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  • 1985-1989  (2)
  • 1910-1914
  • 29.15D  (1)
  • Observation tubes  (1)
  • 1
    ISSN: 1432-0649
    Keywords: 41.80E ; 52.25 ; 29.15D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract First results are presented from an experiment scattering laser light from a relativistic electron beam. The 5 cm diameter continuous electron beam of 28 keV kinetic energy and 2.6 A current presents an electron gas of a density of 8×107 cm−3, from which 20 ns pulses of laser light (490 nm) were scattered at a repetition rate of 15 Hz and an average power of 20 mJ per pulse. The Doppler-shifted wavelength of photons backscattered under 180° was analysed with a Fabry-Perot interferometer. This technique provides, for the first time, a non-destructive measurement of the velocity distribution in an electron beam radially resolved in space. The results presented here comprise the direct measurement of the absolute electron energy and the degree of space-charge compensation in the electron beam. The determination of an upper bound of 10−2 for the ratio of longitudinal to transverse electron temperature implies the first direct measurement of a flattened velocity distribution.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 85 (1985), S. 237-247 
    ISSN: 1573-5036
    Keywords: Fibrescope ; Observation tubes ; Root distribution ; Root growth ; Wheat growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Non-destructive observations of root growth and distribution can be obtained from counting root intercepts with observation tubers inserted in the root zone. This paper describes the technique of inserting clear acrylic tubes horizontally into large undisturbed and repacked soil cores. Counts of roots intersecting scribed lines on the sides of the tubes were made with a fibrescope. Comparison was made between observation root tubes of different diameter (25 and 38.5 mm). The r2 values for the relationships between root intercept counts and destructively determined values of root length density (RLD) ranged from 0.78 to 0.96. The larger diameter tubes had higher r2 values. Theoretical calibration of the technique does not appear to be possible since analysis indicated that fewer roots intersected the scribed lines on the observation tube than would have been expected from a non-disturbed, randomly distributed root system. It is not known if this discrepancy is due to non-randomness or to an artifact associated with the insertion of the observation tube. Roots were not more prolific at the edge of the soil cores. Comparison of values of root length per unit soil surface area, rates of downward root growth and water uptake rates were within the ranges previously reported for wheat roots of field crops grown on clay soils. Observed root growth and distribution was found to be sensitive to four soil and water treatments imposed. It is concluded that the technique will allow quantitative analysis of root growth and distribution in undisturbed soil cores.
    Type of Medium: Electronic Resource
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