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Yoshiki Kusama - One of the best experts on this subject based on the ideXlab platform.

  • observation of the interaction between the geodesic acoustic mode and ambient Fluctuation in the jft 2m tokamak
    Nuclear Fusion, 2006
    Co-Authors: Y Miura, Yoshihiko Nagashima, A Nishizawa, Yoshihiro Hamada, K. Shinohara, K. Kamiya, H. Ogawa, K Hoshino, Yusuke Kawasumi, Yoshiki Kusama
    Abstract:

    The electrostatic and Density Fluctuation are measured simultaneously with a heavy ion beam probe. The electrostatic Fluctuation with the geodesic acoustic mode (GAM) frequency is observed in L-mode plasmas and not in H-mode plasmas. The poloidal and radial structure is consistent with the GAM. So the Fluctuation is concluded to be the GAM.The amplitude of the GAM changes in the radial direction; it is small near the separatrix, has a maximum at 3 cm inside the separatrix and decreases again to 5 cm inside the separatrix.The GAM and the temporal behaviour of the ambient Density Fluctuation show a significant coherence, and the phase of modulation of the ambient Density Fluctuation tends to delay the potential oscillation of the GAM. It is clearly verified that the GAM affects ambient Fluctuation and also the local particle transport through modulation of the amplitude of the ambient Fluctuation.

  • geodesic acoustic mode in jft 2m tokamak plasmas
    Plasma Physics and Controlled Fusion, 2006
    Co-Authors: Y Miura, A Fujisawa, S I Itoh, A Nishizawa, Yoshihiro Hamada, K. Kamiya, K Itoh, H. Ogawa, K Hoshino, Yoshiki Kusama
    Abstract:

    The characteristics of geodesic–acoustic-mode (GAM) are investigated through direct and simultaneous measurement of electrostatic and Density Fluctuations with a heavy ion beam probe.The amplitude of the GAM changes in relation to the radial position; it is small near the separatrix, reaches a local maximum at 3 cm inside the separatrix and then decreases again to 5 cm inside the separatrix. The frequency is constant in the range, though the predicted GAM frequency varies according to the temperature gradient. The correlation length is about 6 cm and comparable to the structure of the amplitude of the GAM. The results indicate the GAM has a radial structure which reflects the local condition at about 3 m inside the separatrix.The phase relation between the GAM oscillation indicates that the GAM is a radial propagating wave.The interaction between the GAM and the ambient Density Fluctuation is shown by the high coherence between the GAM oscillation and the temporal behaviour of the ambient Density Fluctuation. Moreover, the phase relation between the electric field Fluctuation of the GAM ( ) and the amplitude of the Density Fluctuation indicates that the modulation of the ambient Density Fluctuation delays the . The causality between the GAM and the modulation of the Density Fluctuation is revealed.

Peera Pongkitiwanichakul - One of the best experts on this subject based on the ideXlab platform.

  • constraining low frequency alfvenic turbulence in the solar wind using Density Fluctuation measurements
    The Astrophysical Journal, 2009
    Co-Authors: Benjamin D G Chandran, Eliot Quataert, G G Howes, Qian Xia, Peera Pongkitiwanichakul
    Abstract:

    One proposed mechanism for heating the solar wind, from close to the Sun to beyond approx10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves, KAWs) are compressive, the measured Density Fluctuations in the solar wind place an upper limit on the amplitude of KAWs and hence an upper limit on the rate at which the solar wind can be heated by low-frequency, Alfvenic turbulence. We evaluate this upper limit for both coronal holes at 5 R{sub sun} and the near-Earth solar wind. At both locations, the upper limit we find is consistent with models in which the solar wind is heated by low-frequency Alfvenic turbulence. At 1 AU, the upper limit on the turbulent heating rate derived from the measured Density Fluctuations is within a factor of 2 of the measured solar-wind heating rate. Thus, if low-frequency Alfvenic turbulence is the primary mechanism for heating the near-Earth solar wind, KAWs must be one of the dominant sources of solar-wind Density Fluctuations at frequencies approx1 Hz. We also present a simple argument for why Density-Fluctuation measurements do appear to rule out models in which coronal holes are heated by non-turbulent high-frequency waves ('sweeping'), but aremore » compatible with heating by low-frequency Alfvenic turbulence.« less

  • constraining low frequency alfvenic turbulence in the solar wind using Density Fluctuation measurements
    The Astrophysical Journal, 2009
    Co-Authors: Benjamin D G Chandran, Eliot Quataert, G G Howes, Qian Xia, Peera Pongkitiwanichakul
    Abstract:

    One proposed mechanism for heating the solar wind, from close to the sun to beyond ∼ 10 AU, invokes low- frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves) are compressive, the measured Density Fluctuations in the so lar wind place an upper limit on the amplitude of kinetic Alfven waves and hence an upper limit on the rate at which the solar wind can be heated by low- frequency, Alfvenic turbulence. We evaluate this upper limit for both coronal holes at 5R⊙ and in the near- Earth solar wind. At both radii, the upper limit we find is cons istent with models in which the solar wind is heated by low-frequency Alfvenic turbulence. At 1 AU, the upper limit on the turbulent heating rate derived from the measured Density Fluctuations is within a factor of 2 of the measured solar wind heating rate. Thus if low-frequency Alfvenic turbulence contributes to heating the near-Earth solar wind, kinetic Alfven waves must be one of the dominant sources of solar wind Density fluct uations at frequencies ∼ 1 Hz. We also present a simple argument for why Density Fluctuation measurements do appear to rule out models in which the solar wind is heated by non-turbulent high frequency waves "sweeping" through the ion-cyclotron resonance, but are compatible with heating by low-frequency Alfvenic turbulence. Subject headings:

  • constraining low frequency alfvenic turbulence in the solar wind using Density Fluctuation measurements
    arXiv: Solar and Stellar Astrophysics, 2009
    Co-Authors: Benjamin D G Chandran, Eliot Quataert, G G Howes, Qian Xia, Peera Pongkitiwanichakul
    Abstract:

    One proposed mechanism for heating the solar wind, from close to the sun to beyond 10 AU, invokes low-frequency, oblique, Alfven-wave turbulence. Because small-scale oblique Alfven waves (kinetic Alfven waves) are compressive, the measured Density Fluctuations in the solar wind place an upper limit on the amplitude of kinetic Alfven waves and hence an upper limit on the rate at which the solar wind can be heated by low-frequency, Alfvenic turbulence. We evaluate this upper limit for both coronal holes at 5 solar radii and in the near-Earth solar wind. At both radii, the upper limit we find is consistent with models in which the solar wind is heated by low-frequency Alfvenic turbulence. At 1 AU, the upper limit on the turbulent heating rate derived from the measured Density Fluctuations is within a factor of 2 of the measured solar wind heating rate. Thus if low-frequency Alfvenic turbulence contributes to heating the near-Earth solar wind, kinetic Alfven waves must be one of the dominant sources of solar wind Density Fluctuations at frequencies of order 1 Hz. We also present a simple argument for why Density Fluctuation measurements do appear to rule out models in which the solar wind is heated by non-turbulent high-frequency waves ``sweeping'' through the ion-cyclotron resonance, but are compatible with heating by low-frequency Alfvenic turbulence.

Byung Chan Eu - One of the best experts on this subject based on the ideXlab platform.

  • voids generic van der waals equation of state and transport coefficients of liquids
    Physical Chemistry Chemical Physics, 2007
    Co-Authors: Byung Chan Eu
    Abstract:

    In this Perspective, we discuss the role of voids in transport processes in liquids and the manner in which the concept of voids enters the generic van der Waals equation of state and the modified free volume theory. The Density Fluctuation theory is then discussed and we show how the Density Fluctuation theory can be made a molecular theory with the help of the modified free volume theory and the generic van der Waals equation of state. The confluence of the aforementioned three theories makes it possible to calculate the transport coefficients of liquids by using the information on the equilibrium pair correlation function, which can be calculated either by an integral equation theory or Monte Carlo simulations. A number of relations between transport coefficients are also presented, which are derived on the basis of the Density Fluctuation theory. Since they can be used to obtain one transport coefficient from another they can be very useful in handling experimental and theoretical data. An application of the modified free volume theory to polymer melts is discussed as an example for a theory of transport properties of complex liquids.

  • generic van der waals equation of state modified free volume theory of diffusion and viscosity of simple liquids
    Journal of Physical Chemistry B, 2005
    Co-Authors: Rozita Laghaei, And Afshin Eskandari Nasrabad, Byung Chan Eu
    Abstract:

    The shear viscosity formula derived by the Density Fluctuation theory in previous papers is computed for argon, krypton, and methane by using the self-diffusion coefficients derived in the modified free volume theory with the help of the generic van der Waals equation of state. In the temperature regime near or above the critical temperature, the Density dependence of the shear viscosity can be accounted for by ab initio calculations with the self-diffusion coefficients provided by the modified free volume theory if the minimum (critical) free volume is set equal to the molecular volume and the volume overlap parameter (α) is taken about unity in the expression for the self-diffusion coefficient. In the subcritical temperature regime, if the Density Fluctuation range parameter is chosen appropriately at a temperature, then the resulting expression for the shear viscosity can well account for its Density and temperature dependence over the ranges of Density and temperature experimentally studied. In the se...

Jinnouk Gong - One of the best experts on this subject based on the ideXlab platform.

  • exact analytic solution for non linear Density Fluctuation in a λcdm universe
    Journal of Cosmology and Astroparticle Physics, 2016
    Co-Authors: Jaiyul Yoo, Jinnouk Gong
    Abstract:

    We derive the exact third-order analytic solution of the matter Density Fluctuation in the proper-time hypersurface in a ΛCDM universe, accounting for the explicit time-dependence and clarifying the relation to the initial condition. Furthermore, we compare our analytic solution to the previous calculation in the comoving gauge, and to the standard Newtonian perturbation theory by providing Fourier kernels for the relativistic effects. Our results provide an essential ingredient for a complete description of galaxy bias in the relativistic context.

  • relativistic effects and primordial non gaussianity in the matter Density Fluctuation
    Physics Letters B, 2016
    Co-Authors: Jaiyul Yoo, Jinnouk Gong
    Abstract:

    We present the third-order analytic solution of the matter Density Fluctuation in the proper-time hypersurface of nonrelativistic matter flows by solving the nonlinear general relativistic equations. The proper-time hypersurface provides a coordinate system that a local observer can set up without knowledge beyond its neighborhood, along with physical connections to the local Newtonian descriptions in the relativistic context. The initial condition of our analytic solution is set up by the curvature perturbation in the comoving gauge, clarifying its impact on the nonlinear evolution. We compute the effective non-Gaussian parameters due to the nonlinearity in the relativistic equations. With proper coordinate rescaling, we show that the equivalence principle is respected and the relativistic effect vanishes in the large-scale limit.

Stuart D. Bale - One of the best experts on this subject based on the ideXlab platform.

  • Density Fluctuation spectrum of solar wind turbulence between ion and electron scales
    Physical Review Letters, 2012
    Co-Authors: Christopher H. K. Chen, C Salem, J W Bonnell, F S Mozer, Stuart D. Bale
    Abstract:

    We present a measurement of the spectral index of Density Fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be -2.75 +/- 0.06, steeper than predictions for pure whistler or kinetic Alfven wave turbulence, but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the Density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.

  • Density Fluctuation spectrum of solar wind turbulence between ion and electron scales
    Physical Review Letters, 2012
    Co-Authors: Christopher H. K. Chen, J W Bonnell, F S Mozer, C S Salem, Stuart D. Bale
    Abstract:

    We present a measurement of the spectral index of Density Fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be $\ensuremath{-}2.75\ifmmode\pm\else\textpm\fi{}0.06$, steeper than predictions for pure whistler or kinetic Alfv\'en wave turbulence but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the Density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.