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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Evolution of luminous IRAS sources - CCD imaging

The paper presents optical imaging of a sample of 64 luminous IRAS galaxies which cover a wide range of IRAS spectra and luminosity and also include a range of optical types. The objects are almost all in current or recent tidal interaction. The connections between the strength and age of the interaction, the IR spectrum and luminosity, and the optical colors, and other properties of the galaxies are discussed. The principal result is that the powerful IR sources with steep IR spectra are stronger and dynamically younger interacting systems, while the flat IR spectrum objects are older. Star formation, dust obscuration, and the timescales for nuclear activity compared with IR and tidal events are discussed, and a self-consistent evolution scenario connecting the luminous IR sources is described.

Hutchings, J. B.↗
NASA NTRS1979

Energetic binary collisions in rare gas plasmas

Calculations have been made of cross sections for energy and momentum transfer in binary collisions between like pairs of Ar, Kr, and Xe atoms in the energy range from about 1 to 1000 eV. These calculations were made using a classical model with pair interaction potentials for the rare gases developed from experimental sources, e.g., investigations of specific heats, viscosities, solid-state parameters, and scattering data. Cross sections in this energy range have not been available. The cross sections exhibit a rapid decrease from accepted values at thermal energies as the interaction energy increases. This behavior can be used to understand directed beam propagation limits as well as particle propagation within a plasma. Experimental data have also been fit to a theoretical expression for the Ar resonance charge exchange cross section over the same energy range.

Robinson, R. S.↗
NASA NTRS1995

Evolution of the solar wind acceleration region during 1990-1994

The single-station measurements of interplanetary scintillation (IPS) at 2 and 8 GHz have been made at the Kashima Space Research Center of the Communications Research Laboratory in the period from 1990 to 1994. These IPS data are used to study the radial distribution of solar wind velocity and density fluctuations near the sun (i.e. 10-70 Rs), and the long-term variation in these properties. The IPS co-spectrum technique is applied here to estimate the solar wind velocity. Derived velocities show that the solar wind gains a speed significantly in the radial range from 10 to 30 Rs (solar radii). which is much farther than the source surface of the thermally driven solar wind model. From the scintillation index analysis. it is found that the radial fall of density fluctuations is well described by the power-law function. A series of IPS observations reveals that a pronounced change in velocity and turbulence level for this radial range occurs at the polar region of the sun during 1990-1994. That is, the high speed wind and the reduced turbulence region develop there as the solar activity declines. On the other hand, little long-term variation is observed for the solar wind acceleration region at a low latitude. From the comparison with He 1O83 nm observations. it is demonstrated that the change of the solar wind structure is closely linked with the evolution of the coronal hole on the solar surface.

Tokumaru, M.↗
NASA NTRS1972

Wind sensitivity studies of a non-return wind tunnel, with a 216- by 432-mm (8.5- by 17.0-inch) test section, phase 1

The study to develop inlet and exit treatments which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel is reported. The investigation was conducted in the Ames Research Center 40- by 80-Foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios between zero and one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three directions generally less than 1/2 knot (0.26 m/sec) for wind velocities of 15 knots (7.7 m/sec) or less. The loss in total pressure due to the inlet treatment was low: about 0.03 of the test-section dynamic pressure.

Eckert, W. T.↗
NASA NTRS1973

Wind sensitivity studies of a non-return wind tunnel with a 216- by 432-mm (8.5- by 17.0-inches) test section, phase 2

The refinement of inlet and exit treatments were studied which would minimize the effect of external wind on the test-section flow quality of a nonreturn wind tunnel. The investigation was conducted in the Ames Research Center 40- by 80-foot Wind Tunnel which served as the wind source. Several inlets and two exits were tested at wind directions ranging from 0 to 180 degrees and at wind-to-test-section velocity ratios from zero to somewhat greater than one. For the best inlet configuration the flow quality was good, with a velocity deviation in each of the three component directions generally less. The loss in total pressure due to the inlet treatment was low: about 0.035 of the test-section dynamic pressure for the no-wind case.

Eckert, W. T.↗
NASA NTRS1974

Limb darkening of two latitudes of Jupiter at phase angles of 34 and 109 deg

The imaging photopolarimeter aboard Pioneer 10 produced hundreds of red and blue images of Jupiter covering a wide range of phase angles and having good linearity and signal-to-noise characteristics. In this preliminary analysis the limb darkening across two of the red images (at phase angles of about 34 and 109 deg) in both a prominent dark belt and a bright zone are compared with multiple-scattering models. Of the simple models tried, the smallest deviations from the observations result for ones consisting of a thin absorbing layer above a semiinfinite atmosphere of particles scattering according to the Henyey-Greenstein phase function. The asymmetry parameter for the best fits to both the belt and the zone data is in the range g = 0 to 0.25, corresponding to particles small in comparison with the wavelength of red light. The phase integral derived from the models lies in the range of about 1.5 to 1.6, implying a substantial internal heat source for Jupiter.

Tomasko, M. G.↗
NASA NTRS1975

Preliminary evaluation of turbofan cycle parameters and acoustical suppression on the noise and direct operating cost of a commercial Mach 0.85 transport

A study was made of the effects of turbofan cycle parameters and the use of acoustic noise suppression material to quiet 200 passenger, Mach 0.85 trijets having design ranges of 2778, 4630, and 9260 kilometers (1500, 2500, and 5000 n. mi). Aircraft gross weight and direct operating cost, which varied with amount of suppression and cycle selection, are presented as functions of both EPNdB traded and 90 EPNdB contour footprint area. Noise levels 10.9 EPNdB below FAR 36 requirements result in a 5 percent increase in DOC for an aircraft designed for a range of 9260 kilometers (5000 n. mi.). An aircraft designed for a 2778 kilometer (1500 n. mi.) range would have an EPNdB level 14 below FAR 36 for this same economic penalty. In this range of noise level, fan-machinery noise is the principal source.

Eisenberg, J. D.↗
NASA NTRS1974

Relative transition probabilities of cobalt

Results of determinations of neutral-cobalt transition probabilities measured relative to Co I 4150.43 A and Co II 4145.15 A, using a gas-driven shock tube as the spectroscopic light source. Results are presented for 139 Co I lines in the range from 3940 to 6640 A and 11 Co II lines in the range from 3840 to 4730 A, which are estimated to have reliabilities ranging from 8 to 50%.

Roig, R. A.↗
NASA NTRS1974

Microwave profiling of snowpack free-water content

A microwave system is proposed to measure the amount of liquid-phase water in a snowpack operating in the range of 1 to 10 GHz. Attenuation of the beam between source and receivers is produced by the water in the snow. The relationships of frequency, distance, and volume percent of water are calculated for an assumed detector sensitivity, together with the estimated cost of a representative system. A laboratory test is described that shows the attenuation for snow at maximum wetness at 9.35 GHz. A configuration is proposed that involves a vertical tube containing microwave and radioactive sources and another vertical tube containing microwave and gamma-ray detectors, so that density and wetness profiles are obtained simultaneously over essentially the same path.

Linlor, W. I.↗
NASA NTRS1976

Temperature of the atmosphere of Jupiter from Pioneer 10/11 radio occultations

Radio-occultation data from the Pioneer 10 and 11 flybys are analyzed using an integral inversion technique combined with a model for Jupiter's shape based on gravity data in order to account for the oblateness of the planet's atmosphere. The inversion technique defines the center of refraction in terms of the radius of curvature and the normal to the equipotential surface at the closest approach point of the ray. An Abelian inversion of the data obtained during the Pioneer 10 entry, the Pioneer 10 exit, and the Pioneer 11 exit is performed by fixing the center of refraction at some average value for each occultation event. The results for all three measurements are found to be consistent and to show a temperature inversion between the 10-mb and the 100-mb levels, with temperatures of 130 to 170 K at 10 mb and 80 to 100 K at 100 mb. Major sources of error are discussed, and it is concluded that the range of reasonable temperature uncertainties at these levels does not exceed 40 K. It is noted that the temperature inversion was also inferred from Pioneer 10 IR radiometric data.

Kliore, A. J.↗
NASA NTRS1976

A 30-cm diameter argon ion source

A 30 cm diameter argon ion source was evaluated. Ion source beam currents up to 4a were extracted with ion energies ranging from 0.2 to 1.5 KeV. An ion optics scaling relation was developed for predicting ion beam extraction capability as a function of total extraction voltage, gas type, and screen grid open area. Ignition and emission characteristics of several hollow cathode geometries were assessed for purposes of defining discharge chamber and neutralizer cathodes. Also presented are ion beam profile characteristics which exhibit broad beam capability well suited for ion beam sputtering applications.

Sovey, J. S.↗
NASA NTRS1976

Radio observations of interplanetary magnetic field structures out of the ecliptic

New observations of the out-of-the ecliptic trajectories of type 3 solar radio bursts have been obtained from simultaneous direction finding measurements on two independent satellite experiments, IMP-6 with spin plane in the ecliptic, and RAE-2 with spin plane normal to the ecliptic. Burst exciter trajectories were observed which originated at the active region and then crossed the ecliptic plane at about 0.8 AU. A considerable large scale north-south component of the interplanetary magnetic field is followed by the exciters. The apparent north-south and east-west angular source sizes observed by the two spacecraft are approximately equal, and range from 25 deg at 600 KHz to 110 deg at 80 KHz.

Fitzenreiter, R. J.↗
NASA NTRS1976

A 30-cm diameter argon ion source

A 30-cm diameter argon ion source was evaluated. Ion source beam currents up to 4A were extracted with ion energies ranging from 0.2 to 1.5 KeV. An ion optics scaling relation was developed for predicting ion beam extraction capability as a function of total extraction voltage, gas type and screen grid open area. Ignition and emission characteristics of several hollow cathode geometries were assessed for purposes of defining discharge chamber and neutralizer cathodes. Also presented are ion beam profile characteristics which exhibit broad beam capability well suited for ion beam sputtering applications.

Sovey, J. S.↗
NASA NTRS1977

Radio observations of interplanetary magnetic field structures out of the ecliptic

Observations of the out-of-ecliptic trajectories of type III solar radio bursts have been obtained from simultaneous direction-finding measurements in two independent satellite experiments, IMP-6 with spin plane in the ecliptic and RAE-2 with spin plane normal to the ecliptic. Burst-exciter trajectories were observed which originated at the active region and then crossed the ecliptic plane at about 0.8 AU. A considerable large-scale north-south component of the interplanetary magnetic field followed by the exciters is found. The apparent north-south and east-west angular source sizes observed by the two spacecraft are approximately equal, and range from 25 deg at 600 kHz to 110 deg at 80 kHz.

Fitzenreiter, R. J.↗
NASA NTRS1979

Observations of pulsating X-ray binaries 4U0900-40 and 4U1223-62

A sounding-rocket observation of the pulsating X-ray binaries 4U 0900-40 (Vela X-1) and 4U 1223-62 (GX301-2, Wray 977) over the energy range from 0.5 to 27 keV is reported. No short-time-scale periodicities in the range from 2 msec to 20 sec are found for either source, although both exhibit some minor flaring activity on time scales of a few seconds. The data for Vela X-1 suggest that the time-averaged spectra are complex and that the pulse-resolved spectra are also complex and variable, with significant fluctuations above 10 keV. When compared with other observations at different epochs, the spectral data for 4U 1223-62 confirm large variability in both intensity and spectral characteristics. It is concluded that the intrapulse changes observed in the spectral behavior of Vela X-1 must reflect changes in the surface magnetic fields and the plasma flows near the neutron star.

Ku, W. H.-M.↗
NASA NTRS1980

Method and means for helium/hydrogen ratio measurement by alpha scattering

An apparatus for determining helium to hydrogen ratios in a gaseous sample is presented. The sample is bombarded with alpha particles created by a self contained radioactive source and scattering products falling within a predetermined forward scattering angular range impact a detector assembly. Two detectors are mounted in tandem, the first completely blocking the second with respect to incident scattering products. Alpha particle/hydrogen or alpha particle/helium collisions are identified by whether scattering product impacts occur simultaneously in both detectors or only in the first detector. Relative magnitudes of the two pulses can be used to further discriminate against other effects such as noise and cosmic ray events.

Whitehead, A. B.↗
NASA NTRS1980

Design considerations for optical heterodyne receivers: A review

The current state of knowledge concerning optical heterodyne receivers is reviewed. Following a discussion of noise processes in the heterodyne receiver and the manner in which sensitivity is increased through time integration of the detected signal, an expression for the mean square signal current is derived by mixing a coherent local oscillator with a partially coherent, quasimonochromatic source. Then the manner in which the IF signal calculation can be transferred to any convenient plane in the optical front end of the receiver is demonstrated. Using these techniques, a relatively simple equation is obtained for the coherently detected signal from an extended incoherent source and applied to the heterodyne detection of an extended thermal source and to the backscatter lidar problem where the antenna patterns of both the transmitter beam and heterodyne receiver must be taken into account. Finally, the detection of a coherent source is considered and, in particular, a distant point source such as a star or laser transmitter in a long range heterodyne communications system is discussed.

Degnan, J. J.↗
NASA NTRS1981

Studies of bipolar nebulae. VII - The exciting star of OH 0739-14 /equals OH 231.8 plus 4.2/

A spectral classification for the exciting star of the bipolar reflection nebula OH 0739-14, which has also been observed to be an OH/H2O maser source, is obtained from the spectrum of the nebulosity in the range 6000-9000 A. Spectrophotometry of the visible nebula was obtained with the Cassegrain image-tube scanner on the Lick Observatory 3-m telescope at a resolution of approximately 7 A. The red spectrum is found to be distinguished by TiO absorption at the bandheads at 8206, 8303, 8432, 8442 and 8452 A and VO in the 7400 and 7900 A regions. On the basis of the depths of these bandheads and the K I 7699 A and Ca II infrared triplet, OH 0739-14 is determined to be of spectral type M9 III. The underlying star thus represents the coolest known star to occur in a bipolar system.

Cohen, M.↗