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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 4 (1984), S. 177-196 
    ISSN: 1573-4862
    Keywords: Interfaces ; ultrasonics ; partial contact ; quasi-static
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A quasi-static model for the ultrasonic transmission and reflection at imperfect interfaces is developed. The interface is represented by a distributed spring, determined by the change in static compliance of the medium with respect to one with a perfect interface, and a distributed mass, representing excess mass at the interface. Comparison of the model predictions to exact solutions for two simple cases illustrates its accuracy at low frequencies. The spring stiffnesses can be derived from existing solutions for the elastic displacement of materials containing cracks and inclusions under static load. Results for a variety of cases are reviewed. Applications of the model to study the characteristics of partially contacting surfaces in several problem areas of current interest are discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4862
    Keywords: Beam propagation ; bimetallic weld ; Gauss-Hermite beam model ; finite element method ; ultrasonics ; anisotropic medium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract In this paper, predictions of two models for the propagation of ultrasonic beams through a two-dimensional, bimetallic weld geometry are compared. The finite element method can predict beam propagation through quite general geometry with high accuracy. This model, however, requires significant computational time. On the other hand, the approximate Gauss-Hermite model offers considerably greater computational speed, but has lower accuracy in certain regions and cannot treat the most general geometries and inhomogeneities in material properties. This paper compares the performances of the two models for the case of the two-dimensional, bimetallic weld consisting of multiple layers, some of which have anisotropic properties. It is found that the results of the two models are in good agreement in the vicinity of the central ray, and that the deviation increases as one moves away from the axis. Also, as the beam propagates through multiple interfaces, the accuracy of the Gauss-Hermite solution decreases.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of nondestructive evaluation 4 (1984), S. 107-123 
    ISSN: 1573-4862
    Keywords: ultrasonics ; transducers ; focusing ; refractior ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A scalar theory of the propagation of Gaussian ultrasonic beams through lenses and interfaces is presented. For radiation into a fluid, the Fresnel approximation is employed to derive the laws of propagation of Guassian beams (previously employed in the analysis of coherent optical systems). These are then generalized to situations commonly found in nondestructive evaluation by treating the effects of propagation through lenses and through curved interfaces at oblique incidence. A numerical example illustrates the ease with which insight into diffraction phenomena for complex geometries can be gained by this approach. The limitations imposed on the theory by aberrations and the scalar assumption are discussed, and the relationship of the Gaussian theory to the radiation of piston transducers is explored.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 125 (1990), S. 119-128 
    ISSN: 1573-5036
    Keywords: ammonia ; application method ; application rate ; environment ; grassland ; nitrogen ; slurry ; volatilization ; wind speed
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three experiments were conducted to examine the influence of slurry application rate, wind speed and applying slurry in narrow bands on ammonia (NH3) volatilization from cattle slurry surface-applied to grassland. The experiments were conducted in the field using a system of small wind tunnels to measure NH3 loss. There was an inverse relationship between slurry application rate and the proportion of NH4 +-N volatilized. From slurry applied at 20, 40, 60, 80, 100 and 120 m3 ha-1, the respective proportions of NH4 +-N lost by NH3 volatization in 6 days were 60, 56, 49, 40, 44 and 44%. The negative relationship was most pronounced in the first 24 hours after application when 57–77% of the total loss for 6 days occurred. Wind speed had a positive effect on NH3 volatilization, although the effect was small in relation to the total loss; increasing the wind speed from 0.5 to 3.0 m s-1 increased the total 5 day loss by a factor of 0.29. The effect of wind speed was also most pronounced in the first 24 hours when much of the NH3 loss took place. The effect of reducing the surface area of the applied slurry was examined by comparing NH3 volatilization from slurry broadcast across plots with that applied in narrow bands. Although the rate of NH3 volatilization was considerably smaller from the banded application immediately after the slurry was applied, the difference between the treatments progressively narrowed until 2 days after application, after which a higher rate was maintained from the banded slurry. After 5 days the total loss from the banded application was 83% of that from broadcast slurry.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Plant and soil 125 (1990), S. 109-117 
    ISSN: 1573-5036
    Keywords: ammonia ; environment ; grassland ; mechanical separation ; nitrogen ; slurry ; volatilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Three experiments were conducted using a system of small wind tunnels to measure ammonia (NH3) volatilization from cattle slurry after surface application to land. In each experiment slurry was applied at a rate equivalent to 80 m3 ha-1, providing the equivalent of approximately 100 kg NH4 +-N ha-1. The first experiment compared NH3 volatilization from the liquid fraction obtained by mechanical separation of slurry with that from unseparated slurry. The total NH3 loss over six days from unseparated and separated slurry were very similar, being 38 and 35% respectively of the NH4 +-N applied. For the first five hours, the rate of NH3 loss was higher from the unseparated slurry, thereafter it was consistently lower. In the second experiment, slurry was ponded in a tray to examine whether impeded infiltration or changes in the NH4 + concentration or overall pH of the slurry influenced the rapid decline in rate soon after application that is characteristic of NH3 volatilization from animal slurries applied to land. It appeared, however, that other factors such as resistance to diffusion within the slurry and/or at the slurry surface were mostly responsible for the rapid decline in rate. In the third experiment, in which NH3 volatilization was measured from slurry applied to grassland or bare soil, the total loss from slurry applied to grassland was approximately 1.5 times that from slurry applied to bare soil.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-5036
    Keywords: acetylene inhibition ; calcium carbide ; denitrification ; nitrogen ; vegetable production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The use of calcium carbide (CaC2) pellets as a source of acetylene (C2H2) for the C2H2 inhibition technique to measure denitrification in the field was examined in a sandy loam soil cropped to lettuce. CaC2 was used in combination with vented closed chambers. Three grams of 2–4 mm CaC2 pellets were inserted at 7 and 20 cm for raised beds, and 6 and 15 cm for furrows, in four holes located at right angles, 2.5 cm outside a 20 cm dia. chamber pushed 4 cm into the soil. Acetylene concentrations were determined in the centre of the chamber 1.0 and 4.0 hours after applying CaC2, in beds (two dates) and furrows (one date) at different depths to 20 and 15 cm, respectively, for beds and furrows. At soil matric potentials of ca. 0.01 and ca. 0.06 MPa, soil C2H2 concentrations were 〉1.0% (v/v) for all determinations. Weekly measurements of denitrification were made from a sprinkler irrigated lettuce crop for 8 weeks. Measurements were made 24 hours after irrigation and on one occasion 48 hours after. Measured mean rates of denitrification were generally 〈100 g N ha−1 d−1, much less than published data following furrow irrigation of vegetable crops in a nearby region. In another sandy loam soil at ca. 0.08 MPa, soil C2H2 concentrations were ≥2.0 % at 5 and 15 cm, 1.0 and 6.0 hours after adding CaC2. Using CaC2 to generate C2H2 in soil is a convenient approach for field measurements where the C2H2 inhibition technique is used with chambers to determine the nitrous oxide flux. In comparison with C2H2 supply via probe systems, CaC2 overcomes the requirements for cylinders of pressurised C2H2 gas and complex on-site plumbing.
    Type of Medium: Electronic Resource
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