16,568 research outputs found
Slow light in molecular aggregates nanofilms
We study slow light performance of molecular aggregates arranged in nanofilms
by means of coherent population oscillations (CPO). The molecular cooperative
behavior inside the aggregate enhances the delay of input signals in the GHz
range in comparison with other CPO-based devices. Moreover, the problem of
residual absorption present in CPO processes, is removed. We also propose an
optical switch between different delays by exploiting the optical bistability
of these aggregates.Comment: 4 pages, 4 figure
Evaluation of the scattering amplitude in the -channel at finite density
The scattering amplitude in the -channel is studied at
finite baryonic density in the framework of a chiral unitary approach which
successfully reproduces the meson meson phase shifts and generates the
and resonances in vacuum. We address here a new variety of mechanisms
recently suggested to modify the interaction in the medium, as well as
the role of the wave selfenergy, in addition to the wave, in the
dressing of the pion propagators.Comment: 26 pages, 17 figure
Rotating Superconductors and the London Moment: Thermodynamics versus Microscopics
Comparing various microscopic theories of rotating superconductors to the
conclusions of thermodynamic considerations, we traced their marked difference
to the question of how some thermodynamic quantities (the electrostatic and
chemical potentials) are related to more microscopic ones: The electron's the
work function, mean-field potential and Fermi energy -- certainly a question of
general import.
After the correct identification is established, the relativistic correction
for the London Moment is shown to vanish, with the obvious contribution from
the Fermi velocity being compensated by other contributions such as
electrostatics and interactions.Comment: 23 pages 4 fi
The power of low-resolution spectroscopy: On the spectral classification of planet candidates in the ground-based CoRoT follow-up
Planetary transits detected by the CoRoT mission can be mimicked by a
low-mass star in orbit around a giant star. Spectral classification helps to
identify the giant stars and also early-type stars which are often excluded
from further follow-up.
We study the potential and the limitations of low-resolution spectroscopy to
improve the photometric spectral types of CoRoT candidates. In particular, we
want to study the influence of the signal-to-noise ratio (SNR) of the target
spectrum in a quantitative way. We built an own template library and
investigate whether a template library from the literature is able to reproduce
the classifications. Including previous photometric estimates, we show how the
additional spectroscopic information improves the constraints on spectral type.
Low-resolution spectroscopy (1000) of 42 CoRoT targets covering a
wide range in SNR (1-437) and of 149 templates was obtained in 2012-2013 with
the Nasmyth spectrograph at the Tautenburg 2m telescope. Spectral types have
been derived automatically by comparing with the observed template spectra. The
classification has been repeated with the external CFLIB library.
The spectral class obtained with the external library agrees within a few
sub-classes when the target spectrum has a SNR of about 100 at least. While the
photometric spectral type can deviate by an entire spectral class, the
photometric luminosity classification is as close as a spectroscopic
classification with the external library. A low SNR of the target spectrum
limits the attainable accuracy of classification more strongly than the use of
external templates or photometry. Furthermore we found that low-resolution
reconnaissance spectroscopy ensures that good planet candidates are kept that
would otherwise be discarded based on photometric spectral type alone.Comment: accepted for publication in Astronomische Nachrichten; 12 pages, 4
figures, 7 table
An investigation on the modelling of kinetics of thermal decomposition of hazardous mercury wastes
Casimir effect in the nonequilibrium steady-state of a quantum spin chain
We present a fully microscopics-based calculation of the Casimir effect in a
nonequilibrium system, namely an energy flux driven quantum XX chain. The force
between the walls (transverse-field impurities) is calculated in a
nonequilibrium steady state which is prepared by letting the system evolve from
an initial state with the two halves of the chain prepared at equilibrium at
different temperatures. The steady state emerging in the large-time limit is
homogeneous but carries an energy flux. The Casimir force in this
nonequilibrium state is calculated analytically in the limit when the
transverse fields are small. We find that the the Casimir force range is
reduced compared to the equilibrium case, and suggest that the reason for this
is the reduction of fluctuations in the flux carrying steady state.Comment: 11 page
Nonlinear spin-polarized transport through a ferromagnetic domain wall
A domain wall separating two oppositely magnetized regions in a ferromagnetic
semiconductor exhibits, under appropriate conditions, strongly nonlinear I-V
characteristics similar to those of a p-n diode. We study these characteristics
as functions of wall width and temperature. As the width increases or the
temperature decreases, direct tunneling between the majority spin bands
decreases the effectiveness of the diode. This has important implications for
the zero-field quenched resistance of magnetic semiconductors and for the
design of a recently proposed spin transistor.Comment: 5 pages, 3 figure
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