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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Classification of solar flares and the relationship between the first and second phases

A large data base on solar flares obtained during the last solar maximum years makes it necessary to revise the views on the relationship between the impulsive phase and the second phase of flares. Contrary to the view most popular before the launch of the Solar Maximum Mission, it is now known that relativistic electrons and gamma-ray-producing protons and ions are accelerated during the impulsive phase. Because flares producing nuclear gamma-rays are different from ordinary flares, it is concluded that additional processes take place in gamma-ray-line flares. Recent studies have shown that flares with gradual hard X-ray time profiles not only produce nuclear gamma-rays during the impulsive phase but also develop full-fledged second-phase phenomena. It is proposed that filament eruption plays a key role in gamma-ray-line flares. When an erupting filament interacts with an overlaying flare loop, relativistic electrons and energetic protons are produced during the impulsive phase. When the erupting filament fully distends the overlying flare loop, full-fledged second-phase phenomena, such as shocks, interplanetary energetic particles, mass ejections and etc. are observed. When the overlying flare loop is compact and strong enough to suppress the activated filament, gamma-rays are emitted during the first phase but no second-phase phenomena occur.

Bai, T.↗
NASA NTRS1993

The unusual metallic particles in Krymka LL3.0 chondrite

The composition, structure peculiarities, and possible scenario of formation of unusual metallic particles in Krymka LL3.0 are shown. In metal released from gentle crushed after removal of chondrules of Krymka LL3.0 chondrite matter, two types of unusual metallic particles were detected. The first type of particle mainly consists of coarse-grained (greater than or equal to 50 microns) kamacite and fine-grained (less than or equal to 10 microns) Ni-high (approximately 53 wt. percent) taenite. These particles have well-defined zonal structure: kamacite is in central part of particles whereas taenite is in outside and the grains of taenite form the mantle around kamacite. In the second type of particle Fe,Ni-phase contains only fine-grained Ni-rich taenite. In both particle types there are also fine-grained phosphate, troilite, and silicate. Both particle types have mostly rounded to subrounded form.

Fisenko, A. V.↗
NASA NTRS1973

Metallic particles of high cobalt content in Apollo 15 soil samples.

Single phase alpha-kamacite containing more than 3.2 wt % Co and gamma-taenite containing from 30 to 60 wt % Ni from the Apollo 15 soils - 15031, 15071, 15081, 15261, and 15271 - have been examined by metallographic and electron microprobe techniques. In addition two phase alpha + gamma particles from soils 14003, 15071, 15261, and 15271 with Ni and Co contents well outside the meteoritic range have also been examined. Two distinct types of alpha-gamma structure occur, one analogous to 'clear taenite' in ordinary chondrites, and the other analogous to a 'Widmanstaetten' structure in Ni-rich ataxites. The measured Ni gradients in the two-phase particles are very similar to those meteorites having the same structure. However the Co content is much higher than the meteoritic samples, up to 12 wt % in the alpha phase. Approximate phase equilibria data for the Fe-Ni-Co system indicate equilibration of the two-phase particles during cooling to approximately 350 C. Estimates of cooling rates and second-phase growth times indicate that the maximum time necessary for the development of the high-Co two-phase structures is roughly 25 to 100 m.y. These estimates argue for the development of the two-phase structures during formation of the lunar crust, at a depth of 10 to 20 km beneath the moon's surface.

Axon, H. J.↗
NASA NTRS1998

Thermal Decomposition Behavior of Ammonium Perchlorate and of an Ammonium-Perchlorate-Based Composite Propellant

The thermal decomposition of ammonium perchlorate (AP) and ammonium-perchlorate-based composite propellants is studied using the simultaneous thermogravimetric modulated beam mass spectrometry (STMBMS) technique. The main objective of the present work is to evaluate whether the STMBMS can provide new data on these materials that will have sufficient detail on the reaction mechanisms and associated reaction kinetics to permit creation of a detailed model of the thermal decomposition process. Such a model is a necessary ingredient to engineering models of ignition and slow-cookoff for these AP-based composite propellants. Results show that the decomposition of pure AP is controlled by two processes. One occurs at lower temperatures (240 to 270 C), produces mainly H2O, O2, Cl2, N2O and HCl, and is shown to occur in the solid phase within the AP particles. 200(micro) diameter AP particles undergo 25% decomposition in the solid phase, whereas 20(micro) diameter AP particles undergo only 13% decomposition. The second process is dissociative sublimation of AP to NH3 + HClO4 followed by the decomposition of, and reaction between, these two products in the gas phase. The dissociative sublimation process occurs over the entire temperature range of AP decomposition, but only becomes dominant at temperatures above those for the solid-phase decomposition. AP-based composite propellants are used extensively in both small tactical rocket motors and large strategic rocket systems.

Behrens, R.↗
NASA NTRS1989

The 27-28 October 1986 FIRE IFO Cirrus case study: Comparison of radiative transfer theory with observations by satellite and aircraft

Observations of cirrus and altocumulus clouds during the First International Satellite Cloud Climatology Project Regional Experiment (FIRE) are compared to theoretical models of cloud radiative properties. Three tests are performed. First, LANDSAT radiances are used to compare the relationship between nadir reflectance ot 0.83 micron and beam emittance at 11.5 microns with that predicted for model calculations using spherical and nonspherical phase functions. Good agreement is found between observations and theory when water droplets dominate. Poor agreement is found when ice particles dominate, especially using scattering phase functions for spherical particles. Even when compared to a laboratory measured ice particle phase function, the observations show increased side scattered radiation relative to the theoretical calculations. Second, the anisotropy of conservatively scattered radiation is examined using simultaneous multiple angle views of the cirrus from LANDSAT and ER-2 aircraft radiometers. Observed anisotropy gives good agreement with theoretical calculations using the laboratory measured ice particle phase function and poor agreement with a spherical particle phase function. Third, Landsat radiances at 0.83, 1.65, and 2.21 microns are used to infer particle phase and particle size. For water droplets, good agreement is found with King Air FSSP particle probe measurements in the cloud. For ice particles, the LANDSAT radiance observations predict an effective radius of 60 microns versus aircraft observations of about 200 microns. It is suggested that this descrepancy may be explained by uncertainty in the imaginary index of ice and by inadequate measurements of small ice particles by microphysical probes.

Wielicki, Bruce A.↗
NASA NTRS1991

Light scattering by lunar-like particle size distributions

A fundamental input to models of light scattering from planetary regoliths is the mean phase function of the regolith particles. Using the known size distribution for typical lunar soils, the mean phase function and mean linear polarization for a regolith volume element of spherical particles of any composition were calculated from Mie theory. The two contour plots given here summarize the changes in the mean phase function and linear polarization with changes in the real part of the complex index of refraction, n - ik, for k equals 0.01, the visible wavelength 0.55 micrometers, and the particle size distribution of the typical mature lunar soil 72141. A second figure is a similar index-phase surface, except with k equals 0.1. The index-phase surfaces from this survey are a first order description of scattering by lunar-like regoliths of spherical particles of arbitrary composition. They form the basis of functions that span a large range of parameter-space.

Goguen, Jay D.↗
NASA NTRS1978

Radio evidence on the particle distribution functions in the corona following flares

This paper summarizes results of radio studies of the distribution functions (number, energy distribution, and pitch-angle distribution) of the energetic particles that are produced at the time of solar flares. The clues and constraints they impose on the mechanisms of acceleration are considered, bearing in mind that radio evidence implies that there are at least two stages of acceleration in many flares. The distribution functions of the particles resulting from first-phase acceleration, first- and/or second-phase, and second-phase acceleration are discussed.

Dulk, G. A.↗
NASA NTRS1984

Electrical conductivity studies on CuBr containing Al2O3 particles

The conductivity of CuBr was studied and the role of a second phase, Al2O3, dispersed in CuBr was tested. CuBr melts at 493 C and exhibits three phases in the solid state. CuBr is a good ionic conductor with a transport number for copper ions of virtually unity with weighed proportions of the appropriate chemicals used. The CuBr materials were heated above melting point of CuBr, and the samples were sandwiched between copper electrodes. The ac conductivity, was determined at 1 kHz between 25 and 440 C depending on the sample. It was shown that at low temperatures, the conductivity for CuBr (Al2O3) increased by as much as 100, whereas in the beta phase the conductivity of CuBr containing Al2O3 decreased. The electrical conductivity studies are in agreement with earlier data.

Dubec, P. M.↗
NASA NTRS2022

Probing the High-energy Gamma-Ray Emission Mechanism in the Vela Pulsar via Phase-resolved Spectral and Energy-dependent Light-curve Modeling

Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV γ-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to ∼100 GeV) and the Fermi Large Area Telescope to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and current-sheet model, invoking a step function for the accelerating electric field as motivated by kinetic simulations. We include a refined calculation of the curvature radius of particle trajectories in the lab frame, impacting the particle transport, predicted light curves, and spectra. Our model reproduces the decrease of the flux of the first peak relative to the second one, evolution of the bridge emission, near-constant phase positions of peaks, and narrowing of pulses with increasing energy. We can explain the first of these trends because we find that the curvature radii of the particle trajectories in regions where the second γ-ray light-curve peak originates are systematically larger than those associated with the first peak, implying that the spectral cutoff of the second peak is correspondingly larger. However, an unknown azimuthal dependence of the E field, as well as uncertainty in the precise spatial origin of the GeV emission, precludes a simplistic discrimination of emission mechanisms.

Monica Barnard↗
NASA NTRS1987

Growth process of gamma'-particles in a liquid-quenched Ni-15 at percent Al alloy

The growth of gamma-prime particles in a supersaturated Ni-15 at% Al alloy prepared by the liquid-quench method was studied using a magnetic mass balance, transmission electron microscopy, and field ion microscopy. Three stages in the precipitation and growth of these particles are demonstrated. In the first phase, the gamma-prime phase was produced by nucleation of spinodal decomposition of the alloy. In the second stage, spherical gamma-prime particles were arranged at random in the matrix with the size independent of aging time. Then, the Al concentration in the matrix decreased with the -1/3 power of the aging time. These results suggest that the degree of ordering increases with aging time. In the third stage, the particles were coarsened with aging time. They were arranged in the matrix (100) zone and were cubic, with the cube face lying on (100). The interfacial free energy was 28.4 mJ/sq m at 873 K and 22.4 mJ/sq m at 973 K.

Tachikake, A.↗
NASA NTRS1990

The 27-28 October 1986 FIRE IFO cirrus case study - Comparison of radiative transfer theory with observations by satellite and aircraft

Observations of cirrus and altocumulus clouds during the FIRE are compared to theoretical models of cloud radiative properties. Three tests are performed. First, radiances are used to compare the relationship between nadir reflectance ot 0.83 micron and beam emittance at 11.5 microns with that predicted for model calculations using spherical and nonspherical phase functions. Good agreement is found between observations and theory when water droplets dominate. Poor agreement is found when ice particles dominate, especially using spherical-particle phase functions (SPPFs). Even when compared to a laboratory-measured ice-particle phase function (IPPF), the observations show great side-scattered radiation than the theoretical calculations. Second, the anisotropy of conservatively scattered radiation is examined using simultaneous multiple angle views of the cirrus from Landsat and ER-2 aircraft radiometers. Observed anisotropy gives good agreement with theoretical calculations using the laboratory IPPF and poor agreement with an SPPF. Third, Landsat radiances at 0.83, 1.65, and 2.21 microns are used to infer particle phase and size. For water droplets, good agreement is found with particle-probe measurements in the cloud. For ice particles, the Landsat radiance observations predict an effective radius of 60 microns versus aircraft observations of about 200 microns. It is suggested that this discrepancy may be explained by uncertainty in the imaginary index of ice and by inadequate measurements of small ice particles by microphysical probes.

Wielicki, Bruce A.↗
NASA NTRS1979

Energetic particles in solar flares

The principal properties of energetic particles accelerated in solar flares are reviewed. Particular emphasis is placed on the high-energy flare component whose acceleration is often referred to as second-phase acceleration. Stochastic Fermi acceleration is treated analytically, and the results of the computation are compared with particle and gamma-ray data to deduce information on the timing of the acceleration, the spectrum of the particles, and the energy content of the nucleonic component. A discussion of He-3 and heavy element abundances is also presented.

Ramaty, R.↗
NASA NTRS1976

Light scattering by tenuous particles - A generalization of the Rayleigh-Gans-Rocard approach

We consider scattering by arbitrarily shaped particles that satisfy two conditions: (1) that the polarizability of the particle relative to the ambient medium be small compared to 1 and (2) that the phase shift introduced by the particle be less than 2. We solve the integro-differential equation proposed by Shifrin by using the method of successive iterations and then applying a Fourier transform. For the second iteration, results are presented that accurately describe scattering by a broad class of particles. The phase function and other elements of the scattering matrix are shown to be in excellent agreement with Mie theory for spherical scatterers.

Acquista, C.↗
NASA NTRS1982

Second-stage acceleration in a limb-occulted flare

From radio observations it is known that two distinct groups of phenomena occur in large solar flares. The phenomena are related to an impulsive phase of approximately 100 s duration in the early stage of a flare and a following second phase lasting for tens of minutes. A study is presented of the limb-occulted flare event of July 22, 1972, giving particular attention to the second stage particle acceleration. The study takes into account hard X-ray, energetic particle, and radio observations. The conducted analysis shows that second stage acceleration is physically distinct from the impulsive phase, and is characterized by continuous and widespread electron acceleration to high energies, most likely by the type II burst shock wave.

Hudson, H. S.↗
NASA NTRS1985

The energy spectra of solar flare electrons

A survey of 50 electron energy spectra from .1 to 100 MeV originating from solar flares was made by the combination of data from two spectrometers onboard the International Sun Earth Explorer-3 spacecraft. The observed spectral shapes of flare events can be divided into two classes through the criteria of fit to an acceleration model. This standard two step acceleration model, which fits the spectral shape of the first class of flares, involves an impulsive step that accelerates particles up to 100 keV and a second step that further accelerates these particles up to 100 MeV by a single shock. This fit fails for the second class of flares that can be characterized as having excessively hard spectra above 1 MeV relative to the predictions of the model. Correlations with soft X-ray and meter radio observations imply that the acceleration of the high energy particles in the second class of flares is dominated by the impulsive phase of the flares.

Evenson, P. A.↗
NASA NTRSDate not supplied

CFD Comparisons with Updated NASA Juncture Flow Data

The purpose of the NASA Juncture Flow experiment is to acquire high-quality flowfield details deep in the corner of a wing-body junction specifically for the purpose of CFD validation. A second phase of testing was recently completed, which includes both laser doppler velocimetry and particle image velocimetry measurements. This paper describes the recent experiment and its results. It also makes detailed comparisons between the experimental data and a new version of a widely-used CFD turbulence model for Reynolds-averaged Navier-Stokes, which was recently developed to improve separated corner flow predictions. The CFD results generally produce very good qualitative agreement with the experiment, although they are less accurate inside of the separation region, as expected.

Experimental Data↗
NASA NTRS1991

Optical properties of aggregate particles whose outer diameter is comparable to the wavelength

Results are described of numerical calculations of the optical properties (extinction efficiency, single-scattering albedo, phase function, and linear polarization) of aggregate particles whose outer diameter is comparable with the wavelength. Results are presented for two types of particle, one composed of monomers whose radius is small compared with the wavelength and a second containing monomers with larger radii. The shape of the forward-scattered lobe of the phase function is diagnostic of the mean projected area (but differs from that for an equal-area sphere), while the linear polarization, phase function at large scattering angles, and single-scattering albedo depend on the monomer diameter. The wavelength dependence of the extinction efficiency differs markedly from that for equal-area spheres. These results can be used to infer particle properties from remotely sensed data.

West, Robert A.↗