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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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All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Radon emanation from the moon - Spatial and temporal variability.

Observations of Rn-222 and Po-210 on the lunar surface with the orbiting Apollo alpha particle spectrometer reveal a number of features in their spatial distribution and indicate the existence of time variations in lunar radon emission. Localized Rn-222 or Po-210 around the craters Aristarchus and Grimaldi and the edges of virtually all maria indicates time varying radon emission and suggests a correlation between alpha 'hot spots' and sites of transient optical events observed from the earth. In a gross sense, the slower variations of Rn-222 seem to correlate with the distribution of gamma activity.

Gorenstein, P.↗
NASA NTRS1975

Origin of cosmic rays

Based on recent observations of the galactic gas and gamma ray distributions, the galactic cosmic ray distribution is deduced. This distribution is identical to that of supernova remnants (within experimental error), strongly supporting the hypothesis that most observed cosmic rays are produced by supernovas in our own galaxy. The average age of the cosmic ray sources is suggested, from the character of their distribution, to be about 30 million years.

Stecker, F. W.↗
NASA NTRS1976

The relationship between the galactic matter distribution, cosmic ray dynamics, and gamma ray production

Theoretical considerations and analysis of the results of gamma ray astronomy suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density should be enhanced where the matter density is greatest on the scale of galactic arms. This concept has been explored in a galactic model using recent 21 cm radio observations of the neutral hydrogen and 2.6 mm observations of carbon monoxide, which is considered to be a tracer of molecular hydrogen. The model assumes: (1) cosmic rays are galactic and not universal; (2) on the scale of galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3) the cosmic ray scale height is significantly larger than the scale height of the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of about 3:1.

Kniffen, D. A.↗
NASA NTRS1977

Minimum distortion quantizers

The well-known algorithm of Max is used to determine the minimum distortion quantizers for normal, two-sided exponential, and specialized two-sided gamma input distributions and for mean-square, magnitude, and relative magnitude error distortion criteria. The optimum equally-spaced and unequally-spaced quantizers are found, with the resulting quantizer distortion and entropy. The quantizers, and the quantizers with entropy coding, are compared to the rate distortion bounds for mean-square and magnitude error.

Jones, H. W., Jr.↗
NASA NTRS1985

The substitution of nickel for cobalt in hot isostatically pressed powder metallurgy UDIMET 700 alloys

Nickel was substituted in various proportions for cobalt in a series of five hot-isostatically-pressed powder metallurgy alloys based on the UDIMET 700 composition. These alloys were given 5-step heat treatments appropriate for use in turbine engine disks. The resultant microstructures displayed three distinct sizes of gamma-prime particles in a gamma matrix. The higher cobalt-content alloys contained larger amounts of the finest gamma-prime particles, and had the lowest gamma-gamma-prime lattice mismatch. While all alloys had approximately the same tensile properties at 25 and 650 gamma C, the rupture lives at 650 and 760 C peaked in the alloys with cobalt contents between 12.7 and 4.3 pct. Minimum creep rates increased as cobalt contents were lowered, suggesting their correlation with the gamma-prime particle size distribution and the gamma-gamma-prime mismatch. It was also found that, on overaging at temperatures higher than suitable for turbine disk use, the high cobalt-content alloys were prone to sigma phase formation.

Harf, F. H.↗
NASA NTRS1991

GRIS observations of Al-26 gamma-ray line emission from two points in the Galactic plane

Both of the Gamma-Ray Imaging Spectrometer (GRIS) experiment's two observations of the Galactic center region, at l = zero and 335 deg respectively, detected Al-26 gamma-ray line emission. While these observations are consistent with the assumed high-energy gamma-ray distribution, they are consistent with other distributions as well. The data suggest that the Al-26 emission is distributed over Galactic longitude rather than being confined to a point source. The GRIS data also indicate that the 1809 keV line is broadened.

Teegarden, B. J.↗
NASA NTRS1991

Cosmological gamma-ray bursts

The distribution in angle and flux of gamma-ray bursts indicates that the majority of gamma-ray bursters are at cosmological distances, i.e., at z of about 1. The rate is then about 10 exp -8/yr in a galaxy like the Milky Way, i.e., orders of magnitude lower than the estimated rate for collisions between neutron stars in close binary systems. The energy per burst is about 10 exp 51 ergs, assuming isotropic emission. The events appear to be less energetic and more frequent if their emission is strongly beamed. Some tests for the distance scale are discussed: a correlation between the burst's strength and its spectrum; the absorption by the Galactic gas below about 2 keV; the X-ray tails caused by forward scattering by the Galactic dust; about 1 month recurrence of some bursts caused by gravitational lensing by foreground galaxies; and a search for gamma-ray bursts in M31. The bursts appear to be a manifestation of something exotic, but conventional compact objects can provide an explanation. The best possibility is offered by a decay of a bindary composed of a spinning-stellar-mass black-hole primary and a neutron or a strange-quark star secondary. In the final phase the secondary is tidally disrupted, forms an accretion disk, and up to 10 exp 54 ergs are released. A very small fraction of this energy powers the gamma-ray burst.

Paczynski, Bohdan↗
NASA NTRS1993

Optimal thresholds for the estimation of area rain-rate moments by the threshold method

Optimization of the threshold method, achieved by determination of the threshold that maximizes the correlation between an area-average rain-rate moment and the area coverage of rain rates exceeding the threshold, is demonstrated empirically and theoretically. Empirical results for a sequence of GATE radar snapshots show optimal thresholds of 5 and 27 mm/h for the first and second moments, respectively. Theoretical optimization of the threshold method by the maximum-likelihood approach of Kedem and Pavlopoulos (1991) predicts optimal thresholds near 5 and 26 mm/h for lognormally distributed rain rates with GATE-like parameters. The agreement between theory and observations suggests that the optimal threshold can be understood as arising due to sampling variations, from snapshot to snapshot, of a parent rain-rate distribution. Optimal thresholds for gamma and inverse Gaussian distributions are also derived and compared.

Short, David A.↗
NASA NTRS1999

"Novel Techniques in Non-Stationary Analysis of Rotorcraft Vibration Signitures"

This research effort produced new methods to analyze the performance of linear predictors that track non-stationary processes. Specifically, prediction methods have been applied to the vibration pattern of rotorcraft drivetrains. This analysis is part or a larger rotorcraft Health and Usage Monitoring System (HUMS) that can diagnose immediate failures of the subsystems, as indicated by abrupt change in the vibration signature, and prognosticate future health, by examining the vibration patterns against long-term trends. This problem is described by a earlier joint paper co-authored by members of the funding agency and the recipient institutions prior to this grant effort. Specific accomplishments under this grant include the following: (1) Definition of a framework for analysis of non-stationary time-series estimation using the coefficients of an adaptive filter. (2) Description of a novel method of combining short-term predictor error and long-term regression error to analyze the performance of a non-stationary predictor. (3) Formulation of a multi-variate probability density function that quantifies the performance of a adaptive predictor by using the short- and long-term error variables in a Gamma function distribution. and (4) Validation of the mathematical formulations with empirical data from NASA flight tests and simulated data to illustrate the utility beyond the domain of vibrating machinery.

Meng, Teresa↗
NASA NTRS2012

Microwave Properties of Ice-Phase Hydrometeors for Radar and Radiometers: Sensitivity to Model Assumptions

A simplied framework is presented for assessing the qualitative sensitivities of computed microwave properties, satellite brightness temperatures, and radar reflectivities to assumptions concerning the physical properties of ice-phase hydrometeors. Properties considered included the shape parameter of a gamma size distribution andthe melted-equivalent mass median diameter D0, the particle density, dielectric mixing formula, and the choice of complex index of refraction for ice. We examine these properties at selected radiometer frequencies of 18.7, 36.5, 89.0, and 150.0 GHz; and radar frequencies at 2.8, 13.4, 35.6, and 94.0 GHz consistent with existing and planned remote sensing instruments. Passive and active microwave observables of ice particles arefound to be extremely sensitive to the melted-equivalent mass median diameter D0 ofthe size distribution. Similar large sensitivities are found for variations in the ice vol-ume fraction whenever the geometric mass median diameter exceeds approximately 1/8th of the wavelength. At 94 GHz the two-way path integrated attenuation is potentially large for dense compact particles. The distribution parameter mu has a relatively weak effect on any observable: less than 1-2 K in brightness temperature and up to 2.7 dB difference in the effective radar reflectivity. Reversal of the roles of ice and air in the MaxwellGarnett dielectric mixing formula leads to a signicant change in both microwave brightness temperature (10 K) and radar reflectivity (2 dB). The choice of Warren (1984) or Warren and Brandt (2008) for the complex index of refraction of ice can produce a 3%-4% change in the brightness temperature depression.

Microwave properties↗
DOE OSTI2020

AGR-3/4 Modeling and Transport Parameters

Outline AGR-3/4 experiment and objectives Description of AGR-3/4 modeling approach and inputs Source term (release from particles) Temperature profiles Diffusion through concentric rings Adsorption across gaps between rings Simplified Source Model and updated model results Reconstruction of fission product distributions from gamma tomography data

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1992

Two populations of gamma-ray bursts - A solution to the BATSE conundrum

BATSE measurements suggest that the distribution of gamma-ray burst sources is spatially nonuniform, but as yet shows no discernible anisotropy. This is not consistent with the distribution expected solely from a local galactic population of neutron star sources. We suggest, however, that the inconsistency can be reconciled if there are at least two distinct classes of bursts, both of which originate on galactic neutron stars, but which differ by a factor of 10 exp 4, or more, in mean luminosity. We show, as an example, that the observed V/V(max) distributions and anisotropy constraints of gamma-ray bursts are consistent with those expected from a combination of two such classes, resulting from different burst mechanisms on a single galactic, high-velocity, neutron star population.

Lingenfelter, R. E.↗
NASA NTRS1995

GRO: Black hole models for gamma-ray bursts

The Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory (CGRO) has established that the distribution of gamma-ray bursts (GRB's) is isotropic but is bound radially. This finding suggests that the bursts are either cosmological or they originate from an extended Galactic halo. The implied luminosities and the observed variability of the GRB's on time scales as short as one millisecond suggest that they originate from compact objects. We are presently studying black hole models for GRB's. Any such model must produce a non-thermal photon spectrum to agree with the observed properties. For a wide range of burst parameters the assumed bursting source consists of a non-thermal electron-positron-photon plasma of very high density. It seems possible to produce such a plasma in accretion onto black holes. In our on-going work, we are developing the kinetic theory for a non-equilibrium pair plasma. The main new features of our work are as follows: (1) We do not assume the presence of a thermal electron bath. (2) Non-thermal, high-energy pairs are allowed to have an arbitrary concentration and energy distribution. (3) There is no soft photon source in our model; initially all the photons in the plasma are either energetic X-rays or gamma-rays. (4) The initial energy distribution of the pairs as well as photons is arbitrary. (5) We collect the analytical expressions for the kinetic kernels for all relevant processes. And (6) we present a different approach to finding the time-evolution of pair and photon spectra, which is a combination of the kinetic-theory and the non-linear Monte-Carlo schemes. We have developed many Monte-Carlo programs to model various process, to take into account the time evolution, and to incorporate various physical effects which are unique to non-thermal plasmas. The hydrodynamics of fireballs in GRB's was studied before. Applying results from kinetic theory will improve our understanding of these systems.

Ruderman, Malvin↗
NASA NTRS1992

Gamma-ray bursts in the Galactic halo

It is shown here that significant isotropy can be achieved for the angular and luminosity distributions of gamma-ray bursts with a spherically symmetric Galactic halo model for the bursts if the halo extends out beyond 100 kpc. Large halo core radii enhance isotropy, although consistency with observation is possible for core radii as small as 5 kpc if the halo radius is sufficiently large. The intrinsic luminosity distribution of gamma-ray bursts must be treated as a free parameter to fit the observations. If gamma-ray bursts are from the halo, they are likely to be old population H neutron stars, because models based on pulsars escaping from the Galactic plane have strong anisotropies.

Brainerd, J. J.↗
NASA NTRS1991

Cosmic rays in the Small Magellanic Cloud

The SMC is investigated in order to determine whether this galaxy is in dynamic quasi-stable equilibrium between the expansive pressure of the hot cosmic ray gas, the magnetic fields, and the kinetic motion of interstellar gas and the gravitational attraction of matter. It is argued that the cosmic ray density level is three to five times smaller than that which would exist if the galaxy were in approximate dynamic equilibrium and cosmic ray sources were adequate. The scale of coupling between the cosmic rays and matter in the projected dimension that can be observed is less than 0.5 kpc, which is rather small to be consistent with a stable cosmic ray distribution. The observed matter distribution and the calculated cosmic ray density distribution are used to determine the expected gamma ray intensity distribution.

Sreekumar, P.↗
NASA NTRS1988

Intrinsic and artificial bias in the KONUS cumulative number distribution

The known biases affecting the KONUS gamma burst cumulative number distribution are discussed and categorized as intrinsic (unavoidable) and artificial (avoidable). Artificial biases are removed to obtain a revised, more faithful representation of the true KONUS log N-log Pc, where Pc is in counts (1/0.25 s). A low Pc turnover is still apparent in the revised log N-log Pc. Conflicting claims that the KONUS log N-log Pc is compatible with a nearby disk or an isotropic, homogeneous distribution are tested using the revised log N-log Pc and a rigorous treatment of the KONUS intrinsic gamma background bias. The claims are shown to be improbable. Other possibilities and problms concerning log N-log Pc are discussed, but the need for a complete explanation of the low Pc turnover remains.

Jennings, Mark C.↗
NASA NTRS1975

Gamma ray astronomy

A survey of the instruments developed for gamma ray astronomy is given together with a brief summary of the current status of the observational results. These include the studies of galactic gamma ray emission, the diffuse, presumably extragalactic, gamma radiation, and localized gamma ray sources. The study of the spatial distribution of galactic gamma radiation is beginning to provide a new means for the study of galactic structure and dynamics. The diffuse emission may provide evidence of gamma ray emission in the cosmological past, although improved observations must be obtained before the picture can be clarified. The study of localized sources has shown NP0532, the Crab radio pulsar, to be a gamma ray pulsar also and strong emission from Vela may be due to supernova produced cosmic rays interacting with the remnant gas.

Kniffen, D.↗