15,969 research outputs found
Response to tilted magnetic fields in Bi2Sr2CaCu2O8 with columnar defects: Evidence for transverse Meissner effect
The transverse Meissner effect (TME) in the highly layered superconductor
Bi2Sr2CaCu2O(8+y) with columnar defects is investigated by transport
measurements. We present detailed evidence for the persistence of the
Bose-glass phase when H is tilted at an angle theta < theta_c (T) away from the
column direction: (i) the variable-range vortex hopping process for low
currents crosses over to the half-loops regime for high currents; (ii) in both
regimes near theta_c(T) the energy barriers vanish linearly with tan(theta) ;
(iii) the transition temperature is governed by T_{BG}(0) -T_{BG}(theta) sim
|tan(theta)|^{1/\nu_{\perp}} with \nu_{\perp}=1.0 +/- 0.1. Furthermore, above
the transition as theta->\theta_c+, moving kink chains consistent with a
commensurate-incommensurate transition scenario are observed. These results
thereby clearly show the existence of the TME for theta < theta_c(T).Comment: 4 pages, RevTeX, 5 EPS figure
Effect of field tilting on the vortices in irradiated Bi-2212
We report on transport measurements in a Bi-2212 single crystal with columnar
defects parallel to the c-axis. The tilt of the magnetic field away from the
direction of the tracks is studied for filling factors f=B_z/B_phi<1. Near the
Bose Glass transition temperature T_BG, the angular scaling laws are verified
and we find the field independent critical exponents nu'=1.1 and z'=5.30.
Finally, above H_perpC we evidence the signature of a smectic-A like vortex
phase. These experimental results provide support for the Bose Glass theory.Comment: 2 pages LaTeX, 2 EPS figures, uses fleqn and espcrc2 style macros.
Submitted to Proceedings of M2S-HTSC-V
Effective restoration of the U_A(1) symmetry with temperature and density
We investigate the full U(3)U(3) chiral symmetry restoration, at
finite temperature and density, on the basis of a quark model which
incorporates the most relevant properties of QCD in this context: explicit and
spontaneous breaking of chiral symmetry and axial U(1) symmetry breaking. A
specific lattice-inspired behavior of the topological susceptibility, combined
with the convergence of chiral partners, signals the onset of an effective
chiral symmetry restoration. The results suggest that the axial part of the
symmetry is restored before the possible restoration of the full
U(3)U(3) chiral symmetry can occur. This conclusion is valid in the
context of both finite temperature and density.Comment: 5 pages, 2 figures; PRD versio
Chaos and Synchronized Chaos in an Earthquake Model
We show that chaos is present in the symmetric two-block Burridge-Knopoff
model for earthquakes. This is in contrast with previous numerical studies, but
in agreement with experimental results. In this system, we have found a rich
dynamical behavior with an unusual route to chaos. In the three-block system,
we see the appearance of synchronized chaos, showing that this concept can have
potential applications in the field of seismology.Comment: To appear in Physical Review Letters (13 pages, 6 figures
Estado actual da pescaria de camarāo no Banco de Sofala
A summary of the shrimp fishery history as well as the most important recommendations for the period 1977-1990 is presented. During the last years the catch rates have decreased. Although many possible causes can be appointed, such as, weather conditions and increase of effort, there is no clear explanation for it. A relationship between catch rates in the main period of recruitment (January to March) and the level of recruitment of the same year was established. Based on this relationship, the total annual catch is predicted for the level of fishing mortality chosen. Fishing mortality is estimated as 2.28 yearˉ¹ and a gradual reduction of fishing effort is recommended until 2.17 yearˉ¹ calculated as F(sub)0.1
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