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  • 1
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    Seismic-wave traveltimes in random media (1992)
    In:  Geophysical Journal International 110: 29-41
    Details
    Publication Date: 1992
    Keywords: seismic processing/methodology
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    CITATION DEKORP
  • 2
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    Atomic probe microscopy of 3C SiC films grown on 6H SiC substrates (1993)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The surface of 3C SiC films grown on 6H SiC substrates has been studied by atomic probe microscopy in air. Atomic-scale images of the 3C SiC surface have been obtained by STM which confirm the 111 line type orientation of the cubic 3C layer grown on the 0001 plane type surface of the hexagonal 6H substrate. The nearest-neighbor atomic spacing for the 3C layer has been measured to be 3.29 +/- 0.2 A, which is within 7 percent of the bulk value. Shallow terraces in the 3C layer have been observed by STM to separate regions of very smooth growth in the vicinity of the 3C nucleation point from considerably rougher 3C surface regions. These terraces are oriented at right angles to the growth direction. Atomic force microscopy has been used to study etch pits present on the 6H substrate due to high temperature HCl cleaning prior to CVD growth of the 3C layer. The etch pits have hexagonal symmetry and vary in depth from 50 nm to 1 micron.
    Keywords: SOLID-STATE PHYSICS
    Type: Applied Physics Letters (ISSN 0003-6951); 62; 20; p. 2545-2547.
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    A drive unit for the instrument pointing system (1981)
    In:  CASI
    Details
    Publication Date: 2006-01-16
    Description: The requirements, capabilities, and unique design features of the instrument pointing system drive units (DU) are presented. The DU's are identical for all three gimbal axes (elevation, cross elevation, and azimuth) and provide alternating rotation of shaft versus the housing of + or - 180 deg. The design features include: two ball bearing cartridges using cemented carbide balls coated with TiC a layer; redundant brushless torque motors and resolvers; a load by-pass mechanism driven by a dc torque motor to off-load the bearings during ascent/descent, ground transportation, and to provide an emergency breaking capability; and cabling over each gimbal axis by means of cable follow-up consisting of 13 signal and 15 power flat band cable loops. Test results of disturbance torque characteristics are presented.
    Keywords: MECHANICAL ENGINEERING
    Type: NASA. Marshall Space Flight Center The 15th Aerospace Mech. Symp.; p 263-278
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Crystal-melt interface shape of Czochralski-grown large diameter germanium crystals (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Crystal-melt interface shapes of 100 to 200 mm diameter 111-line Ge grown by the Czochralski technique have been examined using the method of fast withdrawal from the melt. Initially, the interface shape is convex, then transforms gradually into a sigmoidal shape, becomes nearly planar at about one third of the final crystal length, and finally assumes a concave profile with progressively increasing curvature. The nearly planar interface has a double-facet structure, with an annular facet at the edge of the crystal in addition to the central (111) facet. Formation of the annular facet is accompanied by a giant oscillation of the pull rate when the maximum average pull rate is exceeded. Such oscillation is detrimental to crystal quality, since it introduces a region of high dislocation density. An average pull rate maximum of 2 cm/h has been found to allow for a smooth growth of 200 mm diameter crystals. The origin of the pull rate perturbation is discussed in terms of an instantaneous change in the equilibrium shape of the meniscus.
    Keywords: SOLID-STATE PHYSICS
    Type: Journal of Crystal Growth (ISSN 0022-0248); 99; 1-4,
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    Development of a relatchable cover mechanism for a cryogenic IR-sensor (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A cover mechanism for use on the Infrared Background Signature Survey (IBSS) cryostat was developed. The IBSS IR-instrument is scheduled for STS launch in early 1991 as a payload of the Shuttle Payload Satellite (SPS) 2. The cover is hinged, with a motorized rope drive. During ground processing, launch, entry, and landing, the cryostat, which houses the IR-instrument, is required to be a sealed vacuum tight container for cooling purposes and contamination prevention. When on orbit, the cover is opened to provide an unobstructed field of view for the IR-instrument. A positive seal is accomplished through the use of latch mechanism. The cover and the latch are driven by a common redundant actuator consisting of dc motors, spur gears, and a differential gear. Hall probe limit switches and position sensors (rotary variable transformer) are used to determine the position of the cover and the latch. The cover mechanism was successfully qualified for thermal vacuum (-25 to 35 C), acoustic noise, vibration (6 Gs sine, 9.7 G RMS) and life cycles. Constricting requirements, mechanical and electronic control design, specific design details, test results of functional performance, and environmental and life tests are described.
    Keywords: MECHANICAL ENGINEERING
    Type: JPL, The 25th Aerospace Mechanisms Symposium; p 125-134
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Three-micron spectroscopy of highly reddened field stars (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Broad absorption features centered at 3.45 microns and at 3.0-3.0 microns towards a number of late-type supergiants in the vicinity of the galactic center were repeatedly reported. Here, 2.0 to 2.5 and 3.0 to 4.0 micron spectra are presented for field late-type highly reddened (A sub V is approximately 17-27) stars located in different regions of the galactic plane more than 20 deg away from the galactic center direction. The observations, made with the 3.6, 2.2, and 1.0 m ESO telescopes at La Silla, Chile, consists of CVF spectra with resolution lambda/delta lambda is approximately or equal to 100 and IRSPEC spectra with resolution lambda/delta lambda is approximately or equal to 700. In the direction of the most highly reddened stars, definitive detections of the 3.45 and the 3.0 to 3.1 micron absorption features are reported. The 3.45 micron feature was attributed to absorption arising in a vibrational transition resulting from the C-H stretching in organic compounds, while the 3.0 to 3.1 micron broader feature are tentatively attributed to O-H bonds. The observations strongly support that the agent producing the 3.45 micron feature, presumably organic molecules, is an important component of the diffuse interstellar medium and is not characteristic only of the galactic center environment.
    Keywords: ASTROPHYSICS
    Type: NASA, Ames Research Center, Interstellar Dust: Contributed Papers; p 29
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 7
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    Electric potential distributions at the interface between plasmasheet clouds (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: At the interface between two plasma clouds with different densities, temperatures, and/or bulk velocities, there are large charge separation electric fields which can be modeled in the framework of a collisionless theory for tangential discontinuities. Two different classes of layers were identified: the first one corresponds to (stable) ion layers which are thicker than one ion Lamor radius; the second one corresponds to (unstable) electron layers which are only a few electron Larmor radii thick. It is suggested that these thin electron layers with large electric potential gradients (up to 400 mV/m) are the regions where large-amplitude electrostatic waves are spontaneously generated. These waves scatter the pitch angles of the ambient plasmasheet electron into the atmospheric loss cone. The unstable electron layers can therefore be considered as the seat of strong pitch angle scattering for the primary auroral electrons.
    Keywords: GEOPHYSICS
    Type: NASA. Marshall Space Flight Center Double Layers in Astrophysics; p 287-294
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    VLBI system for weekly measurement of UT1 and polar motion: Preliminary results (1980)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The DSN implementation of a system for measuring UT1 and polar motion using very long baseline interferometry (VLBI) is currently being tested. The VLBI experiments are being conducted on a weekly basis on each of two intercontinental baselines. During a 17 day period in September 1979, data were obtained for seven consecutive experiments using an early version of that system. Those experiments were used to refine the estimation procedure to be used in the operational system and to provide a preliminary assessment of the performance of the system.
    Keywords: SPACE COMMUNICATIONS, SPACECRAFT COMMUNICATIONS, COMMAND AND TRACKING
    Type: The Telecommun. and Data Acquisition Rept.; p 15-20
    Format: text
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    NASA TECHNICAL REPORTS
  • 9
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    The JPL near-real-time VLBI system and its application to clock synchronization and earth orientation measurements (1983)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The JPL near-real-time VLBI system called Block I is discussed. The hardware and software of the system are described, and the Time and Earth Motion Precision Observations (TEMPO) which utilize Block I are discussed. These observations are designed to provide interstation clock synchronization to 10 nsec and to determine earth orientation (UT1 and polar motion - UTPM) to 30 cm or better in each component. TEMPO results for clock synchronization and UTPM are presented with data from the July 1980-August 1981 analyzed using the most recent JPL solution software and source catalog. Future plans for TEMPO and Block I are discussed.
    Keywords: GEOSCIENCES (GENERAL)
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Experiences with a computer-based study on waste heat usage for integrated agricultural purposes in Mchigan (1977)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Keywords: ENVIRONMENT POLLUTION
    Type: NASA, Washington Proc. of the Conf. on Waste Heat Management and Utilization, Vol. 2,; 23 p
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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