1,791 research outputs found
Experimental investigations of the radio wave attenuation processes through the paths leaving buildings
Digital binary phase-shift keyed signal detector
We have developed the effective algorithm for detecting digital binary phase-shift keyed signals. This algorithm requires a small number of arithmetic operations over the signal period. It can be relatively easy implemented based on the modern programmable logic devices. It also provides high interference immunity by identifying signal presence when signal-to-noise ratio is much less that its working value in the receiving path. The introduced detector has intrinsic frequency selectivity and allows us to form the estimate of the noise level to realize the adaptive determination of decision threshold. In order to get confirmation of the detector operability and performance, we suggest the expressions for false alarm and missing probabilities. In addition, we have examine, both theoretically and experimentally, the influence of the detector parameters on its characteristics
Digital demodulator of the quadrature amplitude modulation signals
In this paper, the digital algorithm and the device for the demodulation of the quadrature amplitude modulation signals are considered. The fundamental advantages of our approach are simple hardware implementation, minimal number of arithmetic operations required over the signal period as well as the potential interference immunity in the presence of Gaussian noise. The expressions have been found for the error probability and their inaccuracy has been estimated. By means of the statistical simulation methods, the practical interference immunity of the introduced demodulator, together with the influence of phase locking errors have been tested. The introduced demodulator can be implemented either as a device independent from the programmable logic devices, or as an installation unit of the receiver equipment
Effect of the Tunneling Conductance on the Coulomb Staircase
Quantum fluctuations of the charge in the single electron box are
investigated. The rounding of the Coulomb staircase caused by virtual electron
tunneling is determined by perturbation theory up to third order in the
tunneling conductance and compared with precise Monte Carlo data computed with
a new algorithm. The remarkable agreement for large conductance indicates that
presently available experimental data on Coulomb charging effects in metallic
nanostructures can be well explained by finite order perturbative results.Comment: 4 pages, 5 figure
Supersymmetry approach to nuclear-spin-polarization-induced quantum dot structure calculations
In nuclear-spin-polarization-induced quantum dots the electrons are confined
through local nuclear spin polarization. The model electron confinement
potential is time-dependent due to the nuclear spin diffusion and relaxation
processes. It can be well-approximated by a Gaussian curve which is not an
exactly solvable potential. We demonstrate that it can also be approximated by
multisoliton potentials for the zero value of the angular momentum and by their
singular analogues for other values of momentum without any loss of
calculational accuracy. We obtain these potentials by supersymmetric (or
equivalently Darboux) transformations from the zero potential. The main
advantage of such potentials is that they are exactly solvable. Time-dependence
of the nuclear-spin-polarization-induced quantum dot energy levels is found.Comment: Physica E (in press) (2005
Darboux transformations of coherent states of the time-dependent singular oscillator
Darboux transformation of both Barut-Girardello and Perelomov coherent states
for the time-dependent singular oscillator is studied. In both cases the
measure that realizes the resolution of the identity operator in terms of
coherent states is found and corresponding holomorphic representation is
constructed. For the particular case of a free particle moving with a fixed
value of the angular momentum equal to two it is shown that Barut-Giriardello
coherent states are more localized at the initial time moment while the
Perelomov coherent states are more stable with respect to time evolution. It is
also illustrated that Darboux transformation may keep unchanged this different
time behavior.Comment: 13 page
Feshbach projection-operator formalism to resonance scattering on Bargmann-type potentials
The projection-operator formalism of Feshbach is applied to resonance
scattering in a single-channel case. The method is based on the division of the
full function space into two segments, internal (localized) and external
(infinitely extended). The spectroscopic information on the resonances is
obtained from the non-Hermitian effective Hamilton operator
appearing in the internal part due to the coupling to the external part. As
well known, additional so-called cut-off poles of the -matrix appear,
generally, due to the truncation of the potential. We study the question of
spurious matrix poles in the framework of the Feshbach formalism. The
numerical analysis is performed for exactly solvable potentials with a finite
number of resonance states. These potentials represent a generalization of
Bargmann-type potentials to accept resonance states. Our calculations
demonstrate that the poles of the matrix obtained by using the Feshbach
projection-operator formalism coincide with both the complex energies of the
physical resonances and the cut-off poles of the -matrix.Comment: 12 pages, 9 figure
Dilepton production in proton-proton collisions at BEVALAC energies
The dilepton production in elementary reactions at
BEVALAC energies GeV is investigated. The calculations
include direct decays of the vector mesons , , and , Dalitz decays of the -, -, -, -, and -mesons, and of the baryon resonances
. The subthreshold vector meson production cross sections in
collisions are treated in a way sufficient to avoid double counting with the
inclusive vector meson production. The vector meson dominance model for the
transition form factors of the resonance Dalitz decays is
used in an extended form to ensure correct asymptotics which are in agreement
with the quark counting rules. Such a modification gives an unified and
consistent description of both radiative decays and meson decays.
The effect of multiple pion production on the experimental efficiency for the
detection of the dilepton pairs is studied. We find the dilepton yield in
reasonable agreement with the experimental data for the set of intermediate
energies whereas at the highest energy GeV the number of
dilepton pairs is likely to be overestimated experimentally in the mass range
MeV.Comment: 25 pages (IOP style), 5 figures, revised manuscript accepted for
publication in JP
Nonlocal supersymmetric deformations of periodic potentials
Irreducible second-order Darboux transformations are applied to the periodic
Schrodinger's operators. It is shown that for the pairs of factorization
energies inside of the same forbidden band they can create new non-singular
potentials with periodicity defects and bound states embedded into the spectral
gaps. The method is applied to the Lame and periodic piece-wise transparent
potentials. An interesting phenomenon of translational Darboux invariance
reveals nonlocal aspects of the supersymmetric deformations.Comment: 15 pages, latex, 9 postscript figure
- …