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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Proton-radiation damage in Gunn oscillators

The irradiation effects of 22 MeV protons on the electrical characteristics of GaAs continuous-wave Gunn oscillators was studied. The radio frequency power output was reduced by 3 decibels at proton fluences in the neighborhood of 1.5 x 10 to the 12th power protons/sq cm. Conductance measurements indicate that the carrier removal rate at high electric fields remained roughly 40 percent less than at low fields. Diode efficiencies of two device groups were found to be monotonically descreasing functions of fluence. Frequency modulation noise was generally unaffected by radiation, but the magnitude of the noise in the noise power spectrum increased significantly. These effects are partially accounted for, in a qualitative fashion, by a model of electron traps having field-dependent net-carrier capture rates and various response times.

Johnson, J. W.↗
NASA NTRS1975

Cosmic ray mass and momentum spectra at mountain altitude

A cosmic ray mass spectrometer using a superconducting magnet, digitized wire spark chambers, and a scintillation counter time of flight system, has been operated at an altitude of 2750 meters. The apparatus is most sensitive to charged particles with momentum to mass ratios between 0.2 and 2.0. Results for the momentum spectra of protons and deuterons are presented, as well as upper limits for H-3 and He-3. The reaction nucleon + nucleon yields deuteron + pion accounts for part of the observed deuteron spectrum in the 0.9 to 3 GeV/c region.-

Barber, H. B.↗
NASA NTRS1985

On the Origin of Triton and Pluto

Lyttleton's (1936) hypothesis that Triton and Pluto originated as adjacent prograde satellites of Neptune is evaluated, and it is shown that with the presently accepted masses of Triton and Pluto-Charon, the momentum and energy exchange required to sell Triton on a retrograde orbit is impossible. The Pluto-Charon system could not have acquired its present angular momentum state during an ejection event unless a physical collision was involved, which is quite unlikely. The simplest hypothesis is that Triton and Pluto are independent representatives of large outer solar system planetesimals. Triton is simply captured, with spectacular consequences that include runaway melting of interior ices and release to the surface of clathrated CH4, CO, and N2. Condensed remnants of this protoatmosphere could account for features in Triton's unique spectrum.

Mckinnon, W. B.↗
NASA NTRS1984

On the origin of Triton and Pluto

Lyttleton's (1936) hypothesis that Triton and Pluto originated as adjacent prograde satellites of Neptune is evaluated, and it is shown that with the presently accepted masses of Triton and Pluto-Charon, the momentum and energy exchange required to set Triton on a retrograde orbit is impossible. The Pluto-Charon system could not have acquired its present angular momentum state during an ejection event unless a physical collision was involved, which is quite unlikely. The simplest hypothesis is that Triton and Pluto are independent representatives of large outer solar system planetesimals. Triton is simply captured, with spectacular consequences that include runaway melting of interior ices and release to the surface of clathrated CH4, CO, and N2. Condensed remnants of this protoatmosphere could account for features in Triton's unique spectrum.

Mckinnon, W. B.↗
NASA NTRS1986

Comets, X-ray bursts, and gamma-ray bursts

The proposal, revived by Tremaine and Zytkow (1985), that accretion of comets by neutron stars may be the origin of gamma-ray bursts is considered. This mechanism has difficulty accounting for the observed gamma-ray spectrum and optical counterparts of the bursts. The survival of comets near supernovae is investigated. Ablation rates and the thermal structure of an ablating surface layer are calculated. In some circumstances, mechanical disruption will erode a comet more rapidly than evaporation. The accretion of comets by neutron stars may produce a class of X-ray burst sources with novel properties.

Katz, J. I.↗
NASA NTRS1995

Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands

Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these Polycyclic Aromatic Hydrocarbons (PAHs) absorb in the visible. C10H8(+) has 12 discrete absorption bands which fall between 6800 and 5000 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBS at 6520, 6151, and 5965 A, other moderately strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 A. If C16H10(+), or a closely related pyrene-like ion is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.

Salama, F.↗
DOE OSTI2013

COLLISIONLESS DAMPING AT ELECTRON SCALES IN SOLAR WIND TURBULENCE

The dissipation of turbulence in the weakly collisional solar wind plasma is governed by unknown kinetic mechanisms. Two candidates have been suggested to play an important role in the dissipation, collisionless damping via wave-particle interactions and dissipation in small-scale current sheets. High resolution spacecraft measurements of the turbulent magnetic energy spectrum provide important constraints on the dissipation mechanism. The limitations of popular fluid and hybrid numerical schemes for simulation of the dissipation of solar wind turbulence are discussed, and instead a three-dimensional kinetic approach is recommended. We present a three-dimensional nonlinear gyrokinetic simulation of solar wind turbulence at electron scales that quantitatively reproduces the exponential form of the turbulent magnetic energy spectrum measured in the solar wind. A weakened cascade model that accounts for nonlocal interactions and collisionless Landau damping also quantitatively agrees with the observed exponential form. These results establish that a turbulent cascade of kinetic Alfven waves that is terminated by collisionless Landau damping is sufficient to explain the observed magnetic energy spectrum in the dissipation range of solar wind turbulence.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

COLLISIONAL RELAXATION OF ELECTRONS IN A WARM PLASMA AND ACCELERATED NONTHERMAL ELECTRON SPECTRA IN SOLAR FLARES

Extending previous studies of nonthermal electron transport in solar flares, which include the effects of collisional energy diffusion and thermalization of fast electrons, we present an analytic method to infer more accurate estimates of the accelerated electron spectrum in solar flares from observations of the hard X-ray spectrum. Unlike for the standard cold-target model, the spatial characteristics of the flaring region, especially the necessity to consider a finite volume of hot plasma in the source, need to be taken into account in order to correctly obtain the injected electron spectrum from the source-integrated electron flux spectrum (a quantity straightforwardly obtained from hard X-ray observations). We show that the effect of electron thermalization can be significant enough to nullify the need to introduce an ad hoc low-energy cutoff to the injected electron spectrum in order to keep the injected power in non-thermal electrons at a reasonable value. Rather, the suppression of the inferred low-energy end of the injected spectrum compared to that deduced from a cold-target analysis allows the inference from hard X-ray observations of a more realistic energy in injected non-thermal electrons in solar flares.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Charge symmetric dissociation of doubly ionized N{sub 2} and CO molecules

We report a comparative study of the features in dissociative double ionization by high energy electron impact of N{sub 2} and CO molecules. The ratio of cross-section of charge symmetric dissociative ionization to non-dissociative ionization (CSD-to-ND ratio) and the kinetic energy release (KER) spectra of dissociation are experimentally measured and carefully corrected for various ion transmission losses and detector inefficiencies. Given that the double ionization cross sections of these iso-electronic diatomics are very similar, the large difference in the CSD-to-ND ratios must be attributable to the differences in the evolution dynamics of the dications. To understand these differences, potential energy curves (PECs) of dications have been computed using multi-reference configuration interaction method. The Franck-Condon factors and tunneling life times of vibrational levels of dications have also been computed. While the KER spectrum of N{sub 2}{sup ++} can be readily explained by considering dissociation via repulsive states and tunneling of meta-stable states, indirect dissociation processes such as predissociation and autoionization have to be taken into account to understand the major features of the KER spectrum of CO{sup ++}. Direct and indirect processes identified on the basis of the PECs and experimental KER spectra also provide insights into the differences in the CSD-to-ND ratios.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
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↗
DOE OSTI2026

Low energy neutron light output characterization of EJ301D and deuterated stilbene with a comparison of light output characterization methods

The neutron-induced light yield of a 2.54 cm diameter by 2.54 cm long right circular cylinder of EJ301D and a (5.08 cm)3 custom made cube of deuterated trans-stilbene-d12 (d-stilbene) were measured over incident neutron energies from 300 keV to 2.2 MeV and 200 keV to 2.4 MeV, respectively. The measurements were performed using a time-of-flight experiment with a Cf-252 source and an approximately 1.5 m flight path. We compare three light output spectrum full energy deposition edge estimation methods: (1) simulating the neutron energy spectrum edge and fitting it to the light output spectrum, (2) using the inflection point of the light output spectrum edge (derivative method, a.k.a. Kornilov’s method), and (3) using an empirical model fit to the edge of the light output spectrum. Both the derivative and equation fit methods do not account for physical processes such as multiple neutron scattering in the detectors. They instead rely on assumptions about the linear shape continuum shape of the light output spectrum and the direct correlation between the location of the spectrum’s inflection point and maximum energy deposition. These assumptions were found to introduce bias into those methods when tested against simulated spectra with known edge locations. When tested against measured spectra the derivative method was found to differ from the simulation fit by greater than 30% at low energies with large discontinuities for adjacent data points above 800 keV incident neutron energy. The empirical equation fitting method was found to also exhibit bias of a similar magnitude, but with significantly more continuous behavior, especially with the lower count data of the smaller volumed EJ301D scintillator. Experimental light output yield for this neutron energy range is reported using the simulated spectrum fitting method because it includes physics neglected by the other methods, and did not exhibit the bias observed in the other methods

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1987

Effect of current on spectrum of breaking waves in water of finite depth

This paper presents an approximate method to compute the mean value, the mean square value and the spectrum of waves in water of finite depth taking into account the effect of wave breaking with or without the presence of current. It is assumed that there exists a linear and Gaussian ideal wave train whose spectrum is first obtained using the wave energy flux balance equation without considering wave breaking. The Miche wave breaking criterion for waves in finite water depth is used to limit the wave elevation and establish an expression for the breaking wave elevation in terms of the elevation and its second time derivative of the ideal waves. Simple expressions for the mean value, the mean square value and the spectrum are obtained. These results are applied to the case in which a deep water unidirectional wave train, propagating normally towards a straight shoreline over gently varying sea bottom of parallel and straight contours, encounters an adverse steady current whose velocity is assumed to be uniformly distributed with depth. Numerical results are obtained and presented in graphical form.

Tung, C. C.↗
NASA NTRS1985

Nonthermal electron-positron pair production and the 'universal' X-ray spectrum of active galactic nuclei

A nonthermal model for power-law X-ray and gamma-ray sources is considered. An initial, primary distribution of relativistic electrons is injected and cooled via Compton scattering of soft photons (produced either externally or by the synchrotron mechanism). The scattered photons, constituting a primary gamma-ray source, produce electron-positron pairs that act as a secondary electron injection, which in turn produce a secondary photon spectrum. Pairs formed by a part of the photon spectrum optically thin to pair production are taken into account. The distribution of particles and photons is obtained, and numerical results as well as analytical solutions to certain special cases are presented. For the case of a delta-function primary electron injection it is found that the photon spectrum in the X-ray region is well approximated by a power law, with the energy spectral index alpha(X) lying in the relatively narrow range 0.5-0.9 as the compactness parameter L(x)/R (where L(x) is the X-ray luminosity and R is the source radius) varies over many orders of magnitude. This is proposed as a possible mechanism to explain the universal X-ray spectra observed from active galactic nuclei.

Zdziarski, A. A.↗
DOE OSTI2017

Gamma-Ray Emission of the Kes 73/1E 1841-045 Region Observed with the Fermi Large Area Telescope

The supernova remnant (SNR) Kes 73 and/or the magnetar 1E 1841-045 at its center can deposit a large amount of energy to the surroundings and is potentially responsible for particle acceleration. Using the data taken with the Fermi Large Area Telescope (LAT), we confirmed the presence of an extended source whose centroid position is highly consistent with this magnetar/SNR pair. Its emission is intense from 100 MeV to >100 GeV. Its LAT spectrum can be decoupled into two components, which are respectively governed by two different mechanisms. According to the young age of this system, the magnetar is seemingly a necessary and sufficient source for the downward-curved spectrum below 10 GeV, as the observed <10 GeV flux is too high for the SNR to account for. On the other hand, the SNR is reasonably responsible for the hard spectrum above 10 GeV. Further studies of this region in the TeV regime is required so that we can perform physically meaningful comparisons of the >10 GeV spectrum and the TeV spectrum.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1985

Energy spectra of high energy atmospheric neutrinos

Focusing on high energy neutrinos ( or = 1 TeV), a new calculation of atmospheric neutrino intensities was carried out taking into account EMC effects observed in P-A collisions by accelerator, recent measurement of primary cosmic ray spectrum and results of cosmic ray muon spectrum and charge ratio. Other features of the present calculation are (1) taking into account kinematics of three body decays of kaons and charm particles in diffusion equations and (2) taking into account energy dependence of kaon production.

Mitsui, K.↗
DOE OSTI2020

$$\varLambda $$ and $$\varSigma $$ Excitations and the Quark Model

Abstract The spectrum of $$\varLambda $$ Λ and $$\varSigma $$ Σ excitations is reviewed taking into account (nearly) all hyperon resonances which were seen in early analyses or in one of the recent partial-wave analyses. The spectrum is compared with the old Isgur–Karl model and the Bonn model. These models allows us to discuss the SU(3) structure of the observed resonances. The SU(3) decomposition is compared with SU(6) relations between the different decay modes. Seven $$\varLambda $$ Λ states are proposed to be classified as SU(3) singlet states. The hyperon spectrum is compared with the spectrum of N and $$\varDelta $$ Δ resonances.

Klempt, E.↗