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NASA NTRS1984

Windblown sand on Venus - Preliminary results of laboratory simulations

Small particles and winds of sufficient strength to move them have been detected from Venera and Pioneer-Venus data and suggest the existence of aeolian processes on Venus. The Venus wind tunnel (VWT) was fabricated in order to investigate the behavior of windblown particles in a simulated Venusian environment. Preliminary results show that sand-size material is readily entrained at the wind speeds detected on Venus and that saltating grains achieve velocities closely matching those of the wind. Measurements of saltation threshold and particle flux for various particle sizes have been compared with theoretical models which were developed by extrapolation of findings from Martian and terrestrial simulations. Results are in general agreement with theory, although certain discrepancies are apparent which may be attributed to experimental and/or theoretical-modeling procedures. Present findings enable a better understanding of Venusian surface processes and suggest that aeolian processes are important in the geological evolution of Venus.

Greeley, R.↗

NASA NTRS1984

The chemical durability of tektites - A laboratory study and correlation with long-term corrosion behavior

Leach tests carried out on tektite specimens (indochinites and australites) under high-dilution conditions show a common behavior characterized by low leach rates (0.00018 g/sq m per d, or 7.2 x 10 to the -12th m/d at 23 C) and an activation energy of (79,600 + or - 700 J/mol). The extent of selective leaching is very small, of the order of 10 to the -8th m. Extrapolation of test results over the lifetime of the tektites gives an excellent agreement with field observations on the extent of corrosion, and this is an important step in establishing the validity of laboratory tests as a basis for the development of models and predictions concerning long-term durabilities at least in the limiting case of high dilution or rapid flow. The results are also shown to be in agreement with various previous observations on the corrosion resistance of tektites. The chemical durability of tektites is observed to be consistent with their composition, highlighting requirements of high corrosion resistance in glasses; these requirements include a silica content in excess of 67 mol percent, an extremely low water content, and an alkali content which is low both absolutely and relative to the di- and poly-valent metal oxide levels. It is shown that artificial glasses which fulfil these criteria are no less corrosion-resistant than the corresponding natural glasses. These conclusions have bearing on the development, as well as on the evaluation, of glasses intended for very long service, such as radioactive waste vitrification media.

Barkatt, A.↗

NASA NTRS1984

Discovery of a shell around Alpha Lyrae

IRAS observations of Alpha Lyrae reveal a large infrared excess beyond 12 microns. The excess over an extrapolation of a 10,000 K blackbody is a factor of 1.3 at 25 microns, 7 at 60 microns, and 16 at 100 microns. The source of 60 microns emission has a diameter of about 20 arcsec. This is the first detection of a large infrared excess from a main-sequence star without significant mass loss. The most likely origin of the excess is thermal radiation from solid particles more than a millimeter in radius, located approximately 85 AU from Alpha Lyr and heated by the star to an equilibrium temperature of 85 K. These results provide the first direct evidence outside of the solar system for the growth of large particles from the residual of the prenatal cloud of gas and dust.

Aumann, H. H.↗

NASA NTRS1983

A program in global biology

NASA's Global Biology Research Program and its goals for greater understanding of planetary biological processes are discussed. Consideration is given to assessing major pathways and rates of exchange of elements such as carbon and nitrogen, extrapolating local rates of anaerobic activities, determining exchange rates of ocean nutrients, and developing models for the global cycles of carbon, nitrogen, sulfur, and phosphorus. Satellites and sensors operating today are covered: the Nimbus, NOAA, and Landsat series. Block diagrams of the software and hardware for a typical ground data processing and analysis system are provided. Samples of the surface cover data achieved with the Advanced Very High Resolution Radiometer, the Multispectral Scanner, and the Thematic Mapper are presented, as well as a productive capacity model for coastal wetlands. Finally, attention is given to future goals, their engineering requirements, and the necessary data analysis system.

Mooneyhan, D. W.↗

NASA NTRS1984

Two multifrequency observations of 3C 371

Observations of 3C371 made at frequencies from the radio to the ultraviolet and coordinated during two short time intervals separated by 3 months are presented. Also presented are 1 keV X-ray flux densities measured at a different time. The multifrequency measurements indicate spectral steepening at visual wavelengths, and that an extrapolation of the ultraviolet continuum falls below the X-ray data. The infrared through X-ray data is explained as relativistically beamed synchrotron self-Compton emission, and source parameters are derived for two possible models. The present ultraviolet spectra both show strong Lyman-alpha emission at the same redshift as weak optical emission lines reported previously. Production of these lines by recombination of gas, after its ionization by the ultraviolet to X-ray continuum radiation, is favored as an explanation. C IV and N V absorption lines are tentatively identified in one ultraviolet spectrum, which, if real, suggest the presence of a hot (about 300,000 K) gaseous halo in 3C 371.

Puschell, J. J.↗

NASA NTRS1984

Electron-impact-excitation cross sections for electronic levels in neon for incident energies between 25 and 100 eV

Absolute differential cross sections (DCS's) for electron-impact excitation of the lowest forty electronic levels in atomic neon have been determined for incident electron energies of 30 and 50 eV, for the four lowest levels at 25 eV, and two levels at 100 eV. The cross sections for these forty electronic levels are grouped into fifteen features, six of which represent excitation to resolved single electronic levels and the remaining nine which contain the unresolved contributions from two or more electronic levels. These DCS's were extrapolated to 0 deg and 180 deg and integrated to yield absolute integral cross sections as a function of incident electron energy. The results are compared to other experimental and theoretical results.

NASA NTRS1984

Far-infrared observations of a star-forming region in the Corona Australis dark cloud

A high-resolution far-IR (40-250-micron) survey of a 0.9-sq-deg section of the core region of the Corona Australis dark cloud (containing very young stellar objects such as T Tauri stars, Herbig Ae and Be stars, Herbig-Haro objects, and compact H II regions) is presented. Two extended far-IR sources were found, one associated with the Herbig emission-line star R CrA and the other with the irregular emission-line variable star TY CrA. The two sources have substantially more far-IR radiation than could be expected from a blackbody extrapolation of their near-IR fluxes. The total luminosities of these sources are 145 and 58 solar luminosity, respectively, implying that the embedded objects are of intermediate or low mass. The infrared observations of the sources associated with R CrA and TY CrA are consistent with models of the evolution of protostellar envelopes of intermediate mass. However, the TY CrA source appears to have passed the evolutionary stage of expelling most of the hot dust near the central source, yielding an age of about 1 Myr.

Cruz-Gonzalez, I.↗

NASA NTRS1984

The influence of neutral winds on He(+) distributions in the equatorial ionospshere

The effects of F-region neutral winds on the distribution of He(+) in the equatorial ionosphere have been examined using a theoretical model and an observational data set. It is shown by the model that components of neutral wind in the magnetic meridian up to only 50 m/s can produce He(+) gradients in the northern and southern sectors of a flux tube that differ by more than 80 percent. This is associated with interhemisphere transport velocities of He(+) as large as 15 m/s at 800 km. A substantial latitude gradient in the He(+) distribution across the dip equator also results from the redistribution of He(+). The changes in the He(+) concentration at the dip equator and the latitude distribution of H(+) in response to different neutral wind components is determined from the model and used to construct longitude distributions of He(+) to compare with observations made at equinox. Good agreement between the calculations and observations is obtained both at the geographic and geomagnetic equators using the relationship between neutral winds, interhemispheric transport velocity and He(+) concentration derived from the model. If these relationships can be extrapolated to accommodate the different conditions expected during solstice, the He(+) distributions expected during this season can also be discussed.

Murphy, J. A.↗

NASA NTRS1984

Infrared observations of the 3C 273 jet

The first infrared (1.25 micron and 2.2 micron) observations of the jet in the quasar 3C 273 are reported. The present data, when combined with previous observations, show that the optical-infrared spectrum is a power law with index approximately equal to that in the radio, but lies a factor of 5 below the extrapolation from the radio. Various emission mechanisms for the optical-infrared jet are discussed, and it is concluded that synchrotron radiation is the most likely. However, the spectra of different parts of the jet are not the same; the radio-infrared index of the inner half is significantly larger (i.e., softer spectrum) than that of the outer half of the jet.

Becklin, E. E.↗

NASA NTRS1984

Relationships between a potential field-source surface model of the coronal magnetic field and properties of the solar wind at 1 AU

A comparison is made between the properties at the source surface of a potential field model of the solar corona and solar wind properties observed with ISEE 3 at 1 AU and extrapolated back to the sun. This is done for three consecutive Carrington rotations in the summer of 1979. The already known properties of a velocity minimum at the interplanetary current sheet and a tendency for the average velocity to increase with longitudinal distance from the current sheet are recovered. A better correlation between source surface properties and velocity is demonstrated by using the field strength on the source surface rather than longitudinal distance from the current sheet. Applying a simple algorithm to distinguish between transient and corotating interplanetary variations substantially increases the correlation. However, given a reasonable estimate of the number of degrees of freedom for the sample, only the correlation between source surface field strength and flow speed after the transients have been eliminated is statistically significant at the 1 percent level.

Suess, S. T.↗

NASA NTRS1982

Numerical analysis of Weyl's method for integrating boundary layer equations

A fast method for accurate numerical integration of Blasius equation is proposed. It is based on the limit interchange in Weyl's fixed point method formulated as an iterated limit process. Each inner limit represents convergence to a discrete solution. It is shown that the error in a discrete solution admits asymptotic expansion in even powers of step size. An extrapolation process is set up to operate on a sequence of discrete solutions to reach the outer limit. Finally, this method is extended to related boundary layer equations.

Najfeld, I.↗

NASA NTRS1984

Absolute measurement of the extreme UV solar flux

A windowless rare-gas ionization chamber has been developed to measure the absolute value of the solar extreme UV flux in the 50-575-A region. Successful results were obtained on a solar-pointing sounding rocket. The ionization chamber, operated in total absorption, is an inherently stable absolute detector of ionizing UV radiation and was designed to be independent of effects from secondary ionization and gas effusion. The net error of the measurement is + or - 7.3 percent, which is primarily due to residual outgassing in the instrument, other errors such as multiple ionization, photoelectron collection, and extrapolation to the zero atmospheric optical depth being small in comparison. For the day of the flight, Aug. 10, 1982, the solar irradiance (50-575 A), normalized to unit solar distance, was found to be 5.71 + or - 0.42 x 10 to the 10th photons per sq cm sec.

Carlson, R. W.↗

NASA NTRS1984

The lightcurve and phase relation of the asteroid 133 Cyrene

The asteroid 133 Cyrene was observed photometrically on 17 nights during oppositions in 1979 and 1980. The synodic period of rotation was found to be 12.708 + or - 0.001 h with an amplitude of 0.30 m during both oppositions. At large phase angles, the phase relation is quite ordinary (0.025 mag/degree); however, the low phase angle observations reveal a dramatic opposition brightening, about 0.2 mag/degree near zero phase angle. The absolute magnitude, V(1,0), extrapolated with the above linear phase coefficient, is 8.40. The following color indices were also measured: B-V = 0.90, U-B = 0.51.

Harris, A. W.↗

NASA NTRS1984

Detection of a sub-milliarcsecond radio component in the RS CVn system HR 1099

The RS CVn system HR 1099 was observed with a five station VLBI array at a frequency of 8.4 GHz during a strong radio outburst of approximately 400 mJy. The data are consistent with a circular Gaussian source of 0.8 + or - 0.12 milli-arcsec (FWHM), corresponding to a linear size of 4 + or - 0.6 x 10 to the 11th cm. This is comparable to the distance between the surfaces of the two stars, or to 75 percent of the diameter of the chromospherically active K star. Extrapolation of published photometric data shows that the starspot formation of HR 1099 was facing toward the observers at the times of observations. The high equivalent brightness temperature, approximately 10 billion K, is consistent with gyrosynchrotron emission from a power-law energy distribution of electrons in a magnetic field of strength about 30 gauss.

Mutel, R. L.↗

NASA NTRS1984

The National Transonic Facility - A research perspective

The capabilities of the National Transonic Facility (NTF) at NASA-Langley and its impact on aerodynamics investigations are surveyed. The fan-driven, closed-circuit transonic wind tunnel has an 8.2 sq ft slotted test section. Trials can be run from Mach 0.2-1.2, pressures of 1-8.9 atm, and temperatures of -320 to 150 F using nitrogen as the working gas. Instrumentation has been developed for monitoring force, pressure, attitude, deformation, temperature, skin friction, flow transition, and flow velocity as well as visualizing flows around the models. Pressures of 15-130 psi are available, as are Re up to 120 million at Mach 1. Correlations are being made with flight data from the Shuttle, 767, X-29A, and TACT aircraft for real-world extrapolations. The NTF, when combined with computational fluid dynamics techniques, will permit testing of aerodynamically sophisticated shapes while narrowing the design goals for each model during basic research in fluid mechanics, transport, and aerodynamic phenomena.

Campbell, J. F.↗

NASA NTRS1984

Coordination of Fe, Ga and Ge in high pressure glasses by Moessbauer, Raman and X-ray absorption spectroscopy, and geological implications

For some time, it has been recognized that the structure of silicate liquids has a great bearing on such magma properties as viscosity, diffusivity, and thermal expansion and on the extrapolation of thermodynamic quantities outside of the experimentally measurable range. In this connection it is vital to know if pressure imposes changes in melt structure similar to the pressure-induced reconstructive transformations in crystals. In the present study on 1 bar and high pressure glasses, an investigation is conducted regarding the coordination of Fe(3+) in Fe silicate glasses by Moessbauer spectroscopy. Raman spectroscopy is employed to explore the coordinations of Ge(4+) in GeO2 glasses and of Ga(3+) in NaGa silicate glasses, while the coordination of Ga(3+) in NaGaSiO4 glasses is studied with the aid of methods of X-ray absorption spectroscopy.

Fleet, M. E.↗

NASA NTRS1986

Three-Dimensional Turbomachine-Blade-Row Analysis Code

Computer program (MERNEW3D) developed that prepares bulk of input data set required for Denton three-dimensional inviscid turbomachine-blade-row analysis code. Denton input generated from minimum of geometry and flow-variable information by using cubic spline curve fits for interpolation and extrapolation. Curve-fitting procedures taken from previously developed and widely used NASA computer program (MERIDL), which performs meridional streamsurface analysis.

Glassman, A. J.↗

NASA NTRS1986

Determining the Temperature Profile in a Cylindrical Sample

Power-series solution extrapolates from axial temperature profile. Thermal profile in homogeneous axisymmetric body determined throughout body if axial temperature profile known at any radius. New theory developed as aid in research on growth of mercury cadmium telluride for infrared detectors. In particular, applicable to Bridgman-Stockbarger growth, in which round cylindrical ampoule of molten ternary semiconductor is solidified directionally, from one end to other.

Clayton, J. C.↗