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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 667 records · Page 37
All sourcesNASA NTRSDOE OSTI
NASA NTRS1973

Smithsonian Astrophysical Observatory's minicomputer vs. the laser

Review of some of the problems encountered in replacing a CDC 6400, that was used for supplying a network of laser tracking stations with predictions, by an 8K Data General 1200 minicomputer with a teletype for I/O. Before the replacement, the predictions were expensive to compute and to transmit, and were clumsy logistically. The achieved improvements are described, along with every step it took to accomplish them, and the incurred costs.

Cherniack, J. R.↗
NASA NTRS1974

A multiwire proportional counter system for high energy astrophysics

Resolution tests of multiwire proportional counter delay line readout systems are reported. The system is being developed at NASA/JSC for use in a large balloon borne magnet spectrometer. The system is ultimately intended for use in Space Shuttle missions. Tests of two different types of delay line and associated electronics carried out in minimum ionizing particle beams (accelerator and sea level cosmic ray) are reported. Resolution performance is shown to be strongly dependent on type of gas mixture and in the case of inclined events upon the propagation velocity of the delay line. The resolution performance achieved for magic gas chamber filling (100 um at normal incidence) is far superior to any other state of the art technique capable of being applied to large geometry factor systems.

Lacy, J. L.↗
NASA NTRS1974

Some magnetic null lines of astrophysical interest. II

A list of magnetic null lines from selected spectroscopic analyses is presented for possible use in detailed studies of magnetic Ap stars. The presented data represent an extension of the magnetic null lines whose usefulness Shore and Adelman (1974) have recently demonstrated for the study of the overall physical conditions prevailing in the atmospheres of peculiar A stars and for testing the consequences of the mechanism of selective elemental diffusion.

Adelman, S. J.↗
NASA NTRS1975

Relativistic astrophysics

The coordinate independence of gravitational radiation and the parameterized post-Newtonian approximation from which it is extended are described. The general consistency of the field equations with Bianchi identities, gauge conditions, and the Newtonian limit of the perfect fluid equations of hydrodynamics are studied. A technique of modification is indicated for application to vector-metric or double metric theories, as well as to scalar-tensor theories.

Smalley, L. L.↗
NASA NTRS1975

Infrared spectra of molecules and materials of astrophysical interest

The vibrational spectra from 4000 to 33 cm-1 of several modecules which may be present in the atmosphere of the Jovian planets are studied to provide vibrational frequencies which can be used to: (1) determine the composition of the cloud covers of several of the planets; (2) provide structural information under favorable circumstances; (3) provide necessary data from which accurate thermodynamic data can be calculated; and (4) furnish information as to the nature of the potential energy function of the molecules and forces acting within them. Some of the molecules are produced photochemically from methane, ammonia, and hydrogen sulfide which are thought to be constituents of the planets with reducing atmospheres. Some of the compounds polymerize under ultraviolet radiation and drop out of the atmospheres. However, planets with a hot base, like that of Jupiter, may rebuild molecules destroyed photochemically.

Durig, J. R.↗
NASA NTRS1975

Free radical OH, a molecule of astrophysical and aeronomic interest

The chemistry and physics of the gaseous OH free radical as it applies to interstellar space, planetary atmospheres, and the sun is presented. Topics considered are: (1) rotational-vibrational transitions; (2) dissociation and ionization processes; (3) spectral characteristics.

Mohan, H.↗
NASA NTRS1975

Sensitivity limits of an infrared heterodyne spectrometer for astrophysical applications

A discussion and an evaluation of the degradation in sensitivity is given for a heterodyne spectrometer employing a HgCdTe photodiode mixer and tunable diode lasers. The minimum detectable source brightness is considered as a function of the mixer parameters, transmission coefficient of the beam splitter, and local oscillator emission powers. The degradation in the minimum detectable line source brightness which results from the bandwidth being a function of the line width is evaluated and plotted as a function of the wavelength and bandwidth for various temperature to mass ratios. It is shown that the minimum achievable degradation in the sensitivity of a practical astronomical heterodyne spectrometer is approximately 30. Estimates of signal-to-noise ratios with which infrared line emission from astronomical sources of interest may be detected are given.

Abbas, M. M.↗
NASA NTRS1975

Infrared, X-ray, and XUV astrophysics

An observational program covering wavelengths from the near infrared to 1 millimeter is reviewed. The program of millimeter observations largely consisted of analyzing previous observations since the summer humidity was too high for new observations. Maps of millimeter emission from W3, Sgr B2, W49 and M42 were made. Five extragalactic sources were detected and are discussed. Energy distributions of several of the discrete sources at the Galactic Center were studied. A 5-year visual/infrared program on Markarian galaxies is discussed which showed the presence of both thermal and nonthermal infrared radiation sources and established correlations between the infrared sources and the emission line regions. The Nova Cygnus 1975, caught during its rise as well as subsequent dimming, is also discussed. Several other continuing programs are described, including studies of dark clouds and CO maser sources.

Source record↗
NASA NTRS1975

The generation of magnetic fields in astrophysical bodies. X - Magnetic buoyancy and the solar dynamo

The magnetic field appearing as bipolar magnetic regions at the surface of the sun represents the lines of force from a general azimuthal field of the order of 100 gauss somewhere beneath the surface. The amplification time, as a consequence of the nonuniform rotation, is of the order of 10 years. But magnetic buoyancy brings the azimuthal field up through much of the convective zone in a time rather less than 10 years, raising the question of where the azimuthal field can be retained long enough to be amplified. We show that magnetic fields can be retained for long periods of time in the stable radiative region beneath the convective zone, but unfortunately the solar dynamo cannot function there because turbulent diffusion is an essential part of its operation. The only possible conclusion appears to be that the dynamo operates principally in the very lowest levels of the convective zone at depths of 150,000 km or more, where the gas density is 0.1 g/cu cm, and the fields are limited to 50 gauss.

Parker, E. N.↗
NASA NTRS1975

Hyperbolic cosmic dust - Its origin and its astrophysical significance

The heliocentric radial distribution of the flux of hyperbolic cosmic dust particles, as measured by the Pioneer 8 and 9 spacecraft, is closely related to the radial variation of the spatial density of source or parent meteoroids. Within the limits of the experimental and theoretical uncertainties the spatial density of parent meteoroids, as deduced from the hyperbolic cosmic dust data, is found to be increasing with increasing heliocentric distance in the neighborhood of one AU. Other recent experimental evidence confirms this result. The new results also suggest that the ratio of the areal density of submicron-sized craters to the areal density of millimeter-sized craters will be less on the north-south faces of lunar rocks than on the east-west faces of the same rocks. The change in ratio is not as large as previously thought. It is noted that the solar system is not presently contributing significant amounts of dust to the interstellar medium though it may once have done so.

Zook, H. A.↗
NASA NTRS1976

Strong scintillations in astrophysics. 4. Cross-correlation between different frequencies and finite bandwidth effects

The cross correlation of the intensity fluctuations between different frequencies and finite bandwidth effects on the intensity correlations based on the Markov approximation were calculated. Results may be applied to quite general turbulence spectra for an extended turbulent medium. Calculations of the cross-correlation function and of finite bandwidth effects are explicitly carried out for both Gaussian and Kolmogorov turbulence spectra. The increases of the correlation scale of intensity fluctuations are different for these two spectra and the difference can be used to determine whether the interstellar turbulent medium has a Gaussian or a Kolmogorov spectrum.

Lee, L. C.↗
NASA NTRS1976

Infrared spectra of molecules and materials of astrophysical interest

The vibrational spectra from 4,000 to 33/cm of several molecules which may be present in the atmosphere of the Jovian planets or exist in outer space were studied. These studies have been made to provide vibrational frequencies which can be used to: (1) determine the composition of the cloud covers of several of the planets, (2) provide structural information under favorable circumstances, (3) provide necessary data from which accurate thermodynamic data can be calculated, and (4) furnish information as to the nature of the potential energy function of the molecules and forces acting within them. Some of the molecules studied can be produced photochemically from methane, ammonia, and hydrogen sulfide which are thought to be constituents of the planets with reducing atmospheres. Some of the compounds will polymerize under ultraviolet radiation and drop out of the atmospheres. However, planets with a hot base, like that of Jupiter, may rebuild molecules destroyed photochemically. These criteria were used in selecting the compounds under study.

Durig, J. R.↗
NASA NTRS1976

Infrared astronomy and high energy astrophysics

Observations of the diffuse far infrared flux from the galactic plane as well as far infrared measurements of the properties of dense molecular clouds, when combined with recent high-energy gamma ray measurements and radio observations of carbon monoxide, can yield new information about the total mass of molecular clouds, the large scale structure of the inner galaxy, and the density of cosmic rays. These observations are discussed.

Fazio, G. G.↗
NASA NTRS1975

Gamma ray astrophysics

Gamma-ray production processes are considered, taking into account Compton scattering between cosmic-ray electrons and starlight microwave background photons, synchrotron radiation, bremsstrahlung interactions, nucleon-antinucleon annihilations, the form of the spectrum from pion production at high energies, and gamma rays from photomeson production at ultrahigh energies. Attention is also given to gamma-ray absorption mechanisms, gamma rays observed from the Galaxy, and extragalactic gamma rays.

Stecker, F. W.↗
NASA NTRS1975

Strong scintillations in astrophysics. II - A theory of temporal broadening of pulses

A theory of temporal broadening of pulses propagating in a turbulent medium is developed on the basis of the Markov approximation. The theory may be applied to quite general turbulence spectra and to thin or thick turbulent regions. Since the basis of the theory is the wave equation, no reliance is placed on geometrical optics and no assumptions are made about the scattered angular spectrum. The observed smearing is found to be the combination of three effects: the dispersion effect, the pure refractive effect, and the diffraction effect. The last of these dominates for typical pulsar parameters. Pulse shapes are calculated for both Gaussian and Kolmogorov turbulence spectra and it is shown how these scale with the various turbulence parameters.

Lee, L. C.↗
NASA NTRS1975

Strong scintillations in astrophysics. III - The fluctuations in intensity

Fluctuations in intensity due to wave propagation in a wide range of turbulent media, are discussed on the basis of a previously developed theory of strong scintillations. An asymptotic analytic solution to the fourth-moment equation is presented, and its range of validity is discussed. Various parameters characterizing the intensity fluctuations, such as scintillation index and correlation scale, are expressed in terms of turbulence parameters for both Gaussian and power-law irregularity spectra as well as for thick and thin turbulent media.

Lee, L. C.↗