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S Ayik - One of the best experts on this subject based on the ideXlab platform.

  • stochastic one body transport and coherent Collision Term
    NONEQUILIBRIUM AND NONLINEAR DYNAMICS IN NUCLEAR AND OTHER FINITE SYSTEMS:International Conference, 2002
    Co-Authors: S Ayik
    Abstract:

    The stochastic one-body transport theory in non-relativistic framework is briefly reviewed, and a coherent damping mechanism arising from the coupling between the mean-field fluctuations and the single-particle motion is discussed. For small amplitude fluctuations, the coherent mechanism appears as a particle-phonon Collision Term in the transport equation for the average density matrix, which play a dominant role in damping of giant resonance excitations and nuclear collective motion at low energies.

  • extended tdhf with a coherent Collision Term
    Physics Letters B, 2000
    Co-Authors: S Ayik
    Abstract:

    Abstract It is shown that the stochastic one-body transport description contains, in addition to incoherent binary Collisions, a coherent damping mechanism due to coupling between mean-field fluctuations and single-particle motion. An extended TDHF model is proposed by incorporating the coherent mechanism into the equation of motion. In the limit of small fluctuations around equilibrium, the collective and single-particle self-energies due to the coherent mechanism are deduced.

  • Collisional damping of nuclear collective vibrations in a non-Markovian transport approach
    Physical Review C, 1998
    Co-Authors: S Ayik, O. Yilmaz, A. Gokalp, P Schuck
    Abstract:

    A detailed derivation of the Collisional widths of collective vibrations is presented in both quantal and semi-classical frameworks by considering the linearized limits of the extended TDHF and the BUU model with a non-Markovian binary Collision Term. Damping widths of giant dipole and giant quadrupole excitations are calculated by employing an effective Skyrme force, and the results are compared with GDR measurements in Lead and Tin nuclei at finite temperature.

  • Finite temperature nuclear response in the extended random phase approximation
    Physical Review C, 1998
    Co-Authors: Denis Lacroix, Ph. Chomaz, S Ayik
    Abstract:

    The nuclear collective response at finite temperature is investigated for the first time in the quantum framework of the small amplitude limit of the extended time-dependent Hartree-Fock approach, including a non-Markovian Collision Term. It is shown that the Collision width satisfies a secular equation. By employing a Skyrme force, the isoscalar monopole, isovector dipole, and isoscalar quadrupole excitations in 40Ca are calculated and important quantum features are pointed out. The Collisional damping due to decay into incoherent two-particle–two-hole states is small at low temperatures but increases rapidly at higher temperatures.

Victor Sofonea - One of the best experts on this subject based on the ideXlab platform.

  • half range lattice boltzmann models for the simulation of couette flow using the shakhov Collision Term
    Physical Review E, 2018
    Co-Authors: Victor E Ambrus, Victor Sofonea
    Abstract:

    The three-dimensional Couette flow between parallel plates is addressed using mixed lattice Boltzmann models which implement the half-range and the full-range Gauss-Hermite quadratures on the Cartesian axes perpendicular and parallel to the walls, respectively. The ability of our models to simulate rarefied flows are validated through comparison against previously reported results obtained using the linearized Boltzmann-BGK equation for values of the Knudsen number (Kn) up to $100$. We find that recovering the non-linear part of the velocity profile (i.e., its deviation from a linear function) at ${\rm Kn} \gtrsim 1$ requires high quadrature orders. We then employ the Shakhov model for the Collision Term to obtain macroscopic profiles for Maxwell molecules using the standard $\mu \sim T^\omega$ law, as well as for monatomic Helium and Argon gases, modeled through ab-initio potentials, where the viscosity is recovered using the Sutherland model. We validate our implementation by comparison with DSMC results and find excellent match for all macroscopic quantities for ${\rm Kn} \lesssim 0.1$. At ${\rm Kn} \gtrsim 0.1$, small deviations can be seen in the profiles of the diagonal components of the pressure tensor, the heat flux parallel to the plates, and the velocity profile, as well as in the values of the velocity gradient at the channel center. We attribute these deviations to the limited applicability of the Shakhov Collision model for highly out of equilibrium flows.

  • BGK models for diffusion in isothermal binary fluid systems
    Physica A-statistical Mechanics and Its Applications, 2001
    Co-Authors: Victor Sofonea, Robert F. Sekerka
    Abstract:

    Two Bhatnagar–Gross–Krook (BGK) models for isothermal binary fluid systems—the classical single relaxation time model and a split Collision Term model—are discussed in detail, with emphasis on the diffusion process in perfectly miscible ideal gases. Fluid equations, as well as the constitutive equation for diffusion, are derived from the Boltzmann equation using the method of moments and the values of the transport coefficients (viscosity and diffusivity) are calculated. The Schmidt number is found to be equal to one for both models. The split Collision Term model allows the two fluid components to have different values of the viscosity, while the single relaxation time model does not have this characteristic. The value of the viscosity does not depend on the density in the split Collision Term model, as expected from the classical kinetic theory developed by Maxwell. Possible extension of BGK models to non-ideal gases and ideal solutions (where the Schmidt number is larger than 1) is also investigated.

W Greiner - One of the best experts on this subject based on the ideXlab platform.

  • microscopic models for ultrarelativistic heavy ion Collisions
    Progress in Particle and Nuclear Physics, 1998
    Co-Authors: Steffen A Bass, H Weber, C Hartnack, J Konopka, M Brandstetter, J Aichelin, Marcus Bleicher, S Soff, Stefan Hofmann, W Greiner
    Abstract:

    In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended Collision Term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the inTermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

Steffen A Bass - One of the best experts on this subject based on the ideXlab platform.

  • microscopic models for ultrarelativistic heavy ion Collisions
    arXiv: Nuclear Theory, 1998
    Co-Authors: Steffen A Bass, M Brandstetter, Marcus Bleicher, Stefan Hofmann, M Belkacem, L Bravina, C Ernst, L Gerland, M Hofmann, J Konopka
    Abstract:

    In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended Collision Term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the inTermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

  • microscopic models for ultrarelativistic heavy ion Collisions
    Progress in Particle and Nuclear Physics, 1998
    Co-Authors: Steffen A Bass, H Weber, C Hartnack, J Konopka, M Brandstetter, J Aichelin, Marcus Bleicher, S Soff, Stefan Hofmann, W Greiner
    Abstract:

    In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended Collision Term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the inTermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

J Konopka - One of the best experts on this subject based on the ideXlab platform.

  • microscopic models for ultrarelativistic heavy ion Collisions
    arXiv: Nuclear Theory, 1998
    Co-Authors: Steffen A Bass, M Brandstetter, Marcus Bleicher, Stefan Hofmann, M Belkacem, L Bravina, C Ernst, L Gerland, M Hofmann, J Konopka
    Abstract:

    In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended Collision Term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the inTermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.

  • microscopic models for ultrarelativistic heavy ion Collisions
    Progress in Particle and Nuclear Physics, 1998
    Co-Authors: Steffen A Bass, H Weber, C Hartnack, J Konopka, M Brandstetter, J Aichelin, Marcus Bleicher, S Soff, Stefan Hofmann, W Greiner
    Abstract:

    In this paper, the concepts of microscopic transport theory are introduced and the features and shortcomings of the most commonly used ansatzes are discussed. In particular, the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) transport model is described in great detail. Based on the same principles as QMD and RQMD, it incorporates a vastly extended Collision Term with full baryon-antibaryon symmetry, 55 baryon and 32 meson species. Isospin is explicitly treated for all hadrons. The range of applicability stretches from $E_{lab} 200$ GeV/nucleon, allowing for a consistent calculation of excitation functions from the inTermediate energy domain up to ultrarelativistic energies. The main physics topics under discussion are stopping, particle production and collective flow.