917 research outputs found
Macroscopic evidence of microscopic dynamics in the Fermi-Pasta-Ulam oscillator chain from nonlinear time series analysis
The problem of detecting specific features of microscopic dynamics in the
macroscopic behavior of a many-degrees-of-freedom system is investigated by
analyzing the position and momentum time series of a heavy impurity embedded in
a chain of nearest-neighbor anharmonic Fermi-Pasta-Ulam oscillators. Results
obtained in a previous work [M. Romero-Bastida, Phys. Rev. E {\bf69}, 056204
(2004)] suggest that the impurity does not contribute significantly to the
dynamics of the chain and can be considered as a probe for the dynamics of the
system to which the impurity is coupled. The () entropy, which measures
the amount of information generated by unit time at different scales of
time and of the observable, is numerically computed by methods of nonlinear
time-series analysis using the position and momentum signals of the heavy
impurity for various values of the energy density (energy per degree
of freedom) of the system and some values of the impurity mass . Results
obtained from these two time series are compared and discussed.Comment: 7 pages, 5 figures, RevTeX4 PRE format; to be published in Phys. Rev.
Directed deterministic classical transport: symmetry breaking and beyond
We consider transport properties of a double delta-kicked system, in a regime
where all the symmetries (spatial and temporal) that could prevent directed
transport are removed. We analytically investigate the (non trivial) behavior
of the classical current and diffusion properties and show that the results are
in good agreement with numerical computations. The role of dissipation for a
meaningful classical ratchet behavior is also discussed.Comment: 10 pages, 20 figure
Short period attractors and non-ergodic behavior in the deterministic fixed energy sandpile model
We study the asymptotic behaviour of the Bak, Tang, Wiesenfeld sandpile
automata as a closed system with fixed energy.
We explore the full range of energies characterizing the active phase. The
model exhibits strong non-ergodic features by settling into limit-cycles whose
period depends on the energy and initial conditions. The asymptotic activity
(topplings density) shows, as a function of energy density , a
devil's staircase behaviour defining a symmetric energy interval-set over which
also the period lengths remain constant. The properties of -
phase diagram can be traced back to the basic symmetries underlying the model's
dynamics.Comment: EPL-style, 7 pages, 3 eps figures, revised versio
Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators
The largest Lyapunov exponent of a system composed by a heavy impurity
embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators
is numerically computed for various values of the impurity mass . A
crossover between weak and strong chaos is obtained at the same value
of the energy density (energy per degree of freedom)
for all the considered values of the impurity mass . The threshold \epsi
lon_{_T} coincides with the value of the energy density at which a
change of scaling of the relaxation time of the momentum autocorrelation
function of the impurity ocurrs and that was obtained in a previous work ~[M.
Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete
Lyapunov spectrum does not depend significantly on the impurity mass . These
results suggest that the impurity does not contribute significantly to the
dynamical instability (chaos) of the chain and can be considered as a probe for
the dynamics of the system to which the impurity is coupled. Finally, it is
shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak
to strong chaos at the same value of the energy density that the crossover
value of largest Lyapunov exponent. Implications of this result
are discussed.Comment: 6 pages, 5 figures, revtex4 styl
Sporadicity and synchronization in one-dimensional asymmetrically coupled maps
A one-dimensional chain of sporadic maps with asymmetric nearest neighbour
couplings is numerically studied. It is shown that in the region of strong
asymmetry the system becomes spatially fully synchronized, even in the
thermodinamic limit, while the Lyapunov exponent is zero. For weak asymmetry
the synchronization is no more complete, and the Lyapunov exponent becomes
positive. In addition one has a clear relation between temporal and spatial
chaos, {\it i.e.}: a positive effective Lyapunov exponent corresponds to a lack
of synchronization and {\it vice versa}Comment: 9 pages + 3 figures (postscript appended uuencoded tar), IOP style
(appended uuencoded compress
Source mechanism of Saturn narrowband emission
Narrowband emission (NB) is observed at Saturn centered near 5 kHz and 20 kHz
and harmonics. This emission appears similar in many ways to Jovian
kilometric narrowband emission observed at higher frequencies, and therefore
may have a similar source mechanism. Source regions of NB near 20 kHz are
believed to be located near density gradients in the inner magnetosphere and
the emission appears to be correlated with the occurrence of large neutral
plasma clouds observed in the Saturn magnetotail. In this work we present
the results of a growth rate analysis of NB emission (~20 kHz) near or
within a probable source region. This is made possible by the sampling of
in-situ wave and particle data. The results indicate waves are likely to be
generated by the mode-conversion of directly generated Z-mode emission to
O-mode near a density gradient. When the local hybrid frequency is close <I>n</I>
<I>f</I><sub>ce</sub> (<I>n</I> is an integer and <I>f</I><sub>ce</sub> is the electron cyclotron frequency)
with <I>n</I>=4, 5 or 6 in our case, electromagnetic Z-mode and weak ordinary
(O-mode) emission can be directly generated by the cyclotron maser
instability
Year in review in Intensive Care Medicine 2012. II: Pneumonia and infection, sepsis, coagulation, hemodynamics, cardiovascular and microcirculation, critical care organization, imaging, ethics and legal issues.
Journal ArticleSCOPUS: re.jSCOPUS: re.jinfo:eu-repo/semantics/publishe
Transport properties in chaotic and non-chaotic many particles systems
Two deterministic models for Brownian motion are investigated by means of
numerical simulations and kinetic theory arguments. The first model consists of
a heavy hard disk immersed in a rarefied gas of smaller and lighter hard disks
acting as a thermal bath. The second is the same except for the shape of the
particles, which is now square. The basic difference of these two systems lies
in the interaction: hard core elastic collisions make the dynamics of the disks
chaotic whereas that of squares is not. Remarkably, this difference is not
reflected in the transport properties of the two systems: simulations show that
the diffusion coefficients, velocity correlations and response functions of the
heavy impurity are in agreement with kinetic theory for both the chaotic and
the non-chaotic model. The relaxation to equilibrium, however, is very
sensitive to the kind of interaction. These observations are used to reconsider
and discuss some issues connected to chaos, statistical mechanics and
diffusion.Comment: 23 pgs with 8 Figure
Planetary Science Virtual Observatory architecture
In the framework of the Europlanet-RI program, a prototype of Virtual
Observatory dedicated to Planetary Science was defined. Most of the activity
was dedicated to the elaboration of standards to retrieve and visualize data in
this field, and to provide light procedures to teams who wish to contribute
with on-line data services. The architecture of this VO system and selected
solutions are presented here, together with existing demonstrators
The prediction of future from the past: an old problem from a modern perspective
The idea of predicting the future from the knowledge of the past is quite
natural when dealing with systems whose equations of motion are not known. Such
a long-standing issue is revisited in the light of modern ergodic theory of
dynamical systems and becomes particularly interesting from a pedagogical
perspective due to its close link with Poincar\'e's recurrence. Using such a
connection, a very general result of ergodic theory - Kac's lemma - can be used
to establish the intrinsic limitations to the possibility of predicting the
future from the past. In spite of a naive expectation, predictability results
to be hindered rather by the effective number of degrees of freedom of a system
than by the presence of chaos. If the effective number of degrees of freedom
becomes large enough, regardless the regular or chaotic nature of the system,
predictions turn out to be practically impossible. The discussion of these
issues is illustrated with the help of the numerical study of simple models.Comment: 9 pages, 4 figure
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