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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 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Relationship between proton motive force and potassium ion transport in Halobacterium halobium envelope vesicles

The permeability of Halobacterium halobium vesicle membranes to potassium ions was investigated, and possible mechanisms for the regulation of the gradient of protons by the transmembrane movement of these ions were studied. The lack of a potassium ion diffusion potential in the absence of valinomycin, light-induced electrical potentials in excess of the chemical potential difference for potassium ions, and direct measurements of potassium ion influx during illumination show that the membranes are relatively impermeable to these ions. As a result of sodium ion extrusion during illumination, chlorine ions and water must be lost and the vesicles collapse. The light-induced collapse of vesicles is diminished only if the influx of potassium ions is increased.

Lanyi, J. K.↗
NASA NTRS1979

Predictions of induced background radiations at gamma/X-ray experiment envelopes in NASA spacecraft

This work seeks to predict secondary radiation levels induced in spacecraft structures by space protons. The radiations analyzed are secondary neutrons from spallation and evaporation reactions and gamma and beta rays from the decay of induced radioactivity, as sources of interfering background to spaceborne measurements of galactic and planetary gamma rays below 10 MeV. The spacecraft considered are the Multi-Mission Spacecraft (MMS) and the Space Shuttle, modeled as spherical shells. The proton environment is that of the South Atlantic Anomaly, as well as cosmic ray protons. The induced radioactivity is analyzed in terms of its interference with various gamma-ray lines of astrophysical interest, as well as its contribution to several spectral regions of the gamma-ray continuum. The buildup of the line and continuum radioactivity background is predicted for a period of nearly 9 months in orbit (approximately 4100 orbits). In addition, background contributions from cosmic ray electron bremsstrahlung and earth gamma-ray albedo are estimated.

Fischbein, W. L.↗
NASA NTRS1981

The 1979-1980 eclipse of Zeta Aurigae. I - The circumstellar envelope

A model of the K-star wind far from the K star, and its interaction with the B star, has been derived from a study of Mg(+) and C(+++) resonance lines in the spectrum of Zeta Aurigae during 1979 and 1980. A mass loss rate from the K star of 2 x 10 to the -8th solar masses/year is suggested by the data; the rate of accretion of the K supergiant's material by the B star then being such that the matter accreted over a period of ten years is of the order of the total mass of the photosphere of the B star.

Chapman, R. D.↗
NASA NTRS1983

Chromospheric emission of W Ursae Majoris-type stars and its relation to the structure of their common envelopes

Short-wavelength IUE spectra of 14 W UMa binary systems were analyzed. All but the A2 V system GK Cep and possibly the A8 system AG Vir show chromospheric and transition-region emission lines. This property extends to at least as early as A8-9. The luminosity in transition-region emission lines is roughly proportional to bolometric luminosity. The strength of transition-region emission relative to chromospheric emission is roughly independent of spectral type and is at least as great as for other stars with enhanced surface activity. The enhanced chromospheric activity and light curve peculiarities of the hotter systems seem to disagree with the predictions of the contract-discontinuity models for contract binary structure.

Eaton, J. A.↗
NASA NTRS1983

Optical features associated with the extended HI envelope of M83

Deep red Schmidt plates (127-04 + RG630) of the galaxy M83 show the presence of extensive faint optical structure well beyond the Holmberg radius of the galaxy. Digital processing has been used to bring these features out in detail. They consist of arc-like structures and clumps of H II regions, which seem to follow the H I distribution and thus are likely to participate in the warping of the H I disk.

Wamsteker, W.↗
NASA NTRS1983

Speculative-theoretical Modeling of the Atmosphere Enveloping a Hypothetical (closed, Thermal) Star

The predictions of theoretical stellar atmospheric structural modeling and the theoretical picture of the local stellar environment as derived from the speculation that stars are (closed, thermal) thermodynamic systems, are summarized. The definition and representation of space- and state-fluxes is discussed and both classical (local thermodynamic equilibrium) and neoclassical (non-local thermodynamic equilibrium) thermal models are addressed.

Source record↗
NASA NTRS1983

Far-ultraviolet emission lines in U Cephei - Evidence for a hot, turbulent circumstellar envelope

The numerous emission lines in the far-UV spectrum which have been found in the Algol-type eclipsing binary U Cephei are similar to those observed in the W Serpentis stars, although they are weaker and appear only during the primary eclipse. The line-emitting region is studied in both emission and absorption.It surrounds the hotter component and extends to a distance of several of its radii. A model is proposed in which the emission originates in a highly turbulent circumstellar region, at an electron temperature of about 10,000 K. The energy needed for ionization is derived from collisions, and is probably extracted from the accretion energy.

Plavec, M. J.↗
NASA NTRS1984

On the dynamics in evaporating cloud envelopes

Cowie and McKee (1977) have conducted an analytical study of the case of an isolated, spherical cloud at rest in an infinite, hot medium. The present investigation is concerned with the theoretical model considered by Cowie and McKee for a thermally evaporating cloud. An analysis is conducted under the same conditions of inviscid flow with temperature equipartition. The current analysis allows for a continuous change in the saturation of the conductivity, rather than abrupt transitions from a classical to a fully saturated regime and back again, as in the model employed by Cowie and McKee. By suitable variable transformations, the momentum and energy equations can be reduced in the inviscid limit to a single equation for the Mach number in terms of a modified radius, and the solutions represented in a phase plane. An analytic model for the structure of the shock layer is developed.

Giuliani, J. L., Jr.↗
NASA NTRS1985

Challenges of developing an electro-optical system for measuring man's operational envelope

In designing work stations and restraint systems, and in planning tasks to be performed in space, a knowledge of the capabilities of the operator is essential. Answers to such questions as whether a specific control or work surface can be reached from a given restraint and how much force can be applied are of particular interest. A computer-aided design system has been developed for designing and evaluating work stations, etc., and the Anthropometric Measurement Laboratory (AML) has been charged with obtaining the data to be used in design and modeling. Traditional methods of measuring reach and force are very labor intensive and require bulky equipment. The AML has developed a series of electro-optical devices for collecting reach data easily, in computer readable form, with portable systems. The systems developed, their use, and data collected with them are described.

Woolford, B.↗
NASA NTRS1985

Electrons and positrons from expanding supernova envelopes in dense clouds

If antiprotons in cosmic rays are produced as secondary particles in sources, it is expected that positrons are also created by the same process. The interstellar spectra of positrons and electrons are calculated by taking into account such sources. Spectra are then compared with observations.

Stephens, S. A.↗
NASA NTRS1985

On the probability density function of the squared envelope of a sum of random phase vectors

Weber et al. (1980) have found that a generic problem arises in the study of multiuser FHMA/MFSK systems. According to this problem, the presence of the other channel users acts as interference to reception of the desired user's transmission. The present investigation is concerned with a recursive solution in which the recursion parameter is the number of vectors in the sum. A mathematical characterization of such a solution is presented, taking into account the simple two-vector case in which a well-known closed form result is possible. Some numerical results are also discussed. It is pointed out that the considered recursive solution provides a break in the bottleneck associated with the exact computation of the error probability performance of multiuser FHMA/MFSK systems and single access MFSK systems corrupted by multitone jamming.

Simon, M. K.↗
NASA NTRS1985

Development of a wind shear performance envelope

It is quite important that the airplane performance during a continuing headwind loss be understood. Lack of consideration of this characteristic can result in assuming almost twice the performance than that which the airplane actually has during severe wind shear at high descent rates. The example data relates to the Boeing 727-200, but the characteristics are applicable to any airplane.

Bliss, J. H.↗
NASA NTRS1985

Automated Portable Test System (APTS) - A performance envelope assessment tool

The reliability and stability of microcomputer-based psychological tests are evaluated. The hardware, test programs, and system control of the Automated Portable Test System, which assesses human performance and subjective status, are described. Subjects were administered 11 pen-and-pencil and microcomputer-based tests for 10 sessions. The data reveal that nine of the 10 tests stabilized by the third administration; inertial correlations were high and consistent. It is noted that the microcomputer-based tests display good psychometric properties in terms of differential stability and reliability.

Kennedy, R. S.↗