2,444 research outputs found
Semiclassical Transition from an Elliptical to an Oval Billiard
Semiclassical approximations often involve the use of stationary phase
approximations. This method can be applied when is small in comparison
to relevant actions or action differences in the corresponding classical
system. In many situations, however, action differences can be arbitrarily
small and then uniform approximations are more appropriate. In the present
paper we examine different uniform approximations for describing the spectra of
integrable systems and systems with mixed phase space. This is done on the
example of two billiard systems, an elliptical billiard and a deformation of
it, an oval billiard. We derive a trace formula for the ellipse which involves
a uniform approximation for the Maslov phases near the separatrix, and a
uniform approximation for tori of periodic orbits close to a bifurcation. We
then examine how the trace formula is modified when the ellipse is deformed
into an oval. This involves uniform approximations for the break-up of tori and
uniform approximations for bifurcations of periodic orbits. Relations between
different uniform approximations are discussed.Comment: LaTeX, 33 pages including 10 PostScript figures, submitted to J.
Phys.
Leading off-diagonal approximation for the spectral form factor for uniformly hyperbolic systems
We consider the semiclassical approximation to the spectral form factor
K(tau) for two-dimensional uniformly hyperbolic systems, and derive the first
off-diagonal correction for small tau. The result agrees with the tau^2-term of
the form factor for the GOE random matrix ensemble.Comment: 8 pages, 3 figure
The semiclassical relation between open trajectories and periodic orbits for the Wigner time delay
The Wigner time delay of a classically chaotic quantum system can be
expressed semiclassically either in terms of pairs of scattering trajectories
that enter and leave the system or in terms of the periodic orbits trapped
inside the system. We show how these two pictures are related on the
semiclassical level. We start from the semiclassical formula with the
scattering trajectories and derive from it all terms in the periodic orbit
formula for the time delay. The main ingredient in this calculation is a new
type of correlation between scattering trajectories which is due to
trajectories that approach the trapped periodic orbits closely. The equivalence
between the two pictures is also demonstrated by considering correlation
functions of the time delay. A corresponding calculation for the conductance
gives no periodic orbit contributions in leading order.Comment: 21 pages, 5 figure
Trace formula for a dielectric microdisk with a point scatterer
Two-dimensional dielectric microcavities are of widespread use in microoptics
applications. Recently, a trace formula has been established for dielectric
cavities which relates their resonance spectrum to the periodic rays inside the
cavity. In the present paper we extend this trace formula to a dielectric disk
with a small scatterer. This system has been introduced for microlaser
applications, because it has long-lived resonances with strongly directional
far field. We show that its resonance spectrum contains signatures not only of
periodic rays, but also of diffractive rays that occur in Keller's geometrical
theory of diffraction. We compare our results with those for a closed cavity
with Dirichlet boundary conditions.Comment: 39 pages, 18 figures, pdflate
Semiclassical Theory of Chaotic Quantum Transport
We present a refined semiclassical approach to the Landauer conductance and
Kubo conductivity of clean chaotic mesoscopic systems. We demonstrate for
systems with uniformly hyperbolic dynamics that including off-diagonal
contributions to double sums over classical paths gives a weak-localization
correction in quantitative agreement with results from random matrix theory. We
further discuss the magnetic field dependence. This semiclassical treatment
accounts for current conservation.Comment: 4 pages, 1 figur
Single chain dimers of MASH-1 bind DNA with enhanced affinity
By designing recombinant genes containing tandem copies of the coding region of the BHLH domain of MASH-1 (MASH-BHLH) with intervening DNA sequences encoding linker sequences of 8 or 17 amino acids, the two subunits of the MASH dimer have been connected to form the single chain dimers MM8 and MM17. Despite the long and flexible linkers which connect the C-terminus of the first BHLH subunit to the N-terminus of the second, a distance of ∼55 Å, the single chain dimers could be produced in Escherichia coli at high levels. MM8 and MM17 were monomeric and no ‘cross-folding' of the subunits was observed. CD spectroscopy revealed that, like wild-type MASH-BHLH, MM8 and MM17 adopt only partly folded structures in the absence of DNA, but undergo a folding transition to a mainly α-helical conformation on DNA binding. Titrations by electrophoretic mobility shift assays revealed that the affinity of the single chain dimers for E box-containing DNA sequences was increased ∼10-fold when compared with wild-type MASH-BHLH. On the other hand, the affinity for heterologous DNA sequences was increased only 5-fold. Therefore, the introduction of the peptide linker led to a 4-fold increase in DNA binding specificity from −0.14 to −0.57 kcal/mo
Particle creation and annihilation at interior boundaries:One-dimensional models
We describe creation and annihilation of particles at external sources in one
spatial dimension in terms of interior-boundary conditions (IBCs). We derive
explicit solutions for spectra, (generalised) eigenfunctions, as well as Green
functions, spectral determinants, and integrated spectral densities. Moreover,
we introduce a quantum graph version of IBC-Hamiltonians.Comment: 32 page
Semiclassical universality of parametric spectral correlations
We consider quantum systems with a chaotic classical limit that depend on an
external parameter, and study correlations between the spectra at different
parameter values. In particular, we consider the parametric spectral form
factor which depends on a scaled parameter difference . For
parameter variations that do not change the symmetry of the system we show by
using semiclassical periodic orbit expansions that the small expansion
of the form factor agrees with Random Matrix Theory for systems with and
without time reversal symmetry.Comment: 18 pages, no figure
Spectral statistics in chaotic systems with a point interaction
We consider quantum systems with a chaotic classical limit that are perturbed
by a point-like scatterer. The spectral form factor K(tau) for these systems is
evaluated semiclassically in terms of periodic and diffractive orbits. It is
shown for order tau^2 and tau^3 that off-diagonal contributions to the form
factor which involve diffractive orbits cancel exactly the diagonal
contributions from diffractive orbits, implying that the perturbation by the
scatterer does not change the spectral statistic. We further show that
parametric spectral statistics for these systems are universal for small
changes of the strength of the scatterer.Comment: LaTeX, 21 pages, 7 figures, small corrections, new references adde
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