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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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Effect of sharply lowered muscular activity on the thyroid gland of the white rat

The effect of hypokinesia on the thyroid gland of 200 white rats was studied. The rats were kept in 16x6x6 cm cages for 90 days. The functional activity of the thyroids increased after 24 hrs of partial immobilization and peaked after 15 days. After 30 days of immobilization, the functional activity returned to normal in one third of the test animals and after 60 days in all animals. After 15 days of immobilization, the test animals began to lose weight (in comparison to the controls) and remained underweight for the rest of the test period (up to 90 days). When returned to normal conditions, they caught up with and even overtook in weight the control animals after about 1 month. All changes produced by hypokinesia were reversible after 1 month.

Bekishev, K.↗
NASA NTRS1980

Friction evaluation of unpaved, gypsum-surface runways at Northrup Strip, White Sands Missile Range, in support of Space Shuttle Orbiter landing and retrieval operations

Friction measurement results obtained on the gypsum surface runways at Northrup Strip, White Sands Missile Range, N. M., using an instrumented tire test vehicle and a diagonal braked vehicle, are presented. These runways were prepared to serve as backup landing and retrieval sites to the primary sites located at Dryden Flight Research Center for shuttle orbiter during initial test flights. Similar friction data obtained on paved and other unpaved surfaces was shown for comparison and to indicate that the friction capability measured on the dry gypsum surface runways is sufficient for operations with the shuttle orbiter and the Boeing 747 aircraft. Based on these ground vehicle friction measurements, estimates of shuttle orbiter and aircraft tire friction performance are presented and discussed. General observations concerning the gypsum surface characteristics are also included and several recommendations are made for improving and maintaining adequate surface friction capabilities prior to the first shuttle orbiter landing.

Yager, T. J.↗
NASA NTRS1979

First spectrum of an extra-solar object in the extreme ultraviolet The white dwarf HZ 43

An EUV instrument is described which has been used to carry out a spectroscopic observation of the hot white dwarf HZ 43. The instrument consists of an EUV telescope and spectrometer housed in a sounding-rocket shell 44 cm in diameter and 176 cm in length. It is noted that HZ 43 was successfully observed for 200 sec and that the EUV spectrum was strongly detected from 170 to 400 A. A second-order image was detected beyond 400 A, and a decrement was observed at 200 A, which corresponds to photoelectric absorption of He II. The observed spectrum is shown to be inconsistent with a coronal model. It is concluded that the surface number density of helium relative to hydrogen must be in the range from 0.00001 to 0.0001 and that an upper limit of 4 x 10 to the 17th per sq cm can be placed on the column density of ionized helium in the intervening interstellar medium.

Malina, R. F.↗
NASA NTRS1979

Interstellar absorption of the extreme ultraviolet flux from two hot white dwarfs

Photometric upper limits on the 300 A flux from the hot white dwarfs Feige 24 and G191-B2B are presented. The limits, which were obtained with a rocket-borne extreme ultraviolet imaging telescope, are interpreted as lower limits on the density of the intervening interstellar matter. The limits are used to investigate the state of interstellar gas within 100 pc. A local clumpiness factor, which is of value in planning future extreme ultraviolet observations, is derived.

Cash, W.↗
NASA NTRS1979

HD 149499 B - The hottest white dwarf

IUE spectra of the white dwarf component of HD 149499, discovered from the Skylab experiments S-019 UV survey, show prominent lines of He II. The star appears to be helium-rich with He/H not less than 1. The ultraviolet fluxes show the temperature to be within the range 70,000-100,000 K, with the most probable value near 85,000 K.

Wray, J. D.↗
NASA NTRS1980

CCD camera systems and support electronics for a White Light Coronagraph and X-ray XUV solar telescope

Two instruments, a White Light Coronagraph and an X-ray XUV telescope built into the same housing, share several electronic functions. Each instrument uses a CCD as an imaging detector, but due to different spectral requirements, each uses a different type. Hardware reduction, required by the stringent weight and volume allocations of the interplanetary mission, is made possible by the use of a microprocessor. Most instrument functions are software controlled with the end use circuits treated as peripherals to the microprocessor. The instruments are being developed for the International Solar Polar Mission.

Harrison, D. C.↗
NASA NTRS1980

Helium runaways in white dwarfs

The long-term evolution of a carbon-accreting white dwarf (M = 0.5 solar mass) has been studied from the onset of accretion to the ignition of helium. The variations in the details of the helium-shell flash have been examined with respect to variations in mass accretion rate. For intermediate rates (10 to the -9th to 10 to the -8th solar mass/yr) the helium flash is potentially explosive, whereas for high rates (5 x 10 to the -8th solar mass/yr) the shell flash is relatively weak. The results are discussed in the context of the long-term evolution of novae.

Taam, R. E.↗
NASA NTRS1980

Ultraviolet spectrum synthesis of the helium white dwarf Ross 640

The UV spectrum of the He-rich white dwarf Ross 640 was used to derive Mg, Si, and Fe abundances by a spectrum synthesis technique. The values obtained were: Mg/He = 6.8 x 10 to the -8th; Si/He = 3.2 x 10 to the -8th; Ca/He = 7.6 x 10 to the -10th; and Fe/He = 2.0 x 10 to the -9th. The abundances indicate the operation of diffusion processes within a helium-rich atmosphere, provided some mechanism exists to deposit metals in the observable layers.

Cottrell, P. L.↗
NASA NTRS1980

Radio and white-light observations of coronal transients

Optical, radio and X-ray evidence of violent mass motions in the corona has existed for some years but only recently have the form, nature, frequency and implication of the transients become obvious. In this paper the observed properties of coronal transients are reviewed, with concentration on the white-light and radio manifestations. The classification according to speeds seems to be meaningful, with the slow transients having thermal emissions at radio wavelengths and the fast ones nonthermal. The possible mechanisms involved in the radio bursts are then discussed and estimates of various forms of energy are reviewed. It appears that the magnetic energy transported from the sun by the transient exceeds that of any other form, and that magnetic forces dominate in the dynamics of the motions. The conversion of magnetic energy into mechanical energy, by expansion of the field, provides a possible driving force for the coronal and interplanetary shock waves.

Dulk, G. A.↗
NASA NTRS1981

A systems approach to mechanisms for a white light coronagraph X-ray XUV telescope

A combined instrument package containing nine mechanisms was designed and developed for the international solar polar mission (ISPM). This complement of instruments, commonly called the CXX, is the only imaging system on either the NASA or ESA spacecraft and consists of a white light coronagraph mounted parallel to a combined X-ray and extreme ultra-violet (XUV) telescope. Requirements for and implementation of mechanisms in the CXX instrument are discussed.

R Mastronardi↗
NASA NTRS1981

The white dwarf companion of the B a 2 star zeta Cap

The Ba II star zeta Cap has a white dwarf companion. Its T (sub eff) is determined to be 22000 K, its mass is approximately one solar mass. The importance of this finding for the explanation of abundance peculiarities is discussed.

Boehm-Vitense, E.↗
NASA NTRS1979

Masses, radii, temperatures, luminosities and surface compositions of white dwarfs

The masses, radii, temperature, luminosities and compositions of white dwarf stars are discussed, with particular emphasis on those areas in which considerable work remains to be done. It is pointed out that radii for stars of known parallax are available, together with masses and their variance. Consideration is then given to the difficulties involved in the determination of the temperatures of the hottest stars and helium stars by means of Stromgren or multichannel photometry, and it is noted that the frequency of binaries among the hottest degenerates seems too high to be due to chance. Results of IUE observations of the UV spectra of three DA and one DO star are discussed, with attention given to the similarities between UV-derived and ground-based determinations of temperatures and surface gravities. The metal abundances of hydrogen and helium degenerate stars are finally considered, and spectral classes and abundances of the helium atmosphere degenerates are tabulated.

Greenstein, J. L.↗
NASA NTRS1979

Instability of g-mode oscillations in white dwarf stars

A white dwarf model with M = 6 solar masses, Te = 12,000 K, and L = 1.2 x 10 to the 31st erg/sec provided by Cox has been tested for linear stability of radial oscillations. The radial mode instability first reported for this model by Cox, et al. (1979) has been confirmed. The growth rates obtained are comparable to the rates found by Cox. A sequence of l = 2 g-modes has also been found to be unstable. The e-folding times range from around 10 to the 11th periods for a 137 second mode (1 radial node) to less than 100 periods for a 629 second mode (17 nodes). It is likely that the latter rate is too high because the eigenfunction has been forced to vanish at the non-zero inner radius of the model, at which the Brunt-Vaisala frequency is barely less than the mode frequency.

Keeley, D. A.↗
NASA NTRS1981

Lanning 14, a new DO white dwarf - Spectrophotometry and atmospheric parameters

Optical spectrophotometric observations are presented and analyzed for Lanning 14, which was recently classified as a DO white dwarf and has one of the strongest He II 4868 absorption lines of any known star, with strong He Bracket lines and weak He I. An effective temperature of 55,000 plus or minus 2500 K, log g near 8, and He/H ratio equal to or greater than 100, have been derived by means of a new grid of hot, high-gravity, mixed-composition models. It is concluded that Lanning 14 is both hotter and more helium-rich than the prototype DO star HZ 21.

Liebert, J.↗
NASA NTRS1981

Observations of the strong ultraviolet absorptions in the spectrum of the DC white dwarf G218-8

The spectrum of the 14th magnitude DC white dwarf G218-8 (EG 245) is described. In the visible spectral region the star has been observed with the IIDS scanner attached to the Kitt Peak National Observatory 2.1 m telescope, where it shows a featureless spectrum. However, the ultraviolet observations using the IUE satellite show that strong absorption lines attributable to neutral carbon are present. G218-8 has an effective temperature near 11,500 K and a helium dominated atmosphere with a carbon-to-helium abundance ratio less than or approximately equal to 0.005.

Wegner, G.↗
NASA NTRS1981

Flow fields within Jupiter's Great Red Spot and White Oval BC

Voyager 1 high-resolution images of Jupiter's Great Red Spot (GRS) and White Oval BC are used to map flow fields within these two areas. The relative vorticity is computed as a function of semi-major axis length and position angle in a coordinate system consisting of concentric ellipses of equal eccentricity. Wind speeds of 110-120 m/s are observed near the outer edge of both features, and along their minor axes relative vorticity profiles reach a maximum of 0.00006/s. Maximum Rossby numbers of 0.36 are computed for flows within both features, and are found to be low, indicating geostrophic constraints on the flow. The difference in streamline curvature within the GRS and the Oval BC is found to compensate for the difference in planetary vorticity at the respective latitudes of the features. Finally, motions within the central region of the GRS are slower and more random than around the spot's outer portion.

Mitchell, J. L.↗
NASA NTRS1981

The Spacelab Lyman alpha and white light coronagraphs program

The Harvard-Smithsonian Center for Astrophysics and the High Altitude Observatory have defined a joint coronagraphs experiment for a future Spacelab mission. The instrumentation package would include an ultraviolet light coronagraph to measure the intensity and profiles of spectral lines formed between 1.2 and 8 solar radii from sun center and a white light coronagraph to measure the intensity and polarization of visible light. The overall goals of the joint program are to use new coronal plasma diagnostic techniques to understand the physical processes and mechanisms operating in the solar corona, to understand the acceleration of high-speed and low-speed solar wind streams and to extrapolate this knowledge to other stars in order to help understand the physics of stellar coronae and stellar mass loss.

Kohl, J. L.↗