20,282 research outputs found
The Development of the Forbush Decrease and the Geomagnetic Storm Fields
Relationships between Forbush decreases and associated geomagnetic storm characteristic
Finite-Temperature and -Density QED: Schwinger-Dyson Equation in the Real-Time Formalism
Based on the real-time formalism, especially, on Thermo Field Dynamics, we
derive the Schwinger-Dyson gap equation for the fermion propagator in QED and
Four-Fermion model at finite-temperature and -density. We discuss some
advantage of the real-time formalism in solving the self-consistent gap
equation, in comparison with the ordinary imaginary-time formalism. Once we
specify the vertex function, we can write down the SD equation with only
continuous variables without performing the discrete sum over Matsubara
frequencies which cannot be performed in advance without further approximation
in the imaginary-time formalism. By solving the SD equation obtained in this
way, we find the chiral-symmetry restoring transition at finite-temperature and
present the associated phase diagram of strong coupling QED.
In solving the SD equation, we consider two approximations:
instantaneous-exchange and -independent ones. The former has a direct
correspondence in the imaginary time formalism, while the latter is a new
approximation beyond the former, since the latter is able to incorporate new
thermal effects which has been overlooked in the ordinary imaginary-time
solution. However both approximations are shown to give qualitatively the same
results on the finite-temperature phase transition.Comment: 28 pages+15 figures (figures: not included, available upon request
The structure of the solar plasma flow generated by solar flares
Geomagnetic storm characteristics for two-dimensional configuration of solar plasma flow generated by solar flare
Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot
A numerical renormalization-group study of the conductance through a quantum
wire side-coupled to a quantum dot is reported. The temperature and the
dot-energy dependence of the conductance are examined in the light of a
recently derived linear mapping between the Kondo-regime temperature-dependent
conductance and the universal function describing the conductance for the
symmetric Anderson model of a quantum wire with an embedded quantum dot. Two
conduction paths, one traversing the wire, the other a bypass through the
quantum dot, are identified. A gate potential applied to the quantum wire is
shown to control the flow through the bypass. When the potential favors
transport through the wire, the conductance in the Kondo regime rises from
nearly zero at low temperatures to nearly ballistic at high temperatures. When
it favors the dot, the pattern is reversed: the conductance decays from nearly
ballistic to nearly zero. When the fluxes through the two paths are comparable,
the conductance is nearly temperature-independent in the Kondo regime, and a
Fano antiresonance in the fixed-temperature plot of the conductance as a
function of the dot energy signals interference. Throughout the Kondo regime
and, at low temperatures, even in the mixed-valence regime, the numerical data
are in excellent agreement with the universal mapping.Comment: 12 pages, with 9 figures. Submitted to PR
Doping evolution of the electronic specific heat coefficient in slightly-doped La2-xSrxCuO4 single crystals
Detailed doping dependence of the electronic specific heat coefficient gamma
is studied for La2-xSrxCuO4 (LSCO) single crystals in the slightly-doped
regime. We find that gamma systematically increases with doping, and
furthermore, even for the samples in the antiferromagnetic (AF) regime, gamma
already acquires finite value and grows with x. This suggests that finite
electronic density of states (DOS) is created in the AF regime where the
transport shows strong localization at low temperatures, and this means the
system is not a real insulator with a clear gap even though it still keeps long
range AF order.Comment: 4 pages, 4 figures, accepted for publication in Journal of Physics:
Conference Series (LT25 proceeding
Comparison of Entropy Production Rates in Two Different Types of Self-organized Flows: B\'{e}nard Convection and Zonal flow
Entropy production rate (EPR) is often effective to describe how a structure
is self-organized in a nonequilibrium thermodynamic system. The "minimum EPR
principle" is widely applicable to characterizing self-organized structures,
but is sometimes disproved by observations of "maximum EPR states." Here we
delineate a dual relation between the minimum and maximum principles; the
mathematical representation of the duality is given by a Legendre
transformation. For explicit formulation, we consider heat transport in the
boundary layer of fusion plasma [Phys. Plasmas {\bf 15}, 032307 (2008)]. The
mechanism of bifurcation and hysteresis (which are the determining
characteristics of the so-called H-mode, a self-organized state of reduced
thermal conduction) is explained by multiple tangent lines to a pleated graph
of an appropriate thermodynamic potential. In the nonlinear regime, we have to
generalize Onsager's dissipation function. The generalized function is no
longer equivalent to EPR; then EPR ceases to be the determinant of the
operating point, and may take either minimum or maximum values depending on how
the system is driven
Spin-charge-lattice coupling near the metal-insulator transition in Ca3Ru2O7
We report x-ray scattering studies of the c-axis lattice parameter in
Ca3Ru2O7 as a function of temperature and magnetic field. These structural
studies complement published transport and magnetization data, and therefore
elucidate the spin-charge-lattice coupling near the metal-insulator transition.
Strong anisotropy of the structural change for field applied along orthogonal
in-plane directions is observed. Competition between a spin-polarized phase
that does not couple to the lattice, and an antiferromagnetic metallic phase,
which does, gives rise to rich behavior for B b.Comment: 6 pages, 4 figures, to appear in Phys. Rev.
Thermal dependence of the zero-bias conductance through a nanostructure
We show that the conductance of a quantum wire side-coupled to a quantum dot,
with a gate potential favoring the formation of a dot magnetic moment, is a
universal function of the temperature. Universality prevails even if the
currents through the dot and the wire interfere. We apply this result to the
experimental data of Sato et al.[Phys. Rev. Lett. 95, 066801 (2005)].Comment: 6 pages, 3 figures. More detailed presentation, and updated
references. Final version
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