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At least 127 records · Page 7
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NASA NTRS1979

Stark-profile calculations for Lyman-series lines of one-electron ions in dense plasmas

The frequency distributions of the first six Lyman lines of hydrogenlike carbon, oxygen, neon, magnesium, aluminum, and silicon ions broadened by the local fields of both ions and electrons are calculated for dense plasmas. The electron collisions are treated by an impact theory allowing (approximately) for level splittings caused by the ion fields, finite duration of the collisions, and screening of the electron fields. These calculations are fully quantum mechanical and include the full Coulomb interaction. Ion effects are calculated in the quasistatic, linear-Stark-effect approximation, using distribution functions of Hooper and Tighe which include correlation and shielding effects. Theoretical uncertainties from the various approximations are estimated, and the scaling of the profiles with density, temperature, and nuclear charge is discussed. A correction for the effects caused by low-frequency field fluctuations is suggested.

Griem, H. R.↗
NASA NTRS1979

Cosmic far-ultraviolet background radiation - Probe of a dense hot intergalactic medium

Line and continuum radiation fluxes have been computed for a wide range of enriched intergalactic medium (IGM) models. Observations of the diffuse extragalactic light at optical and far-ultraviolet wavelengths are found to provide a potentially important probe of a dense hot intergalactic medium. If the diffuse X-ray background is produced by this gas, the models constrain the cosmological density parameter (Omega) to be less than 0.4. The associated Compton distortions of the cosmic blackbody background radiation and the optical depths to distant quasars at X-ray wavelengths are also evaluated.

Sherman, R. D.↗
NASA NTRS1980

The effect of dense cores on the structure and evolution of Jupiter and Saturn

The evolutionary and static models of Jupiter and Saturn were calculated with homogeneous solar composition mantles and dense cores of material consisting of solar abundances of SiO2, MgO, Fe, and Ni. Evolutionary sequences for Jupiter were calculated with cores of mass ranging from 2 to 8% of the Jovian mass; the Saturn sequences ranged from cores of mass of 16 to 22% of total mass. Two envelope mixtures representative of the solar abundances were used: they contained mass fraction of 0.74 and 0.77 of hydrogen, respectively, and 0.24 and 0.21 mass fractions of helium. For Jupiter, the observations of the temperature at 1 bar pressure, of radius and of internal luminosity were best fit by evolutionary models with a core mass of about 6.5% and chemical composition of 0.77 mass fraction of hydrogen and 0.21 mass fraction of helium. The cooling time calculated for Saturn was 2.6 x 10 to the 9th yr, almost a factor of 2 less than the percentage of the solar system.

Grossman, A. S.↗
NASA NTRS1980

Time correlation functions in classical dense fluids

The velocity autocorrelation functions and memory functions of dense classical fluids may be directly obtained from the static radial distribution function g(r) in an approximate way. Following the Mori projection operator formalism, the memory functions may be related to the fluctuating force correlation. At low densities, these functions may be evaluated by following the trajectories of particle pairs in the interatomic potential. At higher densities, the force correlation functions can be evaluated approximately from particle pair trajectories via the potential of the mean force. The results for argon fluids at various densities and temperatures agree satisfactorily with the molecular dynamics and the Enskog values. The decrease of the diffusion coefficient with density is partly due to the nature of g(r) which reflects the stronger clustering of atoms at higher densities.

Tsang, T.↗
NASA NTRS1981

Abundance of atomic carbon /C I/ in dense interstellar clouds

The abundance of interstellar neutral atomic carbon is investigated by means of its ground state fine-structure line emission at 492 GHz using the 91.5 cm telescope of NASAs Kuiper Airborne Observatory. Atomic carbon is found to be very abundant in dense interstellar molecular clouds with column densities of about 10 to the 19th per sq cm. Because the observations have considerably greater column densities than current theories of carbon chemistry, it is suggested that the physical conditions of these clouds are not as simple as assumed in the models. Various situations are discussed which would lead to large C I abundances, including the possibility that the chemical lifetimes of the clouds are relatively short.

Phillips, T. G.↗
NASA NTRS1981

Infrared sources in dense molecular clouds

Recent accomplishments in the infrared study of dense molecular clouds are reviewed, and the outstanding problems in the area are discussed. Such questions as whether clouds are collapsing, how they can be classified, and whether star formation is occurring on the edges of clouds are analyzed. Problems of determining size, energy distribution and luminosity, spectral features, evolutionary state, and energetics of infrared sources are discussed.

Evans, N. J., II↗
NASA NTRS1982

Determination of the temperature of a dense plasma from a spectral line shift

The method of maximum spectral line shift proposed by Bardocz, et al, (1966) was successfully applied in the diagnostics of dense plasmas produced by high power pulse discharges. It is pointed out that the effect of the shock wave pressure on the spectral line shift has to be taken into account in order to obtain accurate results with this method for high power discharges. A pressure dependent function was introduced in the expression given by those authors to provide the necessary correction.

Sultanov, A. M.↗
NASA NTRS1982

Detection of interstellar NH sub 3 in the far-warm and dense gas in Orion-KL

The detection of the (J,K) = a(4,3) yields s(3,3) rotation inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region is reported. The line is in emission and has a FWHM or = to 30 km s 0.15. The far IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3) yields s(3,3) line is very optically thick, and since it is seen in emission, radiative excitation of the (4,3) NH3 level by far IR emission from dust within the source can be ruled out. Radiative excitation via the 10 microns of vibrational transitions of NH3 also seems unlikely. Hence, the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Since the far IR line emission is highly trapped, densities of approximately 10 to the 7th power cu cm are high enough to explain the observations. Shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region.

Townes, C. H.↗
NASA NTRS1982

Stabilized Acoustic Levitation of Dense Materials Using a High-Powered Siren

Stabilized acoustic levitation and manipulation of dense (e.g., steel) objects of 1 cm diameter, using a high powered siren, was demonstrated in trials that investigated the harmonic content and spatial distribution of the acoustic field, as well as the effect of sample position and reflector geometries on the acoustic field. Although further optimization is possible, the most stable operation achieved is expected to be adequate for most containerless processing applications. Best stability was obtained with an open reflector system, using a flat lower reflector and a slightly concave upper one. Operation slightly below resonance enhances stability as this minimizes the second harmonic, which is suspected of being a particularly destabilizing influence.

Gammell, P. M.↗
NASA NTRS1982

Visible light observations of a dense plasmoid associated with a moving Type IV solar radio burst

A coronal transient rising above the eastern limb of the sun was observed simultaneously on April 27, 1980 by the Coronagraph/Polarimeter (C/P) aboard the Solar Maximum Mission spacecraft and by the Culgoora radioheliograph (CRH). The C/P observed an outward-moving loop transient followed by a plasmoid of dense ionized material, while the CRH observed several types of radio bursts, including a moving Type IV burst at 80 MHz whose position coincided with the bright plasmoid. An estimate of the reasonable lower limit of the electron density in the moving Type IV burst indicates that this burst could have resulted from emission at either the fundamental or the second harmonic of the plasma frequency. This is a new result because in the past it was thought that the density in the moving Type IV source region would be too low for plasma radiation.

Stewart, R. T.↗
NASA NTRS1983

Structure of dense molecular gas in TMC 1 from observations of three transitions of HC3N

The Taurus dark cloud complex is a collection of many individual clouds scattered across approximately 50 pc. Within one of these, Heiles Cloud 2, is the dense condensation TMC 1. TMC 1 is one of the few sources in which some of the long carbon chain molecules are found. The present investigation is concerned with a mapping of the density structure in a narrow ridge of the TMC 1 structure. It is shown that the HC3N emission from the J = 5 to 4, J = 9 to 8, and J = 12 to 11 transitions is well matched by a narrow ridge of material at a single density of 50,000-100,000 per cu cm. There is evidence that the HC3N fractional abundance is variable along the ridge. Evidence is also found for the presence of subcondensations within this ridge from maps at individual velocities.

Schloerb, F. P.↗
NASA NTRS1983

Detection of interstellar NH3 in the far-infrared - Warm and dense gas in Orion-KL

Results of an investigation are presented which show the detection of the (J,K) = a(4,3)-s(3,3) rotation-inversion transition of ammonia at 124.6 microns toward the center of the Orion-KL region. The line is found to be in emission and has a FWHM greater than or equal to 30 km/s, while the far-IR ammonia line emission probably comes mainly from the 'hot core', a compact region of warm, very dense gas previously identified by the radio inversion lines of NH3. The a(4,3)-s(3,3) line is very optically thick and it is determined that radiative excitation of the (4,3) NH3 level by far-IR emission from dust within the source can be ruled out. It is concluded that the (4,3) level is probably collisionally excited and the gas in the hot core region is warmer than the dust. Densities of approximately 10 to the 7th/cu cm are high enough to explain the observations, while shock heating by the mass outflow from IRc2 may account for the high gas temperatures in the hot core region.

Townes, C. H.↗
NASA NTRS1983

Scattering of electromagnetic waves from a half space of densely distributed dielectric scatterers

The scattering of a plane wave obliquely incident on a half space of densely distributed spherical dielectric scatterers is studied. The quasi-crystalline approximation is applied to truncate the hierarchy of multiple scattering equations, and the Percus-Yevick and the Verlet-Weis results are used to represent the pair distribution function. The coherent reflected wave is studied with these approximations. The incoherent scattered wave is calculated with the distorted Born approximation. In the low-frequency limit, closed-form expressions are obtained for the effective propagation constants, the coherent reflected wave, and the bistatic scattering coeficients. Results at higher frequencies are calculated numerically. The advantage of the present approach is that, in the low-frequency limit, it reproduces the effects of specular reflection, Fresnel reflection coefficient, Brewster angle, and Clausius-Mosotti relation. In addition to the classical results, the bistatic scattering coefficients are also calculated. The theory is also applied to match backscattering data from dry snow at microwave frequencies.

Tsang, L.↗
NASA NTRS1984

Methyl acetylene as a temperature probe for dense interstellar clouds

Methyl acetylene (propyne) appears to be a convenient and reliable probe of kinetic temperature for dense (few x 10 to the 4th/ cu cm) molecular clouds. A method is presented for fitting a (J + 1) - J K-multiplet to obtain the kinetic temperature from a single observation, facilitating the direct construction of kinetic temperature maps. Observations of Tau MC1, Ori MC1, Sgr B2, DR 21, DR 21 (OH), and S140 are presented to demonstrate the validity of the technique. Determination of methyl acetylene column densities requires, in addition, knowledge of the rotational excitation temperature. The relative abundance of CH3CCH appears to be within a factor of 2 of 2.5 x 10 to the -9th. Because of the large uncertainties in estimates of total gas column density, it is not clear whether there is genuine source-to-source variation in the CH3CCH relative abundance.

Kuiper, T. B. H.↗
NASA NTRS1985

A device for generating motive force through the expansion of a non-elastic dense fluid

A device for generating motive force through the expansion of a dense, nonelastic fluid is described. It consists of an exterior block of a material with a low expansion coefficient, the interior of which is equipped with two circular cavities, both of which are equipped with rotors having blades constantly stressed outward by springs, so that they make contact with the cavity walls. One cavity is heated externally, and both have an exterior wall made of a friction ring which keeps the volume constant when their length varies. These cavities are interconnected by ducts which, at the inlet, are a prolongation of a peripheral groove made in the friction ring. The excess fluid produced by expansion flows through the groove, subsequently entering the cavity again after passing through a cooler located in the exterior part of the block. Both rotors are connected to gears with appropriate ratios which are equipped with a blocking device to guarantee that they always rotate in the same direction.

Muller, L.↗
NASA NTRS1985

Spectral evolution of gamma-rays from adiabatically expanding sources in dense clouds

The excess of antiprotons (P) observed in cosmic ray was attributed to their production in supernova (SN) envelopes expanding in dense clouds. While creating P, gamma rays are also produced and these clouds would shine as gamma-ray sources. The evolution of the gamma-ray spectrum is calculated for clouds of r sub H = 10.000 and 100.000/cu cm.

Stephens, S. A.↗
NASA NTRS1985

Adiabatic deceleration of secondary antiprotons in the envelopes of supernova exploding in dense clouds

On the basis of well established cosmic ray propagation models, the expected flux of antiprotons in cosmic rays within the few-hundred MeV region is small by comparison with the observed flux. Observational data are presently approached through the examination of the possibility of antiproton production by supernova (SN) envelopes during the expansion phase and while undergoing the consequent adiabatic deceleration. In the case of the SN explosions in dense clouds treated, the SN remnant is decelerated within a few thousand years, generating may antiprotons whose spectrum can be calculated by taking all energy loss processes into account and examining the remnant's spectral evolution. Attention is also given to the possibility of obtaining the antiproton spectrum with enhanced flux at low energies.

Stephens, S. A.↗