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At least 217 records · Page 12

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NASA NTRS1984

Evaluation of the radar response to land surfaces and volumes: Examination of theoretical models, target statistics, and applications

Four areas of L-band radar remote sensing of terrain were examined: (1) the behavior of the radar backscatter coefficient of distributed surface and volumes as a function of the targets' dielectric and geometric parameters and as a fnction of their physical parameters; (2) the correspondence of the angular behavior of the relative backscatter coefficient as extracted from SIR-B digital imagery and truck mounted L-band scatterometer measurements for about 100 fields; (3) the statistical behavior of SIR-B image density for targets that appear homogeneous on Thematic Mapper (TM) optical imagery and/or color IR photography; and (4) the applicability of SIR-B imagery both alone and in conjunction with TM imagery for the classification and monitoring of land cover and renewable resources.

Ulaby, F. T.↗

NASA NTRS1985

Examination of returned solar-max surfaces for impacting orbital debris and meteoroids

Previous theoretical studies predicted that in certain regions of earth orbit, the man-made earth orbiting debris environment will soon exceed the interplanetary meteoroid environment for sizes smaller than 1 cm. The surfaces returned from the repaired Solar Max Mission (SMM) by STS 41-C on April 12, 1984, offered an excellent opportunity to examine both the debris and meteoroid environments. To date, approximately 0.7 sq. met. of the thermal insulation and 0.05 sq. met of the aluminum louvers have been mapped by optical microscope for crater diameters larger than 40 microns. Craters larger in diameter than about 100 microns found on the initial 75 micron thick Kapton first sheet on the MEB (Main Electronics Box) blanket are actually holes and constitute perforations through that blanket. The following populations have been found to date in impact sites on these blankets: (1) meteoritic material; (2) thermal paint particles; (3) aluminum droplets; and (4) waste particles.

Kessler, D. J.↗

NASA NTRS1984

A surface-analytical examination of stringer particles in aluminum-lithium-copper alloys

A surface analytical examination of powder metallurgy processed Al-Li-Cu alloys was conducted. The oxide stringer particles often found in these alloys are characterized. Particle characterization is important to more fully understand their impact on the stress corrosion and fracture properties of the alloy. The techniques used where SIMS (Secondary Ion Mass Spectroscopy) and SAM (Scanning Auger Microscopy). The results indicate that the oxide stringer particles contain both Al and LI with relatively high Li content and the Li compounds may be associated with the stringer particles, thereby locally depleting the adjacent matrix of Li solute.

Larson, L. A.↗

NASA NTRS1985

Examination of nonadiabatic effects during an electron beam experiment in the ionosphere

Prompt and delayed echo fluxes and superacceleration of electrons were observed during the sounding rocket flight Several Coordinated Experiments using an electron accelerator. Magnetospheric electric fields parallel to the magnetic field were investigated. The degree of nonadiabatic behavior of the injected electron beam and the return flux was examined. It is shown that the region of strong beam-plasma interaction is limited to 300 km in length along the magnetic field but that backscatter or energetic electrons could occur from much larger distances. By appraising the difference in transit times of 1.9 and 3.9 keV electrons it is established that a continuous backscatter model operating out to several thousand kilometres is not consistent with the observations.

Wilhelm, K.↗

NASA NTRS1986

Re-examination of cumulative fatigue damage analysis: An engineering perspective

A method which has evolved in our laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomena can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading - especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

Manson, S. S.↗

NASA NTRS1986

Transmission electron microscopic examination of phosphoric acid fuel cell components

Transmission electron microscopy (TEM) was used to physically characterize tested and untested phosphoric acid fuel cell (PAFC) components. Those examined included carbon-supported platinum catalysts, carbon backing paper, and Teflon-bonded catalyst layers at various stages of fabrication and after testing in pressurized PAFC's. Applicability of electron diffraction and electron energy loss spectroscopy for identifying the various phases was explored. The discussion focuses on the morphology and size distribution of platinum, the morphology and structural aspects of Teflon in catalyst layers, and the structural evidence of carbon corrosion. Reference is made to other physical characterization techniques where appropriate. A qualitative model of the catalyst layer that emerged from the TEM studies is presented.

Pebler, A.↗

NASA NTRS1986

Lithologic discrimination of volcanic and sedimentary rocks by spectral examination of Landsat TM data from the Puma, Central Andes Mountains

The Central Andes are widely used as a modern example of noncollisional mountain-building processes. The Puna is a high plateau in the Chilean and Argentine Central Andes extending southward from the altiplano of Bolivia and Peru. Young tectonic and volcanic features are well exposed on the surface of the arid Puna, making them prime targets for the application of high-resolution space imagery such as Shuttle Imaging Radar B and Landsat Thematic Mapper (TM). Two TM scene quadrants from this area are analyzed using interactive color image processing, examination, and automated classification algorithms. The large volumes of these high-resolution datasets require significantly different techniques than have been used previously for the interpretation of Landsat MSS data. Preliminary results include the determination of the radiance spectra of several volcanic and sedimentary rock units and the use of the spectra for automated classification. Structural interpretations have revealed several previously unknown folds in late Tertiary strata, and key zones have been targeted to be investigated in the field. The synoptic view of space imagery is already filling a critical gap between low-resolution geophysical data and traditional geologic field mapping in the reconnaissance study of poorly mapped mountain frontiers such as the Puna.

Fielding, E. J.↗

NASA NTRS1986

Re-examination of cumulative fatigue damage analysis - An engineering perspective

A method which has evolved in the laboratories for the past 20 yr is re-examined with the intent of improving its accuracy and simplicity of application to engineering problems. Several modifications are introduced both to the analytical formulation of the Damage Curve Approach, and to the procedure for modifying this approach to achieve a Double Linear Damage Rule formulation which immensely simplifies the calculation. Improvements are also introduced in the treatment of mean stress for determining fatigue life of the individual events that enter into a complex loading history. While the procedure is completely consistent with the results of numerous two level tests that have been conducted on many materials, it is still necessary to verify applicability to complex loading histories. Caution is expressed that certain phenomenon can also influence the applicability - for example, unusual deformation and fracture modes inherent in complex loading especially if stresses are multiaxial. Residual stresses at crack tips, and metallurgical factors are also important in creating departures from the cumulative damage theories; examples of departures are provided.

Manson, S. S.↗

NASA NTRS1986

An examination of vertical circulations associated with heavy snow events along the East Coast

Observational data are presented to show how a particular orientation of upper-level jet streaks (ULJS) associated with a diffluent trough near the East Coast of the U.S. can lead to heavy snowfalls. Surface fronts, precipitation and isobar maps, vertical motion vectors, and geostrophic wind streamlines preceding and during snowstorms on February 11, 1983, February 19, 1979, January 20, 1978, and January 13, 1964 are examined. The interaction of a direct vertical ageostrophic circulation within the confluent entrance of a ULJS over the northeastern U.S. or southeastern Canada and an indirect circulation within the exit region of a ULJS accompanying a trough nearing the East Coast are demonstrated to be conducive to heavy snowfall on the East Coast.

Kocin, Paul J.↗

NASA NTRS1986

Workload - An examination of the concept

The relations between task difficulty and workload and workload and performance are examined. The architecture and limitations of the central processor are discussed. Various procedures for measuring workload are described and evaluated. Consideration is given to normative and descriptive approaches; subjective, performance, and arousal measures; performance operating characteristics; and psychophysiological measures of workload.

Gopher, Daniel↗

NASA NTRS1987

Examination of the physical processes associated with the keyhole region of variable polarity plasma arc welds in aluminum alloy 2219

The morphology and properties of the Variable Polarity Plasma Arc (VPPA) weld composite zone are intimately related to the physical processes associated with the keyhole. This study examined the effects of oxide, halide, and sulfate additions to the weld plate on the keyhole and the weld pool. Changes in both the arc plasma character and the bead morphology were correlated to the chemical environment of the weld. Pool behavior was observed by adding flow markers to actual VPPA welds. A low temperature analog to the welding process was developed. The results of the study indicate that oxygen, even at low partial pressures, can disrupt the stable keyhole and weld pool. The results also indicate that the Marangoni surface tension driven flows dominate the weld pool over the range of welding currents studied.

Walsh, Daniel W.↗

NASA NTRS1987

An examination of possible solar wind sources for a sudden brightening of Comet IRAS-Araki-Alcock

Terrestrial and near-earth measurements are examined in order to investigate possible solar wind sources for the sudden global brightenings noted in Comet IRAS-Araki-Alcock. These brightenings are not found to be associated with increases in the solar wind momentum flux, quantity of solar energetic particles, or solar activity, in contradiction to the proposal of Lutz and Wagner (1986). If a radial alignment of the IMF seen at IMP-8 after about 0800 UT was not responsible for the cometary brightening, then it is suggested that the brightening must have been intrinsic to the comet.

Russell, C. T.↗

NASA NTRS1987

Time-locked time-histories - A new way of examining eye-movement data

A problem often encountered when eye-movement measurement is conducted is the choice of 'indices' or 'statistics' available to present such information. The present study reports the use of the Time-Locked Time-History as a technique of value in the examination and presentation of eye-movement data. Plots created using this technique are labeled time-locked time-histories as they illustrate subject eye lookpoint during a period of time before and after a certain time-locking event. Events that occur with some degree of repetition, such as the onset or termination of control activities, warning signals, or changes in indicator positions may be utilized as time-locking events. The present study reports the use of this technique in an eye-movement study using a secondary task in which the subject must discriminate specific types of information in the display.

Comstock, J. Raymond, Jr.↗

NASA NTRS1988

Examination of Martian sedimentary rocks to understand possible paleo-ocean and its age

It is well known that the terrestrial marine sediments have large cerium anomaly on their chondrite-normalized REE pattern. Siliceous shale and calcaleous sediments have negative Ce-anomaly. Ferromanganese nodule have positive or negative Ce-anomaly. The Ce-anomaly is considered to be a result of tetravalent state of cerium rather than common trivalent. Ferromanganese nodule which formed under reducing condition has negative Ce-anomaly. Then, combined study of Ce-anomaly with Ce isotopes is expected to play an important role in geochemistry. La-138 decays to Ce-138 and Ba-138 with a total half life of about 1 x 10 to the 11th years. Cerium anomalies (positive or negative) are expected in Martian paleo-ocean and in sediments as observed in the terrestrial environment. A list of things to be examined is given.

Tanaka, T.↗

NASA NTRS1989

Re-examination of radiofrequency mass spectrometers: Center Director's Discretionary Fund

The three-stage, two-cycle, Bennett mass spectrometers in use in space and ground experiments today are of the same physical configuration as developed by Bennett in 1950. Sine-wave radiofrequency (RF) is also still used. The literature indicates that the electronics and physical manufacturing capabilities of 1950 technology may have limited the use of other improvements at that time. Therefore, a study, experimental and analytical, was undertaken to examine previously rejected RF approaches as well as new ones. The results of this study indicate there are other approaches which use fewer grids and square wave or a combination of square-wave and sine-wave RF. In regard to suppression of harmonics, none performed better than the three-stage, two-cycle, Bennett mass spectrometer. Use of square-wave RF in the Bennett approach can provide a slightly more compact configuration but no increase in throughput.

Carruth, M. R., Jr.↗

NASA NTRS1989

Examination of stratospheric ozone photochemistry in light of recent data

The consistency of stratospheric ozone photochemistry is examined using data from the Atmospheric Trace Molecule Spectroscopy (ATMOS) and LIMS experiments. The ATMOS experiment measured vertical profiles of important trace constituents and temperature in the stratosphere during 1985. These observations have been used to constrain the levels of odd nitrogen and odd chlorine in a photochemical model. This model yields O3 mixing ratios that are in good agreement with the observations. The deviation in ozone is less than 20 percent except near 52 km. The updated model has also been used in conjunction with the LIMS data to simulate the stratospheric photochemistry corresponding to the 1979 time period.

Natarajan, Murali↗

NASA NTRS1989

Water vapor and methane in the upper stratosphere - An examination of some of the Nimbus 7 measurements

The zonal mean volume mixing ratios of water vapor and methane from January to May, 1979, derived from the Nimbus-7 limb IR monitor of the stratosphere and from stratosphere and mesosphere sounder experiments are investigated. The water vapor mixing ratio of air that enters the stratosphere from the troposphere and the yield of water vapor from photochemical oxidation of methane in the stratosphere are examined. The water vapor yield averaged between 1.5 and 2.0, although variability with time and level was relatively large. It is suggested that water vapor yield increases with height in the 16- to 3-mbar range. The average water vapor mixing ratio fo air entering the stratosphere during the study period was about 3.25 X 10 to the -6th.

Hansen, Anthony R.↗

NASA NTRS1989

Energetics examination of winter blocking simulations in the Northern Hemisphere

Four numerical simulations of the global atmosphere for January 1979 are analyzed to study the formation of blocking in terms of Northern Hemisphere energetics. The Goddard Laboratory for Atmospheres (GLA) 4 x 5 deg latitude-longitude grid general circulation model (GCM) and 2 x 2.5 deg grid GCM are employed with the GLA and Geophysical Fluid Dynamics Laboratory initial datasets. Among four simulations, the simulations by the high resolution GCM produce realistically strong blockings with compatible spectral energetics as in the observed blockings episodes. The latitude-height cross sections of the energy variables of wavenumber 1 is presented to describe the dipole structure of blockings. Blocking development is also examined in time series of barotropic and baroclinic components of energy and associated conversions.

Kung, Ernest C.↗