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At least 973 records · Page 54

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NASA NTRS1982

Glasses of impact origin from Apollo 11, 12, 15, and 16 - Evidence for fractional vaporization and mare/highland mixing

Electron microprobe analyses have been performed on glasses of impact origin in Apollo 11 breccias (10059, 10060, 10061), Apollo 12 soil (12070), and Apollo 15 breccias (15318, 15425, 15426, 15427). These glasses were produced by shock melting of regolith, rather than of rock. Simple concepts for better understanding and interpreting the chemical data from impact glasses have been developed. These concepts are a significant improvement on earlier strategies, which centered principally on cluster analysis. Using ratios of refractory lithophile elements, the compositional effects of fractional vaporization often associated with impact melting to obtain chemical information about the mare and highland components in the regoliths parental to the glasses have been 'seen through'. This method is also applied to the mare-derived impact glasses from Apollo 16 in order to place constraints on the types of volcanic components occurring in Mare Nectaris. Since impact glasses can be used to derive chemical constraints on the indigenous lithologies comprising multi-component regoliths; the frequent occurrence of these glasses, as well as their low masses, should make them critically important for study when small quantities of grab-samples are returned by future unmanned spacecraft from planets, satellites, and asteroids where regoliths are present.

Delano, J. W.↗

NASA NTRS1983

Two hundred passage three-way valve: Fraction collector

This paper describes the design and operation of a fraction collector used to direct flow of separated biological materials from 197 capillary tubes to either a collection tray or to a waste tank. This mechanism uses a 28-volt dc gear motor driving twin cams to force 197 needles through a self-sealing silicone rubber septum, where they inject the material in 197 separate pockets in a collection tray. The position of the collector tray is sensed by two optical limit switches. The time sequences are controlled automatically by an electronics control monitoring module.

Keffer, J. L.↗

NASA NTRS1982

Numerical simulation of crystal fractionation in shergottite meteorites

Cumulus clinopyroxenes in the Shergotty and Zagami meteorites suggest crystal fractionation occurred, possibly by gravitative settling. Numerical models of this process in a nonconvecting environment argue that the small phenocrysts can segregate only under extreme conditions of cooling time or gravitational field strength. Since textures indicate that cooling time was not excessive, a large (planetary) g is required by these models, in agreement with other suggestions that the shergottite parent body may be Mars. Other calculations indicate that it is extremely difficult to produce the observed textures in a convecting environment, unless crystal setting occurred in a quiescent zone at the bottom of the magma chamber.

Grimm, R. E.↗

NASA NTRS1983

Stratospheric sulfuric acid fraction and mass estimate for the 1982 volcanic eruption of El Chichon

The stratospheric sulfuric acid fraction and mass for the 1982 volcanic eruptions of El Chichon are investigated using data from balloon soundings at Laramie (41 deg N) and in southern Texas (27-29 deg N). The total stratospheric mass of these eruptions is estimated to be approximately 8 Tg about 6.5 months after the eruption with possibly as much as 20 Tg in the stratosphere about 45 days after the eruption. Observations of the aerosol in Texas revealed two primary layers, both highly volatile at 150 C. Aerosol in the upper layer at about 25 km was composed of an approximately 80 percent H2SO4 solution while the lower layer at approximately 18 km was composed of a 60-65 percent H2SO4 solution aerosol. It is calculated that an H2SO4 vapor concentration of at least 3 x 10 to the 7th molecules/cu cm is needed to sustain the large droplets in the upper layer. An early bi-modal nature in the size distribution indicates droplet nucleation from the gas phase during the first 3 months, while the similarity of the large particle profiles 2 months apart shows continued particle growth 6.5 months after the explosion.

Hofmann, D. J.↗

NASA NTRS1983

Experimental investigations of trace element fractionation in iron meteorites. II - The influence of sulfur

The partitioning of Ir, Ge, Ga, W, Cr, Au, P, and Ni between solid metal and metallic liquid is investigated as a function of temperature and the S-concentration of the metallic liquid. The partition coefficients for siderophile elements, such as Ir, W, Ga, and Ge, are found to increase by factors of 10-100 as the S-concentration of the metallic liquid increases from 0-30 wt percent. Partition coefficients for other siderophile elements, such as Ni, Au, and P, increase by factors of only 2-3. In contrast, a decrease is seen in the partition coefficients for the more chalcophile element Cr. These experimentally determined coefficients are used in conjunction with a fractional crystallization model to reproduce the geochemical behavior of Ni, P, Au, and Ir during the magmatic evolution of groups IIAB, IIIAB, IVA and IVB iron meteorites. The mean S-concentration for each group increases in the order IVB, IVA, IIIAB, IIAB, which is in accordance with cosmochemical prediction. However, the geochemical behavior of Ge, Ga, W, and Cr cannot be reproduced in an internally consistent way. It is concluded that the magmatic histories of these iron meteorite groups are more complex than has been generally assumed.

Jones, J. H.↗

NASA NTRS1984

Application of a fractional-step method to incompressible Navier-Stokes equation

A numerical method for computing three dimensional, time dependent incompressible flows is presented. The method is based on a fractional step, or time-splitting, scheme in conjunction with the approximate-factorization technique. The use of velocity boundary conditions for the intermediate velocity field leads to inconsistent numerical solutions. Appropriate boundary conditions for the intermediate velocity field are derived and tested. Numerical solutions for flow inside a driven cavity and over a backward-facing step are presented and compared with experimenal data and other numerical results.

Kim, J.↗

NASA NTRS1984

Global variation of the para hydrogen fraction in Jupiter's atmosphere and implications for dynamics on the outer planets

A detailed analysis of the Voyager infrared spectrometer measurements on Jupiter's atmosphere is presented, and possible implications of para hydrogen disequilibrium for the energetics and dynamics of that atmosphere are examined. The method of data analysis is described, and results for the large scale latitude variation of the para hydrogen fraction are presented. The Jovian results show pronounced latitude variation, and are compared with other parameters including wind fields, thermal structure, and various indicators of atmospheric clouds. The problem of equilibration rate is reexamined, and it is concluded that on Jupiter the equilibration time is longer than the radiative time constant at the level of emission to space, but that this inequality reverses at greater depths. A model for the interaction of fluid motions with the ortho-para conversion process is presented, and a consistent mixing length theory for the reacting ortho-para mixture is developed. Several implications of the Jovian data for atmospheric energetics and stability on the outer planets are presented.

Conrath, B. J.↗

NASA NTRS1984

A connection between state-space and doubly coprime fractional representations

Explicit formulas for a doubly coprime fractional representation of the transfer function of a lumped LTI system are given in terms of a stabilizable and detectable state-space realization of the transfer function. These formulas allow existing computational algorithms to be utilized for the purpose of computing doubly coprime factorizations. Several additional implications of this result are briefly discussed, as are some immediate extensions and future research directions.

Nett, C. N.↗

NASA NTRS1985

Modelling Equilibrium and Fractional Crystallization in the System MgO-FeO-CaO-Al2O3-SiO2

A mathematical modelling technique for use in petrogenesis calculations in the system MgO-FeO-CaO-Al2O3-SiO2 is reported. Semiempirical phase boundary and elemental distribution information was combined with mass balance to compute approximate equilibrium crystallization paths for arbitrary system compositions. The calculation is applicable to a range of system compositions and fractionation calculations are possible. The goal of the calculation is the computation of the composition and quantity of each phase present as a function of the degree of solidification. The degree of solidification is parameterized by the heat released by the solidifying phases. The mathematical requirement for the solution of this problem is: (1) An equation constraining the composition of the magma for each solid phase in equilibrium with the liquidus phase, and (2) an equation for each solid phase and each component giving the distribution of that element between that phase and the magma.

Herbert, F.↗

NASA NTRS1985

Nebular volatile fractionations associated with chondrule formation

Chondrules are ubiquitous constituents of primitive solar system matter, indicating that chondrule formation was an important and widespread process in the early history of the solar system. If chondrules formed from fine grained CI like precursors, some volatile fractionation must have accompanied chondrule formation. This is not likely related to a separation of chondrules from gas (and dust, fine enough to be coupled to gas) shortly after formation, a process required by most models of chondrule formation. If chondrules are continuously formed in and removed from a region of the solar nebula, the chemical environment in this region will change. Vaporization of solid increases both oxygen and sulfur in the gas relative to H. Depending on the oxygen/sulfur ratio, which may vary widely as a function of precursor composition and temperature, two cases can be distinguished: (1) sulfur requires reaction with solid to condense, and thus may become much more enriched than 0; (2) if a significant amount of silicate is vaporized together with sulfides and does not recondense, changes in H/O outweigh S enrichment. In combination, these two effects may be able to account for much of the chemical variation among various types of chondrites. Opaque, fine grained matrix in unequilibrated chondrites, which is thought to derive from dust, has indeed been found to have a volatile element abundance complementary to chondrules.

Kracher, A.↗

NASA NTRS1985

About increase of the large transvere momentum processes fraction in hA interactions at energies 5.10(14) - 10(16) eV according to the data on E.A.S. hadrons

The lateral distributions of extensive air showers (EAS) hadrons obtained at Tien-Shan array are compared with the simulations. The simulation data have been treated in the same way as experimental data, including the recording method. The comparison shows that the experimental hadron lateral distributions are wider than simulated ones. On the base of this result the conclusion is drawn that the fraction of processes with large p (perpendicular) increases in hadron-air interactions at energies 5 x 10 to the 14 to 10 to the 16 eV compared with accelerator data in p-p interactions at lower energies.

Danilova, T. V.↗

NASA NTRS1983

Fractional representation theory - Robustness results with applications to finite dimensional control of a class of linear distributed systems

This paper reviews and extends the fractional representation theory. In particular, new and powerful robustness results are presented. This new theory is utilized to develop a preliminary design methodology for finite dimensional control of a class of linear evolution equations on a Banach space. The design is for stability in an input-output sense, but particular attention is paid to internal stability as well.

Nett, C. N.↗

NASA NTRS1986

Effect of volume fraction and size of fine-gamma prime particles on raising the creep strength of a DS nickel-base superalloy

The creep behavior of a directionally solidifified nickel-base superalloy, DKS3, has been investigated as a function of the volume fraction and size of the gamma-prime phase at 760 and 950 C. The dislocation structure and morphology of gamma-prime was examined by transmission electron microscopy at the primary, secondary and tertiary creep stages at 73.8 kgf/sq mm. Experimental results are described in terms of a high temperature creep model in the range of temperatures and applied stresses where shearing of the gamma-prime phase does not control the straining process.

Lin, D. L.↗

NASA NTRS1986

Organic chemistry of Murchison meteorite: Carbon isotopic fractionation

The carbon isotopic composition of individual organic compounds of meteoritic origin remains unknown, as most reported carbon isotopic ratios are for bulk carbon or solvent extractable fractions. The researchers managed to determine the carbon isotopic ratios for individual hydrocarbons and monocarboxylic acids isolated from a Murchison sample by a freeze-thaw-ultrasonication technique. The abundances of monocarboxylic acids and saturated hydrocarbons decreased with increasing carbon number and the acids are more abundant than the hydrocarbon with the same carbon number. For both classes of compounds, the C-13 to C-12 ratios decreased with increasing carbon number in a roughly parallel manner, and each carboxylic acid exhibits a higher isotopic number than the hydrocarbon containing the same number of carbon atoms. These trends are consistent with a kinetically controlled synthesis of higher homologues for lower ones.

Yuen, G. U.↗

NASA NTRS1986

Scattering from nonspherical Chebyshev particles. I - Cross sections, single-scattering albedo, asymmetry factor, and backscattered fraction

Using the extended boundary condition method, scattering calculations from randomly oriented rotationally symmetric nonspherical particles were made, the size parameters (1-25) and the refractive indicies (1.5 0.02i) of which were chosen to relate to the transfer of solar and IR radiation in an aerosol atmosphere. Comparison of computations for 23 Chebyshev shapes to corresponding size-averaged spherical results revealed that nonsphericity increased absorption for size parameters larger than around 10 and decreased the asymmetry factor, and correspondingly increased the backscattered fraction, in the size ranges 8-15. The scattering efficiency was somewhat larger for nonspherical particles, while the single-scattering albedo tended to be smaller, and concavity was shown to almost always enhance spherical-nonspherical differences.

Mugnai, A.↗

NASA NTRS1985

Application of a fractional-step method to incompressible Navier-Stokes equations

Kim, J.↗

NASA NTRS1986

Fractionation of noble gases by thermal escape from accreting planetesimals

Assuming solar initial elemental and isotopic ratios and a determination of the degree of fractionation occurring by competition between gravitational binding and escape, a model is developed for selective noble gas loss through escape during the growth of planetesimals to form the terrestrial planets. Of the two classes of planetesimals that can form on a time scale that is consistent with modern accretion models, one is depleted in neon while the other is neon-rich. The mechanism is noted to be capable of accounting for all known properties of the noble gas volatiles on the terrestrial planets, with only one exception, namely the Ar-36/Ar-38 ratios for Mars and the earth, which are much lower than observed.

Donahue, T. M.↗

NASA NTRS1986

Mass fractionation during transonic escape and implications for loss of water from Mars and Venus

Hydrodynamic escape of hydrogen from a planetary atmosphere can remove heavier gases as well as hydrogen, provided that the escape rate is sufficiently large. Analytic approximations for the degree of mass fractionation of a trace species during hydrodynamic escape are compared with accurate numerical solutions for the case of transonic outflow. The analytic approximations are most accurate when the ratio of molecular weights of the heavier and lighter constituents is large so that nonlinear terms in the momentum equation for the heavy constituent become small. The simplest analytic formula is readily generalized to the case where a heavy constituent is also a major species. Application of the generalized formula to hypothetical episodes of hydrodynamic escape from Venus and Mars suggests that both hydrogen and oxygen could have escaped; thus, substantial quantities of water may have been lost without the need to oxidize large amounts of the crust.

Zahnle, Kevin J.↗