Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “surface texturing”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Algorithmic commonalities in the parallel environment

The ultimate aim of this project was to analyze procedures from substantially different application areas to discover what is either common or peculiar in the process of conversion to the Massively Parallel Processor (MPP). Three areas were identified: molecular dynamic simulation, production systems (rule systems), and various graphics and vision algorithms. To date, only selected graphics procedures have been investigated. They are the most readily available, and produce the most visible results. These include simple polygon patch rendering, raycasting against a constructive solid geometric model, and stochastic or fractal based textured surface algorithms. Only the simplest of conversion strategies, mapping a major loop to the array, has been investigated so far. It is not entirely satisfactory.

Mcanulty, Michael A.↗
NASA NTRS1987

Mercury - Wavelength and longitude dependence of polarization

The polarization-time variations noted in the present linear polarization observations of the integrated Mercury disk, with filters covering the 0.3-1.0 micron bandpass and between 53-130 deg of phase angle, may be accounted for in terms of longitude dependence through the variation of brightness or other properties over the surface. Kepler's equation for the eccentric anomaly was solved for each observation, and the true anomaly was used to find the subsolar longitude. The difference found in the polarization-albedo relations of Mercury and the moon indicates a difference in surface texture and/or composition.

Gehrels, T.↗
NASA NTRS1988

Non-random cratering flux in recent time

Proposed periodic cycles of mass mortality have been linked to periodic changes in the impact flux on Earth. Such changes in the impact flux, however, also should be recorded on the Moon. Previous studies have concluded that the impact flux on the Moon over the last 1 to 2 billion years has been reasonably constant, but sudden changes in the impact flux over time intervals as short as 30 my could not be detected in these studies unless the added crater population greatly exceeded the cumulative cratering record. Consequently this study focuses only on bright-rayed craters larger than 1 km thereby not only limiting the study to recent craters but also largely eliminating contamination by secondary craters. Preservation of ray patterns and other fine-scale surface textures in the ejecta provides first-order culling of craters younger than Tycho, i.e., about 100 my. Although a periodic change in the impact flux in the Earth-Moon system cannot yet be confirmed from the data, a non-random component appears to exist with an increased flux around 7 and 15 my. The concentrations in different quadrants of the lunar hemisphere would be consistent with a shower of debris generally smaller than 0.5 km.

Schultz, P. H.↗
NASA NTRS1989

Evidence for volcanism in NW Ishtar Terra, Venus

Venera 15/16 radar data for an area in NW Ishtar Terra, Venus, show an area with moderate radar return and a smooth textured surface which embays low lying areas of the surrounding mountainous terrain. Although this unit may be an extension of the lava plains of Lakshmi Planum to the southeast, detailed study suggests a separate volcanic center in NW Ishtar Terra. Lakshmi Planum, on the Ishtar Terra highland, exhibits major volcanic and tectonic features. On the Venera radar image radar brightness is influenced by slope and roughness; radar-facing slopes (east-facing) and rough surfaces (approx. 8 cm average relief) are bright, while west-facing slopes and smooth surfaces are dark. A series of semi-circular features, apparently topographic depressions, do not conform in orientation to major structural trends in this region of NW Ishtar Terra. The large depression in NW Ishtar Terra is similar to the calderas of Colette and Sacajawea Paterae, as all three structures are large irregular depressions. NW Ishtar Terra appears to be the site of a volcanic center with a complex caldera structure, possibly more than one eruptive vent, and associated lobed flows at lower elevations. The morphologic similarity between this volcanic center and those of Colette and Sacajawea suggests that centralized eruptions have been the dominant form of volcanism in Ishtar. The location of this volcanic center at the intersection of two major compressional mountain belts and the large size of the calders (with an inferred larg/deep magma source) support a crustal thickening/melting rather than a hot-spot origin for these magmas.

Gaddis, L.↗
NASA NTRS1989

Physical properties of Aten, Apollo and Amor asteroids

Data available on the physical properties of a group of planet-crossing asteroids, the Aten, Apollo, and Amor objects (AAAO) (include data on the taxonomy, mineralogical surface composition, diameter, rotation rate, shape, and surface texture) are presented together with the type of observations used for obtaining these data. These data show that the population of the AAAO is diverse in all of their physical characteristics. This diversity implies that the AAAO come from multiple sources and had different evolutionary histories.

Mcfadden, Lucy-Ann↗
NASA NTRS1991

Low-Thermal-Conduction Links For Silicon Sensors

Simple method of texturing surface of silicon reduces thermal conductivities of links in silicon x-ray calorimeters and infrared bolometers. Gives links high density of phonon scattering sites reducing conduction of heat. Links made shorter and more robust. Used in making x-ray calorimeters and infrared bolometers. Applicable to any microelectronic device in which high degree of thermal isolation needed.

Mott, D. Brent↗
NASA NTRS1991

Atomic oxygen interaction with solar array blankets at protective coating defect sites

Atomic oxygen in the low-Earth-orbital environment oxidizes SiOx protected polyimide Kapton solar array blankets at sites which are not protected such as pin windows or scratches in the protective coatings. The magnitude and shape of the atomic oxygen undercutting which occurs at these sites is dependent upon the exposure environment details such as arrival direction and reaction probability. The geometry of atomic oxygen undercutting at defect sites exposed to atomic oxygen in plasma asher was used to develop a Monte Carlo model to simulate atomic oxygen erosion processes at defect sites in protected Kapton. Comparisons of Monte Carlo predictions and experimental results are presented for plasma asher atomic oxygen exposures for large and small defects as well as for protective coatings on one or both sides of Kapton. The model is used to predict in-space exposure results at defect sites for both directed and sweeping atomic oxygen exposure. A comparison of surface textures predicted by the Monte Carlo model and those experimentally observed from both directed space ram and laboratory plasma asher atomic oxygen exposure indicate substantial agreement.

Banks, Bruce A.↗
NASA NTRS1992

Vapor Deposition Of Metal From Gas/Tungsten Arc

Vacuum gas/tungsten-arc vapor-deposition process yields highly reflective, smooth films reproducing contours of surfaces on which deposited. Rate of deposition controlled precisely, and surface texture varied. Capable of deposition at rates double those of standard sputtering. Useful in making thin metallic coats to serve as electrical conductors, radio reflectors or antenna elements, or optical mirrors of partial or ultrahigh reflectivity, and in making semiconductor devices.

Weeks, Jack L.↗
NASA NTRS1991

Factors controlling lava dome morphology

Research suggests that variations in lava dome morphology on different planets will depend much more critically on local gravity and the style of eruption than on the magma composition, ambient temperature, or the relative roles of convective and radiative cooling. Eruption style in turn reflects differences in tectonic conditions and the ability of magma to exsolve volatiles. Observed crude correlations between silica content and calculated yield strengths for terrestrial lava flows and domes probably are do to differences in extrusion rate and volatile solubility, rather than intrinsic rheological properties. Thus, even after taking the known effect of gravity into account, observed differences in gross dome morphology on different planets cannot by themselves be directly related to composition. Additional information such as the distribution of surface textures and structures, or spectroscopic data will be needed to conclusively establish dome compositions.

Fink, Jonathan↗
NASA NTRS1991

Character of the opposition effect and negative polarization

Photometric and polarimetric properties at small phase angles were measured for silicates with controlled surface properties in order to distinguish properties that are associated with surface reflection from those that are associated with multiple scattering from internal grain boundaries. These data provide insight into the causes and conditions of photometric properties observed at small phase angles for dark bodies of the solar system. Obsidian was chosen to represent a silicate dielectric with no internal scattering boundaries. Because obsidian is free of internal scatterers, light reflected from both the rough and smooth obsidian samples is almost entirely single and multiple Fresnel reflections form surface facets with no body component. Surface structure alone cannot produce an opposition effect. Comparison of the obsidian and basalt results indicates that for an opposition effect to occur, surface texture must be both rough and contain internal scattering interfaces. Although the negative polarization observed for the obsidian samples indicates single and multiple reflections are part of negative polarization, the longer inversion angle of the multigrain inversion samples implies that internal reflections must also contribute a significant negative polarization component.

Pieters, Carle M.↗
NASA NTRS1992

Small volcanic edifices and volcanism in the plains of Venus

The different types of eruption that have occurred over time in the Venusian plains are considered. The most extensive volcanic units consist of flood lavas, the largest of which have volumes of the order of thousands of cubic kilometers. They are inferred to have erupted at high effusion rates, and they exhibit a range of radar backscatter characteristics indicating different surface textures and ages. Small edifices on the plains occur mainly in clusters associated with fracture belts. The majority are shield volcanos that may be up to a few tens of kilometers across but are generally 10 km or less in diameter. Volcanic domes have diameters up to several tens of kilometers and volumes of the order of 100 cu cm. These are interpreted as being constructed of lava erupted with a relatively high effective viscosity and thus possibly composed of more silicic lava. For many domes, the flanks were unstable during and after eruption and experienced gravity sliding that produced steep scalloped outer margins.

Guest, John E.↗
NASA NTRS1992

Analysis of volcanic surface morphology on Venus from comparison of Arecibo, Magellan, and terrestrial airborne radar data

The paper compares Arecibo Observatory and Magellan radar data for Venus to airborne radar images for potential terrestrial analog surfaces. Volcanic deposits in western Eistla Regio and northern Sedna Planitia are characterized. It is shown that the expected-sense circularly polarized echoes in the 'dark plains' and broad flow aprons of Eistla Regio decrease rapidly with incidence angle. This angular scattering behavior implies surfaces no rougher than terrestrial pahoehoe flows. Polarization ratio comparisons show that the extensive lava flows in Western Eistla Regio and Sedna Planitia are generally consistent with the properties of terrestrial pahoehoe flows, with only limited occurrences of a'a morphology. Three scenarios are suggested. Many of the large flow units in the two study regions were emplaced as complexes of low-effusion rate pahoehoe flows, rather than as higher eruption rate events which might be expected to produce a'a surface textures; the long lava flows were originally emplaced as a'a but have since weathered to a smoother texture; or a combination of atmospheric and magma compositional effects combine to inhibit a'a formation even at high volume eruption rates.

Campbell, Bruce A.↗
NASA NTRS1992

Characterization of selected LDEF-exposed polymeric films

The characterization of selected experimental and commercially available thin polymeric films which received 10 months of exposure to the LEO environment on the Long Duration Exposure Facility is reported. The visual appearance of most specimens changed due to exposure. However, except for a silicon-containing copolymer film, chemical characterization including infrared, thermal, and X-ray photoelectron analyses showed that the molecular structure of the surviving material had not changed significantly in response to exposure. Surface texturing due to atomic oxygen erosion was documented using various microscopic analyses. The possibility of continued post-exposure degradation of some polymeric materials is proposed.

Young, Philip R.↗
NASA NTRS1993

The continuum slope of Mars - Bidirectional reflectance investigations and applications to Olympus Mons

Two primary causes of near-IR continuum slope variations have been observed in an investigation of the bidirectional reflectance characteristics of ferric coatings on the continuum slope of Mars. First, the presence of a thin ferric coating on a dark substrate produces a negative continuum slope due to the wavelength-dependent transparency of the ferric coating. Second, wavelength-dependent directional reflectance occurs when the surface particles are tightly packed, particle sizes are on the order of or smaller than the wavelength of light, or the surface is otherwise smooth on the order of the wavelength of light. Based on these results, the annuli on the flanks of Olympus Mons which are defined by reflectance and continuum slope are consistent with spatial variations in surface texture and possibly with spatial variations in the thickness of a ferric dust coating or rind.

Fischer, Erich M.↗
NASA NTRS1991

Image feature extraction using Gabor-like transform

Noisy and highly textured images were operated on with a Gabor-like transform. The results were evaluated to see if useful features could be extracted using spatio-temporal operators. The use of spatio-temporal operators allows for extraction of features containing simultaneous frequency and orientation information. This method allows important features, both specific and generic, to be extracted from images. The transformation was applied to industrial inspection imagery, in particular, a NASA space shuttle main engine (SSME) system for offline health monitoring. Preliminary results are given and discussed. Edge features were extracted from one of the test images. Because of the highly textured surface (even after scan line smoothing and median filtering), the Laplacian edge operator yields many spurious edges.

Finegan, Michael K., Jr.↗
NASA NTRS1993

Guide to Magellan image interpretation

An overview of Magellan Mission requirements, radar system characteristics, and methods of data collection is followed by a description of the image data, mosaic formats, areal coverage, resolution, and pixel DN-to-dB conversion. The availability and sources of image data are outlined. Applications of the altimeter data to estimate relief, Fresnel reflectivity, and surface slope, and the radiometer data to derive microwave emissivity are summarized and illustrated in conjunction with corresponding SAR image data. Same-side and opposite-side stereo images provide examples of parallax differences from which to measure relief with a lateral resolution many times greater than that of the altimeter. Basic radar interactions with geologic surfaces are discussed with respect to radar-imaging geometry, surface roughness, backscatter modeling, and dielectric constant. Techniques are described for interpreting the geomorphology and surface properties of surficial features, impact craters, tectonically deformed terrain, and volcanic landforms. The morphologic characteristics that distinguish impact craters from volcanic craters are defined. Criteria for discriminating extensional and compressional origins of tectonic features are discussed. Volcanic edifices, constructs, and lava channels are readily identified from their radar outlines in images. Geologic map units are identified on the basis of surface texture, image brightness, pattern, and morphology. Superposition, cross-cutting relations, and areal distribution of the units serve to elucidate the geologic history.

Ford, John P.↗
NASA NTRS1992

The effect of runway surface and braking on Shuttle Orbiter main gear tire wear

In 1988, a 1067 m long touchdown zone on each end of the Kennedy Space Center (KSC) Shuttle Landing Facility (SLF) was modified from its original heavy-broom finish with transverse grooves configuration to a longitudinal corduroy surface texture with no transverse grooves. The intent of this modification was to reduce the spin-up wear on the Orbiter main gear tires and provide for somewhat higher crosswind capabilities at that site. The modification worked well, so it was proposed that the remainder of the runway be modified as well to permit even higher crosswind landing capability. Tests were conducted at the NASA Langley Aircraft Landing Dynamics Facility (ALDF) to evaluate the merit of such a modification. This paper discusses the results of these tests, and explains why the proposed modification did not provide the expected improvement and thus was not implemented. Also, in an ongoing program to evaluate the origin of various tire wear phenomenon, a series of tests was conducted to evaluate the effect of braking on tire wear. Finally, a modified tire is discussed in terms of its wear performance under rollout and braking operations.

Daugherty, Robert H.↗
NASA NTRS1995

Method and apparatus for non-destructive evaluation of composite materials with cloth surface impressions

A method and related apparatus for nondestructive evaluation of composite materials by determination of the quantity known as Integrated Polar Backscatter, which avoids errors caused by surface texture left by cloth impressions by identifying frequency ranges associated with peaks in a power spectrum for the backscattered signal, and removing such frequency ranges from the calculation of Integrated Polar Backscatter for all scan sites on the composite material is presented.

Madras, Eric I.↗