960 research outputs found
Classical-quantum correspondence in bosonic two-mode conversion systems: polynomial algebras and Kummer shapes
Bosonic quantum conversion systems can be modeled by many-particle
single-mode Hamiltonians describing a conversion of molecules of type A
into molecules of type B and vice versa. These Hamiltonians are analyzed in
terms of generators of a polynomially deformed algebra. In the
mean-field limit of large particle numbers, these systems become classical and
their Hamiltonian dynamics can again be described by polynomial deformations of
a Lie algebra, where quantum commutators are replaced by Poisson brackets. The
Casimir operator restricts the motion to Kummer shapes, deformed Bloch spheres
with cusp singularities depending on and . It is demonstrated that the
many-particle eigenvalues can be recovered from the mean-field dynamics using a
WKB type quantization condition. The many-particle state densities can be
semiclassically approximated by the time-periods of periodic orbits, which show
characteristic steps and singularities related to the fixed points, whose
bifurcation properties are analyzed.Comment: 13 pages, 13 figure
Tooth shell technique: A proof of concept with the use of autogenous dentin block grafts
Background
Autogenous bone block graft is considered the gold standard for lateral bony defects. Dentin has been identified to be a suitable autogenous bone graft material due to its structural and chemical similarities to the alveolar bone.
Methods
This proof of concept study describes the clinical application of the tooth shell technique in 24 sites with 27 implants of 22 patients. A tooth shell was fixed laterally to the defect with microscrews. Distance between the shell and the residual bone was filled with particulate remnants of the tooth root. Implant was inserted simultaneously. Cone beam computed tomography was done after implant insertion (T1) and 3 months later at time of implant exposure (T2). Target parameters were biological complications and the resorption of hard tissue graft.
Results
Even though a graft exposure occurred in one case (4.5% on patient-level), all implants showed enough implant stability and were able to be loaded. At T2, the evaluation of the X-rays showed no case with hard tissue loss at the mesial or distal implant shoulder. All implants were completely osseointegrated.
Conclusions
The tooth shell technique showed promising results for the reconstruction of lateral alveolar crest defects. It may be considered to serve as an alternative material to avoid bone harvesting procedures
Quasiclassical analysis of Bloch oscillations in non-Hermitian tight-binding lattices
Many features of Bloch oscillations in one-dimensional quantum lattices with
a static force can be described by quasiclassical considerations for example by
means of the acceleration theorem, at least for Hermitian systems. Here the
quasiclassical approach is extended to non-Hermitian lattices, which are of
increasing interest. The analysis is based on a generalised non-Hermitian phase
space dynamics developed recently. Applications to a single-band tight-binding
system demonstrate that many features of the quantum dynamics can be understood
from this classical description qualitatively and even quantitatively. Two
non-Hermitian and -symmetric examples are studied, a Hatano-Nelson lattice
with real coupling constants and a system with purely imaginary couplings, both
for initially localised states in space or in momentum. It is shown that the
time-evolution of the norm of the wave packet and the expectation values of
position and momentum can be described in a classical picture.Comment: 20 pages, 8 figures, typos corrected, slightly extended, accepted for
publication in New Journal of Physics in Focus Issue on Parity-Time Symmetry
in Optics and Photonic
Wannier-Stark resonances in optical and semiconductor superlattices
In this work, we discuss the resonance states of a quantum particle in a
periodic potential plus a static force. Originally this problem was formulated
for a crystal electron subject to a static electric field and it is nowadays
known as the Wannier-Stark problem. We describe a novel approach to the
Wannier-Stark problem developed in recent years. This approach allows to
compute the complex energy spectrum of a Wannier-Stark system as the poles of a
rigorously constructed scattering matrix and solves the Wannier-Stark problem
without any approximation. The suggested method is very efficient from the
numerical point of view and has proven to be a powerful analytic tool for
Wannier-Stark resonances appearing in different physical systems such as
optical lattices or semiconductor superlattices.Comment: 94 pages, 41 figures, typos corrected, references adde
Resonance solutions of the nonlinear Schr\"odinger equation in an open double-well potential
The resonance states and the decay dynamics of the nonlinear Schr\"odinger
(or Gross-Pitaevskii) equation are studied for a simple, however flexible model
system, the double delta-shell potential. This model allows analytical
solutions and provides insight into the influence of the nonlinearity on the
decay dynamics. The bifurcation scenario of the resonance states is discussed,
as well as their dynamical stability properties. A discrete approximation using
a biorthogonal basis is suggested which allows an accurate description even for
only two basis states in terms of a nonlinear, nonhermitian matrix problem.Comment: 21 pages, 14 figure
Bose-Einstein condensates in accelerated double-periodic optical lattices: Coupling and Crossing of resonances
We study the properties of coupled linear and nonlinear resonances. The
fundamental phenomena and the level crossing scenarios are introduced for a
nonlinear two-level system with one decaying state, describing the dynamics of
a Bose-Einstein condensate in a mean-field approximation (Gross-Pitaevskii or
nonlinear Schroedinger equation). An important application of the discussed
concepts is the dynamics of a condensate in tilted optical lattices. In
particular the properties of resonance eigenstates in double-periodic lattices
are discussed, in the linear case as well as within mean-field theory. The
decay is strongly altered, if an additional period-doubled lattice is
introduced. Our analytic study is supported by numerical computations of
nonlinear resonance states, and future applications of our findings for
experiments with ultracold atoms are discussed.Comment: 12 pages, 17 figure
A Sensitive Faraday Rotation Setup Using Triple Modulation
The utilization of polarized targets in scattering experiments has become a
common practice in many major accelerator laboratories. Noble gases are
especially suitable for such applications, since they can be easily
hyper-polarized using spin exchange or metastable pumping techniques. Polarized
helium-3 is a very popular target because it often serves as an effective
polarized neutron due to its simple nuclear structure. A favorite cell material
to generate and store polarized helium-3 is GE-180, a relatively dense
aluminosilicate glass. In this paper, we present a Faraday rotation method,
using a new triple modulation technique, where the measurement of the Verdet
constants of SF57 flint glass, pyrex glass, and air were tested. The
sensitivity obtained shows that this technique may be implemented in future
cell wall characterization and thickness measurements. We also discuss the
first ever extraction of the Verdet constant of GE-180 glass for four
wavelength values of 632 nm, 773 nm, 1500 nm, and 1547 nm, whereupon the
expected 1/{\lambda}^{2} dependence was observed.Comment: 4 pages, 2 figures Updated version for RSI submissio
Barrier transmission for the Nonlinear Schr\"odinger Equation: Surprises of nonlinear transport
In this communication we report on a peculiar property of barrier
transmission that systems governed by the nonlinear Schroedinger equation share
with the linear one: For unit transmission the potential can be divided at an
arbitrary point into two sub-potentials, a left and a right one, which have
exactly the same transmission. This is a rare case of an exact property of a
nonlinear wave function which will be of interest, e.g., for studies of
coherent transport of Bose-Einstein condensates through mesoscopic waveguideComment: 7 pages, 2 figure
Computing quantum eigenvalues made easy
An extremely simple and convenient method is presented for computing eigenvalues in quantum mechanics by representing position and momentum operators in a simple matrix form. The simplicity and success of the method is illustrated by numerical results concerning eigenvalues of bound systems and resonances for hermitian and non-hermitian Hamiltonians as well as driven quantum systems
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