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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Quantum theory of the dielectric constant of a magnetized plasma and astrophysical applications. I.

A quantum mechanical treatment of an electron plasma in a constant and homogeneous magnetic field is considered, with the aim of (1) defining the range of validity of the magnetoionic theory (2) studying the deviations from this theory, in applications involving high densities, and intense magnetic field. While treating the magnetic field exactly, a perturbation approach in the photon field is used to derive general expressions for the dielectric tensor. Numerical estimates on the range of applicability of the magnetoionic theory are given for the case of the 'one-dimensional' electron gas, where only the lowest Landau level is occupied.

Canuto, V.↗
NASA NTRS1975

An improved method for measuring the magnetic inhomogeneity shift in hydrogen masers

The reported method makes it possible to conduct all maser frequency measurements under conditions of low magnetic field intensity for which the hydrogen maser is most stable. Aspects concerning the origin of the magnetic inhomogeneity shift are examined and the available approaches for measuring this shift are considered, taking into account certain drawbacks of currently used methods. An approach free of these drawbacks can be based on the measurement of changes in a parameter representing the difference between the number of atoms in the involved states.

Reinhardt, V. S.↗
NASA NTRS1993

Magnetic field properties of the intermediate transition of the Venus ionosheath

Results of a statistical analysis of the magnetic properties of the intermediate transition of the Venus ionosheath based on the magnetic field data of the Pioneer Venus Orbiter are reported. It is found that the transition is often characterized by a substantial decrease in magnetic field intensity and an accompanying rotation to a direction that is more closely aligned with the sun-Venus axis. In other cases, the 30 kHz bursts occur outside a region of enhanced magnetic field reminiscent of the magnetic barrier external to the Venus dayside ionopause. The rotation of the magnetic field toward the sun-Venus line associated with the 30 kHz bursts is also evident here, but generally the conditions change more gradually. Possible mechanisms of these variations and ionospheric plasma expansion are examined.

Perez-De-tejada, H.↗
NASA NTRS1987

The dynamical oscillation and propulsion of magnetic fields in the convective zone of a star. II - Thermal shadows. III - Accumulation of heat and the onset of the Rayleigh-Taylor instability

The dynamics of thermal shadows which develop in the convective zone of a star around an insulating obstacle such as a horizontal band in intense magnetic field are studied. The depth of the shadow on the cool side of the obstacle is found to depend largely on the width of the obstacle multiplied by the temperature gradient. Thermal shadows pressing fields up to 10,000 G downward against the bottom of the convective zone are produced by the broad bands of the azimuthal field in the sun's convective zone. In the third part, the time-dependent accumulation of heat beneath a thermal barrier simulating such a band in the lower convective zone of the sun is considered. The resulting Rayleigh-Taylor instability is shown to cause tongues of heated gas to penetrate upward through the field, providing the emerging magnetic fields that give rise to the activity of the sun.

Parker, E. N.↗
NASA NTRS1987

Stream structures in the outer heliosphere

Nineteen magnetic clouds are identified in the years from 1978 through 1982 and studied by the superimposed epoch method. The magnetic fluctuations, density, and temperature are enhanced ahead of the clouds preceded by shocks. Strong magnetic field intensities and low proton temperatures are observed in the clouds. A relatively large (2.5%) decrease in cosmic ray intensity is caused by the turbulent sheath behind an interplanetary shock ahead of a magnetic cloud. Only a small (0.5%) decrease in intensity is associated with the magnetic cloud itself. Magnetic clouds can produce geomagnetic activity with a decrease in the Dst index of the order of 100 gammas. The magnitude of the change in Dst index for the case when southward fields arrive first is comparable to that for the case of northward fields first, and the phase is such that geomagnetic activity is associated with the southward fields.

Whang, Y. C.↗
NASA NTRS1977

Magnetic holes in the solar wind

An analysis of high-resolution magnetic field measurements from the Goddard Space Flight Center magnetometer on Explorer 43 showed that low magnetic field intensities (less than 1 gamma) in the solar wind at 1 AU occur as distinct depressions, or 'holes', in otherwise nearly average conditions. These magnetic holes are new kinetic scale phenomena, having a characteristic dimension of the order of 20,000 km. They occurred at a rate of 1.5/d in the 18-day interval (March 18 to April 6, 1971) that was considered. Most magnetic holes are characterized by both a depression in /B/ and a change in the magnetic field direction, and some of these are possibly the result of magnetic merging. However, in other cases the direction, does not change; such holes are not due to merging but might be a diamagnetic effect due to localized plasma inhomogeneities.

Turner, J. M.↗
NASA NTRS1994

Merged interaction regions and large-scale magnetic field fluctuations during 1991: Voyager 2 observations

This paper analyzes Voyager 2 observations of the magnetic field between 33.6 AU and 36.2 AU during 1991 when extraordinary events were observed on the Sun and in the heliosphere. The magnetic field strength signal B(t) has the unusual form of two large transient merged interaction regions (MIRs) on a fluctuating background. The two MIRs moved past the spacecraft in 32 days and 18 days, respectively. The mean field strength in each transient MIR was approx. equals 2.6 times the mean field during the remaining part of the year (0.11 nT). Each of the MIRs is related to a fast stream. The magnetic field is strong throughout each stream, suggesting that the strong fields are carried by the streams as well as produced by shock and stream compression. The fluctuations in B(t) during 1991 are not multifractal, and the MIRs cannot be approximated as multifractal clusters of intense magnetic fields. The distribution of the hour-averaged magnetic field strengths is approximately lognormal over 90% of its intermediate range, and it has an exponential tail for B greater than the average magnetic field strength. The elevation angles of B have a normal distribution with a standard deviation of 16 deg +/- 4 deg. The distributions of the azimuthal angles of B in the ranges 1 deg - 180 deg and 180 deg - 360 deg are approximately normal over a more limited range, and non-Gaussian tails associated with nearly radial magnetic fields; the standard deviations are approx. equal to 40 deg. Individual sectors are present throughout most of the interval, even in the MIRs, but there is no recurrent sector pattern. A model of the large-scale fluctuations in 1991 will have to include both determinaistic and statistical factors.

Burlaga, L. F.↗
NASA NTRS1972

The ring current.

The topology of delta-B (i.e., the observed scalar magnetic field intensity minus a scalar reference field intensity) in the magnetosphere has been established by the Rb magnetometer observations on OGO's 3 and 5. This delta-B topology provides a convenient framework, on the basis of which the complex features found by the earlier magnetic field observations made by Explorers 10, 12, 14, 26 and Electron 2 can be reinterpreted to fit a unified simple picture of the magnetospheric field distortions including the inflation of the equatorial magnetosphere by the ring current. It is proposed that the quiet-time ring current consists of two parts, the inner ring current imbedded deeply inside the plasmapause and the outer ring current flowing in the plasma sheet.

Sugiura, M.↗
NASA NTRS1978

/U,B,K/ coordinates - A natural system for studying magnetospheric convection

The formulation of the magnetospheric convection problem involves a coordinate system consisting of the electric potential, the magnetic field intensity, and the modified longitudinal invariant. The mapping is extended to include all particles and not just those mirroring in the magnetic equator. Equations of motion for the particle mirror points in this representation are presented. The analysis results in a natural division of the magnetosphere into accelerator and dynamo regions and use of the coordinate system permits trajectory-dependent effects to be distinguished from source- or sink-dependent effects. The representation is illustrated by application to the analysis of the nose structure protons observed by Smith and Hoffman (1974).

Whipple, E. C., Jr.↗
NASA NTRS1999

On the Variable Spin-Down of SGR 1900+14

We consider the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14 reported in a companion paper by Woods et al. During an 80 day interval between June 1998 and the large outburst on August 27, 1998, the mean spin-down rate increased by a factor 2.3 resulting in a positive period offset of delta P/P = 1 X 10(exp -4)/ A radiation hydrodynamical outflow associated with the August 27 event could impart the required torque, but only if the dipole magnetic field is stronger than about 10(exp 14) G and the outflow lasts longer than the observed X-ray flare. A positive period increment is also a natural consequence of a gradual plastic deformation of the neutron star crust by an intense magnetic field. Finally, we discuss the relative stability of the long term spin-down rate of SGR 1900+14, and compare the relative spindown rates of the SGRs and the Anomalous X-ray Pulsars.

Thompson, Christopher↗
NASA NTRS1974

Interplanetary stream magnetism: Kinematic effects

The particle density, and the magnetic field intensity and direction are calculated in corotating streams of the solar wind, assuming that the solar wind velocity is constant and radial and that its azimuthal variations are not two rapid. The effects of the radial velocity profile in corotating streams on the magnetic fields were examined using kinematic approximation and a variety of field configurations on the inner boundary. Kinematic and dynamic effects are discussed.

Burlaga, L. F.↗
NASA NTRS1983

Terrestrial versus Jovian VLF chorus - A comparative study

The relevant parameters of the magnetospheres of Jupiter and earth are investigated based on the wave-particle resonant interactions that are believed to be responsible for the generation of VLF chorus emissions observed on Voyager 1. Expressions are derived for the wave-particle interaction length and the nonlinearity parameter, and the values of these parameters are compared with those calculated for the earth's magnetosphere. It is determined that the typical interaction lengths are at least 2-5 times larger in the Jovian than in the terrestrial magnetosphere, and that the wave intensity necessary to reach the threshold of nonlinearity in the Jovian magnetosphere is 5-100 times lower. Measurements by Voyager 1 show that the inferred wave magnetic field intensities of the Jovian chorus are in the range of reported intensities for terrestrial chorus, probably due to the fact that the fluxes of few keV resonant particles found in the Jovian magnetosphere were typically two orders of magnitude higher. Growth rate measurements on Voyager 1 broadband wave data are employed to confirm that the temporal growth rates of Jovian chorus bursts are higher than for the earth.

Inan, U. S.↗
NASA NTRS1991

Microstructure and magnetization of Y-Ba-Cu-O prepared by melt quenching, partial melting and doping

Y-Ba-Cu-O samples prepared by means of a variety of melt-based techniques exhibit high values for their magnetic properties compared with those of samples prepared by solid state sintering. These techniques include single-stage partial melting as well as melt quenching followed by a second heat treatment stage, and they have been applied to the stoichiometric 123 composition as well as to formulations containing excess yttrium or other dopants. The structure of these melt-based samples is highly aligned, and the magnetization readings exhibit large anisotropy. At 77 K and magnetic field intensities of about 2 kOe, diamagnetic susceptibilities as high as -14 x 10(exp -3) emu/g were obtained in the cases of melt-quenched samples and remanent magnetization values as high as 10 emu/g for samples prepared by partial melting.

Hojaji, Hamid↗
NASA NTRS1977

The external magnetic field environment

Calculations were made to predict magnetic field intensities surrounding an aircraft following a lightning strike. Aircraft design and aircraft structural geometry were considered in the computations. A wire grid aircraft model was used to aid in magnetic flux estimation.

Franklin A Fisher↗
NASA NTRS1972

Stellar evolution.

Aspects of normal stellar evolution are discussed together with evolution near the main sequence, stellar evolution from main sequence to white dwarf or carbon ignition, the structure of massive main-sequence stars, and problems of stellar stability and stellar pulsation. Other subjects considered include variable stars, white dwarfs, close binaries, novae, early supernova luminosity, neutron stars, the photometry of field horizontal-branch stars, and stellar opacity. Transport mechanisms in stars are examined together with thermonuclear reactions and nucleosynthesis, the instability problem in nuclear burning shells, stellar coalescence, and intense magnetic fields in astrophysics. Individual items are announced in this issue.

Chiu, H.-Y.↗
NASA NTRS1978

Magnetic fields and flows between 1 and 0.3 AU during the primary mission of Helios 1

Magnetic phenomena and coronal holes observed by Helios 1 during nearly four rotations of the sun are discussed. It is estimated that the magnetic field intensity of open field lines in some of the coronal holes (which changed in shape and latitude from one rotation to the next) was of the order of 10-20 G during the studied period, December 1974 to March 1975. Magnetic field polarity, cold magnetic enhancements, and longitudinal widths of the stream are described. It is concluded that between the sun and 0.3 AU there was a diverging stream surrounded by a thin boundary layer in which there was large velocity shear. There is evidence for compression of the magnetic field in the western boundary layer.

Burlaga, L. F.↗