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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 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Voids in the Ly-alpha forest

The general issue of using the Ly-alpha absorbers in quasar spectra as tracers of the large-scale matter distribution is discussed, emphasizing complications due to evolutionary effects and line blending. Then, a novel method of statistical analysis of the line data appropriate for studying large-scale structure is described. This method circumvents the problem of line blending by truncating the interval distribution at the low end. It also explicitly takes z-dependent effects into account. As an example, the method is applied to an 18-quasar spectrum sample of 417 lines.

Duncan, Robert C.↗
NASA NTRS1990

The Ar/Ca abundance ratio in solar flares

An Ar/Ca abundance ratio of at least 0.56 is derived using the X-ray spectra of solar flares recorded by the SOLFLEX spectrometers on the P78-1 spacecraft. The method involves determining the contribution of the Ar XVII 1s2 1S0-1s4p 1P1 line to a blended feature at 3.2005 A. This contribution is determined by considering the relationship of the other component of the blended feature, namely the Ca XVIII 1s2 2s 2S(1/2)-1s2p2s 2P(3/2) line, to the dielectronic satellite lines of Ca XVII that fall between 3.215 and 3.24 A. It is demonstrated that a broad-wavelength coverage solar X-ray spectrometer experiment is necessary for precise abundance measurements.

Doschek, George A.↗
NASA NTRS1990

Two and three dimensional grid generation by an algebraic homotopy procedure

An algebraic method for generating two- and three-dimensional grid systems for aerospace vehicles is presented. The method is based on algebraic procedures derived from homotopic relations for blending between inner and outer boundaries of any given configuration. Stable properties of homotopic maps have been exploited to provide near-orthogonality and specified constant spacing at the inner boundary. The method has been successfully applied to analytically generated blended wing-body configurations as well as discretely defined geometries such as the High-Speed Civil Transport Aircraft. Grid examples representative of the capabilities of the method are presented.

Moitra, Anutosh↗
NASA NTRS1991

Surface and interfacial properties of carbon fibers

The adhesion strength of AS4 fibers to thermoplastic polymers was determined. The specific polymers were polycarbonate, polyphenylene oxide, polyetherimide, polyphenylene oxide blends with polystyrene, and polycarbonate blends with a polycarbonate-polysiloxan copolymer. Data are also included for polysulfone. It was recognized at the outset that an absolute measure of the fiber matrix adhesion would be difficult. However, it is feasible to determine the fiber bond strengths to the thermoplastics relative to the bond strengths of the same fibers to epoxy polymers. It was anticipated, and in fact realized, that the adhesion of AS4 to the thermoplastic polymers was relatively low. Therefore, further objectives of the study were to identify means of increasing fiber/matrix adhesion and to try to determine why the adhesion of AS4 to thermoplastics is significantly less than to epoxy polymers.

Bascom, Willard D.↗
NASA NTRS1991

Grid generation strategies for turbomachinery configurations

Turbomachinery flow fields involve unique grid generation issues due to their geometrical and physical characteristics. Several strategic approaches are discussed to generate quality grids. The grid quality is further enhanced through blending and adapting. Grid blending smooths the grids locally through averaging and diffusion operators. Grid adaptation redistributes the grid points based on a grid quality assessment. These methods are demonstrated with several examples.

Lee, K. D.↗
NASA NTRS1989

Nitrogen abundances from UV lines of HgMn and standard late-B stars

A recent survey by Roby (1987) discovered that the relatively weak high excitation lines of N 1 near 7468 and 8680 A were undetectable in the majority of HgMn stars, leading to upper limits on the N abundance of roughly ten times below that of the solar N abundance. Standard stars with similar temperatures (10,000 to 13,000 K) did exhibit these same N lines and were found to have roughly solar N abundances. The N abundances were redetermined in two HgMn stars and four standard stars using the strong, low excitation lines of N 1 found in the ultraviolet. The observational data consisted of high quality, high resolution, co-added International Ultraviolet Explorer spectra which was previously collected and reduced. Examination of the spectra plus considerations of signal/noise and severe line blending led to the choice of three promising N 1 lines located at 1742.7, 1745.3 and 1411.9 A. The atomic data for these lines were previously calculated using the best laboratory measurements found in a search of the relevant literature. The chosen N lines turned out to be blended significantly with Fe 2 lines. To obtain the abundances for N synthetic spectra were computed to match the observed spectra. The synthetic spectra were calculated using lie-blanketed model atmospheres, stellar parameters, and abundances for the other elements based upon previous work by S. Adelman. The N abundance was then adjusted to give the best fit of the observed line profiles. In the 2 HgMn stars, the N lines were again found to be undetectable, but the stronger intrinsic strength of the new lines yield more stringent upper limits than those obtained previously. Model atmosphere and abundances were updated in two stars where new results were reported. An additional N 1 line and an additional standard star were added to the program. A line opacity model was developed for a missing feature adjacent to the N 1 line at 1745.2 A, leading to a 25 percent improvement in the determined from this line.

Roby, Scott W.↗
NASA NTRS1991

Silsesquioxane-derived ceramic fibres

Fibers formed from blends of silsesquioxane polymers were characterized to study the pyrolytic conversion of these precursors to ceramics. The morphology of fibers pyrolyzed to 1400 C revealed primarily amorphous glasses whose conversion to beta-SiC is a function of both blend composition and pyrolysis conditions. Formation of beta-SiC crystallites within the glassy phase is favored by higher than stoichiometric C/Si ratios, while carbothermal reduction of Si-O bonds to form SiC with loss of SiO and CO occurs at higher methyl/phenylpropyl silsesquioxane (lower C/Si) ratios. As the carbothermal reduction is assumed to be diffusion controlled, the fibers can serve as model systems to gain understanding of the silsesquioxane pyrolysis behavior, and therefore are useful in the development of polysilsesquioxane-derived ceramic matrices and coatings as well.

Hurwitz, F. I.↗
NASA NTRS1991

A Variational Formalism for the Radiative Transfer Equation: Prelude to Model 3

The MODEL III variational data assimilation model is the third of four general assimilation models designed to blend weather data measured from space based platforms in the meteorological data mainstream in a way that maximizes the information content of the satellite data. Because there are many different observation locations and there are many instruments with different measurement error characteristics, it is also necessary to require that the blending be done to maximize the information content of the data and simultaneously to retain a dynamically consistent and reasonably accurate description of the state of the atmosphere. This is ideally a variational problem for which the data receive relative weights that are inversely proportional to measurement error and are adjusted to satisfy a set of dynamical equations that govern atmospheric processes. The advantage of MODEL III over the previous two models is that radiance, the atmospheric variable measured by satellite, becomes a dependent variable. In the previous versions, mean layer temperatures that had been retrieved from the radiances by some method, were included in the assimilation by substituting them in place of the rawinsonde temperatures. Now both rawinsonde temperatures and satellite radiances are included independently in the assimilation.

Achtemeier, Gary L.↗
NASA NTRS1992

Cell volume control at a surface for three-dimensional grid generation packages

An alternate method of calculating the cell size for orthogonality control in the solution of Poisson's 3D space equations is presented. The method provides the capability to enforce a better initial guess for the grid distribution required for boundary layer resolution. This grid point distribution is accomplished by enforcing grid spacing from a grid block boundary where orthogonality is required. The actual grid spacing or cell size for that boundary is determined by the two or four adjacent boundaries in the grid block definition, which are two dimensional grids. These two dimensional grids are in turn defined by the user using insight into the flow field and boundary layer characteristics. The adjoining boundaries are extended using a multifunctional blending scheme, with user control of the blending and interpolating functions to be used. This grid generation procedure results in an enhanced computational fluid dynamics calculation by allowing a quicker resolution of the configuration's boundary layer and flow field and by limiting the number of grid re-adaptations. The cell size specification calculation was applied to a variety of configurations ranging from axisymmetric to complex three-dimensional configurations. Representative grids are shown for the Space Shuttle and the Langley Lifting Body (HL-20).

Alter, Stephen J.↗
NASA NTRS1992

An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers

The high-resolution laboratory millimeter- and submillimeter-wave spectra of C-12H(3)OH and C-13H(3)OH have been extended to include transitions involving significantly higher angular momentum quantum numbers than studied previously. For C-12H(3)OH, the data set now includes 549 A torsional substate transitions and 524 E torsional substate transitions through J is not greater than 24, exclusive of blends. For C-13H(3)OH the data set now includes 453 A torsional substate transitions and 440 E torsional substate transitions through J is not greater than 24, exclusive of blends. The extended internal axis method Hamiltonian has been used to analyze the transitions to experimental accuracy. The molecular constants determined by this approach have been used to predict accurately the frequencies of many transitions through J = 25 not measured in the laboratory.

Anderson, Todd↗
NASA NTRS1993

Crosslinked polyimides prepared from N-(3-ethynylphenyl)maleimide

The compound N-(3-ethynylphenyl)maleimide (NEPMI) was used to prepare thermally stable, glassy polyimides which did not exhibit glass transition temperatures below 500 C. NEPMI was blended with the maleimide of methylene dianiline (BMI) and heated to form the polyimide. NEPMI was also mixed with Thermid 600 R, a commercially available bisethynyl oligomeric material, and heated to form a thermally stable, glassy polyimide. Lastly, NEPMI was blended with both BMI and Thermid 600 R to form thermally stable, glassy polyimides.

Gerber, Margaret K.↗
NASA NTRS1993

Rapid exploration of curvilinear grids using direct volume rendering

Fast techniques for direct volume rendering over curvilinear grids of hexahedral cells are developed. This type of 3D grid is common in computational fluid dynamics and finite element analysis. Four new projection methods are presented and compared with each other and with previous methods for tetrahedral grids and rectilinear grids. All four methods use polygon-rendering hardware for speed. A simplified algorithm for visibility ordering, which is based on a combination of breadth-first and depth-first searches, is described. A new multi-pass blending method is described that reduces visual artifacts that are introduced by linear interpolation in hardware where exponential interpolation is needed. Multi-pass blending is of equal interest to hardware-oriented projection methods used on rectilinear grids. Visualization tools that permit rapid data banding and cycling through transfer functions, as well as region restrictions, are described.

Vangelder, Allen↗
NASA NTRS1991

Preliminary properties of a resin from ethynyl terminated materials

A blend composed of an ethynyl terminated aspartimide (brittle component) and an ethynyl terminated arylene ether oligomer (tough component) was thermally cured to yield a resin which underwent preliminary evaluation to determine the potential for use in structural applications on aerospace vehicles. The blend exhibited good compression moldability, allowing for fabrication of neat moldings, adhesive specimens and composites at temperatures of 250 C under a pressure of 1.4 MPa (200 psi). Neat resin moldings and adhesive specimens provided relatively high mechanical properties. Composite specimens provided promising results in spite of fiber misalignment, fiber washout, and a small amount of panel warpage.

Hergenrother, Paul M.↗
NASA NTRS1993

Observations of the gaseous Galactic halo toward 3C 273 with the Goddard High Resolution Spectrograph

An analysis of observations of 24 absorption lines produced near zero redshift by Milky Way disk and halo gas along the sight line to 3C 273 is presented. The reduced spectra have a resolution of about 20 km/s (FWHM) with broad wings and an SNR of 13 to 20. The species detected include C II, C II*, C IV, O I, Mg II, Si II, Si IV, S II, Mn II, Fe II, and Ni II. The O I absorption is blended with earth atmospheric emission, and one of the Si IV doublet lines is blended with an intergalactic Lyman-alpha line. Column densities are determined for C II*, C IV, Si II, Si IV, N V, S II, Mn II, and Ni II using standard curve-of-growth techniques and the apparent optical depth method. The column density for S II and a measure of N(H I) from FOS observations of Lyman-alpha reveal a 45-percent overabundance of sulfur compared with neutral hydrogen which is probably due to the presence of S II in ionized gas toward 3C 273.

Savage, Blair D.↗
NASA NTRS1993

Variations of the ultraviolet Fe II and Balmer continuum emission in the Seyfert galaxy NGC 5548

We present measurements of the Balmer continuum/Fe II emission blend between 2160 and 4130 A in the Seyfert galaxy NGC 5548. The measurements are from spectra obtained as part of the combined space-based and ground-based monitoring program of this object in 1988-1989. An iterative scheme is used to determine and subtract the continuum emission underlying the emission blend so as to obtain a light curve sampled once every four days. The small blue bump is an important component of the emission-line cooling, constituting about one third of the line flux in this object. Its flux varies with an amplitude of approximately +/- 20 percent about the mean, similar to the amplitude of the Balmer line variations during the same period. Its light curve resembles that of Ly-alpha, with a lag of about 10 days behind the continuum variations. The bump variation amplitude is independent of the wavelength interval where it is measured, which indicates that both the Balmer continuum and Fe II emission have comparable variation amplitudes. These results suggest that the Fe II UV multiplets and the Balmer continuum are emitted in the same parts of the broad-line region as most other broad emission lines in this object.

Maoz, D.↗
NASA NTRS1950

Starting of rocket engine at conditions of simulated altitude using crude monoethylaniline and other fuels with mixed acid

Experiments were conducted at sea level and pressure altitude of about 55,000 feet at various temperatures to determine starting characteristics of a commercial rocket engine using crude monoethylaniline and other fuels with mixed acid. With crude monoethylaniline, ignition difficulties were encountered at temperatures below about 20 degrees F. With mixed butyl mercaptans, water-white turpentine, and x-pinene, no starting difficulties were experienced at temperatures as low as minus 74 degrees F. Turpentine and x-pinene, however, sometimes left deposits on the injector face. With blends containing furfuryl alcohol and with other blends, difficulties were experienced either from appreciable deposits or from starting.

COMBUSTION - ROCKET ENGINES↗
NASA NTRS1951

Ignition-delay Characteristics in Modified Open-cup Apparatus of Several Fuels with Nitric Acid Oxidants Within Temperature Range 70 to 105 Degrees F

Fluid properties and low-temperature ignition delays were obtained for approximately 90 fuel-oxidant combinations. A red fuming nitric acid containing approximately 3 percent water and 19 percent nitrogen tetroxide froze at approximately -87 degrees F and ignited several low-viscosity fuel blends of aromatic amines in triethylamine at -76 degrees F and lower. With this acid, the following average ignition delays were obtained with a blend of 30 percent o-toluidine in triethylamine: ...

FUEL SYSTEMS - ENGINES, ROCKET↗
NASA NTRS1993

Consortium for materials development in space

During fiscal 1993, the Consortium for Materials Development in Space (CMDS) maintained the organizational structure and project orientation established in prior years. The commercial objectives are improved materials, biomedical applications, and infrastructure and support hardware. Projects include nonlinear optical materials; space materials (specifically polymer foam/films, atomic oxygen and high temperature superconductors); alloyed and blended materials: sintered and alloyed materials; polymer and carbonate blends; electrodeposition; organic separation; materials dispersion and biodynamics; space carriers: Consort, COMET support, Spacehab utilization; and flight services: accelerometers, CMIX, USEC, ORSEP, and Space Experiment Facility (SEF).

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