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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Electronic state and superconductivity of YBa2Cu3-xO7-y (M=Al,Zn and Sn) systems

A series of YBa2Cu(3-x)MxO(7-y) (M=Al,Zn and Sn) single phase samples were prepared, and the measurements of the crystal structure, oxygen content, electric resistivity, thermoelectric power, Mossbauer spectrum, XPS and superconductivity were performed. The experimental results of X ray powder diffraction, Mossbauer spectrum and oxygen content show that the Zn(2+) and the Al(3+) occupy the Cu(2) site in Cu-O planes and the Cu(1) site in Cu-O chains respectively, but the Sn(4+) occupies both the Cu(1) sites. As regards the properties in superconducting state, both the Zn(2+) and the Al(3+) depress T(sub c) strongly, but the Sn(4+) does not. As for the electronic transport properties in normal state, the system doped by Al(3+) displays a rapid increase of resistivity and some electron localization-like effects, and the thermoelectric power enhances obviously; the series contained Zn(2+) almost shows no changes of electric resistivity but the sign of the thermoelectric power is reversed. Other results are given and briefly discussed.

Zhao, Y.↗
NASA NTRS1984

Contamination control and cleanliness level integrity for the Space Shuttle Orbiter PLB, payloads and facilities at KSC

The PLB, its cargo, and payload canister must satisfy the cleanliness requirements of visual clean (VC) level 1, 2, 3, or special as stated in NASA document SN-C-0005A. The specific level of cleanliness is chosen by the payload bay customer for their mission. During orbiter turnaround processing at KSC, the payload bay is exposed to the environments of the Orbiter Processing Facility (OPF) and the Payload Changeout Room (PCR). In supportive response to the orbiter payload bay/facility interface, it is necessary that the facility environment be controlled and monitored to protect the cleanliness/environmental integrity of the payload bay and its cargo. Techniques used to meet environmental requirements during orbiter processing are introduced.

Bartelson, D.↗
NASA NTRS1980

Effect of starting powder characteristics on density, microstructure and low temperature oxidation behavior of a Si3N48w/o Y2O3 ceramic

The densification and oxidation behavior of Si3N4 - 8w/oY2O3 prepared from three commercial starting powders were studied. Bars of SN 402, SN 502, and CP 85/15 were sintered for 3 to 4.5 hours at 1750 C. A second set was hot pressed for 2 hours at 1750 C. The microstructures were studied by transmission electron microscopy and scanning electron microscopy, densities were determined, and the phase compositions were determined by X-ray diffraction. Densification and microstructure were greatly influenced by the starting powder morphology and impurity content. Although SN 402 exhibited the maximum weight lose, the highest sintered and hot pressed densities were obtained with this powder. All powders had both equiaxed and elongated grains. Sintered bars were composed of beta silicon nitride and n-melelite. In contrast, hot pressed bars contained beta silicon nitride, H-phase, and J-phase, but no melelite. Yttria distribution in sintered bars was related to the presence of cation impurities such as Ca, Fe, and Mg. A limited oxidation study at 750 C in air showed no instability in these Si3N4 - 8 w/oY2O3 specimens, regardless of startin powder.

Schuon, S.↗
NASA NTRS1985

Containerless Studies of Nucleation and Undercooling

The long term research goals are to perform experiments to determine the achievable limits of undercooling, the characteristics of heterogeneous nucleation, and the physical properties of significantly undercooled melts. The techniques used are based on the newly developed containerless manipulation methods afforded by acoustic levitation. Ground based investigations involved 0.1 to 2 mm specimens of pure metals and alloys (In, Ga, Sn, Ga-In, ...) as well as glass-forming organic compounds (O-Terphenyl). A currently operating ultrasonic high temperature apparatus has allowed the ground-based levitation of 1 to 2 mm samples of solid aluminum at 550 deg C in an argon atmosphere. Present work is concentrating on the undercooling of pure metal samples (In, Sn), and on the measurements of surface tension and viscosity of the undercooled melts via shape oscillation techniques monitored through optical detection methods. The sound velocity of undercooled O-Terphenyl is being measured in an immiscible liquid levitation cells.

Trinh, E. H.↗
NASA NTRS1985

Search for a shock wave around the Crab Nebula

The region surrounding the Crab Nebula is searched for the existence of a shock wave with the imaging instruments of the Einstein Observatory. The search is complicated by the scattering of nebula and pulsar X-rays from the imperfectly polished surfaces of the telescope mirror, as well as from interstellar grains along the line of sight. Both of these effects lead to the appearance of X-ray emission, in the form of an X-ray halo, beyond the boundaries of the nebula filaments. It is shown that the size, shape, and intensity of the halo around the Crab Nebula, above the contribution of mirror scattering, is consistent with what is expected from the scattering from interstellar grains. The upper limit on the X-ray emission from a shock wave is about 1 percent of the total 0.5-4 keV luminosity of the Crab, or about 2 x 10 to the 35th ergs/sec (assuming a distance of 2.2 kpc). This figure applies to a shell whose angular radius is 9 arcminutes. The upper limit is smaller (larger) for a shell of larger (smaller) size. This upper limit is an order of magnitude or more below the flux of Cas A, Tycho, and Kepler SNRs, which are 2 to 3 times younger, but it is still above that of SN 1006.

Mauche, C. W.↗
NASA NTRS1986

Theoretical Electric Dipole Moments of SiH, GeH and SnH

Accurate theoretical dipole moments (mu(sub c) have been computed for the X(exp 2)Pi ground states of Si(-)H(+)(0.118 D), Ge(+)H(-)(0.085 D) and Sn(+)H(-)(0.357 D). The trend down the periodic table is regular and follows that expected from the electronegativities of the group IV atoms. The dipole moment of 1.24 +/- 0.1 D for GeH recently derived by Brown, Evenson and Sears from the relative intensities of electric and magnetic dipole transitions in the 10 microns spectrum of the X(exp 2)Pi state is seriously questioned.

Pettersson, Lars G. M.↗
NASA NTRS1990

Effect of pretreatment on a platinized tin oxide catalyst used for low-temperature CO-oxidation

A commercial platinized tin oxide catalyst used for low-temperature CO oxidation has been characterized using ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES) and Electron Spectroscopy for Chemical Analysis (ESCA) before and after reduction in 40 Torr of CO for 1 hour at various temperatures from 75 to 175 C. The reduction results in loss of surface oxygen, formation of metallic tin, conversion of platinum oxides to Pt-O-Sn and Pt(OH)2 and a small amount of metallic Pt which alloys with the tin. These results should be useful in understanding how the pretreatment temperature affects the catalytic activity of platinized tin oxide toward CO oxidation.

Drawdy, Jean E.↗
NASA NTRS2016

The Double-Peaked SN 2013ge: A Type Ib/c Sn with an Asymmetric Mass Ejection or an Extended Progenitor Envelope

We present extensive multiwavelength (radio to X-ray) observations of the Type Ib/c supernova (SN Ib c) SN 2013ge from -13 to +457 days relative to maximum light, including a series of optical spectra and Swift UV-optical photometry beginning 2-4 days post-explosion. This data set makes SN 2013ge one of the best-observed normal SNe Ib/c at early times-when the light curve is particularly sensitive to the progenitor configuration and mixing of radioactive elements -and reveals two distinct light curve components in the UV bands. The first component rises over 4-5 days and is visible for the first week post-explosion. Spectra of the first component have blue continua and show a plethora of moderately high velocity (approximately 15,000 km/s) but narrow (approximately 3500 km/s)spectroscopic features, indicating that the line-forming region is restricted. The explosion parameters estimated for the bulk explosion (M(sub ej) approximately 23 solar mass; E(subK) approximately (1-2) x 10(exp 51) erg) are standard for SNe Ib/c, and there is evidence forweak He features at early times-in an object that would have otherwise been classified as Type Ic. In addition,SN 2013ge exploded in a low-metallicity environment (approximately 0.5 atomic mass), and we have obtained some of the deepest radio and X-ray limits for an SN Ib/c to date, which constrain the progenitor mass-loss rate to be M less than 4 x 10(exp -6) solar mass/yr. We are left with two distinct progenitor scenarios for SN 2013ge, depending on our interpretation of the early emission. If the first component is cooling envelope emission, then the progenitor of SN 2013ge either possessed an extended (greater than or approximately 30 solar radius) envelope or ejected a portion of its envelope in the final less than or approximately 1 yr before core collapse. Alternatively, if the first component is due to outwardly mixed Ni-56, then our observations are consistent with the asymmetric ejection of a distinct clump of nickel-rich material at high velocities. Current models for the collision of an SN shock with a binary companion cannot reproduce both the timescale and luminosity of the early emission in SN 2013ge. Finally, the spectra of the first component of SN 2013ge are similar to those of the rapidly declining SN 2002bj.

supernovae: general – supernovae: individual (SN↗
NASA NTRS2017

Effect of Silicon on Activity Coefficients of P, Bl, CD, SN, and AG in Liquid Fe-Si, and Implications for Differentiation and Core Formation

Cores of differentiated bodies (Earth, Mars, Mercury, Moon, Vesta) contain light elements such as S, C, Si, and O. We have previously measured small effects of Si on metal-silicate partitioning of Ni and Co [1,2], and larger effects for Mo, Ge, Sb, As [2]. The effect of Si on many siderophile elements could be an important, and as yet unquantified, influence on the core-mantle partitioning of SE. Here we report new experiments designed to quantify the effect of Si on the partitioning of Bi, Cd, Sn, Ag, and P between metal and silicate melt. The results will be applied to Earth, Mars, Mercury, Moon, and Vesta, for which we have excellent constraints on the mantle Bi, Cd, Sn, Ag, and P concentrations from mantle and/or basalt samples.

Righter, K.↗
NASA NTRS1990

Non-LTE model calculations for SN 1987A and the extragalactic distance scale

This paper presents model atmospheres for the first week of SN 1987A, based on the luminosity and density/velocity structure from hydrodynamic models of Woosley (1988). The models account for line blanketing, expansion, sphericity, and departures from LTE in hydrogen and helium and differ from previously published efforts because they represent ab initio calculations, i.e., they contain essentially no free parameters. The formation of the UV spectrum is dominated by the effects of line blanketing. In the absorption troughs, the Balmer line profiles were fit well by these models, but the observed emissions are significantly stronger than predicted, perhaps due to clumping. The generally good agreement between the present synthetic spectra and observations provides independent support for the overall accuracy of the hydrodynamic models of Woosley. The question of the accuracy of the Baade-Wesselink method is addressed in a detailed discussion of its approximations. While the application of the standard method produces a distance within an uncertainty of 20 percent in the case of SN 1987A, systematic errors up to a factor of 2 are possible, particularly if the precursor was a red supergiant.

Schmutz, W.↗
NASA NTRS1994

Properties of the highly ionized disk and halo gas toward two distant high-latitude stars

Goddard High Resolution Spectrograph (GHRS) intermediate -resolution observations of S III, Si III, Al III, Si IV, C IV, and N V absorption along the sight lines to HD 18100 (l = 217.9 deg, b = -62.7, d = 3.1 kpc, z = -2.8 kpc) and HD 100340 (l = 258.9 deg, b = +61.2 deg, d = 5.3 kpc, z = 4.6 kpc) are presented. These small science aperture spectra have resolutions ranging from 11 to 20 km/s full width at half maximum (FWHM) and S/N from 30 to 65 per diode substep. Strong absorption by moderately and highly ionized gas is seen in each direction. The absorption in the direction of the south Galactic polar region (HD 18100) is kinematically simple, while the absorption in the direction of north Galactic polar region (HD 100304) is kinematically complex. In each case the absorption by the highly ionized gas lies within the velocity range of absorption by neutral and weakly ionized gas. Along each sight line, the velocity dispersion determined from the unsaturated absorption lines increases with the energy required to create each ion. The logarithmic column densities for Al III, Si IV, C IV, and N V are log N(atoms/sq cm = 12.71, 13.10, 13.58, and 12.75 toward HD 18100 and log N = 12.88, 13.31, 13.83, and 13.04 toward HD 100340. Average ionic ratios among these species are very similar along the two sight lines. Differences in profile shape between the absorption for AL II, Si IV, C IV, and N V provide additional support for the claim of Savage, Sembach, & Cardelli (1994) that there exists two types of highly ionized gas in the interstellar medium. One type of highly ionized gas is responsible for the structured Si IV absorption and part of the C IV absorption. In this gas N(C IV)/N(Si IV) approximately 3.0 and N(C IV)/N(N V) greater than 6. The absorption by this gas seems to be associated with some type of self-regulating interface or mixing layer between the warm and hot interstellar medium. The other type of highly ionized gas is responsible for most of the N V absorption, part of the C IV absorption, and has very little associated Si IV absorption. In this gas N(C IV)/N(N V) is approximately 1 to 3. This gas is hot (T greater than 2 x 10(exp 5) K) and may be tracing the cooling gas of supernova (SN) bubbles or a Galactic fountain. The relative mixture of these two types of highly ionized gas varies from one sight line to the next. The two sight lines in this study sample halo gas in the solar neighborhood and have a smaller percentage of the more highly ionized gas than inner Galaxy sight lines.

Savage, Blair D.↗
NASA NTRS1980

Liquid-phase electroepitaxy - Dopant segregation

A theoretical model is presented which accounts for the dopant segregation in liquid-phase electroepitaxy in terms of dopant transport in the liquid phase (by electromigration and diffusion), the growth velocity, and the Peltier effect at the substrate-solution interface. The contribution of dopant electromigration to the magnitude of the effective segregation coefficient is dominant in the absence of convection; the contribution of the Peltier effect becomes significant only in the presence of pronounced convection. Quantitative expressions which relate the segregation coefficient to the growth parameters also permit the determination of the diffusion constant and electromigration mobility of the dopant in the liquid phase. The model was found to be in good agreement with the measured segregation characteristics of Sn in the electroepitaxial growth of GaAs from Ga-As solutions. For Sn in Ga-As solution at 900 C the diffusion constant was found to be 4 x 10 to the -5 sq cm/s and the electromigration velocity (toward the substrate with a positive polarity 2 x 10 to the -5 cm/s current density of 10 A/sq cm.

Lagowski, J.↗
NASA NTRS1990

Narrow circumstellar emission lines in SN 1987A

Low and high dispersion short wavelength prime (SWP) spectra of SN 1987A show that the supernova's progenitor was in a post red giant branch stage of evolution at the time of its demise in February 1987. The development of narrow high temperature emission lines of N 5, N 4, N 3, C 3, He 2 and O 3 were followed since May 1987. Observations through April 1990 are presented. The lines are interpreted as arising in a low density gas surrounding the supernova which was photoionized by the extreme UV pulse at shock breakout. In this picture, their temporal evolution is determined primarily by light travel time effects and recombination. Comparison of models of circumstellar environment with the International Ultraviolet Explorer (IUE) observations are discussed.

Sonneborn, George↗
NASA NTRS1974

A search for X-rays from supernova 1972e with Uhuru and OSO-7

The results of observations performed with X-ray detectors aboard OSO-7 and Uhuru at 13 different times ranging from 16 months before to 2 years after Sn 1972e maximum light are reported. Only one possible (3.2 sigma) positive result was found. The absence of any sizable flux contradicts the model of Shklovsky and imposes limitations on the model of Colgate and McKee.

Canizares, C. R.↗
NASA NTRS1977

Recrystallization as a controlling process in the wear of some f.c.c. metals

Detailed examination of copper specimens after sliding against 440 C steel in liquid methane at speeds up to 25 m/s and loads of up to 2 kg showed the metal comprising the wear surface to possess a fine cell recrystallized structure. Wear proceeded by the plastic shearing of metal in this near surface region without the occurrence of visible metal transfer. A dynamic balance between the intense shear process at the surface and the nucleation of recrystallized grains was proposed to account for the behavior of the metal at the wear surface. Sliding wear experiments were also conducted on Ag, Cu-10% Al, Cu-10% Sn, Ni and Al. It was found that low wear and the absence of heavy metal transfer were associated with those metals observed to undergo recrystallization nucleation without prior recovery.

Bill, R. C.↗
NASA NTRS1990

Platinized tin oxide catalysts for CO2 lasers: Effects of pretreatment

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as PtO2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Gardner, Steven D.↗
NASA NTRS1989

Platinized tin oxide catalysts for CO2 lasers - Effects of pretreatment

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X-ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as Pto2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Gardner, Steven D.↗
NASA NTRS1987

Detection of a very bright source close to the LMC supernova SN 1987A

High angular resolution observations of the supernova in the Large Magellanic Cloud, SN 1987A, have revealed a bright source separated from the SN by approximately 60 mas with a magnitude difference of 2.7 at 656 nm (H-alpha). Speckle imaging techniques were applied to data recorded with the CfA two-dimensional photon counting detector on the CTIO 4 m telescope on March 25 and April 2 to allow measurements in H-alpha on both nights and at 533 nm and 450 nm on the second night. The nature of this object is as yet unknown, though it is almost certainly a phenomenon related to the SN.

Nisenson, P.↗