44,180 research outputs found
A model for the phase separation controlled by doping and the internal chemical pressure in different cuprate superconductors
In the framework of a two-band model, we study the phase separation regime of
different kinds of strongly correlated charge carriers as a function of the
energy splitting between the two sets of bands. The narrow (wide) band
simulates the more localized (more delocalized) type of charge carriers. By
assuming that the internal chemical pressure on the CuO layer due to
interlayer mismatch controls the energy splitting between the two sets of
states, the theoretical predictions are able to reproduce the regime of phase
separation at doping higher than 1/8 in the experimental pressure-doping-
phase diagram of cuprates at large microstrain as it appears in overoxygenated
LaCuO.Comment: 8 pages, 5 figures, submitted to Phys. Rev.
Fuzzy audio similarity measures based on spectrum histograms and fluctuation patterns
Spectrum histograms and fluctuation patterns are representations of audio fragments. By comparing these representations, we can determine the similarity between the corresponding fragments. Traditionally, this is done using the Euclidian distance. We propose fuzzy similarity measures as an alternative. First we introduce some well-known fuzzy similarity measures, together with certain properties that can be desirable or useful in practice. In particular we present several forms of restrictability, which allow to reduce the computation time in practical applications. Next, we show that fuzzy similarity measures can be used to compare spectrum histograms and fluctuation patterns. Finally, we describe some experimental observations for this fuzzy approach of constructing audio similarity measures
Symmetric Diblock Copolymers in Thin Films (I): Phase stability in Self-Consistent Field Calculations and Monte Carlo Simulations
We investigate the phase behavior of symmetric AB diblock copolymers confined
into a thin film. The film boundaries are parallel, impenetrable and attract
the A component of the diblock copolymer. Using a self-consistent field
technique [M.W. Matsen, J.Chem.Phys. {\bf 106}, 7781 (1997)], we study the
ordered phases as a function of incompatibility and film thickness in
the framework of the Gaussian chain model. For large film thickness and small
incompatibility, we find first order transitions between phases with different
number of lamellae which are parallel oriented to the film boundaries. At high
incompatibility or small film thickness, transitions between parallel oriented
and perpendicular oriented lamellae occur. We compare the self-consistent field
calculations to Monte Carlo simulations of the bond fluctuation model for chain
length N=32. In the simulations we quench several systems from to
and monitor the morphology into which the diblock copolymers
assemble. Three film thicknesses are investigated, corresponding to parallel
oriented lamellae with 2 and 4 interfaces and a perpendicular oriented
morphology. Good agreement between self-consistent field calculations and Monte
Carlo simulations is found.Comment: to appear in J.Chem.Phy
Evidence for complex order parameter in La_{1.83}Sr_{0.17}CuO_4
The in-plane magnetic field penetration depth (\lambda_{ab}) in
single-crystal La_{1.83}Sr_{0.17}CuO_4 was investigated by means of the
muon-spin rotation (\muSR) technique. The temperature dependence of
\lambda^{-2}_{ab} has an inflection point around 10-15K, suggesting the
presence of two superconducting gaps: a large gap (\Delta_1^d) with d-wave and
a small gap (\Delta_2^s) with s-wave symmetry. The zero-temperature values of
the gaps at \mu_0H=0.02T were found to be \Delta_1^d(0)=8.2(2)meV and
\Delta_2^s(0)=1.57(8)meV.Comment: 5 pages, 3 figure
--Oscillations for Correlated Electron Pairs in Disordered Mesoscopic Rings
The full spectrum of two interacting electrons in a disordered mesoscopic
one--dimensional ring threaded by a magnetic flux is calculated numerically.
For ring sizes far exceeding the one--particle localization length we
find several --periodic states whose eigenfunctions exhibit a pairing
effect. This represents the first direct observation of interaction--assisted
coherent pair propagation, the pair being delocalized on the scale of the whole
ring.Comment: 4 pages, uuencoded PostScript, containing 5 figures
Exclusive electroproduction revisited: treating kinematical effects
Generalized parton distributions of the nucleon are accessed via exclusive
leptoproduction of the real photon. While earlier analytical considerations of
phenomenological observables were restricted to twist-three accuracy, i.e.,
taking into account only terms suppressed by a single power of the hard scale,
in the present study we revisit this differential cross section within the
helicity formalism and restore power-suppressed effects stemming from the
process kinematics exactly. We restrict ourselves to the phenomenologically
important case of lepton scattering off a longitudinally polarized nucleon,
where the photon flips its helicity at most by one unit.Comment: 22 pages, 1 figur
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