressor-rotor flow which leads to analytical results except in thin edge regions which require numerical solution. For unsteady flow the qualitative nature of the shock-wave motion in a channel depends strongly on the orders of magnitude of the frequency and amplitude of impressed wall oscillations or fluctuations in back pressure. One example of supersonic flow is considered, for a channel with length large compared to its width, including the effect of separation bubbles and the possibility of self-sustained oscillations. The effect of viscosity on a weak shock wave in a channel is discussed.

Adamson, T. C., Jr.↗
NASA NTRS1988

Catastrophic volcanism as a cause of shocked features found at the K/T boundary and in cryptoexplosion structures

The presence of quartz grains containing shock lamellae at the Cretaceous/Tertiary (K/T) boundary is viewed by many as the single most compelling evidence of meteoritic or cometary impact because there is no known endogenous mechanism for producing these features. Similarly the presence of shocked quartz, shatter cones, coesite and stishovite at cryptoexplosion structures is comonly taken as conclusive evidence of impact. However, several recent studies have cast doubt on this interpretation. It is argued that basaltic volcanism, although not normally explosive, can under exceptional circumstances produce overpressures sufficiently high to produce shock features. The exceptional circumstances include a high content of volatiles, usually CO2, and no preestablished pathway to the surface. Rapid cooling of the saturated basaltic magma can occur if it underlies a cooler more evolved magma in a chamber. Initial slow cooling and partial exsolution of the volatiles will cause the density of the basaltic magma to become less than that of the overlying magma, leading to overturning and mixing. Gas will escape the magma chamber along planar cracks once the pressure becomes sufficiently high. In the vicinity of the crack tip there is a smallscale deviatoric stress pattern which is thought to be sufficiently high to produce transient cracks along secondary axes in the quartz crystals, causing the planar features. The CO2-rich fluid inclusions which have been found along planar elements of quartz in basement rocks of the Vredefort Dome were likely to have been emplaced by such a process. If the mechanism described is capable of producing shocked features as above, it would require a reassessment of the origin of many cryptoexplosion structures as well as seriously weakening the case for an impact origin of the K/T event.

Loper, D. E.↗
NASA NTRS1989

Numerical investigation of an internal layer in turbulent flow over a curved hill

The development of an internal layer in a turbulent boundary layer flow over a curved hill is investigated numerically. The turbulence field of the boundary layer flow over the curved hill is compared with that of a turbulent flow over a symmetric airfoil (which has the same geometry as the curved hill except that the leading and trailing edge plates were removed) to study the influence of the strongly curved surface on the turbulence field. The turbulent flow equations are solved by a control-volume based finite difference method. The turbulence is described by a multiple-time-scale turbulence model supplemented with a near-wall turbulence model. Computational results for the mean flow field (pressure distributions on the walls, wall shearing stresses and mean velocity profiles), the turbulence structure (Reynolds stress and turbulent kinetic energy profiles), and the integral parameters (displacement and momentum thicknesses) compared favorably with the measured data. Computational results show that the internal layer is a strong turbulence field which is developed beneath the external boundary layer and is located very close to the wall. Development of the internal layer was more obviously observed in the Reynolds stress profiles and in the turbulent kinetic energy profiles than in the mean velocity profiles. In this regard, the internal layers is significantly different from wall-bounded simple shear layers in which the mean velocity profile characterizes the boundary layer most distinguishably. Development of such an internal layer, characterized by an intense turbulence field, is attributed to the enormous mean flow strain rate caused by the streamline curvature and the strong pressure gradient. In the turbulent flow over the curved hill, the internal layer begin to form near the forward corner of the hill, merges with the external boundary layer, and develops into a new fully turbulent boundary layer as the fluid flows in the downstream direction. For the flow over the symmetric airfoil, the boundary layer began to form from almost the same location as that of the curved hill, grew in its strength, and formed a fully turbulent boundary layer from mid-part of the airfoil and in the downstream region. Computational results also show that the detailed turbulence structure in the region very close to the wall of the curved hill is almost the same as that of the airfoil in most of the curved regions except near the leading edge. Thus the internal layer of the curved hill and the boundary layer of the airfoil were also almost the same. Development of the wall shearing stress and separation of the boundary layer at the rear end of the curved hill mostly depends on the internal layer and is only slightly influenced by the external boundary layer flow.

Kim, S-W.↗