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  • 1
    Electronic Resource
    Electronic Resource
    Ultrasonic scattering from imperfect interfaces: A quasi-static model (1984)
    Springer
    Journal of nondestructive evaluation 4 (1984), S. 177-196 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00566223
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrasonic beam propagation through a bimetallic weld—A comparison of predictions of the Gauss-Hermite beam model and finite element method (1993)
    Springer
    Journal of nondestructive evaluation 12 (1993), S. 151-158 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00567571
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The effects of focusing and refraction on Gaussian ultrasonic beams (1984)
    Springer
    Journal of nondestructive evaluation 4 (1984), S. 107-123 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00566401
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The endosperms of common cereals contain related poly A +RNA sequences (1983)
    Springer
    Theoretical and applied genetics 64 (1983), S. 269-273 
    Details
    ISSN: 1432-2242
    Keywords: Cereal ; mRNA ; Prolamin ; Homology ; Endosperm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary mRNA has been isolated from the developing endosperms of four Triticeae species. Wheat endosperm mRNA has been used as a template to construct a bank of cDNA plasmid clones. More than 95% of these clones hybridized strongly to endosperm poly A+RNA but not to shoot poly A+RNA. 32P-labelled mRNA from species related to wheat was used in filter hybridizations to detect inter-species sequence homologies. The wheat cDNA clones can be grouped into 4 classes: clones hybridizing to wheat RNA only, clones cross-hybridizing to barley endosperm poly A +RNA, clones cross-hybridizing to rye endosperm poly A+ RNA, and clones showing homology to both barley and to rye RNA. Some of the sequence homology has been assigned to storage protein mRNA sequences.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00303777
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    The role of multiple binding sites in the activation of zein gene expression byOpaque-2 (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 723-732 
    Details
    ISSN: 1617-4623
    Keywords: Opaque-2 ; 22 kD α-zeins ; Endosperm ; Transient gene expression ; Particle bombardment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Opaque-2 (O2) encodes a transcriptional activator of the basic domain-leucine zipper (bZIP) class, which controls the expression level in maize endosperm of the 22 kD α-zeins and a number of non-storage proteins. The interaction of the O2 protein at three clustered binding sites on an isolated 22 kD zein gene promoter has been investigated. O2 is shown to transactivate transcription from these sites in tobacco mesophyll protoplasts as well as in maize endosperm cells transformed by particle bombardment. The binding sites have been mutated by base exchanges, singly or in different combinations, to determine their contribution to transactivation in vivo in both the leaf protoplast and the maize endosperm system. The effect of these mutations on binding of O2 in vitro was determined by electrophoretic mobility shift assays (EMSA), using O2 protein expressed inE. coli. Two of the sites seemed to be equally effective in responding to Opaque-2 in vivo in both cell types, although one of them does not contain an ACGT core sequence, and has a lower affinity for O2 in vitro than the ACGT-containing binding site. A third site, which has the lowest affinity of all three, confers no detectable O2-dependent promoter activation alone, but significantly increases activation in combination with either one of the other sites. Hence, weaker O2 binding sites can still mediate major O2-dependent effects when present in target promoters in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02173979
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    The role of multiple binding sites in the activation of zein gene expression by Opaque-2 (1996)
    Springer
    Molecular genetics and genomics 252 (1996), S. 723-732 
    Details
    ISSN: 1617-4623
    Keywords: Key words Opaque-2 ; 22 kD α-zeins ; Endosperm ; Transient gene expression ; Particle bombardment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Opaque-2 (O2) encodes a transcriptional activator of the basic domain-leucine zipper (bZIP) class, which controls the expression level in maize endosperm of the 22 kD α-zeins and a number of non-storage proteins. The interaction of the O2 protein at three clustered binding sites on an isolated 22 kD zein gene promoter has been investigated. O2 is shown to transactivate transcription from these sites in tobacco mesophyll protoplasts as well as in maize endosperm cells transformed by particle bombardment. The binding sites have been mutated by base exchanges, singly or in different combinations, to determine their contribution to transactivation in vivo in both the leaf protoplast and the maize endosperm system. The effect of these mutations on binding of O2 in vitro was determined by electrophoretic mobility shift assays (EMSA), using O2 protein expressed in E. coli. Two of the sites seemed to be equally effective in responding to Opaque-2 in vivo in both cell types, although one of them does not contain an ACGT core sequence, and has a lower affinity for O2 in vitro than the ACGT-containing binding site. A third site, which has the lowest affinity of all three, confers no detectable O2-dependent promoter activation alone, but significantly increases activation in combination with either one of the other sites. Hence, weaker O2 binding sites can still mediate major O2-dependent effects when present in target promoters in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02173979
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    Paper (German National Licenses)
    Fulltext
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