1,934 research outputs found
Concatenated Space Time Block Codes and TCM, Turbo TCM Convolutional as well as Turbo Codes
Space-time block codes provide substantial diversity advantages for multiple transmit antenna systems at a low decoding complexity. In this paper, we concatenate space-time codes with Convolutional Codes (CC), Turbo Convolutional codes (TC), Turbo BCH codes (TBCH), Trellis Coded Modulation (TCM) and Turbo Trellis Coded Modulation (TTCM) schemes for achieving a high coding gain. The associated performance and complexity of the coding schemes is compared
Coulomb Gaps in One-Dimensional Spin-Polarized Electron Systems
We investigate the density of states (DOS) near the Fermi energy of
one-dimensional spin-polarized electron systems in the quantum regime where the
localization length is comparable to or larger than the inter-particle
distance. The Wigner lattice gap of such a system, in the presence of weak
disorder, can occur precisely at the Fermi energy, coinciding with the Coulomb
gap in position. The interplay between the two is investigated by treating the
long-range Coulomb interaction and the random disorder potential in a
self-consistent Hartree-Fock approximation. The DOS near the Fermi energy is
found to be well described by a power law whose exponent decreases with
increasing disorder strength.Comment: 4 pages, revtex, 4 figures, to be published in Phys. Rev. B as a
Rapid Communicatio
Topological Gauge Theory Of General Weitzenbock Manifolds Of Dislocations In Crystals
General Weitzenbock material manifolds of dislocations in crystals Are
proposed, the reference, idealized and deformation states of the bodies in
general case are generally described by the general manifolds, the topological
gauge field theory of dislocations is given in general case,true distributions
and evolution of dislocations in crystals are given by the formulas describing
dislocations in terms of the general manifolds,furthermore, their properties
are discussed.Comment: 10pages, Revte
A QCD Sum Rule Approach to the Contribution to the Radiative Decay
QCD sum rules are used to calculate the contribution of short-distance
single-quark transition , to the amplitudes of the
hyperon radiative decay, . We re-evaluate the
Wilson coefficient of the effective operator responsible for this transition.
We obtain a branching ratio which is comparable to the unitarity limit.Comment: 15 pages, Revtex, 13 figures available as a uuencoded, gz-compressed
ps fil
An observation of spin-valve effects in a semiconductor field effect transistor: a novel spintronic device
We present the first spintronic semiconductor field effect transistor.
The injector and collector contacts of this device were made from magnetic
permalloy thin films with different coercive fields so that they could be
magnetized either parallel or antiparallel to each other in different applied
magnetic fields. The conducting medium was a two dimensional electron gas
(2DEG) formed in an AlSb/InAs quantum well.
Data from this device suggest that its resistance is controlled by two
different types of spin-valve effect: the first occurring at the
ferromagnet-2DEG interfaces; and the second occuring in direct propagation
between contacts.Comment: 4 pages, 2 figure
Chiral Baryon Fields in the QCD Sum Rule
We study the structure of local baryon fields using the method of QCD sum
rule. We only consider the single baryon fields and calculate their operator
product expansions. We find that the octet baryon fields belonging to the
chiral representations [(3,3*)+(3*,3)] and [(8,1)+(1,8)] and the decuplet
baryon fields belonging to the chiral representations [(3,6)+(6,3)] lead to the
baryon masses which are consistent with the experimental data of ground baryon
masses. We also calculate their decay constants, check our normalizations for
baryon fields in PRD81:054002(2010) and find that they are well-defined.Comment: 12 pages, 6 figure, 1 table, accepted by EPJ
Dephasing of Electrons in Mesoscopic Metal Wires
We have extracted the phase coherence time of electronic
quasiparticles from the low field magnetoresistance of weakly disordered wires
made of silver, copper and gold. In samples fabricated using our purest silver
and gold sources, increases as when the temperature
is reduced, as predicted by the theory of electron-electron interactions in
diffusive wires. In contrast, samples made of a silver source material of
lesser purity or of copper exhibit an apparent saturation of
starting between 0.1 and 1 K down to our base temperature of 40 mK. By
implanting manganese impurities in silver wires, we show that even a minute
concentration of magnetic impurities having a small Kondo temperature can lead
to a quasi saturation of over a broad temperature range, while
the resistance increase expected from the Kondo effect remains hidden by a
large background. We also measured the conductance of Aharonov-Bohm rings
fabricated using a very pure copper source and found that the amplitude of the
conductance oscillations increases strongly with magnetic field. This set
of experiments suggests that the frequently observed ``saturation'' of
in weakly disordered metallic thin films can be attributed to
spin-flip scattering from extremely dilute magnetic impurities, at a level
undetectable by other means.Comment: 16 pages, 11 figures, to be published in Physical Review
Effects of Wind Field Inhomogeneities on Doppler Beam Swinging Revealed by an Imaging Radar
In this work, the accuracy of the Doppler beam-swinging (DBS) technique for wind measurements is studied using an imaging radarâthe turbulent eddy profiler (TEP) developed by the University of Mas- sachusetts, with data collected in summer 2003. With up to 64 independent receivers, and using coherent radar imaging (CRI), several hundred partially independent beams can be formed simultaneously within the volume defined by the transmit beam. By selecting a subset of these beams, an unprecedented number of DBS configurations with varying zenith angle, azimuth angle, and number of beams can be investigated. The angular distributions of echo power and radial velocity obtained by CRI provide a unique opportunity to validate the inherent assumption in the DBS method of homogeneity across the region defined by the beam directions. Through comparison with a reference wind field, calculated as the optimal uniform wind field derived from all CRI beams with sufficient signal-to-noise ratio (SNR), the accuracy of the wind estimates for various DBS configurations is statistically analyzed. It is shown that for a three-beam DBS configura- tion, although the validity of the homogeneity assumption is enhanced at smaller zenith angles, the root- mean-square (RMS) error increases because of the ill-conditioned matrix in the DBS algorithm. As ex- pected, inhomogeneities in the wind field produce large bias for the three-beam DBS configuration for large zenith angles. An optimal zenith angle, in terms of RMS error, of approximately 9°â10° was estimated. It is further shown that RMS error can be significantly reduced by increasing the number of off-vertical beams used for the DBS processing
Deformed Oscillator Algebras and Higher-Spin Gauge Interactions of Matter Fields in 2+1 Dimensions
We formulate a non-linear system of equations which describe higher-spin
gauge interactions of massive matter fields in 2+1 dimensional space-time and
explain some properties of the deformed oscillator algebra which underlies this
formulation. In particular we show that the parameter of mass of matter
fields is related to the deformation parameter in this algebra.Comment: LaTex, 12 pages, no figures; Invited talk at the International
Seminar Supersymmetry and Quantum Field Theory dedicated to the memory of
Dmitrij V. Volkov; Kharkov, January 1997; to appear in the proceeding
Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions
We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, , and temperature, , is determined by the
scaling variable (where is the exponent for the temperature
dependence of the inelastic scattering rate) and not by , as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, , and the thermal exponent, ,
in terms of the scaling dimension, , of the interaction strength
and the dynamical exponent (which has the value ), obtaining
and .Comment: 9 pages, 4 figures, submitted to Physical Review
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