3,256 research outputs found
Wavelet transforms in a critical interface model for Barkhausen noise
We discuss the application of wavelet transforms to a critical interface
model, which is known to provide a good description of Barkhausen noise in soft
ferromagnets. The two-dimensional version of the model (one-dimensional
interface) is considered, mainly in the adiabatic limit of very slow driving.
On length scales shorter than a crossover length (which grows with the strength
of surface tension), the effective interface roughness exponent is
, close to the expected value for the universality class of the
quenched Edwards-Wilkinson model. We find that the waiting times between
avalanches are fully uncorrelated, as the wavelet transform of their
autocorrelations scales as white noise. Similarly, detrended size-size
correlations give a white-noise wavelet transform. Consideration of finite
driving rates, still deep within the intermittent regime, shows the wavelet
transform of correlations scaling as for intermediate frequencies.
This behavior is ascribed to intra-avalanche correlations.Comment: RevTeX, 10 pages, 9 .eps figures; Physical Review E, to be publishe
Emission spectrum of quasi-resonant laterally coupled quantum dots
We calculate the emission spectrum of neutral and charged excitons in a pair
of laterally coupled InGaAs quantum dots with nearly degenerate energy levels.
As the interdot distance decreases, a number of changes take place in the
emission spectrum which can be used as indications of molecular coupling. These
signatures ensue from the stronger tunnel-coupling of trions as compared to
that of neutral excitons.Comment: 7 pages, 7 figure
Structure of a liquid crystalline fluid around a macroparticle: Density functional theory study
The structure of a molecular liquid, in both the nematic liquid crystalline
and isotropic phases, around a cylindrical macroparticle, is studied using
density functional theory. In the nematic phase the structure of the fluid is
highly anisotropic with respect to the director, in agreement with results from
simulation and phenomenological theories. On going into the isotropic phase the
structure becomes rotationally invariant around the macroparticle with an
oriented layer at the surface.Comment: 10 pages, 6 figues. Submitted to Phys. Rev.
Direct measurements of the penetration depth in a superconducting film using magnetic force microscopy
We report the local measurements of the magnetic penetration depth
in a superconducting Nb film using magnetic force microscopy (MFM). We
developed a method for quantitative extraction of the penetration depth from
single-parameter simultaneous fits to the lateral and height profiles of the
MFM signal, and demonstrate that the obtained value is in excellent agreement
with that obtained from the bulk magnetization measurements.Comment: 3 pages, 4 figures, submitted to APL on 08/18/0
Bubbling the False Vacuum Away
We investigate the role of nonperturbative, bubble-like inhomogeneities on
the decay rate of false-vacuum states in two and three-dimensional scalar field
theories. The inhomogeneities are induced by setting up large-amplitude
oscillations of the field about the false vacuum as, for example, after a rapid
quench or in certain models of cosmological inflation. We show that, for a wide
range of parameters, the presence of large-amplitude bubble-like
inhomogeneities greatly accelerates the decay rate, changing it from the
well-known exponential suppression of homogeneous nucleation to a power-law
suppression. It is argued that this fast, power-law vacuum decay -- known as
resonant nucleation -- is promoted by the presence of long-lived oscillons
among the nonperturbative fluctuations about the false vacuum. A phase diagram
is obtained distinguishing three possible mechanisms for vacuum decay:
homogeneous nucleation, resonant nucleation, and cross-over. Possible
applications are briefly discussed.Comment: 13 Pages, 16 figures, revtex4, submitted to pr
Long range scattering effects on spin Hall current in -type bulk semiconductors
Employing a nonequilibrium Green's function approach, we examine the effects
of long-range hole-impurity scattering on spin-Hall current in -type bulk
semiconductors within the framework of the self-consistent Born approximation.
We find that, contrary to the null effect of short-range scattering on
spin-Hall current, long-range collisions do produce a nonvanishing contribution
to the spin-Hall current, which is independent of impurity density in the
diffusive regime and relates only to hole states near the Fermi surface. The
sign of this contribution is opposite to that of the previously predicted
disorder-independent spin-Hall current, leading to a sign change of the total
spin-Hall current as hole density varies. Furthermore, we also make clear that
the disorder-independent spin-Hall effect is a result of an interband
polarization directly induced by the dc electric field with contributions from
all hole states in the Fermi sea.Comment: 9 pages, 1 figur
The Lennard-Jones-Devonshire cell model revisited
We reanalyse the cell theory of Lennard-Jones and Devonshire and find that in
addition to the critical point originally reported for the 12-6 potential (and
widely quoted in standard textbooks), the model exhibits a further critical
point. We show that the latter is actually a more appropriate candidate for
liquid-gas criticality than the original critical point.Comment: 5 pages, 3 figures, submitted to Mol. Phy
Kramers-Kronig constrained variational analysis of optical spectra
A universal method of extraction of the complex dielectric function
from
experimentally accessible optical quantities is developed. The central idea is
that is parameterized independently at each node of a
properly chosen anchor frequency mesh, while is
dynamically coupled to by the Kramers-Kronig (KK)
transformation. This approach can be regarded as a limiting case of the
multi-oscillator fitting of spectra, when the number of oscillators is of the
order of the number of experimental points. In the case of the normal-incidence
reflectivity from a semi-infinite isotropic sample the new method gives
essentially the same result as the conventional KK transformation of
reflectivity. In contrast to the conventional approaches, the proposed
technique is applicable, without readaptation, to virtually all types of
linear-response optical measurements, or arbitrary combinations of
measurements, such as reflectivity, transmission, ellipsometry {\it etc.}, done
on different types of samples, including thin films and anisotropic crystals.Comment: 10 pages, 7 figure
Self-organized Pattern Formation in Motor-Microtubule Mixtures
We propose and study a hydrodynamic model for pattern formation in mixtures
of molecular motors and microtubules. The steady state patterns we obtain in
different regimes of parameter space include arrangements of vortices and
asters separately as well as aster-vortex mixtures and fully disordered states.
Such stable steady states are observed in experiments in vitro. The sequence of
patterns obtained in the experiments can be associated with smooth trajectories
in a non-equilibrium phase diagram for our model.Comment: 11 pages Latex file, 2 figures include
Correlated sequential tunneling through a double barrier for interacting one-dimensional electrons
The problem of resonant tunneling through a quantum dot weakly coupled to
spinless Tomonaga-Luttinger liquids has been studied. We compute the linear
conductance due to sequential tunneling processes upon employing a master
equation approach. Besides the previously used lowest-order golden rule rates
describing uncorrelated sequential tunneling (UST) processes, we systematically
include higher-order correlated sequential tunneling (CST) diagrams within the
standard Weisskopf-Wigner approximation. We provide estimates for the parameter
regions where CST effects can be important. Focusing mainly on the temperature
dependence of the peak conductance, we discuss the relation of these findings
to previous theoretical and experimental results.Comment: replaced with the published versio
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