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NASA NTRS1993

X-ray detector physics and applications; Proceedings of the Meeting, San Diego, CA, July 23, 24, 1992

Recent developments in X-ray and hard X-ray imaging detector, high-intensity sources, hard X-ray imaging optics, calibration, and detection technologies are discussed. Particular attention is given to a high-MTF X-ray image intensifier, application of monolithic CdZnTe linear solid state ionization detectors for X-ray imaging, magnetic response of high-Tc superconductors to X-ray radiation and detection of X-rays, laboratory soft X-ray source with foil target, detection of explosive materials using nuclear radiation, energy response of astronomical CCD X-ray detectors, calibration techniques for high-flux X-ray detectors, fabrication of grazing-incidence optics using flow-polishing techniques, and numerical simulations for capillary-based X-ray optics. (No individual items are abstracted in this volume)

Hoover, Richard B.↗

NASA NTRS1994

Oil-And-Gas-Fire Snubber

Flame diverted and extinguished without explosives. Oil-and-gas-fire snubber consists of pipe with two exit branches and large selector valve, positioned over well, on path of escaping fuel. Flame moved to one side; then flow of fuel moved to other side, away from flame. Two versions of snubber have different uses. First used only to extinguish fire. Exit branch only long enough to keep fuel away to prevent reignition. Second needed if well not capped after fire at well extinguished and oil and gas remained present in problem quantities. Exit branch long enough to extend to oil-storage tank, and gas separated from oil and vented or burned at convenient location.

Weinstein, Leonard M.↗

NASA NTRS2012

Comparing Volcanic Terrains on Venus and Earth: How Prevalent are Pyroclastic Deposits on Venus?

In the last several years, astronomers have discovered several exoplanets with masses less than 10 times that of the Earth [1]. Despite the likely abundance of Earth-sized planets, little is known about the pathways through which these planets evolve to become habitable or uninhabitable. Venus and Earth have similar planetary radii and solar orbital distance, and therefore offer a chance to study in detail the divergent evolution of two objects that now have radically different climates. Understanding the extent, duration, and types of volcanism present on Venus is an important step towards understanding how volatiles released from the interior of Venus have influenced the development of the atmosphere. Placing constraints on the extent of explosive volcanism on Venus can provide boundary conditions for timing, volumes, and altitudes for atmospheric injection of volatiles. In addition, atmospheric properties such as near-surface temperature and density affect how interior heat and volatiles are released. Radar image data for Venus can be used to determine the physical properties of volcanic deposits, and in particular, they can be used to search for evidence of pyroclastic deposits that may result from explosive outgassing of volatiles. For explosive volcanism to occur with the current high atmospheric pressure, magma volatile contents must be higher than is typical on Earth (at least 2-4% by weight) [2,3]. In, addition, pyroclastic flows should be more prevalent on Venus than convective plumes and material may not travel as far from the vent source as it would on Earth [3]. Areas of high radar backscatter with wispy margins that occur near concentric fractures on Sapho Patera [4] and several coronae in Eastern Eistla Regio [5] have been attributed to collapse of eruption columns and runout of rough materials.

Carter, Lynn M.↗

NASA NTRS1990

Near-infrared mapping of spiral barred galaxies

In external galaxies, near-infrared emission originates from stellar populations, hot dust, free-free emission from H+ regions, gaseous emission, non-thermal nucleus if any. Because of the low extinction compared to the visible, infrared wavelengths are useful to probe regions obscured by dust such as central parts where starburst phenomena can occur because of the large quantity of matter. The results presented were obtained with a 32 x 32 InSb charge injection device (CID) array cooled at 4K, at the f/36 cassegrain focus of the 3m60 Canada-France-Hawaii telescope with a spatial resolution of 0.5 inches per pixel. The objects presented are spiral barred galaxies mapped at J(1.25 microns), H(1.65 microns) and K(2.2 microns). The non-axisymetric potential due to the presence of a bar induces dynamical processes leading to the confinement of matter and peculiar morphologies. Infrared imaging is used to study the link between various components. Correlations with other wavelengths ranges and 2-colors diagrams ((J-H), (H-K)) lead to the identification of star forming regions, nucleus. Maps show structures connected to the central core. The question is, are they flowing away or toward the nucleus. Observations of M83 lead to several conclusions. The star forming region, detected in the visible and the infrared cannot be very compact and must extend to the edge of the matter concentration. The general shape of the near-infrared emission and the location of radio and 10 micron peaks suggest the confinement of matter between the inner Linblad resonances localized from CO measurements about 100 and 400 pc. The distribution of color indices in the arc from southern part to the star forming region suggests an increasing amount of gas and a time evolution eventually triggered by supernova explosions. Close to the direction of the bar, a bridge-like structure connects the arc to the nucleus with peculiar color indices. Perhaps, this structure can be linked to a height velocity component seen in UV and we can attribute it to a jet and/or a matter flow along the bar toward the nucleus, fuelling it. NGC 1068 is the nearest Seyfert 2 galaxy. It has been a subject of many studies at all wavelengths. This object was mapped at J, H, K, L and M, and in polaro-imagery. Results are given.

Gallais, P.↗

NASA NTRS1985

The coalescence instability in solar flares

The nonlinear coalescence instability of current carrying solar loops can explain many of the characteristics of the solar flares such as their impulsive nature, heating and high energy particle acceleration, amplitude oscillations of electromagnetic and emission as well as the characteristics of two-dimensional microwave images obtained during a flare. The plasma compressibility leads to the explosive phase of loop coalescence and its overshoot results in amplitude oscillations in temperatures by adiabatic compression and decompression. It is noted that the presence of strong electric fields and super-Alfvenic flows during the course of the instability play an important role in the production of nonthermal particles. A qualitative explanation on the physical processes taking place during the nonlinear stages of the instability is given.

Tajima, T.↗

NASA NTRSDate not supplied

Active Volcanoes of Kamchatka as Suitable Terrestrial Analogs for Future Landing Missions and for Change Detection Analysis on Venus

The next decade will see the return to Venus due to a number of missions which have been recently selected and proposed for launch. The selected missions NASA DAVINCI and VERITAS, Roscosmos Venera-D, and ESA EnVision, along with the proposed missions ISRO Shukrayaan- 1, and CNSA VOICE, will open a new era for the exploration of the Earth’s hellish twin planet. These missions will shed new light on the science questions such as: (a) whether recent volcanic activity is locally constrained, or active volcanism occurs on a global scale; (b) the rate of the present-day volcanic activity; (c) the styles of volcanism on Venus, including possible occurrences of pyroclastic/explosive volcanism; and (d) how does the extreme environment on Venus effect volcanic activity. In preparation for these future missions to Venus, the Analogs for VENus’ GEologically Recent Surfaces (AVENGERS) initiative has the scope to select and analyze a number of active terrestrial volcanoes as suitable analogs for the identification and analysis of active volcanism on Venus. The Roscosmos Venera-D is the only mission, among the currently selected or planned mission, equipped with a lander to analyze the elemental and mineralogical composition of the surface. Therefore, it is crucial to find applicable volcanic areas on Earth to perform operational tests such as surface drilling and in-situ elemental composition analysis. To this regard, we propose the analysis of active volcanoes of the Kamchatka Peninsula, which is in a geodynamic setting (subduction) contrasting to that of the volcanic rises on Venus (hot spot). Thus, Kamchatka may represent a helpful geodynamic endmember to put the expected landing site of the Venera-D mission within the context of the entire variety of volcanic landforms and surface chemistry. The Kamchatka Peninsula is located on the eastern margin of the Eurasian plate, in proximity to the Kuril-Kamchatka subduction zone. The frequent eruptions characterizing the volcanoes of the Kamchatka Peninsula make them a suitable terrestrial analog for the possible detection of ongoing eruptions on Venus by future missions, which can be achieved by comparing a sequence of radar images of the same volcano and its surroundings taken at different times. Moreover, it is possible to collect samples of both unweathered and weathered volcanic deposits, to analyze their near infrared spectra in the laboratory for direct comparison with the spectra to be provided by the future missions to Venus. The chemical analyses of Venusian surface materials from the previous Soviet Venera and Vega missions are consistent with that of tholeiitic basalts. Since the volcanism of the Kamchatka Peninsula is characterized by both basaltic lava flows eruptions and pyroclastic activity, performing operational tests in the Kamchatka Peninsula also offers the unique opportunity to provide us the tools to potentially interpret the diverse output given by both effusive and explosive volcanic products.

Piero D'Incecco↗

NASA NTRS1996

Mixing and Transition Control Studied

Considerable progress in understanding nonlinear phenomena in both unbounded and wallbounded shear flow transition has been made through the use of a combination of high- Reynolds-number asymptotic and numerical methods. The objective of this continuing work is to fully understand the nonlinear dynamics so that ultimately (1) an effective means of mixing and transition control can be developed and (2) the source terms in the aeroacoustic noise problem can be modeled more accurately. Two important aspects of the work are that (1) the disturbances evolve from strictly linear instability waves on weakly nonparallel mean flows so that the proper upstream conditions are applied in the nonlinear or wave-interaction streamwise region and (2) the asymptotic formulations lead to parabolic problems so that the question of proper out-flow boundary conditions--still a research issue for direct numerical simulations of convectively unstable shear flows--does not arise. Composite expansion techniques are used to obtain solutions that account for both mean-flow-evolution and nonlinear effects. A previously derived theory for the amplitude evolution of a two-dimensional instability wave in an incompressible mixing layer (which is in quantitative agreement with available experimental data for the first nonlinear saturation stage for a plane-jet shear layer, a circular-jet shear layer, and a mixing layer behind a splitter plate) have been extended to include a wave-interaction stage with a three-dimensional subharmonic. The ultimate wave interaction effects can either give rise to explosive growth or an equilibrium solution, both of which are intimately associated with the nonlinear self-interaction of the three dimensional component. The extended theory is being evaluated numerically. In contrast to the mixing-layer situation, earlier comparisons of theoretical predictions based on asymptotic methods and experiments in wall-bounded shear-flow transition have been somewhat lacking in one aspect or another. The current work strongly suggests that the main weakness is the underlying asymptotic representation of the linear "part" of the problem and not the explicit modeling of the nonlinear/wave-interaction effects. Consequently, the long-wave-length/high-Reynolds-number asymptotic limit for the Blasius boundary-layer stability problem was reexamined, and a new dispersion relationship for the instability waves that is uniformly valid for both the upper- and lower branch regions to the required order of approximation was obtained. A comparison with numerical results, obtained by solving the Orr-Sommerfeld stability problem, shows that the asymptotic formula provides surprisingly good results, even for values of the frequency parameter usually encountered in experimental investigations. This is particularly evident in the dynamically important upper-branch region, where much of the nonlinear interactions in transition experiments are believed to take place. The result is important in that it can be used to greatly improve the accuracy of weakly nonlinear critical-layer-based theories, and a consistent nonlinear theory is currently under evaluation.

Source record↗

NASA NTRS1979

Alphonsus-type dark-halo craters - Morphology, morphometry and eruption conditions

The Alphonsus dark-halo craters are sites of volcanic eruptions with a characteristic crater radius of approximately 1 km. They are characterized by dark haloes ranging from 3 to 4 km, by substantial amounts of nonjuvenile material within the deposits, and by a lack of any associated lava flows or prominent constructional features, such as cones or domes. In the present paper, possible eruption styles are analyzed, using these observational constraints. It is concluded that an eruption process analogous to terrestrial volcanian explosive activity provides the most reasonable explanation for the characteristics of the deposits. The dark-halo craters appear to have formed contemporaneously with the emplacement of lavas in the adjacent Mare Nubium.

Head, J. W., III↗

NASA NTRS1983

Martian rampart crater ejecta - Experiments and analysis of melt-water interaction

The possible effects of explosive water vaporization on ejecta emplacement after impact into a wet target are described. A general model is formulated from analysis of Viking imagery of Mars and experimental vapor explosions as well as consideration of fluidized particulate transport and lobate volcanic deposits. The discussed model contends that as target water content increases, the effects of vapor expansion due to impact increasingly modify the ballistic flow field during crater excavation. This modification results in transport by gravity-driven surface flowage, and is similar to that of atmospheric drag effects on ejecta modelled by Schultz and Gault (1979).

Wohletz, K. H.↗

NASA NTRS1977

Electric currents in cosmic plasmas

It is suggested that dualism is essential for the physics of cosmic plasmas, that is, that some phenomena should be described by a magnetic field formalism, and others by an electric current formalism. While in earlier work the magnetic field aspect has dominated, at present there is a systematic exploration of the particle (or current) aspect. A number of phenomena which can be understood only from the particle aspect are surveyed. Topics include the formation of electric double layers, the origin of 'explosive' events like magnetic substorms and solar flares, and the transfer of energy from one region to another. A method for exploring many of these phenomena is to draw the electric circuit in which the current flows and then study its properties. A number of simple circuits are analyzed in this way.

Alfven, H.↗

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

Calculational investigation of impact cratering dynamics - Material motions during the crater growth period

The considered investigation was conducted in connection with studies which are to provide a better understanding of the detailed dynamics of impact cratering processes. Such an understanding is vital for a comprehension of planetary surfaces. The investigation is the continuation of a study of impact dynamics in a uniform, nongeologic material at impact velocities achievable in laboratory-scale experiments conducted by Thomsen et al. (1979). A calculation of a 6 km/sec impact of a 0.3 g spherical 2024 aluminum projectile into low strength (50 kPa) homogeneous plasticene clay has been continued from 18 microseconds to past 600 microseconds. The cratering flow field, defined as the material flow field in the target beyond the transient cavity but well behind the outgoing shock wave, has been analyzed in detail to see how applicable the Maxwell Z-Model, developed from analysis of near-surface explosion cratering calculations, is to impact cratering

Austin, M. G.↗

NASA NTRS1999

Low-Temperature Oxidation Reactions and Cool Flames at Earth and Reduced Gravity

Non-isothermal studies of cool flames and low temperature oxidation reactions in unstirred closed vessels are complicated by the perturbing effects of natural convection at earth gravity. Buoyant convection due to self-heating during the course of slow reaction produces spatio-temporal variations in the thermal and thus specie concentration fields due to the Arrhenius temperature dependence of the reaction rates. Such complexities have never been quantitatively modeled and were the primary impetus for the development of CSTR's (continuously stirred tank reactors) 30 years ago. While CSTR's have been widely adopted since they offer the advantage of spatial uniformity in temperature and concentration, all gradients are necessarily destroyed along with any structure that may otherwise develop. Microgravity offers a unique environment where buoyant convection can be effectively minimized and the need for stirring eliminated. Moreover, eliminating buoyancy and the need for stirring eliminates complications associated with the induced hydrodynamic field whose influence on heat transport and hot spot formation, hence explosion limits, is not fully realized. The objective of this research is to quantitatively determine and understand the fundamental mechanisms that control the onset and evolution of low temperature reactions and cool flames in both static and flow reactors. Microgravity experiments will be conducted to obtain benchmark data on the structure (spatio-temporal temperature, concentration, flow fields), the dynamics of the chemical fronts, and the ignition diagrams (pressure vs. temperature). Ground-based experiments will be conducted to ascertain the role of buoyancy. Numerical simulations including detailed kinetics will be conducted and compared to experiment.

Pearlman, Howard↗

NASA NTRS1997

Fuel Line Based Acoustic Flame-Out Detection System

An acoustic flame-out detection system that renders a large high pressure combustor safe in the event of a flame-out and possible explosive reignition. A dynamic pressure transducer is placed in the fuel and detects the stabilizing fuel pressure oscillations, caused by the combustion process. An electric circuit converts the signal from the combustion vortices, and transmitted to the fuel flow to a series of pulses. A missing pulse detector counts the pulses and continuously resets itself. If three consecutive pulses are missing, the circuit closes the fuel valve. With fuel denied the combustor is shut down or restarted under controlled conditions.

Puster, Richard L.↗

NASA NTRS2003

The "Supercritical Pile" Model for GRB: Tapping the Proton Energy and Getting the v F(sub V) Peak at Approx. 1 MeV

We propose a process by which the kinetic energy of the protons, that carry most of the energy of GRB relativistic blast waves (RBW) of Lorentz factor is converted explosively into relativistic electrons of the same Lorentz factor, which subsequently produce the observed prompt gamma-ray emission of the burst. This conversion is the result of the combined effects of the reflection of photons produced within the flow by upstream located matter, their re-interception and conversion into e(+) e(-) pairs on the RBW by the p gamma (right arrow) p e(+) e(-) reaction.

Kazanas, D.↗

NASA NTRS1973

Introduction to gasdynamics of explosions

Questions concerning the genesis and sustenance of an explosion are investigated, giving attention to the mechanics of explosions, the gasdynamics of explosions, aspects of technological significance, and future prospects. The dynamics of exothermic processes is discussed together with the most prominent effects of explosions. Blast waves are considered, taking into account conservation principles, blast wave transformation, conservative equations in nondimensional form, the equation of state, Eulerian space profiles, Eulerian time profiles, Lagrangian time profiles, boundary conditions and integral relations, and self-similar flow fields.

Oppenheim, A. K.↗

NASA NTRS1990

Theoretical and experimental studies of baroclinic processes

The geophysical fluid flow simulation code, GEOSIM, is being used to study the phenomenon of vacillation in the baroclinic annulus. Having verified that the code predicts vacillation for the same points as the experiments, the work is aiming toward explaining the mechanics of vacillation and pointing out some of the sensitivities of the results to the numerical method. Researchers are finding that there is a structural change associated with amplitude vacillation, where the structural changes are in the vertical. The results disagree with the premise of Lindzen et al, that the vacillation is due to constructive and destructive interference of neutral modes with different phase speeds. The researchers are continuing to study the Spacelab 3 Geophysical Fluid Flow Cell (GFFC) results with horizontal temperature gradients and heating from below. GEOSIM has been used to compute a wide range of cases, and these are being compared with the observations. The computations and observations compare well, and the model is being used to extend the results beyond cases studied in the experiments and to study the mechanics and predictability of the flows. The study of fully nonlinear baroclinic instability using the GFFC apparatus is proceeding with the numerical code. While the first instability that occurs is of planetary scale, secondary instabilities consisting of small-scale, penetrative convection occurs where cold fluid flows over a warm surface. The simultaneous modeling of the planetary scale and the convective scale is possible because of the nonhydrostatic formulation of the model. Some of these results have been animated on the Stardent computer, which shows the explosive nature of the small-scale convection.

Miller, Tim↗

NASA NTRS2000

Transitional mixing in a binary species supercritical, temporal mixing layer

The turbulent mixing of fluids at high pressure is a topic of much interest as it is relavant both to the natural phenomena and to technical applications. In the realm of technical applications, liquid rocket combustion presents a particular challenge as the operating conditions are supercritical with respect to both fuel and oxidizer, making mandatory the understanding of supercritical fluid behavior for a potentially explosive mixture. In this situation, numerical simulations with validated models can contribute information that would be otherwise impossible to obtain.

supercritical↗