734 research outputs found
The K-sat problem in a simple limit
We compute the thermodynamic properties of the 3-satisfiability problem in
the infinite connectivity limit. In this limit the computations can be strongly
simplified and the thermodynamical properties can be obtained with an high
accuracy. We find evidence for a continuous replica symmetry breaking in the
region of high number of clauses, .Comment: 9 pages, 6 figures. To appear in J. Stat. Phys. Minor change
Stable Solution of the Simplest Spin Model for Inverse Freezing
We analyze the Blume-Emery-Griffiths model with disordered magnetic
interaction that displays the inverse freezing phenomenon. The behavior of this
spin-1 model in crystal field is studied throughout the phase diagram and the
transition and spinodal lines for the model are computed using the Full Replica
Symmetry Breaking Ansatz that always yields a thermodynamically stable phase.
We compare the results both with the formulation of the same model in terms of
Ising spins on lattice gas, where no reentrance takes place, and with the model
with generalized spin variables recently introduced by Schupper and Shnerb
[Phys. Rev. Lett. {\bf 93} 037202 (2004)], for which the reentrance is enhanced
as the ratio between the degeneracy of full to empty sites increases. The
simplest version of all these models, known as the Ghatak-Sherrington model,
turns out to hold all the general features characterizing an inverse transition
to an amorphous phase, including the right thermodynamic behavior.Comment: 4 pages, 4 figure
Complexity of the Sherrington-Kirkpatrick Model in the Annealed Approximation
A careful critical analysis of the complexity, at the annealed level, of the
Sherrington-Kirkpatrick model has been performed. The complexity functional is
proved to be always invariant under the Becchi-Rouet-Stora-Tyutin
supersymmetry, disregarding the formulation used to define it. We consider two
different saddle points of such functional, one satisfying the supersymmetry
[A. Cavagna {\it et al.}, J. Phys. A {\bf 36} (2003) 1175] and the other one
breaking it [A.J. Bray and M.A. Moore, J. Phys. C {\bf 13} (1980) L469]. We
review the previews studies on the subject, linking different perspectives and
pointing out some inadequacies and even inconsistencies in both solutions.Comment: 20 pages, 4 figure
Neural-Based Nonlinear Device Models for Intermodulation Analysis
A new procedure to learn a nonlinear model together with its derivative parameters using a composite neural network is presented.So far neural networks have never been used to extract large-signal device model accounting for distortion parameters.Applying this method to FET devices leads to nonlinear models for current- voltage functions which allow improved prediction of weak and mildly device nonlinearities in the whole bias region. The resulting models have demonstrated to be suitable for both small-signal and large-signal analyses,including intermodulation distortion prediction
The random Blume-Capel model on cubic lattice: first order inverse freezing in a 3D spin-glass system
We present a numerical study of the Blume-Capel model with quenched disorder
in 3D. The phase diagram is characterized by spin-glass/paramagnet phase
transitions of both first and second order in the thermodynamic sense.
Numerical simulations are performed using the Exchange-Monte Carlo algorithm,
providing clear evidence for inverse freezing. The main features at criticality
and in the phase coexistence region are investigated. The whole inverse
freezing transition appears to be first order. The second order transition
appears to be in the same universality class of the Edwards-Anderson model. The
nature of the spin-glass phase is analyzed by means of the finite size scaling
behavior of the overlap distribution functions and the four-spins real-space
correlation functions. Evidence for a replica symmetry breaking-like
organization of states is provided.Comment: 18 pages, 24 figures, 7 table
Breeze analysis by mast and sodar measurements
During the year 1993, field measurements were carried out in a meteorological station located in the neighbourhood of Rome, 10 km from the coast (Tyrrhenian Sea). The monitoring station is composed of a 30 m mast and a three-axial Doppler sodar. A statistical analysis of data has been made in order to obtain the main parameters utilised by the dispersion model. Hourly, seasonal and conditional averages showed the strong influence of sea and land breeze circulation on the local characteristics of the atmospheric boundary layer. Such an aspect has to be considered in the numerical predictions of pollutant dispersion
Diluted one-dimensional spin glasses with power law decaying interactions
We introduce a diluted version of the one dimensional spin-glass model with
interactions decaying in probability as an inverse power of the distance. In
this model varying the power corresponds to change the dimension in short-range
models. The spin-glass phase is studied in and out of the range of validity of
the mean-field approximation in order to discriminate between different
theories. Since each variable interacts only with a finite number of others the
cost for simulating the model is drastically reduced with respect to the fully
connected version and larger sizes can be studied. We find both static and
dynamic evidence in favor of the so-called replica symmetry breaking theory.Comment: 4 pages, 6 figures, 2 table
Phase diagram and complexity of mode-locked lasers: from order to disorder
We investigate mode-locking processes in lasers displaying a variable degree
of structural randomness, from standard optical cavities to multiple-scattering
media. By employing methods mutuated from spin-glass theory, we analyze the
mean-field Hamiltonian and derive a phase-diagram in terms of the pumping rate
and the degree of disorder. Three phases are found: i) paramagnetic,
corresponding to a noisy continuous wave emission, ii) ferromagnetic, that
describes the standard passive mode-locking, and iii) the spin-glass in which
the phases of the electromagnetic field are frozen in a exponentially large
number of configurations. The way the mode-locking threshold is affected by the
amount of disorder is quantified. The results are also relevant for other
physical systems displaying a random Hamiltonian, like Bose-Einstein
condensates and nonlinear optical beams.Comment: 4 pages, 2 figure
The Ising M-p-spin mean-field model for the structural glass: continuous vs. discontinuous transition
The critical behavior of a family of fully connected mean-field models with
quenched disorder, the Ising spin glass, is analyzed, displaying a
crossover between a continuous and a random first order phase transition as a
control parameter is tuned. Due to its microscopic properties the model is
straightforwardly extendable to finite dimensions in any geometry.Comment: 10 pages, 1 figure, 1 tabl
Ising spin glass transition in magnetic field out of mean-field
The spin-glass transition in external magnetic field is studied both in and
out of the limit of validity of mean-field theory on a diluted one dimensional
chain of Ising spins where exchange bonds occur with a probability decaying as
the inverse power of the distance. Varying the power in this long-range model
corresponds, in a one-to-one relationship, to change the dimension in
spin-glass short-range models. Evidence for a spin-glass transition in magnetic
field is found also for systems whose equivalent dimension is below the upper
critical dimension at zero magnetic field.Comment: 5 pages, 1 table, 6 figures, data analysis mistake corrected, new
figures, new scaling approach to critical properties introduce
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