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  • 1
    Electronic Resource
    Electronic Resource
    Reflection of ultrasonic waves from imperfect interfaces: A combined boundary element method and independent scattering model approach (1992)
    Springer
    Journal of nondestructive evaluation 11 (1992), S. 141-149 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; imperfect interfaces ; quasi-static ; reflection coefficients ; spring constants ; independent scattering ; boundary element
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A numerical technique for obtaining interface reflection coefficients for imperfect bonds between similar materials for a wide range of distributed defects is developed. A numerical boundary element method is utilized to find the far-field scattering amplitudes of a single defect for a normally incident plane wave. Then, the normal incidence reflection coefficient for a planar distribution of such defects is obtained from the independent scattering model. As a validation, the reflection coefficients are compared to the quasi-static model results where the latter are available. This establishes the basis for one application of the new model, the determination of spring constants which are not available. Other applications of the model, including studies of the response at frequencies beyond the quasi-static limit, the ratio of longitudinal to transverse wave reflectivities, and the effects of selected multiple scattering are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566405
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  • 2
    Electronic Resource
    Electronic Resource
    Interfacial spring model for ultrasonic interactions with imperfect interfaces: Theory of oblique incidence and application to diffusion-bonded butt joints (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 131-152 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; diffusion bonds ; oblique incidence ; spring model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract The quasi-static distributed spring model is used to derive the ultrasonic reflectivity of an imperfectly-bonded interface as a function of frequency and angle of incidence. The results are then incorporated in a model for the corner reflection from a diffusion-bonded joint between two abutting plates, the corner being defined by the bond plane and the common lower surface plane of the plates. An immersion-inspection geometry is assumed, and seven categories of corner reflections are identified and examined in detail. These fall into two classes: those having parallel incident and exiting rays in water (φ′=φ), and those having nonparallel water rays (φ′ ≠ φ). The φ′ = φ categories are suitable for single probe (pulse-echo) inspections of the joint. Based on the amplitude of the outgoing corner-reflected signal, two φ = φ′ geometries appear promising. These employ, respectively, a corner reflection involving only longitudinal waves with the interface illuminated at near-grazing incidence (LLL), and a corner reflection involving only transverse waves with the interface illuminated at near 45° incidence (TTT). In addition, two practical φ′ ≠ φ geometries are indicated; these both involve mode conversion upon reflection from the interface, with the incident or outgoing longitudinal wave traveling nearly parallel to the interface. Model predictions for LLL and TTT reflections are compared to measurements on diffusion-bonded Inconel specimens, and techniques for applying the model results to more complicated bond geometries are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00565998
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Ultrasonic characterization of tubing pinch welds (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 217-225 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; pinch welds ; solid-state bonds ; grain scattering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Spatially-focused, high-frequency ultrasonic pulses have been used in the evaluation of the quality of stainless steel tubing pinch welds. Experimentally, echoes from the bond plane were generally too weak to observe, except in bond planes with macrocracking. Correlations were therefore sought between bond quality and the amplitude and spectral features of the back-surface echo that has passed through the bond plane twice. Linear scans of the back-surface echo parallel and perpendicular to the tubing axis were made on pinch welds of four classes of bond quality. Trends, with scatter, were observed between the ultrasonic parameters and bond quality. These experimental results were interpreted using the Stanke-Kino theory of ultrasonic attenuation due to grain scattering to relate the microstructural changes caused by the pinch-weld process to the observed ultrasonic signals. The results illustrate the importance of process-related changes in near-bond microstructure in attempts to nondestructively determine bond strength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566004
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  • 4
    Electronic Resource
    Electronic Resource
    Quantitative characterization of flaws near a surface using inverse born approximation (1982)
    Springer
    Journal of nondestructive evaluation 3 (1982), S. 183-188 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; Born inversion ; NDE
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Quantitative reconstruction of volumetric flaws near a surface of an elastic solid has been carried out experimentally by analyzing the scattered ultrasonic waves. The inverse Born approximation (developed for flaws in bulk materials) was tested for the first time in the determination of the size, shape, and orientation of near-surface flaws. We have studied spherical solid inclusions at various depths below the surface. In addition we examined an approximately 2:1 prolate spheroidal inclusion which was located one major axis below the surface. The determination of the flaw's size, shape, and orientation in terms of an equivalent ellipsoid is realized by performing nonlinear least-squares iteration of the one-dimensional Born inversion results obtained at various scattering directions within a finite aperture. The reconstruction is in good agreement with the actual parameters of the flaw.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00565863
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  • 5
    Electronic Resource
    Electronic Resource
    Application of the boundary element method to elastic wave scattering by irregular defects (1990)
    Springer
    Journal of nondestructive evaluation 9 (1990), S. 113-127 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; modeling ; scattering ; boundary element method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A time-harmonic boundary element formulation for elastic wave scattering in 3D is adapted to ultrasonic NDE. Defect classes addressed are volumetric voids and inclusions, and crack-like elliptical voids. For axisymmetric flaws, comparisons are made with method of optimal truncation (MOOT) and transition-matrix calculations. Comparison to experiment is made for more general shapes. For crack-like voids, comparisons are made with the Kirchhoff, geometric theory of diffraction (GTD), and quasistatic asymptotic approximations. The efficiency and usefulness of the boundary element method (BEM) in finding the bounds of applicability of these approximate theories are demonstrated. An example of a flaw characterization technique based on intermediate frequency scattering data simulated by BEM is given. The ability of BEM to handle nonplanar incident fields, as described by a transducer beam model, is shown. Other computational and modeling efficiencies of the BEM are noted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00566388
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    Paper (German National Licenses)
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  • 6
    Electronic Resource
    Electronic Resource
    Backscattered microstructural noise in ultrasonic toneburst inspections (1994)
    Springer
    Journal of nondestructive evaluation 13 (1994), S. 111-136 
    Details
    ISSN: 1573-4862
    Keywords: Ultrasonics ; backscattering ; noise ; backscatter coefficient ; figure-of-merit ; microstructure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A model is presented which relates the absolute backscattered noise level observed in an ultrasonic immersion inspection to details of the measurement system and properties of the metal specimen under study. The model assumes that the backscattered noise signal observed for a given transducer position is an incoherent superposition of echoes from many grains. The model applies to normal-incidence, pulse-echo inspections of weakly-scattering materials using toneburst pulses from either a planar or focused transducer. The model can be used in two distinct ways. Measured noise echoes can be analyzed to deduce a “Figure-of-Merit” (FOM) which is a property of the specimen alone, and which parameterizes the contribution of the microstructure to the observed noise. If the FOM is known, the model can be used to predict the absolute noise levels that would be observed under various inspection scenarios. Tests of the model are reported, using both synthetic noise echoes, and measured noise echoes from metal specimens having simple and complicated microstructures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00728250
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  • 7
    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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  • 8
    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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  • 9
    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)
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  • 10
    Electronic Resource
    Electronic Resource
    A circular dichroic investigation of the secondary structure of lectins (1978)
    New York : Wiley-Blackwell
    Biopolymers 17 (1978), S. 2107-2120 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The far-uv CD spectra of eight lectins are presented. These eight lectins, as well as others previously studied, are grouped into three classes according to their particular CD spectra. The eight lectins studied appeared to have secondary structure dominated by β-pleated sheet, which so far has been true of all lectins. An attempt was made to quantitate the three structural components (α-helix, β-pleated sheet, and aperiodic) in the lectins using the data for reference proteins given by Chen et al. [Biochemistry 13,3350 (1974)]. For lectins in two of the classes, this method proved excellent and values for the three components are given. However, for the third class of lectins, which includes most of the lectins as well as Concanavalin A, this method of analysis proved to be unsatisfactory. This inadequacy was due to two factors: (1) the reference proteins used by Chen and (2) the unusual CD spectra of these lectins manifested by considerable ellipticity above 225 nm in a region where there are no known peptide electronic transitions.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1978.360170906
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    Paper (German National Licenses)
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