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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Dependence of polar hole density on magnetic and solar conditions

Electron densities from the Langmuir probes on the Atmospheric Explorer C and Dynamics Explorer 2 are used for analyzing the behavior of the high-altitude night-side F region polar hole as a function of solar and magnetic activity and of universal time (UT). The polar region of invariant latitude from 70 deg to 80 deg and MLT from 22 to 03 hours is examined. The strongest dependencies are observed in F10.7 and UT; a strong hemispherical difference due to the offset of the magnetic poles from the earth's rotation axis is observed in the UT dependence of the ionization hole. A seasonal variation in the dependence of ion density on solar flux is indicated, and an overall asymmetry in the density level between hemispheres is revealed, with the winter-hole density about a factor of 10 greater in the north than in the south.

Hoegy, W. R.↗
NASA NTRS1983

Turbulent generation of outward-traveling interplanetary Alfvenic fluctuations

Additional evidence is presented for the dynamic alignment of the fluctuating plasma fluid velocity and the fluctuating magnetic field in two-dimensional MHD turbulence. The evidence is seen as indicating that the interplanetary fluctuations need not represent time-asymptotic states. Rather, it is contended that interplanetary Alfvenic fluctuations are generated in situ in the early stage of dynamic alignment. In addition to providing an explanation for inertial-range alignment of the fluctuating plasma fluid velocity and the fluctuating magnetic field in the solar wind, the model presented here accounts for the fact that the sign of this correlation (relative to the direction of the mean magnetic field) corresponds to the observed 'direction of propagation', that is, away from the sun. Evidence is found to support the contention that MHD fluctuations in the solar wind resemble turbulence arising from local stirring of the medium.

Matthaeus, W. H.↗
NASA NTRS2010

Recent Simulation Results on Ring Current Dynamics Using the Comprehensive Ring Current Model

Plasma sheet conditions and electromagnetic field configurations are both crucial in determining ring current evolution and connection to the ionosphere. In this presentation, we investigate how different conditions of plasma sheet distribution affect ring current properties. Results include comparative studies in 1) varying the radial distance of the plasma sheet boundary; 2) varying local time distribution of the source population; 3) varying the source spectra. Our results show that a source located farther away leads to a stronger ring current than a source that is closer to the Earth. Local time distribution of the source plays an important role in determining both the radial and azimuthal (local time) location of the ring current peak pressure. We found that post-midnight source locations generally lead to a stronger ring current. This finding is in agreement with Lavraud et al.. However, our results do not exhibit any simple dependence of the local time distribution of the peak ring current (within the lower energy range) on the local time distribution of the source, as suggested by Lavraud et al. [2008]. In addition, we will show how different specifications of the magnetic field in the simulation domain affect ring current dynamics in reference to the 20 November 2007 storm, which include initial results on coupling the CRCM with a three-dimensional (3-D) plasma force balance code to achieve self-consistency in the magnetic field.

Zheng, Yihua↗
NASA NTRS1988

Auroral E-fields from DE-1 and -2 at magnetically conjugate points

The results of studies of the electric field measurements from the two Dynamics Explorer satellites are reviewed. There are times at which DE-2 measured electric fields at the auroral ionosphere while DE-1 obtained nearly simultaneous measurement at a higher altitude on the same magnetic field lines. When these electric fields are mapped to a common altitude it is found that the large-scale electric fields are similar, but the small-scale electric fields have a larger amplitude at the higher altitude. Through the use of Fourier analysis it is shown that these results are evidence for a magnetic field-aligned potential drop between the two satellites. While these results were made possible by the satellites' altitude separation, it is also possible to take advantage of the fact that the satellites may pass through the same geomagnetic location with a time separation. This was useful for confirming that sinusoidal electric field oscillations which were detected near one conjunction were due to spatial rather than temporal variations, since similar oscillations were found at the same location at different times. The observed spatial oscillations can be explained by a simple model of magnetosphere-ionosphere coupling.

Weimer, D. R.↗
NASA NTRS1985

Conservation laws for relativistic guiding-center plasma

A covariant relativistic formulation is used for self-consistent dynamics of a guiding-center plasma in an electromagnetic field. The reciprocal interactions appear as a magnetization in Maxwell's equations and as field gradient forces in the guiding-center dynamical equation. The ten local conservation laws corresponding to translational and rotational invariance of the Minkowski space are expressed in terms of a symmetric energy-momentum tensor.

Similon, P. L.↗
NASA NTRS1966

Unconventional inertial sensors.

Inertial sensors, discussing magnetic resonance and superconductor gyroscopes, ring lasers, fluid dynamical devices, electrostatic gyroscopes, etc

CRYOGENIC GYROSCOPE↗
NASA NTRS1976

The relationship between the galactic matter distribution, cosmic ray dynamics, and gamma ray production

Theoretical considerations and analysis of the results of gamma ray astronomy suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density should be enhanced where the matter density is greatest on the scale of galactic arms. This concept has been explored in a galactic model using recent 21 cm radio observations of the neutral hydrogen and 2.6 mm observations of carbon monoxide, which is considered to be a tracer of molecular hydrogen. The model assumes: (1) cosmic rays are galactic and not universal; (2) on the scale of galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3) the cosmic ray scale height is significantly larger than the scale height of the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of about 3:1.

Kniffen, D. A.↗
NASA NTRS1977

New aspects of the cosmic-ray modulation in 1974-1975 near solar minimum

Residual cosmic-ray modulation at or near the solar minima of 1965 and 1972-75 is compared on the basis of ground-based and satellite observations of nonrelativistic proton and helium components as well as variations in the relativistic component. It is found that the nonrelativistic fluxes lagged behind the high-energy fluxes to form a hysteresis loop over the period from 1965 to 1973, that the 1975 proton fluxes were about 85% higher than the 1972 level and about 35% higher than the 1965 level, and that the 1975 helium fluxes were about 60% higher than in 1965. Some unique recovery events are discussed, and a time-lag effect dependent on magnetic rigidity is examined which was associated with dynamic changes in the heliosphere. A qualitative explanation is offered for the hysteresis effect.

Garcia-Munoz, M.↗
NASA NTRS1977

SAS-2 gamma-ray results from the galactic plane and their implications for galactic structure and galactic cosmic-ray dynamics

The final SAS-2 results related to high energy galactic gamma-ray emission show a strong correlation with galactic structural features seen at other wavelenghts, when the known gamma-ray sources are subtracted. Theoretical considerations and analysis of the gamma-ray data suggest that the galactic cosmic rays are dynamically coupled to the interstellar matter through the magnetic fields, and hence the cosmic ray density is enhanced where the matter density is greatest on the scale of the galactic arms. This concept has been explored in a galactic model that assumes: (1) cosmic rays are galactic and not universal; (2)on the scale of the galactic arms, the cosmic ray column (surface) density is proportional to the total interstellar gas column density; (3)the cosmic ray scale height is significantly larger than the scale height to the matter; and (4) ours is a spiral galaxy characterized by an arm to interarm density ratio of over 2:1.

Fichtel, C. E.↗
NASA NTRS1978

Search for X-ray emission from AO0235+164

Limits to the first-order Compton scattering, brightness temperature, and angular size of the compact radio source AO0235+164 were calculated on the basis of a flux density of less than about 1 microJy at 10 to the 18th Hz calculated from observations of the source with the rotating modulation collimator aboard the SAS 3 X-ray observatory. It was found that the maximum brightness temperature at this frequency is less than 2.4 times 10 to the 11th K, corresponding to a minimum angular size of 0.38 msec of arc, assuming the synchrotron self-absorption turnover coefficient is 0.5. On the basis of the distance implied by the largest redshift present, the energy contained in relativistic particles and the magnetic field are calculated, and the ratio of particle to magnetic energy is greater than 10, so the dynamics must be particle dominated. This indicates relativistic expansion if the mean energy per particle is comparable to or greater than the rest of those particles that neutralize the electron plasma.

Dennison, B.↗
NASA NTRS1979

Data reduction and analysis for the TRW IMP-7 plasma wave experiment

Highlights from the IMP 7 plasma wave experiment are briefly outlined. The measurements in the tail revealed great complexities involving substorms and fireballs and provided insight into the overall dynamics of the magnetosphere. The low levels of magnetic turbulence may be of significance with respect to the development of tearing mode dissipation for reconnection events. The IMP wave observations in the distant magnetosphere boundary region showed that the boundaries were quite diffuse and frequently purely defined. Finally, nearly simultaneous IMP 7 and 8 comparisons were used to achieve an understanding of shock structure and propagation.

Scarf, F. L.↗
NASA NTRS1980

The physics of plasma injection events

In this paper, plasma injection is defined as an increase of particle flux in a detector of finite bandwidth. Injection can result from dynamic processes or from spacecraft penetration of a quasi-static spatial structure produced by a steady magnetospheric convection pattern. ATS-5 particle spectrograms are found to provide examples of plasma injection events of both sorts. Dynamic injection occurs both with and without local magnetic signatures. For events not associated with clear local magnetic signatures, convection theory with a steady or a time-varying uniform electric field can account for the energy dispersion of injected particles with energy less than 50 keV. The paper concludes with a discussion of the way in which the convection boundaries are related to the substorm injection boundary of Mauk and McIlwain. Several alternative expressions for the local time and K(p) dependence of the injection boundary are given.

Kivelson, M. G.↗
NASA NTRS1981

Phenomena induced by charged particle beams

The injection of energetic particles along the Earth's magnetic field lines is a possible remote sensing method for measuring the electric fields parallel to the magnetic field with good time resolution over the entire magnetic field. Neutralization processes, return-current effects, dynamics of the beams, triggered instabilities, and waves must be investigated before the fundamental question about proper experimental conditions, such as energy, intensity and divergence of the beams, pitch-angle injection, ion species, proper probes and detectors and their location, and rendezvous conditions, can be resolved. An experiment designed to provide a better understanding of these special physical processes and to provide some answers to questions concerning beam injection techniques is described.

Beghin, C.↗
NASA NTRS1984

An Assessment of Integrated Flywheel System Technology

The current state of the technology in flywheel storage systems and ancillary components, the technology in light of future requirements, and technology development needs to rectify these shortfalls were identified. Technology efforts conducted in Europe and in the United States were reviewed. Results of developments in composite material rotors, magnetic suspension systems, motor/generators and electronics, and system dynamics and control were presented. The technology issues for the various disciplines and technology enhancement scenarios are discussed. A summary of the workshop, and conclusions and recommendations are presented.

Keckler, C. R.↗
NASA NTRS1984

DE 1 observations of type 1 counterstreaming electrons and field-aligned currents

Dynamics Explorer 1 satellite observations of plasma and magnetic fields during type one counterstreaming electron events are presented. Counterstreaming electrons are observed at high altitudes in the region of field-aligned current. The total current density computed from the plasma data in the 18-10,000 eV energy range is generally about 1-2 micro-A/sq m. For the downward current, low-energy electrons contribute more than 40 percent of the total plasma current density integrated above 18 eV. For the upward current, such electrons contribute less than 50 percent of that current density. Electron beams in the field-aligned direction are occasionally detected. The pitch angle distributions of counterstreaming electrons are generally enhanced at both small and large pitch angles. STARE simultaneous observations for one DE 1 pass indicated that the field-aligned current was closed through Pedersen currents in the ionosphere. The directions of the ionospheric current systems are consistent with the DE 1 observations at high altitudes.

Lin, C. S.↗
NASA NTRS1986

Geophysical remote sensing

The types of remote sensing images which have applications in geophysical studies are reviewed. Features of the Shuttle Imaging Radar, a synthetic aperture radar, are described and a sample image is provided to illustrate the capabilities for mapping large-scale geological structure. A combined Landsat-Seasat image is shown to yield data on crustal composition. Sea surface topographic features that result from gravitational effects are demonstrated to be amenable to characterization with another Seasat instrument, a radar altimeter. Magsat data allow identification of magnetic perturbations produced by crustal magnetization. Finally, auroral imagery gathered with the Atmospheric Dynamics Explorer are presented which show that the effects of particles bombarding the atmosphere can be detected at UV wavelengths.

Mcpherron, Robert L.↗