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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 NTRS1986

Generalized energetics for linear and nonlinear symmetric instabilities

The generalized energy conservation integral is applied to linear and nonlinear symmetric instabilities (SIs) and conditional symmetric instabilities (CSIs) in uniform and nonuniform basic states. The generalized energy conservation integral for linear SI in nonuniform basic state is refined to include initial thermal-inertial perturbations. A generalized conservation integral is derived for a nonlinear SI with uniform and nonuniform basic states. The integral reveals that: (1) the stability conditions of nonlinear and linear SI are not the same; (2) when the basic state is symmetrically stable the nonlinear evolution of a symmetric disturbance is energetically bounded by its initial energy; and (3) when the basic state is symmetrically unstable the growth of the symmetric perturbation is approximated by the linear SI theory. Precipitative heating is incorporated into the generalized energy integral for nonlinear CSI; the relation between nonlinear evolution of a CSI circulation and precipitative heating is examined.

Xu, Q.↗
NASA NTRS1977

Terminal energy distribution of blast waves from bursting spheres

The calculation results for the total energy delivered to the surroundings by the burst of an idealized massless sphere containing an ideal gas are presented. The logic development of various formulas for sphere energy is also presented. For all types of sphere bursts the fraction of the total initial energy available in the sphere that is delivered to the surroundings is shown to lie between that delivered for the constant pressure addition of energy to a source region and that delivered by isentropic expansion of the sphere. The relative value of E sub/Q increases at fixed sphere pressure/surrounding pressure as sphere temperature increases because the velocity of sound increases.

Adamczyk, A. A.↗
NASA NTRS1990

Dynamics of axisymmetric loops

Time-dependent, 2D MHD simulations in cylindrical geometry are presently employed to study the evolution of a solar magnetic loop in response to rotation within circular sections at the loop ends. While the magnetic energy initially increases as time-squared, and the solution fluctuates at a characteristic loop frequency, the average kinetic energy subsequently increases rapidly and levels off at a higher value that is still substantially lower than the magnetic energy release. Magnetic energy thenceforth increases exponentially with time, and deviations from a force-free field begin to appear. Finally, the current and field are no longer force-free, and the solution becomes highly nonlinear.

Steinolfson, R. S.↗
NASA NTRS1987

Using Enviro-Pod low altitude imagery to inventory building surface materials for an acid rain study - A Baltimore example

Low altitude, oblique and vertical color photography taken from EPA's Enviro-Pod Ka 85 camera system has provided the data for taking an inventory of building surface materials in a test area of downtown Baltimore. Photography was acquired from a gridded flight plan to provide views of all sides of buildings. Color, texture, and linear detail are employed in the photo interpretation aided by contextual reference to a classification of building construction type developed in an earlier study. The work could potentially support a materials inventory initiated by the National Acid Precipitation Assessment Program (NAPAP) by scientists from EPA, Geological Survey, and the Department of Energy. Initial results show the method to be viable. Discrete surface materials such as brick, both bare and painted, stone, and metal are identified.

Ellefsen, Richard↗
NASA NTRS1988

Cascade model of gamma-ray bursts: Power-law and annihilation-line components

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

Harding, A. K.↗
NASA NTRS1989

Cascade model of gamma-ray bursts

If, in a neutron star magnetosphere, an electron is accelerated to an energy of 10 to the 11th or 12th power eV by an electric field parallel to the magnetic field, motion of the electron along the curved field line leads to a cascade of gamma rays and electron-positron pairs. This process is believed to occur in radio pulsars and gamma ray burst sources. Results are presented from numerical simulations of the radiation and photon annihilation pair production processes, using a computer code previously developed for the study of radio pulsars. A range of values of initial energy of a primary electron was considered along with initial injection position, and magnetic dipole moment of the neutron star. The resulting spectra was found to exhibit complex forms that are typically power law over a substantial range of photon energy, and typically include a dip in the spectrum near the electron gyro-frequency at the injection point. The results of a number of models are compared with data for the 5 Mar., 1979 gamma ray burst. A good fit was found to the gamma ray part of the spectrum, including the equivalent width of the annihilation line.

Sturrock, P. A.↗
NASA NTRS1979

Cometary particulate analyzer

A concept for determining the relative abundance of elements contained in cometary particulates was evaluated. The technique utilizes a short, high intensity burst of laser radiation to vaporize and ionize collected particulate material. Ions extracted from this laser produced plasma are analyzed in a time of flight mass spectrometer to yield an atomic mass spectrum representative of the relative abundance of elements in the particulates. Critical aspects of the development of this system are determining the ionization efficiencies for various atomic species and achieving adequate mass resolution. A technique called energy-time focus, which utilizes static electric fields to alter the length of the ion flight path in proportion to the ion initial energy, was used which results in a corresponding compression to the range of ion flight times which effectively improves the inherent resolution. Sufficient data were acquired to develop preliminary specifications for a flight experiment.

Friichtenicht, J. F.↗
NASA NTRS1989

Multiple coherent mode interaction in a developing round jet

The integral energy method has been used in order to study the nonlinear interactions of the large-scale coherent structure in a spatially developing round jet. The streamwise development of a jet is obtained in terms of the mean flow shear layer momentum thickness, the wave mode kinetic energy and the wave mode phase angle. It is shown that the nonlinear interaction between wave modes is dependent on the wave mode phase angles. The initial wave mode phase angles as well as the initial energy densities play a significant role in the streamwise evolution of the large-scale coherent wave modes and the mean flow.

Lee, S. S.↗
NASA NTRS1994

The asymptotic state of rotating homogeneous turbulence at high Reynolds numbers

The long-time, asymptotic state of rotating homogeneous turbulence at high Reynolds numbers has been examined using large-eddy simulation of the incompressible Navier-Stokes equations. The simulations were carried out using 128 x 128 x 512 collocation points in a computational domain that is four times longer along the rotation axis than in the other directions. Subgrid-scale motions in the simulations were parameterized using a spectral eddy viscosity modified for system rotation. Simulation results show that in the asymptotic state the turbulence kinetic energy undergoes a power-law decay with an exponent which is independent of rotation rate, depending only on the low-wavenumber form of the initial energy spectrum. Integral lengthscale growth in the simulations is also characterized by power-law growth; the correlation length of transverse velocities exhibiting much more rapid growth than observed in non-rotating turbulence.

Squires, Kyle D.↗
NASA NTRS1986

Energy broadening due to space-charge oscillations in high current electron beams

During electron beam accelerator operation on Spacelab I, substantial fluxes of electrons were observed with energies greater than the initial beam energy. Numerical calculations are performed for the emission of an unneutralized, one-dimensional electron beam. These calculations show clearly that space charge oscillations, which are associated with the charge buildup on the emitter, strongly modify the beam and cause the returning beam particles to have a distribution of kinetic energies ranging from half to over twice the initial energy.

Katz, I.↗
NASA NTRS2002

RHESSI and Trace Observations of the 21 April 2002 X1.5 Flare

Observations of the X1.5 flare on 21 April 2002 are reviewed using the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Transition Region and Coronal Explorer (TRACE). The major findings are as follows: 1. The 3-25 keV X-rays started 54 mins before the EUV (195 A) emission suggesting that the initial energy release heated plasma directly to 220 MK, well above the 1.6 MK needed to produce the Fe XII (195 A) line. 2. Using coaligned 12-25 keV RHESSI and TRACE images, further evidence is found for the existence of hot (15-20 MK) plasma in the 195 A passband. This hot, diffuse emission is attributed to the presence of the Fe XXIV (192 A) line within the TRACE 195 A passband. 3. The 12-25 keV source centroid moves away from the limb with an apparent velocity of approx. 9.9 km/ s, slowing to approx. 1.7 km/ s after 3 hours, its find altitude being approx. 120 Mm after approx. 12 hours. This suggests that the energy release site moves to higher altitudes in agreement with classical flare models. 4. The 50-100 keV emission correlates well with EUV flare ribbons, suggesting thick-target interactions at the footpoints of the magnetic arcade. The 50-100 keV time profile matches the time derivative of the GOES light curve (Neupert effect), which suggests that the same electrons that produced the thick-target hard X-ray emission also heat the plasma seen in soft X-rays. 5. X-ray footpoint emission has an E(sup -3) spectrum down to approx. 10 keV suggesting a lower electron cutoff energy than previously thought. 6. The hard X-ray (25-200 keV) peaks have FWHM durations of approx. 1 min suggesting a more gradual energy release process than expected. 7. The TRACE images reveal a bright symmetric front propagating away from the main flare site at speeds of greater than or = 120 km/ s. This may be associated with fast CME observed several minutes later by LASCO. 8. Dark sinuous lanes are observed in the TRACE images that extend almost radially from the post-flare loop system. This "fan of spines" becomes visible well into the decay phase of the flare and shows evidence for both lateral and downward motions.

Gallagher, Peter T.↗
NASA NTRS2007

Dynamic Theory of Relativistic Electrons Stochastic Heating by Whistler Mode Waves with Application to the Earth Magnetosphere

In the Hamiltonian approach an electron motion in a coherent packet of the whistler mode waves propagating along the direction of an ambient magnetic field is studied. The physical processes by which these particles are accelerated to high energy are established. Equations governing a particle motion were transformed in to a closed pair of nonlinear difference equations. The solutions of these equations have shown there exists the energetic threshold below that the electron motion is regular, and when the initial energy is above the threshold an electron moves stochastically. Particle energy spectra and pitch angle electron scattering are described by the Fokker-Planck-Kolmogorov equations. Calculating the stochastic diffusion of electrons due to a spectrum of whistler modes is presented. The parametric dependence of the diffusion coefficients on the plasma particle density, magnitude of wave field, and the strength of magnetic field is studies. It is shown that significant pitch angle diffusion occurs for the Earth radiation belt electrons with energies from a few keV up to a few MeV.

Khazanov, G. V.↗
NASA NTRS1973

Nonthermal X-rays and related processes

The hard X-rays associated with solar flares represent the bremsstrahlung of nonthermal electron streams. In the initial phase of the flare, the X-rays probably come from a dense region in the chromosphere, as a consequence of precipitation from the lower corona. A gradual nonthermal X-ray burst may occur in a later phase, probably caused by the electrons responsible for the type 4 burst. The bombardment of the chromosphere during the early phase of the flare releases a large amount of energy there. This energy can support many of the observed flash-phase phenomena. We therefore consider this picture of flare energetics: The energy initially goes into fast particles. These interact with the chromosphere, which expands to form the hot region observed in the corona. This hot region then provides energy for many of the main-phase flare phenomena, such as H-alpha emission. The bulk of the energy in the bombardment must reside in the electron component. A clear test of the whole picture lies in its prediction of a strong infrared excess during the flash phase.

Hudson, H. S.↗
NASA NTRS1990

High pressure gas scintillation drift chambers with wave-shifter fiber readout. II

Results from a prototype high-pressure xenon gas scintillation drift chamber using a novel wave-shifter fiber readout scheme are presented. The primary scintillation light yield was measured to be one photon per 76 + or - 12 eV deposited energy. Initial results on the chamber are presented for two-interaction separation (less than 4 mm in the drift direction and about 7 mm orthogonal to the drift); for position resolution (less than 400 microns rms in the plane orthogonal to the drift direction); and for energy resolution (less than 6 percent FWHM at 122 keV).

Parsons, A.↗
NASA NTRS2006

Dynamic Theory of Relativistic Electrons Stochastic Heating by Whistler Mode Waves with Application to the Earth Magnetosphere

In the Hamiltonian approach an electron motion in a coherent packet of the whistler mode waves propagating along the direction of an ambient magnetic field is studied. The physical processes by which these particles are accelerated to high energy are established. Equations governing a particle motion by group symmetries of the problem were transformed in to a closed pair of nonlinear difference equations. The solutions of these equations have shown there exists the energetic threshold below that the electron motion is regular, and when the initial energy is above the threshold an electron moves stochastically. It is proved that the upper boundary of particle stochastic heating is conditioned by intrinsic property of the particle chaotic motion. Particle energy spectra and pitch angle electron scattering are described by the Fokker-Planck-Kolmogorov equations. It is shown that significant pitch angle diffusion occurs for the Earth radiation belt electrons with energies from a few keV up to a few MeV.

Khazanov, G. V.↗
NASA NTRS1991

Energy degradation of fast electrons in hydrogen gas

An equation is derived for calculating the energy distribution of fast electrons in a partially ionized gas and a method is provided to solve for the electron degradation spectrum and the energy deposition in different forms (ionization, excitation, or heating). As an example, the energy degradation of fast electrons in a gas of pure hydrogen is calculated, considering excitations to the lowest 10 atomic levels. The Bethe approximation and the continuous slowing-down approximation are discussed and it is concluded that these approximations are accurate to the order of 20 percent for electrons with initial energy of greater than about keV. The method and results can be used to determine heating, excitations, and ionizations by high-energy photoelectrons or cosmic-ray particles in various astrophysical circumstances, such as the interstellar medium, supernova envelopes, and QSO emission-line clouds.

Xu, Yueming↗
NASA NTRS2001

Three Dimensional Cross-Sectional Properties From Bone Densitometry

Bone densitometry has previously been used to obtain cross-sectional properties of bone in a single scan plane. Using three non-coplanar scans, we have extended the method to obtain the principal area Moments of inertia and orientations of the principal axes at each cross-section along the length of the scan. Various 5 aluminum phantoms were used to examine scanner characteristics to develop the highest accuracy possible for in vitro non-invasive analysis of mass distribution. Factors considered included X-ray photon energy, initial scan orientation, the included angle of the 3 scans, and Imin/Imax ratios. Principal moments of inertia were accurate to within 3.1% and principal angles were within 1 deg. of the expected value for phantoms scanned with included angles of 60 deg. and 90 deg. at the higher X-ray photon energy. Low standard deviations in error also 10 indicate high precision of calculated measurements with these included angles. Accuracy and precision decreased slightly when the included angle was reduced to 30 deg. The method was then successfully applied to a pair of excised cadaveric tibiae. The accuracy and insensitivity of the algorithms to cross-sectional shape and changing isotropy (Imin/Imax) values when various included angles are used make this technique viable for future in vivo studies.

Cleek, Tammy M.↗