6,218 research outputs found
Scaling behavior of a one-dimensional correlated disordered electronic System
A one-dimensional diagonal tight binding electronic system with correlated
disorder is investigated. The correlation of the random potential is
exponentially decaying with distance and its correlation length diverges as the
concentration of "wrong sign" approaches to 1 or 0. The correlated random
number sequence can be generated easily with a binary sequence similar to that
of a one-dimensional spin glass system. The localization length (LL) and the
integrated density of states (IDOS) for long chains are computed. A comparison
with numerical results is made with the recently developed scaling technique
results. The Coherent Potential Approximation (CPA) is also adopted to obtain
scaling functions for both the LL and the IDOS. We confirmed that the scaling
functions show a crossover near the band edge and establish their relation to
the concentration. For concentrations near to 0 or 1 (longer correlation length
case), the scaling behavior is followed only for a very limited range of the
potential strengths.Comment: will appear in PR
Selective enhancement of topologically induced interface states in a dielectric resonator chain
The recent realization of topological phases in insulators and
superconductors has advanced the quest for robust quantum technologies. The
prospects to implement the underlying topological features controllably has
given incentive to explore optical platforms for analogous realizations. Here
we realize a topologically induced defect state in a chain of dielectric
microwave resonators and show that the functionality of the system can be
enhanced by supplementing topological protection with non-hermitian symmetries
that do not have an electronic counterpart. We draw on a characteristic
topological feature of the defect state, namely, that it breaks a sublattice
symmetry. This isolates the state from losses that respect parity-time
symmetry, which enhances its visibility relative to all other states both in
the frequency and in the time domain. This mode selection mechanism naturally
carries over to a wide range of topological and parity-time symmetric optical
platforms, including couplers, rectifiers and lasers.Comment: 5 pages, 4 figures, + supplementary information (3 pages, 4 figures
Waveguide photonic limiters based on topologically protected resonant modes
We propose a concept of chiral photonic limiters utilising topologically
protected localised midgap defect states in a photonic waveguide. The chiral
symmetry alleviates the effects of structural imperfections and guaranties a
high level of resonant transmission for low intensity radiation. At high
intensity, the light-induced absorption can suppress the localised modes, along
with the resonant transmission. In this case the entire photonic structure
becomes highly reflective within a broad frequency range, thus increasing
dramatically the damage threshold of the limiter. Here we demonstrate
experimentally the principle of operation of such photonic structures using a
waveguide consisting of coupled dielectric microwave resonators.Comment: 6 pages, 4 figure
Experimental observation of the mobility edge in a waveguide with correlated disorder
The tight-binding model with correlated disorder introduced by Izrailev and
Krokhin [PRL 82, 4062 (1999)] has been extended to the Kronig-Penney model. The
results of the calculations have been compared with microwave transmission
spectra through a single-mode waveguide with inserted correlated scatterers.
All predicted bands and mobility edges have been found in the experiment, thus
demonstrating that any wanted combination of transparent and non-transparent
frequency intervals can be realized experimentally by introducing appropriate
correlations between scatterers.Comment: RevTex, 4 pages including 4 Postscript figure
Enhancement of localization in one-dimensional random potentials with long-range correlations
We experimentally study the effect of enhancement of localization in weak
one-dimensional random potentials. Our experimental setup is a single mode
waveguide with 100 tuneable scatterers periodically inserted into the
waveguide. By measuring the amplitudes of transmitted and reflected waves in
the spacing between each pair of scatterers, we observe a strong decrease of
the localization length when white-noise scatterers are replaced by a
correlated arrangement of scatterers.Comment: 4 pages, 6 figure
Computational Modeling of Hip Replacement Surgery: Total Hip Replacement vs. Hip Resurfacing
The motivation of the present work is the computational simulation of hip replacement surgery by means of a finite element approach based on open system thermodynamics. Its key feature is a non-constant material density, which is allowed to adapt with respect to changes in the mechanical loading environment. From a computational point of view, the density is treated as an internal variable. Its evolution is governed by a first order rate equation, the balance of mass, which is enhanced by an additional mass production term to account for growth. An implicit Euler backward scheme is suggested for its time discretization. The algorithmic determination of the material density based on a local Newton iteration is presented. To ensure quadratic convergence of the global Newton Raphson solution scheme, a consistent linearization of the discrete algorithmic equations is carried out. Finally, two alternative medical techniques in hip arthritis are compared, the conventional total hip replacement strategy and the more recent hip resurfacing technology. The result of the suggested remodeling algorithm is shown to agree remarkably well with clinically observed phenomena
Statistics of the electromagnetic response of a chaotic reverberation chamber
This article presents a study of the electromagnetic response of a chaotic
reverberation chamber (RC) in the presence of losses. By means of simulations
and of experiments, the fluctuations in the maxima of the field obtained in a
conventional mode-stirred RC are compared with those in a chaotic RC in the
neighborhood of the Lowest Useable Frequency (LUF). The present work
illustrates that the universal spectral and spatial statistical properties of
chaotic RCs allow to meet more adequately the criteria required by the Standard
IEC 61000-4-21 to perform tests of electromagnetic compatibility.Comment: 6 pages, 9 figure
Schematic baryon models, their tight binding description and their microwave realization
A schematic model for baryon excitations is presented in terms of a symmetric
Dirac gyroscope, a relativistic model solvable in closed form, that reduces to
a rotor in the non-relativistic limit. The model is then mapped on a nearest
neighbour tight binding model. In its simplest one-dimensional form this model
yields a finite equidistant spectrum. This is experimentally implemented as a
chain of dielectric resonators under conditions where their coupling is
evanescent and good agreement with the prediction is achieved.Comment: 17 pages, 15 figure
First experimental realization of the Dirac oscillator
We present the first experimental microwave realization of the
one-dimensional Dirac oscillator, a paradigm in exactly solvable relativistic
systems. The experiment relies on a relation of the Dirac oscillator to a
corresponding tight-binding system. This tight-binding system is implemented as
a microwave system by a chain of coupled dielectric disks, where the coupling
is evanescent and can be adjusted appropriately. The resonances of the finite
microwave system yields the spectrum of the one-dimensional Dirac oscillator
with and without mass term. The flexibility of the experimental set-up allows
the implementation of other one-dimensional Dirac type equations.Comment: 6 figures, 5 page
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