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Results for “decaying mechanism”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

What heated the parent meteorite planets?

The plausibility of the two most wide discussed mechanisms, decay of short-lived Al-26 and solar wind induction heating, for heating the small planetesimals in which the meteorites formed are examined and shown to have significant problems. The main problem for the Al-26 decay mechanism is the fact that eucritic lavas, melted by the mysterious heating mechanism in some early planetesimal, did not contain enough Al-26 to decay to radiogenic Mg-26 when they erupted to their planetesimal surface and cooled. It is necessary to postulate that the lavas lingered underground while their Al-26 decayed away. The solar wind induction heat concept has the problem that astrophysical evidence has made is seem increasingly unlikely that an intense solar wind flux blew past planetesimals in the early solar system. Instead, it was probably collimated in the direction of the sun's poles by the persistence of the solar nebula during the T Tauri epoch.

Wood, John A.↗
NASA NTRS2012

Explaining Polarization Reversals in STEREO Wave Data

Recently Breneman et al. reported observations of large amplitude lightning and transmitter whistler mode waves from two STEREO passes through the inner radiation belt (L<2). Hodograms of the electric field in the plane transverse to the magnetic field showed that the transmitter waves underwent periodic polarization reversals. Specifically, their polarization would cycle through a pattern of right-hand to linear to left-hand polarization at a rate of roughly 200 Hz. The lightning whistlers were observed to be left-hand polarized at frequencies greater than the lower hybrid frequency and less than the transmitter frequency (21.4 kHz) and right-hand polarized otherwise. Only righthand polarized waves in the inner radiation belt should exist in the frequency range of the whistler mode and these reversals were not explained in the previous paper. We show, with a combination of observations and simulated wave superposition, that these polarization reversals are due to the beating of an incident electromagnetic whistler mode wave at 21.4 kHz and linearly polarized, symmetric lower hybrid sidebands Doppler-shifted from the incident wave by +/-200 Hz. The existence of the lower hybrid waves is consistent with the parametric decay mechanism of Lee and Kuo whereby an incident whistler mode wave decays into symmetric, short wavelength lower hybrid waves and a purely growing (zero-frequency) mode. Like the lower hybrid waves, the purely growing mode is Doppler-shifted by 200 Hz as observed on STEREO. This decay mechanism in the upper ionosphere has been previously reported at equatorial latitudes and is thought to have a direct connection with explosive spread F enhancements. As such it may represent another dissipation mechanism of VLF wave energy in the ionosphere and may help to explain a deficit of observed lightning and transmitter energy in the inner radiation belts as reported by Starks et al.

Breneman, A.↗
NASA NTRS1975

Ring current proton decay by charge exchange

Explorer 45 measurements during the recovery phase of a moderate magnetic storm have confirmed that the charge exchange decay mechanism can account for the decay of the storm-time proton ring current. Data from the moderate magnetic storm of 24 February 1972 was selected for study since a symmetrical ring current had developed and effects due to asymmetric ring current losses could be eliminated. It was found that after the initial rapid decay of the proton flux, the equatorially mirroring protons in the energy range 5 to 30 keV decayed throughout the L-value range of 3.5 to 5.0 at the charge exchange decay rate calculated by Liemohn. After several days of decay, the proton fluxes reached a lower limit where an apparent equilibrium was maintained, between weak particle source mechanisms and the loss mechanisms, until fresh protons were injected into the ring current region during substorms. While other proton loss mechanisms may also be operating, the results indicate that charge exchange can entirely account for the storm-time proton ring current decay, and that this mechanism must be considered in all studies involving the loss of proton ring current particles.

Smith, P. H.↗
NASA NTRS2004

A Critical Review of the Transport and Decay of Wake Vortices in Ground Effect

This slide presentation reviews the transport and decay of wake vortices in ground effect and cites a need for a physics-based parametric model. The encounter of a vortex with a solid body is always a complex event involving turbulence enhancement, unsteadiness, and very large gradients of velocity and pressure. Wake counter in ground effect is the most dangerous of them all. The interaction of diverging, area-varying, and decaying aircraft wake vortices with the ground is very complex because both the vortices and the flow field generated by them are altered to accommodate the presence of the ground (where there is very little room to maneuver) and the background turbulent flow. Previous research regarding vortex models, wake vortex decay mechanisms, time evolution within in ground effect of a wake vortex pair, laminar flow in ground effect, and the interaction of the existing boundary layer with a convected vortex are reviewed. Additionally, numerical simulations, 3-dimensional large-eddy simulations, a probabilistic 2-phase wake vortex decay and transport model and a vortex element method are discussed. The devising of physics-based, parametric models for the prediction of (operational) real-time response, mindful of the highly three-dimensional and unsteady structure of vortices, boundary layers, atmospheric thermodynamics, and weather convective phenomena is required. In creating a model, LES and field data will be the most powerful tools.

Sarpkaya, T.↗
NASA NTRS1975

On the stability of plane shocks

In the analysis of shock stability reported, the disturbances are assumed to originate at an arbitrary moving point. A change in the decay mechanism is shown to result from the increasing angle of incidence between the shock and an intersecting cylindrical (or spherical) wave generated behind it. The local reflection coefficient for reflection of a pressure wave from a shock varies strongly with the angle of incidence. At small angles of incidence the reflected wave is very weak and the incident wave decays in a geometric manner.

Van Moorhem, W. K.↗
NASA NTRS1972

Calculations of neutron flux spectra induced in the earth's atmosphere by galactic cosmic rays

Calculations have been carried out to determine the neutron flux induced in the earth's atmosphere by galactic protons and alpha particles at solar minimum for a geomagnetic latitude of 42 N. Neutron flux spectra were calculated using Monte Carlo and discrete ordinates methods, and various comparisons with experimental data are presented. The magnitude and shape of the calculated neutron-leakage spectrum at the particular latitude considered support the theory that the cosmic-ray-albedo-neutron-decay mechanism is the source of the protons and electrons trapped in the Van Allen belts.

Armstrong, T. W.↗
NASA NTRS1977

A search for helium ions in the recovery phase of a magnetic storm

Data from an energetic ion mass spectrometer experiment on the low-latitude polar-orbiting satellite 1971-89A were examined for evidence of helium ions in the region of the ring current during the recovery phase of the December 17-18, 1971 magnetic storm. The principal precipitating ion species with energies between 0.7 and 12 keV were observed to be O+ and H+. No evidence for He+ was obtained. Inferences about the composition of the trapped population are made on the basis of simultaneous observations in the equatorial plane by Explorer 45. Coordinated observations with Explorer 45 and the Fritz Peak Observatory during the period of a stable auroral red arc have provided some information on the ionospheric and magnetospheric processes associated with the arc. A comparison of charge exchange and precipitation lifetimes during the recovery phase of the December 17-18 storm has shown both processes to be of comparable importance as ring current decay mechanisms in the energy range of the observations.

Sharp, R. D.↗
NASA NTRS1983

Some Comments on Longevity by a Technologist

The durability of flywheels was investigated. Since only composite flywheels possess the potential for system energy densities in the range of 20 to 40 W hr/kg, and they are not yet at a level of maturity where a comfortable data base exists, the longevity aspects of the yet to be developed devices is still a speculation. The general methodologies that have been used in some of the more established technology areas to establish some degree of credibility in the ability to predict the upper limits of expected useful life based on the current limiting decay mechanism are outlined.

Thaller, L. H.↗
NASA NTRS1987

A dynamical constraint on particulate sizes for Saturn's B ring spokes

The exponential charge decay time for particulates constituting the spokes in Saturn's B ring is presently proposed as a dynamical time scale for their evolution. Mean particulate radius is determined to be 0.01 + or - 0.03 microns, on the basis of a consideration of solar UV photoemission as the charge decay mechanism which leads to the determination of a dynamical constraint that can be placed on the particulate sizes.

Eplee, Robert E., Jr.↗
NASA NTRS1988

Imaging and spectroscopy of Comet P/Halley

The goals of this investigation are the analysis of a large set of high-resolution echelle/reticon spectra, and the reduction and analysis of a set of narrow-band-filtered charge coupled device (CCD) images of Comet Halley taken during the preperihelion period at Oak Ridge Observatory by Dr. R. E. McCrosky. The scientific objectives associated with these goals are the determination of the spatial distributions of several important radicals, atoms and ions in the coma. These include C2, CN, C3, H2O(+) and CO(+) from the image data. The analysis of the neutral species distribution with Monte Carlo models will aid in the understanding of their production and decay mechanisms as well as serve as an important indicator of the physical conditions in the inner coma. The spatial distributions of the ions will serve as a guide to constrain the complex model necessary for understanding the interaction of the solar wind and the cometary ions. Work during this past year has been devoted largely to the reduction of the standard star photometry for the CCD image data set, as well as the re-flat-fielding of a number of the comet images. We are pleased to report that despite a number of setbacks and the small effort devoted to this work (2 1/2 months for the PI and a generous share of completely unsupported time by Dr. McCrosky) that this portion of the work has been successfully completed. The goals for the upcoming final year of this project (under a new project number) are to complete the calibration of the CCD image data for inclusion in the IHW archive, to analyze a select portion of the neutral radical images with our Monte Carlo models, and to present the results of the 6300/region spectra as a guide to low-resolution spectral observers in order to yield the unambiguous separation of the contributions of cometary O(1D), airglow O(1D), and the numerous NH2 lines in that region of the spectrum.

Combi, Michael R.↗
NASA NTRS1992

High voltage spheres in an unmagnetized plasma - Fluid and PIC simulations

The basic physics involving the interaction of a high voltage sphere with a LEO-Plasma was investigated via computer experiments. Two approaches were used: the fluid description and the more general particle pushing method. Both techniques displayed qualitatively similar features. Thus, the initial time-dependent response of the plasma predicted by the fluid model, including the initial current surge and sheath formation, the formation of ion and electron density shells about the sphere with a double layer potential structure, and the subsequent propagation of the density shells away from the sphere. The PIC results also displayed an oscillatory character and slightly different time constants for the growth and decay mechanisms involved.

Thiemann, H.↗
NASA NTRS1995

Minority-carrier lifetime in InP as a function of light bias

Minority-carrier lifetime in InP is studied as a function of doping level and laser intensity using time-resolved photoluminescence. A continuous wave diode laser illuminates bulk InP and acts as a light bias, injecting a steady-state concentration of carriers. A 200 ps laser pulse produces a small transient signal on top of the steady-state luminescence, allowing lifetime to be measured directly as a function of incident intensity. For p-InP, lifetime increases with light bias up to a maximum value. Bulk recombination centers are presumably filled to saturation, allowing minority carriers to live longer. The saturation bias scales with dopant concentration for a particular dopant species. As light bias is increased for n-InP, minority-carrier lifetime increases slightly but then decreases, suggesting radiative recombination as a dominant decay mechanism.

Yater, Jane A.↗
NASA NTRS1994

Search of the energetic gamma-ray experiment telescope (EGRET) data for high-energy gamma-ray microsecond bursts

Hawking (1974) and Page & Hawking (1976) investigated theoretically the possibility of detecting high-energy gamma rays produced by the quantum-mechanical decay of a small black hole created in the early universe. They concluded that, at the very end of the life of the small black hole, it would radiate a burst of gamma rays peaked near 250 MeV with a total energy of about 10(exp 34) ergs in the order of a microsecond or less. The characteristics of a black hole are determined by laws of physics beyond the range of current particle accelerators; hence, the search for these short bursts of high-energy gamma rays provides at least the possibility of being the first test of this region of physics. The Compton Observatory Energetic Gamma-Ray Experiment Telescope (EGRET) has the capability of detecting directly the gamma rays from such bursts at a much fainter level than SAS 2, and a search of the EGRET data has led to an upper limit of 5 x 10(exp -2) black hole decays per cu pc per yr, placing constraints on this and other theories predicting microsecond high-energy gamma-ray bursts.

Fichtel, C. E.↗
NASA NTRS1996

Testing of hypotheses about altitude decompression sickness by statistical analyses

This communication extends a statistical analysis of forced-descent decompression sickness at altitude in exercising subjects (J Appl Physiol 1994; 76:2726-2734) with a data subset having an additional explanatory variable, rate of ascent. The original explanatory variables for risk-function analysis were environmental pressure of the altitude, duration of exposure, and duration of pure-O2 breathing before exposure; the best fit was consistent with the idea that instantaneous risk increases linearly as altitude exposure continues. Use of the new explanatory variable improved the fit of the smaller data subset, as indicated by log likelihood. Also, with ascent rate accounted for, replacement of the term for linear accrual of instantaneous risk by a term for rise and then decay made a highly significant improvement upon the original model (log likelihood increased by 37 log units). The authors conclude that a more representative data set and removal of the variability attributable to ascent rate allowed the rise-and-decay mechanism, which is expected from theory and observations, to become manifest.

NASA Center JSC↗
NASA NTRS2007

Temperature Dependent E2 Raman Modes in the ZnCoO Ternary Alloy

The anharmonic properties of low and high frequency E2 modes of ZnO and Co doped ZnO were investigated using Raman scattering spectroscopy. We have determined the behavior of frequency, linewidths, and lifetime of E2 modes in the temperature range from 80 to 800 K. In the case of E2(high) mode the frequency shift towards the lower energy side was analyzed in light of the theory of anharmonic phonon-phonon interaction and thermal expansion of the lattice, and the linewidth behavior was analyzed in terms of anharmonic effect of three-phonon decay mechanism. But in the case of E2(low), the linewidth and frequency behaved practically harmonic with respect to temperature and independent of Co substitutions. It is found that the E2(high) phonon anharmonicity is higher for ZnCoO alloys than in pure ZnO and it increases with the compositional disorder. The low temperature lifetime of E2 phonon in ZnO, 1 % and 3% Co doped ZnO were found to be 1.S2, 1.74, and 1.54 ps, respectively.

Samanta, K.↗
NASA NTRS1980

Selective decay hypothesis at high mechanical and magnetic Reynolds numbers

Implications of certain applications of turbulence theory to two-dimensional turbulence and magnetohydrodynamic flow are discussed. It is shown that the use of the Navier-Stokes equation (NSE) for measurements of turbulent fluctuations has been effective only for three-dimensional flows. For two-dimensional flows, used for the study of large-scale motions in the atmosphere or ocean, enstrophy is cascaded to high wave numbers and dissipated at a finite rate even at infinite Re. MHD flows are numerically calculated for the two-dimensional case and analytically for the three-dimensional case, for which discrepancies in the relative rates of energy and cross helicity decay lead to a recommendation that numerical calculations for the three-dimensional case be carried out to determine the precise decayed states.

Matthaeus, W. H.↗
NASA NTRS1980

On the secular decrease in the semimajor axis of Lageos orbit

The semimajor axis of the Lageos orbit is decreasing secularly at the rate of -1.1 mm/day due to an unknown force. Nine possible mechanisms are investigated. Five of the mechanisms, resonance with the Earth's gravitational field, gravitational radiation, the Poynting-Robertson effect, transfer of spin angular momentum to the orbital angular momentum, and drag from near Earth dust are ruled out because they are too small to require unacceptable assumptions to account for the observed rate. Three other mechanisms, the Yarkovsky effect, the Schach effect, and terrestrial radiation pressure could possibly give the proper order of magnitude for the decay rate, but the characteristic signatures of these perturbations do not agree with the observed secular decrease. Atmospheric drag from a combination of charged and neutral particles is the most likely cause for the orbital decay. This mechanism explains at least 71 percent of the observed rate of decrease of the semimajor axis.

Rubincam, D. P.↗