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At least 199 records · Page 11

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NASA NTRS1986

Effect of texture on magnetoacoustic stress measurement in steel

The effect of texture on the general stress measurements of a heavily cold rolled steel plate is analyzed. Changes in the acoustic natural velocity for plate samples with their long axes perpendicular, parallel, and in a 40 degree direction with respect to the rolling axis were measured; graphs of the velocity variations for the three samples are provided. It is observed that the negative minimum change in the acoustic natural velocity under residual compression for the perpendicular sample is about half that of the parallel and 40 degree samples indicating that the functional form of the velocity curve is influenced by the structural properties of the sample; however, the stress measurements are unaffected by the texture.

Namkung, M.↗

NASA NTRS1986

Compositions and textures of relic forsterite in carbonaceous and unequilibrated ordinary chondrites

The compositions and textures of olivines in equilibrated ordinary chondrites, C1, C2, and C3 meteorites are described. The olivines are classified by color into blue, red, or dark olivines. The characteristic features of blue olivines are examined. It is observed that the texture of the olivine: (1) forms cores in single olivine grains; (2) shows subhedral to euhedral boundaries against rim olivines; (3) rarely contains inclusions; (4) has embayments containing olivines similar to that of the rim; and (5) occurs within chondrules. The mode of formation for blue olivines, the relation between blue olivine and high temperature compounds, and modifications in the features of blue olivines are analyzed. It is noted that the olivine is a product of condensation, has been modified by additions of olivine formed from a liquid, and that these olivines represent relic grains that are similar to olivines found in cosmic particles and in cores of some deep sea particles.

Steele, I. M.↗

NASA NTRS1988

Effect of melt spinning on grain size and texture in Ni-Mo alloys

Chill-block melt-spun ribbons of Ni-Mo alloys with Mo contents of 8 to 41.8 wt pct have been examined for microstructure and texture dependence on processing conditions. Linear features observed in grains solidified with a planar liquid-solid interface at the quench side of the ribbons have been identified to be due to the twins on the (111)gamma plane formed during solidification. Grain size variation with the wheel surface speed and the alloy composition has been studied. The crystallographic texture on the quench side and the free surface side of the ribbons has been investigated.

Tewari, S. N.↗

NASA NTRS1988

Texture-based cloud classification

The purpose of the 1988 ASEE Summer Program has been to broaden the application of texture-based cloud classification approaches to lower spatial resolution GOES imagery, and to design texture-based approaches for determining cloud cover over high albedo surfaces.

Welch, Ronald M.↗

NASA NTRS1989

Dynamic crystallization of chondrule melts of porphyritic olivine composition - Textures experimental and natural

A full range of textures characteristic for porphyritic olivine chondrules was reproduced in melts of the same composition, crystallized under dynamic crystallization conditions (under controlled cooling), as determined by electron microprobe analyses. The primary differences between the natural and experimentally produced porphyritic olivine textures were the nature and the extent of matrix crystallization, which reflected the subsolidus or low-temperature cooling history. The most confining limits on the chondrule-forming process were found to be the presence of crystalline precursors for the chondrule melts and the upper temperature limit of melting.

Lofgren, Gary↗

NASA NTRS1991

Texture analysis of radiometric signatures of new sea ice forming in Arctic leads

Analysis of 33.6-GHz, high-resolution, passive microwave images suggests that new sea ice accumulating in open leads is characterized by a unique textural signature which can be used to discriminate new ice forming in this environment from adjacent surfaces of similar radiometric temperature. Ten training areas were selected from the data set, three of which consisted entirely of first-year ice, four entirely of multilayer ice, and three of new ice in open leads in the process of freezing. A simple gradient operator was used to characterize the radiometric texture in each training region in terms of the degree to which radiometric gradients are oriented. New ice in leads has a sufficiently high proportion of well-oriented features to distinguish it uniquely from first-year ice and multiyear ice. The predominance of well-oriented features probably reflects physical processes by which new ice accumulates in open leads. Banded structures, which are evident in aerial photographs of new ice, apparently give rise to the radiometric signature observed, in which the trend of brightness temperature gradients is aligned parallel to lead trends. First-year ice and multiyear ice, which have been subjected to a more random growth and process history, lack this banded structure and therefore are characterized by signatures in which well-aligned elements are less dominant.

Eppler, Duane T.↗

NASA NTRS1992

Statistical Approach To Extraction Of Texture In SAR

Improved statistical method of extraction of textural features in synthetic-aperture-radar (SAR) images takes account of effects of scheme used to sample raw SAR data, system noise, resolution of radar equipment, and speckle. Treatment of speckle incorporated into overall statistical treatment of speckle, system noise, and natural variations in texture. One computes speckle auto-correlation function from system transfer function that expresses effect of radar aperature and incorporates range and azimuth resolutions.

Rignot, Eric J.↗

NASA NTRS1992

Ion Beam Textured and Coated Surfaces Experiment (IBEX)

Ion beam textured and commercial materials suitable for use in space power systems were flown in low Earth orbit on the Long Duration Exposure Facility (LDEF) for 5.8 years. Because of their location on LDEF (98 deg from the ram direction), the 36 materials were primarily exposed to vacuum ultraviolet radiation, thermal cycling, the vacuum of space, the micrometeoroid environment, and grazing incidence atomic oxygen. Measurements of solar absorptance and thermal emittance (pre- and post-flight) showed no changes for almost all of the materials, except for the S-13G and Kapton and coated Kapton samples. The optical property stability of ion beam textured surfaces and most other surfaces indicates that they are functionally durable to the synergistic rigors of the space environment.

Mirtich, Michael J.↗

NASA NTRS1991

A hydrodynamic approach to cosmology - Texture-seeded cold dark matter and hot dark matter cosmogonies

Hydrodynamical simulations of galaxy formation in a texture-seeded cosmology are presented, with attention given to Omega = 1 galaxies dominated by both hot dark matter (HDM) and cold dark matter (CDM). The simulations include both gravitational and hydrodynamical physics with a detailed treatment of collisional and radiative thermal processes, and use a cooling criterion to estimate galaxy formation. Background radiation fields and Zel'dovich-Sunyaev fluctuations are explicitly computed. The derived galaxy mass function is well fitted by the observed Schechter luminosity function for a baryonic M/L of 3 and total M/L of 60 in galaxies. In both HDM and CDM texture scenarios, the 'galaxies' and 'clusters' are significantly more strongly correlated than the dark matter due to physical bias processes. The slope of the correlation function in both cases is consistent with observations. In contrast to Gaussian models, peaks in the dark matter density distributrion are less correlated than average.

Cen, R. Y.↗

NASA NTRS1992

Apollo 15 green glass - Relationships between texture and composition

A suite of 365 Apollo 15 green-glass particles was analyzed by INAA and then described petrographically so that comparisons between composition and physical characteristics could be made. Nonuniform compositional distributions of crystalline and elongate particles were evident, although differences in the distribution of volatile-element coatings and extent of particle breakage were not as striking. A binomial evaluation of these textures on an intergroup basis supports the previously proposed hypothesis that the green-glass groups formed during discrete eruptive events because the groups that were defined compositionally also show significant differences in the average texture and structure of particles. Furthermore, in at least one case (Group D), intragroup differences in the distribution of vitrophyric and vitric particles were apparent. An extension of previous models for pyroclastic volcanism suggests that this feature may indicate that a systematic change in the composition of ejecta occurred as eruption progressed.

Steele, Alison M.↗

NASA NTRS1993

Scene segmentation of natural images using texture measures and back-propagation

Knowledge of the three-dimensional world is essential for many guidance and navigation applications. A sequence of images from an electro-optical sensor can be processed using optical flow algorithms to provide a sparse set of ranges as a function of azimuth and elevation. A natural way to enhance the range map is by interpolation. However, this should be undertaken with care since interpolation assumes continuity of range. The range is continuous in certain parts of the image and can jump at object boundaries. In such situations, the ability to detect homogeneous object regions by scene segmentation can be used to determine regions in the range map that can be enhanced by interpolation. The use of scalar features derived from the spatial gray-level dependence matrix for texture segmentation is explored. Thresholding of histograms of scalar texture features is done for several images to select scalar features which result in a meaningful segmentation of the images. Next, the selected scalar features are used with a neural net to automate the segmentation procedure. Back-propagation is used to train the feed forward neural network. The generalization of the network approach to subsequent images in the sequence is examined. It is shown that the use of multiple scalar features as input to the neural network result in a superior segmentation when compared with a single scalar feature. It is also shown that the scalar features, which are not useful individually, result in a good segmentation when used together. The methodology is applied to both indoor and outdoor images.

Sridhar, Banavar↗

NASA NTRS1992

Lithological and textural controls on radar and diurnal thermal signatures of weathered volcanic deposits, Lunar Crater region, Nevada

Radar backscatter intensity as measured by calibrated synthetic aperture radar (SAR) systems is primarily controlled by three factors: local incidence angle, wavelength-scale roughness, and dielectric permittivity of surface materials. Radar observations may be of limited use for geological investigations of surface composition, unless the relationships between lithology and the above characteristics can be adequately understood. In arid terrains, such as the Southwest U.S., weathering signatures (e.g. soil development, fracturing, debris grain size and shape, and hill slope characteristics) are controlled to some extent by lithologic characteristics of the parent bedrock. These textural features of outcrops and their associated debris will affect radar backscatter to varying degrees, and the multiple-wavelength capability of the JPL Airborne SAR (AIRSAR) system allows sampling of textures at three distinct scales. Diurnal temperature excursions of geologic surfaces are controlled primarily by the thermal inertia of surface materials, which is a measure of the resistance of a material to a change in temperature. Other influences include albedo, surface slopes affecting insolation, local meteorological conditions and surface emissivity at the relevant thermal wavelengths. To first order, thermal inertia variations on arid terrain surfaces result from grain size distribution and porosity differences, at scales ranging from micrometers to tens of meters. Diurnal thermal emission observations, such as those made by the JPL Thermal Infrared Multispectral Scanner (TIMS) airborne instrument, are thus influenced by geometric surface characteristics at scales comparable to those controlling radar backscatter. A preliminary report on a project involving a combination of field, laboratory and remote sensing observations of weathered felsic-to basaltic volcanic rock units exposed in the southern part of the Lunar Crater Volcanic Field, in the Pancake Range of central Nevada is presented. Focus is on the relationship of radar backscatter cross sections at multiple wavelengths, apparent diurnal temperature excursions identified in multi-temporal TIMS images, surface geometries related to weathering style, and parent bedrock lithology.

Plaut, Jeffrey J.↗

NASA NTRS1993

Multiplicity of chondrule heating events and the coarsening of chondrule textures

Our studies of compound chondrules show that most chondrules experienced at least two thermal events that produced appreciable amounts of melt. I suggest that chondrules were subjected to a hierarchy of brief heating events, the number increasing exponentially with decreasing intensity, and that some of intermediate intensity deposited enough heat to partially melt mesostasis glass and promote the growth of mafic mineral grains. This scenario can account for textures that require improbably low monotonic cooling rates in laboratory simulations, and also for the rarity of glassy chondrule textures despite the ease with which these are produced in the laboratory.

Wasson, John T.↗

NASA NTRS1994

Unsupervised texture image segmentation by improved neural network ART2

We here propose a segmentation algorithm of texture image for a computer vision system on a space robot. An improved adaptive resonance theory (ART2) for analog input patterns is adapted to classify the image based on a set of texture image features extracted by a fast spatial gray level dependence method (SGLDM). The nonlinear thresholding functions in input layer of the neural network have been constructed by two parts: firstly, to reduce the effects of image noises on the features, a set of sigmoid functions is chosen depending on the types of the feature; secondly, to enhance the contrast of the features, we adopt fuzzy mapping functions. The cluster number in output layer can be increased by an autogrowing mechanism constantly when a new pattern happens. Experimental results and original or segmented pictures are shown, including the comparison between this approach and K-means algorithm. The system written in C language is performed on a SUN-4/330 sparc-station with an image board IT-150 and a CCD camera.

Wang, Zhiling↗

NASA NTRS1995

Texturing of high T(sub c) superconducting polycrystalline fibers/wires by laser-driven directional solidification in an thermal gradient

This paper summarizes the technique of laser-driven directional solidification in a controlled thermal gradient of yttria stabilized zirconia core coated Y-Ba-Cu-O materials to produce textured high T(sub c) superconducting polycrystalline fibers/wires with improved critical current densities in the extended range of magnetic fields at temperatures greater than 77 K. The approach involves laser heating to minimize phase segregation by heating very rapidly through the two-phase incongruent melt region to the single phase melt region and directionally solidifying in a controlled thermal gradient to achieve highly textured grains in the fiber axis direction. The technique offers a higher grain growth rate and a lower thermal budget compared with a conventional thermal gradient and is amenable as a continuous process for improving the J(sub c) of high T(sub c) superconducting polycrystalline fibers/wires. The technique has the advantage of suppressing weak-link behavior by orientation of crystals, formation of dense structures with enhanced connectivity, formation of fewer and cleaner grain boundaries, and minimization of phase segregation in the incongruent melt region.

Varshney, Usha↗

NASA NTRS1998

Textural and Carbon Isotopic Analyses of Modern Carbonate Microbialites: Possible Ancient and Martian Analogs

Many modem and ancient carbonate deposits around the world have been recognized as microbial buildups or microbialites. Ancient microbialite structures have been divided into two basic categories based on their internal fabric or texture. They include stromatolites which have a predominantly laminated internal fabric and thrombolites which have an open-porous clotted fabric, that lacks laminae. The origin of these two basic microbial fabrics is still being debated in the literature. Understanding the origin and the various microorganisms involved in forming these modem fabrics is the key to the interpretation of similar fabrics in ancient and possibly Martian rocks. Therefore, detailed studies are needed on the microbiological makeup and origin of the fabrics in modem microbialites. Such studies may serve as analogs for ancient and Martian microbialites in the future. The purpose of this study is to examine the textures and carbon isotopic signatures of the following modem microbialites from the Bahamas: 1) a modem subtidal microbialite from Iguana Cay, Bahamas and 2) a modem microbial mat (stromatolite) from a hypersaline pond on Lee Stocking Island, Bahamas.

Thompson, Joel B.↗

NASA NTRS2000

Bayesian Fusion of Color and Texture Segmentations

In many applications one would like to use information from both color and texture features in order to segment an image. We propose a novel technique to combine "soft" segmentations computed for two or more features independently. Our algorithm merges models according to a mean entropy criterion, and allows to choose the appropriate number of classes for the final grouping. This technique also allows to improve the quality of supervised classification based on one feature (e.g. color) by merging information from unsupervised segmentation based on another feature (e.g., texture.)

Manduchi, Roberto↗

NASA NTRS2000

Micromechanical Characterization and Texture Analysis of Direct Cast Titanium Alloys Strips

This research was conducted to determine a post-processing technique to optimize mechanical and material properties of a number of Titanium based alloys and aluminides processed via Melt Overflow Solidification Technique (MORST). This technique was developed by NASA for the development of thin sheet titanium and titanium aluminides used in high temperature applications. The materials investigated in this study included conventional titanium alloy strips and foils, Ti-1100, Ti-24Al-11Nb (Alpha-2), and Ti-48Al-2Ta (Gamma). The methodology used included micro-characterization, heat-treatment, mechanical processing and mechanical testing. Characterization techniques included optical, electron microscopy, and x-ray texture analysis. The processing included heat-treatment and mechanical deformation through cold rolling. The initial as-cast materials were evaluated for their microstructure and mechanical properties. Different heat-treatment and rolling steps were chosen to process these materials. The properties were evaluated further and a processing relationship was established in order to obtain an optimum processing condition. The results showed that the as-cast material exhibited a Widmanstatten (fine grain) microstructure that developed into a microstructure with larger grains through processing steps. The texture intensity showed little change for all processing performed in this investigation.

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