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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 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Large-scale cosmic microwave background anisotropies in isocurvature baryon open universe models

The large-angular-scale cosmic microwave background anisotropy is calculated in a low-density baryon-dominated universe with isocurvature primordial inhomogeneities. In models in which the initial power spectra of perturbations are steeper than white noise, predictions for the quadrupole moment of the anisotropy are found to be in conflict with existing observational limits, if the universe remained fully ionized and Compton drag inhibited growth of inhomogeneities until z = about 100. In order to lower the amplitude of the anisotropy, it is necessary to substantially prolong the duration of the growth phase of density perturbations, while smearing out fine-scale anisotropies, thereby requiring reionization to occur at a redshift smaller than 100, but larger than the redshift of the last scattering surface (in a reionized model).

Gorski, Krzysztof M.↗
NASA NTRS1989

Dynamical evolution of domain walls in an expanding universe

Whenever the potential of a scalar field has two or more separated, degenerate minima, domain walls form as the universe cools. The evolution of the resulting network of domain walls is calculated for the case of two potential minima in two and three dimensions, including wall annihilation, crossing, and reconnection effects. The nature of the evolution is found to be largely independent of the rate at which the universe expands. Wall annihilation and reconnection occur almost as fast as causality allows, so that the horizon volume is 'swept clean' and contains, at any time, only about one, fairly smooth, wall. Quantitative statistics are given. The total area of wall per volume decreases as the first power of time. The relative slowness of the decrease and the smoothness of the wall on the horizon scale make it impossible for walls to both generate large-scale structure and be consistent with quadrupole microwave background anisotropy limits.

Press, William H.↗
NASA NTRS1990

A test of the galactic origin of gamma-ray bursts

Models in which gamma-ray bursters are young neutron stars may be difficult to reconcile with the apparently isotropic distribution of observed bursts. To justify this statement, the distribution of old neutron stars in the Galaxy was calculated by integrating numerically some 90,000 orbits in the Galactic gravitational potential for up to 10 to the 10th yr. Other calculations included the dipole moment in the angular distribution of neutron stars as a convenient measure of their concentration toward the Galactic center, the quadrupole moment in their angular distribution as a convenient measure of their concentration toward the Galactic plane, and the average value of V/Vmax as a convenient measure of the radial distribution of neutron stars. Models that require accretion from a cold circumstellar disk or from a close companion are only marginally consistent with the isotropic distribution of the observed bursts. Models that require accretion of interstellar matter are ruled out due to a very strong dipole anisotropy. Models that suggest the Galactic halo origin of gamma-ray bursts are briefly discussed. The GRANAT and GRO missions should provide evidence for or against the association of gamma-ray bursts with the Galactic disk neutron stars.

Paczynski, Bohdan↗
NASA NTRS1990

The microwave spectrum of the AlO radical

The rotational spectrum of the aluminum monoxide radical in the ground electronic state X 2Sigma(+) was observed in the millimeter- and submillimeter-wave region. Aluminum monoxide radicals were generated directly in a flow reactor absorption cell by the reaction of N2O with aluminum vaporized from a high-temperature crucible. The observed spectrum was analyzed to yield molecular constants including the rotational constant, centrifugal distortion constant, spin-rotation interaction constant, magnetic hyperfine interaction constants, and nuclear quadrupole coupling constant.

Yamada, Chikashi↗
NASA NTRS1989

Possible test at Jupiter of the nonsymmetric gravitational theory

Radiometric data generated during spacecraft flybys of Jupiter have the capability to provide an interesting constraint on the coupling of cosmions in the nonsymmetric gravitational theory (NGT) of Moffat. It is shown that the close flyby of Jupiter by Pioneer 11 could imply a possible limit on the NGT l parameter of the sun of solar l less than 2800 km, a limit which could affect the ability of the NGT to account for the precession of the perihelion of Mercury with a large solar quadrupole moment.

Krisher, Timothy P.↗
NASA NTRS1990

In situ extraction and analysis of volatiles and simple molecules in interplanetary dust particles, contaminants, and silica aerogel

Results are presented for the analyses of eight interplanetary dust particles (IDPs) for the volatile elements H, C, N, O, and S and their molecular species, as well as of the volatiles associated with contaminants (i.e., the compounds used during the collection and curation of IDPs), which were carried out using a laser microprobe interfaced with a quadrupole mass spectrometer. It was found that the volatile species from contaminants were always present in the spectra of IDPs. Despite the contamination problems, several indigenous molecular species could be identified, including OH, CO2 or C2H4, C and CS2, CO2 along with CO (possibly indicating the presence of carbonate), H2S, SO, COS, SO2, and CS2. In some cases, the sulfur components can be attributed to aerosols; however, in one of the IDPs, the presence of H2S, SO, COS, and SO2 indicates the possible presence of elemental sulfur.

Hartmetz, C. P.↗
NASA NTRS1989

Antiferromagnetism in Co-57-doped La2CuO(4-y) studied by Moessbauer spectroscopy

Moessbauer effect studies of Co-57-doped La2CuO(4-y) were performed at temperatures between 4.2 K and room temperature. These confirm the antiferromagnetic ordering of these compounds below room temperature. Temperature dependence of the quadrupole splitting shows that the hyperfine field is at an angle with the c-axis.

Jha, S.↗
NASA NTRS1990

Decomposition of perfluoroalkylpolyethers (PFPE) in ultra-high vacuum under sliding conditions

Reactions of perfluoroalkylpolyethers (PFPE: Fomblin, Demnum and Krytox) were studied during the sliding contact of stainless steel specimens under ultrahigh vacuum conditions. All three fluids reacted with the steel specimens during sliding. Fomblin, which has acetal linkages, decomposed under the sliding conditions generating gaseous products, (COF2 and fluorinated carbons) which were detected by a quadrupole mass spectrometer. Gaseous products were not detected for the Demnum and Krytox fluids. The amount of gaseous products from Fomblin increased with increasing sliding speed. At the end of the sliding experiments, the wear scar and deposits on the specimens were examined by small spot size XPS. The oxide layer on the specimen surface was removed during sliding, and metal fluorides were formed on the worn surface. The surface of the wear scar and deposits were covered with adsorbed PFPE. Based on these results, it was concluded that the decomposition reaction on Fomblin was initiated by contacting the fluid with a fresh metal surface which was formed during sliding.

Mori, Shigeyuki↗
NASA NTRS1989

Testing general relativity in space-borne and astronomical laboratories

The current status of space-based experiments and astronomical observations designed to test the theory of general relativity is surveyed. Consideration is given to tests of post-Newtonian gravity, searches for feeble short-range forces and gravitomagnetism, improved measurements of parameterized post-Newtonian parameter values, explorations of post-Newtonian physics, tests of the Einstein equivalence principle, observational tests of post-Newtonian orbital effects, and efforts to detect quadrupole and dipole radiation damping. Recent numerical results are presented in tables.

Will, Clifford M.↗
NASA NTRS1989

Simulations of light scattering in planetary rings

The current status of efforts to model light scattering in the Uranian and Saturnian rings is briefly reviewed, with an emphasis on the treatment of thin, vertically warped, or clumpy rings. Consideration is given to observations of an opposition surge in the rings (indicating that they are physically thick) and possible reasons for the failure of classical models to predict the forward-scattering characteristics of the B and inner A rings of Saturn, the quadrupole brightness variations in the A ring, the increase in reflectivity with optical depth in the A and B rings, the increase in brightness with solar and observer angle in the B ring, and systematic brightness variations in images of the inner Cassini division. It is pointed out that some of these discrepancies are eliminated by the use of a ray-tracing simulation code which determines the singly scattered light from a layer one or many particles thick.

Dones, L.↗
NASA NTRS1990

Observations of thermal ion influxes about the space shuttle

Ion mass spectrometer measurements made as part of the University of Iowa's Plasma Diagnostic Package on the STS-3 and Spacelab 2 Space Shuttle missions sampled a variety of ion composition and collected ion current responses to gas emissions from the vehicle. The only other shuttle ion measurements were made by an Air Force Geophysics Laboratory (AFGL) quadrupole spectrometer flown on STS-4. Gas emissions change the distribution of the incoming plasma through scattering and charge transfer processes. A background flux of contaminant ion species (mostly relating to water) always exists in the near vicinity of the shuttle with a magnitude which is dependent on the look direction of the spectrometer but which varies differently with changes in the angle of attack than that of the ambient ions. There is a near shuttle wake cavity in the contaminant ion distributions which has a different spatial configuration than the wake of the ambient ions. Although water dumps produce the most persistent ion perturbations, the sources for ion current modification were best delineated from measurements made when only one or two of the Reaction Control System thrusters fired for a relatively long duration. Contaminant ion perturbations associated with such firings were observed to persist for the order of a second after the cessation of the firings. The dense thruster plumes are efficient collisional, charge exchange barriers to the passage of ambient ions. Collected ion current perturbations were more evident for firings of the rear verniers, whose plumes scatter off projecting surfaces, than for the nose thrusters. The effect of the Vernier firings was found to depend not only on the location and attitude of the spectrometer with respect to the shuttle and thruster plume direction, but also on the orientation of the local magnetic field with respect to the shuttle velocity.

Grebowsky, Joe M.↗
NASA NTRS1991

Characterization of a 5-eV neutral atomic oxygen beam facility

An experimental effort to characterize an existing 5-eV neutral atomic oxygen beam facility being developed at Princeton Plasma Physics Laboratory is described. This characterization effort includes atomic oxygen flux and flux distribution measurements using a catalytic probe, energy determination using a commercially designed quadrupole mass spectrometer (QMS), and the exposure of oxygen-sensitive materials in this beam facility. Also, comparisons were drawn between the reaction efficiencies of materials exposed in plasma ashers, and the reaction efficiencies previously estimated from space flight experiments. The results of this study show that the beam facility is capable of producing a directional beam of neutral atomic oxygen atoms with the needed flux and energy to simulate low Earth orbit (LEO) conditions for real time accelerated testing. The flux distribution in this facility is uniform to +/- 6 percent of the peak flux over a beam diameter of 6 cm.

Vaughn, J. A.↗
NASA NTRS1990

Rheological properties, shape oscillations, and coalescence of liquid drops with surfactants

A method was developed to deduce dynamic interfacial properties of liquid drops. The method involves measuring the frequency and damping of free quadrupole oscillations of an acoustically levitated drop. Experimental results from pure liquid-liquid systems agree well with theoretical predictions. Additionally, the effects of surfactants is considered. Extension of these results to a proposed microgravity experiment on the drop physics module (DPM) in USML-1 are discussed. Efforts are also underway to model the time history of the thickness of the fluid layer between two pre-coalescence drops, and to measure the film thickness experimentally. Preliminary results will be reported, along with plans for coalescence experiments proposed for USML-1.

Apfel, R. E.↗
NASA NTRS1990

Analysis of the COS B data for evidence of linear polarization of Vela pulsar gamma rays

The COS B spark chamber telescope observations of the Vela pulsar were analyzed for gamma-ray polarization. No significant quadrupole moment is found in the azimuthal distribution of the electron-positron pair production planes. However, analysis of the sensitivity indicates that even 100-percent polarization would not be detected. Therefore, the null result does not constrain the polarization of the Vela pulsar gamma-ray emission. This result contradicts the report of Caraveo et al. (1988) of possible evidence for polarization of the Vela pulsar gamma rays.

Mattox, John R.↗
NASA NTRS1991

Gravitational lensing by clusters of galaxies - Constraining the mass distribution

The possibility of placing constraints on the mass distribution of a cluster of galaxies by analyzing the cluster's gravitational lensing effect on the images of more distant galaxies is investigated theoretically in the limit of weak distortion. The steps in the proposed analysis are examined in detail, and it is concluded that detectable distortion can be produced by clusters with line-of-sight velocity dispersions of over 500 km/sec. Hence it should be possible to determine (1) the cluster center position (with accuracy equal to the mean separation of the background galaxies), (2) the cluster-potential quadrupole moment (to within about 20 percent of the total potential if velocity dispersion is 1000 km/sec), and (3) the power law for the outer-cluster density profile (if enough background galaxies in the surrounding region are observed).

Miralda-Escude, Jordi↗
NASA NTRS1991

Preliminary results from the COBE differential microwave radiometers - Large angular scale isotropy of the cosmic microwave background

Preliminary but precise micowave maps are presented of the sky, and thus of the early universe, derived as the first results from the Differential Microwave Radiometers experiment aboard COBE. The dipole anisotropy attributed to the motion of the solar system with respect to the CMB reference frame shows strongly in all six sky maps and is consistent with a Doppler-shifted thermal spectrum. The best-fitted dipole has amplitude 3.3 + or - 0.2 mK in the direction (alpha, delta) = 11.2 h + or - 0.2 h, -7 deg + or - 2 deg (J2000) or (l,b) = 265 deg + or - 2 deg, 48 deg + or - 2 deg. There is no clear evidence in the maps for any other large angular-scale feature. Limits on Delta T/T0 of 3 x 10 to the -5th (T0 = 2.735 K), 4 x 10 to the -5th, and 4 x 10 to the -5th are found for the rms quadrupole amplitude, monochromatic fluctuations, and Gaussian fluctuations, respectively. These measurements place the most severe constraints to date on many potential physical processes in the early universe.

Smoot, G. F.↗
NASA NTRS1990

COBE

Preliminary results are presented from COBE's three observational instruments. These are the FIRAS spectrum experiment, which surveyed over 98 percent of the sky, the IR background experiment, DIRBE which surveyed all of the sky, and the DMR anisotropy experiment. It is found that the cosmic microwave background is very close to a blackbody, with a temperature of 2.735 + or - 0.06 K. The only reliably detected background anisotropy is the 3.3 + or - 0.2 mK-amplitude dipole. The rms quadrupole anisotropy is less than 0.00003 with 95-percent confidence. DIRBE results indicate that the IRAS 60-100 micron diffuse-flux calibrations suffer from gain and offset errors.

Wright, Edward L.↗
NASA NTRS1990

Characterization and calibration of the EOIM-III flight mass spectrometer in a high velocity oxygen atom beam

Calibration and characterization of the quadrupole mass spectrometer component of the Evaluation of Oxygen Effects on Materials III (EOIM-III) space-flight experiment are reported in this paper. A high-velocity atom beam system was used to characterize the response of the flight mass spectrometer to high velocity oxygen atoms as well as the reaction/scattering products formed when the atom beam struck a surface. Carbon dioxide, carbon monoxide, and water were observed to form in the mass spectrometer whenever high velocity oxygen atoms were present. The major gaseous products formed from high-velocity atom-beam polymer reactions were easily detected and identified.

Koontz, S. L.↗