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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Comparison of chain sampling plans with single and double sampling plans

The efficiency of chain sampling is examined through matching of operating characteristics (OC) curves of chain sampling plans (ChSP) with single and double sampling plans. In particular, the operating characteristics of some ChSP-0, 3 and 1, 3 as well as ChSP-0, 4 and 1, 4 are presented, where the number pairs represent the first and the second cumulative acceptance numbers. The fact that the ChSP procedure uses cumulative results from two or more samples and that the parameters can be varied to produce a wide variety of operating characteristics raises the question whether it may be possible for such plans to provide a given protection with less inspection than with single or double sampling plans. The operating ratio values reported illustrate the possibilities of matching single and double sampling plans with ChSP. It is shown that chain sampling plans provide improved efficiency over single and double sampling plans having substantially the same operating characteristics.

Stephens, K. S.↗
NASA NTRS1975

The Nakhlites. I - Petrography and mineral chemistry. II - Where, when, and how

The two Nakhlite meteorites (Nakhla and Lafayette) are described, and their possible origin is discussed. It is shown that both objects are cumulates of clinopyroxene with augite as the major mineral and with lesser abundances of olivine, plagioclase, K-feldspar, Fe-Ti oxides, FeS, pyrite, chalcopyrite, and possibly iddingsite. Also, both meteorites are unbrecciated, and their texture is dominated by elongate subhedral to euhedral prisms of clinopyroxene. The data are shown to be compatible with the Nakhlites' being cumulative rocks from a common basaltic parent liquid. It is established that these objects are not of lunar origin, and it is concluded that the position of the parent body relative to other planetary bodies remains to be determined.

Bunch, T. E.↗
NASA NTRS1976

Thorium and uranium variations in Apollo 17 basalts, and K-U systematics

It is found that Apollo 11 low-K and in particular Apollo 17 mare basalts show a wide range of Th/U ratios unlike other rocks; such variations cannot be explained by near surface crystal fractionation. A two-stage fractional crystallization-partial melting model involving a clinopyroxene cumulate as the major phase can explain the variations in Th/U ratios. Due to the Sm-Nd systematics constraint, several source cumulates are invoked to explain the observed Th/U continuum.

Laul, J. C.↗
NASA NTRS1976

Critical review of models for the evolution of high-Ti mare basalts

Current models for the evolution of REE abundances in high-Ti mare basalts are reviewed, the models falling into two classes: simple cumulate remelting models and complex assimilation and hybridization models. Calculations show that the total melting of a cumulate having the modal mineralogy of high-Ti mare basalts can provide for the approximate level of enrichment of REE relative to chondrites, but results in a poor match for the Apollo 17 high-Ti basalt REE pattern.

Drake, M. J.↗
NASA NTRS1977

Lunar igneous rocks and the nature of the lunar interior

Lunar igneous rocks, properly interpreted, can give useful information about mineral assemblages and mineral chemistry as a function of depth in the lunar interior. Though intensely brecciated, terra rocks reveal, in their chemistry, evidence for a magmatic history. Partial melting of feldspathic lunar crustal material occurred in the interval 4.6 to 3.9 Gy. Melting of ilmenite-bearing cumulates at depths near 100 km produced parent magmas for Apollo 11 and 17 titaniferous mare basalts in the interval 3.8 to 3.6 Gy. Melting of ilmenite-free olivine pyroxenites (also cumulates?) at depths greater than 200 km produced low-titanium mare basalts in the interval 3.4 to 3.1 Gy. No younger igneous rocks have yet been recognized among the lunar samples and present-day melting seems to be limited to depths greater than 1000 km.

Hays, J. F.↗
NASA NTRS1977

Application of LANDSAT imagery for snow mapping in Norway

The author has identified the following significant results. During the summer seasons of 1975 and 1976, the snow cover was successfully monitored and measured in the four basins. By using elevation distributions for these basins combined with the measured snow cover percentages, the equivalent snow line altitude was calculated. Equivalent snow line altitude was used in accordance with Mark Meier's definition. Cumulative runoff data were collected for the basins. Tables showing percentage snow cover versus cumulative runoff were worked out for 1975.

Odegaard, H.↗
NASA NTRS1977

Magma oceanography. I - Thermal evolution

Fractional crystallization and flotation of cumulate plagioclase in a cooling 'magma ocean' provides the simplest explanation for early emplacement of a thick feldspar-rich lunar crust. The complementary mafic cumulates resulting from the differentiation of such a magma ocean have been identified as the ultimate source of mare basalt liquids on the basis or rare-earth abundance patterns and experimental petrology studies. A study is conducted concerning the thermal evolution of the early differentiation processes. A range of models of increasing sophistication are considered. The models developed contain the essence of the energetics and the time scale for magma ocean differentiation. Attention is given to constraints on a magma ocean, modeling procedures, single-component magma oceans, fractionating magma oceans, and evolving magma oceans.

Solomon, S. C.↗
NASA NTRS1977

Sr-isotopic constraints on the petrogenesis of Apollo 12 mare basalts

As part of a study of Apollo 12 basalts, crystallization ages and initial Sr-87/Sr-86 (I) were determined for pigeonite basalts 12039 and 12055 and ilmenite basalt 12051. Sr-86/Sr-87 measurements for a larger suite of whole rock and plagioclase samples were obtained, and it is found that I-values for olivine and pigeonite basalts are indistinguishable while I-values for ilmenite basalts are distinctly lower. A self-consistent model for the evolution of the Sr-isotopic composition and REE abundances suggests that basalt was formed by small (2-10%) degrees of melting of cumulate sources composed of varying proportions of olivine, orthopyroxene, and clinopyroxene. This model requires nonchondritic relative abundances of the REE in the parental liquid at the time of formation of the cumulate sources. The model also describes Sr-isotopic composition and REE abundances of Apollo 17 high-Ti basalts and Apollo 15 low-Ti basalts. A lunar 'scenario' involving open system crystallization of a magma ocean from the crust downward is proposed.

Nyquist, L. E.↗
NASA NTRS1978

Zr and Nb partition coefficients - Implications for the genesis of mare basalts, KREEP, and sea floor basalts

The distribution coefficients of Zr and Nb have been found between armalcolite, ilmenite, clinopyroxene, rutile, plagioclase, and a coexisting high-Ti mare basalt melt in the 1105-1128 C temperature range. Henry's Law is not broken over the compositional range evaluated. The distribution coefficients of clinopyroxene are strongly dependent on melt and crystal compositions. The Al2O3 activity in the melt is a strong controlling parameter. It is concluded that: (1) Apollo 11 (low K) and Apollo 17 high-Ti mare basalts may have been generated by the partial melting of an ilmenite-rich cumulate, (2) Apollo 11 (high K) basalts may have been generated by a small amount of partial melting of a more fractionated ilmenite-rich cumulate, (3) KREEP magmas may have been formed as residual melts produced by fractional crystallization of the lunar magma ocean, and (4) anomalous (type II) MOR basalts may have been generated by small degrees of partial melting of a relatively undepleted mantle with clinopyroxene remaining in the residium.

Mccallum, I. S.↗
NASA NTRS1975

Differentiation of a very thick magma body and implications for the source regions of mare basalts

Mass-balance calculations indicate that the molten layer originally covering the moon may have been several hundred kilometers deep. The solidification of this magma ocean involved some unusual effects resulting from the large-pressure differential in the thick magma layer. The sunken cumulates from this differentiation would be more iron-rich, less refractory, and would contain more incompatible elements than would be expected in simple isobaric fractional crystallization and crystal sinking models of magma differentiation. These lower cumulates can have the mineralogical and chemical properties of the source regions of the low-Ti mare basalts.

Walker, D.↗
NASA NTRS1975

Evolution of the moon between 4.6 and 3.3 AE

A model of lunar evolution is proposed. At 4.6 AE an outer shell 60-100 km thick of an initially homogeneous moon was totally molten following accretion. 'Highland basalt' represents remnants of the chilled crust of this molten layer and, therefore, the mean lunar composition. Melt from the partially molten region below the outer shell intruded into it, enriching it in FeO, SiO2, radiogenic, and trivalent trace LIL (large ion lithop) elements. Fractional crystallization of the outer shell produced toward its base a mafic cumulate zone less than 40 km thick, the upper 60 km being anorthosite. The radiogenic elements concentrated together with dense residual melt in the upper parts pf the mafic cumulate zone. Between 4.6 and 4.3 AE a second differentiation led to localized enrichment from below of radiogenic elements in the plagioclase-rich, high-Mg/Mg + Fe residuum below the outer 100-km-thick shell. Melting at these enriched sites at about 4.0 AE produced to KREEP basalts. Later melting at sites of radiogenic element enrichment in the outer 100-km-thick shell produced the mare basalts.

Hollister, L. S.↗
NASA NTRS1975

Crater studies in the Apollo 17 region

As part of crater analysis in the Apollo 17 region, cumulative size-frequency curves were constructed, the density distribution of small craters was determined, and the effects of secondary crater clusters near the landing site were studied. The cumulative curves indicate that the old dark-mantled mare is similar in age to Apollo 11 mare, and that the adjacent young light mare of Central Serenitatis is similar in age to Apollo 15 mare. The old dark-mantled surface is markedly deficient in craters between 100 and 200 m in diameter, and the analysis suggests that this deficiency is a consequence of the old dark mantle which gives rise to an unusually thick unconsolidated layer that causes abnormally rapid degradation of small craters.

Lucchitta, B. K.↗
NASA NTRS1979

Large impact basins on Mercury and relative crater production rates

Mariner 10 revealed evidence for 40 impact basins having diameters greater than or equal to 200 km on the portion of Mercury imaged at sufficient resolution. A log (cumulative number/unit area) vs. log (diameter) plot for the mercurian basins has a least squares slope of -2. Mercury has (in cumulative number/unit area) only 37 percent as many basins as does the Moon over the entire range of diameters greater than or equal to 300 km. If both the Moon and Mercury have had similar preservation times for craters and if common populations of impactors are involved, then Mars crossers may have been a dominant contribution to the basin forming objects.

Frey, H.↗
NASA NTRS1978

A numerical treatment of melt/solid segregation - Size of the eucrite parent body and stability of the terrestrial low-velocity zone

Crystal sinking to form cumulates and melt percolation toward segregation in magma pools can be treated with modifications of Stokes' and Darcy's laws, respectively. The velocity of crystals and melt depends, among other things, on the force of gravity (g) driving the separations and the cooling time of the environment. The increase of g promotes more efficient differentiation, whereas the increase of cooling rate limits the extent to which crystals and liquid can separate. The rate at which separation occurs is strongly dependent on the proportion of liquid that is present. The observation of cumulates and segregated melts among the eucrite meteorites is used as a basis for calculating the g (and planet size) required to perform these differentiations. The eucrite parent body was probably at least 10-100 km in radius. The earth's low velocity zone (LVZ) is shown to be unstable with respect to draining itself of excess melt if the melt forms an interconnecting network. A geologically persistent LVZ with a homogeneous distribution of melt can be maintained with melt fractions only on the order of 0.1% or less.

Walker, D.↗
NASA NTRS1979

The effect of load sequence on the statistical fatigue of composites

A theoretical model to predict the effect of loading sequence on the statistical distributions of the fatigue life and the residual strength under n-stress levels of cyclic loading is derived on the basis of a three-parameter model. In particular, the dual stress fatigue cumulative damage is studied, showing that the Miner's sum (the cumulative damage sum at fatigue failure) is a statistical variable. It is proved theoretically that the Miner's sum is always greater than or equal to unity for the high-low load sequence, while it is always smaller than or equal to unity for the low-high load sequence, with the deviation from unity increasing as the difference between the high and the low stress levels increases. An experimental test program using graphite/epoxy angle-ply laminates, carried out to generate statistically meaningful data for verifying the proposed model, is discussed.

Yang, J. N.↗
NASA NTRS1978

Implications from Luna 24 sample 24170 to U-Pb evolution in the lunar mantle

The concentrations of U, Th and Pb, as well as the Pb isotopic composition, have been determined for a Luna 24 sample from the Mare Crisium area. A relatively recent disturbance to the U-Pb system during meteorite impact or burial in hot ejecta is suggested by the findings. According to three-stage U-Pb evolution model calculations, the source cumulates of the Luna 24 basalt evolved in a U-238/Pb-204 environment much lower than that of the Apollo mare basalts. A laterally heterogeneous lunar magma ocean, U-Pb fractionation during cumulate formation, and/or lack of KREEP addition to the Luna 24 basalt are also reflected in the calculations.

Unruh, D. M.↗
NASA NTRS1978

Origin and history of the adcumulate eucrite, Moama as inferred from REE abundances, Sm-Nd and U-Pb systematics

The abundances of Sm-Nd and U-Pb isotopes and of rare earth elements (REE) in Moama cumulate eucrite were investigated. The Sm-Nd data plotted on a Nd-143/Nd-144 vs Sm-147/Nd-144 evolution diagram define a line with a slope corresponding to an age of 4.58 plus or minus 0.05 billion years and an initial Nd-143/Nd-144 ratio of about 0.50684. Moama was found to contain the lowest overall trivalent REE abundances, the most light REE-depleted abundance pattern, and largest positive Eu anomaly of any eucrite yet studied. The REE data indicate that Moama could have been derived by about 1 to 5% fractional crystallization from a liquid with REE contents similar to Juvinas, or about 20 to 30% fractional crystallization from a Sioux County-like liquid. The data are consistent with the hypothesis that the Moama, Serra de Mage, and Moore county cumulate meteorites could have been derived from the same parent liquid. Results of the U-Th-Pb study indicate that the majority of the Pb in Moama is of terrestrial origin, and suggest that the meteorite has undergone a minor thermal event causing re-equilibration of the U-Pb system.

Hamet, J.↗
NASA NTRS1978

The effect of transponder imperfections on the error probability performance of a satellite communication system

The bit error rate (BER) performance analysis of a data communication system is generally based on the assumption that signal waveforms are ideal and hardware-induced distortion is absent. In a satellite communication system such distortion arises in the satellite transponder, as well as in the transmitter and receiver portions. NASA, which is in the process of developing its Tracking and Data Relay Satellite System (TDRSS), is very much interested in understanding the impact of numerous forms of hardware distortion that have been identified on BER performance. The present paper examines the cumulative impact of nine forms of distortion induced by the transponder on BPSK and QPSK signals. For the present analysis, the transmitter and receiver are assumed to operate in essentially ideal fashions. Computed results indicate that BPSK and QPSK performances are affected in substantially different manners, with QPSK generally more sensitive to a given form of distortion. Cumulative distortion effects are illustrated via computed performance curves.

Weinberg, A.↗