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At least 433 records · Page 24

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NASA NTRS1979

Control of forebody three-dimensional flow separations

Some experiments involving the development of the turbulent symmetric vortex flow about the lee side of a 5 deg semiangle conical forebody at high relative incidence are discussed. The cone was immersed in a Mach 0.6 airstream at a Reynolds number of 13.5 million based on the 1.4 - m axial length of the cone. Novel means of controlling the degree of asymmetry using blowing very close to the nose were investigated. Small amounts of air injected normally or tangentially to the cone surface, but on one side of the leeward meridian and beneath the vortex farthest from the wall, were effective in biasing the asymmetry. With this reorientation of the forebody vortices, the amplitude of the side force could be reduced to the point where its direction was reversed. This phenomenon could be obtained either by changing the blowing rate at constant incidence or by changing incidence at constant blowing rate. Normal injection was more effective than tangential injection. An organized and stable flow structure emerged with the jet vortices positioned above the forebody vortices.

Peake, D. J.↗

NASA NTRS1978

Multiple frequency sounding of a Jovian cloud

A thermal asymmetry displayed in Pioneer 10 45-micron IR radiometric data between the rising and setting limbs of the Jovian South Equatorial Belt (SEB) between -5.0 and -7.0 deg latitude is examined. A high correlation is found between the longitudinal asymmetry of the SEB at 45 microns and the appearance of Jupiter in 5-micron radiation. It is shown that there was a cooler 'obscuring' cloud within the SEB latitude region which correlates highly with the location of relatively reduced intensities at 45 microns. The cloud-top temperature is estimated on the basis of simultaneous 5- and 45-micron observations

Orton, G. S.↗

NASA NTRS1979

Vaporization of comet nuclei - Light curves and life times

The effects of vaporization from the nucleus of a comet are examined and it is shown that a latitude dependence of vaporization can explain the asymmetries in cometary light curves. An attempt is made to explain the observed variation in molecular production rates with heliocentric distance when employing CO2 and clathrate hydrate ice as cometary nuclei substances. The energy balance equation and the vapor pressure equations of water and CO2 are used in calculating the vaporization from a surface. Calculations were carried out from both dry-ice and water-ice nuclei, using a variety of different effective visual albedos, but primarily for a thermal infrared of 0 (emission). Attention is given to cometary lifetimes and light curves and it was determined that the asymmetry in light curves occurs (occasionally) as a 'seasonal' effect due to a variation in the angle between the comet's rotation axis and the sun-comet line.

Cowan, J. J.↗

NASA NTRS1980

Solar coronal holes and cosmic ray intensity variations

A relationship between the (North-South) asymmetry in the areas of the solar polar coronal holes and the (North-South) anisotropy in the cosmic ray intensity is examined. The investigation was extended over a period of two years, using ground based observations of coronal brightness obtained by the K-Coronameter. Periods for study of cosmic ray variations were chosen maximizing the asymmetry of the polar coronal holes. The importance of the role played by coronal holes in the solar modulation of galactic cosmic rays is emphasized.

Venkatesan, D.↗

NASA NTRS1979

Temporal characteristics of the Jovian atmosphere

Drift scans along the central meridian of Jupiter have been obtained at wavelengths of 7.9, 17.8, and 19.7 microns. These observations indicate a significant north-south temperature asymmetry within the Jovian stratosphere but not within its troposphere, results which agree with the recent Voyager 1 observations. Employing a time-dependent stratospheric model, it is found that the observed north-south asymmetry is consistent with seasonal stratospheric variability. In the model, the primary cause for this variability is the time-dependent absorption of sunlight by aerosols.

Caldwell, J.↗

NASA NTRS1980

Detection of mass loss in stellar chromospheres

IUE observations of 47 cool giants have been made in a search for the onset of expansion in the Mg II h and k emission cores. It is found that, in a statistical sense, the longward emission peak becomes dominant above a velocity dividing line in the H-R diagram, which lies close to a temperature dividing line reported by Linsky and Haisch (1979). Also discussed are asymmetries in emission cores, collected asymmetry data including the evaluation of absolute visual magnitude by MK classification, Ca K emission width, and Mg k emission width, and evolutionary implications for the hypothesized supersonic transition locus (Mullan, 1978).

Stencel, R. E.↗

NASA NTRS1980

Iron and titanium distribution on the moon from orbital gamma ray spectrometry with implications for crustal evolutionary models

A set of Fe and Ti maps and regional values are obtained from the Apollo 15 and 16 orbital gamma ray data by energy band analysis. High-Ti basalts predominate the early and late stages of mare volcanism with high-Fe basaltic volcanism in the interim. The first evidence of a high-Ti-KREEP basalt association is found in the Aristarchus region. A N-S asymmetry for Fe and Ti in the east limb and farside highlands complicates the E-W asymmetry for Th but substantiates crustal inhomogeneity. The observed crustal inhomogeneity adds an additional objection to the primitive source model for crustal evolution. The high-Ti-KREEP basalt association and the general trend of decreasing mare basalt Ti with time lend support to the cumulate source model; however, this model cannot account for young, high-Ti maria. The dynamic assimilation model better accounts for chemical variations observed on the moon.

Davis, P. A., Jr.↗

NASA NTRS1980

Minimum energy trap states of dual-spin spacecraft

The general solution to the bearing axis motor torque required to escape a minimum energy trap state is presented for oblate dual-spin spacecraft. A simplified, reduced order analysis of the bearing torque is then obtained for the case of small static imbalances, dynamic imbalances, and asymmetries on the rotor and the stator. This analysis is extended to include large asymmetry on one of the bodies. The results are applied to the design of the Galileo spacecraft.

Hollars, M. G.↗

NASA NTRS1980

Computer modeling of high-efficiency solar cells

Transport equations which describe the flow of holes and electrons in the heavily doped regions of a solar cell are presented in a form that is suitable for device modeling. Two experimentally determinable parameters, the effective bandgap shrinkage and the effective asymmetry factor are required to completely model the cell in these regions. Nevertheless, a knowledge of only the effective bandgap shrinkage is sufficient to model the terminal characteristics of the cell. The results of computer simulations of the effects of heavy doping are presented. The insensitivity of the terminal characteristics to the choice of effective asymmetry factor is shown along with the sensitivity of the electric field and quasielectric fields to this parameter. The dependence of the terminal characteristics on the effective bandgap shrinkage is also presented.

Schartz, R. J.↗

NASA NTRS1981

In-situ measurements of scattering phase functions of stratospheric aerosol particles in Alaska during July 1979

A laser nephelometer developed for airborne measurements of polar scattering diagrams of atmospheric aerosols was flown on the NCAR Sabreliner aircraft to obtain data on light-scattering parameters for stratospheric aerosol particles over Alaska during July 1979. Observed values of the angular variation of scattered-light intensity were compared with those calculated for different values of the asymmetry parameter g in the Henyey-Greenstein phase function. The observations indicate that, for the time and location of the experiments, the Henyey-Greenstein phase function could be used to calculate polar scattering diagrams to within experimental errors for an asymmetry parameter value of 0.49 plus or minus 0.07.

Grams, G. W.↗

NASA NTRS1981

IUE detection of bursts of H Ly-alpha emission from Saturn

A new investigation is reported of the potential sources of Ly-alpha emission in a series of observations of the Saturnian system carried out between January and July 1980 using the short wavelength spectrograph of the IUE Observatory. It is noted that north-south maps of the Ly-alpha emission across the planet disk show pronounced spatial asymmetries in emission brightness. These asymmetries vary to a marked extent on a time scale of days and are interpreted as bursts of Ly-alpha emission of as much as 1 kR brightness averaged over a 6 x 10 arcsec area, above a constant planetary emission level of 700-800 R. In fact, the Ly-alpha emission peaks manifest themselves as essentially point source features in these data; it is pointed out that if the emitting region is smaller than the 6 x 10 arcsec instrumental resolution, the surface brightness must be proportionally higher.

Clarke, J. T.↗

NASA NTRS1981

Collapses of stellar protogalaxies from aspheric initial conditions

Numerical experimens are presented which were intended to verify the independence of bar formation in rotating galaxy models from special initial conditions. Three-dimensional n-body programs were run starting from aspherical initial conditions characterized by particle rotational and peculiar velocities and offsets from sphericity for a set of 100,000 particles. All the initial configurations examined are observed to collapse to a thin form, overshoot, collapse again and again overshoot, with diameters and central densities similar to those observed under spheric initial conditions. Every aspheric collapse is also found to result in bar formation within two rotation periods, which is even sooner than in initially spherical conditions. In the intermediate stages of collapse, transient sheet patterns are found to be destroyed at asymmetries of 2-3%, while transient rings survived asymmetries of 6-7% but not 15-18%. It is noted that the results may be applicable to galaxy formation in the early universe, and possible mechanisms for the arresting of protogalactic collapse are indicated.

Miller, R. H.↗

NASA NTRS1981

Theoretical interpretation of photometric properties of the Martian surface and atmosphere

Earth-based UBV photometry, photographs from the Lowell Observatory, and Mariner 9 data are combined with a new radiative transfer theory to derive physical parameters for the Martian surface and atmosphere, both before and during the 1971 dust storm. Storm dust particles had a single scattering albedo of 0.84 plus or minus 0.02 and an asymmetry factor of 0.35 plus or minus 0.10 in green (V) light. The geometric albedo of Mars was 0.15 and the phase integral 1.83, yielding 0.27 for the Bond albedo. The mean optical thickness of the 'clear' atmosphere averaged over the whole planet was 0.15 plus or minus 0.05 and was not dependent on wavelength. Geometric albedos for the surface are 0.25 (light areas) and 0.17 (dark areas) in V, 0.095 in B, and 0.060 in U. The soil particles are moderately backward scattering with an asymmetry factor of minus 0.20, and therefore rather opaque. The mean surface roughness is 0.57, representing the depth/radius ratio of an average hole, and being only one-half as large as values typical for the moon and asteroids.

Lumme, K.↗

NASA NTRS1981

The C IV 1550 profile in type 1 Seyfert galaxies

The paper presents C IV 1550 A line profiles for the type 1 Seyfert galaxies NGC 5548, Mrk 509, NGC 7469, and MCG-2-58-22. Several line broadening mechanisms and theoretical line profiles are considered, and random motion of discrete clouds is ruled out. A spherical ensemble of discrete clouds with steady outflow or inflow produces a logarithmic profile, but does not account for the highly extended wings. A spherical ensemble with ballistic outflow produces a profile of the first exponential integral function, and fits the observed profile to the continuum level. Although C IV profiles favor the ballistic model, both Mrk 509 and NGC 7469 have significant asymmetry, and Balmer lines with a higher optical depth show higher asymmetry and redshift than all four galaxies.

Wu, C.-C.↗

NASA NTRS1981

The magnetic-anomaly model of the Jovian magnetosphere - A post-Voyager assessment

Predictions previously put forth (Dessler and Vasyliunas, 1979) as tests for the magnetic-anomaly model (in which the anomalously weak magnetic field region in the northern hemisphere of Jupiter influences the outer Jovian magnetosphere by one or more plasma interaction processes) are reexamined in the light of Voyager and other recent observations. With regard to the prediction of a restricted longitude range of enhanced interaction between Io and Jupiter's ionosphere, the longitudinal asymmetries seen both in ground-based observations of sulfur emissions from the Io torus and in Voyager observations of Jovian auroral emissions are found to agree well with the predicted asymmetries.

Vasyliunas, V. M.↗

NASA NTRS1982

Io's hot plasma torus - A synoptic view from Voyager

A study of the morphology of Io's hot plasma torus has encompassed hundreds of Voyager UVS measurements of torus intensity. The long-term average state of the torus can be characterized by an axial asymmetry in the brightness of the prominent S III 685-A feature manifested as an enhancement in brightness whose peak is fixed near 1900 local time. No long-term correlation of brightness with magnetic longitude is present. On time scales of a few Jupiter rotations, the torus can differ markedly from its average axial asymmetry, and its brightness is correlated with magnetic longitude for short times.

Sandel, B. R.↗

NASA NTRS1981

Seasonal variations of total ozone revealed by the Nimbus-4 BUV data set

Backscattered ultraviolet (BUV) data from the Nimbus-4 spacecraft for the period 1970-1977 have been processed to a refined level. The seasonal and interannual variations of total ozone are examined on a global scale, using daily zonal means of 10 deg latitude bands and a time-latitude cross section. A harmonic analysis was performed on the daily zonal means and the amplitude, days of peak ozone values, and percentage of variance were computed for the annual, semiannual and higer harmonics for several years and each year. A clear quasi-biennial oscillation (QBO) was revealed from the tropics to midlatitudes after removing the mean annual wave. Asymmetries in the annual wave in the two hemispheres found earlier for the period 1970-1972 persist through the entire observation period. Interannual variations appear to be the result of the QBO of ozone from low to midlatitudes. Asymmetries in the QBO amplitude phase, and period were also detected in the two hemispheres.

Hilsenrath, E.↗

NASA NTRS1983

The peculiar radio galaxy 3C 433

Radio, optical and X-ray observations are presented of the peculiar radio galaxy 3C 433, a Seyfert 2 object with luminosity an order of magnitude greater than that expected from its complex, shell-type morphology. Observations conducted at 6 and 12 cm with the VLA and at 21 cm with the Westerbork telescope show a striking asymmetry between the northern and southern radio emissions, and an overall X-shaped morphology. Optical observations using the Video Camera and High Gain Video Spectrometer on the 4-m telescope and the Intensified Image Dissector Scanner on the 2.1-m telescope at Kitt Peak confirm the identification of the source with a pair of bright galaxies. Observations in the X-ray from the Einstein Observatory IPC reveal an unresolved source at the position of 3C 433, as well as two serendipitous X-ray sources. The observations may be used to explain the overall structure of the source either in terms of tidal torquing or precessing models of double galaxies; however, it is argued that the tidal torquing model requires fewer assumptions to account for the brightness asymmetry.

Van Breugel, W.↗