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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

The fast decoding of Reed-Solomon codes using Fermat theoretic transforms and continued fractions

It is shown that Reed-Solomon (RS) codes can be decoded by using a fast Fourier transform (FFT) algorithm over finite fields GF(F sub n), where F sub n is a Fermat prime, and continued fractions. This new transform decoding method is simpler than the standard method for RS codes. The computing time of this new decoding algorithm in software can be faster than the standard decoding method for RS codes.

Reed, I. S.↗
NASA NTRS1978

Time-dependence of sea-ice concentration and multiyear ice fraction in the Arctic Basin

Microwave images of sea ice obtained by Nimbus-5 and the NASA CV-990 airborne laboratory are used to determine the time variation of the sea-ice concentration and multiyear ice fraction within the pack ice in the Arctic Basin. The images, constructed from data acquired from the electrically scanned microwave radiometer, are analyzed for four seasons during 1973-1975. Observations indicate significant variations in the sea-ice concentration in the spring, late fall, and early winter. Sea-ice concentrations as low as 50% were detected in large areas in the interior of the Arctic polar sea-ice pack. The applicability of passive-microwave remote sensing for monitoring the time dependence of sea-ice concentration is considered.

Gloersen, P.↗
NASA NTRS1978

Determination of volume fraction in multiphase systems using incomplete pole figures

The determination of the volume fraction of a second phase in a multiphase sample by X-ray diffraction becomes more difficult if the diffracting planes have a preferred orientation. Lopata and Kula have described a method of treating this problem using complete pole figures for each of the phases. With some samples, it is not always possible or convenient to obtain data over the full hemisphere. Equations and an example are given which require X-ray data over a limited range of approximately 0 to 75 deg. This can be obtained by reflection without a specially cut sample or transmission data. A series of Legendre polynomials are fitted to data collected while spinning the sample about its normal. An extrapolation is made possible by introducing two conditions on the end points which must be satisfied if the extrapolation functions are to be valid.

Houska, C. R.↗
NASA NTRS1978

Luna 24: 90-150 micrometer fraction - Implications for remote sampling of regolith

An analysis of the mineral grains and glasses found in the 90 to 150 micron fraction of the Luna 24 core sample is presented and implications for the automatic collection of planetary and asteroidal regoliths are discussed. Electron microprobe analysis for pyroxene, olivine, plagioclase, opaque minerals and glass in samples at various depths indicate that polymineralic grains have compositions similar to those of gabbroic and basaltic fragments from coarser samples, while monomineralic grains contain an additional population of Mg-rich olivines and pyroxene. Most of the glasses are found to be related to mare basalts or local regolith, with nonmare material represented by glasses of highland basalt and low K Fra Mauro composition. It is concluded that as regards mineralogy and petrology, a single grab sample would have been as useful and a series of grab samples on a long traverse would have been more useful than the Luna 24 core sample, with the fine sample being more informative than the coarse.

Papp, H. A.↗
NASA NTRS1978

Fractional crystallization of iron meteorites, an experimental study

Measurements of the distribution coefficients of various elements (Ni, Co, P, Pt, Ir, Ge, Cr, and Au) between solid and liquid phases were made for FeNi alloys. A high thermal gradient crystal growing furnace was employed in order to promote plane front solidification, rapid mixing in the liquid and a minimum of diffusion in the solid. Eight measurements of the nickel distribution coefficient gave an average value of 0.91 plus or minus 0.03 and this value was independent of the Ni concentration in the range 5.5 to 8.75 wt. % Ni. Equilibrium distribution coefficients were also calculated by correcting for the diffusion boundary layer present in the liquid. These values are within 20% of the measured distribution coefficient values. Except for Co and Ni, all the measured distribution coefficient values are closer to 1.0 than those calculated by Scott (1972) for the IIIAB irons. Using the experimental values and the calculated equilibrium values for ternary additions to FeNi melts, it appears that fractional crystallization processes will not explain the observed chemical variations in the major iron meteorite groups. Alternative explanations are suggested which also recognize the fact that cooling rates vary widely in several chemical groups.

Goldstein, J. I.↗
NASA NTRS1978

Sputtering - Its relationship to isotopic fractionation on the lunar surface

Silicon, oxygen, sulfur and, possibly, potassium show systematic enrichment of heavier isotopes with increasing soil maturity, probably as a result of solar-wind sputtering, but such a pattern is not exhibited by solar wind-implanted species. Apparently sputter-erosion is not penetrating to their implantation depth, about 200 A. This suggests that sputtering on the moon is being impeded by deposition of vapor condensate following meteoritic impact. Although neither secular variation in the isotopic composition at the source of regolith carbon, probably the solar wind, nor isotopic fractionation of carbon after implantation in the regolith can be ruled out, carbon isotope systematics currently yield no evidence in support of either process.

Kerridge, J. F.↗
NASA NTRS1979

Decoding of B.C.H. and R.S. codes with errors and erasures using continued fractions

Through the use of continuing fractions, a simplified algorithm for decoding B.C.H. and R.S. codes is developed that corrects both erasures and errors on a finite field GF(q to the m). It is noted that the decoding method is a modification of the Forney-Belekamp technique. Finally, it is believed that the present scheme is both simpler to understand and to implement than more conventional algorithms.

Reed, I. S.↗
NASA NTRS1979

Condensation and fractionation of rare earths in the solar nebula

The condensation behavior of the rare earth elements in the solar nebula is calculated on the basis of the most recent thermodynamic data in order to construct a model explaining group II rare earth element patterns in Allende inclusions. Models considered all involve the removal of large fractions of the more refractory heavy rare earth elements in an early condensate, followed by the condensation of the remainder at a lower temperature. It is shown that the model of Boynton (1975) in which one rare earth element component is dissolved nonideally in perovskite according to relative activity coefficients can not reasonably be made to fit the observed group II patterns. A model in which two rare earth components control the patterns and dissolve ideally in perovskite is proposed and shown to be able to account for the 20 patterns by variations of the perovskite removal temperature and the relative proportions of the two components.

Davis, A. M.↗
NASA NTRS1980

Effects of various assumptions on the calculated liquid fraction in isentropic saturated equilibrium expansions

The saturated equilibrium expansion approximation for two phase flow often involves ideal-gas and latent-heat assumptions to simplify the solution procedure. This approach is well documented by Wegener and Mack and works best at low pressures where deviations from ideal-gas behavior are small. A thermodynamic expression for liquid mass fraction that is decoupled from the equations of fluid mechanics is used to compare the effects of the various assumptions on nitrogen-gas saturated equilibrium expansion flow starting at 8.81 atm, 2.99 atm, and 0.45 atm, which are conditions representative of transonic cryogenic wind tunnels. For the highest pressure case, the entire set of ideal-gas and latent-heat assumptions are shown to be in error by 62 percent for the values of heat capacity and latent heat. An approximation of the exact, real-gas expression is also developed using a constant, two phase isentropic expansion coefficient which results in an error of only 2 percent for the high pressure case.

Bursik, J. W.↗
NASA NTRS1979

A model for chemical and isotopic fractionation in the lunar regolith by impact vaporization

Up until now there has been no complete model of chemical and isotopic fractionation effects which could occur in the lunar regolith as a result of hypervelocity impact vaporization. Previous work on the outlines for such a model are extended and show that impact vaporization could be an efficient mechanism for producing heavy isotope enrichments. Rough qualitative predictions based on the model show a general similarity to the observations on lunar samples.

Housley, R. M.↗
NASA NTRS1980

Siderophile element fractionation in enstatite chondrites

Analysis of the concentration of 10 to 15 siderophile elements was made in the magnetic regions of Abee (E4) and Hvittis (E6). All elements, except Cu, W, and Fe were concentrated in the metal phase; unlike ordinary chondrites, the metal phase Abee and Hvittis consists of homogeneous, uniform grain size kamacite. The Ir/Ni ratio was 25% lower in Abee than in Hvittis, showing that more Ir was lost from Abee during the refractory element fractionation; Abee and other E4-5 members were not depleted in moderately volatile elements. It was concluded that E4-5 and E6 chondrites evolved from two different reservoirs, and that exchange of material among them has not occurred.

Rambaldi, E. R.↗
NASA NTRS1980

Fractional capacity electrolyzer development for CO2 and H2O electrolysis

The electrolyzer module was designed to produce 0.24 kg/d (0.53 lb/d) of breathable oxygen from the electrolysis of metabolic carbon dioxide and water vapor. The fractional capacity electrolyzer module is constructed from three electrochemical tube cells and contains only three critical seals. The module design illustrated an 84 percent reduction in the total number of seals for a one person capacity oxygen generating system based on the solid electrolyte carbon dioxide and water vapor electrolysis concept. The electrolyzer module was successfully endurance tested for 71 days.

Wynveen, R. A.↗
NASA NTRS1980

Empirical ionization fractions in the winds and the determination of mass-loss rates for early-type stars

From a study of the UV lines in the spectra of 25 stars from 04 to B1, the empirical relations between the mean density in the wind and the ionization fractions of O VI, N V, Si IV, and the excited C III (2p 3P0) level were derived. Using these empirical relations, a simple relation was derived between the mass-loss rate and the column density of any of these four ions. This relation can be used for a simple determination of the mass-loss rate from O4 to B1 stars.

Lamers, H. J. G. L. M.↗
NASA NTRS1981

New ionization fractions for the lithium- and helium-like ionization stages of calcium and iron

A reinterpretation of the high resolution X-ray spectra of Ca XIX and Fe XXV, observed during a solar flare on March 25, 1979, is presented. New ionization fractions for Ca XVIII, Ca XIX, Fe XXIV, and Fe XXV are used, and it is shown that the new calculations substantially change the interpretation of the spectra. It is implied that the flare plasma was ionizing during the early phases of the flare, and recombining during the decay phase.

Doyle, J. G.↗
NASA NTRS1981

Studies on the behavior of ammonia and ammonium salts in the atmosphere (1) - Fractional collection of ammonia gas and particulate ammonium

Methods for the fractional collection of trace amounts of atmospheric ammonia gas and ammonium particles on a two staged glass fiber filter are summarized. A standard glass fiber filter washed with distilled water and dried at 120 to 130 C was used. A second filter was impregnated with a mixture of 3% boric acid and 25% glycerin solution. The blank of glass fiber filters impregnated with a mixture of the above solution was very low for ammonia, i.e. 0.06 micrograms in a filter of 47 mm in diameter. The mean concentrations of ammonia and ammonium in air at Kawasaki, a polluted area, were 7.6 and 2.3 micrograms cu m, and those at Sanriku, an unpolluted area 0.9 and 0.2 micrograms cu m, respectively. Ratios of concentration levels of ammonium to total ammonia in the atmosphere were 0.3 and 0.2 for the polluted and unpolluted areas, respectively. Ammonium salts in air at both areas were not correlated with relative humidity. Variations in time of ammonia concentrations and sources in surrounding areas are also considered.

Kiin, K.↗
NASA NTRS1980

The Apollo 16 regolith - Comparative petrology of the greater than 20 micron and 20-10 micron soil fractions, lateral transport and differential volatilization

The present investigation is concerned with questions regarding a preferential transport of finer-grained material on the lunar surface. Attention is also given to a possible appearance of volatization effects in the case of fine-grained glass beads. It is found that preferential lateral transport of fine-grained material is not efficient over the distances required to introduce mare material into the Apollo-16 (A-16) lunar highlands. The presence of granitic glasses found in the 20-10 micron fractions is attributed to comminution of mesostasis. The composition of mesostasis and the silica-rich phases contained within it reported by other investigators supports this conclusion. No evidence could be found of increased volatilization in the finer grained samples.

Kempa, M. J.↗
NASA NTRS1981

Copolyamino acid fractionation and protobiochemistry

Investigation of the origins of living things by the uniquely appropriate method of successive approximation in attempted retracement of steps in molecular evolution has yielded: a comprehensive theoretical flowsheet from archaic inanimate matter to an infrastructured, microscopic, protoreproductive, protometabolic protocell; a laboratory model of the same; and an explanatory assessment of the natural variation component of Darwinian evolution. For each of these, the significance is dependent upon awareness of the intrinsic tendency of amino acids, in mixed sets, to order themselves. Without such awareness, it is believed these vistas would have been delayed for decades. Selfordering would have in turn been difficult to recognize and support were it not for the chromatographic developments in fractionation of copolyamino acids.

Fox, S. W.↗