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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.

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At least 721 records · Page 40
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NASA NTRS1987

Evolution of interstellar pickup ions in the solar wind

A model is constructed for the evolution of an interstellar pickup ion distribution in the solar wind. The model assumes that the ions are immediately isotropized at ionization and follows the subsequent development of the distribution function as the particles are convected with the solar wind. The effects of energy diffusion in an ambient wave field with a power law spectrum, adiabatic deceleration in the expanding solar wind, and continual addition of newly ionized particles are all included in the model. An analytical expression describing the evolution of the distribution function in phase space velocity and heliocentric radius is obtained. The distribution quickly approaches an asymptotic shape in phase space which depends on the relative efficiency of the energy diffusion process compared to that of adiabatic deceleration. At large distances from the sun the density of pickup ions falls as 1/r in this model. An expression for the distribution function at large distances and for large particle speed is presented. The asymptotic shape should describe the distribution of pickup ions in the outer heliosphere and could be used as an input distribution for a model of the anomalous component of heliosphere and could be used as an input distribution for a model of the anomalous component of cosmic rays. Comparison of this work with the recent observation of He(+) at 1 AU implies that the energy diffusion process is very weak inside 1 AU.

Isenberg, Philip A.↗
NASA NTRS1986

Evolution of the zonal mean state in the equatorial middle atmosphere during October 1978-May 1979

The week-to-week evolution of the zonal mean state of the equatorial middle atmosphere is studied using daily mapped temperatures derived with the Limb Infrared Monitor of the Stratosphere (LIMS) instrument on Nimbus 7. The characteristics of the LIMS instrument and rocket data are described. The development of the zonal mean state at low latitudes, and the relation between the evolution of the zonal mean state and extratropical changes are examined. The residual circulation is estimated using a radiative algorithm. Advection by the residual mean circulation, and the role of inertial acceleration in mean meridional circulations are discussed.

Hitchman, Matthew H.↗
NASA NTRS1987

The structure and evolution of seasonal wind anomalies over the near-equatorial eastern Indian and western Pacific Oceans

The longitude-height-time structure and evolution of near-equatorial wind variability over the eastern Indian and western Pacific Oceans are studied using data obtained from a network of eight radiosonde stations extending from southern India to the central Pacific Ocean. The seasonal zonal wind anomalies observed at the cross section beween Trivandrum and Majuro stations are analyzed using an empirical orthogonal function. The Walker Circulation fluctuations are described in terms of standing oscillations in the longitude-height plane, and it is determined that Southern Oscillation propagation anomaly best represents the wind fluctuations. A complex empirical orthogonal function (CEOF) analysis and an El Nino compositing methodology are applied to the seasonal zonal wind anomalies. It is determined that the composite El Nino anomalies correspond to the spatial structure and temporal evolution of anomalies implied by the CEOF analysis.

Gutzler, David S.↗
NASA NTRS1987

Evolution of magnetic cataclysmic binaries

The physics of magnetic cataclysmic binary evolution is considered, and it is suggested that DQ Her stars will not evolve into AM Her stars (assuming that mu1 remains constant throughout their evolution), in contradiction to previous assertions. Four regimes that depend on mu1 values are identified, and it is suggested that the mu1 values of the known DQ Her stars are significantly less than those of the known AM Her stars (unless all known stars of both groups have M1 greater than 1 solar mass). A new way of producing ultrashort period binaries is proposed in which synchronization of the magnetic degenerate dwarfs injects angular momentum into the binary, driving the system apart and producing a synchronization-induced period gap. The secondaries in these binaries are shown to be hydrogen-rich rather than hydrogen depleted or pure helium.

Lamb, D. Q.↗
NASA NTRS1987

Nonlinear evolution of radiation-driven thermally unstable fluids

The nonlinear evolution of a radiation-driven thermally unstable planar fluid is simulated numerically using a semiimplicit finite-difference algorithm. When the equilibrium state of the fluid is perturbed by random initial excitation of the velocity field, dense, cool, two-dimensional structures are found to form in a rarer, warmer surrounding medium. The nonlinear phase of evolution is characterized by the turbulent contraction of the condensed region, accompanied by a significant increase in the amount of energy radiated. It is found that, if the random velocity perturbation has a sufficiently large amplitude, the fluid will not form condensed structures. Finally, the relationship of these results to observations of the solar chromosphere, transition region, and corona is discussed.

Dahlburg, R. B.↗
NASA NTRS1987

Galilean satellite evolution - Observational evidence for secular changes in mean motions

The techniques and data used in previous determinations of the orbital evolution of the Galilean satellites of Jupiter are reviewed, and a new analysis is developed on the basis of Lieske's (1986) collection of 15,711 eclipse observations from the period 1652-1983, photographic observations, and Voyager optical-navigation images (Synnott et al., 1982). The data and results are presented in tables, and the secular changes in the satellite mean motions are found to be smaller than previously determined: e.g., (-7.4 + or - 8.7) x 10 to the -10th/yr for Io and (+8 + or - 42) x 10 to the -9th/yr for the relative evolution between Io and Europa.

Lieske, J. H.↗
NASA NTRS1987

The red/infrared evolution in galaxies - Effect of the stars on the asymptotic giant branch

The effect of including the asymptotic giant branch (AGB) population in a spectral synthesis model of galaxy evolution is examined. Stars on the AGB are luminous enough and also evolve rapidly enough to affect the evolution of red and infrared colors in galaxies. The validity of using infrared colors as distance indicators to galaxies is then investigated in detail. It is found that for z of 1 or less infrared colors of model galaxies behave linearly with redshift.

Chokshi, Arati↗
NASA NTRS1987

Science synergism study for EOS on evolution of desert surfaces

The effectiveness of EOS data as a basis for the study of desert surfaces' evolution is presently evaluated for both long and short term geomorphic evolution. Attention is given to the usefulness of such sensor systems planned for EOS as MODIS for regional vegetation distribution/variability monitoring, HIRIS for visible-near IR observations, TIMS for lithological identification, HMMR and SSMI for soil characteristics, LASA for atmospheric profiles, SAR for surface roughness, ALT for two-dimensional topography, ACR for the calibration of imaging sensors, and ERBE for climate modeling and regional surface albedo variation determinations.

Farr, Tom G.↗
NASA NTRS1986

Convective scale interaction: Arc cloud lines and the development and evolution of deep convection

Information is used from satellite data and research aircraft data to provide new insights concerning the mesoscale development and evolution of deep convection in an atmosphere typified by weak synoptic-scale forcing. The importance of convective scale interaction in the development and evolution of deep convection is examined. This interaction is shown to manifest itself as the merger and intersection of thunderstorm outflow boundaries (arc cloud lines) with other convective lines, areas or boundaries. Using geostationary satellite visible and infrared data convective scale interaction is shown to be responsible for over 85 percent of the intense convection over the southeast U.S. by late afternoon, and a majority of that area's afternoon rainfall. The aircraft observations provided valuable information concerning critically important regions of the arc cloud line: (1) the cool outflow region, (2) the density surge line interface region; and (3) the sub-cloud region above the surge line. The observations when analyzed with rapid scan satellite data, helped in defining the arc cloud line's life cycle as 3 evolving stages.

Purdom, James Francis Whitehurst↗
NASA NTRS1988

The evolution of glutathione metabolism in phototrophic microorganisms

The low molecular weight thiol composition of a variety of phototropic microorganisms is examined in order to ascertain how evolution of glutathione (GSH) production is related to the evolution of oxygenic photosynthesis. Cells were extracted in the presence of monobromobimane (mBBr) to convert thiols (RSH) to fluorescent derivatives (RSmB) which were analyzed by high performance liquid chromatography (HPLC). Significant levels of GSH were not found in green sulfur bacteria. Substantial levels were present in purple bacteria, cyanobacteria, and eukaryotic algae. Other thiols measured included cysteine, gamma-glutamylcysteine, thiosulfate, coenzyme A, and sulfide. Many of the organisms also exhibited a marked ability to reduce mBBr to syn-(methyl,methyl)bimane, an ability which was quenched by treatment with 2-pyridyl disulfide or 5,5 prime-bisdithio - (2-nitrobenzoic acid) prior to reaction with mBBr. These observations indicate the presence of a reducing system capable of electron transfer to mBBr and reduction of reactive disulfides. The distribution of GSH in phototropic eubacteria indicates that GSH synthesis evolved at or around the time that oxygenic photosynthesis evolved.

Fahey, Robert C.↗
NASA NTRS1988

Cosmological parameters and evolution of the galaxy luminosity function

The relationship between the observed distribution of discrete sources of a flux limited sample, the luminosity function of these sources, and the cosmological model is discussed. It is stressed that some assumptions about the form and evolution of the luminosity function must be made in order to determine the cosmological parameters from the observed distribution of sources. Presented is a method to test the validity of these assumptions using the observations. It is shown how, using higher moments of the observed distribution, one can determine, independently of the cosmological model, all parameters of the luminosity function except those describing evolution of the density and the luminosity of the luminosity function. These methods are applied to the sample of approximately 1000 galaxies recently used by Loh and Spillar to determine a value of the cosmological density parameter Omega approx = 1. It is shown that the assumptions made by Loh and Spillar about the luminosity function are inconsistent with the data, and that a self-consistent treatment of the data indicates a lower value of Omega approx = 0.2 and a flatter luminosity function. It should be noted, however, that incompleteness in the sample could cause a flattening of the luminosity function and lower the calculated value of Omega and that uncertainty in the values of these parameters due to random fluctuations is large.

Caditz, David↗
NASA NTRS1988

Convergence of Galerkin approximations for operator Riccati equations: A nonlinear evolution equation approach

An approximation and convergence theory was developed for Galerkin approximations to infinite dimensional operator Riccati differential equations formulated in the space of Hilbert-Schmidt operators on a separable Hilbert space. The Riccati equation was treated as a nonlinear evolution equation with dynamics described by a nonlinear monotone perturbation of a strongly coercive linear operator. A generic approximation result was proven for quasi-autonomous nonlinear evolution system involving accretive operators which was then used to demonstrate the Hilbert-Schmidt norm convergence of Galerkin approximations to the solution of the Riccati equation. The application of the results was illustrated in the context of a linear quadratic optimal control problem for a one dimensional heat equation.

Rosen, I. G.↗
NASA NTRS1988

The atmospheres of the earth and the other planets: Origin, evolution and composition

The current understanding of the composition, chemistry, and structure of the atmospheres of the other planets and the origin, early history, and evolution of the earth's atmosphere is reviewed. The information on the atmospheres of the other planets is based on the successful Mariner, Viking, Pioneer, and Voyager missions to these planets. The information on the origin, early history, and evolution of the atmosphere, which is somewhat speculative, is largely based on numerical studies with geochemical and photochemical models.

Levine, Joel S.↗
NASA NTRS1987

Origin and evolution of fluctuations in the solar wind - Helios observations and Helios-Voyager comparisons

Hour-averaged data from the Helios and Voyager spacecraft are used here to investigate the origin and evolution of low-frequency interplanetary fluctuations from 0.3 to 20 AU. The previously observed evolution toward a less purely Alfvenic state with increasing heliocentric distance is shown to occur more rapidly in the inner heliosphere and in low-speed as well as high-speed streams. It is concluded that outward-traveling flucutations are predominantly generated by the sun, but that in situ turbulence, most likely due to stream shear, generates fluctuations with both inward and outward senses of correlation.

Roberts, D. A.↗
NASA NTRS1987

The evolution of a coronal streamer prior to mass ejection

A model describing the quasi-static evolution of a coronal helmet streamer as it is inflated with excess mass was developed. The model produces a sequence of magnetostatic equilibria for a magnetic field configuration that includes a current sheet in the equatorial plane as well as distributed volume currents. The equilibrium solutions are given as Legendre series, and the height at which the current sheet starts is adjusted iteratively to maintain constant flux in the closed-field region. The model was fit to SMM coronagraph/polarimeter observations showing the slow growth of a coronal streamer prior to its disruption in association with an eruptive prominence and mass ejection on August 18, 1980. The results suggest that the early phase of this event is consistent with the quasi-static evolution of the corona in response to the slow addition of mass to the closed-field region of the streamer.

Wolfson, Richard↗
NASA NTRS1988

Evidence for a scaling solution in cosmic-string evolution

Numerical simulations are used to study the most fundamental issue of cosmic-string evolution: the existence of a scaling solution. Strong evidence is found that a scaling solution does indeed exist. This justifies the main assumption on which the cosmic-string theories of galaxy formation is based. The main conclusion coincides with that of Albrecht and Turok (1985) but the results are not consistent with theirs. In fact, the results indicate that the details of string evolution are very different from the standard dogma.

Bennett, David P.↗
NASA NTRS1988

On wind-type flows in astrophysical jets. III - Temporal evolution of perturbations and the formation of shocks

The temporal evolution of disturbances in a spherically symmetric polytropic wind from a central object is studied. Such disturbances may be due to localized momentum addition/subtraction, as, for example, by MHD waves, heating/cooling mechanisms in the outflow, or localized deviations from spherical symmetric expansion. The evolution of an initial perturbed state to a continuous or discontinuous final equilibrium state, as predicted by previous analytic calculations for stationary flows, is followed. It is shown that some of the predicted discontinuous equilibrium states are not physically accessible, while the attainment of the remaining equilibrium states depends on both the temporal and the spatial parameters characterizing the perturbation. The results are derived for solar conditions, but in fact can be applied to outflows in other astrophysical systems. In particular, applications to the solar wind and flows in astrophysical jets are discussed.

Trussoni, E.↗
NASA NTRS1988

The evolution of molecular clouds

The problem of the structure and evolution of molecular clouds is reviewed, with particular emphasis given to the relationship with star formation. The basic hypothesis is that magnetic fields are the primary agents for supporting molecular clouds, although damped Alfven waves may play an important role in the direction parallel to the field lines. This picture naturally leads to a conception of 'bimodal star formation'. It is proposed that high-mass stars form from the overall gravitational collapse of a supercritical cloud, whereas low-mass stars form from small individual cores that slowly condense by ambipolar diffusion from a more extended envelope until they pass the brink of graviational instability and begin to collapse dynamically from 'inside-out'. The evidence that the infall stage of protostellar evolution is terminated by the development of a powerful stellar wind is reviewed.

Shu, Frank H.↗