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At least 631 records · Page 35

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NASA NTRS1976

A fast transient source of hard X-rays at high galactic latitude

An extremely short-lived transient X-ray source has been detected with the SAS-3 satellite at a high galactic latitude (about -51 deg). The source, designated MX 2346-65, had a duration of between 45 s and 2200 s as well as a very hard spectrum. This source had not been detected in previous sky surveys and was not seen again by SAS-3 in 7 days of further periodic observations. Possible explanations of this type of event are discussed.

Rappaport, S.↗

NASA NTRS1976

Mutual phenomena of the Galilean satellites in 1973. III - Final results from 91 light curves

This paper presents an analysis of photoelectric light curves of 91 mutual eclipses and occultations of the Galilean satellites that occurred from June to December 1973. From the deepest curves, radii and standard errors are deduced for J2, J3, and J4. It is shown that the substantial differences between the depths and midtimes observed and those predicted by Sampson's theory can be used in a clear and definite way to revise the orbital constants of that theory. The present analysis, which reduces all the data provided by these mutual events in one body, diminishes the latitude and longitude residuals of the unrevised theory by as much as a factor of about 10. The resulting overall consistency and the demonstrated inadequacy of an explanation based solely on surface-brightness variations argue that these corrections do represent the dominant effects required to account for the light curves. In order that these mutual events can be used with other astrometric data, the separations between a satellite pair at midevent are given. A small systematic (with solar phase angle) and unexplained difference in the longitude corrections is found for Io and Europa as obtained from nearly simultaneous pairs of occultations and eclipses.

Aksnes, K.↗

NASA NTRS1976

Variations in the ultraviolet Mg II lines of beta Persei

Copernicus satellite observations have been used to study changes in the Mg II lines in the neighborhood of 2800 A in Algol during eclipse. The resonance lines near 2800 A show doubling near the bottom of primary eclipse. A possible explanation is that emission from component B fills the line centers; the absolute magnitude thus derived for component B agrees with other values in the literature.

Chen, K.-Y.↗

NASA NTRS1976

Pressure transition of AlP to a conductive phase

A direct simultaneous electric resistance method of comparison with ZnS and GaP is used to show that AlP becomes conductive at a pressure equal to or less than that of ZnS, which has been shown to transform at a pressure slightly less than that for ZnS and at a pressure considerably less than that for GaP. There are two possible explanations for this behavior: (1) the conductive phase of AlP observed is not the beta-tin phase, or (2) the theoretical predictions are in error.

Wanagel, J.↗

NASA NTRS1976

An analysis of the generation of subharmonics in aeroengine ducts and methods of their prevention

When the fans of aero-engine ducts go supersonic they often produce radiation at the subharmonics of blade passage frequency known as Multiple Pure Tones. It has been shown that the conventional explanation that these MPTs are created by the shock waves is inadequate. An alternative mechanism based on the concept of 'strong interaction' between the harmonics during resonance is proposed. Expression for the governing equation for such an interaction is derived. The results show an improved agreement with observed data. The analysis has also led to several practical suggestions for the suppression of noise.

Vaidya, P. G.↗

NASA NTRS1976

The strange case of the missing apocentric librators in the 3:2 resonance

From a comparison of the 2:1 and 3:2 resonances (in the asteroidal belt) two possible explanations to the absence of 3:2 apocentric librators are suggested. The first one is that such 3:2 resonant motion is dynamically unstable. The second interpretation requires the absence of near-circular orbits originally at 4 AU. The latter view, if correct, is inconsistent with cosmogonic models which predict the original orbits of the asteroids to be nearly circular.

Ip, W.-H.↗

NASA NTRS1976

Io sheath-accelerated electrons and ions

Recent results available from more rigorously analyzed Pioneer 10 data and the preliminary results of Pioneer 11 are used to further revise the satellite Io sheath acceleration model. The revised model is then employed to suggest an explanation for a number of earth-based and Pioneer 10 and 11 observations and to discuss other phenomena which might be detectable with future experiments. Particle acceleration near Io is discussed for the cases of negative sheath (face toward Jupiter) and positive sheath (face away from Jupiter). Io sputtering may explain the presence of atomic hydrogen and sodium in the vicinity of Io, and the accelerated particles may be important to the formation of the Io ionosphere. Directed fluxes of 100-keV electrons in the flux tube may lead to the decametric radio emissions, Jovian atmospheric heating, and optical and X ray emissions. Satellite modulation of decametric radio emissions is discussed.

Shawhan, S. D.↗

NASA NTRS1976

Re-examination of compliant wall experiments in air with water substrates

A possible alternative explanation is proposed for compliant wall drag reductions measured in previous investigations. Standing waves were observed to form on the surfaces of compliant wall models in air with water substrates as the freestream velocity was increased from 15 to 30 m/s. These waves resembled sine waves with half of the wave protruding over the upstream portion of the model and the other half being recessed over the downstream end of the model. These data coupled with results of recent drag reduction experiments suggest that standing waves could have caused a shift in the model center of gravity creating a bending moment that was interpreted as a reduction in the skin friction drag.

Hefner, J. N.↗

NASA NTRS1975

On the origin of molecular 'handedness' in living systems

Elementary particle effects (beta-decay) provide only a weakly handed radiation in the biologically effective energy ranges. Global magnetic effects coupled to sunlight are randomized by paleomagnetic reversals. A persistent terrestrial handed bias at possible local biopoetic sites offers a more promising explanation for the origin of the 'handedness' of the molecules found among living systems on earth. Magnetite in lava flows maintains a handed bias for surface catalysis through many magnetic reversals. Indirect evidence for the hypothesis that magnetite contaminated with sulfur is a possible biopoetic site (Granick, 1957) has been provided by the molecular structure of ferredoxin - a single strand of the 14 primordial amino acids wrapped around an FeS core. Lava flows have been suggested as biopoetic sites by Fox (1964), since their temperature and chemical composition might allow for the rapid synthesis of prebiotic compounds at the surface of the primitive earth. The additional fact that magetite in lava flows also provides a persistent handed site for surface catalysis offers a further argument for the experimental investigation of this specific biopoetic environment.

Noyes, H. P.↗

NASA NTRS1976

Secular resonance, solar spin down, and the orbit of Mercury

A mechanism is investigated which may provide an evolutionary explanation for the large mean eccentricity and inclination of Mercury. It is proposed that if the gravitational field of the rapidly rotating early sun had a larger second-degree harmonic, the decreasing value of this harmonic during the subsequent solar spindown would drive Mercury through two secular resonances with Venus, one involving a commensurability in the apsidal motion of the two planets and the other involving their nodal rates. An analysis is performed, showing that these resonances could increase both the inclination and eccentricity of Mercury at nearly the same time, that an initial solar rotational period of 5.5 hr or less would guarantee passage through the resonances, and that a spindown time of about 1 million years could have produced the observed inclination and eccentricity.

Ward, W. R.↗

NASA NTRS1976

Vortex shedding from a blunt trailing edge with equal and unequal external mean velocities

A flow-visualization study has shown that strong Karman vortices develop behind the blunt trailing edge of a plate when the free-stream velocities over both surfaces are equal and that the vortices tend to disappear when the surface velocities are unequal. This observation provides an explanation for the occurence and disappearance of certain discrete tones often found to be present in the noise spectra of coaxial jets. Both the vortex formation and the tones occur at a Strouhal number based on the lip thickness and the average of the external steady-state velocities of about 0.2. Results from theoretical calculations of the vortex formation, based on an inviscid incompressible analysis of the motion of point vortices, were in good agreement with the experimental observations.

Boldman, D. R.↗

NASA NTRS1976

The Skylab barium plasma injection experiments. II - Evidence for a double layer

Television observations of a barium-plasma flux tube extending from near 4500 km to near 10,000 km during a magnetic substorm and dawn-sector auroral display indicated several interesting anomalous events. Beyond 5500 km, there was a rapid increase in brightness accompanied by flux-tube splitting and diffusion, leaving behind a truncated single flux tube. From the orientation of the flux tube compared with theoretical field models, the presence of a substantial field-aligned current sheet is deduced. A suggested explanation of these phenomena is given in terms of a plasma potential double layer.

Wescott, E. M.↗

NASA NTRS1976

Traps in Al2O3 detected by tunneling

A structure, quite different from inelastic tunneling peaks, has been observed in electron-tunneling spectra of MOM junctions. A capacitance peak is associated with this structure, which is attributed to traps in the oxide at energies smaller than those previously reported. The C-V characteristics calculated using a single-energy trap model agree with experimental results; however, no satisfactory explanation has yet been found to account for the strong temperature dependence of the trap energy levels.

Skarlatos, Y.↗

NASA NTRS1976

Exoelectron emission from a clean, annealed magnesium single crystal during oxygen adsorption

Exoelectron emission has been observed from a clean, annealed Mg (0001) surface during oxygen and chlorine adsorption at pressures of 0.000065 N/sq m and lower. The studies were performed in an ultrahigh vacuum system. The crystals were cleaned by argon-ion bombardment and annealed at 300 C. Auger electron spectroscopy was used to verify surface cleanliness, and low-energy electron diffraction was used to verify that the surface was annealed. The emission was found to be dependent on oxygen arrival rate. Two peaks were observed in the electron emission with exposure. Evidence is presented that the formation of the second peak corresponds to oxidation of the Mg surface. The results verify that electron emission occurs from a strain-free surface simply upon adsorption of oxygen. A qualitative explanation for the mechanisms of emission in terms of chemical effects is presented.

Ferrante, J.↗

NASA NTRS1976

A technique for optimizing the design of power semiconductor devices

A technique is described that provides a basis for predicting whether any device design change will improve or degrade the unavoidable trade-off that must be made between the conduction loss and the turn-off speed of fast-switching high-power thyristors. The technique makes use of a previously reported method by which, for a given design, this trade-off was determined for a wide range of carrier lifetimes. It is shown that by extending this technique, one can predict how other design variables affect this trade-off. The results show that for relatively slow devices the design can be changed to decrease the current gains to improve the turn-off time without significantly degrading the losses. On the other hand, for devices having fast turn-off times design changes can be made to increase the current gain to decrease the losses without a proportionate increase in the turn-off time. Physical explanations for these results are proposed.

Schlegel, E. S.↗

NASA NTRS1976

A computational system for aerodynamic design and analysis of supersonic aircraft. Part 2: User's manual

An integrated system of computer programs was developed for the design and analysis of supersonic configurations. The system uses linearized theory methods for the calculation of surface pressures and supersonic area rule concepts in combination with linearized theory for calculation of aerodynamic force coefficients. Interactive graphics are optional at the user's request. This user's manual contains a description of the system, an explanation of its usage, the input definition, and example output.

Middleton, W. D.↗

NASA NTRS1976

Comment on 'Kp dependence on sectors, by I. B. McDiarmid and E. E. Budzinski

A suggestion by McDiarmid and Budzinski that an annual variation of geomagnetic activity can explain a sector polarity asymmetry is shown not to be necessary. The correct explanation is that the Kp-index exhibits systematic errors that enhance the UT variation during Toward polarity and decrease the UT variation during Away polarity.

Svalgaard, L.↗

NASA NTRS1976

Investigation of LANDSAT imagery on correlations between ore deposits and major shield structures in Finland

The author has identified the following significant results. Based on tests, it is obvious that practically all major LANDSAT winter linears found are geologically significant features. Most of them are chains of bogs, lakes, rivers, and cultivated areas covered by ice and/or snow, i.e., unforested linear topographic lows. They need no explanation other than that they are extensive fracture zones of the basement.

Tuominen, H. V.↗