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At least 973 records · Page 54

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NASA NTRS1990

A search for ultraviolet-excess objects (Kondo, Noguchi, and Maehara 1984): Documentation for the machine-readable version

A list of 1186 ultraviolet-excess objects (designated KUV) was compiled as a result of a search conducted with the 105-cm Schmidt telescope of the Kiso station of the Tokyo Astronomical Observatory. This document describes the machine readable version of the KUV survey list and presents a sample listing showing the logical records as they are recorded in the machine readable catalog. The KUV data include equatorial coordinates, magnitudes, color indices, and identifications for previously cataloged objects.

Warren, Wayne H., Jr.↗

NASA NTRS1991

Experimental modelling of lightning interaction phenomena with a free potential conducting objects

Laboratory experiments were conducted to investigate the physical processes of the development of air discharge and its interaction with free potential conducting objects. The space-time development of lightning in gaps was recorded by a motion picture camera and an optoelectronic transducer. The electric field at different points in the gap was measured using a Pockels device both in the leader stage and in the stage of the return stroke. Experimental results of the streamer zone length measurements in the gaps with lengths up to 65 meters are presented. The physical processes occurring during the interaction of positive and negative long sparks with isolated objects were investigated. The striking probability of isolated conducting spheres with different diameters and the dependence of the strike on the location of the gap are investigated.

Chernov, E. N.↗

NASA NTRS1990

Segmentation, modeling and classification of the compact objects in a pile

The problem of interpreting dense range images obtained from the scene of a heap of man-made objects is discussed. A range image interpretation system consisting of segmentation, modeling, verification, and classification procedures is described. First, the range image is segmented into regions and reasoning is done about the physical support of these regions. Second, for each region several possible three-dimensional interpretations are made based on various scenarios of the objects physical support. Finally each interpretation is tested against the data for its consistency. The superquadric model is selected as the three-dimensional shape descriptor, plus tapering deformations along the major axis. Experimental results obtained from some complex range images of mail pieces are reported to demonstrate the soundness and the robustness of our approach.

Gupta, Alok↗

NASA NTRS1991

Accretion disk emission from a BL Lacertae object

It is suggested here that the UV and X-ray emission of BL Lac objects may originate in an accretion disk. Using detailed calculations of accretion disk spectra, the best-measured ultraviolet and soft X-ray spectra of the BL Lac object PKS 2155-304 are fitted, and the mass and accretion rate required is determined. The ultraviolet through soft X-ray continuum is well fitted by the spectrum of an accretion disk, but near-Eddington accretion rates are required to produce the soft X-ray excess. A hot disk or corona could Comptonize soft photons from the cool disk and produce the observed power-law spectrum in the 1-10 keV range. The dynamic time scale in the disk regions that contribute most of the observed ultraviolet and soft X-ray photons are consistent with the respective time scales for intensity variations observed in these two wave bands; the mass derived from fitting the continuum spectrum is consistent with the limit derived from the fastest hard X-ray variability.

Wandel, Amri↗

NASA NTRS1991

Faint Object Camera observations of a globular cluster nova field

The Faint Object Camera onboard Hubble Space Telescope has obtained U and B images of the field of Nova Ophiuchi 1938 in the globular cluster M14 (NGC 6402). The candidate for the quiescent nova suggested by Shara et al. (1986) is clearly resolved into at least six separate images, probably all stellar, in a region of 0.5 arcsec. Although two of these objects are intriguing as they are somewhat ultraviolet, the actual nova counterpart remains ambiguous, as none of the images in the field has a marked UV excess. Many stars within the 1.4 arcsec (2 sigma) uncertainty of the nova outburst position are viable counterparts if only astrometric criteria are used for selection. The 11 x 11 arcsec frames easily resolve several hundred stars in modest exposures, implying that HST even in its current optical configuration will be unique for studies of very crowded fields at moderate (B = 22) limiting magnitudes.

Margon, Bruce↗

NASA NTRS1991

The redshift of the X-ray selected BL Lacertae object H0414 + 009

The X-ray selected BL Lac object H0414 + 009 has a redshift of 0.287; the optical spectrum is well described by the sum of a standard elliptical galaxy plus a relatively flat power law. The galaxy contributes about 40 percent of the light in the spectrum in the rest-frame V band, and is one of the most luminous galaxies known. The properties of H0414 + 009 are similar in all respects to a previously studied object, 1E 1415 + 259 at z = 0.237. If X-ray selected BL Lacs continue to be found in such bright galaxies, then the properties of studying their luminosity function and evolution are considerably enhanced. There is also possible evidence for intrinsic X-ray absorption by a warm medium, as has been found in several other BL Lacs.

Halpern, Jules P.↗

NASA NTRS1991

Young stellar objects detected by IRAS

Fluxes of 453 IRAS point sources selected for proximity to dense gas have been accurately determined by co-adding IRAS data. From this set, 258 sources are detected in all four bands: 12, 25, 60, and 100 microns. As distance from dense molecular material increases, these sources exhibit systematic trends in color and a markedly decreasing luminosity. These trends are broadly consistent with expected evolutionary changes in these stars, with younger objects found closer to dense gas. These data suggest a subtle variation on the criterion for identifying the youngest objects detectable by IRAS, in addition to that of steeply rising spectra: a color temperature which is uniform across all four IRAS bands in the range 40-50 K. These characteristics are used as a criterion to select point sources as candidate very young pre-main-sequence stars.

Clark, Frank O.↗

NASA NTRS1990

An optimal sensing strategy of a proximity sensor system for recognition and localization of polyhedral objects

An algorithm is presented for the recognition and localization of thre-dimensional polyhedral objects based on an optical proximity sensor system capable of measuring the depth and orientation of a local area of an object surface. Emphasis is given to the determination of an optimal sensor trajectory or an optimal probing, for efficient discrimination among all the possible interpretations. The determination of an optimal sensor trajectory for the next probing consists of the selection of optimal beam orientations based on the surface normal vector distribution of the multiple interpretation image (MII) and the selection of an optimal probing plane by projecting the MII onto the projection plane perpendicular to a selected beam orientation and deriving the optimal path on the projection plane. The selection of optimal beam orientation and probing plane is based on the measure of discrimination power of a cluster of surfaces of an MII. Simulation results are shown.

Lee, Sukhan↗

NASA NTRS1990

Real-time motion tracking of three-dimensional objects

The problem in which the three-dimensional motion of an object corresponding to a known polyhedral model is to be computed using only the motion of edge features in a continuous stream of two-dimensional images is considered. Advantage is taken of the spatiotemporal density of the input signal and the limitations of long-range trajectory-prediction methods are avoided. Two parallel algorithms which use feature-based, short-range (spatiotemporally local) motion processes to achieve real-time tracking of modeled objects are presented. Both algorithms have been implemented and tested on a tightly coupled multiprocessor system consisting of an Aspex Pipe for low-level, image-feature computations and a Sequent Symmetry for high-level, model-based computations. An analysis is given of the actual performance limits of each method using the current hardware configuration.

Verghese, Gilbert↗

NASA NTRS1991

Gravitational microlensing of high-redshift supernovae by compact objects

An analysis of the effect of microlensing by a cosmologically dominant density of compact objects is performed, using high-redshift Type Ia supernovae (SN Ia's) as probes. The compact objects are modeled as a three-dimensional distribution of point masses, and Monte Carlo simulations are done to calculate the resulting amplification probability distributions for several column densities and cosmologies. By combining these distributions with the intrinsic SN Ia luminosity function and comparing with the results for a perfectly smooth universe, estimates are made of the number of supernovae that would need to be observed to confirm or rule out this lensing scenario. It is found that about 1000 SN Ia's with redshifts of z = 1 would be needed to perform this test, which is beyond what current searches can hope to accomplish. Observations of many fewer high-redshift supernovae, used merely as standard candles, appears a promising way of distinguishing between different cosmological models.

Rauch, Kevin P.↗

NASA NTRS1991

Far-ultraviolet spectroscopy of the quasar UM 675 with the faint object spectrograph on the Hubble Space Telescope

To investigate the far-UV spectral properties of a QSO and to look for evidence of He I 584 A emission and absorption the Faint Object Spectrograph aboard the HST was used to observed UM 675. Light is detected down to 520 A in the object in the rest frame and limits are set to He I emission, the He I Gunn-Peterson effect at z = 2.148, and Ly-alpha absorption at z roughly 0.5.

Beaver, E. A.↗

NASA NTRS1991

Collisions of giant stars with compact objects - Hydrodynamical calculations

Smooth particle hydrodynamics are used here to model encounters between an 0.8 solar mass giant star and a 1.4 solar mass compact object on a parabolic orbit. It is found that all encounters with periastron distance r(p) less than about 2.5 stellar radii R(G) lead to significant disruption of the stellar envelope, including some mass loss. When r(p)/R(G) is less than about 0.5, the envelope is completely destroyed during the collision. About 40 percent of the gas escapes, while the rest forms a massive disk around the compact object, leaving behind the bare stellar core on a highly eccentric orbit. Subsequent close passages lead to continuous extraction of gas from the disk at a large rate, and the binary orbit may eventually stabilize while still retaining a large eccentricity. It is suggested that many globular cluster pulsars may have been spun up by accretion from a massive disk rather than from a binary companion, thereby providing a possible solution to the birthrate problem.

Rasio, Frederic A.↗

NASA NTRS1990

Evaluating scheduling algorithms for traffic with heterogeneous performance objectives

Two types of network traffic are considered: traffic with deadlines, for which the most important performance objective is based on loss rate, and packets without deadlines, for which the most important performance objective is based on mean delay. An optimal scheduling algorithm is presented to minimize weighted loss rate and weighted mean delay in the queues that form at the switches and at the network access points of a packet-switched network, where weights reflect the relative importance of packets. Although not practical for implementation, the algorithm is intended as a standard for the comparison of the performance of other scheduling algorithms. The algorithm is more general and lower computational complexity than previously published algorithms, enabling performance evaluation of some important scenarios that could not previously have been considered. Using the optimal performance results of this algorithm, the performance of the first-come-first-served, static priority, and earliest deadline first scheduling algorithms is evaluated. The results suggest that network efficiency could be improved by using a more sophisticated heuristic scheduling algorithm rather than one of the aforementioned algorithms.

Peha, Jon M.↗

NASA NTRS1992

Acoustic Measurement Of Periodic Motion Of Levitated Object

Some internal vibrations, oscillations in position, and rotations of acoustically levitated object measured by use of microphone already installed in typical levitation chamber for tuning chamber to resonance and monitoring operation. Levitating acoustic signal modulated by object motion of lower frequency. Amplitude modulation detected and analyzed spectrally to determine amplitudes and frequencies of motions.

Watkins, John L.↗

NASA NTRS1991

Infrared observations of solar system objects

This is an ongoing groundbased infrared study of solar system objects. This is a broadbased program with the overall objective of studying the spectral and physical properties of small solar system bodies. The work spans the entire solar system from a study of the mineralogy of Mercury, to several studies of asteroids, and to studies of Triton, Pluto, and Charon. From these studies, it is hoped that a better understanding of the origin and evolution of these bodies and how they fit into the context of the origin and evolution of the solar system as a whole will be gained.

Lebofsky, Larry A.↗

NASA NTRS1991

Aries x ray objective grating spectrograph

This investigation was initiated in June of 1983. An Aries payload involving a single Wolter 1 telescope was developed and flown under a previous contract and the objective of this work was to add two additional mirrors, nested inside of the then existing mirror and add 12 objective reflection gratings to convert the telescope into a spectrograph. A summary of major milestones in the investigation are given. Results of efforts under this contract prior to 1987 are presented in the form of four reprints of published papers attached to this report. Results of the gamma-ray research are also included in the form of an attached reprint. A summary of other work under the contract since 1987 is given.

Catura, R. C.↗

NASA NTRS1991

On the Concept of Varying Influence Radii for a Successive Corrections Objective Analysis

There has been a long standing concept by those who use successive corrections objective analysis that the way to obtain the most accurate objective analysis is first, to analyze for the long wavelengths and then to build in the details of the shorter wavelengths by successively decreasing the influence of the more distant observations upon the interpolated values. Using the Barnes method, the filter characteristics were compared for families of response curves that pass through a common point at a reference wavelength. It was found that the filter cutoff is a maximum if the filter parameters that determine the influence of observations are unchanged for both the initial and corrections passes. This information was used to define and test the following hypothesis. If accuracy is defined by how well the method retains desired wavelengths and removes undesired wavelengths, then the Barnes method gives the most accurate analyses if the filter parameter on the initial and corrections passes are the same. This hypothesis does not follow the usual conceptual approach to successive corrections analysis.

Achtemeier, Gary L.↗

NASA NTRS1992

NASA TSRV essential flight control system requirements via object oriented analysis

The objective was to analyze the baseline flight control system of the Transport Systems Research Vehicle (TSRV) and to develop a system specification that offers high visibility of the essential system requirements in order to facilitate the future development of alternate, more advanced software architectures. The flight control system is defined to be the baseline software for the TSRV research flight deck, including all navigation, guidance, and control functions, and primary pilot displays. The Object Oriented Analysis (OOA) methodology developed is used to develop a system requirement definition. The scope of the requirements definition contained herein is limited to a portion of the Flight Management/Flight Control computer functionality. The development of a partial system requirements definition is documented, and includes a discussion of the tasks required to increase the scope of the requirements definition and recommendations for follow-on research.

Duffy, Keith S.↗