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  • OPTICS  (3)
  • Key words.Plastic regimes, kinematically determined, granular materials, optimal systems, exact solutions.  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Zeitschrift für angewandte Mathematik und Physik 48 (1997), S. 1-8 
    ISSN: 0044-2275
    Keywords: Key words.Plastic regimes, kinematically determined, granular materials, optimal systems, exact solutions.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics , Physics
    Notes: Abstract. For axially symmetric flow of dilatant granular materials, the velocity equations uncouple from the stress equations in certain plastic regimes, and assuming dilatant double shearing a set of three first order partial differential equations are obtained. These equations turn out to be deceptive because although simple in appearance, the determination of simple exact solutions is non-trivial. Here we show that all the known functional forms of existing solutions also arise systematically by consideration of the "optimal systems" of the classical Lie symmetries which indicates that any further solution types most likely arise from non-classical symmetries. For one of the known families we present a special case which admits a particularly simple closed form expression, which has not been previously given in the literature. For this particular special case the integral curves (streamlines) can be readily obtained as well as a simple analytical "approximation" for the particle paths. The streamlines and the validity of the analytical approximation are shown graphically.
    Type of Medium: Electronic Resource
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  • 2
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    In:  Other Sources
    Publication Date: 2019-07-13
    Description: The problem of making very large glass mirrors for astronomical telescopes is examined, and the advantages of honeycomb mirrors made of borosilicate glass are discussed. Thermal gradients in the glass that degrade the figure of thick borosilicate mirrors during use can be largely eliminated in a honeycomb structure by internal ventilation (in air) or careful control of the radiation environment (in space). It is expected that ground-based telescopes with honeycomb mirrors will give better images than those with solid mirrors. Materials, techniques, and the experience that has been gained making trial mirrors and test castings as part of a program to develop 8-10-m-diameter lightweight mirrors are discussed.
    Keywords: OPTICS
    Type: International Conference on Advanced Technology Optical Telescopes; Mar 11, 1982 - Mar 13, 1982; Tucson, AZ
    Format: text
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  • 3
    Publication Date: 2019-07-13
    Description: Single silica fibers of the type developed for communications are useful in the design of astronomical spectrographs. They can be used to couple light from many objects over a wide field to a single spectrograph, or to eliminate wavelength errors from image motion and gravitational flexure. For many applications it will be advantageous to use small lenses to make the most efficient coupling into and out of a fiber. If the telescope pupil is imaged on the fiber core, an efficient coupling can be made that preserves image size over a certain range. This method is demonstrated by a laboratory test using sapphire spheres as coupling lenses.
    Keywords: OPTICS
    Type: Instrumentation in astronomy V; Sep 07, 1983 - Sep 09, 1983; London
    Format: text
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  • 4
    Publication Date: 2019-07-13
    Description: The making of large astronomical mirrors with borosilicate glass honeycomb structure is discussed. Particular attention is given to a single casting technique for making borosilicate honeycomb mirror blanks up to 7 meters in diameter. Current work on the development of this technique involves the casting of blanks 60 cm in diameter which have the full thickness (33 cm), cell size (15 cm), and faceplate thickness (2.5 cm) needed for a 1.8-m mirror.
    Keywords: OPTICS
    Type: Instrumentation for astronomy with large optical telescopes; Sep 08, 1981 - Sep 10, 1981; Zelenchukskaya; USSR
    Format: text
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