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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H-beta in luminosity. We show how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of Ne v emission in particular will distinguish shrouded AGNs from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Voit, G. M.↗
NASA NTRS1990

Lyman alpha radiation in external galaxies

The Ly alpha line of atomic hydrogen is often a luminous component of the radiation emitted by distant galaxies. Except for those galaxies which have a substantial central source of non-stellar ionizing radiation, most of the Ly alpha radiation emitted by galaxies is generated within regions of the interstellar medium which are photoionized by starlight. Conversely, much of the energy radiated by photoionized regions is carried by the Ly alpha line. Only hot, massive stars are capable of ionizing hydrogen in the interstellar medium which surrounds them, and because such stars are necessarily short-lived, Ly alpha emission traces regions of active star formation. Researchers argue that the strength of the Ly alpha emission observed from external galaxies may be used to estimate quantitatively the dust content of the emitting region, while the Ly alpha line profile is sensitive to the presence of shock waves. Interstellar dust particles and shock waves are intimately associated with the process of star formation in two senses. First, both dust particles and shock waves owe their existence to stellar activity; second, they may both serve as agents which facilitate the formation of stars, shocks by triggering gravitational instabilities in the interstellar gas that they compress, and dust by shielding star-forming molecular clouds from the ionizing and dissociative effects of external UV radiation. By using Ly alpha observations as a probe of the dust content in diffuse gas at high redshift, we might hope to learn about the earliest epochs of star formation.

Neufeld, David A.↗
NASA NTRS1993

Infrared fine-structure line diagnostics of shrouded active galactic nuclei

Far-infrared spectroscopy of celestial objects will improve dramatically in the coming decade, allowing astronomers to use fine-structure line emission to probe photoionized regions obscured in the optical band by thick clouds of dust. The ultraluminous far-IR galaxies revealed by IRAS, quasar-like in luminosity but smothered in molecular gas, probably conceal either immense starbursts or luminous active nuclei. In both scenarios, these objects ought to produce copious infrared fine-structure emission with several lines comparable to H(beta) in luminosity. This paper shows how these lines, if detected, can be used to determine the electron densities and far-IR obscurations of shrouded photoionized regions and to constrain the shape and ionization parameter of the ionizing spectra. The presence of (Ne V) emission in particular will distinguish shrouded AGN's from shrouded starbursts. Since all active galaxies photoionize at least some surrounding material, these diagnostics can also be applied to active galaxies in general and will aid in studying how an active nucleus interacts with the interstellar medium of its host galaxy.

Voit, G. M.↗
NASA NTRS1986

Jet activity in the symbiotic variable R Aquarii

Low-resolution ultraviolet spectra of the R Aquarii jet have been obtained with the International Ultraviolet Explorer (IUE). The most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.

Michalitsianos, A. G.↗
NASA NTRS1965

The aurora.

Visible and invisible aurora discussing morphology, occurrence, magnetic activity, absorption, geophysical and energy particle

AURORAL IONIZATION↗
NASA NTRS1983

The line continuum luminosity ratio in AGN: Or on the Baldwin Effect

The luminosity dependence of the equivalent width of CIV in active galaxies, the "Baldwin" effect, is shown to be a consequence of a luminosity dependent ionization parameter. This law also agrees with the lack of a "Baldwin" effect in Ly alpha or other hydrogen lines. A fit to the available data gives a weak indication that the mean covering factor decreases with increasing luminosity, consistent with the inference from X-ray observations. The effects of continuum shape and density on various line ratios of interest are discussed.

Mushotzky, R.↗
NASA NTRS1983

Mode of incorporation of phosphorus in Hg(0.8)Cd(0.2)Te

Selim and Kroeger (1977) have studied the mode of incorporation of phosphorus in CdTe. According to their findings, phosphorus behaves amphoterically in CdTe acting as an acceptor interstitially and on Te lattice sites, and as a triple donor on Cd lattice sites. The present investigation is concerned with the role of phosphorus in Hg(0.8)Cd(0.2)Te, taking into account Hall-effect and mobility measurements on phosphorus-doped crystals quenched from a temperature in the range from 450 to 600 C subsequent to anneals in different partial pressures of Hg. It is found that the behavior of phosphorus in Hg(0.8)Cd(0.2)Te is similar to that established for CdTe, except that all the electrically active phosphorus defect centers in Hg(0.8)Cd(0.2)Te appear to be only singly ionized. At low Hg pressure, phosphorus is incorporated as a single donor occupying Hg lattice sites, and at high Hg pressure, as a single acceptor on interstitial sites and Te lattice sites.

Vydyanath, H. R.↗
NASA NTRS1984

The line continuum luminosity ratio in active galactic nuclei - or, on the 'Baldwin effect'

The luminosity dependence of the equivalent width of CIV in active galaxies, the 'Baldwin' effect, is shown to be a consequence of a luminosity dependent ionization parameter. This law also agrees with the lack of a 'Baldwin' effect in Ly alpha or other hydrogen lines. A fit to the available data gives a weak indication that the mean covering factor decreases with increasing luminosity, consistent with the inference from X-ray observations. The effects of continuum shape and density on various line ratios of interest are discussed. Previously announced in STAR as N83-35975

Mushotzky, R.↗
NASA NTRS1984

Nitriding of titanium and its alloys by N2, NH3 or mixtures of N2 + H2 in a dc arc plasma at low pressures ( or = to torr)

The dc glow discharges in different gas mixtures of Ar + N2, Ar + NH3 or Ar + N2 + H2 result in the surface nitriding of Ti metal and its alloy (Ti6Al4V). Various gas mixtures were used in order to establish the main active species governing the nitriding process, i.e., N, N2, NH, or NH2 as excited or ionized particles. The dc discharge was sampled and analyzed by quadruple mass spectrometry (QPMS) and optical emission spectroscopy (OES), and the nitrided samples were analyzed by scanning electron microscopy (SEM) with an EDAX attachment, microhardness, and Fourier transform infrared reflectance spectrometry (FTIR). It was found that the excited and ionized nitrogen and hydrogen atoms are the main species responsible for the nitriding process in a dc glow discharge.

Avni, R.↗
NASA NTRS1986

Bubbles and braided jets in galaxies with compact radio nuclei

Narrow-band H-alpha CCD images showing ionized gas in organized kiloparsec-scale structures in three galaxies with low-level active nuclei are presented. The edge-on spiral NGC 3079 contains an apparent loop structure which corresponds to previously reported nonthermal radio emission along the minor axis. The optical emission probably results from interaction between the ejected plasma and the ISM in the disk and halo. The S0 galaxy NGC 3998 exhibits an S-shaped structure centered on the nucleus, with no other evidence for spiral structure. In the spiral galaxy NGC 4258, the presence of continuum-free emission-line arms which coincide with the nonthermal radio arms is confirmed. The morphology of the arms suggests the presence of two double-sided jets which braid or wrap around one another and which bifurcate on both sides. It is concluded that the optical and radio emission in NGC 3079 and in NGC 4258 are related, and it is suggested that both are powered by a plasma which flows from the active nucleus and dissipates kinetic energy in the surrounding ISM.

Ford, Holland C.↗
NASA NTRS1987

Geomagnetic activity and local modulations of cosmic rays circa 1 GV

Solar-sector synchronous modulations of the particulate cosmic radiation reaching the earth's atmosphere have been studied using low altitude satellite and surface data. The flux in the broad maximum of the galactic cosmic ray differential spectrum (near GV rigidity) exhibits an intermittent north-south asymmetry (NSA) in mid and high geomagnetic latitudes. During the 1964 and 1965 years of sunspot minimum, this modulation had a negative rigidity dependence and strong correlations with geomagnetic disturbance index (ap) and interplanetary magnetic field direction. Taken together with other features, this ap dependence is consistent with the hypothesis that reconnection of the interplanetary and geomagnetic fields should produce a local NSA independent of much larger scale NSAs associated with cosmic ray gradients in the heliosphere. This finding is also consistent with suggestions that solar activity influence on atmospheric processes may be mediated by the resulting modulations of upper tropospheric ionization.

Ely, J. T. A.↗
NASA NTRS2004

Higher Resolution Observatories of the Accretion Disk in NGC 4261

The physical conditions in the inner parsec of accretion disks believed to orbit the central black holes in active galactic nuclei can be probed by imaging the absorption of background radio emission by ionized gas in the disk. We will present high angular resolution observations of the nearby galaxy NGC 4261 that show evidence for free-free absorption by a thin, nearly edge-on disk at several frequencies. Because free-free absorption is much larger at lower frequencies, the longest possible baselines are needed to provide adequate angular resolution; observing at higher frequencies to improve resolution does not help. We used trans-Pacific baselines and the HALCA satellite to obtain higher resolution than was previously available at 1.6 and 4.9 GHz. The angular width and the depth of the absorption appears to increase with decreasing frequency, as expected.

Jones, D. L.↗
NASA NTRS2011

Ultra-Low-Dropout Linear Regulator

A radiation-tolerant, ultra-low-dropout linear regulator can operate between -150 and 150 C. Prototype components were demonstrated to be performing well after a total ionizing dose of 1 Mrad (Si). Unlike existing components, the linear regulator developed during this activity is unconditionally stable over all operating regimes without the need for an external compensation capacitor. The absence of an external capacitor reduces overall system mass/volume, increases reliability, and lowers cost. Linear regulators generate a precisely controlled voltage for electronic circuits regardless of fluctuations in the load current that the circuit draws from the regulator.

Thornton, Trevor↗
NASA NTRS2018

Optically Inaccessible Flow Visualization using Positron Emission Tomography

Flow visualization is a powerful tool for characterizing fluid dynamics within engineering systems that utilize fluid working media. Recent advances in Positron Emission Tomography (PET) have enhanced its ability to extend beyond the medical field, and offer an alternate vantage point in visualizing optically inaccessible fluid distributions and flow fields within the aerospace field. In light of this prospect an investigation has ensued to parametrically bound the flows that can be sufficiently resolved using current PET technology. Results from an initial series of experiments and analyses performed at the Positron Imaging Centre (PIC) located at the University of Birmingham, UK, will be presented. Discussion will also cover preliminary, on-going, activities associated with assessing the utility of PET technology in zero-gravity propellant gauging, ionization efficiency characterization in electric propulsion devices, and broader industrial applications.

PET↗
NASA NTRSDate not supplied

Medical countermeasures for extraterrestrial environments: Current status and future prospects with focus on acute injuries

In all space exploratory activities involving humans there are associated risks to health and well-being. Exposure to ionizing radiation represents one of the more serious health concerns. Although medical issues can arise shortly following the rare acute exposures, the more likely radiation-associated injuries will manifest in a delayed fashion following sub-acute exposures or protracted exposures to relatively low radiation doses. The radiological conditions that present these health risks during extraterrestrial space travel are presented in this article, along with current physical and medical countermeasures for such exposure contingencies. The aim of this article is to discuss radiation medical countermeasures that may be considered for future space exploration and travel. Biomedical advances have occurred toward the control and minimization of acute, sub-acute, and fractionated radiation exposure injuries, whether they stem from intentional application of radio-therapeutic procedures or unintentional, accidental terrestrial-based exposures. Those advances, based largely on novel bioengineering, genetic, and combinatorial pharmaceutical strategies, are briefly reviewed here, along with the promising prospects of additional, new and improved medical countering systems/agents that will be forthcoming with additional research and development efforts.

Acute/chronic radiation injuries↗
NASA NTRS2016

Superoxide Dismutase Protects Osteoprogenitors from Irradiation with Low-LET but Not High-LET Species

Ionizing radiation-induced bone loss appears to be a two-stage process: first an early increase in pro-resorption cytokines and increased bone resorption by osteoclasts, followed by a decrease in bone formation by osteoblasts. This results in a net loss of mass in mineralized bone tissue. The molecular mechanisms underlying the imbalance in bone remodeling caused by exposure to radiation are not fully understood. We hypothesized that the radiation-induced rise in reactive oxygen species (ROS) damages osteoblast progenitors, leading to a decrease in number and activity of differentiated progeny. We have shown that a diet high in antioxidant capacity prevents radiation-induced bone loss in adult mice (Schreurs et al. 2016) by reducing the early increase in pro-resotption cytokines. Here, we investigated the damaging effects of radiation exposure on cells in the osteoblast lineage, testing if addition of the exogenous antioxidant enzyme, superoxide dismutase (SOD) can mitigate radiation damage. Osteoprogenitors were grown in vitro from the marrow of 16wk old, male C57Bl/6 mice. Cells were irradiated 3 days after plating (day 0) with either gamma (Cs-137, 0.1-5Gy) or iron (Fe-56, 600 MeV/n, 0.5-2Gy), and then grown until day 10. SOD or vehicle was added 2 hours before irradiation (SOD at 200U/ml), twice a day and up to day 5, for a total of 2 days treatment. Cell behavior was assessed by: (a) colony number (counted on day 7), (b) DNA content (surrogate for cell number) to assess cell growth (percent change between day 3 and day 10) and (c) alkaline phosphatase activity (osteoblast differentiation marker). Results show that SOD protected cells from the adverse effects of low-LET ionizing radiation, but not high-LET radiation. These novel results provide an interesting platform to explore further diverse effects and damages caused by low-LET and high-LET, pointing toward different mechanisms and possible intervention strategies for radiation-induced bone loss.

superoxide dismutase↗
NASA NTRS1997

Multifrequency Studies

The present report concerns the following projects 'Multifrequency observations of the BL Lacertae object MK 421"; "EUVE and multifrequency observations of the quasars 3C 273 and 3C 279"; "EUVE observations of the symbiotic star RAquarii"; and "Morphology of the local HI void and ionization of He in the local ISM". The common theme of the above projects is UV observations and analysis of a wide range of astrophysical classes or objects, from the diffuse interstellar medium, to symbiotic stars (R Aqr), to active galactic nuclei (AGNs). Understanding the local (primarily neutral hydrogen or HI) interstellar medium is of great importance to detecting nearby EUV sources. Specifically, the ionization of helium is strongly influencing the extinction in the extreme ultraviolet (EUV) and the optical depth can vary almost by an order of magnitude depending on the degree of ionization of various species including neutral helium Vel ) and singly ionized helium (Hell). The local interstellar medium (ISM) contains a giant void. Understanding the local ISM and the extent of the HI void engulfing the Sun is crucial to our understanding of the EUV emission from nearby strongly EUV-emitting stars like R Aqr, as well as subtracting local absorption effects from absorption effects in distant sources themselves such as quasars, BL Lacertae objects and AGNs in general. A compilation of known properties of the local ISM with appropriate references has been performed. R Aqr is a symbiotic stellar system comprised of a mass-losing approx.1 - 2 solar mass Mira- like long period variable with a 387 day period and a approx. solar mass,) hot companion/accretion disk that is believed to give rise to the symmetrical jet seen at UV, optical radio wavelengths. Recent observations of R Aqr have been conducted at continuum wavelengths with the Very Large Array (VLA) at 7 mm that have resolved the stellar components in RAqr and a geometrical distance of approx. 200pc has been obtained, confirming that R Aqr is the nearest symbiotic star system to the Sun. The status of the local ISM is, therefore, of great importance in attempting to understand the UV properties of the hot companion in R Aqr and its prominent jet. Here a multifrequency approach is required from both ground observations (e.g. with the VLA) as well as from space-borne observations (with the International Ultraviolet Explorer-IUE; and the Hubble Space Telescope-HST). The R Aqr jet has been observed with the VLA B-configuration at two epochs separated by approx. 13.2 yr. Comparison of the resulting 6 cm continuum images show that the radio jet has undergone a lateral counterclockwise rotation of approx. 6 deg - 12 deg on the plane of the sky. Comparison of the most recent radio image with a nearly contemporaneous HSTIFOC ultraviolet image at approx 2330 A suggests that the UV emission lies along the leading edge of the rotating radio jet.

Kafatos, Menas↗
NASA NTRS1972

Effects of interplanetary magnetic field azimuth on auroral zone and polar cap magnetic activity

During relatively quiet times in the period 1964-1968, AE is found to be greater when the interplanetary magnetic field (b sub IMF) is directed toward the sun in Jan., Feb., and Apr., and when B sub IMF is directed away from the sun in Oct. to Dec. Using Murmansk hourly H values and the AE components, AU and AL, it is shown that this sector dependence is present only in the negative H deviations. This observation supports the idea that negative bay magnitudes are determined chiefly by particle-produced ionization, while positive bay magnitudes are rather insensitive to increases in particle precipitation. The ratio of DP2-type magnetic activity in the southern polar cap to that in the northern polar cap is found to be greater by a factor of about 1.75 for B sub IMF toward the sun.

Burch, J. L.↗