1,128 research outputs found
Coarse-Grained Probabilistic Automata Mimicking Chaotic Systems
Discretization of phase space usually nullifies chaos in dynamical systems.
We show that if randomness is associated with discretization dynamical chaos
may survive and be indistinguishable from that of the original chaotic system,
when an entropic, coarse-grained analysis is performed. Relevance of this
phenomenon to the problem of quantum chaos is discussed.Comment: 4 pages, 4 figure
Models of Time Travel and their Consequences
How do we travel through time? We know that we can move forward in it (we have no choice), but can we jump forward in time? Can we go backward in time? It also gives rise to other troubling questions: is time measurable in distinct increments, or does it flow continuously? In Models of Time Travel and their Consequences, Antonio Mantica walks the reader through current understandings of how time functions in Einstein\u27s universe and proposes three distinct models to explain it. Following that, he provides a list of experiments to credit or discredit the models. Appropriate for audiences of any amount of scientific background
Multifractal properties of return time statistics
Fluctuations in the return time statistics of a dynamical system can be
described by a new spectrum of dimensions. Comparison with the usual
multifractal analysis of measures is presented, and difference between the two
corresponding sets of dimensions is established. Theoretical analysis and
numerical examples of dynamical systems in the class of Iterated Functions are
presented.Comment: 4 pages, 3 figure
On the statistical distribution of first--return times of balls and cylinders in chaotic systems
We study returns in dynamical systems: when a set of points, initially
populating a prescribed region, swarms around phase space according to a
deterministic rule of motion, we say that the return of the set occurs at the
earliest moment when one of these points comes back to the original region. We
describe the statistical distribution of these "first--return times" in various
settings: when phase space is composed of sequences of symbols from a finite
alphabet (with application for instance to biological problems) and when phase
space is a one and a two-dimensional manifold. Specifically, we consider
Bernoulli shifts, expanding maps of the interval and linear automorphisms of
the two dimensional torus. We derive relations linking these statistics with
Renyi entropies and Lyapunov exponents.Comment: submitted to Int. J. Bifurcations and Chao
Nonlinear stabilization of tokamak microturbulence by fast ions
Nonlinear electromagnetic stabilization by suprathermal pressure gradients
found in specific regimes is shown to be a key factor in reducing tokamak
microturbulence, augmenting significantly the thermal pressure electromagnetic
stabilization. Based on nonlinear gyrokinetic simulations investigating a set
of ion heat transport experiments on the JET tokamak, described by Mantica et
al. [Phys. Rev. Lett. 107 135004 (2011)], this result explains the
experimentally observed ion heat flux and stiffness reduction. These findings
are expected to improve the extrapolation of advanced tokamak scenarios to
reactor relevant regimes.Comment: 5 pages, 5 figure
Elasto-viscoplastic modeling of subsidence above gas fields in the Adriatic Sea
Abstract. From the analysis of GPS monitoring data collected above gas
fields in the Adriatic Sea, in a few cases subsidence responses have been
observed not to directly correlate with the production trend. Such behavior,
already described in the literature, may be due to several physical
phenomena, ranging from simple delayed aquifer depletion to a much more
complex time-dependent mechanical response of subsurface geomaterials to
fluid withdrawal. In order to accurately reproduce it and therefore to be
able to provide reliable forecasts, in the last years Eni has enriched its
3D finite element geomechanical modeling workflow by adopting an advanced
constitutive model (Vermeer and Neher, 1999), which also considers the
viscous component of the deformation. While the numerical implementation of
such methodology has already been validated at laboratory scale and tested
on synthetic hydrocarbon fields, the work herein presents its first
application to a real gas field in the Adriatic Sea where the phenomenon has
been observed. The results show that the model is capable to reproduce very
accurately both GPS data and other available measurements. It is worth
remarking that initial runs, characterized by the use of model parameter
values directly obtained from the interpretation of mechanical laboratory
tests, already provided very good results and only minor tuning operations
have been required to perfect the model outcomes. Ongoing R&D projects
are focused on a regional scale characterization of the Adriatic Sea basin
in the framework of the Vermeer and Neher model approach
Evidence for a change in the nuclear mass surface with the discovery of the most neutron-rich nuclei with 17<Z <25
The results of measurements of the production of neutron-rich nuclei by the
fragmentation of a 76-Ge beam are presented. The cross sections were measured
for a large range of nuclei including fifteen new isotopes that are the most
neutron-rich nuclides of the elements chlorine to manganese (50-Cl, 53-Ar,
55,56-K, 57,58-Ca, 59,60,61-Sc, 62,63-Ti, 65,66-V, 68-Cr, 70-Mn). The enhanced
cross sections of several new nuclei relative to a simple thermal evaporation
framework, previously shown to describe similar production cross sections,
indicates that nuclei in the region around 62-Ti might be more stable than
predicted by current mass models and could be an indication of a new island of
inversion similar to that centered on 31-Na.Comment: 4 pages, 3 figures, to be published in Physical Review Letters, 200
Estimate of a spatially variable reservoir compressibility by assimilation of ground surface displacement data
Abstract.
Fluid extraction from producing hydrocarbon reservoirs can cause anthropogenic land subsidence. In
this work, a 3-D finite-element (FE) geomechanical model is used to predict the land surface displacements above
a gas field where displacement observations are available. An ensemble-based data assimilation (DA) algorithm
is implemented that incorporates these observations into the response of the FE geomechanical model, thus re-
ducing the uncertainty on the geomechanical parameters of the sedimentary basin embedding the reservoir. The
calibration focuses on the uniaxial vertical compressibility
c
M
, which is often the geomechanical parameter to
which the model response is most sensitive. The partition of the reservoir into blocks delimited by faults moti-
vates the assumption of a heterogeneous spatial distribution of
c
M
within the reservoir. A preliminary synthetic
test case is here used to evaluate the effectiveness of the DA algorithm in reducing the parameter uncertainty
associated with a heterogeneous
c
M
distribution. A significant improvement in matching the observed data is
obtained with respect to the case in which a homogeneous
c
M
is hypothesized. These preliminary results are
quite encouraging and call for the application of the procedure to real gas fields
- …