La crisis de la deuda soberana o pública: el caso de España

The sovereign debt crisis is often evoked as one of the main causes of the economic difficulties faced by net importing countries and as the rationale behind the austerity measures imposed on their residents. Nothing seems more evident than a country whose global, commercial and financial, imports exceed its global exports has to finance its deficit through a foreign loan. This inevitably leads to the formation of an external debt. Yet, things are less straightforward than they might appear, and a rigorous analysis is called for to verify whether any country’ sovereign debt is ever justifiable. The paper shows that it is because net global imports are paid twice that net importing countries run up a sovereign debt. The case of Spain is symptomatic and provides statistical confirmation of the pathological increase in the country’s external debtLa crisis de la deuda soberana suele considerarse como una de las principales causas de las dificultades económicas a las que se enfrentan los países importadores netos. Constituye asimismo la razón que justifica las medidas de austeridad impuestas a sus residentes. Nada parece más evidente que un país, cuyas importaciones globales, comerciales y financieras, exceden sus exportaciones globales, tenga que financiar su déficit mediante un préstamo extranjero. Lo que conduce inevitablemente a la formación de la deuda exterior. Sin embargo, la realidad es más compleja de lo que parece. De ahí que sea necesario un análisis riguroso que aclare si la deuda soberana de cada país está justificada. Este artículo muestra que no lo está, desde el momento en que los países importadores netos se encuentran con una deuda soberana debido al doble coste de las importaciones globales netas. El caso espa˜nol es sintomático y aporta confirmación estadística del aumento patológico de la deuda exterior del paí

Exit time of turbulent signals: a way to detect the intermediate dissipative range

The exit time statistics of experimental turbulent data is analyzed. By looking at the exit-time moments (Inverse Structure Functions) it is possible to have a direct measurement of scaling properties of the laminar statistics. It turns out that the Inverse Structure Functions show a much more extended Intermediate Dissipative Range than the Structure Functions, leading to the first clear evidence of the universal properties of such a range of scales.Comment: 4 RevTeX pages (3 eps figures included

Predictability: a way to characterize Complexity

Different aspects of the predictability problem in dynamical systems are reviewed. The deep relation among Lyapunov exponents, Kolmogorov-Sinai entropy, Shannon entropy and algorithmic complexity is discussed. In particular, we emphasize how a characterization of the unpredictability of a system gives a measure of its complexity. Adopting this point of view, we review some developments in the characterization of the predictability of systems showing different kind of complexity: from low-dimensional systems to high-dimensional ones with spatio-temporal chaos and to fully developed turbulence. A special attention is devoted to finite-time and finite-resolution effects on predictability, which can be accounted with suitable generalization of the standard indicators. The problems involved in systems with intrinsic randomness is discussed, with emphasis on the important problems of distinguishing chaos from noise and of modeling the system. The characterization of irregular behavior in systems with discrete phase space is also considered.Comment: 142 Latex pgs. 41 included eps figures, submitted to Physics Reports. Related information at this http://axtnt2.phys.uniroma1.i

Linear and nonlinear information flow in spatially extended systems

Infinitesimal and finite amplitude error propagation in spatially extended systems are numerically and theoretically investigated. The information transport in these systems can be characterized in terms of the propagation velocity of perturbations $V_p$. A linear stability analysis is sufficient to capture all the relevant aspects associated to propagation of infinitesimal disturbances. In particular, this analysis gives the propagation velocity $V_L$ of infinitesimal errors. If linear mechanisms prevail on the nonlinear ones $V_p = V_L$. On the contrary, if nonlinear effects are predominant finite amplitude disturbances can eventually propagate faster than infinitesimal ones (i.e. $V_p > V_L$). The finite size Lyapunov exponent can be successfully employed to discriminate the linear or nonlinear origin of information flow. A generalization of finite size Lyapunov exponent to a comoving reference frame allows to state a marginal stability criterion able to provide $V_p$ both in the linear and in the nonlinear case. Strong analogies are found between information spreading and propagation of fronts connecting steady states in reaction-diffusion systems. The analysis of the common characteristics of these two phenomena leads to a better understanding of the role played by linear and nonlinear mechanisms for the flow of information in spatially extended systems.Comment: 14 RevTeX pages with 13 eps figures, title/abstract changed minor changes in the text accepted for publication on PR

Active vs passive scalar turbulence

Active and passive scalars transported by an incompressible two-dimensional conductive fluid are investigated. It is shown that a passive scalar displays a direct cascade towards the small scales while the active magnetic potential builds up large-scale structures in an inverse cascade process. Correlations between scalar input and particle trajectories are found to be responsible for those dramatic differences as well as for the behavior of dissipative anomalies.Comment: Revised version, Phys. Rev. Lett., in pres