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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Solution of elliptic partial differential equations by fast Poisson solvers using a local relaxation factor. 1: One-step method

An algorithm for solving a large class of two- and three-dimensional nonseparable elliptic partial differential equations (PDE's) is developed and tested. It uses a modified D'Yakanov-Gunn iterative procedure in which the relaxation factor is grid-point dependent. It is easy to implement and applicable to a variety of boundary conditions. It is also computationally efficient, as indicated by the results of numerical comparisons with other established methods. Furthermore, the current algorithm has the advantage of possessing two important properties which the traditional iterative methods lack; that is: (1) the convergence rate is relatively insensitive to grid-cell size and aspect ratio, and (2) the convergence rate can be easily estimated by using the coefficient of the PDE being solved.

Chang, S. C.↗
NASA NTRS1984

Comparison of theoretical and flight-measured local flow aerodynamics for a low-aspect-ratio fin

Flight test and theoretical aerodynamic data were obtained for a flight test fixture mounted on the underside of an F-104G aircraft. The theoretical data were generated using two codes, a two dimensional transonic code called Code H, and a three dimensional subsonic and supersonic code call wing-body. Pressure distributions generated by the codes for the flight test fixture as well as boundary layer displacement thickness generated by the two dimensional code were compared to the flight test data. The two dimensional code pressure distributions compared well except at the minimum pressure point and trailing edge. Shock locations compared well except at high transonic speeds. The three dimensional code pressure distributions compared well except at the trailing edge of the flight test fixture. The two dimensional code does not predict displacement thickness of the flight test fixture well.

Johnson, J. B.↗
NASA NTRS1985

Candidate galaxies for study of the local velocity field and distance scale using Space Telescope. I - The most easily resolved. II - The more difficult cases. III - Galaxies in the Virgo cluster core

A subset of 1246 Shapley-Ames galaxies is presented which holds promise for some degree of useful resolution by the Space Telescope. The 95 candidate galaxies easiest to resolve are described and illustrated first. Many of these can be readily resolved into brightest stars from the ground with presently available telescopes at a few sites, while others might be resolved from the ground into at least the brightest blue supergiants. Then, 152 additional candidates are presented which can only be adequately studied with the Space Telescope. Finally, the most promising galaxies for studies of the resolved stellar content that occur in the central six degree core of the Virgo cluster are given. These are expected to be useful for any direct attack on the distance to the cluster itself.

Sandage, A.↗
NASA NTRS1985

Influence of local land-surface processes on the Indian monsoon - A numerical study

Integrations made with general circulation models to investigate the influence of changes in the land-surface fluxes, over the Indian subcontinent, on the monsoon circulation and rainfall are presented. The experiments conducted include: (1) a control, (2) increased land-surface albedo, (3) increased land-surface albedo and reduced land-surface roughness, and (4) increased land-surface albedo, reduced surface roughness, and no evapotranspiration. A comparison of ensemble means of the data is provided; a decrease in rainfall is observed when the surface albedo is increased and the surface roughness reduced. Low surface roughness makes the horizontal transport of planetary boundary layer (PBL) westerly, reducing cross-isobaric moisture and thereby rainfall. Evapotranspiration had no influence on rainfall because of the PBL motion and moisture convergence. The correlation between surface albedo, surface roughness and vegetation is examined.

Sud, Y. C.↗
NASA NTRS1985

Selective broadcast interconnection - A novel scheme for fiber-optic local-area networks

A passive, unswitched scheme is introduced for directly interconnecting N stations, each of which has C transmitters and receivers. Implementations using fiber optics with spatial multiplexing and optionally wavelength multiplexing are discussed. This scheme utilizes the same resources as standard topologies with C parallel buses but outperforms them in two respects: (1) the aggregate throughput is proportional to C squared rather than to C; and (2) the power of each transmitter need reach only N/C, instead of N, receivers.

Marhic, M. E.↗
NASA NTRS1986

Black holes and local dark matter

Two independent constraints are placed on the amount of dark matter in black holes contained in the galactic disk. First, gas accretion by black holes leads to X-ray emission which cannot exceed the observed soft X-ray background. Second, metals produced in stellar processes that lead to black hole formation cannot exceed the observed disk metal abundance. Based on these constraints, it appears unlikely that the missing disk mass could be contained in black holes. A consequence of this conclusion is that at least two different types of dark matter are needed to solve the various missing mass problems.

Hegyi, D. J.↗
NASA NTRS1985

An attempt to localize and identify the gravity sensing mechanism of plants

The oxidation and transport of indole-3-acetic acid (IAA) in Zea mays is examined towards an understanding of the gravity-influenced promotion of growth in plants. An enzyme that oxidizes IAA to a nongrowth-promoting species has been partially purified, and determined to be stimulated by a lipoidal factor. Data suggest that the upward transport of IAA in the stele and outward movement from the stele into the mesophyll cortex is metabolically mediated, and possibly affected by the gravitational stimulus. It is postulated that hormone assymmetries can arise by 'potential-gating' of the transport channels between the various plant tissues.

Bandurski, R. S.↗
NASA NTRS1985

Cytochemical localization of calcium in cap cells of primary roots of Zea mays L

The cellular distribution of Ca in caps of primary roots of Zea mays was examined during the onset and early stages of gravicurvature to determine its possible role in root gravitropism. Staining becomes associated with the portion of the cell wall adjacent to the distal end of the cell after five minutes, and persists throughout the onset of gravicurvature. The outermost peripheral cells of roots oriented horizontally and vertically secrete Ca through plasmodesmata-like channels in their cell walls. Data suggest that Ca is not transported laterally through the columella tissue,but rather that the movement of Ca to the lower side of caps of horizontally-oriented roots is at least partially through and/or on the mucilage of the cap, and via an electrochemical gradient. An important role in root gravitropism is indicated for Ca secretion by peripheral cells.

Moore, R.↗
NASA NTRS1986

A theoretical study of the production and decay of localized electron density enhancements in the polar ionosphere

Uniform convection patterns were introduced into a high latitude time-dependent F region model (HLTD) to study if soft auroral particle precipitation is a necessary precondition to blob formation in the ionosphere. Attention was limited to the conditions leading to the formation of parent blobs (dimensions of at least 10 km) due to plasma instabilities. Consideration was given to the effects of discrete auroral structures and to different O(+) precipitation ionization rate profiles during solar maximum conditions in the thermosphere. Blobs were assumed to be produced on the dayside due to ionization caused by sun-aligned arcs. The simulations indicated that parent blobs would form whenever plasma flux tubes in the ionosphere were exposed to soft particle precipitation lasting more than 10 min. The blobs cease to exist when convected to a region with a high particle production rate where the background particle density exceeds that of the blobs. Conditions wherein either hard or soft particle production can produce blobs are outlined.

Sojka, J. J.↗
NASA NTRS1987

Localized Densification of Tile for Impact Resistance

Densification process increases impact resistance of lightweight, porous silica tile without appreciably raising weight. Colloidal suspension of silica used to increase density of small portion of tile to be strengthened. Process controls penetration of suspension laterally and vertically so densification limited to volume where needed. Insures weight increased only minimally. See also "Attaching Metal Fasteners to Silica Tiles" (MSC-20537).

Smiser, Laurence W.↗
NASA NTRS1986

Solution of elliptic partial differential equations by fast Poisson solvers using a local relaxation factor. 2: Two-step method

A two-step semidirect procedure is developed to accelerate the one-step procedure described in NASA TP-2529. For a set of constant coefficient model problems, the acceleration factor increases from 1 to 2 as the one-step procedure convergence rate decreases from + infinity to 0. It is also shown numerically that the two-step procedure can substantially accelerate the convergence of the numerical solution of many partial differential equations (PDE's) with variable coefficients.

Chang, S. C.↗
NASA NTRS1986

Local interstellar gasdynamical stability in spiral arm flow

The stability of two-dimensional interstellar gas flow passing through a spiral potential has been investigated. The background flow is assumed to move in a tightly wound potential, which may be regarded as external or self-generated. The unperturbed flow, which may be time dependent, is self-gravitating and satisfies the Roberts equations of motion. A polytropic, single-fluid assumption has been used. Magnetic effects are not considered. The motivation behind this work is to try to understand how much of the diversity of spiral arm morphology can be understood by large scale gas dynamical processes alone. To this end, it is suggested that spurring and feathering, and forming molecular cloud complexes may be closely related in the sense of having dynamically similar origins.

Balbus, S. A.↗
NASA NTRS1986

Comparison of theoretical and flight-measured local flow aerodynamics for a low-aspect-ratio fin

Flight test and theoretical aerodynamic data were obtained for a flight test fixture mounted on the underside of an F-104G aircraft. The theoretical data were generated using two codes: a two-dimensional transonic code called code H, and a three-dimensional subsonic and supersonic code called wing-body. Pressure distributions generated by the codes for the flight test fixture, as well as compared with the flight-measured data. The two-dimensional code pressure distributions compared well except at the minimum pressure point and the trailing edge. Shock locations compared well except at high transonic speeds. However, the two-dimensional code did not adequately predict the displacement thickness of the flight test fixture. The three-dimensional code pressure distributions compared well except at the trailing edge of the flight test fixture.

Johnson, J. Blair↗
NASA NTRS1986

Local network interconnection through a satellite point-to-multipoint link

Four architectures to implement a point to multipoint satellite link protocol for communication services offered by the Telecom 1 satellite network are presented. A safe communication service with error correction and flow control facilities is described. It is shown that a time transparent communication system combines simplicity and cost advantages.

Duarte, O. Muniz Bandeira↗
NASA NTRS1987

Local-scale stratigraphy of grooved terrain on Ganymede

The surface of the Jovian satellite, Ganymede, is divided into two main units, dark terrain cut by arcuate and subradial furrows, and light terrain consisting largely of areas with pervasive U-shaped grooves. The grooved terrain may be subdivided on the basis of pervasive morphology of groove domains into four terrain types: (1) elongate bands of parallel grooves (groove lanes); (2) polygonal domains of parallel grooves (grooved polygons); (3) polygonal domains of two orthogonal groove sets (reticulate terrain); and (4) polygons having two to several complexly cross-cutting groove sets (complex grooved terrain). Reticulate terrain is frequently dark and not extensively resurfaced, and grades to a more hummocky terrain type. The other three grooved terrain types have almost universally been resurfaced by light material during their emplacement. The sequence of events during grooved terrain emplacement has been investigated. An attempt is made to integrate observed geologic and tectonic patterns to better constrain the relative ages and styles of emplacement of grooved terrain types. A revised model of grooved terrain emplacement is proposed and is tested using detailed geologic mapping and measurement of crater density.

Murchie, Scott L.↗
NASA NTRS1986

The local interstellar medium. IV - The line of sight to Upsilon Scorpii

Profile fitting of Copernicus UV absorption lines separates out four components in the line of sight to Upsilon Sco. Velocities for three of the components, including the two components associated with major H I and H II regions, are in excellent agreement with the corresponding components in the nearby line of sight to Lambda Sco. The velocity of the remaining component is between the velocities of the two remaining Lambda Sco components. Column densities of the various ionization stages of C, N, Si, S, and Ar in the major H I and H II regions are in reasonable agreement with those determined from the Lambda Sco observations, with four notable exceptions. In Upsilon Sco there is more N II and substantially less S III in the H I component and significantly less N I and Si III in the H II component.

Eder, D. C.↗
NASA NTRS1986

The effect of local advection on the inference of soil moisture from thermal infrared radiances

The degree to which the GOES-VISSR infrared data can be used to infer area-averaged soil moisture is explored for a five-day case study period. Chosen variables are transformed and incorporated into a multiple linear regression. The actual observations, rather than a simplified model, are used to determine the relationship between soil moisture and GOES-IR radiance. It is shown that a depletion coefficient of 0.92 produces an index of ground truth which is best correlated with soil moisture as inferred from GOES thermal infrared data. When all individual daily soil estimates during the case study period are averaged at each point and compared to the average observed soil moisture, the data correlate at 0.85. This implies that the algorithm can distinguish at least four categories of soil moisture.

Wetzel, Peter J.↗