Results for “source zone” — Page 24

NASA NTRS1987

Transform fault earthquakes in the North Atlantic: Source mechanisms and depth of faulting

The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

Bergman, Eric A.↗

NASA NTRS1988

Transform fault earthquakes in the North Atlantic - Source mechanisms and depth of faulting

The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

Bergman, Eric A.↗

NASA NTRS1992

Analysis and modification of a single-mesh gear fatigue rig for use in diagnostic studies

A single-mesh gear fatigue rig was analyzed and modified for use in gear mesh diagnostic research. The fatigue rig allowed unwanted vibration to mask the test-gear vibration signal, making it difficult to perform diagnostic studies. Several possible sources and factors contributing to the unwanted components of the vibration signal were investigated. Sensor mounting location was found to have a major effect on the content of the vibration signal. In the presence of unwanted vibration sources, modal amplification made unwanted components strong. A sensor location was found that provided a flatter frequency response. This resulted in a more useful vibration signal. A major network was performed on the fatigue rig to reduce the influence of the most probable sources of the noise in the vibration signal. The slave gears were machined to reduce weight and increase tooth loading. The housing and the shafts were modified to reduce imbalance, looseness, and misalignment in the rotating components. These changes resulted in an improved vibration signal, with the test-gear mesh frequency now the dominant component in the signal. Also, with the unwanted sources eliminated, the sensor mounting location giving the most robust representation of the test-gear meshing energy was found to be at a point close to the test gears in the load zone of the bearings.

Zakrajsek, James J.↗

NASA NTRS1975

A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona

A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a source of initial arrivals. Results obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 900 m from the rim crest and to a depth of at least 800 m beneath the crater floor.

Ackermann, H. D.↗

NASA NTRS1980

Spacelab experiment: ALAE, Atmospheric Lyman-Alpha Emissions

A spectrophotometer associated with two absorption cells, one filled with hydrogen and the other with deuterium, is described for use in studying various sources of Lyman-alpha emission in the atmosphere, in the interplanetary medium, and possibly in the galactic medium. As the result of charge exchange, Lyman-alpha emission is possibly present in auroral zones, equatorial zones, and at the foot of the polar cusp, where the solar wind interacts directly with the neutral atmosphere. Some emission is also expected from the plasma guns on board Spacelab. The use of the absorption cell is also a test for determining if the presence of geocoronal and interplanetary emission will prevent future astronomical observations of Lyman-alpha emissions.

Source record↗

NASA NTRS1986

Numerical analysis of SSME preburner injector atomization and combustion processes

The coaxial spray injection and combustion flowfields of a Space Shuttle Main Engine preburner injector element have been analyzed using a three-phase numerical code. The processes of atomization, evaporation, secondary droplet breakup, and multispecies chemistry, as well as turbulent diffusion, are included. The model produced realistic pictures of the complex internal flowfield, including liquid jet length, spray shape, flame-zone size and characteristics, and predicted temperatures that seem to be in agreement with test data envelopes. It predicted an external group combustion type of flame. Salient combustion and mixing features are discussed and sources of uncertainty are pointed out for future studies.

Liang, P. Y.↗

NASA NTRS1985

Mechanisms for chromospheric heating

A nonthermal energy source is required to heat the solar chromosphere and corona. A survey is made of the properties of waves that propagate along magnetic flux tubes, which may transport the needed energy from the convection zone to the chromosphere. It is next explored how convective motions can generate those waves. Finally, various mechanisms by which these waves may develop small scale structures and dissipate via viscosity and resistivity are discussed.

Stein, R. F.↗

NASA NTRS1991

Evidence of auroral plasma cavities at Uranus and Neptune from radio burst observations

Radio bursts originating from the stronger magnetic polar regions of both Uranus and Neptune were detected by the planetary radio astronomy experiment during the Voyager 2 encounters with the planets. It has previously been demonstrated that these bursts are beamed into a broad, hollow emission pattern from their auroral sources. It is now shown that the bursts at both planets also manifest similar detailed patterns, with the waves beamed into two separate and distinct radiation cones at intermediate wave frequencies. This double-cone emission pattern is predicted by relativistic cyclotron resonance theory, and application of this theory to the observed emission pattern yields the plasma density structure within the radio source region. Calculations indicate that at both Uranus and Neptune the plasma-to-cyclotron frequency ratio can drop well below 0.01 within the active region. Such low values indicate that the southern auroral zones at both planets contain an auroral plasma cavity that is similar to that found in earth's nightside auroral zone.

Farrell, W. M.↗

NASA NTRS1988

Driving forces: Slab subduction and mantle convection

Mantle convection is the mechanism ultimately responsible for most geological activity at Earth's surface. To zeroth order, the lithosphere is the cold outer thermal boundary layer of the convecting mantle. Subduction of cold dense lithosphere provides tha major source of negative buoyancy driving mantle convection and, hence, surface tectonics. There are, however, importnat differences between plate tectonics and the more familiar convecting systems observed in the laboratory. Most important, the temperature dependence of the effective viscosity of mantle rocks makes the thermal boundary layer mechanically strong, leading to nearly rigid plates. This strength stabilizes the cold boundary layer against small amplitude perturbations and allows it to store substantial gravitational potential energy. Paradoxically, through going faults at subduction zones make the lithosphere there locally weak, allowing rapid convergence, unlike what is observed in laboratory experiments using fluids with temperature dependent viscosities. This bimodal strength distribution of the lithosphere distinguishes plate tectonics from simple convection experiments. In addition, Earth has a buoyant, relatively weak layer (the crust) occupying the upper part of the thermal boundary layer. Phase changes lead to extra sources of heat and bouyancy. These phenomena lead to observed richness of behavior of the plate tectonic style of mantle convection.

Hager, Bradford H.↗

NASA NTRS1981

Energetic particle precipitation at middle and low latitudes

The results from rocket observations of the nighttime electron density profile in the upper E region (120 to 200 km) over Wallops Island, Virginia are discussed. The observations demonstrated the importance of atmospheric tides in the formation of the intermediate layer near 150 km. These observations also show that, except perhaps on geomagnetically quiet nights, energetic particles are the dominant ionization source in the layer. Using rocket, satellite, and ground-based observations it is possible to study the global morphology of particle precipitation. It is found that, just as there are northern and southern auroral zones, there are also mid-latitude, low-latitude, and equatorial zones of precipitation. The evidence for these zones and the properties of the precipitating particles are summarized.

Smith, L. G.↗

NASA NTRS1984

Recombination stellar wind model for the coronae of early-type stars

The wind structures of early-type stars which have base coronal zones are discussed. The calculations give rise to what is called a recombination stellar wind structure because of the transition from a coronally driven wind to a radiatively driven wind. The coronal X-rays are a dominant factor in determining the wind structure because of their effect on the ionization structure, which in turn determines the heating, cooling, and the attenuating properties of the stellar wind. The decreased continuum opacity allows for an increase in the emergent X-ray flux at energies less than 1 keV. The X-ray spectra are compared with those observed with the IPC instrument on the Einstein Observatory and are found to be in excellent agreement. This shows that contrary to earlier analyses, base coronae are not ruled out by the existing IPC X-ray data. The predicted emergent X-ray luminosities are in agreement with the observed values. However, the incident X-ray luminosities from the base coronal zones can be three to four orders of magnitude larger. This suggests that the X-ray IPC spectra reflect the absorption properties of the wind and not the nature of the X-ray source.

Waldron, W. L.↗

NASA NTRS1991

Observations of the freeze/thaw performance of lithium fluoride by motion picture photography

To gain direct observation of the molten salt phase change, a novel containerless technique was developed where the high surface tension of lithium fluoride was used to suspend a bead of the molten salt inside a specially designed wire cage. By varying the current passing through the wire, the cage also served as a variable heat source. In this way, the freeze/thaw performance of the lithium fluoride could be photographed by motion picture photography without the influence of container walls. The motion picture photography of the lithium fluoride sample revealed several zones during the phase change, a solid zone and a liquid zone, as expected, and a slush zone that was predicted by thermal analysis modeling.

Jaworske, D. A.↗

NASA NTRS2014

High Resolution Mapping of Soils and Landforms for the Desert Renewable Energy Conservation Plan (DRECP)

The Desert Renewable Energy Conservation Plan (DRECP), a major component of California's renewable energy planning efforts, is intended to provide effective protection and conservation of desert ecosystems, while allowing for the sensible development of renewable energy projects. This NASA mapping report was developed to support the DRECP and the Bureau of Land Management (BLM). We outline in this document remote sensing image processing methods to deliver new maps of biological soils crusts, sand dune movements, desert pavements, and sub-surface water sources across the DRECP area. We focused data processing first on the largely unmapped areas most likely to be used for energy developments, such as those within Renewable Energy Study Areas (RESA) and Solar Energy Zones (SEZs). We used imagery (multispectral and radar) mainly from the years 2009-2011.

Mapping↗

NASA NTRS2015

Ocean Color Measurements with the Operational Land Imager on Landsat-8: Implementation and Evaluation in SeaDAS

The Operational Land Imager (OLI) is a multispectral radiometer hosted on the recently launched Landsat8 satellite. OLI includes a suite of relatively narrow spectral bands at 30 m spatial resolution in the visible to shortwave infrared, which makes it a potential tool for ocean color radiometry: measurement of the reflected spectral radiance upwelling from beneath the ocean surface that carries information on the biogeochemical constituents of the upper ocean euphotic zone. To evaluate the potential of OLI to measure ocean color, processing support was implemented in Sea-viewing Wide Field-of-View Sensor (SeaWiFS) Data Analysis System (SeaDAS), which is an open-source software package distributed by NASA for processing, analysis, and display of ocean remote sensing measurements from a variety of spaceborne multispectral radiometers. Here we describe the implementation of OLI processing capabilities within SeaDAS, including support for various methods of atmospheric correction to remove the effects of atmospheric scattering and absorption and retrieve the spectral remote sensing reflectance (Rrs; sr−1). The quality of the retrieved Rrs imagery will be assessed, as will the derived water column constituents, such as the concentration of the phytoplankton pigment chlorophyll a.

Measurements↗

NASA NTRS2018

Numerical Investigation of Ion Transport in the MOMA Ion Mass Spectrometer

The Mars Organic Molecule Analyzer (MOMA) is a miniature ion trap mass spectrometer designed for the upcoming ExoMars Rover mission. The spectrometer uses laser desorption to ionize a Martian soil sample within an instrument internal clean zone maintained at ambient Martian pressure. A high-speed aperture valve transiently opens to allow ionized constituents, along with the ambient gas, to enter a vacuum cavity containing a linear ion trap mass spectrometer. The ambient clean zone and the vacuum cavity are connected via a few centimeter long aperture valve ion guide tube. In this paper, we present results from a recently completed numerical investigation of ion transport from the ion source across the ion guide. Specifically, we focus on collisional coupling between ions and the neutral molecules flowing into the vacuum cavity. The simulation domain contains the ambient region, and we consider the variation in ion conductance with ambient pressure. We also analyze the impact of a fixed potential bias applied to the aperture valve. Simulations are performed with a two-dimensional axisymmetric PIC / DSMC code Starfish. Numerical results are compared to experimental data.

Breida, Lubos↗

NASA NTRSDate not supplied

Particulate Emission and Optical Measurements in n-Heptane Low-Swirl Non-Premixed Flames at Elevated Pressures

A series of ground combustion tests conducted at elevated pressures demonstrates in-chamber optical measurements of soot emissions, combined with conventional gaseous and particle emissions sampling techniques. Utilizing a micro-radial-entry counter-swirl (MRX) burner, we successfully stabilized an n-heptane low-swirl, non-premixed spray flame across a wide range of equivalence ratios at pressures reaching 250 psia. Our optical diagnostics feature a temporally gated diffused-backlight illumination extinction imaging (DBI-EI) system, equipped with a 470-nm strobe high-intensity LED array as the illumination source, along with a line-of-sight telecentric camera. By accessing the flame tube, the pulsed DBI-EI provides illuminating optical extinction images, enabling experimental estimation of soot volume fractions within the reaction zone. This imaging technique will allow for real-time observation of soot formation dynamics occurring above the air-blast fuel injector. To further enhance our analysis, we employed simultaneous gaseous and particulate extractive diagnostics, interpreting in-flame particulate information through CO2 sampling, exhaust particle sizing, and particle counting. The processed dataset reveals a promising application of DBI-EI for propulsion emission analysis in high-pressure environments, where optical beam-steering effects can significantly impact results. This report is essential to bridging the divide between in-flame optical diagnostics and exhaust extractive measurements. By achieving an understanding of non-premixed combustion emission characteristics, we attempt to provide invaluable data for computer code validation, advancing the field of combustion research and supporting the development of cleaner, more efficient engines.

high-pressure flame↗

NASA NTRSDate not supplied

Particulate Emission and Optical Measurements in n-Heptane Low-Swirl Non-Premixed Flames at Elevated Pressures

A series of ground combustion tests conducted at elevated pressures demonstrates in-chamber optical measurements of soot emissions, combined with conventional gaseous and particle emissions sampling techniques. Utilizing a micro-radial-entry counter-swirl (MRX) burner, we successfully stabilized an n-heptane low-swirl, non-premixed spray flame across a wide range of equivalence ratios at pressures reaching 250 psia. Our optical diagnostics feature a temporally gated diffused-backlight illumination extinction imaging (DBI-EI) system, equipped with a 470-nm strobe high-intensity LED array as the illumination source, along with a line-of-sight telecentric camera. By accessing the flame tube, the pulsed DBI-EI provides illuminating optical extinction images, enabling experimental estimation of soot volume fractions within the reaction zone. This imaging technique will allow for real-time observation of soot formation dynamics occurring above the air-blast fuel injector. To further enhance our analysis, we employed simultaneous gaseous and particulate extractive diagnostics, interpreting in-flame particulate information through CO2 sampling, exhaust particle sizing, and particle counting. The processed dataset reveals a promising application of DBI-EI for propulsion emission analysis in high-pressure environments, where optical beam-steering effects can significantly impact results. This report is essential to bridging the divide between in-flame optical diagnostics and exhaust extractive measurements. By achieving an understanding of non-premixed combustion emission characteristics, we attempt to provide invaluable data for computer code validation, advancing the field of combustion research and supporting the development of cleaner, more efficient engines.

high-pressure flame↗

NASA NTRS1991

South Pacific convergence zone and global scale circulations (Jul. 1987 - Jul. 1991). Observational and modeling studies of heat, moisture, precipitation, and global-scale circulation patterns (Jul. 1990 - Jul. 1993)

Several research projects were worked on between August 1990 and May 1991. Topics covered included observational and modeling studies of relationships between tropical heat sources and subtropical jet streams, the intraseasonal (30 to 60 day) oscillation near the equator, and precipitation over tropical oceans. Current research activities and plans for the coming year are outlined.

Vincent, Dayton G.↗