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  • Electronic Resource  (3)
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  • 2000-2004  (3)
  • 2001  (3)
  • PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics  (2)
  • AMS Classification. 65L05; 22E60.  (1)
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  • Electronic Resource  (3)
  • E-Resource
  • Loose Leaf
Years
  • 2000-2004  (3)
Year
  • 2001  (3)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Foundations of computational mathematics 1 (2001), S. 129-160 
    ISSN: 1615-3383
    Keywords: AMS Classification. 65L05; 22E60.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Abstract. In this paper we develop in a systematic manner the theory of time-stepping methods based on the Cayley transform. Such methods can be applied to discretize differential equations that evolve in some Lie groups, in particular in the orthogonal group and the symplectic group. Unlike many other Lie-group solvers, they do not require the evaluation of matrix exponentials. Similarly to the theory of Magnus expansions in [13], we identify terms in a Cayley expansion with rooted trees, which can be constructed recursively. Each such term is an integral over a polytope but all such integrals can be evaluated to high order by using special quadrature formulas similar to the construction in [13]. Truncated Cayley expansions (with exact integrals) need not be time-symmetric, hence the method does not display the usual advantages associated with time symmetry, e.g., even order of approximation. However, time symmetry (with its attendant benefits) is attained when exact integrals are replaced by certain quadrature formulas.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 20 (2001), S. 105-122 
    ISSN: 1434-6036
    Keywords: PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: In order to describe the thermodynamics of the glassy systems it has been recently introduced an extra parameter, the effective temperature which generalizes the fluctuation-dissipation theorem (FDT) to off-equilibrium systems and supposedly describes thermal fluctuations around the aging state. Using this concept we investigate the applicability of a zeroth thermodynamic law for non-equilibrium systems. In particular we study two coupled systems of harmonic oscillators with Monte Carlo dynamics. We analyze in detail two types of dynamics: 1) sequential dynamics where the coupling between the subsystems comes only from the Hamiltonian and 2) parallel dynamics where there is a further coupling between the subsystems arising from the dynamics. We show that the coupling described in the first case is not enough to make asymptotically the effective temperatures of the two interacting subsystems equalize, the reason being the too small thermal conductivity between them in the aging state. This explains why different interacting degrees of freedom in structural glasses may stay at different effective temperatures without never mutually thermalizing.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 21 (2001), S. 115-120 
    ISSN: 1434-6036
    Keywords: PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We study the most suitable procedure to measure the effective temperature in off-equilibrium systems. We analyze the stationary current established between an off-equilibrium system and a thermometer and the necessary conditions for that current to vanish. We find that the thermometer must have a short characteristic time-scale compared to the typical decorrelation time of the glassy system to correctly measure the effective temperature. This general conclusion is confirmed analyzing an ensemble of harmonic oscillators with Monte Carlo dynamics as an illustrative example of a solvable model of a glass. We also find that the current defined allows to extend Fourier's law to the off-equilibrium regime by consistently defining effective transport coefficients. Our results for the oscillator model explain why thermal conductivities between thermalized and frozen degrees of freedom in structural glasses are extremely small.
    Type of Medium: Electronic Resource
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