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At least 325 records · Page 18

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NASA NTRS1974

Calculation of a realistic gradient as a function of radial distance from the sun

Numerical calculations of radial gradients of galactic cosmic ray protons have been performed for a model of the interplanetary cavity which includes processes of diffusion along the spiral interplanetary magnetic field lines, convection, and adiabatic energy change. The increasing spiral nature of the field lines with increasing distance from the sun results in the bulk of the modulation region being beyond the earth. The radial gradients for this model are found to be small near the earth and out to a few AU, increasing as one approaches the boundary.

Lezniak, J. A.↗

NASA NTRS1974

Propagation of transverse waves in a radially expanding plasma

Investigation of the properties of low-frequency transverse waves in an expanding plasma. The wave vector, the background magnetic field, and the streaming velocity of the plasma are all assumed to lie along the radial direction. Expressions are presented for the radial dependence of the amplitude and phase of left and right circularly polarized waves, correct to first order in the wave frequency divided by the proton cyclotron frequency. Differences in the phase velocities of these two circular polarizations result in a Faraday rotation that can be substantial for typical interplanetary conditions near 1 AU. The implications of these results for a realistic solar wind model with the interplanetary magnetic field along the spiral direction are also considered.

Solodyna, C. V.↗

NASA NTRS1974

A technique for generating shear waves in cylindrical shells under radial impact

Experimental techniques are developed to study and measure the shear-wave velocity in an aluminum cylindrical shell subjected to a radial impact. The radial impact is obtained by exploding an electrical detonator inserted in plastic plugs mounted on the end of the shell. Strain gages, mounted on the outside surface of the shell at various axial locations, are used to obtain oscilloscope traces from which the shear-wave velocity can be calculated.

Blum, A.↗

NASA NTRS1974

Heavy ion beam probe measurements of radial potential profiles in the modified Penning discharge

A heavy ion beam probe was used to examine the radial potential profile of a plasma in the modified Penning discharge. The plasma has strong (approximately kV) electrostatic potentials near the anode ring which can be a large fraction of the injected ion beam energy. A primary (singly ionized) thallium ion beam is injected through the plasma in the midplane of a double Penning anode ring. After passage through the plasma, primary and secondary (doubly ionized) ions are detected with either a set of flat probes or an electrostatic energy analyzer. A calculation of the primary orbit through the plasma is performed to obtain an approximation to the measured primary beam trajectory. As the real radial potential profile is unknown, an adjustable model is used in the computer program. The adjustable potential profile is varied until the best agreement between measured and calculated trajectories is obtained. Secondary orbits are also predicted using the best fitting adjustable profile. The calculations indicate that secondary beams originating at more than one point in the plasma can be simultaneously observed at the electrostatic analyzer with certain primary beam initial conditions.

Kambic, G. X.↗

NASA NTRS1975

Fluctuations and the radial variation of the interplanetary magnetic field

Correlations between fluctuations in the solar wind velocity and interplanetary magnetic field can influence the observed average interplanetary magnetic field and its variation with heliocentric radius. The average radial magnetic field still varies as inversely with the square of the radius, but, depending on the radial variation of the correlations, the average azimuthal field could depart from the 1/r dependence expected for an Archimedian spiral. This effect could account in part for those observations which indicate a steeper than 1/r dependence for the average azimuthal interplanetary magnetic field.

Jokipii, J. R.↗

NASA NTRS1976

The radial variation of solar flare proton anisotropies observed in deep space on Pioneers 10 and 11

The anisotropy of solar-flare protons (greater than 3 MeV) was evaluated at the time of maximum for each of 24 events measured by Pioneers 10 and 11 and was observed to decrease gradually between 1 and 4.7 AU. Since diffusive streaming is related directly to the effective diffusion coefficient parallel to the interplanetary spiral magnetic field, these observations provide a measure of the radial dependence of interplanetary diffusion parameters. Analysis of these results suggests that the spiral field increases gradually with heliocentric distance. An expression is given for the radial dependence of that field.

Mccarthy, J.↗

NASA NTRS1976

Radial variation of solar-wind parameters

It is demonstrated that since fluctuations in the solar wind are not small, they can have important effects on the observed average values of parameters in the solar wind and their radial variation. The effect is distinct from the dynamical effect of waves and turbulence, and results from the averaging process. It is concluded that, for example, the average density of the solar wind need not vary as the inverse square of distance, even if the average velocity is constant and radial. The effect on thermal anisotropies might also be important. The magnitudes of the effects depend on presently unknown correlations between fluctuations in the solar wind.

Jokipii, J. R.↗

NASA NTRS1976

Losses in radial inflow turbines

A study was conducted to determine experimentally and theoretically the losses in radial inflow turbine nozzles. Extensive experimental data was obtained to investigate the flow behavior in a full-scale radial turbine stator annulus. A theoretical model to predict the losses in both the vaned and vaneless regions of the nozzle was developed. In this analysis, the interaction effects between the stator and the rotor are not considered. It was found that the losses incurred due to the end wall boundary layers can be significant, especially if they are characterized by a strong crossflow. The losses estimated using the analytical study are compared with the experimentally determined values.

Khalil, I. M.↗

NASA NTRS1976

Nonaxisymmetric incompressible hydrostatic pressure effects in radial face seals

A flat seal having an angular misalinement is analyzed, taking into account the radial variations in seal clearance. An analytical solution for axial force, tilting moment, and leakage is presented that covers the whole range from zero to full angular misalinement. Nonaxisymmetric hydrostatic pressures due to the radial variations in the film thickness have a considerable effect on seal stability. When the high pressure is on the outer periphery of the seal, both the axial force and the tilting moment are nonrestoring. The case of high-pressure seals where cavitation is eliminated is discussed, and the possibility of dynamic instability is pointed out.

Etsion, I.↗

NASA NTRS1976

Effects of stream-associated fluctuations upon the radial variation of average solar-wind parameters

The effects of nonlinear fluctuations due to solar wind streams upon radial gradients of average solar wind parameters are computed, using a numerical MHD model for both spherically symmetric time dependent and corotating equatorial flow approximations. Significant effects of correlations are found between fluctuations upon the gradients of azimuthal magnetic fields, radial velocity, density and azimuthal velocity. Between 400 to 900 solar radii stream interactions have transferred the major portion of the angular momentum flux to the magnetic field; at even greater distances the plasma again carries the bulk of the angular momentum flux. The average azimuthal component of the magnetic field may decrease as much as 10% faster than the Archimedean spiral out to 6 AU due to stream interactions, but this result is dependent upon inner boundary conditions.

Goldstein, B. E.↗

NASA NTRS1977

An investigation of viscous losses in radial inflow turbine nozzles

A theoretical model is developed to predict losses in radial inflow turbine nozzles. The analysis is presented in two parts. The first one evaluates the losses which occur across the vaned region of the nozzle, while the second part deals with the losses which take place in the vaneless field. It is concluded that the losses in a radial nozzle would not be greatly affected by the addition of a large vaneless space.

Khalil, I.↗

NASA NTRS1976

Radial diffusion in Jupiter's magnetosphere

Radial phase-space density profiles for equatorially mirroring particles are computed from data obtained by Pioneer 10. The profiles are consistent only with radial diffusion subject to nonadiabatic losses. It is suggested that these losses are due to pitch-angle scattering by whistler turbulence.

Baker, D. N.↗

NASA NTRS1976

Multiple-satellite studies of magnetospheric substorms - Radial dynamics of the plasma sheet

The radial dynamics of the nighttime plasma sheet during substorms is examined. The spatial dependence of plasma sheet variations at different radial distances is studied on the basis of simultaneous recordings from two closely spaced satellites. The simultaneous measurements of the plasma sheet behavior earthward and tailward of r = 15 earth radii confirm substorm models which predict a thinning of the near-earth plasma sheet before the formation of an X-type neutral line, followed by a thickening on the earthward side and a further thinning on the tailward side. Temporal correlations between the plasma sheet variations and substorm development on the ground are studied by obtaining accurate timing of individual substorm expansion onsets. In particular, during multiple onset storms, the near-earth plasma sheet is found to experience a series of multiple expansions and contractions, which usually occur in a one-to-one relationship with ground Pi 2 bursts and are well correlated with auroral zone and low-altitude magnetic disturbances.

Pytte, T.↗

NASA NTRS1977

A determination of the L dependence of the radial diffusion coefficient for protons in Jupiter's inner magnetosphere

In a previous paper (Thomsen et al., 1977), a technique was proposed for estimating the radial diffusion coefficient (n) in the inner magnetosphere of Jupiter from the observations of the sweeping effect of the inner Jovian satellites on the fluxes of the energetic charged particles. The present paper extends this technique to permit the unique identification of the parameters D sub O and n, where the diffusion coefficient is assumed to be of the form D = D sub O L to the nth. The derived value of D sub O depends directly on assumptions regarding the nature and efficiency of the loss mechanism operating on the particles, while the value of n depends only on the assumed width of the loss region. The extended technique is applied to the University of Iowa Pioneer 11 proton data, leading to values of n of about O and D(6) of about 3 x 10 to the -8th (R sub J)-squared/sec, when satellite sweepup losses are assumed to be the only loss operating on the protons. The small value of n is strong evidence that the radial diffusion is driven by ionospheric winds.

Thomsen, M. F.↗

NASA NTRS1977

Linear radial and nonradial modes of oscillation of hot white dwarfs

Low-order linear radial and nonradial quadrupole modes of oscillation of hot white dwarfs with hydrogen envelopes are evaluated in the quasi-adiabatic approximation. Luminosities range from 10 to the 36th to 10 to the 38th power. Masses range between 0.6 and 1.4 solar masses. Models are found with unstable radial modes as high as the third harmonic. The first nonradial quadrupole gravity mode is always unstable. The results may be relevant to pulsating X-ray sources in general and are specifically applied to Cen X-3, Her X-1, and SMC X-1.

Degregoria, A. J.↗

NASA NTRS1978

Performance with and without inlet radial distortion of a transonic fan stage designed for reduced loading in the tip region

A transonic compressor stage designed for a reduced loading in the tip region of the rotor blades was tested with and without inlet radial distortion. The rotor was 50 cm in diameter and designed for an operating tip speed of 420 m/sec. Although the rotor blade loading in the tip region was reduced to provide additional operating range, analysis of the data indicates that the flow around the damper appears to be critical and limited the stable operating range of this stage. For all levels of tip and hub radial distortion, there was a large reduction in the rotor stall margin.

Schmidt, J. F.↗

NASA NTRS1978

Spectral line shapes in spherically symmetric radially moving clouds

We present a method for the analysis of spectral line shapes arising in homogeneous, moving gas clouds in which velocity and molecular line excitation have power-law dependences on radial distance from the center. Analytical expressions are obtained for radial flows, for both optically thick and optically thin lines. The additional case of an optically thick line from a differentially rotating cloud is considered qualitatively. The method is applied to the interpretation of the C(12)O line observed in the direction of the Kleinmann-Low infrared nebula in Orion. While gravitational collapse and accelerated outflows would produce lines qualitatively similar to the observed profile, it does not appear to be possible to fit either model to the observations in detail.

Kuiper, T. B. H.↗

NASA NTRS1978

The radial gradients and collisional properties of solar wind electrons

The plasma electron detector on Mariner 10 is used to obtain measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. The observations show quantitatively that the core of the electron distribution function can be described as collisional at least for radial distances within 1 AU, since with a very few well-marked exceptions associated with high-speed streams, the Coulomb collisional momentum relaxation length is less than the density scale height at all times and all radial distances at which data were obtained. It is found that the Coulomb energy exchange collisions between the core and the (test) halo population are negligible. The power law exponent of the core temperature is about -0.3, whereas the halo temperature is almost independent of heliocentric distance.

Ogilvie, K. W.↗