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NASA NTRS1972

Possible production mechanisms of lunar magnetic fields.

Demonstration of the impossibility of the production of local surface magnetic fields on the moon by conduction currents in the lunar soil and in local lunar atmospheres by volcanic eruption. However, it is suggested that convection currents produced by the ionization (by radiation and/or by triboelectric effects) of volcanic-ash-particle flows may produce the local magnetic fields of about 1000 gamma that are believed to have existed on the moon about 3.5 x 10 to the 9th years ago. A simple electrogasdynamic model for such flows and experiments for further investigation of this hypothesis are discussed.

Cap, F. F.↗

NASA NTRS1973

Barium release system

A chemical system is described for releasing a good yield of free barium neutral atoms and barium ions in the upper atmosphere and interplanetary space for the study of the geophysical properties of the medium. The barium is released in the vapor phase so that it can be ionized by solar radiation and also be excited to emit resonance radiation in the visible range. The ionized luminous cloud of barium becomes a visible indication of magnetic and electrical characteristics in space and allows determination of these properties over relatively large areas at a given time.

Lewis, B. W.↗

NASA NTRS1979

Observations of the motion and distribution of the ionized gas in the central parsec of the Galaxy

High spatial and spectral resolution observations of Ne II (12.8 microns) emission show a complex array of small sources of various velocities within the central 20 arcsec of the Galaxy. More extended clouds of ionized gas are seen outside this region. Many of the localized sources are associated with 10-micron continuum peaks. Clouds in the central region appear to be rotating about an axis tilted 60 to 90 deg from that of galactic rotation. Their velocity distribution indicates a mass of about 8 million solar masses for the central parsec (diameter) of the Galaxy. Sensitive searches for more highly ionized species in the galactic center indicate that the region is ionized by radiation with a cooler spectrum than that found in other H II regions.

Lacy, J. H.↗

NASA NTRS1980

Observations of the motion and distribution of the ionized gas in the central parsec of the Galaxy. II

Observations of infrared fine-structure line emission from compact clouds of ionized gas within Sgr A West are presented. These clouds have diameters of 0.1-0.5 pc, internal velocity dispersions of 100 km/s (FWHM), and line center velocities up to + or - 260 km/s. Their masses are not accurately determined but are probably between 0.1 and 10 solar masses. They are ionized by radiation like that of stars of effective temperature not greater than 35,000 K. The clouds are shown to have lifetimes of 10,000 yr and so must be generated and dissipated at a rate of a few per 1000 yr. From analysis of the distribution of the velocities of the clouds, a most probable mass distribution is derived which includes a central pointlike mass of several x 10 to the 6th solar masses in addition to several x 10 to the 6th solar masses of stars within 1 pc of the center.

Lacy, J. H.↗

NASA NTRS1981

Modulation of Venus ion densities associated with solar variations

The dayside ion concentrations in the Venus ionosphere obtained by the Pioneer Venus orbiter ion mass spectrometer exhibit a modulation corresponding to the 27-day solar variation. Comparisons were made of the amplitudes of modulation of CO(2(+), C(+), and O2(+), with the amplitudes of the 27-day variation in the 10.7-cm solar radio flux and the simultaneously measured EUV fluxes at He II (304 A) and Lyman-beta(1026 A), together with a theoretical analysis of the effects of solar variability on the ionosphere and neutral atmosphere of Venus. This analysis leads to the conclusion that the observed modulation of dayside ion densities is primarily due to the variability in the ionizing EUV radiations and, to a much lesser extent, the result of the variability with solar activity of the neutral atmosphere via the variability in exospheric temperature. In this connection, it is also shown theoretically why the percentage variation of exospheric temperature on Venus (as observed in the ONMS data) for a given variation in the 10.7-cm radio flux is only half of the exospheric temperature variation for earth.

Bauer, S. J.↗

NASA NTRS1983

The opacity of the universe and the strong equivalence principle

A possible explanation of why the advanced solutions of Maxwell's equations are not observed in nature is by way of absorption by an opaque universe. As Davies has shown, the ever expanding, general relativistic cosmological models fail to provide the needed absorption. The absorption mechanism calling for an interplay between local physics and cosmology, is usually developed adopting the strong equivalence principle, SEP, which precludes such interplay. It is shown that complete absorption of electromagnetic radiation by ionized intergalactic plasma is obtained provided a violation of the SEP, of the order of the Hubble's constant, is allowed to occur. The same degree of violation was previously found to be compatible with a large body of observational data.

Canuto, V. M.↗

NASA NTRS1984

The laboratory simulation of unmagnetized supernova remnants Absence of a blast wave

Supernova remnants are experimentally simulated by irradiating spherical targets with eight-beam carbon dioxide laser in a chamber containing finite amounts of neutral gas, the gas being ionized by radiation from the hot target. The expansion velocities of the target plasmas are approximately the same as the expansion velocities of supernova ejecta and the experiment is successfully scaled to the case of a supernova remnant in an unmagnetized, low-density, interstellar medium. No sweep-up of the ambient plasma is detected, indicating that no hydrodynamic shock wave is formed to couple the target ejecta to the ambient gas. The experiment implies that if supernova ejecta couple to the interstellar medium, magnetic-field effects may be crucial to the physical description.

Borovsky, J. E.↗

NASA NTRS1985

Stochastic particle acceleration in flaring stars

The acceleration of electrons by the Fermi-Parker mechanisms in a quasistationary turbulent plasma of dimension l, mean magnetic field strength B, and mean number density n are considered. The electrons suffer radiative and ionization losses and have a scattering mean free path that increases linearly with their momentum. Analytic solutions for the steady-state electron energy spectra are presented. The spectra are characterized by an exponential cutoff above a given momentum determined by the synchrontron or the confinement time, depending on the physical characteristics of the accelerating region.

Bogdan, T. J.↗

NASA NTRS1988

The rebound shock model for solar spicules - Dynamics at long times

The spicule model due to Hollweg is extended and developed. The dynamics is emphasized here; radiative and ionization losses, heat conduction, and nonshock heat input, are not included. In the model, a series of rebound shocks results in chromospheric material with spicule-like properties below a raised transition region. The shocks result from a single quasi-impulsive source in the photosphere. It is found that at long times, the model approaches a new hydrostatic equilibrium with the transition region remaining raised, and with a region of shock-heated chromosphere below it. Attention is given to the variation of the properties of the model in response to different values for the magnitude and location of the source, and to different initial transition region heights. It is concluded that the model is capable of generating structures with properties consistent with observations of spicules (with the exception of temperature) when only the dynamics is considered.

Sterling, Alphonse C.↗

NASA NTRS1989

Rotational and vibrational nonequilibrium effects in rarefied, hypersonic flow

Results are reported for an investigation into the methods by which energy transfer is calculated in the Direct Simulation Monte Carlo method. Description is made of a recently developed energy exchange model that deals with the translational and rotational modes. A new model for simulating the transfer of energy between the translational and vibrational modes is also explained. This model allows the vibrational relaxation time to follow the temperature dependence predicted by the Landau-Teller theory at moderate temperatures. For temperatures in excess of about 8000K the vibrational model is extended to include an empirical result for the relaxation time. The effect of introducing these temperature dependent collision numbers into the DSMC technique is assessed by making calculations representative of the stagnation streamline of a hypersonic space vehicle. Both thermal and chemical nonequilibrium effects are included while the flow conditions have been chosen such that ionization and radiation may be neglected. The introduction of these new models is found to significantly affect the degree of thermal nonequilibrium observed in the flowfield. Larger, and more widely ranging, differences in the results obtained with the different energy exchange probabilities are found when a significant amount of internal energy is included in the calculation of chemical nonequilibrium.

Boyd, Iain D.↗

NASA NTRS1991

A parametric study of dissociation and ionization models at 12 km/sec

Thermochemical nonequilibrium-solution dependence on available models for the chemical reaction rates is examined. Solutions from the Kang and Dunn (1973) reaction-rate set, the Park rate set of 1987, and the Park rate set of 1991 are compared. The blunt-nosed, axisymmetric geometry considered is a 60-deg sphere cone with nose radius of 1.07 m and cicular aft skirt. The nonequilibrium test case is 12 km/sec entry into the earth's atmosphere at 80 km altitude. The model variations are implemented into the Langley aerothermodynamics upwind relaxation algorithm code. While variations in the reaction rates have no effect on the surface pressure distribution and little effect on the convective heating, the effect on degree of ionization and radiative heating can be a factor of three.

Mitcheltree, R. A.↗

NASA NTRS1991

Analysis of model Titan atmospheric components using ion mobility spectrometry

The Gas Chromatograph-Ion Mobility Spectrometer (GC-IMS) was proposed as an analytical technique for the analysis of Titan's atmosphere during the Cassini Mission. The IMS is an atmospheric pressure, chemical detector that produces an identifying spectrum of each chemical species measured. When the IMS is combined with a GC as a GC-IMS, the GC is used to separate the sample into its individual components, or perhaps small groups of components. The IMS is then used to detect, quantify, and identify each sample component. Conventional IMS detection and identification of sample components depends upon a source of energetic radiation, such as beta radiation, which ionizes the atmospheric pressure host gas. This primary ionization initiates a sequence of ion-molecule reactions leading to the formation of sufficiently energetic positive or negative ions, which in turn ionize most constituents in the sample. In conventional IMS, this reaction sequence is dominated by the water cluster ion. However, many of the light hydrocarbons expected in Titan's atmosphere cannot be analyzed by IMS using this mechanism at the concentrations expected. Research at NASA Ames and PCP Inc., has demonstrated IMS analysis of expected Titan atmospheric components, including saturated aliphatic hydrocarbons, using two alternate sample ionizations mechanisms. The sensitivity of the IMS to hydrocarbons such as propane and butane was increased by several orders of magnitude. Both ultra dry (waterless) IMS sample ionization and metastable ionization were successfully used to analyze a model Titan atmospheric gas mixture.

Kojiro, D. R.↗

NASA NTRS1991

Method and apparatus for increasing resistance of bipolar buried layer integrated circuit devices to single-event upsets

Bipolar transistors fabricated in separate buried layers of an integrated circuit chip are electrically isolated with a built-in potential barrier established by doping the buried layer with a polarity opposite doping in the chip substrate. To increase the resistance of the bipolar transistors to single-event upsets due to ionized particle radiation, the substrate is biased relative to the buried layer with an external bias voltage selected to offset the built-in potential just enough (typically between about +0.1 to +0.2 volt) to prevent an accumulation of charge in the buried-layer-substrate junction.

Zoutendyk, John A.↗

NASA NTRS1994

Application of electron paramagnetic resonance imaging to the characterization of the Ultem(R) exposed to 1 MeV electrons. Correlation of radical density data to tiger code calculations

A major long-term goal of the Materials Division at the NASA Langley Research Center is the characterization of new high-performance materials that have potential applications in the aircraft industry, and in space. The materials used for space applications are often subjected to a harsh and potentially damaging radiation environment. The present study constitutes the application of a novel technique to obtain reliable data for ascertaining the molecular basis for the resilience and durability of materials that have been exposed to simulated space radiations. The radiations of greatest concern are energetic electrons and protons, as well as galactic cosmic rays. Presently, the effects of such radiation on matter are not understood in their entirety. It is clear however, that electron radiation causes ionization and homolytic bond rupture, resulting in the formation of paramagnetic spin centers in the polymer matrices of the structural materials. Since the detection and structure elucidation of paramagnetic species are most readily accomplished using Electron Paramagnetic Resonance (EPR) Spectroscopy, the NASA LaRC EPR system was brought back on-line during the 1991 ASEE term. The subsequent 1992 ASEE term was devoted to the adaptation of the EPR core system to meet the requirements for EPR Imaging (EPRI), which provides detailed information on the spatial distribution of paramagnetic species in bulk media. The present (1994) ASEE term was devoted to the calibration of this EPR Imaging system, as well as to the application of this technology to study the effects of electron irradiation on Ultem(exp R), a high performance polymer which is a candidate for applications in aerospace. The Ultem was exposed to a dose of 2.4 x 10(exp 9) Rads (1-MeV energy/electron) at the LaRC electron accelerator facility. Subsequently, the exposed specimens were stored in liquid nitrogen, until immediately prior to analyses by EPRI. The intensity and dimensions of the EPR Images that were generated for the irradiated specimens showed that the electrons penetrated the material to a depth of approximately 0.125 inch. These data show a very high degree of correlation to the energy deposition profile as predicted by the Tiger Code, a Monte Carlo code that provides guidelines for the transport of electrons in matter. Subsequent efforts will focus on delineating the transport properties of energetic protons in Ultem(R).

Suleman, Naushadalli K.↗

NASA NTRS1994

Hubble Space Telescope images of the Seyfert galaxies NGC 5929 and MCG 8-11-11

We present the initial results of a program to obtain high resolution images of Seyfert galaxies with the Planetary Camera aboard the Hubble Space Telescope (HST). In this paper we discuss the images of the type 2 Seyfert NGC 5929 and the type 1.5 Seyfert MCG 8-11-11 (= UGC 3374). The images were obtained in the emission lines of (O III) lambda lambda 4959 and 5007 A and H alpha + (N II) lambda lambda 6548 and 6583 A and their adjacent continua. The high-excitation gas in the narrow line region (NLR) of NGC 5929 is resolved into individual clouds in the central 1 sec .5. Although the (O III) emission is clearly not spherically symmetric with respect to the nucleus, it does not define a distinct 'bicone' morphology, as observed by the HST in a few other Seyfert galaxies. We find no direct evidence for the reddening and/or obscuration effects characteristic of a dusty torus, which, in the context of 'unified models', is expected to obscure the active galactic nucleus (AGN) in type 2 Seyfert galaxies. The correspondence between the emission line gas and the radio morphology suggests that the structure of the NLR in NGC 5929 is governed by matter ejected from the AGN. A comparison of the recombination rate of hydrogen in the brightest emission line cloud with an upper limit on the ionizing luminosity emitted toward Earth provides no evidence that the central ionizing source radiates anisotropically. The images of MCG 8-11-11 show only an unresolved nuclear source. No emission line gas associated with the extended radio source is detected. We estimate upper limits on the intensity of extended line emission in this galaxy and examine their significance.

Bower, Gary A.↗

NASA NTRS2000

Neutrons in Space: Shield Models and Design Issues

The normal working and living areas of the astronaut are designed to provide an acceptable level of protection against the hazards of ionizing space radiation. Attempts to reduce the exposures require intervening shield materials to reduce the transmitted radiation. An unwelcome side effect of the shielding is the production of neutrons, which are themselves dangerous particles that can be (but are not always) more hazardous than the particles that produced them. This is especially true depending on the choice of shield materials. Although neutrons are not a normal part of the space environment, this paper focuses on them as principle component of astronaut exposure in the massive spacecraft's required for human space travel and habitation near planetary surfaces or other large bodies of material in space.

Wilson, J. W.↗

NASA NTRS2003

On the Determination of Ejecta Structure and Explosion Asymmetry from the X-ray Knots of Cassiopeia A

We present a detailed analysis of Chandra X-ray spectra from individual ejecta knots in the supernova remnant Cassiopeia A. The spectra are fitted to give the electron temperature T(sub e), and (single) ionization age n(sub e)t. These quantities are compared with the predictions of self similar hydrodynamic models incorporating time dependent ionization and radiation losses, and Coulomb electron-ion equilibration behind the reverse shock, for a variety of different ejecta density profiles described by a uniform density core and a power law envelope. We find that the ejecta close to the 'jet' region in the NE, but not actually in the jet itself, have a systematically shallower outer envelope than ejecta elsewhere in the remnant, and we interpret this as being due to more energy of the initial explosion being directed in this polar direction as opposed to equatorially. The degree of asymmetry we infer is at the low end of that generally modelled in asymmetric core-collapse simulations, and may be used to rule out highly asymmetric explosion models.

Laming, J. Martin↗

NASA NTRS2004

The Interaction of Hot and Cold Gas in the Disk and Halo of Galaxies

Most of the thermal energy in the Galaxy and perhaps most of the baryons in the Universe are found in hot (log T approximately 5.5 - 7) gas. Hot gas is detected in the local interstellar medium, in supernova remnants (SNR), the Galactic halo, galaxy clusters and the intergalactic medium (IGM). In our own Galaxy, hot gas exists in large superbubbles up to several hundred pc in diameter that locally dominate the interstellar medium (ISM) and determine its thermal and dynamic evolution. While X-ray observations using ROSAT, Chandra and XMM have allowed us to make dramatic progress in mapping out the morphology of the hot gas and in understanding some of its spectral characteristics, there remain fundamental questions that are unanswered. Chief among these questions is the way that hot gas interacts with cooler phase gas and the effects these interactions have on hot gas energetics. The theoretical investigations we proposed in this grant aim to explore these interactions and to develop observational diagnostics that will allow us to gain much improved information on the evolution of hot gas in the disk and halo of galaxies. The first of the series of investigations that we proposed was a thorough exploration of turbulent mixing layers and cloud evaporation. We proposed to employ a multi-dimensional hydrodynamical code that includes non-equilibrium ionization (NEI), radiative cooling and thermal conduction. These models are to be applied to high velocity clouds in our galactic halo that are seen to have O VI by FUSE (Sembach et ai. 2000) and other clouds for which sufficient constraining observations exist.

Slavin, Jonathan↗