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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3692-3697 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Effects of shear flow are investigated in melts of diblock copolymers in the homogeneous disordered phase near the microphase separation transition point. Simple approximate expressions are given for the anisotropic scattering intensity in nonlinear regimes under shear. A non-Newtonian effect and a normal stress effect are also examined, which are caused by deformations of the critical fluctuations in shear. An explicit expression is also found for the critical part of the complex shear modulus. This paper is a generalization of recent work by Fredrickson and Larson.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 1122-1125 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Late stages are examined in the spinodal decomposition process of polymer blends. The coarsening due to surface tension is much delayed in the entangled case even on the dimensionless time scale. Before its inception the hydrodynamic interaction is strongly suppressed and the coarsening should be analogous to that of the kinetic Ising model.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 117 (2002), S. 2359-2367 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using molecular dynamics simulations, we study dynamics of a model polymer melt composed of short chains with bead number N=10 in supercooled states. In quiescent conditions, the stress relaxation function G(t) is calculated, which exhibits a stretched exponential relaxation on the time scale of the α relaxation time τα and ultimately follows the Rouse dynamics characterized by the time τR∼N2τα. After application of shear γ(overdot), transient stress growth σxy(t)/γ(overdot) first obeys the linear growth ∫0tdt′G(t′) for strain less than 0.1 but saturates into a non-Newtonian viscosity for larger strain. In steady states, shear thinning and elongation of chains into ellipsoidal shapes take place for shear γ(overdot) larger than τR−1. In such strong shear, we find that the chains undergo random tumbling motion taking stretched and compact shapes alternatively. We examine the validity of the stress–optical relation between the anisotropic parts of the stress tensor and the dielectric tensor, which are violated in transient states due to the presence of a large glassy component of the stress. We furthermore introduce time-correlation functions in shear to calculate the shear-dependent relaxation times, τα(T,γ(overdot)) and τR(T,γ(overdot)), which decrease nonlinearly as functions of γ(overdot) in the shear-thinning regime. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 8788-8795 
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 51 (1983), S. 601-632 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mutual friction parametersB and B′ for a moving vortex are calculated near the superfluid transition. They are proportional to the kinetic coefficient associated with the order parameter and, asT →λ, diverge as (Tλ − T)−1/3, in agreement with experiment. The nonlinear couplings between the order parameter Ψ and the entropym, both the reversible one and the one in the free energy, are found to be crucial in the mutual friction near the λ point. These couplings were neglected in a previous paper by the author. First, the reversible coupling in the dynamic equations makes the chemical potential deviation long-ranged and causes the dissipation to take place only near the vortex core. Second,B′ can diverge asT → Tλ only in the presence of the coupling of the formm|Ψ|2 in the free energy. Thus theE model of Halperin et al., where the latter coupling is absent, cannot explain the critical anomaly ofB′. The helical mode of a single vertex line is also investigated and its dispersion relation is found to be quite different from that at low temperatures. This mode has the same time scale as that of the second-sound mode when the wave vectors are of the order of the inverse correlation length, thus obeying the usual dynamic scaling law. The time correlation functions of the displacement fluctuations of a vortex line are also obtained. The force acting on a moving vortex is calculated and is found to be equal to the classical Magnus force.
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  • 7
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract By assuming a phenomenological Ginzburg-Landau-Wilson free energy for3He-4He mixtures near the critical surface of the superfluid transition we can express thermodynamic derivatives of the form (∂a/∂b) c,d in terms of a correlation function of ¦ψ¦2, where Gy is the order parameter. Herea, b, c, and d are any four of the quantities entropys, number densityn, molar concentrationX, temperatureT, pressurep, and chemical potential difference Δ=μ3−μ4. Relationships among these thermodynamic derivatives are those of the Pippard-Buckingham-Fairbank approximation in the3He-4He case. Some combinations of the coefficients in the free energy are equal to derivatives on the critical surface and remain invariant with respect to renormalization group transformations. A general scheme is also developed to give correlation function expressions for thermodynamic derivatives.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 53 (1983), S. 189-220 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new formalism is presented to study the critical and tricritical dynamics of3He-4He mixtures near the superfluid transition for arbitrary concentration. In this fluid two conserved variables, the molar concentrationX and the entropys, are twofold coupled to a complex order parameter ψ first in the dynamic equations reversibly and second in the free energy dissipatively. However, at an intermediate concentrationX=X D (which is 0.37 at the saturated vapor pressure) a linear combination ofX ands is found to be asymptotically decoupled from ψ both reversibly and dissipatively. There, dynamic renormalization group equations reduce to those of pure4He (or those of the F model) and some dynamic properties are common to those of pure4He. For example, atX≈X D , the gradient ∇(T−T λ ) under heat flow goes to zero without3He mass flow, whereT λ is the critical temperature, dependent onX, and the thermodiffusion ratio loses the singularity with the critical exponent α. Our dynamic renormalization group equations take into account the above two nonlinear couplings and can be used for any concentrations. Furthermore, using a linear response scheme, general relations are obtained among the kinetic coefficients. As a result the thermal conductivity on the λ line is found to be exactly proportional toX −1 at smallX. The coefficient in front ofX −1 can be expressed in terms of the diffusion constant of an isolated3He molecule in4He.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Interface fluctuations and kinetics of nucleating droplets are studied in4He and3He-4He mixtures at ultralow temperatures in the dissipationless regime. We firstly discuss the droplet number density arising as quantum fluctuations and secondly derive the Rayleigh-Plesset equation for a droplet in a metastable fluid. This equation, which is well-known in classical hydrodynamics, governs kinetics of domain growth at very low temperatures. Thirdly, the quantum nucleation rate is shown to be much enhanced by high-frequency acoustic or electric field, however small its amplitude is, when the period of oscillation 2π/ω is shorter than the time τ s of tunnelling through the potential barrier. Fourthly, we examine equilibrium fluctuations of a planar interface which macroscopically separates two phases. The correlation function of the interface displacement is shown to cross over from the classical expression into a newly found quantum expression as the temperature is lowered.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 18 (1978), S. 475-499 
    ISSN: 1572-9613
    Keywords: Master equation for μ-space fluctuations ; BoltzmannLangevin equation ; molecular chaos ; nonequilibrium long-range correlations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A master equation is derived microscopically to describe the fluctuating motion of the particle density in μ. space. This equation accounts for the drift motion of particles and is valid for any inhomogeneous gas. The Boltzmann equation is obtained from the first moment of this equation by neglecting the second cumulant (the pair correlation function). The successive moments form coarse-grained BBGKY-like hierarchy equations, in which small spatial regions with rij < the force range are smeared out. These hierarchy equations are convenient for investigating the nonequilibrium long-range pair correlation function, which arises mainly from sequences of isolated binary collisions and gives rise to the much-discussed long-time tail and the logarithmic term in the density expansion of transport coefficients. It is shown to have a spatial long tail, like the Coulombic potential, in a steady laminar flow. The stochastic nature of the nonlinear Boltzmann-Langevin equation is also investigated; the random source term is found to be expressed as a linear superposition of Poisson random variables and to become Gaussian in special cases.
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