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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial & engineering chemistry 51 (1959), S. 1265-1266 
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Mathematical geology 17 (1985), S. 797-811 
    ISSN: 1573-8868
    Keywords: indicator function ; variogram ; spatial autocorrelation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Mathematics
    Notes: Abstract Flat variograms often are interpreted as representing a lack of spatial autocorrelation. Recent research in earthquake engineering shows that nearby field noise can substantially mask a prominent spatial autocorrelation and result in what appears to be a purely random spatial process. A careful selection of threshold in assigning an indicator function can yield an indicator variogram which reveals underlying spatial autocorrelation. Although this application involves use of seismic data, the results are relevant to geostatistical applications in general.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 1980-11-01
    Description: Soils cultivated for 60 yr were compared with uncultivated forested soils at 10 sites in Appalachian Quebec. All soils belonged to the Humo-Ferric Podzol Great Group, five sets of comparisons being located on the Ascot soil series and five on the Greensboro. Comparisons were made between corresponding soil horizons, analytical data being derived from the bulking and analysis of six sample cores per horizon. Cultivation increased weight of soil in the solum and in the whole profile of both the Greensboro and the two soil series combined; bulk density was slightly affected. Field capacity, permanent wilting point and available water of the surface and sub-surface layers, in the solum and in the whole profile, were significantly increased by cultivation. The increase of available water was accompanied by a corresponding decrease in gravitational water. The content fine clay was significantly decreased in the surface layer and in the solum, while it was increased significantly in the C horizon by cultivation which also decreased the acidity of the surface and sub-surface in both series. There was a marked increase in organic matter content, but the level of fulvic acid was relatively unaffected by cultivation, indicating that the increased H/F ratio was primarily due to an increase in humic acid. Generally, Al content was not significantly changed, while significant increases in Fe and Mn were observed in the surface and solum of cultivated profiles. A deduction is made that cultivation has regraded podzol profiles into Dystric Brunisol ones which have started to evolve already toward kinds of Luvisolic profiles.
    Print ISSN: 0008-4271
    Electronic ISSN: 1918-1841
    Topics: Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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  • 4
    Publication Date: 1985-11-01
    Print ISSN: 1874-8961
    Electronic ISSN: 1874-8953
    Topics: Geosciences , Mathematics
    Published by Springer
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  • 5
    Publication Date: 1967-08-01
    Print ISSN: 1047-4838
    Electronic ISSN: 1543-1851
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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  • 6
    Publication Date: 1957-05-01
    Print ISSN: 0027-0644
    Electronic ISSN: 1520-0493
    Topics: Geography , Geosciences , Physics
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  • 7
    Publication Date: 2019-06-28
    Description: An experimental investigation of the influence of lateral feel system characteristics on fighter aircraft roll flying qualities was conducted using the variable stability USAF NT-33. Forty-two evaluation flights were flown by three engineering test pilots. The investigation utilized the power approach, visual landing task and up-and-away tasks including formation, gun tracking, and computer-generated compensatory attitude tracking tasks displayed on the Head-Up Display. Experimental variations included the feel system frequency, force-deflection gradient, control system command type (force or position input command), aircraft roll mode time constant, control system prefilter frequency, and control system time delay. The primary data were task performance records and evaluation pilot comments and ratings using the Cooper-Harper scale. The data highlight the unique and powerful effect of the feel system of flying qualities. The data show that the feel system is not 'equivalent' in flying qualities influence to analogous control system elements. A lower limit of allowable feel system frequency appears warranted to ensure good lateral flying qualities. Flying qualities criteria should most properly treat the feel system dynamic influence separately from the control system, since the input and output of this dynamic element is apparent to the pilot and thus, does not produce a 'hidden' effect.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-179445 , H-1584 , NAS 1.26:179445 , CALSPAN-7205-26
    Format: application/pdf
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  • 8
    Publication Date: 2019-06-28
    Description: Digital flight control systems are popular for their flexibility, reliability, and power; however, their use sometimes results in deficient handling qualities, including pilot-induced oscillation (PIO), which can require extensive redesign of the control system. When redesign is not immediately possible, temporary solutions, such as the PIO suppression (PIOS) filter developed for the Space Shuttle, have been proposed. To determine the effectiveness of such PIOS filters on more conventional, high-performance aircraft, three experiments were performed using the NASA F-8 digital fly-by-wire and USAF/Calspan NT-33 variable-stability aircraft. Two types of PIOS filters were evaluated, using high-gain, precision tasks (close formation, probe-and-drogue refueling, and precision touch-and-go landing) with a time delay or a first-order lag added to make the aircraft prone to PIO. Various configurations of the PIOS filter were evaluated in the flight programs, and most of the PIOS filter configurations reduced the occurrence of PIOs and improved the handling qualities of the PIO-prone aircraft. These experiments also confirmed the influence of high-gain tasks and excessive control system time delay in evoking pilot-induced oscillations.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 83-2107
    Format: text
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  • 9
    Publication Date: 2019-06-28
    Description: An investigation of pilot-induced oscillation suppression (PIOS) filters was performed using the USAF/Flight Dynamics Laboratory variable stability NT-33 aircraft, modified and operated by Calspan. This program examined the effects of PIOS filtering on the longitudinal flying qualities of fighter aircraft during the visual approach and landing task. Forty evaluations were flown to test the effects of different PIOS filters. Although detailed analyses were not undertaken, the results indicate that PIOS filtering can improve the flying qualities of an otherwise unacceptable aircraft configuration (Level 3 flying qualities). However, the ability of the filters to suppress pilot-induced oscillations appears to be dependent upon the aircraft configuration characteristics. Further, the data show that the filters can adversely affect landing flying qualities if improperly designed. The data provide an excellent foundation from which detail analyses can be performed.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Format: text
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  • 10
    Publication Date: 2019-06-28
    Description: An investigation of pilot-induced oscillation suppression (PIOS) filters was performed using the USAF/Flight Dynamics Laboratory variable stability NT-33 aircraft, modified and operated by Calspan. This program examined the effects of PIOS filtering on the longitudinal flying qualities of fighter aircraft during the visual approach and landing task. Forty evaluations were flown to test the effects of different PIOS filters. Although detailed analyses were not undertaken, the results indicate that PIOS filtering can improve the flying qualities of an otherwise unacceptable aircraft configuration (Level 3 flying qualities). However, the ability of the filters to suppress pilot-induced oscillations appears to be dependent upon the aircraft configuration characteristics. Further, the data show that the filters can adversely affect landing flying qualities if improperly designed. The data provide an excellent foundation from which detail analyses can be performed.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-163116 , NAS 1.26:163116 , REPT-6645-F-9
    Format: application/pdf
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