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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Acta mechanica 60 (1986), S. 199-215 
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Creep buckling of columns is analyzed for materials obeying nonlinear single memory integral constitutive laws. There have been two basic methods to analyze creep buckling of columns; the Rabotnov and Shesterikov's linearized dynamical approach and Hoff's quasistatic nonlinear approach, the former predicts critical buckling loads and the latter yields critical buckling times. The two theories are generally believed to be independent of each other. Through investigation of creep phenomena other than steady creep, the two different creep stability criteria are found to be correlated and thus the linear treatment is justified by a nonlinear approach. It is also shown that the Hoff's approach can be used to derive critical creep buckling loads. The missing link between the two theorees is found in this paper.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-4943
    Keywords: lens proteins ; β-crystallins ; ultracentrifugation ; intrinsic viscosity ; amino acid compositions ; heterogeneity ; reassociation ; aggregation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A detailed investigation of the hydrodynamic and aggregation behaviors has been made on the β-crystallins of bovine lens. Results from this study indicated that βH (high-molecular-weight β-crystallin) and βL (low-molecular-weight β-crystallin) exhibited considerable heterogeneity in their native structures and subunit polypeptides. Low-speed sedimentation equilibrium showed a heterogeneous paucidisperse system in each β-crystallin fraction. Viscosity and circular dichroism studies pointed to a compact and globular shape and the presence of β-sheet and β-turns in these crystallins. Dissociation of βH by urea and guanidinium HCl followed by reassociation during gel-filtration chromatography produced an elution pattern with two fractions corresponding to βL crystallin and high-molecular-weight aggregates without the formation of native βH. By contrast, under similar treatment, about 60% βL reassociated into the correct native structure and the rest into high-molecular-weight fractions. Amino acid analyses of βH and βL and their corresponding subunit polypeptides demonstrated the close similarity of these crystallins. Trace element analyses indicated that both Ca and Mg are present in βH and βL crystallins and may be involved in maintaining the native quarternary structures of these proteins.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Für die statistischen Eigenschaften der Spannung an der Wellenfront eines plötzlich belasteten halbunendlichen Stabes aus viskoelastischem Werkstoff mit Potenzgesetz werden analytische und numerische Lösungen angegeben. Temperatur und daher temperaturempfindliche Werkstoffparameter werden zufallsabhängig angenommen. Eine kritische Zeit, bei der die Mittelwertsfunktionen die deterministischen Lösungen schneiden und die Varianzen ein Maximum annehmen, wird festgestellt.
    Notes: Summary Analytical and numerical solutions are presented for the statistical properties of the stress at the wave front in a suddenly loaded semi-infinite rod of a viscoelastic material with a stress power constitutive law. The temperature and accordingly the temperature sensitive material parameters are assumed to be random. A critical time is observed, where the mean solutions cross the deterministic solutions and the variance is a maximum.
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  • 4
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Eindimensionale Spannungs- und Temperaturfelder in einem plötzlich belasteten und/oder erwärmten, halbunendlichen Stab aus nichtlinearem, viskoplastischen Material werden mit Hilfe der gekoppelten thermodynamischen Theorie untersucht. Der Wärmetransport gehorcht dem modifizierten Fourierschem Wärmeleitungsgesetz und erfolgt daher eher durch Wellenausbreitung als durch Diffusion. Die Aufbringung thermischer oder mechanischer Störungen am Ende des Stabs läßt zwei Wellenfronten entstehen, mit welchen die Störungen fortschreiten. Feldlösungen für Spannungen und Temperatur werden durch numerische Integration längs der fünf Charakteristiken der beschreibenden Gleichungen erhalten und die Resultate für einige lineare und nichtlineare viskoelastische Modelle angegeben.
    Notes: Summary One-dimensional stress and temperature fields in a suddenly loaded and/or heated semi-infinite rod of nonlinear thermoviscoelastic material are studied using coupled thermomechanical theory. The transport of heat is governed by the modified Fourier heat conduction law, and thus proceeds by wave propagation rather than by diffusion. The application of thermal and mechanical disturbances at the end of the rod gives rise to two wave fronts along which these disturbances propagate. Field solutions for the stress and temperature are obtained by numerical integration along the five characteristics of the governing equations, and results are presented for several linear and nonlinear viscoelastic models.
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  • 5
    ISSN: 1619-6937
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Description / Table of Contents: Zusammenfassung Mit Hilfe der Thermodynamik werden einfache Integrale enthaltende Werkstoffbeziehungen für das nichtlineare thermoviskoelastische Verhalten unter beliebigen Spannungs- und Temperaturverläufen entwickelt und die thermomechanisch gekoppelte Energiegleichung wird angegeben. Im Detail werden der thermodynamisch-einfache Werkstoff, die modifizierte Überlagerung und das isotrope Spannungs-Potenzgesetz diskutiert. Damit thermische Störungen sich mit endlicher Geschwindigkeit ausbreiten, wird ein modifiziertes Fouriersches Wärmeleitgesetz verwendet. Unter Verwendung des nichtlinearen thermoviskoelastischen Spannungs-Potenzgesetzes, der linearisierten Energiegleichung und des modifizierten Wärmeleitgesetzes werden Lösungen der eindimensionalen Wellenfrontausbreitung erhalten.
    Notes: Summary Thermodynamic theory is used to develop single integral constitutive relations for the nonlinear thermoviscoelastic response to arbitrary stress and temperature histories; the thermomechanically coupled energy equation is also obtained. The thermorheologically simple material, modified superposition and the isotropic stress power law are discussed in detail. A modified Fourier heat conduction law is employed to ensure that the propagation of thermal disturbances takes place at a finite velocity. Using the nonlinear thermoviscoelastic stress power law along with the linearized energy equation and modified Fourier law, one-dimensional wave front solutions are obtained.
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  • 6
    ISSN: 1432-1084
    Keywords: MRI ; Knee joint ; Three-dimensional reconstruction: preprocessing, segmentation, shading, surface rendering, volume rendering, hybrid rendering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract We tried to improve the basic three-dimensional reconstruction technique by comparing preprocessing, segmentation, shading and rendering techniques in 15 examples of MR investigations of the knee joint. We conclude that signal-normalising, combined threshold and tracking segmentation, grey-level-gradient shading, and combined surface and volume rendering (i. e. hybrid rendering) are the methods of choice for the three-dimensional reconstruction process.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 0167-4838
    Keywords: (Duck) ; Isozyme distribution ; Lactate dehydrogenase ; Protein evolution ; Subunit crosslinking ; ε-Crystallin
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0014-5793
    Keywords: (Reptile) ; Crystallin ; Microheterogeneity ; Multigene family ; Sequence homology ; Subunit structure
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0428
    Keywords: Diabetic nephropathy ; albuminuria ; aldose reductase inhibitors ; prostaglandins
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effect of two structurally unrelated aldose reductase inhibitors, sorbinil and ponalrestat, on glomerular prostaglandin production and urinary albumin excretion was investigated in rats with diabetes induced by streptozotocin. It was found that both aldose reductase inhibitors, when administered from the time of induction of the diabetes, significantly decreased the raised urinary albumin excretion in the diabetic rats, although it remained elevated compared with non-diabetic rats. Glomerular prostaglandin E and 6-ketoprostaglandin F1α production was significantly increased in glomeruli obtained from the diabetic rats. Inhibition of aldose reductase caused a reduction in the raised glomerular prostaglandin production, although this remained above that observed in the non-diabetic rats. Subsequent experiments were performed to determine whether the effects of the aldose reductase inhibitors could be explained by effects on glomerular filtration rate. It was found that ponalrestat, at a dose which markedly reduced urinary albumin excretion, did not significantly affect glomerular filtration rate in non-diabetic rats, rats with untreated streptozotocin-induced diabetes and rats with diabetes partially treated with low dose insulin. Glomerular sorbitol concentrations were significantly elevated in untreated diabetic rats as early as two weeks after the induction of diabetes. It is concluded that the administration of aldose reductase inhibitors from the time of induction of diabetes significantly reduces glomerular prostaglandin production and urinary albumin excretion. The latter effect is not due to an effect on glomerular filtration rate. Increased polyol pathway activity may account in part for the increased glomerular prostaglandin production and urinary albumin excretion in early experimental diabetes.
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