4,170 research outputs found
On the Fictitious Play and Channel Selection Games
Considering the interaction through mutual interference of the different
radio devices, the channel selection (CS) problem in decentralized parallel
multiple access channels can be modeled by strategic-form games. Here, we show
that the CS problem is a potential game (PG) and thus the fictitious play (FP)
converges to a Nash equilibrium (NE) either in pure or mixed strategies. Using
a 2-player 2-channel game, it is shown that convergence in mixed strategies
might lead to cycles of action profiles which lead to individual spectral
efficiencies (SE) which are worse than the SE at the worst NE in mixed and pure
strategies. Finally, exploiting the fact that the CS problem is a PG and an
aggregation game, we present a method to implement FP with local information
and minimum feedback.Comment: In proc. of the IEEE Latin-American Conference on Communications
(LATINCOM), Bogota, Colombia, September, 201
Temporal relation between quiet-Sun transverse fields and the strong flows detected by IMaX/SUNRISE
Localized strongly Doppler-shifted Stokes V signals were detected by
IMaX/SUNRISE. These signals are related to newly emerged magnetic loops that
are observed as linear polarization features. We aim to set constraints on the
physical nature and causes of these highly Doppler-shifted signals. In
particular, the temporal relation between the appearance of transverse fields
and the strong Doppler shifts is analyzed in some detail. We calculated the
time difference between the appearance of the strong flows and the linear
polarization. We also obtained the distances from the center of various
features to the nearest neutral lines and whether they overlap or not. These
distances were compared with those obtained from randomly distributed points on
observed magnetograms. Various cases of strong flows are described in some
detail. The linear polarization signals precede the appearance of the strong
flows by on average 84+-11 seconds. The strongly Doppler-shifted signals are
closer (0.19") to magnetic neutral lines than randomly distributed points
(0.5"). Eighty percent of the strongly Doppler-shifted signals are close to a
neutral line that is located between the emerging field and pre-existing
fields. That the remaining 20% do not show a close-by pre-existing field could
be explained by a lack of sensitivity or an unfavorable geometry of the
pre-existing field, for instance, a canopy-like structure. Transverse fields
occurred before the observation of the strong Doppler shifts. The process is
most naturally explained as the emergence of a granular-scale loop that first
gives rise to the linear polarization signals, interacts with pre-existing
fields (generating new neutral line configurations), and produces the observed
strong flows. This explanation is indicative of frequent small-scale
reconnection events in the quiet Sun.Comment: 11 pages, 8 figure
Ghost-gluon coupling, power corrections and from twisted-mass lattice QCD at
A non-perturbative calculation of the ghost-gluon running QCD coupling
constant is performed using twisted-mass dynamical fermions. The
extraction of in the chiral limit reveals the presence of
a non-perturbative OPE contribution that is assumed to be dominated by a
dimension-two \VEV{A^2} condensate. In this contest a novel method for
calibrating the lattice spacing in lattice simulations is presented.Comment: 7 pages, 4 figures, XXVIII International Symposium on Lattice Field
Theory 201
Nonlinear Schr\"odinger Equation with Spatio-Temporal Perturbations
We investigate the dynamics of solitons of the cubic Nonlinear Schr\"odinger
Equation (NLSE) with the following perturbations: non-parametric
spatio-temporal driving of the form , damping, and a
linear term which serves to stabilize the driven soliton. Using the time
evolution of norm, momentum and energy, or, alternatively, a Lagrangian
approach, we develop a Collective-Coordinate-Theory which yields a set of ODEs
for our four collective coordinates. These ODEs are solved analytically and
numerically for the case of a constant, spatially periodic force . The
soliton position exhibits oscillations around a mean trajectory with constant
velocity. This means that the soliton performs, on the average, a
unidirectional motion although the spatial average of the force vanishes. The
amplitude of the oscillations is much smaller than the period of . In
order to find out for which regions the above solutions are stable, we
calculate the time evolution of the soliton momentum and soliton
velocity : This is a parameter representation of a curve which is
visited by the soliton while time evolves. Our conjecture is that the soliton
becomes unstable, if this curve has a branch with negative slope. This
conjecture is fully confirmed by our simulations for the perturbed NLSE.
Moreover, this curve also yields a good estimate for the soliton lifetime: the
soliton lives longer, the shorter the branch with negative slope is.Comment: 21 figure
When Does Output Feedback Enlarge the Capacity of the Interference Channel?
In this paper, the benefits of channel-output feedback in the Gaussian interference channel (G-IC) are studied under the effect of additive Gaussian noise. Using a linear deterministic (LD) model, the signal to noise ratios (SNRs) in the feedback links beyond which feedback plays a significant role in terms of increasing the individual rates or the sum-rate are approximated. The relevance of this work lies on the fact that it identifies the feedback SNRs for which in any G-IC one of the following statements is true: (a) feedback does not enlarge the capacity region; (b) feedback enlarges the capacity region and the sum-rate is greater than the largest sum-rate without feedback; and (c) feedback enlarges the capacity region but no significant improvement is observed in the sum-rate
Imaging of high-Z material for nuclear contraband detection with a minimal prototype of a Muon Tomography station based on GEM detectors
Muon Tomography based on the measurement of multiple scattering of
atmospheric cosmic ray muons in matter is a promising technique for detecting
heavily shielded high-Z radioactive materials (U, Pu) in cargo or vehicles. The
technique uses the deflection of cosmic ray muons in matter to perform
tomographic imaging of high-Z material inside a probed volume. A Muon
Tomography Station (MTS) requires position-sensitive detectors with high
spatial resolution for optimal tracking of incoming and outgoing cosmic ray
muons. Micro Pattern Gaseous Detector (MPGD) technologies such as Gas Electron
Multiplier (GEM) detectors are excellent candidates for this application. We
have built and operated a minimal MTS prototype based on 30cm \times 30cm GEM
detectors for probing targets with various Z values inside the MTS volume. We
report the first successful detection and imaging of medium-Z and high-Z
targets of small volumes (~0.03 liters) using GEM-based Muon Tomography
Equilibrium tuned by a magnetic field in phase separated manganite
We present magnetic and transport measurements on La5/8-yPryCa3/8MnO3 with y
= 0.3, a manganite compound exhibiting intrinsic multiphase coexistence of
sub-micrometric ferromagnetic and antiferromagnetic charge ordered regions.
Time relaxation effects between 60 and 120K, and the obtained magnetic and
resistive viscosities, unveils the dynamic nature of the phase separated state.
An experimental procedure based on the derivative of the time relaxation after
the application and removal of a magnetic field enables the determination of
the otherwise unreachable equilibrium state of the phase separated system. With
this procedure the equilibrium phase fraction for zero field as a function of
temperature is obtained. The presented results allow a correlation between the
distance of the system to the equilibrium state and its relaxation behavior.Comment: 13 pages, 5 figures. Submited to Journal of Physics: Condensed Matte
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