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At least 235 records · Page 13

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NASA NTRS1978

The bearing of spinel cataclasites on the crust-mantle structure of the moon

Subsolidus thermodynamic calculations have been made to define the temperature and pressure conditions required to equilibrate lunar spinel cataclasites (olivine + high alumina orthopyroxene + pleonaste spinel + plagioclase + or - cordierite) that occur as clasts in 15445, 73263, and 72435. The results, which are subject to modification by improved thermodynamic data and experiment, indicate that those samples that are cordierite-free and of high Mg/(Mg + Fe) were derived from the lower crust and possibly from a high-velocity zone of the uppermost mantle. However, the cordierite-bearing type in 72435,8 /low Mg/(Mg + Fe)/ resided in the upper levels of the crust prior to excavation by impact. Consideration of the relevant supersolidus phase equilibria indicates that the whole-rock chemistry of all spinel cataclasites can only be explained by pleonaste spinel accumulation. These materials are interpreted to be primordial cumulate rocks formed during the differentiation of the lunar magma ocean.

Herzberg, C. T.↗

NASA NTRS1979

A survey of interstellar C I - Insights on carbon abundances, UV grain albedos, and pressures in the interstellar medium

Interstellar atomic carbon has been sampled over 33 different paths with visual extinctions ranging from about 0.15 to 1.5 mag. The trend of C I vs different forms of hydrogen is found to be steep and somewhat erratic. It is concluded that the observed behavior can be explained by strong differences in the responses of C I, H I, and H2 equilibria to physical conditions, together with marked variations of these conditions within different interstellar clouds.

Jenkins, E. B.↗

NASA NTRS1979

Formation, support and stability of quiescent prominences

The most prevalent hypotheses and theories that treat the formation and support of quiescent prominences are reviewed, along with current ideas concerning the stability of such prominences. Observational clues to the formation of quiescent prominences are described, condensation of coronal material is examined, and injection mechanisms of prominence formation are considered. Questions pertaining to the support and stability of quiescent prominences are discussed in terms of magnetohydrostatic equilibrium, prominence equilibria, and breakdown of stability conditions.

Tandberg-Hanssen, E.↗

NASA NTRS1979

Advanced methods for preparation and characterization of infrared detector materials

Crystal growth of Hg sub 1-x Cd sub x Te and density measurements of ingot slices are discussed. Radial compositional variations are evaluated from the results of infrared transmission edge mapping. The pseudo-binary HgTe-CdTe phase diagram is examined with reference to differential thermal analysis measurements. The phase equilibria calculations, based on the 'regular association solution' theory (R.A.S.) are explained and, using the obtained R.A.S. parameters, the activities of Hg, Cd, and Te vapors and their partial pressures over the pseudo-binary melt are calculated.

Lehoczy, S. L.↗

NASA NTRS1980

The properties of clusters in the gas phase. IV - Complexes of H2O and HNOx clustering on NOx/-/

Thermodynamic quantities for the gas-phase clustering equilibria of NO2(-) and NO3(-) were determined with high-pressure mass spectrometry. A comparison of values of the free energy of hydration derived from the data shows good agreement with formerly reported values at 296 K. New data for larger NO2(-) and NO3(-) hydrates as well as NO2(-)(HNO2)n were obtained in this study. To aid in understanding the bonding and stability of the hydrates of nitrite and nitrate ions, CNDO/2 calculations were performed, and the results are discussed. A correlation between the aqueous-phase total hydration enthalpy of a single ion and its gas-phase hydration enthalpy was obtained. Atmospheric implications of the data are also briefly discussed.

Lee, N.↗

NASA NTRS1979

Basaltic volcanism - The importance of planet size

The volumetrically abundant basalts on the earth, its moon, and the eucrite parent planet all have chemical compositions that are controlled to a large extent by dry, low-pressure, crystal-liquid equilibria. Since this generalization is valid for these three planetary bodies, we infer that it may also apply to the other unsampled terrestrial planets. Other characteristics of basaltic volcanism show variations which appear to be related to planet size: the eruption temperatures, degrees of fractionation, and chemical variety of basalts and the endurance of basaltic volcanism all increase with planet size. Although the processes responsible for chemical differences between basalt suites are known, no simple systematization of the chemical differences between basalts from planet to planet has emerged.

Walker, D.↗

NASA NTRS1980

Trace elements as quantitative probes of differentiation processes in planetary interiors

The characteristic trace element signature that each mineral in the source region imparts on the magma constitutes the conceptual basis for trace element modeling. It is shown that abundances of trace elements in extrusive igneous rocks may be used as petrological and geochemical probes of the source regions of the rocks if differentiation processes, partition coefficients, phase equilibria, and initial concentrations in the source region are known. Although compatible and incompatible trace elements are useful in modeling, the present review focuses primarily on examples involving the rare-earth elements.

Drake, M. J.↗

NASA NTRS1980

The role of P2O5 in silicate melts

Phase equilibria data in the systems SiO2-P2O5, P2O5-M(x)O(y), and P2O5-M(x)O(y)-SiO2 are employed in conjunction with chromatographic and spectral data to investigate the role of P2O5 in silicate melts. P2O5 depolymerizes pure SiO2 melts by entering the network as a four-fold coordinated cation, but polymerizes melts in which an additional metal cation other than silicon is present. In this complex system P2O5 acts to increase phase separation by further enrichment of the high charge density cations Ti, Fe, Mg, Mn, Ca, in the ferrobasaltic liquid. The dual behavior of P2O5 is explained in a model which requires complexing of phosphate anions and metal cations in the melt. This interaction destroys Si-O-M-O-Si bonds polymerizing the melt. The higher concentration of Si-O-M-O-Si bond complexes in immiscible ferrobasaltic liquids relative to their conjugate immiscible granite liquids explains the partitioning of P2O5 into the ferrobasaltic liquid.

Ryerson, F. J.↗

NASA NTRS1980

Numerical studies of new stellarator concepts

A three-dimensional computer code has been developed to study the magnetohydrodynamic equilibrium and stability of a diffuse or sharp boundary plasma in toroidal geometry. It is shown how equilibria with net toroidal current identically zero can be determined and how growth rates of instabilities can be calculated. Applications are made to an l = 2, 3 stellarator configuration that offers the possibility of achieving a critical value as high as 10% for the plasma parameter

Bauer, F.↗

NASA NTRS1980

Nepheline and sodalite in a barred olivine chondrule from the Allende meteorite

The discovery of nepheline and sodalite in association with glass in a barred olivine chondrule from the Allende C3V meteorite is reported, and the possible origin of the minerals is discussed. Scanning electron microscope/energy dispersive analysis indicates that the major minerals of the chondrule are olivine, bronzite and chromite, with olivine bars separated by glass of nearly pure plagioclase composition. The olivine is observed to have a composition richer in Fe than that predicted from olivine-liquid equilibria, indicating, along with the presence of plagioclase glass and small amounts of subcalcic diopside, the nonequilibrium crystallization of the barred olivine chondrule. The textural features of the chondrule are consistent with a liquid origin for nepheline and sodalite from the chondrule-forming liquid under nonequilibrium conditions.

Lumpkin, G. R.↗

NASA NTRS1980

Subcritical transition to turbulence in plane channel flows

A linear three dimensional mechanism for the transition of plane Poiseuille flows to turbulence is presented which provides good agreement with experimental observations. The mechanism is based on the evolution of states within a band of quasi-equilibria which slowly approach the stable upper branch solutions for the evolution of flow energy but which are strongly unstable to infinitesimal three-dimensional disturbances. Numerical simulation has shown that if two-dimensional flow persists long enough for the three-dimensional perturbations to attain finite amplitude, the resulting three dimensional flow quickly develops a turbulent character with nonperiodic behavior, and thus transition can be predicted from knowledge of the initial two- and three-dimensional energies and time scales. The mechanism predicts transition to turbulence at Reynolds numbers greater than 1000, as observed in experiments, and implies higher threshold three-dimensional energies in plane Couette flow.

Orszag, S. A.↗

NASA NTRS1980

Lunar highland melt rocks - Chemistry, petrology and silicate mineralogy

A selected suite containing several of the largest samples of lunar highland melt rocks includes impact melt specimens (anorthositic gabbro, low-K Fra Mauro) and volcanic specimens (intermediate-K Fra Mauro). Although previous assumptions of LKFM volcanism have fallen into disfavor, no fatal arguments against this hypothesis have been presented, and the evidence of a possibly 'inherited igneous' olivine-plagioclase cosaturation provides cause for keeping a volcanic LKFM hypothesis viable. Comparisons of silicate mineralogy with melt rock compositions provide information on the specimen's composition and cooling history. Plagioclase-rock compositions can be matched to the experimentally determined equilibria for appropriate samples to identify melt rocks with refractory anorthitic clasts. Olivine-rock compositions indicate that melt rock vitrophyres precipitate anomalously Fe-rich olivine; the cause of this anomaly is not immediately evident. The Al-Ti and Ca-Fe-Mg zonation in pyroxene provide information on relative cooling rates of highland melt rocks, but Cr- and Al-content (where Al-rich low-Ca pyroxene cores are preserved in rapidly cooled samples) can be correlated with composition of the host rock.

Vaniman, D. T.↗

NASA NTRS1982

Simultaneous stabilization and simultaneous pole placement by nonswitching dynamic compensation

The 'simultaneous stabilization problem' is defined and theorems are proposed for its solution. The problem consists in answering the question: given an r-tuple G sub 1(s), G sub r(s) of p x m proper transfer functions, does there exist a compensator K(s) such that the closed loop systems G sub 1(s) (I+K(s)G sub 1(s)) (-1), G sub r(s) (I+K(s) G sub r(s)) (-1) are (internally) stable. This question arises in reliability theory, where G sub 2(s), G sub r(s) represents a plant G sub 1(s) operating in various modes of failure and K(s) is a nonswitching stabilizing compensator. It is important in the stability analysis and design of a plant which can be switched into various operating modes. The simultaneous stabilization problem can also apply to the stabilization of a nonlinear system which is linearized at several equilibria. Conditions are defined for pole placement and the generalized Sylvestor matrix is discussed.

Ghosh, B. K.↗

NASA NTRS1981

Chaotic /strange/ and periodic behavior in instability saturation by the oscillating two-stream instability

The nonlinear Schroedinger equation with linear growth and damping is truncated to three waves. The resulting system of nonlinear ordinary differential equations describes the excitation of linearly damped waves by the oscillating two-stream instability driven by a linearly unstable pump wave. This system represents a simple model for the nonlinear saturation of a linearly unstable wave. The model is examined analytically and numerically as a function of the dimensionless parameters of the system. It is found that the model can exhibit a wealth of characteristic dynamical behavior including stationary equilibria, Hopf bifurcations to periodic orbits, period doubling bifurcations, chaotic solutions characteristic of a strange attractor, tangent bifurcations from chaotic to periodic solutions, transient chaos, and hysteresis. Many of these features are shown to be explainable on the basis of one-dimensional maps. In the case of chaotic solutions, evidence for the presence of a strange attractor is provided by demonstrating Cantor set-like structure (i.e., scale invariance) in the surface of section.

Russell, D. A.↗

NASA NTRS1981

Two-phase models of quasar emission line regions

It is demonstrated that the emitting gas in clouds of quasar emission line regions must be confined by a hot intercloud medium, provided only that the heating mechanisms are strong enough to drive the low-density intercloud gas above a few tens of millions degrees K. The study of the thermal properties of the gas presented includes heating by photoionization, Compton scattering, suprathermal particles, absorption of radio frequency radiation, cloud friction, thermal conduction, and shocks. Cooling curves for photoionized gases are presented, and phase diagrams analogous to the pressure-temperature diagrams used in studying the interstellar medium are constructed for various conditions. It is shown that two-phase equilibria occur over a wide range of mean density, but over a much narrower range of pressure. The implications of these results for the emission line region are discussed, and it is shown that the emission clouds may be short-lived.

Krolik, J. H.↗

NASA NTRS1981

Eruptive solar magnetic fields

The quasi-steady evolution of solar magnetic fields in response to gradual photospheric changes is considered, with particular attention given to the threshold of a sudden eruption in the solar atmosphere. The formal model of an evolving, force-free field dependent on two Cartesian coordinates is extended to a field which is not force free but in static equilibrium with plasma pressure and gravity. The basic physics is illustrated through the evolution of a loop-shaped electric current sheet enclosing a potential bipolar field with footpoints rooted in the photosphere. A free-boundary problem is posed and then solved for the equilibrium configuration of the current sheet in a hydrostatically supported isothermal atmosphere. As the footpoints move apart to spread a constant photospheric magnetic flux over a larger region, the equilibria available extend the field to increasing heights.

Low, B. C.↗

NASA NTRS1980

Spinel cataclasites in 15445 and 72435 - Petrology and criteria for equilibrium

The problem of establishing the existence of equilibrium among the coexisting phases in the rock is addressed by presenting petrographic and mineral chemistry data on a new spinel cataclasite from 15445 (clast H) and data more extensive than those previously available on two clasts in 72435. Criteria useful in reconstructing the original petrology of these and other spinel cataclasites are analyzed by considering equilibrium among the different phases, that is, the mono- or polymict nature of these cataclasized samples. Finally, the role of impact processes in disturbing the equilibria is discussed.

Baker, M. B.↗

NASA NTRS1981

Mathematical modeling and computer simulation of isoelectric focusing with electrochemically defined ampholytes

A mathematical model of isoelectric focusing at the steady state has been developed for an M-component system of electrochemically defined ampholytes. The model is formulated from fundamental principles describing the components' chemical equilibria, mass transfer resulting from diffusion and electromigration, and electroneutrality. The model consists of ordinary differential equations coupled with a system of algebraic equations. The model is implemented on a digital computer using FORTRAN-based simulation software. Computer simulation data are presented for several two-component systems showing the effects of varying the isoelectric points and dissociation constants of the constituents.

Palusinski, O. A.↗