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  • Other Sources  (21)
  • 1990-1994  (21)
  • 1
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    Heliocentric distance dependencies of the C2 lifetime and C2 parent production rate in comet P/Brorsen-Metcalf (1989o) (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Comet P/Brorsen-Metcalf (1989o) has been extensively observed in the visible and in the ultraviolet during its latest apparition of summer 1989. In this paper we report a preliminary determination of the C2 production rates and lifetimes and we compare those rates to the H2O production rates obtained from UV data.
    Keywords: ASTROPHYSICS
    Type: Lunar and Planetary Inst., Asteroids, Comets, Meteors 1991; p 345-348
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  • 2
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    Results of an A109 simulation validation and handling qualities study (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The results for the validation of a mathematical model of the Agusta A109 helicopter, and subsequent use of the model as the baseline for a handling qualities study of cockpit centerstick requirements, are described. The technical approach included flight test, non-realtime analysis, and realtime piloted simulation. Results of the validation illustrate a time- and frequency-domain approach to the model and simulator issues. The final A109 model correlates well with the actual aircraft with the Stability Augmentation System (SAS) engaged, but is unacceptable without the SAS because of instability and response coupling at low speeds. Results of the centerstick study support the current U.S. Army handling qualities requirements for centerstick characteristics.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Vertica (ISSN 0360-5450); 14; 2, 19; 217-235
    Format: text
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  • 3
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    Nonlinear modeling of a long flexible manipulator and control by inertial devices (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The authors consider the modeling and control of a planar, long flexible manipulator that is representative of current space-based robotic arms. The arm is equipped with three actuators: 1) a shoulder motor; 2) a torque wheel at the tip; and 3) a proof-mass actuator at the tip. The goal is to investigate the potential use of inertial devices as control inputs for maneuvering tasks and vibration suppression. The parameters used for the inertial devices at the tip are comparable to those specified for the Mini-Mast facility at the Langley Research Center. A nonlinear distributed parameter model is obtained by the extended Hamilton principle. The associated eigenvalue/eigenfunction problem is solved and a finite-dimensional state space model is assembled. A preliminary design of a linear quadratic regulator is used, and computer simulation results illustrate the benefits of using the proposed actuators.
    Keywords: CYBERNETICS
    Type: In: 1992 American Control Conference, 11th, Chicago, IL, June 24-26, 1992, Proceedings. Vol. 2 (A93-22776 07-63); p. 1695-1699.
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  • 4
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    Single-input/single-output transfer functions for a flexible slewing link (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Truncated linear models based on constrained and unconstrained mode expansions for a flexible link with torque actuation at its hub led us to examine the behavior of the open-loop-zeros of five commonly used SISO transfer functions. We arrive at new conclusions with regard to minimum- and non-minimum-phase zeros, and passivity of the transfer functions. The flexible-to-rigid inertia (FRI) ratio plays an important role in the determination of these characteristics. This paper illustrates how the zero locations of some of the transfer functions are dramatically affected by the FRI ratio. We also investigate the performance of a hub angle, hub rate, and relative tip position static feedback controller based on a reduced-order constrained mode model when applied to both unconstrained and constrained mode models of the same dimension. Simulations indicate that the constrained model can be stable while the unconstrained model is not for high FRI ratios. Our findings can provide useful information to designers in cases where the controller is sensitive to the 1ocation of the plant's zeros.
    Keywords: CYBERNETICS
    Type: Journal of Robotic Systems (ISSN 0741-2223); 10; 7; p. 913-929.
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  • 5
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    High resolution imaging of galaxy cores (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Surface photometry data obtained with the Faint Object Camera of the Hubble Space Telescope in the cores of ten galaxies is presented. The major results are: (1) none of the galaxies show truly 'isothermal' cores, (2) galaxies with nuclear activity show very similar light profiles, (3) all objects show central mass densities above 10 exp 3 solar masses/cu pc3, and (4) four of the galaxies (M87, NGC 3862, NGC 4594, NGC 6251) show evidence for exceptional nuclear mass concentrations.
    Keywords: ASTROPHYSICS
    Type: Astronomical Journal (ISSN 0004-6256); 106; 4; p. 1371-1393, 1707,
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  • 6
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    High-resolution imaging of the Pluto-Charon system with the Faint Object Camera of the Hubble Space Telescope (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Images of the Pluto-Charon system were obtained with the Faint Object Camera (FOC) of the Hubble Space Telescope (HST) after the refurbishment of the telescope. The images are of superb quality, allowing the determination of radii, fluxes, and albedos. Attempts were made to improve the resolution of the already diffraction limited images by image restoration. These yielded indications of surface albedo distributions qualitatively consistent with models derived from observations of Pluto-Charon mutual eclipses.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 435; 1; p. L75-L78
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  • 7
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    Imaging of four planetary nebulae in the Magellanic Clouds using the Hubble Space Telescope Faint Object Camera (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Using the Faint Object Camera on-board the Hubble Space Telescope, we have obtained images of four planetary nebulae (PNe) in the Magellanic Clouds, namely N2 and N5 in the SMC and N66 and N201 in the LMC. Each nebula was imaged through two narrow-band filters isolating forbidden O III 5007 and H-beta, for a nominal exposure time of 1000 s in each filter. In forbidden O III, SMC N5 shows a circular ring structure, with a peak-to-peak diameter of 0.26 arcsec and a FWHM of 0.35 arcsec while SMC N2 shows an elliptical ring structure with a peak-to-peak diameter of 0.26 x 0.21. The expansion ages corresponding to the observed structures in SMC N2 and N5 are of the order of 3000 yr. LMC N201 is very compact, with a FWHM of 0.2 arcsec in H-beta. The Type I PN LMC N66 is a multipolar nebula, with the brightest part having an extent of about 2 arcsec and with fainter structures extending over 4 arcsec.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 398; 1; p. L41-L44.
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  • 8
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    A new minimum-time control law for a one-mode model of a flexible slewing structure (1993)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: We describe the construction of a new minimum-time control law for a single-axis, undamped, one-mode model of a flexible slewing structure. The set of necessary and sufficient conditions for optimality are developed using phase-plane techniques, and are given in terms of the vibration frequencies and the rigid-body states. This effectively provides the switching hypersurface in four-dimensional space. The resulting control strategy has the advantage that can be implemented on-line since no a priori computation of switching times is required.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Automatic Control (ISSN 0018-9286); 38; 1; p. 142-146.
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  • 9
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    Faint Object Camera observations of M87 - The jet and nucleus (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: UV and optical images of the central region and jet of the nearby elliptical galaxy M87 have been obtained with about 0.1 arcsec resolution in several spectral bands with the Faint Object Camera (FOC) on the HST, including polarization images. Deconvolution enhances the contrast of the complex structure and filamentary patterns in the jet already evident in the aberrated images. Morphologically there is close similarity between the FOC images of the extended jet and the best 2-cm radio maps obtained at similar resolution, and the magnetic field vectors from the UV and radio polarimetric data also correspond well. We observe structure in the inner jet within a few tenths arcsec of the nucleus which also has been well studied at radio wavelengths. Our UV and optical photometry of regions along the jet shows little variation in spectral index from the value 1.0 between markedly different regions and no trend to a steepening spectrum with distance along the jet.
    Keywords: ASTROPHYSICS
    Type: Astronomy and Astrophysics (ISSN 0004-6361); 261; 2; p. 393-404.
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  • 10
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    Momentum management in redundant manipulators for vibration suppression (1993)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This research project dealt with the development of control methodologies which would effectively use existing inertial devices as control actuators in the manipulation of Remote Manipulator System (RMS)-type robotic arms. The existing devices proposed to be investigated are the Torque-Wheel (TW) and the Proof-Mass actuator (PM). This report presents a succinct summary of our results.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA-CR-194112 , NAS 1.26:194112
    Format: application/pdf
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