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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
NASA NTRS1948

Ditching Tests of Two Models of the Army B-36 Airplane

The ditching characteristics of the Army B-36 airplane were determined by testing 1/20- and 1/30-scale dynamic models in calm water in Langley tank no. 2 and at the outdoor catapult. The scope of the tests consisted of ditching the models at various conditions of simulated damage, landing attitudes, and speeds, with various flap settings using several degrees of restraint of the flap hinges. The ditching behavior was evaluated from recordings of deceleration, length of run, and motions of the models. The results showed that the airplane should be ditched at an attitude of about 9 deg with flaps full down. The probable ditching behavior will be a smooth run with a maximum longitudinal deceleration of 3g to 4g and a landing run of 4 to 5 fuselage lengths. Structural failure of the underside of the fuselage will not seriously affect the behavior of the airplane.

Fisher, Lloyd J.↗
NASA NTRS2011

Solar Wind Strahl Observations and Their Implication to the Core-Halo Formation due to Scattering

A study of the kinetic properties of the strahl electron velocity distribution functions (VDF?s) in the solar wind is presented. This study focuses on the mechanisms that control and regulate the electron VDF?s and the stability of the strahl electrons in the solar wind; mechanisms that are not yet well understood. Various parameters are investigated such as the strahl-electron density, temperature anisotropy, and electron heat-flux. These parameters are used to investigate the stability of the strahl population. The analysis check for whether the strahl electrons are constrained by some instability (e.g., the whistler or KAW instabilities), or are maintained by other types of processes. The electron heat-flux and temperature anisotropy are determined by modeling of the 3D-VDF?s from which the moments properties of the various populations are obtained. The results of this study have profound implication on the current hypothesis about the probable formation of the solar wind halo electrons produced from the scattering of the strahl population. This hypothesis is strengthened by direct observations of the strahl electrons being scattered into the core-halo in an isolated event. The observation implies that the scattering of the strahl is not a continuous process but occurs in bursts in regions where conditions for wave growth providing the scattering are optimum. Sometimes, observations indicate that the strahl component is anisotropic (Tper/Tpal approx. 2). This provides a possible free energy source for the excitation of whistler waves as a possible scattering mechanism, however this condition is not always observed. The study is based on high time resolution data from the Cluster/PEACE electron spectrometer.

Vinas, Adolfo F.↗
NASA NTRS2003

Bayes Error Rate Estimation Using Classifier Ensembles

The Bayes error rate gives a statistical lower bound on the error achievable for a given classification problem and the associated choice of features. By reliably estimating th is rate, one can assess the usefulness of the feature set that is being used for classification. Moreover, by comparing the accuracy achieved by a given classifier with the Bayes rate, one can quantify how effective that classifier is. Classical approaches for estimating or finding bounds for the Bayes error, in general, yield rather weak results for small sample sizes; unless the problem has some simple characteristics, such as Gaussian class-conditional likelihoods. This article shows how the outputs of a classifier ensemble can be used to provide reliable and easily obtainable estimates of the Bayes error with negligible extra computation. Three methods of varying sophistication are described. First, we present a framework that estimates the Bayes error when multiple classifiers, each providing an estimate of the a posteriori class probabilities, a recombined through averaging. Second, we bolster this approach by adding an information theoretic measure of output correlation to the estimate. Finally, we discuss a more general method that just looks at the class labels indicated by ensem ble members and provides error estimates based on the disagreements among classifiers. The methods are illustrated for artificial data, a difficult four-class problem involving underwater acoustic data, and two problems from the Problem benchmarks. For data sets with known Bayes error, the combiner-based methods introduced in this article outperform existing methods. The estimates obtained by the proposed methods also seem quite reliable for the real-life data sets for which the true Bayes rates are unknown.

Tumer, Kagan↗
NASA NTRS2014

Predicting Ground Delay Program at an Airport Based on Meteorological Conditions

In this paper, we present two supervised-learning models, logistic regression and decision tree, to predict occurrence of ground delay program at an airport based on meteorological conditions and scheduled traffic demand. Such predictive capabilities can help the Federal Aviation Administration traffic managers and airline dispatchers to prepare mitigation strategies to reduce the impact of adverse weather. The models are applied to predict ground delay program occurrence at two major U.S. airports: Newark Liberty Intl. and San Francisco Intl. airports. The logistic regression model estimates the probability that a ground delay program will occur during a given hour. Decision tree, on the other hand, classifies an hour as a ground delay program or not based on the input variables. Results indicate that both models perform significantly better than a purely random prediction of ground delay program occurrence at the two airports. The logistic regression model performs better than the decision tree model. The degree to which various input variables impact the probability of ground delay program vary between the two airports. While the enroute convective weather is a dominant factor causing ground delay programs at New York airports, poor visibility and low cloud ceiling caused by marine stratus are major drivers of ground delay programs at San Francisco Intl. airport.

traffic flow management↗
NASA NTRS1972

Thermal evolution of the moon.

The thermal history and current state of the lunar interior are investigated using constraints imposed by recent geological and physical data. Theoretical temperature models are computed taking into account different initial conditions, heat sources, differentiation and simulated convection. To account for the early formation of the lunar highlands, the time duration of magmatism and present-day temperatures estimated from lunar electrical conductivity profiles, it is necessary to restrict initial temperatures and abundances of radioactive elements. Successful models require that the outer half of the moon initially heated to melting temperatures, probably due to rapid accretion. Differentiation of radioactive heat sources toward the lunar surface occurred during the first 1.6 billion years. Temperatures in the outer 500 km are currently low, while the deep interior (radius less than 700 to 1000 km) is warmer than 1000 C, and is of primordial material.

Toksoz, M. N.↗
NASA NTRS1976

Effects of 1- and 2-MeV electrons on photomultiplier tubes

Various types of photomultiplier tubes useful for space applications were irradiated with 1- and 2-MeV electrons at Van Allen radiation belt fluxes of 100,000 to 10 millions electrons/sq cm-sec. The increase in the dark current due to electron irradiation was observed at various bias voltages under worst-case conditions (no shielding). Results were presented in the form of dark current plotted against electron flux. All the tubes tested showed extremely large increases in dark current. Tube types 541A, 6217, 6199, and 6903 exhibited the largest increases under irradiation, whereas type 1P22 was affected the least. All the damage observed was transient. The luminescence produced in the optical window probably accounts for a large part of the dark-current increases, but there were some effects possibly due to direct irradiation of the photocathode and dynode chain.

Beatty, M. E., III↗
NASA NTRS1978

Effect of filtration on rolling-element-bearing life in contaminated lubricant environment

Fatigue tests were conducted on groups of 65 millimeter-bore ball bearings under four levels of filtration with and without a contaminated MIL-L-23699 lubricant. The baseline series used noncontaminated oil with 49 micron absolute filtration. In the remaining tests contaminants of the composition found in aircraft engine filters were injected into the filter's supply line at a constant rate of 125 milligrams per bearing-hour. The test filters had absolute particle removal ratings of 3, 30, 49, and 105 microns (0.45, 10, 30, and 70 microns nominal), respectively. Bearings were tested at 15,000 rpm under 4580 newtons radial load. Bearing life and running tract condition generally improved with finer filtration. The 3 and 30 micron filter bearings in a contaminated lubricant had statistically equivalent lives, approaching those from the baseline tests. The experimental lives of 49 micron bearings were approximately half the baseline bearing's lives. Bearings tested with the 105 micron filter experienced wear failures. The degree of surface distress, weight loss, and probable failure mode were found to be dependent on filtration level, with finer filtration being clearly beneficial.

Loewenthal, S. H.↗
NASA NTRS1979

Reaction rate and products for the reaction O/3P/ + H2CO

A study of reaction kinetics of O + H2CO in a discharge-flow system using mass spectrometric detection of reactants and products is presented. It was performed under both oxygen-atom-rich and formaldehyde-rich conditions over the 296 to 437 K range, showing that the global bimolecular rate constant is in agreement with other studies. This study differs from others in that the reaction products can be observed, and a substantial yield of a primary reaction product was measured with a mass spectral peak at m/e=44. This suggests that the global reaction rate probably consists of combination, as well as of simple abstraction. For the combination, one hypothesis is that triplet dioxymethylene is formed which polymerizes to triplet formic acid; the vibrationally excited triplet formic acid may decompose to form several sets of products, including HCO + OH and HCO2 + H.

Chang, J. S.↗
NASA NTRS1984

Ion cyclotron waves as a possible source of resonant auroral radar echoes

Some auroral radar Doppler data which show the presence of spectra not previously discussed are described. The data were obtained during highly distributed magnetic conditions with a relatively small 50 MHz radar pointed northeast of Ithaca, New York. The data are characterized by strong discrete echoes and display spectral peaks which are even narrower than type 1 and are centered at a considerably smaller Doppler shift. These echoes were present simultaneously with and adjacent in range to the commonly observed auroral spectra, and were probably obtained from a height of about 140 km or higher, well above the center of the auroral electrojet. The results are compared with existing electrojet instability theories, and other plasma instabilities which might be important are discussed. The Doppler shift suggests that the narrow spectra might be caused by ion cyclotron waves generated by field-aligned currents, but the observations cannot be fully explained by any of the theories.

Fejer, B. G.↗
NASA NTRS2005

Comparative Planetary Mineralogy: Valence State Partitioning of Cr, Fe, Ti, and V Among Crystallographic Sites in Olivine, Pyroxene, and Spinel from Planetary Basalts

We have considered the valence-state partitioning of Cr, Fe, Ti, and V over crystallographic sites in olivine, pyroxene, and spinel from planetary basalts. The sites that accommodate these cations are the M2 site (6-8 coordinated) and M1 site (6 coordinated) in pyroxene, the M2 site (6-8 coordinated) and M1 site (6 coordinated) in olivine, and the tetrahedral and octahedral sites in spinel. The samples we studied are basalts from Earth, Moon, and Mars, which have fO2 conditions that range from IW-2 (Moon) to IW+6 (Earth) with Mars somewhere between at IW to IW+2. In this range of fO2 the significant elemental valences are (from low to high fO2) Ti4+, V3+, Fe2+, Cr2+, Cr3+, V3+, V4+, and Fe3+. V2+ and Ti3+ play a minor role in the phases considered for the Moon, and are probably in very low concentrations. V5+ plays a minor role in these phases in terrestrial basalts because it is probably in lower abundance than V4+ and it has an ionic radii that is so small (0.054 nm, 6- coordinated,[1]) that it is almost at the lower limit for octahedral coordination. The role of Cr2+ in the Moon is significant, as Sutton et al. [2] found that lunar olivine contains mostly Cr2+ while coexisting pyroxene contains mostly Cr3+. Hanson one vacancy only accommodates one V4+. Thus more vacancies are required in V4+ substitutions into olivine. In the Moon V3+ is much more abundant than V4+ [7, 8]. Thus in lunar chromite V3+ follows Cr3+, whereas in Earth V4+ (which is much greater in abundance than V3+) follows Ti4+ (eg in ulv spinel). We could go on in this vein for some time but space limitations do not permit us to do so.

Papike, J. J.↗
NASA NTRS2006

Reliability of Radioisotope Stirling Convertor Linear Alternator

Onboard radioisotope power systems being developed and planned for NASA s deep-space missions would require reliable design lifetimes of up to 14 years. Critical components and materials of Stirling convertors have been undergoing extensive testing and evaluation in support of a reliable performance for the specified life span. Of significant importance to the successful development of the Stirling convertor is the design of a lightweight and highly efficient linear alternator. Alternator performance could vary due to small deviations in the permanent magnet properties, operating temperature, and component geometries. Durability prediction and reliability of the alternator may be affected by these deviations from nominal design conditions. Therefore, it is important to evaluate the effect of these uncertainties in predicting the reliability of the linear alternator performance. This paper presents a study in which a reliability-based methodology is used to assess alternator performance. The response surface characterizing the induced open-circuit voltage performance is constructed using 3-D finite element magnetic analysis. Fast probability integration method is used to determine the probability of the desired performance and its sensitivity to the alternator design parameters.

Shah, Ashwin↗
NASA NTRS1971

A proposed criterion for aircraft flight in turbulence

A proposed criterion for aircraft flight in turbulent conditions is presented. Subjects discussed are: (1) the problem of flight safety in turbulence, (2) new criterion for turbulence flight where existing ones seem adequate, and (3) computational problems associated with new criterion. Primary emphasis is placed on catastrophic occurrences in subsonic cruise with the aircraft under automatic control. A Monte Carlo simulation is used in the formulation and evaluation of probabilities of survival of an encounter with turbulence.

Porter, R. F.↗
NASA NTRS1971

Relationship between Fe /+/ ions and equatorial spread F.

Evaluation of observations from the retarding potential analyzer on Ogo 6 near the magnetic equator, demonstrating an intimate relationship between the presence of Fe(+) ions and irregularities in the total ion concentration. The ionospheric irregularities (or structure) are probably another manifestation of equatorial spread F, although this has not yet been verified. Nearly half the nighttime equatorial crossings below 700 km exhibit both Fe(+) and structure, but only 10% of the passes without Fe(+) have structure. Approximately one-third of the passes with Fe(+) are not structured, which indicates that Fe(+) may be a necessary but not sufficient condition for structure formation. The Atlantic region shows an extremely high and detailed correlation between Fe(+) ions and the irregularities.

Hanson, W. B.↗
NASA NTRS1985

Applications of Fuzzy Clustering Techniques to Stratified by Tropopause MSU Temperature Retrievals

The fuzzy partitioned clustering method was applied to predict tropopause height only using microwave information with an eye towards using it on real data under cloudy conditions. In the second stage stratified by tropopause regression temperature retrievals included using only the three or four microwave channels for each 40 mb range. The first step in the experiment is the fuzzy partitioned clustering of the microwave brightness temperatures. This method is a combination of standard hard clustering and discriminant analysis. The fuzzy partitioned clustering uses all the generated probabilities of membership of each pattern vector in any of the given clusters. These probabilities are generated by discriminant analysis to locate the correct cluster. The ultimate goal of standard discriminant analysis is to provide the unique (correct) cluster to which the pattern vector belongs. It was only the maximum of all the generated probabilities. The method uses all the probabilities and weight the regressions generated within each cluster. These regression formulas predict the tropopause height from the microwave brightness temperatures. In the second step the microwave regression temperature retrievals are stratified by tropopause height every 40 mb. The control experiment is defined, the data are stratified by land/ocean, summer/winter, and latitude bands.

Munteanu, M. J.↗
NASA NTRS1985

Influence of meteorological conditions on aerosol vertical distribution and composition off the northeast American coastline

The size distribution and composition of lower tropospheric aerosols were measured off the northeast American coastline under clear air and disturbed meteorological conditions. Under the clear air conditions observed on 5 August 1982, with air flow from west to east, sulfate-rich stratified layers are the dominant feature of aerosol distribution in the lowest 3000 m of the troposphere. The encroachment of a warm frontal system over the study area on 9 August 1982 resulted in dramatic changes in aerosol distribution and composition prior to any precipitation, probably due to increased vertical mixing and dilution of pollutant aerosols. Chloride becomes the dominant water soluble anion in the lower 3000 m, primarily due to a several fold decrease in sulfate. Although these results are limited to only two sets of measurements, the data indicate the variability which can occur in the tropospheric vertical aerosol distributions at remote locations. A knowledge of the structure and stability of these stratified layers is of particular importance to studies of the ocean-troposphere chemistry problem.

Sebacher, D. I.↗
NASA NTRS1986

Evolution and infrared spectra of brown dwarfs

Self-consistent models are constructed for the structure, evolution, and observable properties of degenerately cooling objects, or 'brown dwarfs'. Model atmospheres composed of a range of likely gaseous and particulate opacity sources are calculated in order to provide a boundary condition for interior temperature-pressure profiles and to determine the emergent spectra for such objects. The radius derived from the interior models is combined with the emergent fluxes calculated from the atmosphere model to fit the data of McCarthy, Probst, and Low (1985) and to derive the luminosity and mass of VB 8B. The latter is found to be most probably an 0.05 solar mass object with effective temperature in the 1200-1500 K range and an atmosphere which very likely contains particulate absorbers. Key changes in chemical oxidation state and condensation of major constituents during the evolution of brown dwarfs are presented.

Lunine, Jonathan I.↗
NASA NTRS1988

Sampling the ancient volatile-rich areas of Mars

Viking images clearly show areas with a high density of fluidized craters that also display a significant number of wrinkle ridges. Fluidized crater ejecta morphology may indicate that the target material was rich in volatiles at the time of the impact. Therefore, these areas are of the utmost importance in deciphering both the Martian tectonic evolution and the amount of subsurface water, at times when more favorable conditions for life to evolve did exist on Mars. Although a large number of extensional features are associated with Tharsis and Elysium geologic activity, the planet-wide distribution of ridges suggests that Mars' tectonic history is far more complex than the Tharsis-dominated scenario indicates. Like on the Moon and Mercury, ridges on Mars were formed under compressive stresses, probably as a result of thrust-fault mechanism, although surface expressions and direct causes vary. Martian ridges are most easily seen on smooth plains of volcanic origin, but the majority of the 16,000 mapped and classified compressive features are located in the old terrains, far beyond Tharsis influence.

Chicarro, A. F.↗
NASA NTRS1920

The testing of balloon fabrics

Report describes methods and materials used in waterproofing and fireproofing airplane fabrics using dopes. The determination of the probable life of a balloon fabric in service by experimental means is of great value in choosing the most suitable fabrics for a given purpose and in pointing the way to improvements in compounding and construction. The usefulness of exposure to the weather for this purpose has been amply demonstrated. Various attempts have been made to reproduce by artificial means the conditions promoting deterioration in service, but without marked success. Exposure to the weather remains the most satisfactory method for this purpose, and a consideration of the characteristics of such tests is therefore important. This report presents the results of a typical series of exposure tests made in 1917.

Edwards, Junius David↗