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Effect of the boundary condition on the vortex patterns in mesoscopic three-dimensional superconductors - disk and sphere
The vortex state of mesoscopic three-dimensional superconductors is
determined using a minimization procedure of the Ginzburg-Landau free energy.
We obtain the vortex pattern for a mesoscopic superconducting sphere and find
that vortex lines are naturally bent and are closest to each other at the
equatorial plane. For a superconducting disk with finite height, and under an
applied magnetic field perpendicular to its major surface, we find that our
method gives results consistent with previous calculations. The matching
fields, the magnetization and , are obtained for models that differ
according to their boundary properties. A change of the Ginzburg-Landau
parameters near the surface can substantially enhance as shown here.Comment: 7 pages, 4 figures (low resolution
The Average Kinetic Energy of the Superconducting State
Isothermal magnetization curves are plotted as the magnetization times the
magnetic induction, , versus the applied field, H. We show
here that this new curve is the average kinetic energy of the superconducting
state versus the applied field, for type-II superconductors with a high
Ginzburg-Landau parameter . The maximum of occurs at
a field, , directly related to the upper critical field, ,
suggesting that may be extracted from such plots even in cases when
it is too high for direct measurement. We obtain these plots both
theoretically, from the Ginzburg-Landau theory, and experimentally, using a
Niobium sample with , and compare them.Comment: 11 pages, 9 postscript figure
Little-Parks oscillations near a persistent current loop
We investigate the Little-Parks oscillations caused by a persistent current
loop set on the top edge of a mesoscopic superconducting thin-walled cylinder
with a finite height. For a short cylinder the Little-Parks oscillations are
approximately the same ones as the standard effect, as there is only one
magnetic flux piercing the cylinder. For a tall cylinder the inhomogeneity of
the magnetic field makes different magnetic fluxes pierce the cylinder at
distinct heights and we show here that this produces two distinct Little-Parks
oscillatory regimes according to the persistent current loop. We show that
these two regimes, and also the transition between them, are observable in
current measurements done in the superconducting cylinder. The two regimes stem
from different behavior along the height, as seen in the order parameter,
numerically obtained from the Ginzburg-Landau theory through the finite element
methodComment: 13 pages, 12 figure
Vortex Lines or Vortex-Line Chains at the Lower Critical Field in Anisotropic Superconductors?
The vortex state at the lower critical field, H_{c1}, in clean anisotropic
superconductors placed in an external field tilted with respect to the axis of
anisotropy (c-axis) is considered assuming two possible arrangements: dilute
vortex-lines or dilute vortex-line chains. By minimizing the Gibbs free
energies in the London limit for each possibility we obtain the corresponding
lower critical fields as a function of the tilt angle. The equilibrium
configuration at H_{c1} for a given tilt angle is identified with that for
which H_{c1} is the smallest. We report results for parameter values typical of
strong and moderate anisotropy. We find that for strong anisotropy vortex-line
chains are favored for small tilt angles (< 7.9^o) and that at 7.9^o there is
coexistence between this configuration and a vortex-line one. For moderate
anisotropy we find that there is little difference between the vortex-line and
the vortex-chain lower critical fields.Comment: 5 pages, 4 figures, accepted to appear on Physica
Implications of Screen Use in Young Children\u27s Occupations
Introduction:
OTs need to address both the duration and quality of screen media children use, to promote their development and participation in healthy occupations
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