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  • Articles: DFG German National Licenses  (6)
  • Physical Chemistry  (3)
  • ultrasonics  (3)
  • 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
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 16 (1984), S. 867-878 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of OH reactions with furan (k1), thiophene (k2), and tetrahydrothiophene (k3), have been investigated over the temperature range 254-425 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by timeresolved resonance fluorescence spectroscopy. The following Arrhenius expressions adequately describe the measured rate constants as a function of temperature (units are cm3 molecule-1 S-1): k1 = (1.33 ± 0.29) × 10-11 exp[(333 ± 67)/T], k2 = (3.20 ± 0.70) × 10-12 exp[(325 ± 71)/T], k3 = (1.13 ± 0.35) × 10-11 exp[(166 ± 97)/T]. The results are compared with previous investigations and their implications regarding reaction mechanisms and atmospheric residence times are discussed.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 16 (1984), S. 1623-1636 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The kinetics of OH reactions with 1-4 carbon aliphatic thiols have been investigated over the temperature range 252-430 K. OH radicals were produced by flash photolysis of water vapor at λ 〉 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2-4.6 × 10-11 cm3 molecule-1 s-1, -Eact = 0.6-1.0 kcal/mol, A = 0.6-1.2 × 10-11 cm3 molecule-1 s-1. CH3SH and CH3SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Chemical Kinetics 17 (1985), S. 1281-1297 
    ISSN: 0538-8066
    Keywords: Chemistry ; Physical Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Absolute rate coefficients for the reaction of OH with HCl (k1) have been measured as a function of temperature over the range 240-1055 K. OH was produced by flash photolysis of H2O at λ 〉 165 nm, 266 nm laser photolysis of O3/H2O mixtures, or 266 nm laser photolysis of H2O2. OH was monitored by time-resolved resonance fluorescenceor pulsed laser-induced fluorescence. In many experiments the HCl concentration was measured in situ in the slow flow reactor by UV photometry. Over the temperature range 240-363 K the following Arrhenius expression is an adequate representation of the data: k1 = (2.4 ± 0.2) × 10-12 exp[-(327 ± 28)/T]cm3 molecule-1 s-1. Over the wider temperature range 240-1055 K, the temperature dependence of k1 deviates from the Arrhenius form, but is adequately described by the expression k1 = 4.5 × 10-17 T1.65 exp(112/T) cm3 molecule-1 s-1. The error in a calculated rate coefficient at any temperature is 20%.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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