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  • Geophysics  (191)
  • COMPOSITE MATERIALS  (9)
  • Astrophysics
  • Seismology
  • 2000-2004  (198)
  • 1990-1994  (10)
  • 1
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    In:  Geophys. J. Int., San Francisco, Pergamon, vol. 143, no. 3, pp. 629-661, pp. L15303, (ISSN: 1340-4202)
    Publication Date: 2000
    Keywords: Hypocentral depth ; CRUST ; earth mantle ; Seismology ; Rheology ; Lithosphere ; GJI
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  • 2
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    In:  Geophys. Res. Lett., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 31, no. 9, pp. 1-4, pp. L09611
    Publication Date: 2004
    Description: Backazimuth estimates derived from surface wave polarization can be used to test association of an observed surface wave with a seismic event. However, commonly used techniques for estimating the backazimuth are subject to a number of errors and are often inaccurate. We evaluate the performance of a new algorithm for determining Rayleigh wave propagation direction from the cross-correlation of the horizontal and Hilbert transformed vertical seismograms. This proves to be more accurate and much less error-prone than current automatic processing procedures, and the cross-correlation value provides a good measure of the reliability of the backazimuth estimate. Consequently, the new algorithm will permit more reliable event association at a lower magnitude threshold.
    Keywords: Horizontal to vertical spectral ratio ; Nakamura ; Spectrum ; NOISE ; Site amplification ; Surface waves ; Polarization ; Rayleigh waves ; Correlation ; Hilbert transform ; 7200 ; Seismology ; 7219 ; Seismology: ; Nuclear ; explosion ; seismology ; 7255 ; Surface ; waves ; and ; free ; oscillations ; GRL
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  • 3
    Publication Date: 2001
    Keywords: paleo ; Seismology ; Geol. aspects ; 7221 ; Seismology ; Paleoseismology ; 1829 ; Hydrology ; Groundwater ; hydrology ; 7294 ; Instruments ; and ; techniques
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  • 4
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    In:  Bull. Seism. Soc. Am., Washington D.C., Bundesanstalt für Geowissenschaften und Rohstoffe, vol. 90, no. 2, pp. 494-499, pp. L09611
    Publication Date: 2000
    Keywords: Seismology ; Seismics (controlled source seismology) ; Spectrum ; Source ; BSSA
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  • 5
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    Phillips Laboratory Air Force Systems Command
    In:  scientific report, Hanscom Air Force Base, Phillips Laboratory Air Force Systems Command, vol. C 560, 183 pp., no. PL-TR-91-2161, pp. 1143-1146 (SL3.8), (ISBN 3-933346-037)
    Publication Date: 1991
    Keywords: Magnitude ; Energy (of earthquakes) ; Nuclear explosion ; Seismology ; Seismic arrays ; Data analysis / ~ processing
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  • 6
    Publication Date: 2011-08-24
    Description: To use graphite polyetheretherketone (PEEK) material on highly curved surfaces requires that the material be drapable and easily conformable to the surface. This paper presents the mechanical property characterization and impact resistance results for laminates made from two types of graphite/PEEK materials that will conform to a curved surface. These laminates were made from two different material forms. These forms are: (1) a fabric where each yarn is a co-mingled Celion G30-500 3K graphite fiber and PEEK thermoplastic fiber; and (2) an interleaved material of Celion G30-500 3K graphite fabric interleaved with PEEK thermoplastic film. The experimental results from the fabric laminates are compared with results for laminates made from AS4/PEEK unidirectional tape. The results indicate that the tension and compression moduli for quasi-isotropic and orthotropic laminates made from fabric materials are at least 79 percent of the modulus of equivalent laminates made from tape material. The strength of fabric material laminates is at least 80 percent of laminates made from tape material. The evaluation of fabric material for shear stiffness indicates that a tape material laminate could be replaced by a fabric material laminate and still maintain 89 percent of the shear stiffness of the tape material laminate. The notched quasi-isotropic compression panel failure strength is 42 to 46 percent of the unnotched quasi-isotropic laminate strength. Damage area after impact with 20 ft-lbs of impact energy is larger for the co-mingled panels than for the interleaved panels. The inerleaved panels have less damage than panels made from tape material. Residual compression strength of quasi-isotropic panels after impact of 20 ft-lbs of energy varies between 33 percent of the undamaged quasi-isotropic material strength for the tape material and 38 percent of the undamaged quasi-isotropic material strength for the co-mingled fabric material.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of the American Helicopter Society (ISSN 0002-8711); 39; 1; p. 24-30
    Format: text
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  • 7
    Publication Date: 2013-08-29
    Description: Progress on two programs to evaluate structural composite components in flight service on Bell 206L and Sikorsky S-76 commercial helicopters is described. Forty ship sets of composite components that include the litter door, baggage door, forward fairing, and vertical fin have been installed on Bell Model 206L helicopters that are operating in widely different climates. Component installation started in 1981 and selected components were removed and tested at prescribed intervals over a ten year evaluation. Four horizontal stabilizers and eleven tail rotor spars that are production components on the S-76 helicopter were tested after prescribed periods of service to determine the effects of the operating environment on their performance. Concurrent with the flight evaluation, materials used to fabricate the components were exposed in ground racks and tested at specified intervals to determine the effects of outdoor environments. Results achieved from 123,000 hours of accumulated service on the Bell 206L components and 53,000 hours on the Sikorsky S-76 components are reported. Seventy-eight Bell 206L components were removed and tested statically. Results of seven years of ground exposure of materials used to fabricate the Bell 206L components are presented. Results of tests on four Sikorsky S-76 horizontal stabilizers and eleven tail rotor spars are also presented. Panels of material used to fabricate the Sikorsky S-76 components that were exposed for six years were tested and results are presented.
    Keywords: COMPOSITE MATERIALS
    Type: NASA. Langley Research Center, Eighth DOD(NASA)FAA Conference on Fibrous Composites in Structural Design, Part 2; p 393-428
    Format: text
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  • 8
    Publication Date: 2013-08-31
    Description: Ancient geologic and hydrologic phenomena on Mars observed through the magnetic data provide windows to the ancient past through the younger Argyre and Hellas impacts, the northern plains basement and the rock materials that mantle the basement, and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes). These signatures, coupled with highly degraded macrostructures (tectonic features that energetic planet during its embryonic development (0.5 Ga or so of activity) with an active dynamo and magnetosphere. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Tern. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated I through impact crater and elemental information. This region records many unique characteristics, including predominately Noachian materials, a highland-lowland boundary region that is distinct from other boundary regions, the presence of very few macrostructures when compared to the rest of the cratered highlands, the largest region of fretted terrain on Mars, outflow channels such as Mamers Valles that do not have obvious origins, and distinct albedo, thermal inertia, gravity, magnetic, and elemental signatures.
    Keywords: Geophysics
    Type: Workshop on Hemispheres Apart: The Origin and Modification of The Martian Crustal Dichotomy; 13-14; LPI-Contrib-1213
    Format: application/pdf
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  • 9
    Publication Date: 2017-10-02
    Description: NASA Langley and the U.S. Army have jointly sponsored programs to assess the effects of realistic flight environments and ground-based exposure on advanced composite materials and structures. Composite secondary structural components were initially installed on commercial transport aircraft in 1973; secondary and primary structural components were installed on commercial helicopters in 1979; and primary structural components were installed on commercial aircraft in the mid-to-late 1980's. Service performance, maintenance characteristics, and residual strength of numerous components are reported. In addition to data on flight components, 10 year ground exposure test results on material coupons are reported. Comparison between ground and flight environmental effects for several composite material systems are also presented. Test results indicate excellent in-service performance with the composite components during the 15 year period. Good correlation between ground-based material performance and operational structural performance has been achieved.
    Keywords: COMPOSITE MATERIALS
    Type: AGARD, The Utilization of Advanced Composites in Military Aircraft; 13 p
    Format: text
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  • 10
    Publication Date: 2017-10-02
    Description: NASA has identified the development of an autonomously operating spacecraft as a necessity for an expanded program of missions exploring the Solar System. The Autonomous Sciencecraft Experiment (ASE) has been selected for flight demonstration by NASA s New Millennium Program (NMP) as part of the Space Technology 6 (ST6) mission. ASE is scheduled to fly on the US Air Force Research Laboratory (AFRL) Techsat-21 constellation in 2006. Tech- Sat-21 consists of three satellites flying in a variable-geometry formation in Earth orbit. Each satellite is equipped with X-band Synthetic Aperture Radar, yielding high spatial resolution images (approx. 3 m) of the Earth s surface. The constellation will fly at an altitude of 550 km, in a 35.4 inclination circular orbit, yielding exact repeat-track observations every 13 days. Prior to full deployment, elements of the versatile ASE spacecraft command and control software, image formation software and science processing software will be utilized and tested on two very different platforms in 2003: AirSAR and EO-1 (described below). Advantages of Autonomous Operations: ASE will demonstrate advanced autonomous science data acquisition, processing, and product downlink prioritization, as well as autonomous spacecraft command and control, and fault detection. The advantages of spacecraft autonomy are to future missions include: (a) making the best use of reduced downlink; (b) the overcoming of communication delays through decisionmaking in situ, enabling fast reaction to dynamic events; (c) an increase of science content per byte of returned data; and (d) an avoidance of return of null (no-change/no feature) datasets: if there is no change detectable between two scenes of the same target, there is no need to return the second dataset.
    Keywords: Astrophysics
    Type: Lunar and Planetary Science XXXIV; LPI-Contrib-1156
    Format: text
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