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At least 937 records · Page 52

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NASA NTRS1974

Vortex age as a wake turbulence scaling parameter

Tests were conducted in the Virginia Tech Stability Wind Tunnel to determine the significance of vortex age as a scaling parameter in wake turbulence development and dissipation. Vortex structure was measured over a range of three angles of attack, three free-stream speeds, and seven downstream positions from 2 to 30 chordlengths using an NACA 0012 wing and a five hole yawhead probe. The resulting data indicates that vortex age is not a self-sufficient scaling parameter but a free-stream velocity influence also exists at higher angles of attack which cannot be explained in terms of Re or M.

Marchman, J. F., III↗

NASA NTRS1973

Argon in Apollo 15 green glass spherules /15426/ - Ar-40-Ar-39 age and trapped argon

The results of thermal-release argon analyses of neutron-irradiated green glass spherules separated from the lunar sample 15426 are discussed. It is shown that the gas-retention age determined by the Ar-40-Ar-39 method is similar to that of local mare basalts, and differs from the ages of Appenine Front samples recovered from the same region as 15426. Trapped argon is present in near-surface regions of the spherules, and can be resolved into at least two components requiring separate origins: a shallow (0.1 micron) component with Ar-40/Ar-39 not less than 30, and a deeper (2.0 micron) component with an Ar-40/Ar-39 ratio of 2.9. The ratio of trapped Ar-40 to Ar-36 is higher than in any lunar soil samples, and suggests that the trapped gas was implanted early in the spherules history.

Podosek, F. A.↗

NASA NTRS1974

On the age of the Onverwacht Group, Swaziland sequence, South Africa

Some rocks of the Onverwacht Group, South Africa, have been analyzed for Rb and Sr concentrations and Sr isotopic composition. These rocks include volcanic rocks, layered ultramafic differentiates and cherty sediments. Whole rock data indicate that the Rb-Sr isotopic systems in many samples were open and yield no reasonable isochron relationships. However, the data of mineral separates from a basaltic komatiite define a good isochron of 3.50 (plus or minus .2) b.y. with an initial Sr-87/Sr-86 ratio of 0.70048 plus or minus 5. The orthodox interpretation of this age is the time of the low grade metamorphism. It is reasonable to assume that the age of 3.50 b.y. might also represent the time of initial Onverwacht volcanism and deposition. The initial Sr-87/Sr-86 ratio obtained above is important to an understanding of the Sr isotopic composition of the Archean upper mantle.

Jahn, B.-M.↗

NASA NTRS1973

The abundance and age distributions of 500 F stars in the solar neighbourhood

The uvby catalog of Perry has been used, in conjunction with theoretical uvby colors and stellar evolutionary tracks, to obtain the metal abundance distribution and age distribution of F and G type dwarf stars within 100 pc of the sun. Eighty-three per cent of stars with spectral type F5-G2 have metal content within a factor of 2.5 of the solar abundance, and only 2% have less than one-quarter the solar abundance. The metal abundance distribution, which contains more metal-rich stars than found in previous investigations of F and G dwarfs, has also been compared with the observed metal abundance distribution of G and K giants and the model galaxy calculations of Truran and Cameron (1971). A comparison of the age distribution with evolutionary calculations implies that the rate of star formation in the galaxy may not have decreased by a large factor in the last 10 billion years.

Clegg, R. E. S.↗

NASA NTRS1974

Ar-40/Ar-39 chronology and cosmic ray exposure ages of the Apollo 15 samples

The Ar-40*/Ar-39* thermal release patterns of igneous soil fragments, rake basalts, and large crystalline rocks are by and large well defined. Shock deformations of up to moderate intensities have no observable effects on the Ar-40*/Ar-39* release patterns. Neither do the Ar-40* diffusion losses have any relationship with the shock intensities. The peak of the magnetic activity in Palus Putredinis occurred at 3.33 plus or minus 0.02 Gy, lava flows continuing up to 3.13 Gy but at much reduced intensity. No correlation between the crystallization ages and the petrographic rock types was observed. The cosmic ray exposure gas indicate a mature regolith around the Hadley Rille-Apennine Front region. The exposure ages of the Apollo 15 samples cannot reliably be used to obtain the time of prominent cratering events at this site.

Husain, L.↗

NASA NTRS1974

Rb-Sr age of lunar igneous rocks 62295 and 14310

Measurements of Rb-Sr ages of crystallization performed on igneous lunar highland rocks 62295 and 14310 are reported. Lunar sample 62295 is a mesostasis-rich spinel-troctolite very-high-alumina basalt exhibiting a variable igneous structure. Sample 14310 is a feldspathic KREEP-rich basalt. The determined ages probably date the cooling of shock melts.

Mark, R. K.↗

NASA NTRS1974

Effects of leaf age within growth stages of pepper and sorghum plants on leaf thickness, water, chlorophyll, and light reflectance

Pepper and sorghum plants (characterized by porous and compact leaf mesophylls, respectively) were used to study the influence of leaf age on light reflectance. Measurements were limited to the upper five nodal positions within each growth stage, since upper leaves make up most of the reflectance surfaces remotely sensed. The increase in leaf thickness and water content with increasing leaf age was taken into consideration, since each of these factors affects the reflectance as well as the selection of spectral wavelength intervals for optimum discrimination of vegetation.

Gausman, H. W.↗

NASA NTRS1974

Problems in the interpretation of lunar mare stratigraphy and relative ages indicated by ejecta from small impact craters

The numbers of large ejecta blocks in excess of several meters in diameter ('blockiness') around the rims of small craters in southeastern Mare Serenitatis exceed those around similar craters in southern Mare Imbrium (and some other regions) at all but the final stages of crater degradation. Terrestrial explosion crater analogs, studies of impact processes, and a layered mare model suggest that the nature of the layering in the subsurface, including lavas, ejecta and buried regolith horizons, could account for the variable blockiness of crater ejecta and, possibly, for some variation in crater size-frequency distributions. Such effects would limit the reliability and utility of counting postmare craters for the purpose of estimating the relative ages of mare surfaces. Similarly, comparisons of the effects of progressive degradation on small impact craters to determine relative or absolute ages of individual craters may be limited by the influence of stratigraphy on ejecta fragment size distributions, which would in turn affect micrometeorite erosion rates and regolith production models.

Young, R. A.↗

NASA NTRS1977

Measurement of vortex velocities over a wide range of vortex age, downstream distance and free stream velocity

A wind tunnel test was conducted to obtain vortex velocity signatures over a wide parameter range encompassing the data conditions of several previous researchers while maintaining a common instrumentation and test facility. The generating wing panel was configured with both a revolved airfoil tip shape and a square tip shape and had a semispan aspect of 4.05/1.0 with a 121.9 cm span. Free stream velocity was varied from 6.1 m/sec to 76.2 m/sec and the vortex core velocities were measured at locations 3, 6, 12, 24 and 48 chordlengths downstream of the wing trailing edge, yielding vortex ages up to 2.0 seconds. Wing pitch angles of 6, 8, 9 and 12 deg were investigated. Detailed surface pressure distributions and wing force measurements were obtained for each wing tip configuration. Correlation with vortex velocity data taken in previous experiments is good. During the rollup process, vortex core parameters appear to be dependent primarily on vortex age. Trending in the plateau and decay regions is more complex and the machanisms appear to be more unstable.

Rorke, J. B.↗

NASA NTRS1976

On the age of Rhodesian greenstone belts

Isochron ages and initial Sr-87/Sr-86 ratios are derived from Rb-Sr isotopic analyses on metavolcanic rocks from some greenstone belts of the Rhodesian Archean craton. Three mineral isochron ages (about 2.4 billion years) are tentatively suggested to represent the time of an important low-grade metamorphic event.

Jahn, B.-M.↗

NASA NTRS1977

Ar-40 intercept values and young apparent /K-40/-/Ar-40/ ages of five Apollo 15 fines

Correlations between Ar-40 and Ar-36 from size fractions of three Apollo 15 fines (15071, 15421, 15501) have been obtained. The Ar-40 intercept values of these fines and of 15091 and 15601 are generally lower than what one would expect for fines resulting from the comminution of rocks having ages of about 3.3 billion yr, typical for basalts of the landing site. This is interpreted to be the result of contamination by ray material from the Copernican age (equal or less than about 1 billion yr) craters, Autolycus and Aristillus, north of the landing site.

Jordan, J. L.↗

NASA NTRS1976

Accelerated heat-aging studies on fluororubber in various media

Heat-aging studies were conducted on fluororubber (copolymers of vinylidene fluoride and perfluoropropylene) using N,N-dicinnamylidene-1,6-hexanediamine, a Schiff's base of 1,6-hexanediamine, and MgO as acid acceptor. The principal technique employed was chemical stress relaxation for determining network changes brought about in the heat-aged fluororubber. This technique was backed up by swelling measurements, gel permeation chromatography, and IR spectroscopy. Stress relaxation curves are plotted for a wide range of variation in parameters (time, crosslinking density, state of curing, temperature, intermittent and continuous relaxation).

Kalfayan, S. H.↗

NASA NTRS1976

Rb-Sr ages and isotopic systematics of some Serenitatis mare basalts

Rb/Sr isotopic data and internal isochron ages are presented for some mare basalts from the Taurus-Littrow region. It is found that in age and in trace- and major-element chemistry as well as in Rb-Sr isotopic systematics, the Serenitatis mare basalts closely resemble the low-K Tranquility basalts, suggesting that over a wide region on the moon volcanism occurred at a discrete period 3.7-3.8 AE ago.

Murthy, V. R.↗

NASA NTRS1976

Rb-Sr age of troctolite 76535

Rb-Sr systematics is studied for the lunar troctolite 76535 in phases covering a wide range of Rb and Sr concentrations. A line is obtained corresponding to an age of 4.61 plus or minus 0.07 AE and an initial Sr-87/Sr-86 of 0.69900 plus or minus 0.00003. The Rb-Sr age of 4.55 plus or minus 0.10 AE for the dunite (72417) and that of the troctolite are in approximate agreement and permit an interpretation that these rocks formed during a single major lunar differentiation which presumbly produced an anorthositic-gabbroic lunar crust and layered upper mantle.

Papanastassiou, D. A.↗

NASA NTRS1976

The morphological evolution of mare-highland contacts - A potential measure of relative mare surface age

The uniform breaks in slopes along many mare-highland contacts may be debris aprons transported primarily by impact erosion at relatively slow rates. Other suggestions, such as the 'high lava mark' hypothesis, appear inadequate to explain all of the unique characteristics of these widespread features. There is a reasonable correlation of overall slope form (profile) and apron distribution with established mare age provinces. Distinctive debris aprons in the younger maria could represent the initial stages of lunar slope degradation produced mainly by the postmare impact flux. The growth of debris aprons must be qualitatively related to the impact flux recorded on adjacent mare surfaces and could provide an approximate means of extrapolating relative mare ages to highland scarps and crater walls. By combining detailed measurements of lunar slopes with development of a realistic model for impact modification of these features, approximate limits for the cumulative lunar flux distribution through time might be derived.

Young, R. A.↗

NASA NTRS1977

On the structure of contact binaries. II - Zero-age models

Zero-age models of contact binaries of roughly solar composition are constructed on the basis of contact discontinuity hypothesis. With this formulation, systems with common radiative envelopes can be constructed as well as systems with common convective envelopes. Two models with total masses, respectively, of 1.5 and 3 solar masses are presented explicitly; both binary models have a mass ratio chosen equal to 0.5. The properties of the interior structure of these models are compared with the properties of zero-age single stars which have masses corresponding to the individual components. The predictions of the theory are compared with the empirical period-color relationship found by Eggen (1961, 1967) for W Ursae Majoris stars. The agreement with observations is satisfactory.

Lubow, S. H.↗

NASA NTRS1978

Imbrian-age highland volcanism on the moon - The Gruithuisen and Mairan domes

The Gruithuisen and Mairan domes on the moon represent morphologically and spectrally distinct nonmare extrusive volcanic features of Imbrian age. The composition, morphology, and age relationships of the domes indicate that nonmare extrusive volcanism in the northern Procellarum region of the moon continued until about 3.3 x 10 to the 9th to 3.6 x 10 to the 9th years ago and was partially contemporaneous with the emplacement of the main sequence of mare deposits.

Head, J. W., III↗

NASA NTRS1977

Steady state, exposure age, and growth of agglutinates in lunar soils

Mineralogical evolution of lunar soils as a function of agglutinate content can be described with the help of a two-component model. Steady-state condition of exposed lunar soils can be achieved only by the balance of comminution, agglutination, and replenishment processes. Rate of replenishment depends on the meteoroid flux and the nature of the substrate which varies both in space and time. Rates of agglutination and comminution depend not only on the micrometeoritic flux but also on the chemical and modal composition of an exposed soil. It is concluded from modeling the above that steady-state condition of lunar soils is independent of its maturity or exposure age. Agglutinate content of a lunar soil can be used to estimate the relative exposure age of the soil only if the soil is in a non-steady-state condition.

Basu, A.↗