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At least 919 records · Page 51
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Spectral analysis of groove spacing on Ganymede

A quantitative analysis of groove spacing on Ganymede is described. Fourier transforms of a large number of photometric profiles across groove sets are calculated and the resulting power spectra are examined for the position and strength of peaks representing topographic periodicities. The geographic and global statistical distribution of groove wavelengths are examined, and these data are related to models of groove tectonism. It is found that groove spacing on Ganymede shows an approximately long-normal distribution with a minimum of about 3.5 km, a maximum of about 17 km, and a mean of 8.4 km. Groove spacing tends to be quite regular within a single groove set but can vary substantially from one groove set to another within a single geographic region.

Grimm, R. E.↗
NASA NTRS1984

Polyimides containing oxyethylene units. II - Polymerization of 3.3', 4.4'-benzophenonetetra carboxylic dianhydride and pyromellitic dianhydride

The study is concerned with the polymerization of diamines 2a-d with readily available dianhydrides, i.e., 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) and pyromellitic dianhydride (PMDA). The synthesis and polymerization of asymmetric diamines containing substituted alkylene ether linkages are also investigated. It is assumed that the flexibility introduced into the polymer chain through the use of such diamines would result in moderate glass transition temperatures that would allow the systems to be melt processed. Mixtures of diamines are also copolymerized so as to further disrupt the polymer's symmetry and recurrence regularity. The properties of the resulting polymers are briefly discussed.

Harris, F. W.↗
NASA NTRS1983

Impedance properties of circular microstrip antenna

A moment method solution to the input impedance of a circular microstrip antenna excited by either a microstrip feed or a coaxial probe is presented. Using the exact dyadic Green's function and the Fourier transform the problem is formulated in terms of Richmond's reaction integral equation from which the unknown patch current can be solved for. The patch current is expanded in terms of regular surface patch modes and an attachment mode (for probe excited case) which insures continuity of the current at probe/patch junction, proper polarization and p-dependance of patch current in the vicinity of the probe. The input impedance of a circular microstrip antenna is computed and compared with earlier results. Effect of attachment mode on the input impedance is also discussed.

Deshpande, M. D.↗
NASA NTRS1984

CCD use at Lick Observatory

The CCD detector and data handling system in regular use at Lick Observatory are described. A grism system has been installed on the automated Cassegrain spectrograph at the Shane 3-meter telescope. A very compact CCD cooling system has been developed using a commercial gas expansion refrigerator; the dewar is a cylinder 15 cm in diameter and 6 cm high. The data acquisition computer, an LSI 11/23 with 256 kbyte RAM, 160 Mbyte Winchester disk, and color video display, provides for FITS format magnetic tape storage as well as preliminary analysis of images and spectra. The 3-meter telescope spectrographic system uses a 500 x 500 pixel thinned CCD. Design information and operational experience for these detector systems are presented along with some results to illustrate the quality of the data being obtained and the current limitations of the CCD detectors and data system.

Lauer, T. R.↗
NASA NTRS1985

Star formation in grand design and flocculent spiral galaxies

An examination is conducted of the colors and neutral hydrogen contents of spiral galaxies which have been classified in the Elmegreen and Elmegreen arm morphology system. Using these data, possible differences between the star formation activity in spiral galaxies with and without classic spiral arms are delineated. At the same revised Hubble type, spiral galaxies with regular global arm patterns (the grand design spirals) are bluer than spiral galaxies lacking such patterns (the flocculent spirals) by a small, but statistically significant amount (approximately 0.05 in B-V and approximately 0.15 in U-V). The neutral hydrogen contents of the two groups are roughly similar, implying the star formation rate averaged over a Hubble time has been approximately the same in grand design and flocculent systems. The color differences can be explained either by using an initial mass function in the flocculent spiral galaxies which is deficient in massive stars by a factor of 2 compared with the grand design systems, or by a decrease of 30 percent in the ratio of recent to past star formation rates in flocculent galaxies. The possibility is discussed that systematic Hubble type misclassifications significantly affect these conclusions.

Romanishin, W.↗
NASA NTRS1985

A shadowed flow in the stem of the Crab nebula?

The faint radio and emission line 'jet' outward from the northern boundary of the Crab Nebula which appears as a neat right cylinder is modelled here as the convected margin of a gas cloud that accidentially cast its shallow across the nearly ballistic flow of the stellar envelope ejected in the supernova explosion. It is shown that this model is consistent with known data on the jet, and that it accounts for the strikingly regular geometrical features in a natural way. In contrast, flow instability models do not easily result in so neat a cylinder.

Morrison, P.↗
NASA NTRS1984

Timber inventory using Landsat

The results of recent efforts to apply Landsat MSS imagery, in concert with topological maps, to forestry timber inventories via the FOCIS program are reported. FOCIS (Forests Classification and Inventory System) was defined for inventorying the lumber volume of coniferous tree types in rugged terrain regions. Data from four bands serve as input for unsupervised clustering and iterative labeling of the elevation, slope angle, and subregions of interest. Simulated photographic maps are generated which serve as overlays for regular maps for assessing timber harvests and sales goals. Sample procedures followed in mapping the Eldorado region forests in the Sierra Nevada mountains are discussed.

Strahler, A. H.↗
NASA NTRS1985

A VLSI design of a pipeline Reed-Solomon decoder

A pipeline structure of a transform decoder similar to a systolic array was developed to decode Reed-Solomon (RS) codes. An important ingredient of this design is a modified Euclidean algorithm for computing the error locator polynomial. The computation of inverse field elements is completely avoided in this modification of Euclid's algorithm. The new decoder is regular and simple, and naturally suitable for VLSI implementation.

Shao, H. M.↗
NASA NTRS1984

The origin and evolution of planetary rings

Roche (1847) suggested that Saturn's rings may be the fragments of a disrupted satellite rather than the uncoagulated remnant of a circumplanetary disk from which the regular satellites formed. In order to address this unresolved central issue, attention is given to the dynamical processes of viscous spreading, gas drag, particulate coagulation, and the effect of further matter infall from heliocentric orbit onto the planet/disk, all of which act on a gas/solid disk in Keplerian motion. In view of these considerations, it is suggested that rings were created by the disruption of large satellites which were less sensitive to the destructive processes present during the planet's formation. This hypothesis explains the presence of shepherd satellites, such as large collision fragments, which coexist in the same orbital range as the ring particles.

Harris, A. W.↗
NASA NTRS1985

Space platforms and autonomy

Potential applications for autonomous space platforms (SP) are discussed. The platforms are assumed to have long in-service lifetimes and therefore be flexible as to configuration modification and payload changeout. Higher degrees of autonomy, particularly from ground control, are made possible because of the rapid increase of microprocessor power and artificial intelligence advances. Functioning independently, the platforms are to rely only on periodic refurbishment visits by, e.g., the Orbiter. The Manned Space Station (MSS) will be the most complex structure, involving multifacted man-machine interfaces. The SP can be subsystems of the MSS (or other platforms), handling communications enunciation, data acquisition, analysis and telemetry, fault detection and isolation, systems monitoring and control, etc. The SP adopted will depend in all cases on costs vs benefits analyses to determine the worth of removing the function(s) from direct, regular human intervention.

Easter, R. W.↗
NASA NTRS1985

VLSI architectures for computing multiplications and inverses in GF(2m)

Finite field arithmetic logic is central in the implementation of Reed-Solomon coders and in some cryptographic algorithms. There is a need for good multiplication and inversion algorithms that are easily realized on VLSI chips. Massey and Omura recently developed a new multiplication algorithm for Galois fields based on a normal basis representation. A pipeline structure is developed to realize the Massey-Omura multiplier in the finite field GF(2m). With the simple squaring property of the normal-basis representation used together with this multiplier, a pipeline architecture is also developed for computing inverse elements in GF(2m). The designs developed for the Massey-Omura multiplier and the computation of inverse elements are regular, simple, expandable and, therefore, naturally suitable for VLSI implementation.

Wang, C. C.↗
NASA NTRS1985

Elastic constant versus temperature behavior of three hardened maraging steels

Elastic constants of three maraging steels were determined by measuring ultrasonic velocities. Annealed steels show slightly lower bulk moduli and considerably lower shear moduli than hardened steels. All the elastic constants (Young's modulus, shear modulus, bulk modulus and Poisson's ratio) show regular temperature behavior between 76 and 400 K. Young's modulus and the shear modulus increase with increasing yield strength, but the bulk modulus and Poisson's ratio are relatively unchanged. Elastic anisotropy is quite small.

Ledbetter, H. M.↗
NASA NTRS1985

A global climatology of total ozone from the Nimbus 7 total ozone mapping spectrometer

A global climatology of total column ozone has been computed from 4 years of daily observations by the total ozone mapping spectrometer aboard the Nimbus 7 polar-orbiting satellite. Observations were made at local noon; no observations are available in polar regions during the polar night. The orbital data have been area averaged onto a regular 5 deg by 5 deg latitude-longitude grid. The global coverage is more than 90 percent complete during the last 3 observing years (October 1979 to September 1982) and approximately 70 percent complete during the first year (October 1978 to September 1979). Global maps of the temporal mean and rms variance and the amplitude and phase of the annual and semiannual harmonics are presented. Similar analyses of the zonal mean values are given along with a time-latitude section of the zonal-mean total ozone. This climatology should be useful both for validating numerical models and for inspiring theoretical analyses.

Bowman, K. P.↗
NASA NTRS1985

Lidar observations of vertically organized convection in the planetary boundary layer over the ocean

Observations of a convective planetary boundary layer (PBL) were made with an airborne, downward-looking lidar system over the Atlantic Ocean during a cold air outbreak. The lidar data revealed well-organized, regularly spaced cellular convection with dominant spacial scales between two and four times the height of the boundary layer. It is demonstrated that the lidar can accurately measure the structure of the PBL with high vertical and horizontal resolution. Parameters important for PBL modeling such as entrainment zone thickness, entrainment rate, PBL height and relative heat flux can be inferred from the lidar data. It is suggested that wind shear at the PBL top may influence both entrainment and convective cell size.

Melfi, S. H.↗
NASA NTRS1985

Microwave inversion of leaf area and inclination angle distributions from backscattered data

The backscattering coefficient from a slab of thin randomly oriented dielectric disks over a flat lossy ground is used to reconstruct the inclination angle and area distributions of the disks. The disks are employed to model a leafy agricultural crop, such as soybeans, in the L-band microwave region of the spectrum. The distorted Born approximation, along with a thin disk approximation, is used to obtain a relationship between the horizontal-like polarized backscattering coefficient and the joint probability density of disk inclination angle and disk radius. Assuming large skin depth reduces the relationship to a linear Fredholm integral equation of the first kind. Due to the ill-posed nature of this equation, a Phillips-Twomey regularization method with a second difference smoothing condition is used to find the inversion. Results are obtained in the presence of 1 and 10 percent noise for both leaf inclination angle and leaf radius densities.

Lang, R. H.↗
NASA NTRS1985

Theoretical Problems in Materials Science

Interactions between theoretical physics and material sciences to identify problems of common interest in which some of the powerful theoretical approaches developed for other branches of physics may be applied to problems in materials science are presented. A unique structure was identified in rapidly quenched Al-14% Mn. The material has long-range directed bonds with icosahedral symmetry which does not form a regular structure but instead forms an amorphous-like quasiperiodic structure. Finite volume fractions of second phase material is advanced and is coupled with nucleation theory to describe the formation and structure of precipitating phases in alloys. Application of the theory of pattern formation to the problem of dendrite formation is studied.

Langer, J. S.↗
NASA NTRS1985

Thermal and Solutal Convection Damping Using an Applied Magnetic Field

Samples of eutectic Bi/Mn alloy were directionally solidified in the presence of a transverse magnetic field to determine if gravity-induced convection effects could be reduced or eliminated. The microstructure of Bi/MnBi is characterized by a regular, aligned-rod eutectic morphology that is sensitive to growth conditions. This, combined with ferromagnetism of one of the components, MnBi, can be used to eliminate whether convection effects are significant enough to be effected by the presence of a static, homogeneous, magnetic field.

Pirich, R. G.↗
NASA NTRS1985

Particle generation experience in Langley's 16-foot transonic tunnel

The Langley 16-Foot Transonic Tunnel is a single-return, continuous-flow, atmospheric tunnel which uses air exchange for cooling. The tunnel speed is continuously variable from Mach 0 to 1.30. The test section is a regular octagon in cross-section with slots at the corners of the octagon. The laser velocimeter optics, laser, photomultipliers, etc. are mounted in the test section plenum chamber which surrounds the test section. The test volume is approximately a 1-meter cube about the tunnel center line centered on tunnel station 40.84 meters. The seeding system particle generators are mounted on the upstream side of the fourth set of turning vanes approximately 49 meters upstream of the test volume. At this point the tunnel has a diameter of 17.68 meters which meant that installation of the generators was a difficult procedure. It might be noted that particle generation had to be continuous as when the generators were turned off the data rate rapidly deteriorated to zero.

Reubush, D. E.↗