49,387 research outputs found
Critical state analysis of orthogonal flux interactions in pinned superconductors
We show that, based on the critical state model for flux-line pinning in hard
superconductors, one can assess the magnetic moment relaxation induced by the
oscillations of a perpendicular magnetic field. Our theory follows a recent
proposal of using phenomenological 2D modeling for the description of crossed
field dynamics in high-T superconductors [{\tt arXiv:cond-mat/0703330}].
Stationary regimes with either saturation to metastable configurations, or
complete decay to the thermodynamic equilibrium are obtained. The transition
between both types of response is related to the disappearance of a flux free
core within the sample. As a common feature, a step-like dependence in the time
relaxation is predicted for both cases. The theory may be applied to long bars
of arbitrary and non homogeneous cross section, under in-plane magnetic field
processes.Comment: 11 figures, submitte
Two-dimensional Einstein manifolds in geometrothermodynamics
We present a class of thermodynamic systems with constant thermodynamic
curvature which, within the context of geometric approaches of thermodynamics,
can be interpreted as constant thermodynamic interaction among their
components. In particular, for systems constrained by the vanishing of the
Hessian curvature we write down the systems of partial differential equations.
In such a case it is possible to find a subset of solutions lying on a
circumference in an abstract space constructed from the first derivatives of
the isothermal coordinates. We conjecture that solutions on the characteristic
circumference are of physical relevance, separating them from those of pure
mathematical interest. We present the case of a one-parameter family of
fundamental relations that -- when lying in the circumference -- describe a
polytropic fluid
A random laser tailored by directional stimulated emission
A disordered structure embedding an active gain material and able to lase is
called random laser (RL). The RL spectrum may appear either like a set of sharp
resonances or like a smooth line superimposed to the fluorescence. A recent
letter accounts for this duality with the onset of a mode locked regime in
which increasing the number of activated modes results in an increased inter
mode correlation and a pulse shortening ascribed to a synchronization
phenomenon. An extended discussion of our experimental approach together with
an original study of the spatial properties of the RL is reported here.Comment: 9 Pages; 16 Figure
Scattering approach to fidelity decay in closed systems and parametric level correlations
This paper is based on recent work which provided an exact analytical
description of scattering fidelity experiments with a microwave cavity under
the variation of an antenna coupling [K\"ober et al., Phys. Rev. E 82, 036207
(2010)]. It is shown that this description can also be used to predict the
decay of the fidelity amplitude for arbitrary Hermitian perturbations of a
closed system. Two applications are presented: First, the known result for
global perturbations is re-derived, and second, the exact analytical expression
for the perturbation due to a moving S-wave scatterer is worked out. The latter
is compared to measured data from microwave experiments, which have been
reported some time ago. Finally, we generalize an important relation between
fidelity decay and parametric level correlations to arbitrary perturbations.Comment: 20 pages, 2 figures, research article, (v2: stylistic changes, ref.
added
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