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At least 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

The inconsistency between proton charge exchange and the observed ring current decay

The equatorial pitch-angle distributions of ring-current ions observed during a storm recovery phase at L values between 3 and 4 are compared with the pitch-angle distributions predicted by proton charge exchange with neutral hydrogen. Large disagreements are found, and three alternative explanations are explored. (1) A strong proton source acts to mask the effects of charge exchange. It is believed that the required strong continual source with a unique pitch-angle and energy dependence is unrealistic at these low L values. (2) Presently accepted neutral hydrogen density models have densities well over an order of magnitude too large for a storm recovery phase. No evidence is known to support the required large errors in the densities. (3) The ring current at particle energies not exceeding 50 keV was dominated by some ion species other than protons during the storm recovery phase. Such ions must have much longer lifetimes for charge exchange with hydrogen than do protons. This alternative is strongly favored, with He(+) being an attractive candidate.

Lyons, L. R.↗
NASA NTRS1976

Silicon monoxide in the 4 micron infrared spectrum of long-period variables

The first-overtone sequence of vibration-rotation transitions of the free radical silicon monoxide are shown to have extreme phase-dependent variations in the spectra of two M-type long-period variables, Omicron Ceti and R Leonis, and the mild S-type long-period variable, Chi Cygni. At maximum light, the SiO band heads are not detectable. Near minimum light, the band heads of (Si-25)O are detected in the 4-micron spectra of all three stars. The band heads of the terrestrially less abundant isotopic species, (Si-29)O and (Si-30)O, are detected in Chi Cygni. Possible explanations of the phase-dependent behavior are discussed, and the role of the stellar chromosphere is considered.

Hinkle, K. H.↗
NASA NTRS1976

Reassessment of roles of oxygen and ultraviolet light in Precambrian evolution

It is argued that the transition to an oxidizing atmosphere preceded the origin of eukaryotic cells, which in turn must have preceded the origin of metazoa. Moreover, the number of methods by which organisms can protect themselves from harmful UV radiation is sufficiently large to suggest that solar UV, even when the atmosphere was anaerobic, was not such as to control the distribution and diversification of life. An alternative explanation for the late and sudden appearance of metazoa in lower Cambrian sediments is proposed, which is related to the mechanisms by which fully mature eukaryotic cells probably originated. There was probably a protracted evolution of modern genetic systems based on mitosis in cells which acquired organelles (e.g., plastids and mitochondria) by hereditary endosymbiosis. The origin of hard parts underlies the Cambrian explosion of metazoans.

Margulis, L.↗
NASA NTRS1976

High-velocity interstellar clouds

Interstellar absorption line studies have revealed that rapidly moving clouds within one kiloparsec of the sun have considerably less depletion of heavy elements than in the low-velocity diffuse clouds, and their density is somewhat greater and their thickness smaller. Evaporation of interstellar grains, resulting from grain-grain collisions in interstellar shocks, may provide a possible explanation for the observations. Some problems involved in this mechanism are discussed, particularly the likely dominant importance of the interstellar magnetic field in confining the grains within the shocked layer and in accelerating them through the associated electric field, thus offsetting the frictional force of the gas.

Spitzer, L.↗
NASA NTRS1976

Model for thickness dependence of radiation charging in MOS structures

The model considers charge buildup in MOS structures due to hole trapping in the oxide and the creation of sheet charge at the silicon interface. The contribution of hole trapping causes the flatband voltage to increase with thickness in a manner in which square and cube dependences are limiting cases. Experimental measurements on samples covering a 200 - 1000 A range of oxide thickness are consistent with the model, using independently obtained values of hole-trapping parameters. An important finding of our experimental results is that a negative interface charge contribution due to surface states created during irradiation compensates most of the positive charge in the oxide at flatband. The tendency of the surface states to 'track' the positive charge buildup in the oxide, for all thicknesses, applies both in creation during irradiation and in annihilation during annealing. An explanation is proposed based on the common defect origin of hole traps and potential surface states.

Viswanathan, C. R.↗
NASA NTRS1977

The high energy astronomy observatories

The forthcoming NASA project of orbiting High Energy Astronomy Observatories (HEAO's) designed to probe the universe by tracing celestial radiations and particles is outlined. Solutions to engineering problems concerning HEAO's which are integrated, yet built to function independently are discussed, including the onboard digital processor, mirror assembly and the thermal shield. The principle of maximal efficiency with minimal cost and the potential capability of the project to provide explanations to black holes, pulsars and gamma-ray bursts are also stressed. The first satellite is scheduled for launch in April 1977.

Neighbors, A. K.↗
NASA NTRS1977

Preliminary findings of the Viking gas exchange experiment and a model for Martian surface chemistry

Earlier results reported from the Viking Lander-1 experiment are reexamined and interpreted in terms of a model of the Martian soil surface morphology and chemistry. Major events in the gas exchange experiment (GEX) first cycle are tabulated and data are presented on the sample processing and transport environments experienced by the soil samples. Oxygen and CO2 evolved from humidified Martian soil in GEX and slight changes in N2 present are investigated. A soil model involving iron oxide coating on silicate material is entertained to yield a mechanistic explanation of the experimental findings, and invocation of biotic processes is eschewed.

Oyama, V. I.↗
NASA NTRS1976

Coronal X-ray enhancements associated with H-alpha filament disappearances

The X-ray telescope experiment aboard the Skylab/ATM mission provided high-resolution soft X-ray images of the lower corona away from active regions, revealing frequent large-scale transient X-ray enhancements which could often be associated with the disappearance of H-alpha filaments. The X-ray emitting structures featured peak brightnesses similar to those of nonflaring active region structures, durations from 3 to 40 hours, shapes that in general outlined the preexisting H-alpha filaments to as large as 400,000 km, apparent expansion velocities of the order of tens of km/sec, and observed peak temperatures of the order of a few million degrees. One such event is described and analyzed in detail. Two explanations of the events are discussed: (1) excess cool material is present in the filament cavity, contributing to the X-ray enhancement, and (2) the enhancement is due to the compression of preexisting material by a changing magnetic field.

Webb, D. F.↗
NASA NTRS1976

The Jovian magnetosphere and magnetopause

The characteristics of the planet Jupiter's inner magnetosphere are examined, taking into account the Pioneer 10 and 11 magnetometer data. Data on the reliability of spherical harmonic expansions are presented in a table. The properties of the Jovian magnetosheath and magnetopause are described. Bow shock and magnetopause crossings were securely identified in plasma data and were usually identified in plasma data and were usually identifiable in the magnetometer data. Explanations for the large number of observed crossings are discussed. It is pointed out that in the case of the outer magnetosphere the observed field strength is nearly an order of magnitude larger than would be expected from Jupiter's dipole moment. The distinguishing characteristics of the magnetic field in the middle magnetosphere are also considered.

Davis, L., Jr.↗
NASA NTRS1976

The cause of the nova outburst

A large number of models are evolved for thermonuclear runaways in the hydrogen-rich envelopes of 1.00-solar-mass carbon-oxygen white dwarfs. Models characterized by enhanced CNO abundances satisfy the observations of the common nova outburst, ejecting from 10 to the 27th to 10 to the 29th power g at velocities of 200 to 2400 km/s and kinetic energies of 10 to the 44th to 10 to the 45th power erg. The theoretical light curves are similar to the observed light curves of common novae during the early stages of the outbursts. Explanations are given for the continuous ejection of mass which is observed for long times after the initial outbursts, for the relationship between maximum magnitude and the decline to minimum, and for the constant luminosity phase of the outburst and the oval shapes of the ejected nebulae. The analysis is extended to models with extreme enhancements of C-12 and to models which include infalling material in the evolution. The extreme C-12 studies result in outbursts which reach near-supernova proportions, while the accretion models result in light curves which resemble observed light curves quite closely. The accretion studies also demonstrate the need for enhanced abundances.

Starrfield, S.↗
NASA NTRS1977

Production of C-14 and neutrons in red giants

We have examined the effects of mixing various amounts of hydrogen-rich material into the intershell convective region of red giants undergoing helium shell flashes. We find that significant amounts of C-14 can be produced via the N-14(n, p)C-14 reaction. If substantial portions of this intershell region are mixed out into the envelopes of red giants, then C-14 may be detectable in evolved stars. We find a neutron flux many orders of magnitude above the flux required for the classical s-process, and thus an intermediate neutron process (i-process) may operate in evolved red giants. In all cases studied we find substantial enhancements of O-17. These mixing models offer a plausible explanation of the observations of enhanced O-17 in the carbon star IRC 10216. For certain physical conditions we find significant enhancements of N-15 in the intershell region.

Cowan, J. J.↗
NASA NTRS1977

Binary X-ray pulsars

Recent progress in the study of the pulse profiles of the nine known binary X-ray pulsars is discussed. The sources considered include SMC X-1, Her X-1, Cen X-3, A0535+26, GX1+4, 3U 0900-40, A1118-61, GX301-2, and 3U 0352+30. Sample X-ray profiles for these sources are provided, and general features exhibited by the profiles are identified. It is noted that the apparent existence of a gap in the period distribution of X-ray pulsars, in the range from about 5 to 100 sec, seems to be genuine within obvious statistical limitations and is probably not an observational effect. Two explanations for the production of X-ray pulsations are examined: one requiring a temporal modulation of mass accretion onto the surface of a neutron star and another requiring the funnelling of matter along magnetic field lines to the neutron star's surface.

Rappaport, S.↗
NASA NTRS1977

What's new on the moon. II

Apollo missions and returned lunar samples have provided new information about the moon, the earth, the sun, and the universe. Analyses show that all the planets were formed by the rapid accumulation of small bodies into larger ones about 4.6 billion years ago. The existence of simple molecules formed by reactions between the soil particles and atoms of carbon, oxygen, and nitrogen that have come from the sun, suggests that the basic ingredients for life are common in the universe. The ratio of hydrogen to helium in the solar wind reaching the moon is found to be 20 to 1, whereas the earth-based measurements show this ratio to be 10 to 1. Although the moon does not have any magnetic field at the present, the analyses revealed the existence of such a field three billion years ago. The understanding of the reasons for the disappearance of this field is vital for understanding planetary magnetic fields. The determination of the chemical composition of the whole moon, the explanation of the moon's observed asymmetry, and the understanding of the nature of moon's interior will have to be achieved by future, possibly unmanned, missions.

French, B. M.↗
NASA NTRS1977

Narrow radio recombination lines from ionization fronts

Model weak D-type ionization fronts are used to show that narrow H I radio recombination lines, such as those observed in the directions of several galactic H II regions, may be formed in the outermost layers of an ionization front bounding an H II region. Four model ionization fronts are computed with different values of magnetic-field strength, ionizing photon energy, and initial conditions. The recombination line strengths given by the models are compared with observed line strengths for the H II region NGC 2024, and the observed line profiles are found to be about twice as broad as the model profiles. Some likely explanations for the discrepancy are considered, particularly a variation in front velocity over the observing beam width (Stark broadening is ruled out).

Hill, J. K.↗
NASA NTRS1977

A high-resolution infrared spectrum of IRC +10216

The IR-emitting core and shell of IRC +10216 are investigated using a high-resolution spectrum covering the wavelength interval between 3 and 5 microns. Line identifications made or confirmed include those due to (C-12)(O-16), (C-13)(O-16), (C-12)(O-17), and (C-12)(O-18). A mean heliocentric velocity of about -32 km/s is obtained from the 42 least blended (C-12)O and (C-13)O lines, and the following isotopic abundance ratios are derived by comparing equivalent widths of the observed lines: C-12/C-13, C-12/C-14, O-16/O-17, and O-17/O-18. The structure of the expanding gas shell is examined, an explanation is offered for the lack of P Cygni profiles in the spectrum, and an unsuccessful search for other molecules is briefly discussed. It is concluded that a low C-12/C-13 ratio is not necessarily a signature of a carbon star.

Barnes, T. G.↗
NASA NTRS1977

New aspects of the cosmic-ray modulation in 1974-1975 near solar minimum

Residual cosmic-ray modulation at or near the solar minima of 1965 and 1972-75 is compared on the basis of ground-based and satellite observations of nonrelativistic proton and helium components as well as variations in the relativistic component. It is found that the nonrelativistic fluxes lagged behind the high-energy fluxes to form a hysteresis loop over the period from 1965 to 1973, that the 1975 proton fluxes were about 85% higher than the 1972 level and about 35% higher than the 1965 level, and that the 1975 helium fluxes were about 60% higher than in 1965. Some unique recovery events are discussed, and a time-lag effect dependent on magnetic rigidity is examined which was associated with dynamic changes in the heliosphere. A qualitative explanation is offered for the hysteresis effect.

Garcia-Munoz, M.↗
NASA NTRS1977

Superconductivity in sputtered CuMo6S8

The superconducting transition temperature and the superconducting upper critical fields for sputtered films of copper-containing ternary molybdenum chalcogenides (chevrel phases) were determined. The theory presented by Werthamer, Helfand, and Hohenberg (WHH) (1966) was used to make computer-generated plots of the superconducting upper critical field values versus the superconducting transition temperature values for various values of the Maki paramagnetic pair-breaking parameter and the spin-orbit scattering parameter. The interpretation of the graph suggests that the experimental data for at least one sample are above the maximum WHH theoretical limit in the lower temperature range. Possible explanations of this situation are discussed. In other calculations, a scaling law was found suitable for determining pinning force densities; this data was used to calculate critical current values. The relation between resistivity and temperature was studied.

Alterovitz, S.↗
NASA NTRS1977

Whole-disk polarization measurements of Uranus at visible wavelengths

The whole-disk polarization of Uranus was measured over two apparitons in blue and red light. The blue polarization becomes negative near the 0.5-deg phase, indicating non-Rayleigh scattering. The red polarization phase curve shows positive polarization smaller than suggested by Rayleigh scattering models. An explanation of these data is that the blue and red radiation is scattered by the CH4 haze layer that has been suggested to reside high in the atmosphere of Uranus. As expected, there is no whole-disk circular polarization, an observation which confirms other observations and theoretical predictions.

Michalsky, J. J.↗