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  • Other Sources  (3,478)
  • NASA Technical Reports  (3,478)
  • ASTROPHYSICS  (2,348)
  • ELECTRONICS AND ELECTRICAL ENGINEERING  (602)
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  • NASA Technical Reports  (3,478)
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  • 2010-2014
  • 1990-1994  (1,975)
  • 1980-1984  (1,503)
  • 1970-1974
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  • 1
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    YBCO superconducting ring resonators at millimeter-wave frequencies (1991)
    In:  Other Sources
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    Publication Date: 2011-12-09
    Description: 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.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Microwave Theory and Techniques (ISSN 0018-9480); 39; 1480-148
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  • 2
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    High-voltage 6H-SiC p-n junction diodes (1991)
    In:  Other Sources
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    Publication Date: 2011-12-09
    Description: A chemical vapor deposition (CVD) process has been used to produce device structures of n- and p-type 6H-SiC epitaxial layers on commercially produced single-crystal 6H-SiC wafers. Mesa-style p-n junction diodes were successfully fabricated from these device structures using reactive ion etching, oxide passivation, and electrical contact metallization techniques. When tested in air, the 6H-SiC diodes displayed excellent rectification characteristics up to the highest temperature tested, 600 C. To observe avalanche breakdown of the p-n junction diodes, testing under a high-electrical-strength liquid was necessary. The avalanche breakdown voltage was 1000 V representing the highest reverse breakdown voltage to be reported for any CVD-grown SiC diode.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Applied Physics Letters (ISSN 0003-6951); 59; 1770-177
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  • 3
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    New channelised coplanar waveguide to rectangular waveguide post and slot couplers (1991)
    In:  Other Sources
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    Publication Date: 2011-12-09
    Description: Two new coplanar waveguide to rectangular waveguide couplers with coupling through a post and a slot are experimentally demonstrated. The couplers operate over the Ku-band transmission and X-band reception frequencies that are designated for satellite communications. The measured insertion loss and return loss are about 1 dB, respectively, for both couplers.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Electronics Letters (ISSN 0013-5194); 27; 856-858
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  • 4
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    The best-fit universe (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Inflation provides very strong motivation for a flat Universe, Harrison-Zel'dovich (constant-curvature) perturbations, and cold dark matter. However, there are a number of cosmological observations that conflict with the predictions of the simplest such model: one with zero cosmological constant. They include the age of the Universe, dynamical determinations of Omega, galaxy-number counts, and the apparent abundance of large-scale structure in the Universe. While the discrepancies are not yet serious enough to rule out the simplest and most well motivated model, the current data point to a best-fit model with the following parameters: Omega(sub B) approximately equal to 0.03, Omega(sub CDM) approximately equal to 0.17, Omega(sub Lambda) approximately equal to 0.8, and H(sub 0) approximately equal to 70 km/(sec x Mpc) which improves significantly the concordance with observations. While there is no good reason to expect such a value for the cosmological constant, there is no physical principle that would rule out such.
    Keywords: ASTROPHYSICS
    Type: In: Primordial nucleosynthesis and evolution of early universe; Proceedings of the International Conference, Tokyo, Japan, Sept. 4-8, 1990 (A93-17626 05-90); p. 337-350.
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  • 5
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    Pulsar polarization measurements and the nonsymmetric gravitational theory (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Because of the breakdown of the Einstein equivalence principle in the nonsymmetric gravitational theory (NGT) of Moffat, orthogonally polarized electromagnetic waves can propagate at different velocities in a gravitational field. Moffat has proposed that galactic dark matter, in the form of cosmions, may act as a significant source of gravity in the NGT. We discuss how observations of the highly polarized radiation from distant pulsars could provide significant limits on the strength of the coupling of cosmions in the NGT.
    Keywords: ASTROPHYSICS
    Type: Physical Review D - Particles and Fields, 3rd Series (ISSN 0556-2821); 44; 8; p. R2211-R2213.
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  • 6
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    Cosmic evolution of Quasar radio structure (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We discuss the results of a survey of Quasar radio structures over redshifts from 0.6 to 3.7. There are clear evolutionary trends in size and luminosity, which suggest that the duty cycle of individual Quasars has increased over cosmic time. This affects source count statistics and gives clues on the evolution of Quasar environments.
    Keywords: ASTROPHYSICS
    Type: In: The space distribution of quasars; Proceedings of the Workshop, Victoria, Canada, June 3-5, 1991 (A93-28776 10-90); p. 331, 332; Discuss
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  • 7
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    Hybrid solution for high-speed target acquisition and identification systems (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A typical hierarchy for a general object recognition problem consists of object detection, classification and identification. This paper establishes necessary building blocks required for high-speed object recognition applications. An architecture that combines digital and optical processing, exploiting current image processing techniques for detection and classification, and optical processing hardware is described. An optical processing scheme is suggested for the identification aspect. Numerical results of each proposed concept are presented.
    Keywords: CYBERNETICS
    Type: In: Applications of artificial intelligence IX; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991. Pt. 1 (A93-25397 08-63); p. 81-91.
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  • 8
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    Non-parametric analysis of LANDSAT maps using neural nets and parallel computers (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Nearest neighbor approaches and a new neural network, the Binary Diamond, are used for the classification of images of ground pixels obtained by LANDSAT satellite. The performances are evaluated by comparing classifications of a scene in the vicinity of Washington DC. The problem of optimal selection of categories is addressed as a step in the classification process.
    Keywords: CYBERNETICS
    Type: ; : Problems in the ae
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  • 9
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    Are there two disk star cluster systems in the LMC? (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The surface distribution of star clusters in the LMC has revealed the existence of two elliptical systems superimposed. A small surface density outer ellipse outlining the large system and a higher density elliptical inner system. The major axis of the two subsystems form an angle of 60 deg. The central subsystem contains all youngest populous globular star clusters from both the stellar and dynamical point of view. The large outer system seems to contain all old globular clusters, showing a dumpy distribution and outlining two arms at the northeast and southwest. The small LMC clusters were found to have masses less than 1000 solar masses and are distributed all over the large elliptical system.
    Keywords: ASTROPHYSICS
    Type: In: The formation and evolution of star clusters (A93-48676 20-90); p. 407-409.
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  • 10
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    Early phases of LMC star clusters? (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: On the basis of optical and IUE observations we have investigated the possibility that some of the very young stellar systems of the LMC, such as SL360, may be regarded as globular clusters at the very early phases of their dynamical evolution after the gas cloud expulsion.
    Keywords: ASTROPHYSICS
    Type: In: The formation and evolution of star clusters (A93-48676 20-90); p. 404-406.
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  • 11
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    Wiener-matrix image restoration beyond the sampling passband (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A finer-than-sampling-lattice resolution image can be obtained using multiresponse image gathering and Wiener-matrix restoration. The multiresponse image gathering weighs the within-passband and aliased signal components differently, allowing the Wiener-matrix restoration filter to unscramble these signal components and restore spatial frequencies beyond the sampling passband of the photodetector array. A multiresponse images can be reassembled into a single minimum mean square error image with a resolution that is sq rt A times finer than the photodetector-array sampling lattice.
    Keywords: CYBERNETICS
    Type: In: Infrared imaging systems: Design, analysis, modeling, and testing II; Proceedings of the Meeting, Orlando, FL, Apr. 3-5, 1991 (A93-38351 15-35); p. 237-248.
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  • 12
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    High-temperature superconducting superconductor/normal metal/superconducting devices (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We describe the fabrication and characterization of superconductor/normal metal/superconductor (SNS) devices made with the high-temperature superconductor (HTS) YBa2Cu3O(7-x). Structures of YBa2Cu3O(7-x)/Au/Nb on c-axis-oriented YBa2Cu3O(7-x) were made in both sandwich and edge geometries in order to sample the HTS material both along and perpendicular to the conducting a-b planes. These devices display fairly ideal Josephson properties at 4.2 K. In addition, devices consisting of YBa2Cu3O(7-x)/YBa2Cu3O(y)/YBa2Cu3O(7-x), with a 'normal metal' layer of reduced transition temperature YBa2Cu3O(7-x) were fabricated and show a great deal of promise for applications near 77 K. Current-voltage characteristics like those of the Resistively-Shunted Junction model are observed, with strong response to 10 GHz radiation above 60 K.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Superconductivity applications for infrared and microwave devices II; Proceedings of the Meeting, Orlando, FL, Apr. 4, 5, 1991 (A93-27243 09-33); p. 192-196.
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  • 13
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    Coplanar waveguide microwave filter of YBa2Cu3O7 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Thin film low-pass microwave filters have been made with laser-ablated YBa2Cu3O(7-delta) (YBCO) deposited on LaAlO3 substrates, using a coplanar waveguide structure. The coplanar waveguide sections had dimensions suited for integrated circuits. Measured losses in liquid nitrogen were superior to the loss in a similar thin-film copper filter throughout the 0 to 9.5 GHz pass-band. A simple transmission-line model is adequate for filter design using YBCO films with repeatable characteristics. The measured filters demonstrate the performance of fully patterned YBCO after sealing in space-qualifiable hermetic packages. Five packaged filters of this design were delivered to the Naval Research Laboratory as candidates for space flight in the High Temperature Superconductivity Space Experiment.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Superconductivity applications for infrared and microwave devices II; Proceedings of the Meeting, Orlando, FL, Apr. 4, 5, 1991 (A93-27243 09-33); p. 95-100.
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  • 14
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    A high-efficiency 59- to 64-GHz TWT for intersatellite communications (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The design of a 75-W, 59- to 64- GHz TWT with a predicted overall efficiency in excess of 40 percent is described. This intersatellite communications TWT, designated Model 961HA, employs a coupled-cavity slow-wave structure with a two-step velocity taper and an isotropic graphite multistage depressed collector (MDC). Because the RF efficiency of this TWT is less than 8 percent, an MDC design providing a very high collector efficiency was necessary to achieve the overall efficiency goal of 40 percent.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: ; : Computational meth
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  • 15
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    Spatial deadlocks in task-level planning (1991)
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    Publication Date: 2011-08-24
    Description: We will formulate the problem of resolving spatial (space occupancy and support-stability) interactions in terms of tools developed in Operating Systems for the problems of deadlocks and synchronization. We show how to construct state graphs and to detect resource contentions and deadlocks from these state graphs. We describe an algorithm, called CONTAC, to deal with deadlocks where 'processes' represent the ordered motions of parts. The algorithm is a monitor-like process using preventative preemptive protocol to resolve higher-degree deadlocks. We develop the representation for knowledge about current allocations, pending requests, and synchronization constraints, to generate a contention-free sequence of actions. In this paper we focus on modeling deadlocks which are manifestations of spatial interactions.
    Keywords: CYBERNETICS
    Type: In: Intelligent robotics; Proceedings of the International Symposium, Bangalore, India, Jan. 2-5, 1991 (A93-49350 21-63); p. 505-516.
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  • 16
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    Why did Halley hiccup? (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The outburst of Halley comet that occurred in February 1991 when the comet was over 14 AU from the sun, between the orbits of Saturn and Uranus, is described. This region of the solar system was known to be so cold that a comet nucleus would be totally inert there. On February 12th, 1991 Halley brightened by a factor of about 300, and a dust coma was observed around the nucleus. Different explanations of the comet's strange behavior are suggested.
    Keywords: ASTROPHYSICS
    Type: Nature (ISSN 0028-0836); p. 793, 794.
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  • 17
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    Application of Ka-band MMIC technology for an orbiter/ACTS communications experiment (1991)
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    Publication Date: 2011-08-24
    Description: A proposed Ka-band communications experiment between the Shuttle Orbiter and the Advanced Communications Technology Satellite (ACTS) is described. Monolithic Microwave Integrated Circuit (MMIC) technology is used in both the Orbiter and on the ground. A 25 dB gain circularly polarized phased array transmits low-bit-rate television to ground stations at the Johnson Space Center and the Lewis Research Center.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 231-242.
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  • 18
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    Phase shifter technology assessment - Prospects and applications (1991)
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    Publication Date: 2011-08-24
    Description: Capabilities and limitations of MMIC phase shifter technology at microwave and millimeter wave frequencies are reviewed. MMIC-based phase arrays make it possible to integrate active elements at the array face, i.e., to incorporate transmit power amplifiers and/or low noise amplifiers at each antenna element. Active elements make it possible to increase power efficiency and reliability and provide graceful degradation. Monolithic integration of the various transmit/receive functions including phase shifting is considered to be feasible through at least the lower millimeter-wave frequency range (about 30-100 GHz). MMIC integration also allows more flexibility in array design including those that are intended for airborne conformal applications.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 288-302.
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  • 19
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    Ka-band MMIC array feed development for deep space applications (1991)
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    Publication Date: 2011-08-24
    Description: Ka-band MMIC transmitter arrays are under development at NASA Jet Propulsion Laboratory for future deep space and ground communication needs. A high efficiency full aperture active antenna array is desired to demonstrate solid state array technology for future NASA missions. This paper reports on a 5 watt Ka-band phased array feed and a full aperture active array for a mobile terminal which are being developed to characterize the design tradeoffs and potential of solid state Ka-band MMIC array communication systems.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 243-247.
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  • 20
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    Horizontal-branch evolution with time-dependent convective overshooting (1991)
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    Publication Date: 2011-08-24
    Description: Horizontal-branch (HB) sequences have been computed for different rates of convective overshooting at the edge of the convective core. We find that the convective core undergoes a series of 'breathing pulses' during most of the HB phase. The average behavior of these sequences closely mimics the behavior of sequences computed with canonical semiconvection.
    Keywords: ASTROPHYSICS
    Type: In: The formation and evolution of star clusters (A93-48676 20-90); p. 299-301.
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  • 21
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    Search-based model identification of smart-structure damage (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper describes the use of a combined model and parameter identification approach, based on modal analysis and artificial intelligence (AI) techniques, for identifying damage or flaws in a rotating truss structure incorporating embedded piezoceramic sensors. This smart structure example is representative of a class of structures commonly found in aerospace systems and next generation space structures. Artificial intelligence techniques of classification, heuristic search, and an object-oriented knowledge base are used in an AI-based model identification approach. A finite model space is classified into a search tree, over which a variant of best-first search is used to identify the model whose stored response most closely matches that of the input. Newly-encountered models can be incorporated into the model space. This adaptativeness demonstrates the potential for learning control. Following this output-error model identification, numerical parameter identification is used to further refine the identified model. Given the rotating truss example in this paper, noisy data corresponding to various damage configurations are input to both this approach and a conventional parameter identification method. The combination of the AI-based model identification with parameter identification is shown to lead to smaller parameter corrections than required by the use of parameter identification alone.
    Keywords: CYBERNETICS
    Type: In: Smart structures and materials; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-32726 12-39); p. 33-39.
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  • 22
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    Mixed application MMIC technologies - Progress in combining RF, digital and photonic circuits (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Approaches for future 'mixed application' monolithic integrated circuits (ICs) employing optical receive/transmit, RF amplification and modulation and digital control functions are discussed. We focus on compatibility of the photonic component fabrication with conventional RF and digital IC technologies. Recent progress at Honeywell in integrating several parts of the desired RF/digital/photonic circuit integration suite required for construction of a future millimeter-wave optically-controlled phased-array element are illustrated.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 223-230.
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  • 23
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    Millimeter-wave pseudomorphic HEMT MMIC phased array components for space communications (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Recent advances in pseudomorphic HEMT MMIC (PMHEMT/MMIC) technology have made it the preferred candidate for high performance millimeter-wave components for phased array applications. This paper describes the development of PMHEMT/MMIC components at Ka-band and V-band. Specifically, the following PMHEMT/MMIC components will be described: power amplifiers at Ka-band; power amplifiers at V-band; and four-bit phase shifters at V-band. For the Ka-band amplifier, 125 mW output power with 5.5 dB gain and 21 percent power added efficiency at 2 dB compression point has been achieved. For the V-band amplifier, 112 mW output power with 6 dB gain and 26 percent power added efficiency has been achieved. And, for the V-band phase shifter, four-bit (45 deg steps) phase shifters with less than 8 dB insertion loss from 61 GHz to 63 GHz will be described.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Monolithic microwave integrated circuits for sensors, radar, and communications systems; Proceedings of the Meeting, Orlando, FL, Apr. 2-4, 1991 (A93-25776 09-33); p. 184-192.
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  • 24
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    Molecular hydrogen emission in L1448 associated with a highly collimated molecular outflow (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A near-infrared camera was used to search for jets around low-luminosity embedded infrared sources in nearby molecular clouds. The near-infrared offers the advantage that the extinction is very low compared with the optical. A jet is detected in molecular hydrogen at 2.12 microns toward a source in L1448. Given the sample size this indicates a detection rate of no more than a couple percent. The average visual extinction in L1448 is roughly 5 mag. The properties of the molecular hydrogen emission are similar to those measured for known Herbig-Haro objects, suggesting the jet is a buried Herbig-Haro object/jet that would be visible in the optical if the extinction were lower. The L1448 jet coincides with the unusual CO outflow that is highly collimated and contains high-velocity CO 'bullets'. The properties of the L1448 source suggest it defines a transition case between molecular outflows and Herbig-Haro jets, combining the characteristics of both.
    Keywords: ASTROPHYSICS
    Type: Societa Astronomica Italiana, Memorie (ISSN 0037-8720); 62; 4, 19
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  • 25
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    Ultraviolet flares from RS CVn-type stars and related systems (1991)
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    Publication Date: 2011-08-24
    Description: Properties and parameters of UV flares have been observed from RS CVn systems approximately once per few days observing time. The peak flare luminosities are five or six orders of magnitude more intense than the most energetic solar flares. The nonradiative energy losses, e.g., turbulence and flows, are likely to be at least comparable to the radiative loss.
    Keywords: ASTROPHYSICS
    Type: Societa Astronomica Italiana, Memorie (ISSN 0037-8720); 62; 291-305
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  • 26
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    Maximum entropy method applied to deblurring images on a MasPar MP-1 computer (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A statistical inference method based on the principle of maximum entropy is developed for the purpose of enhancing and restoring satellite images. The proposed maximum entropy image restoration method is shown to overcome the difficulties associated with image restoration and provide the smoothest and most appropriate solution consistent with the measured data. An implementation of the method on the MP-1 computer is described, and results of tests on simulated data are presented.
    Keywords: CYBERNETICS
    Type: In: Image understanding in the '90s: Building systems that work; Proceedings of the Meeting, McLean, VA, Oct. 18, 19, 1990 (A93-20261 06-63); p. 138-146.
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  • 27
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    The cosmic neutrino background (1991)
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    Publication Date: 2011-08-24
    Description: The cosmic neutrino background is expected to consist of relic neutrinos from the big bang, of neutrinos produced during nuclear burning in stars, of neutrinos released by gravitational stellar collapse, and of neutrinos produced by cosmic ray interactions with matter and radiation in the interstellar and intergalactic medium. Formation of baryonic dark matter in the early universe, matter-antimatter annihilation in a baryonic symmetric universe, and dark matter annihilation could have also contributed significantly to the cosmic neutrino background. The purpose of this paper is to review the properties of these cosmic neutrino backgrounds, the indirect evidence for their existence, and the prospects for their detection.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 497-511.
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  • 28
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    The X-ray flux dipole of AGNs as an indicator of the local gravitational field (1991)
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    Publication Date: 2011-08-24
    Description: We have investigated the dipole anisotropy of the sky X-ray flux from nearby AGNs to compare with the peculiar motion of the Local Group (LG) using a more extensive sample than that of Miyaji and Boldt (1990). We have sampled 56 low redshift emission-line AGNs (z less than 0.06) from the HEAO 1 A-2 experiment with a flux limit lower than that of Piccinotti et al. (1982) and with a lower galactic latitude cutoff. Our sample shows a significant dipole anisotropy whose apex is only about 30 deg away from the direction of the Local Group's peculiar motion for the objects with z less than 0.015. The dipole growth vs. redshift shows a sharp rise between z = 0.006 and z = 0.015; the amplitude of the dipole is 40 +/- 10 percent of the corresponding monopole at z = 0.015. The outer redshift cutoff is consistent with the results obtained from analyses using optical and IRAS galaxies. The present sample strengthens our previous conclusion that X-ray emission from AGNs traces the underlying mass distribution as strongly as optical and IR emission from galaxies.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 431-434.
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    The missing mass in clusters of galaxies and elliptical galaxies (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: We review the available data for the existence of dark matter in clusters of galaxies and elliptical galaxies. While the amount of dark matter in clusters is not well determined, both the X-ray and optical data show that more than 50 percent of the total mass must be dark. There is in general fair agreement in the binding mass estimates between the X-ray and optical techniques, but there is not detailed agreement on the form of the potential or the distribution of dark matter. The X-ray spectral and spatial observations of elliptical galaxies demonstrate that dark matter is also required in these objects and that it must be considerably more extended than the stellar distribution.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 394-404.
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    Evidence for evolution of the luminosity function of clusters of galaxies (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: From an all sky, X-ray flux limited sample of clusters of galaxies evidence for a significant deficit in the number of high luminosity clusters is found in the redshift range z approximately 0.1 to 0.2 compared with numbers of nearby clusters. This indicates that the X-ray luminous clusters are undergoing strong evolution. The strength of the effect is consistent with hierarchical merging models. The implications of such strong evolution for clusters are discussed.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 343-346.
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    Spectral-luminosity evolution of active galactic nuclei and the cosmic X-ray background (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Black hole accretion disk dynamo processes are generally regarded as the central power source for AGN (Rees, 1984). If the precursor active galaxies for such AGN are formed at redshift z greater than about 4 and contain initial central seed black holes about 10 exp 6 solar masses, then the Eddington limited X-ray radiation emitted during their lifetime will undergo the phenomenon of 'spectral-luminosity evolution'. When accretion disks are first formed at the onset of galaxy formation, the accretion rate occurs at high values of luminosity/size compactness parameter L/R greater than 10 exp 30 erg/cm-sec. Such high values of L/R generate dynamic constraints which suppress nonthermal black hole accretion disk dynamo processes in favor of thermal processes. This causes the spectrum of X-radiation emitted by early AGN to be predominantly thermal. A superposition of such thermal, comptonized PAG sources can account for the residual cosmic X-ray background and can act as a source of X-ray heating of the intergalactic medium for z greater than about 4.
    Keywords: ASTROPHYSICS
    Type: In: After the first three minutes; Proceedings of the 1st Astrophysics Workshop, Univ. of Maryland, College Park, Oct. 15-17, 1990 (A93-23605 07-90); p. 339-342.
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    Coaxial line configuration for microwave power transmission study of YBa2Cu3O(7-delta) thin films (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-12-09
    Description: Microwave transmission measurements through YBa2Cu3O(7-delta) (YBCO) high-transition-temperature superconducting thin films on lanthanum aluminate (LaAlO3) have been performed in a coaxial line at 10 GHz. LaAlO3 substrates were ultrasonically machined into washer-shaped discs, polished, and coated with laser-ablated YBCO. These samples were mounted in a 50-ohm coaxial air line to form a short circuit. The power transmitted through the films as a function of temperature was used to calculate the normal state conductivity and the magnetic penetration depth for the films.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Applied Superconductivity (ISSN 1051-8223); 1; 178-180
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  • 33
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    Regular variability of the shape of the primary minimum of the orbital light curve of SS 433 with the phase of the precessional period (1991)
    In:  CASI
    Details
    Publication Date: 2009-11-16
    Description: The regular variations of the shape of the primary minimum of the orbital 13.082-day light curve of SS 433 with the phase of the 162.5-day processional period were discovered by analysis of the photometrical databank. The regular variability of the shape of the primary minimum of the discovered light curve of SS 433 reflects displacement with the 26-day double orbital period of at least two hot bright spots on the surface of the processional accretional disk and their eclipse by a normal star. Other aspects of the investigation are further discussed.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 65-67
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    Custom microcircuits (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The goals of this program are to develop custom microcircuit technology, also known as Application Specific Integrated Circuit (ASIC) technology, for use in flight and ground programs. Supporting this effort are activities to investigate the effects of the space environment, and particularly ionizing radiation, on microcircuits and to develop a space qualification methodology. Another aspect of the program emphasizes innovative applications of custom microcircuit technology to image and signal processing and communications.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Center for Space Microelectronics Technology; p 83-87
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  • 35
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    Hydrodynamic study of Supernova 1987A: The phase of a wave of cooling and recombination (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The dependence of the bolometric light curve and of the effective temperature on the density distribution in a progenitor, its chemical composition, mass, radius, and explosion energy is studied. It is shown that, just before the supernova 1987 A outburst, the outside layers of the blue supergiant Sk-69.202 deg had a density distribution similar to that of the polytropic model with an index of n equals 3, a chemical composition with a mass fraction of hydrogen of the order of 0.1, and a relative helium abundance of about 0.9.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 403-409
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    Basic physics and cosmology from pulsar timing data (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Radio pulsars provide unparalleled opportunities for making measurements of astrophysically interesting phenomena. The author concentrates on two particular applications of high precision timing observations of pulsars: tests of relativistic gravitation theory using the binary pulsar 1913+16, and tests of cosmological models using timing data from millisecond pulsars. New upper limits are presented for the energy density of a cosmic background of low frequency gravitational radiation.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 385-393
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  • 37
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    Gas flow and generation of x ray emission in WR+OB binaries (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The supersonic flow of the ionized gas in WR+OB binaries and X-ray generation are considered. X-ray emission is caused by gas heating up to temperatures of 10(exp 7) to 10(exp 8) K behind the front of shock waves. These are found in the collision of gas flowing out from the WR star with either the OB star's surface or the gas of the OB star's wind. The distribution of temperature and concentration behind the shock front are obtained. Using these distributions, the spectral power of bremsstrahlung X-ray emission of hot gas is calculated. Possible reasons that lead to a considerable difference between the observed parameters of X-ray emission of the WR binary of V 444 Cygni and the theoretically expected are discussed.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 394-402
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    X ray radiation from Supernova 1987A. The results of the Kvant module in 1987-1989 (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The results of two years of SN1987A hard X-ray observations by the HEXE instrument aboard the Kvant module are summarized. By May to June 1989, the hard x-ray flux had declined more than 8.5 times in comparison with the maximum of the x-ray light curve. The upper limit of the ratio of Co-57/Co-56 abundances at the level of ratio of Fe-57/Fe-56 abundances at the Earth is a factor of 1.5.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 368-384
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  • 39
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    The peculiar velocity field predicted from the distribution of IRAS galaxies (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: It is noted, in the wake of the recent completion of a redshift survey of about 2300 IRAS galaxies with a characteristic depth of about 4000 km/sec, that the redshift distribution obtained is entirely consistent with that of the observed optical galaxies in the direction of the Great Attractor. The IRAS velocity field also qualitatively reproduces recent observations of the spiral and elliptical galaxies. Although it is not possible to rule out the existence of excess mass in the galactic plane in the direction of the Great Attractor, this is not needed to explain the observed peculiar velocities.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 356-367
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  • 40
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    Extragalactic x ray source counts (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Extragalactic x-ray source counts carry information about the luminosity function and cosmic evolution of galaxies, BL Lac objects, Seyfort galaxies, and quasars. We discuss two available x-ray source samples with complete optical identifications and redshifts. We find evidence for instrumental bias in the detection of clusters for cosmic evolution of quasars, and of absorption effects in low luminosity Seyfert galaxies. Modest spectral and density evolution of Seyfort galaxies would allow the soft x-ray background to be made up entirely of discrete sources. We present a source count prognosis for the Advanced X-ray Astrophysics Facility (AXAF) energy range 0.5 to 10 keV.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 336-343
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    Ultraluminous infrared galaxies (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: One of the major discoveries of the the IRAS all-sky survey was a population of sources having the bolometric luminosities of quasars, but where more than 90 percent of the luminosity emerges in the infrared. These objects, more numerous than quasars, are found exclusivly in interacting/merging galaxies that are extremely rich in interstellar gas. We have accumulated evidence that suggests that these systems are indeed quasars, obscured by many tens of magnitudes of extinction. We suggest that these Ultraluminous Infrared Galaxies are the formation stage of quasars, and that colliding galaxies, ultraluminous infrared galaxies, and quasars might be linked through an evolutionary sequence where the infrared bright phase is one in which the quasar is formed in the nucleus of a merger system, and is enshrouded in gas and dust, while the UV excess quasars are at the end state of quasar evolution where most of the enveloping dust cloud has been dissipated, and the quasar is visible directly.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 344-355
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    The PSR 2127+12 as an indicator of a massive blac k hole in the core of globular cluster M 15 (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The 110-millisecond pulsar PSR 2127+12 in the core of the globular cluster M15 is distinguished by having a negative period derivative P approximately equals -2 x 10(exp -17). This value cannot be provided by acceleration in the mean gravitational potential of the core. A flyby of a star approximately equal to 300 AU away could explain the P observed, but the probability of such an event is small, approximately equal to 10(exp -13). We suggest that the pulsar motion is governed by the presence of a moderately massive (approximately equals 2 divided by 3 x 10(exp 4) solar mass) black hole in the clusters center. The idea is further supported by an observed post-collapse morphology of the M15 core.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 316-321
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    On the observational appearances of a freely precessing neutron star in Hercules X-1 (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Evidence for neutron star free precession is discussed, which is often presumed to be responsible for the observed 35-day cycle in Hercules X-1. The precise formula for the period derivative due to free precession is obtained under assumption that the precession period is much longer than that of the neutron star rotation. The optical light curves to be seen from the binary, with freely precessing accretion neutron star are simulated numerically. This simulation takes into account the reflection effect on the surface of the secondary component and on the accretion disk itself for different diagrams of x-ray emission.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 307-315
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  • 44
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    The large-scale surface brightness distribution of the x ray background (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The x-ray background (XRB) and the microwave background are the dominant isotropic radiation fields available for measurement. There was extensive work on trying to determine the physical origin of the background. That is, whether it is due to a superposition of numerous faint well-known sources, such as active galaxies, an early unidentified population of AGN at high redshift, a new population of objects, or to truly diffuse processes or to a superposition of these. However, while of great intrinsic interest, these studies were not aimed at using the XRB to provide the cosmological information that was gleaned from the microwave background. An alternate approach is presented, which uses the available information on the large, greater than 5 deg, scale distribution of the sky flux to see if the XRB can provide such constraints.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 285-296
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  • 45
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    The evolution of the gravitational radiation from stellar components of galaxies (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The evolution is discussed of gravitational waves spectra produced by binary stars, supernova explosions, and coalescences of binary compact stars in outer galaxies. These spectra are integrated over a simple model of the universe to give an estimate of the stochastic gravitational wave background due to astrophysical sources.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 261-269
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  • 46
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    Quasi-periodic oscillations in low-mass x ray binaries (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Variability on short time scales in the x-ray flux is a very general property of binary x-ray sources. Not until after the discovery of intensity-dependent quasi-periodic oscillations (QPO) and associated red noise form luminous low-mass x-ray binaries were systematic studies of the shape of the power-spectral components made. A brief account is given of the main developments since this discovery which have led to a new picture of the properties of low-mass x-ray binaries.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 251-260
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    Gravitational lenses: The current sample, recent results, and continuing searches (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Gravitational lensing is one of the topics in astrophysics that was quite extensively discussed over time before it was actually discovered. Ten years after the discovery of the first one, it is interesting to note how the field has developed. After an initial slow rate of discovery, the last few years have seen an explosion in the number of reported cases. Attention was drawn to the first few cases because quasars at the same red shift, with similar optical spectra, were observed with angular separations of only a few arc seconds. Most observational effort has been devoted to searching for new candidate lens systems and carefully measuring their properties, both to test whether they are indeed lensed and to provide constraints for modeling. A classification of the lenses is into rings, arcs, multiples, and doubles, where the progression is from sources close to the optical axis to far from the optical axis. The known candidate systems are listed. The searches for gravitational lenses are proving to be successful, and more lenses continue to be discovered serendipitously. Many searches are under way, along with instruments that will routinely increase the resolution of astronomical imaging.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 192-203
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    On two-dimensional relativistic stellar winds (1991)
    In:  CASI
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    Publication Date: 2006-06-13
    Description: Stellar wind is of great interest, because many of the astrophysical systems possess wind like structures. For a long time only nonrelativistic winds have been studied. However, recently it was proposed by Kennel et al. that the relativistic pulsar wind with the plasma, consisting of electrons and positrons, can be responsible for the observed features of the Crab nebula. The study of Kennel et al. revealed the inconsistency of the assumption of the wind zero temperature with the observational data. It has been shown that only for high relativistic temperatures can high Mach numbers be reached, which allows the possibility of a shock formation. The analysis of Kennel et al. was extended into the 2-D case by using conventional magnetohydrodynamic equations for a relativistic plasma with an isotropic relativistic temperature. The state equation is assumed polytropic.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 108-111
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    The cyclotron absorption line and eclipse transition phenomena of 4U 1538-52 (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Observations of the eclipsing binary X ray pulsar, 4U 1538-52 have revealed a cyclotron absorption feature at 20 keV in the x ray spectrum. The pulse phase dependence of the intensity and spectrum can be mimicked by a model of x ray emission from thin accretion heated slabs at the magnetic poles of a rotating neutron star with its magnetic dipole axis inclined at 45 deg from the rotation axis. The observations also yielded data on the eclipse transitions which show that the radial density function at the base of the supersonic wind of the O-type supergiant primary has the form of an exponential like that which characterizes the density run in the similar region of the O-type supergiant primary of Cen X-3. As in the Cen X-3 system, the scale height of the exponential implies a temperature in the base region much greater than that of the supersonic wind.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 77-86
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  • 50
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    Chaotic inflationary universe and the anisotropy of the large-scale structure (1991)
    In:  CASI
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    Publication Date: 2006-06-13
    Description: It has been realized that the inflationary universe is in fact chaotic, that globally it is strongly inhomogeneous, and that the inflation in the universe as a whole is eternal. In such a picture the region available to modern observations is just a tiny part of the universe, in which inflation finished about 10(exp 10) years ago. In spite of the great popularity of the chaotic inflationary universe models, it is usually taken for granted that their specific features (such as strong global inhomogeneity of the universe) can hardly lead to any observable consequences. The argument is that all that is seen is just a tiny part of the universe, a region about 10(exp 28) cm, and the typical scales of considerable inhomogeneities are much greater than this size. In contrast to this opinion, an attempt is made to show that such observable consequences can really exist. The phenomenon closely connected with the origin of structure (galaxies, clusters, etc.) in the observable region is discussed. The main idea considered is the vacuum fluctuations evolution on the inhomogeneous background.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 68-76
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    Turbulization of shear flows in astrophysics (1991)
    In:  CASI
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    Publication Date: 2006-06-13
    Description: The problem of instability in shear flows is treated in a number of works which present a global analysis of irrotational (potential) modes in a 2-D compressible shear flow, implying that, in the presence of reflecting boundaries, those modes can increase and that the characteristic time of the increase is several orders as high as the dynamic time in the medium. Due to the slowness of the increase of irrotational modes and to the problematic character of the theory's applicability for thin accretion disks, an attempt was made to develop an alternative theory of turbulization shear flows. It is quite contrary to the above theory. Instead of the global analysis, a local one is made far from the flow boundaries. Instead of irrotational perturbations, vortical ones are examined. Lastly, the medium is considered to be incompressible. The flow in the accretion disk can be modeled by a plane Couette flow, without regard for boundary conditions: it can be modeled by a plane shear flow in infinite incompressible fluid. According to this scenario, there is a critical perturbation level in the free shear flow. If the level of initial perturbations exceeds the critical one, the flow is turbulized.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 55-64
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  • 52
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    Manifestations of dynamo driven large-scale magnetic field in accretion disks of compact objects (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A turbulent dynamo nonlinear theory of turbulence was developed that shows that in the compact objects of accretion disks, the generated large-scale magnetic field (when the generation takes place) has a practically toroidal configuration. Its energy density can be much higher than turbulent pulsations energy density, and it becomes comparable with the thermal energy density of the medium. On this basis, the manifestations to which the large-scale magnetic field can lead at the accretion onto black holes and gravimagnetic rotators, respectively, are presented.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 46-54
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  • 53
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    The shock breakout in SN1987A modelled with the time-dependent radiative transfer (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: A fully implicit high-order scheme was developed for the independent multi-group radiative transfer coupled with implicit hydrodynamics. The application of this scheme to the SN1987A explosion shows that shortly after the shock breakout a dense shell forms. A gasdynamic code describing the time dependent radiation transport in the multi-group approximation with variable Eddington factors was developed. Results and other aspects of the project are presented.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 39-45
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  • 54
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    Axially symmetrical supernova remnants (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: The origin of cylindrically symmetric supernova remnants (SNR's) is discussed. The results of numerical simulations of two most distinguished barrel-like SNR's SN1006 and G296.5+10.0 are presented.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 19-27
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    On the evolution of pulsars (1991)
    In:  CASI
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    Publication Date: 2006-06-13
    Description: Data from a previous investigation on the angle chi between the axis of rotation and the magnetic dipole axis, determined from polarization observations, provides a complete catalog which makes it possible to carry out a detailed comparison of the theoretical results of this present investigation with the observed distribution of radio pulsars over the angel chi. Before such a comparison is made, the main features of a theory for pulsar evolution is described.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 9-13
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  • 56
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    Instabilities in SN1987A and other supernovae (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: While giving a remarkably good description of many aspects of SN1987A, calculations assuming spherical symmetry have a number of flaws. Many of these problems naturally disappear in the development of a 2-D calculation, as nonspherical instabilities grow. This nonspherical behavior, made evident in SN1987A, has implications for other types of supernovae.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Societ Perspectives; p 1-8
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    The spin down of the radio pulsars: Braking index (1991)
    In:  CASI
    Details
    Publication Date: 2006-06-13
    Description: Presently, the value of the retardation dP/dt is well known for most radio pulsars. It is negative for all cases except one and is of the order of 10(exp -15). That single case is when the pulsar, which is located in the star globular system, can have a considerable acceleration leading to the opposite sign of P'= dP/dt due to the Doppler effect. Careful measurements of the period, P, also allow one to determine the variation of this retardation with the course of time- P'' = d(exp 2)P/dt(exp 2). The results of these measurements are usually represented in the form of the dimensionless retardation index n = omega'' omega/omega(exp 2)= 2 - P''P/P(exp 2) (omega is the angular velocity). The data for 21 pulsars are given. The parameter, n, is strongly undetermined both in value and sign in all cases except for four pulsars. Changes of the rotation period, P, and the inclination angle, chi, the angle between the axes of rotation and the magnetic moment are caused by two processes: the regular retardation and nutation due to deviation from the strict spherical shape of the neutron star. Losses which are caused by the currents flowing in the magnetosphere of the neutron star and by being closed on the star surface are considered. Such losses are critical for the neutron star magnetosphere which is full of dense plasma. Since the radio emission is generated in the dense plasma of the polar magnetosphere, then practically all radio pulsars are retarded by the current mechanism. The formula for the braking index is presented along with other aspects of the investigation.
    Keywords: ASTROPHYSICS
    Type: NAS-NRC, High-Energy Astrophysics. American and Soviet Perspectives; p 14-18
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    Detection and analysis of radio frequency lightning emissions (1982)
    In:  CASI
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    Publication Date: 2006-02-14
    Description: The feasibility study of detection of lightning discharges from a geosynchronous satellite requires adequate ground-based information regarding emission characteristics. In this investigation, a measurement system for collection of S-band emission data is set up and calibrated, and the operations procedures for rapid data collection during a storm activity developed. The system collects emission data in two modes; a digitized, high-resolution, short duration record stored in solid-state memory, and a continuous long-duration record on magnetic tape. Representative lightning flash data are shown. Preliminary results indicate appreciable RF emissions at 2 gHz from both the leader and return strokes portions of the cloud-to-ground discharge with strong peaks associated with the return strokes.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 20 p
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    The design and evaluation of superconducting connectors (1982)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The development of a superconducting connector for superconducting circuits on space flights is described. It is proposed that such connectors be used between the superconducting readout loop and the SQUID magnetometer in the Gravity Probe B experiment. Two types of connectors were developed. One type employs gold plated niobium wires making pressure connections to gold plated niobium pads. Lead-plated beryllium-copper spring contacts can replace the niobium wires. The other type is a rigid solder or weld connection between the niobium wires and the niobium pads. A description of the methods used to produce these connectors is given and their performance analyzed.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 10 p
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    Kinetic theory in astrophysics and cosmology (1982)
    In:  CASI
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    Publication Date: 2006-02-14
    Description: Results associated with exact solution of the Einstein-Boltzmann and Einstein-Maxwell-Boltzmann equations are presented. The generalization of Ehler's killing vector approach for the distribution function to charged particles is considered.
    Keywords: ASTROPHYSICS
    Type: Alabama Univ. in Huntsville The 1981 NASA(ASEE Summer Fac. Fellowship Program; 21 p
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    The 10 January 1986 disconnection event in Comet Halley (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The disconnection event (DE) in the plasma tail of Comet Halley on January 9-12, 1986 is examined. The distances between the comet head and the disconnected tail are measured for a series of images for that time period and then extrapolated to the nucleus to determine the disconnection time: January 9.60 +/- 0.2 days. The approximate solar-wind conditions at the time of the DE were obtained by corotation of IMP-8 satellite data in earth orbit to Comet Halley. At the time of the DE, Comet Halley is inferred to have been close to a magnetic-sector boundary and a high-speed stream-compression region. However, a heliographic latitude separation of 22 degrees (between the comet and IMP-8) and gaps in the IMP-8 data render a more definitive statement about the linkage of the DE to external conditions quite difficult. It is not possible to resolve the effects of magnetic changes associated with the sector boundary and plasma pressure in the compression region.
    Keywords: ASTROPHYSICS
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    The future of cometary plasma research (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Advances in the acquisition and analysis of cometary data are reviewed with attention given to current research and projects under development. The need for supplementing the present cometary data is underscored by discussing observational missions from the ground and earth orbit such as the Giotto Extended Mission and the Comet Rendezvous Asteroid Flyby. The interpretation of Comet Halley data is characterized as advanced with respect to both complete observational data and sophisticated modeling.
    Keywords: ASTROPHYSICS
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    A nonradial pulsation model for the rapidly rotating Delta Scuti star Kappa(2) Bootis (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A sectorial nonradial pulsation model is used to construct theoretical line profiles which mimic the variations for Kappa(2) Boo. Synthetic spectra generated with the appropriate Teff and log g are used as input. It is found that the data can be reproduced by the combination of a high-degree l is approximately equal to 12 mode with P(osc) aproximately equal to 0.071 d, and a low-degree mode, l is approximately equal to 0-2 with P(osc) approximately equal to 0.071-0.079 d. The projected rotational velocity (v sin i - 115 +/-5 km/s) was determined by fitting synthetic line profiles to the observed spectra. The velocity amplitude of the high-degree oscillations is estimated to be about 3.5 km/s. It is found that the ratio of the horizontal and radial pulsation amplitudes is small (about 0.02) and consistent with p-mode oscillations. Comparisons are made with models invoking starspots, and it is impossible to fit the observations of Kappa(2) Boo by a starspot model without assuming unrealistic values of radius or equatorial velocity.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 103; 1250-125
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    New insights from a statistical analysis of IUE spectra of dwarf novae and nova-like stars. I - Inclination effects in lines and continua (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: IUE observations of dwarf novae at maximum at quiescence and novalike objects at the high brightness state are analyzed for effects of the inclination angle on the emitted continuum and line radiation. A clear pattern in the continuum flux distribution is exhibited only by dwarf novae at maximum where some 80 percent of the non-double-eclipsing systems show essentially identical distributions. This result is not in disagreement with theoretical expectations. All classes of objects exhibit a clear, but in each case different, dependence of the line radiation on the inclination angle.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 252; 1, De
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    Post irradiation effects (PIE) in integrated circuits (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Post-irradiation effects (PIE) ranging from normal recovery to catastrophic failure have been observed in integrated circuits during the PIE period. Data presented show failure due to rebound after a 10 krad(Si) dose. In particular, five device types are investigated with varying PIE response. Special attention has been given to the HI1-507A analog multiplexer because its PIE response is extreme. X-ray diffraction has been uniquely employed to measure physical stress in the HI1-507A metallization. An attempt has been made to show a relationship between stress relaxation and radiation effects. All data presented support the current MIL-STD Method 1019.4 but demonstrate the importance of performing PIE measurements, even when mission doses are as low as 10 krad(Si).
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); 38; 1584-158
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    Bench-level characterization of a CMOS standard-cell D-latch using alpha-particle sensitive test circuits (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A methodology is described for predicting the SEU susceptibility of a standard-cell D-latch using an alpha-particle sensitive SRAM, SPICE critical charge simulation results, and alpha-particle interaction physics. Measurements were made on a 1.6-micron n-well CMOS 4-kb test SRAM irradiated with an Am-241 alpha-particle source. A collection depth of 6.09 micron was determined using these results and TRIM computer code. Using this collection depth and SPICE derived critical charge results on the latch design, an LET threshold of 34 MeV sq cm/mg was predicted. Heavy ion tests were then performed on the latch and an LET threshold of 41 MeV sq cm/mg was determined.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); 38; 1486-149
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    Update on parts SEE suspectibility from heavy ions (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: JPL and the Aerospace Corporation have collected a fourth set of heavy ion single event effects (SEE) test data. Trends in SEE susceptibility (including soft errors and latchup) for state-of-the-art parts are displayed. All data are conveniently divided into two tables: one for MOS devices, and one for a shorter list of recently tested bipolar devices. In addition, a new table of data for latchup tests only (invariably CMOS processes) is given.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); 38; 1529-153
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    Characterization of resonant tunneling diodes for microwave and millimeter-wave detection (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors report on the direct detection capabilities of resonant tunneling diodes in the 10-100 GHz range. An open circuit voltage sensitivity of 1750 mV/mW (in Ka-band) was measured. This is higher than the sensitivity of comparatively based commercially available solid-state detectors. The detector properties are a strong function of diode bias and the measured tangential signal sensitivity (-32 dBm at Ka-band with 1-MHz bandwidth) and the dynamic range (25 dB) of the diode are smaller compared to other solid-state detectors.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Microwave Theory and Techniques (ISSN 0018-9480); 39; 1876-188
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    On optimal infinite impulse response edge detection filters (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The authors outline the design of an optimal, computationally efficient, infinite impulse response edge detection filter. The optimal filter is computed based on Canny's high signal to noise ratio, good localization criteria, and a criterion on the spurious response of the filter to noise. An expression for the width of the filter, which is appropriate for infinite-length filters, is incorporated directly in the expression for spurious responses. The three criteria are maximized using the variational method and nonlinear constrained optimization. The optimal filter parameters are tabulated for various values of the filter performance criteria. A complete methodology for implementing the optimal filter using approximating recursive digital filtering is presented. The approximating recursive digital filter is separable into two linear filters operating in two orthogonal directions. The implementation is very simple and computationally efficient, has a constant time of execution for different sizes of the operator, and is readily amenable to real-time hardware implementation.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Pattern Analysis and Machine Intelligence (ISSN 0162-8828); 13; 1154-117
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    A resistive-gate In(0.53)Ga(0.47)As/InP heterostructure CCD (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The first InGaAs/InP charge-coupled device is demonstrated, exhibiting a charge transfer efficiency (CTE) of 0.98 at 13 MHz and 1 GHz. Cooling the device improves the CTE to greater than 0.99 at 13-MHz clock frequency. The 0.76-eV In(0.53)Ga(0.47)As bandgap makes this structure applicable to direct-detection short-wavelength infrared imagers.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Electron Device Letters (ISSN 0741-3106); 12; 688-690
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    Inhomogeneous structure in the chromospheres of dwarf M stars (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Linear combinations of observed spectra of the H-alpha and Ca-II resonance and IR lines from the chromospheres of a quiet (Gl 1) and an active (Gl 735) dwarf-M star are compared with the corresponding spectra from a star of intermediate activity (Gl 887). It is shown that the intermediate spectra cannot be explained as a simple juxtaposition of the extreme chromospheric states. It is concluded that the range of observed strengths of chromospheric activity indicators in dwarf-M stars is due, at least in part, to changes in the radial structure of the chromospheric heating function and not to changes in the area filling factor.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 253; 575-578
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    Cometary apparitions - 1990-2010 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Osculating orbital elements are listed (chronologically by perihelion passage time) for all periodic comets expected to arrive at perihelion during the 1990-2010 interval. Plots which make it possible to readily determine the earth-based viewing conditions of a particular cometary apparition are presented. These plots are drawn in a rotating coordinate system so that the sun-earth line is fixed for each apparition.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 2 (A93-13551 02-90); p. 1281-1308.
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    Cometary plasma waves and instabilities (1991)
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    Publication Date: 2011-08-24
    Description: Various plasma waves and instabilities that have been observed near comets are discussed. Observational results are ordered by plasma parameters and compared with specific instabilities. The variation in the cometary ion and electron beam densities and velocities are studied by examining regions far from and near the comet nucleus. Spacecraft observations relevant to nonlinear wave evolution, wave cascading, and the development of turbulence are reviewed. The implications of the results for wave-particle interactions - linear, nonlinear, resonant, and nonresonant - and their effects on stochastic particle acceleration are addressed. Higher-frequency ELF/VLF wave observations are also reviewed, and comparisons between the various measurements are made.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 2 (A93-13551 02-90); p. 1171-1210.
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    Cometary activity, discrete outgassing areas, and dust-jet formation (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Conceptual models for various types of features observed in cometary comae (jets, spirals, halos, fans, etc.), their computer simulation, and the hydrodynamic models for jet formation are critically reviewed, and evidence for anisotropic, strongly collimated flows of ejecta emanating from discrete active regions (vents) on the rotating cometary nuclei is presented. Techniques employed to generate synthetic comet images that simulate the features observed are described, and their relevance to the primary objects of coma-morphology studies is discussed. Modeling of temporal variations in the water emission from discrete active regions suggests that production curves asymmetric with respect to perihelion should be commonplace. Critical comparisons with the activity profiles of Enke's comet and with light curves of disappearing comets and comets that undergo outbursts are presented. Recent developments in the understanding of the processes that cause the nongravitational perturbations of cometary motions are reviewed, and the observed discontinuities are identified with the birth of new sources and/or deactivation of old vents.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 2 (A93-13551 02-90); p. 769-823.
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    Dynamical history of the Oort cloud (1991)
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    Publication Date: 2011-08-24
    Description: An overview of recent dynamical studies on the Oort cloud of comets surrounding the solar system is presented. Cometary orbits in the cloud evolve under the complex interaction of stellar, galactic, and giant molecular cloud perturbations, as well as planetary and nongravitational perturbations when the orbits reenter the planetary region. There is mounting evidence for a dense, inner Oort cloud of comets which acts as a reservoir to replenish the outer cloud as comets there are stripped away. A ring of comets beyond the orbit of Neptune, which may be the source of the short-period comets, is also likely. Temporal variations in the flux of comets from the Oort cloud into the planetary region by a factor of 50 percent are typical, and by factors of 20 to 200 are possible. Comets in the Oort cloud are processed by galactic cosmic rays, heated by nearby supernovae, eroded by interstellar dust impacts, and disrupted by mutual collisions.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 1 (A93-13551 02-90); p. 463-486.
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    On the integration of reinforcement learning and approximate reasoning for control (1991)
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    Publication Date: 2011-08-24
    Description: The author discusses the importance of strengthening the knowledge representation characteristic of reinforcement learning techniques using methods such as approximate reasoning. The ARIC (approximate reasoning-based intelligent control) architecture is an example of such a hybrid approach in which the fuzzy control rules are modified (fine-tuned) using reinforcement learning. ARIC also demonstrates that it is possible to start with an approximately correct control knowledge base and learn to refine this knowledge through further experience. On the other hand, techniques such as the TD (temporal difference) algorithm and Q-learning establish stronger theoretical foundations for their use in adaptive control and also in stability analysis of hybrid reinforcement learning and approximate reasoning-based controllers.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 2 (A93-13001 02-63); p. 1900-1904.
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    An experimental evaluation of uncertainty models for a flexible structure control problem (1991)
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    Publication Date: 2011-08-24
    Description: The authors describe results in applying robust control techniques of an active precision truss structure at the Jet Propulsion Laboratory. The active structure incorporates piezoelectric members which serve as both structural and actuator/sensor elements. Several characterizations of uncertainty are studied and the controllers are compared experimentally.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 2 (A93-13001 02-63); p. 1658, 1659.
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    Control of discrete event systems modeled as hierarchical state machines (1991)
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    Publication Date: 2011-08-24
    Description: The authors examine a class of discrete event systems (DESs) modeled as asynchronous hierarchical state machines (AHSMs). For this class of DESs, they provide an efficient method for testing reachability, which is an essential step in many control synthesis procedures. This method utilizes the asynchronous nature and hierarchical structure of AHSMs, thereby illustrating the advantage of the AHSM representation as compared with its equivalent (flat) state machine representation. An application of the method is presented where an online minimally restrictive solution is proposed for the problem of maintaining a controlled AHSM within prescribed legal bounds.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 2 (A93-13001 02-63); p. 1499-1504.
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    Permanent magnets composed of high temperature superconductors (1991)
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    Publication Date: 2011-08-24
    Description: A study of persistent, trapped magnetic field has been pursued with high-temperature superconducting (HTS) materials. The main effort is to study the feasibility of utilization of HTS to fabricate magnets for various devices. The trapped field, when not in saturation, is proportional to the applied field. Thus, it should be possible to replicate complicated field configurations with melt-textured YBa2Cu3O7 (MT-Y123) material, bypassing the need for HTS wires. Presently, materials have been developed from which magnets of 1.5 T, at 77 K, can be fabricated. Much higher field is available at lower operating temperature. Stability of a few percent per year is readily attainable. Results of studies on prototype motors and minimagnets are reported.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Journal of Applied Physics (ISSN 0021-8979); 70; 6501-650
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    The temperature of the circumstellar envelope of Alpha Orionis (1991)
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    Publication Date: 2011-08-24
    Description: The processes that heat and cool the circumstellar envelope of Alpha Ori are analyzed and the temperature calculated as a function of distance from the star. Cooling by fine structure lines is included for the first time in a general way in the theory of the thermal balance of a circumstellar envelope. Adiabatic cooling, dust-drag heating, and various line coolants contribute in the outer envelope, whereas the fine structure lines of O I and Si II and adiabatic cooling are dominant in the inner envelope. The rotational levels of CO cool the gas only at very small and at very large distances; elsewhere they provide a small amount of heating. The temperature declines very rapidly at first and then varies roughly as r exp -1/2 in the outer envelope. At very large distances, the temperature distribution flattens out due to photoelectron heating and reaches a minimum of about 4 K at about 250 arcsec.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 606-616
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    10 micron spectra of protostars and the solid methanol abundance (1991)
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    Publication Date: 2011-08-24
    Description: A search has been made for the strong C-O stretching absorption of solid methanol near 9.8 microns toward the heavily obscured protostars AFGL 961, AFGL 2591, the BN object and Mon R2 IRS 3. There is no clear evidence for this feature in the spectra, resulting in very conservative upper limits to the methanol abundance of 6 percent to 17 percent relative to solid H2O toward these objects. This is well below previous estimates of 50-80 percent obtained toward W33 A, NGC 7538 IRS 9, AFGL 2136, and W3 IRS 5, which were based on the assignment of the interstellar 6.85 microns absorption feature to the methanol C-H bending mode. This study shows that such high methanol abundances are not a characteristic of all interstellar ices.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 523-529
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    On the evolution of gravitationally unstable protostellar disks (1991)
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    Publication Date: 2011-08-24
    Description: 2D, N-body simulations of the nonlinear development of long-wavelength instabilities predicted to occur early in the formation stage of protostellar disks forming single stars are presented under conditions of controlled energy loss. It is found that the thermodynamics and long-term evolution of gravitationally unstable disks are intimately coupled: the global evolution rate is linearly proportional to the rate at which dissipated energy reaches and escapes from the surfaces of the disk. An upper limit is obtained to the rate at which energy is lost if it is assumed that the disk maintains vertical isothermality.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 382; 530-543
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    The accumulation and structure of comets (1991)
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    Publication Date: 2011-08-24
    Description: The paper reviews evidence for the accumulation of the terrestrial planets and comets from solid grains, with emphasis on the various proposals for the formation of cometary nuclei. With three exceptions, all hypotheses conclude or imply that a single compact object forms. Several hypotheses start with Goldreich-Ward-type gravitational instabilities. The collapse for this case also occurs at low velocities in the cm/s to m/s range. Experiment and theory show that under these conditions, low-density, filamentary clusters form that are fractal aggregates with a fractal dimension approximately equal to 2. In order to form cometary nuclei, the initial temperature must be about 50 K and not undergo a significant temperature rise during the accumulation process. The calculations show that accumulation will occur at low temperatures. Models of cometary nuclei are reviewed, and a simple model of the structure that results fom the accumulation of fluffy aggregates is described.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 1 (A93-13551 02-90); p. 335-359.
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    Direct adaptive impedance control of manipulators (1991)
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    Publication Date: 2011-08-24
    Description: An adaptive scheme for controlling the end-effector impedance of robot manipulators is presented. The proposed control system consists of three subsystems: a simple filter which characterizes the desired dynamic relationship between the end-effector position error and the end-effector/environment contact force, an adaptive controller which produces the Cartesian-space control input required to provide this desired dynamic relationship, and an algorithm for mapping the Cartesian-space control input to a physically realizable joint-space control torque. The controller does not require knowledge of either the structure or the parameter values of the robot dynamics, and it is implemented without calculation of the robot inverse kinematic transformation. As a result, the scheme represents a very general and computationally efficient approach to controlling the impedance of both nonredundant and redundant manipulators. Furthermore, the method can be applied directly to trajectory tracking in free-space motion by removing the impedance filter.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 3 (A93-13001 02-63); p. 2410-2415.
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    Dynamic coordination of a self-reconfigurable manipulator system (1991)
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    Publication Date: 2011-08-24
    Description: The authors present the dynamic coordination of a self-reconfigurable manipulator system capable of changing its mechanical structure according to given task requirements. The self-reconfiguration is achieved by reconfiguring the topology of a dual-arm system through serial, parallel, and bracing structures. Particular emphasis is placed on the dynamic coordination of two arms having three different dual-arm topologies. The authors develop the Cartesian space dynamic models of a dual-arm system of three dual-arm topologies and derive the kinematic and dynamic constraints imposed on two arms in cooperation. Dual-arm dynamic manipulabilities are defined to quantify the dynamic performance of three dual-arm topologies in terms of the efficiency of generating Cartesian accelerations. A methodology of selecting serial, parallel, and bracing structures based on dual-arm dynamic manipulabilities is provided.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 3 (A93-13001 02-63); p. 2404-2409.
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  • 86
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    Robust controller design for structures with displacement sensors (1991)
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    Publication Date: 2011-08-24
    Description: The passivity theorem may be used to design robust controllers for structures with positive transfer functions. The authors obtain a similar result for systems with displacement sensors. In order to illustrate the ideas discussed, a specific second-order dynamic system is considered.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 2 (A93-13001 02-63); p. 1625, 1626.
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  • 87
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    Cometary orbital dynamics and astrometry (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: An overview of research on cometary orbital dynamics and astrometry is presented, with emphasis on the nongravitational acceleration model which provides accurate orbits and ephemerides, and on new asymmetric models that represent the cometary outgassing phenomena more closely. Using a combination of long-focus telescopes, CCD detectors, microdensitometer reductions, and modern star catalogs, cometary astrometric data that are accurate to the subarcsecond level can be generated.
    Keywords: ASTROPHYSICS
    Type: In: Comets in the post-Halley era. Vol. 1 (A93-13551 02-90); p. 3-17.
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  • 88
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    Active noise control - Piezoceramic actuators in fluid/structure interaction models (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A model for a 2-D acoustic cavity with a flexible boundary (a beam) controlled via piezoceramic patches producing bending moments in the beam is considered. The associated control problem for this fluid/structure interaction system to reduce the acoustic pressure in the cavity involves unbounded control inputs. Approximation methods in the context of an LQR state space formulation are discussed, and numerical results are presented to demonstrate the effectiveness of this approach in computing feedback controls for noise reduction.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 3 (A93-13001 02-63); p. 2328-2333.
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  • 89
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    A self-reconfigurable manipulator system with dextrous bracing structure (1991)
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    Publication Date: 2011-08-24
    Description: The authors present a dextrous bracing structure of a dual-arm system as a means of implementing a self-reconfigurable manipulator system. The dextrous bracing structure allows a dual-arm system to relocate the bracing point between two arms, select the type of contact as the bracing point, and lock or release the joints of individual arms. The self-reconfigurable dual-arm system is now capable of reconfiguring its topology through serial, parallel and bracing structures, supporting general types of contact, rigid or sliding, as well as locking or releasing some of its joints as needed. The focus is on an analysis of the effects of the dextrous bracing on the performance of a dual-arm system in terms of dual-arm manipulabilities and resistivities. The analysis shows that a self-reconfigurable dual-arm system with a dextrous bracing structure gives continuously varying performance characteristics ranging from serial to parallel structures.
    Keywords: CYBERNETICS
    Type: In: IEEE Conference on Decision and Control, 30th, Brighton, United Kingdom, Dec. 11-13, 1991, Proceedings. Vol. 1 (A93-13001 02-63); p. 1033-1038.
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  • 90
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    Synchrotron emission as a tracer of the outflow in M82 (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The discovery of radio synchrotron emission from the outflow in M82 is reported. It is found that the outflow in M82 is visible in synchrotron radiation. IC losses are evident in the steepening of the radio spectrum, though this process is not a major contributor to the observed halo X-ray emission. Particle acceleration and/or diffusion in the wind may be important. Outflow speeds of 1000-3000 km/s are inferred from the spectral index profiles, which significantly exceeds the optically determined values. The fraction of the wind energy in the form of relativistic particles is consistent with a supernova origin. A termination shock produced by the intergalactic medium may be shaping the observed halo of M82.
    Keywords: ASTROPHYSICS
    Type: In: The interstellar disk-halo connection in galaxies (A93-18998 05-90); p. 281-285.
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  • 91
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    High current, high bandwidth laser diode current driver (1991)
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    Publication Date: 2011-08-24
    Description: A laser diode current driver has been developed for free space laser communications. The driver provides 300 mA peak modulation current and exhibits an optical risetime of less than 400 ps. The current and optical pulses are well behaved and show minimal ringing. The driver is well suited for QPPM modulation at data rates up to 440 Mbit/s. Much previous work has championed current steering circuits; in contrast, the present driver is a single-ended on/off switch. This results in twice the power efficiency as a current steering driver. The driver electrical efficiency for QPPM data is 34 percent. The high speed switch is realized with a Ku-band GaAsFET transistor, with a suitable pre-drive circuit, on a hybrid microcircuit adjacent to the laser diode.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: In: Free-space laser communication technologies III; Proceedings of the Meeting, Los Angeles, CA, Jan. 21, 22, 1991 (A93-18923 05-74); p. 412-420.
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  • 92
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    The effect of the changing polarity and neutral sheet of the IMF on the cosmic ray diurnal anisotropy at neutron monitor energies (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A drift with a simulated wavy neutral sheet have been used to study the effects of the reversal of the solar magnetic field every 11 years and the changes in the waviness of the heliospheric neutral sheet, corresponding to changes in solar activity, on the diurnal anisotropy at an energy of 20 GeV. The results indicate that the long-term behavior of the diurnal anisotropy, especially the phase shift from one solar minimum period to another, which seems to depend on the polarity of the IMF, has a theoretical explanation in the drift picture of the modulation of cosmic rays in the heliosphere.
    Keywords: ASTROPHYSICS
    Type: Planetary and Space Science (ISSN 0032-0633); 39; 1233-123
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  • 93
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    Linear system theory (1991)
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    Publication Date: 2011-08-24
    Description: The aim of this book is to provide a systematic and rigorous access to the main topics of linear state-space system theory in both the continuous-time case and the discrete-time case; and the I/O description of linear systems. The main thrusts of the work are the analysis of system descriptions and derivations of their properties, LQ-optimal control, state feedback and state estimation, and MIMO unity-feedback systems.
    Keywords: CYBERNETICS
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  • 94
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    Energetic water-group ions at Comet Giacobini-Zinner - An overview of observations by the EPAS instrument (1991)
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    Publication Date: 2011-08-24
    Description: An overview is presented of the observations of energetic (45-480 keV) cometary water group ions made by the EPAS instrument on the ICE spacecraft during the fly-by of Comet Giacobini-Zinner in September 1985. The discussion covers ion observations in the large-scale ion pick-up region surrounding the comet on about 10 exp 6 km spatial scales, observations of the cometary shock at about 100,000 km and the region of slowed mass-loaded flows which occur downstream, and the finite gyroradius effects which occur near the closest approach.
    Keywords: ASTROPHYSICS
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  • 95
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    YBa2Cu3O(7-delta)/Au/Nb sandwich geometry SNS weak links on c-axis oriented YBa2Cu3O(7-delta) (1991)
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    Publication Date: 2011-08-19
    Description: Sandwich geometry superconductor/normal metal/superconductor structures have been fabricated on LaAlO3 and cubic zirconia with laser-ablated, c-axis-oriented YBa2Cu3O(7-delta) base electrodes, 100-600 A of Au, and Nb counter electrodes, all formed in situ without breaking vacuum. Junctions range in size from 5 to 50 micron on a side. Four probe I-V measurements at 4.2 K show RnA products as low as 6 x 10 to the -9th sq cm and critical current densities up to 5.2 kA/sq cm. AC Josephson steps were observed with the application of 10-GHz radiation. The temperature dependence of Jc and the observation of the AC Josephson effect suggest that true supercurrents are present and that they do indeed represent the characteristics of the YBa2Cu3O(7-delta)/Au/Nb structure. The best results were obtained when the devices were annealed at about 450 C in O2 for 30 min after Au deposition.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Magnetics (ISSN 0018-9464); 27; 1335-133
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    Determination of surface resistance and magnetic penetration depth of superconducting YBa2Cu3O(7-delta) thin films by microwave power transmission measurements (1991)
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    Publication Date: 2011-08-19
    Description: A novel waveguide power transmission measurement technique was developed to extract the complex conductivity of superconducting thin films at microwave frequencies. The microwave conductivity was taken of two laser ablated YBa2Cu3O(7-delta) thin films on LaAlO3 with transition temperatures of approximately 86.3 and 82 K, respectively, in the temperature range 25 to 300 K. From the conductivity values, the penetration depth was found to be approximately 0.54 and 0.43 micron, and the surface resistance (R sub s) to be approximately 24 and 36 micro-Ohms at 36 GHz and 76 K for the two films under consideration. The R sub s values were compared with those obtained from the change in the Q-factor of a 36 GHz Te sub 011-mode (OFHC) copper cavity by replacing one of its end walls with the superconducting sample. This technique allows noninvasive characterization of high transition superconducting thin films at microwave frequencies.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Magnetics (ISSN 0018-9464); 27; 1284-128
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  • 97
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    Shielding and flux trapping properties of high temperature superconductors in the shape of hollow cylinders (1991)
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    Publication Date: 2011-08-19
    Description: Allowing for a field-dependent critical current density, the authors calculate the magnetic field that can be supported by hollow cylinders of varying wall thickness. An adiabatically stable field of 1.0 T can be shielded by or trapped in a cylinder with a wall thickness of 0.4 cm if the critical current density varies linearly with magnetic field and has a value of 104 A/sq cm at a field of 1.0 T. Such a current density appears to be within reach of present state-of-the-art melt-processed YBa2Cu3O7 (123) materials.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Magnetics (ISSN 0018-9464); 27; 1047
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  • 98
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    Resonant-tunnelling diode oscillator using a slot-coupled quasioptical open resonator (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A resonant-tunneling diode has oscillated at X-band frequencies in a microwave circuit consisting of a slot antenna coupled to a semiconfocal open resonator. Coupling between the open resonator and the slot oscillator improves the noise-to-carrier ratio by about 36 dB relative to that of the slot oscillator alone in the 100-200 kHz range. A circuit operating near 10 GHz has been designed as a scale model for millimeter- and submillimeter-wave applications.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Electronics Letters (ISSN 0013-5194); 27; 647-649
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  • 99
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    A field induced guide-antiguide modulator of GaAs-AlGaAs (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A guide-antiguide modulator of GaAs-AlGaAs using the electric-field-induced waveguide concept was demonstrated. The device was formed with a central waveguide electrode sandwiched between two antiguide electrodes on the surface of a p-i-n multiple quantum well (MQW). Switching between lateral guiding and antiguiding was accomplished by reverse biasing either the central electrode or the adjacent electrodes to increase the index beneath these respective regions. The on-off ratio was measured to be 20:1 with a propagation loss of the on-state of about 5 dB/mm.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Photonics Technology Letters (ISSN 1041-1135); 3; 141-143
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  • 100
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    Noise-driven radiative shocks - A new model for the optical quasi-periodic oscillations of the AM Herculis objects (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model for the 0.3-1.2 Hz optical quasi-periodic oscillations (QPOs) observed in a number of AM Her-type binary systems has been developed. It is suggested that the observed optical modulation is the result of shock oscillations induced by nonsteady accretion flows. It is shown that time-dependent models of radiative shock waves in nonsteady accretion flows onto magnetic white dwarfs with mass 0.6 solar mass and magnetic field strength of 30 MG can produce optical QPOs similar to those observed in the AM Her objects. Theoretical calculations have shown that oscillations cannot be sustained for these white dwarf parameters when the accretion rate is constant.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 375; L31-L34
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