11,726 research outputs found
Nesting symmetries and diffusion in disordered d-wave superconductors
The low-energy density of states (DOS) of disordered 2D d-wave
superconductors is extremely sensitive to details of both the disorder model
and the electronic band structure. Using diagrammatic methods and numerical
solutions of the Bogoliubov-de Gennes equations, we show that the physical
origin of this sensitivity is the existence of a novel diffusive mode with
momentum close to which is gapless only in systems with a global
nesting symmetry. We find that in generic situations, the DOS vanishes at the
Fermi level. However, proximity to the highly symmetric case may nevertheless
lead to observable non-monotonic behavior of the DOS in the cuprates
Validation of a physically-based solid oxide fuel cell anode model combining 3D tomography and impedance spectroscopy
This study presents a physically-based model for the simulation of impedance spectra in solid oxide fuel cell (SOFC) composite anodes. The model takes into account the charge transport and the charge-transfer reaction at the three-phase boundary distributed along the anode thickness, as well as the phenomena at the electrode/electrolyte interface and the multicomponent gas diffusion in the test rig. The model is calibrated with experimental impedance spectra of cermet anodes made of nickel and scandia-stabilized zirconia and satisfactorily validated in electrodes with different microstructural properties, quantified through focused ion beam SEM tomography. Besides providing the material-specific kinetic parameters of the electrochemical hydrogen oxidation, this study shows that the correlation between electrode microstructure and electrochemical performance can be successfully addressed by combining physically-based modelling, impedance spectroscopy and 3D tomography. This approach overcomes the limits of phenomenological equivalent circuits and is suitable for the interpretation of experimental data and for the optimisation of the electrode microstructure
On the Bethe Ansatz for the Jaynes-Cummings-Gaudin model
We investigate the quantum Jaynes-Cummings model - a particular case of the
Gaudin model with one of the spins being infinite. Starting from the Bethe
equations we derive Baxter's equation and from it a closed set of equations for
the eigenvalues of the commuting Hamiltonians. A scalar product in the
separated variables representation is found for which the commuting
Hamiltonians are Hermitian. In the semi classical limit the Bethe roots
accumulate on very specific curves in the complex plane. We give the equation
of these curves. They build up a system of cuts modeling the spectral curve as
a two sheeted cover of the complex plane. Finally, we extend some of these
results to the XXX Heisenberg spin chain.Comment: 16 page
Joint Probabilities Reproducing Three EPR Experiments On Two Qubits
An eight parameter family of the most general nonnegative quadruple
probabilities is constructed for EPR-Bohm-Aharonov experiments when only 3
pairs of analyser settings are used. It is a simultaneous representation of 3
Bohr-incompatible experimental configurations valid for arbitrary quantum
states.Comment: Typo corrected in abstrac
Test anxiety, working memory, and cognitive performance: Supportive effects of sequential demands
Substantial evidence suggests that test anxiety is associated with poor performance in complex tasks. Based on the differentiation of coordinative and sequential demands on working memory (Mayr & Kliegl, 1993), two studies examined the effects of sequential demands on the relationship between test anxiety and cognitive performance. Both studies found that high sequential demands had beneficial effects on the speed and accuracy of the performance of test-anxious participants. It is suggested that the more frequent memory updates associated with high sequential demands may represent external processing aids that compensate for the restricted memory capacity of individuals with high test anxiet
Antimatter, Lorentz Symmetry, and Gravity
A brief introduction to the Standard-Model Extension (SME) approach to
testing CPT and Lorentz symmetry is provided. Recent proposals for tests with
antimatter are summarized, including gravitational and spectroscopic tests.Comment: Presented at the 12th International Conference on Low Energy
Antiproton Physics, Kanazawa Japan, March 6-11, 2016, Accepted for
publication in JPS Conference Proceeding
Fast atom diffraction inside a molecular beam epitaxy chamber, a rich combination
Two aspects of the contribution of grazing incidence fast atom diffraction
(GIFAD) to molecular beam epitaxy (MBE) are reviewed here: the ability of GIFAD
to provide \emph{in-situ} a precise description of the atomic-scale surface
topology, and its ability to follow larger-scale changes in surface roughness
during layer-by-layer growth. Recent experimental and theoretical results
obtained for the He atom beam incident along the highly corrugated direction of the (24) reconstructed GaAs(001) surface are
summarized and complemented by the measurements and calculations for the beam
incidence along the weakly corrugated [010] direction where a periodicity twice
smaller as expected is observed. The combination of the experiment, quantum
scattering matrix calculations, and semiclassical analysis allows in this case
to reveal structural characteristics of the surface. For the in situ
measurements of GIFAD during molecular beam epitaxy of GaAs on GaAs surface we
analyse the change in elastic and inelastic contributions in the scattered
beam, and the variation of the diffraction pattern in polar angle scattering.
This analysis outlines the robustness, the simplicity and the richness of the
GIFAD as a technique to monitor the layer-by-layer epitaxial growth
Inhomogeneous Magnetic-Field Response of YBa2Cu3Oy and La2-xSrxCuO4 Persisting above the Bulk Superconducting Transition Temperature
We report that in YBa2Cu3Oy and La2-xSrxCuO4 there is a spatially
inhomogeneous response to magnetic field for temperatures T extending well
above the bulk superconducting transition temperature Tc. An inhomogeneous
magnetic response is observed above Tc even in ortho-II YBa2Cu3O6.50, which has
highly ordered doping. The degree of the field inhomogeneity above Tc tracks
the hole doping dependences of both Tc and the density of the superconducting
carriers below Tc, and therefore is apparently coupled to superconductivity.Comment: Modified discussio
Linear quadrilateral lattice equations and multidimensional consistency
It is shown that every scalar linear quadrilateral lattice equation lies
within a family of similar equations, members of which are compatible between
one another on a higher dimensional lattice. There turn out to be two such
families, a natural parametrisation is given for each.Comment: 7 pages, 1 figur
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