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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 865 records · Page 48
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Physics of heavy ions (1989-1990)

The results from studies on polar wind ion heating due to kinetic ion beam instabilities and the effects of such ion heating on the outflow of O(+) in the polar wind are presented and discussed. First, the linear instabilities associated with an O(+) and H(+) polar wind plasma in the presence of O(+) and H(+) beams for a range of O(+)/H(+) beam densities, T(sub e)/T(sub i), and ion beam speeds were examined. Then, nonlinear heating of the polar wind ions was studied, using numerical simulations. The O(+) and H(+) polar wind ions were modeled by isotropic Maxwellian distributions, and the electrons, O(+) beams, and H(+) beams were modeled by drifting Maxwellian distributions. The effects of the kinetic ion heating on the outflow of the polar wind ions were examined from the ionosphere, using a time-dependent hydrodynamic model. A numerical code to solve the O(+) and H(+) continuity and momentum equations in a flux tube from ionospheric to magnetospheric altitudes were developed. The effects of ion heating were included by allowing for the altitudinal variation of the ion temperatures in the momentum equation. The ion temperature profiles were specified based on the ion heating characteristics found from previous kinetic simulations. It was assumed that heating occurred above 1500 km and increased to a saturated value of temperature that was obtained directly from the kinetic simulation study. The characteristics of the dynamical polar wind without ion heating were studied, and a flux tube on closed field lines that suddenly became open at t = 0 was simulated. Then, the effects of ion heating were included. To gain some physical insight, two limiting cases were considered: preferential H(+) heating and preferential O(+) heating. How O(+) heating can lead to enhanced polar wind O(+) fluxes in the polar magnetosphere is shown.

Ashour-Abdalla, M.↗
NASA NTRS1991

VHF discharges in storm cells producing microbursts

An experiment was carried out in which 3-D mapping of VHF sources was compared to a 3-D description of the reflectivity and dynamics of associated cloud cells observed by a radar network. Data from 61 microbursts were analyzed and it was found that, in 93 pct. of the cases, electrical activity precedes outflow development. The results confirm that the peak in intracloud activity precedes the maximum value of the outflow.

Laroche, P.↗
NASA NTRS1990

On the nature and implications of starburst-driven galactic superwinds

Optical spectroscopic data are presented on the ionized nebulae associated with 14 galaxies that are strong far-IR emitters. It is found that the data provide both qualitative and quantitative support for the 'superwind' model in which the kinetic energy provided by SNe and winds from massive stars in a central starburst drives a large-scale outflow that can shock heat and accelerate ambient interstellar and circumgalactic gas. Clear kinematic signatures of an outflow along the galaxy's minor axis are found for the three nearest far-IR galaxies (FIRGs). The FIRG nebulae are highly overpressured relative to the Galactic ISM, with the pressure dropping systematically with distance from the nucleus. Superwinds are energetically adequate to power both the observed optical and X-ray nebulae, and the relative emission-line intensities and their radial variations are consistent with ionization by wind-driven shocks, but not with photoionization by normal O stars or an AGN. The possible astrophysical implications of superwinds are discussed.

Heckman, Timothy M.↗
NASA NTRS1991

Critical points in the 16-moment approximation

The singular points in steady state, field-aligned plasma transport models based on velocity moment theory are examined. In particular, two separate singular points in the equations obtained from the 16-moment approximation are identified. These equations are presented in a form that makes the singularities apparent, and they are solved in a simple illustrative case. The singular points, one occurring at the sonic point and the other at a critical value of the parallel heat flux, give rise to different outflow regimes, characterized generically by different asymptotic behavior. The existence of the different outflow regimes separated by the heat flux critical point has been only hinted at in previous discussions of numerical simulation of the polar wind.

Yasseen, F.↗
NASA NTRS1991

Two micron morphology of candidate protostars

Results of a deep near-infrared imaging survey of low-luminosity cold IRAS sources in the Taurus dark cloud are discussed. The images involved identify the compact sources energizing the IRAS sources, identify infrared nebulosity around numbers of the invisible sources, and reveal the large-scale (about 1000 to 10,000 AU) morphology of this nebulosity. Some of the invisible sources show a clear bipolar or monopolar morphology suggesting a close relation of the nebulosity with a bipolar mass outflow. It is concluded that the nebulosity is likely due to scattering of radiation from the central source by the dust associated with the mass outflow extending to the poles of a circumstellar dust disk.

Tamura, Motohide↗
NASA NTRS1991

Theoretical description of spectral line profiles of parent molecules in cometary comae

The present overview of cometary spectral-line profiles obtainable through advancements in high-resolution spectroscopic studies, which allow the retrieval of coma kinematic properties from velocity-resolved spectral-line profiles, incorporates the most important gas dynamic processes into an outflow model which is tailored to the interpretation of spectroscopic observations of parent molecules. The model is then used to study the influence on parent-molecule spectral line profile formation of the field-of-view, the expansion velocity, the kinetic temperature, and the anisotropic outflow distributions.

Hu, Hong-Yao↗
NASA NTRS1991

Numerical models of extragalactic radio sources

When supercomputer-implemented numerical simulations analyzing the nonlinear physics inherent in the hydrodynamic and MHD equations are applied to extragalactic radio sources, many of the complex structures observed on telescopic images are reproduced. Attention is presently given to recently obtained results from 2D and 3D numerical simulations of the formation and evolution of extended radio morphologies; these numerical models allow the exploration of such physical phenomena as the role of magnetic fields in the dynamics and emissivity of extended radio galaxies, intermittent outflow from the cores of active galaxies, fluid-jet instabilities, and the bending of collimated outflows by motion through the intergalactic medium.

Burns, Jack O.↗
NASA NTRS1991

Role of groundwater in formation of Martian channels

A global 3-D model of groundwater flow has been used to study possible behavior of groundwater on Mars and its role in creating fluvial features. Conclusions drawn from an earlier 2-D groundwater model are supplemented and expanded. Topical headings are discussed as follows: timescales of groundwater flow; wet areas on Mars and location of outflow channels; implications for valley networks; the enigma of Hellas; absence of fluvial or periglacial features on Syrtis Major; development of chaotic terrain and associated outflow channels; and structurally controlled valley networks.

Howard, Alan D.↗
NASA NTRS1991

Spatially resolved quantitative spectroscopy of comets

The chemical composition of cometary nuclei and the velocity field of the ejected daughter species were investigated through conventional, high-resolution spectroscopy and indirectly by imaging the dissociation radicals in the outflowing cometary comae. Gas production rates and comae symmetries were studied, and coma outflow mechanisms were modeled.

Spinrad, Hyron↗
NASA NTRS1992

Duration and rates of discharge: Maja Valles, Mars

The 1600 km-long Maja Valles outflow system of Mars consists of three major divisions including the upper valley on Lunae Planum, the canyon section across Xanthe Terra, and the lower valley across western Chryse Planitia. Although water released from the source in Juventae Chasma could reach the terminus of the present day valley system in central Chryse Planitia within 44 hours, the original outflow did not traverse the Martian surface in a direct path. It ponded along its course on northern Lunae Planum and near the western edge of Chryse Planitia significantly prolonging the lifetime of surface flow. Calculation of pond volumes and discharge rates through various parts of the channel system indicates that water flowed through this system for nearly a (terrestrial) year. Discharge rates from the various basins along the Maja channels and the maximum flow rates within the various channels are calculated. With this data, it is possible to place reasonable estimates of the minimum length of time required to drain the various impoundments and the duration of flow in various parts of the channel system. The results of these calculations are discussed.

Dehon, R. A.↗
NASA NTRS1991

A numerical simulation of magnetic reconnection and radiative cooling in line-tied current sheets

Radiative MHD equations are used for an optically thin plasma to carry out a numerical experiment related to the formation of 'postflare' loops. The numerical experiment starts with a current sheet that is in mechanical and thermal equilibrium but is unstable to both tearing-mode and thermal-condensation instabilities. The current sheet is line-tied at one end to a photospheric-like boundary and evolves asymmetrically. The effects of thermal conduction, resistivity variation, and gravity are ignored. In general, reconnection in the nonlinear stage of the tearing-mode instability can strongly affect the onset of condensations unless the radiative-cooling time scale is much smaller than the tearing-mode time scale. When the ambient plasma is less than 0.2, the reconnection enters a regime where the outflow from the reconnection region is supermagnetosonic with respect to the fast-mode wave speed. In the supermagnetosonic regime the most rapidly condensing regions occur downstream of a fast-mode shock that forms where the outflow impinges on closed loops attached to the photospheric-like boundary. A similar shock-induced condensation might occur during the formation of 'postflare' loops.

Forbes, T. G.↗
NASA NTRS1992

Nimbus-7 total ozone observations of western North Pacific tropical cyclones

The Nimbus-7 Total Ozone Mapping Spectrometer (TOMS) was used to map the distribution of total ozone around western North Pacific tropical cyclones from 1979 to 1982. The strong correlation between total ozone distribution and tropopause height found in the subtropical and midlatitudes made it possible for TOMS to monitor the propagation of upper-tropospheric waves and the mutual adjustment between these waves and tropical cyclones during their interaction. Changes in these total ozone patterns reflect the 3D upper-tropospheric transport processes that are involved in tropical cyclone intensity and intensity and motion changes. The total ozone distributions indicate that: (1) the mean upper-tropospheric circulations associated with western North Pacific and Atlantic tropical cyclones are similar; (2) more intense tropical cyclones have higher tropopauses around their centers; (3) more intense tropical cyclones have higher tropopauses on the anticyclonic-shear side of their outflow jets, which indicate that the more intense tropical cyclones have stronger outflow channels than less intense systems; (4) tropical cyclones that intensify (do not intensify) are within 10 deg (15 deg) latitude of weak (strong) upper-tropospheric troughs that are moderately rich (very rich) in total ozone; and (5) tropical cyclones turn to the left (right) when they move within approximately 15 deg latitude downstream of an ozone-poor (ozone-rich) upper-tropospheric ridge (trough).

Stout, John↗
NASA NTRS1992

The kinematics of the extended gas in the Seyfert galaxy NGC 3516

Long-slit spectroscopy of the extended gas in the Seyfert galaxy NGC 3516 reveals considerable substructure in the narrow emission lines with several kinematically distinct components visible in H-alpha and N II lambda 6583. The velocity measurements cover almost all of the 3 kpc scale, Z-shaped emission-line structure seen in narrow-band images and suggest that a significant rotational component is present. At large radii, strong deviations from this rotation are observed, indicating that a radial component of motion to the gas is also required to adequately describe the velocity field. There is a clear antisymmetry in these deviations with the velocities being blueshifted with respect to 'normal' galactic rotation on the southwest side of the nucleus and redshifted with respect to it on the northeast side. Although several models can be invoked to explain the observed velocities, the symmetries in the kinematics and emission-line morphology are most easily explained by a bent bipolar mass outflow from the nucleus. In this simple model, gas is ejected out of the plane of the stellar disk and is then slowed by gravitational forces. As the gas trajectory begins to bend, significant velocity deviations are produced. These observations provide some of the best kinematic evidence for mass outflow, although indirect arguments suggest they may be a common feature in many Seyfert galaxies.

Mulchaey, John S.↗
NASA NTRS1992

Observations of the structure and vertical transport of the polar upper ionosphere with the EISCAT VHF radar. II - First investigations of the topside O(+) and H(+) vertical ion flows

EISCAT VHF radar was used to investigate the vertical flows of H(+) and O(+) ions in the topside high-latitude ionosphere. The radar transmitted a single long pulse to probe the ionosphere from 300 to 1200 km altitude. A calculation scheme is developed to deduce the H(+) drift velocity from the coupled momentum equations of H(+), O(+), and the electrons, using the radar data and a neutral atmosphere model. The H(+) vertical drift velocity was expressed as a linear combination of the different forces acting on the plasma. Two nights, one very quiet, one with moderate magnetic activity, were used to test the technique and to provide a first study of the morphology and orders of magnitudes of ion outflow fluxes over Tromso. O(+) vertical flows were found to be downward or close to zero most of the time in the topside ionosphere; they appeared to be strongly correlated with magnetic activity during the disturbed night. H(+) topside ion fluxes were always directed upward, with velocity reaching 500-1000 m/s. A permanent outflow of H(+) ions is inferred.

Wu, Jian↗
NASA NTRS1992

Venusian sinuous rilles

After a preliminary assessment of venusian channels, it now seems to be clear that the channels have distinctive classes, which imply a wide range of formation parameters and formation mechanisms. They include outflow channels mainly formed by mechanical erosion from very high discharge flow, and canali-type channels requiring either constructional process or mechanical erosion by rather exotic low-viscosity lava such as carbonatite or sulfur. Here we focus on venusian sinuous rilles. Venusian sinuous rilles are generally simple, and originate from a collapsed source. They are shallow and narrow downstream. The venusian sinuous rilles are distinct from canali-type channels, which exhibit almost constant morphologies throughout their entire length, and from outflow channels, which are characterized by wide anastomosing reaches. The lunar sinuous rilles could have been formed initially as constructional channels. However, incision was caused by the long flow duration and high temperatures of eruption, along with relatively large discharge rates, possibly assisted by a low viscosity of the channel-forming lava. Channel narrowing and levee formation suggest relatively fast cooling. The venusian channels could have had a similar sequence of formation including rapid cooling. Assuming the substrate is typical tholeiitic lava, the flowing lavas' temperatures have to be higher than the melting temperature of the substrate. The flow should have a low viscosity to cause turbulence and keep a high Reynolds number to sustain efficient thermal erosion. Determining eruption conditions also provide insights to estimate lava composition. Assuming a channel is formed mostly by thermal erosion, the channel's length and longitudinal profile are functions of lava properties. The depth profiles of the channel are measured by radar foreshortening methods and stereo images. Eruption conditions of channel forming lava can be estimated by the methods developed by Hulme.

Komatsu, G.↗
NASA NTRS1993

HST/FOS spectra of PG 1351+64: An intrinsic absorber at low redshift

A 1 A resolution spectra of the nearby (z = 0.08797) Seyfert galaxy PG 1351+64 taken with the Faint Object Spectrograph (FOS) onboard the Hubble Space Telescope is presented. Spectral coverage runs from 1200-3200 A in the observed frame and includes emission and absorption features due to Ly-alpha, N 5, Si 4, C 4, and Mg 2. Three distinct intrinsic absorption systems in Ly-alpha, N 5, Si 4, and C 4, and tentatively in Mg 2, at velocities of 900 km/s, 1630 km/s, and 2900 km/s (plus or minus 100 km/s) relative to the emission-line redshift of the QSO were detected. The maximum relative velocity of these absorbers is less than 5000 km/s and therefore does not meet Weymann, Carswell, & Smith's criteria for Broad-Absorption-Line (BAL) QSO's at high-z. However, the absorptions are almost certainly intrinsic to the QSO given the low redshift of this object. In addition, PG 1351+64 is marginally radio-quiet, as are all BALQSO's, based on recent estimates of the radio-loud/radio-quiet dividing line. The narrow velocity width, less than 500 km/s, and low outflow velocities of the absorption systems are more similar to so called 'associated absorbers' seen at high-z in radio-loud quasars, but whose absorptions are thought to arise in clouds much farther from the nucleus (greater than 1 kpc) than are BAL clouds (1-10 pc). Despite the qualitative resemblance to the associated absorbers, the absorption systems in PG 1351+64 appear to be the low-luminosity analogs of BALQSO absorption troughs. The lower observed outflow velocities in PG 1351+64 are due to the much lower luminosity of the nuclear source in comparison to the high-z, high-luminosity BALQSO's. In addition, 'satellite' emission lines displaced 4000-5000 km/s blueward and redward of the Mg 2 emission were discovered.

Granados, Arno↗
NASA NTRS1993

The vertical disk structure of the edge-on spiral galaxy NGC 3079

NGC 3079 is an edge-on SB(s)c galaxy at a redshift of 1225 km/s relative to the Local Group. Earlier researchers found a spectacular 'figure-eight' radio structure aligned along the minor axis of the galaxy, centered on the nucleus, and extending 3 kpc above and below the plane. The geometry of this structure and the evidence of unusually high nuclear gas velocities suggest that a wind-type outflow from the nucleus is taking place. The disk of NGC 3079 is also remarkable: it is extremely rich in H 2 regions and is the only unambiguous example of a galaxy outside M31 and our own Galaxy to exhibit 'Heiles-like' shells. Other researchers have also identified a nebulosity with a ragged X-shaped morphology formed by a system of lumpy filaments with individual lengths of 3 - 5 kpc. They suggest that this material is ambient halo gas entrained into the boundary layers of the nuclear outflow. The complex structure of the line emission in NGC 3079 makes this object an ideal target for an imaging spectroscopic study. The present paper reports the preliminary results of such a study.

Veilleux, S.↗
NASA NTRS1992

Segmented multigrid domain decomposition procedure for incompressible viscous flows

In this paper, the Navier-Stokes (NS) equations are approximated with a reduced NS system, that represents the lowest-order terms in an asymptotic Re expansion. This system allows for simplified boundary conditions, more generality in the location of the outflow boundary, and insures mass conservation in all subdomain grid interfaces, and also at the outflow boundary. The higher-order NS diffusion terms are included through a deferred corrector, in chosen subdomains, when required.

Srinivasan, Kumar↗