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  • Springer  (3)
  • University of Michigan Press  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    ISSN: 1435-1528
    Keywords: Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner's damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 36 (1997), S. 585-589 
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; viscoelasticity ; constitutive equations ; irreversibility ; integral models ; thermorheological behavior
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract In this work, entanglements in a polymer melt are modeled as a system of parallel springs which form and decay spontaneously. The springs are assumed to be nonlinear, and a certain fraction of them is torn apart by a certain strain. Based on these assumptions, a model of behavior in simple shear is developed. This model is shown to predict a behavior comprising that of a Wagner fluid, and is generalized to a tensorial model of single integral type. The integrand depends on a product of a material function, modeling reversible behavior, and a material functional which takes irreversible processes into account. Irreversibility of network disentanglement, which may occur when deformation changes or reverses direction, can be modeled in this way. It is shown that the two well-known Wagner constitutive equations with and without irreversibility assumptions are special cases of the model developed. In case of a deformation which does not change directions, the new material function and the material functional are multiplied to yield Wagner’s damping function. When the rate of spring formation is a function of temperature, the developed model is shown to predict thermorheologically simple behavior. A constitutive equation for non-isothermal flow of polymers is developed with this assumption.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Rheologica acta 37 (1998), S. 182-188 
    ISSN: 1435-1528
    Keywords: Key words Polymer melts ; viscoelasticity ; birefringence ; elongational flow
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Abstract Birefringence in liquid polymers offers the possibility of obtaining information about stress in complex flows. In this work, this is done for extensional flows of polyisobutylene in a “breathing bubble” rheometer. In this type of rheometer, a bubble consisting of an incompressible, low-viscosity fluid (usually water) is injected into the sample with a nozzle. Expanding or collapsing the bubble by adding or removing water induces biaxial or uniaxial extension in the surrounding sample. The pressure difference between the bubble and the surroundings can be measured and compared to the predictions of constitutive equations. This measurement only gives one integral value for a complex flow history. In this paper, the birefringence around the bubble is measured in order to learn more about the flow. This is done by comparing pressure and birefringence results to those of standard constitutive equations for a polyisobutylene sample. A good agreement between the pressure and optical measurements and the theory is found with a single value of the stress-optical constant.
    Type of Medium: Electronic Resource
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  • 4
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    Unknown
    University of Michigan Press
    Publication Date: 2024-04-05
    Description: In Europe’s recent history, there have been several challenges to the strength of the European Union—Brexit, COVID, financial crises, and global tensions—bringing an increased need to understand the ways that the European Union (EU) could successfully stay together or fall apart. In examining how the European Union has changed since 1993, important puzzles have emerged, including how national government functions are transferred to the EU without reforming the EU, how increased transparency is announced while decisions are approved in informal meetings, and how the effects of the polarizing rise of Euroscepticism can be managed to still promote the formation of solidarity and trust among Europeans. To understand these puzzles, Thomas König introduces a new theory of (supra)national partyism to help explain the causes and consequences of choices made by political leaders for Europe. He uses a game-theoretical perspective to look at how conditions for leaders change through accessions of new members, shocks, and crises, and separates institutional choices into two different games played by office- and policy-seeking political leaders—the interstate summit game and the national game of party competition. The Dynamics of European Integration reveals how the reorganization of electoral systems can harness dissensus and polarization among diverse national constituencies to enable the promotion of solidarity and trust in the EU.
    Keywords: European integration, institutional choices, dynamic analysis, post-Maastricht period, partyism, liberal intergovernmentalism, postfunctionalism, affective polarization, European identity, game-theory, technocracism, camp-building, governance design, transfer of policy competences, political leaders, interstate bargains, causes and consequences, Brexit, COVID, financial crisis, global tension, supranational partyism, national partyism, game theory ; thema EDItEUR::J Society and Social Sciences::JP Politics and government ; thema EDItEUR::J Society and Social Sciences::JP Politics and government::JPS International relations::JPSL Geopolitics ; thema EDItEUR::N History and Archaeology::NH History::NHD European history
    Language: English
    Format: image/jpeg
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