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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 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

1300 micron continuum and C(O-18) line mapping of the giant molecular cloud cores in Orion, W49, and W51

Observations of the 1300-micron continuum emission and the C(O-18) spectral-line emission from three well-studied giant molecular cloud cores: Orion, W49, and W51 are presented. The observations were obtained at the Five College Radio Astronomy Observatory, and they provide a means to examine the consistency of these two methods to trace the column density structure of molecular clouds. A good general correlation is found between the 1300-micron continuum, which traces the column density of dust, and the C(O-18) J = 2-1 line emission, which traces the column density of molecular gas, when the effects of source temperature are taken into consideration. Moreover, nominal values for the gas and dust abundances and the dust properties reproduce the observed continuum-to-line ratios. Thus, no strong C(O-18) abundance gradients within sources has been found, and it appears that either the C(O-18) emission lines or the submillimeter dust emission may used to derive the mass column density within molecular clouds accurately.

Schloerb, F. Peter↗
NASA NTRS1987

A satellite-asteroid mystery and a possible early flux of scattered C-class asteroids

The C spectral class implied by the neutral spectra and low albedo of probably capture-originated satellites orbiting Saturn, Jupiter, and Mars is noted to contradict evidence that class-C objects are native only to the outer half of the asteroid belt. It is presently suggested that Jupiter resonances may have scattered a high flux of C-type objects out of the belt as well as throughout the primordial solar system, at the close of planet accretion, when extended atmospheres could figure in their capture. The largest scattered object fluxes come from the resonance regions primarily populated by C-class objects, lending support to the Pollack et al. (1979) capture scenario invoking extended protoatmospheres.

Hartmann, William K.↗
NASA NTRS1987

Spaceborne Imaging Radar-C instrument

The present discussion of the Spaceborne Imaging Radar-C (SIR-C) hardware design, subsystem functional design, and interfaces with the NASA Space Shuttle, gives attention to antenna characteristics and to instrument performance parameter characteristics in the C- and L-bands. The SIR-C antenna is a dual-frequency, dual-polarization distributed array antenna whose distribution of transmit/receive modules improves the system noise figure and eliminates the need for a single, high-power RF source. Phase shifters for individual subarrays allow electronic beam steering in elevation and azimuth.

Huneycutt, Bryan L.↗
NASA NTRS1987

Surface catalytic degradation study of two linear perfluoropolyalkylethers at 345 C

Thin-liquid-film degradation studies of two commercially available perfluoropolyalkylether fluids (PFAE) were performed at 345 C, in nitrogen and air atmospheres, on iron and 440 C stainless steel surfaces. It was found that one fluid degraded on both iron and 440 C stainless steel surfaces in an air atmosphere, whereas the other fluid did not degrade. Chemical analysis revealed that the test fluid degraded to lower molecular weight products and that the degradation was accompanied by the formation of a brownish deposit on both the iron and 440 C stainless steel surfaces. Surface analysis of the deposit revealed a susbstantial amount of iron oxide (Fe2O3). It was hypothesized that the fluid which degraded did so because of its acetal structure. The other fluid, lacking the acetal structure, did not degrade.

Morales, Wilfredo↗
NASA NTRS1988

Synthesis and characterization of high-T(sub c) screen-printed Y-Ba-Cu-O films on alumina

Thick films of YBa2Cu3O(sub 7-x) have been deposited on highly polished alumina substrates by the screen printing technique. To optimize the post-printing heat treatment, the films were baked at various temperatures for different lengths of time and oxygen-annealed at a lower temperature. The resulting films were characterized by electrical resistivity measurements, x-ray diffraction, and optical and scanning electron microscopy. Properties of the films were found to be highly sensitive to the post-printing thermal treatment. Films baked for 15 min at 1000 C in oxygen were hard, adherent, near single phase, and superconducting with T(sub c)(onset) approx 96 K, T(sub c)(zero) approx 66 K and Delta T sub c (10 to 90 percent) approx 10 K.

Bansal, Narottam P.↗
NASA NTRS1988

Isotopic anomalies of Ne, Xe, and C in meteorites. I - Separation of carriers by density and chemical resistance

The carriers of presolar noble gases were studied by isotopically analyzing 19 separates from the Murray and Murchison C2 chondrites for Ne, Xe, C, and N. It is found that the carriers of Ne-E(H) and Xe-S are resistant to HCl, HF, boiling HClO4, and CrO3-H2SO4, and thus must be either diamond or some resistant carbide or oxide. The carrier of Ne-E(L) may be some form of amorphous carbon with delta C13 of about +340 percent. A new carbon component, C theta, found as 0.2-2-micron inclusions in Murchison spinel, is amorphous and contains little or no noble gas. A new heavy nitrogen component is found which has an abundance of about 1 ppm in the bulk meteorite, combusts at 450-500 C, and may be associated wtih isotopically normal carbon or with C-alpha.

Ming, Tang↗
NASA NTRS1988

Sole means navigation through hybrid Loran-C and GPS

A minimum of four GPS range measurements or two Loran-C time differences are normally required for a position solution for en route navigation, area navigation, and nonprecision approaches. This paper describes a new technique that hybridizes GPS and Loran-C used in the pseudorange mode to process efficiently all available navigation information. Emphasis is placed on combined GPS and Loran-C timing, both for the ground/space facilities and the user. The hybrid system has the potential to solve the GPS and Loran-C integrity problems; more range measurements are available than are required for the navigation solution.

Van Graas, Frank↗
NASA NTRS1988

The anomalous C 4 intensity ratio in symbiotic stars

The C IV lambda lambda 1548.2,1550.8 resonance doublet in a symbiotic stars was shown to exhibit anomalous line intensity ratios in which I (lambda 1548.2)/I(lambda 1550.8) less than 1, or less than the optically-thick limit of unity. The R Aquarii-central HII region and RX Puppis exhibit this phenomena. The I(lambda 1548.2)/I(lambda 1550.8) ratio in RX Puppis is found to vary inversely with the total C IV line intensity, and with the FES-visual light, as the object declined over a 5 yr period following a brightening in UV and optical emission which peaked in 1982. This doublet intensity behavior could be explained by a wind which has a narrow velocity range of 600 approx. less than sup v wind approx. less than 1000 km/sec, or by the pumping of the Fe II (mul. 45.01) transition a sup 4 F sub 9/2 - y sup 4 H(o) sub 11/2 by C IV lambda 1548.2, which effectively scatters C IV photons into the Fe II spectrum in these objects.

Michalitsianos, A. G.↗
NASA NTRS1989

The C-12/C-13 abundance ratio in Comet Halley

The individual (C-13)N rotational lines in Comet Halley are resolved using high-resolution spectra of the CN B2Sigma(+)-X2Sigma(+) (0,0) band. The observe C-12/C-13 abundance ratio excludes a site of origin for the comet near Uranus and Neptune and suggests a condensation environment quite distinct from other solar system bodies. Two theories are presented for the origin of Comet Halley. One theory suggest that the comet originated 4.5 Gyr ago in an inner Oort cloud at a heliocentric distance greater than 100 AU where chemical fractionation led to the C-13 enrichment in the CN parent molecule prior to condensation of the comet nucleus. According to the other, more plausible theory, the comet nucleus condensed relatively recently from the interstellar medium which has become enriches in C-13 and was subsequently gravitationally captured by the solar system.

Wyckoff, Susan↗
NASA NTRS1989

Human mononuclear cell function after 4 C storage during 1-G and microgravity conditions of spaceflight

To investigate the possibility of restoring immune competence of crewmembers during a prolonged spaceflight by infusions of autologous blood components, the effect of storage at 4 C aboard Space Shuttle Columbia (Mission 61-c) on the activity of human peripheral blood mononuclear cells (PBMNCs), stored as leukocyte concentrates in autologous plasa, was investigated. The results of preflight storage at 4 C demonstrated a progressive daily loss in mitogen-stimulated protein synthesis, and thymidine uptake, as well as a progressive reduction in the percentage of PBMNCs expressing cell-surface phenotype markers. The ability of PBMNCs stored at 4 C for 8 d in Columbia's middeck, to become activated and proliferate in vitro was similar to that of cells that remained for 7 d on ground.

Meehan, Richard↗
NASA NTRS1989

Shuttle-C, evolution to a heavy lift launch vehicle

NASA is defining an unmanned, expendable derivative of the Space Shuttle, called Shuttle-C, that can provide a near-term heavy lift launch capability. The major Shuttle-C program guidelines and objectives are outlined, and the background to the concept is reviewed. Possible Shuttle-C payloads and a typical mission are briefly described. The present status and goals of the Shuttle-C concept are considered.

Harsh, Marcellus G.↗
NASA NTRS1990

XTRN - Automatic Code Generator For C Header Files

Computer program XTRN, Automatic Code Generator for C Header Files, generates "extern" declarations for all globally visible identifiers contained in input C-language code. Generates external declarations by parsing input text according to syntax derived from C. Automatically provides consistent and up-to-date "extern" declarations and alleviates tedium and errors involved in manual approach. Written in C and Unix Shell.

Pieniazek, Lester A.↗
NASA NTRS1989

Shuttle C: Heavy-lift vehicle of the 1990's

The unmanned, Shuttle-C, a low cost evolution of the U.S. Space Shuttle is described. It is capable of delivering 45,400 to 77,100 kg payloads by 1994. The Shuttle-C's design is evolved directly from the Space Shuttle. The payload carrier, the only new element of the Shuttle-C, is a cylindrical payload bay 4.6 m in diameter by 25 m in length. Diagrams of similarities and differences betwen the Shuttle and Shuttle-C are presented. A typical mission profile is illustrated. Payload carrying abilities and other applications are described.

Lee, Thomas J.↗
NASA NTRS1990

Progress of research of high-T(sub c) superconductors

The research of high T(sub c) superconductors has made big progress in these last few years. New materials were found and the systematic investigations of these materials must contribute to understanding the mechanism of high T(sub c) superconductivity. The critical currents in thin films, bulks and tapes increased drastically, and the origin of flux pinning will be clarified in the near future. These progressions gives a view of a bright future of high T(sub c) superconductivity in both the basic and application research areas. Recent activities in research of high T(sub c) superconductivity and superconductors in Japan are overviewed.

Tanaka, Shoji↗
NASA NTRS1988

Synthesis and characterization of high-T(c) screen-printed Y-Ba-Cu-O films on alumina

Thick films of YBa2Cu3O(sub 7-x) have been deposited on highly polished alumina substrates by the screen printing technique. To optimize the post-printing heat treatment, the films were baked at various temperatures for different lengths of time and oxygen-annealed at a lower temperature. The resulting films were characterized by electrical resistivity measurements, X-ray diffraction, and optical and scanning electron microscopy. Properties of the films were found to be highly sensitive to the post-printing thermal treatment. Films baked for 15 min at 1000 C in oxygen were hard, adherent, near single phase, and superconducting with T(sub c) (onset) approx 96 KK, T(sub c) (zero) approx 66 K and Delta T sub c (10 to 90 percent) approx 10 K.

Bansal, Narottam P.↗
NASA NTRS1990

Reduced pressure MOCVD of C-axis oriented BiSrCaCuO thin films

BiSrCaCuO thin films were deposited on MgO (100) single-crystal substrates by metalorganic chemical vapor deposition at 500 C and 2 torr using fluorinated beta-diketonate complexes of Sr, Ca, and Cu and triphenylbismuth. An inverted vertical reaction chamber allowed uniform film growth over large areas (7.7 cm diameter). The as-deposited films were amorphous mixtures of oxides and fluorides; a two-step annealing protocol (750 C + 850-870 C) was developed which gives c-axis oriented films of Bi2Sr2Ca1Cu2O(x). The postannealed films showed onsets in the resistive transition of 110 K, and zero resistivity was achieved by 83 K. Critical current densities as high as 11,000 A/sq cm were obtained at 25 K.

Hamaguchi, Norihito↗
NASA NTRS1990

A Probable Approx. 2400 Year Solar Quasi-cycle in Atmospheric Delta C-14

A 2200 to 2600 year quasi-periodicity is present in atmospheric delta C-14 records after removal of long-term trends due to the geomagnetic dipole amplitude variation. This periodicity consists of both a long-term variation of the mean and a superposed, approximately recurring pattern of century-scale variations. The strongest of these latter variations occur near maxima of the approx. 2400 year delta C-14 cycles. The residual record can be modeled to first order as an amplitude modulation of a century-scale periodic forcing function by a approx. 2400 year periodic forcing function. During the last millennium, the largest century-scale variations (occurring near the most recent 2400 year delta C-14 maximum) are known to be mainly a consequence of the pronounced Maunder, Sporer, and Wolf solar activity minima, as verified by independent proxy solar activity records. Therefore, during this period, amplitude modulation has been occurring primarily in the sun and not in the terrestrial radiocarbon system. It is therefore inferred that the approx. 2400 year forcing function is mainly solar although some secondary terrestrial feedback into the delta C-14 record is likely. This conclusion has implications for the predictability of future pronounced solar activity minima and for the interpretation of certain minor Holocene climatic variations.

Hood, L. L.↗
NASA NTRS1990

Thermal stability of the microstructure of an aged Nb-Zr-C alloy

The effects of thermal aging with and without an applied stress on the microstructure of a Nb-Zr-C alloy containing 0.9 wt percent Zr and 0.06 wt percent C were studied. Chemical analysis, metallographic examination, energy dispersive x-ray spectra of the bulk material, and chemical and x-ray analyses of the phase-extracted residue were used to characterize the microstructure. The samples examined were from a creep strength study involving hot and cold working, and various combinations of exposure to temperatures ranging from 1350 to 1755 K with and without applied load for times as long as 34,000 plus hours. The results showed that the initial microstructure consisted primarily of orthorombic precipitates of Nb sub 2 C which were partially or completely transformed to face-centered cubic carbides of nb and Zr, (Zr, Nb)C, upon prolonged exposure to elevated temperatures. Furthermore, it was found that the microstructure of the alloy is extremely stable owing to the very finely distributed precipitates throughout its matrix and along the grain boundaries. The lattice parameters of the cubic carbides were determed to vary from 0.458 to 0.465 nm as the Zr/Nb ratio varied from 38/62 to 75/25.

Uz, Mehmet↗