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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

On an apparent discrepancy between pulsation and evolution masses for Cepheids.

Results of new theoretical pulsation calculations in the linear nonadiabatic approximation are presented. Emphasis is placed on the location of blue edges (the borderline between stability and instability against pulsation) for pulsation in the fundamental mode. The results of evolutionary calculations for the helium-burning phase are introduced, and a theoretical period-luminosity relationship is obtained for Cepheids that lie on the blue edge of the instability strip. The theoretical results are then compared with current estimates of the intrinsic bulk properties of 13 Cepheids, and it is shown how theoretical and observational properties may be reconciled without assuming significant mass loss or the necessity of major adjustments in the theory. Finally, it is argued that the required revision in Cepheid luminosities lies within the observational uncertainties.

Iben, I., Jr.↗
NASA NTRS1972

Search for a Venus halo effect during 1970.

Photometric observations of Venus during 1970 inferior conjunction, in contrast to observations made during the 1969 inferior conjunction, show no evidence of a Venus halo effect at 158 phase angle. The upper limit to brightening is about 0.005 mag but can still be reconciled with earlier results. Because of the importance of the question of H2O-ice in the Venus clouds, further observations are encouraged to remove the marginality of most observations to date.

Ward, D.↗
NASA NTRS1972

Lunar composition as a clue to the early history of the solar system.

The apparent conflict of the low iron content of the moon with the hypothesis of lunar capture is shown to be reconcilable if, in the inner solar system, iron condensations are assumed to conglomerate into planetary cores before the silicates condense to form a number of iron-poor moons. In the outer solar system, there would be no such fractionation, and, in the asteroid belt, the situation should be intermediate and quite complex. A crucial parameter is the ratio of coalescence time to cooling time, which depends on the density of the solar nebula. Also of importance are nonuniform cooling and condensation, as well as the outward transport of volatiles and their dissipation from the solar system. The model can explain also other features of the planets and asteroids.

Singer, S. F.↗
NASA NTRS1972

Radon-222 in the lunar atmosphere.

In 1969 Yeh and Van Allen set upper limits for the alpha-particle emissivity of the moon. The equilibrium surface activity reported by Turkevich et al. (1970) for each alpha active Rn-222 daughter at Mare Tranquillitatis cannot be reconciled with existing diffusion theory. The data, therefore, suggest that earth based diffusion constants are not applicable in the vacuum conditions of the moon, or that there are substantial variations in the uranium content of the moon over relatively small distances.

Brodzinski, R. L.↗
NASA NTRS1972

Corotation of an intermittent solar wind source

The measured electron content of the solar wind in mid-1970 exhibited a region of relatively high electron density that reappeared at intervals of about 27.8 days. It is shown that the repeating event cannot be reconciled with the concept of a long-enduring steady flow, even though the recurrence period is close to the rotation period of the sun. This evidence of transients is inferred from the short duration of each appearance of the interval of higher density; each should last for roughly one corotation interval if it is caused by a steady stream. The radio path was approximately 0.8 AU long, and the corotation interval exceeded 3 days. Other aspects of the content data patterns support the view that such transient events are common in the solar wind. The mid-1970 repeating event is an unusually good example of the intermittent character of flow regions in the solar wind that fluctuate on a time scale of days but endure as identifiable regions for many months. A sputtering corotating source of thin solar plasma streams could explain this series of events; it could also be explained in terms of a stream that is steady in density and speed but undulating north-south so that it passes into and out of the 0.8 AU radio path in a matter of a day or less.

Croft, T. A.↗
NASA NTRS1973

Lunar evolution - How well do we know it now.

The currently known astronomical, chemical, and magnetic data are not uniquely indicative of an extensively and globally molten moon. It is argued that an accretional layering occurred in the moon, but at temperatures below solidus. The excess mass in the near side of the moon compatible with a 2-km displacement in the center of mass relative to the center of figure and the moment of inertia data is considered to be due to Fe-FeS liquid formation and inhomogeneous segregation. These Fe-FeS bodies, termed 'fescons,' are shown to be capable of accounting for the presently available magnetization data, by acting as small regenerative dynamos with a time-stability less than that of the terrestrial equivalent. The chemical characteristics of the highly differentiated materials, are considered to be due to small-scale localized melting caused by collisional events, from sources in which accessory phases play a significant role. Mare basalts are considered to be melts in the overlying material produced at a later time by K-40 radioactivity in the fescons. Some consequences of the present hypothesis are suggested. It is concluded that these and other characteristics of the lunar materials are reconcilable with a 'cold' moon, such as discussed by Urey over the past two decades.

Murthy, V. R.↗
NASA NTRS1973

Effects of atmospheric moisture on rock resistivity.

This study examines the changes in resistivity of rock samples as induced by atmospheric moisture. Experiments were performed on samples of hematitic sandstone, pyrite, and galena. The sandstone underwent a change in resistivity of four orders of magnitude when it was measured in a vacuum of 500 ntorr and in air of 37% relative humidity. Pyrite and galena showed no variations in resistivity when they were measured under the same conditions. These results, plus others obtained elsewhere, indicate that rocks of the resistive type are affected in their electrical properties by atmospheric moisture, whereas rocks of the conductive type are not. The experimental evidence obtained is difficult to reconcile with a model of aqueous electrolytic conduction on the sample surface. It is instead suggested that adsorbed water molecules alter the surface resistivity in a manner similar to that observed in semiconductors and insulators.

Alvarez, R.↗
NASA NTRS1973

Electrostatic Hellmann-Feynman theorem applied to long-range interatomic forces - The hydrogen molecule.

The use of the electrostatic Hellmann-Feynman theorem for the calculation of the leading term in the 1/R expansion of the force of interaction between two well-separated hydrogen atoms is discussed. Previous work has suggested that whereas this term is determined wholly by the first-order wavefunction when calculated by perturbation theory, the use of the Hellmann-Feynman theorem apparently requires the wavefunction through second order. It is shown how the two results may be reconciled and that the Hellmann-Feynman theorem may be reformulated in such a way that only the first-order wavefunction is required.

Steiner, E.↗
NASA NTRS1973

Structure in the nonlinear saturation spectrum of parametric instabilities.

The nonlinear saturation spectrum of the decay instability is obtained in the limit of small spontaneous emission, for comparable ion and electron temperatures, from numerical solutions of a kinetic equation based on an accurate expression for the nonlinearity. The spectral energy occupies several pairs of isolated saucer-shaped regions in wave-vector space. The regions increase in thickness, angular diameter, and number as the pump power is increased. The theory thus predicts the generation of waves propagating in directions which can differ substantially from the direction of the pump field. Ionospheric observations confirm this prediction; they were difficult to reconcile with the predictions of previous theories based on an approximated expression for the nonlinearity. The present work also corrects the results of previous one-dimensional theories that used an accurate expression for the nonlinearity and predicted 'spectral lines' in the limit of vanishing spontaneous emission.

Fejer, J. A.↗
NASA NTRS1972

Jupiter's great red spot revisited

On the original Taylor column theory of Jupiter's Great Red Spot, the fixed latitude of the Spot is taken to imply that the Taylor column in Jupiter's atmosphere is associated with a disturbance such as a topographic feature of the surface Q underlying the atmosphere. The alternative suggestion that the Taylor column is produced by a solid raft floating at depth in the atmosphere is somewhat easier to reconcile with the approximately 10s difference between the respective rotation periods P sub S and P sub R of the Red Spot and of the radio sources, but it does not account so readily for the fixed latitude of the Spot unless it can be shown that the raft is in stable equilibrium under the north-south components of the dynamical forces, including wind effects, acting upon it. A slight wavering of the upper end of the Taylor column relative to the lower end could account at least in part for the most rapid variations in P sub S, but the slow large-amplitude variations in P sub S must reflect changes in the longitudinal motion of either the surface Q or of the raft. By generalizing the Proudman-Taylor theorem to the case of a non-homogeneous fluid it is shown that the Taylor column theory does not imply very special and therefore unlikely horizontal and vertical temperature variations in Jupiter's atmosphere, thus refuting a widely-held belief to the contrary.

Hide, R.↗
NASA NTRS1973

Energetic electrons in the midlatitude nighttime E region

Nike Apache 14.439 was launched from Wallops Island at 0003 EST on 1 November 1972, a very disturbed night (K sub P = 8). A Geiger counter in the payload detected electrons ( keV) with a maximum flux of 1086 + or -261/sq cm/sec/ster. The height-averaged ionization rate in the upper E region is calculated from the measured electron density profile and has a value of 35 1/cu/cm/sec. The ionization rate can be reconciled with the observed flux of electrons ( 70 2 keV) if the spectrum ( keV) is of the form J ( E) = J sub O exp(-E/E sub O) with E sub O equal to 8.3 keV. The ionization rate on this and other nights is found to be strongly dependent on geomagnetic activity. It is suggested that energetic electrons are the principal source of ionization at midlatitudes in the upper E region near midnight, even under rather quiet geomagnetic conditions.

Smith, L. G.↗
NASA NTRS1973

The size of NGC 1068 at 10 microns

The data presented show that a majority of the 10-micron emission from NGC 1068 comes from an area with a diameter of about 60 pc. The measurements described were made at 10 microns on two nights at the 200-inch Hale telescope. The data obtained agree with the results obtained by Stein et al. (1973). An approach to reconcile the new data with the variability observed by Rieke and Low (1972) is also discussed.

Becklin, E. E.↗
NASA NTRS1974

The Regulus occultation light curve and the real atmosphere of Venus

An inversion of the light curve observed during the July 7, 1959, occultation of Regulus by Venus leads to the conclusion that the light curve cannot be reconciled with models of the Venus atmosphere based on spacecraft observations. The event occurred in daylight and, under the subsequently difficult observation conditions, it seems likely that the Regulus occultation light curve is marred by a systematic errors in spite of the competence of the observers involved.

Veverka, J.↗
NASA NTRS1974

Magnetopause reconnection rate

Discussion of certain aspects of the magnetic field reconnection process at the magnetopause. It is argued that the upper limits on reconnection derived by Petschek (1964), on the one hand, and Yeh and Axford (1970) and Sonnerup (1970), on the other, may be reconciled, at least qualitatively. Further, the possibility that magnetopause reconnection proceeds at this upper limit remains a real one. It is demonstrated that under the same assumptions as those used by Petschek (1964, 1966) the theoretical upper limit on the electric field component parallel to the X type magnetic null line is proportional to sin squared (theta/2) when the magnetic fields on the two sides of the magnetopause have equal magnitude. Finally, it is shown that when the magnetic field outside the magnetopause is weaker than the field inside that surface, reconnection may cease altogether for cos theta greater than the ratio of the outside field to the inside one.

Sonnerup, B. U. O.↗
NASA NTRS1974

Cross-flow effects on the boundary layer in a plane of symmetry

The validity of 'effective cone analysis' in estimating the boundary-layer properties of bodies in hypersonic flow is discussed. Simple formulas are derived for noncircular cones at angles of attack and are used to show that effective cone analysis only accounts for the increase in the local edge Reynolds number due to the angle of attack. A correction factor depending on the cross flow produced by the transverse curvature of the body and on the angle of attack is shown to reconcile the effective cone approach with the predictions of exact theory.

Agnone, A.↗
NASA NTRS1974

Far-infrared emission from H II regions. II - Multicolor photometry of selected sources and 2.2 min resolution maps of M42 and NGC 2024

Medium- and broad-bandwidth photometric measurements have been made of seven compact H II regions at wavelengths between 30 and 650 microns. The results are consistent with the hypothesis that the far-infrared flux is continuum radiation from dust grains. Color temperatures range from 33 to 85 K. For most of the sources, the infrared flux is low enough so that the dust could conceivably be mixed with the ionized gas. In at least one case, however, the far-infrared spectrum and luminosity of the source cannot be reconciled with reasonable grain models unless the far-infrared flux comes from a shell surrounding the H II region. M42 (Orion) and NGC 2024 (Orion B) have been mapped at 90 microns with a resolution (half-power beam diameter) of 2.2 min. Although the peak far-infrared brightness in M42 occurs at the position of the Kleinmann-Low infrared nebula, most of the flux originates in a more extended (about 6 x 8 min) source. The energy for the diffuse component could be supplied by the stars in the Trapezium cluster. However, the single early-type star visible in NGC 2024 is not luminous enough to account for either the infrared flux or the observed free-free flux.

Harper, D. A.↗
NASA NTRS1974

Orbit-spectrum sharing between the fixed-satellite and broadcasting-satellite services with applications to 12 GHz domestic systems

A systematic, tutorial analysis of the general problem of orbit-spectrum sharing among inhomogeneous satellite system is presented. Emphasis is placed on extrapolating and applying the available data on rain attenuation and on reconciling differences in the results of various measurements of the subjective effects of interference on television picture quality. An analytic method is presented for determining the approximate values of the intersatellite spacings required to keep mutual interference levels within prescribed limits when many dissimilar satellites share the orbit. A computer model was developed for assessing the interference compatibility of arbitrary configurations of large numbers of geostationary satellite systems. It is concluded that the band from 11.7 c GHz can be shared effectively by broadcasting-satellite and fixed-satellite systems. Recommendations for future study are included.

Reinhart, E. E.↗
NASA NTRS1974

Interaction of metagalactic X-UV radiation with galactic hydrogen

Calculations show that the existence of a metagalactic X-UV flux of the intensity required to explain the high-latitude soft X-ray observations, plus a reasonable extrapolation toward lower energies, is consistent with the existence of neutral hydrogen in galaxies. Shielding by H II slabs can be effective both in the solar neighborhood and in the peripheries of galaxies out to a radius of 30 to 40 kpc. At earlier cosmological epochs shielding is less efficient. The soft X-ray spectrum as observed by Yentis et al. (1972) is difficult to reconcile with a purely extragalactic origin for the flux. A local source of ionization also may be necessary to explain the pulsar dispersion data.

Hill, J. K.↗