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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Large-amplitude magnetic variations in quasi-parallel shocks - Correlation lengths measured by ISEE 1 and 2

Wide separations up to more than 1 earth radius between ISEE 1 and 2 during the second half of 1978 have been used to measure the correlation length of magnetic pulsations in quasiparallel shocks. When the two spacecraft were less than a few hundred km apart, magnetic oscillations measured by magnetometers on both spacecraft exhibited virtually identical waveforms, but at distances of several thousand km, the two time series of field variation showed no detailed similarily at all. The correlation coefficients of the pulsations dropped from close to 1.0 for spacecraft separations of less than 100 km to 0.2 for separations of greater than 800 km. A correlation length of several hundred km may be related to the gyroradius of return protons with energy typical of the peaks of diffuse and beam ion distributions.

Greenstadt, E. W.↗
NASA NTRS1984

Comparison of the solar cosmic ray events on May 7, 1978, and November 22, 1977

Neutron monitor data from the IMP 7 and 8 satellites are used in the present analysis of the cosmic ray events of Nov. 22, 1977, and May 7, 1978, in order to determine the energy spectra of the solar protons from 50 MeV to 10 GeV, together with pitch angle distributions, intensity-time profiles, and anisotropy-time profiles. The solar proton energy spectra obtained agree with the overlapping energy range when the pitch angle distribution is taken into account, and it is noted that the energy spectra covering three decades of energy and eight of intensity, together with their time variations, were very similar for the two events. The May 1978 event is important for the study of solar particle acceleration and their subsequent injection into the interplanetary medium. Although the solar proton propagation of the November 1977 event was diffusive, the solar particle injection was also time-extended and energy-dependent.

Debrunner, H.↗
NASA NTRS2015

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forwardforward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

Parker, L. Neergaard↗
NASA NTRS2015

The Advanced Composition Explorer Shock Database and Application to Particle Acceleration Theory

The theory of particle acceleration via diffusive shock acceleration (DSA) has been studied in depth by Gosling et al. (1981), van Nes et al. (1984), Mason (2000), Desai et al. (2003), Zank et al. (2006), among many others. Recently, Parker and Zank (2012, 2014) and Parker et al. (2014) using the Advanced Composition Explorer (ACE) shock database at 1 AU explored two questions: does the upstream distribution alone have enough particles to account for the accelerated downstream distribution and can the slope of the downstream accelerated spectrum be explained using DSA? As was shown in this research, diffusive shock acceleration can account for a large population of the shocks. However, Parker and Zank (2012, 2014) and Parker et al. (2014) used a subset of the larger ACE database. Recently, work has successfully been completed that allows for the entire ACE database to be considered in a larger statistical analysis. We explain DSA as it applies to single and multiple shocks and the shock criteria used in this statistical analysis. We calculate the expected injection energy via diffusive shock acceleration given upstream parameters defined from the ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) data to construct the theoretical upstream distribution. We show the comparison of shock strength derived from diffusive shock acceleration theory to observations in the 50 keV to 5 MeV range from an instrument on ACE. Parameters such as shock velocity, shock obliquity, particle number, and time between shocks are considered. This study is further divided into single and multiple shock categories, with an additional emphasis on forward-forward multiple shock pairs. Finally with regard to forward-forward shock pairs, results comparing injection energies of the first shock, second shock, and second shock with previous energetic population will be given.

Parker, L. Neergaard↗
NASA NTRS2004

Diffuse Galactic Continuum Gamma Rays. A Model Compatible with EGRET Data and Cosmic-ray Measurements

We present a study of the compatibility of some current models of the diffuse Galactic continuum gamma-rays with EGRET data. A set of regions sampling the whole sky is chosen to provide a comprehensive range of tests. The range of EGRET data used is extended to 100 GeV. The models are computed with our GALPROP cosmic-ray propagation and gamma-ray production code. We confirm that the "conventional model" based on the locally observed electron and nucleon spectra is inadequate, for all sky regions. A conventional model plus hard sources in the inner Galaxy is also inadequate, since this cannot explain the GeV excess away from the Galactic plane. Models with a hard electron injection spectrum are inconsistent with the local spectrum even considering the expected fluctuations; they are also inconsistent with the EGRET data above 10 GeV. We present a new model which fits the spectrum in all sky regions adequately. Secondary antiproton data were used to fix the Galactic average proton spectrum, while the electron spectrum is adjusted using the spectrum of diffuse emission it- self. The derived electron and proton spectra are compatible with those measured locally considering fluctuations due to energy losses, propagation, or possibly de- tails of Galactic structure. This model requires a much less dramatic variation in the electron spectrum than models with a hard electron injection spectrum, and moreover it fits the y-ray spectrum better and to the highest EGRET energies. It gives a good representation of the latitude distribution of the y-ray emission from the plane to the poles, and of the longitude distribution. We show that secondary positrons and electrons make an essential contribution to Galactic diffuse y-ray emission.

Strong, Andrew W.↗
NASA NTRS1985

Sulfate-reducing bacteria: Microbiology and physiology

The sulfate reducing bacteria, the first nonphotosynthetic anaerobic bacteria demonstrated to contain c type cytochromes, perform electron transfer coupled to phosphorylation. A new bioenergetic scheme for the formation of a proton gradient for growth of Desulfovibrio on organic substrates and sulfate involving vectors electron transfer and consistent with the cellular localization of enzymes and electron transfer components was proposed. Hydrogen is produced in the cytoplasm from organic substrates and, as a permease molecule diffuses rapidly across the cytoplasmic membrane, it is oxidized to protons and electrons by the periplasmic hydrogenase. The electrons only are transferred across the cytoplasmic membrane to the cytoplasm where they are used to reduce sulfate to sulfide. The protons are used for transport or to drive a reversible ATPOSE. The net effect is the transfer of protons across the cytoplasmic membrane with the intervention of a proton pump. This type of H2 cycling is relevant to the bioenergetics of other types of anaerobic microorganisms.

Peck, H. D.↗
DOE OSTI2025

Water Dynamics of Superacid Aromatic Proton Exchange Membranes for Fuel Cell Applications

Proton exchange membranes (PEMs) with high conductivity are of critical importance for the development of fuel cells, electrolyzers, and other electrochemical technologies. In this research, poly(1,1,2,2-tetrafluoro-2-phenoxyethane-1-sulfonic acid) (PTPS) with an aromatic polymer main chain and a perfluorinated superacidic polymer side chain was synthesized. The water dynamics of PTPS were characterized across various length scales using a combination of Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR) and compared with Nafion, a standard perfluorinated PEM, and sulfonated poly(ether sulfone) (SPES 40), an aromatic PEM without perfluorinated superacid side chains. The T 1 and T 2 relaxation times of water in the samples probed by NMR increase from SPES 40 to PTPS to Nafion, indicating that the local motion of the water molecules becomes faster. This trend corresponds well with the relative fraction of bulk-like water determined using FTIR. At larger length scales, the diffusion coefficient of water was characterized using pulsed-field gradient NMR (PFG-NMR). At a longer diffusion time (Δ = 100 ms), PTPS has a smaller diffusion coefficient compared with both Nafion and SPES 40, due to restricted diffusion, and this effect is also evident in the proton conductivity of the hydrated membranes. From this comparison, it is apparent that the aromatic backbone and side chain type greatly influence the water dynamics in PEMs at various length scales and the water dynamics significantly impact the bulk proton conductivity. These insights will lead to new designs for aromatic PEMs and help to identify bottlenecks in current materials.

25 ENERGY STORAGE↗
NASA NTRS1989

Energetic particle diffusion coefficients upstream of quasi-parallel interplanetary shocks

The properties of about 30 to 130-keV/e protons and alpha particles upstream of six quasi-parallel interplanetary shocks that passed by the ISEE 3 spacecraft during 1978-1979 were analyzed, and the values for the upstream energegic particle diffusion coefficient, kappa, in these six events were deduced for a number of energies and upstream positions. These observations were compared with predictions of Lee's (1983) theory of shock acceleration. It was found that the observations verified the prediction of the A/Q dependence (where A and Q are the particle atomic mass and ionization state, respectively) of kappa for alpha and proton particles upstream of the quasi-parallel shocks.

Tan, L. C.↗
NASA NTRS1982

Diffusion and viscosity coefficients for helium

The first order Boltzmann-Fokker-Planck equation is solved numerically to obtain diffusion and viscosity coefficients for a ternary gas mixture composed of electron, protons, and helium. The coefficients are tabulated for five He/H abundances ranging from 0.01 to 10 and for both He II and He III. Comparison with Burgers's thermal diffusion coefficients reveals a maximum difference of 9-10% for both He II and He III throughout the range of helium abundances considered. The viscosity coefficients are compared to those of Chapman and Cowling and show a maximum difference of only 5-6% for He II but 15-16% for He III. For the astrophysically important gas mixtures, it is concluded that the results of existing studies which employed Burgers's or Chapman and Cowling's coefficients will remain substantially unaltered.

Roussel-Dupre, R.↗
NASA NTRS1972

A self-consistent model for Jupiter's radiation belts

The solar wind is assumed to be a sufficient source for the radiation belts of Jupiter, with radial diffusion as the process for getting the solar wind fluxes into the inner regions of the radiation belts. The process of a radial diffusion source is combined with pitch-angle diffusion losses to estimate an upper limit to the proton and electron fluxes. The upper limit to the integral proton and electron fluxes in the outer zone scale as L to the -6th power throughout the outer zone, assuming that the magnetic moment is conserved. It is important that these fluxes are above the stably trapped flux levels in the outer regions of the belts; the instability will work because the energies of the particles are above the critical value required.

Thorne, R. M.↗
NASA NTRS1979

Temperature anisotropy of the Jovian sulfur nebula

The apparent paradox between the reported observation of a 3-eV gyration energy of Jupiter's ionized sulfur nebula and its observed thickness is discussed. An observation of the thickness of the cloud taken nearly edge-on is presented and shown to imply a large bounce-averaged anisotropy of the sulfur in temperature. These observations are used to construct a self-consistent model of the sulfur nebula in which the sulfur ions are injected by Io as ions and remain sufficiently collisionless in the magnetosphere to maintain the anisotropy for a time longer than a characteristic diffusion time. It is also shown that the proton-electron plasma is collisionally thermalized and provides an adequate means of tapping the rotational energy of the planet to provide the power radiated in the sulfur lines.

Eviatar, A.↗
NASA NTRS1980

Cusp proton signatures and the interplanetary magnetic field

The variation of proton average energy with latitude in the cusp has been suggested as an indicator of the means of particle entry. If magnetic merging is the principal means of particle entry, the proton average energy should fall with increasing latitude; if diffusion is the principal means, the average energy should first fall and then briefly rise as a function of latitude, showing a 'V' signature. In the present work, 60 selected cusp passes of the AE-D satellite for which IMP-J interplanetary or magnetosheath magnetic-field data were available were examined. About one-third of these passes showed clear or likely merging-type energy dispersions; a third showed clear or likely V-type energy dispersions, and a third showed unclear or no energy dispersions. The results are strongly correlated with the IMF - the merging signatures are associated with southward IMF and the V signatures with northward IMF. Unclear cases are associated with unsteady or weakly northward IMF.

Reiff, P. H.↗
NASA NTRS1983

High energy spectrum of spherically accreting black holes

Spherically accreting black holes may sustain strong collisionless shocks, downstream of which the fluid approximation is not valid. The proton-electron Coulomb exchange provides for the downstream matter diffusion into the hole. Energy conversion efficiencies upward of 10-30 percent are obtained, with most of the luminosity in hard X-rays and gamma-rays. The whole spectrum and its application for radio-quiet QSO's and galactic X- and gamma-ray sources are discussed.

Meszaros, P.↗
NASA NTRS1988

Solar-cycle modulation of galactic cosmic rays

This paper describes a numerical solution of the spherically-symmetric, time-dependent, cosmic-ray modulation equation, compares it to data taken near the ecliptic, and probes the physical mechanisms responsible for the solar-cycle variations in the cosmic-ray intensity. With a physically defensible diffusion coefficient and other reasonable parameters, the spectra of protons and electrons can be simulated simultaneously over the cycle, the radial intensity gradients for particles greater than about 100 MeV, the overall intensity variation during the cycle, and the time lag in the recovery of low-energy particles behind high-energy ones, known commonly as the 'hysteresis.' The results suggest that cosmic-ray variations near the ecliptic are dominated by turbulent scattering regions in the heliosphere, overwhelming any effects of gradient and curvature drifts.

Perko, John S.↗
NASA NTRS1997

Gamma-rays from supernova remnants and the signatures of diffusive shock acceleration

A nonlinear shock acceleration model which generates non-thermal proton distributions and includes a self-consistent determination of shock hydrodynamics, is considered. Gamma ray spectra are obtained for supernova remnants, allowing for the cessation of acceleration to high energies due to the finite ages and the sizes of the remnants. Gamma ray spectral cutoffs can be observed in the TeV range for reasonable remnant parameters and deviations from power law behavior are found at all energies from 1 MeV to cutoff. Correlated observations by the International Gamma Ray Astrophysics Laboratory, Whipple and other instruments may provide stringent constraints to understanding supernova remnants.

Baring, Matthew G.↗