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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Clusters of DNA damage induced by ionizing radiation: formation of short DNA fragments. II. Experimental detection

The basic 30-nm chromatin fiber in the mammalian cell consists of an unknown (possibly helical) arrangement of nucleosomes, with about 1.2 kb of DNA per 10-nm length of fiber. Track-structure considerations suggest that interactions of single delta rays or high-LET particles with the chromatin fiber might result in the formation of multiple lesions spread over a few kilobases of DNA (see the accompanying paper: W.R. Holley and A. Chatterjee, Radiat. Res. 145, 188-199, 1996). In particular, multiple DNA double-strand breaks and single-strand breaks may form. To test this experimentally, primary human fibroblasts were labeled with [3H]thymidine and exposed at 0 degrees C to X rays or accelerated nitrogen or iron ions in the LET range of 97-440 keV/microns. DNA was isolated inside agarose plugs and subjected to agarose gel electrophoresis under conditions that allowed good separation of 0.1-2 kb size DNA. The bulk of DNA remained in the well or migrated only a small distance into the gel. It was found that DNA fragments in the expected size range were formed linearly with dose with an efficiency that increased with LET. A comparison of the yield of such fragments with the yield of total DNA double-strand breaks suggests that for the high-LET ions a substantial proportion (20-90%) of DNA double-strand breaks are accompanied within 0.1-2 kb by at least one additional DNA double-strand break. It is shown that these results are in good agreement with theoretical calculations based on treating the 30-nm chromatin fiber as the target for ionizing particles. Theoretical considerations also predict that the clusters will contain numerous single-strand breaks and base damages. It is proposed that such clusters be designated "regionally multiply damaged sites." Postirradiation incubation at 37 degrees C resulted in a decline in the number of short DNA fragments, suggesting a repair activity. The biological significance of regionally multiply damaged sites is presently unknown.

Non-NASA Center↗
NASA NTRS1973

Ionic migration and weathering in frozen Antarctic soils

Soils of continental Antarctica are forming in one of the most severe terrestrial environments. Continuously low temperatures and the scarcity of water in the liquid state result in the development of desert-type soils. In an earlier experiment to determine the degree to which radioactive Na(Cl-36) would migrate from a shallow point source in permafrost, movement was observed. To confirm this result, a similar experiment involving (Na-22)Cl was conducted. Significantly less movement of the Na-22 ion was observed. Ionic movement in the unfrozen interfacial films at mineral surfaces in frozen ground is held to be important in chemical weathering in Antarctic soils.

Ugolini, F. C.↗
NASA NTRS2015

Failure Analysis Results and Corrective Actions Implemented for the Extravehicular Mobility Unit 3011 Water in the Helmet Mishap

Water entered the Extravehicular Mobility Unit (EMU) helmet during extravehicular activity (EVA) no. 23 aboard the International Space Station on July 16, 2013, resulting in the termination of the EVA approximately 1 hour after it began. It was estimated that 1.5 liters of water had migrated up the ventilation loop into the helmet, adversely impacting the astronaut's hearing, vision, and verbal communication. Subsequent on-board testing and ground-based test, tear-down, and evaluation of the affected EMU hardware components determined that the proximate cause of the mishap was blockage of all water separator drum holes with a mixture of silica and silicates. The blockages caused a failure of the water separator degassing function, which resulted in EMU cooling water spilling into the ventilation loop, migrating around the circulating fan, and ultimately pushing into the helmet. The root cause of the failure was determined to be ground-processing shortcomings of the Airlock Cooling Loop Recovery (ALCLR) Ion Filter Beds, which led to various levels of contaminants being introduced into the filters before they left the ground. Those contaminants were thereafter introduced into the EMU hardware on-orbit during ALCLR scrubbing operations. This paper summarizes the failure analysis results along with identified process, hardware, and operational corrective actions that were implemented as a result of findings from this investigation.

Steele, John↗
NASA NTRS1989

The ultraviolet variability of HD 45166 (qWR + B8 V) - Evidence for stellar wind radiative instabilities

High-resolution IUE spectroscopy of the low-mass qWR star HD 45166, obtained at several epochs during 1980-1988, reveals a complex pattern of variability in its stellar wind emission lines, P Cygni profiles, and highly ionized photospheric absorption spectrum. The most intensive observations, obtained during a 36 hr continuous run in February 1988, show the presence of discrete absorption components (DACs) in the C IV 1550 resonance doublet. These DACs can blend to give the appearance of a well-developed P Cygni absorption profile seen at some other times, roughly doubling the column density of the ground state C(3+) ions in the wind. In the 1988 spectra, two principal features are seen, at about -950 km/s and -750 km/s, with column densities of about 14.0 and 14.7 dex/sq cm, respectively. Both features migrate in velocity with accelerations of about 140 cm/sq sec, implying a recurrence time scale of about 1.6 days and a lifetime of about 3 days for the DACs. A striking characteristic of the acceleration is its slowness. The pattern of DAC variability in HD 45166 is similar to that found for O-type stars and provides further evidence that the DACs are not mass-conserving features but rather that a given feature is formed by different material at different times. It is concluded that the C IV DAC variability observed in HD 45166 results from structural changes in the wind arising from radiative instabilities.

Willis, Allan J.↗
NASA NTRS2000

Growth and Characterization of III-V Semiconductors for Device Applications

The research goal was to achieve a fundamental understanding of the physical processes occurring at the surfaces and interfaces of epitaxially grown InGaAs/GaAs (100) heterostructures. This will facilitate the development of quantum well devices for infrared optical applications and provide quantitative descriptions of key phenomena which impact their performance. Devices impacted include high-speed laser diodes and modulators for fiber optic communications at 1.55 micron wavelengths and intersub-band lasers for longer infrared wavelengths. The phenomenon of interest studied was the migration of indium in InGaAs structures. This work centered on the molecular beam epitaxy reactor and characterization apparatus donated to CAU by AT&T Bell Laboratories. The material characterization tool employed was secondary ion mass spectrometry. The training of graduate and undergraduate students was an integral part of this program. The graduate students received a thorough exposure to state-of-the-art techniques and equipment for semiconductor materials analysis as part of the Master''s degree requirement in physics. The undergraduates were exposed to a minority scientist who has an excellent track record in this area. They also had the opportunity to explore surface physics as a career option. The results of the scientific work was published in a refereed journal and several talks were presented professional conferences and academic seminars.

Williams, Michael D.↗
NASA NTRS1981

Determination of water-soluble ions in soils from the dry valleys of Antarctica

The soil chemistry of the dry valleys of Antarctica was studied. These valleys furnish a terrestrial analog for the surface of Mars. The abundance of the water-soluble ions magnesium, calcium, potassium, sodium chloride, and nitrate in soil samples was determined. All samples examined contained water-soluble salts reflecting the aridity of the area. Movement of salts to low-lying areas was verified. Upward ionic migration was evident in all core samples. Of all cations observed, sodium showed the greatest degree of migration.

Bustin, R.↗
NASA NTRS1986

Xenon-Ion Drilling of Tungsten Films

High-velocity xenon ions used to drill holes of controlled size and distribution through tungsten layer that sheaths surface of controlled-porosity dispenser cathode of traveling wave-tube electron emitter. Controlled-porosity dispenser cathode employs barium/calcium/ aluminum oxide mixture that migrates through pores in cathode surface, thus coating it and reducing its work function. Rapid, precise drilling technique applied to films of other metals and used in other applications where micron-scale holes required. Method requires only few hours, as opposed to tens of hours by prior methods.

Garner, C. E.↗
NASA NTRS2011

Polymeric Materials With Additives for Durability and Radiation Shielding in Space

Polymeric materials are attractive for use in space structures because of their light weight and high strength In addition, polymers are made of elements with low atomic numbers (Z), primarily carbon (C), hydrogen (H), oxygen (0), and nitrogen (N) which provide the best shielding from galactic cosmic rays (GCR) (ref. 1). Galactic cosmic rays are composed primarily of nuclei (i.e., fully ionized atoms) plus a contribution of about 2% from electrons and positrons. There is a small but significant component of GCR particles with high charge (Z > 10) and high energy (E >100 GeV) (ref. 2). These so-called HZE particles comprise only 1 to 2% of the cosmic ray fluence but they interact with very high specific ionization and contribute 50% of the long- term dose to humans. The best shield for this radiation would be liquid hydrogen, which is not feasible. For this reason, hydrogen-containing polymers make the most effective practical shields. Moreover, neutrons are formed in the interactions of GCR particles with materials. Neutrons can only lose energy by collisions or reactions with a nucleus since they are uncharged. This is a process that is much less probable than the Coulombic interactions of charged particles. Thus, neutrons migrate far from the site of the reaction in which they were formed. This increases the probability of neutrons reaching humans or electronic equipment. Fast neutrons (> 1 MeV) can interact with silicon chips in electronic equipment resulting in the production of recoil ions which can cause single event upsets (SEU) in sensitive components (ref. 3). Neutrons lose energy most effectively by elastic collisions with light atoms, particularly hydrogen atoms. Therefore, hydrogen-containing polymers are not only effective in interacting with GCR particles; they are also effective in reducing the energy of the neutrons formed in the interactions.

Kiefer, Richard↗
NASA NTRS2017

Iodine Beam Dump Design and Fabrication

During the testing of electric thrusters, high-energy ions impacting the walls of a vacuum chamber can cause corrosion and/or sputtering of the wall materials, which can damage the chamber walls. The sputtering can also introduce the constituent materials of the chamber walls into an experiment, with those materials potentially migrating back to the test article and coating it with contaminants over time. The typical method employed in this situation is to install a beam dump fabricated from materials that have a lower sputter yield, thus reducing the amount of foreign material that could migrate towards the test article or deposit on anything else present in the vacuum facility.

Polzin, K. A.↗
NASA NTRS2002

Enlargement of Step-Free SiC Surfaces by Homoepitaxial Web-Growth of Thin SiC Cantilevers

Lateral homoepitaxial growth of thin cantilevers emanating from mesa patterns that were reactive ion etched into on-axis commercial SiC substrates prior to growth is reported. The thin cantilevers form after pure stepflow growth removes almost all atomic steps from the top surface of a mesa, after which additional adatoms collected by the large step-free surface migrate to the mesa sidewall where they rapidly incorporate into the crystal near the top of the mesa sidewall. The lateral propagation of the step-free cantilevered surface is significantly affected by pregrowth mesa shape and orientation, with the highest lateral expansion rates observed at the inside concave comers of V-shaped pregrowth mesas with arms lengthwise oriented along the {1100} direction. Complete spanning of the interiors of V's and other mesa shapes with concave comers by webbed cantilevers was accomplished. Optical microscopy, synchrotron white beam x-ray topography and atomic force microscopy analysis of webbed regions formed over a micropipe and closed-core screw dislocations show that c-axis propagation of these defects is terminated by the webbing. Despite the nonoptimized process employed in this initial study, webbed surfaces as large as 1.4 x 10(exp -3) square centimeters, more than four times the pregrowth mesa area, were grown. However, the largest webbed surfaces were not completely free of bilayer steps, due to unintentional growth of 3C-SiC that occurred in the nonoptimized process. Further process optimization should enable larger step-free webs to be realized.

Neudeck, Philip G.↗
NASA NTRS1981

Ohmic contacts to GaAs for high-temperature device applications

Ohmic contacts to n-type GaAs were developed for high temperature device applications up to 300 C. Refractory metallizations were used with epitaxial Ge layers to form the contacts: TiW/Ge/GaAs, Ta/Ge/GaAs, Mo/Ge/GaAs, and Ni/Ge/GaAs. Contacts with high dose Si or Se ion implantation of the Ge/GaAs interface were also investigated. The contacts were fabricated on epitaxial GaAs layer grown on N+ or semi-insulating GaAs substrates. Ohmic contact was formed by both thermal annealing (at temperatures up to 700 C) and laser annealing (pulsed Ruby). Examination of the Ge/GaAs interface revealed Ge migration into GaAs to form an N+ doping layer. The specific contact resistances of specimens annealed by both methods are given.

Anderson, W. T., Jr.↗
NASA NTRS2010

Distribution of Chromosome Breakpoints in Human Epithelial Cells Exposed to Low- and High-LET Radiation

Low-and high-LET radiations produced distinct breakpoint distributions. The difference of the breakpoint distributions between low-and high-LET only appeared in break ends involved in interchromosome exchanges. The breakpoint distributions for break ends participating in intrachromosome exchanges were similar. Gene-rich regions do not necessarily have more chromosome breaks. High-LET appeared to produce long live (data not shown) or longer live breaks that can migrate a longer distance before rejoining with other breaks. Domains occupied by different segments of the chromosomes may be responsible for the breakpoint distribution. The dose responses for interchromosomal exchanges were linear in all four exposures. However, the dose response for intrachromosomal exchanges were none linear. Increasing dose of high dose rate exposure (Fe-ions or -rays) increase the fraction of cells with intrachromosome aberrations, whereas increasing dose of low dose rate exposure (neutrons or -rays) does not affect the fraction of cells with intrachromosome aberrations.

Hada, Megumi↗
NASA NTRS2014

Lithium-Based High Energy Density Flow Batteries

Systems and methods in accordance with embodiments of the invention implement a lithium-based high energy density flow battery. In one embodiment, a lithium-based high energy density flow battery includes a first anodic conductive solution that includes a lithium polyaromatic hydrocarbon complex dissolved in a solvent, a second cathodic conductive solution that includes a cathodic complex dissolved in a solvent, a solid lithium ion conductor disposed so as to separate the first solution from the second solution, such that the first conductive solution, the second conductive solution, and the solid lithium ionic conductor define a circuit, where when the circuit is closed, lithium from the lithium polyaromatic hydrocarbon complex in the first conductive solution dissociates from the lithium polyaromatic hydrocarbon complex, migrates through the solid lithium ionic conductor, and associates with the cathodic complex of the second conductive solution, and a current is generated.

Bugga, Ratnakumar V.↗
NASA NTRS1995

Study of Luminescence Characteristics of Trivalent Terbium in Silicate Glass

An important use of silicate glasses doped with terbium oxide (Tb2O3) is their use as fiber optic sensors for high-resolution imaging applications requiring the detection of x-rays (e.g. tomography and radiography). The x-ray radiation is absorbed by the glass, producing electron-hole pairs (excitons). The excitons migrate through the glass matrix and then recombine, emitting characteristic Tb(3+) luminescence in the optical wavelength region. This emission is due to forbidden transitions of 4f electrons and therefore has a long decay time. Long decay time is undesirable when imaging transient events since it results in blurring in time of the images. It has been reported elsewhere that in crystals Tb(3+) ions can act both as luminescence centers and as fluorescence traps. These traps can capture excitons and delay their recombination. This delayed fluorescence is seen as a long lived, secondary component to the luminescence decay curve, or afterglow. Such a secondary decay component to the luminescence decay of Tb(3+) has been observed before in soda glass following pulsed optical excitation. In order to determine the conditions under which afterglow occurs, an understanding of the material's luminescent properties is required.

West, Mike S.↗
NASA NTRS2004

Lunar and Planetary Science XXXV: Dust: Theory and Experiments

The titles in this section include: 1) Experimental Study of the Radiation Pressure Forces on Isolated Micron-size Dust Particles; 2) Migration of Dust Particles and Their Collisions with the Terrestrial Planets; 3) Chemical In-Situ Analysis of Interplanetary and Interstellar Meteoroids; 4) Mass Spectrometer Calibration of Cassini Cosmic Dust Analyzer for Methane Ice via Laser Ablation; 5) Comparative Effects of 10.2 eV Photon and 200 keV Proton Irradiation on Condensed CO; 6) Experimental Studies on Heated and Unheated He-Irradiated Olivine Grains at Moderate He-Ion Fluences: Analogues to Radiation Damage in IDPs; 7) Impact Studies Using a One Stage Light Gas Gun; 8) Condensation Kinetics of Metallic Iron: An Experimental Study.

Source record↗
NASA NTRSDate not supplied

A materials-informatics based study of solid electrolytes and protective coatings for Li batteries

All-solid-state batteries with Li metal anode can address the safety issues surrounding traditional Li-ion batteries as well as the demand for higher energy densities. However, the development of solid electrolytes and protective coatings simultaneously possessing high ionic conductivity and wide electrochemical stability has proven to be a challenge. Here, we present a data-driven approach to explore the Li compound space for promising solid electrolytes and coatings. This is accomplished through the generation of a large database of battery-related materials properties of Li compounds by computing Li+ migration barriers using bond-valence-based pair potentials, and stability windows using density functional theory energies. Using this database, we implement machine learning models that can accurately predict migration barriers and electrochemical stability windows for any new Li compound. Through feature engineering, we ensure that our models are both accurate and interpretable. We perform feature importance analysis on our models to highlight materials properties that can be tuned for future design of coatings/electrolytes. Our database and informatics approach provide a valuable tool for the rapid discovery of new solid-state battery chemistries.

Solid state batteries↗
NASA NTRS1974

The 15 cm diameter ion thruster research

The startup reliability of a 15 cm diameter mercury bombardment ion thruster which employs a pulsed high voltage tickler electrode on the main and neutralizer cathodes is examined. Startup of the thruster is achieved 100% of the time on the main cathode and 98.7% of the time on the neutralizer cathode over a 3640 cycle test. The thruster was started from a 20 C initial condition and operated for an hour at a 600 mA beam current. An energy efficiency of 75% and a propellant utilization efficiency of 77% was achieved over the complete cycle. The effect of a single cusp magnetic field thruster length on its performance is discussed. Guidelines are formulated for the shaping of magnetic field lines in thrusters. A model describing double ion production in mercury discharges is presented. The production route is shown to occur through the single ionic ground state. Photographs of the interior of an operating-hollow cathode are presented. A cathode spot is shown to be present if the cathode is free of low work-function surfaces. The spot is observed if a low work-function oxide coating is applied to the cathode insert. Results show that low work-function oxide coatings tend to migrate during thruster operation.

Wilbur, P. J.↗
NASA NTRS1990

Platinized tin oxide catalysts for CO2 lasers: Effects of pretreatment

Platinized tin oxide surfaces used for low-temperature CO oxidation in CO2 lasers have been characterized before and after reduction in CO at 125 and 250 C using ion scattering spectroscopy (ISS) and X ray photoelectron spectroscopy (XPS). XPS indicates that the Pt is present initially as PtO2. Reduction at 125 C converts the PtO2 to Pt(OH)2 while reduction at 250 C converts the PtO2 to metallic Pt. ISS shows that the Pt in the outermost atomic layer of the catalyst is mostly covered by substrate species during the 250 C reduction. Both the ISS and XPS results are consistent with Pt/Sn alloy formation. The surface dehydration and migration of substrate species over surface Pt and Sn appear to explain why a CO pretreatment at 250 C produces inferior CO oxidation activities compared to a 125 C pretreatment.

Gardner, Steven D.↗