43,765 research outputs found
An experimental SMI adaptive antenna array for weak interfering signals
A modified sample matrix inversion (SMI) algorithm designed to increase the suppression of weak interference is implemented on an existing experimental array system. The algorithm itself is fully described as are a number of issues concerning its implementation and evaluation, such as sample scaling, snapshot formation, weight normalization, power calculation, and system calibration. Several experiments show that the steady state performance (i.e., many snapshots are used to calculate the array weights) of the experimental system compares favorably with its theoretical performance. It is demonstrated that standard SMI does not yield adequate suppression of weak interference. Modified SMI is then used to experimentally increase this suppression by as much as 13dB
Obtaining pressure versus concentration phase diagrams in spin systems from Monte Carlo simulations
We propose an efficient procedure for determining phase diagrams of systems
that are described by spin models. It consists of combining cluster algorithms
with the method proposed by Sauerwein and de Oliveira where the grand canonical
potential is obtained directly from the Monte Carlo simulation, without the
necessity of performing numerical integrations. The cluster algorithm presented
in this paper eliminates metastability in first order phase transitions
allowing us to locate precisely the first-order transitions lines. We also
produce a different technique for calculating the thermodynamic limit of
quantities such as the magnetization whose infinite volume limit is not
straightforward in first order phase transitions. As an application, we study
the Andelman model for Langmuir monolayers made of chiral molecules that is
equivalent to the Blume-Emery-Griffiths spin-1 model. We have obtained the
phase diagrams in the case where the intermolecular forces favor interactions
between enantiomers of the same type (homochiral interactions). In particular,
we have determined diagrams in the surface pressure versus concentration plane
which are more relevant from the experimental point of view and less usual in
numerical studies
Meson Masses and Mixing Angles in 2+1 Flavor Polyakov Quark Meson Sigma Model and Symmetry Restoration Effects
The meson masses and mixing angles have been calculated for the scalar and
pseudoscalar sector in the framework of the generalized 2+1 flavor Polyakov
loop augmented quark meson linear sigma model. We have given the results for
two different forms of the effective Polyakov loop potential. The comparison of
results with the existing calculations in the bare 2+1 quark meson linear sigma
model, shows that the restoration of chiral symmetry becomes sharper due to the
influence of the Polyakov loop potential. We find that inclusion of the
Polyakov loop in quark meson linear sigma model together with the presence of
axial anomaly, triggers an early and significant melting of the strange
condensate. We have examined how the inclusion of the Polyakov loop
qualitatively and quantitatively affects the convergence in the masses of the
chiral partners in pseudoscalar (, , , ) and scalar
(, , ,) meson nonets as the temperature is varied on
the reduced temperature scale. The role of anomaly in determining the
isoscalar masses and mixing angles for the pseudoscalar ( and )
and scalar ( and )meson complex, has also been investigated in the
Polyakov quark meson linear sigma model. The interplay of chiral symmetry
restoration effects and the setting up of restoration trend has been
discussed and analyzed in the framework of the presented model calculations.Comment: 15 pages, 8 figures, 4 table
Adaptive antenna arrays for satellite communications: Design and testing
When two separate antennas are used with each feedback loop to decorrelate noise, the antennas should be located such that the phase of the interfering signal in the two antennas is the same while the noise in them is uncorrelated. Thus, the antenna patterns and spatial distribution of the auxiliary antennas are quite important and should be carefully selected. The selection and spatial distribution of auxiliary elements is discussed when the main antenna is a center fed reflector antenna. It is shown that offset feeds of the reflector antenna can be used as auxiliary elements of an adaptive array to suppress weak interfering signals. An experimental system is designed to verify the theoretical analysis. The details of the experimental systems are presented
Design of blended rolled edges for compact range main reflectors
A procedure to design blended rolled edge terminations for arbitrary rim shape compact range main reflectors is presented. The reflector may be center-fed or offset-fed. The design procedure leads to a reflector which has a continuous and smooth surface. This procedure also ensures small diffracted fields from the junction between the paraboloid and the blended rolled edge while satisfying certain constraints regarding the maximum height of the reflector and minimum operating frequency of the system. The prescribed procedure is used to design several reflectors and the performance of these reflectors is presented
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