SEARCH · Engineering Papers

Results for “surface morphologies”

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.

SourceResearch connectionFrom yearThrough year

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

At least 379 records · Page 21

All sources NASA NTRS DOE OSTI

NASA NTRS1987

Characterization of ion beam modified ceramic wear surfaces using Auger electron spectroscopy

An investigation of the surface chemistry and morphology of the wear surfaces of ceramic material surfaces modified by ion beam mixing has been conducted using Auger electron spectroscopy and secondary electron microscopy. Studies have been conducted on ceramic/ceramic friction and wear couples made up of TiC and NiMo-bonded TiC cermet pins run against Si3N4 and partially stabilized zirconia disc surfaces modified by the ion beam mixing of titanium and nickel, as well as ummodified ceramic/ceramic couples in order to determine the types of surface changes leading to the improved friction and wear behavior of the surface modified ceramics in simulated diesel environments. The results of the surface analyses indicate that the formation of a lubricating oxide layer of titanium and nickel, is responsible for the improvement in ceramic friction and wear behavior. The beneficial effect of this oxide layer depends on several factors, including the adherence of the surface modified layer or subsequently formed oxide layer to the disc substrate, the substrate materials, the conditions of ion beam mixing, and the environmental conditions.

Wei, W.↗

NASA NTRS1988

Effect of surface tension anisotropy on cellular morphologies

A three-dimensional weakly nonlinear analysis for conditions near the onset of instability at the crystal-melt interface was carried out to second order, taking into account the effects of latent heat generation and surface-tension anisotropy of the crystal-melt interface; particular consideration was given to the growth of a cubic crystal in the 001-, 011-, and 111-line directions. Numerical calculations by McFadden et al. (1987), performed for an aluminum-chromium alloy with the assumption of a linear temperature field and an isotropic surface tension, showed that only hexagonal nodes (and not hexagonal cells) occurred near the onset of instability. The results of the present analysis indicate that the nonlinear temperature field (which occurs when thermal conductivities of the crystal and the melt are different and/or the latent heat effects are not negligible) can modify this result and, for certain alloys and processing conditions, can cause the occurrence of hexagonal cells near the onset of instability.

Mcfadden, G. B.↗

NASA NTRS1994

The RSA survey of dwarf galaxies, 1: Optical photometry

We present detailed surface photometry, based on broad B-band charge coupled device (CCD) images, of about 80 dwarf galaxies. Our sample represents approximately 10% of all dwarf galaxies identified in the vicinity of Revised Shapley-Ames (RSA) galaxies on high resolution blue photographic plates, referred to as the RSA survey of dwarf galaxies. We derive global properties and radial surface brightness profiles, and examine the morphologies. The radial surface brightness profiles of dwarf galaxies, whether early or late type, display the same varieties in shape and complexity as those of classical giant galaxies. Only a few are well described by a pure r(exp 1/4) law. Exponential profiles prevail. Features typical of giant disk galaxies, such as exponential profiles with a central depression, lenses, and even, in one case (IC 2041), a relatively prominent bulge are also found in dwarf galaxies. Our data suggest that the central region evolves from being bulge-like, with an r(exp 1/4) law profile, in bright galaxies to a lens-like structure in dwarf galaxies. We prove detailed surface photometry to be a helpful if not always sufficient tool in investigating the structure of dwarf galaxies. In many cases kinematic information is needed to complete the picture. We find the shapes of the surface brightness profiles to be loosely associated with morphological type. Our sample contains several new galaxies with properties intermediate between those of giant and dwarf ellipticals (but no M32-like objects). This shows that such intermediate galaxies exist so that at least a fraction of early-type dwarf ellipticals is structurally related to early-type giants instead of belonging to a totally unrelated, disjunct family. This supports an origin of early-type dwarf galaxies as originally more massive systems that acquired their current morphology as a result of substantial, presumable supernova-driven, mass loss. On the other hand, several early-type dwarfs in our sample are merger candidates. Merger events may lead to anisotropic velocity distributions in systems of any luminosity, including dwarfs. The RSA sample of dwarf galaxies is more likely to contain mergers because, in contrast to earlier dwarf galaxy surveys that have focused on clusters and rich groups of galaxies, the RSA dwarfs are typically located in low density environments. The occurrence of mergers among dwarf galaxies is of interest in connection with the rapid evolution of faint blue galaxy counts at redshift z less than 1 which suggests that dwarf galaxies were about five times more numerous in the recent past. Finally, our sample contains several examples of late-type dwarfs and 'transition' types that are potential precursors of nucleated early-type dwarfs. All the above processes--mass loss, mergers, astration--are likely to have contributed to the formation of the current population of diffuse early-type dwarfs. A few new redshifts of dwarf galaxies are reported in this paper.

Vader, J. Patricia↗

NASA NTRS2003

Step Bunching and Solution Flow

Imagine a sequence of equidistant steps parallel to one another on a crystal face growing from solution. Steps may be one or part of a lattice spacing high. With such ideal morphology, the most perfect material is expected to be produced. Sometimes this happens. Much more often, however, steps form bunches, acquire wavy shapes and interlace. With time, these spontaneous perturbations may be increased in amplitude, i.e. the stepped surface becomes morphologically unstable. Interferometric studies of Y.G. Kuznetsov, L.N. Rashkovich, P.G. Vekilov and N.A. Booth and the author demonstrated that the step bunching depends at least on direction and rate of solution flow over the interface, supersaturation and presence of impurities. In particular, if solution and step flow are parallel to one another, the steps convene into bunches. If these flows are antiparallel, the bunches disappear. As the step train propagates, the overall bunch height often increases infinitely. However, we have found recently that if the flow rate is large enough, (approximately 1 meter per second), the bunch height may be limited. All these phenomena come from interaction between steps. The interaction mechanisms are still not fully understood. I plan to overview major approaches to the still unresolved problem on how these dissipative structures on growing crystal face appear and evolve.

Chernov, A. A.↗

NASA NTRS2000

Coma Morphology Due to an Extended Active Region and Implications for the Spin State of Comet Hale-Bopp

We show that the circular character of continuum structures observed in the coma of comet Hale-Bopp around the perihelion passage is most likely due to a dust jet from a large extended active region on the surface. Coma morphology due to a wide jet is different from that due to a narrow jet. The latter shows foreshortening effects due to observing geometry, wider jet produces more circular features. This circularization effect provides a self-consistent explanation for the evolution of near-perihelion coma morphology. No changes in the direction of the rotational angular momentum vector are required during this period in contrast to the models of Schleicher et al. This circularization effect also enables us to produce near-circular coma features in the S-E quadrant during 1997 late February and therefore questions the basic premise on which Sekanina bases his morphological arguments for a gravitationally bound satellite nucleus.

Samarasinha, Nalin H.↗

NASA NTRS2018

Corrosion of Bare Carbon Steel as a Passive Sensor to Assess Moisture Availability for Biological Activity in Atacama Desert Soils

In this work we suggest the corrosion of polished bared metal coupons as a passive sensor to detect or identify the lower limit of water availability that could be suitable for biological activity in the Atacama Desert on soil or solid substrates. For this purpose, carbon steel coupons were deposited in selected sites along a west-east transect and removed at predetermined times for morphological inspection. The advantage of this procedure is that the attributes of the oxide layer (corrosion extent, morphology and oxide phases) can be considered as a fingerprint of the atmospheric moisture history at a given time interval. Two types of coupons were used, a long rectangular shape that are half-buried in a vertical position, and square shape that are deposited on the soil surface. The morphological attributes observed by SEM inspection is correlated to the so-called humectation time which is determined from local meteorological parameters. The main result is that the decreasing trend of atmospheric moisture along the transect is closely related to corrosion behavior and water soil penetration. For instance, while in the coastal site oxide phases formed on the coupon surface rapidly evolve to well- crystallized species, in the driest inland site Lomas Bayas only amorphous oxide is observed.

Caceres, Luis↗

NASA NTRS1994

Hubble Space Telescope photometry of the central regions of Virgo cluster elliptical galaxies. 3: Brightness profiles

We have used the Planetary Camera on the Hubble Space Telescope (HST) to study the morphology and surface brightness parameters of a luminosity-limited sample of fourteen elliptical galaxies in the Virgo cluster. The total apparent blue magnitudes of the galaxies range between 9.4 and 13.4. In this paper, the core brightness profiles are presented, while the overall morphology and the isophotal shapes are discussed in two companion papers (Jaffe et al. (1994); van den Bosch et al. (1994)). We show that, in spite of the spherical aberration affecting the HST primary mirror, deconvolution techniques allow recovery of the brightness profile up to 0.2 arcsec from the center of the galaxies. We find that none of the galaxies has an isothermal core. On the basis of their morphological and photometrical properties, the galaxies can be divided in two physically distinct groups, referred to as Type I and Type II. All of the Type I galaxies are classified as E1 to E3 in the Revised Shapley Ames Catalog (Sandage & Tammann 1981), while Type II galaxies are classified as E5 to E7. The characteristics of Type II galaxies are explained by the presence of disks component on both the 1 arcsec and the 10 arcsec scales, while Type I galaxies correspond to the classical disk-free ellipticals.

Ferrarese, Laura↗

NASA NTRS2017

Detrended Topographic Data of the South-pole Aitken Basin (SPA): Comparisons with Apollo 16 and Schiller-Schickard as Indications of the Formation and Evolution of the Spa Interior

Data from recent lunar orbital missions have provided critical insight into the surface composition, morphology, and geologic history of the Moon. A key region that has benefited from this new data is the South Pole-Aitken Basin (SPA), a key area for future sample return]. A key area of investigation of SPA has been the characterization of its surface, detailing the interior composition, geologic evolution, and possible exposure of deep-seated materials. Recently we have applied a number of datasets to ascertain the origin of surfaces in central SPA and identify units that represent the ancient SPA-derived impact melt and those that represent volcanic activity. Here we apply a technique that utilizes high-resolution topographic data to remove local slopes to highlight subtle topographic variations. Such detrended data allows us to characterize units that are either ancient (SPA impact melt) or that represent subsequent volcanic activity.

Petro, N. E.↗

NASA NTRS1994

Remote sensing of potential lunar resources. 2: High spatial resolution mapping of spectral reflectance ratios and implications for nearside mare TiO2 content`

High spatial resolution maps illustrating variations in spectral reflectance 400/560 nm ratio values have been generated for the following mare regions: (1) the border between southern Mare Serenitatis and northern Mare Tranquillitatis (including the MS-2 standard area and Apollo 17 landing site), (2) central Mare Tranquillitatis, (3) Oceanus Procellarum near Seleucus, and (4) southern Oceanus Procellarum and Flamsteed. We have also obtained 320-1000 nm reflectance spectra of several sites relative to MS-2 to facilitate scaling of the images and provide additional information on surface composition. Inferred TiO2 abundances for these mare regions have been determined using an empirical calibration which relates the weight percent TiO2 in mature mare regolith to the observed 400/560 nm ratio. Mare areas with high TiO2 abundances are probably rich in ilmenite (FeTiO3) a potential lunar resource. The highest potential TiO2 concentrations we have identified in the nearside maria occur in central Mare Tranquillitatis. Inferred TiO2 contents for these areas are greater than 9 wt% and are spatially consistent with the highest-TiO2 regions mapped previously at lower spatial resolution. We note that the morphology of surface units with high 400/560 nm ratio values increases in complexity at higher spatial resolutions. Comparisons have been made with previously published geologic maps, Lunar Orbiter IV, and ground-based images, and some possible morphologic correlatins have been found between our mapped 400/560 nm ratio values and volcanic landforms such as lava flows, mare domes, and collapse pits.

Melendrez, David E.↗

NASA NTRS2017

Environmental Barrier Coating Fracture, Fatigue and High-Heat-Flux Durability Modeling and Stochastic Progressive Damage Simulation

Advanced environmental barrier coatings will play an increasingly important role in future gas turbine engines because of their ability to protect emerging light-weight SiC/SiC ceramic matrix composite (CMC) engine components, further raising engine operating temperatures and performance. Because the environmental barrier coating systems are critical to the performance, reliability and durability of these hot-section ceramic engine components, a prime-reliant coating system along with established life design methodology are required for the hot-section ceramic component insertion into engine service. In this paper, we have first summarized some observations of high temperature, high-heat-flux environmental degradation and failure mechanisms of environmental barrier coating systems in laboratory simulated engine environment tests. In particular, the coating surface cracking morphologies and associated subsequent delamination mechanisms under the engine level high-heat-flux, combustion steam, and mechanical creep and fatigue loading conditions will be discussed. The EBC compostion and archtechture improvements based on advanced high heat flux environmental testing, and the modeling advances based on the integrated Finite Element Analysis Micromechanics Analysis Code/Ceramics Analysis and Reliability Evaluation of Structures (FEAMAC/CARES) program will also be highlighted. The stochastic progressive damage simulation successfully predicts mud flat damage pattern in EBCs on coated 3-D specimens, and a 2-D model of through-the-thickness cross-section. A 2-parameter Weibull distribution was assumed in characterizing the coating layer stochastic strength response and the formation of damage was therefore modeled. The damage initiation and coalescence into progressively smaller mudflat crack cells was demonstrated. A coating life prediction framework may be realized by examining the surface crack initiation and delamination propagation in conjunction with environmental degradation under high-heat-flux and environment load test conditions.

Mechanical creep and fatigue loading condition↗

NASA NTRS1969

Surface features of cultured mammalian cells.

Cultured mammalian cell growth morphology studied in situ with scanning electron microscope, discussing surface morphology changes during mitotic cycle of Chang liver cells

Dalen, H.↗

NASA NTRS2008

Quantitative Morphologic Analysis of Boulder Shape and Surface Texture to Infer Environmental History: A Case Study of Rock Breakdown at the Ephrata Fan, Channeled Scabland, Washington

Boulder morphology reflects both lithology and climate and is dictated by the combined effects of erosion, transport, and weathering. At present, morphologic information at the boulder scale is underutilized as a recorder of environmental processes, partly because of the lack of a systematic quantitative parameter set for reporting and comparing data sets. We develop such a parameter set, incorporating a range of measures of boulder form and surface texture. We use standard shape metrics measured in the field and fractal and morphometric classification methods borrowed from landscape analysis and applied to laser-scanned molds. The parameter set was pilot tested on three populations of basalt boulders with distinct breakdown histories in the Channeled Scabland, Washington: (1) basalt outcrop talus; (2) flood-transported boulders recently excavated from a quarry; and (3) flood-transported boulders, extensively weathered in situ on the Ephrata Fan surface. Size and shape data were found to distinguish between flood-transported and untransported boulders. Size and edge angles (approximately 120 degrees) of flood-transported boulders suggest removal by preferential fracturing along preexisting columnar joints, and curvature data indicate rounding relative to outcrop boulders. Surface textural data show that boulders which have been exposed at the surface are significantly rougher than those buried by fan sediments. Past signatures diagnostic of flood transport still persist on surface boulders, despite ongoing overprinting by processes in the present breakdown environment through roughening and fracturing in situ. Further use of this quantitative boulder parameter set at other terrestrial and planetary sites will aid in cataloging and understanding morphologic signatures of environmental processes.

Ehlmann, Bethany L.↗

NASA NTRS1965

The moon.

Moon structure, origin, morphology and surface properties of polarization, radio and radar wavelength-emission, etc

PLANETARY RADIATION↗

NASA NTRS1971

Mariner Mars 1969 - Atmospheric results

Mars atmospheric data from Mariner flights, discussing north polar haze, bright surface features morphology, multiring structures and water vapor exchange

Leighton, R. B.↗

NASA NTRS1974

Investigation of a glass spherule from the Luna-16 probe

A glass spherule of the form of a flattened spheroid measuring 580 microns in diameter is studied. The spherule is transparent, shiny, and of a yellowish brown tint. It contains a number of central and peripheral spherical bubble-type cavities. The surface and morphology features resemble those of Apollo spherules, but differ in chemical composition, which is close to that of the Luna-16 regolith.

Glass, B. P.↗

NASA NTRS1986

Microwave properties of sea ice in the marginal ice zone

Active microwave properties of summer sea ice were measured. Backscatter data were acquired at frequencies from 1 to 17 GHz, at angles from 0 to 70 deg from vertical, and with like and cross antenna polarizations. Results show that melt-water, snow thickness, snowpack morphology, snow surface roughness, ice surface roughness, and deformation characteristics are the fundamental scene parameters which govern the summer sea ice backscatter response. A thick, wet snow cover dominates the backscatter response and masks any ice sheet features below. However, snow and melt-water are not distributed uniformly and the stage of melt may also be quite variable. These nonuniformities related to ice type are not necessarily well understood and produce unique microwave signature characteristics.

Onstott, R. G.↗

NASA NTRS1991

Radar investigation of asteroids and planetary satellites

Radar reconnaissance of near-Earth asteroids, mainbelt asteroids, the Galilean satellites, the Martian satellites, and large Saturnian satellites, using the Arecibo 13-cm and the Goldstone 3.5-cm systems is discussed. Measurements of echo strength, polarization, delay/Doppler distribution of echo power provide information about dimensions, spin vector, large-scale topography, cm-to-m-scale morphology, and surface bulk density. The observations also yield refined estimates of target orbital elements.

Ostro, Steven J.↗

NASA NTRS1992

Ice in the northern lowlands and southern highlands of Mars and its enrichment beneath the Elysium Lavas

The simultaneously examination of ejecta mobility, crater morphology, and surface features has enabled several conclusions to be drawn regarding the location of subsurface ice in the region. The ice distribution is shown to be highly dependent upon latitude and geological situation; in particular, pronounced differences in the distribution between the highland and lowlands are seen, and concentrations of ice were detected beneath the Elysium lavas.

Cave, Julie A.↗