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NASA NTRS1993

Automata network models of galaxy evolution

Two ideas appear frequently in theories of star formation and galaxy evolution: (1) star formation is nonlocally excitatory, stimulating star formation in neighboring regions by propagation of a dense fragmenting shell or the compression of preexisting clouds; and (2) star formation is nonlocally inhibitory, making H2 regions and explosions which can create low-density and/or high temperature regions and increase the macroscopic velocity dispersion of the cloudy gas. Since it is not possible, given the present state of hydrodynamic modeling, to estimate whether one of these effects greatly dominates the other, it is of interest to investigate the predicted spatial pattern of star formation and its temporal behavior in simple models which incorporate both effects in a controlled manner. The present work presents preliminary results of such a study which is based on lattice galaxy models with various types of nonlocal inhibitory and excitatory couplings of the local SFR to the gas density, temperature, and velocity field meant to model a number of theoretical suggestions.

Chappell, David↗

NASA NTRS1993

Simulation of collisional fragmentation with explosives

For practical reasons, experimental studies of collisional fragmentation must at times rely on explosives to fragment a target body. For example, Housen et al., described experiments in which spheres were fragmented in a pressurized atmosphere. Explosives were used because impacts could not be performed in the pressure chamber. Explosives can also be used to study targets much larger than those which can be disrupted by conventional light-gas guns, thereby allowing size- and rate-effects to be investigated. The purpose of this study is to determine the charge burial depth required to simulate various aspects of collisions.

Housen, Kevin↗

NASA NTRS1981

A cloud/particle model of the interstellar medium - Galactic spiral structure

A cloud/particle model for gas flow in galaxies is developed that incorporates cloud-cloud collisions and supernovae as dominant local processes. Cloud-cloud collisions are the main means of dissipation. To counter this dissipation and maintain local dispersion, supernova explosions in the medium administer radial snowplow pushes to all nearby clouds. The causal link between these processes is that cloud-cloud collisions will form stars and that these stars will rapidly become supernovae. The cloud/particle model is tested and used to investigate the gas dynamics and spiral structures in galaxies where these assumptions may be reasonable. Particular attention is given to whether large-scale galactic shock waves, which are thought to underlie the regular well-delineated spiral structure in some galaxies, form and persist in a cloud-supernova dominated interstellar medium; this question is answered in the affirmative.

Levinson, F. H.↗

NASA NTRS1980

Safety shield for vacuum/pressure-chamber windows

Optically-clear shatter-resistant safety shield protects workers from implosion and explosion of vacuum and pressure windows. Plastic shield is inexpensive and may be added to vacuum chambers, pressure chambers, and gas-filling systems.

Shimansky, R. A.↗

NASA NTRS1987

Observations of absorption lines from highly ionized atoms

In the ultraviolet spectra of hot stars, absorption lines can be seen from highly ionized species in the interstellar medium. Observations of these features which have been very influential in revising the perception of the medium's various physical states, are discussed. The pervasiveness of O 6 absorption lines, coupled with complementary observations of a diffuse background in soft X-rays and EUV radiation, shows that there is an extensive network of low density gas (n approx. few x 0.001/cu cm) existing at coronal temperatures log T = 5.3 or 6.3. Shocks created by supernova explosions or mass loss from early-type stars can propagate freely through space and eventually transfer a large amount of energy to the medium. To create the coronal temperatures, the shocks must have velocities in excess of 150 km/sec; shocks at somewhat lower velocity (v = 100 km/sec) can be directly observed in the lines of Si3. Observations of other lines in the ultraviolet, such as Si 4V and C 5, may highlight the widespread presence of energetic UV radiation from very hot, dwarf stars. More advanced techniques in visible and X-ray astronomical spectroscopy may open up for inspection selected lines from atoms in much higher stages of ionization.

Jenkins, Edward B.↗

NASA NTRS1993

The ring around SN1987A

Stars in the 9-40 solar mass range play a prominent role in the hydrodynamical and chemical evolution of galaxies. Their stellar winds and supernova explosions are believed to create the hot component of the interstellar medium (ISM). In some galactic disks, the kiloparsec sized super bubbles formed around clusters of massive stars may blow out of the disk plane and release hot, metal enriched gas into the galaxy's halo. Additionally, the expanding shock front of a super bubble in the disk may trigger additional star formation. Furthermore, similar processes probably drive the galactic winds associated with star burst nuclei that enrich the intracluster and intergalactic mediums. Nonetheless, the explosion of a blue super giant in the Large Magellanic Cloud (LMC), SN1987A, illuminated the incompleteness of our understanding of massive stars. Evolutionary models of massive stars do not synthesize the observed super giant populations in either the Milky Way or LMC. Our modeling of the formation of SN1987A's ring will improve our knowledge of both the post-main-sequence evolution of massive stars and their coupling to the ISM in galaxies.

Martin, Crystal L.↗

NASA NTRS1972

State-of-technology for joining TD-NiCr sheet.

At the current state-of-technology there are many joining processes that can be used to make sound welds in TD-NiCr sheet. Some of these that are described in this report are electron beam welding (EBW), gas-tungsten arc welding (GTAW), diffusion welding (DFW), resistance spot welding (RSW), resistance seam welding (RSEW), and brazing. Roll welding (RW) and explosion welding (EXW) have not been developed to the point where they can be used to make sound welds in TD-NiCr. Joining work that has previously been done on TD-NiCr by various organizations, both privately supported and under Air Force and NASA contracts, is described in this summary. Current work is also described that is being done at General Dynamics/Convair (under NASA contract) and at NASA/Lewis to develop and evaluate DFW, RSW, RSEW, and brazing. Preliminary comparisons of joining processes are made for typical applications. A brief description of the manufacture of TD-NiCr sheet by a recently standardized process (under NASA contract) also is given.

Holko, K. H.↗

NASA NTRS1981

SAGE measurements of the stratospheric aerosol dispersion and loading from the Soufriere Volcano

Explosions of the Soufriere volcano on the Caribbean Island of St. Vincent reduced two major stratospheric plumes which the stratospheric aerosol and gas experiment (SAGE) satellite tracked to West Africa and the North Atlantic Ocean. The total mass of the stratospheric ejecta measured is less than 0.5% of the global stratospheric aerosol burden. No significant temperature or climate perturbation is expected. It is found that the movement and dispersion of the plumes agree with those deduced from high altitude meteorological data and dispersion theory. The stratospheric aerosol dispersion and loading from the Soufrier volcano was measured.

Mccormick, M. P.↗

NASA NTRS1983

NSI-1 Squib adapter development and final test report for usage on space shuttle gas sampler valve/bottle assembly 3270

The possibility of utilizing the NSI-1 squib in place cartridge assembly 2270 for the function of both events required for the Space Shuttle Gas Sampler Valve/Bottle Assembly 3270 was determined. Additionally, it was a requirement that the closure disk of the NSI-1 squib and explosive residue therefrom be retained from the valve cavity in so far as possible to prevent any significant particulate from scratching the valve bore and causing sample leakage following the postfire 2 event.

Siebel, J. E.↗

NASA NTRS1985

History, design and performance of the space shuttle hazardous gas detection system

The Hazardous Gas Detection System (HGDS) is designed to detect leaks hich could result in pre-launch or in-flight fires or explosions resulting from the presence of cryogenic rocket propellants. The historical development, design, and performance of the HGDS is discussed. Data for response time, detection limits, accuracy, and drift are presented. Finally, present and future applications are discussed, and some general conclusions are drawn.

Helms, W. R.↗

NASA NTRS1989

Narrow ultraviolet emission lines from SN 1987A - Evidence for CNO processing in the progenitor

Results from UV observations of SN 1987A with the IUE satellite are presented, showing that emission lines of He II, C III, N III, N IV, N V, and O III increase in strength with time after May 24, 1987. It is found that increased emission originated in a photoionized low-density circumstellar gas, lost by the progenitor in its red supergiant phase. A nebular analysis reveals a large nitrogen overabundance, indicating that the gas has undergone substantial CNO processing. This suggests that the progenitor of SN 1987A lost much of its hydrogen envelope before the explosion. The findings are consistent with models in which a red supergiant evolves to the blue supergiant stage before exploding.

Fransson, C.↗

NASA NTRS1991

Sources of volcanic aerosols: Petrologic and volcanological constraints

Global climatic effects brought about by volcanism are related to the impact of volcanic gases and their derivative aerosols on the atmosphere, rather than the effects of volcanic ash. Evidence from both historic eruptions and polar ice cores indicate that volcanic sulfur gases are the dominant aerosol-forming component, resulting in produciton of a sulfuric acid-rich stratosphere aerosol that can have profound effects on the earth radiation budget over periods of a few years. Due to highly variable sulfur content of different magma types, the climatic effects do not relate simply to total erupted mass. There is a close relationship between volcanic sulfur yield to the atmospheric and hemispheric surface temperature decrease following an eruption, with up to 1 C surface temperature decrease indicated following a major volcanic event such as the 1815 Tambora eruption. While the erupted mass of HCl and HF is equal to or greater than that of sulfur gases in some volcanic events, the halogens do not form known aerosols nor are they abundant in ice core acidity layers. The early removal of halogens from eruption columns occurs by rain flushing and adsorption onto tephra particles, but the fate of halogens in the atmosphere following very large explosive eruptions is unknown. The CO2 flux to the atmosphere from volcanic eruptions is volumetrically one of the most important of the gas species, but owing to the huge size of the atmospheric reservoir of this gas, the volcanic contribution is likely to have negligible effects.

Sigurdsson, Haraldur↗

NASA NTRS2014

Shockwave Consolidation of Nanostructured Thermoelectric Materials

Nanotechnology based thermoelectric materials are considered attractive for developing highly efficient thermoelectric devices. Nano-structured thermoelectric materials are predicted to offer higher ZT over bulk materials by reducing thermal conductivity and increasing electrical conductivity. Consolidation of nano-structured powders into dense materials without losing nanostructure is essential towards practical device development. Using the gas atomization process, amorphous nano-structured powders were produced. Shockwave consolidation is accomplished by surrounding the nanopowder-containing tube with explosives and then detonating. The resulting shock wave causes rapid fusing of the powders without the melt and subsequent grain growth. We have been successful in generating consolidated nano-structured bismuth telluride alloy powders by using the shockwave technique. Using these consolidated materials, several types of thermoelectric power generating devices have been developed. Shockwave consolidation is anticipated to generate large quantities of nanostructred materials expeditiously and cost effectively. In this paper, the technique of shockwave consolidation will be presented followed by Seebeck Coefficient and thermal conductivity measurements of consolidated materials. Preliminary results indicate a substantial increase in electrical conductivity due to shockwave consolidation technique.

Prasad, Narasimha S.↗

NASA NTRS1983

Cloud-particle galactic gas dynamics and star formation

Galactic gas dynamics, spiral structure, and star formation are discussed in relation to N-body computational studies based on a cloud-particle model of the interstellar medium. On the small scale, the interstellar medium is seen as cloud-dominated and supernova-perturbed. It is noted that the cloud-particle model simulates cloud-cloud collisions, the formation of stellar associations, and supernova explosions as dominant local processes. On the large scale, in response to a spiral galactic gravitational field, global density waves and galactic shocks develop having large-scale characteristics similar to those found in continuum gas dynamical studies. Both the system of gas clouds and the system of young stellar associations forming from the clouds figure in the global spiral structure. However, with the attributes of neither assuming a continuum of gas (as in continuum gas dynamical studies) or requiring a prescribed equation of state (such as the isothermal condition), the cloud-particle picture retains much of the detail lost in earlier work. By detail is meant the small-scale features and structures so important in understanding the local, turbulent state of the interstellar medium as well as the degree of raggedness often seen to be superposed on the global spiral structure.

Roberts, W. W., Jr.↗

NASA NTRS1970

An explosion-proof battery case

Battery case, equipped with relief valve, connector, and two covers, separates the explosive mixture from all potential spark sources. Bottom ends of vent tubes are cemented into cell vents and upper ends fit through the gas barrier cover. This arrangement isolates generated gases from the electric power.

Keathley, W. H.↗

NASA NTRS1973

Development of explosively driven launcher for meteoroid studies

The results of a continuing program to develop an explosively driven 2-stage hypervelocity launcher capable of achieving velocities between 15 and 20 km/sec are described. Previous efforts had identified incomplete barrel collapse as a limiting factor in launcher performance. Correlation of experimental and computational results obtained in the present study indicate that boundary-layer gases within the barrel act to prevent complete closure. Simplified calculations suggest that in-contact explosives may have insufficient energy densities to collapse the barrel against a developed boundary layer. Higher energy densities, sufficient to produce complete closure, were obtained with the use of steel flyer plates accelerated by a phased explosive lens. However, when flat flyer plates were impacted on the barrel, the sides of the barrel were observed to rupture and leak gas prior to barrel closure. A promising solution to this problem (untested) is to produce a symmetrical collapse with a cylindrical tube around the barrel.

Baum, D. W.↗

NASA NTRS1977

Chemical depletion of the ionosphere

A theoretical study of the chemical and gas dynamical processes resulting from the release of reactive gases into the daytime ionosphere is discussed. Only point releases, such as from an explosion or a pulsed jet, are considered. Some scientific uses of the artificial reduction of the ionospheric plasma are considered.

Bernhardt, P. A.↗

NASA NTRS1982

Impact ejecta dynamics in an atmosphere - Experimental results and extrapolations

It is noted that the impacts of 0.635-cm aluminum projectiles at 6 km/sec into fine pumice dust, at 1 atm, generate a ball of ionized gas behind an expanding curtain of upward moving ejecta. The gas ball forms a toroid which dissolves as it is driven along the interior of the ejecta curtain, by contrast to near-surface explosions in which a fireball envelops early-time crater growth. High frame rate Schlieren photographs show that the atmosphere at the base of the ejecta curtain is initially turbulent, but later forms a vortex. These experiments suggest that although small size ejecta may be decelerated by air drag, they are not simply lofted and suspended but become incorporated in an ejecta cloud that is controlled by air flow which is produced by the response of the atmosphere to the impact. The extrapolation of these results to large body impacts on the earth suggests such contrasts with laboratory experiments as a large quantity of impact-generated vapor, the supersonic advance of the ejecta curtain, the lessened effect of air drag due to the tenuous upper atmosphere, and the role of secondary cratering.

Schultz, P. H.↗