654 research outputs found
Fano-type interpretation of red shifts and red tails in hole array transmission spectra
We present a unifying point of view which allows to understand spectral
features reported in recent experiments with two-dimensional arrays of
subwavelength holes in metal films. We develop a Fano analysis of the related
scattering problem by distinguishing two interfering contributions to the
transmission process, namely a non-resonant contribution (direct scattering)
and a resonant contribution (surface plasmon excitation). The introduction of a
coupling strength between these two contributions naturally induces resonance
shifts and asymmetry of profiles which satisfy simple scaling relations. We
also report an experiment to confirm this analysis.Comment: 5 page
Density profile of a strictly two-dimensional Bose gas at finite temperature
We study a Bose-condensed gas at finite temperature, in which the particles
of the condensate and of the thermal cloud are constrained to move in a plane
under radial harmonic confinement and interact via strictly two-dimensional
collisions. The coupling parameters are obtained from a calculation of the
many-body T-matrix and decreases as temperature increases through a dependence
on the chemical potential and on the occupancy of excited states. We discuss
the consequences on the condensate fraction and on the density profiles of the
condensed and thermal components as functions of temperature, within a
simplified form of the two-fluid model.Comment: 12 pages, 4 figure
Relativistic Kinetics of Phonon Gas in Superfluids
The relativistic kinetic theory of the phonon gas in superfluids is
developed. The technique of the derivation of macroscopic balance equations
from microscopic equations of motion for individual particles is applied to an
ensemble of quasi-particles. The necessary expressions are constructed in terms
of a Hamilton function of a (quasi-)particle. A phonon contribution into
superfluid dynamic parameters is obtained from energy-momentum balance
equations for the phonon gas together with the conservation law for superfluids
as a whole. Relations between dynamic flows being in agreement with results of
relativistic hydrodynamic consideration are found. Based on the kinetic
approach a problem of relativistic variation of the speed of sound under phonon
influence at low temperature is solved.Comment: 23 pages, Revtex fil
Feshbach resonance in a strictly two-dimensional atomic Bose gas
We discuss the atom-atom scattering problem across a Feshbach resonance in a
two-dimensional dilute Bose gas at zero temperature, in the limit where the
s-wave scattering length exceeds the width of the vertical confinement. We
determine a tunable coupling-strength parameter and by controlling it we
evaluate how the condensate wave function spreads out with increasing atom-atom
repulsions. We also discuss the stability of the condensate in the
magnetic-field regime where the coupling has become attractive.Comment: 9 pages, 1 figur
Quantum Phase Transitions and Conserved Charges
The constraints on the scaling properties of conserved charge densities in
the vicinity of a zero temperature (), second-order quantum phase transition
are studied. We introduce a generalized Wilson ratio, characterizing the
non-linear response to an external field, , coupling to any conserved
charge, and argue that it is a completely universal function of : this is
illustrated by computations on model systems. We also note implications for
transitions where the order parameter is a conserved charge (as in a
ferromagnet-paramagnet transition).Comment: 19 pages, REVTEX 3.0, 8 uuencoded Postscript figues appended,
YCTP-xxx
Tkachenko waves, glitches and precession in neutron star
Here I discuss possible relations between free precession of neutron stars,
Tkachenko waves inside them and glitches. I note that the proposed precession
period of the isolated neutron star RX J0720.4-3125 (Haberl et al. 2006) is
consistent with the period of Tkachenko waves for the spin period 8.4s. Based
on a possible observation of a glitch in RX J0720.4-3125 (van Kerkwijk et al.
2007), I propose a simple model, in which long period precession is powered by
Tkachenko waves generated by a glitch. The period of free precession,
determined by a NS oblateness, should be equal to the standing Tkachenko wave
period for effective energy transfer from the standing wave to the precession
motion. A similar scenario can be applicable also in the case of the PSR
B1828-11.Comment: 6 pages, no figures, accepted to Ap&S
K Meson Production in the Proton-Proton Reaction at 3.67 GeV/c
The total cross section of the reaction has been determined
for proton--proton reactions with . This represents the
first cross section measurement of the channel near
threshold, and is equivalent to the inclusive cross section at
this beam momentum. The cross section determined at this beam momentum is about
a factor 20 lower than that for inclusive meson production at
the same CM energy above the corresponding threshold. This large difference in
the and meson inclusive production cross sections in proton-proton
reactions is in strong contrast to cross sections measured in sub-threshold
heavy ion collisions, which are similar in magnitude at the same energy per
nucleon below the respective thresholds.Comment: 12 pages, 3 figures Phys. Lett. B in prin
Production of Mesons in the Reaction at 3.67 GeV/c
The ratio of the total exclusive production cross sections for
and mesons has been measured in the reaction at
GeV/c. The observed ratio is
from which the exclusive
meson production cross section is determined to be
. Differential cross section
distributions have been measured. Their shape is consistent with isotropic
meson production.Comment: 14 pages, 5 figures, accepted by Phys.Lett.
Contribution to fusion research from IAEA coordinated research projects and joint experiments
- …