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At least 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Photochemical synthesis of simple organic free radicals on simulated planetary surfaces - An ESR study

Electron spin resonance (ESR) spectroscopy provided evidence for formation of hydroxyl radicals during ultraviolet photolysis (254 nm) at -170 C of H2O adsorbed on silica gel or of silica gel alone. The carboxyl radical was observed when CO or CO2 or a mixture of CO and CO2 adsorbed on silica gel at -170 C was irradiated. The ESR signals of these radicals slowly disappeared when the irradiated samples were warmed to room temperature. However, reirradiation of CO or CO2, or the mixture CO and CO2 on silica gel at room temperature then produced a new species, the carbon dioxide anion radical, which slowly decayed and was identical with that produced by direct photolysis of formic acid adsorbed on silica gel. The primary photochemical process may involve formation of hydrogen and hydroxyl radicals. Subsequent reactions of these radicals with adsorbed CO or CO2 or both yield carboxyl radicals, CO2H, the precursors of formic acid. These results confirm the formation of formic acid under simulated Martian conditions and provide a mechanistic basis for gauging the potential importance of gas-solid photochemistry for chemical evolution on other extraterrestrial bodies, on the primitive earth, and on dust grains in the interstellar medium.

Tseng, S.-S.↗
NASA NTRS2014

Water Transport and the Evolution of CM Parent Bodies

Extraterrestrial water-bearing minerals are of great importance both for understanding the formation and evolution of the solar system and for supporting future human activities in space. Asteroids are the primary source of meteorites, many of which show evidence of an early heating episode and varying degrees of aqueous alteration. The origin and characterization of hydrated minerals (minerals containing H2O or OH) among both the main-belt and near-earth asteroids is important for understanding a wide range of solar system formation and evolutionary processes, as well as for planning for human exploration. Current hypotheses postulate asteroids began as mixtures of water ice and anhydrous silicates. A heating event early in solar system history was then responsible for melting the ice and driving aqueous alteration. The link between asteroids and meteorites is forged by reflectance spectra, which show 3-μm bands indicative of bound OH or H2O on the C-class asteroids, which are believed to be the parent bodies of the carbonaceous chondrites in our collections. The conditions at which aqueous alteration occurred in the parent bodies of carbonaceous chondrites are thought to be well-constrained: at 0-25 C for less than 15 Myr after asteroid formation. In previous models, many scenarios exhibit peak temperatures of the rock and co-existing liquid water in more than 75 percent of the asteroid's volume rising to 150 C and higher, due to the exothermic hydration reactions triggering a thermal runaway effect. However, even in a high porosity, water-saturated asteroid very limited liquid water flow is predicted (distances of 100's nm at most). This contradiction has yet to be resolved. Still, it may be possible for water to become liquid even in the near-surface environment, for a long enough time to drive aqueous alteration before vaporizing or freezing then subliming. Thus, we are using physics- and chemistry-based models that include thermal and fluid transport as well as the effects of relevant chemical reactions, to investigate whether formation of hydrated minerals can occur in the surface and near-surface environments of carbonaceous type asteroids. These models will elucidate how the conditions within the parent body that cause internal aqueous alteration play themselves out at the asteroid's surface. We are using our models to determine whether the heat budget of 20-100-km bodies is sufficient to bring liquid water to the near-surface and cause mineral alteration, or whether additional heat input at the surface (i.e, by impacts) is needed to provide a transient liquid water source for mineral hydration without large- scale liquid water transport.

Coker, R.↗
NASA NTRS2011

ALH84001: The Key to Unlocking Secrets About Mars-15 Years and Counting

From the December 27, 1984 discovery of ALH84001, and its subsequent identification as a sample of Mars in 1993, mystery and debate has surrounded the meteorite. With the realization that the ALH84001 sample was a orthopyroxenite and one of the oldest SNC meteorites (~4.09 Ga) available to study, important and critical information about the Martian hydrosphere and atmosphere along with the early history and evolution of the planet could be obtained by studying the unique carbonate globules (~3.9 Ga) in the sample. The initial work showed the carbonate globules were deposited within fractures and cracks in the host-orthopyroxene by low-temperature aqueous fluids. Ideas that the carbonates were formed at temperatures approaching 800oC were ruled out by later experiments. The 1996 announcement by McKay et al. that ALH84001 contained features which could be interpreted as having a biogenic origin generated considerable excitement and criticism. The NASA Administrator Dan Golden said the 1996 ALH84001 announcement saved NASA s Mars planetary exploration program and injected $6 billion dollars over five years into the scientific research and analysis efforts. All of the original four lines of evidence for possible biogenic features within ALH84001 offered by McKay et al. have withstood the test of time. Criticism has been directed at the interpretation of the 1996 analytical data. Research has expanded to other SNC meteorites. Despite the numerous attacks on the ideas, the debate continues after 15 years. The 2009 paper by Thomas-Keprta et al. on the origins of a suite of magnetites within the ALH84001 has offered strong arguments that some of the magnetites can only be formed by biogenic processes and not from thermal decomposition or shock events which happened to the meteorite. NASA s Astrobiology Institute was formed from the foundation laid by the ALH84001 hypothesis of finding life beyond the Earth. The strong astrobiology outreach programs have expanded because of the work done on the Martian meteorites. Despite the criticism on the biogenic-like features in ALH84001, the meteorite has opened a window into the early history of Mars. Clearly low-temperature fluids have left their signatures within the ALH84001 meteorite and subsequent cratering events on Mars have been recorded on observable features within the meteorite. The 15 years of detailed study on ALH84001 and its unique carbonate globules have clearly shown formational and secondary processes at work on Mars. The evidence for biogenic processes operating on early Mars along with ground water activity within the last 15% of the life of Mars offers clear evidence that another niche for life may be possible within our solar system. Now we need a well-documented Mars sample return mission.

Gibson, Everett K.↗
NASA NTRS2011

ALH84001: The Key to Unlocking Secrets About Mars-15 Years and Counting

From the December 27, 1984 discovery of ALH84001, and its subsequent identification as a sample of Mars in 1993, mystery and debate has surrounded the meteorite [1]. With the realization that the ALH84001 sample was a orthopyroxenite and one of the oldest SNC meteorites (approx.4.09 Ga) [2] available to study, important and critical information about the Martian hydrosphere and atmosphere along with the early history and evolution of the planet could be obtained by studying the unique carbonate globules (approx.3.9 Ga) in the sample [3]. The initial work showed the carbonate globules were deposited within fractures and cracks in the host-orthopyroxene by low-temperature aqueous fluids [4]. Ideas that the carbonates were formed at temperatures [5] approaching 800 C were ruled out by later experiments [6]. The 1996 announcement by McKay et al. [7] that ALH84001 contained features which could be interpreted as having a biogenic origin generated considerable excitement and criticism. The NASA Administrator Dan Golden said the 1996 ALH84001 announcement saved NASAs Mars planetary exploration program and injected $6 billion dollars over five years into the scientific research and analysis efforts [8]. All of the original four lines of evidence for possible biogenic features within ALH84001 offered by McKay et al. have withstood the test of time. Criticism has been directed at the interpretation of the 1996 analytical data. Research has expanded to other SNC meteorites. Despite the numerous attacks on the ideas, the debate continues after 15 years. The 2009 paper by Thomas-Keprta et al. [9] on the origins of a suite of magnetites within the ALH84001 has offered strong arguments that some of the magnetites can only be formed by biogenic processes and not from thermal decomposition or shock events which happened to the meteorite. NASA s Astrobiology Institute was formed from the foundation laid by the ALH84001 hypothesis of finding life beyond the Earth. The strong astrobiology outreach programs have expanded because of the work done on the Martian meteorites. De-spite the criticism on the biogenic-like features in ALH84001, the meteorite has opened a window into the early history of Mars. Clearly low-temperature fluids have left their signatures within the ALH84001 meteorite and subsequent cratering events on Mars have been recorded on observable features within the meteorite. The 15 years of detailed study on ALH84001 and its unique carbonate globules have clearly shown formational and secondary processes at work on Mars. Now we need a well-documented Mars sample return mission.

Gibson, Everett K.↗
NASA NTRS1986

Generic Ada code in the NASA space station command, control and communications environment

The results of efforts to apply powerful Ada constructs to the formatted message handling process are described. The goal of these efforts was to extend the state-of-technology in message handling while at the same time producing production-quality, reusable code. The first effort was initiated in September, 1984 and delivered in April, 1985. That product, the Generic Message Handling Facility, met initial goals, was reused, and is available in the Ada Repository on ARPANET. However, it became apparent during its development that the initial approach to building a message handler template was not optimal. As a result of this initial effort, several alternate approaches were identified, and research is now on-going to identify an improved product. The ultimate goal is to be able to instantly build a message handling system for any message format given a specification of that message format. The problem lies in how to specify the message format, and one that is done, how to use that information to build the message handler. Message handling systems and message types are described. The initial efforts, its results and its shortcomings are detailed. The approach now being taken to build a system which will be significantly easier to implement, and once implemented, easier to use, is described. Finally, conclusions are offered.

Mcdougall, D. P.↗
NASA NTRS1985

The deep structure of lunar basins - Implications for basin formation and modification

Models for the crustal structure in the vicinity of nine impact basins, from an inversion of gravity and topographic data from the lunar nearside are presented. The models display a low-density nonmare crustal layer and a mare basalt layer, both of variable thicknesses. Assuming that topography in mare areas is isostatically compensated before the emplacement of mare basalts and that compensation of mare basalt units may be neglected, a decomposition of the gravity anomaly into contributions from Moho relief and mare fill is permitted. Minimum values for mare basalt thicknesses are obtained but because mare basalts and mantle material are similar in density, the thicknesses of the nonmare crust are estimated. An important constraint is the crustal thickness inferred from the Apollo 12 and 14 landing sites from seismic observations. The crustal thickness model indicates that the crust is thinner beneath each of the major nearside basins than in surrounding areas. New bounds on the volume of material ejected from each basin are derived. The geological implications of structural differences among basins for the processes of basin formation and modification are evaluated as functions of time on the moon.

Bratt, S. R.↗
NASA NTRS1997

Spectral and temporal properties of the black hole candidate systems

Observations of Galactic, and extragalactic black hole candidates show that their spectra can be fitted by the thermal Comptonization spectra in the hard state and two components in the soft state. The first component is a black body shape spectrum and the second component is an extended power law with a spectral index of between 1 and 2. The spectral formation of Comptonized spectra in the presence of thermal and bulk motion is considered. In the soft state, when the disk luminosity is high, the emission region temperature is low. In the limit of low plasma temperature, the theoretical spectrum consists of two components: the soft input photons escaping without significant energy change, and a power law that extends to high energies. The spectral index is in the range between 1 and 2, depending on the mass accretion rate. The extended power law is the result of upscattering of soft disk photons in the bulk flow which takes place in the vicinity of the black hole. In the hard state, the disk luminosity is low, the electron temperature of the emission region is high and the thermal Comptonization is the dominant process in the formation of the resulting spectrum.

Titarchuk, Lev↗
NASA NTRS2008

Tool for Merging Proposals Into DSN Schedules

A Practical Extraction and Reporting Language (Perl) script called merge7da has been developed to facilitate determination, by a project scheduler in NASA's Deep Space Network, of whether a proposal for use of the DSN could create a conflict with the current DSN schedule. Prior to the development of merge7da, there was no way to quickly identify potential schedule conflicts: it was necessary to submit a proposal and wait a day or two for a response from a DSN scheduling facility. By using merge7da to detect and eliminate potential schedule conflicts before submitting a proposal, a project scheduler saves time and gains assurance that the proposal will probably be accepted. merge7da accepts two input files, one of which contains the current DSN schedule and is in a DSN-standard format called '7da'. The other input file contains the proposal and is in another DSN-standard format called 'C1/C2'. merge7da processes the two input files to produce a merged 7da-format output file that represents the DSN schedule as it would be if the proposal were to be adopted. This 7da output file can be loaded into various DSN scheduling software tools now in use.

Khanampornpan, Teerapat↗
NASA NTRSDate not supplied

TPSAS-NF1676L-13393-DND

In the two plus decades since it became evident that polar stratospheric clouds (PSCs) play a major role in the springtime depletion of polar ozone, the detailed composition and morphology of PSCs has been an area of interest. Although our PSC knowledge base is substantial, there is still considerable uncertainty in specific key areas related to their composition and formation. Probably the least well understood of these is the nucleation process responsible for the formation of nitric acid trihydrate (NAT) particles and the circumstances under which NAT formation and growth leads to stratospheric denitrification. CALIOP (Cloud-Aerosol LIdar with Orthogonal Polarization) is an excellent instrument for observing PSCs and has already produced an extensive set of PSC observations with unprecedented spatial and temporal resolution covering five winters. These observations are providing new insight into the key remaining questions regarding PSC composition and formation mechanisms. In this paper, we examine the CALIOP PSC observations in combination with a microphysical model in attempt to better understand the underlying physical mechanisms for NAT nucleation. Of particular interest is the early phase of the 2009-2010 Arctic winter when CALIOP frequently observed extended regions of tenuous NAT clouds, clearly before ice was present in the polar vortex. This provides unprecedented large-scale evidence that ice particles are not the only nuclei on which NAT may form. Microphysical model calculations along backward trajectories from these CALIOP NAT cloud observations are used to investigate possible ice-independent, heterogeneous NAT nucleation mechanisms. These analyses will then be expanded to other winters to assess the overall significance of an ice-independent nucleation mechanism for NAT PSCs.

M C Pitts↗
NASA NTRS2012

Large Impact Basins on Mercury: Global Distribution, Characteristics, and Modification History from MESSENGER Orbital Data

The formation of large impact basins (diameter D greater than or equal to 300 km) was an important process in the early evolution of Mercury and influenced the planet's topography, stratigraphy, and crustal structure. We catalog and characterize this basin population on Mercury from global observations by the MESSENGER spacecraft, and we use the new data to evaluate basins suggested on the basis of the Mariner 10 flybys. Forty-two certain or probable impact basins are recognized a few additional basins that may have been degraded to the point of ambiguity are plausible on the basis of new data but are classified as uncertain. The spatial density of large basins (D greater than or equal to 500 km) on Mercury is lower than that on the Moon. Morphological characteristics of basins on Mercury suggest that on average they are more degraded than lunar basins. These observations are consistent with more efficient modification, degradation, and obliteration of the largest basins on Mercury than on the Moon. This distinction may be a result of differences in the basin formation process (producing fewer rings), greater relaxation of topography after basin formation (subduing relief), and/or higher rates of volcanism during the period of heavy bombardment on Mercury compared to the Moon (burying basin rings and interiors).

Fassett, Caleb I.↗
NASA NTRS1985

Formation and detection of high latitude ionospheric irregularities

Measurements of Total Electron Content (TEC) and airglow variations show that large scale plasma patches appearing in the high-latitude ionsophere have irregular structures evidenced by the satellite phase and amplitude scintillations. Whistler waves, intense quasi-DC electric field, and atmospheric gravity waves can become potential sources of various plamsa instabilities. The role of thermal effects in generating ionospheric irregularities by these sources is discussed. Meter-scale irregularities in the ionospheric E and F regions can be excited parametrically with lower hybrid waves by intense whistler waves. Ohmic dissipation of Pedersen current in the electron gas is able to create ionospheric F region irregularities in plasma blobs or plasma patches (i.e., high ambient plasma density environment) with broad scale lengths ranging from tens of meters to a few kilometers. Through the neutral-charged particle collisions, gravity waves can excite large-scale (less than tens of kilometers) ionospheric irregularities simultaneously with forced ion acoustic modes in the E region. The large-scale ionospheric density fluctuations produced in the E region can extend subsequently alogn the earth's magnetic field to the F region and the topside ionospheric regions. These mechanisms characterized by various thermal effects can contribute additively with other processes to the formation of ionospheric irregularities in the high latitude region.

Lee, M. C.↗
NASA NTRS2011

Effect of Reverse Bias Stress on Leakage Currents and Breakdown Voltages of Solid Tantalum Capacitors

The majority of solid tantalum capacitors are produced by high-temperature sintering of a fine tantalum powder around a tantalum wire followed by electrolytic anodization that forms a thin amorphous Ta2O5 dielectric layer and pyrolysis of manganese nitrite on the oxide to create a conductive manganese dioxide electrode. A contact to tantalum wire is used as anode terminal and to the manganese layer as a cathode terminal of the device. This process results in formation of an asymmetric Ta -- Ta2O5 -- MnO2 capacitor that has different characteristics at forward (positive bias applied to tantalum) and reverse (positive bias applied to manganese cathode) voltages. Reverse bias currents might be several orders of magnitude larger than forward leakage currents so I-V characteristics of tantalum capacitors resemble characteristics of semiconductor rectifiers. Asymmetric I-V characteristics of Ta -- anodic Ta2O5 systems have been observed at different top electrode materials including metals, electrolytes, conductive polymers, and manganese oxide thus indicating that this phenomenon is likely related to the specifics of the Ta -- Ta2O5 interface. There have been multiple attempts to explain rectifying characteristics of capacitors employing anodic tantalum pentoxide dielectrics. A brief review of works related to reverse bias (RB) behavior of tantalum capacitors shows that the mechanism of conduction in Ta -- Ta2O5 systems is still not clear and more testing and analysis is necessary to understand the processes involved. If tantalum capacitors behave just as rectifiers, then the assessment of the safe reverse bias operating conditions would be a relatively simple task. Unfortunately, these parts can degrade with time under reverse bias significantly, and this further complicates analysis of the I-V characteristics and establishing safe operating areas of the parts. On other hand, time dependence of reverse currents might provide additional information for investigation of the processes under reverse bias conditions. In practice, there were instances when, due to unforeseen events, the system operated at conditions when capacitors experience periodically a relatively small reverse bias for some time followed by normal, forward bias conditions. In such a case an assessment should be made on the degree to which these capacitors are degraded by application of low-voltage reverse bias, and whether this degradation can be reversed by normal operating conditions. In this study, reverse currents in different types of tantalum capacitors were monitored at different reverse voltages below 15%VR and temperatures in the range from room to 145 C for up to 150 hours to get better understanding of the degradation process and determine conditions favorable to the unstable mode of operation. The reversibility of RB degradation has been evaluated after operation of the capacitors at forward bias conditions. The effect of reverse bias stress (RBS) on reliability at normal operating conditions was evaluated using highly accelerated life testing at voltages of 1.5VR and 2 VR and by analysis of changes in distributions of breakdown voltages. Possible mechanisms of RB degradation are discussed.

Teverovsky, Alexander A.↗
NASA NTRS1995

Solar wind theory and modelling

The outflow of coronal plasma into interplanetary space is a consequence of the coronal heating process. Therefore the formation of the corona and the acceleration of the solar wind should be treated as a single problem. Traditionally the mass or particle flux emanating from the extended corona has been thought of as being determined by the coronal temperature or scale height and the coronal (base) density. This argument follows from considerations of the momentum balance of the corona-wind system from which one obtains models of a close to hydrostatic corona out to the critical point where the flow becomes supersonic. With this approach to the acceleration of the wind is has been difficult to reconcile the relatively small variation observed in the proton flux at 1 AU with the predicted exponential dependence of the proton flux on the coronal temperature. In this talk we would like to emphasize another approach in which coronal energetics play the primary role. The deposition of energy into the corona through some 'mechanical' energy flux is balanced by the various energy sinks available to the corona and the sum of these processes determine the coronal structure, i.e. its temperature and density. The corona loses energy through heat conduction into the transition region, through radiative losses, and through the gravitational potential energy and kinetic energy put into the solar wind itself. We will show from a series of models of the chromosphere transition region-corona-solar wind system that most of the energy deposited in a magnetically open region will go into the solar wind, with roughly half going into kinetic energy and half into lifting the plasma out of the solar gravity field. The coronal base density will adjust itself in such a way that the heat conductive flux flowing into the transition region is radiated away in the upper chromosphere. The coronal temperature is set by the requirements that most of the deposited energy goes into accelerating the solar wind; the coronal scale height will adjust itself so that the solar wind energy losses conform to the amplitude of the input energy. These processes are modified by the 'mode' of energy deposition, and we will show the effects on coronal structure of changing the parameters describing coronal heating as well as the effects of including a helium fluid in the models. However, the location, scale height and/or form of the energy deposition (i.e. heating or direct acceleration) are not too important for the solar wind, the coronal density and temperature structure will vary with the 'mode' of energy deposition, but the solar wind mass flux depends mainly on the amplitude of the energy flux.

Hansteen, Viggo H.↗
NASA NTRS1977

Formation of integrated optics components by multiphoton photorefractive processes

Phase holograms have been formed in pure outdiffused LiNbO3 waveguides using the photorefractive effect initiated by two-photon absorption. Efficient holograms were recorded with two guided waves, of less than 100 W peak power, and less than 10 microJ optical energy. This technique automatically compensates for wave front perturbations in the guide and allows the formation of various integrated components such as wavelength multiplexers and optical switches.

Verber, C. M.↗
NASA NTRS1999

The Role of Calcium in the Response of Osteoblasts to Mechanical Stimulation

A major biomedical concern in the exploration and development of space is the rapid loss of bone associated with extended periods of spaceflight. Mineral content, bone formation, matrix protein production and total body calcium are all reduced during long-term periods of weightlessness. These effects of weightlessness appears to be due to decreases in the anabolic function of osteoblasts and osteocytes rather than changes in the resorptive activity of osteoclasts. Conversely, subjecting the skeleton to exogenous mechanical loading increases matrix protein synthesis and bone formation rate, a process which also appears mediated through osteogenic cells. Osteoblasts have been shown to respond to a number of types of mechanical stimulation. However recently we have demonstrated that osteoblasts respond to fluid shear, but not physiologic levels of mechanical strain, with increases in expression of the matrix protein, osteopontin. We have also shown similar responses in other markers for the anabolic response in bone. The expression of the early response gene, c-fos, and the inducible-isoform of the prostaglandin synthetic enzyme, cyclooygenase-2 (COX-2), both increase rapidly in response to fluid shear, but not strain. How osteoblasts and osteocytes perceive mechanical stimuli and convert this stimulus into a biochemical event within the cell is still unknown. However, examination of the cellular events following mechanical stimulation indicate that two of the earliest responses are a rapid increase in intracellular calcium ([Ca(2+)](sub i)) and a reorganization of the actin cytoskeleton. The increase in [Ca(2+)](sub i) is dependent on the presence of extracellular Ca(2+), suggesting the activation of membrane Ca(2+) channel. We have previously characterized a mechanosensitive, cation-selective channel (MSCC) in osteoblast-like clonal cells, which we postulate is important in this early response to mechanical loading. Using an antisense oligodeoxynucleotide strategy, we have tentatively identified this channel as an isoform of the alc subunit of the dihydropyridine-sensitive, voltage sensitive Ca(2+) channel (VSCC). However, a major component in this mechanically induced rise in [Ca(2+)](sub i) is the release of Ca(2+) from intracellular stores. The actin cytoskeleton also rapidly responds to fluid shear with an increase in stress fiber formation and a realignment of the cell parallel to the direction of flow. To ascertain whether these two observations are related and how they effect shear-induced gene expression, we examined the role of Ca(2+) channels and intracellular Ca(2+) release on cytoskeletal reorganization and the resultant increases in the expression and production of c-fos and COX-2 in response to fluid shear.

Duncan, R. L.↗
NASA NTRS1999

Airborne Observations of Aerosol Emissions from F-16 Aircraft

We presented results from the SASS Near-Field Interactions Flight (SNIF-III) Experiment which was conducted during May and June 1997 in collaboration with the Vermont and New Jersey Air National Guard Units. The project objectives were to quantify the fraction of fuel sulfur converted to S(VI) species by jet engines and to gain a better understanding of particle formation and growth processes within aircraft wakes. Size and volatility segregated aerosol measurements along with sulfur species measurements were recorded in the exhaust of F-16 aircraft equipped with F-100 engines burning fuels with a range of fuel S concentrations at different altitudes and engine power settings. A total of 10 missions were flown in which F-16 exhaust plumes were sampled by an instrumented T-39 Sabreliner aircraft. On six of the flights, measurements were obtained behind the same two aircraft, one burning standard JP-8 fuel and the other either approximately 28 ppm or 1100 ppm S fuel or an equal mixture of the two (approximately 560 ppm S). A pair of flights was conducted for each fuel mixture, one at 30,000 ft altitude and the other starting at 35,000 ft and climbing to higher altitudes if contrail conditions were not encountered at the initial flight level. In each flight, the F-16s were operated at two power settings, approx. 80% and full military power. Exhaust emissions were sampled behind both aircraft at each flight level, power setting, and fuel S concentration at an initial aircraft separation of 30 m, gradually widening to about 3 km. Analyses of the aerosol data in the cases where fuel S was varied suggest results were consistent with observations from project SUCCESS, i.e., a significant fraction of the fuel S was oxidized to form S(VI) species and volatile particle emission indices (EIs) in comparably aged plumes exhibited a nonlinear dependence upon the fuel S concentration. For the high sulfur fuel, volatile particle EIs in 10-second-old-plumes were 2 to 3 x 10 (exp 17) / kg of fuel burned and exhibited no obvious trend with engine power setting or flight altitude. In contrast, about 8-fold fewer particles were observed in similarly aged plumes from the same aircraft burning fuel with 560 ppm S content and EIs of 1 x 10(exp 15)/ kg of fuel burned were observed in the 28 ppm S fuel case. Moreover, data recorded as a function of plume age indicates that formation and growth of the volatile particles proceeds more slowly as the fuel S level is reduced. For example, ultrafine particle concentrations appear to stabilize within 5 seconds after emission in the 1100 ppm S cases but are still increasing in 20-second old plumes produced from burning the 560 ppm S fuel.

Anderson, B. E.↗
NASA NTRS1984

Simultaneous junction formation

High-risk, high-payoff improvements to a baseline process sequence of simultaneous junction formation of silicon solar cells are discussed. The feasibility of simultaneously forming front and back junctions of solar cells using liquid dopants on dendritic web silicon was studied. Simultaneous diffusion was compared to sequential diffusion. A belt furnace for the diffusion process was tested.

Campbell, R. B.↗
NASA NTRS2002

Method for improving the performance of oxidizable ceramic materials in oxidizing environments

Improved adhesion of thermal barrier coatings to nonmetallic substrates using a dense layer of ceramic on an underlying nonmetallic substrate that includes at least one oxidizable component. The improved adhesion occurs because the application of the dense ceramic layer forms a diffusion barrier for oxygen. This diffusion barrier prevents the oxidizable component of the substrate from decomposing. The present invention applies ceramic by a process that deposits a relatively thick and dense ceramic layer on the underlying substrate. The formation of the dense layer of ceramic avoids the problem of void formation associated with ceramic formation by most prior art thermal decomposition processes. The formation of voids has been associated with premature spalling of thermal barrier layers and other protective layers applied to substrates.

Nagaraj, Bangalore A.↗