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At least 721 records · Page 40
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NASA NTRS1977

Petrology of 78155 - An early, thermally metamorphosed polymict breccia

Polymict breccia 78155, which has a bulk composition of anorthositic norite, was brecciated and thermally metamorphosed before the final lunar bombardment of 4.0-3.9 eons. The constituents of the granoblastic matrix and the characteristics of the clasts and the mafic silicates are described. The clasts represent the lunar crust prior to 4.2 eons, the age of the granoblastic matrix. The persistence of uninverted pigeonite in matrix and clasts indicates that metamorphism was at a very high temperature and may have been terminated catastrophically. Evidence that the rock was further brecciated after thermal metamorphism is reported.

Bickel, C. E.↗
NASA NTRS1977

Remanent magnetization stratigraphy of lunar cores

Depth dependent fluctuations have been observed in the natural remanent magnetizations (NRM) of drive cores and drill strings from Apollo 16 and 17 missions. Partial demagnetization of unstable secondary magnetizations and identification of characteristic error signals from a core which is known to have been recently disturbed allow us to identify and isolate the stable NRM stratigraphy in double drive core 60010/60009 and drill strings 60002-60004. The observed magnetization fluctuations persist after normalization to take into account depth dependent variations in the carriers of stable NRM. We tentatively ascribe the stable NRM stratigraphy to instantaneous records of past magnetic fields at the lunar surface and suggest that the stable NRM stratigraphy technique could develop as a new relative time-stratigraphic tool, to be used with other physical measurements such as relative intensity of ferromagnetic resonance and charged particle track density to study the evolution of the lunar regolith.

Banerjee, S. K.↗
NASA NTRS1978

A historical overview of stall/spin characteristics of general aviation aircraft

Even today, stall/spin accidents involving general aviation aircraft account for more fatal and serious injuries than any other kind of accident. The classic stall/spin accident is one in which the pilot stalls the aircraft at too low an altitude to affect recovery. The primary attention in the investigation is given to aerodynamic considerations, although it is recognized that human factors and pilot training are also very important aspects of the total problem. A review of some 70 years of flight indicates that incorporation of the proper combination of aerodynamic parameters to provide good stall/spin avoidance has persistently remained an elusive goal for designers of general aviation aircraft.

Anderson, S. B.↗
NASA NTRS1978

Flying qualities of an aircraft with strong lateral-directional coupling

Flying qualities of aircraft with strong lateral-directional coupling may be unsatisfactory without command and stability augmentation. Although sensitivity to stability derivative variation may be decreased by such a flight control system (FCS), deficiencies associated with control derivative uncertainty may persist or worsen. This is especially true in systems with necessarily high gains, e.g., the Space Shuttle Entry FCS. Effects of stability/control derivative variations on the flying qualities of the Space Shuttle (with and without FCS) have been investigated, and the unaugmented Space Shuttle has been simulated in flight using Princeton's Variable-Response Research Aircraft (VRA).

Stengel, R. F.↗
NASA NTRS1975

The effects of Al/3+/, Cr/3+/, and Ti/3+/ on the stability of armalcolite

Experimental studies on the binary system FeTi2O5-MgTi2O5 yield unrealistically high values for the lower thermal stabilities of lunar armalcolites, since these typically contain 10-15 mole% (Al, Cr, Ti/3+/)2TiO5 components. Pure binary Fe0.5Mg0.5Ti2O5 begins to break down at 1010 + or - 20 C whereas Fe0.5Mg0.5Ti2O5)0.85(Ti2/3+/TiO5)0.15 persists to approximately 900 C and (Fe0.5Mg0.5Ti2O5)0.84(Al2TiO5)0.04(Cr2TiO5)0.03(Ti2/3+/TiO5)0.09 (a model Apollo 17 armalcolite) remains stable down at least to 850 C. The lower thermal stability of the model Apollo 17 armalcolite is raised by approximately 35 C per kilobar of load pressure. The breakdown curve intersects the solidus of likely source materials for high-Ti lunar basalts at 9-10 kbar; thus, the maximum depth at which this armalcolite is stable is 180-200 km. Subsolidus isochemical reaction of Ti/3+/ and Fe/2+/ components in armalcolite can yield rutile and metallic Fe. This assemblage could be misidentified as due to an externally imposed reduction.

Kesson, S. E.↗
NASA NTRS1978

Orbital elements of 4U 0115+63 and the nature of the hard X-ray transients

Extended SAS 3 timing observations of the hard transient X-ray source 4U 0115+63 are reported, and a definitive measurement of the binary orbit of this transient source is presented. It is shown that this source is in a long orbit (period of approximately 24.3 days) that is moderately eccentric (e about 0.34) and that the mean value of the rate of decrease of the pulse period is consistent with the expected spinup of a rotating neutron star that is accreting from a disk. A distance of about 2.5 kpc is inferred, and the B-star optical counterpart is estimated to have an absolute magnitude of approximately -1.5 and a mass of at least 5 solar masses. It is suggested that the companion is a Be star which does not fill its Roche lobe and that the eccentricity and transient nature of the source result from the large orbital separation. It is proposed that hard X-ray transients as a class are collapsed stars (perhaps all neutron stars) in binary systems that are substantially wider than the more persistent X-ray binaries and that the large orbital separation, the small radius of the companion, or both, result in episodic rather than continuous mass transfer onto the X-ray star.

Rappaport, S.↗
NASA NTRS1978

The X-ray source Serpens X-1 - Ariel 5 observations and discussion of models for the spectrum and time variability

Experimental data from Ariel 5 on the spectral shape and time variability of Ser X-1 are presented, and possible explanations for the observations are discussed in terms of current theoretical suggestions for source emission. The observations are summarized in the form of a light curve for 3-7.6-keV photons. The data are fitted with a power law of index -2.3, which yields a hydrogen column density of (1.1 + or - 0.4) x 10 to the 22nd power atoms/sq cm. No persistent periodicity of amplitude greater than 5% of the steady flux is found, but evidence of statistically significant burst activity is obtained. Various emission mechanisms are considered for the time-averaged spectrum and the X-ray bursts. It is suggested that the inverse Compton mechanism is a likely cause for the emission from this source and that the source is radiating near the Eddington limit.

Coe, M. J.↗
NASA NTRS1978

Rare-earth abundances in chondritic meteorites

Fifteen chondrites, including eight carbonaceous chondrites, were analyzed for rare earth element abundances by isotope dilution. Examination of REE for a large number of individual chondrites shows that only a small proportion of the analyses have flat unfractionated REE patterns within experimental error. While some of the remaining analyses are consistent with magmatic fractionation, many patterns, in particular those with positive Ce anomalies, can not be explained by known magmatic processes. Elemental abundance anomalies are found in all major chondrite classes. The persistence of anomalies in chondritic materials relatively removed from direct condensational processes implies that anomalous components are resistant to equilibrium or were introduced at a late stage of chondrite formation. Large-scale segregation of gas and condensate is implied, and bulk variations in REE abundances between planetary bodies is possible.

Evensen, N. M.↗
NASA NTRS1978

Gravity as a biochemical determinant

Hypogravity effects on the biochemistry of living organisms are surveyed, and the differences found under orbital, clinostat, and flotation conditions are examined. Changes can be transient - such as altered serum hormone and electrolyte levels in man - and disappear shortly after return to earth, or changes can be more persistent or permanent, as seems to be the case for changes in the skeletal system mineral and protein constituents for humans who have been in space. While plant ethylene and peroxidase both increase under orbital, clinostat, or flotation conditions, 3-PGA-dehydrogenase increases under orbital but not clinostat conditions and cytochrome C reductase and malic dehydrogenase are affected by clinostat but not actual free fall conditions. Reasons for these discrepancies are considered.

Siegel, S. M.↗
NASA NTRS1978

Recent results from observations of 4U1700-37 using SAS-3

SAS-3 observations of a complete orbital cycle (approximately 3.5 d) of the X-ray source 4U1700-37 are presented. A persistent, approximately sinusoidal modulation of approximately 60% amplitude is present in the data at 97 m. Satellite orbital effects are ruled out by using other detectors pointed away from the source but sampled at the same time. The effect of such a long rotation period (if indeed the period is rotational) on current ideas involving accretion torques and stellar wind is discussed.

Matilsky, T.↗
NASA NTRS1978

A 4.8 hour periodicity in the spectra of Cygnus X-3

The X-ray binary Cyg X-3 has been observed on three occasions during 1975 and 1976 by the GSFC Cosmic X-Ray Spectroscopy Experiment on OSO 8. The X-ray spectra from all three observations can be represented by power-law continua with strong iron line emission. Comparisons of spectra taken within the same observation at various phases of the 4.8 hour period reveal a relative excess of low-energy X-ray emission near zero phase (i.e., the minimum) of the 4.8 hour modulation. In addition, the centroid of the line emission is observed to vary in phase with the 4.8 hour cycle. The possibility of persistent thermal X-ray emission from material surrounding the binary system is introduced in an effort to account for the observed effects.

Becker, R. H.↗
NASA NTRS1978

The discovery of a 97 minute periodicity in 4U 1700-37

SAS 3 observations of a complete orbital cycle (about 3.5 days) of the X-ray source 4U 1700-37 are presented. A persistent, approximately sinusoidal modulation of about 60% amplitude is present in the data at 97 minutes. Satellite orbital effects are ruled out by using other detectors pointed away from the source but sampled at the same time. The effect of such a long rotation period (if indeed the period is rotational) on current ideas involving accretion torques and stellar wind is discussed.

Matilsky, T.↗
NASA NTRS1978

Effect of tropospheric aerosols upon atmospheric infrared cooling rates

An investigation has been made of the impact of wind-blown dust particles upon local climate of arid regions. The case of Northwest India is specifically considered, where a dense layer of dust persists for several months during the summer. In order to examine the effect of this dust layer on the infrared radiative flux and cooling rates, a method is presented for calculating the IR flux within a dusty atmosphere which allows the use of gaseous band models and is applicable in the limit of small single scattering albedo and pronounced forward scattering. The participating components of the atmosphere are assumed to be water vapor and spherical quartz particles only. The atmospheric window is partially filled by including the water vapor continuum bands for which empirically obtained transmission functions have been used. It is shown that radically different conclusions may be drawn on dust effects if the continuum absorption is not considered. The radiative transfer model, when applied to a dusty atmosphere, indicates that there is a moderate enhancement in the atmospheric greenhouse and a 10% increase in the mean IR radiative cooling rate, relative to the dust free case, within the lower troposphere. These results have been compared with previous work by other authors in the context of the possibility of dust layers inhibiting local precipitation.

Harshvardhan, MR.↗
NASA NTRS1978

The magnetopause energetic electron layer. I - Observations along the distant magnetotail

Instrumentation aboard Imp 8 was used to study the magnetopause energetic electron layer along the distant magnetotail, and the observations are discussed. The inner edge of the layer corresponds to the magnetopause boundary, and energetic electrons within the layer persistently stream tailward along local magnetosheath field lines. Pitch angles of electrons along the dusk magnetopause are often restricted to values less than approximately 40 deg, while along the dawnside of the tail somewhat larger pitch angles are normally seen. The differential energy spectra of electrons in the layer, the intensity enhancements, and the average directional intensities are characterized.

Baker, D. N.↗
NASA NTRS1978

Intense magnetic fields at 1 AU: Solar cycle 20

Of the intense magnetic fields (greater than 13 gamma) observed at 1 AU during solar cycle 20 (1973-1975), 92% were associated with shocks, stream interfaces, or cold magnetic enhancements (CMEs). Most (52%) of the magnetic field intensity enhancements occurred at stream interfaces; 27% occurred behind shocks without interfaces; and 11% occurred in CMEs. The most intense fields (25 gamma to 37 gamma) followed shocks. Magnetic field intensities at interfaces did not exceed 25 gamma, suggesting a mechanism such as a magnetoacoustic wave limits the intensity ahead of streams. Intense magnetic fields persist longest behind shocks.

Burlaga, L. F.↗
NASA NTRS1977

Objective tropical cyclone analysis and forecasting technique using conventional and Nimbus-5 electrically scanning microwave radiometer measurements

The ADAPT empirical analysis programs, based on finding an optimal representation of the data in the Karhunen-Loeve sense, were applied to 120 observations of twenty-nine 1973 and 1974 Pacific tropical cyclones. Each observation consists of NIMBUS-5 electrically scanning microwave radiometer (ESMR) radiation measurements at 267 grid points covering and surrounding the tropical cyclone plus nine other non-satellite derived descriptors. Analysis and forecast algorithms to estimate storm motion and intensity were developed for times ranging from the observation time up to 72 hours later. The 24 hr wind speed forecasts with an accuracy of 11.7 knots and position forecasts with accuracies 15% better than persistence were demonstrated using independent tests.

Hunter, H. E.↗
NASA NTRS1979

An objective method for forecasting tropical cyclone intensity and motion using Nimbus-5 ESMR measurements and non-satellite derived descriptors

An empirical analysis program, based on finding an optimal representation of the data was applied to 120 observations of 29 1973 and 1974 North Pacific tropical cyclones. Each observation consists of a field of Nimbus-5 Electrically Scanning Microwave Radiometer radiation measurements at 267 grid points covering and surrounding the tropical cyclone plus nine other non-satellite derived discriptors. Forecast algorithms to estimate storm intensity and motion at 12, 24, 48, and 72 hours after each observation were developed using an independent eigen screening analysis. These algorithms were based on best track data. Independent testing of these algorithms showed that the performance of most of these algorithms were better than persistence and the algorithms forecasting 24, 48, and 72 hour maximum wind speed were better than those made operationally by the Joint Typhoon Warning Center for 1973 and 1974 that did not use best track data.

Hunter, H. E.↗
NASA NTRS1979

Aircraft vortex marking program

A simple, reliable device for identifying atmospheric vortices, principally as generated by in-flight aircraft and with emphasis on the use of nonpolluting aerosols for marking by injection into such vortex (-ices) is presented. The refractive index and droplet size were determined from an analysis of aerosol optical and transport properties as the most significant parameters in effecting vortex optimum light scattering (for visual sighting) and visual persistency of at least 300 sec. The analysis also showed that a steam-ejected tetraethylene glycol aerosol with droplet size near 1 micron and refractive index of approximately 1.45 could be a promising candidate for vortex marking. A marking aerosol was successfully generated with the steam-tetraethylene glycol mixture from breadboard system hardware. A compact 25 lb/f thrust (nominal) H2O2 rocket chamber was the key component of the system which produced the required steam by catalytic decomposition of the supplied H2O2.

Pompa, M. F.↗