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

Myotonic dystrophy type 1 and high ventricular vulnerability at the electrophysiological evaluation: ICD yes or not?

A significant number of sudden death (SD) is observed in myotonic dystrophy (DM1) despite pacemaker implantation and some consider the ICD to be the preferential device in patients with conduction disease. According to the latest guidelines, prophylactic ICD implantation in patients with neuromuscular disorder should follow the same recommendations of non-ischemic dilated cardiomyopathy, being reasonable when pacing is needed. We here report a case of DM1 patient who underwent ICD implantation even in the absence of conduction disturbances on ECG and ventricular dysfunction/fibrosis at cardiac magnetic resonance. The occurrence of syncope, non-sustained ventricular tachycardias at 24-Holter ECG monitoring and a family history of SD resulted associated with ventricular fibrillation inducibility at electrophysiological study, favouring ICD implantation. On our advice, DM1 patient with this association of SD risk factors should be targeted for ICD implantation

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

Estimating the trace of matrix functions with application to complex networks

The approximation of trace(f(Ω)), where f is a function of a symmetric matrix Ω, can be challenging when Ω is exceedingly large. In such a case even the partial Lanczos decomposition of Ω is computationally demanding and the stochastic method investigated by Bai et al. (J. Comput. Appl. Math. 74:71–89, 1996) is preferred. Moreover, in the last years, a partial global Lanczos method has been shown to reduce CPU time with respect to partial Lanczos decomposition. In this paper we review these techniques, treating them under the unifying theory of measure theory and Gaussian integration. This allows generalizing the stochastic approach, proposing a block version that collects a set of random vectors in a rectangular matrix, in a similar fashion to the partial global Lanczos method. We show that the results of this technique converge quickly to the same approximation provided by Bai et al. (J. Comput. Appl. Math. 74:71–89, 1996), while the block approach can leverage the same computational advantages as the partial global Lanczos. Numerical results for the computation of the Von Neumann entropy of complex networks prove the robustness and efficiency of the proposed block stochastic method

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

Implementation of an elasto-viscoplastic constitutive law in Abaqus/Standard for an improved characterization of rock materials

Subsidence modeling is an important activity in the oil and gas industry, for the environmental and operational implications associated to this phenomenon. Abaqus/Standard has been used for many years in Eni as the main numerical simulator for studying the geomechanical behavior of reservoirs. The results of a large campaign of acquisition of subsidence monitoring data in conjunction with the advanced analysis of laboratory experiments have shown that, in some cases, an improved mechanical characterization can be tailored to better capture the complex behavior of the reservoir rock under the effect of underground fluid withdrawal. In this work we first present an implementation in Abaqus/Standard of an elasto-viscoplastic model – namely the Vermeer and Neher model – as user defined material by means of the UMAT subroutine. Next, we provide the results of various simulations of laboratory tests that were performed to investigate its capability to identify the main features of the behavior of reservoir sands, also including time dependency. Finally, we show a preliminary application to a synthetic, nonetheless realistic, reservoir model that has been performed to assess the capabilities of the elasto-viscoplastic model in the simulation of subsidence evolution

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