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At least 343 records · Page 19

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NASA NTRS1982

On the reality of a boundary in the H-R diagram between late-type stars with and without high temperature outer atmospheres

The Linsky-Haisch hypothesis (1979) that a boundary exists in the H-R diagram separating yellow giants from red giants and supergiants is tested. IUE 1150-2000 A low-resolution spectra of 10 stars chosen to constitute a reverse bias sample are presented and discussed. Despite the bias, weak C IV emission indicative of high-temperature plasma was observed in four of the six stars chosen to be probable red stars, while no C IV emission was detected in the four stars chosen to be yellows. In a second test using the entire sample of 39 stars, nearly all of the yellow giants and supergiants were found to have an emission feature at 1549 A, which is attributed to C IV. The large magnitude dispersion could be attributed to temporal or spatial variability, differing magnetic field strengths and geometries, or age-related effects during post-main-sequence evolution. It is concluded that the Linsky-Haisch transition region boundary is a real phenomenon.

Simon, T.↗

NASA NTRS1983

Plasmapause diffusion

The Bohm diffusion coefficient and observed electrostatic wave scattering are used as the bases of estimates of the smoothing effect that diffusion may have on steep plasmapause density gradients. The estimate for diffusion resulting from scattering by observed electrostatic waves is found to be much lower than that of the perpendicular Bohm diffusion coefficient for characteristic plasma temperatures and magnetic fields. This diffusion rate estimate may be too small, however, if the wave amplitudes are significantly higher for steep plasmapauses. The effects are therefore negligible for most considerations of macroscopic plasmapause dynamics, but may be significant in limiting drift wave instabilities and similar phenomena driven by the steepness of the plasmapause density gradient.

Horwitz, J. L.↗

NASA NTRS1982

The upper atmospheres of the earth and planets; Proceedings of the Topical Meeting, Ottawa, Canada, May 16-June 2, 1982

Various topics concerned with the upper atmosphere of the earth and planets are discussed. The atmospheres of the terrestrial planets are addressed, emphasizing Venus. The energy budget of the mesosphere and thermosphere is considered, discussing current and particles as energy sources, the radiation field, and neutral atmosphere dynamics. The results of Pre-Map Project One are covered, and the International Reference Ionosphere is discussed, including electron density profiles, the lower ionosphere, the plasmasphere, plasma temperature profiles, and ion composition. Finally, the mass spectroscopy of atmospheres is treated.

Barth, C. A.↗

NASA NTRS1983

Closed coronal structures. V - Gasdynamic models of flaring loops and comparison with SMM observations

A time-dependent one-dimensional code incorporating energy, momentum and mass conservation equations, and taking the entire solar atmospheric structure into account, is used to investigate the hydrodynamic response of confined magnetic structures to strong heating perturbations. Model calculation results are compared with flare observations which include the light curves of spectral lines formed over a wide range of coronal flare temperatures, as well as determinations of Doppler shifts for the high temperature plasma. It is shown that the numerical simulation predictions are in good overall agreement with the observed flare coronal plasma evolution, correctly reproducing the temporal profile of X-ray spectral lines and their relative intensities. The predicted upflow velocities support the interpretation of the blueshifts as due to evaporation of chromospheric material.

Peres, G.↗

NASA NTRS1984

Deposition stress effects on thermal barrier coating burner rig life

A study of the effect of plasma spray processing parameters on the life of a two layer thermal barrier coating was conducted. The ceramic layer was plasma sprayed at plasma arc currents of 900 and 600 amps onto uncooled tubes, cooled tubes, and solid bars of Waspalloy in a lathe with 1 or 8 passes of the plasma gun. These processing changes affected the residual stress state of the coating. When the specimens were tested in a Mach 0.3 cyclic burner rig at 1130 deg C, a wide range of coating lives resulted. Processing factors which reduced the residual stress state in the coating, such as reduced plasma temperature and increased heat dissipation, significantly increased coating life.

Watson, J. W.↗

NASA NTRS1984

An X-ray study of the remnant of SN 185 A.D.

High-resolution X-ray maps obtained with the Einstein Observatory of the supernova remnant RCW 86 are presented. Analysis of the spatial and spectral properties of the remnant yield a total X-ray emitting mass of not greater than about 5 solar masses and a surrounding mean interstellar density of about 0.3/cu cm. A revision of the generally accepted distance of 2.5 kpc downward to not greater than about 1 kpc is strongly suggested by the data. The diameter (about 13 pc) and X-ray plasma temperature (about 1 keV) are consistent with the identification of the remnant with the supernova of 185 A.D. The observed apparent magnitude of SN 185 coupled with the new distance, the implied explosion energy and ejected mass derived from a Sedov analysis, and the lack of any compact remnant are all characteristic of a Type I event.

Pisarski, R. L.↗

NASA NTRS1984

The two-lobe structure of the distant (at least 200 earth radii) magnetotail

Data from a 5 mos ISEE-3 passage through the magnetotail at distances beyond 60 earth radii (ER) are examined statistically to determine the tail structure out to 238 ER, the extent of the lobe and plasmasheet deviations from normal positions. The data include field and electron plots and plasma temperatures and densities. The maximum thickness of the plasmasheet was found to be similar to near-earth conditions, i.e., 9-15 ER, and was accompanied by an N-S dimension of 53-59 ER. No filamentary structures were derived, and the two-lobe structure was preserved. Possible causes of the asymmetry between the N-S and E-W scales are discussed.

Tsurutani, B. T.↗

NASA NTRS1984

Deposition stress effects on the life of thermal barrier coatings on burner rigs

Watson, J. W.↗

NASA NTRS1985

Equatorial trapped plasmasphere ion distributions and transverse stochastic acceleration

Observations by the DE 1 and SCATHA satellites have revealed ion distribution functions in the equatorial plasmasphere which are sharply peaked at 90 deg pitch angle. The pitch angle anisotropy increases with increasing energy for the observed distributions. Also observed by SCATHA and earlier spacecraft are cyclotron harmonic emissions which are closely confined to the plasmasphere equator. It is demonstrated here that the observed highly anisotropic ion distribution at thermal energies can be explained, as the consequence of the nonlinear evolution of an initially Maxwellian distribution with a characteristic plasmasphere thermal plasma temperature by stochastic acceleration, using the observed levels of wave turbulence.

Curtis, S. A.↗

NASA NTRS1986

Contribution to the study of the electric arc: Erosion of metallic electrodes

A procedure is described for determining the extent of arc electrode erosion (excluding erosion due to transfer of material) from measurements of emitted spectral beam intensity. The relation between emission intensity and plasma temperature is ascertained. Experimental study of several combinations of monometallic electrodes shows that the method is suitable for determining cathode erosion, although the anode metal affects the extent of erosion. Combinations of electrodes which lead to low erosion of silver are reported.

Castro, A.↗

NASA NTRS1985

Short wavelength laser calculations for electron pumping in Be I and B I isoelectronic sequences (Z greater than or equal to 18 and less than or equal to 36)

There has been considerable interest in creating large laser gains in the X-ray region from atomic transitions in ne-like ions formed in high-temperature plasmas. Although the Ne-like ions habe received the most attention, it is also possible to produce population inversions in ions of other isoelectronic sequences. Accordingly, it is shown that certain levels of the 2s3p and 2s(2)3p configurations in the Be I and B I isoelectronic sequences can be inverted by collisional pumping relative to levels of the 2s3s and 2s(2)3s configurations. Level populations and gain coefficients were calculated for the most promising transitions, and opacities were calculated for 2s2p-2s3s and 2s(2)2p-2s(2)3s transitions.

Feldman, U.↗

NASA NTRS1984

Deposition stress effects on the life of thermal barrier coatings on burner rigs

Watson, J. W.↗

NASA NTRS1986

The structure of the static corona and transition region

Static models of coronal loops are investigated. For loops that are low-lying with heights above the chromosphere below about 5000 km, it is shown that a new type of solution appears to the static equations, in addition to the well-known coronal loop solution. The new solution is characterized by a maximum plasma temperature less than about 100,000 K. The structure and properties of these cool solutions are discussed. The differential emission measure Q(T) expected for a magnetic arcade, which must naturally contain both hot and cool loops, is calculated. It is shown that the cool loops have a dramatic effect on the form of Q(T) in the lower transition region. In particular, they can account for the observed rise in Q at low T, which has long been thought to be incompatible with the static-loop model. Finally, the implications of the cool loops on other observations of both the solar and stellar coronae and transition regions are discussed.

Antiochos, S. K.↗

NASA NTRS1987

Plasma Rocket With Hybrid Exhaust Plume

Proposed plasma rocket, described in report, generates hybrid exhaust plume comprising annular layer of relatively cool neutral gas around plasma core. Plasma and gas intermix, providing gradual radial transition between the two. Amount of gas injected adjusted to control propulsive efficiency; relatively cool gas boundary layer at surface of nozzle insulates nozzle from high plasma temperature.

Chang, Franklin R.↗

NASA NTRS1987

Effect of double layers on magnetosphere-ionosphere coupling

The Earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths. These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. A number of models of microscopic turbulence will be introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, the effects of a double layer electric field which scales with the plasma temperature and Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than in the resistive model leading to the possibility of narrow, intense current structures.

Lysak, Robert L.↗

NASA NTRS1986

Observation and interpretation of Zeta Aurigae stars

The ultraviolet observations of four Zeta Aurigae stars are reviewed. A, probably oversimplified, interpretation of the observations points to a straight forward connection between the spectral type of the B star and the amount of high temperature plasma in the systems.

Chapman, R. D.↗

NASA NTRS1987

Low-energy X-ray observations of the Wolf 630 system

The Exosat channel multiplier array is used to resolve the septuplet of M dwarfs into three components (Wolf 630ABab, Wolf 629ab, and VB 8AB) with widely different X-ray characteristics. An isothermal plasma temperature of between 800,000 and 550,000 K (which is very low in the known range of coronal temperatures) is found for any relatively quiescent state of VB 8. It is shown from the count rate during 18,112 sec of effective exposure with Exosat that VB 8 flared once in 0.05-2 keV flux.

Johnson, Hugh M.↗

NASA NTRS1987

Effect of double layers on magnetosphere-ionosphere coupling

The dynamic aspects of auroral current structures are reviewed with emphasis on consequences for models of microscopic turbulence (MT). A number of models of MT are introduced into a large-scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. The effect of a double layer (DL) electric field which scales with the plasma temperature and the Debye length is compared with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is shown that the DL model is less diffusive than the resistive model, indicating the possibility of narrow intense current structures.

Lysak, Robert L.↗