44,941 research outputs found
Blind adaptive equalizer for broadband MIMO time reversal STBC based on PDF fitting
In this paper, we propose a new blind adaptive technique used for the equalisation of space-time block coded (STBC) signals transmitted over a dispersive MIMO channel. The proposed approach is based on minimising the difference between the probability density function (PDF) of the equalizer output — estimated via the Parzen window method — and a desired PDF based on the source symbols. The cost function combines this PDF fitting with an orthogonality criterion derived from the STBC structure of the transmitted data in order to discourage the extraction of identical signals. This cost function motivates an effective and low-cost stochastic gradient descent algorithm for adapting the equaliser. The performance is demonstrated in a number of simulations and benchmarked against other blind schemes for the equalisation of STBC over broadband MIMO channels
A parabolic free boundary problem with Bernoulli type condition on the free boundary
Consider the parabolic free boundary problem For a
realistic class of solutions, containing for example {\em all} limits of the
singular perturbation problem we prove that one-sided
flatness of the free boundary implies regularity.
In particular, we show that the topological free boundary
can be decomposed into an {\em open} regular set (relative to
) which is locally a surface with H\"older-continuous space
normal, and a closed singular set.
Our result extends the main theorem in the paper by H.W. Alt-L.A. Caffarelli
(1981) to more general solutions as well as the time-dependent case. Our proof
uses methods developed in H.W. Alt-L.A. Caffarelli (1981), however we replace
the core of that paper, which relies on non-positive mean curvature at singular
points, by an argument based on scaling discrepancies, which promises to be
applicable to more general free boundary or free discontinuity problems
Biological effects of prolonged expoure of small animals to unusual gaseous environments semiannual report, 1 sep. 1964 - 28 feb. 1965
Biological effect of prolonged exposure of man and small animals to pure oxygen and helium - oxygen environmen
Galactic Globular Cluster Stars: from Theory to Observation
We use evolutionary calculations presented in a recent paper (Cassisi et al.
1998) to predict B,V,I magnitudes for stars in galactic globulars. The effect
of the adopted mixing length on stellar magnitudes and colors is discussed,
showing that the uncertainty on such a theoretical parameter prevents the use
of MS stars as bona fide theoretical standard candles. However, comparison with
Hipparcos data for field subdwarfs discloses a substantial agreement between
theory and observation. Present predictions concerning the magnitude of TO and
of HB stars are compared with similar results appeared in the recent
literature. We present and discuss a theoretical calibration of the difference
in magnitude between HB and TO as evaluated with or without element
sedimentation. Finally we use theoretical HB magnitudes to best fit the CM
diagram of M68 and M5, taken as representative of metal poor and intermediate
metallicity galactic globulars, deriving an age of 111.0 Gyr and
101.0 Gyr, respectively, for the adopted chemical compositions, plus an
additional uncertainty of 1.4 Gyr if the uncertainty on the chemical
composition is taken into account. This result is discussed on the basis of
current evaluations concerning cluster ages and distance moduli.Comment: 8 pages, 13 postscript figures, 6 postscript tables To be published
on Astronomy & Astrophysics Supplement Serie
Hopping conductivity in heavily doped n-type GaAs layers in the quantum Hall effect regime
We investigate the magnetoresistance of epitaxially grown, heavily doped
n-type GaAs layers with thickness (40-50 nm) larger than the electronic mean
free path (23 nm). The temperature dependence of the dissipative resistance
R_{xx} in the quantum Hall effect regime can be well described by a hopping law
(R_{xx} \propto exp{-(T_0/T)^p}) with p=0.6. We discuss this result in terms of
variable range hopping in a Coulomb gap together with a dependence of the
electron localization length on the energy in the gap. The value of the
exponent p>0.5 shows that electron-electron interactions have to be taken into
account in order to explain the occurrence of the quantum Hall effect in these
samples, which have a three-dimensional single electron density of states.Comment: 5 pages, 2 figures, 1 tabl
Potential landscapes and induced charges near metallic islands in three dimensions
We calculate electrostatic potential landscapes for an external probe charge
in the presence of a set of metallic islands. Our numerical calculation in
three dimensions (3D)uses an efficient grid relaxation technique. The
well-known relaxation algorithm for solving the Poisson equation in two
dimensions is generalized to 3D. In addition,all charges on the system, free as
well as induced charges,are determined accurately and self-consistently to
satisfy the desired boundary conditions. This allows the straightforward
calculation of the potential on the outer boundary using the free space
electrostatic Green's function,as well as the calculation of the entire
capacitance matrix of the system. Physically interesting examples of nanoscale
systems are presented and analyzed.Comment: 6 pages, 6 figures, submitted to PR
Evaluation of the micro-carburetor
A prototype sonic, variable-venturi automotive carburetor was evaluated for its effects on vehicle performance, fuel economy, and exhaust emissions. A 350 CID Chevrolet Impala vehicle was tested on a chassis dynamometer over the 1975 Federal Test Procedure, urban driving cycle. The Micro-carburetor was tested and compared with stock and modified-stock engine configurations. Subsequently, the test vehicle's performance characteristics were examined with the stock carburetor and again with the Micro-carburetor in a series of on-road driveability tests. The test engine was then removed from the vehicle and installed on an engine dynamometer. Engine tests were conducted to compare the fuel economy, thermal efficiency, and cylinder-to-cylinder mixture distribution of the Micro-carburetor to that of the stock configuration. Test results show increases in thermal efficiency and improvements in fuel economy at all test conditions. Improve fuel/air mixture preparation is implied from the information presented. Further improvements in fuel economy and exhaust emissions are possible through a detailed recalibration of the Micro-carburetor
Effective coupling between two Brownian particles
We use the system-plus-reservoir approach to study the dynamics of a system
composed of two independent Brownian particles. We present an extension of the
well-known model of a bath of oscillators which is capable of inducing an
effective coupling between the two particles depending on the choice made for
the spectral function of the bath oscillators. The coupling is non-linear in
the variables of interest and an exponential dependence on these variables is
imposed in order to guarantee the translational invariance of the model if the
two particles are not subject to any external potential. The effective
equations of motion for the particles are obtained by the Laplace transform
method and besides recovering all the local dynamical properties for each
particle we end up with an effective interaction potential between them. We
explicitly analyze one of its possible forms.Comment: 4 pages, 1 figur
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