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  • 2005-2009
  • 2000-2004  (4)
  • 2001  (4)
  • PACS. 31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates – 33.80.Wz Other multiphoton processes  (2)
  • PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics  (2)
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  • 2005-2009
  • 2000-2004  (4)
Jahr
  • 2001  (4)
Schlagwörter
  • 1
    Digitale Medien
    Digitale Medien
    Validity of the zero-thermodynamic law in off-equilibrium coupled harmonic oscillators (2001)
    Springer
    The European physical journal 20 (2001), S. 105-122 
    Details
    ISSN: 1434-6036
    Schlagwort(e): PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01313919
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  • 2
    Digitale Medien
    Digitale Medien
    Heat transfer and Fourier's law in off-equilibrium systems (2001)
    Springer
    The European physical journal 21 (2001), S. 115-120 
    Details
    ISSN: 1434-6036
    Schlagwort(e): PACS. 64.70.Pf Glass transitions – 05.70.Ln Nonequilibrium and irreversible thermodynamics
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: 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.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01315082
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  • 3
    Digitale Medien
    Digitale Medien
    Selective preparation of ground state wave-packets: a theoretical analysis of femtosecond pump-dump-probe experiments on the potassium dimer (2001)
    Springer
    The European physical journal 14 (2001), S. 167-172 
    Details
    ISSN: 1434-6079
    Schlagwort(e): PACS. 31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates – 33.80.Wz Other multiphoton processes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: We present simulations on pump-dump-probe experiments performed on the potassium dimer. The interaction of two time-delayed laser pulses prepares vibrational wave packets in the electronic ground state. The quantum calculations reveal to what extent it is possible to prepare a ground state superposition of states with high versus low vibrational quantum numbers by changing the pump-dump delay time. It is shown that transient signals may exhibit interference effects which are due to characteristics of ground state wave-packets composed of two components showing different vibrational dynamics. In this way the signals are able to yield information about vibrational overtone motion.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100530170214
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  • 4
    Digitale Medien
    Digitale Medien
    Femtosecond pump-probe fluorescence signals from classical trajectories: comparison with wave-packet calculations (2001)
    Springer
    The European physical journal 15 (2001), S. 413-422 
    Details
    ISSN: 1434-6079
    Schlagwort(e): PACS. 31.70.Hq Time-dependent phenomena: excitation and relaxation processes, and reaction rates – 33.80.Wz Other multiphoton processes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: A classical approach to simulate femtosecond pump-probe experiments is presented and compared to the quantum mechanical treatment. We restrict the study to gas-phase systems using the I2 molecule as a numerical example. Thus, no relaxation processes are included. This allows for a direct comparison between purely quantum mechanical results and those obtained from classical trajectory calculations. The classical theory is derived from the phase-space representation of quantum mechanics. Various approximate quantum mechanical treatments are compared to their classical counterparts. Thereby it is demonstrated that the representation of the radial density as prepared in the pump-process is most crucial to obtain reliable signals within the classical approach.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/s100530170158
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