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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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NASA NTRS1991

Summary of completed project

The primary goal of the work in this proposal has been the determination of the requirement for acceleration of particles, especially electrons, during solar flares. This is one of the important and yet unsolved problems in solar flares and other astronomical objects. This is done by detailed theoretical investigation of interaction of accelerated particles with ambient plasma including interaction with particles, waves, and large scale magnetic fields. Comparison with observed impulsive phase radiation such as X-rays, gamma-rays, microwaves, and type III radiation is used for constraining the models and for determination of the characteristics of the accelerated particles. Steady state and time-dependent numerical codes have been developed based on the Fokker-Planck method for study of the particle acceleration and transport during a flare. Using these, the correlation between characteristics of radiation at various wavelengths have been investigated and some constraints have been set on the model parameters. During the last three year period of this grant, dissertation research of three graduate students have been partially supported by this grant. Each of these theses has dealt with various observed properties of flare emission with particular emphasis on the interrelationship between radiation in at least two energy bands: X-rays and gamma-rays, X-rays and microwaves, and X-rays and type III radiation. This has allowed considerable tightening of constraints on models, and inclusion of wave particle interaction has allowed direct calculations of acceleration processes.

Petrosian, Vahe↗
NASA NTRS1993

Numerical solutions of the complete Navier-Stokes equations

The objective of this study is to compare the use of assumed pdf (probability density function) approaches for modeling supersonic turbulent reacting flowfields with the more elaborate approach where the pdf evolution equation is solved. Assumed pdf approaches for averaging the chemical source terms require modest increases in CPU time typically of the order of 20 percent above treating the source terms as 'laminar.' However, it is difficult to assume a form for these pdf's a priori that correctly mimics the behavior of the actual pdf governing the flow. Solving the evolution equation for the pdf is a theoretically sound approach, but because of the large dimensionality of this function, its solution requires a Monte Carlo method which is computationally expensive and slow to coverage. Preliminary results show both pdf approaches to yield similar solutions for the mean flow variables.

Hassan, H. A.↗
NASA NTRS1994

A machine-learning apprentice for the completion of repetitive forms

Forms of all types are used in businesses and government agencies, and most of them are filled in by hand. Yet much time and effort has been expended to automate form-filling by programming specific systems or computers. The high cost of programmers and other resources prohibits many organizations from benefiting from efficient office automation. A learning apprentice can be used for such repetitious form-filling tasks. In this paper, we establish the need for learning apprentices, describe a framework for such a system, explain the difficulties of form-filling, and present empirical results of a form-filling system used in our department from September 1991 to April 1992. The form-filling apprentice saves up to 87 percent in keystroke effort and correctly predicts nearly 90 percent of the values on the form.

Hermens, Leonard A.↗
NASA NTRS1995

Thrust measurements of a complete axisymmetric scramjet in an impulse facility

This paper describes tests which were conducted in the hypersonic impulse facility T4 on a fully integrated axisymmetric scramjet configuration. In these tests the net force on the scramjet vehicle was measured using a deconvolution force balance. This measurement technique and its application to a complex model such as the scramjet are discussed. Results are presented for the scramjet's aerodynamic drag and the net force on the scramjet when fuel is injected into the combustion chambers. It is shown that a scramjet using a hydrogen-silane fuel produces greater thrust than its aerodynamic drag at flight speeds equivalent to 260 m/s.

Paull, A.↗
NASA NTRS1993

X-ray emission from a complete sample of Abell clusters of galaxies

The Rosat all sky survey is used to investigate the X-ray properties of a sample of Abell clusters with measured redshifts and accurate positions. The sample comprises the 145 clusters within a 561 square degree region at high galactic latitude. The mean redshift is 0.17. The sample mean exposure time is higher than average and its mean galactic column density is very low. These together produce a flux limit of about 4.2 x 10(exp -13) erg/sq cm/s in the 0.5 to 2.5 keV energy band. By analyzing the excess of positive fluctuations of the X-ray flux at the cluster positions, compared with the fluctuations of randomly drawn background fields, it is possible to extend these results below the nominal flux limit. It is found that 80 of richness R equal to or greater than 0 and 86 of R equal to or greater than 1 clusters are X-ray emitters with fluxes above 1.10 to the power of minus 13 erg/sq cm/s. Nearly 90 of the clusters meeting the requirements to be in Abell's statistical sample emit above the same level. It is concluded that almost all Abell clusters are real clusters and the Abell catalogue is not strongly contaminated by projection effects. The Kaplan-Meier product limit estimator is used to calculate the cumulative X-ray luminosity function. It is shown that the shape of the luminosity functions are similar for different richness classes, but the characteristic luminosities of richness 2 clusters are about twice of those of richness 1 clusters which are in turn about twice of those of richness zero clusters. This result is another manifestation of the luminosity richness relation for Abell cluster.

Briel, Ulrich G.↗
NASA NTRS1995

Completing below-ground carbon budgets for pastures, recovering forests, and mature forests of Amazonia

This progress report covers the following efforts initiated for the year: year-round monthly soil CO2 flux measurements were started in both primary and secondary forests and in managed and degraded pastures; root sorting and weighing has begun and all four ecosystems at Paragominas have been analyzed through samples; regional modeling of soil water dynamics and minimum rooting depth has been done and the RADAMBRASIL soils database has been digitized and a 20 year record of the precipitation for the region has been produced, along with a hydrological ('bucket-tipping') model that will run within a GIS framework; prototype tension lysimeters have been designed and installed in soil pits to begin assessing the importance of DOC as a source of organic matter in deep soils; and many publications, listed in this document, have resulted from this year's research. Two of the papers published are included with this annual report document.

Davidson, Eric A.↗
NASA NTRS1993

Numerical simulation of a complete STOVL aifcraft in ground effect

The aerodynamic environment encountered by powered-lift aircraft operating in ground effect is unique among flight vehicles. It is characterized by low forward speed with embedded regions of high subsonic or supersonic jet flows. During ground effect operations, complex recirculating flows generated by the jets produce large changes in the aerodynamic loads on the flight vehicle. Analytic prediction and small-scale experimental methods have produced mixed results in this flight regime, with the result that costly full-scale powered tests are required to evaluate the performance of candidate designs. The ability to accurately predict vehicle performance without resorting to full-scale tests will be critical to future powered-lift aircraft projects. This paper summarizes efforts to predict the flow field about a powered-lift aircraft, the YAV-8B Harrier, in low level jet-borne flight by solution of the Reynolds-averaged Navier-Stokes equations. Results are compared to infrared images of the NASA YAV-8B Harrier V/STOL Systems Research Aircraft (VSRA) under similar flight conditions.

Smith, Merritt H.↗
NASA NTRS1994

A complete southern sky redshift survey

We discuss a magnitude-limited redshift survey covering a region around the south Galactic pole (SSRS2). The survey includes 3592 galaxies and covers a region of 1.13 sr to a limiting m(sub B(0)) = 15.5, directly comparable to CfA2. Together, CfA2 and SSR2 cover more than a third of the sky. The northern and southern surveys are remarkably similar. Both contain voids with diameters as large as 5000 km/s. The southern survey contains the Southern Wall, similar to the northern Great Wall. The distributions of velocity dispersions for systems extracted from the SSRS2 and CfA2 surveys are also remarkably similar. For the SSRS2, an inhomogeneity-independent technique yields Schechter luminosity function parameters M(sup *) = -19.50 and alpha = -1.20 (H(sub O) = 100 h km/s/Mpc, h = 1 unless otherwise specified). The steep faint-end slope is probably attributable to bluer galaxies. By examining the normalized density fluctuations in the SSRS2 and CfA2 surveys, we suggest that the combined sample is not yet large enough to be 'fair.' There are large fluctuations in shells at 10,000 km/s.

Da Costa, L. Nicolaci↗
NASA NTRS1994

The complete Einstein Observatory X-ray survey of the Orion Nebula region.

We have analyzed archival Einstein Observatory images of a roughly 4.5 square degree region centered on the Orion Nebula. In all, 245 distinct X-ray sources have been detected in six High Resolution Imager (HRI) and 17 Imaging Proportional Counter (IPC) observations. An optical database of over 2700 stars has been assembled to search for candidate counterparts to the X-ray sources. Roughly half the X-ray sources are identified with a single Orion Nebula cluster member. The 10 main-sequence O6-B5 cluster stars detected in Orion have X-ray activity levels comparable to field O and B stars. X-ray emission has also been detected in the direction of four main-sequence late-B and early-A type stars. Since the mechanisms producing X-rays in late-type coronae and early-type winds cannot operate in the late-B and early-A type atmospheres, we argue that the observed X-rays, with L(sub X) approximately = 3 x 10(exp 30) ergs/s, are probably produced in the coronae of unseen late-type binary companions. Over 100 X-ray sources have been associated with late-type pre-main sequence stars. The upper envelope of X-ray activity rises sharply from mid-F to late-G, with L(sub x)/L(sub bol) in the range 10(exp -4) to 2 x 10(exp -3) for stars later than approximately G7. We have looked for variability of the late-type cluster members on timescales of a day to a year and find that 1/4 of the stars show significantly variable X-ray emission. A handful of the late-type stars have published rotational periods and spectroscopic rotational velocities; however, we see no correlation between X-ray activity and rotation. Thus, for this sample of pre-main-sequence stars, the large dispersion in X-ray activity does not appear to be caused by the dispersion in rotation, in contrast with results obtained for low-mass main-sequence stars in the Pleiades and pre-main-sequence stars in Taurus-Auriga.

Gagne, Marc↗
NASA NTRS1994

The X-ray spectra of blazars: Analysis of the complete EXOSAT archive

We analyzed the 0.1-10 keV spectra of 26 blazars (21 BL Lac objects and 5 highly polarized quasars), on the basis of 93 exposures taken from the EXOSAT archives. Fits were performed first with a single power-law model. Indications are found that better fits can be obtained with models where the slope steepens at higher energies. We therefore considered a broken power law and found that in a large fraction of the spectra the fit is significantly improved. Fits with a power law + oxygen edge at 0.6 keV are also explored.

Sambruna, Rita M.↗
NASA NTRS1994

A study of ultraviolet absorption lines through the complete Galactic halo by the analysis of HST faint object spectrograph spectra of active Galactic nuclei, 1

The ultraviolet (1150 - 2850 A) spectra of a number of active galactic nuclei (AGNs) observed with the Hubble Space Telescope (HST) Faint Object Spectrograph (FOS) have been used to study the properties of the Galactic halo. The objects that served as probes are 3C 273, PKS 0454-220, Pg 1211+143, CSO 251, Ton 951, and PG 1351+640. The equivalent widths of certain interstellar ions have been measured, with special attention paid to the C IV/C II and Si IV/Si II ratios. These ratios have been intercompared, and the highest values are found in the direction of 3C 273, where C IV/C II = 1.2 and Si IV/Si II greater than 1. These high ratios may be due to a nearby supernova remnant, rather than to ionized gas higher up in the Galactic halo. Our data give some support to the notion that QSO metal-line systems may arise from intervening galaxies which contain high supernova rates, galactic fountains, and turbulent mixing layers.

Burks, Geoffrey S.↗
NASA NTRS1995

Numerical solutions of the complete Navier-Stokes equations

A compressible turbulence model based on the kappa-zeta (enstrophy) model of Robinson et al. is developed. The model incorporates a new compressibility correction model that is quite different from previous models. Results are compared to the mixing layer data compiled by Settles and Dodson. It is shown that the predictions of the theory are in good agreement with experiment. Moreover, the present model is superior to the kappa-epsilon model with traditional compressibility corrections.

Hassan, H. A.↗
NASA NTRS1995

Statistical analysis of interplanetary shock waves observed during a complete solar activity cycle

During the Helios mission a total of 391 fast forward non-corotating interplanetary shock waves was identified. For most of the 12 years between 1974 and 1986 unique shock detection was possible for more than 80 % of the time. The occurrence rate (in shocks per day) varied from 0.02 at activity minimum in 1976 to 0.17 in 1979 and 0.22 in 1982 with a significant drop to 0.13 in 1980, i.e. right at activity maximum. The average properties of all events as functions of solar distance. phase in the solar cycle, heliographic and -magnetic latitude and others are discussed.

Khalisi, E.↗
NASA NTRS1996

Numerical solutions of the complete Navier-Strokes equations

This report describes the development of an enstrophy model capable of predicting turbulence separation and its application to two airfoils at various angles of attack and Mach numbers. In addition, a two equation kappa-xi model with a tensor eddy viscosity was developed. Plans call for this model to be used in calculating three dimensional turbulent flows.

Hassan, H. A.↗
NASA NTRS1991

High-Moisture Diet for Laboratory Rats: Complete Blood Counts, Serum Biochemical Values, and Intestinal Enzyme Activity

Rats were fed an irradiated high-moisture diet (KSC-25) with or without access to a water bottle. Physiologic values were compared between these two groups and a group of rats fed a purified diet. Hematologic and serum biochemical values, urine specific gravity, and intestinal enzyme activities were determined from samples collected from the three groups of rats. Sprague Dawley rats (n=32) fed the irradiated high-moisture diet with or without a water bottle were the test animals. Rats (n=16) fed an irradiated purified diet and water provided via a water bottle were the control group. The purified diet formulation, modified AIN-76A, is a commonly used purified diet for laboratory rodents. All rats remained alert and healthy throughout the study. A comparison of the physiologic values of rats in this study with reported normal values indicated that all of the rats in the study were in good health. Significant differences (P less than 0.05) of the physiologic values from each rat group are reported.

Battles, August H.↗
NASA NTRS1996

Towards a complete conceptual model of substorm onsets and expansions

Observational results from the CRRES satellite near times of substorm onsets support the theoretical premise that substorms initiate near the inner edge of the plasma sheet. The region is connected latitudinally to the equatorward-most pre-breakup arc. During the growth phase, the inner edge of the plasma sheet moves towards the earth. This motion is modulated by various cavity oscillations of the magnetosphere-ionosphere coupled magnetosphere. This modulation can locally reverse the background convection electric field. The reversed convection taps energy stored in the inner-edge region of the plasma sheet. The near earth plasma sheet moves out of equilibrium with the lobes, and a rarefaction is launched tailward. This allows current driven dissipation to grow and a near-earth X-line to form. A model is presented which explains the observations of the CRRES satellite, and can account for the behavior associated with auroral intensification and substorm onset.

Erickson, Gary M.↗
NASA NTRS1997

Numerical Solutions of the Complete Navier-Stokes Equations

This report details the development of a new two-equation turbulence closure model based on the exact turbulent kinetic energy k and the variance of vorticity, zeta. The model, which is applicable to three dimensional flowfields, employs one set of model constants and does not use damping or wall functions, or geometric factors.

Robinson, David F.↗