SEARCH · Engineering Papers

Results for “cumulative”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 667 records · Page 37

All sources NASA NTRS DOE OSTI

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

Genesis of the Angra dos Reis and other achondritic meteorites

Major, minor, and trace element abundances were determined in seven Angra dos Reis samples, which included whole rocks, fassaite (clinopyroxene), olivine, and whitlockite separates, via sequential instrumental neutron activation analysis. The rare earth element abundance patterns and the trace element abundance patterns of this achondritic meteorite are discussed. A two-stage crystal-liquid fractionation model with source material containing olivine, orthopyroxene, and clinopyroxine is presented for the genesis of Angra dos Reis. Multilinear regression analysis was used to estimate possible composition and properties of the parent magmas. Angra dos Reis was compared with other achondrites, cumulate eucrites and nakhlites in particular. It is thought that the unique Angra dos Reis could not be related to those achondrites by crystal-liquid fractionation of the same parent body.

Ma, M.-S.↗

NASA NTRS1977

Measured oxygen fugacities of the Angra dos Reis achondrite as a function of temperature

Measurements of the oxygen fugacity, f(O2), as a function of temperature, T, were made on an interior bulk sample of the cumulate achondrite, Angra dos Reis. Data clustered between the f(O2)-T relationship of the iron-wustite assemblage and 1.2 log atm units above iron-wustite. Interpretation of the data indicates that, throughout most of the cooling history of the meteorite, f(O2) values were defined by equilibria involving iron-bearing species at values close to the f(O2) of the assemblage iron-wustite. Measured f(O2) data are compatible with crystallization and cooling at pressures greater than 50 bars.

Brett, R.↗

NASA NTRS1977

Happy Canyon - A new type of enstatite achondrite

Mineralogical and chemical characteristics of the Happy Canyon meteorite, found in 1971 near Wayside, Texas, show it to be a new type of enstatite achondrite occupying the gap between the recrystallized enstatite chondrites and the igneous, crystalline, unbrecciated enstatite chondrites. Although the bulk composition of the specimen is consistent with that of an E6 enstatite chondrite, it has a crystal cumulate texture. There are minor amounts of metal and troilite which have survived extensive weathering. The Happy Canyon meteorite may represent an E6 composition which has melted and reprecipitated at a slightly higher oxidation state, possibly in the core of a small parent body.

Olsen, E. J.↗

NASA NTRS1977

Polarization loss of a satellite - Data collection sensor link

It is noted that the stringent economy of data-collection systems consisting of several widely dispersed satellite-monitored sensor platforms can be partially achieved by using an inexpensive linearly polarized antenna on each platform and that due to Faraday rotation of the ionosphere, the satellite antenna must be circularly polarized to avoid a prohibitive polarization loss. The cumulative probability distribution of polarization loss between a linearly polarized platform antenna and an elliptically polarized satellite antenna is computed for satellite-antenna axial ratios of 3 and 4 dB. The results indicate that a polarization loss of 4.5 dB must be expected for a reliability of 85% and an axial ratio of 3 dB. It is suggested that the conventional assignment of a 3-dB polarization loss to the communication link considered may not insure the required link reliability.

Estep, H.↗

NASA NTRS1977

The parabolic approximation for sound propagation in a stratified moving medium

Propagation of sound in a stratified moving medium is discussed through an extension of the parabolic approximation to the acoustic equations of motion for short wavelengths. The parabolic approximation is related to the theory of geometric acoustics, and it is shown that it yields an improvement in accuracy over geometric theory. Also, the approximation corrects cumulative failures of geometric theory which occur when sound propagates many wavelengths from its source. The theory is illustrated by application to simple examples of quasi-plane wave propagation.

Myers, M. K.↗

NASA NTRS1977

The Lewis Research Center geomagnetic substorm simulation facility

A simulation facility was established to determine the response of typical spacecraft materials to the geomagnetic substorm environment and to evaluate instrumentation that will be used to monitor spacecraft system response to this environment. Space environment conditions simulated include the thermal-vacuum conditions of space, solar simulation, geomagnetic substorm electron fluxes and energies, and the low energy plasma environment. Measurements for spacecraft material tests include sample currents, sample surface potentials, and the cumulative number of discharges. Discharge transients are measured by means of current probes and oscilloscopes and are verified by a photomultiplier. Details of this facility and typical operating procedures are presented.

Berkopec, F. D.↗

NASA NTRS1977

Monte Carlo simulation of wave sensing with a short pulse radar

A Monte Carlo simulation is used to study the ocean wave sensing potential of a radar which scatters short pulses at small off-nadir angles. In the simulation, realizations of a random surface are created commensurate with an assigned probability density and power spectrum. Then the signal scattered back to the radar is computed for each realization using a physical optics analysis which takes wavefront curvature and finite radar-to-surface distance into account. In the case of a Pierson-Moskowitz spectrum and a normally distributed surface, reasonable assumptions for a fully developed sea, it has been found that the cumulative distribution of time intervals between peaks in the scattered power provides a measure of surface roughness. This observation is supported by experiments.

Levine, D. M.↗

NASA NTRS1977

Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies

There are many similarities between lunar samples and stone meteorites. Lunar samples, especially from the highlands, indicate that they have been affected by complex and repeated impact processes. Similar complex and repeated impact processes have also been operative on the achondritic and chondritic meteorites. Similarities between lunar and meteoritic rocks are discussed as follows: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes; (2) Chondrules are present in lunar meteorites, as well as in a few achondritic and most chondritic meteorites. They apparently crystallized spontaneously from molten highly supercooled droplets which may have formed from impact melts or, perhaps, volcanic processes (as well as from the solar nebula, in the case of meteoritic chondrites); (3) Lithic fragments vary from little modified (relative to the apparent original texture) to partly or completely melted and recrystallized lithic fragments. Their detailed study allows conclusions to be drawn about their parent rock types and their origin, thereby gaining insight into preimpact histories of lunar and meteoritic breccias. There is evidence that cumulate rocks were involved in the early history of both moon and parent meteorite bodies.

Prinz, M.↗

NASA NTRS1977

Results from the Apollo passive seismic experiment

Recent results from the Apollo Seismic Network suggest that primitive differentiation occurred in the outer shell of the moon to a depth of approximately 300 km and the central region of the moon is presently molten to a radius of between 200 and 300 km. If early melting to a depth of 300 to 400 km was a consequence of accretional energy, very short accretion times are required. It was shown that the best model for the zone of original differentiation is a crust 40 to 80 km thick, ranging in composition from anorthositic gabbro to gabbro, and overlying an ultramafic cumulate about 250 km thick. The best candidate for the molten core appears to be iron or iron sulphide. A new class of seismic signals recently were identified that may correspond to shallow moonquakes. These are rare, but much more energetic than the more numerous, deep moonquakes.

Latham, G.↗

NASA NTRS1977

A plant canopy light absorption model with application to wheat

From the light absorption model the absorption of light in the photosynthetically active region of the spectrum was calculated for a Penjamo wheat crop for several situations including: (1) the percent absorption of the incident radiation by a canopy having a four layer structure; (2) the percent absorption of light by the individual layers within a four layer canopy and by the underlying soil; (3) the percent absorption of light by each vegetative canopy layer for variable sun angle; and (4) the cumulative solar energy absorbed by the developing wheat canopy as it progresses from a single layer through its growth stages to a three layer canopy. This calculation was also presented as a function of the leaf area index.

Chance, J. E.↗

NASA NTRS1977

Rare earth and trace element geochemistry of a fragment of Jurassic seafloor, Point Sal, California

Rocks from an ophiolite suite once on the seafloor were analyzed for rare earth elements (REE), Sc, Co, Na2O, Cr, Zn and FeO. Strontium isotope exchange noted in some of the lavas is attributed to basalt-seawater interaction; the Ce abundance in smectite- and zeolite-bearing lavas may also be due to prolonged exposure to seawater. The higher grades of metamorphic rock, however, show no variation from the usual flat or slightly light REE depleted profiles. Plutonic igneous rock, all light REE depleted, have total REE abundances varying by a factor of 100 between the dunites and diorites. In order of decreasing REE abundance are hornblende, clinopyroxene, plagioclase, orthopyroxene and olivine. Calculations of REE contents of liquids in equilibrium with early cumulative clinopyroxenes suggest that the parent to the stratiform sequence was more depleted in light REE than the parent to the lava pile.

Menzies, M.↗

NASA NTRS1977

Moon-Mercury - Large impact structures, isostasy and average crustal viscosity

It is shown that Mercury's surface has only 70% as many large craters (of at least 200 km in diameter) as the moon. The density of Mercurian impact craters having diameters over 400 km is 30% of that of the moon, and for craters with diameters between 400 and 700 km, Mercurian density is 21% of that of the moon. The size-frequency distribution curve of Mercury is the same as the lunar cumulative -2 slope. The Mercurian curve, however, lies well below the 10% surface saturation level of the lunar curve. This may indicate that the old, heavily-cratered Mercurian terrain is not presently in a state of cratering equilibrium. The differences in crater and basin densities observed between Mercury and the moon may be functions of crater-production rates or of different crustal histories. The total isostatic compensation of impact craters having diameters of about 800 km suggests that the average viscosity of the Mercurian crust during approximately the past 4 eons was the same as that of the moon.

Schaber, G.↗

NASA NTRS1978

A 'chondritic' eucrite parent body - Inference from trace elements

Thirty-three elements were analyzed by radiochemical and instrumented neutron activation in four eucrites - Juvinas (brecciated), Ibitira (vesicular, unbrecciated) and Moore County and Serra de Mage (both cumulate, unbrecciated). Nebular and planetary effects are distinguished in the C1-normalized abundance patterns arranged in the order of volatility. Lithophile, chalcophile, and siderophile patterns are discussed; the stepped lithophile pattern reveals the dominance of nebular processes while the siderophile pattern retains little sign of nebular processes and instead reflects planetary metal-silicate partition. Volatiles were apparently accreted as a fractionated C3-like component, and consistent but subtle C1-normalized abundance differences between eucrites result from crystal/liquid differentiation.

Morgan, J. W.↗

NASA NTRS1977

Continuous and cyclic thermal exposure induced degradation in boron reinforced 6061 aluminum composites

Boron reinforced 6061 aluminum (B/Al) composite was continuously exposed at 728 K for up to 240 hours and cyclically exposed between 293 K and 728 K for up to 6000 three-minute cycles. Room temperature tensile strengths were measured and the specimens were metallographically examined. The data suggest that, in addition to AlB2 formation, magnesium in the matrix diffused to the reaction layer and formed (Al,Mg)B2. This formation could weaken the matrix and embrittle the reaction layer. Continuous exposure degraded the strength of the B/Al specimens about 28% in 240 hours. However, the fracture mode, one indicative of high strength interfaces, did not change. The strength degradation was attributed to crack initiation in the brittle reaction layer causing stress concentrations in the fibers. Cyclic exposure degraded the strength of the B/Al about 34% in 6000 cycles. The fracture mode of the cyclic exposure specimens showed transition toward a mode characteristic of low interfacial strength. The lower interfacial strengths were attributed to stress fields induced by differential thermal expansion. Cyclic exposure degraded the strength of the B/Al specimens more than continuous exposure for similar cumulative exposure times.

Olsen, G. C.↗

NASA NTRS1977

Laboratory duplication of comb layering in the Rhum pluton

A description is provided of the texture of harrisite comb layers, taking into account the results of crystallization experiments at controlled cooling rates, which have reproduced the textural change from 'cumulate' to comb-layered harrisite. Melted samples of harrisite were used in the dynamic crystallization experiments considered. The differentiation of a cooling rate run with respect to olivine grain size and shape is shown and three possible origins of hopper olivine in differentiated crystallization runs are considered. It is found that olivine nucleation occurred throughout cooling, except for the incubation period during early cooling. The elongate combed olivines in harrisite apparently grew as the magma locally supercooled to at least 30 C. It is suggested that the branching crystals in most comb layers, including comb-layered harrisite, probably grew along thermal gradients.

Donaldson, C. H.↗

NASA NTRS1977

Different ages of lunar light plains

The crater populations of 18 lunar light plains (Cayley plains) show a variation in relative ages by a factor of about 4 in crater frequency in regions in the surroundings of the Orientale and Imbrium basin, and by a factor of greater than 25 for more distant sites. Thus the idea of a moon-wide synchronism in the emplacement of the lunar light plains with the formation of the basins Imbrium or Orientale cannot be supported. Some light plains are younger than the youngest basin Orientale. Since these plains cannot have been emplaced by any other basin-forming event and local impact-derived origin can certainly be excluded, an endogenic (magmatic) origin is proposed for these plains. Age determination data (D sub L values) by Soderblom and Lebofsky (1972) and Soderblom and Boyce (1972) are shown to be correlated with own cumulative crater frequency data (N) for surfaces younger than about 3.8 b.y. It is found that D sub L is proportional to the 0.6 power of N. For ages greater than 3.8 b.y., the D sub L data by those authors, especially their light plains data, are incompatible with the present crater frequency data.

Neukum, G.↗

NASA NTRS1977

Ionizing radiation effects on SBP9900 microprocessor

The radiation resistance of a 16-bit microprocessor based on integrated injection logic technology has been investigated. Cumulative fluences of 10 to the 12th power to 10 to the 14th power e/sq cm were used in the radiation-resistance study. Complete failure of the microprocessor was noted at a fluence level of 1.2 times 10 to the 14th power e/sq cm. Though the radiation resistance of the microprocessor makes it suited for space applications, reductions in the power dissipation of the device are needed.

Stanley, A. G.↗