1,700 research outputs found
State Concentration Exponent as a Measure of Quickness in Kauffman-type Networks
We study the dynamics of randomly connected networks composed of binary
Boolean elements and those composed of binary majority vote elements. We
elucidate their differences in both sparsely and densely connected cases. The
quickness of large network dynamics is usually quantified by the length of
transient paths, an analytically intractable measure. For discrete-time
dynamics of networks of binary elements, we address this dilemma with an
alternative unified framework by using a concept termed state concentration,
defined as the exponent of the average number of t-step ancestors in state
transition graphs. The state transition graph is defined by nodes corresponding
to network states and directed links corresponding to transitions. Using this
exponent, we interrogate the dynamics of random Boolean and majority vote
networks. We find that extremely sparse Boolean networks and majority vote
networks with arbitrary density achieve quickness, owing in part to long-tailed
in-degree distributions. As a corollary, only relatively dense majority vote
networks can achieve both quickness and robustness.Comment: 6 figure
Statistical physics of independent component analysis
Statistical physics is used to investigate independent component analysis
with polynomial contrast functions. While the replica method fails, an adapted
cavity approach yields valid results. The learning curves, obtained in a
suitable thermodynamic limit, display a first order phase transition from poor
to perfect generalization.Comment: 7 pages, 1 figure, to appear in Europhys. Lett
Les bassins quaternaires du Sahel central de la Tunisie : genèse et évolution des sebkhas en contexte décrochant compressif et distensif
Les études géologiques et les profils sismiques du Sahel central de la Tunisie suggèrent que la genèse et l'évolution des lagunes côtières et des sebkhas de cette région ont été contrôlés par une tectonique décrochante compressive post-villafranchienne, suivie de mouvements distensifs décrochants d'âge tyrrhénie
Nonlinear force-free and potential field models of active-region and global coronal fields during the Whole Heliospheric Interval
Between 2008/3/24 and 2008/4/2, the three active regions NOAA active regions
10987, 10988 and 10989 were observed daily by the Synoptic Optical Long-term
Investigations of the Sun (SOLIS) Vector Spectro-Magnetograph (VSM) while they
traversed the solar disk. We use these measurements and the nonlinear
force-free magnetic field code XTRAPOL to reconstruct the coronal magnetic
field for each active region and compare model field lines with images from the
Solar Terrestrial RElations Observatory (STEREO) and Hinode X-ray Telescope
(XRT) telescopes. Synoptic maps made from continuous, round-the-clock Global
Oscillations Network Group (GONG) magnetograms provide information on the
global photospheric field and potential-field source-surface models based on
these maps describe the global coronal field during the Whole Heliospheric
Interval (WHI) and its neighboring rotations. Features of the modeled global
field, such as the coronal holes and streamer belt locations, are discussed in
comparison with extreme ultra-violet and coronagraph observations from STEREO.
The global field is found to be far from a minimum, dipolar state. From the
nonlinear models we compute physical quantities for the active regions such as
the photospheric magnetic and electric current fluxes, the free magnetic energy
and the relative helicity for each region each day where observations permit.
The interconnectivity of the three regions is addressed in the context of the
potential-field source-surface model. Using local and global quantities derived
from the models, we briefly discuss the different observed activity levels of
the regions.Comment: Accepted for publication in the Solar Physics Whole Heliospheric
Interval (WHI) topical issue. We had difficulty squeezing this paper into
arXiv's 15 Mb limit. The full paper is available here
ftp://gong2.nso.edu/dsds_user/petrie/PetrieCanouAmari.pd
Field Theoretical Analysis of On-line Learning of Probability Distributions
On-line learning of probability distributions is analyzed from the field
theoretical point of view. We can obtain an optimal on-line learning algorithm,
since renormalization group enables us to control the number of degrees of
freedom of a system according to the number of examples. We do not learn
parameters of a model, but probability distributions themselves. Therefore, the
algorithm requires no a priori knowledge of a model.Comment: 4 pages, 1 figure, RevTe
Information measures based on Tsallis' entropy and geometric considerations for thermodynamic systems
An analysis of the thermodynamic behavior of quantum systems can be performed
from a geometrical perspective investigating the structure of the state space.
We have developed such an analysis for nonextensive thermostatistical
frameworks, making use of the q-divergence derived from Tsallis' entropy.
Generalized expressions for operator variance and covariance are considered, in
terms of which the fundamental tensor is given.Comment: contribution to 3rd NEXT-SigmaPhi International Conference (August
2005, Kolymbari, Greece
Storage and recall of weak coherent optical pulses with an efficiency of 25%
We demonstrate experimentally a quantum memory scheme for the storage of weak
coherent light pulses in an inhomogeneously broadened optical transition in a
Pr^{3+}: YSO crystal at 2.1 K. Precise optical pumping using a frequency stable
(about 1kHz linewidth) laser is employed to create a highly controllable Atomic
Frequency Comb (AFC) structure. We report single photon storage and retrieval
efficiencies of 25%, based on coherent photon echo type re-emission in the
forward direction. The coherence property of the quantum memory is proved
through interference between a super Gaussian pulse and the emitted echo.
Backward retrieval of the photon echo emission has potential for increasing
storage and recall efficiency.Comment: 5,
A survey on fiber nonlinearity compensation for 400 Gbps and beyond optical communication systems
Optical communication systems represent the backbone of modern communication
networks. Since their deployment, different fiber technologies have been used
to deal with optical fiber impairments such as dispersion-shifted fibers and
dispersion-compensation fibers. In recent years, thanks to the introduction of
coherent detection based systems, fiber impairments can be mitigated using
digital signal processing (DSP) algorithms. Coherent systems are used in the
current 100 Gbps wavelength-division multiplexing (WDM) standard technology.
They allow the increase of spectral efficiency by using multi-level modulation
formats, and are combined with DSP techniques to combat the linear fiber
distortions. In addition to linear impairments, the next generation 400 Gbps/1
Tbps WDM systems are also more affected by the fiber nonlinearity due to the
Kerr effect. At high input power, the fiber nonlinear effects become more
important and their compensation is required to improve the transmission
performance. Several approaches have been proposed to deal with the fiber
nonlinearity. In this paper, after a brief description of the Kerr-induced
nonlinear effects, a survey on the fiber nonlinearity compensation (NLC)
techniques is provided. We focus on the well-known NLC techniques and discuss
their performance, as well as their implementation and complexity. An extension
of the inter-subcarrier nonlinear interference canceler approach is also
proposed. A performance evaluation of the well-known NLC techniques and the
proposed approach is provided in the context of Nyquist and super-Nyquist
superchannel systems.Comment: Accepted in the IEEE Communications Surveys and Tutorial
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