36,875 research outputs found
Instanton Approach to Josephson Tunneling between Trapped Condensates
An instanton method is proposed to investigate the quantum tunneling between
two weakly-linked Bose-Einstein condensates confined in double-well potential
traps. We point out some intrinsic pathologies in the earlier treatments of
other authors and make an effort to go beyond these very simple zero order
models. The tunneling amplitude may be calculated in the Thomas-Fermi
approximation and beyond it; we find it depends on the number of the trapped
atoms, through the chemical potential. Some suggestions are given for the
observation of the Josephson oscillation and the MQST.Comment: 20 pages, Revtex4, 6 figures. Abbreviated version accepted by Eur.
Phys. J
Testing Lorentz invariance by use of vacuum and matter filled cavity resonators
We consider tests of Lorentz invariance for the photon and fermion sector
that use vacuum and matter-filled cavities. Assumptions on the wave-function of
the electrons in crystals are eliminated from the underlying theory and
accurate sensitivity coefficients (including some exceptionally large ones) are
calculated for various materials. We derive the Lorentz-violating shift in the
index of refraction n, which leads to additional sensitivity for matter-filled
cavities ; and to birefringence in initially isotropic media. Using published
experimental data, we obtain improved bounds on Lorentz violation for photons
and electrons at levels of 10^-15 and below. We discuss implications for future
experiments and propose a new Michelson-Morley type experiment based on
birefringence in matter.Comment: 15 pages, 8 table
“Though this be madness, yet there is method in’t.” A counterfactual analysis of Richard Wagner’s Tannhäuser
Much like Wagner himself, the eponymous hero of Tannhäuser treads a path of stark contrasts and
rapid swings. From Wartburg to the Venusberg and to the Vatican, the gifted bard transforms from
self-centered artist to seduced disciple, disillusioned devotee, hopeful lover, self-loathing pilgrim and
finally redeemed martyr. He tries everything and everything is trying. These contrasts reach a peak in
the opera‟s central episode, the song contest at Wartburg. Tannhäuser has just been welcomed at the
court, received Elisabeth‟s favor and affection, and is ready to compete for the contest‟s prize, one as
lofty as possibly the princess‟ hand. Instead of securing his reintegration to Wartburg with a brilliant
performance, however, he spoils the event with insolent remarks and the exhibitionist disclosure of
his Venusberg experience. His behavior offends his peers, scandalizes the court, breaks Elisabeth‟s
heart, and brings him to the edge of death. Why would Tannhäuser sacrifice everything for nothing
Faraday waves on a viscoelastic liquid
We investigate Faraday waves on a viscoelastic liquid. Onset measurements and
a nonlinear phase diagram for the selected patterns are presented. By virtue of
the elasticity of the material a surface resonance synchronous to the external
drive competes with the usual subharmonic Faraday instability. Close to the
bicriticality the nonlinear wave interaction gives rise to a variety of novel
surface states: Localised patches of hexagons, hexagonal superlattices,
coexistence of hexagons and lines. Theoretical stability calculations and
qualitative resonance arguments support the experimental observations.Comment: 4 pages, 4figure
Once again: Instanton method vs. WKB
A recent analytic test of the instanton method performed by comparing the
exact spectrum of the Lam potential (derived from representations
of a finite dimensional matrix expressed in terms of generators) with
the results of the tight--binding and instanton approximations as well as the
standard WKB approximation is commented upon. It is pointed out that in the
case of the Lam potential as well as others the WKB--related method
of matched asymptotic expansions yields the exact instanton result as a result
of boundary conditions imposed on wave functions which are matched in domains
of overlap.Comment: 10 pages, no figures. References list revised according to JHE
Lagrangian Statistics of Navier-Stokes- and MHD-Turbulence
We report on a comparison of high-resolution numerical simulations of
Lagrangian particles advected by incompressible turbulent hydro- and
magnetohydrodynamic (MHD) flows. Numerical simulations were performed with up
to collocation points and 10 million particles in the Navier-Stokes
case and collocation points and 1 million particles in the MHD case. In
the hydrodynamics case our findings compare with recent experiments from
Mordant et al. [1] and Xu et al. [2]. They differ from the simulations of
Biferale et al. [3] due to differences of the ranges choosen for evaluating the
structure functions. In Navier-Stokes turbulence intermittency is stronger than
predicted by a multifractal approach of [3] whereas in MHD turbulence the
predictions from the multifractal approach are more intermittent than observed
in our simulations. In addition, our simulations reveal that Lagrangian
Navier-Stokes turbulence is more intermittent than MHD turbulence, whereas the
situation is reversed in the Eulerian case. Those findings can not consistently
be described by the multifractal modeling. The crucial point is that the
geometry of the dissipative structures have different implications for
Lagrangian and Eulerian intermittency. Application of the multifractal approach
for the modeling of the acceleration PDFs works well for the Navier-Stokes case
but in the MHD case just the tails are well described.Comment: to appear in J. Plasma Phy
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