27,575 research outputs found
Hard Thermal Loops in the n-Dimensional phi3 Theory
We derive a closed-form result for the leading thermal contributions which
appear in the n-dimensional phi3 theory at high temperature. These
contributions become local only in the long wavelength and in the static
limits, being given by different expressions in these two limits.Comment: 3 pages, one figure. To be published in the Brazilian Journal of
Physic
Analytic Solution for the Critical State in Superconducting Elliptic Films
A thin superconductor platelet with elliptic shape in a perpendicular
magnetic field is considered. Using a method originally applied to circular
disks, we obtain an approximate analytic solution for the two-dimensional
critical state of this ellipse. In the limits of the circular disk and the long
strip this solution is exact, i.e. the current density is constant in the
region penetrated by flux. For ellipses with arbitrary axis ratio the obtained
current density is constant to typically 0.001, and the magnetic moment
deviates by less than 0.001 from the exact value. This analytic solution is
thus very accurate. In increasing applied magnetic field, the penetrating flux
fronts are approximately concentric ellipses whose axis ratio b/a < 1 decreases
and shrinks to zero when the flux front reaches the center, the long axis
staying finite in the fully penetrated state. Analytic expressions for these
axes, the sheet current, the magnetic moment, and the perpendicular magnetic
field are presented and discussed. This solution applies also to
superconductors with anisotropic critical current if the anisotropy has a
particular, rather realistic form.Comment: Revtex file and 13 postscript figures, gives 10 pages of text with
figures built i
Latitudinal properties of the solar wind from studies of ionic comet tails
A statistical analysis is presented of the orientations of ionic comet tails in the solar wind. The analysis indicates that the radial solar wind speed is not necessarily higher near the solar poles than near the equator. The results refer to a long-term, global flow pattern and do not refer to short-term variations of solar wind speed
Review: Observations of recent comets, ion tails
Photographic plates of the moving structures in the cometary tail are examined. Several divergent explanations for the case of comet Kohoutek are presented. It is suggested that these hypotheses be tested by observing the motion of the material spectroscopically by means of the Doppler effect
Theory of Type-II Superconductors with Finite London Penetration Depth
Previous continuum theory of type-II superconductors of various shapes with
and without vortex pinning in an applied magnetic field and with transport
current, is generalized to account for a finite London penetration depth
lambda. This extension is particularly important at low inductions B, where the
transition to the Meissner state is now described correctly, and for films with
thickness comparable to or smaller than lambda. The finite width of the surface
layer with screening currents and the correct dc and ac responses in various
geometries follow naturally from an equation of motion for the current density
in which the integral kernel now accounts for finite lambda. New geometries
considered here are thick and thin strips with applied current, and `washers',
i.e. thin film squares with a slot and central hole as used for SQUIDs.Comment: 14 pages, including 15 high-resolution figure
On the Free Energy of Noncommutative Quantum Electrodynamics at High Temperature
We compute higher order contributions to the free energy of noncommutative
quantum electrodynamics at a nonzero temperature . Our calculation includes
up to three-loop contributions (fourth order in the coupling constant ). In
the high temperature limit we sum all the {\it ring diagrams} and obtain a
result which has a peculiar dependence on the coupling constant. For large
values of ( is the magnitude of the noncommutative
parameters) this non-perturbative contribution exhibits a non-analytic behavior
proportional to . We show that above a certain critical temperature, there
occurs a thermodynamic instability which may indicate a phase transition.Comment: 28 pages, 37 figures. Matches published version in Nuclear Physics
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