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Eun Jin Kim - One of the best experts on this subject based on the ideXlab platform.
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Self-Consistent Theory of turbulent transport in the solar tachocline - II. Tachocline confinement
Astronomy & Astrophysics, 2006Co-Authors: Nicolas Leprovost, Eun Jin KimAbstract:Aims. We provide a Consistent Theory of the tachocline confinement (or anisotropic momentum transport) within a hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant value during the sun's evolution. Methods. Starting from the first principle with the physically plausible assumption that turbulence is driven externally (e.g. by plumes penetrating from the convection zone), we derive turbulent (eddy) viscosity in the radial (vertical) and azimuthal (horizontal) directions by incorporating the crucial effects of shearing due to radial and latitudinal differential rotations in the tachocline. Results. We show that the simultaneous presence of both shears effectively induces a much more efficient momentum transport in the horizontal plane than in the radial direction. In particular, in the case of strong radial turbulence (driven by overshooting plumes from the convection zone), the ratio of the radial to horizontal eddy viscosity is proportional to ${\cal A}^{-1/3}$, where ${\cal A}$ is the strength of the shear due to radial differential rotation. In comparison, in the case of horizontally driven turbulence, this ratio becomes of order $-\epsilon^2$, with negative radial eddy viscosity. Here, ϵ ($\ll 1$) is the ratio of the radial to latitudinal shear. The resulting anisotropy in momentum transport could thus be strong enough to operate as a mechanism for the tachocline confinement against spreading.
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Self-Consistent Theory of turbulent transport in the solar tachocline
2006Co-Authors: Eun Jin KimAbstract:Aims. We provide a Consistent Theory of the tachocline confinement (or anisotropic momentum transport) within a hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant value during the sun’s evolution. Methods. Starting from the first principle with the physically plausible assumption that turbulence is driven externally (e.g. by plumes penetrating from the convection zone), we derive turbulent (eddy) viscosity in the radial (vertical) and azimuthal (horizontal) directions by incorporating the crucial effects of shearing due to radial and latitudinal differential rotations in the tachocline. Results. We show that the simultaneous presence of both shears effectively induces a much more efficient momentum transport in the horizontal plane than in the radial direction. In particular, in the case of strong radial turbulence (driven by overshooting plumes from the convection zone), the ratio of the radial to horizontal eddy viscosity is proportional to A−1/3, where A is the strength of the shear due to radial differential rotation. In comparison, in the case of horizontally driven turbulence, this ratio becomes of order − 2, with negative radial eddy viscosity. Here, ( 1) is the ratio of the radial to latitudinal shear. The resulting anisotropy in momentum transport could thus be strong enough to operate as a mechanism for the tachocline confinement against spreading.
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Self-Consistent Theory of turbulent transport in the solar tachocline. II. Tachocline confinement
Astronomy and Astrophysics - A&A, 2006Co-Authors: Nicolas Leprovost, Eun Jin KimAbstract:We provide a Consistent Theory of the tachocline confinement (or anisotropic momentum transport) within an hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5\% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant value during the sun's evolution. Starting from the first principle with the physically plausible assumption that turbulence is driven externally (e.g. by plumes penetrating from the convection zone), we derive turbulent (eddy) viscosity in the radial (vertical) and azimuthal (horizontal) directions by incorporating the crucial effects of shearing due to radial and latitudinal differential rotations in the tachocline. We show that the simultaneous presence of both shears induces effectively a much more efficient momentum transport in the horizontal plane than in the radial direction. In particular, in the case of strong radial turbulence (driven by overshooting plumes from the convection zone), the ratio of the radial to horizontal eddy viscosity is proportional to ${\cal A}^{-1/3}$, where ${\cal A}$ is the strength of the shear due to radial differential rotation. In comparison, in the case of horizontally driven turbulence, this ratio becomes of order $-\epsilon^2$, with negative radial eddy viscosity. Here, $\epsilon$ ($\ll 1$) is the ratio of the radial to latitudinal shear. The resulting anisotropy in momentum transport could thus be sufficiently strong to operate as a mechanism for the tachocline confinement against spreading.
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Self-Consistent Theory of turbulent transport in the solar tachocline. I. Anisotropic turbulence
Astronomy & Astrophysics, 2005Co-Authors: Eun Jin KimAbstract:We present a self-Consistent Theory of turbulent transport in the solar tachocline by taking into account the effect of the radial differential rotation on turbulent transport. We show that the shearing by the radial differential rotation leads to reduction in turbulent transport of particles and momentum and the amplitude of turbulent flow via shear stabilization. The degree of reduction depends on the direction as well as the quantity that is transported. Specifically, particle transport in the vertical (radial) direction, orthogonal to the shear flow, is reduced with the scaling A -2 while it is less reduced in the horizonal plane with the scaling A -4/3 . Here, A is shearing rate, representing the radial differential rotation. A similar, but weaker, anisotropy also develops in the amplitude of turbulent flow. The results suggest that the radial differential rotation in the tachocline can cause anisotropy in turbulence intensity and particle transport with weaker turbulence in the radial direction even in the absence of density stratification and even when the turbulence is mainly driven radially by plumes from the convection zone. We also assess the efficiency of the transport by a meridional circulation by taking into account the interaction with the radial differential rotation. Implications for mixing and angular momentum transport in the solar interior is discussed.
Nicolas Leprovost - One of the best experts on this subject based on the ideXlab platform.
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Self-Consistent Theory of turbulent transport in the solar tachocline - II. Tachocline confinement
Astronomy & Astrophysics, 2006Co-Authors: Nicolas Leprovost, Eun Jin KimAbstract:Aims. We provide a Consistent Theory of the tachocline confinement (or anisotropic momentum transport) within a hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant value during the sun's evolution. Methods. Starting from the first principle with the physically plausible assumption that turbulence is driven externally (e.g. by plumes penetrating from the convection zone), we derive turbulent (eddy) viscosity in the radial (vertical) and azimuthal (horizontal) directions by incorporating the crucial effects of shearing due to radial and latitudinal differential rotations in the tachocline. Results. We show that the simultaneous presence of both shears effectively induces a much more efficient momentum transport in the horizontal plane than in the radial direction. In particular, in the case of strong radial turbulence (driven by overshooting plumes from the convection zone), the ratio of the radial to horizontal eddy viscosity is proportional to ${\cal A}^{-1/3}$, where ${\cal A}$ is the strength of the shear due to radial differential rotation. In comparison, in the case of horizontally driven turbulence, this ratio becomes of order $-\epsilon^2$, with negative radial eddy viscosity. Here, ϵ ($\ll 1$) is the ratio of the radial to latitudinal shear. The resulting anisotropy in momentum transport could thus be strong enough to operate as a mechanism for the tachocline confinement against spreading.
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Self-Consistent Theory of turbulent transport in the solar tachocline. II. Tachocline confinement
Astronomy and Astrophysics - A&A, 2006Co-Authors: Nicolas Leprovost, Eun Jin KimAbstract:We provide a Consistent Theory of the tachocline confinement (or anisotropic momentum transport) within an hydrodynamical turbulence model. The goal is to explain helioseismological data, which show that the solar tachocline thickness is at most 5\% of the solar radius, despite the fact that, due to radiative spreading, this transition layer should have thickened to a much more significant value during the sun's evolution. Starting from the first principle with the physically plausible assumption that turbulence is driven externally (e.g. by plumes penetrating from the convection zone), we derive turbulent (eddy) viscosity in the radial (vertical) and azimuthal (horizontal) directions by incorporating the crucial effects of shearing due to radial and latitudinal differential rotations in the tachocline. We show that the simultaneous presence of both shears induces effectively a much more efficient momentum transport in the horizontal plane than in the radial direction. In particular, in the case of strong radial turbulence (driven by overshooting plumes from the convection zone), the ratio of the radial to horizontal eddy viscosity is proportional to ${\cal A}^{-1/3}$, where ${\cal A}$ is the strength of the shear due to radial differential rotation. In comparison, in the case of horizontally driven turbulence, this ratio becomes of order $-\epsilon^2$, with negative radial eddy viscosity. Here, $\epsilon$ ($\ll 1$) is the ratio of the radial to latitudinal shear. The resulting anisotropy in momentum transport could thus be sufficiently strong to operate as a mechanism for the tachocline confinement against spreading.
E. E. Saperstein - One of the best experts on this subject based on the ideXlab platform.
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Self-Consistent Theory of finite Fermi systems and Skyrme–Hartree–Fock method
Physics of Atomic Nuclei, 2016Co-Authors: E. E. Saperstein, S. V. TolokonnikovAbstract:Recent results obtained on the basis of the self-Consistent Theory of finite Fermi systems by employing the energy density functional proposed by Fayans and his coauthors are surveyed. These results are compared with the predictions of Skyrme–Hartree–Fock Theory involving several popular versions of the Skyrme energy density functional. Spherical nuclei are predominantly considered. The charge radii of even and odd nuclei and features of low-lying 2+ excitations in semimagic nuclei are discussed briefly. The single-particle energies ofmagic nuclei are examined inmore detail with allowance for corrections to mean-field Theory that are induced by particle coupling to low-lying collective surface excitations (phonons). The importance of taking into account, in this problem, nonpole (tadpole) diagrams, which are usually disregarded, is emphasized. The spectroscopic factors of magic and semimagic nuclei are also considered. In this problem, only the surface term stemming from the energy dependence induced in the mass operator by the exchange of surface phonons is usually taken into account. The volume contribution associated with the energy dependence initially present in the mass operator within the self-Consistent Theory of finite Fermi systems because of the exchange of high-lying particle–hole excitations is also included in the spectroscopic factor. The results of the first studies that employed the Fayans energy density functional for deformed nuclei are also presented.
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Spectroscopic factors of magic and semimagic nuclei within the self-Consistent Theory of finite Fermi systems
EPL (Europhysics Letters), 2014Co-Authors: N. V. Gnezdilov, E. E. Saperstein, S. V. TolokonnikovAbstract:A scheme is presented to find single-particle spectroscopic factors (SF) of magic and semimagic nuclei within the self-Consistent Theory of finite Fermi systems (TFFS). In addition to the energy dependence of the mass operator Σ induced by the surface-phonon coupling effects which are commonly considered in this problem, the in-volume energy dependence of the operator Σ inherent in the self-Consistent TFFS is also taken into account. This dependence arises due to the effect of high-lying particle-hole excitations and persists in nuclear matter. The self-Consistent basis of the energy density functional method by Fayans et al. is used. Both the surface and in-volume contributions to the SFs turned out to be of comparable magnitude. The results for magic 40,48Ca and 208Pb nuclei and semimagic lead isotopes are presented.
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Quadrupole moments of spherical semi-magic nuclei within the self-Consistent Theory of Finite Fermi Systems
The European Physical Journal A, 2012Co-Authors: S. V. Tolokonnikov, Sergei Kamerdzhiev, D. Voitenkov, S. Krewald, E. E. SapersteinAbstract:The quadrupole moments of odd neighbors of semi-magic lead and tin isotopes and $N=50,N=82$ isotones are calculated within the self-Consistent Theory of Finite Fermi Systems based on the Energy Density Functional by Fayans et al. Two sets of parameters, DF3 and DF3-a, fixed previously are used. They differ by the spin-orbit and effective tensor force parameters, the latter being significantly bigger in the DF3-a functional. Results for the two functionals turned out to be rather different. The functional DF3-a leads to quadrupole moments in reasonable agreement with the experimental ones for most nuclei examined.
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Self-Consistent Theory of finite Fermi systems and radii of nuclei
Physics of Atomic Nuclei, 2011Co-Authors: E. E. Saperstein, S. V. TolokonnikovAbstract:Present-day self-Consistent approaches in nuclear Theory were analyzed from the point of view of describing distributions of nuclear densities. The generalized method of the energy density functional due to Fayans and his coauthors (this is the most successful version of the self-Consistent Theory of finite Fermi systems) was the first among the approaches under comparison. The second was the most successful version of the Skyrme-Hartree-Fock method with the HFB-17 functional due to Goriely and his coauthors. Charge radii of spherical nuclei were analyzed in detail. Several isotopic chains of deformed nuclei were also considered. Charge-density distributions ρch(r) were calculated for several spherical nuclei. They were compared with model-independent data extracted from an analysis of elastic electron scattering on nuclei.
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Self-Consistent Theory of temperature effects in superfluid nuclei
Physics of Atomic Nuclei, 1994Co-Authors: M. V. Zverev, E. E. SapersteinAbstract:A self-Consistent Theory of finite Fermi systems is developed for superfluid nuclei at nonzero temperatures. Calculations are carried out for a chain of even Sn isotopes. The temperature dependence of the energy gap {Delta}(T) turns out to be similar to the square-root behavior known from the BCS Theory. The critical temperature {Tc} at which pairing disappears varies from one nucleus to another because of a change in the level structure near the Fermi surface. However, the relation between {Tc} and {Delta}(0) proves to be close to that predicted by the BCS Theory: {Tc} = 0.57{Delta}(0). The self-Consistent Theory confirms the main result, in which calculations were performed in the approximation of a fixed nuclear mean field: the size of a superfluid nucleus decreases with temperature. 13 refs., 6 figs., 3 tabs.
Ivar Martin - One of the best experts on this subject based on the ideXlab platform.
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Self-Consistent Theory of molecular switching
Physical Review B: Condensed Matter and Materials Physics (1998-2015), 2008Co-Authors: Fabio Pistolesi, Yaroslav Blanter, Ivar MartinAbstract:We study the model of a molecular switch comprised of a molecule with a soft vibrational degree of freedom coupled to metallic leads. In the presence of strong electron-ion interaction, different charge states of the molecule correspond to substantially different ionic configurations, which can lead to very slow switching between energetically close configurations (Franck-Condon blockade). Application of transport voltage, however, can drive the molecule far out of thermal equilibrium and thus dramatically accelerate the switching. The tunneling electrons play the role of a heat bath with an effective temperature dependent on the applied transport voltage. Including the transport-induced ``heating" selfConsistently, we determine the stationary current-voltage characteristics of the device, and the switching dynamics for symmetric and asymmetric devices. We also study the effects of an extra dissipative environment and demonstrate that it can lead to enhanced non-linearities in the transport properties of the device and dramatically suppress the switching dynamics.
Victor Galitski - One of the best experts on this subject based on the ideXlab platform.
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Self-Consistent Theory of ferromagnetism on the surface of a topological insulator
Physical Review B, 2014Co-Authors: Dmitry K. Efimkin, Victor GalitskiAbstract:The Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between magnetic impurities, mediated by Dirac surface states on the surface of a topological insulator, leads to impurities ferromagnetic ordering. We present a self-Consistent Theory of the ordering, which takes into account a gap in the surface spectrum induced by the exchange field of magnetic impurities. We show that the gap does not change the general structure of RKKY interaction but considerable influences its strength. This feedback can be both positive and negative, depending on the ratio between the chemical potential and the gap, and it qualitatively modifies the temperature dependence of the spin polarization of magnetic impurities. The resulting unusual temperature dependence can be directly measured in angle resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM) experiments.
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a self Consistent Theory for graphene transport
Proceedings of the National Academy of Sciences of the United States of America, 2007Co-Authors: Shaffique Adam, Victor Galitski, Euyheon Hwang, Das S SarmaAbstract:We demonstrate theoretically that most of the observed transport properties of graphene sheets at zero magnetic field can be explained by scattering from charged impurities. We find that, contrary to common perception, these properties are not universal but depend on the concentration of charged impurities nimp. For dirty samples (250 × 1010 cm−2 < nimp < 400 × 1010 cm−2), the value of the minimum conductivity at low carrier density is indeed 4e2/h in agreement with early experiments, with weak dependence on impurity concentration. For cleaner samples, we predict that the minimum conductivity depends strongly on nimp, increasing to 8e2/h for nimp ≈ 20 × 1010 cm−2. A clear strategy to improve graphene mobility is to eliminate charged impurities or use a substrate with a larger dielectric constant.