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At least 235 records · Page 13

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NASA NTRS1988

The Earth Radiation Budget Experiment

The Earth Radiation Budget Experiment (ERBE) data studied at present are as follows: (1) Solar Data from ERBS, NOAA-9, and NOAA-10. The solar total irradiance data obtained by the ERBE solar monitors serve as a calibration check on the earth viewing radiometers, as well as provide the experimental value of the solar constant needed in the net radiation computations. (2) The collocated satellite altitude irradiances from ERBS and Nimbus-7 Earth Radiation Budget Measurements are investigated. The sun-synchronous, near-local-noon Nimbus-7 satellite has coincident orbital intersections with the non-sun-synchronous ERBS spacecraft. The objective here is to compare the WFOV and MFOV (wide and medium field-of-view) observations of the ERBS/ERBE, and the Nimbus-7 ERB data sets at the points of their orbital intersections. (3) Globally and zonally averaged ERBE/ERBS data are examined. Investigations of the globally and zonally averaged ERB obtained from the ERBS SCANNER, MFOV and WFOV and the Nimbus-7 WFOV is being carried out to assess the sensor performance.

Mecherikunnel, A. T.↗

NASA NTRS1989

Effect of contrast on the perception of direction of a moving pattern

A series of experiments examining the effect of contrast on the perception of moving plaids was performed to test the hypothesis that the human visual system determines the direction of a moving plaid in a two-staged process: decomposition into component motion followed by application of the intersection-of-contraints rule. Although there is recent evidence that the first tenet of the hypothesis is correct, i.e., that plaid motion is initially decomposed into the motion of the individual grating components, the nature of the second-stage combination rule has not yet been established. It was found that when the gratings within the plaid are of different contrast the preceived direction is not predicted by the intersection-of-constraints rule. There is a strong (up to 20 deg) bias in the direction of the higher-constrast grating. A revised model, which incorporates a contrast-dependent weighting of perceived grating speed as observed for one-dimensional patterns, can quantitatively predict most of the results. The results are then discussed in the context of various models of human visual motion processing and of physiological responses of neurons in the primate visual system.

Stone, L. S.↗

NASA NTRS1990

Extensions of algebraic image operators: An approach to model-based vision

Researchers extend their previous research on a highly structured and compact algebraic representation of grey-level images which can be viewed as fuzzy sets. Addition and multiplication are defined for the set of all grey-level images, which can then be described as polynomials of two variables. Utilizing this new algebraic structure, researchers devised an innovative, efficient edge detection scheme. An accurate method for deriving gradient component information from this edge detector is presented. Based upon this new edge detection system researchers developed a robust method for linear feature extraction by combining the techniques of a Hough transform and a line follower. The major advantage of this feature extractor is its general, object-independent nature. Target attributes, such as line segment lengths, intersections, angles of intersection, and endpoints are derived by the feature extraction algorithm and employed during model matching. The algebraic operators are global operations which are easily reconfigured to operate on any size or shape region. This provides a natural platform from which to pursue dynamic scene analysis. A method for optimizing the linear feature extractor which capitalizes on the spatially reconfiguration nature of the edge detector/gradient component operator is discussed.

Lerner, Bao-Ting↗

NASA NTRS1989

Superclustering in the explosion scenario. II - Prolate spheroidal shells from superconducting cosmic strings

If galaxies form on shells, then clusters of galaxies should form at the vertices where three shells intersect. Weinberg, Ostriker, and Dekel (WOD, 1989) studied this picture quantitatively and found that an intersecting spherical shell model reproduces many of the properties of the observed distribution of galaxy clusters, but that too much superclustering is produced. In this paper, the WOD analysis is repeated with prolate spheroids that could be created by superconducting cosmic strings. It is found that most of the attractive features of the WOD model are maintained in the more general case and there is slight improvement in some aspects, but that the overall problem of excessive superclustering is not really alleviated.

Borden, David↗

NASA NTRS1989

Growth of Greenland ice sheet - Measurement

Measurements of ice-sheet elevation change by satellite altimetry show that the Greenland surface elevation south of 72 deg north latitude is increasing. The vertical velocity of the surface is 0.20 + or - 0.06 meters/year from measured changes in surface elevations at 5906 intersections between Geosat paths in 1985 and Seasat in 1978, and 0.28 + or - 0.02 meters/year from 256,694 intersections of Geosat paths during a 548-day period of 1985 to 1986.

Zwally, H. Jay↗

NASA NTRS1990

Drag on the Lageos satellite

The drag data on the Lageos satellite collected between 1976 and 1987 are analyzed, and the cause of fluctuations observed at times when the orbit intersects the earth's shadow is investigated. The average drag on the Lageos consists of three types of drag: the Yarkovsky thermal drag, which accounts for about 70 percent of the observed drag; the neutral particle drug, accounting for about 14 percent of the drag for a hydrogen number density of 5 x 10 to the 9th/cu m; and the charged particle drag, which accounts for 12 percent of average drag at a number density of 3 x 10 to the 9th and a temperature of 5000 K in the plasmasphere for a satellite potential of -1 V. The observed drag agrees with the particle environment at the Lageos altitude and the drag models. However, the fluctuations in Lageos's along-track acceleration when the orbit intersects the earth's shadow are still not well understood.

Rubincam, David Parry↗

NASA NTRS1989

Applications of algebraic image operators to model-based vision

A highly structured and compact algebraic representation of grey-level images is expanded. Addition and multiplication are defined for the set of all grey-level images, which can then be described as polynomials of two variables. Utilizing this new algebraic structure, an innovative, efficient edge-detection scheme is devised. A robust method for linear feature extraction is developed by combining the techniques of a Hough transform and a line follower with this new edge detection scheme. The major advantage of this feature extractor is its general, object-independent nature. Target attributes, such as line segment lengths, intersections, angles of intersection, and endpoints are derived by the feature extraction algorithm and employed during model matching. The feature extractor and model matcher are being incorporated into a distributed robot-control system.

Lerner, Bao-Ting↗

NASA NTRS1990

Effect of contrast on the perceived direction of a moving plaid

A series of experiments examining the effect of contrast on the perception of moving plaids is performed. This was done to test the hypothesis put forth by Adelson and Movshon (1982) that the human visual system determines the direction of a moving plaid in a two-staged process: decomposition into component motion followed by application of the intersection of constraints rule. When the gratings within the plaid are of different contrast, the perceived direction is not predicted by the intersection of constraints rule. There is a strong (up to 20 deg) bias in the direction of the higher-contrast grating. A revised model, which incorporates a contrast-dependent weighting of perceived grating speed as observed for one-dimensional patterns (Thompson, 1982), can quantitatively predict most of the results. Results are discussed in the context of various models of human visual motion processing and of physiological responses of neurons in the primate visual system.

Stone, L. S.↗

NASA NTRS1990

Convection in Neptune's magnetosphere

It is assumed that nonthermal escape from Triton's atmosphere produces a co-orbiting torus of unionized gas (presumably nitrogen and hydrogen) that subsequently becomes ionized by electron impact to populate a partial Triton plasma torus analogous to the Io plasma torus in Jupiter's magnetosphere. Centrifugal and magnetic-mirror forces confine the ions to a plasma sheet located between the magnetic and centrifugal equators. The ionization rate, and hence the torus ion concentration, is strongly peaked at the two points (approximately 180 deg apart in longitude) at which Triton's orbit intersects the plasma equator. During the course of Neptune's rotation these intersection points trace out two arcs roughly 75 deg in longitudinal extent, which we take to be the configuration of the resulting (partial) plasma torus. The implied partial ring currents produce a quadrupolar (four-cell) convection system that provides rapid outward transport of plasma from the arcs. Ring-current shielding, however, prevents this convection system from penetrating very far inside the plasma-arc distance. It is suggested that this convection/shielding process accounts for the radial confinement of trapped particles (150 keV or greater) within L = 14.3 as observed by the Voyager LECP instrument.

Hill, T. W.↗

NASA NTRS1990

On the large-scale structures formed by wakes of open cosmic strings

Large-scale structures of the universe have been variously described as sheetlike, filamentary, cellular, bubbles or spongelike. Recently cosmic strings became one of viable candidates for a galaxy formation scenario, and some of the large-scale structures seem to be simply explained by the open cosmic strings. According to this scenario, sheets are wakes which are traces of moving open cosmic strings where dark matter and baryonic matter have accumulated. Filaments are intersections of such wakes and high density regions are places where three wakes intersect almost orthogonally. The wakes formed at t sub eq become the largest surface density among all wakes, where t sub eq is the epoch when matter density equals to radiation density. If we assume that there is one open cosmic string per each horizon, then it can be explained that the typical distances among wakes, filaments and clusters are also approx. 10(exp 2) Mpc. This model does not exclude a much more large scale structure. Open cosmic string may move even now and accumulate cold dark matter after its traces. However, the surface density is much smaller than the ones formed at t sub eq. From this model, it is expected that the typical high density region will have extended features such as six filaments and three sheets and be surrounded by eight empty regions (voids). Here, the authors are mainly concerned with such structures and have made numerical simulations for the formation of such large scale structures.

Hara, Tetsuya↗

NASA NTRS1987

Method for fastening aircraft frame elements to sandwich skin panels covering same using woven fiber connectors

This invention relates to improvements in the method by which elongate frame elements such as the spars in aircraft wings are fastened to the skin panels covering same where these skin pane]s are of the sandwich type having inner and outer facesheets with a core bonded therebetween, such method consisting of preparing the panel to receive its frame elements by cutting elongate grooves spanwise through the inner facesheet and the core therebeneath while leaving the outer facesheet intact; bridging the gap thus produced in the inner facesheet with one bundle of filaments adhesively bonded thereto, the latter being contained in a woven connector in the form of a strap or band running lengthwise of the groove, and this filament bundle farming an endless strand of yarn that is laid back and forth transversely across the gap in side-by-side parallel rows but which are parted at intervals for the side-by-side lays of at least one other similar yarn strand to pass therebetween in intersecting relation; adhesive]y-bonding the skin panel core exposed within the groove to one or both sides of the frame element located proximal thereto using two endless strands of yarn laid back and forth to define a pair of intersecting webs arranged in spaced substantially parallel relation to one another that form a part of the connector and pass through the spaces between the first-mentioned yarn strands.

Paul J Jonas↗

NASA NTRS1990

Line-drawing algorithms for parallel machines

The fact that conventional line-drawing algorithms, when applied directly on parallel machines, can lead to very inefficient codes is addressed. It is suggested that instead of modifying an existing algorithm for a parallel machine, a more efficient implementation can be produced by going back to the invariants in the definition. Popular line-drawing algorithms are compared with two alternatives; distance to a line (a point is on the line if sufficiently close to it) and intersection with a line (a point on the line if an intersection point). For massively parallel single-instruction-multiple-data (SIMD) machines (with thousands of processors and up), the alternatives provide viable line-drawing algorithms. Because of the pixel-per-processor mapping, their performance is independent of the line length and orientation.

Pang, Alex T.↗

NASA NTRS1990

Numerical modeling of the atmosphere with an isentropic vertical coordinate

A theta-coordinate model simulating the nonlinear evolution of a baroclinic wave is presented. In the model, vertical discretization maintains important integral constraints such as conservation of the angular momentum and total energy. A massless-layer approach is used in the treatment of the intersections of coordinate surfaces with the lower boundary. This formally eliminates the intersection problem, but raises other computational problems. Horizontal discretization of the continuity and momentum equations in the model are designed to overcome these problems. Selected results from a 10-day integration with the 25-layer, beta-plane version of the model are presented. It is concluded that the model can simulate the nonlinear evolution of a baroclinic wave and associated dynamical processes without major computational difficulties.

Hsu, Yueh-Jiuan G.↗

NASA NTRS1991

Multiple shock-shock interference on a cylindrical leading edge

The details of an experimental study of shock wave interference heating on a cylindrical leading edge representative of the cowl of a rectangular hypersonic engine inlet are presented. This Mach 8 study has provided the first detailed pressure and heat transfer rate distributions on a cylinder resulting from a two-dimensional shockwave interference pattern created by two incident oblique shock waves intersecting the cylinder bow shock wave. The peak heat transfer rate was 38 times the undisturbed flow stagnation point level and occurred when the two oblique shock waves coalesced prior to intersecting the cylinder bow shock wave. Development of pressure deflection diagrams identified a new interference pattern consisting of concomitant supersonic jets separated from each other by a shear layer and submerged in the subsonic region between the bow shock wave and body.

Wieting, Allan R.↗

NASA NTRS1991

Cleavage crystallography of liquid metal embrittled aluminum alloys

The crystallography of liquid metal-induced transgranular cleavage in six aluminum alloys having a variety of microstructures has been determined via Laue X-ray back reflection. The cleavage crystallography was independent of alloy microstructure, and the cleavage plane was 100-plane oriented in all cases. It was further determined that the cleavage crystallography was not influenced by alloy texture. Examination of the fracture surface indicated that there was not a unique direction of crack propagation. In addition, the existence of 100-plane cleavage on alloy 2024 fracture surfaces was inferred by comparison of secondary cleavage crack intersection geometry on the 2024 surfaces with the geometry of secondary cleavage crack intersections on the test alloys.

Reynolds, A. P.↗

NASA NTRS1991

Preliminary 1:500,000-scale geologic mapping of Claritas Fossae, Mars

The Claritas Fossae system is a complex, linear fracture zone that extends from its northern intersection with Noctis Labyrinthus 1800 km south-southeast to its southern intersection with Thaumasia Fossae. The width of the fracture zone varies from 150 km in the north to 550 km in the south; topographic relief, based on radar data from Earth, is 1.0 to 1.5 km. Claritas Fossae and its coincident ridge or rise have been interpreted to be a horst with more than 8 km of vertical uplift, the greatest such uplift on Mars. Viking orbital images of sufficiently high resolution exist to provide the basis only for two 1:500,000 scale photomosaic base maps of Claritas Fossae. They extend en in echelon east and west, i.e., the southeast corner of the northern and western quadrangle (MTM-30102) is coincident with the northwest corner of the eastern and southern quadrangle (MTM-25107). Preliminary geologic maps of the two quadrangles were prepared. Materials in the quadrangles are Noachian and Hesperian age, and the quadrangles are characterized by the widespread occurrence of fractured and cratered plateau material, the oldest material in the map areas. Other information about the quadrangles is presented.

Underwood, James R., Jr.↗

NASA NTRS1992

A new method for recognizing quadric surfaces from range data and its application to telerobotics and automation

A feature set of two dimensional curves is obtained after intersecting symmetric objects like spheres, cones, cylinders, ellipsoids, paraboloids, and parallelepipeds with two planes. After determining the location and orientation of the objects in space, these objects are aligned so as to lie on a plane parallel to a suitable coordinate system. These objects are then intersected with a horizontal and a vertical plane. Experiments were carried out with range images of sphere and cylinder. The 3-D discriminant approach was used to recognize quadric surfaces made up of simulated data. Its application to real data was also studied.

Alvertos, Nicolas↗

NASA NTRS1992

Adjustable steam producing flexible orifice independent of fluid pressure

A self-adjusting choke for a fluids nozzle includes a membrane constructed of a single piece of flexible or elastic material. This flexible material is shaped to fit into the outlet of a nozzle. The body of the membrane has at least two flow channels, from one face to the other, which directs two streams of water to cross at the opening of the nozzle or at some point beyond. The elasticity and thickness of the membrane is selected to match the range of expected pressures and fluid velocities. The choke may have more than two flow channels, as long as they are aligned adjacent to one another and directed towards each other at the exit face. In a three orifice embodiment, one is directed upward, one is directed downward, and the one in the middle is directed forward. In this embodiment all three fluid streams intersect at some point past the nozzle opening. Under increased pressure the membrane will deform causing the orifices to realign in a more forward direction, causing the streams to intersect at a smaller angle. This reduces the force with which the separate streams impact each other, still allowing the separate streams to unify into a single stable spiralling stream in spite of the increased pressure.

Morrison, Andrew D.↗