7,686 research outputs found
Local transport in a disorder-stabilized correlated insulating phase
We report the experimental realization of a correlated insulating phase in 2D
GaAs/AlGaAs heterostructures at low electron densities in a limited window of
background disorder. This has been achieved at mesoscopic length scales, where
the insulating phase is characterized by a universal hopping transport
mechanism. Transport in this regime is determined only by the average electron
separation, independent of the topology of background disorder. We have
discussed this observation in terms of a pinned electron solid ground state,
stabilized by mutual interplay of disorder and Coulomb interaction.Comment: 4+delta pages, 4 figures, To appear in the Physical Review B (Rapid
Comm
Localisation of partial discharge sources using radio fingerprinting technique
Partial discharge (PD) is a well-known indicator of the failure of insulators in electrical plant. Operators are pushing toward lower operating cost and higher reliability and this stimulates a demand for a diagnostic system capable of accurately locating PD sources especially in ageing electricity substations. Existing techniques used for PD source localisation can be prohibitively expensive. In this paper, a cost-effective radio fingerprinting technique is proposed. This technique uses the Received Signal Strength (RSS) extracted from PD measurements gathered using RF sensors. The proposed technique models the complex spatial characteristics of the radio environment, and uses this model for accurate PD localisation. Two models were developed and compared: k-nearest neighbour and a feed-forward neural network which uses regression as a form of function approximation. The results demonstrate that the neural network produced superior performance as a result of its robustness against noise
Effect of Proximity Coupling of Chains and Planes on the Penetration Depth Anisotropy in Y_1Ba_2Cu_3O_7
We calculate the penetration depth in the , and
directions for a simple model of YBaCuO. In this model there are
two layers---representing a CuO plane and a CuO chain---per unit cell.
There is a BCS--like pairing (both wave and wave are considered)
interaction localised in the CuO planes. The CuO chains become
superconducting at temperatures lower than because of their proximity to
the planes, and there is an induced gap in the chains. Since the temperature
dependence of the penetration depth in the direction (along the chains) is
sensitive to the size of the induced gap, the difference between the shapes of
the penetration depth curves in the and directions reveals a great deal
about the nature of the condensate in the chains. We find that in our proximity
model there are always regions of the chain Fermi surface on which the induced
gap is much smaller than , so that the temperature dependence of
is always different than that of . Experimental
observations of the of the anisotropy show nearly identical temperature
dependences. The main result of our paper, then, is that a simple proximity
model in which the pairing interaction is localized to the planes, and the
planes are coherently coupled to the chains cannot account for the superfluid
on the chains.Comment: 24 Pages, Submitted to Phys. Rev.
An integrable multicomponent quad equation and its Lagrangian formulation
We present a hierarchy of discrete systems whose first members are the
lattice modified Korteweg-de Vries equation, and the lattice modified
Boussinesq equation. The N-th member in the hierarchy is an N-component system
defined on an elementary plaquette in the 2-dimensional lattice. The system is
multidimensionally consistent and a Lagrangian which respects this feature,
i.e., which has the desirable closure property, is obtained.Comment: 10 page
An efficient Fredholm method for calculation of highly excited states of billiards
A numerically efficient Fredholm formulation of the billiard problem is
presented. The standard solution in the framework of the boundary integral
method in terms of a search for roots of a secular determinant is reviewed
first. We next reformulate the singularity condition in terms of a flow in the
space of an auxiliary one-parameter family of eigenproblems and argue that the
eigenvalues and eigenfunctions are analytic functions within a certain domain.
Based on this analytic behavior we present a numerical algorithm to compute a
range of billiard eigenvalues and associated eigenvectors by only two
diagonalizations.Comment: 15 pages, 10 figures; included systematic study of accuracy with 2
new figures, movie to Fig. 4,
http://www.quantumchaos.de/Media/0703030media.av
On the precision of chiral-dispersive calculations of scattering
We calculate the combination (the Olsson sum rule)
and the scattering lengths and effective ranges , and ,
dispersively (with the Froissart--Gribov representation) using, at
low energy, the phase shifts for scattering obtained by Colangelo,
Gasser and Leutwyler (CGL) from the Roy equations and chiral perturbation
theory, plus experiment and Regge behaviour at high energy, or directly, using
the CGL parameters for s and s. We find mismatch, both among the CGL
phases themselves and with the results obtained from the pion form factor. This
reaches the level of several (2 to 5) standard deviations, and is essentially
independent of the details of the intermediate energy region ( GeV) and, in some cases, of the high energy behaviour assumed. We discuss
possible reasons for this mismatch, in particular in connection with an
alternate set of phase shifts.Comment: Version to appear in Phys. Rev. D. Graphs and sum rule added. Plain
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