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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 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Current sheet crossings in the distant magnetotail

A computer search of crossings of the field reversal region in the middle of the distant magnetotail has been done with ISEE-3 data. It is found that the instantaneous direction of the magnetic field at the crossings Bz is northward on average at a distance of 220 earth radii, with moderate values of the plasma flow. This result suggests that the magnetic field lines are closed; since the flow is tailward, the Dungey (1961) model with a steady state reconnection line across the magnetotail earthward of the spacecraft is invalidated. The present result gives strong support to a model in which tailward boundary layer flow provides the viscous interaction proposed by Axford and Hines (1961). At higher values of the plasma velocity, negative values of Bz are found.

Heikkila, W. J.↗
NASA NTRS1974

Structures in a non-magnetic solar corona

A fluid mechanical convective instability is examined under the conditions found in the solar corona. Linearized density perturbations are shown to grow as they are carried outward by the solar wind. The non-linear instability may be proposed as a cause of coronal structures in nonmagnetic stars, or in regions of the solar corona with weak magnetic fields.

Cross, M. A.↗
NASA NTRS1974

Analysis of cross beam runs taken at Haswell Field site, October 1969

A series of cross beam experiments was conducted at the ESSA field site at Haswell, Colorado. Both the optical visual and infrared units were operated on a comparison basis. A data report of the initial auto- and cross-correlation evaluation of these tests is presented. The original test data from the Haswell tests were recorded on F M magnetic tape. A copy of the original tapes was made and employed for the present analysis. The tapes were played back at 60 inches per second for analysis. Some of the infrared units runs (Run Nos. 8,25,40,41,42,43,44,45) were played back at 30 inches per second in order to gain sufficient averaging time. The averaging time was nominally 3200 seconds real time at 60 inches per second and 1600 seconds real time at 30 inches per second. These averaging times correspond to 100 seconds of averaging time of the correlator.

Huff, L. L.↗
NASA NTRS1983

Venus' nighttime horizontal plasma flow, 'magnetic congestion', and ionospheric hole production

A simple rectilinear, two-dimensional MHD model is used to investigate the effects of field-aligned plasma loss and cooling on a dense plasma convecting across a weak magnetic field, in order to illumine the Venus nighttime phenomena of horizontal plasma flow, magnetic congestion and ionospheric hole production. By parameterizing field-aligned variations and explicitly solving for cross magnetic field variations, it is shown that the abrupt horizontal enhancements of the vertical magnetic field, as well as sudden decreases of the plasma density to very low values (which are characteristic of ionospheric holes), can be produced in the presence of field-aligned losses.

Grebowsky, J. M.↗
NASA NTRS1989

On the source of cross-grain lineations in the central Pacific gravity field

The source of cross-grain lineations in marine gravity field observed in central Pacific was investigated by comparing multiple collinear gravity profiles from Geosat data with coincident bathymetry profiles, in the Fourier transform domain. Bathymetric data were collected by multibeam sonar systems operating from two research vessels, one in June-August 1985, the other in February and March 1987. The results of this analysis indicate that the lineations are superficial features that appear to result from a combination of subsurface and surface loads supported by a thin (2 km to 5 km) lithosphere.

Mcadoo, David C.↗
NASA NTRS1982

Diffusion processes in the magnetopause boundary layer

A quantitative estimate is calculated for the effect of wave-particle scattering on the structure of the magnetopause boundary layer. It is assumed that large cross-B electric fields are absent in the observed penetration of magnetosheath plasma into the magnetopause boundary layer, thus allowing for cross-field transport comparable to 10% of the Bohm diffusion. It is shown that magnetosheath ions, resonant with low frequency electrostatic waves, can account for the typical boundary layer thickness when transported at 10% of the diffusion rate 1000 sq km/sec. The conditions are required to occur at all local times and under all interplanetary conditions. Significant mass and momentum transfer are then possible across the magnetopause when field merging is not occurring.

Tsurutani, B. T.↗
NASA NTRS1973

Steady-state hot-ion plasma produced by crossed electric and magnetic fields

Results of initial diagnostics on the Lewis Research Center hot-ion-plasma source (HIP-1) are reported. The mirror-contained plasma was heated by applying a radial electric field similar to that used in the ORNL burnout experiments. An electrostatic neutral particle analyzer was used to make a parametric study of ion energy distributions in both hydrogen and euterium plasmas. Ion temperatures as high as 2 keV were measured in plasmas with electron densities greater than 10 to 12th power/cu cm. The performance of the device was found to be extremely sensitive to a magnetic field. There are indications that ion heating was reduced when the size of the Larmor orbit was larger than the region of a strong radial electric field.

Sigman, D. R.↗
NASA NTRS1981

Look direction dependence of radar backscattering cross section for agricultural fields

Analysis of multifrequency-multipolarization scatterometer data acquired by NASA Johnson Space Center during the 1978 Colby Agricultural Soil Moisture Experiment provides evidence that the effects of row orientation remain quite severe for relatively bare fields over a wide range of radar frequencies. In addition, Seasat satellite radar imagery from areas in Louisiana shows dominant row orientation effects even beneath substantial amounts of vegetation cover. The multiparameter nature of the Colby data set, and the continuous angular change in field patterns observed in the Louisiana test area provide much finer definition of microwave sensitivity to row orientation than has been possible in the past.

Waite, W. P.↗
NASA NTRS1979

Apparatus for measuring an aircraft's speed and height

An apparatus for measuring aircraft horizontal speed and height above ground without the need for airborne cooperative devices is presented. Two ground level TV cameras separated by a measured distance and pointed at zenith are placed in line with the projection of the expected path of the aircraft. Speed is determined by measuring the time that it takes the aircraft to travel between the fields of view of the two TV cameras using zenith crossings as the reference points. Height is determined by correlating the speed with the time required to cross the field of view of either of the two cameras.

Young, W. R.↗
NASA NTRS1984

The effect of line-tying on the radiative MHD stability of coronal plasmas with radial pressure profile

The role of photospheric line-tying, i.e., solar coronal loop structures, was investigated in terms of the effect on radiative modes and the influence that different radial pressure profiles exert on the effects of line-tying on radiative MHD stability. Energy is assumed dissipated by heat conduction and radiation and zero- and first-order solutions are obtained for the radiative time scales. Line-tying is a magnetic tension in the zero-order MHD mode and produces stability. Heat conduction occurs along bent field lines in first-order MHD modes when plasmas cross the field lines. Irradiated cool-core loops can experience MHD instabilities in the cylinder center, while line-tying can stabilize the plasma in the surrounding hot medium. Line-tying also adds stability to magnetosonic and condensation modes.

An, C.-H.↗
NASA NTRS1983

On the injection boundary model and dispersing ion signatures at near-geosynchronous altitudes

A simple particle drift model is used to investigate the applicability of the injection boundary concept to the ion dispersion event observed on March 22 (day 81), 1979. The model consists of a dipole magnetic field with a uniform cross-tail electric field plus a corotation field. A full spectrum of particles from 100 eV to 32 keV is injected at the Kp = 6 - Mauk and McIlwain injection boundary at the time of substorm onset on this day (1100 UT). A new approach is presented for displaying the model-produced ion drift trajectories to make the large scale spatial characteristics of the evolving energy distributions easier to envision and to facilitate the comparison of the model results with experimental observations. The resultant prediction for the dispersion signature is compared with Scatha mass spectrometer measurements, and a 2.0 kV/Re cross-tail convection electric field is found to give a good fit to the observed dispersion signature. It is determined that for this particular event, injection only at that portion of the injection boundary close to 1800 local time is required to produce the dispersion curve.

Strangeway, R. J.↗
NASA NTRS1987

Dihedral corner reflector backscatter using higher order reflections and diffractions

The uniform theory of diffraction (UTD) plus an imposed edge diffraction extension is used to predict the backscatter cross sections of dihedral corner reflectors which have right, obtuse, and acute included angles. The UTD allows individual backscattering mechanisms of the dihedral corner reflectors to be identified and provides good agreement with experimental cross-section measurements in the azimuthal plane. Multiply reflected and diffracted fields of up to third-order are included in the analysis for both horizontal and vertical polarizations. The coefficients of the uniform theory of diffraction revert to those of the geometrical theory of diffraction (GTD) in far-field cross-section analyses, but finite cross sections can be obtained everywhere by considering mutual cancellation of diffractions from parallel edges. Analytic calculations are performed using UTD coefficients; hence the accuracy required in angular measurements is more critical as the distance increases. The common far-field approximation that all rays to the observation point are parallel is too gross an approxiation for the angular parameters in the UTD coefficients in the far field.

Griesser, Timothy↗
NASA NTRS2003

Ion Velocity Distributions Within LLBL and Their Possible Implication to Multiple Reconnections

We analyze two LLBL crossings made by Interball Tail satellite under southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-ty and (c) distributions with three components one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tube consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in LLBL indicate that a significant part of LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection X-ray lines between magnetosheath and magnetospheric flux tubes.

Vaisberg, O. L.↗
NASA NTRS1972

Ion-quadrupole effects in ion-molecule collisions.

Ion-quadrupole effects are investigated via numerical calculations of capture cross sections and computer-plotter studies of ion trajectories in the quadrupole field. Capture cross sections are roughly equal to Langevin values for low rotational temperatures; a large fraction of multiple reflection captures are calculated corresponding to formation of ion-molecule complexes.

Dugan, J. V., Jr.↗
NASA NTRS1986

Compton scattering in strong magnetic fields

The relativistic cross section for Compton scattering by electrons in strong magnetic fields is derived. The results confirm and extend earlier work which has treated only transitions to the lowest or first excited Landau levels. For the teragauss field strengths expected in neutron star magnetospheres, the relative rates for excited state transitions are found to be significant, especially for incident photon energies several times the cyclotron frequency. Since these transitions must result in the rapid emission of one or more cyclotron photons as well as the Compton-scattered photon, the scattering process actually becomes a photon 'splitting' mechanism which acts to soften hard photon spectra, and also provides a specific mechanism for populating higher Landau levels in the electron distribution function. The results should be significant for models of gamma-ray bursters and pulsating X-ray sources.

Daugherty, Joseph K.↗
NASA NTRS2013

The Force-Free Magnetosphere of a Rotating Black Hole

We revisit the Blandford-Znajek process and solve the fundamental equation that governs the structure of the steady-state force-free magnetosphere around a Kerr black hole. The solution depends on the distributions of the magnetic field angular velocity and the poloidal electric current. These are not arbitrary. They are determined self-consistently by requiring that magnetic field lines cross smoothly the two singular surfaces of the problem: the inner "light surface" located inside the ergosphere and the outer "light surface" which is the generalization of the pulsar light cylinder.We find the solution for the simplest possible magnetic field configuration, the split monopole, through a numerical iterative relaxation method analogous to the one that yields the structure of the steady-state axisymmetric force-free pulsar magnetosphere. We obtain the rate of electromagnetic extraction of energy and confirm the results of Blandford and Znajek and of previous time-dependent simulations. Furthermore, we discuss the physical applicability of magnetic field configurations that do not cross both "light surfaces."

Contopoulos, Ioannis↗
NASA NTRS1997

Convection in an Infinite Vertical Cylinder in the Presence of a Horizontal Magnetic Field

The use of a magnetic field to suppress convection in low gravity materials processing is an area of active research. This study aims to investigate some of the basic features of an verse magnetic field on convective motion in electrically conducting melts. The geometry considered is in infinite vertical column of liquid metal with an axial temperature gradient and an imposed transverse magnetic field. The incipience and azimuthal orientation of convective roM is investigated. The governing transport equations are nondimensionalized, linearized and the eigen value problem is solved to determine the most physically significant states. The analysis shows that the initial degeneracy (with no magnetic field) is removed by the presence of a magnetic field and the primary convection roll aligns itself so that its plane is perpendicular to the applied magnetic field. A cross over to another mode is also found when the strength of the magnetic field is increased. Velocity distributions are presented corresponding to the lowest modes and the system behavior within limit s of non-linearity is discussed.

Mazuruk, Konstantin↗