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At least 1,225 records · Page 68

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NASA NTRS1990

The polar-ring galaxies NGC 2685 and NGC 3808B (VV 300)

Polar-ring galaxies (PRG) are among the most interesting examples of interaction between galaxies. A PRG is a galaxy with an elongated main body surrounded by a ring (or a disk) of stars, gas, and dust rotating in a near-polar plane (Schweizer, Whitmore, and Rubin, 1983). Accretion of matter by a massive lenticular galaxy from either intergalactic medium or a companion galaxy is usually considered as an explanation of the observed structure of PRG. In the latter case there are two possibilities: capture and merging of a neighbor galaxy, and accretion of mass from a companion galaxy during a close encounter. Two PRG formation scenarios just mentioned are illustrated here by the results of our observations of the peculiar galaxies NGC 2685 and NGC 3808B.

Reshetnikov, V. P.↗

NASA NTRS1991

An overview of the neuron ring model

The Neuron Ring model employs an avalanche structure with two important distinctions at the neuron level. Each neuron has two memory latches; one traps maximum neuronal activation during pattern presentation, and the other records the time of latch content change. The latches filter short term memory. In the process, they preserve length 1 snapshots of activation theory history. The model finds utility in pattern classification. Its synaptic weights are first conditioned with sample spectra. The model then receives a test or unknown signal. The objective is to identify the sample closest to the test signal. Class decision follows complete presentation of the test data. The decision maker relies exclusively on the latch contents. Presented here is an overview of the Neuron Ring at the seminar level.

Taber, Rod↗

NASA NTRS1990

Documentation for the token ring network simulation system

A manual is presented which describes the language features of the Token Ring Network Simulation System. The simulation system is a powerful simulation tool for token ring networks which allows the specification of various Medium Access Control (MAC) layer protocols as well as the specification of various features of upper layer ISO protocols. In addition to these features, it also allows the user to specify message and station classes virtually to any degree of detail desired. The choice of a language instead of an interactive system to specify network parameters was dictated by both flexibility and time considerations. The language was developed specifically for the simulation system, and is very simple. It is also user friendly in that language elements which do not apply to the case at hand are ignored rather than treated as errors.

Peden, Jeffery H.↗

NASA NTRS1991

I-BIEM calculations of the frequency dispersion and AC current distribution at disk and ring-disk electrodes

The Iterative Boundary Integral Equation Method (I-BIEM) has been applied to the problem of frequency dispersion at a disk electrode in a finite geometry. The I-BIEM permits the direct evaluation of the AC potential (a complex variable) using complex boundary conditions. The point spacing was made highly nonuniform, to give extremely high resolution in those regions where the variables change most rapidly, i.e., in the vicinity of the edge of the disk. Results are analyzed with respect to IR correction, equipotential surfaces, and reference electrode placement. The current distribution is also examined for a ring-disk configuration, with the ring and the disk at the same AC potential. It is shown that the apparent impedance of the disk is inductive at higher frequencies. The results are compared to analytic calculations from the literature, and usually agree to better than 0.001%.

Boris D Cahan↗

NASA NTRS1990

Recent findings on angular distributions of dayside ring current energetic ions

The angular distributions observed in the equatorial region for energetic protons, helium ions, and carbon-nitrogen-oxygen ions are investigated. The anisotropy index for the ions in the equatorial magnetosphere between L shells is examined, and a variety of angular distributions different from simple pancake distributions are presented. The survey reveals unusual angular distributions which suggest for the first time a net field-aligned transport of energetic ring current ions and a sharp intensity enhancement over a pitch angle range centered at 90 deg. The latter reflects a sharp boundary of ring curent energetic ions at L of roughly 3 and 4, plausibly due to the addition of a newly injected population.

Lui, A. T. Y.↗

NASA NTRS1991

Examination of a vortex-ring interaction phenomenon in an axisymmetric flow

Unsteady separated flow in an axisymmetric configuration is investigated, with the objective of analyzing vortex-ring formation and break-up and the ensuing interactions believed to be leading to breakdown of laminar flow. The model problem considered is an idealized representation of a combustor with a centerbody. Direct solution of the time-dependent incompressible Navier-Stokes equations is employed, with central-differencing for all spatial derivatives, to determine the response of this flow for Re = 2000, 5000 and 10,000. The last case revealed a rather novel unsteady vortex-ring interaction phenomenon. This case has been further investigated using third-order accurate upwind differencing for the convective terms. The flow is interrogated carefully by examining the corresponding instantaneous vorticity, stream-function and velocity fields, as well as by tracking mass-less marker particles in some of the critical regions. Such detailed examination is deemed essential, prior to assigning fundamental physical relevance to the observed vortex-interaction phenomenon.

Ghia, U.↗

NASA NTRS1991

An unusually strong Einstein ring in the radio source PKS1830 - 211

High-resolution radio images of PKS1830 - 211 are obtained to study the possibility that the double structure is a gravitationally lensed object. The VLBI observations, taken from interferometric radiotelescope networks, reveal an elliptical ring that connects two bright spots of similar composition. Because the lens and the lensed object are closely aligned, and because of the structure of the two spots, the source is concluded to be a radio Einstein ring. The source is found to be close to the galactic plane, and the lens and the lensed object are extragalactic. The source is also found to be unusually bright, suggesting that it is aligned with a bright background source or amplified by some mechanism related to a source that is not so bright.

Jauncey, D. L.↗

NASA NTRS1991

Micrometeorite erosion of the man rings as a source of plasma in the inner Saturnian plasma torus

Micrometeorite bombardment is presently suggested to be a source of water molecules and molecular ions in the region between the outer edge of the main rings of Saturn and Encedalus, adding to those neutrals and plasma that are generated by the sputtering of icy satellites. In view of uncertainties concerning the magnitude and distribution of the ring source, an examination is conducted of limiting cases. The implications of such cases for the Cassini division are calculated, and a discussion of their possible relevance to the region's neutral and plasma cloud is presented.

Pospieszalska, M. K.↗

NASA NTRS1991

Properties of the SN 1987A circumstellar ring and the distance to the Large Magellanic Cloud

The distance to SN 1987A was determined by comparing the angular size of its circumstellar ring, measured from an HST image obtained in a narrow forbidden O III 5007 A filter, with its absolute size derived from an analysis of the light curves of narrow UV lines measured with the IUE. The analysis confirms that the observed elliptical structure is a circular ring seen at a mean inclination of i = 42.8 + or - 2.6 deg and provides a determination of its absolute diameter of (1.27 + or - 0.07) x 10 to the 18th cm. Its ratio to the angular diameter of 1.66 + or - 0.03 arcsec gives an accurate determination of the distance to SN 1987A, i.e., d(1987A) = 51.2 + or - 3.1 kpc.

Panagia, N.↗

NASA NTRS1991

YBCO superconducting ring resonators at millimeter-wave frequencies

Microstrip ring resonators operating at 35 GHz were fabricated from laser ablated YBCO films deposited on lanthanum aluminate substrates. They were measured over a range of temperatures and their performances compared to identical resonators made of evaporated gold. Below 60 Kelvin the superconducting strip performed better than the gold, reaching an unloaded Q approximately 1.5 times that of gold at 25 K. A shift in the resonant frequency follows the form predicted by the London equations. The Phenomenological Loss Equivalence Method is applied to the ring resonator and the theoretically calculated Q values are compared to the experimental results.

Chorey, Christopher M.↗

NASA NTRS1992

Inflatable Rings For Temporary Sealing

Inflatable rings seal joint. After inflation, space pressurized to test for leakage through joint. Rings protect surface of aperture from contact with metal structure of plug, and accommodate out-of-roundness and irregular surface contours without leaking. Pressure seal requires no preparation or cleanup.

Lesh, Paul L.↗

NASA NTRS1992

Injection seeded single mode alexandrite ring laser for lidar applications

Along with many spectroscopic applications, atmospheric lidar measurements require a tunable, narrow band laser with a very high degree of spectral purity. A standing wave pulsed alexandrite laser tuned by injection seeding with an AlGaAs laser diode has demonstrated high stability. The standing wave cavity, however, poses several difficulties in light of the single mode operation and efficient seeding beam into the cavity. In order to overcome these problems and to operate the high power alexandrite laser in a single axial mode with a high spectral purity, a new ring laser system is being developed. The design features of the ring laser and some measurements of the laser characteristics are presented.

Lee, H. Sang↗

NASA NTRS1991

Particle sizes of the Uranus delta ring's inner diffuse companion through comparison of RSS and PPS Voyager occultation data

In January, 1976, Voyager 2's photopolarimeter and UV spectrometer observed Delta Sagitarii and Beta Persei during their occultation by the Uranian delta ring. An inner diffuse companion of this ring was detected and found to have an average width of 12 km. By comparing the widths and equivalent depths of the two sets of data, it is established that the particles making the greatest contribution to the integrated opacities of the companion are of greater-than-several-cm sizes. The particles appear to be located away from the photopolarimetry edges, where there may be particles smaller than those observed elsewhere.

Hui, John↗

NASA NTRS1991

Nonlinear satellite wakes in planetary rings. I - Phase-space kinematics

The explicit expression presently derived for the phase-space density of a planetary ring subjected to perturbations by a proximate satellite recovers the usual perturbed-streamline equations by drawing first-order moments of the phase-space density. The surface density obtained is positive-definite in virtue of taking the ring particles' finite-velocity dispersion into account. The satellite-wake local mean velocity components deviate from the streamline equations' sinusoidal form; this deviation grows as the wake moves downstream from the shepherding satellite.

Stewart, Glen R.↗

NASA NTRS1990

Uranus - The planet, rings and satellites

The present overview of available data regarding Uranus and its planetary structures encompasses ground- and space-based observations of the planet with specific attention given to the interpretation of Voyager 2 data. A brief examination of historical observations is given which includes its discovery, position determination, and the related discoveries of Uranus' five large satellites and rings. The observational data preceding the Voyager 2 mission are reviewed in terms of the planetary interior, atmosphere, and magnetosphere. The Voyager 2 mission is given detailed treatment with descriptions of NASA's development and deployment of the spacecraft as well as detailed data from the Uranus encounter. Reference is given to structure and composition of Uranus' atmosphere, valid models of the interior, and wave-particle interactions in the magnetosphere. The structures of the rings and satellites are examined with reference to specific observational requirements from future missions.

Miner, Ellis D.↗

NASA NTRS1992

Performance of a K-band superconducting annular ring antenna

Superconducting annular ring antennas operating in the TM12 mode at 21 GHz are designed and fabricated on a lanthanum aluminate substrate using a YBCO high-temperature superconducting thin film. The efficiencies and far-field antenna patterns are measured and compared with an identical antenna patterned with silver. The resonant frequencies and experimental far-field patterns agree well with published models, and efficiency measurements show a maximum improvement of 6 percent at 20 K in the efficiency of the HTS antenna when compared to the silver ring at the same temperature.

Richard, M. A.↗

NASA NTRS1992

Ring-array processor distribution topology for optical interconnects

The existing linear and rectangular processor distribution topologies for optical interconnects, although promising in many respects, cannot solve problems such as clock skews, the lack of supporting elements for efficient optical implementation, etc. The use of a ring-array processor distribution topology, however, can overcome these problems. Here, a study of the ring-array topology is conducted with an aim of implementing various fast clock rate, high-performance, compact optical networks for digital electronic multiprocessor computers. Practical design issues are addressed. Some proof-of-principle experimental results are included.

Li, Yao↗

NASA NTRS1992

Ringed impact craters on Venus: An analysis from Magellan images

We have analyzed cycle 1 Magellan images covering approximately 90 percent of the venusian surface and have identified 55 unequivocal peak-ring craters and multiringed impact basins. This comprehensive study (52 peak-ring craters and at least 3 multiringed impact basins) complements our earlier independent analysis of Arecibo and Venera images and initial Magellan data and that of the Magellan team.

Alexopoulos, Jim S.↗