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  • 1
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    Using color-color diagrams to test models for the 'blue bump' (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Color-color diagrams are used to study the set of accretion disk plus power-law models and to determine whether they can adequately fit the optical/UV continua of a sample of 34 quasars, and the soft X-ray excesses measured for seven of the sample objects by Masnou et al. (1991). The loci of pure disk models for cos theta is greater than 0 are virtually superimposed on each other regardless of cos theta, demonstrating that a given observed spectrum cannot be described by a unique combination of S and cos theta. The distributions of model and data colors are found to overlap, showing that the disk plus power-law models do fit the distribution of data colors. For six of the seven objects, the soft X-ray excesses may be fit with an accretion disk plus power-law model without requiring the assumption of super-Eddington accretion; this shows the utility of employing Kerr disks.
    Keywords: ASTROPHYSICS
    Type: In: Testing the AGN paradigm; Proceedings of the 2nd Annual Topical Astrophysics Conference, Univ. of Maryland, College Park, Oct. 14-16, 1991 (A93-29801 11-90); p. 208-211.
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  • 2
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    The variability of the solar diameter (1991)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It is argued here that most of the variation in observations of the solar radius of over three centuries measure properties of the sun's limb darkening function and are affected by many sources of degradation of the solar image. They do not directly measure a true solar radius. From a long series of visual observations made by a single observer as well as recent photoelectric observations, evidence is found for periodicities in the apparent radius that occur in both modern and historical records. The magnitude of the observed variations is quite different in visual and photoelectric observations, suggesting that the process responsible for the periodicities is either one that modifies the solar limb darkening function or one that causes systematic variations in image blurring by the earth's atmosphere. A connection between solar magnetic activity an apparent radius seems likely, with evidence for such a relation dating back as fast as the Maunder minimum.
    Keywords: SOLAR PHYSICS
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  • 3
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    Short-term changes in solar oscillation frequencies and solar activity (1991)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: It is shown that the frequencies of solar rho-mode oscillations change significantly over periods as short as one month. These changes correlate significantly with variations in the strength of surface solar activity as measured by the average, over the sun's visible surface, of the magnitude of the line-of-sight magnetic field component from magnetograms. The frequency and mean magnetic variations are found to obey a linear relationship. It is seen that the mean frequency shift at any time depends on the history of solar activity over an interval of, at most, several months prior to the measurement and conclude that the dominant mechanism of the frequency shift is correlated with surface magnetic activity.
    Keywords: SOLAR PHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 373; L81-L84
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  • 4
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    Research related to ground effect machines (1959)
    In:  Other Sources
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    Publication Date: 2011-08-11
    Keywords: unknown
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  • 5
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    An airborne FLIR detection and warning system for low altitude wind shear (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: It is shown through some preliminary flight measurement research that a forward looking infrared radiometer (FLIR) system can be used to successfully detect the cool downdraft of downbursts (microbusts/macrobursts) and thunderstorm gust front outflows that are responsible for most of the low altitude wind shear (LAWS) events. The FLIR system provides a much greater safety margin for the pilot than that provided by reactive designs such as inertial air speed systems. Preliminary results indicate that an advanced airborne FLIR system could provide the pilot with remote indication of microburst (MB) hazards along the flight path ahead of the aircraft. Results of a flight test of a prototype FLIR system show that a minimum warning time of one to four minutes (5 to 10 km), depending on aircraft speed, is available to the pilot prior to the microburst encounter.
    Keywords: AIR TRANSPORTATION AND SAFETY
    Type: NASA. Langley Research Center, Airborne Wind Shear Detection and Warning Systems: Third Combined Manufacturers' and Technologists' Conference, Part 2; p 637-677
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  • 6
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    Report on the international Cambodian crater expedition, 1992 (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: It has been proposed that Tonle Sap, a lake in Cambodia, 100 km long and 30 km wide, marks the location of an elongate basin formed by the oblique impact of a comet or asteroid. The impact is considered to have produced melted ejecta found now as tektites over much of southeast Asia and Australia. The location of the lake, its approximate age, its size, and the orientation of its long axis (toward Australia) are consistent with this hypothesis. Our scientific objectives were to find impact or shock metamorphosed rocks unambiguously related to the Tonle Sap basin, to collect samples of rocks that may represent those melted to produce Australasian tektites, and to learn as much as possible about Cambodian geology. Using 1:200,000-scale geologic maps with fairly detailed descriptions of the rock units, we selected a number of acceptable 'phnoms' (hills that rise abruptly out of the surrounding plain) that may contain rocks affected by the postulated Tonle Sap impact. A map of central Cambodia is shown, and the locations of sites where samples were collected are indicated. A list of those sites, together with a description of the rocks reported to be present at each site, is given. No obviously shock-metamorphosed or suevite-like rocks were observed. Recent alluvium surrounding Tonle Sap is judged to be lake sediment deposited when the lake surface was at a higher elevation.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., International Conference on Large Meteorite Impacts and Planetary Evolution; p 36-37
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  • 7
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    Near net shape processing: A necessity for advanced materials applications (1993)
    In:  Other Sources
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    Publication Date: 2013-08-29
    Description: High quality discrete parts are the backbones for successful operation of equipment used in transportation, communication, construction, manufacturing, and appliances. Traditional shapemaking for discrete parts is carried out predominantly by machining, or removing unwanted material to produce the desired shape. As the cost and complexity of modern materials escalates, coupled with the expense and environmental hazards associated with handling of scrap, it is increasingly important to develop near net shape processes for these materials. Such processes involve casting of liquid materials, consolidation of powder materials, or deformation processing of simple solid shapes into the desired shape. Frequently, several of these operations may be used in sequence to produce a finished part. The processes for near net shape forming may be applied to any type of material, including metals, polymers, ceramics, and their composites. The ability to produce shapes is the key to implementation of laboratory developments in materials science into real world applications. This seminar presents an overview of near net shapemaking processes, some application examples, current developments, and future research opportunities.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA. Langley Research Center, National Educators' Workshop. Update 92: Standard Experiments in Engineering Materials Science and Technology; p 1-3
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  • 8
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    Small-scale experiments in STOVL ground effects (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A series of tests has been completed in which suckdown and fountain forces and pressures were measured on circular plates and twin-tandem-jet generic STOVL (short takeoff and vertical landing) configurations. The tests were conducted using a small-scale hover rig, for jet pressure ratios up to 6 and jet temperatures up to 700 F. The measured suckdown force on a circular plate with a central jet was greater than that found with a commonly used empirical prediction method. The present data showed better agreement with other sets of data. The tests of the generic STOVL configurations were conducted to provide force and pressure data with a parametric variation of parameters so that an empirical prediction method cold be developed. The effects of jet pressure ratio and temperature were found to be small. Lift improvement devices were shown to substantially reduce the net suckdown forces.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: SAE PAPER 901060
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  • 9
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    Prediction techniques for jet-induced effects in hover on STOVL aircraft (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Prediction techniques for jet induced lift effects during hover are available, relatively easy to use, and produce adequate results for preliminary design work. Although deficiencies of the current method were found, it is still currently the best way to estimate jet induced lift effects short of using computational fluid dynamics. Its use is summarized. The new summarized method, represents the first step toward the use of surface pressure data in an empirical method, as opposed to just balance data in the current method, for calculating jet induced effects. Although the new method is currently limited to flat plate configurations having two circular jets of equal thrust, it has the potential of more accurately predicting jet induced effects including a means for estimating the pitching moment in hover. As this method was developed from a very limited amount of data, broader applications of the method require the inclusion of new data on additional configurations. However, within this small data base, the new method does a better job in predicting jet induced effects in hover than the current method.
    Keywords: AERONAUTICS (GENERAL)
    Type: NASA-TM-102818 , A-90146 , NAS 1.15:102818
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  • 10
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    Forces and pressures induced on circular plates by a single lifting jet in ground effect (1991)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: NASA Ames is conducting a program to develop improved methods for predicting suckdown and hot-gas ingestion on jet V/STOL aircraft when they are in ground effect. As part of that program a data base is being created that provides a systematic variation of parameters so that current empirical prediction procedures can be modified. The first series of tests in this program is complete. This report is one of three that presents the data obtained from tests conducted at Lockheed Aeronautical Systems - Rye Canyon Facility and the High Bay area of the 40 by 80 foot Wind Tunnel at Ames Research Center. Suckdown on two circular plates is examined.
    Keywords: AERODYNAMICS
    Type: NASA-TM-102816 , A-90142 , NAS 1.15:102816
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